RT Journal Article
SR Electronic
T1 Metabolic Intermediate Complex Formation of Human Cytochrome P450 3A4 by Lapatinib
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 1022
OP 1030
DO 10.1124/dmd.110.037531
VO 39
IS 6
A1 Hideo Takakusa
A1 Michelle D. Wahlin
A1 Chunsheng Zhao
A1 Kelsey L. Hanson
A1 Lee Sun New
A1 Eric Chun Yong Chan
A1 Sidney D. Nelson
YR 2011
UL http://dmd.aspetjournals.org/content/39/6/1022.abstract
AB 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.