Enhancement of transfection activity in HEK293 cells by lipoplexes containing cholesteryl nitrogen-pivoted aza-crown ethers

Abstract

Two nitrogen-pivoted aza-crown ethers (aza-CEs) linked to the cholesteryl-fused ring system N-(cholesteryloxycarbonyl)aza-15-crown-5 and N-(cholesteryloxycarbonyl)aza-18-crown-6 have been incorporated into cationic liposomes containing the cytofectin 3β[N-(N′,N′-dimethylaminopropane) carbamoyl] cholesterol (Chol-T) and the neutral co-lipid dioleoylphosphatidylethanolamine. These novel liposomes form stable complexes with plasmid DNA and afford it good protection from serum nuclease digestion. Ethidium displacement studies suggest that the DNA is more loosely packed in aza-CE containing lipoplexes, a finding which is supported by band shift assays that reveal N/P end point ratios of 2:1, 3:1 and 3.5:1 for Chol-T control liposomes, aza-15-crown-5 and aza-18-crown-6 containing liposomes, respectively. The transfection activities of crown ether-containing lipoplex formulations in the human embryonic kidney cell line HEK293 are twofold greater than those achieved by Chol-T lipoplexes not containing the aza-CEs. This observation may be attributable to the more loosely packed DNA, which facilitates disassembly, and to endosomal perturbations caused by macrocycle entrapped cations.