NMR reveals the allosteric opening and closing of Abelson tyrosine kinase by ATP-site and myristoyl pocket inhibitors

Successful treatment of chronic myelogenous leukemia is based on inhibitors binding to the ATP site of the deregulated breakpoint cluster region (Bcr)-Abelson tyrosine kinase (Abl) fusion protein. Recently, a new type of allosteric inhibitors targeting the Abl myristoyl pocket was shown in preclinical studies to overcome ATP-site inhibitor resistance arising in some patients. Using NMR and small-angle X-ray scattering, we have analyzed the solution conformations of apo Abelson tyrosine kinase (c-Abl) and c-Abl complexes with ATP-site and allosteric inhibitors. Binding of the ATP-site inhibitor imatinib leads to an unexpected open conformation of the multidomain SH3-SH2-kinase c-Abl core, whose relevance is confirmed by cellular assays on Bcr-Abl. The combination of imatinib with the allosteric inhibitor GNF-5 restores the closed, inactivated state. Our data provide detailed insights on the poorly understood combined effect of the two inhibitor types, which is able to overcome drug resistance

Structural resemblances and comparisons of the relative pharmacological properties of imatinib and nilotinib

Although assessments of indices of drug similarity are becoming increasingly important, such comparisons are frequently qualitative and involve subjective preconceptions. In this study two tyrosine kinase inhibitors are compared on the basis of structural similarity, target selectivity and general biological activity in patients. The benchmark compound imatinib, is a BCR-ABL1 kinase inhibitor used as front-line treatment of chronic myelogenous leukemia (CML), where most newly-diagnosed chronic phase patients achieve excellent, durable responses. However, some patients do not tolerate imatinib and others may develop secondary resistance, as a consequence of the emergence of imatinib-resistant, mutant forms of BCR-ABL1. Nilotinib is a novel compound used to treat CML, discovered in a medicinal chemistry programme where the imatinib structure was re-engineered, based upon an understanding of the crystallographic binding mode of imatinib. Whereas structure-activity relationships were followed to optimise potency and selectivity towards BCR-ABL1, as well as biopharmaceutical properties, there was no such constraint on off-target activities. This resulted in significant structural differences between imatinib and nilotinib, which areis reflected in the marked differences between the drugs in terms ofin their preclinical pharmacology and side-effect profiles in imatinib-resistant and –intolerant patients, who show a lack of cross-intolerance between the two compounds

Characterization of AMN107, a selective inhibitor of native and mutant Bcr-Abl

SummaryThe Bcr-Abl tyrosine kinase oncogene causes chronic myelogenous leukemia (CML) and Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL). We describe a novel selective inhibitor of Bcr-Abl, AMN107 (IC50 < 30 nM), which is significantly more potent than imatinib, and active against a number of imatinib-resistant Bcr-Abl mutants. Crystallographic analysis of Abl-AMN107 complexes provides a structural explanation for the differential activity of AMN107 and imatinib against imatinib-resistant Bcr-Abl. Consistent with its in vitro and pharmacokinetic profile, AMN107 prolonged survival of mice injected with Bcr-Abl-transformed hematopoietic cell lines or primary marrow cells, and prolonged survival in imatinib-resistant CML mouse models. AMN107 is a promising new inhibitor for the therapy of CML and Ph+ ALL