Pharmacokinetics, Metabolism, and Excretion of [¹⁴C]Axitinib, a Vascular Endothelial Growth Factor Receptor Tyrosine Kinase Inhibitor, in Humans

Abstract

The disposition of a single oral dose of 5 mg (100 mCi) of [ 14 C]axitinib was investigated in fasted healthy human subjects (N = 8). Axitinib was rapidly absorbed, with a median plasma T max of 2.2 hours and a geometric mean C max and half-life of 29.2 ng/ml and 10.6 hours, respectively. The plasma total radioactivity-time profile was similar to that of axitinib but the AUC was greater, suggesting the presence of metabolites. The major metabolites in human plasma (0-12 hours), identified as axitinib N-glucuronide (M7) and axitinib sulfoxide (M12), were pharmacologically inactive, and with axitinib comprised 50.4%, 16.2%, and 22.5% of the radioactivity, respectively. In excreta, the majority of radioactivity was recovered in most subjects by 48 hours postdose. The median radioactivity excreted in urine, feces, and total recovery was 22.7%, 37.0%, and 59.7%, respectively. The recovery from feces was variable across subjects (range, 2.5%-60.2%). The metabolites identified in urine were M5 (carboxylic acid), M12 (sulfoxide), M7 (N-glucuronide), M9 (sulfoxide/N-oxide), and M8a (methylhydroxy glucuronide), accounting for 5.7%, 3.5%, 2.6%, 1.7%, and 1.3% of the dose, respectively. The drug-related products identified in feces were unchanged axitinib, M14/15 (mono-oxidation/sulfone), M12a (epoxide), and an unidentified metabolite, comprising 12%, 5.7%, 5.1%, and 5.0% of the dose, respectively. The proposed mechanism to form M5 involved a carbon-carbon bond cleavage via M12a, followed by rearrangement to a ketone intermediate and subsequent Baeyer-Villiger rearrangement, possibly through a peroxide intermediate. In summary, the study characterized axitinib metabolites in circulation and primary elimination pathways of the drug, which were mainly oxidative in nature.

In Vitro Kinetic Characterization of Axitinib Metabolism

“…Chemical inhibition studies suggested minor roles for CYP2C19 and CYP2D6; however, when using recombinant enzymes only CYP2C19 was shown to form metabolites at a CL int contribution greater than 0.3%. Conversely, a role for CYP1A2 could not be shown through inhibition by furafylline in HLMs, but studies using recombinant enzymes have demonstrated that CYP1A2 was the only enzyme that formed M12a, an in vivo metabolite of axitinib in humans (Smith et al, 2014). Axitinib metabolism in HLMs was inhibited by ,10%, each by montelukast and sulfaphenazole, selective inhibitors for CYP2C8 and CYP2C9, respectively.…”

“…These glucuronides were identified as Glu1, Glu2, and Glu3 (Supplemental Table 3). Glu2 was subsequently identified as axitinib N-glucuronide (M7), a major circulating metabolite in humans (Smith et al, 2014). Therefore, M7 was prepared biosynthetically as an authentic standard for further in vitro evaluation.…”

“…P450 and UGT Kinetic Studies. Since the biotransformation and human absorption, distribution, metabolism, and excretion studies of axitinib indicated that the sulfoxide (M12) and N-glucuronide (M7) metabolites of axitinib were the major circulating metabolites in plasma (Smith et al, 2014), additional enzyme kinetic studies were conducted in the microsomal and recombinant enzyme systems that formed these metabolites. Recombinant CYP3A4, 3A5, 2C19, HLMs, and rUGT 1A1, 1A3, and 1A9 enzymes were used to estimate enzyme kinetic determinations of axitinib metabolism.…”

“…2), which were chemically synthesized for the [ 14 C]axitinib human absorption, distribution, metabolism, and excretion study, were used to confirm the in vitro structures (Smith et al, 2014). These in vitro metabolites are in agreement with in vivo metabolites (e.g., M12, M8a, M12a/M14, and M15) observed in human excreta as determined from a human mass balance study following administration of [ 14 C]axitinib (Smith et al, 2014). Nonspecific Binding of Axitinib in HLMs.…”

“…The characterization of axitinib, [ 14 C]axitinib, axitinib N-glucuronide (M7), axitinib sulfoxide (M12), and benzynirvinol synthesis or biosynthesis (M7) is described below and has been described previously (Smith et al, 2014). [ 14 C] axitinib GMP material was prepared at Amersham (Buckinghamshire, United Kingdom) for Pfizer, La Jolla, CA.…”