Combination of an antiandrogen and a 5 alpha-reductase inhibitor: a further step towards total androgen blockade?

While the elimination of androgens of testicular origin can be easily achieved by orchiectomy or medical castration with LHRH agonists, the action of adrenal androgen precursors which are converted into the active androgen 5 alpha-dihydrotestosterone (DHT) in the prostatic tissue itself can be partially neutralized by antiandrogens which compete with DHT for binding to the androgen receptor. In order to increase the efficiency of androgen blockade, we have used 4-MA, an inhibitor of 5 alpha-reductase, the enzyme which converts testosterone into DHT, to reduce intracellular DHT concentrations and thus facilitate the action of the antiandrogen Flutamide. The present data show that the inhibitory effects of 4-MA (17 beta, N,N-diethylcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one) and of the antiandrogen Flutamide are additive on prostatic growth and on androgen-sensitive prostatic binding protein mRNA levels in the rat, thus clearly suggesting that such a combination could provide the basis for a further improvement in the therapy of prostate cancer.