19-oxygenations of 3-deoxy androgens, potent competitive inhibitors of estrogen biosynthesis, with human placental aromatase.
Aromatase is a cytochrome P450 enzyme complex that catalyzes the conversion of androst-4-ene-3,17-dione (AD) to estrone through three sequential oxygenations of the 19-methyl group. To gain insight into the ability of 3-deoxy derivative of AD, compound 1, and its 5-ene isomer 4, which are potent competitive inhibitors of aromatase, to serve as a substrate, we studied their 19-oxygenation by human placental aromatase and the metabolites isolated were analyzed by gas chromatography-mass spectrometry. Inhibitors 1 and 4 were found to be oxygenated with aromatase to produce the corresponding 19-hydroxy derivatives 2 and 5 and 19-oxo derivatives 3 and 6 as well as the 17beta-reduced 19-hydroxy compounds 7 and 8. Kinetic studies indicated that the 5-ene steroid 4 was surprisingly a good substrate for the aromatase-catalyzing 19-oxygenation with the V(max) value of 45 pmol/min per mg prot which was approx. four times higher than that of the other. The relative K(m) value for steroids 1 and 4 obtained in this study is opposite from the relative K(i) value obtained previously in the inhibition study. The results reveal that there is a difference between a binding suitable for serving as an inhibitor of aromatase and a binding suitable for serving as a substrate of the enzyme in the 3-deoxy steroid series and the C-3 carbonyl group of AD is essential for a proper binding as a substrate to the active site of aromatase.
Numazawa
M
M
Tohoku College of Pharmacy, 4-1 Komatsushima-4-chome, Aobaku, Japan. numazawa@tohoku-pharm.ac.jp
Nagaoka
M
M
Morio
M
M
Kamiyama
T
T
D000728:Androgens / Q000378:metabolism* / Q000494:pharmacology; D000735:Androstenedione / Q000031:analogs & derivatives* / Q000378:metabolism; D000906:Antibodies / Q000494:pharmacology; D001141:Aromatase / Q000276:immunology / Q000378:metabolism*; D047072:Aromatase Inhibitors; D020847:Estrogen Receptor Modulators / Q000737:chemistry* / Q000494:pharmacology; D004967:Estrogens / Q000096:biosynthesis*; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D007700:Kinetics; D015394:Molecular Structure; D010920:Placenta / Q000201:enzymology*; D011485:Protein Binding; D013379:Substrate Specificity
D000728:Androgens; D000906:Antibodies; D047072:Aromatase Inhibitors; D020847:Estrogen Receptor Modulators; D004967:Estrogens; D000735:Androstenedione; D001141:Aromatase