Abstract 4911: Metabolic activation of sunitinib: Implications for sunitinib-induced toxicities
Authors: Jackson Klarissa D. , Amaya Gracia M. , Durandis Rebecca , Wines Kahari J. , Abouda Arsany A. , Starks Samuel A. , Daniels R. Nathan 
Published: August 2018

Abstract
Purpose: Sunitinib is a multi-targeted tyrosine kinase inhibitor approved for the treatment of renal cell carcinoma, gastrointestinal stromal tumors, and pancreatic neuroendocrine tumors. However, clinical use of sunitinib is associated with potentially fatal idiosyncratic liver injury. The mechanisms of this toxicity are unknown. We hypothesized that sunitinib undergoes metabolic activation to form chemically reactive, potentially toxic metabolites, which may contribute to the development of sunitinib-induced liver injury. The purpose of this study was to define the role of cytochrome P450 (CYP) enzymes in the metabolism and bioactivation of sunitinib to provide insight into the mechanisms of drug toxicity.
Methods: Metabolic incubations were performed using individual recombinant P450 enzymes, human liver microsomal fractions, and P450-selective chemical inhibitors. To assess reactive metabolite formation, glutathione (GSH) and a chemical derivative of GSH, dansyl-GSH, were used as trapping agents to detect reactive metabolite-GSH conjugates. Sunitinib metabolites were analyzed by liquid chromatography-tandem mass spectrometry.
Results: Recombinant CYP3A4 was the major enzyme to form the primary active metabolite N-desethyl-sunitinib. Recombinant CYP1A2 generated the highest levels of reactive metabolites trapped as GSH conjugates, with minor contributions from CYP2D6 and CYP3A4. Detection of reactive metabolite dansyl-GSH conjugates from incubations with dansyl-GSH confirmed the generation of reactive metabolites by CYP1A2. In human liver microsomal incubations, the CYP3A inhibitor ketoconazole reduced formation of N-desethyl-sunitinib by 88%, while the CYP1A2 inhibitor furafylline decreased generation of reactive metabolite-GSH conjugates by 62%, compared to control levels. Quinidine (CYP2D6 inhibitor) and ketoconazole (CYP3A inhibitor) also decreased GSH conjugate formation by 54 and 52%, respectively, compared to control. Kinetic assays with recombinant P450s revealed that the overall enzyme efficiency (kcat/Km) for converting sunitinib to reactive metabolite-GSH conjugates was in the following order: CYP1A2 &gt; CYP3A4 &gt; CYP2D6.
Conclusions: Collectively, these data indicate that CYP1A2 and CYP3A4 are important contributors to metabolic activation of sunitinib to generate reactive, potentially toxic metabolites. Factors that alter CYP1A2 and CYP3A4 activity may affect patient risk for sunitinib toxicity. Future studies will focus on examining the impact of P450 genetic variations and environmental factors on sunitinib metabolism and toxicity.
Citation Format: Klarissa D. Jackson, Gracia M. Amaya, Rebecca Durandis, Kahari J. Wines, Arsany A. Abouda, Samuel A. Starks, R. Nathan Daniels. Metabolic activation of sunitinib: Implications for sunitinib-induced toxicities [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4911.