The radiosensitization effect of NS398 on esophageal cancer stem cell-like radioresistant cells

This study aimed to investigate the cancer stem cell (CSC) properties of radioresistant esophageal cancer cells and the radiosensitization effect of NS398, a cyclooxygenase (COX)-2 inhibitor, on them. Fractionated irradiation was applied to acquire radioresistant esophageal cancer cells. Clone formation assay was employed to detect cell radiosensitivity and cloning formation ability. Cell viability was determined by methyl tetrazolium colorimetry assay. Cell cycle distribution and apoptosis were detected by flow cytometry. Tumorigenicity was investigated by xenograft tumorigenicity assay. Expression levels of β-catenin were detected by reverse transcription polymerase chain reaction or Western blot. As results, radioresistant Eca109R50Gy cells were obtained through fractional irradiation from Eca109 cells; Eca109R50Gy cells displayed higher ability of proliferation, colony-formation, and 40 times tumorigenic ability as high as that of the Eca109 cells in vivo. Meantime stem cell marker β-catenin was elevated in Eca109R50Gy cells. All of the above implied that Eca109R50Gy cells have some properties of CSCs. NS398 enhanced the radiosensitivity of Eca109R50Gy cells accompanied by down-regulating the expression of β-catenin. In conclusion, radioresistant Eca109R50Gy cells carried some CSC-like properties; NS398 enhanced the radiosensitivity of CSC-like Eca109R50Gy cells and this function may partly through down-regulating the expression of β-catenin. These findings both stress the important role of CSCs in esophageal cancer radioresistance and provide new insight on possible application of COX-2 inhibitors on CSCs.