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Department of Pharmacology,
Toxicology, and Therapeutics, University of
Kansas Medical Center, Kansas City 66160-7417.
Abstract
5
alpha-Dihydrotestosterone, the principal
androgen mediating prostate growth and function
in the rat, is formed from testosterone by
steroid 5 alpha-reductase. The inactivation of 5
alpha-dihydrotestosterone involves reversible
reduction to 5 alpha-androstane-3 beta,17
beta-diol by 3 beta-hydroxysteroid
oxidoreductase followed by 6 alpha-, 7 alpha-,
or 7 beta-hydroxylation. 5 alpha-Androstane-3
beta,17 beta-diol hydroxylation represents the
ultimate inactivation step of
dihydrotestosterone in rat prostate and is
apparently catalyzed by a single, high-affinity
(Km approximately 0.5 microM) microsomal
cytochrome P450 enzyme. The present studies were
designed to determine if 5 alpha-androstane-3
beta,17 beta-diol hydroxylation by rat prostate
microsomes is inhibited by agents that are known
inhibitors of androgen-metabolizing enzymes.
Inhibitors of steroid 5 alpha-reductase
(4-azasteroid analogs; 10 microM) or inhibitors
of 3 beta-hydroxysteroid oxidoreductase (trilostane,
azastene, and cyanoketone; 10 microM) had no
appreciable effect on the 6 alpha-, 7 alpha-, or
7 beta-hydroxylation of 5 alpha-androstane-3
beta,17 beta-diol (10 microM) by rat prostate
microsomes. Imidazole-type antimycotic drugs (ketoconazole,
clotrimazole, and miconazole; 0.1-10 microM) all
markedly inhibited 5 alpha-androstane-3 beta,17
beta-diol hydroxylation in a
concentration-dependent manner, whereas
triazole-type antimycotic drugs (fluconazole and
itraconazole; 0.1-10 microM) had no inhibitory
effect. The rank order of inhibitory potency of
the imidazole-type antimycotic drugs was
miconazole greater than clotrimazole greater
than ketoconazole. In the case of clotrimazole,
the inhibition was shown to be competitive in
nature, with a Ki of 0.03 microM. The
imidazole-type antimycotic drugs inhibited all
three pathways of 5 alpha-androstane-3 beta,17
beta-diol hydroxylation to the same extent,
which provides further evidence that, in rat
prostate microsomes, a single cytochrome P450
enzyme catalyzes the 6 alpha-, 7 alpha-, and 7
beta-hydroxylation of 5 alpha-androstane-3
beta,17 beta-diol. These studies demonstrate
that certain imidazole-type compounds are potent,
competitive inhibitors of 5 alpha-androstane-3
beta,17 beta-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.