Radio-sensitizing prostate cancer cells: A possible role for zoledronic acid and pravastatin (ZoPra)

Abstract

Prostate cancer is highly prevalent in men worldwide and in Lebanon specifically. Radiotherapy is one of the first-line treatments aimed at reducing tumor size and further disease progression. Its efficacy relies on the radio sensitivity of tumor cells and the patient. However, it’s significantly reduced by the radioresistance of tumor cells and deleterious effects on surrounding normal cells. Radioresistance of tumor cells is brought about by the hyperactivation of non-homologous end-joining DNA repair proteins, pATM and H2AX, that increase repair signaling and recognition respectively. Therefore, targeting these proteins in tumor cells to impede resistance is of high importance. Bisphosphonates such as Zoledronic acid are widely used in the treatment of bone loss-related diseases. Statins, such as Pravastatin, are used in the management of lipid levels. Recently, a combination of both ZoPra was shown to radioprotect normal tissues and radiosensitize cancer cells. Therefore, the aim of this study is to assess the effect of Zoledronic acid and Pravastatin, alone and in combination on the radio-response of human prostate cancer cell lines, DU-145 and PC-3, in vitro, on a cellular and molecular level. The cytotoxic effect of different concentrations of Zoledronic acid and Pravastatin were tested using MTT assay. The optimum concentration of both was determined to be 1 μM and was therefore used in further experiments. Cells were treated with 1 μM Zoledronic acid and Pravastatin, alone and in combination, prior to a 2 Gy irradiation. Clonogenic assay was performed to assess cell survival and colony forming ability in both cell lines with treatment. Immunofluorescence analysis of pATM and γH2AX was performed to study DNA DSB repair kinetics. Pre-treatment with 1 μM ZoPra prior to a 2 Gy irradiation was shown to radiosensitize DU-145 and PC3 cell lines. The treatment was shown to increase the residual number of γH2AX foci. A significant decrease in cell survival in both cell lines was observed. This study presents novel findings on the potential use of ZoPra as a radio-sensitizing agent for radio-resistant prostate cancer cells.