High-throughput fluorescence polarization assay to identify inhibitors of Cbl(TKB)-protein tyrosine kinase interactions

The casitas B-lineage lymphoma (Cbl) proteins play an important role in regulating signal transduction pathways by functioning as E3 ubiquitin ligases. The Cbl proteins contain a conserved tyrosine kinase binding (TKB) domain that binds more than a dozen proteins, including protein tyrosine kinases (PTKs), in a phosphorylation-dependent manner. The cell surface expression levels of the PTKs are regulated by Cbl-mediated ubiquitination, internalization, and degradation. Dysfunction in this signaling cascade has resulted in prolonged activation of the PTKs and, therefore, has been implicated in inflammatory diseases and various cancers. Due to this negative regulatory function, Cbl has been largely ignored as a therapeutic target. However, recent studies, such as the identification of (i) gain of function c-Cbl mutations in subsets of myeloid cancer and (ii) c-Cbl as a prostate basal cell marker that correlates with poor clinical outcome, suggest otherwise. Here we report the development of a competitive high-throughput fluorescence polarization assay in a 384-well format to identify inhibitors of Cbl(TKB). The high-throughput screen readiness of the assay was demonstrated by screening the Prestwick Chemical Library.