Androgen Receptor Variants Occur Frequently in Castration Resistant Prostate Cancer Metastases

Although androgens are depleted in castration resistant prostate cancer (CRPC), metastases still express nuclear androgen receptor (AR) and androgen regulated genes. We recently reported that C-terminal truncated constitutively active AR splice variants contribute to CRPC development. Since specific antibodies detecting all C-terminal truncated AR variants are not available, our aim was to develop an approach to assess the prevalence and function of AR variants in prostate cancer (PCa).Using 2 antibodies against different regions of AR protein (N- or C-terminus), we successfully showed the existence of AR variant in the LuCaP 86.2 xenograft. To evaluate the prevalence of AR variants in human PCa tissue, we used this method on tissue microarrays including 50 primary PCa and 162 metastatic CRPC tissues. RT-PCR was used to confirm AR variants. We observed a significant decrease in nuclear C-terminal AR staining in CRPC but no difference between N- and C-terminal AR nuclear staining in primary PCa. The expression of the AR regulated proteins PSA and PSMA were marginally affected by the decrease in C-terminal staining in CRPC samples. These data suggest that there is an increase in the prevalence of AR variants in CRPC based on our ability to differentiate nuclear AR expression using N- and C-terminal AR antibodies. These findings were validated using RT-PCR. Importantly, the loss of C-terminal immunoreactivity and the identification of AR variants were different depending on the site of metastasis in the same patient.We successfully developed a novel immunohistochemical approach which was used to ascertain the prevalence of AR variants in a large number of primary PCa and metastatic CRPC. Our results showed a snapshot of overall high frequency of C-terminal truncated AR splice variants and site specific AR loss in CRPC, which could have utility in stratifying patients for AR targeted therapeutics

A phase I dose-escalation study of enzalutamide in combination with the AKT inhibitor AZD5363 (capivasertib) in patients with metastatic castration-resistant prostate cancer.

Background Activation of the PI3K/AKT/mTOR pathway through loss of phosphatase and tensin homolog (PTEN) occurs in approximately 50% of patients with metastatic castration-resistant prostate cancer (mCRPC). Recent evidence suggests that combined inhibition of the androgen receptor (AR) and AKT may be beneficial in mCRPC with PTEN loss.Patients and methods mCRPC patients who previously failed abiraterone and/or enzalutamide, received escalating doses of AZD5363 (capivasertib) starting at 320 mg twice daily (b.i.d.) given 4 days on and 3 days off, in combination with enzalutamide 160 mg daily. The co-primary endpoints were safety/tolerability and determining the maximum tolerated dose and recommended phase II dose; pharmacokinetics, antitumour activity, and exploratory biomarker analysis were also evaluated.Results Sixteen patients were enrolled, 15 received study treatment and 13 were assessable for dose-limiting toxicities (DLTs). Patients were treated at 320, 400, and 480 mg b.i.d. dose levels of capivasertib. The recommended phase II dose identified for capivasertib was 400 mg b.i.d. with 1/6 patients experiencing a DLT (maculopapular rash) at this level. The most common grade ≥3 adverse events were hyperglycemia (26.7%) and rash (20%). Concomitant administration of enzalutamide significantly decreased plasma exposure of capivasertib, though this did not appear to impact pharmacodynamics. Three patients met the criteria for response (defined as prostate-specific antigen decline ≥50%, circulating tumour cell conversion, and/or radiological response). Responses were seen in patients with PTEN loss or activating mutations in AKT, low or absent AR-V7 expression, as well as those with an increase in phosphorylated extracellular signal-regulated kinase (pERK) in post-exposure samples.Conclusions The combination of capivasertib and enzalutamide is tolerable and has antitumour activity, with all responding patients harbouring aberrations in the PI3K/AKT/mTOR pathway.Clinical trial number NCT02525068

Analytical Validation and Clinical Qualification of a New Immunohistochemical Assay for Androgen Receptor Splice Variant-7 Protein Expression in Metastatic Castration-resistant Prostate Cancer.

Background The androgen receptor splice variant-7 (AR-V7) has been implicated in the development of castration-resistant prostate cancer (CRPC) and resistance to abiraterone and enzalutamide.Objective To develop a validated assay for detection of AR-V7 protein in tumour tissue and determine its expression and clinical significance as patients progress from hormone-sensitive prostate cancer (HSPC) to CRPC.Design, setting, and participants Following monoclonal antibody generation and validation, we retrospectively identified patients who had HSPC and CRPC tissue available for AR-V7 immunohistochemical (IHC) analysis.Outcome measurements and statistical analysis Nuclear AR-V7 expression was determined using IHC H score (HS) data. The change in nuclear AR-V7 expression from HSPC to CRPC and the association between nuclear AR-V7 expression and overall survival (OS) was determined.Results and limitations Nuclear AR-V7 expression was significantly lower in HSPC (median HS 50, interquartile range [IQR] 17.5-90) compared to CRPC (HS 135, IQR 80-157.5; p<0.0001), and in biopsy tissue taken before (HS 80, IQR 30-136.3) compared to after (HS 140, IQR 105-167.5; p=0.007) abiraterone or enzalutamide treatment. Lower nuclear AR-V7 expression at CRPC biopsy was associated with longer OS (hazard ratio 1.012, 95% confidence interval 1.004-1.020; p=0.003). While this monoclonal antibody primarily binds to AR-V7 in PC biopsy tissue, it may also bind to other proteins.Conclusions We provide the first evidence that nuclear AR-V7 expression increases with emerging CRPC and is prognostic for OS, unlike antibody staining for the AR N-terminal domain. These data indicate that AR-V7 is important in CRPC disease biology; agents targeting AR splice variants are needed to test this hypothesis and further improve patient outcome from CRPC.Patient summary In this study we found that levels of the protein AR-V7 were higher in patients with advanced prostate cancer. A higher level of AR-V7 identifies a group of patients who respond less well to certain prostate cancer treatments and live for a shorter period of time

Expression of androgen receptor splice variants in clinical breast cancers

Published: November 05, 2015The importance of androgen receptor (AR) signaling is increasingly being recognized in breast cancer, which has elicited clinical trials aimed at assessing the efficacy of androgen deprivation therapy (ADT) for metastatic disease. In prostate cancer, resistance to ADT is frequently associated with the emergence of androgen-independent splice variants of the AR (AR variants, AR-Vs) that lack the LBD and are constitutively active. Women with breast cancer may be prone to a similar phenomenon. Herein, we show that in addition to the prototypical transcript, the AR gene produces a diverse range of AR-V transcripts in primary breast tumors. The most frequently and highly expressed variant was AR-V7 (exons 1/2/3/CE3), which was detectable at the mRNA level in &#x003E; 50% of all breast cancers and at the protein level in a subset of ER&#x03B1;-negative tumors. Functionally, AR-V7 is a constitutively active and ADT-resistant transcription factor that promotes growth and regulates a transcriptional program distinct from AR in ER&#x03B1;-negative breast cancer cells. Importantly, we provide ex vivo evidence that AR-V7 is upregulated by the AR antagonist enzalutamide in primary breast tumors. These findings have implications for treatment response in the ongoing clinical trials of ADT in breast cancer.Theresa E. Hickey, Connie M. Irvine, Heidi Dvinge, Gerard A. Tarulli, Adrienne R. Hanson, Natalie K. Ryan, Marie A. Pickering, Stephen N. Birrell, Dong Gui Hu, Peter I. Mackenzie, Roslin Russell, Carlos Caldas, Ganesh V. Raj, Scott M. Dehm, Stephen R. Plymate, Robert K. Bradley, Wayne D. Tilley, Luke A. Selt

Hyperglycemia and prostate cancer recurrence in men treated for localized prostate cancer.

Background:Obesity is consistently linked with prostate cancer (PCa) recurrence and mortality, though the mechanism is unknown. Impaired glucose regulation, which is common among obese individuals, has been hypothesized as a potential mechanism for PCa tumor growth. In this study, we explore the relationship between serum glucose at time of treatment and risk of PCa recurrence following initial therapy.Methods:The study group comprised 1734 men treated with radical prostatectomy (RP) or radiation therapy (RT) for localized PCa between 2001-2010. Serum glucose levels closest to date of diagnosis were determined. PCa recurrence was determined based on PSA progression (nadir PSA+2 for RT; PSA0.2 for RP) or secondary therapy. Multivariate Cox regression was performed to determine whether glucose level was associated with biochemical recurrence after adjusting for age, race, body mass index, comorbidity, diagnosis of diabetes, Gleason Sum, PSA, treatment and treatment year.Results:Recurrence was identified in 16% of men over a mean follow-up period of 41 months (range 1-121 months). Those with elevated glucose (100 mg/dl) had a 50% increased risk of recurrence (HR 1.5, 95% CI: 1.1-2.0) compared with those with a normal glucose level (<100 mg/dl). This effect was seen in both those undergoing RP (HR 1.9, 95% CI: 1.0-3.6) and those treated with RT (HR 1.4, 95% CI: 1.0-2.0).Conclusions:Glucose levels at the time of PCa diagnosis are an independent predictor of PCa recurrence for men undergoing treatment for localized disease

Intense exercise for survival among men with metastatic castrate-resistant prostate cancer (INTERVAL-GAP4): A multicentre, randomized, controlled phase III study protocol

Introduction: Preliminary evidence supports the beneficial role of physical activity on prostate cancer outcomes. This phase III randomised controlled trial (RCT) is designed to determine if supervised high-intensity aerobic and resistance exercise increases overall survival (OS) in patients with metastatic castrate-resistant prostate cancer (mCRPC). Methods and analysis: Participants (n=866) must have histologically documented metastatic prostate cancer with evidence of progressive disease on androgen deprivation therapy (defined as mCRPC). Patients can be treatmentnaive for mCRPC or on first-line androgen receptor-targeted therapy for mCRPC (ie, abiraterone or enzalutamide) without evidence of progression at enrolment, and with no prior chemotherapy for mCRPC. Patients will receive psychosocial support and will be randomly assigned (1:1) to either supervised exercise (high-intensity aerobic and resistance training) or self-directed exercise (provision of guidelines), stratified by treatment status and site. Exercise prescriptions will be tailored to each participant’s fitness and morbidities. The primary endpoint is OS. Secondary endpoints include time to disease progression, occurrence of a skeletal-related event or progression of pain, and degree of pain, opiate use, physical and emotional quality of life, and changes in metabolic biomarkers. An assessment of whether immune function, inflammation, dysregulation of insulin and energy metabolism, and androgen biomarkers are associated with OS will be performed, and whether they mediate the primary association between exercise and OS will also be investigated. This study will also establish a biobank for future biomarker discovery or validation. Ethics and dissemination: Validation of exercise as medicine and its mechanisms of action will create evidence to change clinical practice. Accordingly, outcomes of this RCT will be published in international, peer-reviewed journals, and presented at national and international conferences. Ethics approval was first obtained at Edith Cowan University (ID: 13236 NEWTON), with a further 10 investigator sites since receiving ethics approval, prior to activation. Trial registration number: NCT02730338

Second-Generation HSP90 Inhibitor Onalespib Blocks mRNA Splicing of Androgen Receptor Variant 7 in Prostate Cancer Cells.

Resistance to available hormone therapies in prostate cancer has been associated with alternative splicing of androgen receptor (AR) and specifically, the expression of truncated and constitutively active AR variant 7 (AR-V7). The transcriptional activity of steroid receptors, including AR, is dependent on interactions with the HSP90 chaperone machinery, but it is unclear whether HSP90 modulates the activity or expression of AR variants. Here, we investigated the effects of HSP90 inhibition on AR-V7 in prostate cancer cell lines endogenously expressing this variant. We demonstrate that AR-V7 and full-length AR (AR-FL) were depleted upon inhibition of HSP90. However, the mechanisms underlying AR-V7 depletion differed from those for AR-FL. Whereas HSP90 inhibition destabilized AR-FL and induced its proteasomal degradation, AR-V7 protein exhibited higher stability than AR-FL and did not require HSP90 chaperone activity. Instead, HSP90 inhibition resulted in the reduction of AR-V7 mRNA levels but did not affect total AR transcript levels, indicating that HSP90 inhibition disrupted AR-V7 splicing. Bioinformatic analyses of transcriptome-wide RNA sequencing data confirmed that the second-generation HSP90 inhibitor onalespib altered the splicing of at least 557 genes in prostate cancer cells, including AR. These findings indicate that the effects of HSP90 inhibition on mRNA splicing may prove beneficial in prostate cancers expressing AR-V7, supporting further clinical investigation of HSP90 inhibitors in malignancies no longer responsive to androgen deprivation. Cancer Res; 76(9); 2731-42. ©2016 AACR