Androgen Receptor Antagonists (Antiandrogens) Structure-Activity Relationships

Prostate cancer, acne, seborrhea, hirsutism, and androgenic alopecia are well recognized to depend upon an excess or increased sensitivity to androgens or to be at least sensitive to androgens. It thus seems logical to use antiandrogens as therapeutic agents to prevent androgens from binding to the androgen receptor. The two predominant naturally occurring androgens are testosterone (T) and dihydrotestosterone (DHT). DHT is the more potent androgen in vivo and in vitro. All androgen-responsive genes are activated by androgen receptor (AR) bound to either T or DHT and it is believed that AR is more transcriptionally active when bound to DHT than T. The two classes of antiandrogens, presently available, are the steroidal derivatives, all of which possess mixed agonistic and antagonistic activities, and the pure non-steroidal antiandrogens of the class of flutamide and its derivatives. The intrinsic androgenic, estrogenic and glucocorticoid activities of steroidal derivatives have limited their use in the treatment of prostate cancer. The non-steroidal flutamide and its derivatives display pure antiandrogenic activity, without exerting agonistic or any other hormonal activity. Flutamide (89) and its derivatives, Casodex (108) and Anandron (114), are highly effective in the treatment of prostate cancer. The combination of flutamide and Anandron with castration has shown prolongation of life in prostate cancer. Furthermore, combined androgen blockade in association with radical prostatectomy or radiotherapy are very effective in the treatment of localized prostate cancer. Such an approach certainly raises the hope of a further improvement in prostate cancer therapy. However, all antiandrogens, developed so-far display moderate affinity for the androgen receptor, and thus moderate efficacy in vitro and in vivo. There is thus a need for next-generation antiandrogens, which could display an equal or even higher affinity for AR compared to the natural androgens, and at the same time maintain its pure antiandrogenic activity, and thus providing improved androgen blockade using possibly antiandrogens alone.