Characterization of Cationic Liposome-Mediated Gene TransferIn Vivoby Intravenous Administration

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Abstract
Physicochemical properties of the cationic liposomes, including structure of the cationic lipids, cationic lipid-to-DNA ratio, liposome particle size, and inclusion of the helper lipids, were studied for their effect on the level, site, and duration time of gene expression in vivo by intravenous administration. Using a cytomegalovirus (CMV)-driven gene expression system containing either the luciferase or green fluorescence protein gene as a reporter and two cationic lipids [N-(2,3-dioleoyloxy)propyl-N,N,N-trimethylammonium chloride (DOTMA) and 1,2-dioleoyloxy-3-trimethylammonium propane (DOTAP)], we demonstrated in vivo by a single intravenous injection of DNA/liposome complexes into mice, that cationic liposomes are capable of transfecting cells in organs such as the lung, heart, liver, spleen, and kidney. Transfection efficiency is determined mainly by the structure of the cationic lipid and the ratio of cationic lipid to DNA. Although the presence of cholesterol in DOTAP liposomes did not affect transfection activity, inclusion of dioleoylphosphatidylethanolamine (DOPE) into either DOTAP or DOTMA liposomes significantly decreases liposome transfection activity in vivo. Results from time course show that gene expression in different organs is transient, with a peak level between 4 and 24 hr, dropping to less than 1% of the peak level by day 4. Experiments with repeated injections showed that the peak level of gene expression could be regained by subsequent injection. Cationic liposomes have been studied as a potential carrier for delivering genes to cells for the purpose of gene therapy. This report summarizes our studies on the identification of the physicochemical factors that are important in determining the in vivo gene delivery efficiency of cationic liposomes by intravenous administration. The results show that some of the physicochemical parameters of cationic liposomes required for an optimal transfection in vivo are different from those for optimal in vitro transfection. The data support the notion that cationic liposomes can be an efficient carrier for in vivo gene delivery.

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