CeO ₂ Nanoparticles Initiate Selective Radiation-Induced Death of Cancer Cells through Redox, Cell Cycle, and DNA Repair Disruptions

Citrate-stabilized cerium oxide nanoparticles (CeO 2 NPs) with ultrasmall size (2–4 nm) were synthesized and comprehensively characterized, demonstrating high colloidal stability and favorable redox properties. Their radioprotective and radiosensitizing potential was evaluated in aqueous systems and in vitro using human mesenchymal stem cells (hMSCs) and MCF-7 breast cancer cells. CeO 2 NPs exhibited concentration-dependent catalytic activity, efficiently scavenging hydrogen peroxide and hydroxyl radicals under X-ray irradiation. In hMSCs, CeO 2 NPs promoted proliferation, reduced apoptosis, and attenuated DNA double-strand breaks, thereby conferring radioprotection. In contrast, in MCF-7 cells, CeO 2 NPs enhanced ROS accumulation, disrupted cell-cycle checkpoints, increased γ-H2AX foci, and sensitized cells to radiation-induced apoptosis. Gene expression profiling revealed differential regulation of oxidative stress and apoptosis pathways consistent with selective protection of normal cells and radiosensitization of cancer cells. These findings highlight the dual redox-dependent activity of CeO 2 NPs and support their potential application as nanomaterials for radioprotection and radiosensitization.