THE RATIO OF INITIAL RESIDUAL DNA-DAMAGE PREDICTS INTRINSIC RADIOSENSITIVITY IN 7 CERVIX CARCINOMA CELL-LINES/

The single-cell gel electrophoresis (comet) assay was used to measure radiation-produced DNA double-strand breaks (dsbs) in a series of seve n cervical tumour cell lines (ME180, HT3, C33A, C41, SiHa, MS751 and C aSki). The proportion of DNA dsbs was measured immediately after radia tion treatment (initial damage) and 16 h later after incubation at 37 degrees C (residual damage). Linear dose-response curves were seen for initial (slopes 0.23-0.66) and residual (slopes 0.16-0.87) DNA dsbs. Neither of the slopes of the linear regression analysis on the initial and on the residual DNA dsbs dose-response curves (range 0-80 Gy) cor related with SF2 (surviving fraction at 2 Gy) measured after high- (HD R) or low-dose-rate (LDR) irradiation. An association was evident betw een SF2 after HDR and LDR irradiation and the ratio of the absolute le vel of initial and residual damage after a single dose of 60 Gy. Howev er, a significant correlation was found between HDR (r = -0.78, P = 0. 04) and LDR (r = -0.86, P = 0.03) SF2 values and the ratio of the slop es of the initial and residual DNA dsbs dose-response curves (range 0. 47-0.99), representing the fraction of DNA damage remaining. These res ults indicate that the neutral comet assay can be used to predict radi osensitivity of cervical tumour cell lines by assessing the ratio of i nitial and residual DNA dsbs.