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 antiproliferative
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.
Methods: The present study was performed at the Institute of Biotechnology, affiliated
to Urmia University, Urmia, Iran in the year 2013. In this laboratory experiment, malignant
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 evaluated
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.
Results: Cell viabilities were found to be 59.8% and 17.5% for 50 μM DHA in combination
with doses of 2 and 10 Gy respectively. Using 100 μM DHA diminished cell viability
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.
Conclusion: Our study indicates that DHA decreases colorectal cancer cells proliferation
and could provide a new radiosensitizer drug to enhance the efficacy of colorectal
cancer radiotherapy