Androgen Receptor Variants Research Articles

Evolution of androgen receptor variant (ARV) profiles in serial metastatic solid and liquid biopsies in metastatic castrate resistant prostate cancer (mCRPC) treated with abiraterone acetate/ prednisone (AA/P).

e16559 Background: ARVs that develop early during treatment with abiraterone acetate/ prednisone (AA/P) may play a role in treatment resistance. We evaluated metastatic site and whole blood mRNA expression of full-length AR (AR-FL) and ARVs to characterize treatment-emergent ARVs (TE-ARVs) from men with mCRPC pre- and post- 12 weeks of AA/P collected in a prospective clinical trial (NCT#01953640). Methods: RNAseq performed on paired metastatic site biopsy (n = 40) and whole blood (n = 25) passed quality control. Reads were aligned to the GRCh38 reference genome with the spliced-alignment TopHat2 package. AR-FL or ARVs were detected if ≥ 2 splice reads aligned to unique splice junctions for AR-FL, AR-8, AR-45, AR-23, AR-V3, AR-V5V6, AR-V7, AR-V8, AR-V9, AR-V10, AR-V12, AR-V13, and AR-V14, and normalized to splice reads per million (SRPM). Cox proportional hazard regression analysis was performed on AR-FL and AR-Vs with ≥1 SRPM for association with time to treatment change (TTTC). Results: In metastatic site biopsies post-AA/P, the average number of splice reads was 27,376,541 (range 7,753,998 to 62,456,773). The median number of ARVs detected was 2 (range 0-8), with a total of total of 110 ARVs identified (Table). Dynamic shifts in ARV profiles were observed post-AAP, with 41 TE-ARVs identified in 17 unique patients. The most common TE-ARV was AR-8 (n = 8), followed by AR-45 (n = 5), AR-23 (n = 5), and AR-V7 (n = 4). The presence of AR-V7 post-AAP was adversely associated with TTTC (hazard ratio 2.46, p = 0.013). The identification of early TE- ARV was not associated with TTTC. In whole blood samples, post-AA/P detection of AR-FL was low (n = 3) and no ARVs were detected. Conclusions: No specific patterns were observed in ARV profiles obtained in the metastatic biopsies after 12 weeks of treatment with AA/P. Clinical trial information: 01953640. [Table: see text]

Phase 1b/2 study of enzalutamide (ENZ) with LY3023414 (LY) or placebo (PL) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) after progression on abiraterone.

5009 Background: Preclinical and phase 1 results suggest PI3K/mTOR pathway inhibition may enhance androgen receptor inhibition. We report the results of a double-blind, placebo-controlled, randomized Phase 1b/2 study of ENZ±LY (a dual PI3K/mTOR inhibitor) in pts with mCRPC who progressed on abiraterone. Methods: Phase 1b pts received single-agent LY 200 mg twice daily (BID) for 1 wk prior to starting LY+ENZ. Phase 2 pts were randomized 1:1 to 160 mg daily ENZ with PL or 200 mg BID LY on a 28-d cycle. The primary objective was progression-free survival (PFS: serological, radiographic [rPFS], or death) by PCWG2 criteria. Secondary objectives were rPFS, safety, decline in PSA, and PK. Exploratory biomarker analyses included outcomes by presence of androgen receptor variant 7 (AR-V7). 92 primary PFS events were needed for the study to have at least 80% power at one-sided alpha=0.20. Results: LY+ENZ was tolerable during Phase 1b with 1 dose limiting toxicity observed in 13 enrolled pts. Mean LY exposures remained in an efficacious range despite a 30% average decrease when combined with ENZ. In Phase 2, 129 pts were randomized to LY+ENZ (N=65) and PL+ENZ (N=64) (Table). Median PCWG2-PFS was 3.7 mos (LY+ENZ) vs 2.9 mos (PL+ENZ) (HR 0.66, 95% CI 0.43, 0.99; p-value 0.0208). Conclusions: Combination LY+ENZ had a clinically manageable safety profile. The primary end-point of PCWG2-PFS was met and is supported by a clinically meaningful delay in rPFS in AR-V7 negative pts. The biomarker data provide important insights to inform future development strategies. Clinical trial information: NCT02407054. [Table: see text]

Preclinical investigation of a small molecule inhibitor of p300/CBP reveals efficacy in patient-derived prostate tumor explants.

e16534 Background: Growth and survival of prostate cancer cells are initially dependent upon androgens, and androgen deprivation therapy (ADT) is used to control tumor growth. Unfortunately, resistance to ADT inevitably occurs, and patients relapse with lethal castrate-resistant prostate cancer (CRPC). Increased expression of the androgen receptor (AR) and constitutively active AR variants are hallmarks of CRPC, and treatments targeting aberrant AR signaling are urgently required. CCS1477 is an inhibitor of p300/CBP currently in a Phase I/IIa study for CRPC. CCS1477 enhances degradation of numerous cellular proteins including the AR and AR variants in prostate cancer cells. Our preclinical studies with this compound demonstrated potent single-agent efficacy of CCS1477 using in vitro and in vivo models of prostate cancer and, when used in combination, CCS1477 enhances the efficacy of enzalutamide, a clinical AR antagonist. Understanding the response of clinical tumors to CCS1477, and their potential adaptive evolution, is essential to personalize treatment and predict potential resistance mechanisms. Methods: To assess CCS1477 in human disease, we used a unique model in which clinical prostate tumors from radical prostatectomy are cultured as explants with maintenance of tissue integrity, cell proliferation and androgen signaling. Tumors from 13 patients were cultured in the absence or presence of CCS1477 (10µM) or enzalutamide (10µM) for 48 or 72 hours; micromolar doses were selected to account for altered small molecule uptake and penetration into tissues compared to cell lines, as previously reported. Proliferation, apoptosis and androgen signaling were all analyzed post-culture. Results: Whereas the tumor explants exhibited highly heterogenous proliferative responses to enzalutamide, tumors from all patients exhibited a marked antiproliferative response to CCS1477 (mean reduction in Ki67 immunoreactivity of > 90% compared to vehicle control; p < 0.0005). Culture with CCS1477 was associated with repression of androgen signaling in the prostate tissues, measured by expression and secretion of the clinical biomarker prostate specific antigen (PSA). Conclusions: The consistent and pronounced efficacy of CCS1477 in this patient-derived model would support further investigation of this class of epigenetic agents in the castrate-sensitive prostate cancer setting.

An open label phase 1/2A study to evaluate the safety, pharmacokinetics, pharmacodynamics, and preliminary efficacy of TRC253, an androgen receptor antagonist, in patients with metastatic castration-resistant prostate cancer.

e16542 Background: TRC253 is a high-affinity, orally active small molecule antagonist of the androgen receptor (AR) and specific mutated variants of AR that does not possess agonist activity towards either wild type or mutated AR. TRC253 inhibits AR nuclear translocation as well as AR binding to DNA and is a transcription antagonist. TRC253 treatment is efficacious in an LNCaP xenograft model driven by F877L mutant AR. Methods: In P1 dose escalation, pts with mCRPC previously treated with an AR inhibitor were assigned to increasing TRC253 doses of 40-320 mg daily. Dose escalation followed single-pt dose escalation design for the 40, 80 mg cohorts and expanded to 3+3 design in the 160, 240, 280, and 320 mg cohorts to assess safety, determine the recommended phase 2 dose (RP2D), and evaluate prostate-specific antigen response at week 12. Toxicity and efficacy assessments used NCI-CTCAE v4.03 and PCWG3 criteria, respectively. Pts were centrally screened by circulating tumor DNA using the BEAMing digital PCR assay. Results: Twenty-two pts were enrolled in phase 1 at TRC253 doses of 40 (n = 1), 80 (n = 1), 160 (n = 2), 240 (n = 6), 280 (n = 4), and 320 mg (n = 8) daily in 28-day cycles. One DLT of G3 QTcF prolongation occurred at 320 mg. No drug-related SAEs were reported. Drug-related AEs ≥ G2 included QTcF prolongation (2 G2, 2 G3), elevated lipase (1 G3), fatigue (4 G2), arthralgia (1 G2), diarrhea (1 G2), and platelet count decrease (1 G2). One pt on study had AR F877L at baseline and remained on treatment for 49 wks with PR by RECIST. The remaining 21 pts did not have AR F877L at baseline and of these, 48% (10) remained on study > 6 cycles and one pts had a > 50% decrease in PSA. Target PK exposures were achieved consistently at 280 mg. 280 mg was selected as the RP2D based on safety and PK data. Conclusions: TRC253 daily at 280 mg was well-tolerated and selected as the RP2D. P2 dose expansion is currently enrolling 2 cohorts: 15 pts with AR F877L and 30 pts without AR F877L. The objectives of P2 include collection of additional data for safety, PK, PET and efficacy of TRC253 in mCRPC pts with specific AR mutations. Clinical trial information: NCT02987829.

Cigarette smoking augments androgen receptor activity and promotes resistance to antiandrogen therapy.

Cigarette smoking is associated with worse outcomes in prostate cancer, whose growth is dependent on androgen receptor (AR) signaling. We aimed to elucidate the biological effect of cigarette smoking on AR signaling and its clinical influence on oncological outcome. Gene expression levels after exposure to tobacco smoke condensate (TSC) were evaluated by quantitative real-time polymerase chain reaction and Western blot analysis in prostate cancer cells. Cellular sensitivities to enzalutamide and docetaxel after TSC exposure were evaluated using a prostate cancer cell proliferation assay. Prognosis was compared between current smokers and nonsmokers when treated with AR-axis-targeting (ARAT) agent enzalutamide and docetaxel. Expression of AR variants as well as prostate-specific antigen was augmented after TSC exposure, which occurred after Akt phosphorylation. These inductions were suppressed by Akt inhibitor LY294002 as well as antioxidant N-acetylcysteine. Consistently, TSC exposure augmented cellular resistance to enzalutamide. In clinical data, cigarette smoking was associated with worse progression-free survival and cancer-specific survival when patients with prostate cancer were treated with ARAT agents but not docetaxel. It was suggested that cigarette smoking leads to detrimental oncological outcome when prostate cancer patients are treated with ARAT agents through induction of aberrant AR signaling. Accordingly, we recommend that patients with advanced prostate cancer should refrain from cigarette smoking.

Androgen receptor variant 7 (AR-V7) in sequencing therapeutic agents for castratrion resistant prostate cancer: A critical review.

Background:androgen receptor variant 7 (AR-V7) has been suggested as potential marker for treatment selection in men with metastatic castration-resistant prostate cancer (mCRPC). The aim of the present review is to critically analyze: frequency of the AR-V7 expression in mCRPC cases—impact of AR-V7 expression on abiraterone, enzalutamide, and taxane therapy.Methods:we searched in the Medline and Cochrane Library database from the literature of the past 10 years. We critically evaluated the level of evidence according to the European Association of Urology (EAU) guidelines.Results:12 clinical trials were selected. The determination of AR-V7 in peripheral blood using circulating tumor cells mRNA seems to be the preferred method. At baseline, the mean percentage of cases with AR-V7 positivity was 18.3% (range 17.8%–28.8%). All data on mCRPC submitted to enzalutamide or abiraterone reported a significantly (P <.05) lower clinical progression-free survival (CPFS) and overall survival (OS) in AR-V7+ than AR-V7− cases (CPFS hazard ratio [HR]: 2.3; 95% CI 1.1–4.9; OS HR: 3.0; 95% CI 1.4–6.3). In mCRPC cases submitted to chemotherapies data are not homogeneous and some studies showed no association between CPFS or OS and AR-V7 status (OS HR 1.6; 95% CI 0.6–4.4; P = .40).Conclusions:the suggestion is that taxane therapy is more efficacious than abiraterone or enzalutamide for men with AR-V7+ CRPC. On the contrary, clinical outcomes did not seem to differ significantly on the basis of the type of therapy used among AR-V7− cases.

Androgen receptor-modulatory microRNAs provide insight into therapy resistance and therapeutic targets in advanced prostate cancer

Androgen receptor (AR) signalling is a key prostate cancer (PC) driver, even in advanced ‘castrate-resistant’ disease (CRPC). To systematically identify microRNAs (miRs) modulating AR activity in lethal disease, hormone-responsive and -resistant PC cells expressing a luciferase-based AR reporter were transfected with a miR inhibitor library; 78 inhibitors significantly altered AR activity. Upon validation, miR-346, miR-361-3p and miR-197 inhibitors markedly reduced AR transcriptional activity, mRNA and protein levels, increased apoptosis, reduced proliferation, repressed EMT, and inhibited PC migration and invasion, demonstrating additive effects with AR inhibition. Corresponding miRs increased AR activity through a novel and anti-dogmatic mechanism of direct association with AR 6.9 kb 3′UTR and transcript stabilisation. In addition, miR-346 and miR-361-3p modulation altered levels of constitutively active AR variants, and inhibited variant-driven PC cell proliferation, so may contribute to persistent AR signalling in CRPC in the absence of circulating androgens. Pathway analysis of AGO-PAR-CLIP-identified miR targets revealed roles in DNA replication and repair, cell cycle, signal transduction and immune function. Silencing these targets, including tumour suppressors ARHGDIA and TAGLN2, phenocopied miR effects, demonstrating physiological relevance. MiR-346 additionally upregulated the oncogene, YWHAZ, which correlated with grade, biochemical relapse and metastasis in patients. These AR-modulatory miRs and targets correlated with AR activity in patient biopsies, and were elevated in response to long-term enzalutamide treatment of patient-derived CRPC xenografts. In summary, we identified miRs that modulate AR activity in PC and CRPC, via novel mechanisms, and may represent novel PC therapeutic targets.

4 - Predicting abiraterone acetate treatment resistance from blood-circulating androgen receptor variants in castration-resistant prostate cancer

4 - Predicting abiraterone acetate treatment resistance from blood-circulating androgen receptor variants in castration-resistant prostate cancer

A novel CRISPR-engineered prostate cancer cell line defines the AR-V transcriptome and identifies PARP inhibitor sensitivities.

Resistance to androgen receptor (AR)-targeted therapies in prostate cancer (PC) is a major clinical problem. A key mechanism of treatment resistance in advanced PC is the generation of alternatively spliced forms of the AR termed AR variants (AR-Vs) that are refractory to targeted agents and drive tumour progression. Our understanding of how AR-Vs function is limited due to difficulties in distinguishing their discriminate activities from full-length AR (FL-AR). Here we report the development of a novel CRISPR-derived cell line which is a derivative of CWR22Rv1 cells, called CWR22Rv1-AR-EK, that has lost expression of FL-AR, but retains all endogenous AR-Vs. From this, we show that AR-Vs act unhindered by loss of FL-AR to drive cell growth and expression of androgenic genes. Global transcriptomics demonstrate that AR-Vs drive expression of a cohort of DNA damage response genes and depletion of AR-Vs sensitises cells to ionising radiation. Moreover, we demonstrate that AR-Vs interact with PARP1 and PARP2 and are dependent upon their catalytic function for transcriptional activation. Importantly, PARP blockade compromises expression of AR-V-target genes and reduces growth of CRPC cell lines suggesting a synthetic lethality relationship between AR-Vs and PARP, advocating the use of PARP inhibitors in AR-V positive PC.

Differential expression of androgen receptor variants in hormone-sensitive prostate cancer xenografts, castration-resistant sublines, and patient specimens according to the treatment sequence.

Androgen receptor variants (AR-vs), especially AR-v7 and AR-v 5, 6, and 7 exon-skipped (AR-v567es), are reportedly key players in the development of castration-resistant prostate cancer (CRPC). We previously established a mouse xenograft model (JDCaP) from a metastatic skin lesion from a Japanese patient with CRPC and that was revealed to exhibit androgen sensitivity. In the present study, we established multiple castration-resistant xenograft models from JDCaP mice to investigate the biological features of CRPC. Tissue from JDCaP mice was transplanted into male and female nude mice, and after serial passaging, castration-resistant sublines (JDCaP-CR2M and JDCaP-CR4M in male mice, JDCaP-CR2F and JDCaP-CR4F in female mice) were established. We investigated anti-androgen and testosterone sensitivity and the messenger RNA expression pattern of full-length AR and AR-vs. In addition, we compared AR protein levels of patient specimens among primary, local-recurrent, and two skin-metastatic tumors. All JDCaP-CR sublines showed continuous growth following the administration of bicalutamide, although the effects of testosterone varied among sublines. Parental JDCaP and JDCaP-CR2M, JDCaP-CR4M, and JDCaP-CR4F sublines expressed AR-v7, whereas JDCaP-CR2F exhibited elevated AR-v567es expression resulting from genomic deletion, which was confirmed by DNA sequencing. Moreover, we confirmed AR-v7 expression in the tumor of the original patient after androgen-deprivation therapy. Each JDCaP-CR subline showed different AR-v-expression patterns, with JDCaP-CR2F expressing AR-v567es due to genomic deletion. Our results indicated that AR-vs emerged after androgen-deprivation therapy and appeared essential for acquisition of castration resistance.

SAT-330 Preclinical Screen of Patient CRPC Tumors Shows Sensitivity to Bromodomain Inhibitors Includes AR-null and Neuroendocrine Disease

Castration-resistant prostate cancer (CRPC) remains a lethal disease despite the introduction of second generation androgen receptor (AR) directed therapies. Resistance to AR directed therapies, such as abiraterone and enzalutamide, emerges through diverse alterations in the AR pathway or transition to aggressive AR-null phenotypes. Although bromodomain and extra-terminal (BET) inhibitor therapies are in current clinical trials for CRPC, understanding of the full spectrum of patient responders is limited by a lack of models for preclincial testing. Thus, the goal of this study was to examine the efficacy of BET inhibitors in a panel of patient-derived models of CRPC, including AR-null and neuroendocrine differentiated tumors that are inherently resistant to AR-directed therapy. To rapidly screen the sensitivity of tumors to BET inhibitors, we used ex vivo cultures of patient-derived xenograft tissue from the MURAL (Melbourne Urological Research Alliance) cohort of patient tumors and treated them with JQ1. Changes in proliferation and apoptosis were measured using histology for Ki67 and cleaved caspase 3. Consistent with previous studies, our results showed that all AR-positive tumors were sensitive to JQ1, with decreases in proliferation and increases in apoptosis. Importantly, this includes tumors from patients who failed abiraterone and/or enzalutamide and have diverse alterations of the AR, including mutations, genomic amplifications and expression of truncated AR variants. Surprisingly, 50% of AR null tumors were just as sensitive to BET inhibitors and AR-positive tumors. This includes tumors with large cell and small cell neuroendocrine histopathology, which are inherently resistant to AR-directed therapies. We also assessed intra-patient heterogeneity by examining tumors from different metastases of the same patient. We observed consistent responses in one patient, but divergent responses in another, likely due to differences in AR status. Collectively, our data show that BET inhibitors are promising treatments for tumors with diverse mechanisms of resistance to AR-directed therapies; however, the responses of AR-null tumors are more heterogeneous. Therefore, further studies to identify biomarkers of responsiveness to BET inhibitors in AR-null and neuroendocrine tumors are warranted.

Androgen receptor variant 12 promotes migration and invasion by regulating MYLK in gastric cancer.

Androgen receptor (AR) and its variants (AR-Vs) promote tumorigenesis and metastasis in many hormone-related cancers, such as breast, prostate and hepatocellular cancers. However, the expression patterns and underlying molecular mechanisms of AR in gastric cancer (GC) are not fully understood. This study aimed to detect the expression of AR-Vs in GC and explored their role in metastasis of GC. Here, the AR expression form was identified in GC cell lines and tissues by RT-PCR and qPCR. Transwell assays and experimental lung metastasis animal models were used to assess the function of AR in cell migration and invasion. Downstream targets of AR were screened by bioinformatics, and identified by luciferase reporter assays and electrophoretic mobility shift assays. AR-v12 was identified as the main expression form in GC cell lines and tissues. Different from full length of AR, AR-v12 was localized to the nucleus independent of androgen. Upregulation of AR-v12 in primary GC tissues was significantly associated with metastasis. Overexpression of AR-v12 promoted migration and invasion independent of androgen. Knockdown of AR-v12 inhibited migration and invasion in vitro, as well as metastasis in vivo. Furthermore, AR-v12, serving as a transcription factor, promoted metastasis through regulating the promoter activity of MYLK. In AR-v12 overexpressing cells, knockdown of MYLK inhibited cell migration and invasion, while in AR-v12 knocked-down cells, overexpression of MYLK promoted cell migration and invasion. Collectively, our study demonstrates that AR-v12 is highly expressed in GC tissues and promotes migration and invasion through directly regulating MYLK. Copyright © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

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

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

Human placental androgen receptor variants: Potential regulators of male fetal growth

IntroductionNumerous studies show that males have increased intrauterine growth compared to females, and that pregnancy complications may further these growth differences, but the regulatory mechanisms underlying these differences remain unknown. We propose that these growth outcomes may be due to sex-specific differences in androgen sensitivity – giving rise to altered growth signalling pathways – mediated by the differential expression of placental androgen receptor (AR) variants. MethodsPlacental protein and mRNA were used to identify AR protein variant levels and AR-downstream target gene expression, and were then analysed against neonatal measurements. Dihydrotestosterone (DHT)-induced AR protein variant expression and downstream growth factors were examined in vitro. ResultsFour known AR variants (AR-FL, AR-V1, AR-V7, and AR-45), and three unknown proteins (120, 90 and 55 kDa) immunoreactive to the anti-AR antibody were identified in human placentae. Male placentae from controlled asthmatic pregnancies had increased AR-45 and decreased AR-V1 and AR-V7 nuclear expression. Increased nuclear AR-45 expression was associated with increased insulin-like growth factor 1 (IGF-1), IGF-1 receptor (IGF-1R), and IGF-binding protein 5 (IGFBP-5) mRNA expression and normal male growth. AR-45 mRNA and protein did not change in the presence of uncontrolled maternal asthma and associated with an increase in small for gestational (SGA) male fetuses. In vitro DHT stimulation increased AR-45 protein and IGF-1R and IGFBP-5 mRNA expression. ConclusionsCollectively, our data shows altered AR protein expression and downstream signalling targets may contribute to sex-specific fetal growth outcomes in response to an adverse environment, and that AR-45 appears central in mediating these changes.

Raddeanin A down-regulates androgen receptor and its splice variants in prostate cancer.

Castration‐resistant progression of prostate cancer is a major cause of prostate cancer mortality, and increased expression and activity of the full‐length and the splice variants of androgen receptor (AR) have been indicated to drive castration resistance. Consequently, there is an urgent need to develop agents that can target both the full‐length and the splice variants of AR for more effective treatment of prostate cancer. In the present study, we showed that raddeanin A (RA), an oleanane‐type triterpenoid saponin, suppresses the transcriptional activities of both the full‐length and the splice variants of AR. This is attributable to their decreased expression as a result of RA induction of proteasome‐mediated degradation and inhibition of the transcription of the AR gene. We further showed the potential of using RA to enhance the growth inhibitory efficacy of docetaxel, the first‐line chemotherapy for prostate cancer. This study identifies RA as a new agent to target both the full‐length and the splice variants of AR and provides a rationale for further developing RA for prostate cancer treatment.

Constant Degradation of the Androgen Receptor by MDM2 Conserves Prostate Cancer Stem Cell Integrity.

Prostate cancer stem cells (CSC) are implicated in tumor initiation, cancer progression, metastasis, and the development of therapeutic-resistant disease. It is well known that the bulk of prostate cancer cells express androgen receptor (AR) and that androgens are required for prostate cancer growth, progression, and emergence of castration-resistant disease. In contrast, the small subpopulation of self-renewing CSCs exhibits an AR-negative (AR-) signature. The mechanisms underlying the absence of AR are unknown. Using CSC-like cell models isolated from clinical biopsy tissues, we identify the E3 ligase MDM2 as a key regulator of prostate CSC integrity. First, unlike what has been reported for the bulk of AR+ tumor cells where MDM2 regulates the temporal expression of AR during transcriptional activity, MDM2 in CSCs promoted the constant ubiquitination and degradation of AR, resulting in sustained loss of total AR protein. Second, MDM2 promoted CSC self-renewal, the expression of stem cell factors, and CSC proliferation. Loss of MDM2 reversed these processes and induced expression of full-length AR (and not AR variants), terminal differentiation into luminal cells, and cell death. Selectively blocking MDM2-mediated activity in combination with androgen/AR-targeted therapy may offer a novel strategy for eliminating AR- CSCs in addition to the bulk of AR+ prostate cancer cells, decreasing metastatic tumor burden and inhibiting the emergence of therapeutic resistance.Significance: These findings provide a novel mechanistic aspect of prostate cancer cell stemness that advances our understanding of the diverse transcriptional activity that bypasses AR in contributing to therapeutic resistance, tumor progression, and metastasis.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/6/1124/F1.large.jpg.

ARV7 and ARFL mRNA in blood to predict androgen receptor inhibitors and docetaxel response in castration-resistant prostate cancer patients.

207 Background: The constitutively active androgen receptor (AR) variant 7 ( ARV7) has been associated with AR inhibitors (ARI) resistance, while its role predicting taxanes response remains controversial. We investigated the association between ARV7 and AR full length ( ARFL) expression pre-docetaxel treatment and changes pre- post-treatment in blood with docetaxel activity in metastatic castration-resistant prostate cancer (mCRPC) patients. Methods: ARV7 and ARFL mRNAs were tested by quantitative reverse-transcription PCR in peripheral blood mononuclear cells (PBMC) from mCRPC patients. Measurements were performed before docetaxel treatment and in a subset of patients also post-treatment. A cohort of patients treated with ARI was also included as a control. Results: We included 105 patients: 50 with treated with docetaxel and 55 with ARI. In 28 patients ARV7 and ARFL were evaluated pre and post-docetaxel. High ARV7 correlated with longer PSA-PFS (HR 0.42; 95%CI 0.18-0.99; P= 0.049), radiologic (RX)-PFS (HR 0.32; 95%CI 0.14-0.72; P= 0.006), and overall survival (OS) (HR 0.41; 95%CI 0.18-0.91; P= 0.028) to docetaxel. When relativizing to ARFL we observed that high ARV7/ ARFL ratio also correlated with a better PSA-PFS (HR 0.38; 95%CI 0.17-0.85; P= 0.0179) and RX-PFS (HR 0.43; 95%CI 0.2-0.91; P= 0.0273) to docetaxel. High ARV7 and ARV7/ ARFL were correlated with lower prostatic-specific antigen (PSA) progression-free survival (PFS) to ARI therapy (HR 2.18; 95%CI 1.03-4.6; P= 0.043 and HR 3.84; 95%CI 1.54-9.4; P= 0.004, respectively). ARV7/ ARFL and treatment- ARV7/ARFL interaction were independently associated with better PSA-PFS to docetaxel treatment and lower PSA-PFS to ARI. The increase of ARV7 mRNA levels after docetaxel treatment was indicative of longer OS (HR 0.07; 95%CI 0.008-0.57; P= 0.013). Conclusions: High ARV7 expression and ARV7/ ARFL ratio evaluated in PBMC pre-docetaxel are associated with better clinical outcome in mCRPC patients and lower ARI benefit. The increase of ARV7 levels after docetaxel exposure was also indicative of better outcome.

47 - HSP70/STUB1 complex regulates androgen receptor variants through proteostasis and confers enzalutamide and abiraterone resistance in lethal prostate cancer

47 - HSP70/STUB1 complex regulates androgen receptor variants through proteostasis and confers enzalutamide and abiraterone resistance in lethal prostate cancer

1005 - VERU-111, a novel oral inhibitor of α and β tubulin, inhibits tumor growth in the human castration-resistant AR variant prostate cancer (PCa) model 22Rv1

1005 - VERU-111, a novel oral inhibitor of α and β tubulin, inhibits tumor growth in the human castration-resistant AR variant prostate cancer (PCa) model 22Rv1

Hsp-27 and NF-κB pathway is associated with AR/AR-V7 expression in prostate cancer cells

In the present study, NF-κB inhibitor BAY 11-7082 and/or Hsp-27 inhibitor KRIBB-3 agents were used to investigate the molecular mechanisms mediating androgen receptor expression on prostate cancer cell lines. The decrease observed in androgen receptor and p65 expressions, particularly at 48 h, in parallel with the decrease in the phosphorylation of the p-IKK α/β and p-Hsp-27 proteins in the LNCaP cells, indicated that androgen receptor inactivation occurred after the inhibition of the NF-κB and Hsp-27. In 22Rv1 cells, androgen receptor variant-7 was also observed to be decreased in the combined dose of 48 h. The association of this decrease with the decrease in androgen receptor and p65 expressions is a supportive result for the role of NF-κB signaling in the formation of androgen receptor variant. In androgen receptor variant-7 siRNA treatment in 22Rv1 cell lines, decrease of expression of androgen receptor variant-7 as well as decrease of expression of androgen receptor and p65 were observed. The decrease statistically significant in androgen receptor and p65 expressions was even greater when siRNA treatment was followed with low dose and time (6 h) combined treatment after transfection. We also showed that increased Noxa and decreased Bcl-2 protein level, indicated that apoptotic induction after this combination. In conclusion, inhibition of NF-κB and Hsp-27 is also important, along with therapies for androgen receptor variant-7 inhibition.