Effect of 5-aza-dC and ionizing radiation on colony formation in colon cancer cell lines.

<p>(A) Clonogenic assay of HCT116, SW480, Colo320, and RKO cells treated with 5-aza-dC (0.5 and 1 µM) and/or IR (2 Gy, 5 Gy, and 10 Gy). Clonogenic assay of irradiated (2 Gy, 5 Gy, and 10 Gy) DKO cells. Cells were seeded into 6-well plates (5000 cells/well) and treated with 5-aza-dC/IR. After 2 weeks, cultures were fixed with ethanol and stained with 1.25% crystal violet. Photographs of single colonies are also shown. (B–E) Survival fraction (SF) of HCT116/DKO (B), SW480 (C), Colo320 (D) and RKO (E) cells treated with 5-aza-dC (0.5 and 1 µM) and/or ionizing radiation (IR; 2 Gy, 5 Gy, and 10 Gy). The SF was calculated as mean colonies/seeded cells. The dose enhancement ratio was calculated as the ratio of the SF curve obtained by treatment with a combination of 5-aza-dC and IR to that obtained by treatment with IR alone. Data are expressed as the mean ± standard deviation of three independent experiments. <i>P</i>-values were calculated using Student's <i>t</i>-test. *<i>P</i><0.05; **<i>P</i><0.01; ***<i>P</i><0.001.