ATR and cancer: Similar to induction of replication stress, Western blot analyses also showed a time-dependent, significant increase in levels of phosphorylated Chk1 and Chk2, demonstrating strong activation of both ATR-Chk1 and ATM-Chk2 DDR signaling pathways specifically in the cancer but not noncancerous cells (Fig. 3C, Additional file 3: Figure S3B).