Poly(ethylene glycol)-Grafted Liposomes with Oligopeptide or Oligosaccharide Ligands Appended to the Termini of the Polymer Chains

Abstract

Novel conjugates tailor-made for inclusion in liposomal formulations, containing distearoylphosphatidylethanolamine (DSPE) as a lipid anchor, heterobifunctional polyethylene glycol (PEG) with a molecular weight of 2000 as a linking moiety, and a biological cell adhesive ligand [YIGSR peptide or Sialyl Lewis(X) oligosaccharide (SLX)], were synthesized. They were characterized by NMR, chromatography, and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOFMS). Inclusion of either of the ligand-PEG-lipid conjugates (2 mol %) in a lecithin/cholesterol/ methoxy-PEG2000-DSPE (55:40:3 mole ratio) lipid mixture followed by preparation of unilamellar vesicles (100 nm) resulted in positioning of 55% of the YIGSR and 63% of the SLX ligands on the periphery of the outer surface-grafted polymeric "brush", as determined by a combination of specific enzymatic alterations of each ligand and HPLC. Similar densities of ligand-bearing PEG chains were incorporated into liposomes by simply incubating (37 degrees C, 5 h) either one of the ligand-PEG-lipid conjugates with preformed lipid vesicles. This conjugate insertion process was aggregation free. Using enzymatic derivatization-HPLC, it was demonstrated that all the ligands incorporated into lipid membranes by this new approach were positioned exclusively on the outer leaflet of the liposomal bilayers. Since liposomes of this type are intended for in vivo use as long-circulating, ligand-presenting platforms, the insertion approach is preferable because of the more efficient utilization of ligand-PEG-lipid conjugates.

A Novel Peptide Specifically Binding to Nasopharyngeal Carcinoma For Targeted Drug Delivery

“…The same method was used to prepare a control peptide to replace the L-peptide and couple to NHS-PEG-DSPE for comparison. Peptidyl-PEG-DSPE was transferred to pre-formed liposomes after co-incubation at temperature above the transition temperature of lipid bilayer (27). There were 300 to 500 peptide molecules per liposome, computed as described previously (28).…”

Peptide-Mediated Targeting to Tumor Blood Vessels of Lung Cancer for Drug Delivery

“…The reaction was completed and confirmed by quantitation of the remaining amino groups, measured using a trinitrobenzenesulfonate reagent (37). Peptidyl-PEG/DSPE was transferred to preformed liposomes after coincubation at a temperature above the transition temperature of the lipid bilayer (38). The liposomes had a particle size ranging from 65 to 75 nm in diameter (33).…”

Conjugation of Ligands to the Surface of Preformed Liposomes by Click Chemistry

“…Amide and carbamate bonds were also used, and more recently peptide ligands were coupled to the surface of liposomes via hydrazone and a-oxo hydrazone linkages (12). With the inception of sterically stabilized liposomes (13), ligands were also coupled at the distal end of a PEG spacerarm linked to a hydrophobic anchor (1,14,15). Chemically controlled conjugation between preformed liposomes and ligands should ideally combine several features, such as mild reaction conditions in aqueous media, high yields and chemoselectivity.…”