CHEK1 and head and neck squamous cell carcinoma: Utilising the CHK1 inhibitor PF0477736, it was shown that four out of five HPV-positive HNSCC cell lines (UTSCC45, 93VU147T, UDSCC2 and UMSCC47; but not UPCI-SCC154) were sensitised in the presence of the inhibitor (0.15 μM) because of a reduction in G2M arrest (Ref.