A new liposome-based gene delivery system targeting lung epithelial cells using endothelin antagonist

We formulated a new gene delivery system based on targeted liposomes. The efficacy of the delivery system was demonstrated in in vitro and in vivo models. The targeting moiety consists of a high-affinity 7-amino-acid peptide, covalently and evenly conjugated to the liposome surface. The targeting peptide acts as an endothelin antagonist, and accelerates liposome binding and internalization. It is devoid of other biological activity. Liposomes with high phosphatidyl serine (PS) were specially formulated to help their fusion with the endosomal membrane at low pH and enable release of the liposome payload into the cytoplasm. A DNA payload, pre-compressed by protamine, was encapsulated into the liposomes, which directed the plasmid into the cell's nucleus. Upon exposure to epithelial cells, binding of the liposomes occurred within 5-10 min, followed by facilitated internalization of the complex. Endosomal escape was complete within 30 min, followed by DNA accumulation in the nucleus 2h post-transfection. A549 lung epithelial cells transfected with plasmid encoding for GFP encapsulated in targeted liposomes expressed significantly more protein than those transfected with plasmid complexed with Lipofectamine. The intra-tracheal instillation of plasmid encoding for GFP encapsulated in targeted liposomes into rat lungs resulted in the expression of GFP in bronchioles and alveoli within 5 days. These results suggest that this delivery system has great potential in targeting genes to lungs.