RBIO-05. Mitochondrial complex I inhibitor, IACS synergistically enhances the radio-therapeutic effect for the intracranial S180 sarcoma mouse model

Abstract BACKGROUND Radiotherapy (RT) eliminates cancer cells by inducing DNA damage. However, its efficacy is often reduced by mechanisms such as radiation resistance, effective DNA repair, and hypoxia within tumors. Tumor cells utilize metabolic flexibility, dynamically switching between glycolysis and oxidative phosphorylation (OXPHOS) to survive and resist RT-induced stress. This study investigates how mitochondrial complex I (CI) inhibition by IACS-010759 (IACS) sensitizes tumor cells to RT, focusing on metabolic disruption, DNA damage response, and survival. METHODS The synergy between IACS and RT was assessed in S-180 sarcoma cells with four groups: control, IACS, RT, and RT + IACS. Apoptosis proteins (BAX, BCL-2, cleaved caspase-3) and radiosensitivity markers (SOD2, γH2AX) were analyzed via Western blot. ROS levels were measured by fluorescence, cell cycle by EdU-incorporated flow cytometry, p53 and p21 via Western blot, and stemness by sphere formation. In vivo, mouse intracranial tumor models underwent MRI-based tumor monitoring and survival assessment. RESULTS The RT + IACS group showed heightened apoptosis via BAX/BCL-2 and caspase-3 activation, reduced SOD2, elevated ROS, and persistent γH2AX, indicating impaired DNA repair. Cell cycle analysis indicated G1/G2 phase arrest, which was associated with increased p53 and p21 expression levels, indicating p53/p21-mediated regulation, and stemness was reduced. MRI indicated the greatest tumor reduction and improved survival in the RT + IACS group. CONCLUSION The combination of RT with metabolic inhibition effectively disrupts metabolic flexibility in S180 sarcoma, leading to ROS accumulation, impaired DNA repair, enhanced apoptosis, and reduced tumor stemness. Targeting tumor cell metabolism represents a promising strategy for enhancing RT efficacy by overcoming multiple resistance mechanisms.