Identification of genes inducing resistance to ionizing radiation in human rectal cancer cell lines: re-sensitization of radio-resistant rectal cancer cells through down regulating NDRG1

Background: Resistance to preoperative radiotherapy is a major clinical problem in the treatment for locally advanced rectal cancer. The role of NDRG1 in resistance to ionizing radiation in rectal cancer has not been fully elucidated. This study aimed to investigate the effect of the reduced intracellular NDRG1 expression on radiosensitivity of human rectal cancer cells for exploring novel approaches for treatment of rectal cancer. Methods: Three radio-resistant human rectal cancer cell lines (SNU-61R80Gy, SNU-283R80Gy, and SNU-503R80Gy) were established from human rectal cancer cell lines (SNU-61, SNU-283, and SNU-503) using total 80 Gy of fractionated irradiation. Microarray analysis was performed to identify differently expressed genes in newly established radio-resistant human rectal cancer cells compared to parental rectal cancer cells. Results: A microarray analysis indicated the RNA expression of five genes (NDRG1, ERRFI1, H19, MPZL3, and UCA1) was highly increased in radio-resistant rectal cancer cell lines. Short hairpin RNA-mediated silencing of NDRG1 sensitized rectal cancer cell lines to clinically relevant doses of radiation by causing more DNA double strand breakages to rectal cancer cells when exposed to radiation. Conclusions: Targeting NDRG1 represents a promising strategy to increase response to radiotherapy in human rectal cancer.