RU486 increases radiosensitivity and restores apoptosis through modulation of HPV E6/E7 in dexamethasone-treated cervical carcinoma cells

Objective. Cervical carcinoma tumors containing radioresistant cells are associated with decreased local control and survival. Therefore, strategies to increase cell kill during radiotherapy have a clear rationale. It was previously determined that treatment with the corticosteroid dexamethasone increased radioresistance and decreased apoptosis in C4-1 cervical carcinoma cells. The goal of this study was to determine whether hormone antagonists, specifically Mifepristone (RU486), could reverse the effects of dexamethasone on clonogenic survival and apoptosis following γ-irradiation. Methods. Cervical carcinoma cell line C4-1 cells were exposed to 1 μM dexamethasone in the presence or absence of 1 μM Mifepristone (RU486), a hormone antagonist, and irradiation. Cells were analyzed for steroid-dependent HPV E6/E7 mRNA expression (by Northern blot analysis), clonogenic survival, and apoptosis (by Annexin V staining and the DNA fragmentation assay). In addition, p53 protein levels were determined by Western blot analysis. Results. The hormone antagonist RU486 reversed dexamethasone-dependent upregulation of E6/E7 mRNA and restored radiation-induced p53 expression, apoptosis, and clonogenic survival to levels similar to those observed following irradiation alone. Conclusion. RU486 reverses glucocorticoid- dependent upregulation of HPV E6/E7, which corresponds to restoration of p53 expression, and restores radiosensitivity and apoptosis following γ- irradiation. Therefore, it appears that along with radiation, RU486 may be a beneficial agent in the treatment of hormone-reactive cervical tumors. (C) 2000 Academic Press.