Formulation of cationic liposomes is a key factor that determine the gene knockdown efficiency by cationic liposomes/siRNA complexes (siRNA lipoplexes). Here, to determine the optimal combination of cationic lipid and phospholipid in cationic liposomes for in vitro and in vivo gene knockdown using siRNA lipoplexes, three types of cationic lipid were used, namely 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), dimethyldioctadecylammonium bromide (DDAB) and 11-[(1,3-bis(dodecanoyloxy)-2-((dodecanoyloxy)methyl)propan-2-yl)amino]-N,N,N-trimethyl-11-oxoundecan-1-aminium bromide (TC-1-12). Thereafter, 30 types of cationic liposome composed of each cationic lipid with phosphatidylcholine or phosphatidylethanolamine containing saturated or unsaturated dialkyl chains (C14, C16, or C18) were prepared. The inclusion of phosphatidylethanolamine containing unsaturated and long dialkyl chains with DOTAP- or DDAB-based cationic liposomes induced strong luciferase gene knockdown in human breast cancer MCF-7-Luc cells stably expressing luciferase gene. Furthermore, the inclusion of phosphatidylcholine or phosphatidylethanolamine containing saturated and short dialkyl chains or unsaturated and long dialkyl chains into TC-1-12-based cationic liposomes resulted in high gene knockdown efficacy. When cationic liposomes composed of DDAB/1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), TC-1-12/DOPE and TC-1-12/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine were used, significant gene knockdown occurred in the lungs of mice following systemic injection of siRNA lipoplexes. Overall, the present findings indicated that optimal phospholipids in cationic liposome for in vitro and in vivo siRNA transfection were affected by the types of cationic lipid used.
Keywords: cationic liposome; gene knockdown; lung; phospholipid; siRNA delivery.