In the present study, a non-covalent (biotin–streptavidin) coupling procedure for the preparation of pegylated immunoliposomes is presented, which simplifies the attachment of targeting vectors to sterically stabilized liposomes. A biotinylated poly(ethylene glycol) (PEG)-phospholipid [bio-PEG-distearoylphosphatidylethanolamine (DSPE)] was used as a linker between a streptavidin-conjugated monoclonal antibody (mAb) (i.e. the OX26 mAb raised against the rat transferrin receptor) and 150 nm liposomes. OX26–streptavidin had a biotin binding capacity of two to three biotin molecules per OX26–streptavidin conjugate. Immunostaining experiments with the OX26 mAb followed by fluorescent confocal microscopy revealed immunofluorescence labelling of the transferrin receptor on skeletal muscle, as well as in L6 cells, a continuous cell line derived from rat skeletal muscle. Uptake experiments with L6 cells using the OX26 mAb, fluorescence-labelled OX26–streptavidin or fluorescent OX26-immunoliposomes demonstrated cellular uptake and accumulation within an intracellular compartment of the OX26 mAb and its conjugates. Cellular uptake of OX26 conjugates was sensitive to competition with free OX26 antibody. In summary, these studies describe the design of biotinylated immunoliposomes as a universal drug transport vector and their potential for targeting of the transferrin receptor of skeletal muscle.
Abbreviations used: DSPC, distearoylphosphatidylcholine; FCS, fetal-calf serum; mAb, monoclonal antibody; MBS, m-maleimidobenzoyl-N-hydroxysuccinimide ester; PEG, poly(ethylene glycol); PEG-DSPE, PEG-derivatized distearoylphosphatidylethanolamine; bio-PEG-DSPE, biotinylated PEG-DSPE.