Development and Validation of a Sensitive UHPLC-MS/MS Analytical Method for Fulzerasib in Rat Plasma and its Application to Pharmacokinetics Studies.

Fulzerasib is a novel, potent, and irreversible covalent inhibitor targeting the KRAS G12C mutation, recently approved in China for advanced nonsmall cell lung cancer. This study aimed to develop and fully validate a rapid, specific and sensitive UHPLC-MS/MS method for the quantification of Fulzerasib in rat plasma. Sample preparation was streamlined using a simple protein precipitation technique with acetonitrile. Chromatographic separation was achieved within a 4.0-min run on a C18 column, with verapamil as the internal standard and detection via multiple reaction monitoring. The method was rigorously validated over a linear range of 5 to 5000 ng/mL (R2 > 0.9933), demonstrating excellent accuracy (102%-112.7%) and precision (≤ 10.3% for QCs). Stability was confirmed under various storage and processing conditions. The validated method was successfully applied in the first pharmacokinetic study of Fulzerasib in Sprague-Dawley rats following single intravenous (1 mg/kg) and oral (3 mg/kg) administration. Fulzerasib exhibited favorable pharmacokinetic properties, including low plasma clearance (5.02 mL/min/kg), moderate volume of distribution and notably high oral bioavailability of 38.6%. The established method is reliable, efficient and readily applicable, thereby providing a vital tool for accelerating the ongoing preclinical and translational research of Fulzerasib.