A double transgenic mouse model expressing human pregnane X receptor and cytochrome P450 3A4.

Cytochrome P450 3A4 (CYP3A4), the most abundant human cytochrome P450 in liver, participates in the metabolism of approximately 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 16alpha-carbonitrile, a rodent-specific PXR ligand. Consistent with CYP3A expression, hepatic CYP3A activity increased approximately 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 approximately 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.