Tyrosyl DNA phosphodiesterase 1 (Tdp1) is a promising target for the treatment of cancer, since it plays a key role in the removal of DNA damage generated by the action of topoisomerase 1 (Top1) poisons (irinotecan and topotecan) widely used in anticancer therapy. We have previously shown that the Tdp1 inhibitor, enamine derivative of usnic acid, the agent OL9-116, enhances the antitumor activity of topotecan and studied the pharmacokinetics of the agent. In the present study, we developed and validated an LC-MS/MS methods for the quantification of OL9-116 in mouse lungs, liver, kidneys, Lewis lung carcinoma tumor nodes and studied its distribution in organs of healthy and tumor mice. QuEChERS methodology was selected for sample preparation. Quantification of the compound was performed using SCIEX 6500 QTRAP mass spectrometer in MRM mode following chromatographic separation on a C8 reversed-phase column. Pharmacokinetics of OL9-116 was studied after intragastric administration of the compound to healthy and tumor mice at a dose of 150 mg/kg. It was found that maximal concentration of the agent in organs of healthy mice can reach 100 µg/g followed by its distribution and excretion. In tumor mice we observed increasing concentration of OL9-116 during first 1 h after administration to a level of 5-30 µg/g depending on the tissue (lungs, liver, kidneys, tumor node) and remaining at this level for at least next 12 hours, thus showing a pharmacokinetics profile clearly differing from that of healthy animals.