γH2AX foci at 24 hours after irradiation and cell cycle distribution. DLD-1 cells were treated with 4 Gy of radiation and/or 1 μM of olaparib for 8 h and/or 10nM of CPT for 6 h. (a) Foci of γH2AX and Rad51 in DLD-1 cells treated with various combinations of olaparib, CPT, or irradiation (IR). DAPI(4',6-diamidino-2-phenylindole) was used to stain nucleus. Ola(+): with olaparib. IR(−): without irradiation. (b) Results of cells that were positive for Rad51 foci. (c) Results of cells that were negative for Rad51 foci. (d) Cell cycle distributions.