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Background: Although polycations are among the most efficient nonviral vectors for gene transfer, the gene expression they allow is still too low for in vivo applications. To engineer more potent polycationic vectors, the factors governing the intracellular trafficking of a plasmid complexed with current polycations need to be identified., Methods and Results: The trafficking of plasmid DNA complexed to glycosylated polylysines or polyethylenimine (PEI) derivatives was studied by electron microscopy of human airway epithelial cells. The cellular processing of complexes varied with their size and the polycation derivative used: large complexes (> 200 nm) made with all polycationic vectors studied were internalized by macropinocytosis. In contrast, intermediate (100-200 nm) ligand-coupled polylysine and PEI complexes primarily entered through clathrin-coated pits. Complexes were then found in endosomal vesicles, accumulated in lysosomes or vesicles near the nucleus and their nuclear entry was limited. For the population of small complexes (< or = 100 nm) obtained with PEI derivatives, they were internalized through caveolae and pursued a traffic pattern of potocytosis to the endoplasmic reticulum where their fate remains unclear. Finally, some complexes exited the cells either by regurgitation when PEI derivatives were used or through an exosome-like pathway for glycosylated-polylysine complexes., Conclusions: The different pathways of complex trafficking observed in relation with complex size imply the development and study of vectors forming complexes with definite size. Moreover, the complex exit we describe may contribute to the well-established short-term efficiency of gene transfer based on synthetic vectors. It favors the engineering of vectors allowing repeated treatment., (2005 John Wiley & Sons, Ltd.)

In search of specific and highly selective sugar clusters for cell receptors, such as membrane lectins, various disaccharides were coupled to small peptide cores through an amide bond. In a first step, the reducing disaccharides, i.e. lactose and three different dimannoses, were converted into glycosyl-pyroglutamyl-beta-alanine derivatives. The free carboxylic group of these conjugates was then coupled to the alpha and epsilon amino groups of the core peptide (Lys( n )-Ala-Cys-NH2) with n =1 to 5, with complete substitution leading to homogeneous glycoclusters. The thiol group of the cysteine residue was used to tag the glycosylated oligolysines upon reaction with fluorescein iodoacetamide. The affinity of these glycoclusters towards two plant lectins was assessed by surface plasmon resonance. The selectivity of their cell uptake was investigated by flow cytometry using two types of cells: a human hepatoma cell line (HepG2 cells) expressing the plasma membrane galactose-specific lectin, and monocyte-derived dendritic cells expressing the plasma membrane mannose-specific lectin. The glycoclusters containing four or five disaccharides were shown to bind plant lectins and cell surface membrane lectins with a narrow selectivity and with a high affinity.

Background: We recently designed a cationic polymer called histidylated polylysine made of polylysine partially substituted with histidyl residues which become protonated at slightly acidic pH. This polymer is thought to induce the leakage of acidic vesicles containing plasmid/histidylated polylysine complexes., Methods: and results Here, we have analyzed the ability of histidylated polylysine to transfer reporter or CFTR genes into immortalized cystic fibrosis airway surface epithelial cells (sigmaCFTE29o- cells) and airway gland serous cells (CF-KM4 cells) which are both important targets for cystic fibrosis gene therapy. The luciferase reporter gene expression measured after gene transfer with histidylated polylysine into both cell lines was quite high and similar to that obtained with commercially available vectors. In addition, the level of expression was not dependent on the presence of a membrane disrupting agent such as chloroquine. Histidylated complexes were present in slightly acidic non-lysosomal cellular compartments as shown by a cytological approach using biotinylated plasmid, lysosome-specific antibodies and confocal microscopy. Histidylated complexes appeared to be of small size when prepared at low ionic strength and formed aggregates upon increasing the ionic strength. However, aggregate formation was prevented by the addition of 10% fetal bovine serum. Gene transfer efficiency varied with the size of the complexes and decreased when small particles were used., Conclusions: These results suggest that histidylated polylysine may be an efficient non-viral vector for gene transfer into cystic fibrosis airway surface epithelial cells and airway gland serous cells.

Plasmid/polylysine complexes, which are used to transfect mammalian cells, increase the uptake of DNA, but plasmid molecules are sequestered into vesicles where they cannot escape to reach the nuclear machinery. However, the transfection efficiency increases when membrane-disrupting reagents such as chloroquine or fusogenic peptides, are used to disrupt endosomal membranes and to favor the delivery of plasmid into the cytosol. We designed a cationic polymer that forms complexes with a plasmid DNA (pDNA) and mediates the transfection of various cell lines in the absence of chloroquine or fusogenic peptides. This polymer is a polylysine (average degree of polymerization of 190) partially substituted with histidyl residues which become cationic upon protonation of the imidazole groups at pH below 6.0. The transfection efficiency was optimal with a polylysine having 38 +/- 5% of the epsilon-amino groups substituted with histidyl residues; it was not significantly impaired in the presence of serum in the culture medium. The transfection was drastically inhibited in the presence of bafilomycin A1, indicating that the protonation of the imidazole groups in the endosome lumen might favor the delivery of pDNA into the cytosol.

Nucleic acids (plasmids as well as oligonucleotides) used to specifically express or modulate the expression of a gene, must reach the cytosol and/or the nucleus. Several systems have been developed to increase their uptake and their efficiency. Glycosylated polylysines have been shown to specifically help nucleic acids to be taken up in cells expressing a given cell surface membrane lectin. However, it appeared that the efficiency of the imported nucleic acid was not directly related to the extent of the uptake. Indeed, some glycosylated polylysines bearing sugar moities which are poor ligands of the cell surface lectins of a given cell were found to be more efficient than those bearing better sugar ligands. The interpretation of this paradoxal result is discussed with regards to the nature of the compartment allowing the nucleic acid to cross the membrane and to be delivered in the cytosol on the one hand, and to the presence of intracellular lectins on the other hand.

A polylysine partially substituted with polyhydroxyalkanoyl residues and specially with gluconoyl residues was developed in order to increase the transfection efficiency by decreasing the strength of the electrostatic interactions between the DNA and the cationic polymer. Partially gluconoylated polylysine/DNA complexes were more easily dissociated in solution and their transfection efficiency in the presence of chloroquine, evaluated with HepG2 cells, a human hepatocarcinoma line, was higher when 43 +/- 4% of the epsilon-amino groups of polylysine were blocked with gluconoyl residues. Partially gluconoylated polylysine/plasmid complexes were efficient in transfecting different adherent as well as non-adherent cell lines. Partially gluconoylated polylysine formed highly soluble (above 100 micrograms/ml in DNA) complexes with DNA plasmids. In addition, partially gluconoylated polylysine bearing few lactosyl residues increased the transfection efficiency of HepG2 cells which express a galactose-specific membrane lectin.

We sought to exploit glycosylated poly-L-lysine (pLK) to increase the uptake and biological antisense activity of a phosphorothioate oligonucleotide (pt-odn) [pt-odn complementary to the 3' noncoding region of intercellular adhesion molecule-1 (ICAM-1) (odn(ICAM-1))] complementary to the 3'-noncoding region of ICAM-1 in A549 cells. Dose-dependent inhibition of ICAM-1 expression was obtained (IC50 = 500 nM) through treatment of cells with odn(ICAM-1) complexed with pLK carrying fucose residues in the presence of 100 microM chloroquine. Alteration in the charge ratio between fucosylated pLK and pt-odn had a significant effect on the efficacy of inhibition (optimal conditions, charge ratio = 1.1). This effect was also dependent on the number of fucose moieties per pLK. Free pt-odn or pt-odn complexed with nonglycosylated pLK gave no inhibition at concentrations of < or = 2 microM. Two control pt-odn (one was targeted against an unrelated gene not present in these cells, gag(HIV), and the other had a randomized sequence) gave no inhibition of ICAM-1 expression in the presence or absence of pLK carrying fucose residues at concentrations of < or = 2 microM. When complexed with pLK carrying 100 fucose residues, the amount of cell-associated pt-odn was increased by 15-fold compared with the free pt-odn. Nongycosylated pLK also increased the amount of cell-associated pt-odn by >10 fold but did not alter the biological activity. These results demonstrate clearly the potential of glycosylated pLK as a pt-odn transporter.

To provide an alternative to viral vectors for the transfer of genes into airway epithelial cells in cystic fibrosis (CF), a novel set of substituted polylysines were employed. Polylysine was partially neutralized by blocking a number of positively charged residues with gluconoyl groups. In addition, polylysine was substituted with sugar residues on a specified number of amino groups. Using the gluconoylated polylysine as vector, the pCMVLuc plasmid gave high expression of the reporter gene luciferase in immortalized CF/T43 cells. The luciferase activity was 75-fold greater in the presence of 100 microM chloroquine. Luciferase gene expression persisted at high levels for up to at least 120 hr following transfection. Glycosylated polylysines/pCMVLuc complexes were compared to the gluconoylated polylysine/pCMVLuc complex and beta-Gal-, alpha-Glc-, and Lac-substituted polylysines gave 320%, 300%, and 290%, respectively, higher expression of the reporter gene luciferase. Luciferase expression ranged from 35 to 2 ng of luciferase per milligram of cell protein in the order: beta-Gal = alpha-Glc = Lac > alpha-Gal = Rha = Man > beta-GalNAc > alpha-GalNAc = alpha-Fuc, suggesting that the transfection efficiency is sugar dependent. Most importantly, in primary cultures of both CF and non-CF airway epithelial cells grown from tracheal tissue explants, lactosylated polylysine gave uniformly high expression of luciferase. The glycosylated polylysines provide an attractive nonviral approach for the transfer of genes into airway epithelial cells.

Macrophages are putative target cells for expressing an exogenous gene with therapeutical effects. Knowing that macrophages express membrane lectins mediating endocytosis of their ligands, DNA/glycosylated polylysine complexes were used to transfect human blood monocyte-derived macrophages. Monocytes from human peripheral blood were matured in culture for 7 days to differentiate into macrophage-like cells in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF). Adherent cells, which displayed characteristic macrophage markers, CD 14, CD 11b, HLA-DR, and HLA-ABC antigens and mannose receptor, were transfected by DNA/glycosylated polylysine complexes in the presence of chloroquine. The luciferase reporter gene expression was maximal 24 hr after transfection with a DNA/mannosylated polylysine complex and by using plasmids in which the promoters (either the long terminal repeat of the human immunodeficiency virus or the human cytomegalovirus) drove the luciferase gene expression. Luciferase gene expression was lower when the promoter was the early region of the large T antigen of SV40 virus. Transfection mediated by DNA/mannosylated polylysine complexes was much more efficient than with DEAE-dextran or lipofectin. The possibility of transferring and expressing an exogenous gene into macrophage-like cells by using a nonimmunogenic synthetic vector as a DNA carrier opens new ways to develop nonviral gene therapy strategies.

A process for the selective transfer of genes using glycosylated polylysine was established. Glycosylated polylysines and plasmid DNA form complexes which are taken up by cells expressing surface lectins recognizing the sugar moieties of glycosylated polylysines. Modifications made to this process allow for efficient and specific transfer in in vitro animal cell models.

A DNA delivery system based on the use of polylysine substituted with small recognition signals, such as carbohydrate moieties specifically recognized by membrane lectins present in a given cell line, has been developed [Midoux et al. (1993) Nucleic Acids Res. 21, 871-878]. Human hepatoma (HepG2) cells which express a galactose-specific membrane lectin are efficiently transfected in the presence of chloroquine with pSV2Luc plasmid complexed with a lactosylated polylysine. The optimization of the parameters involved in the formation of DNA/glycosylated polylysine complexes leads to the following conclusions: a high gene transfer efficiency is reached when (i) DNA/glycosylated polylysine complexes are completely retarded when subjected to electrophoresis and when (ii) 31 +/- 4% or 40 +/- 8% of the amino groups of a polylysine having a degree of polymerization (DP) of 190 are substituted with lactosyl or beta-D-galactosyl residues, respectively. In addition, carbohydrate residues bound to polylysine decrease the electrostatic strength between plasmid DNA and glycosylated polylysine, suggesting that the strength of the electrostatic interactions between the plasmid and the glycosylated polylysine plays an important role in the efficiency of the gene expression. The optimal lactosylated polylysine conjugate (polylysine DP 190 substituted with 60 lactosyl residues) transfers a 5 kb and a 12 kb plasmid with a similar efficiency.

Plasmid DNA/glycosylated polylysine complexes were used to transfer in vitro a luciferase reporter gene into human hepatoma cells by a receptor-mediated endocytosis process. HepG2 cells which express a galactose specific membrane lectin were efficiently and selectively transfected with pSV2Luc/lactosylated polylysine complexes in a sugar dependent manner: i) HepG2 cells which do not express membrane lectin specific for mannose were quite poorly transfected with pSV2Luc/mannosylated polylysine complexes, ii) HeLa cells which do not express membrane lectin specific for galactose were not transfected with pSV2Luc/lactosylated polylysine complexes. The transfection efficiency of HepG2 cells with pSV2Luc/lactosylated polylysine complexes was greatly enhanced either in the presence of chloroquine or in the presence of a fusogenic peptide. A 22-residue peptide derived from the influenza virus hemagglutinin HA2 N-terminal polypeptide that mimics the fusogenic activity of the virus, was selected. In the presence of the fusogenic peptide, the luciferase activity in HepG2 cells was 10 fold larger than that of cells transfected with pSV2Luc/lactosylated polylysine complexes in the presence of chloroquine.

Poly-L-lysine modified with mannose derivatives, the residual cationic charges of which being neutralized by N-acylation, were synthesized and used as carriers of a macrophage activator (N-acetylmuramyl dipeptide, MDP). The influence of the acylating agent on the targeting efficiency was investigated: a hydrosolubilizing group such as a gluconoyl moiety led to very efficient carrier conjugates, while an acetyl group did not. The effect of sugar and acyl content of the polymers was assessed using these compounds as inhibitors of red blood cell agglutination by Concanavalin A. The binding and specific endocytosis of poly-L-lysine substituted with several mannose derivatives and gluconoyl residues (GlcAx-, Man(y)-PLK) have been determined by a quantitative flow cytometry analysis. MDP bound to these conjugates was much more efficient in vitro than free MDP in macrophage cytostasis assays.

Mammalian cells express several types of lectins involved in intracellular trafficking, including endocytosis, interorganelle routing and putatively nuclear import. In order to enhance the gene transfer efficiency, glycosylated cationic polymers have been used as nonviral vectors. We developed a simple method to convert reducing saccharides into glycosynthons. Glycosynthons are used to synthesize cationic glycopolymers, called Glycofectins. Glycofectins interact with a plasmid to give a glycoplex, a compacted form of a polymer/DNA complex. The high glycoplex efficiency depends on the sugar involved in the uptake and in the intracellular trafficking of glycoplexes. The present paper deals with glycoplexes, with gene transfer into cystic fibrosis airway epithelial and gland serous cells, and with some of the problems that have to be solved before clinical trials. [ABSTRACT FROM AUTHOR]