CWR-R1 Cells Research Articles

Abstract 2011: MAOA Drives Anti Androgen Therapy Resistance in Advanced Prostate Cancer by Conferring Neuroendocrine Plasticity via a Twist1 BRN2 Signaling Pathway

Abstract Background: Therapy resistance in cancer is often linked to cancer cell state or lineage changes. In prostate cancer (PCa), a subset of castration-resistant prostate cancer (CRPC) loses reliance on the androgen receptor (AR) signaling and gains neuroendocrine (NE) traits through a lineage switch along disease progression. However, the molecular mechanisms driving such cellular lineage plasticity remain unclear. This study investigated the functional and mechanistic role of monoamine oxidase A (MAOA) in driving adenocarcinoma (adeno)-to-NE lineage conversion in CRPC cells upon enzalutamide (ENZ), a FDA-approved newer-generation antiandrogen drug, and evaluated the efficacy of MAOA inhibitors for treating CRPC and overcoming ENZ resistance.Methods: ENZ-resistant C4-2B and CWR-R1 cells (C4-2BENZR and CWR-R1ENZR) CRPC cells were transfected with a PSA promoter-driven GFP expression construct for isolating a PSAlo/− cell population distinct from PSAhi cells, which was used for manipulation of MAOA expression levels and subsequent functional assays in vitro and in vivo. The MAOA expression levels were determined and correlated with NE parameters in PCa clinical samples by immunohistochemistry and data mining of multiple publicly available clinical datasets. Results: MAOA protein expression was significantly upregulated in the PSAlo/− ENZ-resistant cell population, accompanied by concomitant activation of NE markers and downregulation of luminal markers including AR and AR targets, compared to the PSAhi counterpart. Elevated MAOA expression was also found in PCa patient samples associated with NE features from multiple independent cohorts. Silencing MAOA suppressed the proliferation, migration, invasion, stem-like properties and NE plasticity of both PSAlo/- C4-2BENZR and CWR-R1ENZR cells. Moreover, co-culturing adeno LNCaP or C4-2B cells with MAOA-silenced PSAlo/- cells exhibiting a repressed secretory phenotype attenuated acquired induction of NE markers and proliferation of adeno cells as compared to controls. Mechanistically, MAOA induces Twist1, which directly activates the transcription and expression of BRN2, a master neural transcription factor known to confer NE differentiation and anti-AR therapy resistance in CRPC. Further, pharmacological inhibition of MAOA greatly enhanced the growth-inhibitory efficacy of ENZ with ENZ sensitivity restored in ENZ-resistant LuCaP PC PDX-derived organoids as well as a PSAlo/− CWR-R1ENZR xenograft mouse model.Conclusion: Our results suggest MAOA as a potential therapeutic target for reversing ENZ resistance in CRPC treatment by blockade of NE transdifferentiation.Funding Acknowledgements: This work was supported by the NIH/NCI grants R37CA233658 and R01CA258634 (to B. Wu) and the DOD Department of Defense EIRA award W81XWH-21-1-0218 (to J. Wei) Citation Format: Jing Wei, Jing Wang, Chia-hui Chen, Wen Guan, Boyang Wu. MAOA Drives Anti Androgen Therapy Resistance in Advanced Prostate Cancer by Conferring Neuroendocrine Plasticity via a Twist1 BRN2 Signaling Pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2011.

Abstract A059: Epigenetic remodelling by class I HDAC inhibitors increases response to androgen signalling inhibitors in prostate cancer

Abstract Prostate cancer (PCa) is one of the most prevalent cancers in the male population with approximately 1 in 8 men diagnosed with the disease during their lifetime. The treatment options available varies depending on individual circumstances, with surgery or radiotherapy employed as first-line treatments for locally advanced PCa whilst hormone therapies are employed as the disease progresses toward castrate-resistant prostate cancer. Despite the advances in therapies and initial treatment effectiveness, tumours develop resistance and overcoming this resistance proves a major challenge for the treatment of the disease. Dysregulation of chromatin regulatory proteins and the epigenetic landscape are key factors contributing to the development, progression and persistence of PCa. Histone deacetylases (HDACs) are a family of chromatin-modifying proteins which assemble into various transcriptional repressor complexes and mediate gene repression through the removal of acetyl groups from histone tails, subsequently compacting the chromatin landscape impacting on cell proliferation, transcription, replication and DNA repair. Overexpression of HDACs in prostate cancer has been shown to shift the balance of acetylation, resulting in improper gene silencing. Therefore, we hypothesise that restoration of the acetylation homeostasis through HDAC inhibition is a potential therapy to overcome resistance in PCa. Here, we show that the class I HDAC inhibitor Entinostat as a single agent promotes anti-tumour effects in PCa by impairing cell proliferation and inducing apoptosis in a panel of PCa cell lines. Interestingly, we found that combination with the androgen signalling inhibitors (ASIs), Enzalutamide or Abiraterone, further enhances these anti-tumour effects. In vitro analysis of matched parental and Enzalutamide-/Abiraterone-resistant C4-2B and CWRR-1 cells further revealed an enhanced reduction in cell survival following combined Entinostat and ASIs treatments in the resistant models compared to parental. Genomic and transcriptomic analyses uncovered distinct molecular signatures of these resistant models. Treatment with Entinostat alone downregulated androgen receptor (AR) expression and combination with ASI further suppressed AR expression and downstream AR target genes. Taken together, these results demonstrate the potential for Entinostat to synergise with current standard-of-care therapies to target ASI resistance in PCa. In conclusion, this study provides strong evidence suggesting the effectiveness of class I HDAC inhibition by Entinostat in the treatment of castration-resistant prostate cancer and opens the door for further research into combinatorial therapies in targeting resistance. Citation Format: Rachel McCole, Ben McCullough, Judith M. Manley, Nicholas Forsythe, Simon S. McDade, Melissa LaBonte Wilson. Epigenetic remodelling by class I HDAC inhibitors increases response to androgen signalling inhibitors in prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr A059.

Abstract 2650: Targeting the DNA-binding domain of the androgen receptor in castration-resistant prostate cancer

Abstract Background: The androgen receptor (AR), which plays a major role in prostate cancer (PCa), consists of a C-terminal ligand-binding domain (LBD), a hinge domain, a DNA-binding domain (DBD), and an N-terminal domain (NTD). Current AR antagonists and AR signaling inhibitors (ASIs), used in androgen deprivation therapy (ADT) and to prevent disease progression, often fail due to production of alternatively spliced AR variants (AR-Vs) that lack the LBD but retain the DBD, which is essential to AR transcriptional activity. This project examines a series of novel compounds designed to inhibit AR-DNA interaction and study how these compounds affect castration-resistant PCa (CRPC). Methods: Compounds potentially targeting the DBD were used to predict direction and position of compounds when docked to the AR. MTT assays, flow cytometry, immunoblots, qRT-PCR, luciferase assay, and immunofluorescence were used to test compounds on AR and PCa. Drug Affinity Responsive Target Stability (DARTS) tested potential binding of the compounds to the AR. Studies in intact mice were used to determine toxicity of the compounds and the maximum tolerated dose. Results: Of 48 compounds synthesized, C15 had the highest and most consistent efficacy overall. C15 decreased metabolic activity in 22Rv1 and CWR-R1 cells that express AR-Vs and in C4 and C4-2 that do not express AR-Vs. Further, C15 had a reduced effect in AR-null PC3 cells and minimal effect in normal human dermal fibroblast (NHDF) cells. In C4-2 and 22Rv1, C15 significantly reduced PSA mRNA and AR transcriptional activity, and in C4-2, C15 significantly reduced TMPRSS2 and Nrdp1 mRNA levels. C08 and C15 reduced pronase-induced AR proteolysis only when the AR DBD is present. Furthermore, C15 reduces AR binding at the PSA enhancer, but DHT stimulation may weaken this binding inhibition and reduction in AR transcriptional activity. However, combining C15 with an AR inhibitor targeting the LBD (enzalutamide, darolutamide, apalutamide) restores the full inhibitory potential and even reduces metabolic activity and AR transcriptional activity further than either drug alone in both C4-2 and 22Rv1s. No toxicity in intact mice was observed with C15 with the highest dose tested being 50 mg/kg. Conclusion: Our preliminary data demonstrate that C15 directly binds to the DBD of the AR and potently inhibits CRPC cells, including those that express AR-Vs missing the LBD. Although increased DHT levels may weaken C15’s inhibition of the AR DBD, addition of a LBD-targeting AR inhibitor improves the inhibitory potential of both drugs. Based on these results, we conclude that C15 may hold great clinical potential as it successfully inhibits CRPC by targeting the AR DBD with minimal toxicity, and it can improve the effects of standard-of-care LBD-targeting AR inhibitors by reducing AR-V-induced resistance. Citation Format: Thomas M. Steele, Elisabeth A. Messner, Maria Malvina Tsamouri, Salma Siddiqui, Brian Bennion, Ruiwu Liu, Paramita Ghosh. Targeting the DNA-binding domain of the androgen receptor in castration-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2650.

Abstract 6204: Prostate cancer exosomes alter extracellular matrix composition in bone marrow and enhance metastasis

Abstract Introduction: Exosomes produced by neoplastic cells can promote the development of a pro-tumorigenic microenvironment via intercellular communication, and in some cases promote metastasis. The role of exosomes in the spread of prostate cancer, however, remains poorly understood. Here, we show that exosomes derived from enzalutamide resistant prostate cancer cells (EnzR exos) mediate intercellular communication with bone marrow-resident cells, alter the expression of extracellular matrix (ECM) proteins, and enhance metastasis in a clinically relevant mouse model of metastatic prostate cancer. Methods: Exosomes were isolated via ultracentrifugation of conditioned media from enzalutamide resistant CWR-R1 cells. Mice were primed with exosomes via three systemic injections of 10 ug exosomal protein. Exosome-mediated changes in bone marrow ECM composition were assessed via RNA sequencing of CD11b+ bone marrow cells and immunohistochemistry of formalin-fixed, decalcified, paraffin-embedded mouse femurs and tibias. For metastasis studies, intracardiac injection of luciferase-expressing enzalutamide resistant CWR-R1 cells into C.B.-17 SCID mice was used to establish metastatic tumor burden, and animals were monitored via bioluminescence imaging. Exosomal RNA sequencing was performed on EnzR exos and clinical specimens, with exosomes from normal prostate epithelial cells (PNT2) used as a control. Results: Mice primed with EnzR exos developed significantly enhanced metastatic tumor burden compared to unprimed controls. EnzR exo priming also led to decreased expression of thrombospondin-1 in the bone marrow compartment, and increased expression of versican, as determined by RNA sequencing and immunohistochemistry. Exosomal RNA sequencing revealed that five miRNAs were significantly enriched in EnzR exos compared to PNT2 exosome controls. One of these, miR-4443, was found to target thrombospondin-1. Prostate cancer patient serum samples were also enriched in miR-4443 over healthy controls, and exosomal miR-4443 correlated with disease progression. Conclusions: These data indicate that exosomes derived from enzalutamide resistant prostate cancer cells can alter ECM composition in the bone marrow compartment in a pro-tumorigenic manner. Evidence for the clinical relevance of these data was observed in both serum samples and bone biopsies from prostate cancer patients, demonstrating abundant serum exosomal miR-4443 and similarly altered bone marrow ECM composition in advanced prostate cancer patients. Exosomal miR-4443 may be a promising diagnostic and prognostic marker, as well as a potential therapeutic target. Citation Format: Stephen E. Henrich, Kaylin McMahon, Michael Plebanek, Fabio Tavora, Andre De Souza, Anthony Mega, Benedito Carneiro, C. Shad Thaxton. Prostate cancer exosomes alter extracellular matrix composition in bone marrow and enhance metastasis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6204.

Syntaxin 6-mediated exosome secretion regulates enzalutamide resistance in prostate cancer.

Prostate cancer (PCa) deaths are typically the result of metastatic castration-resistant PCa (mCRPC). Recently, enzalutamide (Enz), an oral androgen receptor inhibitor, was approved for treating patients with mCRPC. Invariably, all PCa patients eventually develop resistance against Enz. Therefore, novel strategies aimed at overcoming Enz resistance are needed to improve the survival of PCa patients. The role of exosomes in drug resistance has not been fully elucidated in PCa. Therefore, we set out to better understand the exosome's role in the mechanism underlying Enz-resistant PCa. Results showed that Enz-resistant PCa cells (C4-2B, CWR-R1, and LNCaP) secreted significantly higher amounts of exosomes (2-4 folds) compared to Enz-sensitive counterparts. Inhibition of exosome biogenesis in resistant cells by GW4869 and dimethyl amiloride strongly decreased their cell viability. Mechanistic studies revealed upregulation of syntaxin 6 as well as its increased colocalization with CD63 in Enz-resistant PCa cells compared to Enz-sensitive cells. Syntaxin 6 knockdown by specific small interfering RNAs in Enz-resistant PCa cells (C4-2B and CWR-R1) resulted in reduced cell number and increased cell death in the presence of Enz. Furthermore, syntaxin 6 knockdown significantly reduced the exosome secretion in both Enz-resistant C4-2B and CWR-R1 cells. The Cancer Genome Atlas analysis showed increased syntaxin 6 expressions associated with higher Gleason score and decreased progression-free survival in PCa patients. Importantly, IHC analysis showed higher syntaxin 6 expression in cancer tissues from Enz-treated patients compared to Enz naïve patients. Overall, syntaxin 6 plays an important role in the secretion of exosomes and increased survival of Enz-resistant PCa cells.

Abstract 3005: High density lipoprotein mimics inhibit prostate cancer exosome-mediated communication with myeloid cells

Abstract Introduction: Exosomes are 30-150 nm membrane-bound vesicles that mediate intercellular communication and are secreted in abundance by neoplastic cells. Tumor-derived exosomes are capable of transmitting pro-malignant signals to target cells at local or distant sites to enhance tumor invasiveness and promote metastasis. A sub-set of this pro-malignant intercellular communication is dependent upon target cell cholesterol homeostasis. Here, we show that prostate cancer exosome communication with myeloid cells can be inhibited by treatment with high density lipoprotein mimetic nanoparticles (HDL NPs), which reduce cholesterol in myeloid cells in a targeted fashion. Methods: Exosomes were isolated by ultracentrifugation of conditioned media from enzalutamide resistant CWR-R1 cells and used for all experiments. In vitro assays were conducted using murine bone marrow macrophages obtained from culture of total murine bone marrow in M-CSF for 7 days. Confocal microscopy and flow cytometry were used for in vitro and in vivo uptake assays. Osteoclastogenesis assays were performed using a commercially available TRAP staining kit (Sigma-Aldrich). NF-kB signaling experiments were performed using a reporter human monocyte cell line (THP1-Dual). HDL NPs were synthesized using 5 nm gold nanoparticle templates, apolipoprotein A-1, and phospholipids. Results: HDL NPs were found to inhibit the cellular uptake of prostate cancer exosomes in mouse bone marrow macrophages in vitro. Furthermore, HDL NPs inhibited exosome-induced osteoclastogenesis and exosome-induced monocyte NF-kB signaling. Finally, HDL NP-mediated inhibition of exosome communication was found to be dependent upon scavenger receptor type B-1 (SR-B1). SR-B1 was shown to be expressed ubiquitously in mouse bone marrow macrophages; and HDL NPs were unable to inhibit exosome communication in bone marrow macrophages derived from SR-B1-/- mouse bone marrow. Conclusion: These data demonstrate that HDL NPs inhibit prostate cancer exosome communication with murine myeloid cells, as evidenced by cellular uptake, osteoclastogenesis, and NF-kB signaling. Moreover, SR-B1 is required for HDL NP inhibition of PCa exosome communication. In sum, these results indicate that target cell cholesterol homeostasis may be important for exosome-mediated signaling in prostate cancer, particularly in immune cells and in the bone microenvironment, and that HDL NPs are potent inhibitors of PCa exosome-mediated signaling. Citation Format: Stephen E. Henrich, Kaylin M. McMahon, Michael P. Plebanek, C. Shad Thaxton. High density lipoprotein mimics inhibit prostate cancer exosome-mediated communication with myeloid cells [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 3005.

Chlamydia trachomatis Growth and Cytokine mRNA Response in a Prostate Cancer Cell Line.

In the present paper, we report that C. trachomatis can be efficiently propagated and affect mRNA expression for two major cytokines, relevant to tumor progression, in CWR-R1 cells, a malignant prostate cell line. CWR-R1 and McCoy cells, a classic cell line for chlamydial research, were grown and infected with C. trachomatis under similar conditions. Cell monolayers were harvested for RNA analysis and immunostaining with major outer membrane protein (MOMP) antibody at 24, 48, and 72 hours of the postinfection (hpi) period. It was shown that the infectious cycle of chlamydial pathogen in CWR-R1 cells resembles the progression of C. trachomatis infection in McCoy cells but with a few important differences. First of all, the initial stage of C. trachomatis propagation in CWR-R1 cells (24 hpi) was characterized by larger inclusion bodies and more intense, specific immunofluorescent staining of infected cells as compared with McCoy cells. Moreover, there was a corresponding increase in infective progeny formation in CWR-R1 cells along with mRNA for EUO, a crucial gene controlling the early phase of the chlamydial development cycle (24 hpi). These changes were more minimal and became statistically insignificant at a later time point in the infectious cycle (48 hpi). Altogether, these data suggest that the early phase of C. trachomatis infection in CWR-R1 cells is accompanied by more efficient propagation of the pathogen as compared with the growth of C. trachomatis in McCoy cells. Furthermore, propagation of C. trachomatis in CWR-R1 cells leads to enhanced transcription of interleukin-6 and fibroblast growth factor-2, genes encoding two important proinflammatory cytokines implicated in the molecular mechanisms of chemoresistance of prostate cancer and its ability to metastasize. The possible roles of reactive oxygen species and impaired mitochondrial oxidation in the prostate cancer cell line are discussed as factors promoting the early stages of C. trachomatis growth in CWR-R1 cells.

Abstract 5198: Androgen receptor signaling affects macrophage differentiation in the human prostate cancer microenvironment

Abstract Increasing evidence from epidemiologic and pathologic studies suggests a role of macrophages in the initiation and progression of prostate cancer (PCa). During PCa development, macrophages (CD68+) are recruited into the human prostate cancer microenvironment, including inflammation-associated M1 and cancer-promoting M2 macrophages. Like other prostate cancer-associated stromal cells, macrophages express the androgen receptor (AR); however, its functionality is not known. CD68+ cells generated in vitro from peripheral white blood cells and PMA activated and IFN and LPS polarized human acute monocytic leukemia THP-1 cells also expressed AR. In these cells AR is an 80KD splice variant, lacking parts of exon 1 and exon 2. AR translocated to the nucleus upon testosterone stimulation, which was counteracted by the AR signaling inhibitor RD162. In vitro generated M1 macrophages expressed the M2 markers CD163 and CD206 upon testosterone stimulation, which was reversed by RD162. AR-ChIP sequencing suggested AR regulated Macrophage Triggering Receptor 1 (TREM1) signaling. Expression of key cytokines (e.g., CCL2, CXCL8, CCL7, IL10, IL1B) involved in TREM1 signaling was upregulated upon testosterone stimulation. Actions of these cytokines is generally associated with a protumor phenotype of macrophages. Conditioned medium from macrophages stimulated with testosterone for 8 hrs resulted in enhanced proliferation and migration of human prostate LNCap and CWRR1 cells. In conclusion, AR signaling might affect differentiation of prostate cancer-associated macrophages into cancer-promoting M2, which affects prostate cancer cell proliferation and migration. Maintaining macrophages in M1 might be a novel mechanism of action of androgen receptor inhibitors. Citation Format: Bianca Cioni, Ekatarina Nevedomskaya, Suzan Stelloo, Monique Melis, Johan van Burgsteden, Jeroen de Jong, Henk van der Poel, Jan Paul de Boer, Wilbert Zwart, Andries M. Bergman. Androgen receptor signaling affects macrophage differentiation in the human prostate cancer microenvironment [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 5198.

The Efflux Transporter ABCG2 Maintains Prostate Stem Cells.

This study identifies the mechanism by which the prostate stem cell marker, ABCG2, plays a role in prostate stem cell maintenance and provides a rationale for targeting ABCG2 for differentiation therapy in prostate cancer. Mol Cancer Res; 15(2); 128-40. ©2016 AACR.

Characterization of fibroblast-free CWR-R1ca castration-recurrent prostate cancer cell line.

The previously established CWR-R1 cell line has been used as an in vitro model representing castration-recurrent prostate cancer. Microscopic observation of subconfluent cells demonstrated two distinct cellular morphologies: polygonal closely aggregated epithelial cells surrounded by bipolar fibroblastic cells with long processes. This study sought to establish and characterize a fibroblast-free derivative of the CWR-R1 cell line. The CWR-R1ca cell line was established from CWR-R1 cells by removing fibroblasts using multiple cycles of short-term trypsinization, cloning, and pooling single-cell colonies. Authentication of fibroblast-free CWR-R1ca cells was demonstrated by analyzing the expression of cytodifferentiation and prostate-associated markers, DNA and cytogenetic profiling, and growth pattern in the absence or presence of androgen. CWR-R1ca is an androgen-sensitive cell line that expresses the androgen receptor (AR) and its splice variant 7 and the luminal epithelia markers, CK-8, CK-18, and c-Met. CWR-R1fb fibroblasts isolated from CWR-R1 cells express AR, hepatocyte growth factor-α, and mouse β-actin but not AR-V7 or epithelial markers. Cytogenetic analysis of CWR-R1ca cells revealed a hyperdiploid male with numerical gains in chromosomes 1, 7, 8, 10, 11, and 12, deletion of one chromosome 2 allele, structural abnormalities that include der(1)t(1:4), der(4)t(2:4), der(10)t(4:10), and an unbalanced reciprocal translocation between chromosome 6 and 14. DNA-profiling revealed that CWR-R1ca cells had significant short-tandem repeat marker homology with CWR22Pc and CWR22Rv1 cell lines, which indicated lineage derivation from CWR22 prostate cancer xenografts. CWR-R1ca cells were responsive to the growth stimulatory effects of dihydrotestosterone (DHT) in the femtomolar range. This study establishes CWR-R1ca cells as a fibroblast-free derivative of the castration-recurrent CWR-R1 cell line. Prostate 76:1067-1077, 2016. © 2016 Wiley Periodicals, Inc.

Acquired resistance to the second-generation androgen receptor antagonist enzalutamide in castration-resistant prostate cancer.

Enzalutamide (MDV3100) is a second generation Androgen Receptor (AR) antagonist with proven efficacy in the treatment of castration resistant prostate cancer (CRPC). The majority of treated patients, however, develop resistance and disease progression and there is a critical need to identify novel targetable pathways mediating resistance. The purpose of this study was to develop and extensively characterize a series of enzalutamide-resistant prostate cancer cell lines. Four genetically distinct AR-positive and AR-pathway dependent prostate cancer cell lines (CWR-R1, LAPC-4, LNCaP, VCaP) were made resistant to enzalutamide by long-term culture (> 6 months) in enzalutamide. Extensive characterization of these lines documented divergent in vitro growth characteristics and AR pathway modulation. Enzalutamide-resistant LNCaP and CWR-R1 cells, but not LAPC-4 and VCAP cells, demonstrated increased castration-resistant and metastatic growth in vivo. Global gene expression analyses between short-term enzalutamide treated vs. enzalutamide-resistant cells identified both AR pathway and non-AR pathway associated changes that were restored upon acquisition of enzalutamide resistance. Further analyses revealed very few common gene expression changes between the four resistant cell lines. Thus, while AR-mediated pathways contribute in part to enzalutamide resistance, an unbiased approach across several cell lines demonstrates a greater contribution toward resistance via pleiotropic, non-AR mediated mechanisms.

Gene Expression in Single Cells Isolated from the CWR-R1 Prostate Cancer Cell Line and Human Prostate Tissue Based on the Side Population Phenotype.

Defining biological signals at the single cell level can identify cancer initiating driver mutations. Techniques to isolate single cells such as microfluidics sorting and magnetic capturing systems have limitations such as: high cost, labor intense, and the requirement of a large number of cells. Therefore, the goal of our current study is to identify a cost and labor effective, reliable, and reproducible technique that allows single cell isolation for analysis to promote regular laboratory use, including standard reverse transcription PCR (RT-PCR).In the current study, we utilized single prostate cells isolated from the CWR-R1 prostate cancer cell line and human prostate clinical specimens, based on the ATP binding cassette (ABC) transporter efflux of dye cycle violet (DCV), side population assay. Expression of four genes: ABCG2; Aldehyde dehydrogenase1A1 (ALDH1A1); androgen receptor (AR); and embryonic stem cell marker, Oct-4, were determined.Results from the current study in the CWR-R1 cell line showed ABCG2 and ALDH1A1 gene expression in 67% of single side population cells and in 17% or 100% of non-side population cells respectively. Studies using single cells isolated from clinical specimens showed that the Oct-4 gene is detected in only 22% of single side population cells and in 78% of single non-side population cells. Whereas, AR gene expression is in 100% single side population and non-side population cells isolated from the same human prostate clinical specimen.These studies show that performing RT-PCR on single cells isolated by FACS can be successfully conducted to determine gene expression in single cells from cell lines and enzymatically digested tissue. While these studies provide a simple yes/no expression readout, the more sensitive quantitative RT-PCR would be able to provide even more information if necessary.

XMRV induces cell migration, cytokine expression and tumor angiogenesis: are 22Rv1 cells a suitable prostate cancer model?

22Rv1 is a common prostate cancer cell line used in xenograft mouse experiments as well as in vitro cell culture assays to study aspects of prostate cancer tumorigenesis. Recently, this cell line was shown to harbor multiple copies of a gammaretrovirus, called XMRV, integrated in its genome. While the original prostate cancer xenograft CWR22 is free of any retrovirus, subsequently generated cell lines 22Rv1 and CWR-R1, carry this virus and additionally shed infectious gammaretroviral particles in their supernatant. Although XMRV most likely was generated by recombination events in cell culture this virus has been demonstrated to infect human cells in vitro and 22Rv1 as well as CWR-R1 cells are now considered biosafety 2 reagents. Here, we demonstrate that 22Rv1 cells with reduced retroviral transcription show reduced tumor angiogenesis and increased necrosis of the primary tumor derived from xenografted cells in scid mice when compared to the parental cell line. The presence of XMRV transcripts significantly increases secretion of osteopontin (OPN), CXCL14, IL13 and TIMP2 in 22Rv1 cells. Furthermore, these data are supported by in vitro cell invasion and differentiation assays. Collectively, our data suggest that the presence of XMRV transcripts at least partially contributes to 22Rv1 characteristics observed in vitro and in vivo with regard to migration, invasion and tumor angiogenesis. We propose that data received with 22Rv1 cells or equivalent cells carrying xenotropic gammaretroviruses should be carefully controlled including other prostate cancer cell lines tested for viral sequences.

Abstract A52: Comparison of the efficacy of different mTOR inhibitors for the treatment of prostate cancer

Abstract Background: We previously showed that the mTOR pathway is activated in castration resistant prostate cancer (CRPC) cell lines while its inhibition resulted in upregulation of androgen receptor (AR) signaling, resulting in resistance to mTOR-based therapy (Wang et al., 2008, Oncogene, 27(56):7106-17). mTOR forms two complexes: activation of mTORC1 (mTOR, raptor) increases mRNA translation by phosphorylation of the downstream molecules p70-S6K (S6K) and eIF4E binding protein 1 (4E-BP1), while activation of mTORC2 (mTOR, rictor) leads to activation of Akt, which is also activated by phosphatidylinositol 3-kinase (PI3K). A number of drugs targeting these complexes are currently available, among them, RAD001, which inhibits mTORC1 alone, BEZ235, a dual mTORC1/PI3K inhibitor, and Torin1, an ATP-competitive inhibitor which prevents activation of both mTORC1 and mTORC2. The goal of the present study was to identify the drug that is most effective against PCa either alone or in combination with the AR inhibitor bicalutamide. Results: The drugs were used in a number of cell lines including C4-2 and LNCaP-AI, two CRPC sublines of androgen-dependent LNCaP cells, as well as CWR-R1 and CWR22Rv1, two lines derived from relapsed CWR22 tumors in castrated mice. Another androgen-sensitive cell line, PC-346C, was also used. RAD001 dose responsibly inhibited growth in C4-2 cells, but the other cell lines were resistant to this therapy, either alone or in combination with bicalutamide. In contrast, LNCaP-AI and CWR-R1 cells were also sensitive to BEZ235 and Torin1, but PC-346C cells were resistant to all three. Hence we investigated the molecular mechanism underlying the resistance of these cells to mTOR inhibitors. Clonogenic assays revealed that 20 nM BEZ235 and 25 nM Torin1 are optimal doses that prevent growth of PCa cells, effect comparable of that of 10 nM of RAD001 (physiological concentration in blood of patients under treatment with this drug). Comparison of the downstream targets of the various drugs at these doses revealed that 4E-BP1 and Akt are highly phosphorylated in both C4-2 and PC-346C cells despite RAD001 treatment, whereas BEZ235 and Torin1 inhibited 4E-BP1 phosphorylation. This is despite the fact that AR levels, but not AR transcriptional activity, increased in BEZ235 treated cells, but not in those treated with RAD001 and Torin1. However, phosphorylation of its binding partner eIF4E increased in PC-346C cells but not in C4-2 cells. Conclusion: Phosphorylation of 4E-BP1 and eIF4E, as well as Akt, needs to be downregulated in order for the drug to be effective. The effects of BEZ235 are likely complicated by the increase in AR levels despite the use of bicalutamide. Therefore, a stronger AR inhibitor, such as MDV3100, in combination with this drug, may be required. Acknowledgments: We would like to thank Dr. David Sabatini for the drug Torin1, Novartis Pharmaceuticals for providing BEZ235 and RAD001, and Astra Zeneca, Cheshire, UK, for the drug bicalutamide. CWR-R1 cells were generously provided by Dr Elizabeth Wilson (University of North Carolina), while PC-346C cells were from Dr. W.M. van Weerden, Josephine Nefkens Institute, Erasmus MC, Rotterdam, The Netherlands.

Abstract 2148: Exploitation of androgen receptor splice variant signaling by guanine nucleotide exchange factor Vav3 in castration resistant prostate cancer

Abstract The treatment for advanced or metastatic prostate cancer is androgen deprivation therapy. Patients inevitably relapse and the cancer is now termed androgen-independent or castration resistant (CRPC). CRPC remains dependent on androgen receptor (AR) signaling. One of the proteins implicated in the reactivation of AR transcriptional activity in CRPC is Vav3, a Rho GTPase guanine nucleotide exchange factor. Vav3 is up-regulated in human prostate cancer tumors compared to benign tissue and in preclinical models of prostate cancer progression to CRPC. Vav3 enhances AR activity at both physiological and as well as at subnanomolar androgen concentrations, similar to prostatic microenvironment levels demonstrated in CRPC. Vav3 confers castration resistant growth to a classically androgen dependent cell line in a mouse xenograft model. Thus, elevated levels of Vav3 seem to be pivotal in promoting continued AR signaling in CRPC. We examined the contributions of Vav3 to AR activity and cell proliferation in the CRPC cell lines CWR-22Rv1 and CWR-R1. Knockdown of Vav3 attenuated cell growth and reduced AR activity as compared to the shGFP control. However knockdown of full length AR had little effect, perhaps due to impaired ligand-mediated transcriptional activity of the mutated AR expressed in these cell lines. Because CWR-22Rv1 also express AR splice variants that lack the ligand binding domain and are proposed to underlie CRPC growth, we examined the possibility that Vav3 enhances AR splice variant signaling. The AR splice variant, ARV7 (also known as AR3), exhibits constitutive ligand independent activity and is linked to poor prognosis and survival. Depletion of ARV7 in 22Rv1 and CWR-R1 cell lines resulted in slowed growth and lowered AR activity. Soft agar assays revealed that knockdown of either Vav3 or ARV7 resulted in greatly decreased anchorage independent growth. Vav3 potently enhanced the activity of ARV7 in reporter gene assays. Further, knockdown of Vav3 resulted in lowered levels of nuclear AR splice variants in CWR-22Rv1. Co-immunoprecipitation revealed that ARV7 and Vav3 directly interact. These results suggest that Vav3 may enhance ARV7 activity through increased nuclear localization and that the interaction of Vav3 and ARV7 may be required for robust growth of CRPC cells. These novel data demonstrating interaction between a versatile AR coactivator and an AR splice variant provide insights into the possible mechanisms by which Vav3 exploits and enhances AR splice variant signaling in the progression of prostate cancer malignancy and castration resistance. 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 2148. doi:1538-7445.AM2012-2148

Cadmium Induces p53-Dependent Apoptosis in Human Prostate Epithelial Cells

Cadmium, a widespread toxic pollutant of occupational and environmental concern, is a known human carcinogen. The prostate is a potential target for cadmium carcinogenesis, although the underlying mechanisms are still unclear. Furthermore, cadmium may induce cell death by apoptosis in various cell types, and it has been hypothesized that a key factor in cadmium-induced malignant transformation is acquisition of apoptotic resistance. We investigated the in vitro effects produced by cadmium exposure in normal or tumor cells derived from human prostate epithelium, including RWPE-1 and its cadmium-transformed derivative CTPE, the primary adenocarcinoma 22Rv1 and CWR-R1 cells and LNCaP, PC-3 and DU145 metastatic cancer cell lines. Cells were treated for 24 hours with different concentrations of CdCl2 and apoptosis, cell cycle distribution and expression of tumor suppressor proteins were analyzed. Subsequently, cellular response to cadmium was evaluated after siRNA-mediated p53 silencing in wild type p53-expressing RWPE-1 and LNCaP cells, and after adenoviral p53 overexpression in p53-deficient DU145 and PC-3 cell lines. The cell lines exhibited different sensitivity to cadmium, and 24-hour exposure to different CdCl2 concentrations induced dose- and cell type-dependent apoptotic response and inhibition of cell proliferation that correlated with accumulation of functional p53 and overexpression of p21 in wild type p53-expressing cell lines. On the other hand, p53 silencing was able to suppress cadmium-induced apoptosis. Our results demonstrate that cadmium can induce p53-dependent apoptosis in human prostate epithelial cells and suggest p53 mutation as a possible contributing factor for the acquisition of apoptotic resistance in cadmium prostatic carcinogenesis.

Abstract B47: Identification of novel E2F3 transcriptional targets expands the role of the RB/E2F axis beyond cell cycle control

Abstract The RB/E2F axis is frequently disrupted in multiple tumors. Classical studies reported that the RB tumor suppressor exerts its transcriptional repressor function through an interaction with the E2F family of transcription factors (E2F1-3) to control the timely expression of genes required for DNA replication and cell cycle progression. The E2F3 locus encodes two E2F3 isoforms, a and b, which have unique N-terminal sequences. Multiple studies indicate that E2F3, rather than E2F1 or 2, is elevated in various cancers, including prostate. In prostate tumors elevated E2F3 expression is an independent prognostic factor of clinical outcome, but the direct transcriptional targets of E2F3a and E2F3b have not been characterized. We found that E2F3a and b expression was increased in prostate tumor derived cell lines when compared to non-transformed controls. An expression array analysis following knockdown (k/d) of total E2F3 identified several unexpected targets including Interleukin 6 receptor (IL-6R), a critical component of the IL6 signaling cascade and calpain 2, a protease that is essential in cellular migration and has been shown to be elevated during prostate tumorigenesis. Further studies showed that the two genes were regulated by different E2F3 isoforms- IL6R was a target of E2F3a, while calpain 2 was regulated by E2F3b. Expression of both genes was enhanced by RB ablation. E2F3a-dependent IL-6R regulation was apparent in PC3, LNCaP, CWR-R1, and 22Rv1 cells. Chromatin immunoprecipitation (ChIP) studies identified sequences in the IL-6R promoter that were bound by E2F3. Transient co-transfection studies using an E2F3a expression plasmid showed that E2F3a transactivated the IL-6R promoter in a dose dependent manner. The IL-6R initiated signaling cascade was perturbed following a k/d of E2F3a since the levels of ERK1/2 phosphorylation was reduced. An siRNA-mediated ablation of each isoform revealed that E2F3b, not E2Fa, was effective is reducing calpain 2 levels. ChIP studies indicated that E2F3 binds to the endogenous calpain 2 promoter, and in transient transfection studies E2F3b transactivated the calpain 2 promoter in a dose dependent manner. An analysis of the calpain 2 promoter identified an androgen receptor (AR) half site. Additional transfection studies showed that the AR can cooperate with E2F3b in transactivation of the calpain 2 promoter. Moreover, reduced expression of E2F3b impaired cellular migration in a wound assay. The expression of the E2F3 isoforms has not been previously analyzed in the TRAMP prostate tumor model. Western immunoblot studies of five TRAMP tumors and three age and strain matched prostates showed that TRAMP tumors had highly elevated expression of both E2F3 isoforms. These results indicate that increased expression of both E2F3 isoforms is a feature of human tumor-derived cell lines and the TRAMP mouse model of prostate tumorigenesis. Calpain 2, expression was readily detected in all of the TRAMP tumors, but not in the control tissue. Hence E2F3 overexpression and increased calpain levels are features of human and mouse tumors. This analysis broadens the role of E2F3 in prostate tumorigenesis beyond the regulation of cell cycle progression. E2F3a is a link between the E2F/RB and the IL-6 signaling cascade, while E2F3b regulates expression of a protease that is essential in cell adhesion and migration. Therefore E2F3 deregulation affects multiple signaling networks to promote tumorigenesis. Citation Format: Stephen J. Libertini, Maria Mudryj, Alan P. Lombard, Honglin Chen, Veronica Rodriguez, Carlos Perez-Stable, Bushra al-Bataina, Tilak Koilvaram, Michael George, Allen C. Gao. Identification of novel E2F3 transcriptional targets expands the role of the RB/E2F axis beyond cell cycle control [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr B47.

Abstract IA18: Altered AR gene architecture and splicing in castration-resistant prostate cancer

Abstract Reactivation of the androgen receptor (AR) during androgen depletion therapy (ADT) underlies castration-resistant prostate cancer (CRPCa). Altered splicing of the AR gene and synthesis of constitutively-active COOH-terminally truncated AR variants lacking the AR ligand binding domain has emerged as an important mechanism of ADT-resistance in CRPCa. To understand mechanisms that may promote synthesis of these species, we have been studying the PCa progression models in which altered AR splicing patterns were originally discovered. Remarkably, these models all harbor distinct intragenic rearrangements in the AR gene, which are linked to their individual splicing signatures. For example, the CRPCa 22Rv1 cell line harbors a 35kb intragenic tandem duplication of AR exon 3 and flanking sequences, which results in expression of an exon 3-duplicated full-length AR and multiple truncated AR variant species. The CRPCa LuCaP 86.2 xenograft harbors an 8,579 bp deletion of AR exons 5, 6, and 7, which promotes synthesis of the truncated AR v567es variant. Targeted paired-end re-sequencing of the AR gene in CWR-R1 cells led to the discovery of a 48 kb deletion in AR intron 1, which is linked to a splice switch favoring synthesis of the AR-V7/AR3 variant. Copy number imbalances occur across the length of the AR gene in clinical CRPCa, often concurrent with amplification, indicating complex patterns of intragenic AR gain and loss in human disease. These findings portend ongoing discovery of diverse truncated AR variants in CRPCa and define a new class of AR gene alterations that may drive ADT-resistance at this stage of the disease. Citation Format: Scott M. Dehm. Altered AR gene architecture and splicing in castration-resistant prostate cancer [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr IA18.

AR intragenic deletions linked to androgen receptor splice variant expression and activity in models of prostate cancer progression

Reactivation of the androgen receptor (AR) during androgen depletion therapy (ADT) underlies castration-resistant prostate cancer (CRPCa). Alternative splicing of the AR gene and synthesis of constitutively-active COOH-terminally truncated AR variants lacking the AR ligand binding domain has emerged as an important mechanism of ADT-resistance in CRPCa. In a previous study, we demonstrated that altered AR splicing in CRPCa 22Rv1 cells was linked to a 35 kb intragenic tandem duplication of AR exon 3 and flanking sequences. In this study, we demonstrate that complex patterns of AR gene copy number imbalances occur in PCa cell lines, xenografts, and clinical specimens. To investigate whether these copy number imbalances reflect AR gene rearrangements that could be linked to splicing disruptions, we carried out a detailed analysis of AR gene structure in the LuCaP 86.2 and CWR-R1 models of CRPCa. By deletion-spanning PCR, we discovered a 8,579 bp deletion of AR exons 5, 6, and 7 in the LuCaP 86.2 xenograft, which provides a rational explanation for synthesis of the truncated AR v567es AR variant in this model. Similarly, targeted re-sequencing of the AR gene in CWR-R1 cells led to the discovery of a 48 kb deletion in AR intron 1. This intragenic deletion marked a specific CWR-R1 cell population with enhanced expression of the truncated AR-V7/AR3 variant, a high level of androgen-independent AR transcriptional activity, and rapid androgen independent growth. Together, these data demonstrate that structural alterations in the AR gene are linked to stable gain-of-function splicing alterations in CRPCa.

Dominant-Negative Androgen Receptor Inhibition of Intracrine Androgen-Dependent Growth of Castration-Recurrent Prostate Cancer

BackgroundProstate cancer (CaP) is the second leading cause of cancer death in American men. Androgen deprivation therapy is initially effective in CaP treatment, but CaP recurs despite castrate levels of circulating androgen. Continued expression of the androgen receptor (AR) and its ligands has been linked to castration-recurrent CaP growth.Principal FindingIn this report, the ligand-dependent dominant-negative ARΔ142–337 (ARΔTR) was expressed in castration-recurrent CWR-R1 cell and tumor models to elucidate the role of AR signaling. Expression of ARΔTR decreased CWR-R1 tumor growth in the presence and absence of exogenous testosterone (T) and improved survival in the presence of exogenous T. There was evidence for negative selection of ARΔTR transgene in T-treated mice. Mass spectrometry revealed castration-recurrent CaP dihydrotestosterone (DHT) levels sufficient to activate AR and ARΔTR. In the absence of exogenous testosterone, CWR-R1-ARΔTR and control cells exhibited altered androgen profiles that implicated epithelial CaP cells as a source of intratumoral AR ligands.ConclusionThe study provides in vivo evidence that activation of AR signaling by intratumoral AR ligands is required for castration-recurrent CaP growth and that epithelial CaP cells produce sufficient active androgens for CaP recurrence during androgen deprivation therapy. Targeting intracrine T and DHT synthesis should provide a mechanism to inhibit AR and growth of castration-recurrent CaP.