Quantitative bioanalytical assay for the tropomyosin receptor kinase inhibitor larotrectinib in mouse plasma and tissue homogenates using liquid chromatography-tandem mass spectrometry.

Larotrectinib is a promising tyrosine kinase inhibitor for solid tumors harboring tropomyosin receptor kinase gene fusions. A bioanalytical assay was developed for this drug in small volume samples using a 96-well format to efficiently support multiple mouse studies. The assay was completely validated for mouse plasma and partially for homogenates of eight different tissues: brain, heart, kidneys, liver, lungs, small intestine, spleen, and testes. Proteins in 10-μl samples were precipitated using acetonitrile containing momelotinib as internal standard. Chromatographic separation of analyte and internal standard from endogenous interferences was performed on an ethylene bridged octadecyl silica column using 0.1% (v/v) formic acid (in water) and methanol for gradient elution. Electrospray ionization and selected reaction monitoring on a triple quadrupole mass spectrometer were used for detection. In the range 1-2000 ng/ml the drug could be quantified in all 9 matrices with precisions (within-day and between-day) in the range 2.7-11.1% and accuracies in the range 87.4-101.4%. Compounds were sufficiently stable under all investigated conditions except for kidney homogenate. A pilot pharmacokinetic and tissue distribution study in mice demonstrated the applicability of the new presented assay for larotrectinib.