ABSTRACT
BACKGROUND: The t(9;22) translocation leads to the formation of the chimeric breakpoint cluster region/c-abl oncogene 1 (BCR/ABL) fusion gene on der22, the Philadelphia chromosome. The p185(BCR/ABL) or the p210(BCR/ABL) fusion proteins are encoded as a result of the translocation, depending on whether a "minor" or "major" breakpoint occurs, respectively. Both p185(BCR/ABL) and p210(BCR/ABL) exhibit constitutively activated ABL kinase activity. Through fusion to BCR the ABL kinase in p185(BCR/ABL) and p210(BCR/ABL) "escapes" the auto-inhibition mechanisms of c-ABL, such as allosteric inhibition. A novel class of compounds including GNF-2 restores allosteric inhibition of the kinase activity and the transformation potential of BCR/ABL. Here we investigated whether there are differences between p185(BCR/ABL) and p210(BCR/ABL) regarding their sensitivity towards allosteric inhibition by GNF-2 in models of Philadelphia chromosome-positive acute lymphatic leukemia. DESIGN AND METHODS: We investigated the anti-proliferative activity of GNF-2 in different Philadelphia chromosome-positive acute lymphatic leukemia models, such as cell lines, patient-derived long-term cultures and factor-dependent lymphatic Ba/F3 cells expressing either p185(BCR/ABL) or p210(BCR/ABL) and their resistance mutants. RESULTS: The inhibitory effects of GNF-2 differed constantly between p185(BCR/ABL) and p210(BCR/ABL) expressing cells. In all three Philadelphia chromosome-positive acute lymphatic leukemia models, p210(BCR/ABL)-transformed cells were more sensitive to GNF-2 than were p185BCR/ABL-positive cells. Similar results were obtained for p185(BCR/ABL) and the p210(BCR/ABL) harboring resistance mutations. CONCLUSIONS: Our data provide the first evidence of a differential response of p185(BCR/ABL)- and p210(BCR/ABL)- transformed cells to allosteric inhibition by GNF-2, which is of importance for the treatment of patients with Philadelphia chromosome-positive acute lymphatic leukemia.
Subject(s)
Fusion Proteins, bcr-abl/antagonists & inhibitors , Leukemia, Myelogenous, Chronic, BCR-ABL Positive , Pyrimidines/pharmacology , Allosteric Regulation/drug effects , Allosteric Regulation/physiology , Cell Line, Tumor , Fusion Proteins, bcr-abl/genetics , Humans , Leukemia, Myelogenous, Chronic, BCR-ABL Positive/drug therapy , Leukemia, Myelogenous, Chronic, BCR-ABL Positive/genetics , Pyrimidines/therapeutic useABSTRACT
The BCR/ABL oncogene is responsible for the phenotype of Philadelphia chromosome-positive (Ph+) leukemia. BCR/ABL exhibits an aberrant ABL-tyrosine kinase activity. The treatment of advanced Ph+ leukemia with selective ABL-kinase inhibitors such as Imatinib, Nilotinib and Dasatinib is initially effective but rapidly followed by resistance mainly because of specific mutations in BCR/ABL. Tetramerization of ABL through the N-terminal coiled-coil region (CC) of BCR is essential for the ABL-kinase activation. Targeting the CC-domain forces BCR/ABL into a monomeric conformation reduces its kinase activity and increases the sensitivity for Imatinib. We show that (i) targeting the tetramerization by a peptide representing the Helix-2 of the CC efficiently reduced the autophosphorylation of both unmutated and mutated BCR/ABL; (ii) Helix-2 inhibited the transformation potential of BCR/ABL independently of the presence of mutations; and (iii) Helix-2 efficiently cooperated with Imatinib as revealed by their effects on the transformation potential and the factor-independence related to BCR/ABL with the exception of mutant T315I. These findings support earlier observations that BCR/ABL harboring the T315I mutation have a transformation potential that is at least partially independent of its kinase activity. These data provide evidence that the inhibition of tetramerization inhibits BCR/ABL-mediated transformation and can contribute to overcome Imatinib-resistance.
