Human mass balance, metabolism, and cytochrome P450 phenotyping of lusutrombopag

The human mass balance of lusutrombopag, an orally bioavailable thrombopoietin (TPO) receptor agonist, was characterised in seven healthy male subjects after a single oral dose of [¹⁴C]-lusutrombopag (2 mg, 100 μCi) in solution. Lusutrombopag was the main component in plasma, accounting for 56% of plasma radioactivity AUC_0-∞. In plasma, the half-life of radioactivity (70.7 h) was longer than that of lusutrombopag (25.7 h), suggesting the presence of long circulating metabolites. The main excretion pathway of lusutorombopag was feces, with a radioactivity recovery of approximately 83% within 336 h post-dose. M6 (lusutrombopag-O-propanol or lusutrombopag-O-acetic acid) and M7 (lusutrombopag-O-ethane-1,2-diol) were also identified as main components in feces, accounting for at most 17.9%, and 16.9% of the dose, respectively, and were β-oxidation related metabolites. Our in vitro metabolism study of lusutrombopag indicated that β-oxidation was a subsequent metabolism of ω-oxidation and CYP4 enzymes, including CYP4A11, were the major isozymes contributing to ω-oxidation. In conclusion, lusutrombopag is primarily eliminated via ω-oxidation and excreted in the feces, where CYP4 enzymes play an important role.