Studies directed toward a mechanistic evaluation of aromatase inhibition by androst-5-ene-7,17-dione
作者:Mitsuteru Numazawa、Mii Tachibana
DOI:10.1016/s0039-128x(97)00002-0
日期:1997.7
To gain further insight into the mechanism for inactivation of aromatase by androst-5-ene-7,17-dione (1) and its 19-nor analog 4, 10 beta-oxygenated steroids 5 and 6, Delta(1(10))-steroid 7, and 19-oxo-5 beta,6 beta-epoxy compound 8 were synthesized and tested for their ability to inhibit aromatase in human placental microsomes. all of the steroids studied inhibited the enzyme in a competitive manner with apparent K-i values ranging from 1.1 to 35 mu M. The Delta(1(10))-compound 7 was the most potent inhibitor among them. All of the inhibitors caused a time-dependent inactivation of aromatase in the presence of NADPH in air with the K-inact values ranging from 0.036 to 0.190 min(-1). The substrate and androstenedione protected the inactivation, but a nucleophile, L-cystein, did not, in each case. In contrast, each inhibitor did not cause the time-dependent inactivation in the absence of NADPH. These results show that the 5 beta,6 beta-epoxide 8 and/or the dienone 7 are not a reactive electrophile involved in the irreversible binding to the active site of aromatase during the mechanism-based inactivation caused by the suicide substrates 1 and/or 4. (C) 1997 by Elsevier Science Inc.