Peptide-targeted PEG-liposomes in anti-angiogenic therapy.

Peptides with the RGD amino acid sequence show affinity for the alpha(v)beta(3) integrin, an integrin which is over-expressed on angiogenic endothelium and involved in cell adhesion. A peptide with the sequence ATWLPPR has been demonstrated to show affinity for the vascular endothelial growth factor (VEGF) receptor, a receptor involved in the proliferation of endothelial cells. By coupling these peptides to liposomes, these liposomes can serve as a site-specific drug delivery system to tumor endothelial cells in order to inhibit angiogenesis. In the present study we demonstrate that the coupling of cyclic RGD-peptides or ATWLPPR-peptides to the surface of PEG-liposomes results in binding of these liposomes to endothelial cells in vitro. Subsequent studies with RGD-peptide targeted liposomes in vivo also demonstrate specific binding to the tumor endothelium.