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Identification of human cytochrome P450 isozymes responsible for the in vitro oxidative metabolism of finasteride

Huskey SW, Dean DC, Miller RR, Rasmusson GH, Chiu SH

Drug metabolism and disposition: the biological fate of chemicals, 1995

Abstract

Finasteride, a prescription drug for the treatment of benign prostatic hypertrophy and alleviation of symptoms associated with benign prostatic hypertrophy and alleviation of symptoms associated with benign prostatic hypertrophy, has been shown to be metabolized in rat hepatic microsomes by hydroxylation at the t-butyl group (omega-OH finasteride), followed by further oxidation to the corresponding acid (omega-oic acid finasteride), with omega-aldehyde finasteride as an intermediate. In this study, we identified specific human cytochrome P450 (CYP) isozyme(s) involved in the in vitro metabolism of [14C]finasteride using CYP isozyme-selective inhibitors and microsomes containing specific recombinant human CYP isozymes (expressed in human AHH-1 TK+/-cells). Each of the three steps of the oxidative pathway was examined separately by using [14C]finasteride and its consecutive metabolites (omega-OH finasteride and omega-aldehyde finasteride) as substrates, and human liver microsomes or expressed recombinant CYP isozymes as the enzyme source. Gestodene, a mechanism-based inhibitor of CYP3A isozymes, showed a concentration-dependent inhibition of the oxidative metabolism of [14C]finasteride. In addition, the respective omega-OH finasteride and omega-oic acid finasteride metabolites were generated only by microsomes containing recombinant CYP3A4, but not the other isozymes (CYP1A1, CYP2B6, CYP2C8, CYP2C9, CYP2D6, and CYP2E1). Similar results were obtained for the oxidation of…

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