EPI-001 is a specific inhibitor of the AR (androgen receptor) without inhibiting PR or GR transcriptional activities. EPI-001 selectively interacts with transactivation unit 5 (Tau-5) of the androgen receptor, which is essential for prostate cells to proliferate in the absence of androgens. EPI-001 is active against castration-resistant prostate cancer (CRPC) in xenografts.