Pronounced differences in inhibition potency of lactone and non-lactone compounds for mouse and human coumarin 7-hydroxylases (CYP2A5 and CYP2A6).
1. The structural requirements for a compound to be a potent inhibitor for mouse CYP2A5 and human CYP2A6 enzymes catalysing coumarin 7-hydroxylase activity have been studied. 2. The IC50 of 28 compounds for the pyrazole-treated male DBA/2 mouse and human liver microsomal coumarin 7-hydroxylation were determined at 10 microm coumarin concentration 15 times over Km of coumarin. 3. The three most potent inhibitors for CYP2A5 were gamma-nonanoic lactone, gamma-decanolactone and gamma-phenyl-gamma-butyrolactone with an IC50 = 1.9+/-0.4, 2.1+/-0.2 and 2.4+/-0.3 microM and for CYP2A67-methylcoumarin, butylcyclohexane and indan with an IC50. = 30+/-3.2, 43+/-9 and 50+/-11 microM. 4. Among the 28 compounds studied, only 2-benzoxazolinone, 2-indanone and gamma-valerolactone showed similar inhibitory activity in both species. Indan had a lower IC50 for human than for mouse coumarin 7-hydroxylation, whereas the IC50 of 24 other compounds was higher for human than for mouse coumarin 7-hydroxylation. 5. The largest difference in IC50 between mouse and human activity was observed with 5-substituted phenyl, pentyl, hexyl, heptyl or octyl gamma-lactones or 6-substituted delta-lactones. IC50 of gamma-undecanolactone and gamma-decanolactone was 500 times lower for mouse than human coumarin 7-hydroxylation. 6. The difference in the IC50 between human and mouse coumarin 7-hydroxylation decreased substantially with the corresponding compounds without the lactone ring. 7. It is concluded that certain 5- or 6-position substituted gamma- and delta-lactones are potent inhibitors for mouse CYP2A5 but not for the orthologous human CYP2A6 and that the active site of CYP2A6 could be smaller than the active site of CYP2A5.
Juvonen
R O
RO
Department of Pharmacology, University of Kuopio, Finland. risto.juvonen@uku.fi
Gynther
J
J
Pasanen
M
M
Alhava
E
E
Poso
A
A
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D065637:Cytochrome P-450 CYP2A6; D065607:Cytochrome P-450 Enzyme Inhibitors; D000072467:Cytochrome P450 Family 2; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D007783:Lactones / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008811:Mice, Inbred DBA; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors*
D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D007783:Lactones; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; C585520:Cyp2a5 protein, mouse; D065637:Cytochrome P-450 CYP2A6; D000072467:Cytochrome P450 Family 2