TP53BP1 and lung cancer: In addition, phosphorylation of histone H2AX (γH2AX) and the formation of 53BP1 foci were quantified in Calu-6 and A549 human lung cancer cells as early biomarkers of DNA-DSB formation, following 10 Gy of radiation treatment in the presence and absence of NU5455 (5 μM).