Quantitative analysis of enasidenib in dried blood spots of mouse blood using an increased-sensitivity LC-MS/MS method: Application to a pharmacokinetic study

A simple, sensitive and rapid assay method has been developed and validated as per regulatory guidelines for the estimation of enasidenib on mouse dried blood spots (DBS) using liquid chromatography coupled to tandem mass spectrometry with electrospray ionization in the positive-ion mode. The method employs liquid extraction of enasidenib from DBS disks of mouse whole blood followed by chromatographic separation using 0.2% formic acid-acetonitrile (25:75, v/v) at a flow rate of 1.0 mL/min on an Atlantis dC(18) column with a total run time of 2.0 min. The MS/MS ion transitions monitored were m/z 474.0 -> 267.1 for enasidenib and m/z 309.2 -> 251.3 for the internal standard (warfarin). The assay was linear in the range of 1.01-3044 ng/mL. The within-run and between-run precisions were in the range of 3.18-9.06 and 4.66-8.69%, respectively. Stability studies showed that enasidenib was stable on DBS cards for 1 month. This novel method has been applied to analyze the DBS samples of enasidenib obtained from a pharmacokinetic study in mice.