Topoisomerase I inhibitor 8 is a potent topoisomerase I inhibitor. Topoisomerase I inhibitor 8 is a hexacyclic analogue of camptothecin, and displays cytotoxic effect against tumor cells In Vitro Topoisomerase I inhibitor 8 (compound 57) shows antitumor activities against three cell line cultures with IC 50 s of 0.22 ng/mL (P388), 2.06 ng/mL (HOC-21), 0.17 ng/mL (QG-56), respectively. Topoisomerase I inhibitor 8 results the change in DNA from the supercoiled form to the relaxed form in the presence of topoisomerase I, shows stronger effective than SN-38 , with IC 50 of compound/IC 50 of SN-38=0.51. MCE has not independently confirmed the accuracy of these methods. They are for reference only. IC50& Target:Topoisomerase I