Targeting the fibroblast growth factor pathway in molecular subtypes of castration-resistant prostate cancer

BACKGROUND

Androgen receptor (AR) pathway inhibition remains the cornerstone for prostate cancer therapies. However, castration-resistant prostate cancer (CRPC) tumors can resist AR signaling inhibitors through AR amplification and AR splice variants in AR-positive CRPC (ARPC), and conversion to AR-null phenotypes, such as double-negative prostate cancer (DNPC) and small cell or neuroendocrine prostate cancer (SCNPC). We have shown previously that DNPC can bypass AR-dependence through fibroblast growth factor receptor (FGFR) signaling. However, the role of the FGFR pathway in other CRPC phenotypes has not been elucidated.

METHODS

RNA-Seq analysis was conducted on patient metastases, LuCaP patient-derived xenograft (PDX) models, and CRPC cell lines. Cell lines (C4-2B, VCaP, and 22Rv1) and ex vivo LuCaP PDX tumor cells were treated with enzalutamide (ENZA) and FGFR inhibitors (FGFRi) alone or in combination and sensitivity was determined using cell viability assays. In vivo efficacy of FGFRi in ARPC, DNPC, and SCNPC were evaluated using PDX models.

RESULTS

RNA-Seq analysis of FGFR signaling in metastatic specimens, LuCaP PDX models, and CRPC cell lines revealed significant FGF pathway activation in AR-low PC (ARLPC), DNPC, and SCNPC tumors. In vitro/ex vivo analysis of erdafitinib and CH5183284 demonstrated robust and moderate growth suppression of ARPC, respectively. In vivo studies using four ARPC PDX models showed that combination ENZA and CH5183284 significantly suppressed tumor growth. Additional in vivo studies using four ARPC PDX models revealed that erdafitinib monotherapy was as effective as ENZA in suppressing tumor growth, and there was limited combination benefit. Furthermore, two of three DNPC models and two of four SCNPC models responded to CH5183284 monotherapy, suggesting FGFRi responses were model dependent. RNA-Seq and gene set enrichment analysis of end-of-study ARPC tumors treated with FGFRi displayed decreased expression of E2F and MYC target genes and suppressed G2M checkpoint genes, whereas end-of-study SCNPC tumors had heterogeneous transcriptional responses.

CONCLUSIONS

Although FGFRi treatments suppressed tumor growth across CRPC phenotypes, our analyses did not identify a single pathway or biomarker that would identify tumor response to FGFRi. This is very likely due to the array of FGFR1-4 expression and tumor phenotypes present in CRPC. Nevertheless, our data nominate the FGFR pathway as a clinically actionable target that promotes tumor growth in diverse phenotypes of treatment-refractory metastatic CRPC.

Concurrent Targeting of HDAC and PI3K to Overcome Phenotypic Heterogeneity of Castration-resistant and Neuroendocrine Prostate Cancers

Castration-resistant prostate cancer (CRPC) consists of multiple phenotypic subtypes including androgen receptor (AR)-active prostate cancer (ARPC) and neuroendocrine prostate cancer (NEPC). Tumor cells with these phenotypes can coexist between metastases within a patient and within an individual tumor. Treatments that are effective across CRPC subtypes are currently lacking. Histone deacetylation is crucial for the regulation of chromatin structure and maintenance of cancer cell state and activation of the PI3K/AKT/mTOR signaling cascade is a tumor growth-promoting pathway. We therefore investigated combined targeting of histone deacetylase (HDAC) and PI3K using a rationally designed dual inhibitor, fimepinostat, in CRPC subtypes in vitro and in vivo. Dual HDAC1/2 and PI3K/AKT pathway inhibition by fimepinostat led to robust tumor growth inhibition in both ARPC and NEPC models including cell line- and patient-derived xenografts. HDAC1/2 inhibition combined with PI3K/AKT inhibition was more effective than targeting each pathway alone, producing growth inhibitory effects through cell-cycle inhibition and apoptosis. Molecular profiling revealed on-target effects of combined HDAC1/2 and PI3K/AKT inhibition independent of tumor phenotype. Fimepinostat therapy was also associated with the suppression of lineage transcription factors including AR in ARPC and Achaete-scute homolog 1 (ASCL1) in NEPC. Together, these results indicate that fimepinostat represents a novel therapeutic that may be effective against both ARPC and NEPC through CRPC subtype-dependent and -independent mechanisms.

SIGNIFICANCE

CRPC is a heterogeneous disease constituting multiple phenotypic subtypes that often co-occur within tumors or across metastases in patients. Existing targeted therapies for CRPC do not take this into account. Here we show that fimepinostat, a dual HDAC1/2 and PI3K/AKT inhibitor investigated clinically in other cancer types but not prostate cancer, may overcome this heterogeneity by effectively inhibiting both ARPC and NEPC subtypes of CRPC.

Enhancer profiling identifies epigenetic markers of endocrine resistance and reveals therapeutic options for metastatic castration-resistant prostate cancer patients

Androgen Receptor (AR) signaling inhibitors, including enzalutamide, are treatment options for patients with metastatic castration-resistant prostate cancer (mCRPC), but resistance inevitably develops. Using metastatic samples from a prospective phase II clinical trial, we epigenetically profiled enhancer/promoter activities with H3K27ac chromatin immunoprecipitation followed by sequencing, before and after AR-targeted therapy. We identified a distinct subset of H3K27ac-differentially marked regions that associated with treatment responsiveness. These data were successfully validated in mCRPC patient-derived xenograft models (PDX). In silico analyses revealed HDAC3 as a critical factor that can drive resistance to hormonal interventions, which we validated in vitro . Using cell lines and mCRPC PDX tumors in vitro , we identified drug-drug synergy between enzalutamide and the pan-HDAC inhibitor vorinostat, providing therapeutic proof-of-concept. These findings demonstrate rationale for new therapeutic strategies using a combination of AR and HDAC inhibitors to improve patient outcome in advanced stages of mCRPC.

Response to supraphysiological testosterone is predicted by a distinct androgen receptor cistrome

The androgen receptor (AR) is a master transcription factor that regulates prostate cancer (PC) development and progression. Inhibition of AR signaling by androgen deprivation is the first-line therapy with initial efficacy for advanced and recurrent PC. Paradoxically, supraphysiological levels of testosterone (SPT) also inhibit PC progression. However, as with any therapy, not all patients show a therapeutic benefit, and responses differ widely in magnitude and duration. In this study, we evaluated whether differences in the AR cistrome before treatment can distinguish between SPT-responding (R) and -nonresponding (NR) tumors. We provide the first preclinical evidence to our knowledge that SPT-R tumors exhibit a distinct AR cistrome when compared with SPT-NR tumors, indicating a differential biological role of the AR. We applied an integrated analysis of ChIP-Seq and RNA-Seq to the pretreatment tumors and identified an SPT-R signature that distinguishes R and NR tumors. Because transcriptomes of SPT-treated clinical specimens are not available, we interrogated available castration-resistant PC (CRPC) transcriptomes and showed that the SPT-R signature is associated with improved survival and has the potential to identify patients who would respond to SPT. These findings provide an opportunity to identify the subset of patients with CRPC who would benefit from SPT therapy.

RNA splicing factors SRRM3 and SRRM4 distinguish molecular phenotypes of castration-resistant neuroendocrine prostate cancer

Neuroendocrine (NE) differentiation in metastatic castration-resistant prostate cancer (mCRPC) is an increasingly common clinical feature arising from cellular plasticity. We recently characterized two mCRPC phenotypes with NE features: androgen receptor (AR)-positive NE-positive amphicrine prostate cancer (AMPC) and AR-negative small cell or neuroendocrine prostate cancer (SCNPC). Here, we interrogated the regulation of RE1-silencing transcription factor (REST), a transcriptional repressor of neuronal genes, and elucidated molecular programs driving AMPC and SCNPC biology. Analysis of prostate cancer (PC) cell lines, mCRPC specimens, and LuCaP patient-derived xenograft models detected alternative splicing of REST to REST4 and attenuated REST repressor activity in AMPC and SCNPC. The REST locus was also hypermethylated and REST expression was reduced in SCNPC. While serine/arginine repetitive matrix protein 4 (SRRM4) was previously implicated in alternative splicing of REST in mCRPC, we detected SRRM3 expression in REST4-positive, SRRM4-negative AMPC and SCNPC. In CRPC cell lines, SRRM3 induced alternative splicing of REST to REST4 and exacerbated the expression of REST-repressed genes. Furthermore, SRRM3 and SRRM4 expression defined molecular subsets of AMPC and SCNPC across species and tumor types. Two AMPC phenotypes and three SCNPC phenotypes were characterized, denoted either by REST attenuation and ASCL1 activity or by progressive activation of neuronal transcription factor programs, respectively. These results nominate SRRM3 as the principal REST splicing factor expressed in early NE differentiation and provide a framework to molecularly classify diverse NE phenotypes in mCRPC.

Abstract 1458: Targeting fibroblast growth factor receptors in castration-resistant prostate cancer

Background: Androgen receptor (AR) pathway inhibition remains the cornerstone for prostate cancer therapies. Although AR signaling inhibitors (ARSI), such as enzalutamide (ENZ) and abiraterone (ABI), extend survival in recurrent and castration-resistant prostate cancer (CRPC), durable complete responses are rare. Bypass mechanisms employed by metastatic CRPC include amplification of AR and AR splice variants in AR-high CRPC (ARPC) and conversion to AR-null phenotypes, such as double-negative prostate cancer (DNPC) and small cell or neuroendocrine prostate cancer (SCNPC). We showed previously that DNPC bypasses AR-dependence through fibroblast growth factor (FGF) signaling. However, the utility of targeting the FGF pathway in other molecular subtypes of CRPC remains to be determined.

Methods: RNASeq was conducted on 98 patient metastases, 18 LuCaP patient-derived xenograft (PDX) models and CRPC cell lines. Sensitivity to ARSI and FGFR inhibitors (FGFRi) alone or in combination in cell lines (C4-2B, VCaP, 22Rv1, DU145 and NCIH660) or ex vivo PDX tumor cells (10 ARPC models, 2 DNPC models, and 6 SCNPC models) was measured through CellTitre Glo assays. On-target effects of inhibitors were assessed through immunoblot and qPCR. In vivo efficacy of FGFRi in ARPC and SCNPC was conducted using LuCaP PDX models.

Results: Interrogation of FGF pathway activity and FGFR expression using RNASeq and FGF signature scores in CRPC metastases, LuCaP PDX models and CRPC cell lines revealed upregulated FGF pathway activation in AR-null DNPC and SCNPC and in subsets of ARPC. In vitro/ex vivo analysis of FGFRi (erdafitinib, CH5183284 and rogaratinib) demonstrated robust growth suppression in DNPC and moderate growth suppression in SCNPC. In vivo CH5183284 administration recapitulated the growth suppression observed in vitro for SCNPC LuCaP 93 and LuCaP 173.1 but not for SCNPC LuCaP 49. Furthermore, in vitro/ex vivo analysis of AR-expressing CRPC models determined that combination ARSI (ENZ, ABI or darolutamide) with FGFRi was superior to ARSI or FGFRi monotherapies in a subset of models. Immunoblot and qPCR analyses verified that FGFRi-mediated growth suppression occurs through inactivation of the MAPK/MEK and ERK signal transduction cascade in AR-expressing CRPC. Finally, ARPC LuCaP PDX models treated with combination ARSI and FGFRi showed significant tumor growth inhibition compared to control and monotherapy groups in vivo. Analysis of resistance mechanisms to FGFRi therapy are ongoing.

Conclusions: The emergence of bypass mechanisms that subvert AR-dependence in mCRPC highlights a need for novel therapeutic strategies. Our data nominate the FGF pathway as an actionable target in diverse phenotypes of treatment-refractory mCRPC.

Citation Format: Mark P. Labrecque, Lisha G. Brown, Ilsa M. Coleman, Bryce Lakely, Holly M. Nguyen, Eva Corey, Peter S. Nelson, Colm Morrissey. Targeting fibroblast growth factor receptors in castration-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1458.

Cabozantinib can block growth of neuroendocrine prostate cancer patient-derived xenografts by disrupting tumor vasculature

With the advent of potent second-line anti-androgen therapy, we and others have observed an increased incidence of androgen receptor (AR)-null small cell or neuroendocrine prostate cancer (SCNPC) in metastatic castration-resistant prostate cancer (mCRPC). Our study was designed to determine the effect of cabozantinib, a multi-targeted tyrosine kinase inhibitor that inhibits VEGFR2, MET and RET on SCNPC. Transcriptome analysis of the University of Washington rapid autopsy and SU2C mCRPC datasets revealed upregulated MET and RET expression in SCNPCs relative to adenocarcinomas. Additionally, increased MET expression correlated with attenuated AR expression and activity. In vitro treatment of SCNPC patient-derived xenograft (PDX) cells with the MET inhibitor AMG-337 had no impact on cell viability in LuCaP 93 (MET+/RET+) and LuCaP 173.1 (MET-/RET-), whereas cabozantinib decreased cell viability of LuCaP 93, but not LuCaP 173.1. Notably, MET+/RET+ LuCaP 93 and MET-/RET- LuCaP 173.1 tumor volumes were significantly decreased with cabozantinib treatment in vivo, and this activity was independent of MET or RET expression in LuCaP 173.1. Tissue analysis indicated that cabozantinib did not inhibit tumor cell proliferation (Ki67), but significantly decreased microvessel density (CD31) and increased hypoxic stress and glycolysis (HK2) in LuCaP 93 and LuCaP 173.1 tumors. RNA-Seq and gene set enrichment analysis revealed that hypoxia and glycolysis pathways were increased in cabozantinib-treated tumors relative to control tumors. Our data suggest that the most likely mechanism of cabozantinib-mediated tumor growth suppression in SCNPC PDX models is through disruption of the tumor vasculature. Thus, cabozantinib may represent a potential therapy for patients with metastatic disease in tumor phenotypes that have a significant dependence on the tumor vasculature for survival and proliferation.

Identification of Therapeutic Vulnerabilities in Small-cell Neuroendocrine Prostate Cancer

PURPOSE

Small-cell neuroendocrine prostate cancer (SCNPC) exhibits an aggressive clinical course and incidence rates seem to be increasing following resistance to potent androgen receptor (AR) antagonists. Currently, treatment options are limited and few model systems are available to identify new approaches for treatment. We sought to evaluate commonalities between SCNPC and other aggressive neuroendocrine carcinomas to identify therapeutic targets.

EXPERIMENTAL DESIGN

We generated whole transcriptome RNA-sequencing data from AR-active prostate cancers (ARPCs) and SCNPCs from tumors collected at rapid autopsy and two other neuroendocrine carcinomas, Merkel cell carcinoma (MCC), and small-cell lung cancer. We performed cross-tumor comparisons to identify conserved patterns of expression of druggable targets. We tested inhibitors to highly upregulated drug targets in a panel of prostate cancer cell lines and in vivo patient-derived xenograft (PDX) models.

RESULTS

We identified BCL2 as highly upregulated in SCNPC compared with ARPC. Inhibitors targeting BCL2 induced apoptotic cell death in SCNPC cell lines at nanomolar concentrations while ARPC cell lines were resistant. Treatment with the BCL2 inhibitor navitoclax leads to a reduction of growth of SCNPC PDX tumors in vivo, whereas ARPC PDX models were more resistant. We identified Wee1 as a second druggable target upregulated in SCNPC. Treatment with the combination of navitoclax and the Wee1 inhibitor AZD-1775 repressed the growth of SCNPC PDX resistant to single-agent BCL2 inhibitors.

CONCLUSIONS

The combination of BCL2 and Wee1 inhibition presents a novel therapeutic strategy for the treatment of SCNPC.

Molecular profiling stratifies diverse phenotypes of treatment-refractory metastatic castration-resistant prostate cancer

Metastatic castration-resistant prostate cancer (mCRPC) is a heterogeneous disease with diverse drivers of disease progression and mechanisms of therapeutic resistance. We conducted deep phenotypic characterization of CRPC metastases and patient-derived xenograft (PDX) lines using whole genome RNA sequencing, gene set enrichment analysis and immunohistochemistry. Our analyses revealed five mCRPC phenotypes based on the expression of well-characterized androgen receptor (AR) or neuroendocrine (NE) genes: (i) AR-high tumors (ARPC), (ii) AR-low tumors (ARLPC), (iii) amphicrine tumors composed of cells co-expressing AR and NE genes (AMPC), (iv) double-negative tumors (i.e. AR-/NE-; DNPC) and (v) tumors with small cell or NE gene expression without AR activity (SCNPC). RE1-silencing transcription factor (REST) activity, which suppresses NE gene expression, was lost in AMPC and SCNPC PDX models. However, knockdown of REST in cell lines revealed that attenuated REST activity drives the AMPC phenotype but is not sufficient for SCNPC conversion. We also identified a subtype of DNPC tumors with squamous differentiation and generated an encompassing 26-gene transcriptional signature that distinguished the five mCRPC phenotypes. Together, our data highlight the central role of AR and REST in classifying treatment-resistant mCRPC phenotypes. These molecular classifications could potentially guide future therapeutic studies and clinical trial design.

Abstract 379: Supraphysiological testosterone inhibits tumor growth and is associated with inhibition of ARV7 signaling and DNA damage response in preclinical models of enzalutamide-resistant prostate cancer

Background: Anti-androgen therapies suppress castration-resistant prostate cancer (CRPC) but CRPC cells develop resistance. One of the mechanisms of resistance is through overexpression of androgen receptor (AR) and AR splice variants. In contrast to AR pathway inhibition therapies, recent clinical studies using bipolar androgen therapy demonstrated CRPC inhibition using supraphysiological levels of testosterone (SPT). The objective of this study was to investigate the mechanisms driving SPT-mediated tumor growth inhibition using CRPC patient-derived xenografts (PDX).

Methods: PDXs were implanted in castrated SCID mice and randomized to control or SPT arms. For enzalutamide-resistant (ENZR) PDX studies, mice with established tumors were treated with enzalutamide and randomized to control or SPT upon development of resistance. Tumors were monitored for growth and collected for analyses.

Results: In a SPT preclinical trial using thirteen LuCaP CRPC PDX models, four PDXs responded to SPT treatment while nine demonstrated de novo resistance. Our analysis revealed that responding PDXs had intrinsically higher AR and ARV7 expression compared to non-responding PDXs. Moreover, ARV7 expression was negatively correlated with E2F signaling and proliferation only in responding PDXs, suggesting that the ARV7 program functions differently in responder and non-responder phenotypes. Another PDX trial using ENZR PDXs determined that SPT inhibited the growth of LuCaP 35CR ENZR and LuCaP 96CR ENZR (responders), but not LuCaP 77CR ENZR (non-responder). Serum and intratumoral T were increased in both responders and the non-responder, suggesting that differential T delivery and tumoral retention were not the cause of differential tumor responses. Tumor analyses determined that SPT decreased AR transcript levels, however, nuclear AR protein levels and canonical AR signaling remained high in both responders and the non-responder. Conversely, ARV7 transcript was consistently decreased but the ARV7 program was downregulated only in responders. Additionally, an unbiased pathway analysis of RNASeq revealed that SPT drastically decreased genes associated with E2F-mediated cell cycle progression and proliferation and the DNA damage response (DDR) exclusively in responders. Further support for these pathways driving SPT-mediated tumor inhibition was demonstrated through the resolution of the suppressed ARV7/E2F1/DDR pathways in LuCaP 35CR ENZR upon acquiring SPT resistance, whereas the pathways remained suppressed in LuCaP 96CR ENZR, which exhibited a durable response to SPT.

Conclusion: Our data indicates that SPT therapy inhibits progression of a unique subset of ENZR CRPC and highlights critical roles for ARV7 signaling, DDR and E2F1-mediated proliferation in tumor inhibition.

Citation Format: Hung-Ming Lam, Mark P. Labrecque, Holly M. Nguyen, Lisha G. Brown, Ilsa M. Coleman, Roman Gulati, Bryce Lakely, Daniel Sondheim, Brett Marck, Alvin M. Matsumoto, Elahe A. Mostaghel, Michael T. Schweizer, Peter S. Nelson, Eva Corey. Supraphysiological testosterone inhibits tumor growth and is associated with inhibition of ARV7 signaling and DNA damage response in preclinical models of enzalutamide-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 379.

Abstract 4392: Pre-mRNA splicing factors promote cellular plasticity in castration-resistant prostate cancer

Background: Metastatic castration-resistant prostate cancer (mCRPC) is a heterogeneous disease with poorly understood drivers of disease progression. We recently characterized five mCRPC phenotypes, including an amphicrine phenotype that co-expresses androgen receptor (AR) and neuroendocrine prostate cancer (NEPC) biomarkers. We determined that loss of RE1-silencing transcription factor (REST), a master regulator of neuronal differentiation, drives the amphicrine phenotype, but is not sufficient for prostate cancer (PC) adenocarcinoma to NEPC conversion. Furthermore, loss of REST through SRRM4-mediated splicing of REST pre-mRNA to REST4 has been suggested to drive adenocarcinoma to NEPC conversion. However, the roles of pre-mRNA splicing factors and REST activity in lineage switching require further investigation.

Methods: Transcriptomic (RNASeq) and immunohistochemical/immunofluorescent analysis (IHC and IF) were conducted on amphicrine and NEPC patient metastases, LuCaP patient-derived xenograft (PDX) models and modified CRPC cell lines. The roles of SRRM3 and SRRM4 were examined using overexpression studies in AR-expressing and AR-null CRPC cell lines.

Results: RNASeq, IHC and IF of metastatic specimens, LuCaP PDX models and VCaP cells confirmed the existence of the amphicrine phenotype in vitro and in vivo. Interestingly, transcriptome analysis of amphicrine patient specimens and LuCaP 77CR revealed that loss of REST repressor activity occurred without SRRM4 expression in a subset of tumor specimens. Indeed, BaseScope analysis using primers specific to REST4 and SRRM4 verified that amphicrine 77CR tumors were positive for REST4 expression but negative for SRRM4 expression, suggesting an alternative mechanism of REST splicing. Notably, overexpression of SRRM4 in AR-expressing C4-2B and AR-null PC-3 cells did not induce REST splicing. Moreover, RNASeq of SRRM4-overexpressing cells displayed heterogeneous transcriptome profiles inconsistent with canonical amphicrine or NEPC gene expression profiles. Interestingly, SRRM3 transcript was expressed at high levels in amphicrine and NEPC patient and LuCaP PDX biospecimens that lacked SRRM4 expression, suggesting an SRRM3-mediated mechanism of REST splicing. Studies interrogating the roles of SRRM3 in REST splicing and CRPC cellular plasticity are ongoing.

Conclusions: Our data highlights an unrecognized mechanism of adenocarcinoma to amphicrine or NEPC conversion that hinges on a SRRM3-REST regulatory axis rather than REST-loss or SRRM4-mediated REST splicing. Identifying the mechanisms that may convert adenocarcinoma to treatment-resistant amphicrine or NEPC phenotypes in mCRPC patients will inform treatment and identify potential molecular pathways for therapeutic intervention.

Citation Format: Mark P. Labrecque, Ilsa M. Coleman, Lisha G. Brown, Bryce Lakely, Lori Kollath, Daniel W. Lin, Lawrence D. True, Eva Corey, Peter S. Nelson, Colm Morrissey. Pre-mRNA splicing factors promote cellular plasticity in castration-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4392.

Durable Response of Enzalutamide-resistant Prostate Cancer to Supraphysiological Testosterone Is Associated with a Multifaceted Growth Suppression and Impaired DNA Damage Response Transcriptomic Program in Patient-derived Xenografts

BACKGROUND

Androgen deprivation therapy improves the survival of castration-resistant prostate cancer (CRPC) patients, yet ultimately fails with debilitating side effects. Supraphysiological testosterone (SPT)-based therapy produces clinical responses with improved quality of life in a subset of patients. Currently, no information defines a durable response to SPT.

OBJECTIVE

To identify key molecular phenotypes underlying SPT response to improve patient selection and guide combination treatment to achieve a durable response.

DESIGN, SETTING, AND PARTICIPANTS

A patient-derived xenograft (PDX) preclinical trial was performed with 13 CRPC PDXs to identify molecular features associated with SPT response. Comprehensive intratumoral androgen, tumor growth, and integrated transcriptomic and protein analyses were performed in three PDXs resistant to the newer androgen receptor (AR) pathway inhibitor enzalutamide (ENZ) to define SPT response and resistance.

INTERVENTION

Testosterone cypionate.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

SPT efficacy was evaluated by PDX growth, prostate-specific antigen (PSA) change, and survival. Intratumoral androgens were analyzed using mass spectrometry. Global transcriptome analysis was performed using RNA sequencing, and confirmed by quantitative real-time polymerase chain reaction and immunohistochemistry. Log-rank and Mann-Whitney tests were used for survival and molecular analyses, respectively.

RESULTS AND LIMITATIONS

A durable SPT responder was identified, presenting robust repressions of ARv7 and E2F transcriptional outputs, and a DNA damage response (DDR) transcriptomic program that were altogether restored upon SPT resistance in the transient responder. ENZ rechallenge of SPT-relapsed PDXs resulted in PSA decreases but tumor progression.

CONCLUSIONS

SPT produces a durable response in AR-pathway inhibitor ENZ CRPC that is associated with sustained suppression of ARv7 and E2F transcriptional outputs, and the DDR transcriptome, highlighting the potential of combination treatments that maintain suppression of these programs to drive a durable response to SPT.

PATIENT SUMMARY

Patients with ENZ-resistant prostate cancer have very limited treatment options. Supraphysiological testosterone presents a prominent option for improved quality of life and a potential durable response in patients with sustained suppression on ARv7/E2F transcriptional outputs and DNA repair program.

Abstract IA21: AR is ablated: Now what? Targeting the double-negative phenotype

Background/Introduction: Androgen receptor (AR) signaling is a distinctive feature of prostate cancer (PC) and represents the major therapeutic target for treating metastatic prostate cancer (mPC). Though highly effective, AR antagonism can produce tumors that bypass a functional requirement for AR, often through neuroendocrine (NE) transdifferentiation. Through the molecular assessment of mPCs over two decades, we find that a phenotypic shift has occurred in mPC with the emergence of an AR-null NE-null phenotype. We sought to identify drivers of these “double-negative” PCs (DNPC), with the ultimate objective of developing therapeutic strategies.

Methods: We used genome-wide profiling of copy number (array CGH), mutations (whole-exome sequencing-WES), and gene expression (RNA-seq) to compare the molecular landscapes of AR-active PC (ARPC), NEPC, and DNPC in tumors obtained from 84 consecutive men with mPC undergoing a rapid autopsy. We developed model systems including DNPC patient-derived xenografts (PDX) and cell lines that are devoid of AR activity and lack NE features. Using these models, we tested therapeutics hypothesized to inhibit the activity of pathways preferentially active in DNPC.

Results: In the era prior to the approval of the AR pathway antagonists enzalutamide and abiraterone, most CRPCs were ARPCs (85%) with rare NEPCs (10%) and rarer DNPCs (5%). In the contemporary era (2012-2016), we observed a shift in tumor phenotypes with a higher representation of DNPCs. Gene expression programs of the tumors classified by IHC supported these distinct subtypes. DNPCs did not exhibit GR activity or PI3K/AKT activation but were notable for high MAPK and FGF pathway activity. Models systems recapitulated these findings. FGFR antagonists differentially repressed the growth of DNPC tumors in vitro and in vivo.

Conclusions: Though the majority of mPCs that resist AR targeting retain AR signaling, an increasingly common subtype of mPC exhibits a DNPC phenotype. Our results indicate that at least a subset of these DNPCs are driven by FGF signaling and MAPK activation. Targeting the FGF axis may represent a therapeutic approach for those cancers resistant to AR-directed therapies and may circumvent treatment resistance if combined with initial AR pathway blockade.

Citation Format: Colm Morrissey, Eric G. Bluemn, Ilsa M. Coleman, Jared M. Lucas, Roger T. Coleman, Robin Tharakan, Daniella Bianchi-Frias, Ruth F. Dumpit, Arja Kaipainen, Alexandra N. Corella, Yu Chi Yang, Michael D. Nyquist, Elahe Mostaghel, Xiaotun Zhang, Eva Corey, Lisha G. Brown, Holly M. Nguyen, Michael Schweizer, Lawrence D. True, Paul S. Rennie, Robert L. Vessella, Peter S. Nelson. AR is ablated: Now what? Targeting the double-negative phenotype [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr IA21.

Abstract 1092: Defining the molecular phenotypes of metastatic castration-resistant prostate cancer sensitive to FGF pathway inhibition

Background: Widespread and long-term use of first-and second-line androgen-deprivation therapy (ADT) is changing the molecular and phenotypic landscapes of prostate cancer. Observations made through our longstanding rapid autopsy and patient-derived xenograft (PDX) programs at the University of Washington support a shift in metastatic castration-resistant prostate cancer (mCRPC) towards androgen receptor (AR)-null phenotypes, such as neuroendocrine (NEPC) and double negative (DNPC). Currently, there are no effective therapies for AR-null mCRPC. We showed previously that DNPC (AR-null, NE-null) bypasses AR-dependence through fibroblast growth factor (FGF) signaling. However, the role of the FGF pathway in other molecular mCRPC subtypes remains to be determined.

Methods and Results: Here, we define four mCRPC subtypes that can be categorized by the presence or absence of functioning AR or RE1-silencing transcription factor (REST). Transcriptomic analysis of mCRPC specimens showed that AR and REST activity define four emerging mCRPC phenotypes: adenocarcinoma (AR+/REST+), amphicrine (tumor cells that co-express AR and NE markers, AR+/REST-), DNPC (AR-/REST+) and NEPC (AR-/REST-). Immunohistochemistry of mCRPC and PDX models for AR, prostate specific antigen, synaptophysin, chromogranin, and other clinically relevant markers accurately reflected the AR/REST transcriptomic signature classifications. Furthermore, loss of REST activity can, at least in part, be attributed to alternative splicing of REST mRNA by serine/arginine repetitive matrix protein 4 (SRRM4), leading to the translation of a truncated REST protein. PCR analysis of mCRPC identified the REST splice variant exclusively in amphicrine and NEPC specimens. RNA sequencing/GSEA, qPCR and immunoblot analyses determined that overexpression of SRRM4 or siRNA knockdown of REST in C4-2B (AR+) and PC-3 (AR-) prostate cancer cells promotes expression of neuroendocrine markers. Finally, we are conducting preclinical testing of the FGFR inhibitor CH5183284 in multiple PDX models representing the four mCRPC subtypes described above to delineate the impact of FGF pathway inhibition in all mCRPC subtypes.

Conclusions: Our data highlight the importance of AR and REST transcriptional programs in maintaining phenotypic stability in mCRPC and explain the phenotypic heterogeneity of mCRPC in the post-abiraterone/enzalutamide era. Understanding the mCRPC subtypes that depend on the FGF pathway for survival and proliferation will inform treatment and lead to the development of novel therapies for advanced disease.

Citation Format: Mark P. Labrecque, Lisha G. Brown, Ilsa M. Coleman, Lawrence D. True, Lori Kollath, Bryce Lakely, Yu C. Yang, Holly M. Nguyen, Eva Corey, Peter S. Nelson, Colm Morrissey. Defining the molecular phenotypes of metastatic castration-resistant prostate cancer sensitive to FGF pathway inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1092.

Androgen Receptor Pathway-Independent Prostate Cancer Is Sustained through FGF Signaling

Androgen receptor (AR) signaling is a distinctive feature of prostate carcinoma (PC) and represents the major therapeutic target for treating metastatic prostate cancer (mPC). Though highly effective, AR antagonism can produce tumors that bypass a functional requirement for AR, often through neuroendocrine (NE) transdifferentiation. Through the molecular assessment of mPCs over two decades, we find a phenotypic shift has occurred in mPC with the emergence of an AR-null NE-null phenotype. These "double-negative" PCs are notable for elevated FGF and MAPK pathway activity, which can bypass AR dependence. Pharmacological inhibitors of MAPK or FGFR repressed the growth of double-negative PCs in vitro and in vivo. Our results indicate that FGF/MAPK blockade may be particularly efficacious against mPCs with an AR-null phenotype.

LuCaP Prostate Cancer Patient-Derived Xenografts Reflect the Molecular Heterogeneity of Advanced Disease an--d Serve as Models for Evaluating Cancer Therapeutics

BACKGROUND

Metastatic prostate cancer is a common and lethal disease for which there are no therapies that produce cures or long-term durable remissions. Clinically relevant preclinical models are needed to increase our understanding of biology of this malignancy and to evaluate new agents that might provide effective treatment. Our objective was to establish and characterize patient-derived xenografts (PDXs) from advanced prostate cancer (PC) for investigation of biology and evaluation of new treatment modalities.

METHODS

Samples of advanced PC obtained from primary prostate cancer obtained at surgery or from metastases collected at time of death were implanted into immunocompromised mice to establish PDXs. Established PDXs were propagated in vivo. Genomic, transcriptomic, and STR profiles were generated. Responses to androgen deprivation and docetaxel in vivo were characterized.

RESULTS

We established multiple PDXs (LuCaP series), which represent the major genomic and phenotypic features of the disease in humans, including amplification of androgen receptor, PTEN deletion, TP53 deletion and mutation, RB1 loss, TMPRSS2-ERG rearrangements, SPOP mutation, hypermutation due to MSH2/MSH6 genomic aberrations, and BRCA2 loss. The PDX models also exhibit variation in intra-tumoral androgen levels. Our in vivo results show heterogeneity of response to androgen deprivation and docetaxel, standard therapies for advanced PC, similar to the responses of patients to these treatments.

CONCLUSIONS

The LuCaP PDX series reflects the diverse molecular composition of human castration-resistant PC and allows for hypothesis-driven cause-and-effect studies of mechanisms underlying treatment response and resistance. Prostate 77: 654-671, 2017. © 2017 The Authors. The Prostate Published by Wiley Periodicals, Inc.

Characterization of an Abiraterone Ultraresponsive Phenotype in Castration-Resistant Prostate Cancer Patient-Derived Xenografts

Purpose: To identify the molecular signature associated with abiraterone acetate (AA) response and mechanisms underlying AA resistance in castration-resistant prostate cancer patient-derived xenografts (PDXs).Experimental Design: SCID mice bearing LuCaP 136CR, 77CR, 96CR, and 35CR PDXs were treated with AA. Tumor volume and prostate-specific antigen were monitored, and tumors were harvested 7 days after treatment or at end of study for gene expression and immunohistochemical studies.Results: Three phenotypic groups were observed based on AA response. An ultraresponsive phenotype was identified in LuCaP 136CR with significant inhibition of tumor progression and increased survival, intermediate responders LuCaP 77CR and LuCaP 96CR with a modest tumor inhibition and survival benefit, and LuCaP 35CR with minimal tumor inhibition and no survival benefit upon AA treatment. We identified a molecular signature of secreted proteins associated with the AA ultraresponsive phenotype. Upon resistance, AA ultraresponder LuCaP 136CR displayed reduced androgen receptor (AR) signaling and sustainably low nuclear glucocorticoid receptor (nGR) localization, accompanied by steroid metabolism alteration and epithelial-mesenchymal transition phenotype enrichment with increased expression of NF-κB-regulated genes; intermediate and minimal responders maintained sustained AR signaling and increased tumoral nGR localization.Conclusions: We identified a molecular signature of secreted proteins associated with AA ultraresponsiveness and sustained AR/GR signaling upon AA resistance in intermediate or minimal responders. These data will inform development of noninvasive biomarkers predicting AA response and suggest that further inhibition along the AR/GR signaling axis may be effective only in AA-resistant patients who are intermediate or minimal responders. These findings require verification in prospective clinical trials. Clin Cancer Res; 23(9); 2301-12. ©2016 AACR.

Substantial interindividual and limited intraindividual genomic diversity among tumors from men with metastatic prostate cancer

Tumor heterogeneity may reduce the efficacy of molecularly guided systemic therapy for cancers that have metastasized. To determine whether the genomic alterations in a single metastasis provide a reasonable assessment of the major oncogenic drivers of other dispersed metastases in an individual, we analyzed multiple tumors from men with disseminated prostate cancer through whole-exome sequencing, array comparative genomic hybridization (CGH) and RNA transcript profiling, and we compared the genomic diversity within and between individuals. In contrast to the substantial heterogeneity between men, there was limited diversity among metastases within an individual. The number of somatic mutations, the burden of genomic copy number alterations and aberrations in known oncogenic drivers were all highly concordant, as were metrics of androgen receptor (AR) activity and cell cycle activity. AR activity was inversely associated with cell proliferation, whereas the expression of Fanconi anemia (FA)-complex genes was correlated with elevated cell cycle progression, expression of the E2F transcription factor 1 (E2F1) and loss of retinoblastoma 1 (RB1). Men with somatic aberrations in FA-complex genes or in ATM serine/threonine kinase (ATM) exhibited significantly longer treatment-response durations to carboplatin than did men without defects in genes encoding DNA-repair proteins. Collectively, these data indicate that although exceptions exist, evaluating a single metastasis provides a reasonable assessment of the major oncogenic driver alterations that are present in disseminated tumors within an individual, and thus may be useful for selecting treatments on the basis of predicted molecular vulnerabilities.

Addition of PSMA ADC to enzalutamide therapy significantly improves survival in in vivo model of castration resistant prostate cancer

BACKGROUND

Despite multiple new therapies available to patients with advanced castration-resistant prostate cancer (CRPC), the overall survival benefit still remains relatively short. Therefore, it is important to investigate additional treatment options that could achieve greater efficacy. Because of tumor heterogeneity and the development of resistance to treatment with single agents, combination therapies using existing drugs with new agents can potentially broaden individual therapeutic windows and achieve improved efficacy and safety profiles. The objective of the current studies was to evaluate the efficacy of combination of enzalutamide (ENZ) with prostate specific membrane antigen antibody drug conjugate (PSMA ADC) to inhibit CRPC patient-derived xenografts (PDX) in a preclinical setting.

METHODS

Subcutaneous LuCaP 96CR prostate cancer PDX bearing mice were treated with a single dose of PSMA ADC (2.0 mg/kg) or 5 days a week ENZ (50 mg/kg) as monotherapy or with a combination of these two agents. The effects of the PSMA ADC+ENZ combination were compared to PSMA ADC alone, ENZ alone, and placebo control. IHC analyses were performed to determine PSMA, AR, ARV7, and GR expression and effects on proliferation.

RESULTS

All treatments inhibited tumor progression but with different efficacy. At 6 weeks, in the control and ENZ groups all tumors were progressing, while in the PSMA ADC group only 5/11 were progressing, two remained unchanged and four tumors had decreased tumor volume. Moreover, all animals in the PSMA ADC+ENZ group had smaller tumors at week 6 when compared to their size at enrollment (week 0). A 14-week followup showed that all three treatments resulted in significant survival benefits but the combination effects were the most pronounced resulting in PSMA ADC+ENZ versus ENZ HR = 0.093 (P = 0.0045) and PSMA ADC+ENZ versus PSMA ADC HR = 0.051 (P = <0.0001) with no deaths observed in the combination group.

CONCLUSIONS

Our results clearly indicate that the combination of PSMA ADC+ENZ possesses strong antitumor activity and significantly improves survival over ENZ monotherapy using the LuCaP 96CR PDX model. These results provide a strong rationale for clinical testing of PSMA ADC in combination with ENZ and/or other androgen-directed treatment strategies.

Epithelial mesenchymal-like transition occurs in a subset of cells in castration resistant prostate cancer bone metastases

TGFβ is a known driver of epithelial-mesenchymal transition (EMT) which is associated with tumor aggressiveness and metastasis. However, EMT has not been fully explored in clinical specimens of castration-resistant prostate cancer (CRPC) metastases. To assess EMT in CRPC, gene expression analysis was performed on 149 visceral and bone metastases from 62 CRPC patients and immunohistochemical analysis was performed on 185 CRPC bone and visceral metastases from 42 CRPC patients. In addition, to assess the potential of metastases to seed further metastases the mitochondrial genome was sequenced at different metastatic sites in one patient. TGFβ was increased in bone versus visceral metastases. While primarily cytoplasmic; nuclear and cytoplasmic Twist were significantly higher in bone than in visceral metastases. Slug and Zeb1 were unchanged, with the exception of nuclear Zeb1 being significantly higher in visceral metastases. Importantly, nuclear Twist, Slug, and Zeb1 were only present in a subset of epithelial cells that had an EMT-like phenotype. Underscoring the relevance of EMT-like cells, mitochondrial sequencing revealed that metastases could seed additional metastases in the same patient. In conclusion, while TGFβ expression and EMT-associated protein expression is present in a considerable number of CRPC visceral and bone metastases, nuclear Twist, Slug, and Zeb1 localization and an EMT-like phenotype (elongated nuclei and cytoplasmic compartment) was only present in a small subset of CRPC bone metastases. Mitochondrial sequencing from different metastases in a CRPC patient provided evidence for the seeding of metastases from previously established metastases, highlighting the biological relevance of EMT-like behavior in CRPC metastases.

High-Resolution Genomic Profiling of Disseminated Tumor Cells in Prostate Cancer

Circulating tumor cells and disseminated tumor cells (DTCs) are of great interest because they provide a minimally invasive window for assessing aspects of cancer biology, including tumor heterogeneity, a means to discover biomarkers of disease behavior, and a way to identify and prioritize therapeutic targets in the emerging era of precision oncology. However, the rarity of circulating tumor cells and DTCs poses a substantial challenge to the consistent success in analyzing their molecular features, including genomic aberrations. Herein, we describe optimized and robust methods to reproducibly detect genomic copy number alterations in samples of 2 to 40 cells after whole-genome amplification with the use of a high-resolution single-nuclear polymorphism-array platform and refined computational algorithms. We have determined the limit of detection for heterogeneity within a sample as 50% and also demonstrated success in analyzing single cells. We validated the genes in genomic regions that are frequently amplified or deleted by real-time quantitative PCR and nCounter copy number quantification. We further applied these methods to DTCs isolated from individuals with advanced prostate cancer to confirm their highly aberrant nature. We compared copy number alterations of DTCs with matched metastatic tumors isolated from the same individual to gain biological insight. These developments provide high-resolution genomic profiling of single and rare cell populations and should be applicable to a wide-range of sample sources.

SRRM4 Expression and the Loss of REST Activity May Promote the Emergence of the Neuroendocrine Phenotype in Castration-Resistant Prostate Cancer

PURPOSE

The neuroendocrine phenotype is associated with the development of metastatic castration-resistant prostate cancer (CRPC). Our objective was to characterize the molecular features of the neuroendocrine phenotype in CRPC.

EXPERIMENTAL DESIGN

Expression of chromogranin A (CHGA), synaptophysin (SYP), androgen receptor (AR), and prostate-specific antigen (PSA) was analyzed by IHC in 155 CRPC metastases from 50 patients and in 24 LuCaP prostate cancer patient-derived xenografts (PDX). Seventy-one of 155 metastases and the 24 LuCaP xenograft lines were analyzed by whole-genome microarrays. REST splicing was verified by PCR.

RESULTS

Coexpression of CHGA and SYP in >30% of cells was observed in 22 of 155 metastases (9 patients); 11 of the 22 metastases were AR(+)/PSA(+) (6 patients), 11/22 were AR-/PSA- (4 patients), and 4/24 LuCaP PDXs were AR(-)/PSA(-). By IHC, of the 71 metastases analyzed by whole-genome microarrays, 5 metastases were CHGA(+)/SYP(+)/AR(-), and 5 were CHGA(+)/SYP(+)/AR(+). Only CHGA(+)/SYP(+) metastases had a neuroendocrine transcript signature. The neuronal transcriptional regulator SRRM4 transcript was associated with the neuroendocrine signature in CHGA(+)/SYP(+) metastases and all CHGA(+)/SYP(+) LuCaP xenografts. In addition, expression of SRRM4 in LuCaP neuroendocrine xenografts correlated with a splice variant of REST that lacks the transcriptional repressor domain.

CONCLUSIONS

(i) Metastatic neuroendocrine status can be heterogeneous in the same patient, (ii) the CRPC neuroendocrine molecular phenotype can be defined by CHGA(+)/SYP(+) dual positivity, (iii) the neuroendocrine phenotype is not necessarily associated with the loss of AR activity, and (iv) the splicing of REST by SRRM4 could promote the neuroendocrine phenotype in CRPC.

Efficacy studies of an antibody-drug conjugate PSMA-ADC in patient-derived prostate cancer xenografts

BACKGROUND

It is timely and important to develop new treatment modalities for advanced prostate cancer, because even the newly FDA approved treatments, despite providing significant survival benefits, do not constitute cure of this disease. Antibody drug conjugates (ADCs) represent a promising approach to cancer therapy. Prostate-specific membrane antigen (PSMA) is expressed in advanced prostate cancer and targeting this protein is used for imaging of advanced prostate cancer as well as development of targeting strategies. The objective of our studies was to evaluate the efficacy of PSMA ADC against a series of patient-derived prostate cancer xenografts (LuCaP 58, LuCaP 77, LuCaP 96CR, and LuCaP 105) with different characteristics, including varying levels of PSMA expression and responses to androgen suppression.

METHODS

Mice bearing subcutaneous LuCaP prostate cancer-derived xenografts received PSMA antibody monomethyl auristatin E (MMAE) drug conjugate (PSMA ADC) in which the antibody and MMAE are linked via a protease-cleavable linker. PSMA ADC dose ranged from 1 to 6 mg/kg. Unmodified PSMA mAb + free MMAE at the amount equivalent to those contained in 6 mg/kg PSMA ADC was used as control. All treatments were administered once a week via tail-vein injections and repeated four times once a week and tumor responses were monitored for 10 weeks. IHC analyses were performed to determine PSMA and AR expression and effects on proliferation.

RESULTS

Treatment responses varied widely across the tumor models, from complete tumor regressions in LuCaP 96CR to largely unimpeded tumor progression of LuCaP 58, which had the lowest baseline level of PSMA expression. Intermediate antitumor effects were seen for LuCaP 77 and LuCaP 105 tumors, despite their having similar basal expression of PSMA as LuCaP 96CR. Interestingly, we detected substantial differences in responses even within the same model, indicating that PSMA expression is not the only factor involved in treatment outcomes.

CONCLUSIONS

Our results show high efficacy of PSMA ADC in advanced prostate cancer but also considerable variability in effects despite PSMA expression. Further studies to identify tumor characteristics that are predictive of treatment response are ongoing.

Managerial practices regarding workers working while ill

Surveillance data indicate that handling of food by an ill worker is a cause of almost half of all restaurant-related outbreaks. The U.S. Food and Drug Administration (FDA) Food Code contains recommendations for food service establishments, including restaurants, aimed at reducing the frequency with which food workers work while ill. However, few data exist on the extent to which restaurants have implemented FDA recommendations. The Centers for Disease Control and Prevention's Environmental Health Specialists Network (EHS-Net) conducted a study on the topic of ill food workers in restaurants. We interviewed restaurant managers (n = 426) in nine EHS-Net sites. We found that many restaurant policies concerning ill food workers do not follow FDA recommendations. For example, one-third of the restaurants' policies did not specifically address the circumstances under which ill food workers should be excluded from work (i.e., not be allowed to work). We also found that, in many restaurants, managers are not actively involved in decisions about whether ill food workers should work. Additionally, almost 70% of managers said they had worked while ill; 10% said they had worked while having nausea or "stomach flu," possible symptoms of foodborne illness. When asked why they had worked when ill, a third of the managers said they felt obligated to work or their strong work ethic compelled them to work. Other reasons cited were that the restaurant was understaffed or no one was available to replace them (26%), they felt that their symptoms were mild or not contagious (19%), they had special managerial responsibilities that no one else could fulfill (11%), there was non-food handling work they could do (7%), and they would not get paid if they did not work or the restaurant had no sick leave policy (5%). Data from this study can inform future research and help policy makers target interventions designed to reduce the frequency with which food workers work while ill.

Abstract 735: Evaluation of cabozantinib in combination with abiraterone, enzalutamide or docetaxel in a castration-resistant prostate cancer xenograft in vivo

New second-generation hormonal therapy agents abiraterone (abi) and enzalutamide (enz), and standard chemotherapy docetaxel (doc) provide survival benefits for patients with castration-resistant prostate cancer (CRPC). However, despite these survival benefits, CRPC is still an incurable disease. Therefore, combination treatments with other agents are under consideration to potentially improve patient outcome. Cabozantinib (cabo), an inhibitor of tyrosine kinases including MET, VEGFR2, RET, KIT and AXL, has shown activity as monotherapy in clinical investigations in CRPC. Our objective was to evaluate effects of cabo in combination with abi, enz or doc on a CRPC xenograft tumors in vivo.

Mice with subcutaneous LuCaP 35CR CRPC patient-derived xenograft tumors were treated with abi (0.5 mmol/kg), enz (50 mg/kg), doc (10 mg/kg) or cabo (10 mg/kg) monotherapies or with combinations of cabo with abi, enz or doc. Mice were treated for 4 weeks (wks) and followed for additional 6 wks. After 4 wks of treatment abi and enz exhibited limited activity in this model (∼20% inhibition of tumor volume (TV), not significant), doc exhibited ∼40% TV inhibition (P=0.017), and cabo exhibited ∼60% TV inhibition (P&lt;0.001) vs untreated tumors. Combination of cabo with each of these agents provided reduction in TV vs single agent treatments: ∼40% inhibition vs abi only, P=0.0039; ∼60% inhibition vs enz only, P&lt;0.0001; and ∼70% inhibition vs doc only, P&lt;0.0001. When the tumors were followed for 6 wks after discontinuation of the treatment, all treated tumors started to grow at rates similar to the untreated tumors, indicating presence of viable tumor cells. At the end of the study (10 wks) there were survival benefits for monotherapies, and further survival benefits were detected for combination of enz+cabo vs enz as a monotherapy (medium survival 5.7 vs 3.5 wks, P=0.0087) and doc+cabo vs doc as monotherapy (medium survival 4.75 vs 3.5 wks, P=0.0003), however survival of animals treated with the combinations was not significantly different from the survival of animals treated with cabo monotherapy. In the second study, where mice were treated for up to 18 wks, there were significant survival benefits detected for enz+cabo vs enz (median survival 15.5 vs 6.5 wks; P=0.0039), and for doc+cabo vs doc (median survival 15 vs 6.8 wks; P=0.0008); however, the cabo combinations with enz and doc had survival times similar to cabo monotherapy (16 wks). No significant effects on survival were detected for abi+cabo vs abi as monotherapy. Cabo at 10 mg/kg administered long term did not result in decreased body weight in comparison to non-treated mice. These preliminary data indicate that combinations of cabo with enz, doc or abi are active in the subcutaneous LuCaP 35CR xenograft model. Further analyses of the data and tumors are ongoing.

Citation Format: Holly M. Nguyen, Lisha G. Brown, Jessica L. Olson, Dana T. Aftab, Robert L. Vessella, Eva Corey. Evaluation of cabozantinib in combination with abiraterone, enzalutamide or docetaxel in a castration-resistant prostate cancer xenograft in vivo. [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 735. doi:10.1158/1538-7445.AM2014-735

Abstract 737: Assessment of cabozantinib activity in diverse prostate cancer xenograft models

Cabozantinib (cabo), an inhibitor of tyrosine kinases including MET, VEGFR2, RET, KIT, and AXL, is undergoing clinical investigation in patients with castration-resistant prostate cancer (CRPC). A phase II randomized discontinuation trial of cabo showed clinical activity in CRPC patients. However, not all patients responded to cabo, and most of the responding patients eventually experienced disease progression. The objective of our study was to evaluate the efficacy of cabo in a preclinical setting using xenograft models of CRPC with differential phenotypes to obtain insight into which tumor types might be sensitive to cabo, and to investigate mechanisms of action of this agent.

We used LuCaP 35CR, a PTEN- ERG+ Rb+ CRPC patient-derived xenograft (PDX) that exhibits amplification of the androgen receptor (AR); LuCaP 96CR, a PTEN+ ERG- Rb+ CRPC PDX with high levels of intra-tumoral androgens; LuCaP 86.2, a PTEN- ERG+ Rb- CRPC PDX that expresses the AR v5-7 variant and is not responsive to endocrine therapy; and LuCaP 93, a PTEN- ERG- Rb- neuroendocrine CRPC PDX. Expression of cabo targets in these models was determined by qPCR. Animals were treated with 30 mg/kg cabo p.o. for six weeks (5d on/2d off), and tumor volume (TV), serum PSA and body weights were monitored. IHC and expression arrays were used to analyze effects of cabo. Cabo was effective in halting tumor growth in all four PDXs. Significant inhibition of TV was evident after one week of cabo treatment compared to control groups. PSA values were also significantly lower after one week of the treatment in all three adenocarcinomas. Furthermore, cabo treatment resulted in significant survival benefits in LuCaP 35CR, LuCaP 96CR and LuCaP 93 without significant decreases in body weight. IHC analysis showed decreased microvessel density in all cabo-treated groups vs control groups, suggesting effects on tumor environment. qPCR analysis showed that all models expressed some cabo targets though at different levels, but we did not observe any associations between magnitude of cabo effects and levels of the its targets in the tumors; inhibition of LuCaP 93, which expresses the highest levels of cabo targets, was similar to that of LuCaP 96CR, which expresses low levels of cabo targets. Our analyses of expression profiles of tumors following cabo treatment showed very little overlap between the models. However, E2F1 signaling, was inhibited by cabo in Rb- PDXs LuCaP 93 and LuCaP 86.2, but not in the Rb+ PDXs LuCaP 35CR and LuCaP 96CR. Also, expression of genes regulated by androgen was increased in the Rb- tumors and decreased (LuCaP 35CR) or was not altered (LuCaP 96CR) in the Rb+ tumors, and the levels of nuclear AR showed a similar pattern. Further investigations are ongoing to obtain more detailed insight into mechanisms of cabo effects.

Citation Format: Lisha G. Brown, Holly M. Nguyen, Ilsa M. Coleman, Peter S. Nelson, Robert L. Vessella, Dana T. Aftab, Eva Corey. Assessment of cabozantinib activity in diverse prostate cancer xenograft models. [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 737. doi:10.1158/1538-7445.AM2014-737

Prostate cancer derived prostatic acid phosphatase promotes an osteoblastic response in the bone microenvironment

Approximately 90 % of patients who die of prostate cancer (PCa) have bone metastases, often promoting osteoblastic lesions. We observed that 88 % of castration-resistant PCa (CRPC) bone metastases express prostatic acid phosphatase (PAP), a soluble secreted protein expressed by prostate epithelial cells in predominately osteoblastic (n = 18) or osteolytic (n = 15) lesions. Additionally, conditioned media (CM) of an osteoblastic PCa xenograft LuCaP 23.1 contained significant levels of PAP and promoted mineralization in mouse and human calvaria-derived cells (MC3T3-E1 and HCO). To demonstrate that PAP promotes mineralization, we stimulated MC3T3-E1 cells with PAP and observed increased mineralization, which could be blocked with the specific PAP inhibitor, phosphonic acid. Furthermore, the mineralization promoted by LuCaP 23.1 CM was also blocked by phosphonic acid, suggesting PAP is responsible for the mineralization promoting activity of LuCaP 23.1. In addition, gene expression arrays comparing osteoblastic to osteolytic CRPC (n = 14) identified betacellulin (BTC) as a gene upregulated during the osteoblastic response in osteoblasts during new bone formation. Moreover, BTC levels were increased in bone marrow stromal cells in response to LuCaP 23.1 CM in vitro. Because new bone formation does occur in osteoblastic and can occur in osteolytic CRPC bone metastases, we confirmed by immunohistochemistry (n = 36) that BTC was highly expressed in osteoblasts involved in new bone formation occurring in both osteoblastic and osteolytic sites. These studies suggest a role for PAP in promoting the osteoblastic reaction in CRPC bone metastases and identify BTC as a novel downstream protein expressed in osteoblasts during new bone formation.

Abstract 849: Cabozantinib (XL184) inhibits growth of prostate cancer in the bone and results in an altered bone environment

There is a critical need for novel effective therapies for advanced prostate cancer (PCa) and associated bone metastases. A great deal of focus is being placed on investigations into the use of small molecule kinase inhibitors. Cabozantinib (XL184) is a small molecule kinase inhibitor which potently inhibits MET and VEGF receptor 2 (VEGFR2). In a phase 2 adaptive randomized discontinuation trial cabozantinib has demonstrated encouraging signs of clinical benefit in patients with metastatic castration-resistant PCa. Complete or partial resolution of lesions was evident in 82 of 110 (76%) patients with bone metastases as assessed by bone scan. The objectives of our preclinical studies were to investigate the efficacy of cabozantinib on growth of androgen-sensitive and castration-resistant PCa in the bone and on the bone itself. For our in vivo studies we used the androgen-sensitive LuCaP 23.1 PCa xenograft that elicits an osteoblastic reaction in the bone, and the castration-resistant C4-2B PCa xenograft that elicits mixed osteolytic/osteoblastic lesions. Cabozantinib inhibited growth of LuCaP 23.1 in the bone as demonstrated by serum PSA levels (control: 20.1± 0.8ng/ml vs. cabozantinib: 1.5 ±0.4ng/ml, P=0.020). Micro-CT analysis of trabecular bone showed that LuCaP 23.1 growth in the bone resulted in significant increases in bone volume (BV: 7.6 fold increase vs non-tumored tibiae; P=0.017). These increases were attenuated by cabozantinib (BV: 1.3 fold increase vs non-tumored tibiae, P=0.0021). Micro-CT analysis also showed that cabozantinib treatment affected normal bone. BV in non-tumored tibiae from mice treated with cabozantinib was 1.8 fold higher than BV of non-tumored tibiae from untreated mice (P=0.013). To evaluate the effects on osteoblasts in vitro we used MC3T3 cells. In concordance with the detected effects on normal bone, cabozantinib increased alkaline phosphatase activity in MC3T3 cells (1-3 μM, 1.5-2.2 fold increases, ANOVA P&lt;0.0001) and their mineralization (3 μM: 2.2 fold increase, P=0.0023). In the castration-resistant model, C4-2B, cabozantinib treatment also significantly decreased tumor growth based on serum PSA (control: 24.93±6.80 ng/ml vs. cabozantinib: 5.77±1.29 ng/ml, P=0.0096). Micro-CT assessment of tibiae from the C4-2B study and further analyses of all generated tissues are ongoing to further investigate the mechanisms underlying cabozantinib efficacy.In summary, our preclinical results show that cabozantinib is an effective inhibitor of androgen-sensitive as well as castration-resistant PCa in the bone. Importantly our data also indicate that cabozantinib treatment results in increases in bone formation which might be particularly beneficial to patients with advanced PCa who are on androgen ablation therapy and experiencing decreases in bone mineral density and increased frequency of skeletal-related events.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 849. doi:1538-7445.AM2012-849

Abstract 1937: Nemo-like kinase expression is altered during prostate cancer progression

MAPKs have been implicated in cancer progression. We have previously shown that Nemo-like kinase (NLK) inhibits androgen receptor signaling and induces apoptosis in prostate cancer cell in vitro. The objective of this study was to investigate NLK expression in clinical samples of primary prostate cancer and in prostate cancer xenografts using immunohistochemistry. TMAs containing primary prostate cancer samples and prostate cancer xenograft tissues were used. Our data show that NLK immunoreactivity is 0.34 higher in primary prostate cancer vs. normal prostate epithelium (p=0.01) but our analysis did not reveal any significant correlations of NLK immunoreactivity with PSA, Gleason score or recurrence of the disease. When we examined NLK immunoreactivity in prostate cancer xenografts our results show that there are signficant differences in cellular localization of NLK between xenografts that respond well to castration vs. those that do not. Xenografts that respond well to castration exhibit lower levels of NLK in nucleoplasm and higher leves of NLK in nucleoli vs. xenografts that do not respons well to castration (t=−4.211, p&lt;.0001, and z=3.994, p&lt;.0001 respectively). Our in vitro studies show that DHT increases localization of NLK in nucleoli of LNCaP. NLK levels in nucleoli negatively correlate with levels of nucleophosmin, a protein involved in regulation of proliferation, in the xenografts and in LNCaP cells in vitro. Interestingly we have also shown that in vitro NLK stimulates wnt signaling in LNCaP cells and this effecst in dependent on expresison of androgen receptor. In summary our data show that NLK expression is altered during prostate cancer progression and that NLK alters androgen receptor and wnt signaling pathways. Further studies to investigate mechanisms of NLK effects and NLK involvement in response to androgen ablation in prostate cancer are ongoing.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1937. doi:10.1158/1538-7445.AM2011-1937

The expression of osteoclastogenesis-associated factors and osteoblast response to osteolytic prostate cancer cells

BACKGROUND

Prostate cancer (PCa) has a propensity to metastasize to bone. Tumor cells replace bone marrow and can elicit an osteoblastic, osteolytic, or mixed bone response. Our objective was to elucidate the mechanisms and key factors involved in promoting osteoclastogenesis in PCa bone metastasis.

METHODS

We cultured osteoblast-like MC3T3-E1 cells with conditioned medium (CM) from PC-3 and C4-2B cells. MC3T3-E1 mineralization decreased in the presence of PC-3 CM, whereas C4-2B CM had no effect on mineralization. Using oligo arrays and validating by real-time PCR, we observed a decrease in the expression of mineralization-associated genes in MC3T3-E1 cells grown in the presence of PC-3 CM. In addition, PC-3 CM induced the expression of osteoclastogenesis-associated genes IGFBP-5, IL-6, MCP-1, and RANKL while decreasing OPG expression in MC3T3-E1 cells. Furthermore, CM from MC3T3-E1 cells cultured in the presence of PC-3 CM, in association with soluble RANKL, increased osteoclastogenesis in RAW 264.7 cells. Investigation of PCa metastases and xenografts by immunohistochemistry revealed that the osteoclastic factor IL-6 was expressed in the majority of PCa bone metastases and to a lesser extent in PCa soft tissue metastases. In vitro it was determined that soluble IL-6R (sIL-6R) was necessary for IL-6 to inhibit mineralization in MC3T3-E1 cells.

RESULTS

PC-3 cells inhibit osteoblast activity and induce osteoblasts to produce osteoclastic factors that promote osteoclastogenesis, and one of these factors, IL-6, is highly expressed in PCa bone metastases.

CONCLUSIONS

IL-6 may have an important role in promoting osteoclastogenesis in PCa bone metastasis through its' interaction with sIL-6R.

Nemo-like kinase induces apoptosis and inhibits androgen receptor signaling in prostate cancer cells

BACKGROUND

The mitogen-activated protein kinases (MAPKs) regulate cell growth, differentiation, and stress responses, and many critical signaling pathways are subject to cross-regulation by MAPK signaling. Previous studies have yielded evidence of cross-talk between the MAPK pathways and androgen receptor (AR) signaling, which plays a critical role in growth control of both normal prostate and prostate cancer (PCa). Objective of this study was to evaluate the expression of MAPK-like protein nemo-like kinase (NLK) in PCa and its effects on AR-mediated transcription.

METHODS

Real-time PCR and IHC were used to evaluate levels of NLK in prostatic samples. Effects of over-expression of NLK on apoptosis and proliferation were determined using Western blot and flow cytometry. Effects on AR signaling were evaluated using over-expression and knockdown of NLK in PCa cells in combination with PCR, Western blotting and reporter assays.

RESULTS

Our results show that the expression of NLK is decreased in PCa metastases in comparison to normal prostate epithelium and primary PCa. Our results also show that over-expression of NLK resulted in induction of apoptosis, which was more pronounced in AR-expressing LNCaP versus AR-negative PC-3 cells. Higher levels of NLK decreased levels of AR mRNA and protein as well as inhibited AR-mediated transcription.

CONCLUSIONS

NLK expression is altered during PCa progression and it is involved in regulation of AR signaling in these cells. A deeper understanding of the roles of NLK in regulation of AR-mediated transcription and control of PCa progression may point the way to new modes of therapeutic intervention in this disease.

Host-derived RANKL is responsible for osteolysis in a C4-2 human prostate cancer xenograft model of experimental bone metastases

BACKGROUND

C4-2 prostate cancer (CaP) cells grown in mouse tibiae cause a mixed osteoblastic/osteolytic response with increases in osteoclast numbers and bone resorption. Administration of osteoprotegerin (OPG) blocks these increases, indicating the critical role of RANKL in osteolysis in this model. The objective of our study was to investigate whether RANKL expressed by tumor cells (human origin) directly stimulates osteolysis associated with the growth of these cells in bone or whether the increased osteolysis is caused by RANKL expressed by the host environment cells (murine origin). The relative contribution of tumor-vs. host-derived RANKL has been difficult to establish, even with human xenografts, because murine and human RANKL are both capable of stimulating osteolysis in mice, and the RANKL inhibitors used to date (OPG and RANK-Fc) inhibit human and murine RANKL.

METHODS

To address this question we used a neutralizing, antibody (huRANKL MAb), which specifically neutralizes the biological activities of human RANKL and thereby the contribution of C4-2 derived RANKL in this tibial injection model of experimental bone metastases.

RESULTS

Administration of huRANKL MAb did not inhibit the osteolytic response of the bone to these cells, or affect the establishment and growth of the C4-2 tumors in this environment.

CONCLUSION

In conclusion, our results suggest that in this model, murine RANKL and not the tumor-derived human RANKL is the mediator of the osteolytic reaction associated with C4-2 growth in bone. We hypothesize that C4-2 cells express other factor/s inducing host production of RANKL, thereby driving tumor-associated osteolysis.

Inhibition of androgen-independent prostate cancer by estrogenic compounds is associated with increased expression of immune-related genes

The clinical utility of estrogens for treating prostate cancer (CaP) was established in the 1940s by Huggins. The classic model of the anti-CaP activity of estrogens postulates an indirect mechanism involving the suppression of androgen production. However, clinical and preclinical studies have shown that estrogens exert growth-inhibitory effects on CaP under low-androgen conditions, suggesting additional modes whereby estrogens affect CaP cells and/or the microenvironment. Here we have investigated the activity of 17beta estradiol (E2) against androgen-independent CaP and identified molecular alterations in tumors exposed to E2. E2 treatment inhibited the growth of all four androgen-independent CaP xenografts studied (LuCaP 35V, LuCaP 23.1AI, LuCaP 49, and LuCaP 58) in castrated male mice. The molecular basis of growth suppression was studied by cDNA microarray analysis, which indicated that multiple pathways are altered by E2 treatment. Of particular interest are changes in transcripts encoding proteins that mediate immune responses and regulate androgen receptor signaling. In conclusion, our data show that estrogens have powerful inhibitory effects on CaP in vivo in androgen-depleted environments and suggest novel mechanisms of estrogen-mediated antitumor activity. These results indicate that incorporating estrogens into CaP treatment protocols could enhance therapeutic efficacy even in cases of advanced disease.

Administration of zoledronic acid enhances the effects of docetaxel on growth of prostate cancer in the bone environment

Background

After development of hormone-refractory metastatic disease, prostate cancer is incurable. The recent history of chemotherapy has shown that with difficult disease targets, combinatorial therapy frequently offers the best chance of a cure. In this study we have examined the effects of a combination of zoledronic acid (ZOL), a new-generation bisphosphonate, and docetaxel on LuCaP 23.1, a prostate cancer xenograft that stimulates the osteoblastic reaction when grown in the bone environment.

Methods

Intra-tibial injections of LuCaP 23.1 cells were used to generate tumors in the bone environment, and animals were treated with ZOL, docetaxel, or a combination of these. Effects on bone and tumor were evaluated by measurements of bone mineral density and histomorphometrical analysis.

Results

ZOL decreased proliferation of LuCaP 23.1 in the bone environment, while docetaxel at a dose that effectively inhibited growth of subcutaneous tumors did not show any effects in the bone environment. The combination of the drugs significantly inhibited the growth of LuCaP 23.1 tumors in the bone.

Conclusion

In conclusion, the use of the osteolysis-inhibitory agent ZOL in combination with docetaxel inhibits growth of prostate tumors in bone and represents a potential treatment option.

Comparison of Fc-osteoprotegerin and zoledronic acid activities suggests that zoledronic acid inhibits prostate cancer in bone by indirect mechanisms

Zoledronic acid (ZA) has been shown to inhibit prostate tumor growth in vitro and have beneficial effects in patients with advanced prostate cancer (CaP). The aim of this study was to determine whether ZA exhibits direct anti-tumor effects on CaP cells in vivo. To distinguish the effects of inhibition of osteolysis and direct anti-tumor activity of ZA in vivo, we compared the results of treatment with ZA and osteoprotegerin (Fc-OPG), which inhibits osteolysis, but without significant direct anti-tumor effects. In vitro Fc-OPG had no significant effects on C4-2 proliferation, whereas ZA decreased proliferation. However, both agents decreased tumor growth in bone. Moreover, both increased bone volume and prevented the overall decreases in BMD associated with growth of C4-2 cells in bone. Our study provides novel and significant observations that the in vivo effects of ZA are consistent with indirect effects mediated by osteoclasts.

Metastases of prostate cancer express estrogen receptor-beta

OBJECTIVES

To examine estrogen receptor-beta (ERbeta) expression in prostate cancer (CaP) metastases, thereby providing a basis for conducting estrogen therapy studies in patients with metastatic CaP. Advanced androgen-independent CaP is a serious health problem with no effective treatment at present. Estrogens have been reported to inhibit the growth of CaP cells in androgen-free environments. Recent reports have shown that the prostatic epithelium and primary CaP cells express ERbeta, with decreased expression of ERbeta accompanying CaP progression. It has been proposed that ERbeta may play a role in the growth regulation of prostate cells. The targeting of ERs by selective ER modulators might be an effective method of treating advanced CaP.

METHODS

The anti-ERbeta antibody GC17 was used in immunohistochemistry to characterize the expression of ERbeta in CaP metastasis specimens (n = 60) obtained from 20 patients who had died of CaP. Statistical analyses were performed to evaluate the association of ERbeta expression with clinical parameters, including prostate-specific antigen levels, radiotherapy, and estrogen exposure.

RESULTS

Nuclear ERbeta staining was detected in all bone CaP metastases (33 of 33) and nonosseous CaP metastases (27 of 27). However, a large variability in the percentage of immunoreactive cells (5% to 100%) was found among patients, as well as among individual patient samples. A statistically significant negative association between nuclear ERbeta staining and estrogen exposure (P = 0.05) was detected.

CONCLUSIONS

Our data have shown that ERbeta is expressed in CaP metastases, validating the initiation of studies to evaluate selective ER modulators for treatment of advanced CaP.

Osteoprotegerin in prostate cancer bone metastasis

Osteoprotegerin (OPG), a critical regulator of osteoclastogenesis, is expressed by prostate cancer cells, and OPG levels are increased in patients with prostate cancer bone metastases. The objective of this study was to investigate the effects of OPG overexpression on prostate cancer cells and prostate cancer/bone cell interactions in vitro and in vivo. OPG-transfected C4-2 cells expressed 8.0 ng OPG per mL per 10(6) cells, whereas no OPG was detected in the media of C4-2 cells transfected with a control plasmid. OPG overexpressed by C4-2 cells protected these cells from tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis and decreased osteoclast formation. Subcutaneous OPG-C4-2 and pcDNA-C4-2 tumors exhibited similar growth and take-rate characteristics. However, when grown in bone, tumor volume was decreased in OPG-C4-2 versus pcDNA-C4-2 (P=0.0017). OPG expressed by C4-2 cells caused increases in bone mineral density (P=0.0074) and percentage of trabecular bone volume (P=0.007), and decreases in numbers of osteoblasts and osteoclasts when compared with intratibial pcDNA-C4-2 tumors (P=0.003 and P=0.019, respectively). In summary, our data show that increased expression of OPG in C4-2 cells does not directly affect proliferation of prostate cancer cells but indirectly decreases growth of C4-2 tumors in the bone environment. Our data also show that OPG expressed by C4-2 cells inhibits bone lysis associated with C4-2 bone metastasis, which results in net increases in bone volume. We therefore hypothesize that OPG expressed in prostate cancer patient bone metastases may be at least partially responsible for the osteoblastic character of most prostate cancer bone lesions.

Prostate cancer expression of runt-domain transcription factor Runx2, a key regulator of osteoblast differentiation and function

BACKGROUND

Prostate cancer (CaP) bone metastases express numerous proteins associated with bone cells. Specific transcription factors, including Runx2, regulate the expression of many bone-related factors in osteoblasts. Expression of these transcription factors in CaP may be linked to the ability of CaP bone metastases to influence bone remodeling.

METHODS

CaP tissues and cell lines were analyzed for expression of Runx2 mRNA by RT-PCR and in situ hybridization, and protein by immunohistochemistry, Western blotting, and electrophoretic mobility shift assays (EMSA).

RESULTS

Runx2 mRNA and protein were detected in CaP tissues and cell lines. A specific Runx2: OSE2 complex could be formed with PC-3 nuclear extracts.

CONCLUSIONS

Expression of Runx2 in CaP may be the molecular switch that is associated with expression of various bone-specific factors in CaP. In turn, expression of these factors can influence bone remodeling and possibly play a role in the growth and survival of CaP in bone.

Zoledronic acid exhibits inhibitory effects on osteoblastic and osteolytic metastases of prostate cancer

PURPOSE

In this study we have examined the effects of zoledronic acid (ZA), a new-generation bisphosphonate, on prostate cancer (CaP) cells in vitro, and on both osteoblastic and osteolytic CaP metastases in animal models.

EXPERIMENTAL DESIGN

In vitro, CaP cells were treated with ZA, and the effects on proliferation, cell cycle, and apoptosis were determined. In vivo, PC-3, and LuCaP 23.1 s.c. and tibial tumors were treated with ZA. Effects on bone and tumor were determined by histomorphometry and immunohistochemistry.

RESULTS

ZA decreased proliferation of CaP cells, and caused G(1) arrest and apoptosis of CaP cells in vitro. In vivo, s.c. CaP tumor growth was not affected by ZA. However, growth of osteoblastic and osteolytic metastases of CaP was inhibited significantly in vivo. Matrix metalloproteinase-2, matrix metalloproteinase-9, and Cathepsin K levels were decreased in osteolytic bone metastases after ZA administration.

CONCLUSIONS

In conclusion, we have shown that ZA has significant antitumor effects on CaP cells in vitro and in vivo. Antiosteolytic activity and the antitumor effects of this compound could benefit CaP patients with bone metastases.

Bone morphogenetic protein signaling in prostate cancer cell lines

Prostate cancer is the most commonly diagnosed malignancy in men and is often associated with bone metastases. Prostate cancer bone lesions can be lytic or schlerotic, with the latter predominating. Bone morphogenetic proteins (BMPs) are a family of growth factors, which may play a role in the formation of prostate cancer osteoblastic bone metastases. This study evaluated the effects of BMPs on prostate cancer cell lines. We observed growth inhibitory effects of BMP-2 and -4 on LNCaP, while PC-3 was unaffected. Flow cytometric analysis determined that LNCaP cell growth was arrested in G(1) after bone morphogenetic protein-2 treatment. Treatment of LNCaP and PC-3 with BMP-2 and -4 activated downstream signaling pathways involving SMAD-1, up-regulation of p21(CIP1/WAF1) and changes in retinoblastoma (Rb) phosphorylation. Interestingly, bone morphogenetic protein-2 treatment stimulated a 2.7-fold increase in osteoprotegerin (OPG), a molecule, which inhibits osteoclastogenesis, production in PC-3.

Establishment and characterization of osseous prostate cancer models: intra-tibial injection of human prostate cancer cells

BACKGROUND

To improve the therapy of advanced prostate cancer (CaP), it is critical to develop animal models that mimic CaP bone metastases. Unlike the human disease, CaP xenograft models rarely metastasize spontaneously to bone from the orthotopic site of primary tumor growth.

METHODS

Single-cell suspensions of LNCaP, PC-3, LuCaP 35, and LuCaP 23.1 CaP cells were injected directly into tibia of SCID mice. Immunohistochemistry and bone histomorphometrical analyses were performed to characterize these osseous-CaP models.

RESULTS

LuCaP 23.1 yields an osteoblastic response, LNCaP yields mixed lesions, and LuCaP 35 and PC-3 result in osteolytic responses. We have detected osteoprotegerin, RANK ligand, parathyroid hormone-related protein, and endothelin-1, proteins associated with bone growth and remodeling, in the CaP cells grown in the bone.

CONCLUSIONS

These animal models can be used to study biological interactions, pathways, and potential therapeutic targets, and also to evaluate new agents for treatment and prevention of CaP bone metastasis.

Inhibition of androgen-independent growth of prostate cancer xenografts by 17beta-estradiol

PURPOSE

Estrogen treatment has long been known to be of benefit in prostate cancer (CaP), but its mechanism was thought to involve merely a reduction in androgen levels. However, new evidence indicates that estrogen may exert effects on CaP cells in the absence of androgens.

EXPERIMENTAL DESIGN

Implantation of CaP xenografts (LuCaP 35, LuCaP 49, LuCaP 58, LuCaP 73, PC-3, and LNCaP) into intact and ovariectomized female mice was done to characterize growth and take rates in the absence of androgens. Ovariectomized female mice were supplemented with 17beta-estradiol, and LuCaP 35 CaP xenograft take and growth rates were determined. Reverse transcription-PCR was used to evaluate the presence of the estrogen receptor messages in CaP xenografts.

RESULTS

We have observed significant inhibition of CaP growth in intact versus ovariectomized female animals in five of six CaP xenograft lines. 17beta-Estradiol supplements given to ovariectomized female mice led to inhibition of tumor establishment and diminished growth of LuCaP 35 similar to that observed in intact female mice. Using reverse transcription-PCR, we have shown that these xenografts express the estrogen receptor beta message.

CONCLUSIONS

We have determined that 17beta-estradiol supplementation causes inhibition of CaP growth in an animal model by mechanisms that are independent of androgen action. This gives rise to the possibility that estrogen therapy may be of potential use with hormone-refractory cancers. The xenograft models we describe herein may be useful as well in elucidating the pathways mediating the androgen-independent effects of estrogen on CaP.

The AZFc region of the Y chromosome features massive palindromes and uniform recurrent deletions in infertile men

Deletions of the AZFc (azoospermia factor c) region of the Y chromosome are the most common known cause of spermatogenic failure. We determined the complete nucleotide sequence of AZFc by identifying and distinguishing between near-identical amplicons (massive repeat units) using an iterative mapping-sequencing process. A complex of three palindromes, the largest spanning 3 Mb with 99.97% identity between its arms, encompasses the AZFc region. The palindromes are constructed from six distinct families of amplicons, with unit lengths of 115-678 kb, and may have resulted from tandem duplication and inversion during primate evolution. The palindromic complex contains 11 families of transcription units, all expressed in testis. Deletions of AZFc that cause infertility are remarkably uniform, spanning a 3.5-Mb segment and bounded by 229-kb direct repeats that probably served as substrates for homologous recombination.

A physical map of the human Y chromosome

The non-recombining region of the human Y chromosome (NRY), which comprises 95% of the chromosome, does not undergo sexual recombination and is present only in males. An understanding of its biological functions has begun to emerge from DNA studies of individuals with partial Y chromosomes, coupled with molecular characterization of genes implicated in gonadal sex reversal, Turner syndrome, graft rejection and spermatogenic failure. But mapping strategies applied successfully elsewhere in the genome have faltered in the NRY, where there is no meiotic recombination map and intrachromosomal repetitive sequences are abundant. Here we report a high-resolution physical map of the euchromatic, centromeric and heterochromatic regions of the NRY and its construction by unusual methods, including genomic clone subtraction and dissection of sequence family variants. Of the map's 758 DNA markers, 136 have multiple locations in the NRY, reflecting its unusually repetitive sequence composition. The markers anchor 1,038 bacterial artificial chromosome clones, 199 of which form a tiling path for sequencing.

Optical mapping of BAC clones from the human Y chromosome DAZ locus

The accurate mapping of clones derived from genomic regions containing complex arrangements of repeated elements presents special problems for DNA sequencers. Recent advances in the automation of optical mapping have enabled us to map a set of 16 BAC clones derived from the DAZ locus of the human Y chromosome long arm, a locus in which the entire DAZ gene as well as subsections within the gene copies have been duplicated. High-resolution optical mapping employing seven enzymes places these clones into two contigs representing four distinct copies of the DAZ gene and highlights a number of differences between individual copies of DAZ.

Four DAZ genes in two clusters found in the AZFc region of the human Y chromosome

The DAZ genes are candidate fertility factors that lie within the human Y chromosome's AZFc region, whose deletion is a common cause of spermatogenic failure. The number of DAZ genes has been difficult to determine, in part because the nucleotide sequences of the DAZ genes are nearly identical. Here, fluorescence in situ hybridization and characterization of BAC clones revealed four full-length DAZ genes on the human Y chromosome. They exist in two clusters, each comprising an inverted pair of DAZ genes (3' <-- 5'::5' --> 3'). Analysis of genomic sequences and testicular transcripts suggested that three or four DAZ genes are translated. Each gene contains at least seven tandem copies of a previously described, 2.4-kb repeat unit that encodes 24 amino acids. In addition, two DAZ genes contain tandem copies of a 10.8-kb repeat unit that encodes the RNA-binding domain, which appears to be multimerized in some DAZ proteins. Combining our present results with previous studies, we can reconstruct several steps in the evolution of the DAZ genes on the Y chromosome. In the ancestral Y-chromosomal DAZ gene, amplification of both intragenic repeats began before the human and cynomolgus (Old World) monkey lineages diverged. During subsequent evolution, an inverted duplication of this modified gene occurred. Finally, the resulting two-gene cluster was duplicated, generating the two-cluster/four-gene arrangement found on modern human Y chromosomes.

Mechanistic studies of the effects of anti-factor H antibodies on complement-mediated lysis

We have recently reported that complement factor H, a negative regulator of complement-mediated cytotoxicity, is produced and secreted by most bladder cancers. This observation was exploited in the development of the BTA stat and BTA TRAK diagnostic assays, both of which make use of two factor H-specific monoclonal antibodies in sandwich format. Here we show that both antibodies exert interesting effects on the biochemistry of complement activation in in vitro systems. Antibody X13.2 competes with C3b for association with factor H and strongly inhibits factor H/factor I-mediated cleavage of C3b, thereby evidently inactivating a negative regulator of complement; yet, the antibody strongly inhibits complement-mediated lysis as well. Conversely, antibody X52. 1, which does not compete with C3b and has no effect on solution-phase cleavage of C3b, is capable of enhancing complement-mediated lysis of various cell types, including cancer cells, by over 10-fold. Our observations indicate that it is possible to deconvolute the biochemical roles of factor H in complement by means of appropriate inhibitors, a finding with potentially valuable implications for both basic research and cancer therapy.

Introduction of Tomato Yellow Leaf Curl Virus in Florida and Implications for the Spread of This and Other Geminiviruses of Tomato

In July 1997, symptoms characteristic of tomato yellow leaf curl virus (TYLCV-Is) were observed on one tomato plant in a field in Collier County, Florida, and on several tomato plants in a retail garden center in Sarasota, Florida. Amplification with three sets of primers, analysis of amplified fragments using restriction enzyme digestion, and hybridization with a clone of TYLCV-Is indicated that TYLCV-Is was present in symptomatic plants. The sequence of a 1,300-bp amplified fragment was 99% identical to TYLCV-Is from the Dominican Republic and 98% identical to an isolate from Israel. It appears that TYLCV-Is entered the United States in Dade County, Florida, in late 1996 or early 1997. Subsequently, infected tomato transplants produced for retail sale at two Dade County facilities were rapidly distributed via retail garden centers throughout the state. Infected plants purchased by homeowners and placed in and around homes appeared to be the source of TYLCV-Is for nearby commercial nurseries and production fields. It appears that transplants have played a role in the movement of this and probably other geminiviruses. A number of regulatory procedures, as well as field management practices, were implemented in the 1997-98 production season to minimize the movement of TYLCV-Is within and out of the state.

Men with infertility caused by AZFc deletion can produce sons by intracytoplasmic sperm injection, but are likely to transmit the deletion and infertility

Deletion of the AZFc region of the Y chromosome is the most frequent molecularly defined cause of spermatogenic failure. We report three unrelated men in whom azoospermia or severe oligozoospermia was caused by de-novo AZFc deletions, and who produced sons by intracytoplasmic sperm injection (ICSI). We employed polymerase chain reaction (PCR) assays to examine the Y chromosomes of their four infant sons. All four sons were found to have inherited the Y chromosome deletions. Such sons are likely to be infertile as adults. This likelihood should be taken into account when counselling couples considering ICSI to circumvent infertility due to severe oligozoospermia or non-obstructive azoospermia.