CHEK1 and lung cancer: Given the important role of ATM phosphorylation at Ser1981 in activating the ATM protein and subsequent the ATM signaling pathway [5, 20], it is possible that inhibiting the ATR-CHK1 pathway with caffeine enhances the cisplatin-induced activation of the ATM signal pathway, which further induces expression of important pro-apoptotic proteins, including PUMA, to result in an increase in apoptosis of these lung cancer cells.