302 - Energy and ROS Metabolism in Radioresistant Brain Tumor Cells

Abstract

Background Intra-tumoral genetic and functional heterogeneity correlates with cancer clinical prognoses. Radioresistant brain tumor cells (rBTCs) are considered to play a major role in recurrence after radiotherapy. Understanding the mechanism for radioresistance in rBTCs will aid development of effective novel therapies for brain tumors. However, metabolic properties in rBTCs have not been well investigated. Therefore, we evaluated the metabolic state and reactive oxygen species (ROS) levels in rBTCs. Methods We used two brain tumor cell lines, ONS-76 and A172. Radioresistant clones ONS-F8 and A172-K were isolated from ONS-76 and A172 cells, respectively. To estimate oxidative phosphorylation state, mitochondria volume and mitochondria ROS production were measured by a fluorescence method. To estimate glycolytic activity, lactate production was measured. To investigate whether an energetic state influences the radioresistance, we performed clonogenic survival assays after treating cells with a metabolic modifier dichloroacetate (DCA). Results Radioresistant clones ONS-F8 and A172-K showed smaller mitochondria volume and lower production of mitochondria ROS than control ONS-76 and A172 cells. ONS-F8 and A172-K cells also showed enhanced lactate production. Radiosensitivity was increased in ONS-F8 cells after DCA treatment. Interestingly, DCA treatment did not increase DNA fragmentation in ONS-F8 cells but enhanced the number of DNA double-strand breaks at 24 h after irradiation. Conclusion Our results demonstrated that both ONS-76 and A172 cell lines were composed of heterogeneous cells with varying radiosensitivity. Radioresistant clones ONS-F8 and A172-K had low oxidative phosphorylation activity and a high dependency on glycolysis in energy metabolism. This tendency may contribute to radioresistance in brain tumor cells.