Multiple pathways coordinating reprogramming of endothelial cells into osteoblasts by BMP4

Cell type transition occurs during normal development and under pathological conditions. In prostate cancer bone metastasis, prostate cancer-secreted BMP4 induces endothelial cell-to-osteoblast (EC-to-OSB) transition. Such tumor-induced stromal reprogramming supports prostate cancer progression. We delineate signaling pathways mediating EC-to-OSB transition using EC lines 2H11 and SVR. We found that BMP4-activated pSmad1-Notch-Hey1 pathway inhibits EC migration and tube formation. BMP4-activated GSK3β-βcatenin-Slug pathway stimulates Osx expression. In addition, pSmad1-regulated Dlx2 converges with the Smad1 and β-catenin pathways to stimulate osteocalcin expression. By co-expressing Osx, Dlx2, Slug and Hey1, we were able to achieve EC-to-OSB transition, leading to bone matrix mineralization in the absence of BMP4. In human prostate cancer bone metastasis specimens and MDA-PCa-118b and C4-2b-BMP4 osteogenic xenografts, immunohistochemical analysis showed that β-catenin and pSmad1 are detected in activated osteoblasts rimming the tumor-induced bone. Our results elucidated the pathways and key molecules coordinating prostate cancer-induced stromal programming and provide potential targets for therapeutic intervention.

Radium-223 Treatment Increases Immune Checkpoint Expression in Extracellular Vesicles from the Metastatic Prostate Cancer Bone Microenvironment

PURPOSE

Radium-223 prolongs survival in a fraction of men with bone metastatic prostate cancer (PCa). However, there are no markers for monitoring response and resistance to Radium-223 treatment. Exosomes are mediators of intercellular communication and may reflect response of the bone microenvironment to Radium-223 treatment. We performed molecular profiling of exosomes and compared the molecular profile in patients with favorable and unfavorable overall survival.

EXPERIMENTAL DESIGN

We performed exosomal transcriptome analysis in plasma derived from our preclinical models (MDA-PCa 118b tumors, TRAMP-C2/BMP4 PCa) and from the plasma of 25 patients (paired baseline and end of treatment) treated with Radium-223. All samples were run in duplicate, and array data analyzed with fold changes +2 to -2 and P < 0.05.

RESULTS

We utilized the preclinical models to establish that genes derived from the tumor and the tumor-associated bone microenvironment (bTME) are differentially enriched in plasma exosomes upon Radium-223 treatment. The mouse transcriptome analysis revealed changes in bone-related and DNA damage repair-related pathways. Similar findings were observed in plasma-derived exosomes from patients treated with Radium-223 detected changes. In addition, exosomal transcripts detected immune-suppressors (e.g., PD-L1) that were associated with shorter survival to Radium-223. Treatment of the Myc-CaP mouse model with a combination of Radium-223 and immune checkpoint therapy (ICT) resulted in greater efficacy than monotherapy.

CONCLUSIONS

These clinical and coclinical analyses showed that RNA profiling of plasma exosomes may be used for monitoring the bTME in response to treatment and that ICT may be used to increase the efficacy of Radium-223.

Cabozantinib Reverses Renal Cell Carcinoma-mediated Osteoblast Inhibition in Three-dimensional Coculture In Vitro and Reduces Bone Osteolysis In Vivo

Renal cell carcinoma bone metastases (RCCBM) are typically osteolytic. We previously showed that BIGH3 (beta Ig-h3/TGFBI), secreted by 786-O renal cell carcinoma, plays a role in osteolytic bone lesion in RCCBM through inhibition of osteoblast (OSB) differentiation. To study this interaction, we employed three-dimensional (3D) hydrogels to coculture bone-derived 786-O (Bo-786) renal cell carcinoma cells with MC3T3-E1 pre-OSBs. Culturing pre-OSBs in the 3D hydrogels preserved their ability to differentiate into mature OSB; however, this process was decreased when pre-OSBs were cocultured with Bo-786 cells. Knockdown of BIGH3 in Bo-786 cells recovered OSB differentiation. Furthermore, treatment with bone morphogenetic protein 4, which stimulates OSB differentiation, or cabozantinib (CBZ), which inhibits VEGFR1 and MET tyrosine kinase activities, also increased OSB differentiation in the coculture. CBZ also inhibited pre-osteoclast RAW264.7 cell differentiation. Using RCCBM mouse models, we showed that CBZ inhibited Bo-786 tumor growth in bone. CBZ treatment also increased bone volume and OSB number, and decreased osteoclast number and blood vessel density. When tested in SN12PM6 renal cell carcinoma cells that have been transduced to overexpress BIGH3, CBZ also inhibited SN12PM6 tumor growth in bone. These observations suggest that enhancing OSB differentiation could be one of the therapeutic strategies for treating RCCBM that exhibit OSB inhibition characteristics, and that this 3D coculture system is an effective tool for screening osteoanabolic agents for further in vivo studies.

A Phase II Study of Cabozantinib and Androgen Ablation in Patients with Hormone-Naïve Metastatic Prostate Cancer

PURPOSE

Cabozantinib, an oral inhibitor of c-MET/VEGFR2 signaling, improved progression-free survival (mPFS) but not overall survival (OS) in metastatic castrate-resistant prostate cancer. We evaluated cabozantinib plus androgen deprivation therapy (ADT) in hormone-naïve metastatic prostate cancer (HNMPCa).

PATIENTS AND METHODS

Patients received ADT plus cabozantinib starting at 60 mg daily. The primary endpoint was castrate-resistant PFS by radiographic criteria, clinical progression, or receipt of additional therapy. Secondary endpoints included OS, safety, radiographic responses, and biomarker modulation.

RESULTS

Sixty-two patients received treatment. With a median follow-up of 31.2 months, the mPFS was 16.1 months (95% CI, 14.6-22.7 months), and mOS was not reached. Reductions in PSA ≥ 90%, bone-specific alkaline phosphatase ≥ 50%, and urine N-telopeptides ≥ 50% occurred in 83%, 87%, and 86% of evaluable patients, respectively. Responses in bone scan and measurable disease were observed in 81% of and 90% of evaluable patients, respectively. Most common grade 3 adverse events were hypertension (19%), diarrhea (6%), and thromboembolic events (6%), and dose reductions occurred in 85% of patients. Analysis of baseline cytokine and angiogenic factors (CAFs) revealed that higher plasma concentrations of Lumican, CXCL5, CD25, and CD30 were associated with shorter PFS as was high tumor expression of pFGFR1.

CONCLUSIONS

Cabozantinib plus ADT has promising clinical activity in HNMPCa. CAF profiles and tissue markers suggest candidate prognostic and predictive markers of cabozantinib benefit and provide insights for rational therapy combinations.

Abstract AP21: A NOVEL TARGET FOR OVERCOMING ADAPTIVE RESISTANCE TO ANTI-ANGIOGENIC THERAPY IN OVARIAN CANCER

Anti-angiogenic therapy such as anti-VEGF antibody (AVA) has been being increasingly applied in patients with ovarian cancer, while vast majority developed adaptive resistance, highlighting the need for new therapies. We have screened a cohort of patients with high-grade serous cancer (HGSC) using cDNA-genomic array and immunohistochemistry. Our results indicated that p130cas [Crk-associated substrate], a central node in FAK/Src-mediated angiogenesis, was significantly upregulated in tumor-associated vascular endothelium, and the clinical analysis showed that HGSC patients with increased vascular p130cas have significantly shorter disease-progression survival than those with lower vascular p130cas levels.

Our cell-based studies showed that AVA treatment in endothelial cells led to internalization of a 100-kD fragment of VEGFR2, which was released by caspase-10 cleavage from membrane-tethered VGFR2. This 100-kD form of VEGFR2 bound with TNKS1BP1 (a tankyrase-1-binding protein involved in p53-mediated cell cycle arrest) and internalized into LC3-tagged autophagosomes or translocated into nucleus to initiate cell death. Furthermore, the gene ablation of p130cas with CRISPR/CAS9 in endothelial cells that were originally resistant to AVA therapy re-sensitized them to AVA treatment. Our in vivo studies on targeting vascular p130cas with host-specific siRNA showed a robust inhibition of tumor growth and progression in orthotopic HGSC tumors through initiating autophagy-associated cell death in tumor-associated endothelial cells.

To functionally characterize role of vascular p130cas in angiogenesis, we established the p130casflox/flox-Tie2Cre genomic-engineered mice (GEM) model. Using the ID8 syngeneic model, we found that depletion of vascular p130cas diminished resistance to AVA therapy and compromised angiogenesis by inducing elevated VEGFR2/TNKS1BP1 in autophagosomes and nucleus of tumor-associated endothelial cells, which were followed by cell death. To further explore the therapeutic potential of blocking tumor-associated vascular p130cas as a novel anti-angiogenic strategy, we have constituted a cell-permeable, peptide-nanoparticle complex using a p130cas antagonist encapsulated with biodegradable, long-circulating, core-crosslinked polymeric micelles (CCPM). This CCPM-p130cas antagonist contains a mutated Src-binding domain and is linked with Arg-Gly-Asp (RGD) peptide, which specifically targets angiogenic endothelial cells. We also performed the cell-based studies to show that this CCPM-p130cas antagonist is able to bind to the FAK and Src complex with high affinity and effectively block FAK/Src mediated angiogenic property in endothelial cells. Ongoing studies are focused on investigating the therapeutic efficacy and mechanism of actions for RGD-CCPM-p130cas antagonist as a novel anti-angiogenic therapy to overcome adaptive resistance occurred in patients with HGSC.

In summary, our studies provided new knowledge regarding the pivotal role of vascular p130cas in tumor-associated endothelial vasculature, and the critical pre-clinical evidences for applying the RGD-CCPM-p130cas antagonist as a novel therapeutic for treatment of ovarian cancer.

Citation Format: Yunfei Wen, Alpa M Nick, G Lopez-Berestein, Gary E Gallick, Robert L Coleman Robert , Mien-Chie Hung, and Anil K Sood. A NOVEL TARGET FOR OVERCOMING ADAPTIVE RESISTANCE TO ANTI-ANGIOGENIC THERAPY IN OVARIAN CANCER [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr AP21.

Abstract 385: MTAP gene deficiency creates vulnerability to anti-folate therapy in urothelial bladder carcinoma

Background: The methylthioadenosine phosphorylase (MTAP) gene encodes an essential enzyme for the salvage pathway of adenosine synthesis and is frequently lost in different types of cancer including urothelial bladder carcinoma. Therefore, MTAP-deficient tumors are theoretically very sensitive to anti-folate agents such as pemetrexed that can effectively block the de novo pathway of adenosine synthesis and as a result, create a state of synthetic lethality. We thus hypothesize that tumor MTAP gene deficiency is associated with response to pemetrexed therapy in bladder cancer.

Methods: In this study, we investigated MTAP gene deficiency rates in the TCGA database and confirmed MTAP protein loss by immunohistochemistry using a tumor tissue microarray containing bladder tumor tissues from 151 patients. We then performed in vitro and in vivo studies using MTAP-proficient and MTAP-deficient human bladder cancer cell lines. Functional loss of MTAP was verified with mass spectrometry, which detects its substrate methylthioadenosine (MTA) levels. We also correlated these pre-clinical studies with clinical response data on patients with metastatic bladder cancer treated with pemetrexed.

Results: We identified that 27.8% bladder cancer patients have MTAP protein deficiency, which is consistent with exome sequencing data from the TCGA database. In vitro data showed MTAP-deficient human bladder cancer cell lines were significantly more sensitive to pemetrexed, with IC50 at least 40 times lower than MTAP-proficient cell lines. Subsequent knockdown of the MTAP gene in MTAP-proficient cell lines increased sensitivities to pemetrexed treatment. Consistent with the in vitro data, pemetrexed significantly inhibited the growth of MTAP-deficient or knockdown xenograft tumors but not MTAP-proficient tumors. Furthermore, 4 of 4 (100%) patients with MTAP-deficient metastatic bladder cancer responded to pemetrexed treatment, whereas only 1 of 11 (9%) patients with MTAP-proficient metastatic bladder cancer responded to pemetrexed.

Conclusion: Our data demonstrate that MTAP gene loss in urothelial bladder cancer leads to a metabolic state of synthetic lethality with pemetrexed therapy. Therefore, bladder tumor MTAP loss should be further investigated as a potential biomarker for selection of patients for anti-folate therapy.

Citation Format: Jianfeng Chen, Omar Alhalabi, Guangchun Han, Wei-Lien Wang, Xin-Qiao Zhang, Jian H. Song, Lidia P. Lopez, Sumankalai Ramachandran, Anh G. Hoang, Tyrone Garnett, Matthew Campbell, Amishi Y. Shah, Jennifer Wang, Arlene O. Siefker-Radtke, Shi-Ming Tu, Mark Titus, Charles C. Guo, Gary E. Gallick, Eleni Efstathiou, William F. Benedict, Christopher J. Logothetis, Thai H. Ho, Linghua Wang, Jianjun Gao. MTAP gene deficiency creates vulnerability to anti-folate therapy in urothelial bladder carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 385.

Potentially inappropriate medications defined by STOPP criteria in older patients with breast and colorectal cancer

PURPOSE

Screening for potentially inappropriate medications (PIM) is recommended in older patients with cancer receiving chemotherapy, given the concern for adverse drug reactions, drug-drug interactions and non-adherence. Our objective was to determine the impact of PIM on outcomes in patients with breast and colorectal cancers receiving chemotherapy.

METHODS

We used data from the SEER-Medicare database, including patients >/= 66 years old with a diagnosis of Stage II/III breast and colorectal cancer made between 7/1/2007-12/31/2009. We used modified STOPP criteria to define baseline PIM as a dichotomous variable in the 4 months prior to diagnosis. STOPP criteria was used based on its performance as a robust measure of PIM. Outcomes measures included ER visits, hospitalizations, and death within 3 months from the last chemotherapy, and a composite of the three. We used Chi-square or Fisher's exact test to determine associations of PIM with covariates and outcomes, and Cox proportional hazards (PH) model for the time-to-event analysis.

RESULTS

Final analysis included 1,595 patients with breast cancer and 1,528 patients with colorectal cancer. Frequency of baseline PIM by STOPP was 31.5% in the breast and 30.9% in the colorectal cohort. In the breast cohort, associations with the composite outcome in the Cox PH model included disease stage, comorbidity, medication number and baseline ER visits/hospitalization. Age, gender, race, comorbidity and baseline ER visits/hospitalization were associated in the colorectal cohort. PIM was not associated with outcomes in either cohort, aside from hospitalization in the breast.

CONCLUSIONS

We found no consistent association between pre-chemotherapy PIM defined by STOPP and outcomes.

Potentially inappropriate medication use in older patients with breast and colorectal cancer

BACKGROUND

The objective of this study was to determine patient characteristics associated with potentially inappropriate medication (PIM) use and its impact on outcomes for patients with breast or colorectal cancer receiving adjuvant chemotherapy.

METHODS

The Surveillance, Epidemiology, and End Results database, linked to Medicare claims, was used. The cohort included patients who were 66 years old or older and were diagnosed with stage II or III breast or colorectal cancer between July 1, 2007, and December 31, 2009. The Drugs to Avoid in the Elderly (DAE) list and the Beers criteria were used to identify PIM use. Univariate/multivariate logistic regression determined the association of baseline PIMs with covariates. Event-free survival (EFS) was defined as the time from chemotherapy initiation to the first emergency room (ER) visit, hospitalization, death, or a composite until 3 months after chemotherapy. Cox proportional hazards modeling determined the association of PIMs with EFS.

RESULTS

The analysis included 1595 patients with breast cancer and 1528 patients with colorectal cancer. The baseline PIM frequencies were 22.2% (according to the DAE list) and 27.6% (according to the Beers criteria) in the breast cohort and 15.5% (according to the DAE list) and 24.8% (according to the Beers criteria) in the colorectal cohort. Among patients with breast cancer, 37.5% had at least 1 adverse outcome; associations included the use of ≥5 medications, an advanced stage, higher comorbidity, and prior ER visits/hospitalizations. Baseline PIM use according to the DAE list was associated with an increased risk of death in patients with breast cancer. Among patients with colorectal cancer, 45% had at least 1 adverse outcome, and associations included the use of ≥5 medications, older age, female sex, and higher comorbidity. A time-to-event analysis revealed no association between baseline PIM use and most outcomes.

CONCLUSIONS

These findings require further prospective confirmation, but they support a correlation between polypharmacy and adverse outcomes for cancer patients and call into question the association with PIMs. Cancer 2018;124:3000-7. © 2018 American Cancer Society.

Organelle-Derived Acetyl-CoA Promotes Prostate Cancer Cell Survival, Migration, and Metastasis via Activation of Calmodulin Kinase II

Although emerging evidence suggests a potential role of calcium/calmodulin-dependent kinase II (CaMKII) in prostate cancer, its role in prostate cancer tumorigenesis is largely unknown. Here, we examine whether the acetyl CoA-CaMKII pathway, first described in frog oocytes, promotes prostate cancer tumorigenesis. In human prostate cancer specimens, metastatic prostate cancer expressed higher levels of active CaMKII compared with localized prostate cancer. Correspondingly, basal CaMKII activity was significantly higher in the more tumorigenic PC3 and PC3-mm2 cells relative to the less tumorigenic LNCaP and C4-2B4 cells. Deletion of CaMKII by CRISPR/Cas9 in PC3-mm2 cells abrogated cell survival under low-serum conditions, anchorage-independent growth and cell migration; overexpression of constitutively active CaMKII in C4-2B4 cells promoted these phenotypes. In an animal model of prostate cancer metastasis, genetic ablation of CaMKII reduced PC3-mm2 cell metastasis from the prostate to the lymph nodes. Knockdown of the acetyl-CoA transporter carnitine acetyltransferase abolished CaMKII activation, providing evidence that acetyl-CoA generated from organelles is a major activator of CaMKII. Genetic deletion of the β-oxidation rate-limiting enzyme ACOX family proteins decreased CaMKII activation, whereas overexpression of ACOXI increased CaMKII activation. Overall, our studies identify active CaMKII as a novel connection between organelle β-oxidation and acetyl-CoA transport with cell survival, migration, and prostate cancer metastasis.Significance: This study identifies a cell metabolic pathway that promotes prostate cancer metastasis and suggests prostate cancer may be susceptible to β-oxidation inhibitors. Cancer Res; 78(10); 2490-502. ©2018 AACR.

Osteoblast-Secreted Factors Mediate Dormancy of Metastatic Prostate Cancer in the Bone via Activation of the TGFβRIII-p38MAPK-pS249/T252RB Pathway

Bone metastasis from prostate cancer can occur years after prostatectomy, due to reactivation of dormant disseminated tumor cells (DTC) in the bone, yet the mechanism by which DTCs are initially induced into a dormant state in the bone remains to be elucidated. We show here that the bone microenvironment confers dormancy to C4-2B4 prostate cancer cells, as they become dormant when injected into mouse femurs but not under the skin. Live-cell imaging of dormant cells at the single-cell level revealed that conditioned medium from differentiated, but not undifferentiated, osteoblasts induced C4-2B4 cellular quiescence, suggesting that differentiated osteoblasts present locally around the tumor cells in the bone conferred dormancy to prostate cancer cells. Gene array analyses identified GDF10 and TGFβ2 among osteoblast-secreted proteins that induced quiescence of C4-2B4, C4-2b, and PC3-mm2, but not 22RV1 or BPH-1 cells, indicating prostate cancer tumor cells differ in their dormancy response. TGFβ2 and GDF10 induced dormancy through TGFβRIII to activate phospho-p38MAPK, which phosphorylates retinoblastoma (RB) at the novel N-terminal S249/T252 sites to block prostate cancer cell proliferation. Consistently, expression of dominant-negative p38MAPK in C4-2b and C4-2B4 prostate cancer cell lines abolished tumor cell dormancy both in vitro and in vivo Lower TGFβRIII expression in patients with prostate cancer correlated with increased metastatic potential and decreased survival rates. Together, our results identify a dormancy mechanism by which DTCs are induced into a dormant state through TGFβRIII-p38MAPK-pS249/pT252-RB signaling and offer a rationale for developing strategies to prevent prostate cancer recurrence in the bone.Significance: These findings provide mechanistic insights into the dormancy of metastatic prostate cancer in the bone and offer a rationale for developing strategies to prevent prostate cancer recurrence in the bone. Cancer Res; 78(11); 2911-24. ©2018 AACR.

Targeting DNA Damage Response in Prostate Cancer by Inhibiting Androgen Receptor-CDC6-ATR-Chk1 Signaling

Cell division cycle 6 (CDC6), an androgen receptor (AR) target gene, is implicated in regulating DNA replication and checkpoint mechanisms. CDC6 expression is increased during prostate cancer (PCa) progression and positively correlates with AR in PCa tissues. AR or CDC6 knockdown, together with AZD7762, a Chk1/2 inhibitor, results in decreased TopBP1-ATR-Chk1 signaling and markedly increased ataxia-telangiectasia-mutated (ATM) phosphorylation, a biomarker of DNA damage, and synergistically increases treatment efficacy. Combination treatment with the AR signaling inhibitor enzalutamide (ENZ) and the Chk1/2 inhibitor AZD7762 demonstrates synergy with regard to inhibition of AR-CDC6-ATR-Chk1 signaling, ATM phosphorylation induction, and apoptosis in VCaP (mutant p53) and LNCaP-C4-2b (wild-type p53) cells. CDC6 overexpression significantly reduced ENZ- and AZD7762-induced apoptosis. Additive or synergistic therapeutic activities are demonstrated in AR-positive animal xenograft models. These findings have important clinical implications, since they introduce a therapeutic strategy for AR-positive, metastatic, castration-resistant PCa, regardless of p53 status, through targeting AR-CDC6-ATR-Chk1 signaling.

BIGH3 Promotes Osteolytic Lesions in Renal Cell Carcinoma Bone Metastasis by Inhibiting Osteoblast Differentiation

BACKGROUND: Bone metastasis is common in renal cell carcinoma (RCC), and the lesions are mainly osteolytic. The mechanism of bone destruction in RCC bone metastasis is unknown. METHODS: We used a direct intrafemur injection of mice with bone-derived 786-O RCC cells (Bo-786) as an in vivo model to study if inhibition of osteoblast differentiation is involved in osteolytic bone lesions in RCC bone metastasis. RESULTS: We showed that bone-derived Bo-786 cells induced osteolytic bone lesions in the femur of mice. We examined the effect of conditioned medium of Bo-786 cells (Bo-786 CM) on both primary mouse osteoblasts and MC3T3-E1 preosteoblasts and found that Bo-786 CM inhibited osteoblast differentiation. Secretome analysis of Bo-786 CM revealed that BIGH3 (Beta ig h3 protein), also known as TGFBI (transforming growth factor beta-induced protein), is highly expressed. We generated recombinant BIGH3 and found that BIGH3 inhibited osteoblast differentiation in vitro. In addition, CM from Bo-786 BIGH3 knockdown cells (786-BIGH3 KD) reduced the inhibition of osteoblast differentiation compared to CM from vector control. Intrafemural injection of mice with 786-BIGH3 KD cells showed a reduction in osteolytic bone lesions compared to vector control. Immunohistochemical staining of 18 bone metastasis specimens from human RCC showed strong BIGH3 expression in 11/18 (61%) and moderate BIGH3 expression in 7/18 (39%) of the specimens. CONCLUSIONS: These results suggest that suppression of osteoblast differentiation by BIGH3 is one of the mechanisms that enhance osteolytic lesions in RCC bone metastasis, and raise the possibilty that treatments that increase bone formation may improve therapy outcomes.

JAK2-binding long noncoding RNA promotes breast cancer brain metastasis

Conventional therapies for breast cancer brain metastases (BCBMs) have been largely ineffective because of chemoresistance and impermeability of the blood-brain barrier. A comprehensive understanding of the underlying mechanism that allows breast cancer cells to infiltrate the brain is necessary to circumvent treatment resistance of BCBMs. Here, we determined that expression of a long noncoding RNA (lncRNA) that we have named lncRNA associated with BCBM (Lnc-BM) is prognostic of the progression of brain metastasis in breast cancer patients. In preclinical murine models, elevated Lnc-BM expression drove BCBM, while depletion of Lnc-BM with nanoparticle-encapsulated siRNAs effectively treated BCBM. Lnc-BM increased JAK2 kinase activity to mediate oncostatin M- and IL-6-triggered STAT3 phosphorylation. In breast cancer cells, Lnc-BM promoted STAT3-dependent expression of ICAM1 and CCL2, which mediated vascular co-option and recruitment of macrophages in the brain, respectively. Recruited macrophages in turn produced oncostatin M and IL-6, thereby further activating the Lnc-BM/JAK2/STAT3 pathway and enhancing BCBM. Collectively, our results show that Lnc-BM and JAK2 promote BCBMs by mediating communication between breast cancer cells and the brain microenvironment. Moreover, these results suggest targeting Lnc-BM as a potential strategy for fighting this difficult disease.

Endothelial-to-Osteoblast Conversion Generates Osteoblastic Metastasis of Prostate Cancer

Prostate cancer (PCa) bone metastasis is frequently associated with bone-forming lesions, but the source of the osteoblastic lesions remains unclear. We show that the tumor-induced bone derives partly from tumor-associated endothelial cells that have undergone endothelial-to-osteoblast (EC-to-OSB) conversion. The tumor-associated osteoblasts in PCa bone metastasis specimens and patient-derived xenografts (PDXs) were found to co-express endothelial marker Tie-2. BMP4, identified in PDX-conditioned medium, promoted EC-to-OSB conversion of 2H11 endothelial cells. BMP4 overexpression in non-osteogenic C4-2b PCa cells led to ectopic bone formation under subcutaneous implantation. Tumor-induced bone was reduced in trigenic mice (Tie2^cre/Osx^f/f/SCID) with endothelial-specific deletion of osteoblast cell-fate determinant OSX compared with bigenic mice (Osx^f/f/SCID). Thus, tumor-induced EC-to-OSB conversion is one mechanism that leads to osteoblastic bone metastasis of PCa.

Cabozantinib-induced osteoblast secretome promotes survival and migration of metastatic prostate cancer cells in bone

Therapies that target cancer cells may have unexpected effects on the tumor microenvironment that affects therapy outcomes or render therapy resistance. Prostate cancer (PCa) bone metastasis is uniquely associated with osteoblastic bone lesions and treatment with cabozantinib, a VEGFR-2 and MET inhibitor, leads to a reduction in number and/or intensity of lesions on bone scans. However, resistance to cabozantinib therapy inevitably occurs. We examined the effect of cabozantinib on osteoblast differentiation and secretion in the context of therapy resistance. We showed that primary mouse osteoblasts express VEGFR2 and MET and cabozantinib treatment decreased osteoblast proliferation but enhanced their differentiation. A genome-wide analysis of transcriptional responses of osteoblasts to cabozantinib identified a set of genes accounting for inhibition of proliferation and stimulation of differentiation, and a spectrum of secreted proteins induced by cabozantinib, including pappalysin, IGFBP2, WNT 16, and DKK1. We determined that these proteins were upregulated in the conditioned medium of cabozantinib-treated osteoblasts (CBZ-CM) compared to control CM. Treatment of C4-2B4 or PC3-mm2 PCa cells with CBZ-CM increased the anchorage-independent growth and migration of these PCa cells compared to cells treated with control CM. These results suggest that the effect of cabozantinib on the tumor microenvironment may increase tumor cell survival and cause therapy resistance.

Proteomics Profiling of Exosomes from Primary Mouse Osteoblasts under Proliferation versus Mineralization Conditions and Characterization of Their Uptake into Prostate Cancer Cells

Osteoblasts communicate both with normal cells in the bone marrow and with tumor cells that metastasized to bone. Here we show that osteoblasts release exosomes, we termed osteosomes, which may be a novel mechanism by which osteoblasts communicate with cells in their environment. We have isolated exosomes from undifferentiated/proliferating (D0 osteosomes) and differentiated/mineralizing (D24 osteosomes) primary mouse calvarial osteoblasts. The D0 and D24 osteosomes were found to be vesicles of 130-140 nm by dynamic light scattering analysis. Proteomics profiling using tandem mass spectrometry (LC-MS/MS) identified 206 proteins in D0 osteosomes and 336 in D24 osteosomes. The proteins in osteosomes are mainly derived from the cytoplasm (∼47%) and plasma membrane (∼31%). About 69% of proteins in osteosomes are also found in Vesiclepedia, and these canonical exosomal proteins include tetraspanins and Rab family proteins. We found that there are differences in both protein content and levels in exosomes isolated from undifferentiated and differentiated osteoblasts. Among the proteins that are unique to osteosomes, 169 proteins are present in both D0 and D24 osteosomes, 37 are unique to D0, and 167 are unique to D24. Among those 169 proteins present in both D0 and D24 osteosomes, 10 proteins are likely present at higher levels in D24 than D0 osteosomes based on emPAI ratios of >5. These results suggest that osteosomes released from different cellular state of osteoblasts may mediate distinct functions. Using live-cell imaging, we measured the uptake of PKH26-labeled osteosomes into C4-2B4 and PC3-mm2 prostate cancer cells. In addition, we showed that cadherin-11, a cell adhesion molecule, plays a role in the uptake of osteosomes into PC3-mm2 cells as osteosome uptake was delayed by neutralizing antibody against cadherin-11. Together, our studies suggest that osteosomes could have a unique role in the bone microenvironment under both physiological and pathological conditions.

Androgen receptor inhibitor-induced "BRCAness" and PARP inhibition are synthetically lethal for castration-resistant prostate cancer

Cancers with loss-of-function mutations in BRCA1 or BRCA2 are deficient in the DNA damage repair pathway called homologous recombination (HR), rendering these cancers exquisitely vulnerable to poly(ADP-ribose) polymerase (PARP) inhibitors. This functional state and therapeutic sensitivity is referred to as "BRCAness" and is most commonly associated with some breast cancer types. Pharmaceutical induction of BRCAness could expand the use of PARP inhibitors to other tumor types. For example, BRCA mutations are present in only ~20% of prostate cancer patients. We found that castration-resistant prostate cancer (CRPC) cells showed increased expression of a set of HR-associated genes, including BRCA1, RAD54L, and RMI2 Although androgen-targeted therapy is typically not effective in CRPC patients, the androgen receptor inhibitor enzalutamide suppressed the expression of those HR genes in CRPC cells, thus creating HR deficiency and BRCAness. A "lead-in" treatment strategy, in which enzalutamide was followed by the PARP inhibitor olaparib, promoted DNA damage-induced cell death and inhibited clonal proliferation of prostate cancer cells in culture and suppressed the growth of prostate cancer xenografts in mice. Thus, antiandrogen and PARP inhibitor combination therapy may be effective for CRPC patients and suggests that pharmaceutically inducing BRCAness may expand the clinical use of PARP inhibitors.

Dual Inhibition of EGFR and c-Src by Cetuximab and Dasatinib Combined with FOLFOX Chemotherapy in Patients with Metastatic Colorectal Cancer

Purpose: Aberrant activation of the intracellular tyrosine kinase Src has been implicated as a mechanism of acquired chemotherapy resistance in metastatic colorectal cancer (mCRC). Here, the oral tyrosine kinase Src inhibitor, dasatinib, was investigated in combination with FOLFOX and cetuximab.Experimental Design: We performed a phase IB/II study of 77 patients with previously treated mCRC. Primary objectives were to determine the maximum tolerated dose, dose-limiting toxicities (DLT), pharmacodynamics, and efficacy. Using a 3 + 3 design, patients received FOLFOX6 with cetuximab and escalating doses of dasatinib (100, 150, 200 mg daily), followed by a 12-patient expansion cohort at 150 mg. Phase II studies evaluated FOLFOX plus dasatinib 100 mg in KRAS c12/13^mut patients or in combination with cetuximab if KRAS c12/13^WT FAK and paxillin were utilized as surrogate blood biomarkers of Src inhibition, and paired biopsies of liver metastases were obtained in patients in the expansion cohort.Results: In phase IB, the DLTs were grade 3/4 fatigue (20%) and neutropenia (23%). In phase II, grade 3/4 fatigue (23%) and pleural effusions (11%) were present. Response rates were 20% (6 of 30) in the phase IB escalation and expansion cohort and 13% (3 of 24) and 0% (0 of 23) in the KRAS c12/13^WT and mutant cohorts of phase II, respectively. Median progression-free survival was 4.6, 2.3, and 2.3 months, respectively. There was no evidence of Src inhibition based on surrogate blood biomarkers or paired tumor biopsies.Conclusions: The combination of dasatinib plus FOLFOX with or without cetuximab showed only modest clinical activity in refractory colorectal cancer. This appears to be primarily due to a failure to fully inhibit Src at the achievable doses of dasatinib. The combination of dasatinib plus FOLFOX with or without cetuximab did not show meaningful clinical activity in refractory colorectal cancer due to failure to fully inhibit Src. Clin Cancer Res; 23(15); 4146-54. ©2017 AACR.

The combination of serum insulin, osteopontin, and hepatocyte growth factor predicts time to castration-resistant progression in androgen dependent metastatic prostate cancer- an exploratory study

BACKGROUND

We hypothesized that pretreatment serum levels of insulin and other serum markers would predict Progression-free survival (PFS), defined as time to castration-resistant progression or death, in metastatic androgen-dependent prostate cancer (mADPC).

METHODS

Serum samples from treatment-naïve men participating in a randomized phase 3 trial of ADT +/- chemotherapy were retrospectively analyzed using multiplex assays for insulin and multiple other soluble factors. Cox proportional hazards regression models were used to identify associations between individual factor levels and PFS.

RESULTS

Sixty six patients were evaluable (median age = 72 years; median prostate surface antigen [PSA] = 31.5 ng/mL; Caucasian = 86 %; Gleason score ≥8 = 77 %). In the univariable analysis, higher insulin (HR = 0.81 [0.67, 0.98] p = 0.03) and C-peptide (HR = 0.62 [0.39, 1.00]; p = 0.05) levels were associated with a longer PFS, while higher Hepatocyte Growth Factor (HGF; HR = 1.63 [1.06, 2.51] p = 0.03) and Osteopontin (OPN; HR = 1.56 [1.13, 2.15]; p = 0.01) levels were associated with a shorter PFS. In multivariable analysis, insulin below 2.1 (ln scale; HR = 2.55 [1.24, 5.23]; p = 0.011) and HGF above 8.9 (ln scale; HR = 2.67 [1.08, 3.70]; p = 0.027) levels were associated with longer PFS, while adjusted by OPN, C-peptide, trial therapy and metastatic volume. Four distinct risk groups were identified by counting the number of risk factors (RF) including low insulin, high HGF, high OPN levels, and low C-peptide levels (0, 1, 2, and 3). Median PFS was 9.8, 2.0, 1.6, and 0.7 years for each, respectively (p < 0.001).

CONCLUSION

Pretreatment serum insulin, HGF, OPN, and C-peptide levels can predict PFS in men with mADPC treated with ADT. Risk groups based on these factors are superior predictors of PFS than each marker alone.

Chitosan nanoparticle-mediated delivery of miRNA-34a decreases prostate tumor growth in the bone and its expression induces non-canonical autophagy

While several new therapies are FDA-approved for bone-metastatic prostate cancer (PCa), patient survival has only improved marginally. Here, we report that chitosan nanoparticle-mediated delivery of miR-34a, a tumor suppressive microRNA that downregulates multiple gene products involved in PCa progression and metastasis, inhibited prostate tumor growth and preserved bone integrity in a xenograft model representative of established PCa bone metastasis. Expression of miR-34a induced apoptosis in PCa cells, and, in accord with downregulation of targets associated with PCa growth, including MET and Axl and c-Myc, also induced a form of non-canonical autophagy that is independent of Beclin-1, ATG4, ATG5 and ATG7. MiR-34a-induced autophagy is anti-proliferative in prostate cancer cells, as blocking apoptosis still resulted in growth inhibition of tumor cells. Thus, combined effects of autophagy and apoptosis are responsible for miR-34a-mediated prostate tumor growth inhibition, and have translational impact, as this non-canonical form of autophagy is tumor inhibitory. Together, these results provide a new understanding of the biological effects of miR-34a and highlight the clinical potential for miR-34a delivery as a treatment for bone metastatic prostate cancer.

Yes-mediated phosphorylation of focal adhesion kinase at tyrosine 861 increases metastatic potential of prostate cancer cells

To study the role of FAK signaling complexes in promoting metastatic properties of prostate cancer (PCa) cells, we selected stable, highly migratory variants, termed PC3 Mig-3 and DU145 Mig-3, from two well-characterized PCa cell lines, PC3 and DU145. These variants were not only increased migration and invasion in vitro, but were also more metastatic to lymph nodes following intraprostatic injection into nude mice. Both PC3 Mig-3 and DU145 Mig-3 were specifically increased in phosphorylation of FAK Y861. We therefore examined potential alterations in Src family kinases responsible for FAK phosphorylation and determined only Yes expression was increased. Overexpression of Yes in PC3 parental cells and src-/-fyn-/-yes-/- fibroblasts selectively increased FAK Y861 phosphorylation, and increased migration. Knockdown of Yes in PC3 Mig-3 cells decreased migration and decreased lymph node metastasis following orthotopic implantation of into nude mice. In human specimens, Yes expression was increased in lymph node metastases relative to paired primary tumors from the same patient, and increased pFAK Y861 expression in lymph node metastases correlated with poor prognosis. These results demonstrate a unique role for Yes in phosphorylation of FAK and in promoting PCa metastasis. Therefore, phosphorylated FAK Y861 and increased Yes expression may be predictive markers for PCa metastasis.

Identification of Bone-Derived Factors Conferring De Novo Therapeutic Resistance in Metastatic Prostate Cancer

Resistance to currently available targeted therapies significantly hampers the survival of patients with prostate cancer with bone metastasis. Here we demonstrate an important resistance mechanism initiated from tumor-induced bone. Studies using an osteogenic patient-derived xenograft, MDA-PCa-118b, revealed that tumor cells resistant to cabozantinib, a Met and VEGFR-2 inhibitor, reside in a "resistance niche" adjacent to prostate cancer-induced bone. We performed secretome analysis of the conditioned medium from tumor-induced bone to identify proteins (termed "osteocrines") found within this resistance niche. In accordance with previous reports demonstrating that activation of integrin signaling pathways confers therapeutic resistance, 27 of the 90 osteocrines identified were integrin ligands. We found that following cabozantinib treatment, only tumor cells positioned adjacent to the newly formed woven bone remained viable and expressed high levels of pFAK-Y397 and pTalin-S425, mediators of integrin signaling. Accordingly, treatment of C4-2B4 cells with integrin ligands resulted in increased pFAK-Y397 expression and cell survival, whereas targeting integrins with FAK inhibitors PF-562271 or defactinib inhibited FAK phosphorylation and reduced the survival of PC3-mm2 cells. Moreover, treatment of MDA-PCa-118b tumors with PF-562271 led to decreased tumor growth, irrespective of initial tumor size. Finally, we show that upon treatment cessation, the combination of PF-562271 and cabozantinib delayed tumor recurrence in contrast to cabozantinib treatment alone. Our studies suggest that identifying paracrine de novo resistance mechanisms may significantly contribute to the generation of a broader set of potent therapeutic tools that act combinatorially to inhibit metastatic prostate cancer.

Integrating Murine and Clinical Trials with Cabozantinib to Understand Roles of MET and VEGFR2 as Targets for Growth Inhibition of Prostate Cancer

PURPOSE

We performed parallel investigations in cabozantinib-treated patients in a phase II trial and simultaneously in patient-derived xenograft (PDX) models to better understand the roles of MET and VEGFR2 as targets for prostate cancer therapy.

EXPERIMENTAL DESIGN

In the clinical trial, radiographic imaging and serum markers were examined, as well as molecular markers in tumors from bone biopsies. In mice harboring PDX intrafemurally or subcutaneously, cabozantinib effects on tumor growth, MET, PDX in which MET was silenced, VEGFR2, bone turnover, angiogenesis, and resistance were examined.

RESULTS

In responsive patients and PDX, islets of viable pMET-positive tumor cells persisted, which rapidly regrew after drug withdrawal. Knockdown of MET in PDX did not affect tumor growth in mice nor did it affect cabozantinib-induced growth inhibition but did lead to induction of FGFR1. Inhibition of VEGFR2 and MET in endothelial cells reduced the vasculature, leading to necrosis. However, each islet of viable cells surrounded a VEGFR2-negative vessel. Reduction of bone turnover was observed in both cohorts.

CONCLUSIONS

Our studies demonstrate that MET in tumor cells is not a persistent therapeutic target for metastatic castrate-resistant prostate cancer (CRPC), but inhibition of VEGFR2 and MET in endothelial cells and direct effects on osteoblasts are responsible for cabozantinib-induced tumor inhibition. However, vascular heterogeneity represents one source of primary therapy resistance, whereas induction of FGFR1 in tumor cells suggests a potential mechanism of acquired resistance. Thus, integrated cross-species investigations demonstrate the power of combining preclinical models with clinical trials to understand mechanisms of activity and resistance of investigational agents.

ALG-2 activates the MVB sorting function of ALIX through relieving its intramolecular interaction

The modular adaptor protein ALIX is critically involved in endosomal sorting complexes required for transport (ESCRT)-mediated multivesicular body (MVB) sorting of activated epidermal growth factor receptor (EGFR); however, ALIX contains a default intramolecular interaction that renders ALIX unable to perform this ESCRT function. The ALIX partner protein ALG-2 is a calcium-binding protein that belongs to the calmodulin superfamily. Prompted by a defined biological function of calmodulin, we determined the role of ALG-2 in regulating ALIX involvement in MVB sorting of activated EGFR. Our results show that calcium-dependent ALG-2 interaction with ALIX completely relieves the intramolecular interaction of ALIX and promotes CHMP4-dependent ALIX association with the membrane. EGFR activation induces increased ALG-2 interaction with ALIX, and this increased interaction is responsible for increased ALIX association with the membrane. Functionally, inhibition of ALIX activation by ALG-2 inhibits MVB sorting of activated EGFR as effectively as inhibition of ALIX interaction with CHMP4 does; however, inhibition of ALIX activation by ALG-2 does not affect cytokinetic abscission or equine infectious anemia virus (EIAV) budding. These findings indicate that calcium-dependent ALG-2 interaction with ALIX is specifically responsible for generating functional ALIX that supports MVB sorting of ubiquitinated membrane receptors.

The transcription factors Ik-1 and MZF1 downregulate IGF-IR expression in NPM-ALK⁺ T-cell lymphoma

Background

The type I insulin-like growth factor receptor (IGF-IR) tyrosine kinase promotes the survival of an aggressive subtype of T-cell lymphoma by interacting with nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) oncogenic protein. NPM-ALK⁺ T-cell lymphoma exhibits much higher levels of IGF-IR than normal human T lymphocytes. The mechanisms underlying increased expression of IGF-IR in this lymphoma are not known. We hypothesized that upregulation of IGF-IR could be attributed to previously unrecognized defects that inherently exist in the transcriptional machinery in NPM-ALK⁺ T-cell lymphoma.

Methods and results

Screening studies showed substantially lower levels of the transcription factors Ikaros isoform 1 (Ik-1) and myeloid zinc finger 1 (MZF1) in NPM-ALK⁺ T-cell lymphoma cell lines and primary tumor tissues from patients than in human T lymphocytes. A luciferase assay supported that Ik-1 and MZF1 suppress IGF-IR gene promoter. Furthermore, ChIP assay showed that these transcription factors bind specific sites located within the IGF-IR gene promoter. Forced expression of Ik-1 or MZF1 in the lymphoma cells decreased IGF-IR mRNA and protein. This decrease was associated with downregulation of pIGF-IR, and the phosphorylation of its interacting proteins IRS-1, AKT, and NPM-ALK. In addition, overexpression of Ik-1 and MZF1 decreased the viability, proliferation, migration, and anchorage-independent colony formation of the lymphoma cells.

Conclusions

Our results provide novel evidence that the aberrant decreases in Ik-1 and MZF1 contribute significantly to the pathogenesis of NPM-ALK⁺ T-cell lymphoma through the upregulation of IGF-IR expression. These findings could be exploited to devise new strategies to eradicate this lymphoma.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0324-2) contains supplementary material, which is available to authorized users.

Abstract IA11: The role of bone microenvironment in the lethal progression of prostate cancer

Lethal prostate cancer (PCa) is clinically characterized by bone-homing and bone- forming metastases, and bone is frequently the initial organ involved in castrate-resistant progression. These clinical observations led investigators to develop bone-tropic radiopharmaceuticals to treat men with advanced PCa. The ability of the bone-homing alpha emitter (RAD-223) to prolong progression free and overall survival establishes the therapeutic relevance of targeting bone 1.

The long accepted paradigm of PCa progression has been dominated by the model of evolution from androgen dependence to androgen independence under the selective pressure of castration. Thus, Src family kinases (SFKs) were investigated experimentally and clinically for the treatment of putative “androgen independent” PCa, as SFKs play a role in both tumor growth and bone turnover. The roles of SFKs in migration, invasion, survival of tumor cells, and osteoclast and osteoblast function in tumor microenvironment were supported by numerous clinical and laboratory observations 2, 3. Despite promising phase I /II reports of dasatinib, a multikinase and potent SFK inhibitor, in men with advanced PCa 4, 5, a phase III trial failed to yield the expected survival advantage 6. The result of this trial highlights the difficulties in translating data from cell line models to biologically heterogeneous clinical PCa and in transitioning from phase I/II to phase III clinical trials. The efficacy of dasatinib was not observed likely due to persistent AR signaling, which remains the primary driver of progression in bone by the transition from paracrine to intracrine androgen signaling 7. Based on these considerations, we are testing the efficacy of an androgen biosynthesis inhibitor in combination with dasatinib to better understand the relevance of mechanism(s). A co–clinical investigational strategy is being applied to better define biomarkers to predict clinical efficacy.

These studies also highlight the importance of preclinical work that utilizes models that better reflect the heterogeneity of PCa. This problem is partly overcome by patient- derived xenografts (PDX) 8, 9 10. These models reflect many aspects of PCa in bone and can be used to identify therapy targets and better identify both mechanisms of drug efficacy and development of resistance. Studies in PDX have led to identification of FGF signaling as a therapy target 11. Additional studies in PDX implicated the tumor microenvironment in the striking bone responses observed with cabozantinib 13.

These observations led us to propose a model of prostate cancer progression founded on the hypothesis that cancer progresses from being an endocrine-driven cancer (Dihydrotestosterone-dependent) to paracrine/intracrine driven (microenvironment-dependent), and then finally to a cell autochthonous phase 12. Continued studies should lead to decisions on therapy treatment that are based on an understanding of markers that predict disease progression. This new paradigm will also result in more effective therapy combinations.

References

1. Parker C, Sartor O. Radium-223 in prostate cancer. N Engl J Med. 2013;369: 1659-1660.

2. Park SI, Zhang J, Phillips KA, et al. Targeting SRC family kinases inhibits growth and lymph node metastases of prostate cancer in an orthotopic nude mouse model. Cancer Res. 2008;68: 3323-3333.

3. Lee YC, Huang CF, Murshed M, et al. Src family kinase/abl inhibitor dasatinib suppresses proliferation and enhances differentiation of osteoblasts. Oncogene. 2010;29: 3196-3207.

4. Yu EY, Massard C, Gross ME, et al. Once-daily dasatinib: expansion of phase II study evaluating safety and efficacy of dasatinib in patients with metastatic castration-resistant prostate cancer. Urology. 2011;77: 1166-1171.

5. Araujo JC, Mathew P, Armstrong AJ, et al. Dasatinib combined with docetaxel for castration-resistant prostate cancer: results from a phase 1-2 study. Cancer. 2012;118: 63-71.

6. Araujo JC, Trudel GC, Saad F, et al. Docetaxel and dasatinib or placebo in men with metastatic castration-resistant prostate cancer (READY): a randomised, double-blind phase 3 trial. Lancet Oncol. 2013;14: 1307-1316.

7. Efstathiou E, Titus M, Tsavachidou D, et al. Effects of abiraterone acetate on androgen signaling in castrate-resistant prostate cancer in bone. J Clin Oncol. 2012;30: 637-643.

8. Aparicio A, Tzelepi V, Araujo JC, et al. Neuroendocrine prostate cancer xenografts with large-cell and small-cell features derived from a single patient's tumor: morphological, immunohistochemical, and gene expression profiles. Prostate. 2011;71: 846-856.

9. Roychowdhury S, Iyer MK, Robinson DR, et al. Personalized oncology through integrative high-throughput sequencing: a pilot study. Sci Transl Med. 2011;3: 111ra121.

10. Li ZG, Mathew P, Yang J, et al. Androgen receptor-negative human prostate cancer cells induce osteogenesis in mice through FGF9-mediated mechanisms. J Clin Invest. 2008;118: 2697-2710.

11. Corn PG, Wang F, McKeehan WL, Navone N. Targeting fibroblast growth factor pathways in prostate cancer. Clin Cancer Res. 2013;19: 5856-5866.

12. Logothetis CJ, Gallick GE, Maity SN, et al. Molecular classification of prostate cancer progression: foundation for marker-driven treatment of prostate cancer. Cancer Discov. 2013;3: 849-861.

13. Varkaris A. et al. Abstract, Prostate Cancer Foundation 2013.

Citation Format: Christopher Logothetis, Gary E. Gallick, Sue-Hwa Lin, Nora Navone. The role of bone microenvironment in the lethal progression of prostate cancer. [abstract]. In: Abstracts: AACR Special Conference on Cellular Heterogeneity in the Tumor Microenvironment; 2014 Feb 26-Mar 1; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(1 Suppl):Abstract nr IA11. doi:10.1158/1538-7445.CHTME14-IA11

Secretome analysis of an osteogenic prostate tumor identifies complex signaling networks mediating cross-talk of cancer and stromal cells within the tumor microenvironment

A distinct feature of human prostate cancer (PCa) is the development of osteoblastic (bone-forming) bone metastases. Metastatic growth in the bone is supported by factors secreted by PCa cells that activate signaling networks in the tumor microenvironment that augment tumor growth. To better understand these signaling networks and identify potential targets for therapy of bone metastases, we characterized the secretome of a patient-derived xenograft, MDA-PCa-118b (PCa-118b), generated from osteoblastic bone lesion. PCa-118b induces osteoblastic tumors when implanted either in mouse femurs or subcutaneously. To study signaling molecules critical to these unique tumor/microenvironment-mediated events, we performed mass spectrometry on conditioned media of isolated PCa-118b tumor cells, and identified 26 secretory proteins, such as TGF-β2, GDF15, FGF3, FGF19, CXCL1, galectins, and β2-microglobulin, which represent both novel and previously published secreted proteins. RT-PCR using human versus mouse-specific primers showed that TGFβ2, GDF15, FGF3, FGF19, and CXCL1 were secreted from PCa-118b cells. TGFβ2, GDF15, FGF3, and FGF19 function as both autocrine and paracrine factors on tumor cells and stromal cells, that is, endothelial cells and osteoblasts. In contrast, CXCL1 functions as a paracrine factor through the CXCR2 receptor expressed on endothelial cells and osteoblasts. Thus, our study reveals a complex PCa bone metastasis secretome with paracrine and autocrine signaling functions that mediate cross-talk among multiple cell types within the tumor microenvironment.

Abstract 4056: Differential phosphorylation of focal adhesion kinase and activation of Yes kinase are associated with increased metastatic potential of prostate cancer

Metastatic Prostate Cancer (PCa) is the second leading cause of cancer related-deaths in men in the United States. Understanding the molecular events critical to PCa metastasis should lead to novel therapies for treatment of metastatic disease. To assess molecular alterations required for increased PCa cell migration, a critical step in metastasis, multiple rounds of selection of PC3 and DU145 PCa cells were performed using a modified Boyden chamber assay. Highly migratory cells (termed PC3-Mig-3 and DU145-Mig-3) were obtained, a phenotype that has remained stable. PC3-Mig-3 and DU145-Mig-3 cells were also increased in invasiveness, decreased in adhesion and proliferation; thus acquiring additional properties of metastatic cells. Following orthotopic injection into nude mice, migratory variants were significantly increased in number of lymph node metastases (P&lt;0.05). In examining signaling pathways associated with migration and invasion, we determined both PC3-Mig-3 and DU145-Mig-3 were increased in phosphorylation of FAK at tyrosine 861, but not other sites of FAK phosphorylation, relative to their isogenic parental cells. Overexpression a FAK Y861F mutant in PC3-Mig-3 cells decreased migration, demonstrating the importance of pY861 in migratory and invasive potential. Further, expression of FAK pY861 in human PCa lymph node metastases correlated with decreased overall patient survival, suggesting phosphorylation of FAK Y861 may be a predictive biomarker of clinical outcome. To examine potential mechanisms of differential phosphorylation of FAK Y861, the expression and activity of Src family tyrosine kinases was determined. The expression and activity of the Src family kinase, Yes, but not other members of the Src family, were increased in both migratory variants. This increased Yes expression correlated with increased Yes mRNA expression throughout PCa progression as determined from Oncomine. To determine the role Yes kinase in FAK Y861 phosphorylation, Yes was silenced by shRNA expression in PC3-Mig-3 cells. Decreased Yes expression led to both decreased migration, and selectively decreased phosphorylation of FAK Y861. Overexpression of Yes kinase in PC3 parental cells led to specific increased phosphorylation of FAK Y861. These results suggest: the new models of migration we developed have similar alterations as those that occur during PCa progression in men with PCa; Yes activation may play a unique role in PCa progression by leading to differential phosphorylation of FAK Y861; FAK Y861 phosphorylation is important in metastatic potential of PCa cells; and that Yes and FAK may be important markers of metastatic potential of PCa cells. Further studies are designed to investigate specific signaling pathways affected by increased Yes expression and FAK Y861 phosphorylation.

Citation Format: Tanushree Chatterji, Jian H. Song, Nila U. Parikh, Chien-Jui Cheng, Sue-Hwa Lin, Gary E. Gallick. Differential phosphorylation of focal adhesion kinase and activation of Yes kinase are associated with increased metastatic potential of prostate cancer. [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 4056. doi:10.1158/1538-7445.AM2014-4056

RSK promotes prostate cancer progression in bone through ING3, CKAP2, and PTK6-mediated cell survival

Prostate cancer has a proclivity to metastasize to bone. The mechanism by which prostate cancer cells are able to survive and progress in the bone microenvironment is not clear. Identification of molecules that play critical roles in the progression of prostate cancer in bone will provide essential targets for therapy. Ribosomal S6 protein kinases (RSK) have been shown to mediate many cellular functions critical for cancer progression. Whether RSK plays a role in the progression of prostate cancer in bone is unknown. IHC analysis of human prostate cancer specimens showed increased phosphorylation of RSK in the nucleus of prostate cancer cells in a significant fraction of human prostate cancer bone metastasis specimens, compared with the primary site or lymph node metastasis. Expression of constitutively active myristylated RSK in C4-2B4 cells (C4-2B4/RSK) increased their survival and anchorage-independent growth compared with C4-2B4/vector cells. Using an orthotopic bone injection model, it was determined that injecting C4-2B4/RSK cells into mouse femurs enhanced their progression in bone compared with control cells. In PC3-mm2 cells, knockdown of RSK1 (RPS6KA1), the predominant RSK isoform, but not RSK2 (RPS6KA2) alone, decreased anchorage-independent growth in vitro and reduced tumor progression in bone and tumor-induced bone remodeling in vivo. Mechanistic studies showed that RSK regulates anchorage-independent growth through transcriptional regulation of factors that modulate cell survival, including ING3, CKAP2, and PTK6. Together, these data provide strong evidence that RSK is an important driver in prostate cancer progression in bone.

IMPLICATIONS

RSK, an important driver in prostate cancer progression in bone, has promising potential as a therapeutic target for prostate cancer bone metastasis.

Cadherin-11 in renal cell carcinoma bone metastasis

Bone is one of the common sites of metastases from renal cell carcinoma (RCC), however the mechanism by which RCC preferentially metastasize to bone is poorly understood. Homing/retention of RCC cells to bone and subsequent proliferation are necessary steps for RCC cells to colonize bone. To explore possible mechanisms by which these processes occur, we used an in vivo metastasis model in which 786-O RCC cells were injected into SCID mice intracardially, and organotropic cell lines from bone, liver, and lymph node were selected. The expression of molecules affecting cell adhesion, angiogenesis, and osteolysis were then examined in these selected cells. Cadherin-11, a mesenchymal cadherin mainly expressed in osteoblasts, was significantly increased on the cell surface in bone metastasis-derived 786-O cells (Bo-786-O) compared to parental, liver, or lymph node-derived cells. In contrast, the homing receptor CXCR4 was equivalently expressed in cells derived from all organs. No significant difference was observed in the expression of angiogenic factors, including HIF-1α, VEGF, angiopoeitin-1, Tie2, c-MET, and osteolytic factors, including PTHrP, IL-6 and RANKL. While the parental and Bo-786-O cells have similar proliferation rates, Bo-786-O cells showed an increase in migration compared to the parental 786-O cells. Knockdown of Cadherin-11 using shRNA reduced the rate of migration in Bo-786-O cells, suggesting that Cadherin-11 contributes to the increased migration observed in bone-derived cells. Immunohistochemical analysis of cadherin-11 expression in a human renal carcinoma tissue array showed that the number of human specimens with positive cadherin-11 activity was significantly higher in tumors that metastasized to bone than that in primary tumors. Together, these results suggest that Cadherin-11 may play a role in RCC bone metastasis.

Targeting SRC and tubulin in mucinous ovarian carcinoma

PURPOSE

To investigate the antitumor effects of targeting Src and tubulin in mucinous ovarian carcinoma.

EXPERIMENTAL DESIGN

The in vitro and in vivo effects and molecular mechanisms of KX-01, which inhibits Src pathway and tubulin polymerization, were examined in mucinous ovarian cancer models.

RESULTS

In vitro studies using RMUG-S and RMUG-L cell lines showed that KX-01 inhibited cell proliferation, induced apoptosis, arrested the cell cycle at the G2-M phase, and enhanced the cytotoxicity of oxaliplatin in the KX-01-sensitive cell line, RMUG-S. In vivo studies showed that KX-01 significantly decreased tumor burden in RMUG-S and RMUG-L mouse models relative to untreated controls, and the effects were greater when KX-01 was combined with oxaliplatin. KX-01 alone and in combination with oxaliplatin significantly inhibited tumor growth by reducing cell proliferation and inducing apoptosis in vivo. PTEN knock-in experiments in RMUG-L cells showed improved response to KX-01. Reverse phase protein array analysis showed that in addition to blocking downstream molecules of Src family kinases, KX-01 also activated acute stress-inducing molecules.

CONCLUSION

Our results showed that targeting both the Src pathway and tubulin with KX-01 significantly inhibited tumor growth in preclinical mucinous ovarian cancer models, suggesting that this may be a promising therapeutic approach for patients with mucinous ovarian carcinoma.

Inhibition of cell adhesion by a cadherin-11 antibody thwarts bone metastasis

Cadherin-11 (CDH11) is a member of the cadherin superfamily mainly expressed in osteoblasts but not in epithelial cells. However, prostate cancer cells with a propensity for bone metastasis express high levels of cadherin-11 and reduced levels of E-cadherin. Downregulation of cadherin-11 inhibits interaction of prostate cancer cells with osteoblasts in vitro and homing of prostate cancer cells to bone in an animal model of metastasis. These findings indicate that targeting cadherin-11 may prevent prostate cancer bone metastasis. To explore this possibility, a panel of 21 monoclonal antibodies (mAb) was generated against the extracellular (EC) domain of cadherin-11. Two antibodies, mAbs 2C7 and 1A5, inhibited cadherin-11-mediated cell-cell aggregation in vitro using L-cells transfected with cadherin-11. Both antibodies demonstrated specificity to cadherin-11, and neither antibody recognized E-cadherin or N-cadherin on C4-2B or PC3 cells, respectively. Furthermore, mAb 2C7 inhibited cadherin-11-mediated aggregation between the highly metastatic PC3-mm2 cells and MC3T3-E1 osteoblasts. Mechanistically, a series of deletion mutants revealed a unique motif, aa 343-348, in the cadherin-11 EC3 domain that is recognized by mAb 2C7 and that this motif coordinated cell-cell adhesion. Importantly, administration of mAb 2C7 in a prophylactic setting effectively prevented metastasis of PC3-mm2 cells to bone in an in vivo mouse model. These results show that targeting the extracellular domain of cadherin-11 can limit cellular adhesion and metastatic dissemination of prostate cancer cells.

IMPLICATIONS

Monotherapy using a cadherin-11 antibody is a suitable option for the prevention of bone metastases.

Molecular classification of prostate cancer progression: foundation for marker-driven treatment of prostate cancer

Recently, many therapeutic agents for prostate cancer have been approved that target the androgen receptor and/or the prostate tumor microenvironment. Each of these therapies has modestly increased patient survival. A better understanding of when in the course of prostate cancer progression specific therapies should be applied, and of what biomarkers would indicate when resistance arises, would almost certainly improve survival due to these therapies. Thus, applying the armamentarium of therapeutic agents in the right sequences in the right combination at the right time is a major goal in prostate cancer treatment. For this to occur, an understanding of prostate cancer evolution during progression is required. In this review, we discuss the current understanding of prostate cancer progression, but challenge the prevailing view by proposing a new model of prostate cancer progression, with the goal of improving biologic classification and treatment strategies. We use this model to discuss how integrating clinical and basic understanding of prostate cancer will lead to better implementation of molecularly targeted therapeutics and improve patient survival.

Increased serum insulin-like growth factor-1 levels are associated with prolonged response to dasatinib-based regimens in metastatic prostate cancer

BACKGROUND

Dasatinib, an inhibitor of Src-family kinases, combined with docetaxel in men with castrate-resistant prostate cancer (CRPC), affects bone turnover markers in a phase I/II clinical trial in metastatic CRPC. Only a subset of men benefit from this therapy, and predictive markers are lacking. We hypothesized a role for insulin-like growth factor-1 (IGF-1) as a predictive marker, since IGF-1 is important in both prostate cancer progression and bone development. Hence, we determined the association of IGF-1 expression to treatment response, and whether this expression resulted from tumor cells, the microenvironment, or their interactions.

METHODS

We measured serum IGF-1 levels in men with CRPC treated with dasatinib plus docetaxel. To investigate the source of IGF-1, we utilized two different mouse models harboring human prostate cancer cells, and used species-specific IGF-1 ELISA kits (mouse vs. human).

RESULTS

In men with CRPC, an increase in IGF-1 levels after one cycle of treatment with dasatinib and docetaxel is associated with a higher response rate and longer duration of treatment. Xenograft experiments with subcutaneous and intratibial injection of prostate cancer cells suggest that direct interaction of prostate cancer cells with bone microenvironment is necessary for IGF-1 induction, is entirely host-derived, and occurs only in mice that respond to dasatinib-based therapy.

CONCLUSION

Our results support a role for serum IGF-1 as a potential biomarker for benefit from dasatinib-based combination treatments in CRPC.

Src inhibitors in suppression of papillary thyroid carcinoma growth

BACKGROUND

Papillary thyroid carcinoma is the most common thyroid malignancy. Most papillary thyroid carcinomas contain BRAF mutations or RET/PTC rearrangements, thus providing targets for biologic therapy. Our previous studies had suggested papillary thyroid carcinomas (PTCs) with a BRAF mutation and the RET/PTC1 rearrangement have different sensitivities to MEK1/2 inhibitors, suggesting different signaling transduction pathways were involved.

METHODS

Src signaling transduction pathway in PTC cells was examined using Src inhibitors (PP2, SU6656, or dasatinib) and si-Src RNA in vitro by Western blot analysis and proliferation analysis. An orthotopic xenograft mouse model was used for the in vivo studies using dasatinib.

RESULTS

In PTC cells, Src inhibitors suppressed p-Src and p-FAK and inhibited cell growth. In addition, significant suppression and extension of the p-ERK1/2 dephosphorylation were detected in RET/PTC1-rearranged cells in combination with an MEK inhibitor (CI-1040). The Src family kinase/ABL inhibitor, dasatinib, significantly decreased tumor volume in mice inoculated with PTC cells carrying the RET/PTC1 rearrangement. In BRAF-mutated PTC cells, Src inhibitors effectively suppressed p-Src expression and dasatinib significantly decreased tumor volume with twice daily treatment.

CONCLUSION

Src inhibitors effectively inhibited the Src signaling transduction pathway in PTC cells in vitro and dasatinib suppressed tumor growth in vivo. These results suggested that Src signaling transduction pathway plays an important role in regulating growth in PTC cells. Combination of Src and MEK1/2 inhibitors extended the dephosphorylation of extracellular signal-regulated kinase (ERK)1/2 in PTCs carrying the RET/PTC1 rearrangement suggesting that combination therapy with complementary inhibitors of other signaling transduction pathways may be needed to effectively suppress growth and induce apoptosis in these cells.

RSK promotes G2/M transition through activating phosphorylation of Cdc25A and Cdc25B

Activation of the mitogen-activated protein kinase (MAPK) cascade in mammalian cell lines positively regulates the G2/M transition. The molecular mechanism underlying this biological phenomenon remains poorly understood. Ribosomal S6 kinase (RSK) is a key downstream element of the MAPK cascade. Our previous studies established roles of RSK2 in Cdc25C activation during progesterone-induced meiotic maturation of Xenopus oocytes. In this study we demonstrate that both recombinant RSK and endogenous RSK in Xenopus egg extracts phosphorylate all three isoforms of human Cdc25 at a conserved motif near the catalytic domain. In human HEK293 and PC-3mm2 cell lines, RSK preferentially phosphorylates Cdc25A and Cdc25B in mitotic cells. Phosphorylation of the RSK sites in these Cdc25 isoforms increases their M-phase-inducing activities. Inhibition of RSK-mediated phosphorylation of Cdc25 inhibits G2/M transition. Moreover, RSK is likely to be more active in mitotic cells than in interphase cells, as evidenced by the phosphorylation status of T359/S363 in RSK. Together, these findings indicate that RSK promotes G2/M transition in mammalian cells through activating phosphorylation of Cdc25A and Cdc25B.

Serum insulin to predict time to castration-resistant progression and overall survival in metastatic androgen-dependent prostate cancer (mADPCa)

e16038

Background: Duration of response to androgen-deprivation therapy (ADT) is highly variable in patients with mADPC and prognostic markers are needed. Insulin resistance and hyperinsulinemia may contribute to prostate cancer progression. We hypothesized that pretreatment serum insulin levels would predict time to castration-resistant progression (PFS) and overall survival (OS). Methods: Sera from men treated on a randomized phase 3 trial of first line ADT vs. ADT plus chemotherapy were retrospectively analyzed using a multiplex ELISA for cytokines and angiogenic factors (CAFs). Univariate and multivariate Cox proportional hazards regression models were used to identify associations between CAFs and PFS/OS. Results: 66 pts were evaluable, 86% Caucasian, median age 72 yrs, median PSA 31.5ng/mL, 77% Gleason score of ≥8, and 53% high volume metastatic disease (HVM). Thirty-five pts received ADT; 31 pts received ADT+chemo. In univariate analysis, higher pretreatment insulin and C-peptide were positively correlated with PFS, whereas higher hepatocyte-growth factor (HGF), osteopontin (OPN) and HVM were negatively correlated with PFS. In multivariate analysis, only higher insulin was associated with longer PFS (HR=0.72, 95%CI 1.32 -0.87; p<0.001), whereas higher HGF and OPN were associated with reduced PFS (HR=1.82, 95%CI 0.59-2.83, p<0.01 and HR=1.81, 95%CI 1.18-2.47, p<0.001, respectively). Higher Insulin and Program Death 1 (PD1) were associated with longer OS on multivariate analysis (HR=0.78 p<0.02 and HR=0.55 p<0.02, respectively), whereas HVM and higher OPN were associated with reduced OS (HR=2.28 p<0.01 and HR=1.60 p<0.02). Using low insulin, high HGF and high OPN as 3 independent risk factors (RF), 3 distinct risk groups could predict PFS: good (zero RF), intermediate (1 or 2 RF) and poor risk (3 RF), with median PFS of 6.90, 1.97, and 0.86 years, respectively (p<0.001). Conclusions: Higher pretreatment insulin was associated with prolonged PFS and OS in men with mADPC treated with ADT. Our data suggest that insulin levels are a biomarker for sensitivity to ADT and highlight the complex interactions between metabolism and PCa progression.

Ligand-independent activation of MET through IGF-1/IGF-1R signaling

The receptor tyrosine kinase, MET, has been implicated in tumorigenesis and metastasis of many solid tumors, by multiple mechanisms, including cross talk with epidermal growth factor receptor. In this study, we examined the role of insulin-like growth factor receptor-1 (IGF-1R) signaling in MET activation, focusing on prostate cancer cells. Stimulation of the prostate cancer cell line PC3 with IGF-1 induces a delayed phosphorylation of MET at multiple sites (indicative of full activation), reaching a maximum 18 hr after IGF-1 addition. MET activation does not require the sole MET ligand hepatocyte growth factor (HGF), but does require transcription to occur. Furthermore, direct injection of IGF-1 is sufficient to induce MET activation in vivo, in a PC3 xenograft model. Pharmacologic or genetic inhibition of the tyrosine kinase, Src, abolishes MET phosphorylation, and expression of activated Src is sufficient to induce Met phosphorylation in the absence of IGF-1 stimulation. Activated MET is essential for IGF-1-mediated increased migration of PC3 cells, demonstrating an important biologic effect of IGF-1-mediated MET activation. Finally, we demonstrate that IGF-1-induced delayed MET activation occurs in multiple cell lines which express both the receptors, suggesting that IGF-1R-mediated MET activation may contribute to tumorigenic properties of multiple cancer types when both growth factor receptors are expressed. The results further suggest that MET may be activated by multiple receptor tyrosine kinase receptors, and dual targeting of these receptors may be important therapeutically.

Abstract 3783: Talin-1 phosphorylation promotes invasion and migration of prostate tumor cells through activation of β1 integrins

Integrins have been shown to play a critical role in cell survival. We recently demonstrated that integrins are constitutively activated in highly metastatic prostate cancer cell PC3-mm2. Activation of integrins increases their binding affinity with extracellular matrix, resulting in increased migration and cancer metastasis. Talin is a 270 kDa cytoskeletal protein that has been shown to regulate integrin activity. Previous reports showed that the S425 residue in the N-terminal domain of talin was phosphorylated by Cdk5 to increase talin stability. In this study, we determined whether talin S425 phosphorylation regulates β1 integrin activation. We found that β1 integrin activation in prostate tumor cells correlates with talin S425 phosphorylation but not total talin levels. To examine the role of talin-pS425 in β1 integrin activation, endogenous talin-1 in PC3-mm2 cells was knocked down by shRNA, followed by re-expression of a phosphorylation-deficient S425A or phosphorylation-mimicking S425D talin-1 mutant. Re-expressing phosphorylation-deficient S425A-talin-1 in talin-1-knockdown PC3-mm2 cells showed reduced activation of β1 integrins, and decreased migration and invasion, compared to cells re-expressing wild type talin-1. In contrast, re-expressing the phosphorylation-mimicking S425D mutant in talin-1-knockdown PC3-mm2 cells restored β1 integrin activation and increased migratory and invasive properties of these cells. Inhibition of Cdk5 by roscovitine, a Cdk5 inhibitor, decreases talin-1 S425 phosphorylation and also inhibits downstream integrin signaling, including FAK and Src phosphorylation. Treatment of PC3-mm2 cells with roscovitine decreases β1 integrin activation and migration of PC3-mm2 cells. These results suggest that phosphorylation of talin-1 at S425 plays a role in promoting β1 integrin activation, leading to increased metastatic potential of prostate tumor cells.

Citation Format: Jung-Kang Jin, Yu-Chen Lee, Sue-Hwa Lin, Gary E. Gallick. Talin-1 phosphorylation promotes invasion and migration of prostate tumor cells through activation of β1 integrins. [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 3783. doi:10.1158/1538-7445.AM2013-3783

Targeting constitutively activated β1 integrins inhibits prostate cancer metastasis

Disseminated prostate cancer cells must survive in circulation for metastasis to occur. Mechanisms by which these cells survive are not well understood. By immunohistochemistry of human tissues, we found that levels of β1 integrins and integrin-induced autophosphorylation of FAK (pFAK-Y397) are increased in prostate cancer cells in primary prostate cancer and lymph node metastases, suggesting that β1 integrin activation occurs in metastatic progression of prostate cancer. A conformation-sensitive antibody, 9EG7, was used to examine β1 integrin activation. We found that β1 integrins are constitutively activated in highly metastatic PC3 and PC3-mm2 cells, with less activation in low metastatic LNCaP and C4-2B4 cells. Increased β1 integrin activation as well as the anoikis resistance in prostate cancer cells correlated with metastatic potential in vivo. Knockdown of β1 integrin abrogated anoikis resistance in PC3-mm2 cells. In agreement with β1 integrin activation, PC3-mm2 cells strongly adhered to type I collagen and fibronectin, a process inhibited by the β1 integrin-neutralizing antibody mAb 33B6. mAb 33B6 also inhibited the phosphorylation of β1 integrin downstream effectors, focal adhesion kinase (FAK) and AKT, leading to a 3-fold increase in PC3-mm2 apoptosis. Systemic delivery of mAb 33B6 suppressed spontaneous metastasis of PC3-mm2 from the prostate to distant lymph nodes following intraprostatic injection and suppressed metastasis of PC3-mm2 to multiple organs following intracardiac injection. Thus, constitutively activated β1 integrins play a role in survival of PC3-mm2 cells in circulation and represent a potential target for metastasis prevention.

Serum insulin-like growth factor-1 levels in response to dasatinib-based regimens in bone-metastatic prostate cancer

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Background: Dasatinib, an inhibitor of Src-family kinases, combined with docetaxel in men with castrate-resistant prostate cancer (CRPC), affects bone turnover markers. Only a subset of men benefit from this therapy, and predictive markers are lacking. We hypothesized a role for insulin-like growth factor-1 (IGF-1) as a predictive marker, since IGF-1 is important in both prostate cancer (PCa) progression and bone development. Hence, we determined the association of IGF-1 expression to treatment response, and whether this expression resulted from tumor cells, the microenvironment, or their interactions. Methods: We first measured serum IGF-1 levels in men with CRPC treated with dasatinib plus docetaxel. To investigate the source of IGF-1, we utilized different mouse models harboring human PCa cells, and used species-specific IGF-1 ELISA kits (mouse vs. human). Results: In men with CRPC, an increase in IGF-1 levels after one cycle of treatment is associated with a higher response rate and longer duration of treatment with docetaxel and dasatinib. Xenograft experiments with subcutaneous, and intratibial injection of PCa cells and treatment of mice with dasatinib-based combinations suggest that direct interaction of PCa cells with bone microenvironment is necessary for IGF-1 induction, is entirely host-derived, and occurs only in mice that respond to dasatinib-based therapy. Conclusions: Our results support a role for serum IGF-1 as a potential biomarker for dasatinib-based combination treatments in CRPC. Inoculation of human PCa cells into murine hosts was essential in determining that IGF-1 results from the bone microenvironment. Further studies are warranted to validate these findings in a larger cohort of patients in a prospective manner.

Modulation of soluble c-Met, bone turnover markers, angiogenic factors, and c-Met in men with mCRPC treated with cabozantinib

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Background: Cabozantinib (cabo) is a multi-TKI against c-Met and VEGFR2. Cabo elicits striking changes in bone scans (BS), reductions in soft-tissue mets, and improves bone pain in mCRPC. This unique response is unlinked from PSA and suggests that targets of Cabo reside in the bone microenvironment. To explore the underlying mechanisms of Cabo activity, we examined changes in soluble c-Met, angiogenic factors, bone specific alkaline phosphatase (BAP), and tumor specific c-Met signaling in men on Cabo. Methods: A phase II cohort of docetaxel pretreated men with mCRPC received Cabo. Response was assessed q6 wks by BS and CT scan. Blood and trans-iliac bone marrow biopsies (BMs) were collected pretreatment and at wk 6. Soluble c-Met was measured by ELISA, angiogenic factors by multiplex immunoassay, and tumor c-Met/phospho c-Met expression by IHC. Results: 21 patients with bony mets were evaluated; 38% also had soft tissue mets. 13/21 (62%) pts experienced an improvement (PRs + CRs) in BS and 2/8 (25%) achieved a PR in soft tissue mets. 12/20 (60%) pts had reductions in BAP on therapy (median reduction 48.5%). VEGFR2 levels decreased in response to therapy (p<0.0001) and VEGF levels increased (p<0.085). Soluble c-Met levels increased on therapy (p<0.009). Pretreatment BMs containing >5% tumor involvement (median 80%) were evaluable for 10 patients, 9 of whom also had a 6 wk BM. High intensity, tumor-specific expression of c-Met was detectable in 8/10 (80%) of pretreatment tumors (median involvement 60%) and increased in 4/9 (45%) pts at 6 wks (median increase 30%). Activated phospho c-Met was detectable in 9/10 (90%) of pretreatment tumors (median involvement 80%) and decreased in 5/9 (56%) pts (median reduction 30%) at 6 wks. Conclusions: The results of our study suggest that changes in soluble markers of c-Met, bone turnover, and angiogenesis are linked to Cabo activity. Analyses of BMs demonstrate high c-Met activation in pretreatment mets and suggest Cabo-mediated inhibition at 6 wks. These data support the hypothesis that c-Met contributes to “driver” signaling networks in mCRPC and suggest that biomarkers of stromal cell function should be prioritized for further study.

Resistance to BRAF inhibition in BRAF-mutant colon cancer can be overcome with PI3K inhibition or demethylating agents

PURPOSE

Vemurafenib, a selective inhibitor of BRAF(V600), has shown significant activity in BRAF(V600) melanoma but not in less than 10% of metastatic BRAF(V600) colorectal cancers (CRC), suggesting that studies of the unique hypermethylated phenotype and concurrent oncogenic activation of BRAF(mut) CRC may provide combinatorial strategies.

EXPERIMENTAL DESIGN

We conducted comparative proteomic analysis of BRAF(V600E) melanoma and CRC cell lines, followed by correlation of phosphoinositide 3-kinase (PI3K) pathway activation and sensitivity to the vemurafenib analogue PLX4720. Pharmacologic inhibitors and siRNA were used in combination with PLX4720 to inhibit PI3K and methyltransferase in cell lines and murine models.

RESULTS

Compared with melanoma, CRC lines show higher levels of PI3K/AKT pathway activation. CRC cell lines with mutations in PTEN or PIK3CA were less sensitive to growth inhibition by PLX4720 (P = 0.03), and knockdown of PTEN expression in sensitive CRC cells reduced growth inhibition by the drug. Combined treatment of PLX4720 with PI3K inhibitors caused synergistic growth inhibition in BRAF-mutant CRC cells with both primary and secondary resistance. In addition, methyltransferase inhibition was synergistic with PLX4720 and decreased AKT activation. In vivo, PLX4720 combined with either inhibitors of AKT or methyltransferase showed greater tumor growth inhibition than PLX4720 alone. Clones with acquired resistance to PLX4720 in vitro showed PI3K/AKT activation with EGF receptor (EGFR) or KRAS amplification.

CONCLUSIONS

We show that activation of the PI3K/AKT pathway is a mechanism of both innate and acquired resistance to BRAF inhibitors in BRAF(V600E) CRC and suggest combinatorial approaches to improve outcomes in this poor prognosis subset of patients.

Abstract A53: Crosstalk between IGFR and MET in prostate cancer

Background: Ligand independent receptor tyrosine kinase activation can be mediated by activation through other growth factor receptors. Understanding this cross-talk has implications in the use of combination therapies, as growth factor receptors often stimulate overlapping signaling pathways.

Purpose: To examine crosstalk between IGF-R1 and MET in prostate cancer (PCa) cells.

Experimental procedures: IGF was added to PC3 prostate cancer cells and phosphorylation of c-Met and activation of signaling proteins was examined by immunoblotting various times thereafter. Activation of MET was determined by immunoblotting with antibodies to the tyrosine phosphorylation sites, Y1234/Y1235 and Y1349. To determine the requirement of transcription for c-Met activation, experiments were performed in the presence of actinomycin D. To determine the requirement of IGFR and/or Src in c-Met phosphorylation, IGF was added to PC3 cells with stable knockdown of IGFR or Src by expression of an shIGFR or shSrc construct. Rescue experiments were performed by expressing an sh-insensitive mouse c-Src. To determine the biological effect of MET activation, PC3 cells and PC3 cells with stable knockdown of c-Met were stimulated with IGF and allowed to migrate in Boyden chambers for various times thereafter.

Results: We demonstrate that addition of 100ng/ml of IGF to culture media of PC3 cells (IGF was chosen because it is abundant in the sera of prostate cancer patients), induces MET tyrosine kinase activation beginning 18 hours after addition and sustained for a minimum of 6 hrs thereafter. Multiple sites on Y1234/Y1235 and Y1349 are phosphorylated, suggesting full MET activation, a conclusion supported by increased migration of cells after c-Met phosphorylation. Phosphorylation of MET is not due to the presence of HGF, which was undetectable in cells by quantitative RT-PCR and in media by ELISA, but requires IGF-1R activation, as IGFR stable knock down or the addition of the IGFR-1R inhibitor BMS754807 inhibited MET phosphorylation. We demonstrated that transcription is also required for MET activation, as MET was not tyrosine phosphorylated in cells grown in the presence of actinomycin D. As other groups have shown delayed activation of MET by EGF required the tyrosine kinase, Src, we performed the experiments in the presence of the pan Src Family Kinase inhibitor, dasatinib, and demonstrated that MET phosphorylation was abolished. We demonstrate that Src itself is required for MET phosphorylation, as a stable shSrc knockdown cell line inhibited IGF-induced MET activation, whereas expression of mouse Src (insensitive to sh knockdown) restores MET phosphorylation in the presence of IGF.

Conclusion: We demonstrate that IGF induces MET activation through a ligand-independent mechanism requiring gene transcription following activation of IGF-1R and Src.

Citation Format: Andreas S. Varkaris, Sanchaika Gaur, Nila Parikh, Christopher Logothetis, Gary E. Gallick. Crosstalk between IGFR and MET in prostate cancer. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr A53.

Relationship of Src activity and prior oxaliplatin on outcomes after hepatectomy for metastatic colorectal cancer

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Background: The nonreceptor tyrosine kinase Src regulates pathways critical to tumor proliferation, chemoresistance, and epithelial-to-mesenchymal transition. In vitro, Src is activated after acute oxaliplatin exposure and in acquired oxaliplatin resistance, but not after 5-FU alone. Activation of Src and its substrate FAK in metastatic colorectal cancer treated with oxaliplatin has not been studied in human specimens. Methods: Samples from 170 hepatic resections from two cohorts of patients with metastatic colorectal cancer were examined by IHC for expression of activated Src (pSrc) and FAK (total and pFAK). In the first cohort (n=50), tissue was collected at consecutive hepatic resections before and after oxaliplatin. Patients in the second cohort (n=120) were compared based on whether or not oxaliplatin was administered after resection. IHC was graded semi-quantitatively, 0 to 4 based on intensity (first cohort), and by automated image analysis (second cohort). Results: In the first cohort, pFAK expression increased after oxaliplatin exposure (mean IHC score 2.04 vs. 1.18, p<0.01). In the second cohort, Src activation was correlated with pFAK expression (p<0.01). Patients pretreated with oxaliplatin demonstrated increased expression of activated FAK (p=0.02) compared to 5-FU alone or irinotecan regimens. There was a weak association between total Src expression and the number of oxaliplatin cycles (p=0.06). Among patients in the second cohort, five-year relapse-free survival was inversely related to levels of pFAK (21.1%, 16.5%, and 7.4% for low, medium, and high levels of pFAK, respectively; p=0.02) and of pSrc (19.6%, 13.6%, and 8.2% for low, medium, and high levels of pSrc, respectively; p= 0.01). Conclusions: Patients treated with neoadjuvant oxaliplatin demonstrated increased Src signaling in liver metastases, a finding associated with worse relapse-free survival. These results are consistent with prior in vitro studies correlating oxaliplatin exposure with Src pathway activation and support the idea that inhibition of Src, when used in combination with platinum chemotherapy, warrants further investigation in patients with metastatic colorectal cancer.