03716nas a2200421   4500008004100000022001400041245018800055210006900243260001500312300001200327490000900339520244300348653001202791653002702803653001102830653001902841653003102860653001202891653001202903653001402915653000902929653002102938653002002959653003002979653002503009653002003034653001303054653002603067100002003093700002003113700001903133700001503152700001903167700001603186700001903202700001903221856005403240       2001                        eng d  a0006-300200ap-Nitrophenylcarbonyl-PEG-PE-liposomes: fast and simple attachment of specific ligands, including monoclonal antibodies, to distal ends of PEG chains via p-nitrophenylcarbonyl groups.0 apNitrophenylcarbonylPEGPEliposomes fast and simple attachment of  c2001 Apr 2  a397-4110 v15113 a<p>We have attempted to simplify the procedure for coupling various ligands to distal ends of liposome-grafted polyethylene glycol (PEG) chains and to make it applicable for single-step binding of a large variety of a primary amino group-containing substances, including proteins and small molecules. With this in mind, we have introduced a new amphiphilic PEG derivative, p-nitrophenylcarbonyl-PEG-1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (pNP-PEG-DOPE), synthesized by reaction of DOPE with excess of bis(p-nitrophenylcarbonyl)-PEG in a chloroform/triethylamine mixture. pNP-PEG-DOPE readily incorporates into liposomes via its PE residue, and easily binds primary amino group-containing ligands via its water-exposed pNP groups, forming stable and non-toxic urethane (carbamate) bonds. The reaction between the pNP group and the ligand amino group proceeds easily and quantitatively at pH around 8.0, and remaining free pNP groups are promptly eliminated by spontaneous hydrolysis. Therefore, pNP-PEG-DOPE could serve as a very convenient tool for protein attachment to the distal ends of liposome-grafted PEG chains. To investigate the applicability of the suggested protocol for the preparation of long-circulating targeted liposomes, we have coupled several proteins, such as concanavalin A (ConA), wheat germ agglutinin (WGA), avidin, monoclonal antimyosin antibody 2G4 (mon2G4), and monoclonal antinucleosome antibody 2C5 (mon2C5) to PEG-liposomes via terminal pNP groups and studied whether the specific activity of these immobilized proteins is preserved. The method permits the binding of several dozens protein molecules per single 200 nm liposome. All bound proteins completely preserve their specific activity. Lectin-liposomes are agglutinated by the appropriate polyvalent substrates (mannan for ConA-liposomes and glycophorin for WGA-liposomes); avidin-liposomes specifically bind with biotin-agarose; antibody-liposomes demonstrate high specific binding to the substrate monolayer both in the direct binding assay and in ELISA. A comparison of the suggested method with the method of direct membrane incorporation was made. The effect of the concentration of liposome-grafted PEG on the preservation of specific protein activity in different coupling protocols was also investigated. It was also shown that pNP-PEG-DOPE-liposomes with and without attached ligands demonstrate increased stability in mouse serum.</p>10aAnimals10aAntibodies, Monoclonal10aAvidin10aDrug Stability10aHydrogen-Ion Concentration10aLectins10aLigands10aLiposomes10aMice10aModels, Chemical10aNitro Compounds10aPhosphatidylethanolamines10aPolyethylene Glycols10aProtein Binding10aProteins10aSurface-Active Agents1 aTorchilin, V, P1 aLevchenko, T, S1 aLukyanov, A, N1 aKhaw, B, A1 aKlibanov, A, L1 aRammohan, R1 aSamokhin, G, P1 aWhiteman, K, R  uhttp://microfluidicsciences.com/drupal/?q=node/30