S39625 is an E-ring camptothecin keto analogue. S39625 is stable, potent, and selective topoisomerase I inhibitor without being substrates of drug efflux transporters. Nanomolar concentrations of S39625 induces intense and persistent histone gamma-H2AX. The chemical stability of the keto analogues and the ability of S39625 to produce high levels of persistent Top1-DNA cleavage complex and its potent antiproliferative activity against human cancer cell lines make S39625 a promising new anticancer drug candidate. Histone gamma-H2AX could be used as a biomarker for the upcoming clinical trials of S39625.
