Mechanism-based inhibition of CYP3A4 and CYP3A5 by seven inhibitors

Abstract

We evaluated the potential for inhibition of CYP3A4 and CYP3A5 using seven mechanism-based inhibitors: troleandomycin (TAO), erythromycin (ERY), 6′, 7′-dihydroxybergamottin (DHB), diltiazem (DIL), verapamil (VER), ethynyl estradiol (EE) and ritonavir. These inhibitors were preincubated with NADPH and recombinant enzymes (CYP3A4 and CYP3A5) for 20 minutes. Enzyme activity was determined by 1-hydroxy triazolam (1-OH TRZ) formation from triazolam (250μM). Using recombinant enzymes, IC50 values were reduced by preincubation with inhibitors. IC50 values with preincubation with CYP3A4 using TAO, ERY, DHB, DIL, VER, EE and ritonavir were: 1.7, 2.9, 0.9, 7, 3.3, 4.4 and 0.06 μM respectively. With CYP3A5, IC50 values with preincubation were: 44.5, 77.5, 1.2, 21.8, 8, 17 and 0.1 μM respectively. The pattern of 1-OH TRZ IC50 values suggested two classes of mechanism-based inhibitors, with nonmacrolides showing less than a 4-fold difference between CYP3A4 and CYP3A5, and macrolides showing more than a 25-fold difference. Individuals polymorphically expressing CYP3A5 in significant amounts may have greater susceptibility to interactions involving nonmacrolide mechanism-based inhibitors than that seen with reversible inhibitors. However, macrolide mechanism-based inhibitors may be less susceptible to interactions in these subjects. Clinical Pharmacology & Therapeutics (2004) 75, P83–P83; doi: 10.1016/j.clpt.2003.11.316