To enhance gene transfection to hepatocytes by cationic liposomes, it is necessary to overcome a number of barriers existing in the process from administration to gene expression. Recently we and other group have demonstrated that the escape of plasmid DNA (PDNA)/cationic liposome complexes (lipoplexes) from the endosome to cytoplasm was rate limiting. In this study, to enhance transfection efficiency by promoting the release of lipoplexes from the endosome to cytoplasm, we proposed utilizing the "proton sponge effect". Here, we synthesized a novel pH-sensitive histidine-modified galactosylated cholesterol derivative (Gal-His-C4-Chol), for a more efficient gene delivery to hepatocytes. Liposomes containing Gal-His-C4-Chol showed much greater transfection activity than conventional Gal-C4-Chol liposomes based on a receptor-mediated mechanism in HepG2 cells. Hence, this finding should contribute to the development of gene therapy using cationic liposomes toward their clinical application. (c) 2006 Elsevier B.V. All rights reserved.