p450 - publications
The Effect of Ritonavir on Human CYP2B6 Catalytic Activity: Heme Modification Contributes to the Mechanism-Based Inactivation of CYP2B6 and CYP3A4 by Ritonavir.
Drug Metab Dispos. 2013 Jul 25;
Authors: Lin HL, D'Agostino J, Kenaan C, Calinski D, Hollenberg PF
The mechanism-based inactivation of human CYP2B6 by ritonavir (RTV) in a reconstituted system was investigated. The inactivation is time-, concentration- and NADPH-dependent and exhibits a KI of 0.9 μM, a k inact of 0.05 min(-1) and a partition ratio of 3. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis showed that the protonated molecular ion of RTV exhibits an m/z at 721 and its two major metabolites are an oxidation product with MH(+) at m/z 737 and a decarbamoylated product with MH(+) at m/z 580. Inactivation of CYP2B6 by incubation with 10 μM RTV for 10 min resulted in 50% loss of catalytic activity and native heme, but no modification of the apoprotein was observed. RTV was found to be a potent mixed-type reversible inhibitor (K i = 0.3 μM) and a type II ligand (K s = 1.6 μM) of CYP2B6. Although previous studies have demonstrated that RTV is a potent mechanism-based inactivator of CYP3A4, the molecular mechanism responsible for the inactivation has not been determined. Here, we provide evidence that RTV-inactivation of CYP3A4 is due to heme destruction with the formation of a heme-protein adduct. Similar to CYP2B6, there is no significant modification of the apoprotein. Furthermore, LC-MS/MS analysis revealed that both CYP3A4 and human liver microsomes form an RTV-GSH conjugate having a MH(+) at m/z 858 during metabolism of RTV, suggesting the formation of an isocyanate intermediate leading to formation of the conjugate.
PMID: 23886699 [PubMed - as supplied by publisher]