Novel pyridinium-based cationic lipids as gene delivery vectors

Background: For the past two decades, cationic lipids have remained one of the most widely used non-viral gene delivery vectors due in large to their safety and ease of use despite having low efficiency. We and others believe that the key to improving the effectiveness of non-viral agents is unlocking the still unsolved mechanism behind lipid gene delivery. Our objective is the rational design, synthesis and evaluation of the DNA complexation and in vitro delivery efficiency of novel lipid vectors in an effort to gain structure-function data which may give insight towards the non-viral mechanism. Objectives: Here we report preliminary data on two novel pyridinium-based cationic lipid vectors, designated as TFSA (saturated acyclic structure) and TFUA (unsaturated acyclic structure), both possessing a pyridinium headgroup with a delocalized positive charge, and two saturated (TFSA) or monounsaturated (TFUA) C15 hydrophobic alkyl chains. In the case of the unsaturated analogue, the double bonds are located at the terminal ends of the alkyl chains. Methods: Liposomes were prepared from these novel pyridinium-based cationic lipids in combination with a commercial vector, EPC, together with a co-lipid, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) or cholesterol. Lipid-DNA complexes (lipoplexes) were then formulated by incubating the liposomes with plasmid DNA. Lipoplexes were characterized by gel retardation, DNAse I degradation, as well as biocompatibility and β-galactosidase (β-gal) transfection assays using Chinese Hamster Ovarian (CHO-K1) cells. Fluorescent GFP-plasmid DNA was used to track DNA inside cells using epifluorescence microscopy. Results: The novel lipid formulations were shown to effectively complex DNA and protect it from DNAse I degradation. They were biocompatible with CHO-K1 cells, and performed better when they were formulated with cholesterol over DOPE as co-lipid. Furthermore, the formulation containing the unsaturated compound (TFUA/EPC/DOPE) revealed transfection efficiencies far above TFSA/EPC/DOPE, and superior to the commercial transfection agent EPC formulated alone with DOPE. Results from the GFP-plasmid tracking experiments were consistent with the relative β-gal expressions observed in the transfection assay. Conclusions: These preliminary results suggest that our novel pyridinium-based cationic lipid vectors are effective gene transfer agents, suitable for further investigations into the mechanism of non-viral gene delivery.