Blood

The leukemogenic tyrosine kinase Bcr-AbI contains a highly conserved inhibitor-binding pocket (IBP), which serves as a binding site for imatinib mesylate. Mutations at the IBP may lead to resistance of the AbI kinase against imatinib mesylate. To examine the mechanisms of imatinib mesylate binding and resistance in more detail, we created several point mutations at amino acid positions 315 and 380 of AbI, blocking the access to the IBP and rendering Bcr-AbI imatinib mesylate-resistant. Moreover, introduction of a mutation destabilizing the inactive conformation of AbI (Asp276Ser/GIu279Ser) also led to imatinib mesylate resistance, suggesting that the inhibitor required inactivation of the kinase prior to binding. These Bcr-AbI mutants were then used to evaluate the binding mode and specificity of 2 compounds, PP1 and CGP76030, originally characterized as Src kinase inhibitors. Both compounds inhibited Bcr-AbI in a concentration-dependent manner by overlapping binding modes. However, in contrast to imatinib mesylate, PP1 and CGP76030 blocked cell growth and survival in cells expressing various inhibitor-resistant AbI mutants. Studies on the potential signaling mechanisms demonstrated that in cells expressing inhibitor-resistant Bcr-AbI mutants, PP1 and CGP76030 inhibited the activity of Src family tyrosine kinases and Akt but not signal transducer and activator of transcription-5 (STAT5) and JUN kinase (Jnk). The results suggest that the use of Src kinase inhibitors is a potential strategy to prevent or overcome clonal evolution of imatinib mesylate resistance in Bcr-AbI(+) leukemia. (C) 2003 by The American Society of Hematology