Binding characteristics of seven inhibitors of human aromatase: a site-directed mutagenesis study.

Aromatase, a cytochrome P450, catalyzes three consecutive hydroxylation reactions converting C19 androgens to aromatic C18 estrogenic steroids. In this study, eight human aromatase mutants (I133Y, I133W, F235L, I395F, I474Y, I474W, I474M, and I474N) were prepared to evaluate the active site and a proposed hydrophobic pocket of the enzyme that exists in an aromatase model based on the X-ray structure of cytochrome P450cam. In addition, the binding characteristics of three steroidal inhibitors [4-hydroxyandrostenedione, 7alpha-(4'-amino)phenylthio-1,4-androstandiene-3,17-dione, and bridge (2,19-methyleneoxy)androstene-3,17-dione (MDL 101,003)] and four nonsteroidal inhibitors [aminoglutethimide, CGS 20267, ICI D1033, and vorozole (R83842)] were investigated through inhibitory profile studies on the eight new and three previously generated mutants (P308F, D309A, and T310S). The latter analyses have provided a molecular basis regarding how seven aromatase inhibitors with different structures bind to the active site of aromatase.