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

Evaluation of the Mass Balance and Metabolic Profile of Futibatinib in Healthy Participants

Futibatinib, a selective, irreversible fibroblast growth factor receptor 1-4 inhibitor, was recently approved for FGFR2 rearrangement-positive cholangiocarcinoma. This Phase I study evaluated the mass balance and metabolic profile of 14 C-futibatinib single oral 20-mg dose in healthy participants (n = 6). Futibatinib was rapidly absorbed; median time to peak drug concentration was 1.0 hours. The mean elimination half-life in plasma was 2.3 hours for futibatinib, and 11.9 hours for total radioactivity. Mean recovery of total radioactivity was 70% of the dose, with 64% recovered in feces and 6% in urine. The major excretion route was fecal; negligible levels were excreted as parent futibatinib. Futibatinib was the most abundant plasma component, comprising 59% of circulating radioactivity (CRA). The most abundant metabolites were cysteinylglycine-conjugated futibatinib in plasma (13% CRA) and reduction of desmethyl futibatinib in feces (17% of dose). In human hepatocytes, 14 C-futibatinib metabolites included glucuronide and sulfate of desmethyl futibatinib, whose formation was inhibited by 1-aminobenzotriazole (a pan-cytochrome P450 inhibitor), and glutathione- and cysteine-conjugated futibatinib. These data indicate the primary metabolic pathways of futibatinib are O-desmethylation and glutathione conjugation, with cytochrome P450 enzyme-mediated desmethylation as the main oxidation pathway. 14 C-futibatinib was well tolerated in this Phase 1 study.

Validated UPLC-MS/MS Method for Determination of Futibatinib and Its Pharmacokinetics in Beagle Dogs

Futibatinib, a highly selective, irreversible potent fibroblast growth factor receptor (FGFR) inhibitor, has been proved to be effective in clinical trials of intrahepatic cholangiocarcinoma (ICCA) patients. An ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method to determine the concentration of futibatinib in beagle dog plasma was developed and validated for the study of pharmacokinetics. After the plasma protein was removed by acetonitrile precipitation, futibatinib was detected and derazantinib was used as the internal standard (IS). Futibatinib and IS were separated in an UPLC BEH C18 column (2.1 mm × 50 mm, 1.7 μm) with acetonitrile and 0.1% formic acid as the mobile phase, and the flow rate was 0.3 mL/min. Under the positive ion condition of an electrospray spray ion (ESI+) source, multireaction detection was used, and the ion pairs for futibatinib and IS were m/z 418.99 ⟶ 295.97 and 468.96 ⟶ 382.00, respectively. Futibatinib had a good linear relationship in the linear range of 0.5∼100 ng/mL; the lower limit of quantification (LLOQ) was 0.5 ng/mL. The RSDs of the intraday and interday precision were all less than 10.70%, and the RE value of accuracy was between −3.87% and 3.28%. The extraction recovery of futibatinib was more than 80%, and the matrix effect was around 100%, and futibatinib was found to be stable under four experimental conditions. The new optimized and validated UPLC-MS/MS method was an effective tool to determine the concentration of futibatinib in plasma and has been successfully applied to the pharmacokinetics of futibatinib in beagle dogs. This method would also be used to study drug-drug interaction (DDI).

Metabolic Activation of the Acrylamide Michael Acceptor Warhead in Futibatinib to an Epoxide Intermediate Engenders Covalent Inactivation of Cytochrome P450 3A

Futibatinib (FUT) is a potent inhibitor of fibroblast growth factor receptor (FGFR) 1-4 that is currently under clinical investigation for intrahepatic cholangiocarcinoma. Unlike its predecessors, FUT possesses an acrylamide warhead which enables it to bind covalently to a free cysteine residue in the FGFR kinase domain. However, it remains uninterrogated if this electrophilic α,β-unsaturated carbonyl scaffold could also directly or indirectly engender off-target covalent binding to nucleophilic centres on other cellular proteins. Here, we discovered that FUT inactivated both cytochrome P450 3A (CYP3A) isoforms with K _I, k _inact, and partition ratio of 12.5 and 51.4 µM, 0.25 and 0.06 min^-1 and ~52 and ~58 for CYP3A4 and CYP3A5, respectively. Along with its time-, concentration- and cofactor-dependent inhibitory profile, FUT also exhibited several cardinal features that were consistent with mechanism-based inactivation. Moreover, the nature of inactivation was unlikely to be pseudo-irreversible and instead arose from the covalent modification of the P450 apoprotein and/or its heme moiety due to the lack of substantial enzyme activity recovery following dialysis and chemical oxidation as well as the absence of the diagnostic Soret peak in spectral analyses. Finally, utilizing GSH trapping and high-resolution mass spectrometry, we illuminated that while the acrylamide moiety in FUT could nonenzymatically conjugate to GSH via Michael addition, it was not implicated in the covalent inactivation of CYP3A. Rather, we surmised that it likely stemmed from the metabolic activation of its acrylamide covalent warhead to a highly electrophilic epoxide intermediate that could covalently modify CYP3A and culminate in its catalytic inactivation. Significance Statement In this study, we reported for the first time the inactivation of CYP3A by FUT. Furthermore, using FUT as an exemplary targeted covalent inhibitor, our study revealed the propensity for its acrylamide Michael acceptor moiety to be metabolically activated to a highly electrophilic epoxide. Due to the growing resurgence of covalent inhibitors and the well-established toxicological ramifications associated with epoxides, we advocate that closer scrutiny be adopted when profiling the reactive metabolites of compounds possessing an α,β-unsaturated carbonyl scaffold.