| Title | Inhibition and stimulation of intestinal and hepatic CYP3A activity: studies in humanized CYP3A4 transgenic mice using triazolam. | | Author(s) | van Waterschoot RA, Rooswinkel RW, Sparidans RW, van Herwaarden AE, Beijnen JH, Schinkel AH | | Institution | The Netherlands Cancer Institute. | | Source | Drug Metab Dispos 2009 Sep 14. | | Abstract | CYP3A4 is an important determinant of drug-drug interactions. Here, we evaluated whether Cyp3a(-/-) and CYP3A4 transgenic (CYP3A4-Tg) mice can be utilized 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 human and mouse, but triazolam metabolism in microsomes derived from CYP3A4-Tg "humanized" mice closely resembled that in human microsomes. Interestingly, 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 co-administered triazolam with the prototypical CYP3A inhibitor ketoconazole, which increased triazolam exposure in all CYP3A-proficient mouse strains but not in Cyp3a(-/-) mice. We further found that the anti-cancer drug gefitinib is a potent stimulator of 1'-OH triazolam formation, in vitro. Importantly, also in vivo we could demonstrate 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 utilized to study drug-drug interactions. The data clarify that also for drugs that are not P-glycoprotein substrates, intestinal metabolism can be more important than hepatic metabolism after oral administration. | | Language | ENG | | Pub Type(s) | JOURNAL ARTICLE
| | PubMed ID | 19752211 |
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