An analytical method was developed for measuring the effect of OATP1B2 deficiency on plasma levels of the kinase inhibitor regorafenib and its metabolites regorafenib-N-oxide, N-desmethyl-regorafenib-N-oxide, and regorafenib-N-β-glucuronide (RG) in mice. Compounds were separated by liquid chromatography and monitored by a triple quadrupole mass spectrometer in the selected reaction monitoring mode after positive electrospray ionization. All calibration curves were linear in the selected concentration range (R2 ≥ 0.99). The lower limit of quantification was 5 ng/mL for the four analytes. Within-day precisions, between-day precisions, and accuracies were 2.59–6.82%, 3.97–11.3%, and 94.5–111%, respectively. The identification and structure elucidation of RG, isolated from human urine, was performed by NMR. Compared with wild-type mice given regorafenib (10 mg/kg), deficiency of the drug transporter OATP1B2 in vivo had minimal effects on plasma levels of parent drug and the metabolite regorafenib-N-oxide, and N-desmethyl-regorafenib-N-oxide. However, the area under the curve and peak levels of RG were increased by 5.6-fold and 5.1-fold, respectively, in OATP1B2-knockout mice. In conclusion, our analytical method allowed accurate and precise quantitation of regorafenib and its main metabolites in mouse plasma, and is suitable for evaluation of transporter-dependent pharmacokinetic properties of these agents in vivo.

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Journal Journal of Chromatography. B, Analytical Technologies in the Biomedical and Life Sciences
Fu, Q. (Qiang), Chen, M. (Mingqing), Hu, S, McElroy, C.A. (Craig A.), Mathijssen, A.H.J, Sparreboom, A, & Baker, S.D. (2018). Development and validation of an analytical method for regorafenib and its metabolites in mouse plasma. Journal of Chromatography. B, Analytical Technologies in the Biomedical and Life Sciences, 1090, 43–51. doi:10.1016/j.jchromb.2018.05.005