RU 56279 is an androgen receptor (AR) antagonist with strong and systemic anti-androgenic activity. RU 56279 is also a common, potent and long-lasting anti-androgen metabolite of RU 56187 and RU 58841 (HY-10561) in vivo. RU 56279 can be used as an AR ligand to construct an AR-targeted prodrug system for the study of AR-positive tumor cells[1][2].