Quantification of the irreversible fibroblast growth factor receptor inhibitor futibatinib by UPLC-MS/MS: Application to the metabolic stability assay in human liver microsomes for the estimation of its in vitro hepatic intrinsic clearance

Futibatinib (FUT) is a potent irreversible inhibitor of Fibroblast Growth Factor receptor 1-4 currently under clinical investigation for the treatment of cholangiocarcinoma. However, there remains a paucity of information pertaining to its hepatic metabolism. In this study, our overarching aims were to systematically develop and validate a novel ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) analytical method to quantify FUT for the subsequent application to the metabolic stability assay. Chromatographic separation was achieved on a C₁₈ column and a gradient elution system comprising 0.1% formic acid in water (A) and acetonitrile (B). Positive electrospray ionization in conjunction with multiple reaction monitoring (MRM) mode was harnessed for the selective and sensitive quantification of FUT (m/z 419.2 → 296.0) and erdafitinib (m/z 447.0 → 362.0; internal standard). The retention time was 1.49 min for FUT and 1.29 min for erdafitinib. The calibration curve was linear from 0.003 to 3 µM (r² > 0.99) and the lower limit of quantification was 0.003 µM. The intra-day and inter-day precision (% RSD) and accuracy (% bias) were all < 11.4% and < 11.3% respectively. Quality control samples were determined to be stable under several conditions routinely employed in sample preparation and UPLC-MS/MS analyses. Moreover, the liver microsomal matrix did not adversely affect the quantification of FUT. Following which, the in vitro microsomal intrinsic clearance (CL_int) of FUT was calculated from our metabolic stability assay to be 29.3 µL/min/mg, thereby suggesting that it was a medium clearance drug. Finally, extrapolating the CL_int with human scaling factors yielded an estimated in vitro hepatic intrinsic clearance value of 2075 mL/min. Our study reports the first UPLC-MS/MS method and offers a specific, sensitive and rapid means of determining FUT human liver microsomal stability.