Insights into immuno-oncology drug development landscape with focus on bone metastasis

Bone is among the main sites of metastasis in breast, prostate and other major cancers. Bone metastases remain incurable causing high mortality, severe skeletal-related effects and decreased quality of life. Despite the success of immunotherapies in oncology, no immunotherapies are approved for bone metastasis and no clear benefit has been observed with approved immunotherapies in treatment of bone metastatic disease. Therefore, it is crucial to consider unique features of tumor microenvironment in bone metastasis when developing novel therapies. The vicious cycle of bone metastasis, referring to crosstalk between tumor and bone cells that enables the tumor cells to grow in the bone microenvironment, is a well-established concept. Very recently, a novel osteoimmuno-oncology (OIO) concept was introduced to the scientific community. OIO emphasizes the significance of interactions between tumor, immune and bone cells in promoting tumor growth in bone metastasis, and it can be used to reveal the most promising targets for bone metastasis. In order to provide an insight into the current immuno-oncology drug development landscape, we used 1stOncology database, a cancer drug development resource to identify novel immunotherapies in preclinical or clinical development for breast and prostate cancer bone metastasis. Based on the database search, 24 immunotherapies were identified in preclinical or clinical development that included evaluation of effects on bone metastasis. This review provides an insight to novel immuno-oncology drug development in the context of bone metastasis. Bone metastases can be approached using different modalities, and tumor microenvironment in bone provides many potential targets for bone metastasis. Noting current increasing interest in the field of OIO, more therapeutic opportunities that primarily target bone metastasis are expected in the future.

Abstract 5740: Identification of genetic signatures in bone metastasis of breast and prostate cancer

Bone metastases (BM) cause high mortality and are present in 70-90% of advanced breast and prostate cancer patients. Cancer is a complex genetic disease, and no single gene has been shown to be solely responsible for the initiation, growth or progression of cancer. Therefore, more complete understanding of the multiple genes responsible for disease progression, and more specifically, for the development of BM is needed to support development of diagnostic tools and novel therapeutics for BM.

The aim of this study was to identify genetic signatures specific for BM in solid tumors, more specifically in breast cancer (BC) and prostate cancer (PC).

Genetic data was obtained from cBioPortal. A dataset of 500 metastatic solid tumors was used based on availability of metastasis-specific biopsy data (Robinson et al. Integrative clinical genomics of metastatic cancer, Nature 2017). Altogether 40 of the patients (8%) had BM, of which 27 (67,5%) with PC and 8 (20%) with BC. All cancer biopsy samples were grouped to ‘BM-only’ (n = 40) and ‘no-BM’ (n = 460) groups, indicating the presence or absence of BM. The same comparisons were made separately for BC and PC. To confirm cancer type specificity of the findings, the BC and PC BM-only data were compared. Only significant findings (p<0.05) are reported. Finally, the impact of identified altered genes on clinical outcome (survival) was analyzed more broadly in BC (13 studies, over 7 000 samples) and PC (19 studies, over 6 000 samples) specific datasets.

Altogether 48 genetic alterations including mutations and gene-fusions were identified in BM-only group. From the 48 genes, 8 and 3 corresponded to genetic alterations observed in BC and PC, respectively, when comparing BM-only and no-BM groups. None of these genes overlapped in BC and PC BM-only samples. In BC, the identified 8 genes were GPR139, RASIP1, DTHD1, GGT7, LONP2, ATG4B, PI15 and MKRN3. Of these, GPR139 was associated with improved relapse-free survival, RASIP1 with decreased disease-free survival, GGT7 with improved disease-free survival, and PI15 with lower overall survival when comparing patients with altered or unaltered genes across BC cohorts. In PC, the 3 genes were RNF139, KRTAP4-7 and ZNF516. Of these, RNF139 was associated with decreased overall, disease and progression free survival across PC cohorts.

The study identified four genetic alterations in BC (GPR139, RASIP1, GGT7, PI15) and one in PC (RNF139) that were associated with altered survival in patients. Best to our knowledge, none of these genes have been associated with BM earlier. Further studies are warranted to understand significance of these genes for developing novel therapeutics or diagnostic tools for bone metastatic cancers.

Citation Format: Tiina E. Kähkönen, Jussi M. Halleen, Jenni Bernoulli. Identification of genetic signatures in bone metastasis of breast and prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5740.

Abstract 2870: Limited data from clinical trials assessing immunotherapy effects on bone metastases

Bone metastases are a significant cause of mortality in many major cancers. They are difficult to treat and their response rate to standard-of-care therapies is low. Immunotherapies have been approved as stand-alone therapies or in combination with other therapies for the treatment of advanced or metastatic breast, prostate and lung cancer and melanoma patients. It is unclear if approved immunotherapies affect bone metastases.

In this study, relevant scientific publications were evaluated for feasibility to perform a meta-analysis about immunotherapy efficacy on bone metastases. A PubMed search for approved immunotherapies for each of the above-mentioned cancer indications on September 21, 2020 resulted in 561 relevant scientific publications. From these, the criteria for the selection of publications for this study were: 1) patients had detectable bone metastases, 2) patients received at least one immunotherapy treatment, 3) therapy effects for bone metastases was followed, 4) the study was published between 2010-2020. Based on these criteria only six eligible studies were identified.

Treatment with atezolizumab and nab-paclitaxel increased median overall survival in PD-L1+ bone metastatic tripe-negative breast cancer patients compared to nab-paclitaxel treatment only (Schmid et al., 2020). In metastatic castration-resistant prostate cancer patients with bone-predominant disease, pembrolizumab increased disease control rate and median overall survival compared to patients without bone metastases (Antonarakis et al., 2019). In non-small cell lung cancer patients, long-term survivors (LTS, over 24 months) had fewer bone metastases than non-LTS (Pawel et al., 2019). Upon progression, LTS treated with atezolizumab had less cases with liver and bone metastases compared to non-LTS, whereas the incidence was similar in patients treated with docetaxel. In melanoma, complete radiographic responses in bone metastatic patients were not observed when the patients were treated with pembrolizumab (Lee et al., 2017), progressive disease was observed with ipilimumab in combination with radiation therapy (Sundahl et al., 2018), and patients progressed at bone and other metastatic sites with ipilimumab in combination with Bacillicus Calmette-Guérin (Da Gama Duarte et al., 2018).

Only about 1% (6/561) of publications with approved immunotherapies in breast, prostate and lung cancer and melanoma patients reported results on bone metastases. No conclusion can be drawn about the efficacy due to the limited number of eligible studies. Clinical trials with immunotherapies specifying effects on bone metastases are warranted as they would allow to better understand metastasis-specific responses, improve patient selection in future clinical studies, and ultimately help in providing more effective treatments for patients with life-threatening bone metastases.

Citation Format: Tiina E. Kähkönen, Jussi M. Halleen, Jenni Bernoulli. Limited data from clinical trials assessing immunotherapy effects on bone metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2870.

Osteoimmuno-Oncology: Therapeutic Opportunities for Targeting Immune Cells in Bone Metastasis

Immunotherapies provide a potential treatment option for currently incurable bone metastases. Bone marrow is an important secondary lymphoid organ with a unique immune contexture. Even at non-disease state immune cells and bone cells interact with each other, bone cells supporting the development of immune cells and immune cells regulating bone turnover. In cancer, tumor cells interfere with this homeostatic process starting from formation of pre-metastatic niche and later supporting growth of bone metastases. In this review, we introduce a novel concept osteoimmuno-oncology (OIO), which refers to interactions between bone, immune and tumor cells in bone metastatic microenvironment. We also discuss therapeutic opportunities of targeting immune cells in bone metastases, and associated efficacy and safety concerns.

Abstract 6286: The effects of prednisone, abiraterone acetate and radium-223 dichloride on bone in the intratibial LNCaP prostate cancer model

Radium-223 dichloride (Ra-223) is a targeted alpha therapy that binds to newly formed bone matrix in bone metastases and induces double-stranded DNA breaks in cancer cells, osteoblasts, and osteoclasts. Ra-223 showed survival benefit in patients with bone-metastatic castration-resistant prostate cancer in a pivotal phase 3 trial. Recently, in a phase 3 trial of Ra-223 in combination with abiraterone acetate (AA) and prednisone/prednisolone (P), an increased risk of fractures was observed, which could be largely diminished by concurrent administration of bone resorption-inhibiting bisphosphonates or denosumab.

The aim of this study was to investigate the effects of vehicle, Ra-223, AA, P, AA/P, and Ra-223/AA/P on bone using a mouse model mimicking osteoblastic prostate cancer bone metastases.

Male NOD.scid mice were injected intratibially with LNCaP cells. Following stratification based on serum PSA and total bone volume of the tumor-bearing tibia, mice were treated for 28 days. Serum TRACP 5b and PSA levels were measured at multiple time points. At sacrifice, hind limbs were collected to analyze healthy and tumor-bearing bone structure, quality and formation rate by microCT, 3-point bending assay and dynamic histomorphometry, respectively. Also, Ra-223 incorporation was measured.

Treatment with AA/P reduced Ra-223 incorporation to bone. PSA levels were similarly reduced at sacrifice upon Ra-223, AA, AA/P, and Ra-223/AA/P treatment indicating the absence of triple combination-specific additive anti-tumor effects. Bone resorption marker TRACP 5b levels increased transiently during the first two weeks of Ra-223/AA/P treatment. Neither bone structure or bone biomechanical quality in healthy or tumor-bearing tibia were affected by Ra-223/AA/P. Regarding dynamic bone formation, trabecular mineralizing surface (MS) was reduced in all groups containing Ra-223, while periosteal MS was reduced in all groups receiving P. However, only Ra-223/AA/P reduced both trabecular and periosteal MS. In line with the inhibition of dynamic bone formation, Ra-223/AA/P treatment decreased the number of osteoblasts.

The AA/P treatment-induced reduction of Ra-223 incorporation may mediate the lack of additive anti-tumor effects in the Ra-223/AA/P group. Regarding bone health, Ra-223/AA/P specifically induced a transient increase in bone resorption and inhibited both periosteal and trabecular new bone formation but did not lead to structural or biomechanical bone changes. This preclinical mechanism may nevertheless contribute to the increased fragility observed in the clinics and may explain the beneficial clinical effects of bone resorption-inhibiting bisphosphonates and denosumab. However, several species- and model-related factors may limit the translational relevance of these findings.

Citation Format: Mari I. Suominen, Matias Knuuttila, Birgitta Sjöholm, Esa Alhoniemi, Dominik Mumberg, Jussi M. Halleen, Sanna-Maria Käkönen, Arne Scholz. The effects of prednisone, abiraterone acetate and radium-223 dichloride on bone in the intratibial LNCaP prostate cancer model [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6286.

Abstract 1634: Orthotopic and bone metastasis prostate cancer models using the 22Rv1 cell line

Prostate cancer is the most common cancer in men. Upon diagnosed malignancy the growth of the tumors is androgen driven in a majority of the cases. For that reason, the tumors are treated with androgen deprivation therapy (ADT) to stop or reduce tumor growth. Later, the tumors often become resistant to ADT and at this stage the disease is described as castration-resistant prostate cancer (CRPC). Bone metastasis is one of the hallmark of disease progression. Metastatic disease can be either androgen sensitive or castration resistant (mCRPC) in which the mortality rate is over 50%. Prostate cancer metastases are commonly formed in bones.

The 22Rv1 human prostate carcinoma cell line is androgen sensitive and shown to express androgen receptor (AR). The 22Rv1 cells are an invaluable model system to study AR function, the efficacy of existing drugs and to design novel anti-AR therapies that also target non-truncated regions of AR. The aim of this study was to establish predictive orthotopic and intratibial preclinical in vivo prostate cancer models that can be used in drug development when targeting cancer cells and their local environment.

Male athymic nude mice (5-6 weeks old) and NOG mice (over 20 weeks old) were used in the study. 2.5 × 105 22Rv1 cells were inoculated orthotopically into the prostate of NOG mice, and 0.5 × 106 cells were inoculated intratibially into the bone marrow cavity of athymic nude mice. 22Rv1 human prostate cancer cells (ATCC) were cultured in RPMI 1640 medium supplemented with 10% iFBS, 2 mM L-Glutamine, 10 mM HEPES, 1 mM sodium pyruvate, 4500 mg/l D-Glucose and P/S. Tumor growth was followed by PSA measurements using Human PSA ELISA assay. In addition, in the intratibial model, tumor-induced bone changes were monitored by X-ray imaging of the hind limbs. Prostates and hind limbs were collected at sacrifice, fixed in 10% NBF, and processed to paraffin blocks for further histological analysis. Sections of prostate were stained with hematoxylin-eosin (HE) and AR. Tumor-bearing and contralateral (healthy) tibias were stained with HE - OrangeG, MGT, TRAP, and AR. For enhanced visualization of tumor models in 3D, we reconstructed the tissue from serial sections using a tailored computational pipeline based on applying a deformable model for corresponding points from adjacent sections.

The observed tumor take rate was 100% in both models. Confirmed by IHC, tumors formed in both the orthotopic and intratibial models expressed AR. 22Rv1 cells formed osteoblastic - lytic mixed bone lesions in the intratibial model. Based on lesion areas, randomization of the tumor bearing mice in the intratibial model can be done after 2 weeks from cancer cell inoculation. In conclusion, both presented models are suited to test the anticancer efficacy of new drug candidates. In addition, the intratibial model can be used to test the efficacy of novel drug candidates on prostate cancer cells in bone metastatic microenvironment.

Citation Format: Justyna Zdrojewska, Tiina E. Kähkönen, Jenni H. Mäki-Jouppila, Masi Valkonen, Pekka Ruusuvuori, Jussi M. Halleen, Jenni Bernoulli. Orthotopic and bone metastasis prostate cancer models using the 22Rv1 cell line [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1634.

Abstract 5026: Efficacy of anti-PD-1, IDO inhibitor, chemotherapy and bone-targeting agent on tumor growth in a syngeneic bone metastasis model of triple-negative breast cancer

Triple-negative breast cancer (TNBC) is an aggressive cancer with treatment options limited to standard-of-care chemotherapy. TNBC patients develop metastases in high incidence, and almost all patients have bone metastases at end-stage disease. Bone metastases are mainly osteolytic, causing severe bone loss that can be prevented by bone-targeting agents. Currently, there is no efficient cure for bone metastases. Activation of the patient’s own immune system by immunotherapies is widely studied in various cancers, but their efficacy on bone metastases is not well established. In this study, we aimed to evaluate the efficacy of immunotherapies in comparison to standard-of-care compounds in a preclinical TNBC bone metastasis model. Mouse 4T1-GFP TNBC cells were inoculated intracardially to immunocompetent female Balb/c mice to model bone metastasis. Treatment of single agents of chemotherapy (cyclophosphamide, 100 mg/kg), bone-targeting agent (zoledronic acid, 0.1 mg/kg), and immunotherapies programmed cell death 1 antibody (mouse anti-PD-1, 10 mg/kg) and indoleamine-pyrrole 2,3-dioxygenase (IDO) inhibitor (epacadostat, 100 mg/kg), and the combination of anti-PD-1 and epacadostat were started on the day following the cancer cell inoculations. The study was terminated about 2 weeks after the inoculations. Tumor burden was evaluated at sacrifice by GFP imaging in skeleton and soft tissues, and tumor-induced bone loss by X-ray imaging. Tumor infiltrating lymphocytes (TILs) were evaluated by immunohistochemical stainings of CD3+, CD4+ and CD8+ T cells. Cyclophosphamide decreased skeletal tumor burden and the area of tumor-induced osteolytic bone lesions. It also decreased the number of soft tissue metastases in ovaries and adrenal glands. Zoledronic acid decreased osteolytic lesion area but had no effect on tumor burden. Anti-PD-1, epacadostat and their combination had no effect on tumor burden, on the development of osteolytic lesions, or on the number of soft tissue metastases. Low number or no TILs were observed in the tumors growing in bone obtained from vehicle-treated mice. Immunotherapies did not prevent tumor growth in bone or tumor-induced bone changes in the syngeneic TNBC model. This is probably a consequence of the low number of TILs in the tumors growing in bone. Further studies are needed to evaluate the effects of treatment combinations and to increase the responsiveness to immunotherapies especially in bone metastases.

Citation Format: Tiina Emilia Kähkönen, Mari I. Suominen, Jenni H. Mäki-Jouppila, Jussi M. Halleen, Jenni Bernoulli. Efficacy of anti-PD-1, IDO inhibitor, chemotherapy and bone-targeting agent on tumor growth in a syngeneic bone metastasis model of triple-negative breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5026.

Immunotherapies and Metastatic Cancers: Understanding Utility and Predictivity of Human Immune Cell Engrafted Mice in Preclinical Drug Development

Metastases cause high mortality in several cancers and immunotherapies are expected to be effective in the prevention and treatment of metastatic disease. However, only a minority of patients benefit from immunotherapies. This creates a need for novel therapies that are efficacious regardless of the cancer types and metastatic environments they are growing in. Preclinical immuno-oncology models for studying metastases have long been limited to syngeneic or carcinogenesis-inducible models that have murine cancer and immune cells. However, the translational power of these models has been questioned. Interactions between tumor and immune cells are often species-specific and regulated by different cytokines in mice and humans. For increased translational power, mice engrafted with functional parts of human immune system have been developed. These humanized mice are utilized to advance understanding the role of immune cells in the metastatic process, but increasingly also to study the efficacy and safety of novel immunotherapies. From these aspects, this review will discuss the role of immune cells in the metastatic process and the utility of humanized mouse models in immuno-oncology research for metastatic cancers, covering several models from the perspective of efficacy and safety of immunotherapies.

Abstract B144: Lack of immunotherapy efficacy in a syngeneic bone metastasis model of triple-negative breast cancer

Background: Triple-negative breast cancer (TNBC) is an aggressive cancer with treatment options limited to standard-of-care chemotherapy. TNBC patients develop metastases in high incidence, and almost all patients have bone metastases at end-stage disease. Bone metastases are mainly osteolytic, causing severe bone loss that can be prevented by bone-targeted agents. Currently, there is no efficient cure for bone metastases. Activation of the patient’s own immune system by immunotherapies is widely studied in various cancers, but their efficacy on bone metastases is not well established. In this study, we aimed to evaluate the efficacy of immunotherapies in comparison to standard-of-care compounds in a preclinical TNBC bone metastasis model. Materials and methods: Mouse 4T1-GFP TNBC cells were inoculated intracardially to immunocompetent female Balb/c mice to model bone metastasis. Treatment of single agents of chemotherapy (cyclophosphamide, 100 mg/kg), bone-targeting agent (zoledronic acid, 0.1 mg/kg), and immunotherapies programmed cell death 1 antibody (mouse anti-PD-1, 10 mg/kg) and indoleamine-pyrrole 2,3-dioxygenase (IDO) inhibitor (epacadostat, 100 mg/kg), and the combination of anti-PD-1 and epacadostat were started on the day following the cancer cell inoculations. The study was terminated 12-13 days after the inoculations. Tumor burden was evaluated by GFP imaging and tumor-induced bone loss by X-ray imaging at sacrifice. Tumor infiltrating lymphocytes (TILs) were evaluated by immunohistochemical stainings of CD3+, CD4+ and CD8+ T cells. Results: Cyclophosphamide decreased skeletal tumor burden and the area of tumor-induced osteolytic bone lesions. Zoledronic acid decreased the area of osteolytic lesions but had no effect on skeletal tumor burden. Anti-PD-1, epacadostat and their combination had no effect on skeletal tumor burden or in the development of osteolytic lesions. Low number or no TILs were observed in the tumors growing in bone obtained from vehicle-treated mice. Conclusions: Immunotherapies did not prevent tumor growth in bone or tumor-induced bone changes in the syngeneic TNBC model. This is probably caused by the low number of TILs in the tumors growing in bone. Further studies are needed to evaluate the effects of treatment combinations and to increase the responsiveness to immunotherapies especially in bone metastases.

Citation Format: Tiina E Kähkönen, Mari I Suominen, Jenni HE Mäki-Jouppila, Jussi M Halleen, Jenni Bernoulli. Lack of immunotherapy efficacy in a syngeneic bone metastasis model of triple-negative breast cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr B144. doi:10.1158/1535-7163.TARG-19-B144

Abstract B143: Establishment of primary tumor models of TNBC and ER+/HER2- breast cancer in humanized mice and validation of pembrolizumab efficacy

Background: Immunotherapy is an emerging treatment option for different subtypes of breast cancer. Pembrolizumab (Keytruda®) targets PD-1 expressing T cells in tumors and mediates anti-tumor effects. Targeting PD-1 has shown promising results in advanced breast cancer and is being evaluated in clinical trials in triple-negative breast cancer (TNBC) and in estrogen receptor positive, human epidermal growth factor 2 negative (ER+/HER2-) breast cancer patients. Immunotherapy is not yet an established treatment option for early breast cancer. The aim of this study was to establish preclinical primary tumor models for TNBC and ER+/HER2- in humanized mice, and to evaluate efficacy of pembrolizumab in the models. Materials and methods: Immunodeficient CIEA NOG female mice engrafted with human CD34+ hematopoietic stem cells (huNOG mice) were inoculated orthotopically into mammary fat pad with either MDA-MB-231(SA) (TNBC) or MCF-7 (ER+/HER2-) human breast cancer cells. The mice receiving MCF-7 cells were implanted with estradiol (E2) releasing pellets before cancer cell inoculation to support tumor growth. The mice were treated with pembrolizumab (5 mg/kg) or isotype control in a Q5D schedule. The treatments were started 3 or 14 days after cancer cell inoculation in the TNBC and ER+/HER2- models, respectively. Tumor growth was monitored by caliper measurements, and the study was terminated at 3 weeks (TNBC model) or 7 weeks (ER+/HER2- model). Tumors were collected and analyzed immunohistochemically for tumor-infiltrating lymphocytes (TILs), and hematological analysis was performed from the mice in the ER+/HER2- model. Results: Tumors responded to pembrolizumab treatment in the TNBC model. Three out of eight mice responded to the treatment and one of them had a tumor rejection. Pembrolizumab treatment was associated with decrease in CD8+ TILs and granzyme B+ cells in the tumor. In the ER+/HER2- model, E2 supplementation was essential for tumor growth. However, E2 caused a decrease in the clinical condition, including decrease in white and red blood cells, leading to early sacrifices. Only modest responses for pembrolizumab were observed in a few mice and the results did not reach statistical significance. No major changes were observed in TILs due to pembrolizumab treatment. Conclusions: In the established breast cancer models in humanized mice, pembrolizumab decreased tumor growth in the TNBC model but induced only minor tumor responses in the ER+/HER2- model. Estrogen was essential for ER+/HER2- tumor growth but induced severe anemia and had immunomodulatory effects potentially influencing the lack of pembrolizumab efficacy in the model.

Citation Format: Tiina E Kähkönen, Mari I Suominen, Jenni HE Mäki-Jouppila, Azusa Tanaka, Philip Dube, Michael Seiler, Jussi M Halleen, Jenni Bernoulli. Establishment of primary tumor models of TNBC and ER+/HER2- breast cancer in humanized mice and validation of pembrolizumab efficacy [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr B143. doi:10.1158/1535-7163.TARG-19-B143

Abstract LB-A01: Establishment of a novel prostate cancer bone metastasis model in humanized mice and early efficacy results of pembrolizumab

Background: Programmed cell death 1 (PD-1) and programmed death ligand 1 (PD-L1) expression is typically low in primary prostate cancer but increases at advanced stages. However, targeting PD-1 or PD-L1 has not proven efficacy in prostate cancer patients, and recent clinical trials are directed to combination therapies. About 85% of advanced prostate cancer patients develop skeletal metastases, and the focus in this context should be addressed to the treatment of these metastases. These efforts have been hindered by the lack of relevant preclinical bone metastasis models in immunocompetent mice. We aimed to establish a prostate cancer bone metastasis model in humanized mice and to assess pembrolizumab efficacy in the established model. Materials and methods: Two million LNCaP human prostate cancer cells were inoculated into tibia bone marrow of male CIEA NOG® mice engrafted with human CD34+ hematopoietic stem cells to generate humanized mice. Serum prostate-specific antigen (PSA) levels were measured at 4 weeks, and the mice were allocated to receive either pembrolizumab (anti-PD-1, Keytruda®, 5 mg/kg, Q5D) or human IgG4 isotype control for 6 weeks. Tumor growth was monitored by measuring serum PSA levels. Tumor-induced bone changes were monitored by measuring serum levels of the bone formation marker N-terminal propeptide of type I procollagen (PINP), and by X-ray imaging of tibia. Changes in quantity of circulating T cells was monitored by flow cytometry. At study termination, tissue samples were collected for histological and immunohistochemical evaluation of tumor-infiltrating lymphocytes (TILs). Results: A tumor take of 90% was observed in the humanized mice evaluated by serum PSA levels at endpoint. No significant differences were observed in serum PSA levels, but in a few mice treated with pembrolizumab, only modest tumor growth was observed. Intratibial LNCaP tumors induced osteoblastic-mixed lesions as evaluated by X-ray imaging. No differences were observed in the bone lesion area or in serum PINP levels between the isotype control and pembrolizumab groups. No changes in circulating levels of CD4+, CD8+, or CD4+CD8+ cells were observed. Histology will be performed to confirm tumor morphology and overall tumor viability, and immunohistochemical analysis will reveal the quantity and location of TILs in the tumor. Conclusions: A novel preclinical model of bone metastasis in humanized mice was established. Intratibial prostate cancer tumors induced osteoblastic mixed bone lesions and increased serum PSA levels, mimicking the clinical situation in patients. Resembling recent clinical findings, no or modest responses with pembrolizumab as monotherapy were observed.

Citation Format: Tiina E Kähkönen, Mari I Suominen, Jenni HE Mäki-Jouppila, Azusa Tanaka, Philip Dube, Jussi M Halleen, Jenni Bernoulli. Establishment of a novel prostate cancer bone metastasis model in humanized mice and early efficacy results of pembrolizumab [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr LB-A01. doi:10.1158/1535-7163.TARG-19-LB-A01

Abstract 4588: Characterization of anti-CTLA-4 effects on tumor growth and immune microenvironment in a syngeneic CT26.WT colon carcinoma mouse model

Colorectal cancer is the third most common type of cancer and one of the leading causes of cancer related deaths. It is a group of various diseases at molecular level, which can make targeted drug development challenging. However, novel therapeutics including immunotherapies have shown their potential to be utilized in the future also when treating colorectal cancer. One promising example is ipilimumab, a monoclonal antibody targeting CTLA-4 (cytotoxic T lymphocyte antigen-4, also known as CD152). CTLA-4 is a cell surface receptor expressed on activated T and B lymphocytes. It regulates immunological tolerance and downregulates immune responses. The aim of the study was to characterize the effects of anti-CTLA-4 on tumor growth, survival and tumor immune microenvironment of mice subcutaneously inoculated with mouse colon carcinoma CT26.WT cells.

CT26.WT cells were subcutaneously inoculated into female Balb/c mice (n=27). Body weights and tumor dimensions were determined two times a week during the course of the study. The mice were randomized to three groups (n=9/group) with similar tumor volume and variation and dosing was started when an average tumor size of approximately 50 mm³ was reached (day 7). Anti-CTLA-4 antibody (9D9, 10 mg/kg), an isotype control (mouse IgG2b) and vehicle (PBS) were administered (i.p.) twice a week. Tumor growth and survival were followed for 26 days after inoculation of the cancer cells. The mice were sacrificed individually when the maximum tumor volume (1500 mm³) was reached, the tumors were ulcerated or at the latest on study day 26. Tumor samples were collected for histological and immunohistochemical analysis and stained for helper T cells (CD4), cytotoxic T cells (CD8), myeloid-derived suppressor cells (MDSC; CD11b), tumor-associated macrophages (F4/80), and inflammatory monocytes and neutrophils (FCGR1/CD64) for characterization of tumor immune microenvironment.

Maximum tumor volume and tumor ulceration were observed the earliest on study day 17. Anti-CTLA-4 suppressed tumor growth, and all mice in the group receiving anti-CTLA-4 were still in the study on day 26. Only one and four mice were left in the vehicle and isotype control groups, respectively. Immunohistochemical staining suggested an increase of CD4+ tumor-infiltrating lymphocytes (TILs) in anti-CTLA-4 treated mice. Furthermore, more TAMs were observed in tumors of anti-CTLA-4 treated mice, especially in the borderlines of necrotic areas. Large quantity of CD11b+ MDSCs and inflammatory cells were observed in CT26.WT tumors.

CT26.WT subcutaneous model can be utilized for studying the effects of immunotherapies, and anti-CTLA-4 treatment suppressed tumor growth in this model. CT26.WT tumors represent a highly immunogenic hot tumor type with high immune cell infiltration, associated with a good efficacy of anti-CTLA-4 treatment in the model.

Citation Format: Jenni H. Mäki-Jouppila, Tiina E. Kähkönen, Mari I. Suominen, Jussi M. Halleen, Jenni Bernoulli. Characterization of anti-CTLA-4 effects on tumor growth and immune microenvironment in a syngeneic CT26.WT colon carcinoma mouse model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4588.

Abstract 2161: In vitro osteoblast assays for studying the effects of cancer therapeutics on bone biology

Bone cell activity is an important factor in regulating bone metastases from tumor cells in the skeletal environment. When cancer cells home to bone they secrete factors that stimulate osteoclast activity leading to increased bone resorption. Bone then releases stimulatory factors that in turn promote the growth and proliferation of cancer cells. This process is called the vicious cycle often leading to osteolytic lesions in bone when osteoclastic bone resorption exceeds osteoblastic bone formation. Osteolytic lesions are common in breast and lung cancer and multiple myeloma. There is a vicious cycle between cancer cells and bone cells also in the context of osteoblastic lesions. In osteoblastic metastases, the vicious cycle observed in osteolytic disease takes place but in addition to this cancer cells produce osteoblast-stimulating factors including bone morphogenetic protein (BMP), epidermal growth factor (EGF) and platelet derived growth factor (PDGF). Osteoblasts also influence osteoclasts by producing RANKL, which stimulates osteoclast differentiation. Many cancer patients with bone metastasis have both osteolytic and osteoblastic lesions. This is common for example in prostate cancer. Our aim was to establish an in vitro cell culture model to study the effects of compounds on osteoblast differentiation and activity.

A mouse osteoblast progenitor cell line KS483 was used in the study. BMP-2 was used as a test compound and was added in the beginning of culture and simultaneously with culture medium change every 3-4 days. Ascorbic acid was added into the cell culture medium at day 4. In the osteoblast differentiation assay, the activity of cellular alkaline phosphatase (ALP), a marker of osteoblast differentiation, was measured at day 8 from cell lysates. Total protein content was measured from the same samples. In the osteoblast activity assay, KS483 mouse osteoprogenitor cells were cultured for 13 days, during which N-terminal propeptide of type I procollagen (PINP) secreted into the culture medium was determined at day 11 to demonstrate effects on organic bone matrix formation. β-glycerophosphate was added to the culture at day 11. The cultures were stopped at day 13 by removing the culture media from the wells and adding hydrochloric acid. Calcium deposition, a marker of inorganic bone formation, was determined at the end of the study.

BMP-2 stimulated osteoblast differentiation and activity shown by the increase in ALP, PINP and calcium levels. The results suggest that the KS483 cell line can be used for setting up reliable in vitro models of osteoblast differentiation and activity. These osteoblast assays can be used for studying the effects of compounds on bone formation and cancer related bone events.

Citation Format: Jenni H. Mäki-Jouppila, Jussi M. Halleen, Katja Fagerlund. In vitro osteoblast assays for studying the effects of cancer therapeutics on bone biology [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2161.

Abstract 4850: The relevance of using proper preclinical models when developing therapeutics for localized or bone metastatic prostate cancer

Early stages of prostate cancer are sensitive to androgen deprivation therapy, but upon progression the disease develops to metastatic castration-resistant prostate cancer, where bone is the dominant metastatic site. Despite of recent advances in drug development, the advanced stage is still incurable. Tumor microenvironment in metastatic locations differs from the primary site and may cause resistance to used therapy and modulate tumor properties. Therefore, it is crucial to use proper models in preclinical drug development. Aim of this study was to establish predictive preclinical in vitro and in vivo prostate cancer models that can be used in drug development when targeting cancer cells or tumor microenvironment at different stages. Androgen receptor (AR) positive human prostate cancer cell line LNCaP was used in all studies. In the in vitro assay, the effects of the antiandrogen enzalutamide on viability of LNCaP cells was determined using CellTiter Glo assay in the presence and absence of a synthetic androgen R1881. In two in vivo studies, male NMRI nude mice were used. In a subcutaneous model, part of the mice received dihydrotestosterone (DHT) supplement prior to cancer cell inoculation. In a bone metastasis model, LNCaP cells were inoculated into tibia bone marrow. The mice were randomized to treatment groups based on similar serum PSA levels and cancer-induced changes in bone determined by X-ray imaging at 6 weeks after inoculation of the cancer cells. The mice were treated with 300 kBq/kg of Radium-223 dichloride or vehicle at 6 and 10 weeks. Bone lesions were followed by X-ray imaging during the study. The study was terminated at 12 weeks after inoculation of the cancer cells and the tibias were removed for histological analysis and AR staining. In the in vitro assay, 0.1 and 0.01 nM R1881 increased LNCaP cell viability, and enzalutamide reduced cell viability in the presence of R1881 compared to the group with only R1881. In the subcutaneous model, tumors formed within 2-3 weeks after inoculation and the maximum tumor volume was reached within 10-12 weeks. LNCaP tumors grew in NMRI nude mice without DHT supplement, but DHT supplement supported tumor growth. In the bone metastasis model, LNCaP tumors induced osteoblastic-mixed bone lesions without additional androgen supplement, and immunohistochemical staining demonstrated strong AR expression. Radium-223 dichloride reduced the progression of tumor-induced bone lesions, decreased serum PSA levels, and decreased tumor area analyzed by histology. This study showcases relevant models that can be used at different phases of preclinical drug development when evaluating efficacy or safety of new therapeutics as mono- or combination therapies. The choice of a preclinical model and key readouts should be carefully selected based on whether developing therapeutics for localized or metastatic prostate cancer.

Citation Format: Tiina E. Kähkönen, Jenni H.E. Mäki-Jouppila, Mari I. Suominen, Jussi M. Halleen, Jenni Bernoulli. The relevance of using proper preclinical models when developing therapeutics for localized or bone metastatic prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4850.

Abstract 4616: Establishment of a metastatic orthotopic model of pancreatic ductal adenocarcinoma (PDAC) for drug development

Ductal adenocarcinoma of the pancreas (PDAC) has the worst survival prognosis (<5%) of all common gastrointestinal malignancies. PDAC is typically diagnosed at a very late stage when the tumor has already metastasized to other organs, at which point the treatment can no longer prolong the survival of the patients. To date, surgical resection is the only curative approach present, provided that the cancer is detected at a very early stage. Nonetheless, less than 20% of diagnosed patients qualify for the surgery and majority of these patients will eventually develop recurrence. Despite our advancing knowledge of the tumor biology of PDAC as well as recent improvements in diagnosis, the prognosis remains strikingly poor. The median survival observed after surgery followed by chemotherapy is about 20 months.The aim of this study was to establish an orthotopic model of PDAC that could be used to study efficacy of new potential treatments. Female athymic nude mice (Hsd: Athymic Nude-Foxn1nu) were used in this study. MiaPaCa-2-Luc human PDAC cells were injected to surgically exposed caudal part of the pancreas. At the time of inoculation, the animals were 4-5 weeks of age. To validate the model, the current standard-of-care (SOC) treatment (combination of nab-paclitaxel and gemcitabine) was used. During the study, tumor burden was quantified by imaging the bioluminescence signal emitted by the MiaPaCa-2-luc cells using IVIS Lumina II imaging system. After 30 days in study, tumor growth in the surgical area was observed. The mice were stratified to treatment groups based on similar intensity of the bioluminescent readout. Imaging was performed every second week after inoculation of the cells. The SOC treatment was initiated two weeks post inoculation and was administered twice a week over a period of 4-5 weeks. The observed tumor take rate was 100%. At sacrifice, tumor weight and volume were lower in the group receiving the SOC treatment as compared to the vehicle treated group. Although there were no differences in body weights, mice receiving the SOC treatment gained less weight when comparing the body weights obtained at endpoint relative to baseline. As confirmed by histological analyses at endpoint, the MiaPaCa-2-luc cells induced micrometastasis to other visceral organs including liver. In conclusion, a metastatic orthotopic PDAC model was established successfully and validated with the SOC treatment that slowed down disease progression. Therefore, this orthotopic model provides a promising tool for testing new treatments against PDAC in vivo.

Citation Format: Justyna Zdrojewska, Jenni H.E. Mäki-Jouppila, Jussi M. Halleen, Jenni Bernoulli. Establishment of a metastatic orthotopic model of pancreatic ductal adenocarcinoma (PDAC) for drug development [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4616.

Abstract 2814: Systemic and local bone metastasis models for immuno-oncology drug development

Bone metastases are common and count 30-70% of metastases in breast, lung, and bladder cancer, and 80% of multiple myeloma patients have bone disease. Despite recent progress in cancer treatment, bone metastases remain incurable. Novel immunotherapies have the potential to cure also bone metastatic disease. Here we have established and validated syngeneic models with a focus on bone metastasis that could be used in preclinical efficacy studies. Syngeneic models were established for breast (4T1-GFP), multiple myeloma (5TGM1), bladder (MBT-2) and lung cancer (KLN-205). The cells were inoculated into systemic circulation (4T1 intracardially and 5TGM1 into tail vein) or bone marrow (MBT-2 and KLN-205). In the 4T1 model, tumor burden was assessed by ex vivo GFP imaging and in the 5TGM1 model by measuring serum IgG2b paraprotein levels during the study. Tumor-induced bone changes were followed by X-ray imaging in all models. Hind limbs were analyzed by histology and immunohistochemistry for tumor-infiltrating lymphocytes (TILs). The effects of standard-of-care compounds were assessed in the 4T1 (cyclophosphamide, 100 mg/kg or zoledronic acid, 0.1 mg/kg) and 5TGM1 (bortezomib, 1 mg/kg) models. The effect of anti-PD-1 treatment (200 µg/dose) was evaluated in the MBT-2 model. In the 4T1 model, osteolytic bone lesions formed within 13 days. In addition to bone metastases, about 50% of the mice had metastases in lungs, ovaries, kidneys and adrenal glands based on GFP imaging. Cyclophosphamide decreased the tumor burden and the area of osteolytic bone lesions. Zoledronic acid decreased the osteolytic lesion area but had no effect on tumor burden. Low number or no TILs were observed. In the 5TGM1 model, osteolytic lesions were observed and the study was ended at day 35. Metastases in ovaries, kidneys and adrenal glands were observed in about 30% of the mice. Bortezomib decreased serum paraprotein compared to vehicle treated mice. In both models, cachexia and paraplegia were occasionally observed. Moderate number of CD3+ TILs were observed in the tumors. In the intratibial MBT-2 and KLN-205 models, large osteolytic lesions were observed within 25 days, and in the KLN-205 model also lung metastases were observed. Anti-PD-1 treatment decreased osteolytic tumor area in the MBT-2 model. Moderate number of CD3+ and low number of CD4+ and CD8+ TILs were observed in the tumors growing in bone and also in the lung metastases. A high incidence of bone metastases was observed in all models. The use of systemic models allows studying the effects of test compounds in prevention or treatment of metastases. Intratibial models can be used when the primary interest is in tumor growth in bone microenvironment. Mimicking the clinical situation, none of the SOC compounds could prevent tumor growth completely, and therefore combination therapies are warranted for better overall efficacy.

Citation Format: Tiina E. Kähkönen, Mari I. Suominen, Jenni H. Mäki-Jouppila, Jussi M. Halleen, Arne Scholz, Jenni Bernoulli. Systemic and local bone metastasis models for immuno-oncology drug development [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2814.

Abstract 2007: Validation of a preclinical model for bone metastatic triple negative breast cancer

Metastatic breast cancer (MBC) is the most advanced stage of breast cancer, diagnosed as stage IV. Typically, MBC metastases occur in the bones, liver, brain, and lungs. Bone metastases cause significant morbidity and mortality in late-stage breast cancer patients. At present, there is no efficient curative or preventive treatment for bone metastases. Therefore, establishment and validation of well characterized in vivo models of breast cancer bone metastasis is of utmost importance. The aim of this study was to validate an intracardiac model of bone MBC utilizing GFP tagged triple negative (estrogen receptor; ER, progesterone receptor; PR and human epidermal growth factor receptor 2; HER2 negative) human breast cancer cells, which could be used to study efficacy of new potential treatments. Female athymic nude mice (Hsd: Athymic Nude-Foxn1nu) were used in this study. Bone seeking MDA-MB-231(SA)-GFP human breast cancer cells were inoculated into the left cardiac ventricle of 4-6 weeks old female mice. Allocation to treatment groups (n=15) was performed by stratification procedure based on animal weight prior to the beginning of the study. To validate the model, the current standard-of-care (SOC) treatment (Paclitaxel) was administered between study days 13-17 at the therapeutic dose. Serum bone biomarker TRACP5b was measured before cancer cell inoculation and at sacrifice. Planar X-ray of hind limbs and ex vivo fluorescence imaging of the whole body were performed at sacrifice. The observed tumor take rate was 100%. 33% of mice in the vehicle group were cachectic, but mice treated with SOC exhibited only mild and temporary weight loss. Tumors were observed mainly in skeletal sites but also in soft tissues. The SOC treatment decreased both total and skeletal tumor burden. Based on X-ray images, tumor induced osteolytic bone lesions were smaller in the SOC treated group compared to vehicle though no differences were observed in total bone lesion area. Serum TRACP5b was increased in the vehicle group as a result of osteolytic lesions, and decreased with the SOC treatment. In conclusion, an intracardiac model of MBC was successfully validated with the SOC treatment paclitaxel that efficiently inhibited disease progression. Therefore, this intracardiac model provides a promising tool for testing new treatments against bone and soft tissue MBC in vivo.

Citation Format: Justyna Zdrojewska, Mari I. Suominen, Katja M. Fagerlund, Jussi M. Halleen, Jenni Bernoulli, Johann Zimmermann. Validation of a preclinical model for bone metastatic triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2007.

Abstract 4614: Establishment of a HER2 positive breast cancer bone metastasis model for validation of novel therapies

Breast cancers with overexpression of human epidermal growth factor receptor 2 (HER2+) have aggressive clinical behavior, and at advanced stages are associated with increased risk for developing metastases to distant organs including bones, brain and lungs. The aim of this study was to establish a systemic metastasis model for HER2+ breast cancer with a special interest in bone metastasis. The effects of cell number, estrogen supplementation and mouse strain on metastasis formation were studied.

In the study, 5-6 weeks old athymic nude and Rag2 mice (n=10-13 per group) were used. Half of the mice received estrogen supplementation (E2-releasing rods 5µg/day) one week before inoculation of the cancer cells. The mice were inoculated intracardially with 1 or 5 x 105 luciferase-labelled triple-positive (ER, PR positive and HER2 overexpressing) human BT-474 breast cancer cells. The formation of metastases was followed by bioluminescence imaging (BLI) at inoculation and once a week for the duration of the study. At sacrifice, X-ray imaging was performed and the bones were collected for histological analysis.

The formation of bone metastases was observed in all study groups, and bone metastases were dominant in the model. Based on BLI, bone metastases developed in nude mice earlier than in Rag2 mice. However, detection of metastases in Rag2 mice was challenging due to dark fur hindering the signal transmittance. The bone metastases appeared between 7 to 36 days after inoculation of the cancer cells in nude mice and between 20 to 43 days in Rag2 mice. The number of bone metastases was higher in nude mice. E2 supplement accelerated the development of bone metastases in both mouse strains. In nude mice with E2 supplement, bone metastases appeared between 7 to 14 days compared to between 20 to 36 days in mice without E2 supplement. In Rag2 mice with E2 supplement bone metastases formed between 20 to 28 days compared to between 36 to 43 days without E2 supplement. The use of higher cell number accelerated the development of bone metastases but had no major effect on their incidence in both mouse strains. Take rate of bone metastases was 90-100% in nude mice with E2 supplement compared to 30-50% without E2 supplement. In Rag2 mice, the take rate of bone metastases was 50% with E2 supplement. X-ray imaging showed estrogen induced bone growth and large tumor-induced osteolytic lesions in the hind limbs in both strains. Due to the extensive bone lesions and occasional fractures, the first mice were sacrificed 50 days after inoculation of the cancer cells. Both mouse strains occasionally developed metastases in soft tissues including brain and ovaries.

In conclusion, a high rate of bone metastasis was achieved in athymic nude mice supplemented with E2. This model can be used to study the efficacy of anti-cancer, such as HER2-targeted, compounds on tumor growth at metastatic locations or on the prevention of metastasis formation.

Citation Format: Tiina E. Kähkönen, Mari I. Suominen, Jenni H. Mäki-Jouppila, Jussi M. Halleen, Jenni Bernoulli, Derek Grant. Establishment of a HER2 positive breast cancer bone metastasis model for validation of novel therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4614.

Abstract 3936: Efficacy of single agent radium-223 in the syngeneic MBT-2 bladder cancer bone growth model in mice

Radium-223 dichloride (Ra-223, Xofigo®) is a targeted alpha therapy which prolongs the survival of castration-resistant prostate cancer (CRPC) patients with symptomatic bone metastases. As a calcium-mimetic, Ra-223 selectively binds to hydroxyapatite and targets areas of high bone turnover such as bone metastases. Here, we report the effects of Ra-223 on development and progression of osteolytic bone lesions and on survival in the syngeneic intratibial MBT-2 murine bladder cancer model in immunocompetent mice.

Female 5-7-week-old C3H/HeNHsd mice were injected intratibially with 5x105 MBT-2 cells on day 0. The mice were stratified based on body weight (n=40 per group) on day 5 and Ra-223 (300 kBq/kg, i.v.) or vehicle control was administered on days 5, 33, and 61. The tumor-induced osteolytic lesion area was imaged using radiography on days 10, 18, 25, 76, and at sacrifice. The mice were sacrificed when they met the pre-defined sacrifice criteria (> 20% body weight loss, palpable tumor outgrowth from the bone or general deterioration of health status). The study was terminated on day 158.

In this study, the first mice met the sacrifice criteria on study day 24 and the survival curves plateaued at 52% after 84 days in the control group and at 68% after 112 days in the Ra-223 treatment group. Survival on day 40 was significantly improved in the Ra-223 treatment group compared to the vehicle control (p< 0.001), but the effect was not statistically significant at the end of the study. Based on X-ray imaging 25 days after cancer cell inoculation, Ra-223 treatment also significantly decreased the bone lesion area compared to the vehicle treatment (p=0.0041). After initially sacrificing the mice with extensive bone lesions, tumor growth in bone was stabilized around day 25. The main reason for sacrifice at a later stage was breathing difficulties due to lung metastases, and in the Ra-223-treated mice only one mouse was sacrificed due to bone metastases. Ra-223 treatment was well-tolerated; no body weight loss was observed.

In summary, radium-223 dichloride (Xofigo®) demonstrates moderate single agent in vivo efficacy in the intratibial MBT-2 murine bladder cancer model of osteolytic bone metastasis. Retaining a functional immune system in syngeneic mouse models is particularly relevant for the characterization of potential immune-stimulatory effects of Ra-223. The promising results obtained in this model warrant further investigation of Ra-223 in combination with immuno-oncological treatments like checkpoint inhibitors.

Citation Format: Tiina E. Kähkönen, Mari I. Suominen, Jenni H. Mäki-Jouppila, Birgitta Sjöholm, Ilmari Ahonen, Dominik Mumberg, Karl Ziegelbauer, Jussi M. Halleen, Sanna-Maria Käkönen, Arne Scholz. Efficacy of single agent radium-223 in the syngeneic MBT-2 bladder cancer bone growth model in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3936.

Dovitinib dilactic acid reduces tumor growth and tumor-induced bone changes in an experimental breast cancer bone growth model

Advanced breast cancer has a high incidence of bone metastases. In bone, breast cancer cells induce osteolytic or mixed bone lesions by inducing an imbalance in bone formation and resorption. Activated fibroblast growth factor receptors (FGFRs) are important in regulation of tumor growth and bone remodeling. In this study we used FGFR1 and FGFR2 gene amplifications containing human MFM223 breast cancer cells in an experimental xenograft model of breast cancer bone growth using intratibial inoculation technique. This model mimics bone metastases in breast cancer patients. The effects of an FGFR inhibitor, dovitinib dilactic acid (TKI258) on tumor growth and tumor-induced bone changes were evaluated. Cancer-induced bone lesions were smaller in dovitinib-treated mice as evaluated by X-ray imaging. Peripheral quantitative computed tomography imaging showed higher total and cortical bone mineral content and cortical bone mineral density in dovitinib-treated mice, suggesting better preserved bone mass. CatWalk gait analysis indicated that dovitinib-treated mice experienced less cancer-induced bone pain in the tumor-bearing leg. A trend towards decreased tumor growth and metabolic activity was observed in dovitinib-treated mice quantified by positron emission tomography imaging with 2-[¹⁸F]fluoro-2-deoxy-D-glucose at the endpoint. We conclude that dovitinib treatment decreased tumor burden, cancer-induced changes in bone, and bone pain. The results suggest that targeting FGFRs could be beneficial in breast cancer patients with bone metastases.

Abstract 1738: PD-1/PD-L1 expression and tumor-infiltrating immune cells in triple-negative breast cancer: Characterization of preclinical primary tumor and bone metastasis models in humanized mice

Expression of programmed cell death-1 receptor (PD-1), programmed death-ligand 1 (PD-L1) and tumor-infiltrating lymphocytes (TILs) in triple-negative breast cancer (TNBC) have been shown in many studies supporting development of immunotherapies against TNBC. In order to develop novel immunotherapies especially against bone metastatic TNBC, better understanding of PD-1/PD-L1 axis, TILs, and tumor associated macrophages (TAMs) in the bone microenvironment is warranted. Aim of this study was to characterize immune cell reaction between TNBC primary tumor and bone metastasis in humanized mice to support immunotherapy drug discovery against bone metastasis.

MDA-MB-231(SA) human breast carcinoma cells were inoculated into mammary fat pad or tibia of female CIEA NOG mice engrafted with human pluripotent CD34+ cells and tumor growth was followed for 3 weeks. Immunohistochemical stainings of primary tumors and intratibial tumors were performed against human specific antigens to characterize expression of PD-1, PD-L1, Granzyme B, CD4, CD8 and CD68/CD163. TILs and TAMs were assessed by 4-scale immunoscoring system and PD-L1 expression was determined by Tumor Proportion Scoring (TPS). PD-L1 positivity of the TAM's was omitted in TPS interpretation.

Carcinoma cells of orthotopical tumors exhibited mainly low or moderate heterogeneous expression of PD-L1 (TPS score 1-49%). Moderate or high numbers of CD4 and CD8 positive TILs (scoring 2-3) and low PD-1 expression were observed. Granzyme B expression correlated with CD8 positivity. In comparison, when MDA-MB-231(SA) carcinoma cells were inoculated into bone marrow, tumors had corresponding PD-L1 expression and tumor-infiltrating CD4+ and granzyme B+ human immune cells were observed. However, in the bone microenvironment less CD8+ immune cells were observed and PD-1 expression was negative. When analyzing all tumor area, intratumoral and peritumoral variation of the marker expression and cell location of TILs and TAMs was observed especially in the bone tumors but also in the primary tumors. TILs and TAMs occurred in scattered as well as aggregate form in tumor area.

Taken together, TNBC primary tumors and bone metastases had mainly low or moderate, but clear membranous expression of PD-L1. TILs consisted of CD4+, CD8+, and granzyme B+ cells in the primary tumors, but less CD8+ cells were observed in the bone metastases. PD-1 expression was negative in bone metastases. The obtained results comparing primary tumor and bone metastasis highlights the importance of understanding the influence of tumor microenvironment. Immune system is not only strong regulator of cancer progression, but it also regulates bone turnover. Therefore, it is crucial to use predictive preclinical models when assessing novel immunotherapies.

Citation Format: Tiina E. Kähkönen, Mari I. Suominen, Jussi M. Halleen, Azusa Tanaka, Michael Seiler, Teppo Haapaniemi, Jenni Bernoulli. PD-1/PD-L1 expression and tumor-infiltrating immune cells in triple-negative breast cancer: Characterization of preclinical primary tumor and bone metastasis models in humanized mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1738.

Abstract 3859: Hormone receptor and HER2/HER3 expression in preclinical breast cancer models of primary tumor and bone metastasis

Breast cancer expressing estrogen receptor (ER) and progesterone receptor (PR) is classified as hormone receptor positive, and triple-positive breast cancer expresses also human epidermal growth factor receptors (HER2). Despite the hormonal and HER2 targeted treatments, breast cancer metastasizes to bone in high frequency and may develop resistance against the used treatment. Prevention and treatment of bone metastases is challenging and moreover, hormones are strong regulators of both bone and immune system. Aim of the present study was to verify and compare ER, PR, HER2 and also HER3 status in preclinical primary and bone metastasis breast cancer models utilizing immunodeficient and human immune system engrafted mice.

BT-474 human breast cancer cells were inoculated orthotopically into mammary fat pad of placebo or 17β-estradiol (E2) supplemented female immunodeficient NOG mice. In a bone tumor study, BT-474 cells were inoculated into the tibia of female NOG or humanized NOG mice (HSCFTL-NOG-F mice, Taconic Biosciences). Tumor growth was followed for 8 weeks and histopathological tumor evaluation and immunohistochemical stainings for ER, PR, HER2 and HER3 were performed.

Orthotopic tumor growth of BT-474 was hormone dependent and only minor growth was observed in the absence of E2. In the presence of E2 supplement, the orthotopic tumor expressed ER, PR and HER2/HER3. However, in the absence of E2 supplement there was reduced PR expression but no major changes in the ER and HER2/HER3 expression. In contrast, when breast cancer cells were inoculated into the tibia, tumor growth was observed also without E2 supplement. In this case, tumor in the bone was positive for ER and HER2/HER3 but negative for PR. No significant changes were observed between immunodeficient and humanized mice regarding intratibial tumor growth or ER, PR and HER2/HER3 expression.

As a summary, estrogen supplementation is needed to support breast cancer BT-474 tumor growth when cancer cells are inoculated orthotopically into mammary fat pad. In contrast, BT-474 tumor growth was observed in bone also in the absence of supplied E2 in immunodeficient and humanized mice. ER and HER2/HER3 expression was observed in primary and bone tumors, but PR expression was significantly reduced if no estrogen supplement was used. Taking together, when developing new therapies against breast cancer, treatment targets in preclinical models should be carefully verified. Focus should be addressed not only on primary tumor but also on bone metastasis where cancer cells are under influence of different tumor microenvironment and may express differently hormone receptors and HER2/HER3. While hormones influence breast cancer progression, they also regulate bone turnover and immune system, and therefore humanized mouse models provide an essential platform for novel therapy development.

Citation Format: Tiina E. Kähkönen, Mari I. Suominen, Jussi M. Halleen, Jenni H. Mäki-Jouppila, Azusa Tanaka, Michael Seiler, Teppo Haapaniemi, Jenni Bernoulli. Hormone receptor and HER2/HER3 expression in preclinical breast cancer models of primary tumor and bone metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3859.

Abstract 709: Anti-PD-1 therapy reduces bone lesion growth in a novel syngeneic bladder cancer bone metastasis model

Bladder cancer is a common and aggressive type of cancer occurring both in women and in men. At diagnosis, lymph node involvement is frequently observed and in some cases metastatic spread can already be seen at early stage. With advanced stages, the metastatic incidence increases and the most common metastatic sites are bones, lung, liver and peritoneum. Bone metastases count about 50% of all metastases and the 5-year survival rate in metastatic disease is only 15%. Bone metastases are incurable but can be treated to reduce tumor burden in bone, and new therapies such as immunotherapies hold the potential to treat patients with bone metastatic bladder cancer. The aim of the study was to establish a novel syngeneic model for bladder cancer bone metastasis that could be used to study efficacy of new immunotherapies, and to test efficacy of anti-PD-1 therapy in the model.

In the model establishment study, an intratibial injection of varying number of murine MBT-2 bladder cancer cells was given to 5-6 weeks old female C3H/HeN mice. Tumor-induced bone changes were followed by X-ray imaging once a week. At sacrifice, tumor-bearing tibias were collected and evaluated by histology. In the efficacy study, 5x105 MBT-2 cells were used. The mice were stratified to treatment groups based on similar bone lesion areas at 10 days after cancer cell inoculations and treated with anti-PD-1 therapy (RMP1-14) or isotype control (rat IgG2a, 200 µg per dose) at Q3D schedule. Bone lesion growth was followed by X-ray imaging one week after start of treatment and at sacrifice after three weeks on treatment.

In the model establishment study, tumor take rate of 50% was observed. MBT-2 cells induced an osteolytic bone reaction resulting in substantial bone loss in the mice. The osteolytic bone lesions started to be visible between 7-14 days and the maximum duration of the study was 4 weeks from the cancer cell inoculations. Histology confirmed a large tumor and decreased bone mass in the inoculated tibia. In the efficacy study, treatment with anti-PD-1 reduced bone lesion growth. A trend towards decreased bone lesion area was seen already at one week on treatment and a significant reduction of bone lesion area was seen at sacrifice.

A novel syngeneic bladder cancer bone metastasis model was established. According to the observed significant effects on bone lesion growth by anti-PD-1 treatment this model can be used in preclinical efficacy assessment of new immunotherapies as monotherapy or in combination with other therapies.

Citation Format: Tiina E. Kähkönen, Mari I. Suominen, Jussi M. Halleen, Jenni Bernoulli, Arne Scholz. Anti-PD-1 therapy reduces bone lesion growth in a novel syngeneic bladder cancer bone metastasis model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 709.

Abstract 2684: Drug sensitivity profiling of BT-474 breast cancer cell line for identification of novel therapies targeting HER2-positive breast cancer

Developing targeted therapy for breast cancer expressing hormone receptors such as estrogen receptor (ER) and progesterone receptor (PR) as well as human epidermal growth factor receptor 2 (HER2) is essential. However, breast cancer has high susceptibility to spread despite the targeted therapies and metastases often turn resistant to the used treatment. Therefore, new therapies are needed especially at the stage when cancer becomes resistant to hormonal therapy. The aim of the study was to investigate drug sensitivity of BT-474 breast cancer cell line and to recognize possible vulnerabilities especially in HER2+ breast cancer.

BT-474 cell line (ER+, PR+, HER2+) is originally derived from human solid, invasive ductal carcinoma of the breast. Drug sensitivity of the cell line was assessed by screening of a large compound library consisting of many clinically available and emerging anti-cancer drugs including e.g. conventional chemotherapy, metabolic modifiers, kinesin inhibitors, apoptotic modulators, immunomodulators and kinase inhibitors such as HER2, pan-HER2 and EGFR-HER2 inhibitors. A panel of 525 compounds was tested in five concentrations covering a 10.000-fold drug-relevant concentration range in 384-well format. Cells were seeded to pre-drugged plates, followed by cell viability measurements (CellTiter-Glo) after 72 hours. Maximal and minimal responses to drugs were analyzed, the EC50 values were calculated and Drug Sensitivity Score (DSS) was calculated for each drug as a measure of reduced viability. A selective DSS (sDSS) was calculated to identify the selective drug response pattern.

DSS analysis of BT-474 cell line showed sensitivity to conventional chemotherapy including paclitaxel and docetaxel and to kinase inhibitors such as EGFR and HER2 inhibitors neratinib, afatinib, mubritinib, poziotinib, dacomitinib and lapatinib with nanomolar EC50 values. Moreover, BT-474 cells showed sensitivity to PI3K and mTOR inhibitors, such as copanlisib and omipalisib, and to HSP90 and HDAC inhibitors, such as tanespimycin and abexinostat.

Screening of large compound libraries combined with DSS and sDSS analysis enables drug sensitivity profiling of BT-474 breast cancer cells for discovery of novel therapies against HER+ breast cancer. Furthermore, drug sensitivity profiling enables repurposing of existing drugs to new indications and identification of vulnerabilities in different types of cancer cells.

Citation Format: Jenni H. Mäki-Jouppila, Tiina E. Kähkönen, Mari I. Suominen, Jussi M. Halleen, Jenni Bernoulli, Jani Saarela, Katja Fagerlund. Drug sensitivity profiling of BT-474 breast cancer cell line for identification of novel therapies targeting HER2-positive breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2684.

Abstract 1162: Castration-resistant prostate cancer bone metastasis model to assess new therapeutics

The role of androgens in the regulation of growth of primary prostate cancer is well established but less recognized in the context of advanced bone metastatic disease, which is the cause of high morbidity in patients. At advanced stage, prostate cancer cells typically lose their dependence on endogenous androgens leading to metastatic castration resistant prostate cancer (mCRPC). The aim of the study was to establish a novel mCRPC model resembling clinical aspects of the bone metastatic disease, which could be used for the evaluation of efficacy of new therapies.

To obtain a model for castration resistant growth, 5-6 weeks old NOD.Scid male mice were divided into three study groups. Mice in two study groups were castrated either before inoculation of the cancer cells or at four weeks after inoculation when the tumors were already growing. The mice in one study group were left intact. All mice received an intratibial injection of 2x106 VCaP human prostate cancer cells originally derived from vertebral metastatic site. Tumor growth was followed biweekly for 16 weeks by PSA measurements and X-ray imaging of tumor induced bone changes (lesions). At endpoint, androgen dependent organs were weighed and tumor-bearing tibias were subjected to histological evaluation.

At endpoint, a tumor take of 60%, 40% and 50% was observed in the intact mice and in the mice castrated one week before and four weeks after VCaP cell inoculation, respectively. Tumor take was assessed by PSA, X-ray and histology at endpoint. The PSA levels were higher in the intact mice and in the mice castrated at four weeks compared to the mice castrated before cancer cell inoculation. The PSA levels became detectable between 6-8 weeks after cancer cell inoculation in the intact mice and in the mice castrated at four weeks. In the mice castrated before cancer cell inoculation the PSA levels started to increase very late at 14-16 weeks. VCaP cells induced mainly new bone formation, an osteoblastic bone reaction typical for prostate cancer patients. In castrated mice, fewer bone lesions were observed compared to intact mice. The bone lesion areas quantified from X-ray images were larger in the intact mice compared to the mice castrated before cancer cell inoculation. As expected, the weight of androgen dependent organs was lower in the castrated mice compared to the intact mice.

In conclusion, a model mimicking important clinical aspects of castration resistant prostate cancer bone metastases was established. Tumor take and growth rates indicated that early phases of tumor development into the bone are androgen dependent whereas tumor growth at later stage relies on the bone microenvironment. The results highlight the significance of the tumor microenvironment in establishing clinically relevant preclinical models for drug development.

Citation Format: Tiina E. Kähkönen, Mari I. Suominen, Jussi M. Halleen, Jenni Bernoulli, Pascale Lejeune. Castration-resistant prostate cancer bone metastasis model to assess new therapeutics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1162.

Abstract 1677: Differential efficacy of PD-1 targeted immunomodulation in preclinical models of primary and bone metastatic triple-negative breast cancer

Immuno-oncology (IO) has provided groundbreaking results in cancer treatment. Triple-negative breast cancer (TNBC) tumors attract immune cells, and the presence of tumor-infiltrating lymphocytes (TILs) is linked to improved survival. Programmed cell death 1 (PD-1) is expressed by TILs and its ligand (PD-L1) by TNBC cells, and targeting of PD-1 has shown promising results in treatment of patients with primary TNBC. High frequency of bone metastases is typical in TNBC patients. As immune regulation is different in bone than in other organs it is essential to study the efficacy of IO therapies in bone microenvironment. The aim of this study was to assess the efficacy of anti-PD-1 therapy (pembrolizumab, Keytruda) in the growth of primary and bone metastatic TNBC in preclinical models.

MDA-MB-231(SA)-luc human TNBC cells were inoculated into the mammary fat pad (orthotopic model) or tibia bone marrow (bone model) of female huNOG mice engrafted with CD34+ cells from two different donors. Treatments with pembrolizumab or human IgG4 isotype control (5 mg/kg, i.p., Q5D, n=8) were started 3 days after the inoculations. Tumor growth was monitored by bioluminescence imaging (BLI), orthotopic tumor volume by caliper, and tumor induced changes in bone by X-ray imaging for 21-24 days. Tumor samples were processed to immunohistochemical (IHC) analysis of TILs, PD-1 and PD-L1. Bone volume was analyzed ex vivo by micro-computed tomography, and serum TRACP5b values were determined as a marker of osteoclast number.

Tumor growth at treatment start was confirmed by BLI. Pembrolizumab decreased tumor growth in the orthotopic model. 37.5% of the mice had partial response and 12.5% had tumor rejection. The mice exhibited donor-related differences in efficacy but the overall response was similar. IHC showed low to moderate PD-L1 expression in the TNBC tumors (tumor proportion score 1-49%) and moderate number of CD4+ and CD8+ TILs. No PD-1 expression was observed in pembrolizumab treated mice due to antibody blocking of the epitope. In the bone model, pembrolizumab had no effect in tumor growth or any bone parameters studied. PD-L1 expression was comparable in orthotopic and bone tumors. In bone tumors, CD4+ cells were dominant and CD8+ and PD-1+ cells were rarely observed.

In orthotopic model the response rate was similar to what has been observed in TNBC patients, but the bone metastatic growth could not be inhibited by the PD-1 blockage. Bone marrow has a unique microenvironment and immune cell compartment compared to any other organ, and it is known to be involved in immunosurveillance and to favour tumor cells to become immune evasive. The lack of efficacy of immunotherapy in bone compared to orthotopic tumor may be due to these differences. These results highlight the importance of using both orthotopic and metastasis models in preclinical oncology studies.

Citation Format: Tiina E. Kähkönen, Mari I. Suominen, Jussi M. Halleen, Teppo Haapaniemi, Azusa Tanaka, Michael Seiler, Jenni Bernoulli. Differential efficacy of PD-1 targeted immunomodulation in preclinical models of primary and bone metastatic triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1677.

Abstract 1158: Phenotypic screening using AMIDA identifies different drug responses in breast and prostate cancer cell lines in an organotypic cell culture model

Organotypic 3D cell culture models combined with screening modalities and automated high-content image analyses provide tools to gain a spectrum of biologically relevant information simultaneously from drug responses in tumor cells. This includes information about cell growth, death, differentiation and tumor cell invasion.

In this study, we examined the phenotypic drug responses of prostate cancer cell lines PC-3 and LNCaP, and breast cancer cell lines MDA-MB-231 (SA) and MCF-7 cultured in a miniaturized, imaging-optimized, Matrigel-based organotypic screening platform. We demonstrate the use of the 3D cell culture technology combined with automated morphometric image data analysis software AMIDA, for phenotypic, high-content screening. The emerging tumor organoids were treated with the cytostatic drugs doxorubicin, docetaxel and paclitaxel, a selective inhibitor of matrix metalloproteinase-13 (WAY170523), and with ROCK-inhibitors RKI-1447 and Y-27632. Treatments were conducted at seven different drug concentrations for 4-10 days. At the end point, confocal live cell images were captured and analyzed using AMIDA. Among others, the numerical data representing cell growth (Area) and cell invasion (Appendages) were visualized and used for statistics. EC50 values were calculated based on the Area-parameter derived from AMIDA analysis.

All cell lines initially formed multicellular, round organoids. PC-3 cells formed round and well-differentiated structures but spontaneously converted around day 9 of culture into structures showing massive, string-like collective invasion into the surrounding matrix. A different pattern of cell invasion was observed in MDA-MB-231 organoids, which developed strong and multicellular extensions by day 7-8. Interestingly, both ROCK-inhibitors promoted the invasion of PC-3 cells, as detected by phenotypic analysis with AMIDA. In contrast, Y-27632 reduced the invasion of MDA-MB-231 cells, whereas both ROCK-inhibitors induced cell invasion in MCF-7 cells at high concentration. WAY170523 inhibited the invasion of PC-3 cells but not of MDA-MB-231 cells, pointing to a different mechanism of invasiveness. All cell lines were highly sensitive to doxorubicin, docetaxel and paclitaxel at nanomolar range, as detected by the decrease of cell invasion, reduced organoid size, and increased cell death. The breast cancer cells were more sensitive to taxanes than PC-3 cells.

Organotypic 3D cultures combined with high-content phenotypic analysis with AMIDA software provide a quantitative view of drug effects and enable assessment of differential drug responses on various cell lines.

Citation Format: Mervi Toriseva, Katja Fagerlund, Jesse Mattsson, Tiina E. Kähkönen, Ilmari Ahonen, Malin Åkerfelt, Jenni Bernoulli, Jussi M. Halleen, Matthias Nees, Jenni H. Mäki-Jouppila. Phenotypic screening using AMIDA identifies different drug responses in breast and prostate cancer cell lines in an organotypic cell culture model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1158.

Abstract A151: Drug sensitivity profiling of BT-474 breast cancer cell line for identification of novel therapies against HER2-positive breast cancer

Introduction: Targeted therapy for breast cancer expressing hormone receptors such as estrogen receptor (ER) and progesterone receptor (PR), as well as human epidermal growth factor receptor (HER2), is essential. In spite of current targeted therapies, breast cancer has high susceptibility to spread and metastases often turn resistant to the used treatment. Therefore, new therapies are needed, especially when cancer becomes resistant to hormonal therapy. The aim of the study was to investigate drug sensitivity and resistance of BT-474 breast cancer cell line and to recognize possible vulnerabilities, especially in hormone therapy resistant HER2+ breast cancer. Materials and Methods: BT-474 cell line (ER+, PR+, HER2+) is originally derived from human solid, invasive ductal carcinoma of the breast. The drug sensitivity of the cell line was assessed by applying a large panel of drugs covering cancer chemotherapeutics and clinically available and emerging drugs including, e.g., conventional chemotherapy and kinase inhibitors such as HER2, pan-HER2, and EGFR-HER2 inhibitors. Altogether a panel of 525 compounds was tested in five concentrations covering a 10,000-fold drug-relevant concentration range in 384-well format. Cells were seeded to predrugged plates, followed by cell viability measurements (CellTiter-Glo) after 72 hours. Maximal and minimal responses to drugs were analyzed, the EC50 values were calculated, and Drug Sensitivity Score (DSS) was calculated for each drug as a measure of reduced viability. A selective Drug Sensitivity Score (sDSS) was calculated to identify the selective drug response pattern. Results: DSS analysis of BT-474 cell line showed sensitivity to conventional chemotherapy including paclitaxel and docetaxel and to kinase inhibitors such as EGFR inhibitors neratinib and afatinib. In the absence of supplemented estradiol, the cell line was not sensitive to hormonal therapies, including antiestrogens and selective estrogen receptor modulators. However, BT-474 cells were sensitive to HER2, pan-HER2, and EGFR-HER2 inhibitors including mubritinib, poziotinib, dacomitinib, and lapatinib with EC50 range from 2 to 98 nM. The BT-474 cells also showed sensitivity against PI3K and mTOR inhibitors, such as copanlisib and omipalisib. Conclusions: Screening of large compound libraries combined with DSS and sDSS analysis enables drug sensitivity profiling of HER2+ BT-474 breast cancer cells for identification of novel anticancer compounds against breast cancer, especially for the hormonal-resistant stage of the disease. Moreover, the assay enables repurposing of existing drugs to new indications, identification of vulnerabilities in different types of cancer cells, and functional investigation of cellular pathways behind drug sensitivity or resistance.

Citation Format: Jenni Mäki-Jouppila, Tiina Kähkönen, Mari I. Suominen, Katja M. Fagerlund, Jussi M. Halleen, Jani Saarela, Jenni Bernoulli. Drug sensitivity profiling of BT-474 breast cancer cell line for identification of novel therapies against HER2-positive breast cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A151.

Abstract B099: Importance of hormone receptor and HER2/HER3 status verification in preclinical breast cancer models using immunodeficient and humanized mice

Introduction: Breast cancer expressing estrogen receptor (ER) and progesterone receptor (PR) is classified as hormone receptor positive, and triple-positive breast cancer expresses also human epidermal growth factor receptor (HER2). Despite the hormonal and HER2 targeted treatments, breast cancer metastasizes to bone in high frequency and may develop resistance against the used treatment. Prevention and treatment of bone metastases is challenging; moreover, hormones are strong regulators of both bone and immune system. The aim of the present study was to verify ER, PR, HER2, and also HER3 status in preclinical primary and bone metastasis breast cancer models utilizing immunodeficient and human immune system engrafted mice in order to verify predictive models for drug development. Materials and Methods: BT-474 human breast cancer cells were inoculated orthotopically into mammary fat pad of placebo or 17β-estradiol (E2) supplemented female immunodeficient NOG mice. In a bone tumor study, BT-474 cells were inoculated into the tibia of female NOG or humanized NOG mice (HSCFTL-NOG-F mice, Taconic Biosciences). Tumor growth was followed for 8 weeks, and histopathologic tumor evaluation and immunohistochemical stainings for ER, PR, HER2, and HER3 were performed. Results: Orthotopic tumor growth of BT-474 was hormone dependent and only minor growth was observed in the absence of estrogen. In the presence of E2 supplement, the orthotopic tumor expressed ER, PR, and HER2/HER3. However, in the absence of E2 supplement there was reduced PR expression but no major changes in the ER and HER2/HER3 expression. In contrast, when breast cancer cells were inoculated into the tibia, tumor growth was observed also without E2 supplement. In this case, tumor in the bone was positive for ER and HER2/HER3 but negative for PR. No significant changes were observed between immunodeficient and humanized mice regarding intratibial tumor growth and ER, PR, and HER2/HER3 expression. Conclusions: Estrogen supplementation is needed to support breast cancer BT-474 tumor growth when cancer cells are inoculated orthotopically into mammary fat pad. In contrast, BT-474 tumor growth was observed in bone even in the absence of supplied estrogen. ER and HER2/HER3 expression was observed in primary and bone tumors, but PR expression was significantly reduced if no estrogen supplement was used. Differences in tumor growth depending on the site and estrogen level highlight the importance of tumor microenvironment in breast cancer, and also refer why tumor may shift resistant to used hormonal or HER2 targeted therapy. Taking together, when developing new therapies against breast cancer, treatment targets in preclinical models should be carefully verified. Focus should be placed not only on primary tumor but also on bone metastasis where cancer cells are under influence of different tumor microenvironment and may express differently hormone receptors and HER2/HER3. While hormones influence breast cancer progression, they also regulate bone turnover and immune system, and therefore humanized mouse models provide an essential platform for novel therapy development.

Citation Format: Tiina Kähkönen, Mari I. Suominen, Jenni Mäki-Jouppila, Jussi M. Halleen, Azusa Tanaka, Michael Seiler, Teppo Haapaniemi, Jenni Bernoulli. Importance of hormone receptor and HER2/HER3 status verification in preclinical breast cancer models using immunodeficient and humanized mice [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B099.

Abstract 3838: Drug sensitivity profile of 5TGM1 murine multiple myeloma cell line emphasizes the translational potential of the syngeneic in vivo model

Multiple myeloma (MM) is the second most common hematologic malignancy that originates from B-cells (plasma cells) and causes 2% of cancer-related deaths. Symptoms of MM include bone pain caused by multiple osteolytic lesions, pathologic fractures, and hypercalcemia. Typically, MM has a low growth fraction and it is highly dependent on the microenvironment. These properties have made it hard to target by conventional chemotherapy, but could now be exploited by novel stroma-targeting drugs and immunotherapy. These new approaches underline the need for well characterized models with functional immune system and appropriate tumor microenvironment. To gain additional information supporting the use of the syngeneic 5TGM1 murine multiple myeloma model in drug development, we tested drug sensitivity of 5TGM1 cells by screening an extensive panel of drugs.

The compound library consisting of 460 compounds included conventional chemotherapy, kinase inhibitors, metabolic modifiers, rapalogs, differentiating/epigenetic modifiers, kinesin inhibitors, apoptotic modulators, NSAIDs, hormone therapy, immunomodulators and HSP inhibitors. The compounds were tested in five concentrations covering a 10.000-fold drug-relevant concentration range in 384-well format. Cells were seeded to plates with a compound library, followed by cell viability measurements (CellTiter-Glo) after 72 hours. Maximal and minimal responses to drugs were analyzed, and the EC50 values were calculated. Drug Sensitivity Score (DSS) was calculated for each drug as a measure of reduced viability.

According to DSS analysis, 5TGM1 cells showed sensitivity to conventional chemotherapy, such as antimitotic drugs, and kinase inhibitors, such as MEK1/2 inhibitors. In addition, the cells showed particular sensitivity to several HSP90 inhibitors currently in phase I/II clinical development for MM. Lenalidomide and pomalidomide, efficient in treating multiple myeloma in humans, both gave low DSS value indicating that 5TGM1 cells are not sensitive to these drugs, which is expected because they do not bind to murine form of the target cereblon. In contrast, 5TGM1 cells were highly sensitive to the proteasome inhibitor bortezomib (DSS 32.2), which is currently in clinical use.

In conclusion, the murine 5TGM1 cells show sensitivity to various MM drugs used in the clinic and under development. Evaluating the effects of the microenvironment on the growth and drug sensitivity of 5TGM1 cells in vitro and in vivo will be essential. Furthermore, the cell-based compound screening combined with DSS analysis provides a possibility to profile cellular responses to an extensive collection of anti-cancer compounds enabling identification of vulnerabilities in cancer cells and functional investigation of cellular pathways behind drug sensitivity or resistance.

Citation Format: Jenni Mäki-Jouppila, Jenni Bernoulli, Mari I. Suominen, Tiina Kähkönen, Jussi M. Halleen, Sanna Timonen, Elina Huovari, Katja Suomi, Swapnil Potdar, Maria Nurmi, Päivi Östling, Jani Saarela, Katja M. Fagerlund. Drug sensitivity profile of 5TGM1 murine multiple myeloma cell line emphasizes the translational potential of the syngeneic in vivo model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3838. doi:10.1158/1538-7445.AM2017-3838

Abstract 4968: Importance of tumor microenvironment in the preclinical estrogen receptor positive breast cancer- Primary tumor and bone metastasis models

Estrogen receptor positive (ER+) breast cancer has ability to metastasize to bone in high frequency. Bone is known to be fertile soil for metastasized cancer cells to survive and in turn, metastasized tumor cells alter normally balanced bone environment. Prevention and treatment of bone metastasis is challenging and better understanding why bone metastasis are resistant to current therapies is needed. Aim of the present study was to explore the role of tumor microenvironment and estrogen supplementation on growth of primary breast cancer tumor and bone metastasis to establish predictive ER+ breast cancer models for drug development.

ER+ human breast cancer MCF-7 cells were inoculated into mammary fat pad and in the tibia of female athymic nude mice. Mice received either hormonal supplementation (17-beta estradiol pellet, E2) or placebo. Tumor growth was followed for 5 and 9 weeks. From one group, E2 supplementation was removed on study week 5 and tumor growth was followed for 4 weeks. During the study, blood samples were collected for serum steroid concentration measurements and at the end, histopathological evaluation and immunohistochemical (IHC) stainings were performed to examine tumor steroid hormone receptor expression.

Orthotopic MCF-7 tumor growth was clearly hormone dependent. E2 supplementation, that increased serum estradiol for app. 3-fold, supported tumor growth and when E2 was removed, tumor size decreased and no tumor growth was observed thereafter. In the full absence of E2 supplement, no orthotopic tumor growth was observed. In contrast, when MCF-7 cells were inoculated into tibia, tumor growth was observed both with and without E2 supplement. IHC stainings confirmed orthotopic tumor to express ER, PR and AR when animals received E2. After E2 removal, orthotopic tumors expressed still ER and AR but no longer PR. Also intratibial tumors expressed ER and PR in the presence of E2, but no PR in the absence of E2 supplement. E2 is needed to support MCF-7 tumor growth when cancer cells are inoculated orthotopically into mammary fat pad. No orthotopic tumor growth is observed in the absence of E2 supplement. In contrast, in the bone microenvironment, MCF-7 cells form tumor even in the absence of E2 supplement.

Results highlight importance of tumor microenvironment in the breast cancer progression and also refer why tumor in the different sites may be resistant to therapy. Taking together, when developing new therapies against breast cancer, focus should be addressed not only on primary tumor growth but also on bone metastasis where cancer cells are under influence of bone environment.

Citation Format: Jenni Bernoulli, Mari I. Suominen, Tiina Kähkönen, Jenni Mäki-Jouppila, Jussi M. Halleen, Riikka Oksala. Importance of tumor microenvironment in the preclinical estrogen receptor positive breast cancer- Primary tumor and bone metastasis models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4968. doi:10.1158/1538-7445.AM2017-4968

Abstract 1663: Preclinical efficacy model to promote immunotherapy development for prostate cancer

Immunotherapy for prostate cancer has recently emerged as an attractive treatment strategy. Yet, preclinical models where relationship between inflammation, stroma, tumor cells and prostate cancer progression can be studied are limited. GEMM models of prostate cancer are scarce and in xenograft models, even when in humanized mice, the role of immune system in the initiation and in progress of the malignancy cannot be studied. As the requirement to test novel immunotherapies and especially combination treatments is increasing, a preclinical model that takes into account tumor microenvironment and immune system would be highly useful to promote development of novel therapies to combat against prostate cancer. Aim of the present study was to reveal if there is role between the immune system and development of prostate cancer, and secondly, to validate a model to be utilized later in immunotherapy development.

Intact 10-12 weeks old male Noble rats were s.c. implanted with slow-releasing estradiol and testosterone pellets for 6, 13 and 18 weeks. Daily release for testosterone was 0.8 mg and for estradiol 0.08 mg. Control group animals received placebo hormone pellets without hormones. Serum samples were collected during the study to monitor hormone levels, and prostates were removed and processed for histopathological evaluation at the end of the study. Hormonal treatment caused an increase in estradiol to testosterone ratio, and the prostates were enlarged. Imbalance in hormone-milieu induced inflammation in the prostate, followed by formation of prostatic intraepithelial neoplasia (PIN)-like lesions and finally adenocarcinomas in the periurethral region. Inflammatory cells, mainly T-cells were noticed in the vicinity of PIN-like lesions. During the progression of prostate cancer, inflammatory cells disappeared from the adenocarcinoma sites. In the prostate, inflammation consisting of perivascular, stromal and periglandular T-lymphocytes and intraluminal neutrophils remained.

Results of this study indicate significance of hormonal milieu, especially estrogens and androgens, in the development of inflammation and progression of prostate cancer, with a key role for tumor microenvironment. Presence of lymphocytes in the proximity of PIN-like lesions during the early phases of prostate cancer, and their disappearance later in the adenocarcinomas, indicate interaction between innate and adaptive immune system and cancer. Therefore, this preclinical prostate cancer model that combines immune system and cancer can be utilized when new immunotherapies, combination treatments and prevention possibilities against prostate cancer progression are developed.

Citation Format: Mari I. Suominen, Tiina Kähkönen, Yvonne Konkol, Jenni Mäki-Jouppila, Jussi M. Halleen, Jenni Bernoulli. Preclinical efficacy model to promote immunotherapy development for prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1663. doi:10.1158/1538-7445.AM2017-1663

Abstract 4207: Selective drug sensitivity score (DSS) for indolent and aggressive prostate cancer cell lines

Prostate cancer (PC) is the most common malignancy in men and the second leading cause of cancer-related deaths. The majority of the PCs are classified as adenocarcinomas characterized by the expression of androgen receptor (AR) and prostate-specific antigen (PSA). Two of the most commonly used cell lines are LNCaP and PC-3 cells, derived from lymph node and bone metastases, respectively. Also VCaP cells, derived from vertebral metastases, are widely used in prostate cancer research. It has been well established that LNCaP and VCaP cells represent the conventional indolent form of PC expressing AR and PSA and are androgen-dependent. PC-3 cells, on the other hand, do not express AR and PSA, are androgen-independent, and represent the highly aggressive form.

The drug sensitivity of the cell lines was assessed by applying a large panel of drugs covering cancer chemotherapeutics and clinically available and emerging drugs including conventional chemotherapy, kinase inhibitors, metabolic modifiers, rapalogs, differentiating/epigenetic modifiers, kinesin inhibitors, apoptotic modulators, NSAIDs, hormone therapy, immunomodulators and HSP inhibitors. A panel of 460 compounds was tested in five concentrations covering a 10.000-fold drug-relevant concentration range in 384-well format. Cells were seeded to pre-drugged plates, followed by cell viability measurements (CellTiter-Glo) after 72 hours. Maximal and minimal responses to drugs were analyzed, the EC50 values were calculated and Drug Sensitivity Score (DSS) was calculated for each drug as a measure of reduced viability. A selective Drug Sensitivity Score (sDSS) was calculated to identify the selective drug response pattern of each three cancer cell lines.

As expected, the results indicate that LNCaP and VCaP cells in general were more sensitive to drugs of different categories than PC-3 cells. According to DSS analysis, all three cell lines showed sensitivity to conventional chemotherapy and kinase inhibitors. However, PC-3 cells were more sensitive to kinase inhibitors than conventional chemotherapy. Determining sDSS revealed specific sensitivities of each cell line. LNCaP cells were sensitive to kinase inhibitors, such as mTOR and AKT inhibitors. Also VCaP cells showed selective sensitivity to kinase inhibitors, especially Aurora kinase and IGF1R inhibitors. In addition to kinase inhibitors, VCaP cells were selectively sensitive to HDAC inhibitors. Furthermore, PC-3 cells were sensitive to e.g. CDK inhibitors.

We conclude that the cell-based compound screening combined with DSS and sDSS analysis provides a possibility to profile cellular responses to an extensive collection of anti-cancer compounds enabling repurposing of existing drugs to new indications, identification of vulnerabilities in different types of cancer cells and functional investigation of cellular pathways behind drug sensitivity or resistance.

Citation Format: Jenni Mäki-Jouppila, Jenni Bernoulli, Johanna Tuomela, Mari I. Suominen, Jussi M. Halleen, Sanna Timonen, Elina Huovari, Katja Suomi, Swapnil Potdar, Päivi Östling, Jani Saarela, Katja M. Fagerlund. Selective drug sensitivity score (DSS) for indolent and aggressive prostate cancer cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4207. doi:10.1158/1538-7445.AM2017-4207

Abstract 5202: Additive benefits of radium-223 dichloride and bortezomib combination in a syngeneic 5TGM1 multiple myeloma mouse model

Radium-223 dichloride (radium-223, Xofigo®), a targeted alpha-therapy, improves overall survival in prostate cancer patients with bone metastases. It inhibits disease progression by reducing tumor growth and tumor-induced pathological bone reaction in breast and prostate cancer mouse models. Radium-223 is actively incorporated into the bone matrix by osteoblasts. Multiple myeloma (MM) is characterized by increased osteoclast and reduced or no osteoblast activity. Bortezomib (Velcade®), a treatment for MM, restores the impaired osteoblast activity in MM. Here, we report the effects of radium-223, bortezomib and their combination on myeloma cell proliferation in vitro and on myeloma bone disease model in mice.

Proliferation assays were performed with human plasma cell leukemia (JJN-3, L-363), human MM (LP-1, MOLP-8, RPMI-8226 and OPM-2), and mouse MM (5TGM1) cells. Corresponding in vivo effects were studied in a syngeneic 5TGM1 mouse MM model. Female C57BL/KaLwRij mice (7 weeks old, n=15/group) were inoculated with 5TGM1 cells via tail vein and 26 days later, radium-223 (300 kBq/kg, single iv injection) and/or bortezomib (1 mg/kg ip, twice a week; total of 3 doses) or vehicle control were administered. The development of osteolytic lesions was detected by radiography. Hind limbs were used for histological analyses and total activity measurement was performed by a gamma-counter. TRAP-stained osteoclasts were counted at tumor-bone interface.

Bortezomib inhibited proliferation of all cancer cell lines tested at 25 nM (JJN3 and OPM-2 at 2.5 nM) and radium-223 at 0.8 kBq/ml (L-363 and MOLP-8 at 0.2 kBq/ml) concentrations. Additive effects were observed with combination treatment in vitro. The 5TGM1 in vivo model demonstrated that both bortezomib and radium-223 decreased osteolytic lesion area as monotherapy (p<0.05 and p<0.01, respectively), with the combination being more effective than either monotherapy alone (p<0.001). Bortezomib decreased the number of osteoclasts at tumor-bone interface (p<0.05) and an additive decrease was observed with combination therapy (p<0.01) resulting in almost complete eradication of osteoclasts. Incorporation of radium-223 to bone was higher with combination therapy based on total activity measurements. All treatments were well tolerated.

In conclusion, radium-223 dichloride (Xofigo®) therapy in combination with bortezomib decreased osteolytic lesion area and almost completely eradicated tumor-associated osteoclasts in a mouse model of myeloma bone disease. Incorporation of radium-223 to bone matrix was improved, possibly via induction of osteoblast activity by bortezomib. These data suggest that combination of radium-223 and bortezomib could be a new effective therapy in MM, which is currently being investigated in a Phase Ib/II trial in patients with early relapsed MM (NCT02928029).

Citation Format: Mari I. Suominen, Jukka P. Rissanen, Anniina Luostarinen, Katja M. Fagerlund, Birgitta Sjöholm, Esa Alhoniemi, Sanna-Maria Käkönen, Dominik Mumberg, Jussi M. Halleen, Karl Ziegelbauer, Arne Scholz. Additive benefits of radium-223 dichloride and bortezomib combination in a syngeneic 5TGM1 multiple myeloma mouse model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5202. doi:10.1158/1538-7445.AM2017-5202

Abstract LB-132: A new preclinical model for immuno-oncology: Combination of tumor, bone microenvironment and immune system

Breast and other solid tumors commonly metastasize to bone. Bone microenvironment regulates hematopoietic stem cells and thereby immune cell differentiation. Therefore, a system with functional interaction between bone, immune system and cancer is a prerequisite in developing and in preclinical testing of novel immunotherapies against osseous tumors. Our aim was to establish a model where tumor, bone microenvironment and immune system would be combined to functional entity.

An intratibial injection of 1x106 of BT-474 (ER+, PR+, HER2+) human breast cancer cells were given to huNOG mice (HSCFTL-NOG-F, provided by Taconic Biosciences). These humanized mice were produced through engrafting hCD34+ hematopoietic stem cells (HSC) into CIEA NOG mouse® (NOD.Cg-Prkdcscid Il2rgtm1Sug/ JicTac, Taconic Biosciences). The tumor induced bone changes were followed by radiography at 4, 6 and 8 weeks. Bone mineral density (BMD) and bone mineral content (BMC) were quantified by dual x-ray absorptiometry (DXA) at end of study. Bone turnover markers CTX-I, TRACP5b and PINP were measured from serum in the beginning and at sacrifice. Spleen, thymus, lymph nodes and hind limbs were collected, tumor and bone areas, as well as the expression of human CD3, CD4, CD8, CD16/56, CD20, CD45, CTLA-4 and PD-L1 in immune cells was analyzed.

Tumor-induced osteoblastic new bone growth was observed in all tumor-bearing tibias. Osteoblastic and tumor areas were larger in huNOGs compared to NOG mice. Correspondingly, BMC was higher in huNOGs than in NOG mice, while BMD was comparable. Increased BMC was mainly due to a rise in trabecular bone volume quantified from histological sections. Measurements of bone turnover markers revealed an increased bone resorption rate in NOG mice compared to huNOGs. Spleen weight was markedly increased in huNOGs compared to NOG mice. Strong expression of CD3, CD4, CD8 and CD45 was observed in spleen and lymph nodes of huNOG mice indicating high prevalence active human immune cells. CD45-positive tumor-infiltrating lymphocytes (TILs) and CD4-positive T-helper cells were observed in 80% of the mice. Furthermore, PD-L1 was expressed in 50% of tibias and no CTLA-4 expression was observed in this model.

To our knowledge, the first humanized mouse model of tumor growth in bone was established in this study. The model is characterized by tumor growth, extensive tumor-induced osteoblastic changes and tumor-infiltrating human immune cells in bone, and mimics the late stage of breast cancer metastasized to bone. This humanized mouse model provides a completely new platform for preclinical testing of cancer immunotherapies, particularly the therapies targeting cancers metastasizing to or growing in bone.

Citation Format: Tiina E. Kähkönen, Mari I. Suominen, Jenni Mäki-Jouppila, Jussi M. Halleen, Azusa Tanaka, Michael Seiler, Jenni Bernoulli. A new preclinical model for immuno-oncology: Combination of tumor, bone microenvironment and immune system [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-132. doi:10.1158/1538-7445.AM2017-LB-132

Radium-223 Inhibits Osseous Prostate Cancer Growth by Dual Targeting of Cancer Cells and Bone Microenvironment in Mouse Models

Purpose: Radium-223 dichloride (radium-223, Xofigo), a targeted alpha therapy, is currently used for the treatment of patients with castration-resistant prostate cancer (CRPC) with bone metastases. This study examines the mode-of-action and antitumor efficacy of radium-223 in two prostate cancer xenograft models.Experimental Design: Mice bearing intratibial LNCaP or LuCaP 58 tumors were randomized into groups (n = 12-17) based on lesion grade and/or serum PSA level and administered radium-223 (300 kBq/kg) or vehicle, twice at 4-week intervals. X-rays and serum samples were obtained biweekly. Soft tissue tumors were observed macroscopically at sacrifice. Tibiae were analyzed by gamma counter, micro-CT, autoradiography and histology.Results: Radium-223 inhibited tumor-induced osteoblastic bone growth and protected normal bone architecture, leading to reduced bone volume in LNCaP and abiraterone-resistant LuCaP 58 models. Furthermore, radium-223 resulted in lower PSA values and reduced total tissue and tumor areas, indicating that treatment constrains prostate cancer growth in bone. In addition, radium-223 suppressed abnormal bone metabolic activity as evidenced by decreased number of osteoblasts and osteoclasts and reduced level of the bone formation marker PINP. Mode-of-action studies revealed that radium-223 was deposited in the intratumoral bone matrix. DNA double-strand breaks were induced in cancer cells within 24 hours after radium-223 treatment, and PSA levels were significantly lower 72 hours after treatment, providing further evidence of the antitumor effects.Conclusions: Taken together, radium-223 therapy exhibits a dual targeting mode-of-action that induces tumor cell death and suppresses tumor-induced pathologic bone formation in tumor microenvironment of osseous CRPC growth in mice. Clin Cancer Res; 23(15); 4335-46. ©2017 AACR.

Abstract 381: PI3K inhibitor BAY 1082439 and radium-223 dichloride decrease tumor burden and tumor-induced bone formation in an established bone metastatic prostate cancer model in mice

Background and objective: Bone is the most common site of metastasis in prostate cancer (PCa) and results in significant morbidity and poor prognosis. Disseminated PCa cells conquer hematopoietic stem cell niches, and during outgrowth they induce osteoblasts to form new, disorganized bone. Also osteoclasts are activated at a varying degree. PI3K activation has important role in survival and proliferation of PCa cells, mediating critical signaling pathways involving tumor and stromal cell interaction in the bone microenvironment. BAY 1082439 is a highly selective and potent PI3K inhibitor currently in Phase I, with equipotent activity against PI3Kα and PI3Kβ isoforms. Radium-223 dichloride (ra-223/Xofigo) is alpha-emitting calcium mimetic that via efficient osteoaffinity provides targeted radiation therapy against bone metastases. We have previously reported that BAY 1082439 and ra-223 showed synergistic anti-proliferative and apoptosis-inductive effects in vitro in LNCaP PCa cells (Suominen et al, AACR Annual Meeting 2014). Here, we investigated the effects of BAY 1082439 and ra-223 as single agents and in combination in the osteoblastic LNCaP tumors in tibia of male nod.scid mice.

Methods: Tumors were established 6 weeks after inoculation of LNCaP cells. Mice were randomized into four treatment groups (vehicle, ra-223; BAY 1082439 and ra-223 + BAY 1082439) based on serum PSA and bone lesion score. Treatments were continued for six weeks and the efficacy was assessed by the following endpoints biweekly and/or at the end of the study: PSA, bone formation marker PINP, bone lesions and bone volume (measured by microCT), and tumor and bone area by histological analysis.

Results: Both ra-223 and BAY 1082439 monotherapies inhibited tumor growth (reduction 67.9%, p = 0.029 and 67.4%, p = 0.009, respectively). Furthermore, BAY 1082439 monotherapy treatment group displayed 68.8% of necrotic tumor, compared to 6.5% in the control group (p = 0.009). In the combination group, tumor growth was further suppressed (tumor reduction 89%, p = 0.005) and it is noteworthy that 60% of animals had no detectable tumors in histology. All treatments inhibited the tumor-induced bone formation compared to vehicle, and the combination treatment inhibited progression of bone lesions nearly completely. In conclusion, BAY 1082439 and ra-223 as monotherapies decreased tumor burden and tumor-induced bone reaction, and the observed effects were further enhanced by the combination treatment.

Citation Format: Mari I. Suominen, Jukka Morko, Katja M. Fagerlund, Esa Alhoniemi, Dominik Mumberg, Karl Ziegelbauer, Jussi M. Halleen, Arne Scholz, Ningshu Liu. PI3K inhibitor BAY 1082439 and radium-223 dichloride decrease tumor burden and tumor-induced bone formation in an established bone metastatic prostate cancer model in mice. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 381.

Abstract 640: New models of breast and lung cancer bone metastases for preclinical efficacy testing

Introduction

Clinically, bone is a very common site of metastatic spread in many cancers. In breast, and in particular cases of advanced estrogen receptor positive (ER+) cancers, the propensity of bone involvement is 85%. Similarly in lung cancer, 30-40% of patients with advanced disease develop bone metastases, and as recent advances in lung cancer therapies improve survival, the number of patients living with bone metastases is expected to increase. At the same time there is a paucity of especially ER+ and osteoblastic animal models available for the nonclinical evaluation of new treatment strategies. We present herein the development of four mouse models of breast and lung cancer suitable for screening of new therapies.

Experimental procedures

Human breast cancer cell lines BT-474 and MFM-223 and non-small cell lung cancer (NSCLC) cell lines NCI-H226luc and NCI-H322 were used. BT-474 is ER+, i.e. luminal B subtype and MFM-223 is basal subtype with androgen receptor (AR) expression. H226 originates from squamous cell carcinoma and H322 from adenocarcinoma of the lung. The different cell lines were inoculated in the tibia of female nude or NOD.scid mice. Half of the BT-474 inoculated mice had a s.c. slow release 17-beta estradiol pellet implanted. The formation of bone lesions was monitored by X-ray imaging. For H226 transfected with luciferase, tumor growth was also followed by bioluminescence imaging (BLI). Finally, tumor growth and type of bone lesion, i.e. ostelytic or oestoblastic, was confirmed by histology.

Results

Development of bone lesions was successful in 100% and 90% of animals, with or without hormonal supplementation respectively, four weeks after inoculation of BT-474 cells. Bone lesions were detected earlier in mice with estradiol pellet and were of lytic type. In contrast, bone lesions in mice without hormonal supplementation were strongly osteoblastic. For MFM-223, bone lesions were observed 4-6 weeks after inoculation and the success rate was 60% in nude mice and 70% in NOD.scid mice. For both lung cancer cell lines, 100% of the mice developed bone lesions and were detectable already two weeks after inoculation. H226luc cells developed osteoblastic-mixed lesions and H322 cells induced lytic lesions. Very interestingly, H226luc cells also formed lung metastases in all animals, as evidenced by BLI. Some lung metastases were also found in H322 inoculated mice.

Conclusions

Two new osteoblastic models are added to the current scarce selection and altogether four new bone lesion models representing different subtypes of breast and lung cancer were successfully established. The different types of bone reaction in these models offer a platform for studying the underlying pathways resulting in response to treatment in osteoblastic vs. osteolytic tumor microenvironment.

Citation Format: Mari I. Suominen, Urs B. Hagemann, Yvonne Konkol, Jenni Bernoulli, Katja M. Fagerlund, Roger M. Bjerke, Jenny Karlsson, Jussi M. Halleen, Alan Cuthbertson. New models of breast and lung cancer bone metastases for preclinical efficacy testing. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 640.

Abstract 644: Utilizing a novel luciferase labeling technique to establish and validate preclinical models of pancreatic cancer

Bioluminescent-labeling imaging (BLI) allows sensitive non-invasive sequential imaging of tumor development and early metastasis. Current methods for the genetic modification of cells typically use integrating genotoxic viruses that can disrupt the molecular behavior of cancer cell lines due to their random nature of integration. A primary aim of the study was to utilize a non-integrating DNA vector that comprises an S/MAR (Scaffold/Matrix Attachment Region) element to stably genetically modify pancreatic cancer cells to persistently express the reporter gene luciferase without altering the molecular behavior of the cell or altering its sensitivity to therapeutic drug treatments. Once a novel isogenic cell line is generated the cells can subsequently be used in xenograft studies. A second aim was to validate these established models with gemcitabine and test the efficacy of VAL401, formulation of risperidone in rumenic acid. Human BxPC3, Capan-1, MiaPaCa-2 and Panc-1 pancreatic cancer cells were stably transfected with a pSMARt-UBC-Luc DNA vector and cultured for 4 weeks under selection. Colonies that formed after this period were isolated and expanded in normal medium and evaluated for luciferase expression and the molecular integrity of the DNA vector. Efficacy of gemcitabine was tested in these new luciferase expressing cell lines and VAL401 was tested in Capan-1-luc cells. For in vivo studies, BxPC3-luc cells were inoculated orthotopically into the pancreas of athymic nude mice and stratified into groups: control, gemcitabine, VAL401 (1mg/kg, p.o. daily) and VAL401 (2mg/kg, p.o. daily). In vitro validation results indicated that the luciferase transfected cells maintained their original properties with stable expression. Gemcitabine inhibited cell proliferation in all established cell lines. VAL401 inhibited cell proliferation of Capan-1-luc cells at 50 μM concentration. BxPC3-luc cells inoculated orthotopically into the pancreas were followed for 5 weeks with BLI by IVIS, and the results demonstrated high-quality follow-up of tumor growth. BxPC3-luc cells induced growth of pancreatic tumors with high take rate in all groups. Gemcitabine and both studied doses of VAL401 decreased tumor volume, and the same trend was seen in tumor weight and the BLI during the study. In conclusion, both gemcitabine and VAL401 decreased tumor volume and the same trend was observed using BLI. Our results demonstrated that S/MAR DNA vectors are able to produce genetically modified cells without the limitations of random genomic integration, whilst providing extra-chromosomal mitotic stability and high levels of sustained transgene expression. When utilized in orthotopic xenograft studies, these luciferase expressing cells formed a reliable and essentially non-invasive imaging platform that substantially improves the efficacy of testing anticancer drug candidates.

Citation Format: Jenni Bernoulli, Matthias Bozza, Katja M. Fagerlund, Johanna Tuomela, Mari I. Suominen, Suzanne Dilly, George Morris, Jussi M. Halleen, Richard Harbottle. Utilizing a novel luciferase labeling technique to establish and validate preclinical models of pancreatic cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 644.

Abstract B69: VAL401 decreases tumor volume in a xenograft model of pancreatic cancer utilizing a novel improved luciferase labelling technique

Bioluminescent-labelling allows sensitive non-invasive sequential imaging of tumor development and early metastasis. Current methods for the genetic modification of cells typically use integrating genotoxic viruses that can potentially disrupt the molecular behavior of cancer cell lines due to their random nature of integration. VAL401 is the reformulation of a clinical drug to enable use in the treatment of cancer. Preclinical data indicate potential use of the reformulated drug in lung cancer, where many subsets of patients have currently a high unmet medical need. We have utilized a non-viral DNA vector that comprises an S/MAR (Scaffold/Matrix Attachment Region) element to stably modify cells to be further used in xenograft studies to allow long term expression without affecting cell behavior or silencing over cell divisions. Human BxPC3 pancreatic cancer cells were stably transfected with a pSMARt-UBC-Luc and cultured for 4 weeks under selection. Colonies that formed after this period were isolated and expanded in normal medium and evaluated for luciferase expression and molecular integrity of the DNA vector. For in vivo studies, BxPC3 cells were inoculated orthotopically into the pancreas of athymic nude mice. Four experimental groups were included in the study: 1) Control group receiving vehicle; 2) Reference compound gemcitabine (60 mg/kg, q3dx4 i.p, one week pause, q3dx4 i.p.); 3) Test compound VAL401 (1 mg/kg, p.o. daily); 4) Test compound VAL401 (2 mg/kg, p.o. daily). The luciferase transfected cells maintained their original properties with stable expression. Luciferase-labelled BxPC3 cells inoculated orthotopically into the pancreas were successfully followed for 5 weeks with non-invasive bioluminescence imaging by IVIS, and the results demonstrated high-quality follow-up of tumor growth compared with tumor models using non-labelled cells. BxPC3-luc cells induced growth of pancreatic tumors with high take rate in all groups. Gemcitabine and both studied doses of VAL401 decreased tumor volume, and the same trend was seen in tumor weight and the BLI parameters (total flux, area and average radiance) during the study. In conclusion, both gemcitabine and VAL401 decreased tumor volume and same trend was seen in BLI. Our results demonstrated that S/MAR DNA vectors are able to produce genetically modified cells without the limitations of random genomic integration, whilst providing extra-chromosomal mitotic stability and sustained transgene expression at high level. When utilized in orthotopic xenograft studies, these luciferase expressing cells formed a reliable and essential non-invasive imaging platform that improves substantially efficacy testing of anticancer drug candidates.

Citation Format: Mari I. Suominen, Jenni Bernoulli, Suzanne Dilly, Johanna Tuomela, Matthias Bozza, Katja M. Fagerlund, George Morris, Jussi M. Halleen, Richard Harbottle. VAL401 decreases tumor volume in a xenograft model of pancreatic cancer utilizing a novel improved luciferase labelling technique. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B69.

Abstract A109: Radium-223 dichloride inhibits tumor growth and tumor-induced bone growth in osteoblastic prostate cancer models

Radium-223 dichloride (radium-223), an alpha particle-emitting calcium-mimetic, improves overall survival in prostate cancer patients with symptomatic bone metastases. We have defined radium-223 mode-of-action and efficacy in two clinically relevant prostate cancer xenograft models demonstrating PSA expression and osteoblastic growth upon intratibial inoculation of cancer cells. Immunocompromised male mice were inoculated with human LNCaP or patient-derived LuCaP 58 prostate cancer cells in the intratibial compartment and subsequently stratified into treatment groups based on lesion grade and/or serum PSA levels. Radium-223 (300 kBq/kg) or vehicle was administered intravenously, two times at 4-week intervals during the experiment. X-rays and serum samples were obtained biweekly and at sacrifice. Soft tissue tumors were examined macroscopically at sacrifice and tissue samples were collected and processed for γ-counter measurements, micro-CT, autoradiography and histology. Radium-223 treatment inhibited tumor-induced osteoblastic bone growth as indicated by reduced bone volume and surface in LNCaP and LuCaP 58 prostate cancer mouse models. In addition, radium-223 treatment suppressed metabolic activity in bone as evidenced by decreased number of osteoblasts and osteoclasts relative to bone surface and reduced levels of the bone formation marker PINP. Radium-223 resulted in lower PSA values as early as two weeks after the first dose, indicating constrained tumor growth following treatment. This phenomenon was further supported by reduced total bone lesion tissue and tumor area in LNCaP and LuCaP 58 models and increased percentage of necrotic tumor area in the LuCaP 58 model in radium-223-treated mice as compared to vehicle-treated mice. Moreover, DNA double-strand breaks were increased in cancer cells 24 hours post radium-223 treatment in the LuCaP 58 model providing further evidence of anti-tumor effects. Radium-223-treated mice exhibited less visceral metastases in the LuCaP 58 model (not significant). Based on autoradiography, radium-223 was deposited in the intratumoral bone matrix and in conjunction with osteoblasts in osteoblastic metastases. Our results demonstrate that radium-223 dichloride is successfully incorporated into the intratumoral bone matrix and inhibits tumor growth in both cell line- and patient-derived osteoblastic prostate cancer metastasis models. Given the α-particle range of 50-80 μm, potent radiation effects on the tumor microenvironment are evident whereas relevant effects on the more distant bone marrow are not expected. Taken together, radium-223 therapy exhibits a dual mode-of-action that impacts tumor growth and tumor-induced bone reaction, both important players in the destructive vicious cycle of osteoblastic bone metastasis in prostate cancer.

Citation Format: Mari I. Suominen, Katja M. Fagerlund, Dominik Mumberg, Karl Ziegelbauer, Sanna-Maria Käkönen, Jussi M. Halleen, Robert L. Vessella, Arne Scholz. Radium-223 dichloride inhibits tumor growth and tumor-induced bone growth in osteoblastic prostate cancer models. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A109.

Abstract 3246: Novel luciferase labelling technique to improve imaging of orthotopic prostate and pancreatic cancer models

Bioluminescent-labelling allows sensitive non-invasive sequential imaging of tumor development and early metastasis. However, current methods for the genetic modification of cells typically use integrating genotoxic viruses that can potentially disrupt the molecular behavior of cancer cell lines due to their random nature of integration. Here, we utilized a non-viral DNA vector that comprises an S/MAR (Scaffold/Matrix Attachment Region) element to stably modify cells to be further used in xenograft studies to allow long term expression without affecting cell behavior or silencing over cell divisions. Human PC-3 prostate cancer cells and BxPC-3 pancreatic cancer cells were stably transfected with a pCAG-LUC-S/MAR and cultured for 4 weeks under selection. Colonies that formed after this period were isolated and expanded in normal medium and evaluated for luciferase expression and molecular integrity of the DNA vector. For in vivo studies, PC-3 cells were inoculated orthotopically into the prostate, and BxPC-3 cells into the pancreas using athymic and BALB/c nude mice. For comparison, similar experiments with the corresponding study designs were performed with the non-labelled parental cell lines. The luciferase transfected cells maintained their original properties with stable expression. Luciferase-labelled PC-3 and BxPC-3 cells inoculated orthotopically into the prostate and pancreas, respectively, were successfully followed for 5 weeks with non-invasive bioluminescence imaging by IVIS. The results demonstrated high-quality follow-up of tumor growth compared with tumor models using non-labelled cells. In conclusion, S/MAR DNA vectors are able to produce genetically modified cells without the limitations of random genomic integration, whilst providing extra-chromosomal mitotic stability and sustained transgene expression at high level. When utilized in orthotopic xenograft studies, these luciferase expressing cells formed a reliable and essential non-invasive imaging platform that improves substantially efficacy testing of anticancer drug candidates.

Citation Format: Jenni Bernoulli, Johanna Tuomela, Matthias Bozza, Katja M. Fagerlund, Mari I. Suominen, George Morris, Jussi M. Halleen, Richard Harbottle. Novel luciferase labelling technique to improve imaging of orthotopic prostate and pancreatic cancer models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3246. doi:10.1158/1538-7445.AM2015-3246

Abstract 786: Effects of combination treatment with cabozantinib and bortezomib in the 5TGM1 murine multiple myeloma model

Cabozantinib (cabo) is an inhibitor of tyrosine kinases including MET, VEGFR2, RET, and the TAM family kinases TYRO3, AXL, and MER, and has shown clinical activity in patients with castration-resistant prostate cancer and other solid tumors with bone metastases. Multiple myeloma (MM) is a monoclonal B-cell (plasma cell) neoplasia representing ∼2% of all cancer deaths. The clinical hallmark is presence of multiple osteolytic lesions causing bone pain, pathologic fractures, and hypercalcemia. Circulating levels of HGF and VEGF are upregulated in MM patients, and regulation of plasma cell-osteoblast communication by the HGF-MET signaling pathway has been implicated in the development of lytic bone disease in these patients. We have previously shown that cabo is active in the syngeneic 5TGM1 mouse MM model. This study aimed to determine whether combination with bortezomib would yield additional benefit.

Four experimental groups were included: 1) Control group receiving vehicle, 2) Bortezomib (0.5 mg/kg ip twice a week), 3) Cabo (10 mg/kg, PO QD) and 4) Combination (bortezomib + cabo, same doses).

Female C57BL/KaLwRij mice were allocated to treatment groups (n = 15 per group) with equivalent average body weights. At day 0, animals were inoculated with 5TGM1 cells by IV administration. Dosing began at day 1 and continued daily until euthanasia. Body weights were determined twice a week and blood samples were collected at days -1, 16, 23, 35 and at sacrifice for analysis of paraprotein (IgG2b), PINP and TRACP 5b. Development of osteolytic lesions was detected by radiography at day 35 and at sacrifice. Mice were sacrificed individually when they became paraplegic, lost over 20% of body weight, or had severe breathing problems. The maximum length of the study was 70 days.

By study day 35, the osteolytic lesions were not affected by bortezomib, were reduced by cabo alone, and further reduced by the combination treatment. Bortezomib had inhibited the rise in serum IgG2b levels, but cabo and the combination treatment had not. Despite the effects on serum IgG2b, bortezomib did not significantly increase survival, whereas cabo and the combination treatment did. Increased survival with the combination was significant when compared to bortezomib monotherapy, but not when compared to cabo monotherapy. Earlier we have shown that cabo dose-dependently increases the necrotic tumor area in bone, and proposed that the rise in IgG2b was due to lysis of plasma cells and not tumor growth. Consistent with this hypothesis, the IgG2b levels of cabo treated mice were lower at sacrifice than at day 35 in this study.

In summary, cabo increased survival and exhibited bone-protective and anti-tumor effects in this murine model of MM. Combination with bortezomib showed additive effects on survival. Based on these results, further investigation of cabozantinib in multiple myeloma is warranted.

Citation Format: Mari I. Suominen, Katja M. Fagerlund, Esa Alhoniemi, Jukka P. Rissanen, Jussi M. Halleen, Dana T. Aftab. Effects of combination treatment with cabozantinib and bortezomib in the 5TGM1 murine multiple myeloma model. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 786. doi:10.1158/1538-7445.AM2015-786

Abstract 3447: Radium-223 dichloride exhibits dual mode-of-action inhibiting both tumor and tumor-induced bone growth in two osteoblastic prostate cancer models

Radium-223 dichloride (radium-223), an alpha particle-emitting calcium-mimetic, improves overall survival in prostate cancer patients with symptomatic bone metastases. Here, we define radium-223 mode-of-action and efficacy in two clinically relevant prostate cancer xenograft models demonstrating PSA expression and osteoblastic growth upon intratibial inoculation of cancer cells.

Immunocompromized male mice were inoculated with human LNCaP or patient-derived LuCaP 58 prostate cancer cells in the intratibial compartment and subsequently stratified into treatment groups based on lesion grade and/or serum PSA levels. Radium-223 (300 kBq/kg) or vehicle was administered intravenously, two times at 4-week intervals during the experiment. X-rays and serum samples were obtained biweekly and at sacrifice. Soft tissue tumors were examined macroscopically at sacrifice and tissue samples were collected and processed for γ-counter measurements, micro-CT, autoradiography and histology.

Radium-223 treatment inhibited tumor-induced osteoblastic bone growth as indicated by reduced bone volume and surface in LNCaP and LuCaP 58 prostate cancer mouse models. In addition, radium-223 treatment suppressed metabolic activity in bone as evidenced by decreased number of osteoblasts and osteoclasts relative to bone surface and reduced levels of the bone formation marker PINP. Radium-223 resulted in lower PSA values as early as two weeks after the first dose, indicating constrained tumor growth following treatment. This phenomenon was further supported by reduced total tissue and tumor area in tibia in LNCaP and LuCaP 58 models and increased percentage of necrotic tumor area in the LuCaP 58 model in radium-223-treated mice as compared to vehicle-treated mice. Moreover, DNA double-strand breaks were increased in cancer cells 24 hours post radium-223 treatment in the LuCaP 58 model providing further evidence of anti-tumor effects. Radium-223-treated mice exhibited less visceral metastases in the LuCaP 58 model (not significant). Based on autoradiography, radium-223 was deposited in the intratumoral bone matrix and in conjunction with osteoblasts in osteoblastic metastases.

We demonstrate that radium-223 dichloride is successfully incorporated into the intratumoral bone matrix and inhibits tumor growth in both cell line- and patient-derived osteoblastic prostate cancer metastasis models. Given the α-particle range of 50-80 μm, potent radiation effects on the tumor microenvironment are evident whereas relevant effects on the more distant bone marrow are not expected. Taken together, radium-223 therapy exhibits a dual mode-of-action that impacts tumor growth and tumor-induced bone reaction, both important players in the destructive vicious cycle of osteoblastic bone metastasis in prostate cancer.

Citation Format: Mari I. Suominen, Katja M. Fagerlund, Jukka P. Rissanen, Yvonne Konkol, Jukka Morko, Zhiqi Peng, Esa Alhoniemi, Dominik Mumberg, Karl Ziegelbauer, Sanna-Maria Käkönen, Jussi M. Halleen, Robert L. Vessella, Arne Scholz. Radium-223 dichloride exhibits dual mode-of-action inhibiting both tumor and tumor-induced bone growth in two osteoblastic prostate cancer models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3447. doi:10.1158/1538-7445.AM2015-3447

Abstract 734: Effects of Cabozantinib in the 5TGM1 murine multiple myeloma model

Cabozantinib is an inhibitor of tyrosine kinases including MET, VEGFR2, and RET, and has shown clinical activity in patients with castration-resistant prostate cancer and other solid tumors with bone metastases. Multiple myeloma (MM) is the second most common hematologic malignancy, and represents ∼2% of all cancer deaths. MM is a monoclonal B-cell (plasma cell) neoplasia with clinical hallmarks of multiple osteolytic lesions causing bone pain, pathologic fractures, and hypercalcemia. Circulating levels of HGF and VEGF are upregulated in MM patients, and regulation of plasma cell-osteoblast communication by the HGF-MET signaling pathway has been implicated in the development of lytic bone disease in these patients. Thus, our aim was to determine the activity of cabozantinib on bone lesions and tumor burden in the syngeneic 5TGM1 mouse MM model. Four experimental groups were included: negative control group receiving vehicle, positive control group receiving bortezomib (0.5 mg/kg ip twice a week), low dose cabozantinib group (10 mg/kg, PO QD) and high dose cabozantinib group (30 mg/kg, PO QD). Female C57BL/KaLwRij mice were allocated to treatment groups (n=15 per group) with equivalent average body weights. On day 0, animals were inoculated with 5TGM1 mouse myeloma cells by IV administration. Dosing began on day 1 and continued daily until euthanasia at day 35. Body weights were determined twice a week and blood samples were collected on days -1, 15, 22, and 34 for analysis of paraprotein (IgG2b) and TRACP 5b. The development of osteolytic lesions was detected by radiography at the end of the study. Some animals (4/15) were euthanized before the end of the experiment due to paraplegia in control and bortezomib groups, but none in cabozantinib groups. Animals euthanized within four days of the end of the experiment were included in the analysis. Bortezomib reduced serum IgG2b levels and decreased the frequency of soft tissue lesions, but did not show bone protective properties. Cabozantinib exhibited bone protective effects: mean and total area of osteolytic lesions were reduced at the 30 mg/kg dose, and serum TRACP 5b values and osteoclast counts at the tumor-bone interface were reduced at both the 10 and 30 mg/kg doses. Relative bone area did not differ from control according to histomorphometry. The rise in serum IgG2b started earlier than vehicle control in both cabo-treated groups, but a significant difference was not observed in relative IgG2b at sacrifice. Cabozantinib dose dependently increased the necrotic tumor area in bone, indicating the possibility that the rise in IgG2b may have been due to lysis of plasma cells. Both cabozantinib doses decreased the frequency of soft tissue lesions. In summary, cabozantinib showed both bone-protective and anti-tumor effects in this murine model of MM. Based on these promising results, further investigation of cabozantinib in multiple myeloma is warranted.

Citation Format: Mari I. Suominen, Douglas O. Clary, Rami Käkönen, Katja M. Fagerlund, Esa Alhoniemi, Jukka P. Rissanen, Jussi M. Halleen, Dana T. Aftab. Effects of Cabozantinib in the 5TGM1 murine multiple myeloma model. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 734. doi:10.1158/1538-7445.AM2014-734

Abstract 4022: Combination of PI3K inhibitor BAY 1082439 with radium-223 is a promising treatment of cancer with bone metastases

About 80% of advanced prostate, breast and lung cancer patients develop bone metastases, which cause significant morbidity including chronic pain and pathologic fractures. Patients with bone metastases have a poor prognosis and currently there is no curative treatment. This is largely due to the unique biological microenvironments of bone where a wide range of growth factors promote tumor cell survival and tumor cells stimulate bone remodeling.

Activation of PI3K plays important role in prostate and breast cancer cell proliferation, survival and metastasis. PI3K also mediates critical signaling pathways involving tumor and stromal cell interaction, including cancer-induced bone turnover and osteolysis. BAY 1082439 is a highly selective and potent PI3K inhibitor with balanced activity against PI3kα and PI3Kβ isoforms and currently being evaluated in a phase I clinical trial (N. Liu, et al. AACR 2012 Abstract #2799). Radium-223 dichloride (radium-223), a novel therapy recently approved for treatment of castration-resistant prostate cancer (CRPC) with bone metastases, selectively targets bone and kills metastatic cancer cells by the emission of alpha particles (Parker et al. N Engl J Med. 2013; 369:213).

To identify more effective therapy to treat bone metastases, we evaluated the combination of PI3K inhibitor BAY 1082439 and radium-223 in vitro and in the syngeneic 4T1 metastatic breast cancer model in mice. BAY 1082439 and radium-223 showed synergistic anti-proliferative effects in vitro in both hormone receptor positive (HR+, MCF7 and LNCaP) and negative (4T1 and PC3) breast and prostate tumor cell lines. Pronounced synergistic effects on apoptosis induction were observed in MCF7 and LNCaP cell lines. In vivo, combination of BAY 1082439 at the maximum tolerable dose and radium-223 at the efficacious dose was well tolerated. BAY 1082439 significantly decreased whole body tumor burden as single agent (67% reduction, p=0.00156) and more effectively in combination with radium-223 (81% tumor reduction, p=0.0012), while the effect of radium-223 alone was not statistically significant. Furthermore, BAY 1082439 strongly inhibited tumor-induced osteolysis measured by radiography and led to 53.2% (p=0.16) and 84% (p=0.00698) reduction in total osteolytic area as single agent and in combination with radium-223, respectively. The frequency of soft tissue metastases was also decreased by treatment with BAY 1082439 alone (e.g. 73% reduction in kidney, p=0.012) and more pronounced with radium-223 combination treatment (e.g. complete inhibition of kidney metastasis, p=0.0003). In summary, our data indicate synergistic effects of the PI3K inhibitor BAY 1082439 and radium-223 in inhibiting tumor cell proliferation, survival, total and bone marrow tumor burden, and tumor-induced osteolysis, and warrant further clinical evaluation of this promising combination therapy for the treatment of cancer with bone metastases.

Citation Format: Mari I. Suominen, Katja Fagerlund, Enrico Stasik, Andrea Haegebarth, Arne Scholz, Jukka P. Rissanen, Martin Kornacker, Dominik Mumberg, Jussi M. Halleen, Karl Ziegelbauer, Ningshu Liu. Combination of PI3K inhibitor BAY 1082439 with radium-223 is a promising treatment of cancer with bone metastases. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4022. doi:10.1158/1538-7445.AM2014-4022

Abstract 1803: A new spectrum-selective cathepsin inhibitor, VBY-825, inhibits bone destruction in a syngeneic 5TGM1 multiple myeloma mouse model

Multiple myeloma (MM) is the second most common blood cancer after non Hodgkin lymphoma. It is a monoclonal B-cell neoplasia with clinical hallmarks of multiple osteolytic lesions causing bone pain, fractures and hypercalcemia. Chemo- or radiotherapy may induce remissions, but MM is generally thought to be incurable. Our aim was to observe the effects of a cathepsin inhibitor VBY-825 on bone lesions and tumor burden in the syngeneic 5TGM1 mouse MM model using immunocompetent C57BL/KaLwRij mice. VBY-825 is a potent inhibitor of cathepsins K, L, B, V, and S. 5TGM1 cells were inoculated via tail vein in 7 weeks old female C57BL/KaLwRij mice, which were divided to 4 groups: Control group received vehicle of VBY-825 (5% dextrose 10 ml/kg daily), Control group received bortezomib vehicle (3 ml/kg twice a week), Reference group received bortezomib (0.5 mg/kg twice a week) and Study group received VBY-825 (100 mg/kg daily). Administration of all compounds began one day before tumor cell inoculation and continued until day 34. Disease progression was followed by measuring the serum levels of paraprotein (IgG2b) and TRACP 5b, radiography, and body weight. The animals were sacrificed 5 weeks after inoculation, examined macroscopically, and their bones were collected for histomorphometric analysis.

The reference compound bortezomib had no effects on body weight but it delayed the disease progression based on IgG2b measurements. It also decreased the number and total area of osteolytic lesions, but not mean osteolytic lesion area (MOLA). VBY-825 had no effect on body weight or IgG2b level, frequency of soft tissue tumors or intraosseous tumor area. VBY-825 decreased total and MOLA, consistent with inhibited resorption. There was also a trend of increased relative trabecular bone area. Serum TRACP 5b activity in the VBY-825 treated group did not differ from the respective vehicle group, whereas the number of osteoclasts at tumor-bone interface was increased in VBY-825 treated animals. These findings suggest that VBY-825 decreased osteoclast function and resorption activity without decreasing the number of osteoclasts

In conclusion, VBY-825 had no effects on tumor growth but it inhibited bone destruction in this mouse model of MM, which is consistent with its potency on cathepsin S and K, which are known to be important in osteoclast-mediated bone resorption. VBY-825 is a promising candidate for the treatment of tumor-associated bone disease.

Citation Format: Mari I. Suominen, Johanna Tuomela, Esa Alhoniemi, Katja M. Fagerlund, Jukka P. Rissanen, Jussi M. Halleen, Leslie J. Holsinger. A new spectrum-selective cathepsin inhibitor, VBY-825, inhibits bone destruction in a syngeneic 5TGM1 multiple myeloma mouse model. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1803. doi:10.1158/1538-7445.AM2014-1803

Clinical significance of serum BAP, TRACP 5b and ICTP as bone metabolic markers for bone metastasis screening in lung cancer patients

BACKGROUND

We investigated the clinical significance of serum bone-specific alkaline phosphatase (BAP), tartrate-resistant acid phosphatase isoform 5b (TRACP 5b) and type I collagen carboxyterminal telopeptide (ICTP) as bone metabolic markers for bone metastasis (BM) screening in lung cancer patients.

METHODS

Newly diagnosed advanced lung cancer patients with (N = 130) and without (N = 135) BM were enrolled in the study. Serum BAP, TRACP 5b and ICTP were measured before the treatment.

RESULTS

BAP, TRACP 5b and ICTP values were higher in patients with BM compared with patients without BM (all P < 0.0001). Area under ROC curve (AUC) of BAP, TRACP 5b and ICTP was 0.760, 0.753 and 0.835 (all P < 0.0001), respectively. The cut-off values for BAP, TRACP 5b and ICTP were 21.8 μg/l, 7.8 U/l and 8.8 μg/l, respectively. When TRACP 5b and ICTP were combined, AUC was elevated to 0.895 (P < 0.0001), and the cut-off values were TRACP 5b 7.6 U/l and ICTP 8.4 μg/l.

CONCLUSIONS

We conclude that serum BAP, TRACP 5b and ICTP may serve as useful tools for BM screening in lung cancer patients.

Survival benefit with radium-223 dichloride in a mouse model of breast cancer bone metastasis

BACKGROUND

Bone metastases are associated with increased morbidity and poor prognosis in breast cancer patients. Radium-223 dichloride is a calcium mimetic that localizes to bone, providing targeted therapy for skeletal metastasis.

METHODS

We investigated the mode of action of radium-223 dichloride using breast cancer cell, osteoclast, and osteoblast cultures as well as a mouse model of breast cancer bone metastasis. A single dose of radium-223 dichloride was used in three different settings mimicking the prevention or treatment of bone metastasis. Disease progression was monitored using fluorescence and radiographic imaging and histological analyses. The effect of radium-223 dichloride alone and in combination with doxorubicin or zoledronic acid on survival of mice was analyzed by Kaplan-Meier methods. All statistical tests used were two-sided.

RESULTS

Radium-223 dichloride incorporated into bone matrix and inhibited proliferation of breast cancer cells and differentiation of osteoblasts and osteoclasts (all P values < .001) in vitro. In an established bone metastasis setting, radium-223 dichloride prevented tumor-induced cachexia (0/14 vs 7/14 control mice) and decreased osteolysis by 56% and tumor growth by 43% (all P values < .05). Radium-223 dichloride induced double-strand DNA breaks in cancer cells in vivo. Finally, radium-223 dichloride extended survival as a monotherapy (29.2 days, 95% confidence interval [CI] = 26.6 to 31.8 days, P = .039) and in combination with zoledronic acid (31.4 days, 95% CI = 28.8 to 34.0 days, P = .004) or doxorubicin (31.5 days, 95% CI = 29.5 to 33.5 days, P < .001) compared to the vehicle group (24.9 days, 95% CI = 23.4 to 26.4 days). Similar but even more pronounced effects were observed when radium-223 dichloride was administered in a preventive or micrometastatic setting.

CONCLUSIONS

Our findings strongly support the development of radium-223 dichloride for the treatment of breast cancer patients with or at high risk of developing bone metastases.

Abstract LB-105: Radium-223 dichloride monotherapy and combination therapy with zoledronic acid or doxorubicin improve survival in a mouse model of breast cancer bone metastasis

Breast cancer metastasis to bone results in significant morbidity and poor prognosis. Radium-223 dichloride is an alpha-emitting calcium mimetic that localizes to bone and provides targeted radiation therapy. A phase III clinical study on prostate cancer patients with bone metastases showed that radium-223 dichloride improved overall survival (ALSYMPCA, Parker et al. ECCO/ESMO 2011). We have previously reported that radium-223 decreases osteolysis and tumor burden in bone in a mouse model of breast cancer bone metastasis in preventive and micro-metastatic settings (Suominen et al. AACR Annual Meeting 2012), as well as, in mice with established bone metastases (Suominen et al. AACR Annual Meeting 2011).

Here, we investigated the effects of radium-223 dichloride monotherapy compared to and in combination with either doxorubicin or zoledronic acid on survival in a mouse model of established breast cancer bone metastasis. Human MDA-MB-231(SA)/GFP cells were inoculated intracardially into nude mice, and 15 days later, a single dose of vehicle, radium-223 dichloride (300 kBq/kg, iv injection) and/or zoledronic acid (0.1 mg/kg, sc injection) was administered. Doxorubicin (5 mg/kg, ip injection) was administered once weekly. Radium-223 dichloride monotherapy extended time to sacrifice (P = 0.039), unlike doxorubicin or zoledronic acid monotherapy which did not improve survival as compared to the vehicle group. Radium-223 dichloride in combination with zoledronic acid (P = 0.004) or doxorubicin (P &lt; 0.001) also extended time to sacrifice as compared to the vehicle but did not provide additional survival benefit as compared to the radium-223 dichloride monotherapy.

Histological examination revealed that radium-223 dichloride treatment induced tumor cell necrosis in bone metastases. Therefore, the effect of radium-223 dichloride in inducing double-strand breaks in cancer cells was evaluated by immunohistochemical staining of γ-H2AX molecules. A 3-fold increase in the number of tumor cells with double-strand breaks in the radium-223 dichloride-treated as compared to the vehicle control mice was observed (P &lt; 0.001). This finding supports our previous observations that radium-223 dichloride has an effect on both tumor cells and osteoclasts.

In conclusion, radium-223 dichloride therapy alone or in combination with doxorubicin or zoledronic acid increases survival in breast cancer bone metastasis mouse model via dual action by targeting tumor growth and osteolysis, both important players in the destructive vicious cycle of bone metastasis. Our findings strongly support the development of radium-223 dichloride for the treatment of patients with bone metastatic breast cancer.

Citation Format: Mari I. Suominen, Jukka P. Rissanen, Rami Kakonen, Katja M. Fagerlund, Esa Alhoniemi, Dominik Mumberg, Karl Ziegelbauer, Jussi M. Halleen, Sanna-Maria Kakonen, Arne Scholz. Radium-223 dichloride monotherapy and combination therapy with zoledronic acid or doxorubicin improve survival in a mouse model of breast cancer bone metastasis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-105. doi:10.1158/1538-7445.AM2013-LB-105