Because PARP cleavage is always a result of activation of caspases such as caspase-9 and -3, we looked for activation of these caspases in nilotinib-treated cells: caspase-9 and -3 were indeed activated in both BCR-ABL positive and negative ALL cells (Fig. 3C and Fig. 3D), suggesting that the function of XIAP is inhibited by nilotinib, because XIAP specifically inhibits both these caspases [37], [38]. This evidence concerns the gene ABL1 and acute lymphoblastic leukemia.