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In this paper, we evaluate methodologies and null mouse models used to study drug transporter function in vitro and in vivo. P-glycoprotein and MRP null mice have been used to examine many aspects of xenobiotic distribution and bioavailability. Their advantage over conventional models is that they allow the exclusion of transporters from a particular process; however, they cannot be used to study the activity of the transporter that has been deleted. Use of humanized mice permits a logical progression from phenomena in wild-type mice via the effects of removing the mouse transporter to the consequences of replacing it with its human counterpart. [ABSTRACT FROM AUTHOR]

Xenobiotic metabolism and detoxification is regulated by receptors (e.g., PXR, CAR) whose characterization has contributed significantly to our understanding of drug responses in humans. Technologies facilitating the screening of compounds for receptor interactions provide valuable tools applicable in drug development. Most use in vitro systems or mice humanized for receptors in vivo. In vitro assays are limited by the reporter systems and cell lines chosen and are uninformative about effects in vivo. Humanized mouse models provide novel, exciting ways of understanding the functions of these genes. This article evaluates these technologies and current knowledge on PXR/CAR-mediated regulation of gene expression. [ABSTRACT FROM AUTHOR]