Hypoxia-Targeting Strategies in Radiotherapy and Nitroimidazole-Based Radiosensitizers: A Narrative Review and...

Background: Tumor hypoxia is a major determinant of radioresistance, limiting oxygen-mediated fixation of radiation-induced DNA damage and promoting metabolic adaptation, tumor aggressiveness, and treatment failure. Nitroimidazole derivatives and related hypoxia-targeting compounds have been investigated as radiosensitizers because of their oxygen-mimetic properties and selective activation under low-oxygen conditions. Methods: A structured narrative review was conducted to evaluate recent evidence on hypoxia-targeting strategies and nitroimidazole-based radiosensitizers combined with radiotherapy. PubMed and Scopus were searched in March 2026 using terms related to radiotherapy and nitroimidazoles. Studies published within the last five years were included if they investigated hypoxia-targeting compounds, radiosensitization strategies, or dose-response relationships relevant to radiotherapy. Preclinical, computational, and clinical studies were considered. Results: Sixteen studies were included, comprising preclinical, computational, and clinical investigations. Most studies were preclinical and evaluated in vitro cell lines, murine tumor models, or xenografts across multiple tumor types, including head and neck cancer, glioblastoma, breast cancer, colorectal cancer, cervical cancer, renal carcinoma, pancreatic cancer, and ovarian-related models. Nitroimidazole-based and related hypoxia-targeting strategies generally enhanced radiation response under hypoxic conditions, with sensitizer enhancement ratio values ranging from approximately 1.09 to 1.65. In vivo studies reported reductions in tumor growth or tumor volume when radiosensitizers were combined with radiotherapy. Clinical evidence, mainly in head and neck squamous cell carcinoma, showed variable effects on locoregional outcomes. Conclusions: Current evidence supports the biological relevance of hypoxia-targeting strategies for improving radiotherapy response. Nitroimidazole-based compounds show consistent radiosensitizing effects in preclinical models, but clinical translation remains heterogeneous. Future studies should integrate hypoxia imaging, standardized endpoints, advanced drug delivery systems, and clinically relevant radiotherapy models to better define their role in modern radiation oncology.