Cytotoxicity of diphtheria toxin A fragment to toxin-resistant murine cells delivered by pH-sensitive immunoliposomes.
pH-sensitive immunoliposomes composed of dioleoylphosphatidylethanolamine and oleic acid (8:2 molar ratio) mediated the delivery of the cytotoxic fragment A of diphtheria toxin to the cytoplasm of target L-929 cells. Free fragment A, fragment A encapsulated in antibody-free liposomes, or fragment A encapsulated in pH-insensitive immunoliposomes was not effective in the inhibition of the cellular protein synthesis. pH-sensitive immunoliposomes containing diphtheria fragment A were not toxic to nontarget diphtheria-resistant A31 cells or to nontarget diphtheria-sensitive Vero cells. Pretreatment of target L-929 cells with the weak bases NH4Cl or chloroquine, agents which raise the endosome/lysosome pH, blocked the cytotoxic effect of the pH-sensitive immunoliposomes containing fragment A. Excess free antibody or excess empty pH-sensitive immunoliposomes also blocked the cytotoxic effect. Since it is known that fragment A alone cannot cross lipid membranes, the results of this study indicate that pH-sensitive immunoliposomes are able to release the toxin into the cytoplasm, probably by fusing with the endosome membrane following a receptor-mediated endocytosis of the immunoliposome.
D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004167:Diphtheria Toxin / Q000633:toxicity*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007739:L Cells / Q000166:cytology / Q000187:drug effects; D008081:Liposomes; D051379:Mice; D019301:Oleic Acid; D009829:Oleic Acids / Q000008:administration & dosage*; D010446:Peptide Fragments / Q000633:toxicity*; D010714:Phosphatidylethanolamines / Q000008:administration & dosage*; D014709:Vero Cells
D004167:Diphtheria Toxin; D008081:Liposomes; D009829:Oleic Acids; D010446:Peptide Fragments; D010714:Phosphatidylethanolamines; C029795:diphtheria toxin fragment A; D019301:Oleic Acid; C020888:1,2-dielaidoylphosphatidylethanolamine