Ralaniten acetate (developmental code name EPI-506 ) is an experimental nonsteroidal antiandrogen (NSAA) which was developed by ESSA Pharmaceuticals and was under investigation for the treatment of prostate cancer .   It was a successor of EPI-001 and targets the N-terminal domain (NTD) of the androgen receptor (AR). This mechanism of action is believed to allow the drug to block signaling from the AR and its splice variants .   EPI-506 is a derivative of bisphenol A  and a prodrug of ralaniten (EPI-002), one of the four stereoisomers of EPI-001.  The drug reached phase I / II prior to the discontinuation of its development.  It showed signs of efficacy in the form of prostatic specific antigen (PSA) decreases (4–29%) predominantly at higher doses (≥1,280 mg) in some patients but also caused side effects and was discontinued by its developer in favor of next-generation AR NTD inhibitors with improved potency and tolerability .