title: Studies on protein-liposome coupling using novel thiol-reactive coupling lipids: influence of spacer length and polarity.
abstract: To optimize the preparation of immunoliposomes, we investigated the coupling of thiolated IgG and BSA to liposomes using a novel group of coupling lipids. All lipids consist of cholesterol as membrane anchor and a thiol-reactive maleimide headgroup, linked by a spacer that differs in length and polarity (ethylene glycol, tetraethylene glycol, PEG 400, PEG 1000, dodecyl). In addition, lipids differ in the electrophilicity of the maleimide group (p- or m-maleimidobenzoic ester). In the case of BSA, coupling efficiency strongly depended on the electrophilicity of the maleimide group as well as on the spacer polarity: The less electrophilic meta constitution seems to be an advantage over the p-maleimidobenzoic ester, resulting in higher coupling efficiency. Polar spacers (tetraethylene glycol, 46%) achieved a higher coupling efficiency than a nonpolar spacer with approximately the same length (dodecyl, 15%).When liposomes containing coupling lipids with the spacers tetraethylene glycol, PEG 400, and PEG 1000 were linked to BSA, coupling efficiencies were in a medium range and similar (41-46%) but were lower for the short ethylene glycol spacer (30%). In contrast, for IgG coupling efficiencies correlated with increasing spacer length. Best results were obtained using coupling lipids with a long polar spacer (PEG 1000) (65%), whereas a coupling lipid bearing a short spacer (ethylene glycol) resulted in a low coupling efficiency of 12%.
authors.affiliation: Tumor Biology Center, Department of Clinical Research, Breisacherstr. 117, D-79106 Freiburg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Fleiner
authors.forename: P
authors.initials: P
authors.lastname: Benzinger
authors.forename: T
authors.initials: T
authors.lastname: Fichert
authors.forename: U
authors.initials: U
authors.lastname: Massing
mesh_terms: D002784:Cholesterol / Q000737:chemistry; D016503:Drug Delivery Systems; D007074:Immunoglobulin G / Q000737:chemistry*; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry*; D008081:Liposomes / Q000138:chemical synthesis* / Q000276:immunology / Q000493:pharmacokinetics; D008301:Maleimides / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry*; D011506:Proteins / Q000737:chemistry / Q000378:metabolism; D012710:Serum Albumin, Bovine / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry
chemical_list: D007074:Immunoglobulin G; D008055:Lipids; D008081:Liposomes; D008301:Maleimides; D011506:Proteins; D013438:Sulfhydryl Compounds; C043592:maleimide; D012710:Serum Albumin, Bovine; D011092:Polyethylene Glycols; D002784:Cholesterol