Characterization of a novel diolein-based LPDII vector for gene delivery

LPDII vectors are non-viral vehicles for gene delivery comprised of polycation-condensed plasmid DNA (polyplexes) complexed with anionic pH-sensitive liposomes. Here, we describe a novel LPDII formulation containing polyethylenimine (PEI) polyplexes complexed with anionic pH-sensitive liposomes composed of diolein/cholesteryl hemisuccinate (CHEMS) (6:4 mol/mol). The pH-sensitivity of diolein/CHEMS liposomes was evaluated through quantitative fluorescence measurements of calcein release and particle size analysis. The results indicated that diolein/CHEMS liposomes are stable at physiological pH, but undergo rapid aggregation and fluorescence dequenching at pH values < or =5.0. Using a luciferase reporter gene, in vitro transfection of KB oral cancer cells showed that the transfection efficiency of LPDII vectors was superior to other well-characterized polyplexes and lipoplexes. Results further showed that gene delivery using diolein-containing LPDII vectors was dependent on the PEI nitrogen/DNA phosphate (N/P) ratio, the lipid/DNA weight ratio and the cell line being transfected. Replacing PEI with poly-L-lysine as the DNA condensing agent resulted in only a moderate reduction in transfection activity. Moreover, in contrast to LPDII formulations incorporating dioleoylphosphatidylethanolamine (DOPE), the transfection efficiency of diolein-based LPDII vectors was sustained in media containing up to 50% fetal bovine serum. Since diolein-based LPDII vectors mediate efficient gene transfer and retain their transfection activity in the presence of serum, diolein may be a promising alternative to DOPE for the construction of non-viral vectors for in vivo gene delivery.