TP53 and neoplasm: While the tumor cell lines selected exhibited different intrinsic radiosensitivities and had differences in TP53 status (wild-type, mutant nonfunctional, and deleted; Supplemental Table 3), NU5455 enhanced the effect of IR significantly in all DNA-PK–expressing cells with the exception of LoVo, SER80 values (the sensitizing enhancement ratio 80, which is the ratio between radiation doses with and without NU5455 that induced an 80% inhibition of clonogenic cell survival) ranging from 1.5- to 5.0-fold (median 2.3-fold; Figure 2F and Supplemental Figure 7).