Induction of DNA DSB in ATL cells by NK314 or etoposide and comparison of DNA repair capacity in NK314- or etoposide-treated cells after irradiation. (A) After treatment with the indicated concentrations of NK-314 or etoposide, induction of γH2AX⁺ foci was determined by flow cytometry using an H2A.X Phosphorylation Assay Kit. The percentage of γH2AX⁺ foci was calculated by dividing by the number of cells without treatment by the compounds. (B) DNA damage induced by combination treatment with irradiation and the compounds at a dose of 200nM was determined by induction of γH2AX⁺ foci. DNA damage is expressed as relative ratios of number of γH2AX⁺ cells at time points of 5 minutes and 2 hours after treatment divided by that of γH2AX⁺ cells without treatment by the compounds at each time point.