Androgen Receptor Variants Occur Frequently in Castration Resistant Prostate Cancer Metastases

Abstract

BackgroundAlthough 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).Methodology/Principal FindingsUsing 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.ConclusionsWe 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.

Ablation of the oncogenic transcription factor ERG by deubiquitinase inhibition in prostate cancer

“…To further demonstrate the translational potential of deubiquitinase inhibition in a prostate cancer model that is more representative of a human tumor, we tested the effect of WP1130 treatment on LuCaP 86.2 tumors. This tumor line was derived from a metastatic site of a castration-resistant AR-and ERG-positive prostate tumor and has been continuously propagated in mice (25). WP1130 treatment recapitulated the effects observed with the VCaP and 22Rv1-ERG cell line xenografts, i.e., a marked reduction in tumor growth (P = 0.0042) (SI Appendix, Fig.…”

An androgen receptor N-terminal domain antagonist for treating prostate cancer

“…Constitutively active AR splice variants that lack LBD have been shown in clinical samples of CRPC (16)(17)(18)(19)38). Antiandrogens that bind the AR LBD do not inhibit the activity of AR v567es , which lacks LBD and is constitutively both nuclear and active (17).…”

Coregulation of srGAP1 by Wnt and Androgen Receptor Signaling: A New Target for Treatment of CRPC

“…Abiraterone Acetate and Enzalutamide) more effectively block androgen synthesis and to prevent activation of androgen receptor (AR) [7,8]. Although these AR targeting agents extend life of CRPC patients by a few months, resistance to these treatments remains common and currently there is no cure for CRPC [9][10][11][12][13][14][15][16][17][18]. Therefore, understanding the molecular mechanisms leading to CRPC and identifying alternative targets are important in developing more effective treatment for CRPC.…”