Probing the binding pocket of the active site of aromatase with 6-ether or 6-ester substituted androst-4-ene-3,17-diones and their diene and triene analogs.
A series of 6-ester- (3 and 4) and 6-ether- (7 and 8) substituted androst-4-ene-3,17-diones (androstenediones) and their 1,4-diene analogs (5 and 6, and 9 and 10) as well as C6-substituted 4,6-diene and 1,4,6-triene steroids 11 and 12 were synthesized as aromatase inhibitors to gain insight into the structure-activity relationship between various substituents and inhibitory activity. All of the inhibitors synthesized blocked aromatase in a competitive manner. The inhibitory activities of all of the steroids, except for the 6beta-benzoates 4g and 6h and the 6beta-acetate 6a, were fairly effective to very powerful (K(i): 7.0-320 nM). The 6alpha-n-hexanoyloxy- and 6alpha-benzyloxyandrostenediones (3e and 7e) were the most potent inhibitors (K(i): 7.0 nM each). In the series of 4-ene and 1,4-diene steroids, the 6alpha-substituted steroids had higher affinity for the enzyme than the corresponding 6beta-isomers. In the 1,4-diene steroid series, 6beta-substituted steroids 6a, e, g, and 10a, b, e caused a time-dependent inactivation of aromatase, whereas their 6alpha-isomers 5 and 9 essentially did not. The ether-substituted 1,4,6-trienes 12 inactivated the enzyme in a time-dependent manner; in contrast, their 4,6-diene analogs 11 did not. The substrate androstenedione blocked the inactivation, but no significant effect of L-cysteine was observed. Based on molecular modeling with the PM3 method, along with the present inhibition and inactivation results, it is thought that both the steric effects of the 6-substituents as well as the electronic effects of the C-6 oxygen functions play a critical role in the binding of inhibitors to the active site of aromatase.
Numazawa
M
M
Tohoku Pharmaceutical University,4-1 Komatsushima-4-chome, Aobaku, 981-8558, Sendai, Japan. numazawa@tohoku-pharm.ac.jp
Shelangouski
M
M
Nagasaka
M
M
D000735:Androstenedione / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000138:chemical synthesis / Q000378:metabolism / Q000494:pharmacology; D001141:Aromatase / Q000737:chemistry / Q000378:metabolism*; D047072:Aromatase Inhibitors; D001665:Binding Sites; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000378:metabolism / Q000494:pharmacology; D004952:Esters / Q000737:chemistry; D004987:Ethers / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology; D008958:Models, Molecular; D010920:Placenta / Q000201:enzymology; D011485:Protein Binding; D055672:Static Electricity; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D013997:Time Factors
D000970:Antineoplastic Agents; D047072:Aromatase Inhibitors; D004791:Enzyme Inhibitors; D004952:Esters; D004987:Ethers; D000735:Androstenedione; D001141:Aromatase