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ABSORPTION, DISTRIBUTION, METABOLISM, AND EXCRETION

Avasimibe Induces CYP3A4 and Multiple Drug Resistance Protein 1 Gene Expression through Activation of the Pregnane X Receptor

Departments of Pharmacokinetics, Dynamics, and Metabolism (J.S., K.A.R., L.S.), Clinical Pharmacokinetics and Pharmacodynamics (M.A.M.), Molecular Biology (X.Z.), and Experimental Medicine (R.H.S.), Pfizer Global Research and Development, Ann Arbor, Michigan; and Division of Drug Delivery and Disposition (H.W., D.G., S.J., E.L.L.), School of Pharmacy, University of North Carolina, Chapel Hill, North Carolina

In vitro and clinical studies were conducted to characterize the potential of avasimibe, an acyl-CoA/cholesterol acyltransferase inhibitor to cause drug-drug interactions. Clinically, 3- and 6-fold increases in midazolam (CYP3A4 substrate) oral clearance were observed after 50 and 750 mg of avasimibe daily for 7 days, respectively. A 40% decrease in digoxin (P-glycoprotein substrate) area under the curve was observed with 750 mg of avasimibe daily for 10 days. In vitro studies were conducted to define the mechanisms of these interactions. Induction was observed in CYP3A4 activity and immunoreactive protein (EC₅₀ of 200-400 nM) in primary human hepatocytes treated with avasimibe. Rifampin treatment yielded similar results. Microarray analysis revealed avasimibe (1 µM) increased CYP3A4 mRNA 20-fold, compared with a 23-fold increase with 50 µM rifampin. Avasimibe induced P-glycoprotein mRNA by about 2-fold and immunoreactive protein in a dose-dependent manner. Transient transfection assays showed that avasimibe is a potent activator of the human pregnane X receptor (hPXR) and more active than rifampin on an equimolar basis. Drug-drug interaction studies for CYP3A4 using pooled human hepatic microsomes and avasimibe at various concentrations, revealed IC₅₀ values of 20.7, 1.6, and 3.1 µM using testosterone, midazolam, and felodipine as probe substrates, respectively. Our results indicate that avasimibe causes clinically significant drug-drug interactions through direct activation of hPXR and the subsequent induction of its target genes CYP3A4 and multiple drug resistance protein 1.

Address correspondence to: Dr. Jasminder Sahi, Pfizer Global Research and Development, 2800 Plymouth Rd., Ann Arbor MI 48105. E-mail: jasminder.sahi{at}pfizer.com

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