Activation of p53 in response to purine analogs, which is well documented in primary CLL cells [36], was also found to be inhibited by VE-821 (Figure 3D): both p53 phosphorylation and p53 accumulation were indeed strongly reduced by the ATR inhibitor, indicating that ATR plays an important role in stabilizing p53 after purine analog treatment. Here, TP53 is linked to B-cell chronic lymphocytic leukemia.