Tehran University of Medical Sciences Acta Medica Iranica 0044-6025 65 5 2026 07 13 257 264 EN Soraya Emamgholizadeh minaei Department of Medical Physics and Imaging, School of Allied Medical Sciences, Urmia University of Medical Sciences, Urmia, Iran. Mahshid Mohammadian Department of Clinical Biochemistry, Faculty of Medicine, Urmia University of Medical Sciences, Urmia, Iran. Omid Esnaashari Department of Radiation Oncology, Omid Research and Treatment Center, Urmia, Iran Kamal Mostafanezhad Department of Radiation Oncology, Omid Research and Treatment Center, Urmia, Iran 2025 01 08 2025 11 04 Colorectal cancer (CRC) is diagnosed as one of the most prevalent cancers in the world. The application of radiotherapy in cancer treatment might be limited due to its radio resistance. Specific radiosensitizers are important factors in increasing the radiation therapy (RT) efficiency. In this study, Fe3O4@CuS-PEG nanoparticles in combination with the RT were evaluated for the treatment of CRC cells (HT-29 cells). HT-29 cells were treated with 2, 4, and 6 Gy of X-ray irradiation and/or a minimal toxic concentration of Fe3O4@CuS-PEG nanoparticles. The cytotoxic effect of various treatments was evaluated by MTT assay. Moreover, the malondialdehyde (MDA) level, superoxide dismutase (SOD) activity, and lactic acid level were assessed in single and combined treatments. Furthermore, the epidermal growth factor receptor (EGFR) gene expression level was measured by Quantitative Real-time PCR. Based on our results, cytotoxicity of Fe3O4@CuS-PEG nanoparticles was increased in a dose dependent manner. The nanoparticles were less cytotoxic in the concentration of 5 mg/mL compared to other examined concentrations. According to the results of MTT assay, the viability in the combined treatment groups was significantly lower than that of the single treatment groups. EGFR mRNA expression level was downregulated in radiation+nanoparticles groups in all examined doses of radiation. The level of MDA increased in the combined treatments compared to the alone treatments. Moreover, lactic acid level and SOD activity decreased in double agent combination treatments versus radiation alone. Based on our study, Fe3O4@CuS-PEG nanoparticles can be introduced as an effective radiosensitizer agent for targeted treatment of CRC cells. Moreover, combination treatment could efficiently treat cancerous cells and inhibit tumor growth in vitro. https://acta.tums.ac.ir/index.php/acta/article/view/11473 https://acta.tums.ac.ir/index.php/acta/article/download/11473/6047