Abstract: Objective: To detect the effects of melatonin (MLT) combined with radiotherapy on the proliferation and apoptosis of non-small cell lung cancer (NSCLC) H1299 cells,and to explore the role of MLT in regulating the radiosensitivity of H1299 cells. Methods: The H1299 cells were divided into control group,MLT group,irradiation(IR) group and IR+MLT group. The H1299 cells in control group didn't receive any treatment, the H1299 cells in MLT group were treated with different concentrations of MLT (100 and 500 μmol·L^-1),the H1299 cells in IR group were exposed to 6 Gy ¹³⁷Cs γ-ray,and the H1299 cells in IR+MLT group were treated with different concentrations of MLT (100 and 500 μmol·L^-1) and exposed to 6 Gy ¹³⁷Cs γ-ray. Colony formation assay was used to detect the clone numbers of H1299 cells in various groups; Flow cytometry was applied to detect the apoptotic rates of H1299 cells at 24 and 48 h after irradiation; Western blotting method was performed to detect the phosphorylation levels of nuclear factor kappa B (NF-κB) protein in the H1299 cells in various groups. Results: The colony formation assay results showed that compared with IR group,the clone number of H1299 cells in IR+MLT group was significantly decreased(t=7.234,P<0.01).The flow cytometry results showed that the apoptotic rates of H1299 cells in IR group and MLT group at 24 h after irradiation were higher than that in control group (t=5.020,t=13.525,P<0.01); the apoptotic rate of H1299 cells in IR+MLT group at 24 h after irradiation was higher than that in IR group (t=12.884,P<0.01).There was no significant difference in the apoptotic rate of the H1299 cells between IR+MLT group and IR group at 48 h after irradiation(t=0.394,P>0.05).The Western blotting results showed that the phosphorylation level of NF-κB protein in the H1299 cells in IR+MLT group was lower than that in IR group. Conclusion: MLT combined with radiotherapy has obviously inhibitory effect on the human H1299 cells and can increase the radiosensitivity of H1299 cells.

Key words: melatonin, nuclear factor kappa B, cancer,non-small cell lung, proliferation, apoptosis, radiosensitivity