Novel cholesterol spermine conjugates provide efficient cellular delivery of plasmid DNA and small interfering RNA.

New polycationic lipids corresponding to the two different classes of amphiphiles ("head-tail" and "gemini") were designed and used as components of non-viral gene delivery systems. The hydrophobic domain of lipids is based on the cholesterol residue and the hydrophilic one--on the naturally occurring polyamine--spermine. Ester and carbamate linker groups as well as oligomethylene spacers of various lengths were used to connect cholesterol and spermine motifs in order to estimate the structure-activity relationships of novel polycationic lipids and to determine an effective and safe transfectant suitable for the delivery of different nucleic acids. The cationic liposomes composed of the synthesized polycationic lipids and DOPE provided delivery of FITC-labeled oligonucleotide, plasmid DNA and siRNA into HEK293 cells with an efficiency significantly higher than that of Lipofectamine 2000. We found that the transfection activity of polycationic lipids is influenced by a linker type, a spacer length and the amount of cholesterol residues. The lipid containing two cholesterol units, carbamate linker and spacer of six methylene groups demonstrated the best in vitro transfection results among other analogues tested and was defined as a promising candidate for further transfection studies to be hold in vivo.