Radiosensitivity of radioresistant colorectal cancer cells after treatment with docosahexaenoic acid and irradiation

Radiotherapy has been used to treat many types of cancers over the past years. Radiotherapy generates side effects on normal tissues. Radiosensitizer products provide decrease in tumor proliferation and reduce radiation dose in radiotherapy. Docosahexaenoic Acid (DHA) as an omega-3 polyunsaturated fatty acid has anti-proliferative effects on malignant cells. In this study، the effects of DHA accompanied by ionizing radiation on growth rate and survival fraction of HT29 colorectal cancer cells were evaluated. The present study was performed at the Institute of Biotechnology، affiliated to Urmia University، Urmia، Iran in the year 2013. In this laboratory experiment، ma-lignant cells were cultured in RPMI-1640 supplemented with 10% fetal bovine serum. HT-29 cells were cultured at 5105 cells/well into 6-well culture plates for overnight. Thereafter، the cells were pretreated with either 50 or 100 µM DHA for 4 hours and malignant cells were irradiated with either dose of 2 or 10 Gy. Cell viability was evalu-ated by trypan blue staining after 48 hours. Moreover، malignant cells were pretreated with either 50 or 100 µM DHA for 48 hours and irradiated with dose of 2 to 10 Gy. Thereafter، survival rate was evaluated by 3- (4،5-Dimethylthiazol-2-Yl) -2،5-Diphenyltetrazolium Bromide (MTT) assay after 6 days. Cell viabilities were found to be 59. 8% and 17. 5% for 50 µM DHA in combi-nation with doses of 2 and 10 Gy respectively. Using 100 µM DHA diminished cell vi-ability up to 47% and 13. 9% following doses of 2 and 10 Gy respectively. Treatment of cells with DHA accompanied by increasing doses of γ-rays significantly diminished survival rate. In treated cells with 50 and 100 µM DHA، survival rate were measured to be 79. 1%، 57. 6%، 42. 8%، 40. 5%، 34% and 55. 8%، 43. 7%، 33. 6%، 27. 9%، 23. 5% for doses of 2، 4، 6، 8 and 10 Gy respectively. Our study indicates that DHA decreases colorectal cancer cells prolifera-tion and could provide a new radiosensitizer drug to enhance the efficacy of colorectal cancer radiotherapy.