Androgen Receptor Splice Variant 7 Expression Research Articles

Prognostic role of Androgen Receptor splice variant 7 (AR-V7) in the pathogenesis of breast cancer.

The Androgen Receptor (AR) has emerged as an endocrine therapy target in Breast Cancer, exhibiting up to 80% expression in clinical cases. AR-V7, a constitutively activated splice variant of AR with a truncated ligand-binding domain (LBD), demonstrates ligand-independent transcriptional activity and resistance to nonsteroidal antiandrogens like Bicalutamide or Enzalutamide, targeting the LBD. In metastatic prostate cancer, elevated AR-V7 levels lead to therapeutic resistance and increased metastasis. In this study, we evaluated the expression of AR and AR-V7 in cell lines and a cohort of 89 patients undergoing surgical intervention for treatment-naïve breast cancer. Further clinicopathological correlations and survival analysis were performed to evaluate the relationship between the AR and AR-V7 expression and clinical outcomes. AR-V7/AR-FL ratio was elevated in the TNBC cell line and downregulation of AR-FL upon AR antagonists' treatment led to a compensatory increase in AR-V7. Clinical samples showed significantly elevated expression of AR and AR-V7 in tumors compared to control cases. Further clinicopathological correlation revealed aggressive clinical traits, higher pathological grades, and poor survival with AR-V7 expression. Our study unravels AR-V7 as a marker for poor clinical outcomes, predicting breast cancer aggressiveness, and encourages consideration of AR-V7 as a probable target for therapeutic intervention.

Targeting the CLK2/SRSF9 splicing axis in prostate cancer leads to decreased ARV7 expression.

In advanced prostate cancer (PC), in particular after acquisition of resistance to androgen receptor (AR) signaling inhibitors (ARSI), upregulation of AR splice variants compromises endocrine therapy efficiency. Androgen receptor splice variant-7 (ARV7) is clinically the most relevant and has a distinct 3' untranslated region (3'UTR) compared to the AR full-length variant, suggesting a unique post-transcriptional regulation. Here, we set out to evaluate the applicability of the ARV7 3'UTR as a therapy target. A common single nucleotide polymorphism, rs5918762, was found to affect the splicing rate and thus the expression of ARV7 in cellular models and patient specimens. Serine/arginine-rich splicing factor 9 (SRSF9) was found to bind to and increase the inclusion of the cryptic exon 3 of ARV7 during the splicing process in the alternative C allele of rs5918762. The dual specificity protein kinase CLK2 interferes with the activity of SRSF9 by regulating its expression. Inhibition of the Cdc2-like kinase (CLK) family by the small molecules cirtuvivint or lorecivivint results in the decreased expression of ARV7. Both inhibitors show potent anti-proliferative effects in enzalutamide-treated or -naive PC models. Thus, targeting aberrant alternative splicing at the 3'UTR of ARV7 by disturbing the CLK2/SRSF9 axis might be a valuable therapeutic approach in late stage, ARSI-resistant PC.

Caffeic acid phenethyl ester suppresses the expression of androgen receptor variant 7 via inhibition of CDK1 and AKT.

Androgen receptor (AR) splice variant 7 (AR-V7) is capable to enter nucleus and activate downstream signaling without ligand. AR-V7 assists the tumor growth, cancer metastasis, cancer stemness, and the evolvement of therapy-resistant prostate cancer (PCa). We discovered that caffeic acid phenethyl ester (CAPE) can repress the expression and downstream signaling of AR-V7 in PCa cells. CAPE blocked the gene transcription, nuclear localization, and protein abundance of AR-V7. CAPE inhibited the expression of U2AF65, SF2 and hnRNPF, which were splicing factors for AR-V7 intron. Additionally, CAPE decreased protein stability of AR-V7 and enhanced the proteosome-degradation of AR-V7. We observed that CDK1 and AKT regulated the expression and stability of AR-V7 via phosphorylation of Ser81 and Ser213, respectively. CAPE decreased the expression of CDK1 and AKT. Overexpression of CDK1 restored the abundance of AR-V7 in CAPE-treated PCa cells. Overexpression of AR-V7, AKT or CDK1 rescued the proliferation of PCa cells under CAPE treatment. Intraperitoneal injection of 10 mg/kg CAPE retarded the growth of 22Rv1 xenografts in nude mice and suppressed the protein levels of AR-V7, CDK1 and AKT in 22Rv1 xenografts. Our study provided the rationale of applying CAPE for inhibition of AR-V7 in prostate tumors.

Simultaneous detection of tumor-derived mutations in DNA and RNA extracted from a single circulating tumor cell based on droplet digital polymerase chain reaction.

e15053 Background: Androgen receptor splice variant 7 (AR-V7) is a constitutively activated isoform of AR and has been associated with resistance to AR-targeted therapies and development of metastatic castration-resistant prostate cancer. Confirmation of AR-V7 expression is important step in prostate cancer diagnosis and determining the appropriate drug, however, the detection of AR-V7 with tissues has limitations, such as the clinical challenge to poorly accessible tumor tissues before and after therapy. In addition, KRAS mutations serve as a prognostic biomarker for the administration of appropriate anti-cancer drugs in patients with various cancers, including non-small cell lung cancer (NSCLC). Here, we developed the process for the simultaneous detection of AR-V7 and KRAS mutation in CTCs using isolation with CytoGen’s Smart Biopsy™ System with droplet digital polymerase chain reaction (ddPCR) with high sensitivity and specificity, overcoming the limitations of tissue biopsy. Methods: ddPCR assays were performed to detect the KRAS G12C mutation using CTC gDNA and to evaluate the absolute levels of AR-V7 using CTC mRNA. Analytical validation was performed using NSCLC NCI-H358 and prostate cancer 22Rv1 cells (10 and 5 cells each), which harbor KRAS G12C and AR-V7, respectively, spiked into 5 mL of healthy blood to mimic CTC. CTCs were isolated using CytoGen's Smart Biopsy™ System. Oligo-dT magnetic beads were used to isolate mRNA from CTCs, and gDNA was isolated from the mRNA-depleted CTC lysates using the AllPrep DNA/mRNA Nano Kit. PCR and droplet reading for each assay were performed on the QX200 AutoDG Droplet Digital PCR System. Results: As a result of CTC KRAS G12C detection using the ddPCR™ KRAS G12/G13 Screening Kit, the mutated KRAS gene was successfully detected in as few as 5 NCI-H358 cells. In the results of CTC AR-V7 detection using the custom TaqMan ddPCR assay, transcripts (AR-V7 and HPRT1) were successfully detected even with only 5 22Rv1 cells. These results suggest that CytoGen's Smart Biopsy™ System could be applied to the simultaneous detection of DNA/RNA mutated genes in clinical NSCLC and prostate cancer patients with detection technology requiring high sensitivity and specificity. Conclusions: Accurately detecting multiple genetic mutations in CTCs is a challenging because CTCs are very rare in the blood. In this study, we developed the process to simultaneously extract and detect DNA mutations and RNA splicing variants in CTCs using CytoGen's Smart Biopsy™ System. This process, along with the results from our ongoing clinical trials, could provide information for the diagnosis and appropriate treatment of patients with various cancers, including NSCLC and prostate cancer.

Abstract 7505: Detection validation of androgen-receptor splice variant 7 in circulating tumor cells of prostate cancer by double-check assays

Abstract Introduction: Androgen-receptor splice variant 7 (AR-V7) is constitutively activated isoform of AR and has been associated with resistance towards AR targeting therapies and development into mCRPC. Confirmation of AR-V7 expression is important step in prostate cancer diagnosis and determining the drug, but the detection of AR-V7 with tissues has limitations such as clinical challenge to poorly accessible tumor tissues before and after treatment. Here, we developed the method of AR-V7 detection in circulating tumor cells (CTC) after isolation with CytoGen’s Smart BiopsyTM CTC isolator by in vitro assays of qPCR and immunofluorescence (IF) with high sensitivity and specificity, overcoming the limitations of tissue biopsy. Method: qPCR and IF methods were developed for high sensitivity and specificity of AR-V7 detection. Sensitivity and specificity were tested using AR-V7 positive cells (VCaP and 22Rv1) and negative cells (PC-3 and Raji). Limit of detection (LOD) test of AR-V7 expression was performed with AR-V7 positive cells (200 cells to 50 cells, 3 points) mixed with Raji cells (1 × 10^5cells). Then, AR-V7 positive cells (200 cells to 50 cells, 3 points) were spiked into peripheral blood mononuclear cells (PBMC) of blood sample (5mL, healthy donor) to mimic CTC after isolation by CytoGen’s Smart BiopsyTM CTC isolator, subsequently AR-V7 expression was tested with qPCR and IF assay. Results: AR-V7 expression was clearly detected by qPCR and IF in the LOD test of AR-V7 positive cells mixed with Raji cells and was not detected at all in the negative controls. The similar clear results were also observed in the spiking test of AR-V7 positive cells into PBMC isolated by CytoGen’s Smart BiopsyTM CTC isolator, suggesting that clinical samples of prostate cancer could be applied with excellent sensitivity and specificity for AR-V7. Conclusions: AR-V7 expresses only a part of cancer tissue, so it is difficult to accurately diagnose with traditional histological assays. Detection of AR-V7 in intact live CTC isolated by CytoGen’s Smart BiopsyTM CTC isolator might overcome limitations of tissue biopsy. In this study, we developed the method to detect AR-V7 in CTC with high sensitivity and specificity with qPCR and IF assay, and presented the results of verifying AR-V7 expression by double check using two kinds of assays. We plan to conduct clinical validation of the developed method through additional study using patient samples. Citation Format: Hoin Kang, Jihyun Lee, Min Hyung Kim, Soee Kim, Hyoyong Kim, Jubi Lee, Hae Ung Lee, Hai-Chon Lee, Jung Won Kim. Detection validation of androgen-receptor splice variant 7 in circulating tumor cells of prostate cancer by double-check assays [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 7505.

Abstract A080: Establishment and characterization of a panel of prostate cancer XPDX models with differential AR-V7 staining and enzalutamide response

Abstract Background: Truncated androgen receptor splice variant-7 (AR-V7) expression is associated with prostate cancer progression and resistance to AR-directed therapy. To better understand the role of AR-V7 in prostate cancer, we compared IHC-based AR-V7, full length AR and PSMA protein expression in 9 prostate adenocarcinoma (PAC) XPDX and 5 prostate neuroendocrine tumors (PNEC) XPDX models and correlated expression to in vivo sensitivity to enzalutamide. Variability in receptor expression and in vivo enzalutamide sensitivity was further examined in PAC XPDX models when implanted into alternate mouse strains, intact versus castrated (/CX) animals or when conditioned with enzalutamide. Methods: The PAC parental XPDX models ST1273, ST2347 and ST4017 have been previously described, while ST4420, ST6838 and STM344 are newly established. ST1273/EZR, ST2347/EZR and ST4017/EZR are PAC models conditioned with enzalutamide in vivo to manifest enzalutamide drug resistance. Evaluated PNEC XPDX models included ST072, ST072B, ST2403, ST4005C and STM002. All models were characterized using WES and RNAseq and tested for AR-V7, AR and PSMA receptor expression. For in vivo studies, enzalutamide was administered once daily by oral gavage. Endpoints included tumor volume and time from treatment initiation with %T/C values and tumor regression reported at study completion; a T/C of ≤ 20% versus control was considered sensitive. Tumor regression (%T/C<0%) versus Day 0 tumor volume was also reported. Results: PAC and PNEC models were successfully passaged and tested in SCID and nude strains. Most PAC models were AR+/PSMA+ except ST6838 (-/+) and STM344 (-/-); staining was maintained regardless of mouse strain, castration status or enzalutamide conditioning. PNEC models were AR-/PSMA- except ST2403 (-/+). Two PAC models were intrinsically positive for AR-V7, ST4017, established from a patient post ABI/ENZA and ST6838 from a treatment-naïve patient. No PNEC models were AR-V7+. Enzalutamide conditioning in some PAC models induced AR-V7+ staining dependent on duration of treatment and AR status of the parent model. Castration status and mouse strain affected enzalutamide activity in some PAC models, including reduced activity in ST1273/CX mice versus intact male nudes. ST4420 tested in CB-17 SCIDs was more sensitive to treatment than in nudes. Conclusion: We have established and characterized a panel of PAC and PNEC XPDX models in SCID and nude strains focusing on AR-V7, AR and PSMA staining and differential enzalutamide activity based on protein staining, mouse strain and castration status. We also reported induction of AR-V7 expression by chronic enzalutamide administration. These models can be utilized as a valuable tool in better understanding castrate-resistant prostate cancer and in developing novel therapies for enzalutamide-resistant patients. Citation Format: Jim Lund, Johnnie Flores, Alyssa Simonson, Armand Diaz III, Jared Knol, Naveen Kella, Drew Rasco, Kyriakos P Papadopoulos, Mark Campbell, Michael J Wick. Establishment and characterization of a panel of prostate cancer XPDX models with differential AR-V7 staining and enzalutamide response [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A080.

Abstract B068: Treatment combinations targeting MCL-1 and BCL-xL exert synergistic anti-tumor effects in AR-V7 expressing CRPC cell lines

Abstract Therapeutic agents that overcome acquired resistance to current androgen receptor (AR) pathway targeted therapies in patients with castration-resistant prostate cancer (CRPC) remain an unmet clinical need. A multitude of pathways are implicated in acquired treatment resistance, including the PI3K/mTOR/AKT, WNT/β-catenin, and DNA damage repair pathways. Notably, the androgen receptor splice variant 7 (AR-V7) activates the AR pathway in the absence of androgens, playing a crucial role in CRPC progression. An unbiased high throughput drug screen evaluating an array of inhibitors targeting diverse signaling pathways revealed highly synergistic activity of BH3 mimetics in AR-V7 expressing CRPC cell lines (e.g. LNCaP95, 22Rv1, VCaP-CR). Combinations targeting MCL-1 and BCL-xL (S63845 with A-1331852 or Navitoclax) displayed increased antitumor activity compared to those targeting MCL-1 and BCL-2 (S63845 with Venetoclax). Synergy among BCL-xL and MCL-1 targeted combinations was demonstrated using 2D and 3D CellTiter-Glo viability assays. Combination treatments in 3D spheroid cultures of 22RV1 and LNCaP95 cells confirmed the synergy observed in 2D assays. Furthermore, combined BCL-xL and MCL-1 inhibition altered AR-V7 expression and activated c-PARP cleavage. Drug combinations synergistically targeting BCL-xL and MCL-1 should be further explored for the treatment of therapy-resistant CRPC. Citation Format: Giulia C. Napoli, Andres F. Leon, Erica L. Beatson, Keith T. Schmidt, Emily N. Risdon, Cindy H. Chau, Douglas K. Price, William D. Figg. Treatment combinations targeting MCL-1 and BCL-xL exert synergistic anti-tumor effects in AR-V7 expressing CRPC cell lines [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 B068.

Abstract 6542: Detection of androgen receptor splice variants from clinical sequencing

Abstract Androgen receptor (AR) splice variants (AR-Vs) have been widely studied on its important role in prostate cancer (PC) progression. In particular, AR-Vs lacking ligand binding domains, such as AR splice variant 7 (AR-v7) that links exon 3 and cryptic exon 3 or AR variant that losses exons 5 to 7 (ARv567es), have been demonstrated as one of the resistant mechanisms to androgen deprivation therapy in PC. Despite its clinical importance, the current algorithms to detect fusions such as TopHat-Fusion have limitation to detect intra-chromosomal rearrangements including AR-Vs. In this respect, we propose a novel approach to identify AR-Vs from targeted RNA sequencing (RNA-seq) dataset. In short, our two-step approach first gathers soft-clipped or divided reads that are adjacent to the splicing sites of AR-Vs and then yields the number of splitting reads that support the existence of AR-Vs. Next, the algorithm selects the paired-end reads whose one side and the other side are mapped to the preceding and following exons, respectively. The final number of spanning reads are calculated following to the removal of low-quality reads. We validated the proposed approach using two large-scale, independent RNA-seq datasets of PC samples: 34 samples from Seoul National University Hospital (SNUH) and 558 samples from The Cancer Genome Atlas (TCGA) dataset. Overall, our approach successfully identified samples with putative AR-Vs, including AR-v7 and ARv567es. In addition, our approach successfully detected AR-v7 with reliable number of supporting reads, from the RNA-seq dataset of AR-v7-expressing cell line. Finally, statistical analyses of 34 SNUH PC patients suggested potential detection threshold in clinical sequencing settings (at least 10 split reads and 1% proportion). In the SNUH dataset, The AR-v7 positive group, which included 6 patients (17.1%) with values above the threshold, had higher AR-v7 expression levels than the negative group (p=4.8E-04). The similar pattern was also found in the analysis of TCGA dataset. Owing to its flexibility, we also confirmed that the developed approach can be used to detection of other AR-Vs, including AR-v3 and ARv567es. We expect that the further in-depth analyses including larger samples and clinical outcomes can discover clinical applicability of AR-Vs. Citation Format: Suhyun Hwangbo, Sungyoung Lee, Sheehyun Kim, Hongseok Yun. Detection of androgen receptor splice variants from clinical sequencing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6542.

Targeting the radiation-induced ARv7-mediated circNHS/miR-512-5p/XRCC5 signaling with Quercetin increases prostate cancer radiosensitivity

BackgroundRadiation therapy (RT) with androgen deprivation therapy (ADT) is an effective therapy to suppress the locally advanced prostate cancer (PCa). However, we unexpectedly found that RT could also induce the androgen receptor splice variant 7 (ARv7) expression to decrease the radiosensitivity.MethodsThe study was designed to target ARv7 expression with Quercetin or ARv7-shRNA that leads to enhancing and increasing the radiation sensitivity to better suppress the PCa that involved the modulation of the circNHS/miR-512-5p/XRCC5 signaling.ResultsMechanism studies revealed that RT-induced ARv7 may function via altering the circNHS/miR-512-5p/XRCC5 signaling to decrease the radiosensitivity. Results from preclinical studies using multiple in vitro cell lines and in vivo mouse models concluded that combining RT with the small molecule of Quercetin to target full-length AR and ARv7 could lead to better efficacy to suppress PCa progression.ConclusionTogether, these results suggest that ARv7 may play key roles to alter the PCa radiosensitivity, and targeting this newly identified ARv7 mediated circNHS/miR-512-5p/XRCC5 signaling with Quercetin may help physicians to develop a novel RT to better suppress the progression of PCa.

Abstract 3809: Adaptation of prostate cancer cell lines to tumor microenvironment culture conditions induces expression of androgen receptor splice variant 7 and contributes to drug resistance

Abstract The tumor microenvironment (TME) has several characteristics that distinguish it from normal tissue, including elevated interstitial fluid pressures and hypoxic environments. Both pressurized and hypoxic culture conditions can influence gene and protein expression of tumor cells which can result in tumor metastasis and drug resistance. Enzalutamide is effective in treating metastatic castration-resistant prostate cancer (mCRPC), but majority of patients eventually develop resistance to enzalutamide. One of the biomarkers of enzalutamide resistance is the expression of androgen receptor splice variant 7 (AR-V7), but the mechanism of how AR-V7 expression is upregulated in prostate cancer is unclear. To investigate the influence of TME culture conditions on prostate cancer cell lines, 22Rv1 and LNCaP cell lines were incubated under pressurized and hypoxic culture conditions (2 PSI + 1%O2) for a minimum of 7 days. We compared cell growth, morphology changes, gene expression profiles and drug response to enzalutamide treatment. The growth of 22Rv1 and LNCaP cells was markedly inhibited under TME culture conditions, accompanied by distinct changes in cell morphology. 22Rv1 and LNCaP cells cultured under TME conditions exhibited increased resistance to enzalutamide treatment. Higher levels of AR-V7 expression were detected in 22Rv1 and LNCaP cell lines maintained for 7 days in TME culture conditions. RNA-seq data identified 700+ genes that were differentially expressed in 22Rv1 and LNCaP cell lines adapted to TME culture conditions. GSEA analysis identified signaling pathways associated with hypoxia, glycolysis and epithelial-mesenchymal transition were upregulated under TME culture conditions, and the pathways of xenobiotic metabolism and oxidative phosphorylation were downregulated by TME culture conditions. In summary, adaptation to TME culture conditions can promote the expression of AR-V7 in prostate cancer cell lines and can contribute to enzalutamide drug resistance. Adaptation of cell lines to TME culture conditions can provide meaningful insights into mechanisms of drug resistance while providing a novel approach to identify targets and biomarkers of drug resistance. Citation Format: Yunmin Li, Albert Wong, Ann Lu, James Lim. Adaptation of prostate cancer cell lines to tumor microenvironment culture conditions induces expression of androgen receptor splice variant 7 and contributes to drug resistance [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 3809.

M6A-induced repression of SIAH1 facilitates alternative splicing of androgen receptor variant 7 by regulating CPSF1

Androgen receptor splice variant 7 (AR-v7), a constitutively active transcription factor, plays a crucial role in the progression of castration-resistant prostate cancer (CRPC). Here, we found that the cleavage and polyadenylation specificity factor 1 (CPSF1) (the largest subunit of the multi-protein cleavage and polyadenylation specificity complex), regulated by the E3 ubiquitin ligases SIAH1, promoted AR-v7 expression. The data from microarray-based analysis and clinical specimen-based analysis showed that SIAH1 expression was decreased in PCa and was negatively correlated with aggressive phenotypes of PCa. SIAH1 repressed PCa cell growth and invasion under castrate conditions. SIAH1 directly interacted with CPSF1 and promoted ubiquitination and degradation of CPSF1. CPSF1 expression was negatively correlated with SIAH1 expression, but positively with PCa progression. CPSF1 overexpression switched the AR splicing pattern and facilitated the generation of the oncogenic isoform (AR-v7) by binding to the AAUAAA polyadenylation signal contained in AR-cryptic exon CE3. Functionally, SIAH1 acted as a tumor suppressor in PCa pathogenesis by repressing CPSF1-mediated AR-v7 generation. Finally, we demonstrated that m6A methylation was concerned with the repression of SIAH1 in PCa. Our results define SIAH1/CPSF1/AR-v7 axis as a regulatory factor of PCa progression, providing a promising target for treating PCa.

PRIMERA trial (NCT04188275), early survival results from a prospective trial exploring impact of circulating tumor cell detection in castrate resistant prostate cancer patients undergoing abiraterone or enzalutamide I line treatment.

137 Background: Circulating tumor cells (CTC) detection and androgen receptor splice variant 7 (ARV7) expression have been shown to be associated with worse clinical outcomes in metastatic castration resistant prostate cancer (mCRPC) patients undergoing androgen receptor targeted agents (ARTA) treatment, paving the way for alternative treatment options for patients with negative predictive factors. Full-length androgen receptor (ARFL), prostate specific membrane antigen and prostate specific antigen (PSA) may further help to refine prognostic models. In our institution, a prospective observational trial testing CTC detection in mCRPC undergoing ARTA treatment (PRIMERA trial, NCT04188275) terminated the planned enrollment in 2020. Here we present early results of the overall cohort. Methods: PRIMERA (NCT04188275) is a prospective, observational trial enrolling mCRPC patients undergoing ARTA treatment. All patients were treated with either abiraterone or enzalutamide in I line setting. Blood samples to detect CTCs were taken before starting ARTA treatment. Reverse transcription - quantitative real-time PCR (RT-qPCR) was used to determine the CTC expression of PSA, PSMA, AR and ARV7. PSA drop (defined as difference between baseline PSA at ARTA treatment start and PSA at nadir under treatment), progression free and overall survival (PFS and OS) and their correlation with CTC detection were reported. Explorative analysis about AR, PSA and PSMA expression in CTC+ patients were conducted. Results: Overall, 44 patients were included. CTC were detected at treatment start in 19 patients (43,2%), of whom 3(15,78%), 9(63,15%), 15(78,94%) and 14 (73.68%) patients expressed ARV7, ARFL, PSA and PSMA, respectively. Biochemical response was significantly improved in CTC+ vs. CTC- patients, with median PSA drop values of 18.5 vs 2.5 ng/ml (p=0.03). After a median follow up of 18 months, 22 (50%) patients progressed. PFS was significantly longer in CTC- patients (not reached vs 16 months, respectively, p=0.02). Eight (18.2%) patients died, a non-significant trend in terms of overall survival was detected in favor of CTC- patients (not reached vs 29 months, respectively, p=0.05). AR, PSA and PSMA expression in CTC+ had no significant impact on PSA drop, PFS or OS. Conclusions: PRIMERA trial confirmed the CTC detection predictive importance in mCRPC patients. Adequately powered studies will be needed to further explore CTC profiling in this setting. Clinical trial information: NCT04188275.

Ratio of the expression levels of androgen receptor splice variant 7 to androgen receptor in castration refractory prostate cancer.

In clinical samples, the expression of androgen receptor (AR) and of AR splice variant 7 (AR-V7) is higher in castration-resistant prostate cancer (CRPC) compared with that in hormone-sensitive prostate cancer (PCa). However, there are only a few reports on the ratio of the expression levels of AR-V7 to AR (AR-V7/AR) in prostate tissue. The present study evaluated AR-V7/AR expression in various types of human prostate tissues and CRPC cells. Pretreatment prostate tissue samples from patients with benign prostatic hyperplasia (BPH; n=18), Gleason score 7 (n=17), and Gleason score 8–10 (n=26) were collected at the time of prostate biopsy, and tissue samples from CRPC patients (n=10) were collected at the time of transurethral resection of the prostate. Furthermore, androgen-independent LNCaP cells were established. The mRNA expression levels of AR and AR-V7, cell proliferation and prostate-specific antigen (PSA) production were evaluated by reverse transcription quantitative PCR, MTS assay and chemiluminescent enzyme immunoassay, respectively. There was a significant difference in AR-V7/AR expression ratios between the CRPC group and the BPH and pre-treatment PCa groups (CRPC, 7%; BPH and pre-treatment PCa, 1%). Subsequently, we compared the AR and AR-V7 expression levels in CRPC samples with those in the pretreatment prostate tissues from the same patients. The results demonstrated that the AR-V7/AR ratio increased from 3 to 9% after CRPC onset. Furthermore, in vitro experiment demonstrated that AR-V7 expression in LNCaP cells was increased after transforming into CRPC cells. The AR-V7/AR ratio also increased from 0.05 to 0.3%. In addition, small interfering (si)-RNA-mediated knockdown of AR inhibited the proliferation of and PSA production from androgen-independent LNCaP cells; however, AR-V7 knockdown had no effect. Conversely, siRNA-mediated knockdown of both AR and AR-V7 inhibited the proliferation of VCAP cells. In summary, the findings from the present study demonstrated that AR-V7 expression and AR-V7/AR ratio were increased after the onset of CRPC, which had a limited role in CRPC cell proliferation. Further investigation is required to clarify the roles of AR other splice variants and AR-V7 in CRPC.

Exploring the association between metastatic sites and androgen receptor splice variant 7 (AR-V7) in castration-resistant prostate cancer patients: A meta-analysis of prospective clinical trials

BackgroundThe Androgen Receptor Splice Variant 7 (AR-V7) has been associated with poor clinical outcomes in patients with castration-resistant prostate cancer (CRPC). Herein, we performed a meta-analysis aimed at systematically exploring the association between metastatic sites and AR-V7 expression in CRPC patients across prospective clinical trials. MethodsWe retrieved all the relevant prospective clinical trials through PubMed/Medline, Cochrane library, and EMBASE; additionally, proceedings of the main international oncological meetings were also searched for relevant abstracts. Outcomes of interest included metastatic sites (lymph node metastases, any site metastases, visceral metastases, and bone metastases) in AR-V7 positive and AR-V7 negative CRPC patients. Odds Ratios (ORs) and 95 % confidence intervals (CI) were calculated. ResultsOverall, 14 eligible prospective studies involving a total of 1944 CRPC patients (AR-V7 positive: 467; AR-V7 negative: 1477) were included in the analysis. According to our results, no differences between AR-V7 positive and AR-V7 negative CRPC patients were observed in terms of lymph node (OR 1.01; 95 % CI 0.49–2.09) and visceral metastases (OR 1.23; 95 % CI 0.89–1.71). Conversely, AR-V7 positive CRPC patients presented higher rate of any site metastases (OR 2.22; 95 % CI 1.58–3.12) and bone metastases (OR 2.03; 95 % CI 1.42–2.9) compared to AR-V7 negative subjects. ConclusionsThe results of this meta-analysis, the first in literature to be specifically focused on this topic so far, suggest that AR-V7 positivity may be associated with any site metastases and bone metastases; conversely, no association has been highlighted between AR-V7 expression and lymph node or visceral metastases. Although this meta-analysis should be interpreted with caution due to some limitations, our findings confirm that AR-V7 status could designate a unique and peculiar subtype of PC. Further studies aimed at improving and standardizing AR-V7 detection in clinical trials on CRPC patients are warranted.

Final results of a phase I/II prospective dose escalation trial evaluating safety and efficacy of combination 177Lu PSMA 617 and NOX66 in men with end-stage metastatic castration-resistant prostate cancer (LuPIN trial).

103 Background: 177LuPSMA – 617 is a promising therapy for metastatic castrate-resistant prostate cancer (mCRPC). However, treatment resistance occurs frequently and synergistic combination therapy may improve outcomes. We combined 177LuPSMA – 617 with idronoxil (NOX66), an inhibitor of external NADH oxidase type 2 with radio-sensitizing properties. We present the final safety and efficacy results. Methods: Men with progressive mCRPC after androgen signalling inhibition (ASI) and taxane chemotherapy were enrolled. Key inclusion criteria were: PSMA PET/CT intensity SUV max > 15 with no discordant disease on FDG PET/CT, haemoglobin > 100g/L, platelets > 100x109/L and eGFR > 40mls/min. Enrolled patients received up to six doses of 177 Lu-PSMA 617 (7.5Gbq) day 1 every 6 weeks in combination with NOX66 days 1-10 each cycle. Cohort 1 (n = 8) received 400mg NOX66. Following safety reviews the doses were escalated in cohorts 2 (n = 24) and 3 (n = 24) to 800mg and 1200mg of NOX66, respectively. Blood samples were prospectively collected for androgen receptor splice variant 7 (ARV7) expression. PSMA and FDG PET/CT were performed at study entry and on progression. The primary outcomes were safety and tolerability; the secondary outcomes evaluated were efficacy, pain scores, and quality of life. Results: Of the 56 men enrolled, all had received prior treatment with ASI and docetaxel, and 95% (53/56) had prior cabazitaxel. 96% (54/56) patients received ≥2 cycles and 46% (26/56) completed six cycles of treatment. Adverse events are summarized in the table below. PSA responses were as follows: 86% (48/56) had any PSA reduction and 61% (34/56) had > 50% PSA reduction. 84% (47/56) have had PSA progression to date with median follow up 18.9 months (95% CI 11.9-25.8). Median PSA PFS was 7.5 months (95% CI 6.0-9.0). 55% (31/56) have died and median overall survival was 19.7 months (95% CI 10.7-28.7). 34/56 men had baseline pain scores ≥3, of whom 53% (18/34) had significant reduction in pain indicators. There was no correlation between quantitative PET results and either PSA > 50% response, PSA PFS or OS. Conclusions: The combination of 177 Lu-PSMA 617 + NOX66 appears safe and efficacious in men with heavily pre-treated mCRPC. Exploratory analysis of ARV7 expression and quantitative PET imaging markers of treatment response and resistance is in progress. Clinical trial information: ACTRN12618001073291. [Table: see text]

JMJD6 Is a Druggable Oxygenase That Regulates AR-V7 Expression in Prostate Cancer.

Endocrine resistance (EnR) in advanced prostate cancer is fatal. EnR can be mediated by androgen receptor (AR) splice variants, with AR splice variant 7 (AR-V7) arguably the most clinically important variant. In this study, we determined proteins key to generating AR-V7, validated our findings using clinical samples, and studied splicing regulatory mechanisms in prostate cancer models. Triangulation studies identified JMJD6 as a key regulator of AR-V7, as evidenced by its upregulation with in vitro EnR, its downregulation alongside AR-V7 by bromodomain inhibition, and its identification as a top hit of a targeted siRNA screen of spliceosome-related genes. JMJD6 protein levels increased (P < 0.001) with castration resistance and were associated with higher AR-V7 levels and shorter survival (P = 0.048). JMJD6 knockdown reduced prostate cancer cell growth, AR-V7 levels, and recruitment of U2AF65 to AR pre-mRNA. Mutagenesis studies suggested that JMJD6 activity is key to the generation of AR-V7, with the catalytic machinery residing within a druggable pocket. Taken together, these data highlight the relationship between JMJD6 and AR-V7 in advanced prostate cancer and support further evaluation of JMJD6 as a therapeutic target in this disease. SIGNIFICANCE: This study identifies JMJD6 as being critical for the generation of AR-V7 in prostate cancer, where it may serve as a tractable target for therapeutic intervention.

Role of androgen receptor splice variant-7 (AR-V7) in prostate cancer resistance to 2nd-generation androgen receptor signaling inhibitors.

The role of truncated androgen receptor splice variant-7 (AR-V7) in prostate cancer biology is an unresolved question. Is it simply a marker of resistance to 2nd generation androgen receptor signaling inhibitors (ARSi) like Abiraterone Acetate (Abi) and Enzalutamide (Enza) or a functional driver of lethal resistance via its ligand-independent transcriptional activity? To resolve this question, the correlation between resistance to ARSi and genetic chances and expression of full length AR (AR-FL) vs. AR-V7 were evaluated in a series of independent patient-derived xenografts (PDXs). While all PDXs lack PTEN expression, there is no consistent requirement for mutation in TP53, RB1, BRCA2, PIK3CA, or MSH2, or expression of SOX2 or ERG and ARSi-resistance. Elevated expression of AR-FL alone is sufficient for Abi- but not Enza-resistance, even if AR-FL is gain-of-function (GOF) mutated. Enza-resistance is consistently correlated with enhanced AR-V7 expression. In vitro and in vivo growth responses of Abi-/Enza-resistant LNCaP-95 cells in which CRISPR-Cas9 was used to knockout AR-FL or AR-V7 alone or in combination were evaluated. Combining these growth responses with RNAseq analysis demonstrates that both AR-FL and AR-V7 dependent transcriptional complementation are needed for Abi/Enza resistance.

Abstract B21: Circulating tumor cell by microfluidic magnetophoresis-based gene expression changes for monitoring of prognosis in advanced prostate cancer patient: A pilot study

Abstract Introduction: By using the circulating tumor cells (CTCs), we can get useful genomic information that enables monitoring of patients’ prognosis or selecting appropriate treatment over time by repeat biopsy. The aim of this study is to separate CTCs from prostate cancer patients using new microfluidic technique that is based on disposable lateral magnetophoretic microseparator and to assess the gene expression that is specific for prostate cancer using mRNA from isolated CTCs measured by droplet digital PCR (ddPCR) method. We also evaluated the treatment-dependent gene-profile changes in four metastatic castration-resistant prostate cancer patients (mCRPC). Patients and Methods: Total 55 samples of 49 patients who underwent treatment for prostate cancer between 06/2018 and 05/2019 were prospectively enrolled. Approximately 10 mL of whole blood was drawn from prostate cancer patients; Group A, 14 samples (25.4%) with localized stage II-III cancer; Group B, 5 samples (9.1%) with stage IV; Group C, 8 samples (14.5%) with metastatic hormone-sensitive prostate cancer (mHSPC); and Group D, 29 samples (52.7%) with mCRPC. In particular, more than two repeated blood collections were performed for 4 mCRPC. CTCs were positively isolated by using assembly-disposable CTC-μChip. CTCs from 5 mL of blood were used for counting to identify isolated CTC numbers with immunofluorescence detection procedure. CTCs from the remaining 5 mL of blood were used for gene analysis by ddPCR for 6 prostate cancer-related genes, such as androgen receptor (AR), androgen receptor splice variant 7 (AR-V7), prostate specific membrane antigen (PSMA), prostate specific antigen (PSA), cytokeratin-19 (CK-19), and epithelial cell adhesion molecule (EpCAM). Results: We identified the average of 3, 16, 14, and 26 CTCs per 1ml in group A, B, C, and D, respectively (P&amp;lt; 0.01). The gene positive rates of AR, AR-V7, KRT-19, EpCAM, PSA, and PSMA were 85.4% (47/55), 16.4% (9/55), 56.4% (31/55), 92.7% (51/55), 41.8% (23/55), and 50.9% (28/55), respectively. The copy number of PSA, PSAM, and KRT-19 increased in proportion as the clinical stage increased. 92.7% of samples showed EpCAM positive, whereas AR-V7 was a rare event, with only in 9 out 28 samples positive with mCRPC, but not in other stages. In particular, of the four mCRPC patients who repeated blood sampling, the number of CTCs and the expression of AR, PSA, PSMA, and KRT-19 decreased in patients who responded to drug (enzalutamide and docetaxel). On the other hand, patients who were resistant to drug showed increased expression of AR-V7 and KRT-19 with the increased number of CTC. Conclusions: This study demonstrated that CTC-based multigene profiling could be analyzed using ddPCR. We have also identified several genes associated with progression in mCRPC patients initiating enzalutamide or chemotherapy. While this is a pilot study and prospective validation is needed, these findings highlight the potential role for this approach in real-time monitoring of advanced prostate cancer patients. Citation Format: Jae-Seung Chung, Hyungseok Cho, Ki-Ho Han. Circulating tumor cell by microfluidic magnetophoresis-based gene expression changes for monitoring of prognosis in advanced prostate cancer patient: A pilot study [abstract]. In: Proceedings of the AACR Special Conference on Advances in Liquid Biopsies; Jan 13-16, 2020; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(11_Suppl):Abstract nr B21.

The value of AR-V7 in predicting therapeutic efficiency of abiraterone for CRPC patients

Objective Determine the relationship between AR-V7 expression and treatment efficiency of abiraterone. Methods A prospective cohort study was conducted to detect CTCs AR-V7 in newly diagnosed CRPC patients, aged ≥18 years who were admitted to the urologic department of Peking University cancer hospital from January 2016 to January 2019, with one or more systemic metastases. All the patients intended to be treated with abiraterone. According to the AR-V7 status, patients were divided into 2 groups (AR-V7 positive and negative). PSA decline time, PSA PFS, clinical status PFS, imaging PFS and CSS are analyzed and compared by t-test and Chi-square between 2 groups. Result 49 patients were AR-V7 negative and 28 were AR-V7 positive. Compared with AR-V7 positive patients, PSA decline time (72.04±66.92 vs. 190.11±102.44, P=0.000), PSA non-response rate (6.12% vs. 21.4%, P=0.040) are significantly lower in AR-V7 negative patients. PSA PFS(489.17±269.39 vs. 130.56±120, P=0.010), Clinical PFS (551.91±322.05 vs. 261.44±200.85, P=0.018), and Imaging PFS (523.7±223.28 vs. 247.56±202.80, P=0.003) are significantly longer in AR-V7 negative patients. Conclusion Expression status of AR-V7 is related to the response of abiraterone treatment and the prognosis of the patients. Key words: Prostatic neoplasms; Castration resistant prostate cancer; Androgen receptor splice variant 7(AR-V7); Abiraterone

Preliminary results of a prospective assessment of androgen receptor splice variants in mCRPC patients undergoing androgen receptor targeted agents.

246 Background: Different treatment options for metastatic castrate resistant prostate cancer (mCRPC) are currently available, including Androgen Receptor Targeted Agents (ARTA) and Taxane based chemotherapy. However, selection criteria aiming to drive the therapeutic choice in this setting are lacking, and no standardized therapeutic sequence is validated. In our institution, a prospective study testing predictive value of circulating tumor cells (CTC) in patients (pts) receiving a first line ARTA for mCRPC is currently ongoing (PRIMERA). Here, we present preliminary results from the first enrolled cohort. Methods: Pts affected by mCRPC eligible for Androgen Deprivation Therapy (ADT) plus ARTA were prospectively enrolled and underwent baseline determination of androgen-receptor splice variant 7 (AR-V7) and androgen-receptor-full length (ARFL) variants on CTC at baseline (ARTA start). Fisher Exact Test was conducted to explore the correlation between baseline features and CTC detection rate. Results: Overall, 26 pts were enrolled and baseline results are available for 13 pts. CTC were found in 5 (38.5%) pts. No significant difference was reported in terms of CTC detection probability for pts with high vs low burden of disease according to CHARTEED definition (p=0.42), neither for pts with PSA at CRPC diagnosis &lt; or &gt; 10 ng/ml, (p=0.2). However, a PSA &gt; 10 ng/ml at ADT start in metastatic hormone sensitive setting (mHSPC) was significantly related to CTC detection probability (p=0.01). AR-V7 variants were found in 1 out 5 (20%) CTC-positive pts. Conclusions: PSA at ADT start may significantly be related to CTC detection rate. CTC detection could be particularly useful in pts with a high burden of disease at the beginning of systemic therapy. Metastatic disease could remain dormant until development of CRPC status, with consequent release of increased amount of CTC, more likely to be detected in this setting. AR-V7 expression was found in 20% of CTC positive pts, in line with literature data.[Table: see text]