Impact of Inter‐individual Variability in CYP1A2 and CYP3A4 Activity on Sunitinib Metabolism
Authors: Jackson Klarissa D. , Burnham Elizabeth A. , Abouda Arsany A. , Vergne Matthew J. 
Published: April 2020

Sunitinib is an orally administered multi‐targeted tyrosine kinase inhibitor used in the treatment of renal cell carcinoma, gastrointestinal stromal tumors, and other types of cancer. The product label of sunitinib carries a boxed warning for idiosyncratic hepatotoxicity; however, the mechanisms of this toxicity remain unclear. Recent studies suggest that cytochrome P450‐mediated bioactivation may play a role in sunitinib‐induced liver injury. We have previously shown that CYP1A2 and CYP3A4 catalyze the metabolic activation of sunitinib via oxidative defluorination leading to formation of a chemically reactive, potentially toxic quinoneimine metabolite, which was trapped as a glutathione (GSH) conjugate. We hypothesize that inter‐individual variation in CYP1A2 and CYP3A activity affects hepatic exposure to sunitinib reactive metabolites and may influence the risk of developing sunitinib‐induced hepatotoxicity. The goals of this study were to 1) estimate the relative contributions of CYP1A2 and CYP3A to sunitinib metabolism and bioactivation, and 2) determine the impact of CYP1A2 and CYP3A enzyme activity on sunitinib metabolite formation in individual human liver microsomes. Sunitinib (5 ∝M) was incubated over time (0–10 min) with human liver microsomes from a single donor with high CYP1A2 activity (HH581) in the presence and absence of CYP1A2 inhibitor furafylline (25 ∝M) and CYP3A inhibitor ketoconazole (1 ∝M). Relative levels of sunitinib metabolites N‐desethylsunitinib (M1), defluorosunitinib (M3), and quinoneimine‐GSH conjugates (M5) were measured by LC‐MS/MS analysis. Sunitinib (10 ∝M) was also incubated with human liver microsomes from 12 individual donors, and metabolite formation was compared to individual CYP1A2 and CYP3A activities using probe substrates, phenacetin and midazolam, respectively. In human liver microsomes from a single donor with high CYP1A2 activity, co‐incubation with furafylline reduced M3 and M5 formation by 73% and 80%, respectively, compared to control; however, furafylline had a minimal effect on M1 formation (20% reduction). Ketoconazole reduced M1, M3, and M5 formation by 95%, 46% and 40%, respectively, compared to control. In human liver microsomes from 12 individual donors, formation of M3 and M5 was significantly correlated with CYP1A2 activity as estimated by phenacetin O‐deethylation (M3 vs. phenacetin O‐deethylation: r2 = 0.83) and (M5 vs. phenacetin O‐deethylation: r2 = 0.88). M1 formation was highly correlated with CYP3A activity as measured by midazolam 1′‐hydroxylation (r2 = 0.91). Collectively, these findings indicate that CYP1A2 plays a predominate role in sunitinib bioactivation leading to the quinoneimine‐GSH conjugates (M5), while CYP3A is the primary contributor to sunitinib N‐deethylation to form the major active metabolite M1. Future studies will be conducted in human hepatocytes to evaluate the effect of modulating P450 activity on sunitinib‐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 NIH.