title: Efficiency of cytoplasmic delivery by pH-sensitive liposomes to cells in culture.
abstract: The intracellular processing of pH-sensitive liposomes composed of cholesterylhemisuccinate (CHEMS) and dioleoylphosphatidylethanolamine (DOPE) by eukaryotic cell lines has been compared to non-pH-sensitive liposomes made of CHEMS and dioleoylphosphatidylcholine (DOPC). The pH-sensitive liposomes can deliver encapsulated fluorescent molecules [calcein, fluoresceinated dextran, fluoresceinated polypeptide, and diphtheria toxin A chain (DTA)] into the cytoplasm. Cytoplasmic delivery can be blocked in the presence of ammonium chloride or EDTA, indicating that the process requires a low-pH environment and the presence of divalent cations. Inhibition of cellular protein synthesis by DTA delivery from the pH-sensitive liposome is orders of magnitude greater than from the non-pH-sensitive liposome composition. The delivery of DTA into the cytoplasm by pH-sensitive liposomes is at least 0.01% of cell-associated liposomal DTA. There is no significant difference in the degradation rate of bovine serum albumin (BSA) or the rate of acidification of pH-sensitive dye, 8-hydroxy-1,3,6-pyrene-trisulfonate (HPTS), when delivered to cells in pH-sensitive and non-pH-sensitive liposomes. Thus the efficiency of cytoplasmic delivery is less than 10% of the cell-associated liposome contents, which is the smallest difference that can be detected by these two assays. Based upon the various assays used to measure liposome content disposition in the cell, we conclude that the efficiency of cytoplasmic delivery by the CHEMS/DOPE liposomes is greater than 0.01% and less than 10% of the cell-associated liposomal contents.
authors.affiliation: Department of Pharmacy and Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco 94143.
authors.forename: C J
authors.initials: CJ
authors.lastname: Chu
authors.forename: J
authors.initials: J
authors.lastname: Dijkstra
authors.forename: M Z
authors.initials: MZ
authors.lastname: Lai
authors.forename: K
authors.initials: K
authors.lastname: Hong
authors.forename: F C
authors.initials: FC
authors.lastname: Szoka
mesh_terms: D000818:Animals; D001190:Arylsulfonates / Q000494:pharmacology; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D004167:Diphtheria Toxin / Q000494:pharmacology; D004337:Drug Carriers; D006863:Hydrogen-Ion Concentration; D008081:Liposomes; D051379:Mice; D008856:Microscopy, Fluorescence; D012710:Serum Albumin, Bovine / Q000378:metabolism
chemical_list: D001190:Arylsulfonates; D004167:Diphtheria Toxin; D004337:Drug Carriers; D008081:Liposomes; D012710:Serum Albumin, Bovine; C005047:pyranine