Peroxide compounds as potential anti-cancer agents through induction of ferroptosis

Abstract

Ferroptosis is a non-apoptotic form of regulated cell death which is dependent on iron with the appearance of lipid peroxide. Using the strategy of “tert-butylcyclohexyl ring + peroxide + targeting group”, we have synthesized and screened for anticancer activities of a number of 1,2,4,5-tetraoxanes. The phosphonium or quaternary ammonium moiety was found to be the crucial component for improving the selectivity and cytotoxicity. Among the synthesized compounds, tetraoxanes 48 and 37b were found to initiate ferroptosis in MDA-MB-231 breast cancer cells but were 10-fold less cytotoxic towards NIH3T3 cells. In contrast to classical ferroptosis inducers, 48 and 37b did not inhibit system XC– or directly target glutathione peroxidase 4. We found that these two peroxide compounds induced hydroxyl radicals and lipid peroxides in MDA-MB-231 cells, by using HKOH-1r and C11-BODIPY probes, respectively. Experimental data revealed that mitochondria and lysosomes were not the targeting sites of these two peroxide compounds. It is possible that the iron oxidizing property of 1,2,4,5-tetraoxanes culminates in the formation of carbon-centered radicals, which may be the culprit of ROS generation inside the cells. We also illustrated that lipoxygenase participated in the event of ferroptosis upon 1,2,4,5-tetraoxane treatment by exacerbating lipid peroxide production to a lethal level. What’s more, tetraoxane 48 induced DNA damage which could be mitigated by adding ferrostatin-1. We demonstrated that 1,2,4,5-tetraoxanes eradicated not only cancer cells but also cancer stem cells. Unlike paclitaxel, erasin or artesunate, tetraoxanes 48 and 37b were able to wipe out the majority of ovarian cancer stem cells at 5 µM concentration by inducing ferroptosis. These findings potentiate a reactive oxygen species (ROS) inducing therapy for cancer cells by 1,2,4,5-tetraoxanes which trigger off ferroptosis.