G226, a new epipolythiodioxopiperazine derivative, triggers DNA damage and apoptosis in human cancer cells in vitro via ROS generation

Aim: G226 is a novel derivative of epipolythiodioxopiperazines with potent inhibitory activity against cancer cells. Here, we sought to identify potential targets involved in the anti-cancer activity of G226. Methods: Cell proliferation assay was conducted in a panel of 12 human cancer cell lines. The activities of topoisomerase I (Topo I) and Topo II were studied using supercoiled pBR322 DNA relaxation and kDNA decatenation assays. ROS production was assessed with probes DCFH-DA and H&E. Western blot analysis and flow cytometry were used to examine DNA damage, apoptosis and cell cycle changes. Results: G226 displayed potent cytotoxicity in the 12 human cancer cell lines with a mean IC50 value of 92.7 nmol/L. This compound (1-100 mu mol/L) selectively inhibited the activity of Topo II, and elevated the expression of phosphorylated-H2AX in a dose-dependent manner. In Topo II-deficient HL60/MX2 cells, however, G226-induced DNA damage, apoptosis and cytotoxicity were only partially reduced, suggesting that Topo II was not essential for the anti-tumor effects of G226. Furthermore, G226 (0.125-2 mu mol/L) dose-dependently elevated the intracellular levels of H2O2 and O-2(radical) (anion) in the cancer cells, and pretreatment with GSH, NAC or DTT not only blocked G226-induced intracellular accumulation of ROS, but also abrogated G226-mediated phosphorylation of H2AX, apoptosis and cytotoxicity. Conclusion: G226-mediated ROS production contributes to the anti-cancer activity of this compound.