Dihydroartemisinin enhances radiosensitivity of human glioma cells in vitro

Purpose: The antimalarial agent, artemisinin, also confers cancer-specific cytotoxic effects by reacting with ferrous iron atoms to form free radicals. Here, we investigated the radiosensitizing effects of dihydroartemisinin on glioma cells and assessed some possible mechanisms for these effects. Materials and methods: U373MG glioma cells treated with various concentrations of dihydroartemisinin plus radiation, and efficiency of radiosensitization was assessed by clonogenic survival assay. Expression and activity of antioxidant enzymes, glutathione-S-transferase (GST) were quantified by western blot and enzymatic activity analyses, respectively. Results: Dihydroartemisinin showed higher cytotoxicity in the glioma cell lines than in the liver, breast or cervical cancer cell lines. In clonogenic survival assays, treatment with dihydroartemisinin alone dose-dependently reduced the number of U373MG colonies, while treatment with dihydroartemisinin plus γ-irradiation showed far lower clonal survival than cultures treated with radiation or dihydroartemisinin alone. The radiosensitizing effect of dihydroartemisinin was blocked significantly by the free radical scavengers, NAC and TIRON, indicating association with dihydroartemisinin-induced ROS generation. In addition, the radiation-induced expression of endogenous GST was suppressed by treatment with dihydroartemisinin. The radiosensitizing effect of dihydroartemisinin was also markedly enhanced by the addition of holotransferrin Conclusion: Taken together, our results strongly suggest that dihydroartemisinin triggers production of ROS and inhibits GST activity, leading to effective and therapeutically relevant radiosensitization of human glioma cells.