HYDROXYLATION OF 5-ALPHA-ANDROSTANE-3-BETA, 17-BETA-DIOL BY RAT PROSTATE MICROSOMES - POTENT INHIBITION BY IMIDAZOLE-TYPE ANTIMYCOTIC DRUGS AND LACK OF INHIBITION BY STEROID 5-ALPHA-REDUCTASE INHIBITORS

5α-Dihydrotestosterone, the principal androgen mediating prostate growth and function in the rat, is formed from testosterone by steroid 5α-reductase. The inactivation of 5α-dihydrotestosterone involves reversible reduction to 5α-androstane-3β,17β-diol by 3β-hydroxysteroid oxidoreductase followed by 6α-, 7α-, or 7β-hydroxylation. 5α-Androstane-3β,17β-diol hydroxylation represents the ultimate inactivation step of dihydrotestosterone in rat prostate and is apparently catalyzed by a single, high-affinity (Km ~ 0.5 μM) microsomal cytochrome P450 enzyme. The present studies were designed to determine if 5α-androstane-3β,17β-diol hydroxylation by rat prostate microsomes is inhibited by agents that are known inhibitors of androgen-metabolizing enzymes. Inhibitors of steroid 5α-reductase (4-azasteroid analogs; 10 μm) or inhibitors of 3β-hydroxy-steroid oxidoreductase (trilostane, azastene, and cyanoketone; 10 μm) had no appreciable effect on the 6α-, 7α-, or 7β-hydroxylation of 5α-androstane-3β,17β-diol (10 μm) by rat prostate microsomes. Imidazole-type antimycotic drugs (ketoconazole, clotrimazole, and miconazole; 0.1-10 μm) all markedly inhibited 5α-androstane-3β,17β-diol hydroxylation in a concentration-dependent manner, whereas triazole-type antimycotic drugs (fluconazole and itraconazole; 0.1-10 μm) had no inhibitory effect. The rank order of inhibitory potency of the imidazole-type antimycotic drugs was miconazole > clotrimazole > ketoconazole. In the case of clotrimazole, the inhibition was shown to be competitive in nature, with a Ki of 0.03 μm. The imidazole-type antimycotic drugs inhibited all three pathways of 5α-androstane-3β,17β-diol hydroxylation to the same extent, which provides further evidence that, in rat prostate microsomes, a single cytochrome P450 enzyme catalyzes the 6α-, 7α-, and 7β-hydroxylation of 5α-androstane-3β,17β-diol. These studies demonstrate that certain imidazole-type compounds are potent, competitive inhibitors of 5α-androstane-3β,17β-diol hydroxylation by rat prostate microsomes, which is consistent with the effect of these antimycotic drugs on cytochrome P450 enzymes involved in the metabolism of other androgens and steroids. © 1992.