Abstract 238: Androgen insensitivity syndrome germline loss-of-function mutations in the androgen receptor that acquire somatic gain-of-function in prostate cancer

Abstract

Abstract Genomic alterations in the androgen receptor (AR) commonly occur in patients with advanced prostate cancer resistant to androgen deprivation therapies. While still retaining androgen sensitivity, recurring AR mutations become drivers of antiandrogen resistance by causing alterations in the ligand binding pocket that enables one specific antiandrogen to bind that particular mutant receptor in an agonist conformation, thereby aberrantly activating AR transcriptional activity. We chronically treated antiandrogen-sensitive preclinical prostate cancer models (LNCaP-AR and CWR22Pc) with antiandrogens followed by high-throughput sequencing of the AR exons 2-8 to search for novel mutations that may be associated with antiandrogen resistance. The mutation A597T in the DNA binding domain was found in four LNCaP-AR xenograft tumors from mice receiving enzalutamide or ARN-509, while the ligand binding domain mutation P893S was uncovered in CWR22Pc cells treated in vitro with combined androgen depletion and bicalutamide. Recent whole exome sequencing studies of clinical prostate cancer identified single patients with each of these mutations at high allele frequencies and without concurrent AR amplification (www.cBioPortal.org). A597T occurred in a Gleason 6 primary tumor, whereas P893S was found in a patient with metastatic castration resistant prostate cancer who had received bicalutamide during the course of treatment. Remarkably, both A597T and P893S were earlier reported as germline loss-of-function mutations in patients with androgen insensitivity syndrome. Using an AR reporter assay in AR-null cells coupled with overexpression of these AR mutants, we confirmed that P893S is not activated by the androgen dihydrotestosterone (DHT), but nevertheless is potently stimulated by bicalutamide. In silico modeling showed that in contrast to the wild-type AR, cofactor-recruiting helix 12 of the ligand binding domain of P893S substantially drifted away from an agonist conformation when bound to DHT but was able to adopt the active conformation when simulated with bicalutamide. Importantly, overexpression of AR-P893S in CWR22Pc cells conferred bicalutamide resistance in vivo. These findings highlight an unexpected contextual element to the function of AR mutants, and suggest that rare or private AR mutations may nonetheless act as drivers of clinical progression. Citation Format: Philip A. Watson, Minna D. Balbas, Zeda Zhang, Taslima F. Ishmael, Kayla E. Lawrence, John Wongvipat, Sophie D. Sawyers, Yi-Mi Wu, Dan Robinson, Yang Shen, Arul M. Chinnaiyan, Charles L. Sawyers. Androgen insensitivity syndrome germline loss-of-function mutations in the androgen receptor that acquire somatic gain-of-function in 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 238.