Mechanism-Based Inactivation of Cytochrome P450 3A4 by Lapatinib

Abstract

Fatalities stemming from hepatotoxicity associated with the clinical use of lapatinib (Tykerb), an oral dual tyrosine kinase inhibitor (ErbB-1 and ErbB-2) used in the treatment of metastatic breast cancer, have been reported. We investigated the inhibition of CYP3A4 by lapatinib as a possible cause of its idiosyncratic toxicity. Inhibition of CYP3A4 was time-, concentration-, and NADPH-dependent, with k inact ϭ 0.0202 min Ϫ1 and K i ϭ 1.709 M. The partition ratio was approximately 50.9. Addition of GSH did not affect the rate of inactivation. Testosterone protected CYP3A4 from inactivation by lapatinib. The characteristic Soret peak associated with a metabolite-intermediate complex was not observed for lapatinib during spectral difference scanning. However, reduced carbon monoxide (CO)-difference spectroscopy did reveal a 43% loss of the spectrally detectable CYP3A4-CO complex in the presence of lapatinib. Incubation of either lapatinib or its dealkylated metabolite with human liver microsomes in the presence of GSH resulted in the formation of a reactive metabolite (RM)-GSH adduct derived from the O-dealkylated metabolite of lapatinib. In addition, coincubation of lapatinib with ketoconazole inhibited the formation of the RM-GSH adduct. In conclusion, we demonstrated for the first time that lapatinib is a mechanism-based inactivator of CYP3A4, most likely via the formation and further oxidation of its O-dealkylated metabolite to a quinoneimine that covalently modifies the CYP3A4 apoprotein and/or heme moiety.

Pathway-Dependent Inhibition of Paclitaxel Hydroxylation by Kinase Inhibitors and Assessment of Drug–Drug Interaction Potentials

“…For the CYP3A4 pathway, time-dependent inhibition was observed for the majority of selected kinase inhibitors, consistent with literature reports where midazolam is used as a probe substrate (Li et al, 2009a(Li et al, ,b, 2010Teng et al, 2010;Kenny et al, 2012). For some of those kinase inhibitors, inactivation mechanisms were also investigated (Teng et al, 2010;Takakusa et al, 2011). As observed for axitinib in our present study, a majority of those compounds have the potential to form reactive intermediates during P450 catalysis, as evident by the formation of glutathione adducts (Kenny et al, 2012).…”

“…Further investigation of this finding is under way to delineate CYP2C8 inactivation mechanisms. For the CYP3A4 pathway, time-dependent inhibition was observed for the majority of selected kinase inhibitors, consistent with literature reports where midazolam is used as a probe substrate (Li et al, 2009a(Li et al, ,b, 2010Teng et al, 2010;Kenny et al, 2012). For some of those kinase inhibitors, inactivation mechanisms were also investigated (Teng et al, 2010;Takakusa et al, 2011).…”

“…In contrast, most of the selected kinase inhibitors (except sorafenib) showed strong time-dependent inhibition against CYP3A4-mediated paclitaxel metabolism, consistent with the literature reports (Li et al, 2009a;Teng et al, 2010;Filppula et al, 2012;Kenny et al, 2012). For the subsequent drug-drug interaction prediction, inactivation parameters (K I and k inact ) of CYP3A4 by those kinase inhibitors were adapted from the literature reports (Li et al, 2009a;Teng et al, 2010;Filppula et al, 2012;Kenny et al, 2012).…”

“…For the subsequent drug-drug interaction prediction, inactivation parameters (K I and k inact ) of CYP3A4 by those kinase inhibitors were adapted from the literature reports (Li et al, 2009a;Teng et al, 2010;Filppula et al, 2012;Kenny et al, 2012). Because there were no data available for axitinib, we further investigated the kinetics and mechanisms of CYP3A4 inactivation by this drug.…”

Metabolism and Pharmacokinetics of Allitinib in Cancer Patients: The Roles of Cytochrome P450s and Epoxide Hydrolase in its Biotransformation

“…An in vitro investigation showed that lapatinib was metabolized to O-dealkylated lapatinib by CYP3A4 and CYP2C8, and GSH and cysteinyl-glycine conjugates were also observed (Teng et al, 2010). Although allitinib was metabolized by O-dealkylation, like lapatinib, we detected no conjugates formed by the reaction between GSH and the quinone imine intermediate.…”