Epitiostanol

Epitiostanol (INN, JAN) (brand name Thiodrol; developmental code name 10275 S), also known as epithioandrostanol or 2α,3α-epithio-5α-androstan-17β-ol, is a sulfur-containing, steroidal, potent antiestrogen as well as androgen and anabolic steroid that was described in the literature in 1965 and has been marketed in Japan as an antineoplastic agent for the treatment of breast cancer since 1977. The drug has also been found to be effective in the treatment of gynecomastia.[1] Epitiostanol binds directly to the estrogen and androgen receptors, where it acts as an antagonist and an agonist, respectively. The mechanism of action of epitiostanol in breast cancer is multimodal; it directly suppresses tumor growth through local tissue interactions with the estrogen and androgen receptors, and, in premenopausal women, it additionally acts as an antigonadotropin and reduces systemic estrogen levels through activation of the androgen receptor and consequent suppression of the hypothalamic-pituitary-gonadal axis.

Similarly to the case of testosterone (which is closely related structurally), epitiostanol shows poor bioavailability and weak therapeutic activity when taken orally due to extensive first-pass metabolism and must instead be administered via injection. Mepitiostane, a derivative of epitiostanol with a methoxycyclopentane ether substitution at the 17α position, is an oral prodrug of epitiostanol that has subsequently been developed. Another derivative, methylepitiostanol (2α,3α-epithio-17α-methyl-5α-androstan-17β-ol), also referred to as "epistane", has a methyl group at the 17α position and is similarly an oral version of epitiostanol; it has surfaced as a novel designer steroid. The compound may degrade to the controlled anabolic steroid desoxymethyltestosterone.

Epitiostanol and mepitiostane are unique among anabolic steroids in acting as antagonists of the estrogen receptor.