Calcium overload induces reactive oxygen species to enhance glioblastoma radiosensitivity.

Radiotherapy is the primary treatment of glioblastoma, but its efficacy is often limited by tumor cell resistance to radiation. Radiotherapy mainly has its cytotoxic effect through the formation of reactive oxygen species and the damage to DNA. Nevertheless, to overcome the effects of reactive oxygen species-mediated oxidative damage and endoplasmic reticulum stress, tumor cells may activate the repair mechanisms to stress and improve antioxidant defenses. This study innovatively proposes the use of the calcium ionophore ionomycin as a radiosensitizer in glioblastoma. We used U87MG and U251 cell lines as well as subcutaneous xenograft mice as models, and conducted a combined intervention of ionomycin and radiotherapy. Mechanistically, ionomycin selectively disrupted endoplasmic reticulum calcium homeostasis, inducing severe and sustained endoplasmic reticulum stress. When combined with radiotherapy, this led to a marked surge in intracellular reactive oxygen species, and significantly enhanced apoptosis. In vitro , the combination treatment synergistically reduced cell viability, clonogenicity, and proliferation compared with either monotherapy. In vivo , ionomycin combined with radiotherapy substantially suppressed tumor growth and increased intratumoral reactive oxygen species levels and apoptosis. These findings indicate that ionomycin converts repairable adaptive stress into irreversible lethal damage by amplifying reactive oxygen species through an endoplasmic reticulum stress-reactive oxygen species vicious cycle, thereby overcoming antioxidant defenses and enhancing glioblastoma radiosensitivity.