TP53BP1 and head and neck squamous cell carcinoma: Olaparib treatment (1 μM) of HPV-negative HNSCC cells (UTSCC15, UTSCC45 and Cal33) was observed to cause enhanced radiosensitisation through accumulation of DSBs, as revealed by increases in γH2AX/53BP1 foci 24 h post-irradiation (Ref.