Evaluation of the effect of hyperthermia and electron radiation on prostate cancer stem cells

The aim of this study was to investigate the effect of hyperthermia, 6 MeV electron radiation and combination of these treatments on cancer cell line DU145 in both monolayer culture and spheroids enriched for prostate cancer stem cells (CSCs). Flowcytometric analysis of the expression of molecular markers CD133⁺/CD44⁺ was carried out to determine the prostate CSCs in cell line DU145 grown as spheroids in serum-free medium. Following monolayer and spheroid culture, DU145 cells were treated with different doses of hyperthermia, electron beam and combination of them. The survival and self-renewing of the cells were evaluated by colony formation assay (CFA) and spheroid formation assay (SFA). Flowcytometry results indicated that the percentage of CD133⁺/CD44⁺ cells in spheroid culture was 13.9-fold higher than in the monolayer culture. The SFA showed significant difference between monolayer and spheroid culture for radiation treatment (6 Gy) and hyperthermia (60 and 90 min). The CFA showed significantly enhanced radiosensitivity in DU145 cells grown as monolayer as compared to spheroids, but no effect of hyperthermia. In contrast, for the combination of radiation and hyperthermia the results of CFA and SFA showed a reduced survival fraction in both cultures, with larger effects in monolayer than in spheroid culture. Thus, hyperthermia may be a promising approach in prostate cancer treatment that enhances the cytotoxic effect of electron radiation. Furthermore, determination and characterization of radioresistance and thermoresistance of CSCs in the prostate tumor is the key to develop more efficient therapeutic strategies.