The Effect of Ritonavir on Human CYP2B6 Catalytic Activity: Heme Modification Contributes to the Mechanism-Based Inactivation of CYP2B6 and CYP3A4 by Ritonavir
作者:Hsia-lien Lin、Jaime D’Agostino、Cesar Kenaan、Diane Calinski、Paul F. Hollenberg
DOI:10.1124/dmd.113.053108
日期:2013.10
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 K I of 0.9 μ M, a k inact of 0.05 min−1, and a partition ratio of approximately 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 deacylated product with MH+ at m/z 580. Inactivation of CYP2B6 by incubation with 10 μ M RTV for 10 min resulted in an approximately 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 = 0.33 μ M) and a type II ligand (spectral dissociation constant- K s = 0.85 μ M) 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-glutathione 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.
研究了重构系统中利托那韦 (RTV) 对人 CYP2B6 的基于机制的灭活。失活与时间、浓度和 NADPH 相关,K I 为 0.9 μM,k inact 为 0.05 min−1,分配比约为 3。液相色谱-串联质谱 (LC-MS/MS) 分析表明RTV 的质子化分子离子的 m/z 为 721,其两种主要代谢物是 m/z 737 的 MH+ 氧化产物和 m/z 580 的 MH+ 脱酰产物。用 10 μ 孵育可灭活 CYP2B6 M RTV 10 分钟导致催化活性和天然血红素损失约 50%,但未观察到脱辅基蛋白的修饰。 RTV被发现是一种有效的混合型可逆抑制剂(K i = 0.33 μM)和CYP2B6的II型配体(光谱解离常数- K s = 0.85 μM)。尽管之前的研究已经证明RTV是一种有效的基于机制的CYP3A4灭活剂,但导致灭活的分子机制尚未确定。在这里,我们提供的证据表明,RTV CYP3A4 失活是由于血红素破坏并形成血红素蛋白加合物所致。与 CYP2B6 类似,脱辅基蛋白没有显着修饰。此外,LC-MS/MS分析表明,在RTV代谢过程中,CYP3A4和人肝微粒体均形成具有MH+(m/z 858)的RTV-谷胱甘肽缀合物,表明异氰酸酯中间体的形成导致缀合物的形成。