A 48-h YX-2-107 treatment of NSG mice with advanced Ph+ ALL was sufficient to markedly decrease the proportion of S phase cells in the bone marrow, suppress the expression of the CDK4/6 substrates phospho-RB and FOXM1, and induce the preferential degradation of CDK6 over CDK4. This evidence concerns the gene CDK4 and acute lymphoblastic leukemia.