In Vitro Enhancement of Radiosensitivity by the Combination of Celecoxib and Ad-mda7 in Human Breast Cancer Cells / 한국유방암학회지

ABSTRACT

PURPOSE: Celecoxib and Ad-mda7 have shown its ability to enhance radiosensitivity in various cancer cells in vitro. We expected to synergistically enhance radiosensitivity by combing celecoxib and Ad-mda7 in breast cancer cells in vitro. METHODS: MDA-MB-436 and MDA-MB-468 human breast cancer cells were exposed to different doses (0, 2, 4, and 6 Gy) of radiation with or without pretreatment with either Ad-mda7 or celecoxib alone, or with the combination for three days prior to irradiation. Clonogenic cell survival assay was used to compare the radiosensitizing effect. Fluorescence activated cell sorting analysis was performed to assess cell cycle changes and the subdiploid cell population. We determined the prostaglandin E2 (PGE2) concentration before and after the irradiation (2 Gy, 24 hours). We performed western blot analysis of Akt, phosphorylated Akt, beta-catenin, and cyclooxygenase-2 (COX-2). RESULTS: At the sublethal dose of celecoxib and Ad-mda7, the combination showed significantly enhanced radiosensitivity. The enhancement factor for the combination treatment was 1.44 in MDA-MB-468 cells and 1.75 in MDA-MB-436 cells. There were an increased percentage of apoptotic cells in the combination therapy group as compared to the controls, but this was not statistically significant. Cell cycle analysis demonstrated an increase in the G2/M phase of the cell cycle in the combination group compared with controls. The concentration of PGE2 was significantly decreased after the irradiation in both cell lines compared to the controls. Western blot analysis confirmed that this combination treatment effectively suppress the expression of Akt, phosphorylated Akt, and COX-2 in those cell lines, except beta-catenin. CONCLUSION: Cotreatment of Ad-mda7 plus celecoxib definitely showed radioenhancing effect. We presumed that this effect may be the arrest of the cells at the radiosensitive G2/M phase of the cell cycle.