[Steroidal and nonsteroidal antiandrogens: chemical structures, mechanisms of action and clinical applications].

Antiandrogens are defined as substances which prevent androgens from expressing their activity at target sites. Based on their chemical structures, antiandrogens are divided into steroidal and nonsteroidal antiandrogens. In addition to antiandrogenic action, steroidal antiandrogens simulate the negative feedback inhibition of the hypothalamus, resulting in lowering the concentration of plasma testosterone. On the other hand, in nonsteroidal antiandrogens, the androgenic actions are blocked in both hypothalamus and target tissues. Therefore, negative feedback signals are inhibited and production of testosterone is increased in the testis. For the endocrine therapy of prostate cancer, chlormadinone acetate, flutamide and bicalutamide are or will be available in Japan. Antiandrogen is generally used by the combination with surgical or medical castration, namely as total androgen blockade.