Receptor-Mediated Gene Delivery with Non-Viral DNA Carriers

Structure-activity relationships of cationic shell-crosslinked knedel-like nanoparticles: shell composition and transfection efficiency/cytotoxicity

Cationic nanoparticles are a promising class of transfection agents for oligonucleotide and gene delivery, but vary greatly in their effectiveness and cytotoxicity. Recently, we developed a new class of cationic transfection agents based on cationic shell-crosslinked knedel-like nanoparticles (cSCKs) that efficiently transfect mammalian cells with both oligonucleotides and plasmid DNA. In an effort to further improve transfection efficiency without increasing cytotoxicity, we examined the effects of the composition of primary amine (pa), tertiary amine (ta) and carboxylic acid (ca) groups in the shell of these nanoparticles. A series of discrete complexes of the cSCKs with plasmid DNA (pDNA) or phosphorothioate 2'-OMe oliogonucleotides (ps-MeON) were prepared over a broad range of amine to phosphate ratios (N/P ratio) of 4:1-40:1. The sizes of the complexes and the ability of the nanoparticles to completely bind ODNs were found to depend on the cSCK amine to DNA phosphate (N/P) ratio and the cSCK buffering capacity. The cSCKs were then evaluated for their ability to transfect cells with plasmid DNA by monitoring fluorescence from an encoded EGFP, and for delivery of ps-MeON by monitoring luminescence from luciferase resulting from ps-MeON-mediated splicing correction. Whereas the cationic cSCK-pa(25)-ta(75) was found to be best for transfecting plasmid DNA into HeLa cells at an N/P ratio of 20:1, cSCK-pa(50)-ta(50), at an N/P ratio 10:1 was best for ps-MeON delivery. We also found that increasing the proportion of tertiary relative to primary amine reduced the cytotoxicity. These results demonstrate that a dramatic improvement in gene and oligonucleotide delivery efficiency with decreased cytotoxicity in HeLa cells can be achieved by incorporation of tertiary amines into the shells of cSCKs.

Cell-specific targeting of lipid-based carriers for ODN and DNA

It is well recognized that there is an urgent need for non-toxic systemically applicable vectors for biologically active nucleotides to fully exploit the current potential of molecular medicine in gene therapy. Cell-specific targeting of non-viral lipid-based carriers for ODN and DNA is a prerequisite to attain the concentration of nucleic acids required for therapeutic efficacy in the target tissue. In this review we will address the most promising approaches to selective targeting of liposomal nucleic acid carriers in vivo. In addition, the routes of entry and intracellular processing of these carrier systems are discussed as well as physiological factors potentially interfering with the biological and/or therapeutic activity of their nucleotide pay-load.

Targeting of Lipid-Protamine-DNA (LPD) Lipopolyplexes Using RGD Motifs

The incorporation of pegylated lipid into Lipid-Protamine-DNA (LPD-PEG) lipopolyplexes causes a decrease of their in vitro transfection activity. This can be partially attributed to a reduction in particle binding to cells. To restore particle binding and specifically target LPD formulations to tumor cells, the lipid-peptide conjugate DSPE-PEG5K-succinyl-ACDCRGDCFCG-COOH (DSPE-PEG5K-RGD-4C) was generated and incorporated into LPD formulations (LPD-PEG-RGD). LPD-PEG-RGD was characterized with respect to its biophysical and biological properties. The Incorporation of DSPE-PEG5K-RGD-4C ligands into LPD formulations results in a 5 and a 15 fold increase in the LPD-PEG-RGD binding and uptake, respectively, over an LPD-PEG formulation. Enhancement of binding and uptake resulted in a 100 fold enhancement of transfection activity. Moreover, this transfection enhancement was specific to cells expressing appropriate integrin receptors (MDA-MB-231). Huh7 cells, known for their low level of alphavbeta3 and alphavbeta5 integrin expression, failed to show RGD mediated transfection enhancement. This transfection enhancement can be abolished in a competitive manner using free RGD peptide, but not an RGE control peptide. Results demonstrated RGD mediated enhanced LPD-PEG cell binding and transfection in cells expressing the integrin receptor. These formulations provide the basis for effective, targeted, systemic gene delivery.

Cationic lipid-DNA complexes-lipoplexes-for gene transfer and therapy

Cationic lipid-mediated gene transfer and delivery still attract great attention of many gene therapy laboratories. From the point of view of the most important characteristics of lipoplex particles, e.g. its charge and size, we reviewed recent studies available. In general, the paper deals with non-viral systems of gene transfer into eukaryotic cell based on various lipids. Having usually less efficiency in gene transfer, lipid-based gene transfer vehicles (lipoplexes/genosomes) are characterized with certain advantages even over viral ones: they are less toxic and immunogenic, could be targetable and are easy for large-scale production, a size of transferred DNA being quite high. Conditions of DNA condensation during interactions with lipids are described. Results of the studies of mechanism of DNA-lipid complex interactions with the cell membrane and their transport into the nucleus are summarized. Dependence of efficiency of gene transfer on lipoplex structure and physical-chemical properties is reviewed. Advantages and disadvantages of different macromolecule complexes from the point of view of transfection efficiency, possibility of use in vivo, cytotoxicity and targeted gene transfer in certain organs and tissues are also discussed. Results of transfection of different cells using neutral, anion and cation liposomes are reviewed. The conclusion reached was that efficiency and specificity of gene transfer may grow considerably when mixed macromolecule lipid systems including polycations and glycolipids are used.

Synthesis of galactosyl compounds for targeted gene delivery

Cell-specific DNA delivery offers a great potential for targeted gene therapy. Toward this end, we have synthesized a series of compounds carrying galactose residues as a targeting ligand for asialoglycoprotein receptors of hepatocytes and primary amine groups as a functional domain for DNA binding. Biological activity of these galactosyl compounds in DNA delivery was evaluated in HepG2 and BL-6 cells and compared with respect to the number of galactose residues as well as primary amine groups in each molecule. Transfection experiments using a firefly luciferase gene as a reporter revealed that compounds with multivalent binding properties were more active in DNA delivery. An optimal transfection activity in HepG2 cells requires seven primary amine groups and a minimum of two galactose residues in each molecule. The transfection activity of compounds carrying multi-galactose residues can be inhibited by asialofetuin, a natural substrate for asialoglycoprotein receptors of hepatocytes, suggesting that gene transfer by these galactosyl compounds is asialoglycoprotein receptor-mediated. These results provide direct evidence in support of our new strategy for the use of small and synthetic compounds for cell specific and targeted gene delivery.