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  • Title: Studies of the time-dependent inactivation of aromatase by 4beta,5beta-epoxy-6-one and 5beta,6beta-epoxy-4-one steroids under various conditions.
    Author: Numazawa M, Yamada K.
    Journal: Biol Pharm Bull; 1999 Nov; 22(11):1207-11. PubMed ID: 10598029.
    Abstract:
    The time-dependent inactivation of aromatase by epoxy analogs of the good aromatase inhibitors, androst-4-ene-6,17-dione (3) and androst-5-ene-4,17-dione (7), 4beta,5beta-epoxy and 5beta,6beta-epoxy compounds 10 and 13 and their 19-oxo derivatives 11 and 14, was examined in either the presence or absence of NADPH. The 4beta,5beta-epoxy-19-oxo steroid 11 along with the 19-methyl-5beta,6beta-epoxide 13 inactivated human placental aromatase in a mechanism-based manner, in the presence of NADPH, with rate constants for inactivation (k(inact)) of 0.133 min(-1) for steroid 11 and 0.100 min(-1) for steroid 13, whereas the two other steroids, 10 and 14, did not. On the other hand, none of four epoxides studied caused time-dependent inactivation of aromatase in an affinity-labeling manner in the absence of NADPH. These results are the first report showing that inhibitors 11 and 13 are suicide substrates having an epoxyketone structural feature.
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