Adverse drug interactions secondary to induction of drug detoxification genes by ligand activated PXR is an important clinical problem leading to decreased drug efficacy. Despite our ability to use rapid in vitro screens to identify compounds that activate PXR, there is still no way to predict the extent of drug interaction in individual patients. We believe that human variation in PXR expression contributes to the interindividual differences in induction of CYP3A. Moreover, the growing list of drug detoxification genes induced by PXR further justifies the need to determine what is responsible for variable PXR expression. Our prior studies have revealed that sequence variation (SNPs, single nucleotide polymorphisms) in the PXR coding region is not significantly contributing to human variation in PXR expression or human variation in induction of the CYP3A target gene. Our current research is designed to further elucidate the cellular and molecular mechanisms regulating PXR expression. Our prior studies have revealed that there are multiple isoforms of PXR that differ in their amino terminus and in the ligand binding domain. Our current research in Aim 1 is designed to discover the extent to which PXR with different amino termini and different ligand binding domains are expressed in human tissues and whether these PXR splice variants have altered function. We hypothesize that these variant PXRs fine tune PXR activation creating an additional layer of regulation, and ultimately influence the CYP3A inductive phenotype. Towards the goal of understanding factors regulating PXR expression Aims 2 and 4 will determine the role of liver enriched transcriptional factors in regulation of human PXR transcription and PXR expression in human liver. In order to visualize PXR transcriptional activity in mouse tissues, in Aim 3 we will develop a transgenic mouse with the PXR-promoter-driving a luciferase reporter. Bioluminescent imaging through the skin of the mouse will monitor in real-time PXR transcription under the most informative biological conditions-i.e., in a living intact animal. This unique and powerful whole body imaging approach will allow us to visualize PXR transcription in multiple tissues under different physiological and drug treated environments. In total this proposal describes a comprehensive set of experiments to determine how PXR is regulated.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM060346-08
Application #
7214745
Study Section
Pharmacology A Study Section (PHRA)
Program Officer
Okita, Richard T
Project Start
2000-03-01
Project End
2009-03-31
Budget Start
2007-04-01
Budget End
2009-03-31
Support Year
8
Fiscal Year
2007
Total Cost
$277,173
Indirect Cost
Name
St. Jude Children's Research Hospital
Department
Type
DUNS #
067717892
City
Memphis
State
TN
Country
United States
Zip Code
38105
Yasuda, Kazuto; Cline, Cynthia; Lin, Yvonne S et al. (2015) In Vivo Imaging of Human MDR1 Transcription in the Brain and Spine of MDR1-Luciferase Reporter Mice. Drug Metab Dispos 43:1646-54
Brown, Kevin C; Hosseinipour, Mina C; Hoskins, Janelle M et al. (2012) Exploration of CYP450 and drug transporter genotypes and correlations with nevirapine exposure in Malawians. Pharmacogenomics 13:113-21
Nagai, Shinjiro; Takenaka, Kazumasa; Nachagari, Deepa et al. (2011) Deoxycytidine kinase modulates the impact of the ABC transporter ABCG2 on clofarabine cytotoxicity. Cancer Res 71:1781-91
Yang, Xia; Zhang, Bin; Molony, Cliona et al. (2010) Systematic genetic and genomic analysis of cytochrome P450 enzyme activities in human liver. Genome Res 20:1020-36
Lamba, Vishal; Panetta, John C; Strom, Stephen et al. (2010) Genetic predictors of interindividual variability in hepatic CYP3A4 expression. J Pharmacol Exp Ther 332:1088-99
Chaudhry, Amarjit S; Urban, Thomas J; Lamba, Jatinder K et al. (2010) CYP2C9*1B promoter polymorphisms, in linkage with CYP2C19*2, affect phenytoin autoinduction of clearance and maintenance dose. J Pharmacol Exp Ther 332:599-611
Lin, Yvonne S; Yasuda, Kazuto; Assem, Mahfoud et al. (2009) The major human pregnane X receptor (PXR) splice variant, PXR.2, exhibits significantly diminished ligand-activated transcriptional regulation. Drug Metab Dispos 37:1295-304
Perera, M A; Thirumaran, R K; Cox, N J et al. (2009) Prediction of CYP3A4 enzyme activity using haplotype tag SNPs in African Americans. Pharmacogenomics J 9:49-60
Lamba, Jatinder; Lamba, Vishal; Strom, Stephen et al. (2008) Novel single nucleotide polymorphisms in the promoter and intron 1 of human pregnane X receptor/NR1I2 and their association with CYP3A4 expression. Drug Metab Dispos 36:169-81
Yasuda, Kazuto; Ranade, Aarati; Venkataramanan, Raman et al. (2008) A comprehensive in vitro and in silico analysis of antibiotics that activate pregnane X receptor and induce CYP3A4 in liver and intestine. Drug Metab Dispos 36:1689-97

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