title: Modulation of P450 CYP3A4-dependent metabolism by P-glycoprotein: implications for P450 phenotyping.
abstract: Some compounds used for phenotyping of cytochrome P450s are substrates of P-glycoprotein (pgp). It is likely that in these cases, the level of pgp modulates the metabolism of in vivo probes. To address this important issue, we have analyzed the effects of pgp on CYP3A4-mediated reactions in two newly established cell lines (3A4/HR/MDR(-) and 3A4/HR/MDR(+)), which express CYP3A4 in the absence and presence of pgp, respectively. In cultured cells, the presence of pgp increased the apparent K(m) for the 6beta-hydroxylase activity of CYP3A4 toward testosterone and cortisol by a factor of 1.7 and 4, respectively. These steroids are poor and good substrates of pgp, respectively, and cortisol 6beta-hydroxylase has been frequently used as an in vivo probe for CYP3A4. Interestingly, we also found that pgp modulated the inhibition of CYP3A4-mediated metabolism by several compounds in intact cells. Although quinidine inhibited testosterone 6beta-hydroxylase activity in membranes or in intact cells that expressed recombinant CYP3A4 in the absence of pgp, low concentrations of this compound increased CYP3A4 activity in intact cells that expressed pgp. These results imply that pharmacokinetic drug-drug interactions involving CYP3A4 can be influenced by pgp.
authors.affiliation: Department of Dermatology, University Hospital, Rheinland-Westfälische Technische Hochschule (RWTH), Aachen, Germany.
authors.forename: J M
authors.initials: JM
authors.lastname: Baron
authors.forename: L B
authors.initials: LB
authors.lastname: Goh
authors.forename: D
authors.initials: D
authors.lastname: Yao
authors.forename: C R
authors.initials: CR
authors.lastname: Wolf
authors.forename: T
authors.initials: T
authors.lastname: Friedberg
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics* / Q000378:metabolism*; D000935:Antifungal Agents / Q000494:pharmacology; D002316:Cardiotonic Agents / Q000494:pharmacology; D002460:Cell Line; D002478:Cells, Cultured; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism*; D004077:Digoxin / Q000494:pharmacology; D006801:Humans; D006900:Hydroxylation; D007654:Ketoconazole / Q000494:pharmacology; D006899:Mixed Function Oxygenases / Q000235:genetics* / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010641:Phenotype; D013250:Steroid Hydroxylases / Q000378:metabolism; D014162:Transfection
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000935:Antifungal Agents; D002316:Cardiotonic Agents; D015853:Cysteine Proteinase Inhibitors; D004077:Digoxin; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D013250:Steroid Hydroxylases; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C022657:steroid hormone 6-beta-hydroxylase; C510163:CYP3A4 protein, human; D009251:NADPH-Ferrihemoprotein Reductase; D007654:Ketoconazole