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 kinact = 0.0202 min−1 and Ki = 1.709 μM. 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.
Footnotes
↵ The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
This work was supported by the National University of Singapore (NUS) [Grants R-148-000-100-112, R-279-000-249-646, R-148-000-117-133]; the NUS Department of Pharmacy [Final Year Project Grant R-148-000-003-001]; and the Biomedical Research Council, Agency for Science, Technology, and Research.
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.110.065839.
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ABBREVIATIONS:
- P450
- cytochrome P450
- MBI
- mechanism-based inactivator
- RM
- reactive metabolite
- ACN
- acetonitrile
- HLM
- human liver microsome
- LC/MS/MS
- liquid chromatography/tandem mass spectrometry
- Ki
- inactivator concentration at half-maximum rate of inactivation
- kinact
- inactivation rate constant at infinite inactivator concentration
- Kobs
- observed inactivation rate constant
- DMSO
- dimethyl sulfoxide
- ESI
- electrospray ionization
- EP
- entrance potential
- CE
- collision energy
- CXP
- collision cell exit potential
- QTOFMS
- quadrupole, orthogonal acceleration time-of-flight tandem mass spectrometer
- IDR
- idiosyncratic drug reaction
- MIC
- metabolite-intermediate complex
- LAPA
- lapatinib
- i-FIT
- the likelihood that the isotopic pattern of the elemental composition matches a cluster of peaks in the spectrum.
- Received April 25, 2010.
- Accepted July 6, 2010.
- Copyright © 2010 The American Society for Pharmacology and Experimental Therapeutics
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