[Biotinylated pH-sensitive liposomes--containers for guided administration of biologically active substances to the...

The technique is described for obtaining pH-sensitive biotinylated liposomes. The liposomes included phosphatidyl ethanolamine, oleic acid, cholesterol, biotin amidocaproyl phosphatidyl ethanolamine, with a molar ratio of 7:3:3:0.1 or 4:2:4:0.1. The fluorescein stain calcein at ++self-limited concentration, 32-P-dTTP, or DNA was incorporated into the internal liposome medium. The liposomes were stable in neutral or mildly alkaline medium but became leaky and showed agglutination at pH 5.7. Liposomes were agglutinated in the presence of avidin and bound specifically to the layer of avidin on the surface of immunological plates. The apparent liposome affinity to the avidin layer was up to 10(-11) M. The avidin-biotin system allows for specific binding of liposomes to human lymphocytes via biotinylated anti-CD5-antibodies. A simple, convenient, and rapid procedure has been elaborated for the binding of water-soluble substances (plasmid DNA included) to liposomes without DNA destruction.