To investigate the radiosensitizing effect of nitric oxide (NO) combined with radiation on esophageal cancer cell line TE-1. Methods Methyl thiazolyl tetrazolium (MTT) assay was used to assess the effects of NO and radiation on TE-1 cells regarding inhibition of cell proliferation. Flow cytometry was used to examine the effect of NO and radiation on cell apoptosis and cycle. Reverse transcription polymerase chine reaction and Western blot were used to evaluete the effect of NO on mRNA and protein expression of manganese superoxide dismutase (MnSOD). Results NO inhibited the proliferation of TE-1 cells while significantly enhancing their radiosensitivity. The application of NO combined with radiation significantly increased the apoptosis rate and G2/M phase propor-tion of TE-1 cells

with substantial decreases in the MnSOD mRNA and protein expression levels. Conclusions NO reduces the MnSOD mRNA and protein expression levels by affecting TE-1 cell cycle

further inhibiting the apoptosis of esophageal cancer cells and enhancing the killing effect of radiation on esopha-geal cancer cells.