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

Abstract

ABSTRACT:Avasimibe, an acyl-CoA:cholesterol acyltransferase inhibitor, has been previously shown to be a potent inducer of CYP3A4 and multiple drug resistance protein 1. We have further characterized the drug interaction potential of avasimibe by studying the inductive and inhibitory effect of this compound on major drug-metabolizing enzymes. Enzymes known to be involved in the metabolism of drugs likely to be coadministered with avasimibe, such as CYP1A1/2, CYP2C, and CYP2B6, were evaluated further by microarray analysis, Western immunoblotting, and activity assays, using rifampicin and ␤-naphthoflavone as positive controls. No change was observed in CYP1A1/2 mRNA or activity levels after avasimibe treatment. Differential induction of CYP2C9-and CYP2B6-immunoreactive protein and activity was observed depending on drug concentration and donor. Microarray analysis showed a similar increase in CYP2C and CYP2B6 mRNA levels. The inhibition potential of avasimibe on the major drug-metabolizing enzymes was assessed using pooled human liver microsomes. Avasimibe inhibited CYP2C9 (IC 50 2.9 M), CYP1A2 (IC 50 13.9 M), and CYP2C19 (IC 50 26.5 M). A clinical drug interaction study was conducted to determine whether avasimibe might interact with the CYP2C9 substrate warfarin. Volunteers received 750 mg of avasimibe and showed a 54.2% reduction in trough concentrations of S-warfarin and decreased prothrombin times by 12, 15, 19, and 21% on days 6 through 9, respectively. These results demonstrate that avasimibe's inductive spectrum resembles that of rifampin.

CYP Induction-Mediated Drug Interactions: in Vitro Assessment and Clinical Implications

“…In another study with cultured human hepatocytes, protein and activity of CYP2C8 and CYP2C9 were induced by 3-to 5-fold after rifampicin treatment, whereas the protein and activity of CYP3A4 were induced by 10-fold after rifampicin treatment (142). Similar observations of differential induction of CYP genes by rifampicin have been reported by other investigators (133,143). Although the PXR response elements of CYP2C8 and CYP2C9 genes have not been identified, the differential induction between CYP2C and CYP3A genes by rifampicin may reflect the differences in the affinity of PXR/RXR to the responsive elements between CYP2C8/CYP2C9 genes and CYP3A4 genes (144Y146).…”

Regulation of cytochrome P450 2C9 expression in primary cultures of human hepatocytes

“…We further explored the relationship between PXR activation of CYP3A4 and CYP2C9 induction by comparing the concentration-response profiles of CYP3A4 and CYP2C9 catalytic activities in two hepatocyte preparations after treatment with the potent PXR activators rifampin and avasimibe [8,9]. Rifampin and avasimibe produced similar concentration-dependent induction of CYP2C9 activity with comparable EC 50 values.…”

“…Rifampin, a known CYP3A4 inducer, increased the mean systemic clearance of phenytoin, tolbutamide, and S-warfarin (all predominantly metabolized by CYP2C9) by approximately two-fold in clinical studies [4][5][6], suggesting possible coregulation of these two enzymes. This coregulation was given further credence when it was found that medications such as avasimibe and aprepitant induce both CYP3A4 and CYP2C9 activity in humans [7][8][9]. There is some evidence of this coregulation in human hepatocytes as well, although these studies provide somewhat conflicting data.…”

“…The increase in CYP2C9 specific activity after induction with known inducers, e.g. rifampin typically ranges from 1.4-to 6.5-fold [9], relative to clotrimazole and phenobarbital, that can produce up to 15-and 10-fold induction in CYP3A4 catalytic activity, respectively, depending on the basal CYP3A4 activity in individual preparations of hepatocytes [34]. The variability between hepatocyte preparations in the extent of CYP2C9 induction by rifampin was significant, suggesting that induction of CYP2C9 activity could be partially responsible for the noted interpatient variability in clinical studies.…”

“…For example, CYP2C9 and CYP3A4 mRNA have been shown to display similar concentration-and time-dependent induction in response to treatment with the PXR activators rifampin and dexamethasone [11]; treatment of hepatocytes with two traditional Chinese herbal medicines derived from Schisandra chinensis Bail and Glycyrrhiza uralensis Fisch, induced both CYP3A4 and CYP2C9 [37]; calcium channel modulators induced CYP3A4 and CYP2C9 mRNA, protein, and activity [13]; and PXR mediated the induction of CYP2C9 with rifampin, phenobarbital, and hyperforin [22,38]. Clinical trials revealed induction of both CYP3A4 and CYP2C9 after two weeks of aprepitant administration [7] and Sahi et al demonstrated that avasimibe, a potent activator of PXR in vitro, caused increased clearance of CYP3A4 and CYP2C9 substrates in vivo [8,9]. Moreover, significant drug interactions occur in vivo between known activators of PXR and substrates of CYP2C9 [4][5][6]39].…”