Pharmacokinetics, mass balance, and metabolism of [14C]FCN-437c, a selective and potent CDK4/6 inhibitor in humans.

This study investigated the pharmacokinetics, mass balance, and metabolism of [¹⁴C]FCN-437c, a selective and potent CDK4/6 inhibitor, in humans. Six healthy male Chinese subjects were administered a single oral dose of 200 mg [¹⁴C]FCN-437c (120 µCi), and plasma, urine, and feces samples were collected up to 456 h post-dose. The geometric mean C_max of radioactivity in plasma and blood were 706 and 557 ng eq./mL, respectively, with a median T_max of 5.0 h and a geometric mean t_1/2 of 56.5 h in plasma. The primary route of elimination was fecal excretion, accounting for a mean of 77.16% of the dose, whereas urinary excretion constituted a mean of 19.19% of the administered radioactivity. UHPLC-HRMS analysis identified 12 metabolites in human plasma, urine, and feces, with 8 of them being phase I metabolites, and the major metabolic pathways were mono-oxidation and O-dealkylation. Additionally, 4 phase II metabolites were identified, including two glucuronides, one glutathione conjugate, and one cysteine conjugate. The study provides insights into the metabolic stability and clearance mechanisms of FCN-437c in human, which are essential for its further clinical development and dosing regimens.