| Research Abstract |
We studied on a suicide substrate of aromatase and the results obtained are as follows :
1) Androst-4-ene-3,6,17-trione (AT) and 4-hydroxyandrostenedione (4-OHA) are typical aromatase suicide substrates and the mechanisms of inactivation of aromatase were studied by use of the regio- and stereo-specifically labeled inhibitors with ^3H and ^<14>C. The labeled inhibitors were separately incubated with human placental mictosomes under various conditions. AT was aromatized to yield 6-oxoestrogens via 19-hydroxy-and 19-oxo-AT's, and its aromatase-bound metabolite retained 1beta-proton, 19-carbon, and one of three 19-methy1 protons of AT. These show that 19-oxo AT has an important role in the inactivation. On the other hand. the bound metabolite produced from 4-OHA retained the 19-carbon but losed the 1beta-proton, suggesting that new activation process would be involved in the inactivation.
2) 6beta-Alkyl derivatives of androstenedione (A) and 6alpha, 7alpha-cyclopropane derivatives of 3-deoxy A, synthesized in this study, were proven to be potent competitive inhibitors of aromatase. Moreover, androst-5-ene-7, 17-dione, a positional isomer of the natural substrate A, inactivated aromatase in a time-dependent manner. These results demonstrate new structure-activity relationship of aromatase inhibitor. On the other hand, 19-Erhynyl and 19,19-difluoro derivatives of 3-deoxy A or AT were suicide substrates of aromatase, respectively, showing that both 3-deoxy A and AT are oxygenated at C-19 by aromatase reaction.
3) A new aromatase assay method using [1beta-^3H]16alpha-hydroxy A as a substrate, instead of [1beta-^3H]A, was established. It was shown that this would be very useful for the development of efficient aromatase inhibitor which can be used for treatment of breast cancer.
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