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 (CLint) 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 CLint 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.