Department of Medicinal Chemistry, University of Washington, Seattle, WA, USA.
Drug Metab Dispos. 2011 Jun;39(6):1022-30. doi: 10.1124/dmd.110.037531. Epub 2011 Mar 1.
Lapatinib, an oral breast cancer drug, has recently been reported to be a mechanism-based inactivator of cytochrome P450 (P450) 3A4 and also an idiosyncratic hepatotoxicant. It was suggested that formation of a reactive quinoneimine metabolite was involved in mechanism-based inactivation (MBI) and/or hepatotoxicity. We investigated the mechanism of MBI of P450 3A4 by lapatinib. Liquid chromatography-mass spectrometry analysis of P450 3A4 after incubation with lapatinib did not show any peak corresponding to irreversible modifications. The enzymatic activity inactivated by lapatinib was completely restored by the addition of potassium ferricyanide. These results indicate that the mechanism of MBI by lapatinib is quasi-irreversible and mediated via metabolic intermediate complex (MI complex) formation. This finding was verified by the increase in a signature Soret absorbance at approximately 455 nm. Two amine oxidation products of the metabolism of lapatinib by P450 3A4 were characterized: N-hydroxy lapatinib (M3) and the oxime form of N-dealkylated lapatinib (M2), suggesting that a nitroso or another related intermediate generated from M3 is involved in MI complex formation. In contrast, P450 3A5 was much less susceptible to MBI by lapatinib via MI complex formation than P450 3A4. In addition, P450 3A5 had a significantly lower ability than 3A4 to generate M3, consistent with N-hydroxylation as the initial step in the pathway to MI complex formation. In conclusion, our results demonstrate that the primary mechanism for MBI of P450 3A4 by lapatinib is not irreversible modification by the quinoneimine metabolite, but quasi-irreversible MI complex formation mediated via oxidation of the secondary amine group of lapatinib.
拉帕替尼，一种口服乳腺癌药物，最近有报道称其是细胞色素 P450（P450）3A4 的一种基于机制的失活剂，也是一种特发性肝毒物。据推测，形成反应性醌亚胺代谢物与基于机制的失活（MBI）和/或肝毒性有关。我们研究了拉帕替尼对 P450 3A4 的 MBI 机制。用拉帕替尼孵育后 P450 3A4 的液相色谱-质谱分析未显示任何对应于不可逆修饰的峰。拉帕替尼失活的酶活性可通过添加铁氰化钾完全恢复。这些结果表明，拉帕替尼的 MBI 机制是准不可逆的，通过代谢中间复合物（MI 复合物）形成介导。这一发现通过大约 455nm 处特征性 Soret 吸收的增加得到了验证。P450 3A4 代谢拉帕替尼的两种胺氧化产物被表征：N-羟基拉帕替尼（M3）和 N-去烷基化拉帕替尼的肟形式（M2），表明 M3 生成的亚硝基或其他相关中间产物参与了 MI 复合物形成。相比之下，P450 3A5 通过 MI 复合物形成比 P450 3A4 更不易受到拉帕替尼的 MBI。此外，P450 3A5 生成 M3 的能力明显低于 3A4，这与 N-羟化作为 MI 复合物形成途径的初始步骤一致。总之，我们的结果表明，拉帕替尼导致 P450 3A4 的 MBI 的主要机制不是醌亚胺代谢物的不可逆修饰，而是通过拉帕替尼仲胺基团的氧化介导的准不可逆 MI 复合物形成。
