Abstract A163: Development of Grb2 SH3 domain antagonists

Abstract Src-homology 3 (SH3) domains are small modules of about 60 amino acids residues found in proteins that participate in many signaling pathways. As such, SH3 domains are involved in the regulation of several important cellular processes, including cell growth and differentiation, cell movement, protein trafficking and degradation, and immune responses. The adaptor protein Grb2 contains two SH3 domains. The canonical model of Grb2 function relies on the widely confirmed observation that Grb2 SH3 domains are constitutively associated with Sos1, a guanine-nucleotide exchange factor that promotes GDP-GTP exchange on Ras. Upon growth factor receptor activation and tyrosyl phosphorylation, Grb2 brings Sos1 into close proximity of membrane-bound Ras, thereby activating Ras and the downstream MAPK cascade, a well-know oncogenic signaling convergence point. Thus, antagonism of Grb2-Sos interaction is a logical strategy for inhibiting tumor cell growth. Using a short synthetic peptide corresponding to the SH3 domain recognition motif of Sos1 as a starting point, and systematically introducing bridging carbonyl sequences and other modifications, novel antagonists of Sos1-SH3 domain interaction were developed. The performance of these antagonists was systematically evaluated using a solid phase Grb2-Sos1 binding assay and cell lysates prepared from the pheochromocytoma cell line PC12, which has robust expression of both Grb2 and Sos1 proteins. Refinement of candidates identified in initial screens yielded a set of peptidomimetic antagonists with nanomolar IC50 values that were selected for further study. The potency and target selectivity of these compounds suggest that they may have utility as anti-cancer therapeutics for tumors where Grb2-Sos1 interactions are critical for oncogenesis and disease progression. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A163.