Liquid chromatography-tandem mass spectrometric assay for the mutated BRAF inhibitor dabrafenib in mouse plasma

A quantitative bioanalytical liquid chromatography-tandem mass spectrometric (LC-MS/MS) assay for the mutated BRAF inhibitor dabrafenib was developed and validated. Plasma samples were pre-treated using protein precipitation with acetonitrile containing PLX4720 as internal standard. The extract was directly injected into the reversed-phase chromatographic system after dilution with water. The eluate was transferred into the electrospray interface with positive ionization and the analyte was detected in the selected reaction monitoring mode of a triple quadrupole mass spectrometer. The assay was validated in a 2-2000 ng/ml calibration range with r(2)=0.993±0.002 for linear regression with quadratic weighting (n=5). Within day precisions (n=6) were 3.3-5.2%, between day (3 days; n=18) precisions 4.7-8.2%. Accuracies were between 95-104% for the whole calibration range. The drug was sufficiently stable under all relevant analytical conditions. Finally, the assay was successfully used to determine drug pharmacokinetics in mice.