Vascular endothelial growth factor (VEGF) is a small, dimeric protein important for angiogenesis, the formation of new blood vessels. The elegant phage-display studies of Fairbrother and co-workers led to peptide ligands that blocked the receptor binding of VEGF, but with approximately micromolar dissociation constants, which are much weaker than the nano- to picomolar dissociation constants of acceptable drugs. While not a widely used design concept, a ligand that binds irreversibly to its target has several potential advantages over such weakly binding reversible ligands. For reversible binding, the concentration of free ligand must be larger than the dissociation constant in order for the target to be >50% occupied; for a covalent ligand, under ideal conditions the target could be titrated with equimolar ligand. Once tagged, the target is permanently inactivated, an outcome qualitatively different from reversible binding. To create a site on a weakly binding peptide ligand that would carry a covalent labeling reagent, we replaced a residue that does not change the peptide’s affinity for VEGF, but is located within reach of a lysine side chain on the protein. We will describe the interaction of reactively tagged peptides with VEGF, including recent studies in vivo in animal models, with particular focus on a nitroaryl fluoride reagent (see figure).
Fig.1. Marquez et al., Reactive peptide for inhibiting VEGF. Bioconjugate Chem., 2012, 23 (5), pp 1080?1089