*2.2. Cell Culture and Irradiation*

HT29, DLD1, HCT116, SW480, RKO, and LoVo colorectal cancer cells were purchased from the Korean Cell Line Bank (KCLB, Seoul, Korea). These cell lines from passages 4 to 10 were used for the experiments and were maintained in RPMI 1640 medium containing 1% antibiotic-antimycotic (GIBCO) supplemented with 10% FBS. The cells were cultured in a humidified 5% CO<sup>2</sup> atmosphere at 37 ◦C. Cells were exposed to radiation (0~10 Gy) using a Gammacell 3000 Elan irradiator (137Cs γ-ray source; MDS Nordion, Canada).
