Modulation of Cholesterol Metabolism Improves Response to Enzalutamide Treatment in Prostate Cancer

Abstract

Abstract Objectives Prostate cancer (PCa) growth is mediated by androgens via activation of androgen receptor (AR). Accordingly, androgen deprivation therapy (ADT) is the gold standard for the treatment of advanced PCa, but progression to castration-resistant PCa (CRPC) follows. Enzalutamide (ENZ) is an AR antagonist used for the management of CRPC. However, patients acquire resistance to the drug in a short period. As cholesterol metabolism is dysregulated in PCa and lipogenesis is upregulated by AR signaling, we hypothesized that inhibition of cholesteryl ester formation and suppression of lipogenesis by blockage of sterol-O-acyltransferase 1 (SOAT1) could enhance the response to ENZ. Methods The mRNA expression of SOAT1 in PCa patients was analyzed using Oncomine and TCGA database. Survival analysis of TCGA PCa patients data was executed using cBioPortal. 22RV1 cells inherently resistant to ENZ, were challenged to avasimibe (AVA), a pharmacological inhibitor of SOAT1, with or without ENZ. Results We found SOAT1 mRNA is significantly overexpressed in prostate carcinoma compared to the normal tissue in separate datasets (Taylor 3; Grasso; Liu). Analysis of the TCGA PCa dataset among patients who had undergone ADT showed longer disease-free status (P = 0.039) and a trend toward better overall survival status (P = 0.066) in low SOAT1 mRNA expressing patients. Moreover, SOAT1 mRNA expression positively correlated with AR mRNA expression with Pearson coefficient of 0.5 (P = 7.475e-6). We also found that combination of 20 μM ENZ and 2 μM AVA reduced 52% of cell counts after 5 days and 53% of colony formation after 2 weeks, whereas AVA resulted in 20% and 28% reduction, respectively, with no effect from ENZ. Synergism of these two drugs was observed based on MTT assay with Chou-Talalay's combination index method. 4 μM AVA treatment for 24h downregulated AR downstream nkx3.1 mRNA level with no difference in AR or ARV7 mRNA levels. AVA treatment also downregulated lipogenic SCD1 mRNA level, inhibition of which was previously reported to enhance response to ENZ. Conclusions SOAT1 is a potential biomarker predictive of the success of ENZ treatment in PCa according to TCGA data. Our in vitro study further supports that SOAT1-regulated cholesterol metabolism is an important factor for the ENZ response. Funding Sources Purdue Research Foundation, Ralph W. and Grace M. Showalter Research Trust.