Radiosensitizing Effects of Lithium Ascorbate on Normal and Tumor Lymphoid Cells under X-ray Irradiation

The study aimed to assess the radiosensitizing effect of lithium ascorbate on tumor cells. Cancer cells radioresistance is an important factor restraining the success of X-ray therapy. Radiosensitizing drugs make tumor cells more sensitive to ionizing radiation and improve the effectiveness of radiotherapy. Although many chemical substances can potentiate the cytotoxic effects of X-ray radiation, their clinical applications are limited due to possible adverse reactions. Recently, several approaches have been proposed to develop new radiosensitizers that are highly effective and feature low toxicity. Among new enhancers of X-ray therapy, ascorbic acid, and its derivates demonstrate very low toxicity along with a wide therapeutic range. Lithium ascorbate is a promising X-ray therapy enhancer, but its mechanism of action is unknown. This research focuses on the radiosensitizing properties of lithium ascorbate and its effects on both tumor and normal irradiated cells. The viability of the radiosensitized cells was evaluated by fluorescence flow cytometry using Annexin V-FITC Apoptosis Detection Kit and Cellular ROS Assay Kit (Abcam, UK). The test cell cultures included normal human mononuclear and Jurkat cells. Lithium ascorbate sensitizes normal human mononuclear and Jurkat cells towards ionizing radiation. The combined cytotoxic effect of X-ray irradiation (3 Gy) and lithium ascorbate (1,2 mmol/L) substantially exceeds the effects of the individual factors, i.e. synergetic action appears. The major types of cell death were late apoptosis and necrosis caused by excessive production of reactive oxygen species. Lithium ascorbate in combination with X-ray irradiation exhibited the cytotoxic effect on both normal and cancer lymphoid cells by activating reactive oxygen species (ROS)-induced apoptosis. These findings indicate that lithium ascorbate is a promising substance to develop a new radiosensitizing drug.