Study of radiation-induced DNA damage and repair with comet assay in four human tumor cell lines

Objective To establish the relationship between radiosensitivity and radiation-induced DNA damage and repair in four human tumor cell lines by means of comet assay. Methods With the alkaline comet assay,the amounts of DNA single strand breaks (SSB) were quantified. The correlation between a certain DNA damage and the relevant radiation dose was investigated in four human tumor cell lines: the well differentiated nasopharyngeal squamous carcinoma cell line (CNE-1), the esophageal squamous carcinoma cell line (Ec-109), the lung adenocarcinoma cell line (GLC), and the poorly differentiated gastric adenocarcinoma cell line (BGC-823) ,which had been exposed to 6 MV X-ray. In our study, the spontaneous DNA repair of SSB after exposure was also determined for cell lines of CNE-1 and GLC, and the result was compared to that from the clonogenic cell surviving assay.Results The amount of DNA SSB induced by irradiation of a single dose of 16 Gy was definitely detected with the alkaline comet assay in all cell lines. It was found that there was a close association of DNA damage and the delivered dose; that is the larger the dose, the severer the DNA SSB. For the same single dose of 16 Gy according to a descending order, the different DNA damages ranked as: CNE-1Ec-109GLCBGC-823. The Do values of CNE-1, Ec-109, GLC and BGC-823 were 1.25, 1.27, 1.88 and 1.56, respectively. The half repair time was 17.8?min for CNE-1 and 7.4?min for GLC..Conclusions It is concluded that this assay definitely detects, and presents exactly the amount of DNA damage induced by radiation in four human tumor cell lines (CNE-1, Ec-109, GLC and BGC-823), and quantitatively demonstrates the spontaneous repair of DNA damage as well.The radiosensitivity,with different Do values for squamous carcinoma or adenocarcinoma cell lines,is correlative to the ability of DNA-damage repair.