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

Abstract

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 (EC 50 of 200 -400 nM) in primary human hepatocytes treated with avasimibe. Rifampin treatment yielded similar results. Microarray analysis revealed avasimibe (1 M) increased CYP3A4 mRNA 20-fold, compared with a 23-fold increase with 50 M 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 IC 50 values of 20.7, 1.6, and 3.1 M 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.Avasimibe is a sulfamic acid phenyl ester that inhibits acyl-CoA/cholesterol acyltransferase (ACAT), an enzyme that catalyzes the intracellular esterification of cholesterol, thereby reducing intracellular cholesterol ester content. This class of inhibitors reduces the absorption of dietary cholesterol, the secretion of hepatic very low-density lipoproteins into the plasma, and the extent of atherosclerosis (Lee et al., 1996). Avasimibe is currently in clinical trials and the doses being administered to patients are between 50 to 750 mg daily. Avasimibe has been shown to reduce triglycerides at doses between 50 and 500 mg daily (Insull et al., 2001). The pharmacokinetics of avasimibe is characterized by less than proportional increases in systemic exposure with increasing dose, as measured by maximum plasma concentrations (C max ) and the plasma concentration-time area under the curve (AUC). C max values of avasimibe were approximately 0.5 and 1.5 M after multiple oral doses of 50 and 750 mg daily, respectively (Vora et al., 1997). The lack of dose proportionality was most likely due to the poor solubility of the compound. In general, a reduction in AUC after multiple dose administration is consistent with autoinduction of the metabolic pathways of a compound and/or induction of the MDR1 gene product P-glycoprotein.Enzyme induction often results in decreasing plasma drug concentrations and the attenuation of the effect of concomitan...

Effects of Avasimibe on Cytochrome P450 2c9 Expression in Vitro and in Vivo

“…Clinical studies with midazolam (a CYP3A4 substrate) revealed 3-and 6-fold increases in midazolam oral clearance after 50 mg and 750 mg, respectively, of oral avasimibe daily for 7 days (Sahi et al, 2003). When digoxin (a P-glycoprotein substrate) was administered to healthy human volunteers, a 40% decrease in digoxin AUC was observed with 750 mg of avasimibe daily for 10 days (Sahi et al, 2003). These studies confirmed avasimibe to be an inducer of both CYP3A4 and MDR1.…”

“…Induction of CYP3A4 and MDR1 is mediated predominantly through activation of the pregnane X receptor (PXR) (Blumberg et al, 1998;Lehmann et al, 1998). Earlier studies in our laboratory confirmed that avasimibe significantly activates PXR and is more potent than the prototypical CYP3A4 inducer, rifampin (1 M avasimibe Ͼ Ͼ 10 M rifampin) (Sahi et al, 2003).…”

“…In clinical studies, a reduction in avasimibe AUC was found after multiple dose administration, consistent with autoinduction of metabolism or transport (Vora et al, 1997). Clinical studies with midazolam (a CYP3A4 substrate) revealed 3-and 6-fold increases in midazolam oral clearance after 50 mg and 750 mg, respectively, of oral avasimibe daily for 7 days (Sahi et al, 2003). When digoxin (a P-glycoprotein substrate) was administered to healthy human volunteers, a 40% decrease in digoxin AUC was observed with 750 mg of avasimibe daily for 10 days (Sahi et al, 2003).…”

Determination of P-Glycoprotein ATPase Activity Using Luciferase

“…hPXR is a key regulator of both CYP3A4 and MDR1 (P-gp). 34) hPXR mRNA is absent or expressed at only extremely low levels in Caco-2 cells, because in a preliminary experiment, hPXR mRNA was not detected in Caco-2 cells by RT-PCR (data not shown). This result was consistent with the findings of another group, 35) who did not detect hPXR mRNA in Caco-2 cells.…”

Establishment of In Silico Prediction Models for CYP3A4 and CYP2B6 Induction in Human Hepatocytes by Multiple Regression Analysis Using Azole Compounds

“…Several clinically used drugs cause P450 induction, including the antibiotic rifampicin (Niemi et al, 2003), the acyl-CoA/cholesterol acyltransferase inhibitor avasimibe (Sahi et al, 2003), and the dual endothelin receptor antagonist bosentan (Dingemanse and van Giersbergen, 2004). These drugs reduce the plasma concentration of midazolam and/or those of themselves.…”