Pharmacokinetic study of Tdp1 inhibitor resulted in a significant increase in antitumor effect in the treatment of Lewis lung carcinoma in mice by its combination with topotecan

We have previously shown that the Tdp1 inhibitor, enamine derivative of usnic acid, the agent OL9-116, enhances the antitumor activity of topotecan. In the present study, we developed and validated LC-MS/MS method for the quantification of OL9-116 in mouse whole blood and studied pharmacokinetics of the agent. The substance OL9-116 was shown to be stable in the whole blood in vitro. Sample preparation included two steps: mixing 10 mu L of a blood sample with 10 mu L of 0.2 M ZnSO4 aqueous solution, followed by protein precipitation with 100 mu L of acetonitrile containing internal standard. Quantification of the compound was performed using SCIEX 6500 QTRAP mass spectrometer in MRM mode following chromatographic separation on a C8 reversedphase column. The method was validated in terms of selectivity, linearity, accuracy, precision, recovery, and stability of the prepared sample. When the agent OL9-116 was administered intragastrically at a dose of 150 mg/ kg, the maximum concentration in the blood (about 5000 ng/mL) was reached after 2-4 h followed by the distribution and elimination of the compound. A study of the antitumor activity of a combination of OL9-116 and topotecan against Lewis lung carcinoma revealed that administration of topotecan 3 h after OL9-116 resulted in the most pronounced antitumor effect compared to simultaneous or individual administration of both compounds.

Automated summary

We developed and validated an LC-MS/MS method for quantification of OL9-116 in mouse whole blood and studied its pharmacokinetics. OL9-116 was stable in vitro in whole blood. After oral administration of OL9-116 at a dose of 150 mg/kg, the maximum concentration in the blood was reached after 2-4 hours and then distributed and eliminated. Co-administration of topotecan 3 hours after OL9-116 showed the most pronounced antitumor effect compared to simultaneous or individual administration of both compounds.