Metabolism and Disposition of Cabozantinib in Healthy Male Volunteers and Pharmacologic Characterization of Its Major Metabolites

Metabolism and excretion of cabozantinib, an oral inhibitor of receptor tyrosine kinases, was studied in 8 healthy male volunteers after a single oral dose of 175 mg cabozantinib L-malate containing C-14-cabozantinib (100 mu Ci/subject). Total mean radioactivity recovery within 48 days was 81.09%; radioactivity was eliminated in feces (53.79%) and urine (27.29%). Cabozantinib was extensively metabolized with 17 individual metabolites identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in plasma, urine, and feces. Relative plasma radioactivity exposures (analyte AUC(0-t)/total AUC(0-t) for cabozantinib+major metabolites) were 27.2, 25.2, 32.3, 7, and 6% for cabozantinib and major metabolites monohydroxy sulfate (EXEL-1646), 6-desmethyl amide cleavage product sulfate (EXEL-1644), N-oxide (EXEL-5162), and amide cleavage product (EXEL-5366), respectively. Comparable relative plasma exposures determined by LC-MS/MS analysis were 32.4, 13.8, 45.9, 4.9, and 3.1%, respectively. These major metabolites each possess in vitro inhibition potencies <= 1/10th of parent cabozantinib against the targeted kinases MET, RET, and VEGFR2/KDR. In an in vitro cytochrome P450 (CYP) panel, cabozantinib and EXEL-1644 both inhibited most potently CYP2C8 (Ki(app) = 4.6 and 1.1 mu M, respectively). In an in vitro drug transporter panel, cabozantinib inhibited most potently MATE1 and MATE2-K (IC50 = 5.94 and 3.12 mu M, respectively) and was a MRP2 substrate; EXEL-1644 inhibited most potently OAT1, OAT3, OATP1B1, MATE1, and OATP1B3 (IC50 = 4.3, 4.3, 6.1, 16.7, and 20.6 mM, respectively) and was a substrate of MRP2, OAT3, OATP1B1, OATP1B3, and possibly P-gp. Therefore, cabozantinib appears to be the primary pharmacologically active circulating analyte, whereas both cabozantinib and EXEL-1644 may represent potential for drug-drug interactions.