Chemotherapy and the Extra-Tumor Immune Microenvironment: EXTRA-TIME

SUMMARY

Understandably, conventional therapeutic strategies have focused on controlling primary tumors. We ask whether the cost of such strategies is actually an increased likelihood of metastatic relapse.

HTLV-1 infected T cells cause bone loss via small extracellular vesicles

Adult T cell leukemia (ATL), caused by infection with human T cell leukemia virus type 1 (HTLV-1), is often complicated by hypercalcemia and osteolytic lesions. Therefore, we studied the communication between patient-derived ATL cells (ATL-PDX) and HTLV-1 immortalized CD4+ T cell lines (HTLV/T) with osteoclasts and their effects on bone mass in mice. Intratibial inoculation of some HTLV/T lead to a profound local decrease in bone mass similar to marrow-replacing ATL-PDX, despite the fact that few HTLV/T cells persisted in the bone. To study the direct effect of HTLV/T and ATL-PDX on osteoclasts, supernatants were added to murine and human osteoclast precursors. ATL-PDX supernatants from hypercalcemic patients promoted formation of mature osteoclasts, while those from HTLV/T were variably stimulatory, but had largely consistent effects between human and murine cultures. Interestingly, this osteoclastic activity did not correlate with expression of osteoclastogenic cytokine RANKL, suggesting an alternative mechanism. HTLV/T and ATL-PDX produce small extracellular vesicles (sEV), known to facilitate HTLV-1 infection. We hypothesized that these sEV also mediate bone loss by targeting osteoclasts. We isolated sEV from both HTLV/T and ATL-PDX, and found they carried most of the activity found in supernatants. In contrast, sEV from uninfected activated T cells had little effect. Analysis of sEV (both active and inactive) by mass spectrometry and electron microscopy confirmed absence of RANKL and intact virus. Viral proteins Tax and Env were only present in sEV from the active, osteoclast-stimulatory group, along with increased representation of proteins involved in osteoclastogenesis and bone resorption. sEV injected over mouse calvaria in the presence of low dose RANKL caused more osteolysis than RANKL alone. Thus, HTLV-1 infection of T cells can cause release of sEV with strong osteolytic potential, providing a mechanism beyond RANKL production that modifies the bone microenvironment, even in the absence of overt leukemia.

BCAR4 Expression as a Predictive Biomarker for Endocrine Therapy Resistance in Breast Cancer

BACKGROUND

Breast cancer, particularly the estrogen receptor positive (ER+) subtype, remains a leading cause of cancer-related death among women. Endocrine therapy is the most effective treatment for ER+ breast cancer; however, the development of resistance presents a significant challenge. This study explored the role of the breast cancer antiestrogen resistance 4 (BCAR4) gene as a potential driver of resistance and a pivotal biomarker in breast cancer.

PATIENTS AND METHODS

The researchers undertook a comprehensive analysis of 1743 patients spanning 6 independent cohorts. They examined the association of BCAR4 expression with patient outcomes across all breast cancer types and the PAM50 molecular subtypes. The relationship between elevated BCAR4 expression and resistance to endocrine therapy including AIs, the prevailing standard-of-care for endocrine therapy, was also investigated.

RESULTS

This meta-analysis corroborated the link between BCAR4 expression and adverse outcomes as well as resistance to endocrine therapy in breast cancer. Notably, BCAR4 expression is clinically significant in luminal A and B subtypes. Additionally, an association between BCAR4 expression and resistance to AI treatment was discerned.

CONCLUSION

This study expands on previous findings by demonstrating that BCAR4 expression is associated with resistance to newer therapies. The identification of patients with intrinsic resistance to hormone therapy is crucial to avoid ineffective treatment strategies. These findings contribute to our understanding of endocrine therapy resistance in breast cancer and could potentially guide the development of more effective treatment strategies.

Resistance to abemaciclib is associated with increased metastatic potential and lysosomal protein deregulation in breast cancer cells

Cyclin dependent kinase 4 and 6 inhibitors such as abemaciclib are routinely used to treat metastatic estrogen receptor positive (ER+) breast cancer. However, adaptive mechanisms inhibit their effectiveness and allow for disease progression. Using ER+ breast cancer cell models, we show that acquired resistance to abemaciclib is accompanied by increase in metastatic potential. Mass spectrometry-based proteomics from abemaciclib sensitive and resistant cells showed that lysosomal proteins including CTSD (cathepsin D), cathepsin A and CD68 were significantly increased in resistant cells. Combination of abemaciclib and a lysosomal destabilizer, such as hydroxychloroquine (HCQ) or bafilomycin A1, resensitized resistant cells to abemaciclib. Also, combination of abemaciclib and HCQ decreased migration and invasive potential and increased lysosomal membrane permeability in resistant cells. Prosurvival B cell lymphoma 2 (BCL2) protein levels were elevated in resistant cells, and a triple treatment with abemaciclib, HCQ, and BCL2 inhibitor, venetoclax, significantly inhibited cell growth compared to treatment with abemaciclib and HCQ. Furthermore, resistant cells showed increased levels of Transcription Factor EB (TFEB), a master regulator of lysosomal-autophagy genes, and siRNA mediated knockdown of TFEB decreased invasion in resistant cells. TFEB was found to be mutated in a subset of invasive human breast cancer samples, and overall survival analysis in ER+, lymph node-positive breast cancer showed that increased TFEB expression correlated with decreased survival. Collectively, we show that acquired resistance to abemaciclib leads to increased metastatic potential and increased levels of protumorigenic lysosomal proteins. Therefore, the lysosomal pathway could be a therapeutic target in advanced ER+ breast cancer.

Transferrin receptor in primary and metastatic breast cancer: Evaluation of expression and experimental modulation to improve molecular targeting

BACKGROUND

Conjugation of transferrin (Tf) to imaging or nanotherapeutic agents is a promising strategy to target breast cancer. Since the efficacy of these biomaterials often depends on the overexpression of the targeted receptor, we set out to survey expression of transferrin receptor (TfR) in primary and metastatic breast cancer samples, including metastases and relapse, and investigate its modulation in experimental models.

METHODS

Gene expression was investigated by datamining in twelve publicly-available datasets. Dedicated Tissue microarrays (TMAs) were generated to evaluate matched primary and bone metastases as well as and pre and post chemotherapy tumors from the same patient. TMA were stained with the FDA-approved MRQ-48 antibody against TfR and graded by staining intensity (H-score). Patient-derived xenografts (PDX) and isogenic metastatic mouse models were used to study in vivo TfR expression and uptake of transferrin.

RESULTS

TFRC gene and protein expression were high in breast cancer of all subtypes and stages, and in 60-85% of bone metastases. TfR was detectable after neoadjuvant chemotherapy, albeit with some variability. Fluorophore-conjugated transferrin iron chelator deferoxamine (DFO) enhanced TfR uptake in human breast cancer cells in vitro and proved transferrin localization at metastatic sites and correlation of tumor burden relative to untreated tumor mice.

CONCLUSIONS

TfR is expressed in breast cancer, primary, metastatic, and after neoadjuvant chemotherapy. Variability in expression of TfR suggests that evaluation of the expression of TfR in individual patients could identify the best candidates for targeting. Further, systemic iron chelation with DFO may upregulate receptor expression and improve uptake of therapeutics or tracers that use transferrin as a homing ligand.

p38MAPKα Stromal Reprogramming Sensitizes Metastatic Breast Cancer to Immunotherapy

Metastatic breast cancer is an intractable disease that responds poorly to immunotherapy. We show that p38MAPKα inhibition (p38i) limits tumor growth by reprogramming the metastatic tumor microenvironment in a CD4+ T cell-, IFNγ-, and macrophage-dependent manner. To identify targets that further increased p38i efficacy, we utilized a stromal labeling approach and single-cell RNA sequencing. Thus, we combined p38i and an OX40 agonist that synergistically reduced metastatic growth and increased overall survival. Intriguingly, patients with a p38i metastatic stromal signature had better overall survival that was further improved by the presence of an increased mutational load, leading us to ask if our approach would be effective in antigenic breast cancer. The combination of p38i, anti-OX40, and cytotoxic T-cell engagement cured mice of metastatic disease and produced long-term immunologic memory. Our findings demonstrate that a detailed understanding of the stromal compartment can be used to design effective antimetastatic therapies.

SIGNIFICANCE

Immunotherapy is rarely effective in breast cancer. We dissected the metastatic tumor stroma, which revealed a novel therapeutic approach that targets the stromal p38MAPK pathway and creates an opportunity to unleash an immunologic response. Our work underscores the importance of understanding the tumor stromal compartment in therapeutic design. This article is highlighted in the In This Issue feature, p. 1275.

Abstract 251: Inhibition of stromal p38MAPKalpha triggers innate-adaptive anti-tumor immunity in metastatic breast cancer

Metastases are the main cause of death in breast cancer patients. Among breast metastatic sites, bone is the most prevalent site that can also seed secondary metastases. Moreover, once tumor cells reach the bone, the disease is considered incurable and treatments are only palliative. For this reason, new therapies that limit metastatic growth are desperately needed. We previously showed that pharmacological inhibition of p38MAPKα (p38i) limited visceral and bone metastases in several clinically relevant models of breast cancer metastasis. Indeed, we found that this approach had no impact on tumor cells but instead limited the supporting nature of the stromal compartment. These findings led us to ask how p38i impacted the stromal compartment. Using a novel strategy to segregate tumor-infiltrating from non-tumor-infiltrating stromal cells in the bone metastatic site, we carried out single cell RNA sequencing (scRNA-Seq) to investigate how p38i altered immune and non-immune tumor stroma. Our analyses revealed that p38i treatment shifts tumor-associated macrophages in the bone towards a tumor-suppressive phenotype with increased signatures for IFNγ signaling and adaptive immunity. Importantly, the gene signature we identified in bone macrophages under p38i treatment correlated with better survival among patients with luminal B breast tumors. Given the importance of the p38i gene signature in patient samples, we next depleted macrophages and also blocked IFNγ and found both approaches reversed the p38i anti-tumor effect. Because T cells are an important source of IFNγ in vivo, we next assessed whether T cells were required by p38i to limit tumor growth. Depletion of CD4+ T cells, but not CD8+ T cells, blunted the p38i anti-tumor effect. Although p38i did not increase CD4+ T cell infiltration, p38i increased the percentage of activated CD4+ T cells infiltrating bone metastases. The requirement for CD4+ T cells in our model and the lack of evident OX40 ligand in our scRNA-Seq data led us to ask if p38i could be used in combination with immunotherapy to further limit metastases. Indeed, combination of p38i and agonist anti-OX40 (agOX-40) immunotherapy synergistically reduced metastatic growth and increased overall survival in our mouse models. Finally, because our work revealed no obvious role for CD8+ T cells in this model, we next asked if introduction of a CD8+ T cell antigen could further increase the anti-tumor effects of p38i. We thus modified PyMT-BO1 cells to express ovalbumin, which contains a strong CD8 antigen and combined it with p38i and agOX40. This combination led to a greater than 90% cure rate of mice with metastatic lesions. Although the mechanisms by which inhibition of p38MAPKα shapes the metastatic tumor microenvironment are still under investigation, our findings indicate that metastatic breast cancer patients may benefit from immunotherapy when carried out in combination with p38i.

Citation Format: Douglas Vendas Faget, Xianmin Luo, Qihao Ren, Jiayu Ye, Thomas Cole, Zhangting Yao, Bhavna Murali, Xinming Su, Yalin Xu, Joseph B. Monahan, Katherine N. Weilbaecher, David G. DeNardo, Sheila A. Stewart. Inhibition of stromal p38MAPKalpha triggers innate-adaptive anti-tumor immunity in metastatic breast 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 251.

A randomized feasibility study evaluating temozolomide circadian medicine in patients with glioma

Background

Gliomas are the most common primary brain tumor in adults. Current treatments involve surgery, radiation, and temozolomide (TMZ) chemotherapy; however, prognosis remains poor and new approaches are required. Circadian medicine aims to maximize treatment efficacy and/or minimize toxicity by timed delivery of medications in accordance with the daily rhythms of the patient. We published a retrospective study showing greater anti-tumor efficacy for the morning, relative to the evening, administration of TMZ in patients with glioblastoma. We conducted this prospective randomized trial to determine the feasibility, and potential clinical impact, of TMZ chronotherapy in patients with gliomas (NCT02781792).

Methods

Adult patients with gliomas (WHO grade II-IV) were enrolled prior to initiation of monthly TMZ therapy and were randomized to receive TMZ either in the morning (AM) before 10 am or in the evening (PM) after 8 pm. Pill diaries were recorded to measure compliance and FACT-Br quality of life (QoL) surveys were completed throughout treatment. Study compliance, adverse events (AE), and overall survival were compared between the two arms.

Results

A total of 35 evaluable patients, including 21 with GBM, were analyzed (18 AM patients and 17 PM patients). Compliance data demonstrated the feasibility of timed TMZ dosing. There were no significant differences in AEs, QoL, or survival between the arms.

Conclusions

Chronotherapy with TMZ is feasible. A larger study is needed to validate the effect of chronotherapy on clinical efficacy.

Yoga Therapy During Chemotherapy for Early-Stage and Locally Advanced Breast Cancer

Background:

Chemotherapy is associated with decreased quality of life (QOL), fatigue, depression, and weight gain in patients with breast cancer. Weight gain is associated with poorer prognosis. Yoga improves QOL, fatigue, and mood in women with breast cancer but its effect on treatment-related weight gain has not been studied. The aim of this trial was to determine the feasibility of personalized yoga therapy in women receiving treatment for early-stage or locally advanced breast cancer and assess its impact on weight gain.

Methods:

Thirty women were randomized 1:1 to receive yoga therapy by a certified yoga therapist during treatment or a control group. Participants in the yoga arm were asked to complete three 30 minute yoga sessions weekly (which included movement, breath work, mindfulness, and relaxation) throughout adjuvant or neoadjuvant chemotherapy (N = 29) or endocrine (N = 1); the control arm received breast cancer treatment without yoga. For comparability between participants randomized to yoga therapy, the single patient treated with endocrine therapy was excluded from the analysis. Primary outcomes were feasibility and weight change. Additional outcomes were mood, fatigue, QOL, serum tumor necrosis factor-alpha (TNF-alpha), and C-reactive protein (CRP) as immune mediator biomarkers.

Results:

Mean age was 51.6 years, 75.9% were white and 24.1% were people of color, reflecting the cancer center population. 80% had stage II-III disease. Enrollment was completed in 9 months. Compliance was lower than predicted; however, participants participated in on average 1.7 yoga sessions/week for a mean 15.6 weeks duration. There were no adverse events. Control arm participants gained on average 2.63% body weight during treatment while yoga participants lost 0.14% body weight (weight change = −0.36 in yoga arm vs. 2.89 in standard of care arm, Wilcoxon rank sum test P = .024). Control participants reported increased fatigue and decreased QOL, while yoga participants reported no change in QOL. No significant change in TNF-alpha or CRP was noted in either arm.

Conclusion:

This feasibility study suggests that personalized yoga therapy is beneficial for QOL and weight maintenance among women undergoing chemotherapy for early-stage or locally advanced breast cancer. Weight maintenance associated with yoga therapy may be of clinical significance in this population given the poorer prognosis associated with weight gain in breast cancer survivors.

Trial Registration:

NIH Clinicaltrials.gov #NCT03262831; August 25, 2017. https://clinicaltrials.gov/ct2/show/NCT03262831

Breast cancer-derived GM-CSF regulates arginase 1 in myeloid cells to promote an immunosuppressive microenvironment

Tumor-infiltrating myeloid cells contribute to the development of the immunosuppressive tumor microenvironment. Myeloid cell expression of arginase 1 (ARG1) promotes a protumor phenotype by inhibiting T cell function and depleting extracellular l-arginine, but the mechanism underlying this expression, especially in breast cancer, is poorly understood. In breast cancer clinical samples and in our mouse models, we identified tumor-derived GM-CSF as the primary regulator of myeloid cell ARG1 expression and local immune suppression through a gene-KO screen of breast tumor cell-produced factors. The induction of myeloid cell ARG1 required GM-CSF and a low pH environment. GM-CSF signaling through STAT3 and p38 MAPK and acid signaling through cAMP were required to activate myeloid cell ARG1 expression in a STAT6-independent manner. Importantly, breast tumor cell-derived GM-CSF promoted tumor progression by inhibiting host antitumor immunity, driving a significant accumulation of ARG1-expressing myeloid cells compared with lung and melanoma tumors with minimal GM-CSF expression. Blockade of tumoral GM-CSF enhanced the efficacy of tumor-specific adoptive T cell therapy and immune checkpoint blockade. Taken together, we show that breast tumor cell-derived GM-CSF contributes to the development of the immunosuppressive breast cancer microenvironment by regulating myeloid cell ARG1 expression and can be targeted to enhance breast cancer immunotherapy.

Antibiotic-induced disturbances of the gut microbiota result in accelerated breast tumor growth

The gut microbiota's function in regulating health has seen it linked to disease progression in several cancers. However, there is limited research detailing its influence in breast cancer (BrCa). This study found that antibiotic-induced perturbation of the gut microbiota significantly increases tumor progression in multiple BrCa mouse models. Metagenomics highlights the common loss of several bacterial species following antibiotic administration. One such bacteria, Faecalibaculum rodentium, rescued this increased tumor growth. Single-cell transcriptomics identified an increased number of cells with a stromal signature in tumors, and subsequent histology revealed an increased abundance of mast cells in the tumor stromal regions. We show that administration of a mast cell stabilizer, cromolyn, rescues increased tumor growth in antibiotic treated animals but has no influence on tumors from control cohorts. These findings highlight that BrCa-microbiota interactions are different from other cancers studied to date and suggest new research avenues for therapy development.

Targeted Therapy to β3 Integrin Reduces Chemoresistance in Breast Cancer Bone Metastases

Breast cancer bone metastases are common and incurable. Tumoral integrin β3 (β3) expression is induced through interaction with the bone microenvironment. Although β3 is known to promote bone colonization, its functional role during therapy of established bone metastases is not known. We found increased numbers of β3⁺ tumor cells in murine bone metastases after docetaxel chemotherapy. β3⁺ tumor cells were present in 97% of post-neoadjuvant chemotherapy triple-negative breast cancer patient samples (n = 38). High tumoral β3 expression was associated with worse outcomes in both pre- and postchemotherapy triple-negative breast cancer groups. Genetic deletion of tumoral β3 had minimal effect in vitro, but significantly enhanced in vivo docetaxel activity, particularly in the bone. Rescue experiments confirmed that this effect required intact β3 signaling. Ultrastructural, transcriptomic, and functional analyses revealed an alternative metabolic response to chemotherapy in β3-expressing cells characterized by enhanced oxygen consumption, reactive oxygen species generation, and protein production. We identified mTORC1 as a candidate for therapeutic targeting of this β3-mediated, chemotherapy-induced metabolic response. mTORC1 inhibition in combination with docetaxel synergistically attenuated murine bone metastases. Furthermore, micelle nanoparticle delivery of mTORC1 inhibitor to cells expressing activated αvβ3 integrins enhanced docetaxel efficacy in bone metastases. Taken together, we show that β3 integrin induction by the bone microenvironment promotes resistance to chemotherapy through an altered metabolic response that can be defused by combination with αvβ3-targeted mTORC1 inhibitor nanotherapy. Our work demonstrates the importance of the metastatic microenvironment when designing treatments and presents new, bone-specific strategies for enhancing chemotherapeutic efficacy.

Hedgehog-targeted therapeutics uncouple the vicious cycle of bone metastasis

Paracrine Hedgehog (Hh) signaling, in which tumor-derived Hh ligands activate stromal cells, has been implicated in the development and progression of many cancers. Recent data suggest that Hh-targeted therapeutics exert direct effects on host cells, thus interrupting a "vicious cycle" to bone metastasis that involves osteoblasts, osteoclasts, and tumor cells.

In Vivo Tumorigenesis, Osteolytic Sarcomas, and Tumorigenic Cell Lines from Transgenic Mice Expressing the Human T-Lymphotropic Virus Type 1 (HTLV-1) Tax Viral Oncogene

Human T-lymphotropic virus type 1 (HTLV-1) causes adult T-cell leukemia, a disease commonly associated with hypercalcemia and osteolysis. There is no effective treatment for HTLV-1, and the osteolytic mechanisms are not fully understood. Mice expressing the HTLV-1 oncogene Tax, driven by the human granzyme B promoter (Tax+), develop osteolytic tumors. To investigate the progression of the bone-invasive malignancies, wild-type, Tax+, and Tax+/interferon-γ-/- mice were assessed using necropsy, histologic examination, IHC analysis, flow cytometry, and advanced imaging. Tax+ and Tax+/interferon-γ-/- malignancies of the ear, tail, and foot comprised poorly differentiated, round to spindle-shaped cells with prominent neutrophilic infiltrates. Tail tumors originated from muscle, nerve, and/or tendon sheaths, with frequent invasion into adjacent bone. F4/80+ and anti-mouse CD11b (Mac-1)+ histiocytic cells predominated within the tumors. Three Tax+/interferon-γ-/- cell lines were generated for in vivo allografts, in vitro gene expression and bone resorption assays. Two cell lines were of monocyte/macrophage origin, and tumors formed in vivo in all three. Differences in Pthrp, Il6, Il1a, Il1b, and Csf3 expression in vitro were correlated with differences in in vivo plasma calcium levels, tumor growth, metastasis, and neutrophilic inflammation. Tax+ mouse tumors were classified as bone-invasive histiocytic sarcomas. The cell lines are ideal for further examination of the role of HTLV-1 Tax in osteolytic tumor formation and the development of hypercalcemia and tumor-associated inflammation.

Hepatic lipids promote liver metastasis

Obesity predisposes to cancer and a virtual universality of nonalcoholic fatty liver disease (NAFLD). However, the impact of hepatic steatosis on liver metastasis is enigmatic. We find that while control mice were relatively resistant to hepatic metastasis, those which were lipodystrophic or obese, with NAFLD, had a dramatic increase in breast cancer and melanoma liver metastases. NAFLD promotes liver metastasis by reciprocal activation initiated by tumor-induced triglyceride lipolysis in juxtaposed hepatocytes. The lipolytic products are transferred to cancer cells via fatty acid transporter protein 1, where they are metabolized by mitochondrial oxidation to promote tumor growth. The histology of human liver metastasis indicated the same occurs in humans. Furthermore, comparison of isolates of normal and fatty liver established that steatotic lipids had enhanced tumor-stimulating capacity. Normalization of glucose metabolism by metformin did not reduce steatosis-induced metastasis, establishing the process is not mediated by the metabolic syndrome. Alternatively, eradication of NAFLD in lipodystrophic mice by adipose tissue transplantation reduced breast cancer metastasis to that of control mice, indicating the steatosis-induced predisposition is reversible.

Nonalcoholic fatty liver disease promotes liver metastasis in mice, likely due to lipid transfer to tumor cells.

Nanotherapy delivery of c-myc inhibitor targets Protumor Macrophages and preserves Antitumor Macrophages in Breast Cancer

Tumor-associated macrophages (TAMs) enhance tumor growth in mice and are correlated with a worse prognosis for breast cancer patients. While early therapies sought to deplete all macrophages, current therapeutics aim to reprogram pro-tumor macrophages (M2) and preserve those necessary for anti-tumor immune responses (M1). Recent studies have shown that c-MYC (MYC) is induced in M2 macrophages in vitro and in vivo where it regulates the expression of tumor-promoting genes. In a myeloid lineage MYC KO mouse model, MYC had important roles in macrophage maturation and function leading to reduced tumor growth. We therefore hypothesized that targeted delivery of a MYC inhibitor to established M2 TAMs could reduce polarization toward an M2 phenotype in breast cancer models.

Methods: In this study, we developed a MYC inhibitor prodrug (MI3-PD) for encapsulation within perfluorocarbon nanoparticles, which can deliver drugs directly to the cytosol of the target cell through a phagocytosis independent mechanism. We have previously shown that M2-like TAMs express significant levels of the vitronectin receptor, integrin β3, and in vivo targeting and therapeutic potential was evaluated using αvβ3 integrin targeted rhodamine-labeled nanoparticles (NP) or integrin αvβ3-MI3-PD nanoparticles.

Results: We observed that rhodamine, delivered by αvβ3-rhodamine NP, was incorporated into M2 tumor promoting macrophages through both phagocytosis-independent and dependent mechanisms, while NP uptake in tumor suppressing M1 macrophages was almost exclusively through phagocytosis. In a mouse model of breast cancer (4T1-GFP-FL), M2-like TAMs were significantly reduced with αvβ3-MI3-PD NP treatment. To validate this effect was independent of drug delivery to tumor cells and was specific to the MYC inhibitor, mice with integrin β3 knock out tumors (PyMT-Bo1 β3KO) were treated with αvβ3-NP or αvβ3-MI3-PD NP. M2 macrophages were significantly reduced with αvβ3-MI3-PD nanoparticle therapy but not αvβ3-NP treatment.

Conclusion: These data suggest αvβ3-NP-mediated drug delivery of a c-MYC inhibitor can reduce protumor M2-like macrophages while preserving antitumor M1-like macrophages in breast cancer.

Balixafortide (a CXCR4 antagonist) plus eribulin in HER2 negative metastatic breast cancer: Dose-response analysis of efficacy from phase I single-arm trial

e15209

Background: Balixafortide (B) is a potent, selective antagonist of the chemokine receptor CXCR4. High CXCR4 levels correlate with aggressive metastatic phenotypes and poor prognosis in metastatic breast cancer (MBC). Efficacy and safety data were published recently from the Phase 1 trial investigating B + eribulin (E) in patients with HER2 negative MBC1. We report the final efficacy analyses from this trial, including assessment of dose-response. Methods: In this single-arm, dose escalation trial, patients (pts) received E + increasing doses of B using a 3+3 design in 3 parts: Part I (cohorts received low E doses); Part II (dose-escalation cohort for B [1−5.5mg/kg] + 1.4mg/m2 E); Expanded Cohort (EC; 5.5mg/kg B + 1.4mg/m2 E) to confirm safety and efficacy. Results: At entry, all 56 women (age range 33−82 years) were HER2-negative (IHC and/or FISH), CXCR4 positive. The majority were Caucasian. Most pts were heavily pre-treated in the metastatic setting (line of chemotherapy on study: 29% 2nd line, 50% 3rd line, 21% 4th line). 75% were hormone receptor positive and 23% had triple negative breast cancer. Conclusions: A consistent dose response effect for B + E was suggested in heavily pretreated pts with HER2 negative MBC across all efficacy endpoints. A comparison of these efficacy results, and particularly response data, with single agent data for E in similar populations2, 3 showed that pts in the EC had a more profound benefit observed consistently throughout all efficacy endpoints. Further data and analysis will be forthcoming for presentation. 1. 3 patients from Part II also included in EC because they received the B dose selected for EC (5.5mg/kg). 2. Part I was an initial safety run-in with lower E doses, and so is not included in the table. 1. Pernas S et al. Lancet Oncol. 2018; 19: 812−24 2. Cortes J et al. Lancet. 2011; 377: 914−923 3. Kaufman PA et al. J Clin Oncol. 2015; 33: 594−601. Clinical trial information: NCT01837095 . [Table: see text]

Mutation profile differences in younger and older patients with advanced breast cancer using circulating tumor DNA (ctDNA)

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Background: Although the noninvasive nature of ctDNA testing is attractive in an older adult population, less is known regarding the mutation profiles of ctDNA in the older adult breast cancer population as this population is often excluded from studies. Previous tissue testing has shown differences in mutation profiles between older and younger adults with breast cancer. The objective of this study is to assess differences in mutation profiles in the older and younger adult breast cancer population using a ctDNA assay. Methods: Patients (pts) with advanced breast cancer underwent molecular profiling using a plasma-based ctDNA NGS assay (Guardant360) between 5/2015-10/2019 at Siteman Cancer Center. Clinicopathological histories were obtained from the medical record. The results of a multicenter database of pts with advanced breast cancer who had undergone molecular profiling using Guardant360 were obtained. Associations between mutations and age were measured using a Fisher’s exact test. Results: In the single institution cohort, of the 214 patients who underwent testing, 148 (69.16%) were < 65 and 66 (30.84%) ≥ 65 years-old. The most frequently mutated genes in age < 65 pts were TP53 (48.65%), PIK3CA (35.81%), and ESR1 (30.41%) while the most frequently mutated genes in age≥65 pts were PIK3CA (56.06%), TP53 (51.52%), ESR1 (25.76%), and ATM (21.21%). ATM, BRAF and PIK3CA mutations were found more frequently in age≥ 65 pts with ER+ HER2- breast tumors (p < 0.01). MYC and ESR1 mutations were not significantly associated with age, overall or within subtype. Overall ctDNA resulted in change in management in 19.8% pts (40/202). In the larger multicenter cohort, of the 8803 pts who underwent testing, 5367 (61.0%) were < 65 and 3417 (38.8%) ≥ 65 years-old. ATM, ESR1 and PIK3CA mutations were more common in age≥65 pts (p < 0.0001) and MYC mutations were less common in age≥65 pts (p < 0.0001). Conclusions: This study found that ctDNA is a feasible, attractive alternative to traditional biopsies and may identify actionable mutations in older adults with breast cancer. When controlling for subtype, results from a single institution were similar to the larger multicenter cohort showing ATM and PIK3CA were more common in the older adult population. This data suggests there may be additional molecular differences between breast cancer in older compared to younger adults that warrants further investigation.

Mouse model recapitulates the phenotypic heterogeneity of human adult T-cell leukemia/lymphoma in bone

Adult T-cell leukemia/lymphoma has a unique relationship to bone including latency in the marrow, and development of bone invasion, osteolytic tumors and humoral hypercalcemia of malignancy. To study these conditions, we established and characterized a novel mouse model of ATL bone metastasis. Patient-derived ATL cell lines including three that do not express HTLV-1 oncoprotein Tax (ATL-ED, RV-ATL, TL-Om1), an in vitro transformed human T-cell line with high Tax expression (HT-1RV), and an HTLV-1 negative T-cell lymphoma (Jurkat) were injected intratibially into NSG mice, and were capable of proliferating and modifying the bone microenvironment. Radiography, μCT, histopathology, immunohistochemistry, plasma calcium concentrations, and qRT-PCR for several tumor-bone signaling mRNAs were performed. Luciferase-positive ATL-ED bone tumors allowed for in vivo imaging and visualization of bone tumor growth and metastasis over time. ATL-ED and HT-1RV cells caused mixed osteolytic/osteoblastic bone tumors, TL-Om1 cells exhibited minimal bone involvement and aggressive local invasion into the adjacent soft tissues, Jurkat cells proliferated within bone marrow and induced minimal bone cell response, and RV-ATL cells caused marked osteolysis. This mouse model revealed important mechanisms of human ATL bone neoplasms and will be useful to investigate biological interactions, potential therapeutic targets, and new bone-targeted agents for the prevention of ATL metastases to bone.

Parathyroid hormone-related protein promotes bone loss in T-cell leukemia as well as in solid tumors

Parathyroid hormone-related protein (PTHrP) and macrophage inflammatory protein-1α (MIP-1α) are important factors that increase bone resorption and hypercalcemia in adult T-cell leukemia (ATL). We investigated the role of PTHrP and MIP-1α in the development of local osteolytic lesions in T-cell leukemia through overexpression in Jurkat T-cells. Injections of Jurkat-PTHrP and Jurkat-MIP-1α into the tibia and the left ventricle of NSG mice were performed to evaluate tumor growth and metastasis in vivo. Jurkat-pcDNA tibial neoplasms grew at a significantly greater rate and total tibial tumor burden was significantly greater than Jurkat-PTHrP neoplasms. Despite the lower tibial tumor burden, Jurkat-PTHrP bone neoplasms had significantly greater osteolysis than Jurkat-pcDNA and Jurkat-MIP-1α neoplasms. Jurkat-PTHrP and Jurkat-pcDNA cells preferentially metastasized to bone following intracardiac injection, though the overall metastatic burden was lower in Jurkat-PTHrP mice. These findings demonstrate that PTHrP induced pathologic osteolysis in T-cell leukemia but did not increase the incidence of skeletal metastasis.

HTLV-1 viral oncogene HBZ drives bone destruction in adult T cell leukemia

Osteolytic bone lesions and hypercalcemia are common, serious complications in adult T cell leukemia/lymphoma (ATL), an aggressive T cell malignancy associated with human T cell leukemia virus type 1 (HTLV-1) infection. The HTLV-1 viral oncogene HBZ has been implicated in ATL tumorigenesis and bone loss. In this study, we evaluated the role of HBZ on ATL-associated bone destruction using HTLV-1 infection and disease progression mouse models. Humanized mice infected with HTLV-1 developed lymphoproliferative disease and continuous, progressive osteolytic bone lesions. HTLV-1 lacking HBZ displayed only modest delays to lymphoproliferative disease but significantly decreased disease-associated bone loss compared with HTLV-1-infected mice. Gene expression array of acute ATL patient samples demonstrated increased expression of RANKL, a critical regulator of osteoclasts. We found that HBZ regulated RANKL in a c-Fos-dependent manner. Treatment of HTLV-1-infected humanized mice with denosumab, a monoclonal antibody against human RANKL, alleviated bone loss. Using patient-derived xenografts from primary human ATL cells to induce lymphoproliferative disease, we also observed profound tumor-induced bone destruction and increased c-Fos and RANKL gene expression. Together, these data show the critical role of HBZ in driving ATL-associated bone loss through RANKL and identify denosumab as a potential treatment to prevent bone complications in ATL patients.

Assessment of Copper Nanoclusters for Accurate in Vivo Tumor Imaging and Potential for Translation

Nanoparticles have been widely used for preclinical cancer imaging. However, their successful clinical translation is largely hampered by potential toxicity, unsatisfactory detection of malignancy at early stages, inaccurate diagnosis of tumor biomarkers, and histology for imaging-guided treatment. Herein, a targeted copper nanocluster (CuNC) is reported with high potential to address these challenges for future translation. Its ultrasmall structure enables efficient renal/bowel clearance, minimized off-target effects in nontargeted organs, and low nonspecific tumor retention. The pH-dependent in vivo dissolution of CuNCs affords minimal toxicity and potentially selective drug delivery to tumors. The intrinsic radiolabeling through the direct addition of ⁶⁴Cu to CuNC (⁶⁴Cu-CuNCs-FC131) synthesis offers high specific activity for sensitive and accurate detection of CXCR4 via FC131-directed targeting in novel triple negative breast cancer (TNBC) patient-derived xenograft mouse models and human TNBC tissues. In summary, this study not only reveals the potential of CXCR4-targeted ⁶⁴Cu-CuNCs for TNBC imaging in clinical settings, but also provides a useful strategy to design and assess the translational potential of nanoparticles for cancer theranostics.

Balixafortide (a CXCR4 antagonist) + eribulin in HER2-negative metastatic breast cancer (MBC): Survival outcomes of the phase I trial

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Background: Balixafortide (B) is a potent antagonist of the chemokine receptor CXCR4. Preclinical evidence suggests that disrupting CXCR4 dependent pathways prevents development of breast cancer metastases, enhances the cytotoxic effect of chemotherapy and immunotherapy, and counteracts tumor cell evasion of the immune system. Encouraging safety and efficacy data were published recently from the ongoing Phase 1 trial investigating B + eribulin (E) in patients with HER2 negative MBC (Pernas S. et al. Lancet Oncol. 2018; 19: 812−24). The objective response rate, median progression free survival and median overall survival (OS) for the expanded cohort (EC) and the overall efficacy population (OEP) were 37.5% and 29.6%, 6.2 months and 4.5 months, and 18 months and 16.8 months, respectively. Here we report the 18 and 24 months landmark OS data from this trial. Methods: This trial enrolled 56 patients with HER2-negative, CXCR4-positive MBC, previously treated with 1−3 chemotherapy regimens for MBC. A 3+3 dose escalation design was used, followed by an EC. All cohorts received E on days 2 and 9, and B on days 1−3 and 8−10 of 21 day cycles. The association between various baseline biomarkers and treatment outcomes including OS is currently being investigated in a multivariate analysis (MVA). Results: Landmark survival data for the trial are shown in the table. Clinical trial information: NCT01837095. Conclusions: Landmark 18 months and 24 months OS data are consistent with the positive trend of all efficacy read-outs observed in this study and safety information is consistent with what was previously reported. Although inter-trial comparisons should be interpreted with caution, these survival rates, especially for the EC, are higher than those reported for eribulin monotherapy in similar MBC populations. These promising results suggest that B + E could potentially provide a new treatment option in heavily pre-treated patients with HER2 negative MBC and this is currently being investigated in a pivotal, randomized trial.[Table: see text]

Abstract P1-15-05: Is absolute lymphocyte count associated with platinum-sensitivity? A phase II single arm study evaluating the efficacy of neoadjuvant carboplatin and docetaxel in triple negative breast cancer

Background: Platinum-based chemotherapy is still considered investigational for the treatment of sporadic triple negative breast cancer (TNBC). Since patients with TNBC have a high rate of chemotherapy resistance, it is critical to identify platinum-sensitive individuals prior to initiating therapy. Higher absolute lymphocyte count (ALC) is associated with improved clinical response to anthracycline-based chemotherapy, the current standard of care in TNBC. We report the initial results of a phase II single arm study evaluating the efficacy of neoadjuvant carboplatin and docetaxel in TNBC. We also report results of an exploratory analysis assessing whether ALC can be used to predict pathologic complete response (pCR) after treatment with platinum-based chemotherapy.

Patients and Methods: 78 patients with clinical stage II or III TNBC have been enrolled in this ongoing study evaluating the efficacy of neoadjuvant carboplatin and docetaxel (NCT201404107). Patients received docetaxel 75 mg/m2 and carboplatin AUC 6 every three weeks for a total of 6 cycles. Blood samples were collected prior to each cycle, and a posttreatment sample was collected &gt; 3 weeks after completing cycle 6. pCR was defined as no residual invasive disease in the breast, with or without ductal carcinoma in situ, and no tumor deposits in sampled lymph nodes. Baseline characteristics of patients were summarized with descriptive statistics. Univariate and multivariate logistic regression analyses were used to identify factors associated with pCR.

Results: Out of the 78 enrolled patients, 60 have completed all 6 treatment cycles and surgery. The preliminary pCR rate is 46.7%. Age, race, clinical stage, and tumor grade determined at time of diagnosis were not significantly different between pCR patients and non-pCR patients. In univariate analyses, patients with higher ALCs at the posttreatment time point were more likely to have pCR than those who had lower ALCs (OR 5.5, 95% CI 1.5-20.7, p=0.011). Additionally, patients who had higher minimum ALCs were also more likely to have pCR (OR 9.1, 95% CI 1.5-54.9, p=0.016). Baseline ALC values were not associated with pCR. The associations of posttreatment and minimum ALCs to pCR remained statistically significant even after controlling for age and clinical stage at time of diagnosis (posttreatment ALC OR 7.6, 95% CI 1.7-34.8, p=0.009; minimum ALC OR 9.0, 95% CI 1.5-55.2, p=0.018).

Conclusion: The pCR rate of our cohort is similar to that of other trials evaluating neoadjuvant platinum-based chemotherapy in TNBC. Baseline ALC did not predict which patients would achieve pCR. However, the associations of posttreatment and minimum ALCs with pCR indicate patients who are able to maintain a robust population of circulating lymphocytes throughout treatment with platinum-based chemotherapy are more likely to respond favorably. The link between patient immunity and platinum-based chemotherapy suggests addition of immunotherapy agents to neoadjuvant chemotherapy may improve patient outcomes.

Citation Format: Chen I, Guo F, Summa T, Luo J, Ellis MJ, Ma CX, Weilbaecher KN, Naughton MJ, Suresh R, Peterson LL, Cherian MA, Bose R, Frith AE, Hernandez-Aya LF, Gillanders WE, Ademuyiwa FO. Is absolute lymphocyte count associated with platinum-sensitivity? A phase II single arm study evaluating the efficacy of neoadjuvant carboplatin and docetaxel in triple negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-15-05.

Inhibition of the Stromal p38MAPK/MK2 Pathway Limits Breast Cancer Metastases and Chemotherapy-Induced Bone Loss

The role of the stromal compartment in tumor progression is best illustrated in breast cancer bone metastases, where the stromal compartment supports tumor growth, albeit through poorly defined mechanisms. p38MAPKα is frequently expressed in tumor cells and surrounding stromal cells, and its expression levels correlate with poor prognosis. This observation led us to investigate whether inhibition of p38MAPKα could reduce breast cancer metastases in a clinically relevant model. Orally administered, small-molecule inhibitors of p38MAPKα or its downstream kinase MK2 each limited outgrowth of metastatic breast cancer cells in the bone and visceral organs. This effect was primarily mediated by inhibition of the p38MAPKα pathway within the stromal compartment. Beyond effectively limiting metastatic tumor growth, these inhibitors reduced tumor-associated and chemotherapy-induced bone loss, which is a devastating comorbidity that drastically affects quality of life for patients with cancer. These data underscore the vital role played by stromal-derived factors in tumor progression and identify the p38MAPK-MK2 pathway as a promising therapeutic target for metastatic disease and prevention of tumor-induced bone loss.Significance: Pharmacologically targeting the stromal p38MAPK-MK2 pathway limits metastatic breast cancer growth, preserves bone quality, and extends survival. Cancer Res; 78(19); 5618-30. ©2018 AACR.

The β3-integrin endothelial adhesome regulates microtubule-dependent cell migration

Integrin β3 is seen as a key anti-angiogenic target for cancer treatment due to its expression on neovasculature, but the role it plays in the process is complex; whether it is pro- or anti-angiogenic depends on the context in which it is expressed. To understand precisely β3's role in regulating integrin adhesion complexes in endothelial cells, we characterised, by mass spectrometry, the β3-dependent adhesome. We show that depletion of β3-integrin in this cell type leads to changes in microtubule behaviour that control cell migration. β3-integrin regulates microtubule stability in endothelial cells through Rcc2/Anxa2-driven control of active Rac1 localisation. Our findings reveal that angiogenic processes, both in vitro and in vivo, are more sensitive to microtubule targeting agents when β3-integrin levels are reduced.

Perfusion-based fluorescence imaging method delineates diverse organs and identifies multifocal tumors using generic near-infrared molecular probes

Rapid detection of multifocal cancer without the use of complex imaging schemes will improve treatment outcomes. In this study, dynamic fluorescence imaging was used to harness differences in the perfusion kinetics of near-infrared (NIR) fluorescent dyes to visualize structural characteristics of different tissues. Using the hydrophobic nontumor-selective NIR dye cypate, and the hydrophilic dye LS288, a high tumor-to-background contrast was achieved, allowing the delineation of diverse tissue types while maintaining short imaging times. By clustering tissue types with similar perfusion properties, the dynamic fluorescence imaging method identified secondary tumor locations when only the primary tumor position was known, with a respective sensitivity and specificity of 0.97 and 0.75 for cypate, and 0.85 and 0.81 for LS288. Histological analysis suggests that the vasculature in the connective tissue that directly surrounds the tumor was a major factor for tumor identification through perfusion imaging. Although the hydrophobic dye showed higher specificity than the hydrophilic probe, use of other dyes with different physical and biological properties could further improve the accuracy of the dynamic imaging platform to identify multifocal tumors for potential use in real-time intraoperative procedures.

Breast and pancreatic cancer interrupt IRF8-dependent dendritic cell development to overcome immune surveillance

Tumors employ multiple mechanisms to evade immune surveillance. One mechanism is tumor-induced myelopoiesis, whereby the expansion of immunosuppressive myeloid cells can impair tumor immunity. As myeloid cells and conventional dendritic cells (cDCs) are derived from the same progenitors, we postulated that myelopoiesis might impact cDC development. The cDC subset, cDC1, which includes human CD141⁺ DCs and mouse CD103⁺ DCs, supports anti-tumor immunity by stimulating CD8⁺ T-cell responses. Here, to understand how cDC1 development changes during tumor progression, we investigated cDC bone marrow progenitors. We found localized breast and pancreatic cancers induce systemic decreases in cDC1s and their progenitors. Mechanistically, tumor-produced granulocyte-stimulating factor downregulates interferon regulatory factor-8 in cDC progenitors, and thus results in reduced cDC1 development. Tumor-induced reductions in cDC1 development impair anti-tumor CD8⁺ T-cell responses and correlate with poor patient outcomes. These data suggest immune surveillance can be impaired by tumor-induced alterations in cDC development.

Tumors escape the immune system through many mechanisms. Here the authors show that certain tumors inhibit anti-tumor immunity by stopping the production of conventional dendritic cells (cDCs) in the bone marrow, therefore depleting the pool of cDCs available to present antigen to CD8⁺ T cells.

Abstract P5-21-30: Retrospective review of palbociclib (Pal) efficacy and benefit from subsequent treatments following Pal progression in patients (pts) with hormone receptor positive (HR+) and HER2 negative (HER2-) metastatic breast cancer (MBC)

Background

The cyclin-dependent kinase (CDK) 4/6 inhibitor Pal is approved for HR+ HER2- MBC. However, the optimal therapy following Pal progression is unknown. Therefore we conducted this retrospective study to review Pal efficacy and summarize the practice pattern and responses to subsequent treatments post Pal progression.

Methods

We performed a chart review of pts with HR+ HER2- MBC who began Pal treatment at Washington University Siteman Cancer Center between Feb 16, 2015 and July 13, 2016 and collected information on pts demographics, diagnosis, and treatment history. Duration of therapy was used to calculate the progression free survival (PFS) for each regimen. Treatment was considered first-line if administered without any prior systemic therapy or at least 1 year from completion of adjuvant hormonal therapy (HT). Treatments received after progression on 1st line therapy or upon relapse during or within 1 year from the completion of adjuvant HT were considered second-line regimens.

Statistical analyses were performed on SAS software, version 9.4. The Kaplan-Meier method was used to generate time-to-event curves, from which median PFS was calculated. A stratified log-rank test was used for all comparisons, and the P value derived from the comparison was reported.

Results

We completed a chart review for 81 pts (78 female and 3 male; 63 Caucasian, 14 African American, and 4 other races) with HR+ HER2- MBC (68 were ER+PR+, 13 were ER+PR-) who received Pal plus letrozole (n=65) or fulvestrant (n=15) or anastrozole (n=1), with a median age of 62.0 years (range 28.1 - 85.6) at the start of Pal.

The median follow up was 20.0 months (mos) (range 10.8 – 27.9). 25 pts were still on Pal treatment. The median PFS on Pal was 19.9 mos in the first-line setting (n=20), compared to 12.1 mos and 4.4 mos in the second-line (n=14) and subsequent lines (n=47), respectively (p=0.0287). Among the 54 pts who progressed on Pal, 38 moved on to the next treatment. 20 pts received chemotherapy and 16 pts received HT or a HT combination. 2 pts received fulvestrant plus Pal upon progression on letrozole plus Pal, and treatment was still ongoing at 4 mos and 7 mos of follow up, respectively. The most common treatments post Pal were single-agent capecitabine (Cape) (n=9) and the combination of exemestane (Exe) and everolimus (Eve) (n=8). The median PFS was 4.7 mos with Cape compared to 8.4 mos with Exe and Eve (p=0.60). The median PFS was 4.7 mos for the 20 pts who received chemo, whereas the median PFS was 4.9 mos with subsequent HT (n=16) (p=0.75).

Conclusion

Pal plus letrozole or fulvestrant is effective for the treatment of HR+ HER2- MBC, with activity observed beyond the 1st and 2nd line treatment settings. The PFS of Pal observed in this single center retrospective study is consistent with that of published data. Single-agent cape or the Exe and Eve combination were common treatment choices following progression on Pal. Although the study is limited by its small sample size, the median PFS of 8.4 mos with Exe and Eve indicates its potential efficacy in the setting of Pal progression. Additional pts and followup data will be presented.

Citation Format: Xi J, Oza A, Thomas S, Naughton M, Ademuyiwa F, Weilbaecher KN, Suresh R, Bose R, Cherian MA, Hernandez-Aya L, Frith A, Peterson LL, Krishnamurthy J, Ma CX. Retrospective review of palbociclib (Pal) efficacy and benefit from subsequent treatments following Pal progression in patients (pts) with hormone receptor positive (HR+) and HER2 negative (HER2-) metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-21-30.

Bone-Induced Expression of Integrin β3 Enables Targeted Nanotherapy of Breast Cancer Metastases

Bone metastases occur in approximately 70% of metastatic breast cancer patients, often leading to skeletal injuries. Current treatments are mainly palliative and underscore the unmet clinical need for improved therapies. In this study, we provide preclinical evidence for an antimetastatic therapy based on targeting integrin β3 (β3), which is selectively induced on breast cancer cells in bone by the local bone microenvironment. In a preclinical model of breast cancer, β3 was strongly expressed on bone metastatic cancer cells, but not primary mammary tumors or visceral metastases. In tumor tissue from breast cancer patients, β3 was significantly elevated on bone metastases relative to primary tumors from the same patient (n = 42). Mechanistic investigations revealed that TGFβ signaling through SMAD2/SMAD3 was necessary for breast cancer induction of β3 within the bone. Using a micelle-based nanoparticle therapy that recognizes integrin αvβ3 (αvβ3-MPs of ∼12.5 nm), we demonstrated specific localization to breast cancer bone metastases in mice. Using this system for targeted delivery of the chemotherapeutic docetaxel, we showed that bone tumor burden could be reduced significantly with less bone destruction and less hepatotoxicity compared with equimolar doses of free docetaxel. Furthermore, mice treated with αvβ3-MP-docetaxel exhibited a significant decrease in bone-residing tumor cell proliferation compared with free docetaxel. Taken together, our results offer preclinical proof of concept for a method to enhance delivery of chemotherapeutics to breast cancer cells within the bone by exploiting their selective expression of integrin αvβ3 at that metastatic site. Cancer Res; 77(22); 6299-312. ©2017 AACR.

HTLV-1 viral oncogene HBZ induces osteolytic bone disease in transgenic mice

Adult T-cell leukemia/lymphoma (ATL) is an aggressive T cell malignancy that occurs in HTLV-1 infected patients. Most ATL patients develop osteolytic lesions and hypercalcemia of malignancy, causing severe skeletal related complications and reduced overall survival. The HTLV-1 virus encodes 2 viral oncogenes, Tax and HBZ. Tax, a transcriptional activator, is critical to ATL development, and has been implicated in pathologic osteolysis. HBZ, HTLV-1 basic leucine zipper transcription factor, promotes tumor cell proliferation and disrupts Wnt pathway modulators; however, its role in ATL induced osteolytic bone loss is unknown. To determine if HBZ is sufficient for the development of bone loss, we established a transgenic Granzyme B HBZ (Gzmb-HBZ) mouse model. Lymphoproliferative disease including tumors, enlarged spleens and/or abnormal white cell counts developed in two-thirds of Gzmb-HBZ mice at 18 months. HBZ positive cells were detected in tumors, spleen and bone marrow. Importantly, pathologic bone loss and hypercalcemia were present at 18 months. Bone-acting factors were present in serum and RANKL, PTHrP and DKK1, key mediators of hypercalcemia and bone loss, were upregulated in Gzmb-HBZ T cells. These data demonstrate that Gzmb-HBZ mice model ATL bone disease and express factors that are current therapeutic targets for metastatic and bone resident tumors.

Phase I study of the combination of balixafortide (CXCR4 inhibitor) and eribulin in HER2-negative metastatic breast cancer (MBC) patients (pts)

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Background: Balixafortide (POL6326) is a cyclic peptide and a potent, selective antagonist of the chemokine receptor CXCR4. Evidence suggests that CXCR4 inhibition interferes with the tumor-protective microenvironment and sensitizes tumor cells to chemotherapy. The combination of balixafortide (B) and eribulin (E) was safe with early signs of efficacy in the dose escalation part of this study. Methods: The expanded cohort of thisopen label phase I study was designed to assess the anti-tumor activity, safety and pharmacokinetics of the addition of the recommended phase 2 dose (RP2D) of B to E in pts with MBC and with any CXCR4 expression level at the tumor site. Patients received E (1.4 mg/m2) on days 2 and 9, flanked by B (5.5 mg/kg) on days 1-3, and 8-10 of 21-day cycles. Results: 24 pts with relapsed MBC (median age 59 [33-82]) were enrolled in the expanded cohort. Median number of prior chemotherapies for MBC was 2 (range 1-3). 20/24 (83%) pts were ER and/or PR positive; 3/24 (13%) pts had TNBC. Objective response rate (ORR) was 33%. 8/24 (33%) pts achieved a partial response and 4/24 (17%) pts had meaningful (≥ 6 months) stable disease for a Clinical Benefit Ratio of 50%. Median duration of treatment was 15.3 weeks (range 5-40) with 11 pts still on treatment. The most common Gr 3-4 adverse events were neutropenia (9/24, 38%) and leucopenia (3/24, 13%); 2 pts had febrile neutropenia and 1 patient died from sepsis. 15/24 (63%) pts experienced histamine-like infusion reactions related to B that were manageable with anti-histamines. Conclusions: The therapeutic activity of this treatment regimen appears promising with an ORR of 33% in patients with advanced MBC. B (5.5 mg/kg) can be combined safely with E (1.4 mg/m2) and the safety profile resembles E monotherapy as previously reported. This is the first study of the treatment combination of E with B in relapsed MBC pts. Further confirmatory studies are being considered. Clinical trial information: NCT01837095.

Evaluating Acetate Metabolism for Imaging and Targeting in Multiple Myeloma

PURPOSE

We hypothesized that in multiple myeloma cells (MMC), high membrane biosynthesis will induce acetate uptake in vitro and in vivo Here, we studied acetate metabolism and targeting in MMC in vitro and tested the efficacy of ¹¹C-acetate-positron emission tomography (PET) to detect and quantitatively image myeloma treatment response in vivo EXPERIMENTAL DESIGN: Acetate fate tracking using ¹³C-edited-¹H NMR (nuclear magnetic resonance) was performed to study in vitro acetate uptake and metabolism in MMC. Effects of pharmacological modulation of acetate transport or acetate incorporation into lipids on MMC cell survival and viability were assessed. Preclinical mouse MM models of subcutaneous and bone tumors were evaluated using ¹¹C-acetate-PET/CT imaging and tissue biodistribution.

RESULTS

In vitro, NMR showed significant uptake of acetate by MMC and acetate incorporation into intracellular metabolites and membrane lipids. Inhibition of lipid synthesis and acetate transport was toxic to MMC, while sparing resident bone cells or normal B cells. In vivo, ¹¹C-acetate uptake by PET imaging was significantly enhanced in subcutaneous and bone MMC tumors compared with unaffected bone or muscle tissue. Likewise, ¹¹C-acetate uptake was significantly reduced in MM tumors after treatment.

CONCLUSIONS

Uptake of acetate from the extracellular environment was enhanced in MMC and was critical to cellular viability. ¹¹C-Acetate-PET detected the presence of myeloma cells in vivo, including uptake in intramedullary bone disease. ¹¹C-Acetate-PET also detected response to therapy in vivo Our data suggested that acetate metabolism and incorporation into lipids was crucial to MM cell biology and that ¹¹C-acetate-PET is a promising imaging modality for MM. Clin Cancer Res; 23(2); 416-29. ©2016 AACR.

Abstract 2198: Integrin αvβ3-targeted lipase-labile docetaxel-prodrug micelles preferentially treat breast cancer bone metastases

Background: Bone metastases occur in 70% of metastatic breast cancer patients and are a leading cause of morbidity. Current therapies are often palliative, in part due to a lack of specificity for tumor targets within the bone. Integrin αvβ3 is overexpressed on neo-angiogenic blood vessels, tumor-promoting macrophages, osteoclasts, and more aggressive breast cancer cells, making it an attractive therapeutic target.

Objective: The goal of this study was to use Sn2 lipase-labile docetaxel-prodrug nanoparticle, targeted against activated integrin αvβ3, to attenuate breast cancer metastases.

Methods: A novel phospholipid-based micelle (∼12.5 nm) was functionalized with a peptidomimetic for activated integrin αvβ3, and designed to carry either rhodamine for fluorescent labeling or Sn2 lipase-labile prodrug of docetaxel (DTX-PD) for drug delivery. For microscopic localization studies, fluorescently labeled micelles were prepared with or without integrin αvβ3-targeting. C57BL/6 female mice received MMTV-PyMT breast cancer cell line (luciferase-labeled) via intracardiac (IC) injection to achieve tumor metastasis in all major organs. On day 8 post-IC injection, micelle preparations were administered i.v. and circulated within C57BL/6 mice for 3 hours prior to sacrifice and tissue collection. For drug efficacy studies, Sn2 lipase-labile docetaxel-prodrug was incorporated into αvβ3-micelles (αvβ3-DTX-PD). C57BL/6 female mice IC injected with MMTV-PyMT cells (luciferase-labeled) were treated with αvβ3-DTX-PD, or molar equivalent dose of free-DTX, or saline. Beginning on day 4 post-IC injection, mice were treated 3 times, once every 3 days (1.85mg/kg DTX per treatment). On day 12 post-IC injection, metastatic burden in the major organs was analyzed via ex vivo bioluminescent imaging.

Results: Fluorescent histological analysis of the tibiofemoral bone region showed significant colocalization of αvβ3-micelles with breast cancer bone metastases, as compared with non-targeted micelles (6.5-fold increase, p&lt;0.001). αvβ3-micelles did not localize within tumor-free bones. In drug efficacy analysis, αvβ3-DTX-PD micelles significantly attenuated bone metastases (3-fold, p = 0.007) and significantly reduced osteolytic bone destruction as assessed by x-ray analysis (3.5-fold, p = 0.021). Serum chemistry analysis of enzymes indicative of liver damage were elevated in the DTX treated group, but not in αvβ3-DTX-PD or saline treated groups. Interestingly, αvβ3-DTX-PD micelles did not attenuate breast cancer metastases within the liver, lungs, or kidneys. Histological examination of metastatic tumor tissue demonstrated elevated integrin β3 expression in bone metastases, as compared to the other sites.

Conclusion: These findings suggest that the unique elevated expression of integrin αvβ3 within breast cancer bone metastases could be exploited with αvβ3-DTX-PD micelles for effective therapy.

Citation Format: Michael H. Ross, Alison K. Esser, Anne H. Schmieder, Grace Cui, Xiaoxia Yang, Xinming Su, Dipanjan Pan, Gregory M. Lanza, Katherine N. Weilbaecher. Integrin αvβ3-targeted lipase-labile docetaxel-prodrug micelles preferentially treat breast cancer bone metastases. [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 2198.

Antagonizing Integrin β3 Increases Immunosuppression in Cancer

Integrin β3 is critical for tumor invasion, neoangiogenesis, and inflammation, making it a promising cancer target. However, preclinical and clinical data of integrin β3 antagonists have demonstrated no benefit or worse outcomes. We hypothesized that integrin β3 could affect tumor immunity and evaluated tumors in mice with deletion of integrin β3 in macrophage lineage cells (β3KOM). β3KOM mice had increased melanoma and breast cancer growth with increased tumor-promoting M2 macrophages and decreased CD8(+) T cells. Integrin β3 antagonist, cilengitide, also enhanced tumor growth and increased M2 function. We uncovered a negative feedback loop in M2 myeloid cells, wherein integrin β3 signaling favored STAT1 activation, an M1-polarizing signal, and suppressed M2-polarizing STAT6 activation. Finally, disruption of CD8(+) T cells, macrophages, or macrophage integrin β3 signaling blocked the tumor-promoting effects of integrin β3 antagonism. These results suggest that effects of integrin β3 therapies on immune cells should be considered to improve outcomes. Cancer Res; 76(12); 3484-95. ©2016 AACR.

Stromal-Initiated Changes in the Bone Promote Metastatic Niche Development

More than 85% of advanced breast cancer patients suffer from metastatic bone lesions, yet the mechanisms that facilitate these metastases remain poorly understood. Recent studies suggest that tumor-derived factors initiate changes within the tumor microenvironment to facilitate metastasis. However, whether stromal-initiated changes are sufficient to drive increased metastasis in the bone remains an open question. Thus, we developed a model to induce reactive senescent osteoblasts and found that they increased breast cancer colonization of the bone. Analysis of senescent osteoblasts revealed that they failed to mineralize bone matrix and increased local osteoclastogenesis, the latter process being driven by the senescence-associated secretory phenotype factor, IL-6. Neutralization of IL-6 was sufficient to limit senescence-induced osteoclastogenesis and tumor cell localization to bone, thereby reducing tumor burden. Together, these data suggest that a reactive stromal compartment can condition the niche, in the absence of tumor-derived signals, to facilitate metastatic tumor growth in the bone.

Dual-therapy with αvβ3-targeted Sn2 lipase-labile fumagillin-prodrug nanoparticles and zoledronic acid in the Vx2 rabbit tumor model

Fumagillin, an unstable anti-angiogenesis mycotoxin, was synthesized into a stable lipase-labile prodrug and incorporated into integrin-targeted lipid-encapsulated nanoparticles (αvβ3-Fum-PD NP). Dual anti-angiogenic therapy combining αvβ3-Fum-PD NP with zoledronic acid (ZA), a long-acting osteoclast inhibitor with proposed anti-angiogenic effects, was evaluated. In vitro, αvβ3-Fum-PD NP reduced (P<0.05) endothelial cell viability without impacting macrophage viability. ZA suppressed (P<0.05) macrophage viability at high dosages but not endothelial cell proliferation. 3D MR neovascular imaging of rabbit Vx2 tumors showed no effect with ZA, whereas αvβ3-Fum-PD NP alone and with ZA decreased angiogenesis (P<0.05). Immunohistochemistry revealed decreased (P<0.05) microvascularity with αvβ3-Fum-PD NP and ZA and further microvascular reduction (P<0.05) with dual-therapy. In vivo, ZA did not decrease tumor macrophage numbers nor cancer cell proliferation, whereas αvβ3-Fum-PD-NPs reduced both measures. Dual-therapy with ZA and αvβ3-Fum-PD-NP may provide enhanced neo-adjuvant utility if macrophage ZA uptake is increased. From the Clinical Editor: Although anti-angiogenesis is one of the treatment modalities in the fight against cancer, many cancers become resistant to VEGF pathway inhibitors. In this article, the authors investigated the use of dual therapy using fumagillin, integrin-targeted lipid-encapsulated nanoparticles (αvβ3- Fum-PD NP) and zoledronic acid (ZA), in both in-vitro and in-vivo experiments. This combination approach may provide an insight to the design of future drugs against cancers.

Contact-facilitated drug delivery with Sn2 lipase labile prodrugs optimize targeted lipid nanoparticle drug delivery

Sn2 lipase labile phospholipid prodrugs in conjunction with contact-facilitated drug delivery offer an important advancement in Nanomedicine. Many drugs incorporated into nanosystems, targeted or not, are substantially lost during circulation to the target. However, favorably altering the pharmacokinetics and volume of distribution of systemic drug delivery can offer greater efficacy with lower toxicity, leading to new prolonged-release nanoexcipients. However, the concept of achieving Paul Erhlich's inspired vision of a 'magic bullet' to treat disease has been largely unrealized due to unstable nanomedicines, nanosystems achieving low drug delivery to target cells, poor intracellular bioavailability of endocytosed nanoparticle payloads, and the substantial biological barriers of extravascular particle penetration into pathological sites. As shown here, Sn2 phospholipid prodrugs in conjunction with contact-facilitated drug delivery prevent premature drug diffusional loss during circulation and increase target cell bioavailability. The Sn2 phospholipid prodrug approach applies equally well for vascular constrained lipid-encapsulated particles and micelles the size of proteins that penetrate through naturally fenestrated endothelium in the bone marrow or thin-walled venules of an inflamed microcirculation. At one time Nanomedicine was considered a 'Grail Quest' by its loyal opposition and even many in the field adsorbing the pains of a long-learning curve about human biology and particles. However, Nanomedicine with innovations like Sn2 phospholipid prodrugs has finally made 'made the turn' toward meaningful translational success.

CXCR4 Protein Epitope Mimetic Antagonist POL5551 Disrupts Metastasis and Enhances Chemotherapy Effect in Triple-Negative Breast Cancer

The SDF-1 receptor CXCR4 has been associated with early metastasis and poorer prognosis in breast cancers, especially the most aggressive triple-negative subtype. In line with previous reports, we found that tumoral CXCR4 expression in patients with locally advanced breast cancer was associated with increased metastases and rapid tumor progression. Moreover, high CXCR4 expression identified a group of bone marrow-disseminated tumor cells (DTC)-negative patients at high risk for metastasis and death. The protein epitope mimetic (PEM) POL5551, a novel CXCR4 antagonist, inhibited binding of SDF-1 to CXCR4, had no direct effects on tumor cell viability, but reduced migration of breast cancer cells in vitro. In two orthotopic models of triple-negative breast cancer, POL5551 had little inhibitory effect on primary tumor growth, but significantly reduced distant metastasis. When combined with eribulin, a chemotherapeutic microtubule inhibitor, POL5551 additively reduced metastasis and prolonged survival in mice after resection of the primary tumor compared with single-agent eribulin. Hypothesizing that POL5551 may mobilize tumor cells from their microenvironment and sensitize them to chemotherapy, we used a "chemotherapy framing" dosing strategy. When administered shortly before and after eribulin treatment, three doses of POL5551 with eribulin reduced bone and liver tumor burden more effectively than chemotherapy alone. These data suggest that sequenced administration of CXCR4 antagonists with cytotoxic chemotherapy synergize to reduce distant metastases.

Whole Genome Sequence of Multiple Myeloma-Prone C57BL/KaLwRij Mouse Strain Suggests the Origin of Disease Involves Multiple Cell Types

Monoclonal gammopathy of undetermined significance (MGUS) is the requisite precursor to multiple myeloma (MM), a malignancy of antibody-producing plasma B-cells. The genetic basis of MGUS and its progression to MM remains poorly understood. C57BL/KaLwRij (KaLwRij) is a spontaneously-derived inbred mouse strain with a high frequency of benign idiopathic paraproteinemia (BIP), a phenotype with similarities to MGUS including progression to MM. Using mouse haplotype analysis, human MM SNP array data, and whole exome and whole genome sequencing of KaLwRij mice, we identified novel KaLwRij gene variants, including deletion of Samsn1 and deleterious point mutations in Tnfrsf22 and Tnfrsf23. These variants significantly affected multiple cell types implicated in MM pathogenesis including B-cells, macrophages, and bone marrow stromal cells. These data demonstrate that multiple cell types contribute to MM development prior to the acquisition of somatic driver mutations in KaLwRij mice, and suggest that MM may an inherently non-cell autonomous malignancy.

Abstract P3-11-04: Effects of neoadjuvant chemotherapy with or without zoledronic acid on pathological response: A meta-analysis of randomised trials

Background:

The addition of bisphosphonates to adjuvant systemic therapy reduces bone metastases and improves survival in postmenopausal patients with early breast cancer. We have conducted four randomised trials of neoadjuvant chemotherapy (CT) +/- zoledronic (ZA) in stage II/III breast cancer to investigate the potential for enhancing pathological response within the breast and axilla. We report here a meta-analysis of these studies to enable more reliable evaluation of treatment effects and investigate activity in pre-defined subgroups of interest.

Methods:

Individual patient data from four prospective randomized clinical trials reporting the effect of the addition of ZA on pathological response after neoadjuvant CT were pooled. Primary outcomes were pathological complete response in the breast (pCRb) and in the breast and lymph nodes (pCR). A fixed effects Mantel-Haenszel meta-analysis was performed using odds ratios (OR) from multivariate analyses in each study correcting for T-status and ER-status after testing for heterogeneity. Predefined subgroup analyses were performed for postmenopausal women and patients with triple-negative breast cancer.

Results:

pCRb and pCR data were available in 736 and 553 women respectively. A summary of results is shown in the table below. In the total study population, ZA addition to neoadjuvant CT did not increase pCRb/pCR rates (12.9% for CT only vs. 16.0% with CT+ ZA; OR 1.34, 95% C.I. 0.86-2.08). However, in postmenopausal women, the addition of ZA resulted in a doubling of the pCRb rate (8.5% for CT only vs. 17.0% with CT+ ZA; OR 2.72, 95% C.I. 1.15-6.42) and pCR rate (7.8% for CT only vs. 13.6% with CT+ ZA; OR 2.48, 95% C.I. 0.80-7.69). There was significant interaction between menopausal status and ZA benefit (P for interaction=0.047). In patients with triple-negative breast cancer a trend was observed favouring CT+ZA.

Pathological responseCTCT + ZAOdd's Ratio95% C.I.pCRb/totalPercentagepCRb/totalPercentagepCR in breastTotal population48/37312.958/36316.01.340.86-2.08Postmenopausal patients11/1308.524/14117.02.721.15-6.42*Pre/perimenopausal patients34/23214.733/21415.41.030.59-1.79Triple-negative breast cancer13/7018.621/6731.31.990.85-4.66pCR/totalPercentagepCR/totalPercentagepCR in breast and lymph nodesTotal population28/27910.033/27412.01.310.73-2.34Postmenopausal patients7/907.814/10313.62.480.80-7.69Pre/perimenopausal patients19/17810.718/16311.01.000.49-2.08Triple-negative breast cancer9/5217.315/5129.41.800.63-5.21Overview of pCRb and pCR in both treatment arms in the total population and predefined subgroups

Conclusion:

This meta-analysis shows that no overall benefit from the addition of ZA to neoadjuvant CT. However, as has been seen in the adjuvant setting, the addition of ZA to CT in postmenopausal women with early breast cancer appears to specifically increase the effects of CT with increases in pCRb and pCR. Further translational research is warranted to explore the mechanism of these observations and the potential treatment interaction with menopause.

Citation Format: Judith R Kroep, Ayoub Charehbili, Rob E Coleman, Rebecca L Aft, Yoshie Hasegawa, Gerrit-Jan Liefers, Matthew C Winter, Katherine N Weilbaecher, Kohei Akazawa, Samantha Hinsley, Hein Putter, Hans WR Nortier, Norio Kohno. Effects of neoadjuvant chemotherapy with or without zoledronic acid on pathological response: A meta-analysis of randomised trials [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-11-04.

Small Molecule MYC Inhibitor Conjugated to Integrin-Targeted Nanoparticles Extends Survival in a Mouse Model of Disseminated Multiple Myeloma

Multiple myeloma pathogenesis is driven by the MYC oncoprotein, its dimerization with MAX, and the binding of this heterodimer to E-Boxes in the vicinity of target genes. The systemic utility of potent small molecule inhibitors of MYC-MAX dimerization was limited by poor bioavailability, rapid metabolism, and inadequate target site penetration. We hypothesized that new lipid-based MYC-MAX dimerization inhibitor prodrugs delivered via integrin-targeted nanoparticles (NP) would overcome prior shortcomings of MYC inhibitor approaches and prolong survival in a mouse model of cancer. An Sn 2 lipase-labile prodrug inhibitor of MYC-MAX dimerization (MI1-PD) was developed which decreased cell proliferation and induced apoptosis in cultured multiple myeloma cell lines alone (P < 0.05) and when incorporated into integrin-targeted lipid-encapsulated NPs (P < 0.05). Binding and efficacy of NPs closely correlated with integrin expression of the target multiple myeloma cells. Using a KaLwRij metastatic multiple myeloma mouse model, VLA-4-targeted NPs (20 nm and 200 nm) incorporating MI1-PD (D) NPs conferred significant survival benefits compared with respective NP controls, targeted (T) no-drug (ND), and untargeted (NT) control NPs (T/D 200: 46 days vs.

NT/ND

28 days, P < 0.05 and T/D 20: 52 days vs.

NT/ND

29 days, P = 0.001). The smaller particles performed better of the two sizes. Neither MI1 nor MI1-PD provided survival benefit when administered systemically as free compounds. These results demonstrate for the first time that a small molecule inhibitor of the MYC transcription factor can be an effective anticancer agent when delivered using a targeted nanotherapy approach.

Thrombospondin-1 regulates bone homeostasis through effects on bone matrix integrity and nitric oxide signaling in osteoclasts

Thrombospondin-1 (TSP1), an endogenous antiangiogenic, is a widely expressed secreted ligand with roles in migration, adhesion, and proliferation and is a target for new therapeutics. While TSP1 is present in the bone matrix and several TSP1 receptors play roles in bone biology, the role of TSP1 in bone remodeling has not been fully elucidated. Bone turnover is characterized by coordinated activity of bone-forming osteoblasts (OB) and bone-resorbing osteoclasts (OC). TSP1-/- mice had increased bone mass and increased cortical bone size and thickness compared to wild type (WT). However, despite increased size, TSP1-/- femurs showed less resistance to bending than expected, indicative of diminished bone quality and a bone material defect. Additionally, we found that TSP1 deficiency resulted in decreased OC activity in vivo and reduced OC differentiation. TSP1 was critical during early osteoclastogenesis, and TSP1 deficiency resulted in a substantial overexpression of inducible nitric oxide synthase (iNOS). Importantly, administration of a NOS inhibitor rescued the OC function defects of TSP1-/- mice in vivo. To investigate the role of bone-derived TSP1 in osteoclastogenesis, we found that WT pre-OCs had defective iNOS expression when cultured on TSP1-/- bone compared to WT bone, suggesting that TSP1 in bone plays a critical role in iNOS signaling during OC development. These data implicate a new role for TSP1 in bone homeostasis with roles in maintaining bone matrix integrity and regulating OC formation. It will be critical to monitor bone health of patients administered TSP1-pathway directed therapeutics in clinical use and under development.

Abstract 1114: Combination of a novel CXCR4 antagonist with chemotherapy reduces breast cancer bone metastatic tumor burden

Background:

Bone is the most common site of metastasis for patients with breast cancer. Tumor cells migrate to and reside in the protective bone marrow microenvironment niche through adhesive interaction between tumor CXCR4 and stromal CXCL12 (SDF1). CXCL12 is produced by activated osteoblasts, bone marrow and lung stromal cells, and endothelial cells. Nearly 60% of breast cancers express CXCR4 and this is associated with decreased survival. We hypothesized that a Protein Epitope Mimetic (PEM) POL5551, a novel CXCR4 antagonist, will limit the extent of tumor metastasis by disrupting stromal-mediated protection from cytotoxic chemotherapy and in turn may prolong survival.

Approach:

In vitro, POL5551 had no direct cytotoxic activity and did not reduce proliferation of CXCR4+ MDA-MB-231 or 4T1 osteolytic breast cancer cell lines. However, in an in vitro scratch-wound assay POL5551 inhibited migration of MDA-MB-231 cells. In a Gaussia luciferase (GLuc) complementation model in MDA-MB-231 cells, the interaction of CXCL12 with CXCR4, but not CXCR7, was blocked by low nanomolar concentrations of POL5551. At 20 mg/kg administered from day 10 post inoculation, POL5551 displayed no single agent activity on primary tumor xenografts, and in combination with eribulin there was no synergistic effect on primary tumor xenografts. However, continuation of treatment with POL5551 after surgical tumor removal decreased tumor metastasis and prolonged survival to 58 days compared to control at 45 days and eribulin alone at 51 days. Also, POL5551 showed effects on immune infiltration to the primary tumor. To test the hypothesis that CXCR4 antagonism disrupts the protective bone marrow niche in which tumor cells reside and sensitizes them to cytotoxic chemotherapy, we employed a “framing dosing strategy”. In a second model of metastasis produced by intracardiac injection of MDA-MB-231 cells, POL5551 (20 mg/kg, s.c.) was administered to mice with bone metastases 4 hours before and 4 & 18 hours after eribulin chemotherapy (0.2 mg/kg, i.v.). While bone is the predominant site of metastasis with these cell lines, lung and liver metastasis also occurs. POL5551 in combination with eribulin decreased bone tumor burden more than eribulin alone (reduction in leg bone & liver tumor burden, versus control respectively: eribulin alone 58% & 75%, n.s.; POL5551+eribulin: 89% & 86%, P&lt;0.05; n=4-5 mice per group).

Conclusion:

These preclinical data support a synergism of CXCR4 antagonism during chemotherapy for the treatment of metastatic breast cancer. These and additional data support initiation of a Phase I clinical trial to evaluate a related PEM CXCR4 antagonist in combination with eribulin chemotherapy in patients with metastatic breast cancer who have failed at least 2 lines of therapy.

Note: This abstract was not presented at the meeting.

Citation Format: Jingyu Xiang, Michelle A. Hurchla, Kathryn Luker, Garry Douglas, Barbara Romagnoli, Eric Chevalier, Michael Bauer, Johann Zimmermann, Klaus Dembowsky, Gary Luker, Katherine N. Weilbaecher. Combination of a novel CXCR4 antagonist with chemotherapy reduces breast cancer bone metastatic tumor burden. [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 1114. doi:10.1158/1538-7445.AM2014-1114

Abstract 5381: VLA-4 targeted nanoparticles deliver a cMYC-MAX prodrug antagonist extends survival a metastatic myeloma mouse model

Background: While it is well known that MYC oncoprotein drives multiple myeloma (MM) pathogenesis, the development of several small-molecule inhibitors of the c-MYC/MAX interaction has been limited by rapid systemic metabolism, poor bioavailability and the inability of the drug to reach inhibitory concentrations in the tumor.

Objective: The goal of this study was to develop and deliver an effective VLA-4-targeted Sn 2 lipase-labile Myc-inhibitor nanotherapy.

Experimental Methods: A novel Sn 2 phosphatidylcholine-cMyc-Max antagonist prodrug (M1-PD) was designed, synthesized, characterized and evaluated in vitro and in vivo. In vitro, titrated free M1-PD was compared to free Myc-antagonist in human MM cell lines (H929 and U266) and mouse MM (5TGM1). M1-PD was incorporated into two lipid-based nanoparticle genera (&lt;20nm and ∼200nm) that were functionalized for MM targeting using a peptidomimetic VLA-4-lipid ligand. The nanoparticles were physico-chemically characterized and evaluated for their relative pharmacokinetics in vivo. Effectiveness of the two VLA-4-targeted M1-PD nanotherapies were evaluated in MM cell cultures, correlated with VLA-4 expression levels, and then studied in C57BL/KaLwRij mice with metastatic 5TGM1.

Results: Bioactivity of free M1-PD was several orders magnitude more potent that the free cMyc antagonist in cell culture. Binding and efficacy of M1-PD nanoparticles correlated with integrin expression in target cells. VLA-4-M1-PD nanoparticles (&lt;20nm and ∼200nm) equivalently inhibited MM cell growth in vitro compared to controls. In C57BL/KaLwRij mice with metastatic 5TGM1, VLA-4-MI1-PD 20nm micelles conferred significant survival benefit (T/D) over the 20nm targeted no drug (T/ND) or untreated controls (NT/ND) (52 days vs. 29 days, p=0.001) and versus the 200nm VLA-4-MI1-PD nanocolloid and its controls.

Conclusion: These finding support the feasibility of a new VLA-4-directed nanotherapy to deliver lipase-labile cMyc prodrug to disrupt MYC-MAX dimerization and improve MM survival.

Citation Format: Deepti Soodgupta, Dipanjan Pan, Grace Cui, Angana Senpan, Xiaoxia Yang, Samuel A. Wickline, Edward V. Prochownik, Katherine N. Weilbaecher, Michael H. Tomasson, Gregory M. Lanza. VLA-4 targeted nanoparticles deliver a cMYC-MAX prodrug antagonist extends survival a metastatic 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 5381. doi:10.1158/1538-7445.AM2014-5381

Abstract 378: Macrophage ß3 Integrin is an Important Player in Inflammation and Cellular Plasticity

Communication between cells and the surrounding environment is a crucial mechanism for survival. Integrins are membrane-bound molecules that are involved in signaling between the cells and the extracellular matrix, thereby influencing cytoskeletal stability and intracellular signaling. β3 integrin and its binding partner αv form the αvβ3 heterodimer that is expressed in various cells. We and others have described the consequences of its absence in inflammation, atherosclerosis and cancer in vivo. However, the distinct role of this integrin as a signaling molecule and the consequences of its absence for macrophage structure remain mostly elusive.

Our aim is to further characterize the phenotype of β3-deficient (β3-/-) bone marrow-derived macrophages (BMDM) under stimulatory conditions (LPS and LDLs) compared to control cells in vitro.

qPCR, WB, ELISA, migration, proliferation assays were used to investigate β3-/- BMDM and controls (wt BMDM and Raw 264.7).

LPS was described to be not only pro- but also anti-inflammatory in a time-dependent manner. We show that LPS stimulation leads to high expression of pro-inflammatory cytokines (IL-1β and TNFα) shortly after treatment, while expression of anti-inflammatory cytokine (IL-10) arises at a later stage (12h post stimulation). Interestingly, β3-/- BMDM express more IL-1β than controls. IL-10 expression appears much earlier in β3-/- BMDM (6h post stimulation) but is reduced after 12h, indicating a faster and higher cellular response in the absence of the β3 integrin.

OxLDL, the leading cause to foam cell formation, stimulates the expression of IL-1β in controls and β3-/- BMDM with the latter expressing significantly less of this cytokine indicating that lack of β3 causes differential cellular responses after LPS and oxLDL stimulation. Other LDL forms tested (nLDL, acLDL, cLDL) did not have any effect on IL-1β expression.

In addition, we identified a higher proliferation rate in the β3-/- BMDM when cultured with M-CSF and a migration deficit in response to LPS, M-CSF and VEGF.

Taken together, our results show that macrophage β3 deficiency causes differential cellular plasticity depending on the stimulus, with functional consequences that could be essential in inflammation and atherosclerosis.

Abstract 1624: Targeting the Hedgehog pathway to inhibit osteosarcoma growth through dual effects on tumor and microenvironment cells

In addition to serving crucial roles in bone development, Hedgehog (Hh) signaling contributes to the development and progression of many cancers, making it an attractive candidate for treatment of bone-resident cancers. Recent data suggest that Hh-targeted agents exert pluripotent effects on host bone microenvironment cells through both cell-intrinsic and paracrine mechanisms, interrupting the ‘vicious cycle’ of tumor cell, osteoblast (OB), osteoclast (OC), and bone marrow stromal cell (BMSC) interactions in bone metastatic breast cancers. Here, reciprocal stimulation between tumor cells and bone cells enhance both tumor growth and bone pathology. Similarly, development of osteosarcoma (OS), the most common primary bone cancer, is strongly influenced by conditions within surrounding microenvironment providing additional points for therapeutic intervention.

The 5-year survival rate for metastatic OS is under 30%, highlighting the need for novel and targeted treatments. We have demonstrated that mice deficient in the tumor suppressor ARF (p19ARF; p14ARF in humans) have enhanced rates of bone turnover, mimicking the adolescent growth period in which OS is prevalent. By crossing Arf-/- mice with those expressing Tax, an HTLV-1 oncogene that results in osteolytic tumors, we developed a model of high penetrant spontaneous OS that recapitulates many aspects of human disease. Here, suppression of bone turnover with the bisphosphonate zoledronic acid prevented the development of OS, suggesting that enhanced OC activity may stimulate OS growth. In agreement, we found that Tax+Arf-/- OS had increased RANKL-to-OPG ratios resulting in increased osteoclastogenic ability. Compared to normal osteoblasts and mesenchymal stem cell precursors, Tax+Arf-/- OS cells have increased expression of Hh pathway genes and exhibit increased susceptibility to Hh inhibitors (SMO antagonists). In particular, Tax+Arf-/- OS cells express high levels of the Hh ligands Sonic (SHH) and Indian (IHH), suggesting they may stimulate surrounding cells in a paracrine fashion. Notably, BMSC derived from non-tumor bearing Tax+Arf-/- mice also exhibit increased expression of pro-tumorigenic factors (including IL-6 and IGF), generating a fertile ‘soil’. SHH or conditioned media from Tax+Arf-/- OS cells enhanced OC activity and BMSC cell production of pro-tumorigenic growth factors. Furthermore, the increased OB and OC differentiation and activity present in Tax+Arf-/- cells could be abrogated with SMO inhibitors. We have established an OS cell line from Tax+Arf-/- mice (TAN) with the ability to form mineralized tumors upon intratibial injection. Using this model, we hypothesize that treatment with SMO antagonists will decrease OS growth due to both tumor cytotoxic effects and direct effects on host bone microenvironment cells that abrogate the pro-tumor microenvironment.

Citation Format: Michelle Anne Hurchla, Katherine N. Weilbaecher. Targeting the Hedgehog pathway to inhibit osteosarcoma growth through dual effects on tumor and microenvironment cells. [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 1624. doi:10.1158/1538-7445.AM2013-1624

Noncompetitive modulation of the proteasome by imidazoline scaffolds overcomes bortezomib resistance and delays MM tumor growth in vivo

Multiple myeloma (MM) is a malignant disorder of differentiated B-cells for which standard care involves the inhibition of the proteasome. All clinically used proteasome inhibitors, including the chemotherapeutic drug bortezomib, target the catalytic active sites of the proteasome and inhibit protein proteolysis by competing with substrate binding. However, nearly all (~97%) patients become intolerant or resistant to treatments within a few years, after which the average survival time is less than 1 year. We describe herein the inhibition of the human proteasome via a noncompetitive mechanism by the imidazoline scaffold, TCH-13. Consistent with a mechanism distinct from that of competitive inhibitors, TCH-013 acts additively with and overcomes resistance to bortezomib. Importantly, TCH-013 induces apoptosis in a panel of myeloma and leukemia cell lines, but in contrast, normal lymphocytes, primary bone marrow stromal cells (hBMSC), and macrophages are resistant to its cytotoxic effects. TCH-013 was equally effective in blocking MM cell growth in co-cultures of MM cells with hBMSC isolated from CD138 negative bone marrow (BM) samples of MM patients. The cellular activity translated well in vivo where TCH-013 delayed tumor growth in an MM xenograft model to a similar extent as bortezomib.