Figure 3.

DNA repair efficiency and correlation with 5FU sensitivity. Cells were treated with 100 μg/ml 5FU for 24 h and then incubated in fresh drug-free medium for an additional 24 h to allow the repair of 5FU-induced DNA damage. Cells were collected and embedded in agarose plugs which were incubated overnight in lysis buffer (0.4 M EDTA, 2% N-lauryl sarcosine and 1 mg/ml proteinase K) and the DNA fragments were separated by electrophoresis in 0.8% agarose gel using a constant field (0.6 V/cm, 36 h). (A) The gel was stained in ethidium bromide and photographed under UV illumination. (B) FDR, which corresponds to unrepaired (residual) DNA fragments, in the four cell lines was measured using a gel documentation system. (C) Correlation between the unrepaired (residual) DNA fragments and the 5FU IC60 value of the four cell lines was determined. FDR₁₀₀, FDR after treatment with 100 μg/ml 5FU; 5FU, 5-fluorouracil; FDR, fraction of DNA released; IC60, 5FU concentration that results in 40% cell death when compared with control cell growth.