Introduction: Gastric cancer is a major unmet clinical problem worldwide. The frequency of cases varies greatly across different geographic areas. In our country Iran, for example, the incidence of gastric cancer is around 7300 cases per year, and this malignancy is recognized as the most common cancer in men. Pathogenesis of gastric cancer has been linked to, but not limited, Helicobacter pylori and Epstein Barr virus infection. Surgery, chemotherapy and radiotherapy are common treatments for gastric cancer, however, patients with advance tumor stage have low survival rate. Saffron is one of the oldest spices with various pharmacological effects. In traditional medicine, it has been used to cure vomiting, dental and gingival pain, insomnia, depression, seizures, asthma and bronchitis, to name a few. Saffron is composed of at least four active ingredients including safranal (2,6,6-trimethyl-1,3-cyclohexadiene-1-carboxaldehyde), crocin, crocetin and picrocrocin. As a natural monoterpenoid, safranal has great antioxidant potential and reported to be a good therapeutic agent for diseases arising from oxidative stress. In the present study, we aimed to investigate radiosensitivity of safranal on human gastric cancer cells Methods: To assess the effects of safranal in combination with ionizing radiation, MKN-45 cells (a human gastric adenocarcinoma cell line) were pretreated with 1.6 mM and 3.2 mM of safranal for 24 h. Then, cells were exposed to 4, 6 and 8 Gy X-ray and after 48 h recovery, cell viability was determined by resazurin assay. Briefly, 10% v/v resazurin solution was added to cells and after 3 h incubation, absorbance was measured at 600 nm. Results: Obtained results indicated that upon treatment with 1.6 mM safranal followed by 4, 6 and 8 Gy radiation, cell viability was determined as 100%, 99.23% and 89.79% respectively. In addition, after treatment of cells with 3.2 mM safranal followed by 4, 6 and 8 Gy radiation, viability was decreased down to 80.25%, 74.10% and 59.43%, respectively. Conclusion: Treatment of human gastric cancer cells with the higher concentration of safranal and ionizing radiation reduced viability, however, safranal alone also induced considerable toxic effects on MKN-45 cells. To better evaluate radiosensitizing effects of safranal, more investigation on other gastric cancer cell lines is recommended

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