4-Oxygenated androst-5-en-17-ones and their 7-oxo derivatives as aromatase inhibitors.
A series of androst-5-ene-4,7-diones and 4-oxygenated androst-5-enes were synthesized and tested for their ability to inhibit aromatase in human placental microsomes. All of the steroids examined inhibited the enzyme in a competitive manner. The inhibitory activity of 4beta-hydroxy-5-ene steroid 7 (Ki = 25 nM) was much more powerful than that of the parent 5-ene steroid 11 (Ki = 78 nM), whereas 4beta-acetate 8 and 4-oxo analog 5 (Ki = 90 and 120 nM, respectively) were less potent than compound 11. This indicates that a hydrogen bonding between a hydroxy group of the 4beta-ol 7 and a residue of the active site of aromatase plays an important role in its binding. The 5-en-4-one steroid 5 did not cause a time-dependent inactivation of aromatase. In contrast, 5-ene-4,7-dione 13 as well as its 19-hydroxy and 19-oxo analogs 19 and 20 caused the time-dependent inactivation only in the presence of NADPH in air with the k(inact) values ranging from 0.057 to 0.192 min(-1), although their affinities for the enzyme were not high (Ki = 430-6300 nM). The inactivation was prevented by androstenedione, and no significant effect of L-cysteine on the inactivation was observed in each case. These results suggest that oxygenation at C-19 would be at least in part involved in the inactivation caused by the inhibitor 13.
Numazawa
M
M
Tohoku College of Pharmacy, Sendai, Japan.
Tachibana
M
M
Tateda
Y
Y
D047072:Aromatase Inhibitors; D001665:Binding Sites; D003687:Dehydroepiandrosterone / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology; D009249:NADP / Q000378:metabolism; D010920:Placenta / Q000201:enzymology
D047072:Aromatase Inhibitors; D004791:Enzyme Inhibitors; D003687:Dehydroepiandrosterone; D009249:NADP