title: Inhibition and stimulation of intestinal and hepatic CYP3A activity: studies in humanized CYP3A4 transgenic mice using triazolam.
abstract: CYP3A4 is an important determinant of drug-drug interactions. In this study, we evaluated whether cytochrome P450 3A knockout mice [Cyp3a(-/-)] and CYP3A4 transgenic (CYP3A4-Tg) mice can be used to study drug-drug interactions in the liver and intestine. Triazolam was used as a probe drug because it is a highly specific CYP3A substrate and not a P-glycoprotein substrate. Triazolam metabolism was profoundly reduced in Cyp3a(-/-) mice both in vitro and in vivo. In vitro studies revealed clear species differences in humans and mice, but triazolam metabolism in microsomes derived from CYP3A4-Tg "humanized" mice closely resembled that in human microsomes. It is interesting to note that studies with tissue-specific CYP3A4-Tg mice revealed that intestinal CYP3A4 has a major impact on oral triazolam exposure, whereas the effect of hepatic CYP3A4 was limited. To mimic a drug-drug interaction, we coadministered triazolam with the prototypical CYP3A inhibitor ketoconazole, which increased triazolam exposure in all the CYP3A-proficient mouse strains but not in Cyp3a(-/-) mice. We further found that the anticancer drug gefitinib is a potent stimulator of 1'-OH triazolam formation in vitro. It is noteworthy that we could also show in vivo stimulation of triazolam metabolism by gefitinib, resulting in a lower oral triazolam exposure. To our knowledge, this is the first in vivo example of direct stimulation of CYP3A4 activity after oral drug administration. Overall, this study illustrates how Cyp3a(-/-) and CYP3A4-Tg mice can be used to study drug-drug interactions. The data clarify that for drugs that are not P-glycoprotein substrates, intestinal metabolism also can be more important than hepatic metabolism after oral administration.
authors.affiliation: Division of Molecular Biology, The Netherlands Cancer Institute, 1066 CX Amsterdam, The Netherlands.
authors.forename: Robert A B
authors.initials: RA
authors.lastname: van Waterschoot
authors.forename: Rogier W
authors.initials: RW
authors.lastname: Rooswinkel
authors.forename: Rolf W
authors.initials: RW
authors.lastname: Sparidans
authors.forename: Antonius E
authors.initials: AE
authors.lastname: van Herwaarden
authors.forename: Jos H
authors.initials: JH
authors.lastname: Beijnen
authors.forename: Alfred H
authors.initials: AH
authors.lastname: Schinkel
mesh_terms: D000284:Administration, Oral; D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage; D051544:Cytochrome P-450 CYP3A / Q000235:genetics / Q000378:metabolism*; D065692:Cytochrome P-450 CYP3A Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D004347:Drug Interactions; D020536:Enzyme Activators / Q000008:administration & dosage; D004791:Enzyme Inhibitors / Q000008:administration & dosage; D000077156:Gefitinib; D006801:Humans; D006900:Hydroxylation; D007422:Intestines / Q000187:drug effects / Q000201:enzymology*; D007654:Ketoconazole / Q000008:administration & dosage; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008861:Microsomes / Q000201:enzymology; D011799:Quinazolines / Q000008:administration & dosage; D013045:Species Specificity; D013379:Substrate Specificity; D014229:Triazolam / Q000008:administration & dosage / Q000493:pharmacokinetics*; D008565:Membrane Proteins
chemical_list: D000970:Antineoplastic Agents; D051544:Cytochrome P-450 CYP3A; D065692:Cytochrome P-450 CYP3A Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System; D020536:Enzyme Activators; D004791:Enzyme Inhibitors; D000077156:Gefitinib; D007654:Ketoconazole; D011799:Quinazolines; D014229:Triazolam; C510163:CYP3A4 protein, human; C496508:Cyp3a11 protein, mouse; D008565:Membrane Proteins