A) DSB formation and repair. Formation of DSBs was measured at 4°C to prevent repair: H460 cells were exposed to DMSO (black bar) or 25 μM YTR107 (white bar) for 90 min at 37°C, administered 4 Gy at 4°C, and immediately assayed for formation of DNA DSBs using a neutral comet assay (N = 110). Repair of DSBs: Cells were also were exposed to DMSO (bar with horizontel lines) or 25 μM YTR107 (bar with vertical lines) for 30 min at 37°C, administered 4 Gy, incubated at 37°C for 45min and then subjected to a neutral comet assay (N=100). B) YTR107-mediated radiosensitization. H460 cells were exposed to 25 μM YTR107 prior to, during, and for 90 min after irradiation. Colony formation was used to assess survival (+/− SD). C) YTR107-mediated radiosensitization following multiple 2 Gy fractions. For five consecutive days H460 and Calu1 cells were exposed to 0 or 15 μM YTR107 for 30 min prior to, during a 2 Gy fraction, and for 90 after irradiation. Colony formation was used to assess survival (+/− SD). D) Growth of syngeneic Lewis Lung Carcinoma (LLC) tumors is delayed following exposure to YTR107 and factionated x-irradiation. For five consecutive days mice bearing LLC tumors were injected with DMSO or 10 mg/kg YTR107 and administered 2.4 Gy. Fold change in tumor volume +/− SD is shown. Symbols are larger than SD error bars. N= 8 mice per point.