Quantitation of Tucatinib, a Novel Tyrosine Kinase Inhibitor in Dried Blood Spot (DBS) With LC-ESI-MS/MS: Application to a Pharmacokinetic Study in Mice.

Tucatinib (Irbinitinib, ARRY-380), a potent oral, selective HER2 kinase inhibitor that the FDA, has approved for the treatment of HER2-positive metastatic breast cancer and colorectal cancer. Tucatinib provides a powerful, targeted therapy for HER2-positive cancers, showing substantial benefits in survival and disease control, especially for patients with difficult-to-treat brain metastases, extending options beyond standard chemotherapy. This research aimed to create and validate a new rapid, sensitive, and specific LC-MS/MS technique for measuring tucatinib in dried blood spots (DBS) from mice, with afatinib serving as an internal standard (IS) following regulatory guidelines in the linearity range from 0.178 to 1009 ng/mL (r > 0.990). The chromatographic separation of tucatinib and IS was achieved using the Acquity BEH C18 column with an isocratic mobile phase at a flow rate of 0.6 mL/min within 1.15 min total run time and 2 μL injection volume. Detection and quantification of tucatinib and the IS was done by using a triple quadrupole mass spectrometer in multiple reaction monitoring (MRM) mode. Tucatinib remained stable under various storage conditions. Comparison of DBS versus plasma samples concentrations showed a strong correlation, suggesting that DBS can serve as a valid alternative to plasma for pharmacokinetic evaluation.