Abstract
Cytochrome P450 3A4 (CYP3A4), the most abundant human cytochrome P450 in liver, participates in the metabolism of ∼50% of clinically used drugs. The pregnane X receptor (PXR), a member of the nuclear receptor superfamily, is the major activator of CYP3A4 transcription. However, because of species differences in response to PXR ligands, it is problematic to use rodents to assess CYP3A4 regulation and function. The generation of double transgenic mice expressing human PXR and CYP3A4 (TgCYP3A4/hPXR) would provide a solution to this problem. In the current study, a TgCYP3A4/hPXR mouse model was generated by bacterial artificial chromosome transgenesis in Pxr-null mice. In TgCYP3A4/hPXR mice, CYP3A4 was strongly induced by rifampicin, a human-specific PXR ligand, but not by pregnenolone 16α-carbonitrile, a rodent-specific PXR ligand. Consistent with CYP3A expression, hepatic CYP3A activity increased ∼5-fold in TgCYP3A4/hPXR mice pretreated with rifampicin. Most antihuman immunodeficiency virus protease inhibitors are CYP3A substrates and their interactions with rifamycins are a source of major concern in patients coinfected with human immunodeficiency virus and Mycobacterium tuberculosis. By using TgCYP3A4/hPXR mice, human PXR-CYP3A4-mediated rifampicin-protease inhibitor interactions were recapitulated, as the metabolic stability of amprenavir, nelfinavir, and saquinavir decreased 52, 53, and 99%, respectively, in the liver microsomes of TgCYP3A4/hPXR mice pretreated with rifampicin. In vivo, rifampicin pretreatment resulted in an ∼80% decrease in the area under the serum amprenavir concentration-time curve in TgCYP3A4/hPXR mice. These results suggest that the TgCYP3A4/hPXR mouse model could serve as a useful tool for studies on CYP3A4 transcription and function in vivo.
Footnotes
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This study was funded by the National Cancer Institute Intramural Research Program. J.R.I. is grateful to the U.S. Smokeless Tobacco Company for a grant for collaborative research.
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.108.022723.
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ABBREVIATIONS: P450, cytochrome P450; PXR, pregnane X receptor; RIF, rifampicin; PCN, pregnenolone 16α-carbonitrile; BAC, bacterial artificial chromosome; TgCYP3A4, CYP3A4-transgenic mice; hPXR, PXR-humanized mice; TgCYP3A4/hPXR, double transgenic mice expressing human PXR and CYP3A4; HIV, human immunodeficiency virus; PI, protease inhibitor; TB, Mycobacterium tuberculosis; MDZ, midazolam; 1′-OH-MDZ, 1′-hydroxymidazolam; APV, amprenavir; NFV, nelfinavir; SQV, saquinavir; bp, base pair; PCR, polymerase chain reaction; WT, wild-type; mAb, monoclonal antibody; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; LC-MS/MS, liquid chromatography-coupled tandem mass spectrometry; PCR, polymerase chain reaction; AUC, area under the concentration-time curve.
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↵1 Current affiliation: Department of Pharmacology, Toxicology and Therapeutics, University of Kansas Medical Center, Kansas City, Kansas.
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↵2 Current affiliation: Department of Chemical Biology, Laboratory for Cancer Research, College of Pharmacy, Rutgers University, Piscataway, New Jersey.
- Received June 5, 2008.
- Accepted September 12, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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