Glycosylated liposomes with proton sponge capacity: novel hepatocyte- specific gene carriers

Interest in hepatocyte-directed liposomal gene delivery is driven, in part, by the lack of effective treatment for several liver-associated disorders. To impart a hepatocyte targeting capability on DNA-lipoplexes, and to promote early release of cargo DNA from endosomes, novel glycosylated and imidazolylated cholesteryl derivatives have been synthesized and evaluated in vitro. Thus cholesteryl-3β-N-[(lactobionyl) amino] carbamate (Chol-LAC) and cholesteryl-3β-N- [(urocanyl) amino] carbamate (Chol-UAC) have been formulated with the cytofectin cholesteryl-3β-[(N',N'- dimethylaminopropyl) carbamate (Chol-T) and the neutral co-lipid dioleoylphosphatidyl ethanolamine (DOPE). Liposomes, which displayed a buffering capability at endosomal pH, effectively bound DNA at a N/P ratio of 0.8:1 and offered partial protection against serum nuclease digestion. The MTT cell viability assay showed that lipoplexes were well tolerated by human hepatoma cells (HepG2), which were efficiently transfected almost exclusively by asialoglycoprotein receptor (ASGP-R)-mediation, as demonstrated in competition assays. In the ASGP-R-negative human kidney cell line (HEK293) transfection levels were considerably lower (P < 0.001). Therefore the combination of Chol-LAC and Chol- UAC in cationic liposomal formulations may provide a platform for the development of useful hepatotropic gene delivery systems.