ATR and cancer: Recent findings suggest that the p53 signaling pathway is involved in chemosensitization of cancer cells to DNA-damaging agents through DNA damage response sensors ataxia telangiectasia mutated protein (ATM) and ataxia telangiectasia and Rad3-related protein (ATR) and their downstream cell cycle regulator checkpoint kinases 1 and 2 (Chk1 and Chk2) [31,32,33].