Radiosensitization of recombinant human endostatin in human lung squamous cancer cells in vitro

Objective To investigate the radiosensitising effect of recombinant human endostatin (endostar) on human lung squamous cancer cell line H-520 in vitro and its mechanism. Methods H-520 cells in exponential growing phase were treated with endostar alone, irradiation alone, or endostar plus irra-diation. Colony-forming assay was used to investigate the cytotoxicity and radiosensitising effects of endostar. Cell survival fractions of all groups were calculated and cell survival curves were fitted by single-hit multi-tar-get model. Cell apoptosis, cell cycle distribution and activated Caspase expression level were investigated by flow cytometry. Results The D0, Dq, D10 and SF2 values of combined treatment group were much lower than those of irradiation alone group. The sensitization enhancement ratio (SER) was 1.50 (ratio of D0 values). Endnstar induced H-520 cell apoptosis in a dose dependant manner. After administration of endostar, H-520 cell proliferation was inhibited, and cell apoptosis rate and apoptotic bodies were increased. After irradiation of 0 Gy, 2 Gy, 4 Gy and 8 Gy, the apoptosis rate of H-520 cells was 4.27% ±0.29%, 14.3% ±1.15%, 28.49% ± 1.58% and 54.79% ± 1.89% in the radiotherapy alone group, and 22.38% ± 1.61%, 35.01% ±1.16%, 46.83%±2.06% and 64.08%±4.28% in the combined treatment group, respective-ly. The difference between the two groups was significant (t = 19.17, 17.79, 25.64 and 3.44,all P < 0.05 ). Flow cytometric analysis showed that cell cycle distribution changed and G0 + G1 phase arrest oc-curred after endostar treatment, while irradiation induced G2 + M arrest. The expression level of activated Caspase in combination group (62.7% ±1.9% ) was higher compared to the control group ( 12.1%± 0. 1% ) , endostar alone group ( 54.6% ±1.0% ) and irradiation alone group ( 34.1%±1.2% ) ( t = 46.69, 6.55 and 22.54 ; all P < 0.05 ). Conclusion Endostar can enhance the radiosensitivity of H-520 ceils by inhibiting cell proliferation, promoting cell apoptosis and facilitating cell cycle redistribution. Key words: Endostatin;  Cell lines,human lung squamous cell carcinoma;  Radiosensitization; Cell apoptosis;  Cell cycle