A comparative study on three unique galactosylated cationic liposomes with their steically stablized counterparts, in HepG2 cells.
Receptor mediated endocytosis allows for the site specific delivery of exogenous DNA via appropriate ligand-receptor interactions. Various ligands have been used to target the asialoglycoprotein receptor (ASGP-R) present on the hepatocyte cell membrane viz. asialofeutin, asialoorosomucoid, lac-BSA, asialolactoferrin, asialotransferrin, asialo-ceruloplasmin and galactose. The high affinity that the receptor displays for the galactose sugar moiety has led to the development of several new galacto-lipids for the incorporation into liposomes intended for hepatocyte targeting. In this study, three cholesteryl derivatives displaying galactose units linked to the sterol skeleton by different spacer elements have been formulated into cationic liposomes with and without polyethylene glycol (PEG) accessories. The three galactosylated liposomal formulations were prepared using near equimolar amounts of MSO9 (N,N-dimethylaminopropylamidosuccinyl-cholesterylformylhydrazide) and DOPE (dioleoylphosphotidylethanolamine) together with the respective galactose derivative (at 10 mole % w/w) viz. Cholesteryl-3β-N-(4-aminophenyl-β-Dgalactopyranosyl) carbamate; Cholesteryl (1-β-D-galactopyranosyl-1,2,3 triazol-4-yl) carbonate; and Cholesteryl-β-D-galactopyranoside. All liposomes displayed DNA binding, nuclease protective capabilities to plasmid DNA, low cytotoxicity (cell viability being within 60-101 %) and an increase in transfection activities, in the human hepatocellular carcinoma cell line HepG2, which expresses the ASGP-R abundantly. The results obtained correlate well with differences in the spacer element in the 3 galactosylated cholesterol derivatives under study and the presence and absence of 2 mole % DSPE-PEG₂₀₀₀ in the liposome formulations. Overall, it was observed that the cationic liposome containing cholesteryl (1-β-Dgalactopyranosyl- 1,2,3 triazol-4-yl) carbonate (with and without PEGylated accessories), which was synthesised chemically using “click chemistry”, afforded the highest in vitro transfection activity, and may be optimised and studied further. The highest levels of transfection activity, in vitro, were attributed to the increased length of the spacer arm between the galactose moiety and the cholesteryl anchor of the targeting component. Two formulations were then subjected to in vivo studies, using male Sprague Dawley rats which yielded little or no transgene expression.