In contrast, it was additionally observed that the HPV-negative HNSCC cell line was more susceptible to the combination of PARP and WEE1 (MK1775) inhibition, which was suggested to be due to more potent activation of the G2/M checkpoint caused by WEE1 inhibition that is downstream of CHK1. Here, CHEK1 is linked to head and neck squamous cell carcinoma.