Molecular Mechanisms Underlying the Clinical Success of the Cancer Drug Gleevec

Cancer is a serious illness and the second leading cause of death in the US. It is caused by misregulation of the signaling cascades and uncontrolled cell proliferation. Protein kinases are the key players in the regulatory machinery, and in the last 20 years they have become an increasingly important drug targets. The main requirement for such drugs is selectivity: ideally, only one kinase should be affected by an individual drug. The prominent success story is an FDA-approved chronic myeloid leukemia therapeutic Gleevec. Gleevec is a highly specific inhibitor of the Abl kinase and has very little potency towards a closely related Src subfamily of kinases. This specificity is particularly intriguing considering that the drug-binding pockets look nearly identical in these kinases. We combined NMR and pre-steady-state kinetic experiments to monitor Gleevec binding in real time and with residue-specific precision. Our data establish a novel model that fully and quantitatively explains the observed 3000-fold difference in Gleevec's affinities to Abl and Src, solving a long-standing paradox in the field. These results reveal the general principles of kinase-drug interactions and highlight the molecular mechanisms behind nanomolar affinities found in clinically relevant therapeutics.