To identify an effective method of evaluating the radiosensitivity of human tumor cell lines in vitro, the present study adopted mtDNA‑4977‑bp deletion coupled with comet assay. The three human tumor cell lines applied were HepG2, EC‑9706 and MCF‑7. The surviving fraction (SF), ratio of the mtDNA‑4977‑bp deletion and DNA damage were detected by MTT assay, nested polymerase chain reaction (PCR) technique and comet assay, respectively. Clearly, lower SFs were found for the HepG2 and EC‑9706 cells as compared with the MCF‑7 cells following irradiation at doses of 2, 4 and 8 Gy, indicating a higher radiosensitivity for the HepG2 and EC‑9706 cells. Additionally, no significant differences were identified in the mtDNA‑4977‑bp deletions found among HepG2, EC‑9706 and MCF‑7 cells by PCR following 1- or 4‑Gy γ‑ray irradiation, while increased deletion ratios of mtDNA‑4977 bp were observed in HepG2 and EC‑9706 cells following 8‑Gy irradiation, in contrast to decreases in MCF‑7 cells. The most notable differences among these three tumor cell lines were observed by comet assay following 8–Gy γ‑ray irradiation. A combined method of nested PCR and comet assay, therefore, is the most effective and accurate method in evaluating the radiosensitivity of tumor cells.

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