Thiol-containing androgens as suicide substrates of aromatase

Abstract

The thiol-containing androgens 17.beta.-hydroxy-10.beta.-mercaptoestr-4-en-3-one (1) and 19-mercaptoandrost-4-ene-3,17-dione (2) were synthesized and tested in human placental microsomes for their ability to suicide inhibit aromatase. Both compounds showed time-dependent, pseudo-first-order rates of inactivation of aromatase with Ki of 106 and 34 nM and kcat of 3.2 .times. 10-3 and 1.2 .times. 10-3/s, respectively, for 1 and 2 at 30.degree. C. Diffusion dialysis failed to reactivate aromatase previously inactivated by either compound, and both compounds required that NADPH and O2 be present for the time-dependent inactivation of the enzyme. The presence of the substrate, androst-4-ene-3,17-dione (5.0 .mu.M), protected the enzyme from inactivation while Cys (1.0 mM) failed to protect aromatase from inactivation by either compound. The above evidence demonstrates that both compounds are potent suicide inhibitors of aromatase. [The observation that approximately 35% of breast cancers are estrogen dependent has stimulated research into methods of limiting estrogen production.].