198. In Vitro and In Vivo Gene-Transferring Characteristics of Novel Cationic Lipids, DMKD(O,O′-dimyristyl-N-lysyl aspartate) and DMKE(O,O′-dimyristyl-N-lysyl Glutamate)

Abstract

Previously, we introduced a novel cationic lipid consisting of three biocompatible components, lysine, aspartic acid, and two C-14 hydrocarbon chains, named as O,O′-dimyristyl-N-lysyl aspartate (DMKD) as a potent gene transfection reagent. Recently, we have chemically synthesized another gene-transferring cationic lipid consisting of a core of glutamic acid and lysine with two C-14 hydrocarbon chains, assigned the acronym DMKE (O,O′-dimyristyl-N-lysyl glutamate). Biophysical characteristics of the cationic liposomes made of DMKE or DMKD were compared with those of conventional DOTAP liposomes. The DMKE- and DMKD-liposomes exhibited similarly stronger DNA-binding affinity than the DOTAP liposomes. Interestingly, vesicle size changes of DMKE- and DMKD-liposomes by lipoplex formation were far smaller than that of the DOTAP liposomes. Their gene-transferring capabilities were also tested in various cell-lines and compared with the control DOTAP liposomes. Under the same transfection conditions, the order of in vitro gene transfection efficiency was DMKE=DMKD>DOTAP. The pH changes (pH 5.0 – 7.4) in culture media little affected fusigenic activities of all the cationic liposomes. However, cell surface-binding affinities of the DMKE- and DMKE-lipoplexes were similar to each other, but higher than the DOTAP liposomes. In mouse studies, intravenously administered DMKE- and DMKD-lipoplexes did not exhibited superior gene expression in lungs to the DOTAP lipoplexes. Interestingly, they were more favorably transferred to the liver, not to the lungs. Particularly, under the same experimental conditions of intratumoral transfection, the DMKE lipoplexes showed more efficient gene expression in the tumor tissues than the DOTAP- and DMKD-lipoplexes. This study suggests that a small difference in the backbone structure of cationic lipid significantly affects their gene transfection capabilities. The DMKE- and DMKD-liposomes can be utilized as an efficient gene-transferring vector for hepatic or intratumoral transgene expression.