Representative SOID measurement in G2 cells and mitotic cells in the presence of KU55933. KU55933 (10 μM), or their solvent DMSO was treated from 30 min before IR. Two hours later, cells were fixed and subjected to immunofluorescence staining for Ser139-phosphorylated H2AX and Ser10-phosphorylated H3. KU55933 was washed out 30 minutes before fixation to recover the size and the fluorescence intensity of phosphorylated H2AX foci. Numbers indicate the SOID values in each nucleus.