Correlation between cellular radiosensitivity and DNA damage measured by the alkaline comet assay in human cancer cell lines.

In order to evaluate the usefulness of alkaline comet assay as a predictive assay of radiosensitivity, two parameters of comet assay and three parameters of cell survival curve were compared using 13 human cancer cell lines. Colony forming assay was performed after irradiation from 1 Gy to 6 Gy, and determined clonogenic survival parameters, such as D10, Dq and SF2. In comet assay, initial DNA damage (ID) immediatery after X-ray irradiation at dose of 8 Gy and residual damage (RD) at each 30 or 60 min after irradiation were assessed. Thirteen cell lines showed a broad spectrum in D10 value, ranging from 2.74 to 8.18, and Dq value, ranging from 0.29 to 3.42. ID varied from 1.87 to 9.09 among the cell lines, and RD varied from 0.66% to 56.51% at 30 min, and from 0% to 55.58% at 60 min. When cell lines were classified into two groups (group A and group B) according to each own D10 value, the group A, whose D10 value was more than 6, showed higher ID (5.4 + 2.3) than the group B (2.6 + 0.7), whose D10 values was less than 6 (P=0.008). There was, however, no correlation between ID and SF2. When cell lines were classified into two groups according to each own Dq value (group C and group D), the average of RD in group C, whose Dq value was more than 2, was 2.9% at 30 min. Group D whose Dq value is less than 2 was 15.6% at 30 min. The significant difference was observed between group C and group D (p= 0.049). These results suggest that the comet assay might be potential to classify a radiosensitive group according to ID and RD.International Comet Assay Workshop No.