VCaP Cells Research Articles

Abstract 1016: The androgen receptor splice variant AR-V7 associates with the glucocorticoid receptor following androgen blockade

Abstract Expression of the constitutively active androgen receptor splice variant AR-V7 is associated with resistance to anti-androgen therapies and worse clinical outcomes in prostate cancer. Dimerization is a requirement for AR-V7 transcriptional activity, but whether that occurs through homodimerization or heterodimerization remains poorly understood. Because NR3C-family nuclear hormone receptors rely on a highly conserved D-box motif within the DNA-binding domain to mediate dimerization, we hypothesized that AR-V7 can heterodimerize with other NR3C-family nuclear hormone receptors, with a particular interest in the glucocorticoid receptor (GR). Like AR-V7, GR is upregulated in prostate cancer following androgen blockade, regulates canonical AR target genes, and is associated with resistance to anti-androgen therapies. Using NanoBRET technology in HEK293 cells, we found that AR-V7 interacts with liganded NR3C-family nuclear hormone receptors, including the full-length androgen receptor, the progesterone receptor, the mineralocorticoid receptor, and, most notably, GR. Using co-immunoprecipitation and proximity ligation assays, we demonstrate that AR-V7 associates with GR following androgen blockade in both the VCaP cell line and the CWR-22RV1 cell line, two models of prostate cancer that express endogenous AR-V7 and GR. Preliminary ChIP-Seq experiments in these cell lines suggest AR-V7 and GR chromatin occupancy at the same genomic sites in a ligand-dependent manner. Taken altogether, this data suggests AR-V7 can utilize GR as an alternative binding partner to initiate heterodimerization and transcriptional activation. Citation Format: Eric Bueter, David Hosfield, Erin McAuley, Phillip Selman, Geoffrey Greene, Suzanne D. Conzen, Russell Z. Szmulewitz. The androgen receptor splice variant AR-V7 associates with the glucocorticoid receptor following androgen blockade [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 1016.

Abstract 924: The androgen receptor antagonist darolutamide shows strong antitumor efficacy in patient- and cell line-derived xenograft prostate cancer models

Abstract Darolutamide is a structurally unique androgen receptor (AR) antagonist which has recently completed a pivotal clinical phase 3 trial. Here we explored the efficacy of darolutamide in different prostate cancer models and in combination with the ATR inhibitor BAY 1895344. Darolutamide was tested in the patient-derived xenografts LuCaP35 and LuCaP96. The studies were performed with SCID male mice implanted subcutaneously. Oral, twice daily treatment with 100 mg/kg darolutamide started at a mean tumor size of about 150 mm3; the study was stopped 3.5 weeks later. In addition the cell line-derived xenograft LAPC-4 was tested after subcutaneous inoculation of SCID male mice. Oral, daily treatment with 100 mg/kg darolutamide started at a mean tumor size of about 50 mm2. The ATR inhibitor BAY 1895344 was applied at 20 mg/kg, twice daily for 3 days followed by 4 days without treatment. X-ray radiation was performed at 5 Gy, once weekly on days 26 and 33 after start of compound treatment. Efficacy was evaluated by calculating the ΔT/ΔC values. Gene expression analysis was performed on RNA extracted from prostate cancer cells treated with darolutamide and/or BAY 1895344, and analyzed using RT2 Profiler PCR arrays (Qiagen). RNA-seq and AR ChIP-seq (06-680, Millipore) datasets of darolutamide-treated cell lines were used for genome-wide studies. γH2AX (ab2893, abcam) levels were evaluated by Western blot analysis. Darolutamide showed strong anti-tumor activity in the LuCaP96 model (6% ΔT/ΔC). Significant anti-tumor efficacy was also observed in the LAPC-4 model following treatment with darolutamide (36% ΔT/ΔC) or with radiation (19% ΔT/ΔC). Stronger efficacy was observed when combining darolutamide with the ATR inhibitor BAY 1895344 (17% ΔT/ΔC) or with BAY 1895344 plus radiation (1% ΔT/ΔC). RNAseq analysis of LAPC-4 and VCaP cells showed that expression of DNA repair genes was regulated by androgen and efficiently blocked by darolutamide. In line with this, we observed androgen-dependent AR binding close to DNA repair genes, which supports a regulatory role of the AR signalling pathway in the regulation of these genes. We also found that γH2AX levels were increased after treatment with BAY 1895344 alone or in combination with darolutamide. Expression of H2AX was also increased following combination treatment. Notably, darolutamide treatment alone did not have comparable effects on H2AX but strongly reduced androgen-driven expression of several DNA damage response genes. In conclusion, darolutamide demonstrated strong in vivoefficacy in xenograft models as single agent, and enhanced activity in combination with radiation and an ATR inhibitor, with the latter involving down-regulation of DNA repair genes. Together these results suggest broad anti-tumor activity of darolutamide in prostate cancer as a single agent or in combination with other anti-tumor modalities. Citation Format: Pascale Lejeune, Antje Wengner, Simon J. Baumgart, Ekaterina Nevedomskaya, Eva Corey, Dominik Mumberg, Bernard Haendler. The androgen receptor antagonist darolutamide shows strong antitumor efficacy in patient- and cell line-derived xenograft prostate cancer models [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 924.

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

Abstract 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.

Effect of Piceatannol on Cell Cycle Progression in Prostate Cancer Cells (P05-005-19)

ObjectivesPiceatannol (PIC) is a polyphenolic and resveratrol analog that is found in many vegetables consumed by humans. Like resveratrol, PIC has beneficial effects on health due to its anti-inflammatory, anti-oxidative and anti-proliferative features. However, the molecular targets of PIC in prostate cancer (PCa), which is the second most common cancer in men worldwide, are still poorly understood. Preventing cancer through dietary sources is a promising strategy to control diseases. Therefore, the aim of present study was to investigate the molecular mechanistic of actions of PIC in PCa cell lines with different genetic background common to human prostate cancer. MethodsHuman PCa cell lines (PC-3, 22Rv1, LNCaP, and VCaP) were treated with different doses of PIC (5–40 μM) and used for cell viability assay, measurement of total free fatty acids (FFA) and lactate, and cell cycle distribution. ResultsPIC treatment dose- and time-dependently reduced viability in PC-3 (androgen-independent, PTEN null, p53 null) and VCaP cells (androgen-responsive, wild-type PTEN, mutant p53). Because metabolic alterations, such as increased glucose and lipid metabolism are implicated in pathogenesis of in PCa, we tested if PIC could affect these pathways. Results from lactate and total free fatty acid assays in VCaP, 22Rv1 (castration-resistant, wild-type PTEN, mutant p53), and LNCaP (androgen-responsive, PTEN null, wild-type p53) revealed no effect of PIC on these metabolisms. However, PIC treatment delayed cell cycle progression in G0/G1 phase concomitant with the induction of apoptosis in both LNCaP and 22Rv1 cells, suggesting that growth inhibitory effect of PIC in PCa is associated with cell cycle arrest and apoptotic cell death at least LNCaP and 22Rv1 cells. ConclusionsWhile PIC treatment does not alter lipid or glucose metabolism, cell cycle arrest and apoptosis induction are likely important in anti-cancer effects of PIC. Funding SourcesSão Paulo Research Foundation (2018/09793-7).

Targeted Notch1 inhibition with a Notch1 antibody, OMP-A2G1, decreases tumor growth in two murine models of prostate cancer in association with differing patterns of DNA damage response gene expression.

Notch plays a protumorigenic role in many cancers including prostate cancer (PCa). Global notch inhibition of multiple Notch family members using γ-secretase inhibitors has shown efficacy in suppressing PCa growth in murine models. However, global Notch inhibition is associated with marked toxicity due to the widespread function of many different Notch family members in normal cell physiology. Accordingly, in the current study, we explored if specific inhibition of Notch1 would effectively inhibit PCa growth in a murine model. The androgen-dependent VCaP and androgen-independent DU145 cell lines were injected subcutaneously into mice. The mice were treated with either control antibody 1B7.11, anti-Notch1 antibody (OMP-A2G1), docetaxel or the combination of OMP-A2G1 and docetaxel. Tumor growth was measured using calipers. At the end of the study, tumors were assessed for proliferative response, apoptotic response, Notch target gene expression, and DNA damage response (DDR) expression. OMP-A2G1 alone inhibited tumor growth of both PCa cell lines to a greater extent than docetaxel alone. There was no additive or synergistic effect of OMP-A2G1 and docetaxel. The primary toxicity was weight loss that was controlled with dietary supplementation. Proliferation and apoptosis were affected differentially in the two cell lines. OMP-A2G1 increased expression of the DDR gene GADD45α in VCaP cells but downregulated GADD45α in Du145 cells. Taken together, these data show that Notch1 inhibition decreases PCa xenograft growth but does so through different mechanisms in the androgen-dependent VCaP cell line vs the androgen-independent DU145 cell line. These results provide a rationale for further exploration of targeted Notch inhibition for therapy of PCa.

SAT-328 Androgens Modulate the Expression of Prostatic Acid Phosphatase

INTRODUCTION: Prostatic acid phosphatase (PAP) is an acid phosphatase synthesized in prostate epithelial cells that served as the biochemical diagnostic mainstay for prostate cancer for several decades. There are two forms of PAP, secretory(sPAP) and transmembrane (TM-PAP), that are derived from alternative transcripts of the gene. PAP is highly expressed by epithelial cells of the adult prostate, however, the androgenic regulation of prostatic acid phosphatase is not well understood. HYPOTHESIS AND OBJECTIVES: We hypothesized that androgens do not increase PAP expression. Our objectives were to determine the immunohistochemical expression of PAP in human fetal prostate tissue, human bone metastases, and intact and castrated xenograft tumors of human VCaP prostate cancer cells. In addition, the effects of dihydrotestosterone (DHT) onTM- and sPAP expression in vitro were quantified. METHODS: Immunohistochemical staining for PAP, androgen receptor (AR) and Prostate Specific Antigen (PSA) protein expression was carried out on human fetal prostate (9.5, 11.5, 13, 16.5 and 18 weeks of gestational age) and human castration-resistant prostate cancer bone metastases archival specimens obtained with IRB approval. Tissue from human benign prostate and breast cancer metastases were used as controls. For xenograft studies, VCaP cells were inoculated subcutaneously into SCID mice and surgical or sham castration was performed after tumor development. Mouse tumors and weights were measured biweekly and tumor tissue isolated after mouse sacrifice. Isolated tumors were stained for PAP, AR and PSA. RESULTS: PAP expression was an early marker of prostate development and observed in the fetal prostate as early as 11.5 weeks of gestational age. Strong PAP expression was observed in all human castration-resistant prostate cancer bone metastases examined (4/4 specimens). The AR was absent in two of four specimens. PSA was expressed in human castration-resistant bone metastatic prostate specimens; however, the expression was not as strong as PAP. In vivo, castrated VCaP tumors underwent tumor stasis and were significantly smaller compared to intact animals but increased PAP expression was noted after castration. In contrast, PSA and AR expression was reduced in castrated VCaP tumors compared to tumors from intact mice. DHT treatment of VCaP cells increased AR expression while decreasing both sPAP and TM-PAP at doses ranging from 10-7-10-14M for 24 h. CONCLUSIONS: Our findings demonstrate that PAP is expressed early in normal human fetal prostate development and may be a marker of the early stages of differentiation. DHT decreased the expression of both isoforms of PAP in vitro and castration increased PAP expression in vivo. TM-PAP may serve as a potential target for castration-resistant prostate cancer as its expression increases with castration.

SUN-001 Analysis of Isoform Specific Differential Splicing Effects in Prostate Cancer

The androgen receptor (AR) is a hormone activated transcription factor which is important for the growth and progression of prostate cancer (PCa). Metastatic PCa is treated with androgen deprivation therapy (ADT) based regimen but eventually, these tumours develop resistance through multiple mechanisms that reactivate AR. These include expression of constitutively active AR splice variants that lack a ligand binding domain such as AR-V7. To characterize the common and unique activities of AR and AR-V7, we engineered LNCaP and VCaP cell lines that express AR-V7 in response to doxycycline and performed RNA-Seq. Many genes were found to be regulated by both AR and AR-V7, but there were also genes regulated by only one isoform. Moreover, both isoforms altered mRNA splicing of numerous target genes, in some cases without altering overall levels of mRNA. In many cases, the alterations in splicing are AR isoform specific. To understand the differential splicing by AR isoforms, CD44 mini-gene splicing assay and studies of endogenous target genes are being done. The CD44 mini-gene contains an MMTV promoter and is a multi-functional molecule containing two variable exons, v4 and v5 that can be either included or excluded during the splicing process. Both AR and AR-V7 induce transcription from an MMTV promoter. Co-transfection of AR or AR-V7 with the CD44 mini-gene in Hela cells demonstrated that CD44 splicing was altered by AR and its variant AR-V7. R1881 treated samples showed a shift to RNA products resulting from the skipping of both variable exons. Treatment with R1881 showed a decrease in the PSI (Percent Spliced Inclusion) as compared to obtained in the absence of R1881 or AR-V7. In contrast, AR-V7 minimally induced single exon skipping as compared to vehicle. These observations suggest that AR and its variants can have marked effects on RNA splicing to produce radically different proteins with different splicing/inclusion ratio. Analysis of the RNA-Seq data revealed that multiple types of splicing events are affected by the AR isoforms. For instance, whether an isoform favours exclusion or inclusion of a particular exon is event specific. A comparison of splicing in VCaP and LNCaP models showed that only a subset of events were common to the two models. One of the most differentially regulated events in both lines is an exon inclusion/exclusion event in PGAP2. Both isoforms increase the inclusion/exclusion ratio. However, further analysis showed that AR-V7 preferentially increased the levels of inclusion, but did not affect the basal levels of skipping. Also, AR increased the inclusion/skipping ratio through repression of expression of the skipped product. Similar analyses for other splicing events are ongoing. Our studies will provide a better understanding for the molecular basis for isoform specific actions and the role of AR/AR-V7 in the regulation of mRNA transcription and splicing.

MiR-103a-2-5p/miR-30c-1-3p inhibits the progression of prostate cancer resistance to androgen ablation therapy via targeting androgen receptor variant 7.

Androgens and androgen receptors are vital factors involved in prostate cancer progression, and androgen ablation therapies are commonly used to treat advanced prostate cancer. However, the acquisition of androgen ablation therapy resistance remains a challenge. Recently, androgen receptor splicing variants lacking the ligand-binding domain have been reported to play a critical role in the acquisition of androgen ablation therapy resistance. In the present study, we revealed that the messenger RNA expression and the protein levels of an androgen receptor variant 7 (AR-V7) were higher in prostate cancer tissue samples and in the AR-positive prostate cancer cell line, VCaP. In contrast, microRNA (miR)-30c-1-3p/miR-103a-2-5p expression was significantly downregulated in tumor tissues and cells. miR-30c-1-3p/miR-103a-2-5p overexpression could inhibit AR-V7 expression, suppress VCaP cell growth, and inhibit AR-V7 downstream factor expression by directly targeting the 3'-untranslated region of AR-V7. Under enzalutamide (Enza) treatment, the effects of AR-V7 overexpression were the opposite of those of miR-103a-2-5p/miR-30c-1-3p overexpression; more importantly, the effects of miR-103a-2-5p/miR-30c-1-3p overexpression could be significantly reversed by AR-V7 overexpression under Enza. In summary, we demonstrated a novel mechanism of the miR-30c-1-3p/miR-103a-2-5p/AR-V7 axis modulating the cell proliferation of AR-positive prostate cancer cells via AR downstream targets. The clinical application of miR-30c-1-3p/miR-103a-2-5p needs further in vivo validation.

MicroRNA-384 is lowly expressed in human prostate cancer cells and has anti-tumor functions by acting on HOXB7

ObjectivesIn this work, we evaluated the expression of microRNA-384 (miR-384) in human prostate cancer (CAP) cells and its regulatory role on CAP in vitro and in vivo functions. MethodsIn CAP cell lines, miR-384 expression was evaluated by qRT-PCR. In LNCaP and VCaP cells, lentiviral infection was done to overexpress miR-384. The regulatory effects of miR-384 overexpression on CAP in vitro proliferation and migration, and in vivo tumorigenesis, were evaluated, respectively. The targeting of miR-384 on Homeobox b7 gene (HOXB7), was evaluated by dual-luciferase reporter assay and qRT-PCR. In addition, HOXB7 was upregulated in miR-384-overexpressed CAP cells to evaluate the correlated role of HOXB7 in miR-384-mediated CAP proliferation and migration in vitro. ResultsMiR-384 was lowly expressed in CAP cell lines. Lentiviral infection induced miR-384 overexpression inhibited CAP in vitro proliferation and migration, and in vivo tumorigenesis. HOXB7 was directly targeted by miR-384 in CAP cells. In miR-384-overexpressed CAP cells, HOXB7 upregulation reversed the effect of miR-384 by promoting CAP in vitro proliferation and migration. ConclusionMiR-384 was downregulated in CAP cells. MiR-384 overexpression suppressed CAP in vitro and in vivo development, possibly via acting through its downstream target gene of HOXB7.

The influence of treatment sequence in the prognostic value of TMPRSS2-ERG as biomarker of taxane resistance in castration-resistant prostate cancer.

TMPRSS2-ERG expression in blood has been correlated with low docetaxel benefit in metastatic castration-resistant prostate cancer (mCRPC). This multicenter study aimed to prospectively asses its role as a taxane-resistance biomarker in blood and retrospectively in tumors, exploring also the impact of prior abiraterone/enzalutamide (A/E) in patients and in vitro. TMPRSS2-ERG was tested by quantitative reverse-transcription PCR. We included 204 patients (137 blood and 124 tumor samples) treated with taxanes. TMPRSS2-ERG expression was correlated with prostate-specific antigen (PSA)-progression-free survival (PFS), radiological-PFS (RX-PFS), and overall survival (OS). Independent association with survival was evaluated by multivariate Cox modeling. In vitro ERG knockdown and combinatorial and sequential experiments with enzalutamide and docetaxel were performed in VCaP cells. Prior A/E (HR 1.8, 95% CI 1.2-2.8) and blood TMPRSS2-ERG detection (HR 2, 95% CI 1.1-3.7) were independently associated to lower PSA-PFS. In patients without prior A/E, blood and tumor TMPRSS2-ERG independently predicted lower PSA-PFS (HR 3.3, 95% CI 1.4-7.9 and HR 1.8, 95% CI 1.02-3.3, respectively) to taxanes. When prior A/E was administered, TMPRSS2-ERG was not associated with outcome. There was a significant interaction between blood TMPRSS2-ERG and prior A/E related to PSA-PFS (p = 0.032) and RX-PFS (p = 0.009). In vitro stable ERG inhibition did not sensitize VCaP cells to docetaxel. Concomitant enzalutamide and taxanes were synergistic, but prior enzalutamide reduced docetaxel cytotoxicity in VCaP cells. Enzalutamide induced the expression of neuroendocrine markers and reduced that of E-cadherin. We conclude that prior hormone-therapy may influence taxanes response and TMPRSS2-ERG prognostic value. Thus, multiple and sequential biomarkers are needed in CRPC follow-up evaluation.

Discovery and biological evaluation of novel androgen receptor antagonist for castration-resistant prostate cancer

Prostate cancer (PC) is the second most common malignancy in men worldwide. Among current therapies, two antiandrogens, Abiraterone Acetate and Enzalutamide (Enza) have become the standard of care for patients with metastatic castration-resistant prostate cancer (mCRPC). Here, we designed and synthesized a new series of nonsteroidal compounds deriving from the hybridization of Abiraterone (Abi) and Enzalutamide, among which compound 4a featuring the diphenylamine scaffold was identified as a potent and cell selective androgen receptor (AR) antagonist. In cell proliferation assays, compound 4a exhibited better antiproliferative activities than Enzalutamide against AR-overexpressing VCaP cells and 22Rv1 cells bearing H874Y-mutated AR. In addition, 4a suppressed the activity of AR-F876L mutant that confers resistance to Enzalutamide and efficiently blocked R1881-induced PSA and FKBP5 gene expression. In competitive binding assay, compound 4a displayed higher binding affinity to AR than Enzalutamide. These results suggest compound 4a as a potential candidate to treat Enza-resistant CRPC.

Characterization of the ERG-regulated Kinome in Prostate Cancer Identifies TNIK as a Potential Therapeutic Target

Approximately 50% of prostate cancers harbor the TMPRSS2:ERG fusion, resulting in elevated expression of the ERG transcription factor. Despite the identification of this subclass of prostate cancers, no personalized therapeutic strategies have achieved clinical implementation. Kinases are attractive therapeutic targets as signaling networks are commonly perturbed in cancers. The impact of elevated ERG expression on kinase signaling networks in prostate cancer has not been investigated. Resolution of this issue may identify novel therapeutic approaches for ERG-positive prostate cancers. In this study, we used quantitative mass spectrometry-based kinomic profiling to identify ERG-mediated changes to cellular signaling networks. We identified 76 kinases that were differentially expressed and/or phosphorylated in DU145 cells engineered to express ERG. In particular, the Traf2 and Nck-interacting kinase (TNIK) was markedly upregulated and phosphorylated on multiple sites upon ERG overexpression. Importantly, TNIK has not previously been implicated in prostate cancer. To validate the clinical relevance of these findings, we characterized expression of TNIK and TNIK phosphorylated at serine 764 (pS764) in a localized prostate cancer patient cohort and showed that nuclear enrichment of TNIK (pS764) was significantly positively correlated with ERG expression. Moreover, TNIK protein levels were dependent upon ERG expression in VCaP cells and primary cells established from a prostate cancer patient-derived xenograft. Furthermore, reduction of TNIK expression and activity by silencing TNIK expression or using the TNIK inhibitor NCB-0846 reduced cell viability, colony formation and anchorage independent growth. Therefore, TNIK represents a novel and actionable therapeutic target for ERG-positive prostate cancers that could be exploited to develop new treatments for these patients.

Clinical utility of androgen receptor gene aberrations in circulating cell-free DNA as a biomarker for treatment of castration-resistant prostate cancer

The therapeutic landscape of castration-resistant prostate cancer (CRPC) has rapidly expanded. There is a need to develop noninvasive biomarkers to guide treatment. We established a highly sensitive method for analyzing androgen receptor gene (AR) copy numbers (CN) and mutations in plasma circulating cell-free DNA (cfDNA) and evaluated the AR statuses of patients with CRPC. AR amplification was detectable in VCaP cell line (AR amplified) genomic DNA (gDNA) diluted to 1.0% by digital PCR (dPCR). AR mutation were detectable in LNCaP cell line (AR T878A mutated) gDNA diluted to 0.1% and 1.0% by dPCR and target sequencing, respectively. Next, we analyzed AR status in cfDNA from 102 patients. AR amplification and mutations were detected in 47 and 25 patients, respectively. As a biomarker, AR aberrations in pretreatment cfDNA were associated with poor response to abiraterone, but not enzalutamide. In serial cfDNA analysis from 41 patients, most AR aberrations at baseline diminished with effective treatments, whereas in some patients with disease progression, AR amplification or mutations emerged. The analysis of AR in cfDNA is feasible and informative procedure for treating patients with CRPC. cfDNA may become a useful biomarker for precision medicine in CRPC.

The influence of treatment sequence in the prognostic value of TMPRSS2-ERG as a biomarker of taxane resistance in castration-resistant prostate cancer.

235 Background: TMPRSS2-ERG expression at peripheral blood has been correlated with lower docetaxel benefit. This multicenter study prospectively assessed the role of TMPRSS2-ERG mRNA as a taxane-resistance biomarker in blood and retrospectively in tumors, and explored the impact of prior abiraterone/enzalutamide (A/E) in castration-resistant prostate cancer (CRPC) patients and in vitro. Methods: TMPRSS2-ERG was tested by quantitative reverse-transcription PCR. We included 204 patients (137 blood and 124 tumor samples) treated with taxanes. TMPRSS2-ERG expression was correlated with PSA-progression-free survival (PFS), radiological-PFS (RX-PFS), and overall survival (OS). Independent association with survival was evaluated by multivariate Cox modeling. ERG knockdown, combinatorial and sequential experiments with enzalutamide and docetaxel were performed in VCaP cells. Results: In the multivariate analysis prior A/E (HR: 1.833; P = 0.005) and blood TMPRSS2-ERG (HR: 2, 95%CI; 1.1-3.67; P = 0.018) , were independently associated to lower PSA-PFS. In patients without prior A/E, both blood and tumor TMPRSS2-ERG independently predicted lower PSA-PFS (HR 2.92; P = 0.014 and HR 1.82; P = 0.045, respectively) to taxanes. This was not observed in patients with prior A/E. There was a significant interaction between blood TMPRSS2-ERG detection and prior A/E related to PSA-PFS (P = 0.032) and RX-PFS (P = 0.009). In vitro stable ERG inhibition did not sensitize VCaP cells to docetaxel. Concomitant enzalutamide and taxanes were synergistic, but prior enzalutamide reduced docetaxel cytotoxicity in VCaP cells. Enzalutamide induced neuroendocrine markers and reduced E-cadherin expression. Conclusions: Prior hormone-therapy may influence taxanes response and TMPRSS2-ERG prognostic value. Thus, multiple and sequential biomarkers are needed in CRPC follow-up evaluation.

ARV-110: An oral androgen receptor PROTAC degrader for prostate cancer.

259 Background: The Androgen Receptor (AR) remains the principal driver of castration-resistant prostate cancer during the transition from a localized to metastatic disease. Most patients initially respond to inhibitors of the AR pathway, but the response is often relatively short-lived. The majority of patients progressing on enzalutamide or abiraterone exhibit genetic alterations in the AR locus, either in the form of amplifications or point mutations in the AR gene. Given these mechanisms of resistance, our goal is to eliminate the AR protein using the PROteolysis TArgeting Chimera (PROTAC) technology. Methods: Here we report an orally bioavailable small molecule AR PROTAC degrader, ARV-110, that promotes ubiquitination and degradation of AR. This molecule has been characterized in in vitro degradation and functional assays, and DMPK, toxicology and preclinical efficacy studies. Results: ARV-110 robustly degrades AR in all cell lines tested, with an observed half-maximal degradation concentration (DC50) of ~1 nM. ARV-110 treatment leads to highly selective AR degradation, as demonstrated by proteomic studies. In VCaP cells, PROTAC-mediated AR degradation suppresses the expression of the AR-target gene PSA, inhibits AR-dependent cell proliferation, and induces apoptosis at low nanomolar concentrations. Further, ARV-110 degrades clinically relevant mutant AR proteins and retains activity in a high androgen environment. In mouse xenograft studies, greater than 90% AR degradation is observed at a 1 mg/kg PO QD dose. Significant inhibition of tumor growth and AR signaling has been achieved in LNCaP, VCaP and prostate cancer patient derived xenograft (PDX) models. Notably, ARV-110 demonstrates in vivo efficacy and reduction of AR-target gene expression in a long term, castrate, enzalutamide-resistant VCaP tumor model. Conclusions: In summary, we report preclinical data on an orally bioavailable AR PROTAC degrader, ARV-110, that demonstrates efficacy in multiple prostate cancer models. ARV-110 has completed IND-enabling studies and FIH studies are planned for 1Q2019.

Long Noncoding RNA IGF2AS is Acting as an Epigenetic Tumor Suppressor in Human Prostate Cancer

ObjectiveTo assess the expression profile and functional mechanism of long noncoding RNA (lncRNA) insulin growth factor 2 antisense (IGF2AS) in human prostate cancer (PCa). MethodsQuantitative reverse transcriptase-polymerase chain reaction was applied to assess IGF2AS expression in immortal PCa cell lines and in situ human PCa tumors. IGF2AS was overexpressed in VCaP and PC3 cells to assess its effect on PCa cell proliferation and invasion in vitro, and xenograft in vivo. The effect of IGF2AS overexpression on IGF2 was also assessed in PCa cells. Then, IGF2 was upregulated in IGF2AS-overexpressed PCa cells to assess the functional involvement of IGF2 in IGF2AS-mediated PCa cell development. ResultsIGF2AS was downregulated in both PCa cell lines and human PCa tumors. In VCaP and PC3 cells, lentivirus-induced IGF2AS overexpression suppressed cancer cell proliferation and invasion in vitro, and xenograft development in vivo. IGF2 was downregulated by IGF2AS overexpression. Conversely, IGF2 upregulation revered the suppressing function of IGF2AS on PCa proliferation and invasion. ConclusionLncRNA IGF2AS is acting as an epigenetic tumor suppressor in human PCa, likely through inverse regulation on IGF2. IGF2AS/IGF2 axis may be a future therapeutic target for PCa treatment.

Lack of combination effects of soy isoflavones and taxane chemotherapy of castration-resistant prostate cancer.

Patients with cancer, including prostate cancer, often use dietary supplements, such as soy or isoflavones, before, during, or after therapy. There is little information about possible interactions between supplements and cancer chemotherapy. There are some reports suggesting enhancement by genistein of taxane chemotherapy for castrate-resistant prostate cancer (CRPC). We investigated whether physiologically attainable concentrations of soy isoflavones (≤10 μM) interact with taxanes on growth inhibition of CRPC cells in vitro and in vivo in nude mice exposed via the diet, on microtubule disassembly in vitro, and on P-glycoprotein-mediated drug efflux in 22Rv1 cells and CYP3A4 activity in microsomes. Genistein, daidzein, and equol did not affect growth of VCaP, 22Rv1, C4-2, and PC-3 CRPC cells or growth inhibition of these cells by docetaxel and cabazitaxel. These isoflavones did not inhibit microtubule disassembly in vitro or inhibit the microtubule effects of taxanes and genistein did not bind substantially to microtubules. Genistein considerably inhibited P-glycoprotein-mediated drug efflux in 22Rv1 cells and CYP3A4 activity in microsomes. However, dietary supplementation with genistein at 250 and 500 ppm did not affect the tumor growth inhibiting effect of docetaxel on 22Rv1 cells xenografted in nude mice. Our results with relevant cell models and clinically achievable concentrations of soy isoflavones do not support the notion that genistein or other soy isoflavones can enhance the effects of taxane chemotherapy in CRPC cell and xenograft models. Yet, the inhibitory effects of genistein on drug efflux in 22Rv1 cells and on microsomal CYP3A4 activity raise the possibility that genistein can affect taxane effects on CRPC cells in other circumstances than those we studied, which merits further research.

Radiosensitization by a Pyrrole-Imidazole Polyamide Through Interference with DNA Repair

Non-genotoxic small molecules that potentiate the effects of ionizing radiation in malignant cells could be used to augment radiotherapy for solid tumors. Pyrrole-imidazole (Py–Im) polyamides are synthetic non-genotoxic DNA minor groove-binding small molecules with programmable sequence specificity; binding to DNA induces allosteric changes that can interfere with protein-DNA interactions. We hypothesized that Py–Im polyamides can modulate the cellular response to ionizing radiation. The LNCaP and VCaP cell lines were used as model systems. Double (phosphorylated γ-H2AX) and single (XRCC1) DNA strand break foci were quantified by immunofluorescence. Cell viability was measured by xCELLIGence and PrestoBlue assays. Genomic fragmentation was measured by alkaline single cell gel electrophoresis. Gene expression changes were determined by RNA-sequencing. DNA ligase activity was assayed in vitro by gel-shift assay. A cell line expressing siRNA against DNA ligase 3 was used to determine if deficiency in this protein in vivo could potentiate cytotoxicity by a polyamide. Pre-treatment of cells with a Py-Im polyamide prior to exposure to ionizing radiation resulted in a delay in resolution of phosphorylated γ-H2AX foci, increase in XRCC1 foci, and reduced cellular replication potential. Polyamide treatment induced genes related to the ultraviolet radiation response. We observed that the polyamide is almost 10-fold more toxic to a cell line deficient in DNA ligase 3 as compared to the parental cell line. Alkaline single cell gel electrophoresis reveals that the polyamide induces genomic fragmentation in the ligase 3 deficient cell line but not the corresponding parental line. The polyamide interferes sequence-dependently with DNA ligation in vitro . These data support a model where a polyamide may interfere with repair of DNA strand breaks after ionizing radiation. We conclude that Py-Im polyamides may be further explored as sensitizers to genotoxic therapies.

Transcriptional Reprogramming and Inhibition of Tumor-propagating Stem-like Cells by EC-8042 in ERG-positive Prostate Cancer

BackgroundThe TMPRSS2-ERG gene fusion is the most frequent genetic rearrangement in prostate cancers and results in broad transcriptional reprogramming and major phenotypic changes. Interaction and cooperation of ERG and SP1 may be instrumental in sustaining the tumorigenic and metastatic phenotype and could represent a potential vulnerability in ERG fusion–positive tumors. ObjectiveTo test the activity of EC-8042, a compound able to block SP1, in cellular and mouse models of ERG-positive prostate cancer. Design, setting, and participantsWe evaluated the activity of EC-8042 in cell cultures and ERG/PTEN transgenic/knockout mice that provide reliable models for testing novel therapeutics in this specific disease context. Using a new protocol to generate tumor spheroids from ERG/PTEN mice, we also examined the effects of EC-8042 on tumor-propagating stem-like cancer cells with high self-renewal and tumorigenic capabilities. Outcome measurements and statistical analysisThe efficacy of EC-8042 was determined by measuring the proliferative capacity and target gene expression in cell cultures, invasive and metastatic capabilities in chick chorioallantoic membrane assays, and tumor development in mice. Significance was determined using statistical test. Results and limitationsEC-8042 blocked transcription of ERG-regulated genes and reverted the invasive and metastatic phenotype of VCaP cells. EC-8042 blocked the expansion of stem-like tumor cells in tumor spheroids from VCaP cells and mouse-derived tumors. In ERG/PTEN mice, systemic treatment with EC-8042 inhibited ERG-regulated gene transcription, tumor progression, and tumor-propagating stem-like tumor cells. ConclusionsOur data support clinical testing of EC-8042 for the treatment of ERG-positive prostate cancer in precision medicine approaches. Patient summaryIn this study, EC-8042, a novel compound with a favorable pharmacological and toxicological profile, exhibited relevant activity in cell cultures and in vivo in a genetically engineered mouse model that closely recapitulates the features of clinically aggressive ERG-positive prostate cancer. Our data indicate that further evaluation of EC-8042 in clinical trials is warranted.

Abstract B061: Alternative RNA splicing and prostate cancer aggressiveness

Abstract Prostate cancer (PCa) is the most common cancer in men in the United States. Aggressive pathology, metastasis, and drug resistance of cancer cells are the most important prognostic factors for patients with PCa. African Americans (AAs) suffer disproportionately from PCa, with higher aggressiveness, progression, and mortality. A recently published analysis involving our laboratory reported more than 2,500 alternatively RNA spliced (ARS) genes between AA and white PCa biopsy tissue specimens. Subsequent analysis revealed that, among the race-related ARS genes in PCa tissue, 19 are also ARS in breast, lung, and liver cancer. Several of the genes that are ARS across multiple tumor types are important for cancer aggressiveness, including CD44, FN1, and LMO7. We designed PCR primers to further explore the expression of LMO7 variants in preclinical models of white and AA PCa, and found that a LMO7 variant that skips exons 10, 11, and 12 is predominantly expressed in VCaP (white) and MDA PCA 2b (AA) PCa cell lines. In addition, we detected a unique race-related LMO7 splicing event that excludes exons 10 and 11, but preserves exon 12. This event is detected in MDA PCA 2b cells, but not in VCaP cells. Importantly, both of these LMO7 splicing events are in-frame and are not frameshifts leading to truncated or extended C-terminal proteins. These LMO7 variants translate to proteins of 1297 amino acids (missing 344 amino acids coded by skipped exons 10, 11, and 12) and 1287 amino acids (missing 334 amino acids coded by skipped exons 10 and 11), which differ from the full-length LMO7 variant that translates to a protein of 1631 amino acids. Interestingly, the enrichment of these variants in cancer cells suggests an important regulatory role for the amino acids encoded by the skipped exons. Further work to study the impact of LMO7 variants as well as other candidate RNA splice variants on PCa aggressiveness is ongoing, using gene overexpression, gene depletion, and splicing manipulation by siRNA or CRISPR-cas, followed by assessment of resulting alterations in growth, migration, invasion, and drug sensitivity. In summary, we have identified genes that undergo race-related ARS in multiple tumor types and novel ARS events that may functionally contribute to increased tumor aggressiveness, including that of PCa in AA men. Citation Format: Muthana Al Abo, Steven R. Patierno, Jennifer A. Freedman. Alternative RNA splicing and prostate cancer aggressiveness [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 B061.