The effect of 4MA, a potent inhibitor of 5 alpha-reductase, on the growth of androgen-responsive human genitourinary tumors grown in athymic nude mice.

The five alpha-reductase inhibitors are a newly developed family of compounds that block the intracellular conversion of testosterone (T) to dihydrotestosterone (DHT). 17-beta-N, N-Diethylcarbamoyl-4-methyl-4-aza-5-alpha-androstan-3-one (4MA), the most widely studied of these compounds, has been shown to inhibit the androgen-dependent growth of both normal animal tissues and of the Noble tumor, an experimental, hormone-responsive rat neoplasm. 4MA has been found to inhibit androgen-dependent growth without altering plasma levels of T or DHT. In the present study, we assessed the efficacy of 4MA in inhibiting the growth of PC-82 and R198, human androgen-responsive genitourinary malignancies. In the first experiment, 4MA was administered subcutaneously at a dose of 6 mg/kg/day to castrated and hormonally replaced groups of PC-82-bearing male athymic nude mice. 4MA therapy when compared to control therapy caused significant PC-82 growth inhibition in three different groups of hormonally replaced castrated mice: physiologic T-replaced (P less than .001), supraphysiologic T replaced (P less than .001), and supraphysiologic T and DHT replaced (P less than .001). There was no difference between the post therapy plasma levels of T or DHT in the control-treated and 4MA-treated mice. In the second experiment, the effect of 4MA (6 mg/kg/day S.Q.) was compared to that of castration and control therapy on the growth of R198. Both castration and 4MA therapy effectively inhibited R198 growth when compared to control therapy (P = .01 and .02, respectively), but there was no difference in the degree of growth inhibition seen with 4MA or castration (P = .45). Castration and 4MA-therapy significantly lowered plasma T levels when compared to control therapy; castration also significantly lowered plasma DHT levels, while 4MA and control therapy did not. These studies suggest that 4MA is effective in inhibiting the growth of human androgen-responsive tumors grown in athymic nude mice and that further studies with other 5 alpha-reductase inhibitors are indicated.