Evaluation and optimization of different cationic liposome formulations for in vivo gene transfer

Five commonly used cationic liposome formulations were tested for their ability to deliver DNA to established subcutaneous human tumor xenografts in SCID mice. Liposomes were complexed with a mammalian expression plasmid containing the bacterial beta-galactosidase gene and delivered to tumors by direct injection. The optimal lipid to DNA ratios in vivo were markedly different than those observed in vitro for each liposome formulation. Tumor size at the time of inoculation also effected transfection efficiency significantly. Of the five liposome formulations tested, DC-Cholesterol was found to be superior to all others in vivo. Even under optimal conditions however, the efficiency of in vivo transfection was low in our system (approximately 0.3%). Implications of these results for in vivo gene therapy of tumors are discussed.