Trimethyltrienolone

Trimethyltrienolone (developmental code name R-2956 or RU-2956), or 2α,2β,17α-trimethyltrenbolone, also known as 2α,2β,17α-trimethylestra-4,9,11-trien-17β-ol-3-one, is a steroidal antiandrogen derived from testosterone that was first described in 1973 and was one of the earliest antiandrogens to be discovered and developed. It is a derivative of the extremely potent anabolic-androgenic steroid metribolone (R-1881; 17α-methyltrenbolone), and possesses only about 4-fold lower competitive affinity for the androgen receptor (AR) in comparison. Trimethyltrienolone is a powerful and selective antagonist of the androgen receptor (AR) with very low intrinsic androgenic activity and no estrogenic, antiestrogenic, or progestogenic activity. The drug almost completely inhibits dihydrotestosterone (DHT) binding to the AR in vitro at a mere 10-fold molar excess. It was under investigation for potential clinical use, but was abandoned in favor of non-steroidal antiandrogens like flutamide and nilutamide due to their comparative advantage of a complete lack of androgenicity, and hence, was never marketed.