Inhibition of CHK1/2 with AZD7762, inhibition of DNA-PKcs with NU7441 and inhibition of BER with ABT-888 in combination with RT resulted in radiosensitization of radioresistant HNSCC cells, to the extent that they rescued the radioresistant phenotype (Figure 3A). Here, CHEK1 is linked to head and neck squamous cell carcinoma.