Studies on carbohydrate-binding proteins using liposome-based systems--I. Preparation of neoglycoprotein-conjugated liposomes and the feasibility of their use as drug-targeting devices

Effective uptake of N-acetylglucosamine-conjugated liposomes by cardiomyocytes in vitro

A drug delivery system (DDS) that targets the injured myocardium would serve as a novel therapeutic tool for cardiac diseases. To develop such a DDS, we investigated the interaction of 2 types of glycoside-conjugated liposomes containing a fluorescence substrate with cardiomyocytes. Flow cytometry revealed that cardiomyocytes adequately interact with N-acetylglucosamine-conjugated liposomes (GlcNAc-Ls). Furthermore, to confirm whether the agents encapsulated in GlcNAc-Ls affect the intracellular environment of cardiomyocytes, we prepared GlcNAc-Ls-containing pravastatin and examined the effect of pravastatin on cardiomyocytes. Pravastatin is a 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor (statin) and is hydrophilic. It is reported that lipophilic statins enhance nitric oxide (NO) production and inducible nitric oxide synthase (iNOS) expression by interleukin-1beta (IL-1beta)-stimulated cardiomyocytes. The hydrophilic nature of pravastatin prevents its entry into cardiomyocytes; therefore, it cannot enhance both these processes. Treatment with GlcNAc-Ls-containing pravastatin specifically enhanced NO production and iNOS expression by IL-1beta-stimulated cardiomyocytes. Based on these results, we found that cardiomyocytes exhibit a high degree of interaction with GlcNAc-Ls, and GlcNAc-Ls-encapsulated agents can be effectively taken up by cardiomyocytes. We suggest that GlcNAc-Ls can be utilized therapeutically as a DDS for the injured myocardium.

Surface modification of liposomes by saccharides: vesicle size and stability of lactosyl liposomes studied by photon correlation spectroscopy

The cell glycocalyx is an attractive model for surface modification of liposomes, because its hydrated oligosaccharide layer inhibits nonspecific protein adsorption and can provide specificity towards desired sites. Here, we report on the use of lactose as a model saccharide to modify the liposome surface and examine the vesicle size and stability. Two kinds of lactosyl lipids, including lactosyl ether-lipid (6a) and lactosyl ester-lipid (6b), which contain octadecyl and octadecanoyl as the lipid tails, respectively, were synthesized and their liposomes were prepared by the extrusion method. The effects of glycolipid structure, concentration, and the pore size of the extrusion membrane on vesicle size and stability were investigated at room temperature by photon correlation spectroscopy (PCS). All liposomes with 5 or 10 mol% of lactosyl lipids had a narrow size distribution and remained stable at room temperature for at least one month, which is comparable to 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)- and poly(ethylene glycol) (PEG)-liposomes. The maximum incorporation of lactosyl ester-lipid into liposomes was 15 mol%, compared with only 10 mol% for the lactosyl ether-lipid. The lactosyl ester-liposomes had better stability and exhibited less size change than the lactosyl ether-liposomes at 15 or 20 mol% of lactosyl lipids incorporated. This may be attributed to the better structural compatibility of lactosyl ester-lipid with DSPC. The PCS results show that the glycolipid structure and concentrations are major factors that affect vesicle stability, while the pore size of extrusion membranes has no influence.

Targeting of liposomes to melanoma cells with high levels of ICAM-1 expression through adhesive peptides from immunoglobulin domains

The P(0) protein is an immunoglobulin [Ig] superfamily cell adhesion molecule from peripheral nerve myelin. Synthetic peptides derived from the P(0) protein and leukocyte function-associated antigen-1 (LFA-1) were investigated as potential ligands for targeting liposomes to intercellular adhesion molecule-1 (ICAM-1) expressing melanoma cells. Three synthetic P(0) peptides and one LFA-1 peptide were selected for linkage to liposome surfaces. P(0)-peptide-1, from the extracellular Ig-like domain, increased liposome binding to M21 (6.36-fold) and A-375 (1.85-fold) cells compared to control blank liposomes, but did not increase liposome binding to MeM 50-10 cells. P(0)-peptide-3, from the basic intracellular domain, increased binding of liposomes to all three melanoma cell lines nonspecifically due to its high content of positively charged amino acids. LFA-1- and negative control arg-gly-asp (RGD)-peptides did not affect liposome binding to M21 cells. The extent of P(0)-peptide-1-liposome binding to human melanoma cell lines correlated with the level of cellular ICAM-1 expression (r(2) = 0.868). P(0)-peptide-1-mediated targeting of liposomes might, therefore, prove useful in the development of drug delivery systems for treatment of ICAM-1 expressing malignant melanomas.

Endogenous lectins as targets for drug delivery

To minimize side effects of drugs it would be ideal to target them exclusively to those cell types which require treatment. As a means to this end prototypical cellular recognition systems pique our interest to devise biomimetic strategies. Since oligosaccharides of glycoconjugates outmatch other information-carrying biomolecules (proteins, nucleic acids) in theoretical storage capacity by far, work on the sugar code can spark off development of effective targeting devices. Conjugation of custom-made glycan epitopes to proteins or biocompatible non-immunogenic polymeric scaffolds produces neoglycoconjugates with purpose-adaptable properties. In the interplay with endogenous receptors such as lectins, suitable oligosaccharides such as histo-blood group trisaccharides as parts of neoglycoconjugates have already proven their practical applications in histopathology. Elucidation of the structure of cell lectins with currently five main families aids to tailor ligand characteristics rationally. They include the types of functional groups and their topological presentation to optimize the bimolecular binding as well as the optimal spatial clustering and spacer characteristics to exploit cooperativity. Indeed, the potent trivalent cluster glycosides designed for the C-type asialoglycoprotein receptors furnish an instructive example how to turn the theoretical guideline on ligand modification into nM-affinity. By placing emphasis on tissue lectins as targets of neoglycoconjugate-mediated drug delivery, the long-term perspective is opened to likewise test members of these families themselves for routing of therapeutic payloads, aiming at cell addressins. This review illustrates the conceivable potential which work on the sugar code with custom-made neoglycoconjugates and tissue lectins can have in store for drug delivery.

P0 protein mediated targeting of liposomes to melanoma cells with high level of ICAM-1 expression

The feasibility of targeting liposomes reconstituted with P0 protein (P0-liposomes) to melanoma cells with high level of intercellular adhesion molecule-1 (ICAM-1) expression was investigated. P0 protein, an immunoglobulin superfamily (IgSF) cell adhesion molecule from peripheral nerve myelin, was used as a model targeting ligand. Liposome uptake by the cells was quantitated using radioactive lipids. The presence of intact P0 protein in the liposome bilayer increased the extent of interaction of liposomes with human M21 (7.80 fold) and A-375 (4.62 fold) melanoma cells compared to control liposomes of same lipid composition but no P0 protein, whereas with MeM 50-10 melanoma cells no significant increase was found (1.70 fold). The extent of binding of P0-liposomes to the melanoma cells correlated with the level of ICAM-1 expression on cells (r2 = 0.9996). M21 and A-375 cells express ICAM-1 (the percentage of stained cells, PSC, was 95% and 85%, respectively), whereas, MeM 50-10 cells do not. P0 protein also increased the interaction of liposomes with P0 protein expressing CHO-X2 cells (4.36 fold, as a positive control) compared to control liposomes. The indirect flow cytometry experiments using biotinylated P0 protein showed that P0 protein itself in solution also binds to M21 cells but does not bind to MeM 50-10 cells. Preincubation of M21 cells with anti-ICAM-1 monoclonal antibody decreased the binding of biotinylated P0 protein to the M21 cells by 35%. P0 protein or its binding domain(s) that mediate the targeting of liposomes through adhesive interactions may be useful for the development of novel types of drug delivery systems. This approach may have relevance in the treatment of metastatic cancers, inflammation and viral diseases, where cell adhesion proteins are over expressed.

Receptor mediated glycotargeting

Glycotargeting relies on carrier molecules possessing carbohydrates that are recognized and internalized by cell surface mammalian lectins. Numerous types of glycotargeting vehicles have been designed based on the covalent attachment of saccharides to proteins, polymers and other aglycones. These carriers have found their major applications in antiviral therapy, immunoactivation, enzyme replacement therapy and gene therapy. This review compared different types of glycotargeting agents and the lectins which have been successfully targeted to treat both model and human diseases. It may be concluded that the discovery of new mammalian lectins which endocytose their ligands will lead to the rapid development of new glycotargeting agents founded on the principles of carbohydrate-protein interactions.

Mode of action of the anti-influenza virus activity of plant flavonoid, 5,7,4'-trihydroxy-8-methoxyflavone, from the roots of Scutellaria baicalensis

When mouse-adapted influenza virus A/PR/8/34 (A/PR8) (10 PFU/cell) was adsorbed to Madin-Darby canine kidney (MDCK) cells at 4 degrees C for 1 h and incubated at 37 degrees C, release of the virus from the cells was detected in the medium from 4 h after incubation and reached to plateau at 8 h. However, 5,7,4'-trihydroxy-8-methoxyflavone (F36) from the roots of Scutellaria baicalensis significantly reduced this single-cycle replication of A/PR8 from 4 h to 12 h after incubation by dose-dependent manner and the dose which decrease the virus titer one tenth was 11 microM. F36 (50 microM) did not inhibit the adsorption of A/PR8 to MDCK cells, but reduced release of the virus in the medium, when it was added at 0 or 2 h after the incubation. The cell-associated virus determined by sialidase activity was also reduced by F36 treatment at 0 or 2 h. F36 also inhibited the fusion of A/PR8 with liposomes containing bovine brain mixed gangliosides at pH 5.0. However, F36 little affected on the elongation activity of the viral RNA-dependent RNA polymerase in vitro. These results suggest that F36 reduces the replication of A/PR8 by inhibiting the fusion of the virus with endosome/lysosome membrane which occurs at early stage of virus infection cycle. Whereas, when F36 was added to the MDCK cells infected with A/PR8 at 3 or 4 h after incubation, release of the virus in the medium was reduced but the cell-associated virus was increased in comparison with control.(ABSTRACT TRUNCATED AT 250 WORDS)