Development and validation of an LC-MS/MS method to quantify the bromodomain and extra-terminal (BET) inhibitor JQ1 in mouse plasma and brain microdialysate: Application to cerebral microdialysis study

JQ1, is a cell-permeable small-molecule inhibitor of bromodomain and extra-terminal protein (BET) function with reportedly good CNS penetration, however, unbound and pharmacologically active CNS JQ1 exposures have not been characterized. Additionally, no quantitative bioanalytical methods for JQ1 have been described in the literature to support the CNS penetration studies. In the present article, we discuss the development and validation of a sensitive and reliable liquid chromatography-tandem mass spectrometry (LC-MS/MS) quantitative methods to determine JQ1 in mouse plasma and brain microdialysate. JQ1 and the internal standard, dabrafenib (ISTD), were extracted from plasma and microdialysate samples using a simple solid phase extraction protocol performed on an Oasis HLB μElution plate. Chromatographic separation of JQ1 and ISTD was achieved on a reversed phase C₁₂ analytical column with gradient elution profile of mobile phases (MP A: water containing 0.1 % formic acid and MP B: acetonitrile containing 0.1 % formic acid) at a flow rate of 0.6 mL/min. The mass spectrometric detection was performed in the positive MRM ion mode by monitoring the transitions 457.40 > 341.30 (JQ1) and 520.40 > 307.20 (ISTD). The calibration curves demonstrated good linearities over the concentration range of 5-1000 ng/mL for the mouse plasma method (r² ≥ 0.99) and 0.5-500 ng/mL for the microdialysate method (r² ≥ 0.99). The experimental limit of quantification obtained was 5 and 0.5 ng/mL for the mouse plasma and microdialysate method, respectively, with the coefficient of variation less than 10 % for the analyte peak area. All the other validation parameters, including intra-and inter-day accuracy and precision, matrix effect, selectivity, carryover effect, and stability, were within the USFDA bioanalytical guidelines acceptance limits. The LC-MS/MS method was successfully applied to a mouse pharmacokinetic and cerebral microdialysis study to characterize the unbound JQ1 exposure in brain extracellular fluid and plasma.