TP53 and head and neck squamous cell carcinoma: To determine the impact of PARP inhibition on TP53 reactivator-induced HNSCC cell viability, we treated UMSCC1, UMSCC14, and UMSCC-17A with APR-246, 6(5H)-phenanthridinone (PHEN, a PARP-1 inhibitor), or their combination for 72 h.