title: Identification of the human cytochrome P450s responsible for the in vitro metabolism of a leukotriene B4 receptor antagonist, CP-195,543.
abstract: 1. The major human cytochrome P450 (CYP) form(s) responsible for the metabolism of CP-195,543, a potent leukotriene B4 antagonist, were investigated. 2. Incubation of CP-195,543 with human liver microsomes resulted in the formation of three major metabolites, M1-3. M1 and M2 were diastereoisomers and formed by oxidation on the benzylic position. M3 was formed by aromatic oxidation of the benzyl group attached to the 3-position of the benzopyran ring. 3. The results from experiments with recombinant CYPs, correlation studies and inhibition studies with form-selective inhibitors and a CYP3A antibody strongly suggest that the CYP3A4 plays a major role in the metabolism of CP-195,543. Recombinant CYP3A5 did not metabolize CP-195,543. 4. The apparent K(m) and V(max) for the formation of M1-3 in human liver microsomes were determined as 36 microM and 4.1 pmol min(-1) pmol(-1) P450, 44 microM and 10 pmol min(-1) pmol(-1) P450, and 34 microM and 2.0 pmol min(-1) pmol(-1) P450, respectively. The average in vitro intrinsic clearance for M2 was the highest both in human liver microsomes and recombinant CYP3A4 compared with M1 and M3. Intrinsic clearance for M2 in human liver microsomes and recombinant CYP3A4 was 0.231 and 0.736 ml min(-1) pmol(-1) P450, respectively. The intrinsic clearances for M1 and M3 in human liver microsomes and CYP3A4 were 0.114 and 0.060 and 0.197 and 0.088 ml min(-1) pmol(-1) P450, respectively. This suggests that benzylic oxidation is the predominant phase I metabolic pathway of CP-195,543 in man.
authors.affiliation: Department of Pharmacokinetics, Dynamics and Mechanism, Pfizer Global Research and Development, Groton, CT 06340, USA.
authors.forename: S C
authors.initials: SC
authors.lastname: Khojasteh-Bakht
authors.forename: M I
authors.initials: MI
authors.lastname: Rossulek
authors.forename: H G
authors.initials: HG
authors.lastname: Fouda
authors.forename: C
authors.initials: C
authors.lastname: Prakash
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002839:Chromans / Q000378:metabolism* / Q000493:pharmacokinetics; D003374:Coumarins / Q000494:pharmacology; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006801:Humans; D007654:Ketoconazole / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008617:Mephenytoin / Q000494:pharmacology; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism; D008875:Middle Aged; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D011802:Quinidine / Q000494:pharmacology; D018102:Receptors, Leukotriene B4 / Q000037:antagonists & inhibitors*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013426:Sulfaphenazole / Q000494:pharmacology; D013806:Theophylline / Q000031:analogs & derivatives*
chemical_list: D002839:Chromans; D003374:Coumarins; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D018102:Receptors, Leukotriene B4; D011994:Recombinant Proteins; D013426:Sulfaphenazole; D009249:NADP; D003577:Cytochrome P-450 Enzyme System; C030123:coumarin; D013806:Theophylline; C050131:furafylline; C104464:CYP3A protein, human; C510164:CYP3A5 protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D011802:Quinidine; D008617:Mephenytoin; D007654:Ketoconazole; C112776:CP 195543