Recent progress and further application of polyethylene glycol (PEG)-graftedliposomes were reviewed. PEG coating on the liposomal surface reduces the uptake by reticuloendothelial system to prolong the circulation in blood. In addition to the conventional preparation procedure, such as hydration or reversed phase evaporation method, PEG liposomes were also prepared by incubation of PEG-lipid derivatives with pre-formed liposomes. In the latter case, PEG molecules were coated on only outer surface of the liposomal membranes. Encapsulation efficiency, permeability and stability of PEG-grafted liposomes depend on the kind of PEG-lipid derivatives used. Especially, conformational change of grafted PEG from mushroom to brush structure influences on the encapsulation efficiency, permeability and finally the long-circulation properties. Passive targeting with PEG liposomal carrier system has been investigated in the field of cancer chemotherapy. Doxorubicin-encapsulated PEG liposomes(Doxil) in AIDS-related Kaposi's sarcoma is the only PEG liposomal product commercially available. As for active targeting following passive targeting to the target site, two types of PEG-immunoliposomes and ligand-attached liposomes were studied in terms of the targeting and receptor-mediated endocytosis into the target cells. There are many advantages on the use of PEG liposomal formulation for drug delivery, however, questions on the benefit of PEG-coating have been raised from the resent study. In addition to the long-circulation property of PEG liposomes, further functional properties such as degradation or fusogenicity should be required for the PEG liposomal drug delivery in the future.
抄録全体を表示