The Study On The Mechanism Of Celecoxib's Radio-sennsitivity To γ-rays On The SHG44 And U87-MG Glioma Cells

Objective: This study was to investigate the effect of celecoxib, a selective inhibitor of COX-2 enzyme, on glioma cell radiosensitivity. The thesis contained: the drug's influence on the proliferation of glioma cells SHG44 and U87-MG, COX-2 mRNA expression level, cell cycle of the cells and expression level of cell cycle regulatory protein p53,cyclinD₁ and cyclinB₁ after the cells treated by ⁶⁰Co-γirradiation. The data showed a primary investigation of celecoxib's radio sensitizing mechanism.Methods: (1)The effect of celecoxib on the survival fraction of SHG44 and U87-MG cells was investigated with the method of MTT. (2) Microcolony formation assay was used to determine the radiosensitivity of glioma cells and celecoxib's radiation-enhancing effect.(3) Reverse transcriptase PCR (RT-PCR) was adopted to investigate the effect on the expression level of Cox-2 after ⁶⁰Co-γirradiation. (4) Flow cytometric analysis was used to detect the changes of cell cycle distribution induced by celecoxib after ⁶⁰Co-γirradiation. (5)Influence of celecoxib on cell cycle related protein p53, cyclin D₁ and cyclin B₁'s expression level was investigated by Western Blot.Results: (1)Cell proliferation inhibition effect of celecoxib presented a concentration-dependent manner, and the inhibition effect decreased as the concentration increased. Colony formation rate decreased as the celecoxib concentration increase, while decreases as the irradiation dose increase. There was an interaction effect between celecoxib and irradiation. The dose enhancement ratio (DER) increased as the celecoxib concentration increased when the survival rate was 50%; (2) Compared with control group, celecoxib alone could decrease COX-2 mRNA expression level; compared with irradiation treatment alone, celecoxib could decrease radiation-induced COX-2 mRNA expression level; (3) Compared with control group, the percent of cells in G1 phase increased after the celecoxib treated alone; compared with irradiation treatment alone, celecoxib could attenuate radiation-induced G₂/M arrest. (4) p53 or cyclin B₁ level showed no significant change while cyclinD₁ decreased obviously in celecoxib group; Compared with ⁶⁰Co-γirradiation alone group, cyclinB₁ level decreased in the combination group.Conclusions: (1) Celecoxib had no proliferation inhibition effect at a low concentration, while a concentration-dependent inhibition at a high concentration. Besides, celecoxib had the radio-sensitizing effect on both SHG44 and U87-MG cells after they irradiated by ⁶⁰Co-γray; (2) Mechanism of celecoxib's radio-sensitizing effect might be in close relation with the inhibition of COX-2 mRNA expression, even COX-2 protein expression; (3) Celecoxib could induce G1 arrest in both SHG44 and U87-MG cells, and attenuated radiation-induced G₂/M arrest, which probably drived more irradiation damaged cells to enter M phase, finally the cells died because they din't have enough time to repair; (4) Celecoxib could decrease expression level of cyclinD₁;Compaired with irradiation treatment alone, expression level of cyclinD₁ was decreased after combination treatments, which indicated irradiation-induced G₂/M arrest could be attenuated through modulating the expression level of cell cycle key factor cyclinB₁. It possibley induced the radio-sensitizing effect on glioma cells.