Androgen Receptor Splice Variant-7 mRNA Research Articles

The association of AR-V7 with resistance to Abiraterone in metastatic castration-resistant prostate cancer

Background: This paper sought to investigate the association between androgen receptor splice variant 7 (AR-V7) status in circulating tumors cells (CTCs) and resistance to abiraterone (Abi) and docetaxel (Doc) in men with metastatic castration-resistant prostate cancer (mCRPC). Methods: This was a prospective clinical study, newly confirmed mCRPC patients who were randomized going to receive Abi or Doc with age ≥18 years were enrolled to detect the AR-V7 mRNA in CTCs. The association of AR-V7 status with Gleason Score, prostate specific antigen response rate (PSA RR), hormone-sensitive duration time (HSDT), time-to event outcomes, including PSA progression-free survival (PFS), clinical PFS, radiographic PFS and cancer-specific survival (CSS) was examined. Results: 139 patients with mCPRC were enrolled; 67 received Abi and 72 received Doc. The proportion of AR-V7-positive patients was 35.8% in Abi-treated patients and 34.7% in Doc-treated patients. Our results were as follows: (1) among men receiving Abi, AR-V7-positive patients had a higher Gleason Score (8.34 ± 1.03 vs. 7.29 ± 0.76, p = 0.012) and lower PSA RR (20.8% vs. 65.1%, p = 0.001) compared with AR-V7-negative patients; in a multivariable COX model, AR-V7 positivity was an independent risk factor for shorter PSA PFS (p = 0.012), clinical PFS (p = 0.036) and radiographic PFS (p = 0.028); (2) among men receiving Doc, AR-V7-positive patients also had a higher Gleason Score compared with AR-V7-negative patients (8.86 ± 0.66 vs. 7.57 ± 0.94, p < 0.0001), but no differences in PSA RR, PSA PFS, clinical PFS, radiographic PFS or CSS were observed; (3) among AR-V7-positive patients, men receiving Abi had lower a PSA RR compared with men receiving Doc (20.8% vs. 48%, p = 0.046); in a multivariable COX model, Abi was an independent risk factor for shorter PSA PFS (p = 0.040) and clinical PFS (p = 0.046); (4) among AR-V7-negative patients, there were no differences in PSA RR, PSA PFS, clinical PFS, radiographic PFS or CSS between Abi- and Doc-treated patients. Conclusion: AR-V7-positive patients commonly have a higher Gleason Score than AR-V7 negative patients, and AR-V7 positivity is strongly associated with Abi resistance in mCRPC but is not associated with the effectiveness of Doc.

MRNA expressions of androgen receptor and its variants in matched hormone-sensitive and castration-resistant prostate cancer

Objectives: Androgen receptor splice variants (AR-Vs), especially androgen receptor splice variant 7 (AR-V7), are considered as important factors in developing castration-resistance of prostate cancer and also as candidate predictive factors. Our aim was to evaluate changes in the mRNA expression of full-length AR (AR-FL) and AR-Vs in the primary prostate cancers from the same patients before and after ADT.Methods: We compared morphologic differences and evaluated AR-FL, AR-V7, AR-V4, ARv567es, AR-V3 and AR8 mRNA expression in matched samples of primary hormone-sensitive and castration-resistant prostate cancer (CRPC) from 19 patients.Results: mRNA expression of AR-FL, AR-V7, ARv567es and AR-V3 was present in hormone sensitive prostate cancer (HSPC) and was significantly increased in CRPC in 81.2% (13/16). There were strong positive correlations between AR-FL and AR-V7 (r = 0.93, p < .001), ARv567es (r = 0.72, p < .001) and AR-V3 (r = 0.81, p < .001) mRNA expression. AR-V7/AR-FL ratio was more significantly (>30%) increased after ADT in 25% (4/16) of the patients, who showed significantly (p < .001) worse overall survival. Neuroendocrine differentiation was seen in one patient (5.3%) and the Gleason score was increased in 10 (52.6%) patients.Conclusion: We demonstrated that the expression of AR-V7 is present at low levels in HSPC and is increased in CRPC and the increase is an active process possibly related to aggressive clinical course.

Androgen Receptor Modulation Optimized for Response—Splice Variant: A Phase 3, Randomized Trial of Galeterone Versus Enzalutamide in Androgen Receptor Splice Variant-7–expressing Metastatic Castration-resistant Prostate Cancer

Background: Detection of androgen receptor (AR) splice variant-7 (AR-V7) messenger RNA (mRNA) in circulating tumor cells (CTCs) is associated with a suboptimal response to abiraterone and enzalutamide in metastatic castration-resistant prostate cancer (mCRPC). Galeterone inhibits CYP17 and AR, and induces AR protein degradation. We hypothesized that galeterone would be clinically superior to enzalutamide in AR-V7–positive (AR-V7+) mCRPC. Objective: To screen and characterize AR-V7+ mCRPC, and evaluate galeterone compared with enzalutamide. Design, setting, and participants: This was a multicenter randomized phase 3 trial; enzalutamide-, abiraterone-, and chemotherapy-naïve mCRPC patients had AR-V7 prescreening using a CTC-based mRNA assay. Intervention: AR-V7+ patients were randomized (1:1) to open-label galeterone or enzalutamide; planned sample size was 148. Outcome measurements and statistical analysis: The primary endpoint was radiographic progression-free survival (rPFS). Baseline AR-V7 status was correlated with patient characteristics. Results and limitations: Overall, 953 men were prescreened for AR-V7; 323 (34%) had detectable CTCs, and 73/323 had AR-V7 mRNA. The AR-V7+ prevalence was 8% (73/953; 95% confidence interval [CI] 6–10%). AR-V7 was associated with indicators of advanced and high-volume disease at baseline, including higher prostate-specific antigen (PSA) level (p < 0.001), more bone metastases (p < 0.001), docetaxel for hormone-sensitive disease (p < 0.001), prior first-generation androgen deprivation therapy (p < 0.001), and shorter time from diagnosis to enrollment (p < 0.001). Of 73 eligible patients, 38 were randomized to galeterone (n=19) or enzalutamide (n=19); 35 dropped out before randomization. Owing to high censorship for the rPFS events, the data monitoring committee recommended early closure based on interim evidence that the primary endpoint would not be met. The PSA50 values were 2/16 (13%) and 8/19 (42%) for galeterone and enzalutamide respectively (proportion difference=−0.278, 95% CI −0.490 to 0.097). Conclusions: The prevalence of CTC mRNA AR-V7 in first-line mCRPC was 8% (95% CI 6–10%). AR-V7+ was associated with the characteristics of aggressive and advanced disease. These men had rapid disease progression. Development of galeterone will not be pursued. Patient summary: Of men with metastatic castration-resistant prostate cancer, 8% had the androgen receptor splice variant-7 (AR-V7) blood biomarker. The AR-V7+ patients had features of aggressive disease. Thirty-eight men were treated with either galeterone or enzalutamide; the trial was stopped early prior to determining efficacy because too many patients transitioned off the trial due to advancing cancer before having required radiographs.

Role of Circulating Tumor Cells (CTC), Androgen Receptor Full Length (AR-FL) and Androgen Receptor Splice Variant 7 (AR-V7) in a Prospective Cohort of Castration-Resistant Metastatic Prostate Cancer Patients.

Background: Circulating tumor cells (CTC), androgen receptor full-length (AR-FL), and androgen receptor splice variant 7 (AR-V7) are prognostic in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC). AR-V7 seems to predict resistance to androgen-receptor signaling inhibitors (ARSi). Methods: We assessed the association of CTC, AR-FL, and AR-V7 with prostate-specific antigen (PSA) response and overall survival (OS). We used a modified AdnaTest CTC-based AR-FL and AR-V7 mRNA assay. Chi-square test, Fisher Exact test, Kaplan–Meier method, log-rank test, Cox proportional hazards models were used as appropriate. Results: We enrolled 39 mCRPC pts, of those 24 started a first-line treatment for mCRPC (1L subgroup) and 15 had received at least two lines for mCRPC (>2L subgroup). CTC, AR-FL, and AR-V7 were enriched in >2L compared to 1L subgroup. Detection of these biomarkers was associated with a lower percentage of biochemical responses. Only 1/7 AR-V7+ pts had a PSA response and received cabazitaxel. Median OS was 4.7 months (95% CI 0.6–8.9) in AR-V7+ pts and not reached in AR-V7− pts. AR-V7 was the only variable with prognostic significance in the Cox model. Conclusion: AR-V7, CTC, and AR-FL are associated with advanced mCRPC and AR-V7+ predicts for shorter OS.

Plasma extracellular vesicles as phenotypic biomarkers in prostate cancer patients.

The development of phenotypic biomarkers to aid the selection of treatment for patients with castrate-resistant prostate cancer (CRPC) is an important priority. Plasma exosomes have excellent potential as real-time biomarkers to characterize the tumor because they are easily accessible in the blood and contain DNA, RNA, and protein from the parent cell. This study aims to investigate the characteristics of putative prostate-specific plasma extracellular vesicle (EV) markers and their relationship with clinical outcomes. We investigated plasma EVs in a total of 89 patients with prostate cancer (PCa) at different stages of disease progression. EVs were isolated using both precipitation and ultracentrifugation methods; physical characterization was performed using dynamic light scattering, acetylcholinesterase (AChE) activity, and velocity gradients. An immunocapture method was developed for the evaluation of prostate-specific membrane antigen (PSMA)-positive exosomes. Exosomal messenger RNA (mRNA) was quantified using droplet digital polymerase chain reaction for the expression of KLK3 and androgen receptor splice variant 7 (AR-V7) genes, which code prostate-specific antigen (PSA) and AR-V7, respectively. Serum sex steroids were measured using liquid chromatography-tandem mass spectroscopy. Isolated exosomes from patients with CRPC had a smaller hydrodynamic size than those isolated from localized patients with PCa, whileAChE activity showed no difference. Moreover, no differences were observed after initiation of androgen deprivation therapy in serial patient samples. Velocity gradients identified that PSMA-positive exosomes occupied a specific fraction of isolated EVs. A total of 35 patients with CRPC had mRNA analyzed from isolated plasma exosomes. Detectable exosomal KLK3 corresponded with higher concomitant serum PSA measurements, as expected (mean, 112.6 vs 26.61 ng/mL; P = .065). Furthermore, detectable levels of AR-V7 mRNA were associated with a shorter time to progression (median, 16.0 vs 28.0 months; P = .0499). Furthermore, detectable exosomal AR-V7 was significantly associated with testosterone levels below the lower limit of quantification (<0.1 nM). Our results suggest that exosomal AR-V7 is correlated with lower sex steroid levels in CRPC patients with a poorer prognosis. PSMA immunocapture does not appear sufficient to isolate PCa-specific exosomes.

Abstract 2617: A multicenter project to test the validity and logistics surrounding the testing of AR-V7 mRNA expression in circulating tumor cells

Abstract Introduction: The presence of the androgen receptor splice variant 7 (AR-V7) in circulating tumor cells (CTCs) has shown to be associated with resistance to anti-AR treatment with abiraterone or enzalutamide, but not to chemotherapy containing taxanes such as cabazitaxel in patients with metastatic castration-resistant prostate cancer (mCRPC). The primary objective of this project was to set up a validated multi-center pipeline to measure AR-V7 by RT-qPCR in RNA isolated from CellSearch-enriched CTCs. This pipeline included a) the pre-analytical phase (appropriate anonymized sample collection and sample preservation), b) the analytical phase (assay performance with high analytical sensitivity, precision and specificity and c) the post-analytical phase (data evaluation and reporting). Materials and Methods: CellSearch-enirched CTCs from metastatic castration-resistant prostate cancer (mCRPC) patients were characterized by RT-qPCR. To validate the pipeline, we determined the proportion of blood samples from mCRPC patients having three or more CTCs per 7.5 mL of blood for whom an AR-V7 status can be assayed and returned to the clinician within 11 days (design PRELUDE study protocol). Results: In the range of the RNA equivalent of 0.2-12 AR-V7 positive VCaP cells the coefficient of variation (CV) for AR-V7 was 9% (n=37). The limit of detection (LOD) was 0.3 and the limit of quantification (LOQ) 3 cells in the final RT-qPCR. In none of 17 healthy blood donors an AR-V7 signal was detected, showing high diagnostic specificity (100%). No differences were observed between AR-V7 data generated by four different technicians or in two different laboratories. For the 45 patients in the PRELUDE study, thirteen patients were not eligible due to poor RNA quality (n=1) or because the blood sample did not contain enough epithelial signal (n=12). Twenty-two patients were AR-V7 negative and ten AR-V7 positive. The median, 75th and 90th percentile reporting times from blood draw to dissemination of the test results were 7, 8 and 9 days, respectively. Conclusion: This AR-V7 test with validated cut-offs, a strong intra- and inter-laboratory performance and the ability to report the outcome within a clinically acceptable time frame for the large majority of patients, met our pre-specified objectives. The AR-V7 test is now ready to be used in prospective studies (including randomized controlled trials) to test its predictive value for outcome on post-docetaxel (anti-AR of cabazitaxel) treatment. Citation Format: Anieta M. Sieuwerts, Bianca Mostert, Michelle van der Vlugt-Daane, Jaco Kraan, Corine Beaufort, Mai Van, Wendy J. Prager, Bram De Laere, Nick Beije, Paul Hamberg, Hans M. Westgeest, Metin Tascilar, Luc Y. Dirix, Wendy Onstenk, Ronald de Wit, Martijn P. Lolkema, Ron H. Mathijssen, John W. Martens, Stefan Sleijfer. A multicenter project to test the validity and logistics surrounding the testing of AR-V7 mRNA expression in circulating tumor cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2617.

AR-V7 in circulating tumor cells cluster as a predictive biomarker of abiraterone acetate and enzalutamide treatment in castration-resistant prostate cancer patients.

We examined whether androgen receptor splice variant 7 (AR-V7) in circulating tumor cell(CTC)clusters can be used to predict survival in patients with bone metastatic castration resistant-prostate cancer (mCRPC) treated with abiraterone or enzalutamide. We retrospectively enrolled 98 patients with CRPC on abiraterone or enzalutamide, and investigated the prognostic value of CTC cluster detection (+ v -) and AR-V7 detection (+ v -) using a CTC cluster detection - based AR-V7 mRNA assay. We examined ≤50% prostate-specific antigen (PSA) responses, PSA progression-free survival (PSA-PFS), clinical and radiological progression-free survival (radiologic PSF), and overall survival (OS). We then assessed whether AR-V7 expression in CTC clusters identified after On-chip multi-imaging flow cytometry was related to disease progression and survival after first-line systemic therapy. All abiraterone-treated or enzalutamide-treated patients received prior docetaxel. The median follow-up was 20.7 (range: 3.0-37.0) months in the abiraterone and enzalutamide cohorts, respectively. Forty-nine of the 98 men (50.0%) were CTC cluster (-), 23 of the 98 men (23.5%) were CTC cluster(+)/AR-V7(-), and 26 of the 98 men (26.5%) were CTC cluster(+)/AR-V7(+). CTC cluster(+)/AR-V7(+) patients were more likely to have EOD ≥3 at diagnosis (P = 0.003), pain (P = 0.023), higher alkaline phosphatase levels (P < 0.001), and visceral metastases (P < 0.001). On multivariable analysis, pretherapy CTC cluster(+), CTC cluster(+)/AR-V7(-), and ALP >UNL were independently associated with a poor PSA-PFS, radiographic PFS, and OS in abiraterone-treated patients and enzalutamide-treated patients. The CTC clusters and AR-V7-positive CTC clusters detected were important for assessing the response to abiraterone or enzalutamide therapy and for predicting disease outcome.

Prognostic and predictive role of CTCs and AR-V7+ CTCs expression in metastatic catrate resistant prostate cancer (mCRPC): A feasibility study.

367 Background: Circulating tumor cells (CTC) counts ≥ 5/7.5 mL predict shorter survival in patients (pts) with mCRPC. Moreover, the presence of androgen receptor splice variant-7 mRNA (AR-V7) in CTCs is thought to play a relevant role in the development of primary or acquired resistance to enzalutamide (E) or abiraterone (A). We developed a new immunofluorescence-based assay for AR-V7+ CTCs and tested its association with PFS and OS. Methods: We performed a single-centre observational prospective trial enrolling pts with mCRPC candidate to receive E or A. CTC samples have been collected at baseline, after 1 month (mo) and every 3 mos thereafter until progression or at 12 mos without progression. CTCs have been enumerated with CellSearch System. We integrated the standard assay with a mAb able to recognize the AR-V7 protein. Slides from samples underwent automated immunofluorescent staining and AR-V7+ CTCs were enumerated. Results: Since Sep 2016, 31 pts have been enrolled (Table). We compared CTC counts between standard and the integrated assay and found no differences in the mean total CTC number ± (Wilcoxon Signed Rank test, p= 0.31). 16 out of 28 evaluable pts (57%) had ≥ 1 CTCs at baseline, 9 pts (32%) had ≥ 5 CTCs/7.5 ml, 4 pts (14.3%) were AR-V7+ before any exposure to A or E. After a median follow-up time of 8.1 mos, 6 pts have progressed and 4 died. No association has been found between CTCs ≥ 5/7.5 mL and survival. The presence of at least 1 AR-V7+ CTC at baseline did not correlate with PSA response, but had a weak association with shorter PFS (log-rank test, p = 0.055) and a significant impact (p = 0.02) on OS. Conclusions: We developed a new integrated assay for AR-V7+ CTCs, based on an automated platform that permits serial sampling with low inter- / intra-test variability. The clinical utility in anticipating the resistance to E or A is under study. [Table: see text]

Overexpression of nuclear AR-V7 protein in primary prostate cancer is an independent negative prognostic marker in men with high-risk disease receiving adjuvant therapy

BackgroundOverexpression of the androgen receptor (AR) splice variant 7 (AR-V7) has recently been reported to be associated with resistance to antihormonal therapy. Herein, we address the question whether tumor cells with AR-V7 expression can be detected at the time of radical prostatectomy, that is, before long-term hormonal manipulation and castration resistance, and what the potential prognostic impact on the biochemical recurrence (BCR)-free survival may be. MethodsAn anti-AR-V7 antibody was first validated in a training set of prostate cancer specimens by a comparison of AR-V7 protein to AR-V7 mRNA expression. We then analyzed nuclear AR-V7 protein expression in the primary tumors and lymph node metastases from 163 predominantly high-risk patients (cohort I) as well as the primary tumors from patients of a second, consecutive patient cohort (n = 238, cohort II) not selected for any clinicopathological features. Staining results were correlated to patient characteristics and BCR-free patient survival. ResultsHigh nuclear AR-V7 protein expression was detected in approximately 30%–40% of patients in cohort I and II at the time of radical prostatectomy. High baseline expression of nuclear AR-V7 protein was associated with an unfavorable BCR-free survival in the high-risk patient cohort I but not in the unselected consecutive cohort II. Remarkably, AR-V7 was an independent negative prognostic factor in high-risk prostate cancer patients of cohort I who were selected to receive adjuvant treatment. ConclusionsProstate cancer cells with high nuclear AR-V7 protein expression can be detected in a substantial proportion of tumors at the time of radical prostatectomy. The presence of AR-V7-positive tumor cells is associated with an unfavorable prognosis for BCR-free survival in a high-risk patient cohort including a subgroup of patients selected to receive adjuvant therapy, in which AR-V7 was an independent negative prognosticator. Overexpression of nuclear AR-V7 protein hence identifies a subset of tumors with remarkably aggressive growth characteristics among clinically and histologically high-risk patients at the time of radical prostatectomy.

AR-V7 in Peripheral Whole Blood of Patients with Castration-resistant Prostate Cancer: Association with Treatment-specific Outcome Under Abiraterone and Enzalutamide

BackgroundIt has been demonstrated that androgen receptor splice variant 7 (AR-V7) expression in circulating tumor cells (CTCs) predicts poor treatment response in metastatic castration-resistant prostate cancer (mCRPC) patients treated with abiraterone or enzalutamide. ObjectiveTo develop a practical and robust liquid profiling approach for direct quantification of AR-V7 in peripheral whole blood without the need for CTC capture and to determine its potential for predicting treatment response in mCRPC patients. Design, setting, and participantsWhole blood samples from a prospective biorepository of 85 mCRPC patients before treatment initiation with abiraterone (n=56) or enzalutamide (n=29) were analyzed via droplet digital polymerase chain reaction. Outcome measurements and statistical analysisThe association of AR-V7 status with prostate-specific antigen (PSA) response defined by PSA decline ≥50% and with PSA–progression-free survival (PSA-PFS), clinical PFS, and overall survival (OS) was assessed. Results and limitationsHigh AR-V7 expression levels in whole blood were detectable in 18% (15/85) of patients. No patient with high AR-V7 expression achieved a PSA response, and AR-V7 status was an independent predictor of PSA response in multivariable logistic regression analysis (p=0.03). High AR-V7 expression was associated with shorter PSA-PFS (median 2.4 vs 3.7 mo; p<0.001), shorter clinical PFS (median 2.7 vs 5.5 mo; p<0.001), and shorter OS (median 4.0 vs. 13.9 mo; p<0.001). On multivariable Cox regression analysis, high AR-V7 expression remained an independent predictor of shorter PSA-PFS (hazard ratio [HR] 7.0, 95% confidence interval [CI] 2.3–20.7; p<0.001), shorter clinical PFS (HR 2.3, 95% CI 1.1–4.9; p=0.02), and shorter OS (HR 3.0, 95% CI 1.4–6.3; p=0.005). ConclusionsTesting of AR-V7 mRNA levels in whole blood is a simple and promising approach to predict poor treatment outcome in mCRPC patients receiving abiraterone or enzalutamide. Patient summaryWe established a method for determining AR-V7 status in whole blood. This test predicted treatment resistance in patients with metastatic castration-resistant prostate cancer undergoing treatment with abiraterone or enzalutamide. Prospective validation is needed before application to clinical practice.

Melatonin Inhibits Androgen Receptor Splice Variant-7 (AR-V7)-Induced Nuclear Factor-Kappa B (NF-κB) Activation and NF-κB Activator-Induced AR-V7 Expression in Prostate Cancer Cells: Potential Implications for the Use of Melatonin in Castration-Resistant Prostate Cancer (CRPC) Therapy.

A major current challenge in the treatment of advanced prostate cancer, which can be initially controlled by medical or surgical castration, is the development of effective, safe, and affordable therapies against progression of the disease to the stage of castration resistance. Here, we showed that in LNCaP and 22Rv1 prostate cancer cells transiently overexpressing androgen receptor splice variant-7 (AR-V7), nuclear factor-kappa B (NF-κB) was activated and could result in up-regulated interleukin (IL)-6 gene expression, indicating a positive interaction between AR-V7 expression and activated NF-κB/IL-6 signaling in castration-resistant prostate cancer (CRPC) pathogenesis. Importantly, both AR-V7-induced NF-κB activation and IL-6 gene transcription in LNCaP and 22Rv1 cells could be inhibited by melatonin. Furthermore, stimulation of AR-V7 mRNA expression in LNCaP cells by betulinic acid, a pharmacological NF-κB activator, was reduced by melatonin treatment. Our data support the presence of bi-directional positive interactions between AR-V7 expression and NF-κB activation in CRPC pathogenesis. Of note, melatonin, by inhibiting NF-κB activation via the previously-reported MT1 receptor-mediated antiproliferative pathway, can disrupt these bi-directional positive interactions between AR-V7 and NF-κB and thereby delay the development of castration resistance in advanced prostate cancer. Apparently, this therapeutic potential of melatonin in advanced prostate cancer/CRPC management is worth translation in the clinic via combined androgen depletion and melatonin repletion.

Clinical Significance of Androgen Receptor Splice Variant-7 mRNA Detection in Circulating Tumor Cells of Men With Metastatic Castration-Resistant Prostate Cancer Treated With First- and Second-Line Abiraterone and Enzalutamide.

Purpose We reported previously that the detection of androgen receptor splice variant-7 (AR-V7) mRNA in circulating tumor cells (CTCs) correlated with poor outcomes from the use of abiraterone and enzalutamide in patients with castration-resistant prostate cancer (CRPC). Here, we expanded our cohort size to better characterize the prognostic significance of AR-V7 in this setting. Methods We prospectively enrolled 202 patients with CRPC starting abiraterone or enzalutamide and investigated the prognostic value of CTC detection (+ v -) and AR-V7 detection (+ v -) using a CTC-based AR-V7 mRNA assay. We examined ≥ 50% prostate-specific antigen (PSA) responses, PSA progression-free survival, clinical and radiologic progression-free survival, and overall survival. We constructed multivariable models adjusting for PSA, Gleason sum, number of prior hormone therapies, prior abiraterone or enzalutamide use, prior taxane use, presence of visceral metastases, and Eastern Cooperative Oncology Group score. We also separately examined the first-line and second-line novel hormonal therapy (NHT) settings. Results Median follow-up times were 15.0, 21.7, and 14.6 months for CTC-, CTC+/AR-V7- and CTC+/AR-V7+ patients, respectively. CTC+/AR-V7+ patients were more likely to have Gleason scores ≥ 8 ( P = .05), metastatic disease at diagnosis ( P = .01), higher PSA ( P < .01), prior abiraterone or enzalutamide use ( P = .03), prior taxane use ( P = .02), and Eastern Cooperative Oncology Group ≥ 1 ( P = .01). Outcomes for the overall cohort (and separately for the first-line and second-line NHT cohorts) were best for CTC- patients, intermediate for CTC+/AR-V7- patients, and worse for CTC+/AR-V7+ patients. These correlations remained significant in multivariable models. Conclusion This expanded analysis further characterizes the importance of CTC-based AR-V7 mRNA detection in predicting outcomes in patients with CRPC receiving first- and second-line NHT and, to the best of our knowledge, is the first to suggest that this assay be interpreted using three separate prognostic categories: CTC-, CTC+/AR-V7-, and CTC+/AR-V7+.

AR-V7 detection by a novel junction-specific RNA in situ hybridization (RISH) test.

191 Background: Previous studies have reported an association between blood-based detection of androgen receptor splice variant-7 (AR-V7) and resistance to abiraterone/enzalutamide in men with metastatic castration-resistant prostate cancer (mCRPC). Further characterization of AR-V7 and its clinical correlates are necessary but depend on the development of methods that allow for reliable and specific measurement of AR-V7. In this study, we developed and evaluated a novel junction-specific AR-V7 RNA in situ hybridization (RISH) test. Methods: We developed a novel RISH assay targeting single exon-exon junction, allowing for highly-specific detection of mature cytoplasmic AR-FL and AR-V7 mRNA in native cell and tissue environment. We compared quantitative RISH AR-V7 results generated from an automated scoring system with AR-V7 levels quantified by RT-PCR in a panel of cell lines. Using the validated assay, we quantified AR-V7 signals in 58 prostate tumor biopsies. We conducted preliminary evaluation of the clinical correlates of AR-V7 detected. Results: The novel AR-V7 RISH test specifically detected mature cytoplasmic AR-V7 mRNA and did not detect nuclear pre-mRNA. AR-V7 RISH results were highly concordant with RT-PCR results. We generated quantitative AR-FL and AR-V7 data from 93.1% of the clinical specimens examined (54 of 58). Positive AR-V7 signals were detected in 23 specimens, all of which also co-expressed AR-FL. The median AR-V7/AR-FL ratio was 4.6%. Positive detection of AR-V7 was significantly correlated with prior treatment with second-line AR targeting agents and serum PSA ( p &lt;0.05), but not with any other baseline clinical variables. Notably, all castration-sensitive prostate cancer specimens (CSPC) (n = 9) were AR-V7 negative by this method. Association between AR-V7 and treatment outcome has yet to be fully evaluated. Conclusions: We demonstrate for the first time a highly specific and quantifiable AR-V7 RISH test for detection of clinically significant levels of AR-V7 mRNA in prostate tissue specimens. This test may be applied to liquid biopsy specimens to expand the utility. Prospective studies can be designed to evaluate the potential utility of this novel test in drug development and patient management.

Abstract 4965: Analytic validation and clinical qualification of a novel immunohistochemical assay for AR-V7 protein expression in metastatic prostate cancer

Abstract BACKGROUND: The androgen-receptor splice variant 7 (AR-V7) has been implicated in the development of castration resistant prostate cancer (CRPC) and resistance to current therapies including enzalutamide and abiraterone. AR-V7 mRNA expression in circulating tumour cells of patients with CRPC correlated with treatment resistance. However, the importance of AR-V7 has been questioned in light of low AR-V7 mRNA levels relative to the full-length androgen receptor in CRPC and it is critically important to develop validated assays that confirm AR-V7 protein levels and its clinical importance in patients with CRPC. METHODS: Following validation of a monoclonal antibody, immunohistochemical analysis of nuclear AR-V7 (alongside a nuclear AR N-terminal domain antibody; AR-NTD) was performed in a patient cohort identified with matched therapy-naive hormone-sensitive primary prostate cancer (HSPC) and CRPC. We determined the levels of nuclear AR-V7 as patients progressed from HSPC to CRPC. We also determined if AR-V7 expression levels associated with overall survival from time of CRPC biopsy. RESULTS: In our patient cohort (n = 39), nuclear AR-V7 (p = &amp;lt;0.0001) and nuclear AR-NTD (p = 0.0006) increased significantly as patients progressed from HSPC to CRPC. Lower nuclear AR-V7 expression was associated with improved overall survival from time of CRPC biopsy in patient groups divided by the 25th (18.7 vs 9.6 months; HR 0.36 [95% CI 0.17-0.62]; p = 0.002), 50th (13.0 vs 9.8 months; HR 0.60 [95% CI 0.29-1.07]; p = 0.09) or 75th (6.0 vs 11.5 months; HR 0.31 [95% CI 0.04-0.34]; p = 0.0004) percentile of AR-V7 expression. Similarly, a lower nuclear AR-V7 to nuclear AR-NTD ratio was associated with improved overall survival from time of CRPC biopsy in patient groups divided by the 25th (17.8 vs 9.1 months; HR 0.42 [95% CI 0.22-0.78], p = 0.01), 50th (14.0 vs 8.8 months; HR 0.43 [95% CI 0.17-0.69], p = 0.005) and 75th (11.5 vs 7.3 months; HR 0.39 [95% CI 0.09-0.69], p = 0.009) percentile. Nuclear AR-NTD did not associate with overall survival from CRPC biopsy. CONCLUSION: We provide first evidence that expression of nuclear AR-V7 protein not only increases with emerging treatment resistance in CRPC but also is associated with overall survival from time of CRPC biopsy. These data support AR-V7 protein being key to CRPC progression and that agents targeting AR splice variants will be important to improve patient outcome in CRPC. Citation Format: Daniel Nava Rodrigues, Jon Welti, Adam Sharp, Shihua Sun, Ruth Riisnaes, Ines Figueiredo, Zafeiris Zafeiriou, Pasquale Rescigno, Johann S. de Bono, Stephen R. Plymate. Analytic validation and clinical qualification of a novel immunohistochemical assay for AR-V7 protein expression in metastatic prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4965.

Implementing a CTC-based clinical trial assay for selecting AR-V7+ patients for enrollment in a pivotal phase 3 study (ARMOR3-SV).

348 Background: ARMOR3-SV is a randomized phase 3, multi-center study comparing galeterone to enzalutamide in men with metastatic (M1) castrate resistant prostate cancer (CRPC) expressing androgen receptor splice variant-7 mRNA (AR-V7) who have not yet received chemotherapy, or other second generation androgen signaling inhibitors. AR-V7 is a truncated, constitutively active splice variant of the androgen receptor (AR) that lacks the ligand binding domain (LBD) and has been implicated in prostate cancer progression. Recently, the presence of AR-V7 in circulating tumor cells (CTCs) has been associated with a lack of responsiveness to both abiraterone and enzalutamide, whereas galeterone, a selective small molecule that potently degrades the androgen receptor, has demonstrated activity in preclinical model systems expressing AR-V7 and clinically in patients with C-terminal loss, of which AR-V7 is the most common form. Methods: Utilizing the lab test developed at JHU as a model system, we sought to develop a clinical trial assay utilizing immunomagnetic bead isolation of CTCs followed by mRNA isolation and cDNA generation. We then developed a duplexed PCR assay using Taqman chemistry to detect the full-length AR (AR-FL) and AR-V7. Negative patient samples were used to establish the limit of blank and assay cut-off and synthetic oligonucleotides to establish the limit of detection. Results: The AR-FL and AR-V7 assay shows linear response to template dilution to the assay cut-off Ct. Blood spiked with LNCaP and LNCaP95 cells were used to demonstrate assay suitability and sensitivity. We have successfully detected AR-FL and AR-V7 in select CRPC patient samples. We have also demonstrated assay reproducibility and have shown that the assay remains consistent in the presence of select interfering substances. Conclusions: For the ARMOR3-SV trial, this clinical trial assay is being utilized globally at central laboratories to screen patient blood samples for AR-V7 expression in evaluable CTCs as the first criterion for inclusion in this study. Clinical trial information: NCT02438007.

Abstract B173: Galeterone shows anti-tumor activity in multiple pre-clinical models that express androgen receptor splice variants, supporting correlative patient data seen in ARMOR2

Abstract Multiple experimental approaches were used to examine whether and by what mechanism galeterone affects prostate cancer growth in cells and tumors expressing androgen receptor (AR) splice variants, such as AR-V7. Galeterone is a selective, multitargeted, small molecule that disrupts androgen signaling at multiple points in the pathway. ARMOR3-SV is a Phase 3, randomized, open-label, multicenter, controlled clinical trial in metastatic castration resistant prostate cancer (mCRPC) patients whose tumors express AR splice variant-7 mRNA (AR-V7). AR-V7 is a truncated, constitutively active splice variant of the AR that lacks the ligand binding domain (LBD) and has been implicated in prostate cancer progression. The expression of AR-V7 occurs in approximately 14-26% of men with mCRPC prior to second-generation anti-androgens or chemotherapy, and AR-V7 expression has been clinically associated with resistance to enzalutamide (Xtandi) or abiraterone (Zytiga). Here we provide the pre-clinical and clinical rationale for the development of galeterone in mCRPC patients with AR-V7. Our findings show that using multiple pre-clinical approaches, galeterone reduces in vitro prostate cancer cell proliferation, androgen receptor signaling and xenograft tumor growth using cells and tumors that express AR splice variants. Reductions in AR splice variant protein were also observed in cells that also co-express wild-type AR, and prostate cancer cells that lack wild type AR, but transiently express AR splice variant protein. Clinical data further support activity of galeterone in patients with truncated androgen receptors. Galeterone's unique mechanism of AR protein downregulation occurs in both splice variant and wild-type AR, supporting that galeterone-induced AR downregulation is independent of the AR LBD. Because preclinical and clinical data support an opportunity for treatment in this setting, Tokai Pharmaceuticals designed ARMOR3-SV to test galeterone vs. enzalutamide in men with metastatic castration-resistant prostate cancer whose tumors express the AR-V7 splice variant. Citation Format: Douglas B. Jacoby, Amina Zoubeidi, Eva B. Corey, Elahe Mostaghel, Andrew K. Kwegyir-Afful, Senthilmurugan Ramalingam, Vincent Njar. Galeterone shows anti-tumor activity in multiple pre-clinical models that express androgen receptor splice variants, supporting correlative patient data seen in ARMOR2. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B173.

Abstract 2910: Androgen receptor splice variant-7 predicts resistance to enzalutamide in patients with castration-resistant prostate cancer

Abstract Background: Androgen receptor splice variant-7 (AR-V7) is a truncated form of the androgen receptor (AR) protein which lacks the ligand-binding domain, the target of enzalutamide, but remains constitutively active as a transcription factor. Following from preclinical studies implicating AR-V7 as a mechanism of resistance to novel AR-directed therapies, we hypothesized that the presence of AR-V7 in circulating tumor cells (CTCs) from men with advanced prostate cancer would be associated with primary resistance to enzalutamide. Methods: We used quantitative reverse-transcription polymerase-chain-reaction (qRT-PCR) analysis to interrogate CTCs for the presence or absence of AR-V7 from prospectively enrolled patients with metastatic castration-resistant prostate cancer initiating treatment with enzalutamide. We examined associations between AR-V7 status and PSA response rates (the primary clinical endpoint of the study), PSA-progression-free-survival (PSA-PFS), and clinical/radiographic-progression-free-survival (PFS). Multivariable Cox regressions were performed to determine the independent effect of AR-V7 status on clinical outcomes to enzalutamide treatment. A prespecified sample size of 30 patients would yield 85% power to detect a difference in PSA response rates from 10% (in AR-V7-positive men) to 60% (in AR-V7-negative men), using a two-sided α=0.10. Results: Thirty-one (31) enzalutamide-treated patients were enrolled in the study, of which 38.7% (12/31) had detectable AR-V7 mRNA from CTCs. Compared to AR-V7-negative patients, AR-V7-positive men had worse PSA response rates (0% [0/12] vs 52.6% [10/19], P=0.004); in fact, no patient with detectable AR-V7 achieved a PSA response. Furthermore, AR-V7-positive patients had shorter PSA-PFS (median: 1.4 vs 5.9 months, HR 7.4, 95%CI 2.7-20.6, log-rank P&amp;lt;0.001), and shorter PFS (median: 2.1 vs 6.1 months, HR 8.5, 95%CI 2.8-25.4, log-rank P&amp;lt;0.001) than AR-V7-negative patients. In multivariable Cox regression analysis, presence of AR-V7 (HR 3.5, 95%CI 1.2-10.5, P=0.027), baseline PSA level (HR 1.01, 95%CI 1.00-1.01, P=0.042), and prior abiraterone treatment (HR 5.4, 95%CI 1.1-26.5, P=0.039) were all independently predictive of PSA-PFS. Similarly, presence of AR-V7 (HR 3.7, 95%CI 1.2-11.9, P=0.026) and prior abiraterone use (HR 8.7, 95%CI 1.0-75.6, P=0.049) were both independently predictive of PFS in multivariable analysis. Conclusions: Detection of AR-V7 mRNA in circulating tumor cells from patients with metastatic castration-resistant prostate cancer may be associated with primary resistance to enzalutamide. If confirmed by other investigators in larger-scale prospective studies, this could be used as a biomarker to predict enzalutamide resistance (and to direct AR-V7-positive patients away from further AR-targeting therapies). Citation Format: Emmanuel S. Antonarakis, Changxue Lu, Hao Wang, Brandon Luber, Mary Nakazawa, Jeffrey C. Roeser, Yan Chen, Helen L. Fedor, Tamara L. Lotan, Angelo M. De Marzo, John T. Isaacs, William B. Isaacs, Rosa Nadal, Channing J. Paller, Samuel R. Denmeade, Michael A. Carducci, Mario A. Eisenberger, Jun Luo. Androgen receptor splice variant-7 predicts resistance to enzalutamide in patients with castration-resistant prostate cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2910. doi:10.1158/1538-7445.AM2014-2910