Representative confocal microscopy images of γH2AX foci 24 hours post-IR in cells treated with vehicle control, 5 Gy or 5 Gy plus 100 nM KU60648 (added 1 hour before IR) in 143B cells (A) and U2OS cells (B). Quantification of percentage of cells with > 20 γH2AX foci in cells treated with vehicle control, 100 nM KU60648 alone, 5 Gy or 5 Gy plus 100 nM KU60648 in 143B cells (C) and U2OS cells (D). Results are mean ± SD from 2 independent experiments. For each treatment group, >150 and >90 nuclei were counted for 143B and U2OS cells, respectively.