The Generation and Characterization of a Radiation-Resistant Model System to Study Radioresistance in Human Breast Cancer Cells

Abstract

To systematically study the selection of radioresistant cells in clinically advanced breast cancer, a model system was generated by treating MDA-MB231 breast cancer cells with fractionated gamma radiation. A clonogenic assay of the surviving cell populations showed that 2-6 Gy per fraction resulted in a rapid selection of radioresistant populations, within three to five fractions. Irradiation with additional fractions after this initial increase did not increase the radioresistance of the surviving population significantly. Doses of 0.5 and 8 Gy per fraction were not effective in selecting radioresistant cells. To further determine the cause of the changes in radiosensitivity, 15 clones were isolated from the cell populations treated with 40 or 60 Gy with 2 or 4 Gy per fraction, respectively, and were analyzed for radiosensitivity. The average D(10) for these clones was 6.75 +/- 0.36 Gy, which was higher than that for the parental cell population (D(10) = 6.0 +/- 0.2 Gy). The operation of cell cycle checkpoints and the doubling time were similar for both the nonirradiated parental population and the isolated radioresistant subclones. In contrast, a decrease in the apoptotic potential was correlated (r = 0.7, P < 0.01) with increased survival after irradiation, suggesting that apoptosis is an important factor in determining radioresistance under our experimental conditions. We also isolated several subclones from the nonirradiated parental cell population and analyzed them to determine their radiosensitivity after fractionated irradiation. Ten fractions of 4 Gy (40 Gy in total) did not result in a significant increase in the radioresistance of these subclones compared to the irradiated cell populations. The possible mechanisms of the increased radioresistance after fractionated irradiation are discussed.

MiR-593 mediates curcumin-induced radiosensitization of nasopharyngeal carcinoma cells via MDR1

“…Radioresistance occurs in primary IR treatment, and the survived cells may be more resistant to the second IR treatment, thereby leading to radiotherapy failure (12,22,23). In this regard, the exact molecules and signaling pathway involved in radiosensitization should be determined to develop target therapy and enhance the efficacy of radiation.…”

In vitro response of the human breast cancer cell line MDAMB-231 and human peripheral blood mononuclear cells exposed to 60Co at single fraction

“…Radioresistance of MDAMB-231 cells were demonstrated by post-irradiation MTT assay in comparison with radiosensitivity of other cell lines (Hunáková et al, 2000;Andrade et al, 2003). Other studies obtained radiation resistant cell clones of MDAMB-231 selected after gamma fractioned irradiation up to doses of 60 Gy with fractions of 4 Gy/fraction (Pearce et al, 2001). These cells line can be resistant to a fractioned dose as a single fraction gamma irradiation.…”

Alterations of cell cycle control proteins SHP-1/2, p16, CDK4 and cyclin D1 in radioresistant nasopharyngeal carcinoma cells

“…Irradiation was performed with 6 MV X-rays generated by a Siemens Primus H high-energy linear accelerator (Munich, Germany) as previously described (37). The length of the irradiation intervals were dependant on the MUs of LINAC delivered.…”