Abstract

Infigratinib (INF) is a promising selective inhibitor of fibroblast growth factor receptors 1–3 that has recently been accorded both orphan drug designation and priority review status by the US Food and Drug Administration for the treatment of advanced cholangiocarcinoma. Its propensity to undergo bioactivation to electrophilic species was recently expounded upon. However, other than causing aberrant idiosyncratic toxicities, these reactive intermediates may elicit mechanism-based inactivation of cytochrome P450 enzymes. In this study, we investigated the interactions between INF and the most abundant hepatic CYP3A. Our findings revealed that, apart from being a potent noncompetitive reversible inhibitor of CYP3A4, INF inactivated CYP3A4 in a time-, concentration- and NADPH-dependent manner with inactivator concentration at half-maximum inactivation rate constant, maximum inactivation rate constant, and partition ratio of 4.17 µM, 0.068 minute⁻¹, and 41, respectively, when rivaroxaban was employed as the probe substrate. Coincubation with testosterone (alternative CYP3A substrate) or ketoconazole (direct CYP3A inhibitor) attenuated the rate of inactivation, whereas the inclusion of glutathione and catalase did not confer such protection. The lack of enzyme activity recovery after dialysis for 4 hours and oxidation with potassium ferricyanide, coupled with the absence of the characteristic Soret peak signature collectively substantiated that inactivation of CYP3A4 by INF was not mediated by the formation of quasi-irreversible metabolite-intermediate complexes but rather through irreversible covalent adduction to the prosthetic heme and/or apoprotein. Finally, glutathione trapping and high-resolution mass spectrometry experimental results unraveled two plausible bioactivation mechanisms of INF arising from the generation of a p-benzoquinonediimine and epoxide reactive intermediate.