Oligomerization inhibition, combined with allosteric inhibition, abrogates the transformation potential of T3151-positive BCR/ABL

The t(9;22) translocation leads to the formation of the chimeric bcrlabl fusion gene, which encodes the BCR/ABL fusion protein. In contrast to its physiological counterpart c-ABL, the BCR/ABL kinase is constitutively activated, inducing the leukemic phenotype. The N-terminus of c-ABL (Cap region) contributes to the regulation of its kinase function. It is myristoylated, and the myristate residue binds to a hydrophobic pocket in the kinase domain known as the myristoylbinding pocket in a process called 'capping', which results in an auto-inhibited conformation. Because the cap region is replaced by the N-terminus of BCR, the BCR/ABL 'escapes' this auto-inhibition. Allosteric inhibition by myristate 'mimics', such as GNF-2, is able to inhibit unmutated BCR/ABL, but not the BCR/ABL that harbors the 'gatekeeper' mutation T3151. In this study, we analyzed the possibility of increasing the efficacy of allosteric inhibition by blocking BCR/ABL oligomerization. We showed that inhibition of oligomerization was able to not only increase the efficacy of GNF-2 on unmutated BCR/ABL, but also overcome the resistance of BCR/ABL-T3151 to allosteric inhibition. These results strongly suggest that the response to allosteric inhibition by GNF-2 is inversely related to the degree of oligomerization of BCR/ABL. In summary, our observations establish a new approach for the molecular targeting of BCR/ ABL and its resistant mutants represented by the combination of oligomerization and allosteric inhibitors. Leukemia (2009) 23, 2242-2247; doi: 10.1038/leu.2009.194; published online 1 October 2009 Keywords: Philadelphia chromosome-positive leukemia; BCR/ABL; imatinib-resistance; 'gatekeeper' mutation T3151; inhibition of oligomerization; allosteric inhibition