Next, we investigated the effect of inhibiting either Chk1 or Wee1 kinases in HNSCC cells in combination with PBT, with cells positioned either in the entrance plateau at low-LET (2.7 keV/μm), or within the Bragg peak at relatively high-LET (10.8 keV/μm). Here, CHEK1 is linked to head and neck squamous cell carcinoma.