Stimulation-responsive Cationic Lipid Gene Vector Studies

Gene therapy is a very promising method for the treatment of many human diseases,including AIDS, cancer and some genetic disorders. A fundamental engineering challenge of gene-based therapy is the development of safe and effective delivery vectors. Cationic lipids have become the most promising vector in gene delivery for their biocompatibility, none immunity and design/synthesis convenience. It is very important to study the structure-activity relationship of cationic lipid to construct an ideal gene vector.The first chapter in this thesis outlines the research development of cationic lipids and the main obstacles in the process of gene transfection.In the second chapter, two amino acid based amphiphilic molecules bearing a-tocopherol and different hydrophilic headgroups were designed and synthesized. A biodegradable disulfide linkage bridged the hydrophilic amino acids and hydrophobic tails. The target lipids showed good DNA-binding ability, and are able to condense DNA into stable lipoplex nanoparticles. The histidine-containing lipid 2-4a gave higher transfection efficiency than the lysine derivative, which might be attributed to weaker DNA binding. In addition to their low cytotoxicity, these lipoplexes also showed good transfection efficiency, which is comparable with commercially available Lipofectamine. Furthermore, lipid 2-4a has good serum resistance, and the optimized TE was approximately 4.3 times higher than bPEI-25 K in the presence of10% FBS.Based on the research of the second chapter, in the third chapter, several dipeptide-based amphiphilic molecules bearing a-tocopherol and various hydrophilic headgroups were designed and synthesized. A biodegradable disulfide linkage bridged the hydrophilic amino acids and hydrophobic tails. These lipids showed high DNA binding ability and good biocompatibility. The TE of cationic lipid 3-2f was especially high, and was 100 times higher than that of a branched polyethylenimine in the presence of 10% serum.In the fourth chapter, several amino-based amphiphilic molecules bearing a benzyl ester at the terminus of the acyl chain and various hydrophilic headgroups were designed and synthesized. The target lipids showed high DNA binding ability, and were able to condense DNA into stable lipoplex nanoparticles. Phenylalanine containing cationic lipid 4-4c gave the higher transfection efficiency, which might be attributed to its higher DNA binding ability and lower cytotoxicity. Besides their low cytotoxicity, these lipoplexes also showed good transfection efficiency which is comparable to commercially available Lipofectamine 2000. Furthermore, lipid 4-4c has good serum-resistance capability, and the optimized TE was about 2.1 times higher than bPEI 25 k in the presence of 10% serum in Hela cells. The structures of the hydrophilic headgroup significantly affected the TE, and the phenylalanine group was demonstrated to play an important role in the transfection by such a type of lipid.