AR-V7 Expression Research Articles

Androgen production, uptake, and conversion (APUC) genes define prostate cancer patients with distinct clinical outcomes.

BACKGROUNDProstate cancer (PC) is driven by aberrant signaling of the androgen receptor (AR) or its ligands, and androgen deprivation therapies (ADTs) are a cornerstone of treatment. ADT responsiveness may be associated with germline changes in genes that regulate androgen production, uptake, and conversion (APUC).METHODSWe analyzed whole-exome sequencing (WES) and whole-transcriptome sequencing (WTS) data from prostate tissues (SU2C/PCF, TCGA, GETx). We also interrogated the Caris Precision Oncology Alliance (POA) DNA (592-gene/whole exome) and RNA (whole transcriptome) next-generation sequencing databases. Algorithm for Linking Activity Networks (ALAN) was used to quantify all pairwise gene-to-gene associations. Real-world overall survival was determined from insurance claims data using Kaplan-Meier estimates.RESULTSSix APUC genes (HSD3B1, HSD3B2, CYP3A43, CYP11A1, CYP11B1, CYP17A1) exhibited coalescent gene behavior in a cohort of metastatic tumors (n = 208). In the Caris POA dataset, the 6 APUC genes (APUC-6) exhibited robust clustering in primary prostate (n = 4,490) and metastatic (n = 2,593) biopsies. Surprisingly, tumors with elevated APUC-6 expression had statically lower expression of AR, AR-V7, and AR signaling scores, suggesting ligand-driven disease biology. APUC-6 genes instead associated with the expression of alternative steroid hormone receptors, ESR1/2 and PGR. We used RNA expression of AR or APUC-6 genes to define 2 subgroups of tumors with differential association with hallmark pathways and cell surface targets.CONCLUSIONSThe APUC-6-high/AR-low tumors represented a subgroup of patients with good clinical outcomes, in contrast with the AR-high or neuroendocrine PCs. Altogether, measuring the aggregate expression of APUC-6 genes in current genomic tests identifies PCs that are ligand (rather than AR) driven and require distinct therapeutic strategies.FUNDINGNCI/NIH 1R37CA288972-01, NCI Cancer Center Support P30 CA077598, DOD W81XWH-22-2-0025, R01 CA249279.

Research Progress of AR Gene Family in Prostate Cancer Therapy

Prostate cancer (PCa) is a malignancy originating from the epithelial cells of the prostate gland, strongly influenced by androgens, and is one of the most common cancers in men. Androgen deprivation therapy (ADT) is the primary treatment for prostate cancer. However, after prolonged ADT treatment, nearly all patients experience an increase in prostate-specific antigen (PSA) levels and tumor regrowth. The regrowth is primarily driven by the reactivation of androgen signaling pathways within the tumor cells, leading to the development of castration-resistant prostate cancer (CRPC). The overall survival for patients with CRPC is typically less than two years. The reactivation of androgen signaling after ADT is a key mechanism leading to the progression of CRPC. In particular, abnormal expression of androgen receptor (AR) family genes, particularly AKR1C3 and AR-V7, are beleived to play central roles in the emergence of CRPC. Beyond hormonal factors, various molecular mechanisms contribute to the development of castration resistance, such as genetic mutations and the role of the tumor microenvironment. Additionally, dysregulation of signaling pathways and interactions between tumor cells and the surrounding matrix furrher promote tumor survival and growth, even in the absence of androgens. Understanding these mechanisms is essential for developing more effective treatment strategies for CRPC.

MED12 and CDK8/19 Modulate Androgen Receptor Activity and Enzalutamide Response in Prostate Cancer.

Prostate cancer progression is driven by androgen receptor (AR) activity, which is a target for therapeutic approaches. Enzalutamide is an AR inhibitor that prolongs the survival of patients with advanced prostate cancer. However, resistance mechanisms arise and impair its efficacy. One of these mechanisms is the expression of AR-V7, a constitutively active AR splice variant. The Mediator complex is a multisubunit protein that modulates gene expression on a genome-wide scale. MED12 and cyclin-dependent kinase (CDK)8, or its paralog CDK19, are components of the kinase module that regulates the proliferation of prostate cancer cells. In this study, we investigated how MED12 and CDK8/19 influence cancer-driven processes in prostate cancer cell lines, focusing on AR activity and the enzalutamide response. We inhibited MED12 expression and CDK8/19 activity in LNCaP (AR+, enzalutamide-sensitive), 22Rv1 (AR-V7+, enzalutamide-resistant), and PC3 (AR-, enzalutamide-insensitive) cells. Both MED12 and CDK8/19 inhibition reduced cell proliferation in all cell lines, and MED12 inhibition reduced proliferation in the respective 3D spheroids. MED12 knockdown significantly inhibited c-Myc protein expression and signaling pathways. In 22Rv1 cells, it consistently inhibited the AR response, prostate-specific antigen (PSA) secretion, AR target genes, and AR-V7 expression. Combined with enzalutamide, MED12 inhibition additively decreased the AR activity in both LNCaP and 22Rv1 cells. CDK8/19 inhibition significantly decreased PSA secretion in LNCaP and 22Rv1 cells and, when combined with enzalutamide, additively reduced proliferation in 22Rv1 cells. Our study revealed that MED12 and CDK8/19 regulate AR activity and that their inhibition may modulate response to enzalutamide in prostate cancer.

Increased chromatin accessibility mediated by nuclear factor I drives transition to androgen receptor splice variant dependence in castration-resistant prostate cancer.

Androgen receptor (AR) splice variants, of which ARv7 is the most common, are increased in prostate cancer (PC) that develops resistance to androgen signaling inhibitor drugs, but the extent to which these variants drive AR activity, and whether they have novel functions or dependencies, remain to be determined. We generated a subline of VCaP PC cells (VCaP16) that is resistant to the AR inhibitor enzalutamide (ENZ) and found that AR activity was independent of the full-length AR (ARfl), despite its continued high-level expression, and was instead driven by ARv7. The ARv7 cistrome and transcriptome in VCaP16 cells mirrored that of the ARfl in VCaP cells, although ARv7 chromatin binding was weaker, and strong ARv7 binding sites correlated with higher affinity ARfl binding sites across multiple models and clinical samples. Notably, although ARv7 expression in VCaP cells increased rapidly in response to ENZ, there was a long lag before it gained chromatin binding and transcriptional activity. This lag was associated with an increase in chromatin accessibility, with the AR and nuclear factor I (NFI) motifs being most enriched at these more accessible sites. Moreover, the transcriptional effects of combined NFIB and NFIX knockdown versus ARv7 knockdown were highly correlated. These findings indicate that ARv7 can drive the AR program, but that its activity is dependent on adaptations that increase chromatin accessibility to enhance its intrinsically weak chromatin binding.

AR-V7 expression facilitates accelerated G2/M phase transition in castration-resistant prostate cancer

The emergence of AR-V7, a truncated isoform of AR upon androgen deprivation therapy treatment, leads to the development of castration resistant prostate cancer (CRPC). Understanding mechanisms that regulate AR-V7 expression is critical for developing newer therapeutic strategies. In this study, we have investigated the regulation of AR-V7 during cell cycle and identified a distinct pattern of periodic fluctuation, peaking during G2/M phase. This fluctuation correlates with the expression of Cdc-2 like kinase 1 (CLK1) and phosphorylated serine/arginine-rich splicing factor 1 (p-SRSF1) during these phases, pointing towards their role in AR-V7 generation. Functional assays reveal that CLK1 knockdown prolongs the S phase, leading to altered cell cycle distribution and increased accumulation of AR-V7 and pSRSF1 in G1/S phase. Conversely, CLK1 overexpression rescues AR-V7 and p-SRSF1 levels in the G2/M phase, consistent with observed cell cycle alterations upon AR-V7 knockdown and overexpression in CRPC cells. Furthermore, overexpression of kinase-deficient CLK1 mutant leads to diminished AR-V7 levels during G2/M, underlining the essential contribution of CLK1's kinase activity in modulating AR-V7 expression. Collectively, our findings, for the first time, show periodic regulation of AR-V7 expression, its effect on cell cycle progression and the critical role of CLK1-pSRSF1 axis in modulating AR-V7 expression throughout the cell cycle.

Abstract LB027: Identifying natural inhibitors of androgen receptor (AR) and its variants from NCI Natural Product Repository

Abstract Second-generation androgen ablation therapies (ADT), enzalutamide, and abiraterone are initially effective on metastatic castration-resistant prostate cancer (mCRPC). However, nearly 30-40% of patients eventually become resistant to these treatments due to the presence of androgen-receptor variants (AR-V), which lack a ligand-binding domain. The grim reality that metastatic CRPC is virtually incurable for most patients poses a significant challenge for clinicians striving to enhance these individuals' quality of life and lifespan. Considering drug discovery efforts, we partnered with the National Cancer Institute's (NCI) Natural Product Repository, which possesses a diverse collection of natural product extracts derived from plant, marine, and microbial organisms. We developed high-throughput phenotypic screening assays to screen the crude natural product extract libraries on AR and AR-variants CRPC cell lines (C4-2B and 22Rv1). Several extracts inhibited the growth of both CRPC cell lines and were further confirmed for dose-dependent cell viability inhibition assays. Once we determined the IC50 dose, we performed a Western blot analysis that confirmed the inhibition of AR and AR-V7 expression in CRPC cells.In subsequent studies, we narrowed down by fractionating the most potent extracts and confirmed their ability to inhibit AR expression and signaling on CRPC cell lines. Currently, we are characterizing the potent compounds and their inhibitory activity on AR and AR-variants, in vitro and in vivo CRPC models. Many nutraceuticals have been shown to target AR signaling, synthesis, or degradation which effectively inhibited the growth of CRPC. Our collaborative efforts with NCI will permit us find N-terminal AR degrading molecules (AF-1), which are essential for the AR transcriptional activities of CRPC. In sum, discovery of ovel small molecules from our drug development program have the potential to translate these effective natural products into drugs with clinical benefits to treat CRPC. Citation Format: Neha Tyagi, Sepideh Hosseiniporgham, Ashish Tyagi, Balaji Chandrasekaran, Katherine Bonilla, Inna Kriger, James Saccchettini, Chendil Damodaran. Identifying natural inhibitors of androgen receptor (AR) and its variants from NCI Natural Product Repository [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB027.

Abstract LB177: Discovery of HC-4955, a novel AR-V7-targeting PROTAC for the treatment of mCRPC

Abstract Prostate cancer is the second most commonly diagnosed cancer and the second leading cause of cancer death among men worldwide. Androgens play an important role in the development and progression of prostate cancers and targeting androgen receptor (AR) signaling axis over decades has remained a mainstay of prostate cancer therapy. Next generation hormonal agents (NHAs) enzalutamide and abiraterone have brought clinical benefits for metastatic castrate-resistant prostate cancer (mCRPC) patients, AR axis-targeted therapy resistance is inevitable due to AR gene amplification or mutations. AR-V7 is the most clinically relevant AR splice variant associated with endocrine resistance and poor prognosis. AR-V7 constitutively activates AR signaling and lacks the ligand binding domain (LBD) where hormones and AR antagonists interact, resulting in resistance to AR signaling inhibitors (ARSi). Thus, AR-V7 is a promising therapeutic target to address ARSi resistance in mCRPC. We have discovered a highly potent AR-V7 proteolysis targeting chimera (PROTAC), HC-4955 that degrades both the wild-type AR (WT-AR) and AR-V7 mutant. HC-4955 degrades AR-V7 with DC50 < 5 nM. In silico molecular docking analysis predicts the binding of HC-4955 to the N-terminal domain of AR and then the essential amino acids contributed to HC-4955 binding are validated by mutational analysis studies. HC-4955 also potently degrades mutants of AR-LBD mutations including L702H and T878A and these mutations are also associated with ARSi resistance. HC-4955 strongly inhibits proliferation of ARSi-resistant prostate cancer cell lines with IC50 < 10 nM. HC-4955 shows a robust anti-tumor activity in the AR-V7-bearing 22Rv1 cell line derived tumor xenograft (CDX) and patient-derived xenograft (PDX) mouse models, with majority of the tumors completely regressed and > 90% AR-V7 expression decreased at 1-5 mg/kg (QD, PO) in these models. The pre-clinical results support the clinical development of HC-4955 for the treatment of mCRPC. Selected pre-clinical data along with the chemical structure of HC-4955 will be presented. Citation Format: Jing Li, Zhilin Tu, Wu Du, Xi Xiang, Zeyu Wen, Yang You, Lijuan Zhao, Yin Chen, Chengcheng Yang, Hongwei Yuan, Xinghai Li. Discovery of HC-4955, a novel AR-V7-targeting PROTAC for the treatment of mCRPC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB177.

Abstract 7486: Development and analytic validation of an ARv7/PSMA dual biomarker circulating tumor cell assay

Abstract Background Prostate cancer drug targets and biomarkers may be investigated non-invasively on circulating tumor cells (CTCs) obtained via liquid biopsies. PSMA is an important drug target in prostate cancer, and ARv7 is a splice variant that confers resistance to second-generation androgen receptor inhibitors. In this study, we describe the development and analytic validation of a novel assay to quantify ARv7 and PSMA protein expression on CTCs. The assay was validated with blood samples from patients with Stage IV prostate cancer to demonstrate clinical feasibility. To our knowledge, a PSMA/ARv7 dual protein assay for CTCs has not previously been reported. Methods LNCaP (PSMA positive), PC3 (PSMA negative), 22Rv1 (ARv7 positive), and BT474 (ARv7 negative) cells were spiked into healthy donor blood to generate model CTCs. Nucleated cells were collected from these spike-in samples using the AccuCyte® sample preparation kit and spread onto microscope slides. Slides were fixed and stained with antibodies to cytokeratin, EpCAM, and CD45 to detect CTCs and exclude white blood cells (WBCs), and with PSMA and ARv7 to evaluate protein expression on identified CTCs. The slides were imaged with the CyteFinder® automated immunofluorescence scanning microscope that identifies CTCs for confirmation by trained reviewers based on machine learning algorithms and quantitatively measures biomarker signal mean fluorescence intensity (MFI). Results For ARv7/PSMA expression classification of the model CTCs, the dual biomarker assay showed analytic sensitivity of 83%/97% and specificity 98%/99%, yielding accuracy of 90.2%/97.9%, respectively. The dynamic range of MFI for both biomarkers was approximately three orders of magnitude. Inter-run reproducibility CV was 13.6% (ARv7) and 6.9% (PSMA). Slide repeatability mean CV was 11.1% (ARv7) and 12.0% (PSMA). Clinical feasibility of the assay was investigated in 9 progressing Stage IV prostate cancer patient blood samples. CTCs were identified in all clinical samples (median 4, range 1 - 384). Thresholds for biomarker positivity were established based on MFI measurements of positive and negative control cell lines. ARv7 positivity in clinical samples ranged from 33% to 100%, and PSMA positivity ranged from 0% to 75%. Conclusions We have developed a dual ARv7/PSMA assay that simultaneously measures protein expression of both biomarkers on individual CTCs. The assay is accurate and reproducible for the assessment of ARv7 and PSMA expression by liquid biopsy in clinical studies. Citation Format: Jon Ladd, Erin Bayer, Brock Bartels, Eric Kaldjian, Arturo Ramirez. Development and analytic validation of an ARv7/PSMA dual biomarker circulating tumor cell assay [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 7486.

Abstract 1231: First-in-class AR-V7/AR-fl small molecule molecular glue degrader for prostate cancer treatment

Abstract Metastatic castration resistance prostate cancer (mCRPC) is a lethal disease due to the development of treatment to androgen receptor (AR) signaling inhibitors (ARSi) and taxane chemotherapy. Treatment resistance occurs partly due to the expression of AR splice variants that lack the ligand binding domain (LBD) and are constitutively active in the nucleus. AR-V7 is the most prevalent variant conferring clinical resistance to both ARSi and taxanes. Currently, there is no selective AR-V7 inhibitor leaving patients with limited therapeutic options. Thus, the development of selective AR-V7 inhibitors is a high priority, clinically unmet need. To identify AR-V7 pharmacologic inhibitors, we performed a high throughput small molecule phenotypic screen using enzymatic complementation and nuclear AR-V7 as the assay endpoint. Our primary screen of ~170K compounds (z score = 0.8), followed by a cell-toxicity counter screen and a secondary GFP screen identified hit compound 7907, as a dual AR-V7/AR-fl protein degrader, with unique chemotype compared to all known AR modulators. Hit to lead optimization by medicinal chemistry/SAR studies identified lead compound 15, with increased potency compared to 7907. Mechanistically, we showed that compound 15 shortened AR-V7 protein half-life by activating the ubiquitin-proteasome pathway and inducing proteasomal degradation of both AR-V7/AR-fl, without affecting their transcription. Importantly, compound 15 induced degradation occurred within 3hr of treatment and was blocked by the clinically approved proteasome inhibitor, bortezomib. TurboID proximity ligation assay identified distinct E3 ligases, uniquely interacting with AR-V7 or AR-fl. Using AR-V7/AR-fl deletion mutants we further showed that compound 15 activity is mediated by the N-terminal domain of AR, present in both proteins. Remarkably, compound 15 sensitized LNCaP95 cells (endogenous AR-V7/AR-fl expression) to enzalutamide suggesting potential therapeutic synergism and ability to reverse enzalutamide resistance. Ongoing studies aim to narrow down the binding site of compound 15 as well as identify the E3 ligases mediating its activity. Together, these data support a molecular glue degrader mechanism of action, consistent with published studies showing that molecular glue degraders are ideal for targeting classically “undruggable” proteins lacking an LBD or containing intrinsically disordered domains, as is the case for AR-V7. Currently, all AR-directed therapies target the LBD of AR-fl, inhibiting AR signaling. AR-V7 expression is a direct outcome of this inhibition, leading to AR-fl and AR-V7 co-expression in patient tumors. We posit that our drug candidate, by offering dual AR-V7/AR-fl inhibition in a single treatment, has the potential to not only benefit patients with mCRPC but also patients with hormone-sensitive disease, and delay AR-V7 expression. Citation Format: CheukMan C. Au, Catrina Estrella, Prerna Vatsa, Michelle Naidoo, Michael Miller, Peter T. Meinke, David M. Nanus, Paraskevi Giannakakou. First-in-class AR-V7/AR-fl small molecule molecular glue degrader for prostate cancer treatment [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 1231.

Abstract 6562: Comprehensive liquid biopsy: Multi-analyte evaluation of cellular and plasma components of blood in prostate cancer from a single blood collection tube

Abstract Background Liquid biopsy samples offer a non-invasive method for investigating drug targets and biomarkers in solid tumors. In this study, we describe a comprehensive liquid biopsy analysis of whole blood to identify circulating tumor cells (CTCs), large extracellular vesicles and CTC fragments, and CTC-white blood cell hybrids; quantify protein biomarker expression on CTCs; perform targeted mutation profiling on CTCs and cell-free DNA (cfDNA) from plasma; and analyze protein expression on white blood cells (WBCs) from a single 7.5 mL blood sample. This array of tests was applied to blood samples from patients with Stage IV prostate cancer to demonstrate clinical feasibility. Methods A novel dual biomarker CTC assay was developed to measure protein expression of PSMA and ARv7 on CTCs from stage IV prostate cancer patients. Nucleated cells from clinical samples were processed to microscope slides using AccuCyte®, an unbiased, density-based separation method that also allows for plasma collection for downstream analysis. Slides were fixed and stained with antibodies to cytokeratin, EpCAM, and CD45 to detect CTCs and exclude WBCs, and with PSMA and ARv7 to evaluate protein biomarker expression on identified CTCs. The slides were imaged with the CyteFinder® automated immunofluorescence scanning microscope that identifies CTCs for confirmation by trained reviewers and quantitatively measures protein mean fluorescence intensity (MFI) on any cells detected on the slides (CTCs, CTC-WBC hybrids, large extracellular vesicles and CTC fragments and WBCs). Individual CTCs and control pools of WBCs from clinical samples with at least 4 CTCs were picked using CytePicker®, a needle-based system used to isolate single cells. cfDNA was isolated from plasma removed during the AccuCyte® process using a QIAamp MinElute ccfDNA kit. Picked CTCs, WBC pools, and isolated ctDNA were sequenced using the OncoZoom Cancer HotSpot panel from Paragon Genomics. Results Nine progressing Stage IV prostate cancer patient blood samples were stained with a novel PSMA/ARv7 dual biomarker assay. CTCs were identified in all clinical samples (median 4, range 1 - 384). PSMA positivity in clinical samples ranged from 0% to 75%, and ARv7 positivity ranged from 33% to 100%, and. Additional analysis using QuPath was performed to determine PSMA/ARv7 protein expression on WBCs and CTC fragments. ctDNA analysis from 5 individual samples was compared to sequencing results from individual CTCs from the same samples. Conclusions Using a single 7.5 mL blood liquid biopsy, we can measure protein expression on enumerated CTCs and quantify these same protein biomarkers on WBCs and CTC fragments/oncosomes, determine the genetic makeup of the tumor through the sequencing of cfDNA, and monitor genetic mutations in intact CTCs in circulation. Citation Format: Jon Ladd, Erin Bayer, Brock Bartels, Arista Tischner, Rachel Ponting, Eric Kaldjian, Arturo Ramirez. Comprehensive liquid biopsy: Multi-analyte evaluation of cellular and plasma components of blood in prostate cancer from a single blood collection tube [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 6562.

Circulating and Imaging Biomarkers of Radium-223 Response in Metastatic Castration-Resistant Prostate Cancer.

Radium-223 improves overall survival (OS) and reduces skeletal events in patients with bone metastatic castration-resistant prostate cancer (CRPC), but relevant biomarkers are lacking. We evaluated automated bone scan index (aBSI) and circulating tumor cell (CTC) analyses as potential biomarkers of prognosis and activity. Patients with bone metastatic CRPC were enrolled on a prospective single-arm study of standard radium-223. 99mTc-MDP bone scan images at baseline, 2 months, and 6 months were quantitated using aBSI. CTCs at baseline, 1 month, and 2 months were enumerated and assessed for RNA expression of prostate cancer-specific genes using microfluidic enrichment followed by droplet digital polymerase chain reaction. The median OS was 21.3 months in 22 patients. Lower baseline aBSI and minimal change in aBSI (<+0.7) from baseline to 2 months were each associated with better OS (P = .00341 and P = .0139, respectively). The higher baseline CTC count of ≥5 CTC/7.5 mL was associated with worse OS (median, 10.1 v 32.9 months; P = .00568). CTCs declined at 2 months in four of 15 patients with detectable baseline CTCs. Among individual genes in CTCs, baseline expression of the splice variant AR-V7 was significantly associated with worse OS (hazard ratio, 5.20 [95% CI, 1.657 to 16.31]; P = .00195). Baseline detectable AR-V7, higher aBSI, and CTC count ≥5 CTC/7.5 mL continued to have a significant independent negative impact on OS after controlling for prostate-specific antigen or alkaline phosphatase. Quantitative bone scan assessment with aBSI and CTC analyses are prognostic markers in patients treated with radium-223. AR-V7 expression in CTCs is a particularly promising prognostic biomarker and warrants validation in larger cohorts.

Therapeutic Potential of Bipolar Androgen Therapy for Castration-Resistant Prostate Cancer: In Vitro and In Vivo Studies.

Androgen deprivation therapy (ADT) is a primary treatment for advanced prostate cancer (PCa), but resistance often leads to castration-resistant PCa (CRPC). CRPC remains androgen receptor (AR)-dependent, and AR overexpression causes vulnerability to high doses of androgen in CRPC. Bipolar androgen therapy (BAT) refers to the periodic administration of testosterone, resulting in oscillation between supraphysiologic and near-castrate serum testosterone levels. In this study, we evaluated the efficacy of BAT against CRPC in a preclinical setting. To emulate CRPC characteristics, PCa cell lines (LNCaP, VCaP, and 22Rv1) were cultured in phenol red-free RPMI-1640 medium supplemented with 10% dextran-coated charcoal treated FBS (A- cell line). Cell viability, AR, and AR-V7 expression were evaluated using the Cell Counting Kit-8 and Western blotting. In vivo studies involved 12 castrated NOG mice injected with LNCaP/A- cells, treated with testosterone pellets or controls in 2-week cycles. Tumor sizes were measured post a 6-week treatment cycle. Bicalutamide inhibited PCa cell viability but not in the adapted cell lines. Supraphysiologic androgen levels suppressed AR-expressing PCa cell growth in vitro. In vivo, high AR-expressing LNCaP cells proliferated under castrate conditions, while BAT-treated xenografts exhibited significant growth inhibition with low Ki-67 and mitotic indexes and a high cell death index. This study provides preliminary evidence that BAT is effective for the treatment of CRPC through rapid cycling between supraphysiologic and near-castrate serum testosterone levels, inducing an anti-tumor effect.

Abstract A021: Reactive osteogenic-niche regulation of endocrine resistance in prostate cancer bone metastases: Role of tenascin-C induced metabolic shift in regulating therapeutic resistance in prostate cancer

Abstract Background: The main objective of the study is to investigate the regulatory role of reactive osteogenic niche in evolution of therapeutic resistance in prostate cancer bone metastases. Prostate cancer that metastasize to the bone develop into an androgen insensitive/therapeutic resistant state known as metastatic castration resistance prostate cancer (mCRPC). In bone, prostate cancer cells spatially associate with reactive osteogenic niche typified with elevated expression of the repair-associated, extracellular matrix protein- tenascin-C. Our recent finding show that tenascin-C regulates splicing and post-translational stability of therapeutic resistant- androgen receptor splice variant- AR-V7. Expression of AR-V7 and induction of de novo lipogenesis is observed to co-evolve in mCRPC. In this study, we evaluated the role of tenascin-C in regulating de novo lipogenesis in prostate cancer cells and its association with AR-V7 expression. Methods: Immunofluorescence imaging were conducted to assess spatial localization of lipids using BODIPY 493/503 in prostate cancer cells interacting with tenascin-C- expressing osteogenic cells-preosteoblast using a novel heterotypic 3D organoid model. Prostate cancer cells cultured on tenascin-C were subjected to lipidomic analysis using LC-MS for characterization of tenascin-C induced lipid accumulation. RT-qPCR and Western blotting were conducted to evaluate differential regulation of enzymes involved in de novo lipogenesis by tenascin-C. siRNA and small molecular inhibitors were utilized to evaluate molecular association between tenascin-C, enzymes regulating de novo lipogenesis, and AR-V7 in prostate cancer cells. Results: Imaging of heterotypic organoids revealed lipid accumulation in prostate cancer cells interacting with tenascin-C expressing preosteoblasts. Lipidomic analysis confirmed tenascin-C induced enrichment of neutral lipids such as di and triglycerides in prostate cancer cells, a novel finding. Tenascin-C also induced expression of enzymes regulating de novo lipogenesis such as acetyl-CoA carboxylase alpha (ACACA) and fatty acid synthase (FASN) in prostate cancer cells (p˂ 0.01). Assessment of clinical transcriptomic datasets confirm significant upregulation of both tenascin-C and specifically ACACA in prostate cancer bone metastases compared to other visceral metastatic sites (p=1E-10, p=1E-7). Importantly, we observed tenascin-C induced upregulation of ACACA and FASN expression in prostate cancer cells was impeded by AR-V7 knockdown. Conversely, inhibition of ACACA activity (CP-640186 at 0.5 uM) also suppressed AR-V7 protein expression in prostate cancer cells. Conclusions: In summary, this study suggests a complex functional association between a reactive osteogenic niche component -tenascin-C, and AR-V7 expression with de novo lipogenesis in prostate cancer cells. Targeting to uncouple the tenascin-C regulated de novo lipogenesis in prostate cancer cells may be a promising therapeutic strategy to prevent evolution of AR-V7 expression and development of mCRPC. Citation Format: Rintu T. Thomas, David R. Rowley. Reactive osteogenic-niche regulation of endocrine resistance in prostate cancer bone metastases: Role of tenascin-C induced metabolic shift in regulating therapeutic resistance 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 A021.

Abstract A019: Enzalutamide resistance is driven by adaptations that enhance AR splice variant and FOXA1 activities

Abstract Prostate cancer (PCa) that progresses on therapy with an androgen receptor (AR) inhibitor such as enzalutamide (Enz) generally continues to express high levels of transcriptionally active AR, but mechanisms driving this persistent AR activity remain to be established. These tumors also generally express increased levels of AR splice variants that lack the ligand binding domain and hence have androgen-independent activity (with ARv7 being the most common), but the extent to which these variants contribute to AR activity, and their dependence on the full length AR (ARfl), also remain unclear. We found Enz treatment initially suppressed AR activity in VCaP cells, despite an increase in ARv7 splice variant, while Enz-resistant VCaP cells (VCaPEnzR) generated by prolonged culture in Enz had restoration of AR transcriptional activity. Notably, this restored AR activity was not associated with further increases in ARv7 expression. However, by ChIP-seq we found it was associated with increased ARv7 chromatin binding, with ARv7 binding at a subset of the sites occupied by ARfl, but not at any unique sites. Moreover, approaches using RNAi and an AR degrader targeting ARfl showed that ARv7 was the major driver of AR transcriptional activity in the VCaPEnzR cells, despite much higher levels of ARfl expression, and was not dependent on ARfl. ATAC-seq showed there was a global increase in chromatin accessibility in the VCaPEnzR cells, with the greatest increase being at ARv7 sites. This suggested these sites had decreased nucleosome occupancy, which was confirmed by MNase-seq. As FOXA1 can act as a pioneer factor to open chromatin, we next carried out FOXA1 ChIP-seq. This showed increased FOXA1 binding across all FOXA1 sites in the VCaPEnzR cells versus parental VCaP, with the greatest increases being at ARv7 binding sites and at sites that showed the greatest increases in accessibility by ATAC-seq. Notably, frameshift mutations in the C-terminus of FOXA1 are found at increased frequency in castration-resistant prostate cancer (CRPC) and may enhance FOXA1 activity, but FOXA1 was not mutated in the VCaPEnzR versus parental VCaP cells. Mass spectrometry then identified posttranslational modifications (PTMs) in FOXA1 that have been previously reported in PCa, including K270 methylation that can impair FOXA1 chromatin binding, but this was not consistently decreased in VCaPEnzR cells. In contrast, we found consistent increases in phosphorylation at C-terminal sites including T334 and Y429. Notably, the Y429 phosphorylation was reported previously to enhance FOXA1 chromatin binding and estrogen receptor activity. Together these findings indicate that progression to Enz-resistance is dependent on adaptations that enhance ARv7 activity. These adaptations include increasing chromatin accessibility at ARv7 binding sites, which may be driven by PTMs in FOXA1. Citation Format: Betul Ersoy-Fazlioglu, Larysa Poluben, Mannan Nouri, Henry W. Long, Joshua W. Russo, Steven P. Balk. Enzalutamide resistance is driven by adaptations that enhance AR splice variant and FOXA1 activities [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 A019.

PD04-09 COMBINATION TREATMENT WITH HSP70/STUB1 MODULATOR AND ENZALUTAMIDE YIELDS SYNERGISTIC ACTIVITY IN ADVANCED PROSTATE CANCER

You have accessJournal of UrologyCME1 Apr 2023PD04-09 COMBINATION TREATMENT WITH HSP70/STUB1 MODULATOR AND ENZALUTAMIDE YIELDS SYNERGISTIC ACTIVITY IN ADVANCED PROSTATE CANCER Pengfei Xu, Joy C. Yang, Bo Chen, Christopher Nip, Shu Ning, Allen C. Gao, Hao Shao, Jason Gestwicki, Christopher P. Evans, and Chengfei Liu Pengfei XuPengfei Xu More articles by this author , Joy C. YangJoy C. Yang More articles by this author , Bo ChenBo Chen More articles by this author , Christopher NipChristopher Nip More articles by this author , Shu NingShu Ning More articles by this author , Allen C. GaoAllen C. Gao More articles by this author , Hao ShaoHao Shao More articles by this author , Jason GestwickiJason Gestwicki More articles by this author , Christopher P. EvansChristopher P. Evans More articles by this author , and Chengfei LiuChengfei Liu More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003228.09AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Ubiquitin proteasome system is suppressed in enzalutamide resistant prostate cancer cells and that the HSP70/STUB1 machinery is involved in androgen receptor (AR) and AR variant protein stabilization. Targeting HSP70 could be a valuable strategy to overcome the resistance of androgen receptor signaling inhibitors (ARSI) in advanced prostate cancer. In this study, we tested novel HSP70/STUB1modulators in enzalutamide resistant cells and patient-derived prostate cancer cell models. METHODS: Expression of AR-V7, HSP70 and STUB1 were determined by qRT-PCR and western blot. Expression of HSP70 and STUB1 was down-regulated using specific siRNA. HSP70/STUB1 and AR-V7 interaction was determined by co-immunoprecipitation and dual immunofluorescence. Tumor organoids were established from the patient derived xenografts (PDX) and the viability was stained by LIVE/DEAD™ Cell Imaging Kit. The effects of HSP70 inhibitors on enzalutamide sensitivity were examined in cell line model and patient-derived cell models. RESULTS: A novel HSP70 inhibitor JG98 significantly suppressed drug resistant C4-2B MDVR and CWR22Rv1 cell growth and enhanced enzalutamide treatment (p<0.001). JG98 also suppressed the PDX derived organoid growth and induced organoid death in a dose dependent manner (p<0.001). Mechanistically, JG98 suppressed AR/AR-V7 expression in resistant cells and promoted STUB1 entering into the nucleus and bound to AR-V7. Knockdown of STUB1 diminished the anti-cancer effect and AR-V7 inhibition by JG98. A more potent HSP70 inhibitor JG231 was developed from JG98. JG231 significantly improved the drug solubility and showed better pharmacokinetic characteristics than JG98. Moreover, JG231 effectively suppressed the cell growth and enhanced enzalutamide treatment in resistant cells and PDX derived prostate cancer cells (p<0.001). CONCLUSIONS: The HSP70/STUB1 machinery involved in AR/AR-V7 regulation and enzalutamide resistance. Targeting HSP70 by novel HSP70/STUB1 modulators overcome the ARSI resistance and improve their therapy. Source of Funding: This work was supported in part by grants NIH/NCI R37CA249108 (C, Liu) and R01CA251253 (C, Liu) © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e145 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Pengfei Xu More articles by this author Joy C. Yang More articles by this author Bo Chen More articles by this author Christopher Nip More articles by this author Shu Ning More articles by this author Allen C. Gao More articles by this author Hao Shao More articles by this author Jason Gestwicki More articles by this author Christopher P. Evans More articles by this author Chengfei Liu More articles by this author Expand All Advertisement PDF downloadLoading ...

Expression and Therapeutic Targeting of TROP-2 in Treatment-Resistant Prostate Cancer.

Men with metastatic castration-resistant prostate cancer (mCRPC) frequently develop resistance to androgen receptor signaling inhibitor (ARSI) treatment; therefore, new therapies are needed. Trophoblastic cell-surface antigen (TROP-2) is a transmembrane protein identified in prostate cancer and overexpressed in multiple malignancies. TROP-2 is a therapeutic target for antibody-drug conjugates (ADC). TROP-2 gene (TACSTD2) expression and markers of treatment resistance from prostate biopsies were analyzed using data from four previously curated cohorts of mCRPC (n = 634) and the PROMOTE study (dbGaP accession phs001141.v1.p1, n = 88). EPCAM or TROP-2-positive circulating tumor cells (CTC) were captured from peripheral blood for comparison of protein (n = 15) and gene expression signatures of treatment resistance (n = 40). We assessed the efficacy of TROP-2-targeting agents in a mouse xenograft model generated from prostate cancer cell lines. We demonstrated that TACSTD2 is expressed in mCRPC from luminal and basal tumors but at lower levels in patients with neuroendocrine prostate cancer. Patients previously treated with ARSI showed no significant difference in TACSTD2 expression, whereas patients with detectable AR-V7 expression showed increased expression. We observed that TROP-2 can serve as a cell surface target for isolating CTCs, which may serve as a predictive biomarker for ADCs. We also demonstrated that prostate cancer cell line xenografts can be targeted specifically by labeled anti-TROP-2 agents in vivo. These results support further studies on TROP-2 as a therapeutic and diagnostic target for mCRPC.

LOX-1 Activation by oxLDL Induces AR and AR-V7 Expression via NF-κB and STAT3 Signaling Pathways Reducing Enzalutamide Cytotoxic Effects.

The oxidized low-density lipoprotein receptor 1 (LOX-1) is one of the most important receptors for modified LDLs, such as oxidated (oxLDL) and acetylated (acLDL) low-density lipoprotein. LOX-1 and oxLDL are fundamental in atherosclerosis, where oxLDL/LOX1 promotes ROS generation and NF-κB activation inducing the expression of IL-6, a STAT3 activator. Furthermore, LOX-1/oxLDL function has been associated with other diseases, such as obesity, hypertension, and cancer. In prostate cancer (CaP), LOX-1 overexpression is associated with advanced stages, and its activation by oxLDL induces an epithelial-mesenchymal transition, increasing angiogenesis and proliferation. Interestingly, enzalutamide-resistant CaP cells increase the uptake of acLDL. Enzalutamide is an androgen receptor (AR) antagonist for castration-resistant prostate cancer (CRPC) treatment, and a high percentage of patients develop a resistance to this drug. The decreased cytotoxicity is promoted in part by STAT3 and NF-κB activation that induces the secretion of the pro-inflammatory program and the expression of AR and its splicing variant AR-V7. Here, we demonstrate for the first time that oxLDL/LOX-1 increases ROS levels and activates NF-κB, inducing IL-6 secretion and the activation of STAT3 in CRPC cells. Furthermore, oxLDL/LOX1 increases AR and AR-V7 expression and decreases enzalutamide cytotoxicity in CRPC. Thus, our investigation suggests that new factors associated with cardiovascular pathologies, such as LOX-1/oxLDL, may also promote important signaling axes for the progression of CRPC and its resistance to drugs used for its treatment.

Using the AR-V7 biomarker to determine treatment in metastatic castrate resistant prostate cancer, a feasibility randomised control trial, conclusions from the VARIANT trial [version 2; peer review: 2 approved

Prostate cancer is the most commonly diagnosed malignancy in the UK. Castrate resistant prostate cancer (CRPC) can be difficult to manage with response to next generation hormonal treatment variable. AR-V7 is a protein biomarker that can be used to predict response to treatment and potentially better inform management in these patients.Our aim was to establish the feasibility of conducting a definitive randomised controlled trial comparing the clinical utility of AR-V7 biomarker assay in personalising treatments for patients with metastatic CRPC within the United Kingdom (UK) National Health Service (NHS). Due to a number of issues the trial was not completed successfully, we aim to discuss and share lessons learned herein. We conducted a randomised, open, feasibility trial, which aimed to recruit 70 adult men with metastatic CRPC within three secondary care NHS trusts in the UK to be run over an 18-month period. Participants were randomised to personalised treatment based on AR-V7 status (intervention) or standard care (control). The primary outcome was feasibility, which included: recruitment rate, retention and compliance. Additionally, a baseline prevalence of AR-V7 expression was to be estimated. Fourteen participants were screened and 12 randomised with six into each arm over a nine-month period. Reliability issues with the AR-V7 assay meant prevalence was not estimated. Due to limited recruitment the study did not complete to target. Whilst the trial did not complete to target, we have ascertained that men with advanced cancer are willing to take part in trials utilising biomarker guided treatment. A number of issues were identified that serve as important learning points in future clinical trials.

Prostate fibroblasts enhance androgen receptor splice variant 7 expression in prostate cancer cells

Androgen receptor splice variant (AR-V) expression has been associated with prostate cancer (PCa) progression to castration-resistant PCaduring androgen deprivation therapy, which reduces androgen production and inhibits androgen action in PCa cells. However, the mechanisms whereby aberrant AR-V expression is increased in PCa are still largely unknown. Fibroblasts in tumor stroma influence PCa initiation and aggressiveness, and which may play a crucial role in eliciting genetic changes during malignant transformation in human prostate epithelium. Here, our aim was to determine whether prostate fibroblasts in tumor stroma induce aberrant AR-V7 expression in PCa cells under low androgen concentration. We performed in vitro experiments using androgen-sensitive, AR-positive PCa cell lines (LNCaP and 22Rv1 cells), commercially available prostate stromal cells (PrSC), and primary cultured prostate fibroblasts (pcPrF) from PCa specimens collected from biopsies of patients with advanced PCa. PCa cells were cocultured with each of the three fibroblast lines (PrSC, pcPrF-M37, and pcPrF-M48). The proliferation under low androgen concentration of LNCaP and 22Rv1 cells cocultured with PrSC, pcPrF-M37, or pcPrF-M48 was significantly increased compared to that of PCa cells cultured alone. Androgen receptor-full length (AR-FL) protein expression was increased in LNCaP and 22Rv1 cells cocultured with PrSC, pcPrF-M37, or pcPrF-M48. AR-V7 protein expression was increased in 22Rv1 cells cocultured with PrSC, pcPrF-M37, or pcPrF-M48. Under low androgen concentration, AR-V7 protein expression was slightly detected in LNCaP cells cocultured with PrSC or pcPrF-M37. Cytokine array analysis revealed that monocyte chemotactic protein-1 (MCP-1) and interleukin-8 (IL-8) levels in the conditioned medium of 22Rv1 cells cocultured with PrSC, pcPrF-M37, or pcPrF-M48 were increased under low androgen concentration. High IL-8 concentration (30 ng/ml) resulted in significantly increased protein expression of AR-FL, AR-V7, and phospho-NF-κB p65 in 22Rv1 cells. In contrast, IL-8 antibody (1 µg/ml) decreased AR-V7 protein expression in 22Rv1 cells cocultured with PrSC, pcPrF-M37, or pcPrF-M48. pcPrF from PCa specimens increase the expression of aberrant AR-V7 in PCa cells. IL-8 may be a target for preventing the expression of aberrant AR-Vs in PCa.

Synthesis and biological activity of 21,22-cyclosteroids and their derivatives

Synthesis of 21,22-cyclosteroids has been achieved starting from pregnenolone acetate. The key transformation was the Kulinkovich reaction of 17-vinyl steroids with esters. The resulting cyclopropanols were further subjected to three-membered ring-opening under various conditions including to base-, palladium or visible light-promoted isomerization and cross-coupling reaction. A number of steroidal Δ2-6-ketones and 3β-hydroxy-Δ5-enes with functional groups at C-21 - C-23 have been synthesized via the 21,22-cyclosteroids. The antiproliferative and antihormonal activity of the obtained compounds on the cell lines of prostate (22Rv1) and breast (MCF-7) cancer was studied. The androgen receptor activity was assessed by reporter assay when the expression of signalling proteins was evaluated by immunoblotting. (20S,22R)–22-Acetoxy-21,22-cyclo-5α-cholest-5-ene with the moderate antiandrogenic potency revealed IC50 values of 18.4 ± 1.2 and 14.6 ± 1.4 µM against MCF-7 and 22Rv1 cells, respectively, and its effects on the expression of AR-V7, cyclin D1 and BCL2 were explored.