Lapatinib Metabolism in CYP3A5‐Genotyped Primary Human Hepatocytes

Abstract

Drug‐induced liver injury is associated with the oral tyrosine kinase inhibitor lapatinib, which is used in metastatic breast cancer therapy. Lapatinib is extensively metabolized by cytochrome P450 (CYP) 3A4 and CYP3A5 to yield an O‐debenzylated metabolite (Lap‐OH), which can undergo further oxidation to a reactive quinoneimine. We hypothesized that polymorphic expression of CYP3A5 may contribute to individual differences in lapatinib bioactivation and influence hepatic exposure to reactive, potentially toxic metabolites. The objective of this study was to assess the metabolism of lapatinib in CYP3A5‐genotyped human hepatocyte cultures, and evaluate whether CYP3A5 genotype and activity lead to differences in lapatinib metabolite formation. Commercially available human hepatocytes were obtained from XenoTech (pooled) and BioIVT (individual). CYP3A5 genotype (*1/*1, *1/*3, and *3/*3) and donor characteristics (sex, age, ethnicity) were provided by the companies. Lapatinib (10 μM) was incubated with genotyped human hepatocytes in suspension for 2 h. Separate incubations were carried out to measure CYP3A and CYP3A5‐selective activity using probe substrates, midazolam (2.5 μM) and T‐5 (5 μM), respectively. Metabolite formation was analyzed by liquid chromatography‐tandem mass spectrometry. The results from experiments with genotyped human hepatocytes from pooled donors showed that formation of Lap‐OH was higher in CYP3A5 expressers (CYP3A5 *1/*1 and CYP3A5*1/*3 donors) compared to CYP3A5 non‐expressers (CYP3A5*3/*3 donors). CYP3A activity, as measured by midazolam 1’‐hydroxylation, and CYP3A5‐selective activity, as measured by T‐5 N‐oxidation, were also higher in CYP3A5 expressers (*1/*1 and *1/*3) compared to non‐expressers (*3/*3). In incubations with single‐donor human hepatocytes (n = 15), the levels of Lap‐OH generated were 2.2‐fold higher in CYP3A5 expressers compared to non‐expressers (p = 0.0497). Moreover, formation of Lap‐OH was 2.5‐fold higher in hepatocytes from female donors compared to males (p = 0.0390). Collectively, these results indicate that CYP3A5 genotype and donor sex influence lapatinib bioactivation in human hepatocyte cultures. Future studies will examine the cytotoxicity of lapatinib in primary human hepatocytes to determine the impact of CYP3A5 genotype, sex, and other individual factors on lapatinib‐induced hepatocellular injury.Support or Funding InformationThis research is funded by the National Cancer Institute of the National Institutes of Health (K01CA190711). Research reported here is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.