ATR and B-cell chronic lymphocytic leukemia: Interestingly, both checkpoint kinases 1 and 2 (Chk1 and Chk2) were phosphorylated in the presence of MLN4924, further suggesting that targeting NAE induced activity of both ATM (ataxia telangiectasia mutated) and ATR (ataxia telangiectasia and Rad3 related) activity in CLL cells (Figure 2a).