Isoaspartate-glycine-arginine: A new tumor vasculature-targeting motif

Asparagine deamidation in peptides or in fibronectin fragments containing the asparagine-glycine-arginine sequence generates isoaspartate-glycine-arginine (isoDGR), a new alpha v beta 3 integrin-binding motif. Because alpha v beta 3 is expressed in angiogenic vessels, we hypothesized that isoDGR-containing peptides could be exploited as ligands for targeted delivery of drugs to tumor neovasculature. We found that a cyclic Ciso DGRC peptide coupled to fluorescent nanoparticles (quantum dots) could bind alpha v beta 3 integrin and colocalize with anti-CD31, anti-alpha v beta 3, kind anti-alpha 5 beta 1 antibodies in human renal cell carcinoma tissue sections, indicating that this peptide could efficiently recognize endothelial cells of angiogenic vessels. Using Ciso DGRC fused to tumor necrosis factor alpha (TNF) we observed that ultralow doses (1-10 pg) of this product (called iso DGR-TNF), but not. of TNT, or CDGRC-TNF fusion protein, were sufficient to induce antitumor effects when administered alone or in combination with chemotherapy to tumor-hearing mice. The antitumor activity of iso DGR-TNF was efficiently inhibited by coadministration with an excess of free Ciso DGRC, its expected for ligand-directed targeting mechanisms. These results suggest. that isoDGR is a novel tumor vasculature-targeting motif. Peptides containing isoDGR could be exploited as ligands for targeted delivery of drugs, imaging agents, or other compounds to tumor vasculature.