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<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.