Allosteric Inhibition of Bcr-Abl Kinase by High-Affinity Monobody Inhibitors Directed to the SH2-Kinase Interface
Bcr-Abl is a constitutively active kinase that causes chronic myelogenous leukemia (CML). We have shown that a tandem fusion of two designed binding proteins, termed monobodies, respectively directed to the interaction interface between the SH2 and kinase domains and to the phosphotyrosine-binding site of the SH2 domain inhibits the of Bcr-Abl kinase activity. Because the latter monobody inhibits processive phosphorylation by Bcr-Abl and the SH2-kinase interface is occluded in the active kinase, it remained undetermined whether targeting the SH2-kinase interface alone was sufficient for Bcr-Abl inhibition. To address this question, we generated new, higher-affinity monobodies, with single nanomolar KD values, targeting the kinase-binding surface of SH2. Structural and mutagenesis studies revealed the molecular underpinnings of the monobody-SH2 interactions. Importantly, the new monobodies inhibited Bcr-Abl kinase activity in vitro and in cells, and they potently induced cell death in CML cell lines. This work provides strong evidence for the SH2-kinase interface as a pharmacologically tractable site for allosteric inhibition of Bcr-Abl.
Record created on 2016-04-28, modified on 2016-08-09