CHEK1 and pancreatic neoplasm: To determine the role of APE2 in the ATR DDR pathway in pancreatic cancer cells, we first established that H2O2 triggered Chk1 and RPA32 phosphorylation in human pancreatic cancer PANC1 cells and that ATR-specific inhibitor VE-822 prevented H2O2-induced Chk1 and RPA32 phosphorylation (Figure 1A).