Pharmacokinetic Study Of Irinotecan By Co-administered Thalidomide

Irinotecan, a semisynthetic derivative of camptothecin, is a broad-spectrum antineoplastic agent of the topoisomerase I inhibitor class and its clinical application was widespread. Myelosuppression and delayed diarrhea are its critically adverse reactions, especially delayed diarrhea which was the most significant one of the factors why its clinical application was hindered. The intestinal mucosa was usually injured by the active metabolite SN-38, the ionic transport was abnormal in the intestinal tract, and delayed diarrhea was induced because of the excessive water and electrolytes secreted into the intestinal tract. Delayed diarrhea could be reduced if the concentration of SN-38 was decreased.Thalidomide with antiangiopoiesis and immunoloregulation properties has been demonstrated antineoplastic activity. It has been confirmed that irinotecan intestinal toxicity was relieved by co-administrated thalidomide in several clinical trials. However, the mechanisms are unknown. To provide the evidence for clinical medication and to perfect the chemotherapy to insure the safety and efficacy of irinotecan, the study should be established to investigate the interaction between irinotecan and thalidomide.Healthy male Sprague Dawley rats were randomized to two groups with one group receiving CPT-11 at 10mg·kg^-1 by i.v. and the other group receiving CPT-11 at 20mg·kg^-1 by i.v., both groups in combination with thalidomide (20mg·kg^-1 by i.p. given 30min prior to CPT-11 injection). Either of the two doses has a control group which is administrated the same dose CPT-11 in combination with DMSO whose administration is the same as thalidomide. Blood samples were collected at 0.083, 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, 10 and 12h following CPT-11 injection. The plasma concentrations were determined and pharmacokinetics parameters were fitted to inspect the change of pharmacokinetics of both CPT-11 and SN-38 by the DASver2.0 software.To support the study of pharmacokinetics of irinotecan, a LC-MS/MS method was established for simultaneous determination of CPT-11 and its active metabolite SN-38. The ESI tandem quadrupole mass spectrometer was used in the methodology of biopharmaceutical analysis. Solid phase extraction was utilized for the sample preparation. The gradient mobile phase was consisted of 5mM ammonium formiate solution pH3.0 (A) and 0.1%formic acid in methanol (B). The gradient process was shown below. During 0-0.5min, the ratio of A:B stepped from 70:30 to 0:100. During 0.5-6min, the ratio of A:B sustained at 0:100. During 6-6.5min, the ratio of A:B stepped from 0:100 to 70:30. During 6.5-10min, the ratio of A:B sustained at 70:30. The total time of the analysis was 10min, the flow rate was 0.25mL·min^-1 and the column temperature was 30℃. The MRM mode was used in the data acquiring. The parent ion of CPT-11 was m/z 587.7 [M+H]⁺, the linear range of standard curve of plasma sample was 1.0-2000ng·mL^-1, and the r²â‰¥0.999. The parent ion of SN38 was m/z 393.1[M+H]⁺, the linear range of standard curve of plasma sample was 0.5-100ng·mL^-1, and the r²â‰¥0.999. This method was applied to the study suitably.Between the both doses combined with thalidomide by i.p., the C_max of CPT-11 was increased significantly (p<0.05) of both doses, its AUC_0-t was increased in both groups, but AUC_{20mg·kg^-1} was increased without statistical significance, the AUC_0-t of SN38 was decreased significantly (p<0.05) of both doses, its C_max was decreased in both groups, but its C_max of the dose of 10 mg·kg^-1 was decreased without statistical significance. The results of pharmacokinetics in rats indicated that co-administrated thalidomide could increase the C_max significantly (p<0.05) and the AUC_0-t of CPT-11 to some extent and attenuate the AUC_0-t significantly (p<0.05) and the C_max of SN-38 to some extent. The pharmacokinetic study revealed the mechanism of action that the delayed diarrhea of irinotecan could be prevented by thalidomide.The experimental results provides reasonable data for clinical trial. To put the clinical trial in progress, the protocol was layinged to provide references in the study.