Design of fusogenic liposomes using a poly(ethylene glycol) derivative having amino groups

As a novel fusogenic liposome, we designed liposomes modified with poly(gly cidol) having beta-alanine residues, which is a poly(ethylene glycol) deriv ative with positively charged groups. The polymer-modified liposomes of egg yolk phosphatidylcholine (EYPC) and dioleoylphosphatidylethanolamine (DOPE ) were prepared by reverse phase evaporation. Fusion of the polymer-modifie d liposomes with anionic liposomes consisting of phosphatidic acid and DOPE was investigated. Fusion ability of the polymer-modified liposomes increas ed with increasing amount of the polymer fixed on the liposome. Also, inclu sion of DOPE was necessary for the generation of the fusion ability of the polymer-modified liposomes. CV1 cells treated with the polymer-modified DOP E/EYPC liposomes containing calcein displayed diffuse fluorescence, suggest ing that calcein was introduced into the cytoplasm. In contrast, only punct ual fluorescence was observed in the cells treated with the polymer-modifie d EYPC liposomes containing calcein, indicating that calcein remained in th e endosome and/or lysosome. In addition, COS1 cells were transfected effici ently by treatment with the polymer-modified EYPC/DOPE liposomes containing pSV2cat plasmid, whereas the transfection was not induced by treatment wit h the polymer-modified EYPC liposomes. Close correlation between fusion abi lity of the polymer-modified liposomes and their ability to deliver their c ontents to the cytoplasm implies that membrane fusion plays an important ro le in the liposome-mediated cytoplasmic delivery. (C) 2000 Elsevier Science B.V. All rights reserved.