Induction of Cytochrome P450 (CYP) 1A2 and CYP3A Influences Sunitinib Metabolism and Bioactivation in Primary Human Hepatocytes.

Sunitinib is an orally administered tyrosine kinase inhibitor used to treat renal cell carcinoma, gastrointestinal stromal tumors, and pancreatic neuroendocrine tumors. The product label for sunitinib carries a boxed warning for idiosyncratic hepatotoxicity; however, the mechanisms of this toxicity remain unclear. We have previously shown that cytochrome P450 (CYP) 1A2 and CYP3A4 catalyze the metabolic activation of sunitinib via oxidative defluorination to form a chemically reactive, potentially toxic quinoneimine, trapped as a glutathione (GSH) conjugate. The purpose of this study was to determine the effects of CYP1A2 and CYP3A induction on sunitinib bioactivation in human hepatocytes in vitro. Sandwich-cultured human hepatocytes from a single donor were pretreated with CYP1A2 and CYP3A inducers, omeprazole (50 μM) and rifampicin (25 μM), respectively, for 72 hours followed by incubation with sunitinib (10 μM) for 24 hours. Sunitinib metabolites were analyzed by liquid chromatography - tandem mass spectrometry. CYP1A2 induction by omeprazole reduced sunitinib levels by 48% and increased formation of the primary active metabolite N-desethylsunitinib (M1) by 2.0-fold, compared to control without inducer. CYP3A induction by rifampicin caused depletion of sunitinib by 93% and led to a corresponding increase in M1 formation by 4.9-fold. For defluorosunitinib (M3), omeprazole increased M3 levels by 7.4-fold, but rifampicin decreased M3 formation by 72%, compared to control. In addition, we identified a putative quinoneimine-cysteine conjugate (M6) of sunitinib in hepatocytes formed as a downstream metabolite of the quinoneimine-GSH conjugate. Omeprazole increased M6 formation by 7.7-fold, but rifampicin had a minimal effect on M6. The non-selective P450 inhibitor 1-aminobenzotriazole (1 mM) reduced each of these metabolites (M1, M3, M6), confirming the involvement of P450-mediated metabolism. Collectively, these findings indicate that induction of CYP3A enhances sunitinib metabolic clearance via N-dealkylation to M1, and CYP1A2 induction increases sunitinib bioactivation to the reactive, potentially toxic quinoneimine metabolite. Modulation of P450 activity due to enzyme induction or other environmental and genetic factors may influence the risk of metabolism-mediated adverse reactions associated with sunitinib.