Validated LC-MS/MS Method for the Determination of Paxalisib on Mouse Dried Blood Spots: An Application to Pharmacokinetic Study in Mice

Paxalisib is a dual PI3K/mTOR inhibitor, being used in advanced cancer treatment. In this research, we report a validated LC-MS/MS method for quantifying paxalisib from mouse dried blood spot (DBS). We validated the method in-line with the FDA guidelines. Liquid-liquid extraction technique was used to extract paxalisib from the DBS discs. We used a Chromolith RP-18 end cap (100 × 4.6 mm) column and isocratic mobile phase for the chromatographic separation of paxalisib and the internal standard (IS, dasatinib). The flow was 0.80 mL/min. In the optimized chromatographic conditions, the retention of paxalisib and the IS was ~2.13 and 2.06 min, respectively. Each injection total run time was 2.50 min. The MS/MS ion transitions monitored were m/z 383.2 → 309.1 and 488.1 → 410.1 for paxalisib and the IS, respectively. We have used a broad calibration range (1.24-3762 ng/mL) with a determination coefficient (r²) of 0.995. All the validation parameters assessed met the acceptance criteria, and hematocrit had no effect on DBS Paxalisib concentrations. We have used the validated method to derive the intravenous and oral pharmacokinetic parameters by quantifying paxalisib in mouse blood and correlated with mice pharmacokinetic data.