Effect of the combination of cationic lipid and phospholipid on gene-knockdown using siRNA lipoplexes in breast tumor cells and mouse lungs

Previously, using three types of cationic lipids, the effect of phospholipids in liposomal formulations on gene-knockdown efficacy was determined after in vitro and in vivo transfection with small interfering RNA (siRNA)/cationic liposome complexes (siRNA lipoplexes) containing various cationic lipids and phospholipids. In the present study, six other types of cationic lipids, namely N,N-dimethyl-N-tetradecyltetradecan-1-aminium bromide, N-hexadecyl-N,N-dimethylhexadecan-1-aminium bromide (DC-1-16), 2-[bis{2-(tetradecanoyloxy)ethyl}amino]-N,N,N-trimethyl-2-oxoethan-1-aminium chloride (DC-6-14), 1,2-di-O-octadecenyl-3-trimethylammonium propane chloride (DOTMA), 1,2-distearoyl-3-trimethylammonium-propane chloride (DSTAP) and 1,2-dioleoyl-3-dimethylammonium-propane were selected, and the effect of phospholipids in liposomal formulations containing each cationic lipid on gene-knockdown was evaluated. A total of 30 types of cationic liposomes composed of each cationic lipid with phosphatidylethanolamine containing unsaturated or saturated diacyl chains (C14, C16 or C18) were prepared. Regardless of the type of cationic lipid, the inclusion of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) in the liposomal formulations resulted in injectable size of siRNA lipoplexes after mixing of siRNA and cationic liposomes. Transfection of their lipoplexes with luciferase (Luc) siRNA into human breast cancer MCF-7-Luc cells stably expressing Luc led to a strong knockdown of Luc. Furthermore, the systemic injection of siRNA lipoplexes composed of DC-1-16, DC-6-14, DOTMA or DSTAP with DOPE resulted in siRNA accumulation in the lungs. Significant gene-knockdown was observed in the lungs of mice following the systemic injection of siRNA lipoplexes containing DC-1-16 and DOPE. Cationic liposomes composed of DC-1-16 and DOPE serve as potential carriers for in vitro and in vivo siRNA transfection.