| To systematically study the selection of radioresistant cells with γ-radiation treatments, a model system was generated by treating MDA-MB231, a clinically advanced breast cancer cell line, with fractionated γ-radiation. The surviving populations were analyzed by clonogenic assay for resistance to ionizing radiation. Doses between 2 and 6 Gy resulted in a rapid increase in the radioresistance of the population. Continued fractionation did not significantly increase the radioresistance of the population after this initial increase. Doses of 0.5 or 8 Gy/fraction were significantly inferior at selecting radioresistant cells compared to the intermediate doses utilized.; In order to determine the cause of the change in radiosensitivity, fifteen clones were isolated from the populations treated with 40 Gy by 2 Gy/fraction or 60 Gy by 4 Gy/fraction and analyzed for resistance to ionizing radiation. Eleven of these clones were more radioresistant than the parental cell line and four were somewhat more radiosensitive. Five clones were also isolated from the parental cell line, none of which were more radioresistant than the parental population.; Each clone was characterized to determine the cause of their different radiosensitivities. (Abstract shortened by UMI.)... |
