Ligands for the tyrosine kinase p56(lck) SH2 domain: Discovery of potent dipeptide derivatives with monocharged, nonhydrolyzable phosphate replacements

p56(lck) is a member of the src family of tyrosine kinases. Through modular binding units called SH2 domains, p56(lck) promotes phosphotyrosine-depend ent protein-protein interactions and plays a critical role in signal transd uction events that lead to T-cell activation. Starting from the phosphoryla ted dipeptide (2), a high-affinity ligand for the p56(lck) SH2 domain, we h ave designed novel dipeptides that contain monocharged, nonhydrolyzable pho sphate group replacements and bind to the protein with K-D's in the low mic romolar range. Replacement of the phosphate group in phosphotyrosine-contai ning sequences by a (R/S)-hydroxyacetic (compound 8) or an oxamic acid (com pound 10) moiety leads to hydrolytically stable, monocharged ligands, with 83- and 233-fold decreases in potency, respectively. This loss in binding a ffinity can be partially compensated for by incorporating large lipophilic groups at the inhibitor N-terminus. These groups provide up to 13-fold incr eases in potency depending on the nature of the phosphate replacement. The discovery of potent (2-3 mu M), hydrolytically stable dipeptide derivatives , bearing only two charges at physiological pH, represents a significant st ep toward the discovery of compounds with cellular activity and the develop ment of novel therapeutics for conditions associated with undesired T-cell proliferation.