Development and validation of an HPLC-MS/MS method for the determination of filgotinib, a selective Janus kinase 1 inhibitor: Application to a metabolic stability study

Filgotinib is a selective Janus kinase 1 inhibitor drug which is currently under investigation for the treatment of rheumatoid arthritis and Crohn s disease. The aim of the present study was to develop an accurate, simple and sensitive LC-MS/MS method for the determination of filgotinib (FLG) in human liver microsomes (HLMs) and its application to a metabolic stability study. Chromatographic separation was carried on using of a reversed phase C18 column. The mobile phase was mixture of acetonitrile and ammonium formate (10 mM, pH 3.8) (30:70, v/v), under isocratic elution at a flow rate of 0.3 mL/min. Veliparib was used as internal standard. FLG was extracted from HLMs by precipitation. An electrospray ionization source was used to assay of FLG. The assay of FLG at m/z 426 -> 358 and 426 -> 291 for FLG and IS at 245 -> 145 and 245 -> 84 was attained through MRM. The linearity of the investigated method was observed from 5 to 500 ng/mL (correlation coefficient r(2) = 0.999). The LOD was 1.43 ng/mL, while the LOQ was 4.46 ng/mL. The investigated method exhibited good recovery (98.42-108.6%) and precision (ranged from 0.88% to 4.7%). The investigated method was successfully employed for a metabolic stability study of FLG in the HLMs matrix. The metabolic stability of FLG was evaluated by measuring two parameters, in vitro t(1/2) (48.47 min) and intrinsic clearance (14.294/min/mg). The results of the metabolic study confirm that FLG is execrated from the human body at a slower rate compared to related tyrosine kinase inhibitors. Therefore, drug plasma levels and kidney function should be monitored due to potential bioaccumulation.