Abstract LB-200: Regulation of intracellular androgen availability by glucuronidation in prostate tumor cells may contribute to loss of circulating androgen dependence in prostate cancer

Abstract

Abstract Recurrence of prostate cancer following androgen deprivation therapy is a serious clinical problem because tumor cells that resume growth are highly aggressive. Growth and survival of prostate epithelial cells is normally dependent on intracellular androgen levels that regulate androgen receptor (AR) gene transcription. The potency and availability of androgens is partly controlled at the cellular level by inactivation and excretion of excess quantities. UDP-glucose dehydrogenase (UGDH) provides UDP-glucuronate precursors for androgen inactivation by a family of UDP-glucuronosyltransferase (UGT) enzymes, which catalyze the transfer of glucuronate to a hydroxyl moiety on a broad range of steroid substrates, thereby irreversibly inactivating them. Levels of UGDH and UGT2B isozymes are androgen controlled and regulate tumor cell growth, but the role of glucuronidation in maintenance of prostate cancer hormone sensitivity is not well understood. In this study, we used an isogenic LNCaP cell culture model to test the effect of androgen deprivation on glucuronidation and AR function. LNCaP C33 androgen dependent and C81 androgen independent cells were selected for 15 days in androgen free media supplemented with charcoal-stripped serum and decrements of dihydrotestosterone (DHT). Selection in the absence of DHT virtually eliminated UGDH expression, and significantly increased UGT2B expression, specifically in C33 cells. DHT addition to these cells after selection elevated UGDH 4-fold, and suppressed UGT expression by 50%. The degree to which DHT regulation of these hormone glucuronidation enzymes could be restored decreased with selection dose. AR protein levels were not altered, so we used chromatin immunoprecipitation and luciferase reporter expression to evaluate AR activity at the PSA promoter. Less AR bound to the PSA enhancer in C81 cells than in C33 cells. In C81 cells, DHT addition also did not stimulate appreciable AR binding. Therefore, the diminished dependence of these cells on exogenous androgens is likely due to reduced binding of the AR to its target response elements. Importantly, DHT-restored AR binding to the PSA promoter was significantly diminished following low or no androgen selection. Selection in decreasing androgen also reduced the magnitude of luciferase reporter activity upon DHT stimulation, specifically in C33 cells. Results are consistent with loss of AR activity, but not expression, after prolonged low androgen selection, concurrent with enhanced basal UGDH and UGT function. We propose that ligand-dependent and independent function of the AR results from altered DHT availability, which implicates glucuronidation enzymes in the intracellular steroid fluxes that govern AR transcriptional activity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-200.