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Introduction: Nowadays, cancer is the second cause of mortality in the world and among its variants the most common cancer in women is the breast cancer. One of the methods for cancer treatment is radioth-erapy, in which to enhance the efficiency of radiation therapy some of radio sensitizer can be used for enhancing tumor cell radiosensitivity. Some nanopa-rticles can be considered as a sensitizer because they enhance the cytotoxicity due to oxidative stress and increase the free radicals, especially reactive oxygen species (ROS), within cells resulting in cell death. In this study, elevated synergistic effect of TiO2 nanoparticles as radiosensitizer was evaluated in presence of cobalt-60 gamma rays on human breast cancer cell line. Materials & Methods: After cell culture, the human breast adenocarcinoma cell line (MCF-7 cells) was exposed to 2 Gy of radiation and 30 µg/ml concentration of the aforementioned nanoparticles. Viability was calculated using (3-[4, 5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) MTT assay. Findings: Viability of cells in presence of gamma radiation and the nanoparticles, sig-nificantly reduced compared to the viability of cells exposed only to radiation or nano-particle, alone. The effect may dependent on nanoparticle crystals type and conce-ntration. Discussion & Conclusion: Nano-TiO2 inc-reased sensitivity of breast cancer cells to gamma radiation, due to an increase in ROS production and cytotoxicity. Anatase crystals have more severe effects than rutile crystal because of having a larger surface area and creation of more free radicals. Therefore, this nanoparticle has the potent-ial to be used as a radiosensitizer.

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Introduction: Nowadays, cancer is the second cause of mortality in the world. Gastric cancer has a high mortality rate (about 70%) which is more common in men and has a higher incidence in eastern Asian countries. One of the methods for cancer treatment is radiotherapy, in which to enhance the efficiency of radiation therapy some of radio-sensitizer agents can be used to enhance tumor cell radiosensitivity. Some nanoparticles can be considered as a sensitizer because of enhancing the cytotoxicity to oxidative stress and increasing free radicals especially ROS within cells, resulting to cell death. In this study, synergistic effect of TiO2 nanoparticles as a radio-sensitizer agent was evaluated in the presence of cobalt-60 gamma rays on human gastric cancer cell line. Materials and Methods: After cell culture, MKN-45 cells were exposed to 2 Gy of radiation and 30 µg/ml concentration of nanoparticles. Viability was calculated using MTT assay. Findings: Exposing cultured cells to nanoparticles alone resulted to a mean decrease of 70% in cell survival. Viability of cells in presence of gamma radiation and nanoparticles was significantly reduced compared to the viability of cells exposed only to radiation or nanoparticle, alone. The effect was dependent both on the nanoparticle crystal type and concentration. Discussion & Conclusion: Nano-TiO2 increased the sensitivity of gastric cancer cells to gamma radiation, due to an increase in the ROS production and cytotoxicity. Anatase crystals have more severe effects than rutile crystal because of having a larger surface area and creation of more free radicals. Therefore, this nanoparticle has the potential to be used as a radio-sensitizer.