• Susan P Rhodes, Jennifer N Otten, Gary P Hingorani, Dylan P Hartley, and Ronald B Franklin.
• Array BioPharma Inc., 3200 Walnut Street, Boulder, Colorado 80301, USA. Susan.Rhodes@arraybiopharma.com
• J Pharmacol Toxicol Methods. 2011 May 1;63(3):223-6.

IntroductionThe human nuclear receptors pregnane X receptor (PXR), constitutive androstane receptor (CAR), and aryl hydrocarbon receptor (AhR) are known to regulate gene expression of the cytochrome P450 (CYP) enzymes, 3A4, 2B6, and 1A2, respectively. In conventional CYP induction studies, the activity of each CYP enzyme is assessed in a separate incubation with the appropriate marker substrate. The objective of this study was to assess, simultaneously, the induction of CYP3A4, CYP2B6, and CYP1A2 activity in cultured human hepatocytes treated with various prototypical ligands of PXR, CAR, and AhR by utilizing an optimized substrate cocktail, as well as a rapid, sensitive liquid chromatography-mass spectrometry method.MethodsTo evaluate the xenobiotic-mediated induction of hepatocellular gene expression, the prototypical inducers rifampicin (10 μM) and phenobarbital (1 mM) were used for CYP3A4, CITCO (1 μM) and artemisinin (50 μM) were used for CYP2B6, and 3-methylcholanthrene (1 μM) and omeprazole (50 μM) were utilized for induction of CYP1A2. Primary human hepatocytes were treated with each compound for 48h, followed by a 30-min incubation of the hepatocyte culture along with the addition of three marker substrates for specific CYP activity: midazolam (CYP3A4; 5 μM), bupropion (CYP2B6; 50 μM), and phenacetin (CYP1A2; 100μM). The assessment of CYP activity was performed with a rapid, sensitive liquid chromatography-tandem mass spectrometry method which simultaneously assessed activity of CYP3A4, CYP2B6, and CYP1A2 in a single 3-min method by examining the formation of the probe substrate metabolites, 1'-hydroxymidazolam, hydroxybupropion, and acetaminophen, respectively.ResultsThe average fold-induction of CYP3A4, CYP2B6, and CYP1A2 activity was comparable between the cocktail and the conventional assay.DiscussionThe combination of three marker substrates in a single 30-min incubation, in addition to a rapid, sensitive LC-MS/MS method, resulted in an efficient and robust method for assessing cytochrome P450 induction as compared to the conventional methodology.Copyright © 2010 Elsevier Inc. All rights reserved.

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