ATR and B-cell chronic lymphocytic leukemia: In line with this, we observed that phosphorylation of H2AX (γH2AX) induced by UV-C in CLL cells was completely prevented for up to 60 min by two selective ATR inhibitors, VE-821 and AZ20 [28, 29], used at 10 and 1 μM, respectively (Figure 2B).