Targeted gene transfer into hepatoma cells with lipopolyamine-condensed DNA particles presenting galactose ligands: a stage toward artificial viruses

Cationic liposomes for gene delivery

Cationic liposome-DNA complexes (lipoplexes) constitute a potentially viable alternative to viral vectors for the delivery of therapeutic genes. This review will focus on various parameters governing lipoplex biological activity, from their mode of formation to in vivo behaviour. Particular emphasis is given to the mechanism of interaction of lipoplexes with cells, in an attempt to dissect the different barriers that need to be surpassed for efficient gene expression to occur. Aspects related to new trends in the formulation of lipid-based gene delivery systems aiming at overcoming some of their limitations will be covered. Finally, examples illustrating the potential of cationic liposomes in clinical applications will be provided.

Lipoplexes with biotinylated transferrin accessories: Novel, targeted, serum-tolerant gene carriers

Novel transfecting assemblies comprising biotinylated cationic liposomes, DNA and tribiotinylated transferrin-streptavidin (streptavidin(bio3-transferrin)) accessories have been prepared, characterized and evaluated for toxicity and DNA delivery capability in human cervical carcinoma cells (HeLa). Two new lipophilic cholesteryl-based biotin derivatives, biotinylcholesterylformylhydrazide (MSB1) and aminohexanoylbiotinylcholesterylformylhydrazide (MSB2) provided docking points for streptavidin(bio3-transferrin) on cationic liposomes which were formulated with N,N-dimethylaminopropylaminylsuccinylcholesterylformylhydrazide (MS09) and dioleoylphosphatidylethanolamine (DOPE) in a 2:48:50 molar ratio. Ethidium dye displacement assays and gel retardation studies suggest that in ternary complexes, the DNA is electrostatically bound to the cationic liposomes while transferrins remain liposome-bound through streptavidin-biotin interactions. Assemblies fully protected plasmid DNA from serum nuclease digestion over a range of liposome:pGL3 DNA ratios (3-8:1, w/w) and exhibited low growth inhibition of HeLa cells (circa 5%) at the optimal transfection composition for streptavidin(bio3-transferrin):liposome:pGL3 DNA of 10:6:1 (w/w/w). Transfection levels, which were twice those of untargeted lipoplexes containing MSB1 or MSB2, were not significantly diminished in the presence of 10% foetal bovine serum. Excess transferrin (200 microg per well) reduced transfection levels to those of untargeted complexes, supporting the notion that at least 50% of ternary complexes gained entry into the cervical carcinoma cells by receptor mediation. Conversely, transfection levels with untargeted lipoplexes were only slightly reduced in the presence of transferrin at the same concentration.

Ligand-Targeted Delivery of Therapeutic siRNA

RNA interference (RNAi) is a post-transcriptional gene-silencing phenomenon that is triggered by double-stranded RNA (dsRNA). Since many diseases are associated with the inappropriate production of specific proteins, attempts are being made to exploit RNAi in a clinical settings. However, before RNAi can be exploited as therapeutically, several obstacles must be overcome. For example, small interfering RNA (siRNA) is unstable in the blood stream so any effects of injected siRNA are only transient. Accordingly, methods must be developed to prolong its activity. Furthermore, the efficient and safe delivery of siRNA into target tissues and cells is critical for successful therapy. Any useful delivery method should be designed to target siRNA to specific cells and to promote gene-silencing activity once the siRNA is inside the cells. Recent chemical modifications of siRNA have overcome problems associated with the instability of siRNA, and various ligands, including glycosylated molecules, peptides, proteins, antibodies and engineered antibody fragments, appear to be very useful or have considerable potential for the targeted delivery of siRNA. The use of such ligands improves the efficiency, specificity and, as a consequence, the safety of the corresponding delivery systems.

Intracellular trafficking of nonviral vectors

Nonviral vectors continue to be attractive alternatives to viruses due to their low toxicity and immunogenicity, lack of pathogenicity, and ease of pharmacologic production. However, nonviral vectors also continue to suffer from relatively low levels of gene transfer compared to viruses, thus the drive to improve these vectors continues. Many studies on vector-cell interactions have reported that nonviral vectors bind and enter cells efficiently, but yield low gene expression, thus directing our attention to the intracellular trafficking of these vectors to understand where the obstacles occur. Here, we will review nonviral vector trafficking pathways, which will be considered here as the steps from cell binding to nuclear delivery. Studies on the intracellular trafficking of nonviral vectors has given us valuable insights into the barriers these vectors must overcome to mediate efficient gene transfer. Importantly, we will highlight the different approaches used by researchers to overcome certain trafficking barriers to gene transfer, many of which incorporate components from biological systems that have naturally evolved the capacity to overcome such obstacles. The tools used to study trafficking pathways will also be discussed.

Genetic modification of hematopoietic stem cells with nonviral systems: past progress and future prospects

Serious unwanted complications provoked by retroviral gene transfer into hematopoietic stem cells (HSCs) have recently raised the need for the development and assessment of alternative gene transfer vectors. Within this context, nonviral gene transfer systems are attracting increasing interest. Their main advantages include low cost, ease of handling and large-scale production, large packaging capacity and, most importantly, biosafety. While nonviral gene transfer into HSCs has been restricted in the past by poor transfection efficiency and transient maintenance, in recent years, biotechnological developments are converting nonviral transfer into a realistic approach for genetic modification of cells of hematopoietic origin. Herein we provide an overview of past accomplishments in the field of nonviral gene transfer into hematopoietic progenitor/stem cells and we point at future challenges. We argue that episomally maintained self-replicating vectors combined with physical methods of delivery show the greatest promise among nonviral gene transfer strategies for the treatment of disorders of the hematopoietic system.

A cationic cytofectin with long spacer mediates favourable transfection in transformed human epithelial cells

The synthesis and transfection potential of a novel cationic cholesterol cytofectin with a dimethylamino head group and a long 12 atom, 15A spacer incorporating relatively polar amido and dicarbonyl hydrazine linkages are reported. Thus N,N-dimethylaminopropylamidosuccinylcholesterylformylhydrazide (MS09) in equimolar admixture with dioleoylphosphatidylethanolamine (DOPE) forms stable unilamellar liposomes (80-150 nm) which cluster into very effective transfecting, serum nuclease-resistant, lipoplexes with DNA (180-200 nm) at a liposome+/DNA- molar charge ratio of 2.8:1 (12:1, w/w). Gel retardation and ethidium displacement assays confirmed that DNA was fully liposome-associated and maximally compacted at this ratio. Transfection levels in three human transformed epithelial cell lines, as established by luciferase transgene activity, was found to be optimal at this charge ratio and in the following order: cervical carcinoma (HeLa)>oesophageal carcinoma (SNO)>hepatoblastoma (HepG2). Activity in the murine fibroblast line NIH-3T3 was comparable to that in HepG2 cells. MS09 lipoplexes achieved approximately three-times and two-times greater activity than Lipofectin complexes in HeLa and SNO cells, respectively, whilst comparable levels were recorded in HepG2 and NIH-3T3 cells. MS09 lipoplexes were well tolerated by HepG2, HeLa and SNO cells with cell numbers found to be 80, 85 and 75% of untreated cultures, respectively, at the optimal transfection concentration. These lipoplexes also exhibited high activity in the presence of 10% foetal bovine serum (FBS) in HeLa (17% inhibition) and HepG2 (33% inhibition) cells.

Galactosylated polyethylenimine-graft-poly(vinyl pyrrolidone) as a hepatocyte-targeting gene carrier

Polyethylenimine (PEI) has been used for the gene delivery system in vitro and in vivo since it has high transfection efficiency owing to proton buffer capacity. However, the use of PEI for gene delivery is limited due to cytotoxicity, non-specificity and unnecessary interaction with serum components. To overcome cytotoxicity and non-specificity, PEI was coupled with poly(vinyl pyrrolidone) (PVP) as the hydrophilic group to reduce cytotoxicity and lactose bearing galactose group for hepatocyte targeting. The galactosylated-PEI-graft-PVP (GPP) was complexed with DNA, and GPP/DNA complexes were characterized. GPP showed good DNA binding ability, high protection of DNA from nuclease attack. The sizes of DNA complexes show tendency to decrease with an increase of charge ratio and had a minimum value around 59 nm at the charge ratio of 40 for the GPP-1/DNA complex (PVP content: 4.1 mol%). The GPP showed low cytotoxicity. And GPP/DNA complexes were mediated by asialoglycoprotein receptors (ASGP-R)-mediated endocytosis. Also, the transfection efficiency of GPP-1/DNA complex at charge ratio of 40 in the HepG2 was higher than that of PEI/DNA one.

Characteristics and biodistribution of soybean sterylglucoside and polyethylene glycol-modified cationic liposomes and their complexes with antisense oligodeoxynucleotide

A novel cationic liposome modified with soybean sterylglucoside (SG) and polyethylene glycol-distearoylphosphatidylethanolamine (PEG-DSPE) as a carrier of antisense oligodeoxynucleotide (ODN) for hepatitis B virus (HBV) therapy was constructed. Characteristics of the cationic liposomes modified with SG and PEG (SG/PEG-CL) and their complexes with 15-mer phosphorothioate ODN (SG/PEG-CL-ODN complex) were investigated by incorporation efficiency, morphology, electrophoresis, zeta potentials, and size analysis. Antisense activity of the liposomes and ODN complexes was determined as hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) in HepG2 2.2.15 cells by ELISA. Their tissue and intrahepatic distribution were evaluated following intravenous injection in mice. The complexes gained high incorporation efficiency and intact vesicular structure with mean size at approximately 200 nm. The SG/PEG-CL-ODN complexes enhanced the inhibition of both HBsAg and HBeAg expression in the cultured HepG2 2.2.15 cells relative to free ODN. The uptake of SG/PEG-CL and nonmodified cationic liposomes (CL) was primarily by liver, spleen, and lung. Furthermore, the concentration of SG/PEG-CL was significant higher than that of CL in hepatocytes at 0.5 hr postinjection. The biodistribution of SG/DSPE-CL-ODN complex compare with free ODN showed that liposomes enhanced the accumulation of ODN in the liver and spleen, while decreasing its blood concentration. SG/PEG-CL-mediated ODN transfer to the liver is an effective gene delivery method for cell-specific targeting, which has a potential for gene therapy of HBV infections. SG and PEG-modified cationic liposomes have proven to be an alternative carrier for hepatocyte-selective drug targeting.

Synthetic, self-assembly ABCD nanoparticles; a structural paradigm for viable synthetic non-viral vectors

Gene therapy research is still in trouble owing to a paucity of acceptable vector systems to deliver nucleic acids to patients for therapy. Viral vectors are efficient but may be too dangerous. Synthetic non-viral vectors are inherently safer but are currently not efficient enough to be clinically viable. The solution for gene therapy lies with improved synthetic non-viral vectors systems. This review is focused on synthetic cationic liposome/micelle-based non-viral vector systems and is a critical review written to illustrate the increasing importance of chemistry in gene therapy research. This review should be of primary interest to synthetic chemists and biomedical researchers keen to appreciate emerging technologies, but also to biological scientists who remain to be convinced about the relevance of chemistry to biology.

Hepatocytes targeting of cationic liposomes modified with soybean sterylglucoside and polyethylene glycol

AIM

In this study, a hepatocyte-specific targeting technology was developed by modifying cationic liposomes with soybean sterylglucoside (SG) and polyethylene glycol (PEG) (C/SG/PEG-liposomes).

METHODS

The liposomal transfection efficiencies in HepG(2) 2.2.15 cells were estimated with the use of fluorescein sodium (FS) as a model drug, by flow cytometry. The antisense activity of C/SG/PEG-liposomes entrapped antisense oligonucleotides (ODN) was determined as HBsAg and HBeAg in HepG(2) 2.2.15 cells by ELISA. The liposome uptake by liver and liver cells in mice was carried out after intravenous injection of (3)H-labeled liposomes.

RESULTS

C/SG-liposomes entrapped FS were effectively transfected into HepG(2) 2.2.15 cells in vitro. C/SG/PEG-liposomes entrapped ODN, reduced the secretion of both HBsAg and HBeAg in HepG(2) 2.2.15 cells when compared to free ODN. After in vivo injection of (3)H-labeled C/SG/PEG-liposomes, higher radiation accumulation was observed in the hepatocytes than non-parenchymal cells of the liver.

CONCLUSION

C/SG/PEG-liposomes mediated gene transfer to the liver is an effective gene-delivery method for hepatocytes-specific targeting, which appears to have a potential for gene therapy of HBV infections.

Ligands of the asialoglycoprotein receptor for targeted gene delivery, part 1: Synthesis of and binding studies with biotinylated cluster glycosides containing N-acetylgalactosamine

In order to develop the non-viral Bioplex vector system for targeted delivery of genes to hepatocytes, we have evaluated the structure-function relationship for a number of synthetic ligands designed for specific interaction with the hepatic lectin ASGPr. Biotinylated ligand derivatives containing two, three or six beta-linked N-acetylgalactosamine (GalNAc) residues were synthesized, bound to fluorescent-labeled streptavidin and tested for binding and uptake to HepG2 cells using flow cytometry analysis (FACS). Uptake efficiency increased with number of displayed GalNAc units per ligand, in a receptor dependent manner. Thus, a derivative displaying six GalNAc units showed the highest uptake efficacy both in terms of number of internalizing cells and increased amount of material taken up per each cell. However, this higher efficiency was shown to be due not so much to higher number of sugar units, but to higher accessibility of the sugar units for interaction with the receptor (longer spacer). Improving the flexibility and accessibility of a trimeric GalNAc ligand through use of a longer spacer markedly influenced the uptake efficiency, while increasing the number of GalNAc units per ligand above three only provided a minor contribution to the overall affinity. We hereby report the details of the chemical synthesis of the ligands and the structure-function studies in vitro.

A bio-recognition device developed onto nano-crystals of carbonate apatite for cell-targeted gene delivery

The DNA delivery to mammalian cells is an essential tool for analyzing gene structure, regulation, and function. The approach holds great promise for the further development of gene therapy techniques and DNA vaccination strategies to treat and control diseases. Here, we report on the establishment of a cell-specific gene delivery and expression system by physical adsorption of a cell-recognition molecule on the nano-crystal surface of carbonate apatite. As a model, DNA/nano-particles were successfully coated with asialofetuin to facilitate uptake by hepatocyte-derived cell lines through the asialoglycoprotein receptor (ASGPr) and albumin to prevent non-specific interactions of the particles with cell-surface. The resulting composite particles with dual surface properties could accelerate DNA uptake and enhance expression to a notable extent. Nano-particles coated with transferrin in the same manner dramatically enhanced transgene expression in the corresponding receptor-bearing cells and thus our newly developed strategy represents a universal phenomenon for anchoring a bio-recognition macromolecule on the apatite crystal surface for targeted gene delivery, having immediate applications in basic research laboratories and great promise for gene therapy.

Enhanced hepatocyte-selective in vivo gene expression by stabilized galactosylated liposome/plasmid DNA complex using sodium chloride for complex formation

In this study, we demonstrated that the presence of an essential amount of sodium chloride (NaCl) during the formation of cationic liposome/plasmid DNA complexes (lipoplexes) stabilizes the lipoplexes according to the surface charge regulation (SCR) theory. Fluorescence resonance energy transfer analysis revealed that cationic liposomes in an SCR lipoplex (5 and 10 mM NaCl solution in lipoplex) increased fusion. Also, aggregation of SCR lipoplexes was significantly delayed after exposure to saline (150 mM NaCl) as a model of physiological conditions. After intraportal administration, the hepatic transfection activity of galactosylated SCR lipoplexes (5 and 10 mM NaCl solution in lipoplex) was approximately 10- to 20-fold higher than that of galactosylated conventional lipoplexes in mice. The transfection activity in hepatocytes of galactosylated SCR lipoplexes was significantly higher than that of conventional lipoplexes, and preexposure to competitive asialoglycoprotein-receptor blocker significantly reduced the hepatic gene expression, suggesting that hepatocytes are responsible for high hepatic transgene expression of the galactosylated SCR lipoplexes. Pharmacokinetic studies both in situ and in vivo demonstrated a higher tissue binding affinity and a greater expanse of intrahepatic distribution by galactosylated SCR lipoplexes. Moreover, enhanced transfection activity of galactosylated SCR lipoplexes was observed in HepG2 cells, and investigation of confocal microscopic images showed that the release of plasmid DNA in the cell was markedly accelerated. These characteristics partly explain the mechanism of enhanced in vivo transfection efficacy by galactosylated SCR lipoplexes. Hence, information in this study will be valuable for the future use, design, and development of ligand-modified lipoplexes for in vivo applications.

Polyethyleneimine grafted with pluronic P85 enhances Ku86 antisense delivery and the ionizing radiation treatment efficacy in vivo

In an effort to improve the efficacy of antisense delivery, we evaluated polyethyleneimine (PEI, 2 kDa) alone or grafted with nonionic amphiphilic block copolymer Pluronic (P85) as a carrier for Ku86 antisense oligonucleotide (ASO) delivery. Ku86 is an abundant nuclear protein that plays an important role in nonhomologous DNA end joining and has implications in tumorigenesis and acquired drug resistance. Transfection of adherent and suspension cell lines with Ku86 ASOs complexed with P85-g-PEI (2 kDa) conjugates was associated with a specific decrease in Ku86 mRNA levels (EC50<75 nM and EC50<250 nM, respectively, n=3). More importantly, no requirement for reduced serum conditions was necessary during transfection. In contrast, whereas Ku86 ASOs complexed with PEI (2 kDa) alone were effective in decreasing Ku86 mRNA levels in adherent cell lines (EC50<75 nM, n=3), the formulation did not produce any detectable decrease in Ku86 mRNA levels in suspension cell lines. Transfection of adherent cell lines with 500 nM Ku86 ASOs formulated with P85-g-PEI (2 kDa) was associated with a specific decrease (<10% remaining of control) in Ku86 protein expression and a two-fold increased cell death after treatment with ionizing radiation (IR). In athymic nude mice bearing subcutaneous human HT29 colon adenocarcinoma xenografts, Ku86 ASO-P85-g-PEI (2 kDa) administration (15 mg/kg, subcutaneously) with a Q1D x 7 treatment schedule, when combined with a single dose of IR (6 Gy), caused a significant inhibition of HT29 tumor growth compared with mismatch- and naked antisense-pretreated control groups (time from 200 to 1000 mm3, 126.9 versus 84.18 and 87.76 days, P<0.005). A potentiation of the antitumor activity was observed in all mice treated with Ku86 ASO-P85-g-PEI (2 kDa) formulation; however, tumor growth inhibition was reversible upon treatment cessation. No morbidity/mortality or changes in histopathology were observed under this treatment regiment. Our results indicate that P85-g-PEI (2 kDa) conjugates may increase the efficacy of Ku86 ASO delivery in management of resistant malignancies, thus providing a rationale for their evaluation in cancer patients in combination with conventional anticancer therapies.

Advanced strategies in liposomal cancer therapy: problems and prospects of active and tumor specific drug release

Tumor specific drug delivery has become increasingly interesting in cancer therapy, as the use of chemotherapeutics is often limited due to severe side effects. Conventional drug delivery systems have shown low efficiency and a continuous search for more advanced drug delivery principles is therefore of great importance. In the first part of this review, we present current strategies in the drug delivery field, focusing on site-specific triggered drug release from liposomes in cancerous tissue. Currently marketed drug delivery systems lack the ability to actively release the carried drug and rely on passive diffusion or slow non-specific degradation of the liposomal carrier. To obtain elevated tumor-to-normal tissue drug ratios, it is important to develop drug delivery strategies where the liposomal carriers are actively degraded specifically in the tumor tissue. Many promising strategies have emerged ranging from externally triggered light- and thermosensitive liposomes to receptor targeted, pH- and enzymatically triggered liposomes relying on an endogenous trigger mechanism in the cancerous tissue. However, even though several of these strategies were introduced three decades ago, none of them have yet led to marketed drugs and are still far from achieving this goal. The most advanced and prospective technologies are probably the prodrug strategies where non-toxic drugs are carried and activated specifically in the malignant tissue by overexpressed enzymes. In the second part of this paper, we review our own work, exploiting secretory phospholipase A2 as a site-specific trigger and prodrug activator in cancer therapy. We present novel prodrug lipids together with biophysical investigations of liposome systems, constituted by these new lipids and demonstrate their degradability by secretory phospholipase A2. We furthermore give examples of the biological performance of the enzymatically degradable liposomes as advanced drug delivery systems.

Lipid Carrier Systems for Targeted Drug and Gene Delivery

For effective chemotherapy, it is necessary to deliver therapeutic agents selectively to their target sites, since most drugs are associated with both beneficial effects and side effects. The use of lipid dispersion carrier systems, such as lipid emulsions and liposomes, as carriers of lipophilic drugs has attracted particular interest. A drug delivery system can be defined as a methodology for manipulating drug distribution in the body. Since drug distribution depends on the carrier, administration route, particle size of the carrier, lipid composition of the carrier, electric charge of the carrier and ligand density of the targeting carrier, these factors must be optimized. Recently, the lipid carrier system has also been applied to gene delivery systems for gene therapy. However, in both drug and gene medicine cases, a lack of cell-selectivity limits the wide application of this kind of drug and/or gene therapy. Therefore, lipid carrier systems for targeted drug and gene delivery must be developed for the rational therapy. In this review, we shall focus on the progress of research into lipid carrier systems for drug and gene delivery following systemic or local injection.

What Role Can Chemistry Play in Cationic Liposome‐Based Gene Therapy Research Today?

Gene therapy research is still in trouble owing to a paucity of acceptable vector systems to deliver nucleic acids to patients for therapy. Viral vectors are efficient but may be too dangerous for routine clinical use. Synthetic non-viral vectors are inherently much safer but are currently not efficient enough to be clinically viable. The solution for gene therapy lies with improved synthetic non-viral vectors based upon well-found platform technologies and a thorough understanding of the barriers to efficient gene delivery and expression (transfection) relevant to clinical applications of interest. Here we introduce and interpret synthetic non-viral vector systems through the ABCD nanoparticle structural paradigm that represents, in our view, an appropriate lens through which to view all synthetic, non-viral vector systems applicable to in vitro use or in vivo applications and gene therapy. Our intention in introducing this paradigm is to shift the focus of organic and physical chemists away from the design of yet another cytofectin, and instead encourage them to appreciate the wider challenges presented by the need to produce tool kits of meaningful chemical components from which to assemble viable, tailor-made nanoparticles for in vivo applications and gene therapy, both now and in the future.

Targeting of Polyplexes: Toward Synthetic Virus Vector Systems

Dominating issues in gene vector optimization are specific in recognizing the target cells and exploiting the proper intracellular trafficking routes. Any progress in this area will result in improved specific gene transfer, reduce the required therapeutic vector doses and, in consequence, lower the overall toxicity to the host. To provide polyplexes with the ability to distinguish between non-target and target cells, cell-binding ligands have been incorporated which recognize target-specific cellular receptors. In addition, polyplex domains with unspecific binding capacity (such as surface charges) have to be shielded or removed. Cell-binding ligands can be small molecules, vitamins, carbohydrates, peptides or proteins such as growth factors or antibodies. Such ligands have been incorporated into polyplexes after chemical conjugation to cationic polymers. The choice of the ligand and physical properties of the DNA formulation strongly influence extracellular routing (circulation in blood, tissue distribution), uptake and intracellular delivery of polyplexes. Recent efforts are discussed that aim at the development of polyplexes into virus-like supramolecular complexes; such particles should undergo structural changes compatible with extracellular and intracellular targeting.

Structural investigations of DNA-polycation complexes

The internal structure of DNA-polycation complexes is investigated by synchrotron small-angle X-ray scattering (SAXS). Hexagonal packing of DNA is observed for DNA complexed with poly-L-lysine (PL), poly-L-arginine (PA), spermine (Sp), and linear and branched polyethyleneimine (lPEI and bPEI, respectively). Variations in the internal spacings and degree of long-range ordering are dependent on both polycation type and concentration of added salt. With increasing concentration of monovalent salt, a discontinuous phase transition is observed from compact to loose bundles and finally to an isotropic network phase. This salt-induced melting transition was found to be universal for all polyplexes studied and is in quantitative agreement with a simple free energy model based solely on electrostatic and entropic contributions. Using the osmotic stress method, bulk modulus (K) is measured for PL-DNA and PA-DNA polyplexes at various salt concentrations. With increasing osmotic force, we show that the salt-induced melting transition is shifted and compression in the loose bundle regime is in qualitative agreement with our model.

Polynorbornene polycationic polymers as gene transfer agents. Influence of the counterion for in vitro transfection

Polycationic derivatives of polynorbornene with different non-cytotoxic counterions, have been prepared by organometallic polymerization of methyleneammonium norbornene and subsequent exchange of the counterion. In this paper the effect of the counterion on the polycationic polymer binding onto plasmid DNA was studied via different ethidium bromide assays, heparin displacement and protection against degradation by DNAse. According to the nature of the counterions and consequently the size of the polymer particles, their complexation with the DNA led to aggregates with variable binding affinity for the plasmid. The relative transfection efficiency of each polyplex was compared, on the basis of reporter gene expression, in cells in culture. The nature of the counterion was seen to affect gene delivery. The order of transfection efficiency of the counterions studied at equivalent charge ratios (NH3+/PO4-) is lactobionate, acetate, chloride. The results obtained with the polynorbornene methyleneammonium lactobionate and acetate are particularly encouraging.

Engineering synthetic vectors for improved DNA delivery: insights from intracellular pathways

Significant progress has been made in the area of nonviral gene delivery to date. Yet, synthetic vectors remain less efficient by orders of magnitude than their viral counterparts. Research continues toward unraveling and overcoming various barriers to the efficient delivery of DNA, whether in plasmid form encoding a gene or as an oligonucleotide for the selective inhibition of target gene expression. Novel components for overcoming these hurdles are continually being incorporated into the design of synthetic vectors, leading to increasingly more virus-like particles. Despite these advances, general principles defining the design of synthetic vectors are yet to be developed fully. A more quantitative analysis of the cellular uptake and intracellular processing of these vectors is required for the rational manipulation of vector design. Mathematical frameworks with a more conceptual basis will help obtain an integrated perspective on these complex systems. In this review, we critically examine the progress made toward the improved design of synthetic vectors by the strategic exploitation of intracellular mechanisms and explore newer possibilities to overcome obstacles in the practical realization of this field.

A New Triantennary Galactose-Targeted PEGylated Gene Carrier, Characterization of Its Complex with DNA, and Transfection of Hepatoma Cells

Nonviral gene vectors remain inefficient in vivo largely because of their rapid clearance from the circulation and also their nonspecific association with the extracellular matrix. To overcome such drawbacks, cationic lipoplexes are now frequently coated with hydrophilic polymers such as PEGs to reduce nonspecific interactions, and ligands are also linked to their surface to obtain cell-specific gene transfer. In view of the development of vectors for systemic gene delivery, we have designed and studied lipoplexes that carry a triantennary galactosyl ligand attached to the distal end of a (PEG)45-conjugated lipid. We incorporated this targeted PEGylated lipid into lipoplexes using two strategies of formulation, i.e., using either preformed micelles or liposomes. We demonstrated that the incorporation of PEG chains stabilized lipoplexes and masked, but only partially, the positive charges exposed on the surface of the particles. We have also shown that incorporation into lipoplexes of a lipidated PEG chain, bearing a ligand at its distal end, yielded particles that exhibited an accessible ligand throughout the whole range of cationic lipid to DNA ratios. We obtained a targeted transfection in HepG2 cells with one of the formulations. Our results strengthen the validity of using a ligand carried by a long PEG spacer arm for targeted gene transfer.

Tissue and intrahepatic distribution and subcellular localization of a mannosylated lipoplex after intravenous administration in mice

We have previously reported that, unlike a lipoplex and mannosylated (Man) lipoplex underwent gene transfer to liver nonparenchymal cells (NPC) that possess mannose receptors after intravenous administration in mice. In this study, the tissue, intrahepatic distribution, and subcellular localization of the lipoplex after intravenous administration were investigated. DC-Chol liposome was selected as a cationic liposomes. After administration of lipoplex and Man lipoplex, the high gene expression was observed in the lung and liver, respectively. After administration of [32P]Man lipoplex, about 80% of [32P]plasmid DNA (pDNA) was accumulated in the liver. As for the intrahepatic distribution, the NPC/parenchymal cells (PC) ratio of [32P]Man lipoplex was 9.64, whereas the NPC/PC ratio of [32P]lipoplex was 1.93. The radioactivity in the cytosolic fraction of liver homogenate of [111In]Man lipoplex was two-fold higher than that of [111In]lipoplex, indicating that Man liposomes facilitate the release of pDNA into the cytosolic space. However, a rapid sorting of the radioactivity from endosomes to lysosomes was observed with the [111In]Man lipoplex. Also, amplification of pDNA by PCR suggested that the Man lipoplex is more rapidly degraded within the intracellular vesicles than the lipoplex. These results suggested that modulation of its intracellular sorting could improve the transfection efficiency of Man lipoplex.

Targeted gene delivery into HepG2 cells using complexes containing DNA, cationized asialoorosomucoid and activated cationic liposomes

Unilamellar activated cationic liposomes containing 3beta[N-(N',N'-dimethylaminopropane)-carbamoyl] cholesterol, dioleoyl phosphatidylethanolamine (DOPE) and the N-hydroxysuccinimide ester of cholesteryl hemisuccinate (4:5:1, molar ratio) have been prepared and their DNA-binding capacity has been assessed in a gel retardation assay. Ternary complexes composed of activated cationic liposomes, carbodiimide-cationized asialoorosomucoid (Me+AOM) and pRSVL plasmid DNA were assembled for receptor-mediated DNA delivery into cells expressing the asialoglycoprotein receptor (ASGP-R). Binding of complexes in which Me+AOM was replaced by fluoresceinated Me+AOM (FMe+AOM) to the human hepatocellular cell line HepG2 at 4 degrees C was severely reduced by co-incubation with asialoorosomucoid (AOM). Moreover, assemblies containing liposomes, pRSVL DNA and Me+AOM (8:1:4, w/w/w) promoted high levels of luciferase activity in this cell line (1.3 x 10(7) relative light units/mg soluble cell protein). Assays conducted in the presence of a hundred-fold excess of the ligand AOM afforded considerably lower levels of transfection (2.5 x 10(5) relative light units/mg soluble cell protein). In contrast, the highest level of luciferase activity achieved with liposome, pRSVL DNA, AOM complexes was only a quarter of the best levels obtained with liposome, pRSVL DNA, Me+AOM assemblies. These findings strongly support the notion that complexes gain entry into hepatocyte-derived cells by ASGP-R mediation and that they are potentially useful gene carriers to liver hepatocytes.

On the interpretation of Raman spectra of 1-aminooxy-spermine/DNA complexes

By FT-Raman spectroscopy, we have investigated the effect of 1-aminooxy-spermine (AOSPM) on aggregation and stability of calf-thymus DNA and selected oligonucleotide chains. AOSPM is able to mimic spermine in some macromolecular interactions, but is unable to substitute polyamines to maintain cell proliferation, suggesting pharmacological applications. Raman spectra of solutions containing AOSPM and either genomic DNA or two 15mer oligodeoxyribonucleotides, with GC or AT sequences, were recorded. Precipitation was observed for calf-thymus DNA, aggregated structures and appearance of several Z marker bands were observed for the 15mer GC sequence, and no macromolecular changes were detected for the 15mer AT sequence. Specific binding sites between the aminooxy group and the base residues were also evidenced. Assignment of the AOSPM Raman bands was supported on a normal mode calculation for the molecule NH(2)-O-CH(3), as a model. The theoretical results, in combination with the analysis of the Raman bands, demonstrated that the aminooxy group played a relevant role in the AOSPM-DNA interaction. Preferential binding by the major groove was evidenced in the absence of macromolecular changes. When either precipitation or aggregation occurred, the interaction involved both the major and minor grooves. The specific interaction between AT/GC base pairs and the aminooxy group has also been theoretically investigated. The biological relevance of this work is discussed.

Interactions of heparin with human skin cells: Binding, location, and transdermal penetration

The development of new materials for tissue engineering of skin substitutes requires an increasing knowledge of their interactions with human skin cells. Since carbohydrate recognition is involved in numerous biologic processes, including skin regeneration, the aim of this study was to identify sugar receptors expressed at the surface of human dermic and epidermic cells. Binding of fluorescent sugar-polyhydroxyethylacrylamide derivatives was analyzed by flow cytofluorimetry on cultured human skin fibroblasts, keratinocytes, and melanocytes. We observed that these three cell types express a membrane receptor specific for GlcNAc6S. Since the polysaccharide heparin contains this sugar moiety, we further investigated the interactions of heparin with skin cells. We analyzed the in vitro cell binding and ex vivo diffusion with the Franz cell of heparin and of two other polysaccharides of similar molecular weight, dextran and chondroitin sulfate. We found evidence of the preferential binding of heparin on keratinocytes and its high transcutaneous penetration of skin. Altogether, our results describe the affinity of heparin for human skin cells and suggest it may be an excellent candidate for use in the skin delivery of drugs or cosmetics and also as an active component in engineered skin.

Visualization of transfection of hepatocytes by galactosylated chitosan-graft-poly(ethylene glycol)/DNA complexes by confocal laser scanning microscopy

Dual-labeled galactosylated chitosan-graft-poly(ethylene glycol) (PEG) (GCP)/DNA complexes were prepared and their hepatocyte-specific delivery and cellular distribution were investigated by confocal laser scanning microscopy (CLSM). The complexes were transfected into hepatocyte through specific interaction of galactose moiety of the GCP and asialoglycoprotein receptors (ASGPR) of the hepatocytes. The GCP/DNA complexes taken up by the hepatocytes were rapidly released into the cytoplasm, but nuclear trafficking of the released complexes was slow and rate-limiting process. The more efficient transfection of the complex occurred in the human-derived HepG2 cells than in primary hepatocytes.

Lattice model for the kinetics of rupture of fluid bilayer membranes

We have constructed a model for the kinetics of rupture of membranes under tension, applying physical principles relevant to lipid bilayers held together by hydrophobic interactions. The membrane is characterized by the bulk compressibility (for expansion) K, the thickness 2h(t) of the hydrophobic part of the bilayer, the hydrophobicity sigma, and a parameter gamma characterizing the tail rigidity of the lipids. The model is a lattice model which incorporates strain relaxation, and considers the nucleation of pores at constant area, constant temperature, and constant particle number. The particle number is conserved by allowing multiple occupancy of the sites. An equilibrium "phase diagram" is constructed as a function of temperature and strain with the total pore surface and distribution as the order parameters. A first-order rupture line is found with increasing tension, and a continuous increase in protopore concentration with rising temperature till instability. The model explains current results on saturated and unsaturated phosphatidylcholine lipid bilayers and thicker artificial bilayers made of diblock copolymers. Pore size distributions are presented for various values of area expansion and temperature, and the fractal dimension of the pore edge is evaluated.

Calcium phosphate nanoparticles as novel non-viral vectors for targeted gene delivery

Calcium phosphate nanoparticles present a unique class of non-viral vectors, which can serve as efficient and alternative DNA carriers for targeted delivery of genes. In this study we report the design and synthesis of ultra-low size, highly monodispersed DNA doped calcium phosphate nanoparticles of size around 80 nm in diameter. The DNA encapsulated inside the nanoparticle is protected from the external DNase environment and could be used safely to transfer the encapsulated DNA under in vitro and in vivo conditions. Moreover, the surface of these nanoparticles could be suitably modified by adsorbing a highly adhesive polymer like polyacrylic acid followed by conjugating the carboxylic groups of the polymer with a ligand such as p-amino-1-thio-beta-galactopyranoside using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride as a coupling agent. We have demonstrated in our studies that these surface modified calcium phosphate nanoparticles can be used in vivo to target genes specifically to the liver.

Synthesis of antisense oligonucleotides conjugated to a multivalent carbohydrate cluster for cellular targeting

Carrier-mediated delivery holds great promise for significantly improving the cellular uptake and therefore the therapeutic efficacy of antisense oligonucleotides in vivo. A multivalent carbohydrate recognition motif for the asialoglycoprotein receptor has been designed for tissue- and cell-specific delivery of antisense drugs to parenchymal liver cells. To combine low molecular weight with high receptor affinity, the synthetic ligand contains three galactosyl residues attached to a cholane scaffold via epsilon-aminocapramide linkers. Three-dimensional structural calculations indicate that this unique design provides proper spacing and orientation of the three galactosyl residues to accomplish high affinity binding to the receptor. Covalent conjugation of the bulky carbohydrate cluster to oligonucleotides has been achieved by solid-phase synthesis using low-loaded macroporous resins and optimized synthesis protocols.

Evaluation of lipid-based reagents to mediate intracellular gene delivery

We characterized different cationic lipid-based gene delivery systems consisting of both liposomes and nonliposomal structures, in terms of their in vitro transfection activity, resistance to the presence of serum, protective effect against nuclease degradation and stability under different storage conditions. The effect of lipid/DNA charge ratio of the resulting complexes on these properties was also evaluated. Our results indicate that the highest levels of transfection activity were observed for complexes prepared from nonliposomal structures composed of FuGENE 6. However, their DNA protective effect was shown to be lower than that observed for cationic liposome formulations when prepared at the optimal (+/-) charge ratio. Our results suggest that lipoplexes are resistant to serum up to 30% when prepared at a 2:1 lipid/DNA charge ratio. However, when they were prepared at higher (+/-) charge ratios, they become sensitive to serum for even lower concentrations (10%). Replacement of dioleoyl-phosphatidylethanolamine (DOPE) by cholesterol enhanced the resistance of the complexes to the inhibitory effect of serum. This different biological activity in the presence of serum was attributed to different extents of binding of serum proteins to the complexes, as evaluated by the immunoblotting assay. Studies on the stability under storage show that lipoplexes maintain most of their biological activity when stored at -80 degrees C, following their fast freezing in liquid nitrogen.

Gene therapy as an alternative to liver transplantation

Liver transplantation has become a well-recognized therapy for hepatic failure resulting from acute or chronic liver disease. It also plays a role in the treatment of certain inborn errors of metabolism that do not directly injure the liver. In fact, the liver maintains a central role in many inherited and acquired genetic disorders. There has been a considerable effort to develop new and more effective gene therapy approaches, in part, to overcome the need for transplantation as well as the shortage of donor livers. Traditional gene therapy involves the delivery of a piece of DNA to replace the faulty gene. More recently, there has been a growing interest in the use of gene repair to correct certain genetic defects. In fact, targeted gene repair has many advantages over conventional replacement strategies. In this review, we will describe a variety of viral and nonviral strategies that are now available to the liver. The ever-growing list includes viral vectors, antisense and ribozyme technology, and the Sleeping Beauty transposon system. In addition, targeted gene repair with RNA/DNA oligonucleotides, small-fragment homologous replacement, and triplex-forming and single-stranded oligonucleotides is a long-awaited and potentially exciting approach. Although each method uses different mechanisms for gene repair and therapy, they all share a basic requirement for the efficient delivery of DNA.

Prospects for cationic polymers in gene and oligonucleotide therapy against cancer

Gene and antisense/ribozyme therapy possesses tremendous potential for the successful treatment of genetically based diseases, such as cancer. Several cancer gene therapy strategies have already been realized in vitro, as well as in vivo. A few have even reached the stage of clinical trials, most of them phase I, while some antisense strategies have advanced to phase II and III studies. Despite this progress, a major problem in exploiting the full potential of cancer gene therapy is the lack of a safe and efficient delivery system for nucleic acids. As viral vectors possess toxicity and immunogenicity, non-viral strategies are becoming more and more attractive. They demonstrate adequate safety profiles, but their rather low transfection efficiency remains a major drawback. This review will introduce the most important cationic polymers used as non-viral vectors for gene and oligonucleotide delivery and will summarize strategies for the targeting of these agents to cancer tissues. Since the low efficiency of this group of vectors can be attributed to specific systemic and subcellular obstacles, these hurdles, as well as strategies to circumvent them, will be discussed. Local delivery approaches of vector/DNA complexes will be summarized and an overview of the principles of anticancer gene and antisense/ribozyme therapy as well as an outline of ongoing clinical trials will be presented.

Polyamine structural effects on the induction and stabilization of liquid crystalline DNA: potential applications to DNA packaging, gene therapy and polyamine therapeutics

DNA undergoes condensation, conformational transitions, aggregation and resolubilization in the presence of polyamines, positively charged organic molecules present in all cells. Under carefully controlled environmental conditions, DNA can also transform to a liquid crystalline state in vitro. We undertook the present work to examine the ability of spermidine, N4-methylspermidine, spermine, N1-acetylspermine and a group of tetramine, pentamine and hexamine analogs of spermine to induce and stabilize liquid crystalline DNA. Liquid crystalline textures were identified under a polarizing microscope. In the absence of polyamines, calf thymus DNA assumed a diffused, planar cholesteric phase with entrapped bubbles when incubated on a glass slide at 37 degrees C. In the presence of spermidine and spermine, the characteristic fingerprint textures of the cholesteric phase, adopting a hexagonal order, were obtained. The helical pitch was 2.5 micro m. The final structures were dendrimeric and crystalline when DNA was treated with spermine homologs and bis(ethyl) derivatives. A cholesteric structure was observed when DNA was treated with a hexamine at 37 degrees C. This structure changed to a hexagonal dendrimer with fluidity on prolonged incubation. These data show a structural specificity effect of polyamines on liquid crystalline phase transitions of DNA and suggest a possible physiological function of natural polyamines.

Repeated cationic multilamellar liposome-mediated gene transfer enhanced transduction efficiency against murine melanoma cell lines

We investigated whether repeated cationic multilamellar liposome-mediated gene transfers enhanced the transduction efficiency against murine melanoma cell lines and experimental subcutaneous melanoma. In the former, the murine melanoma cell line, B16F10, was transfected by our original cationic multilamellar liposomes containing pVLacZ, which express beta-galactosidase in eukaryotic cells. Cells were exposed to the liposomes in a single, double, or triple procedure during the cell logarithmic proliferative period. We then evaluated the transduction efficiency by X-gal staining and beta-galactosidase assay. The number of positive cells and level of beta-galactosidase activity were significantly increased by repeated exposures compared with a single one. Cells transfected by the fluorescently labeled cationic liposome containing pEGFP-C1 showed both an increased uptake of liposomes and an increased number of EGFP expression cells following repeated exposures. In the latter, murine subcutaneous melanomas, which were made by transplantation of B16F10 in C57BL6 mice, were transfected by same liposomes. Subcutaneous melanomas were exposed to the liposomes in a single, double, or triple procedure. We then evaluated the transduction efficiency by the beta-galactosidase assay. The level of beta-galactosidase activity was significantly increased by repeated exposures compared with a single one. The results indicate that repeated exposures to the liposomes enhanced the transduction efficiency toward murine melanoma cells and experimental subcutaneous melanoma, and may provide a basis for the repeated-exposure protocol for human trials.

Liver- and lobe-selective gene transfection following the instillation of plasmid DNA to the liver surface in mice

The present study has undertaken the liver- and lobe-selective gene transfections following the instillation of plasmid DNA (pDNA) to the liver surface in mice. The luciferase levels produced in the applied (left) liver lobe at 6 h after liver surface instillation of pDNA were significantly higher than those produced in the other tissues assayed, and ranged from 8.5-fold higher in other liver lobes to 320-fold higher in other tissues. After small intestine surface instillation of pDNA, the gene expression was a little detected in the tissues assayed. Following liver surface instillation of pDNA at a time from 2 to 48 h or at a volume from 15 to 120 microl, the gene expressions of the applied liver lobe were always significantly higher than those of other liver lobes and other tissues. We demonstrated the novel liver- and lobe-selective gene transfection utilizing the instillation to the liver surface.

Nonviral approaches satisfying various requirements for effective in vivo gene therapy

Development of an efficient method of gene introduction to target cells is the key issue in treating genetic and acquired diseases by in vivo gene therapy. Although various nonviral approaches have been developed, any method needs to be optimized in terms of the target disease and transgene product. The most important information required is (i) target cell-specificity of gene transfer, (ii) efficiency, (iii) duration of transgene expression, and (iv) the number of transfected cells following in vivo application of a vector. These characteristics are determined by the properties of the vector used, as well as the route of its administration, biodistribution, interaction with biological components and the nature of the target cells. Cell-specific gene transfer can be achieved by controlling the tissue disposition of plasmid DNA (pDNA), although the interaction of the pDNA complex with biological components might limit the specificity. Various approaches have been reported to increase the efficiency of transgene expression, from cationic lipids/polymers to physical stimuli, but some of those are ineffective under in vivo conditions. The duration of transgene expression is a complex function involving variables including the cell type, transfection method, and plasmid construct. Immune response often reduces the level and duration of transgene expression. In addition, the number of transfected cells is important, especially in cases in which the therapeutic protein localizes within the target cells. Successful clinical application of nonviral gene delivery methods rely on the development of such methods optimized for a particular target disease.

Role of intracellular cationic liposome-DNA complex dissociation in transfection mediated by cationic lipids

The cationic lipid-mediated gene transfer process involves sequential steps: internalization of the cationic lipid-DNA complexes inside the cells via an endocytosis-like mechanism, escape from endosomes, dissociation of the complex, and finally entry of free DNA into the nucleus. However, cationic lipid-DNA complex dissociation in the cytoplasm and the ability of the subsequently released DNA to enter the nucleus have not yet been demonstrated. In this report we showed, using confocal laser scanning analysis, that microinjection of a double fluorescent-labeled cationic lipid-pCMV-LacZ plasmid complex into the cytoplasm of HeLa cells results in efficient complex dissociation. However, the released DNA did not enter the nucleus, and no significant transfection could be detected. In contrast, nuclear microinjection of the cationic lipid-pCMV-LacZ plasmid complex resulted in efficient complex dissociation and transfection of all the cells. Taken together, the data suggest that intracellular dissociation of the cationic lipid-DNA complex is not a limiting step for transfection as previously thought.

Nucleic acid biotechnology

Driven by advances in the acquisition of genetic sequence information and the ability to manipulate small quantities of nucleic acid, a number of technologies are emerging that exploit nucleic acids for research, diagnostic, and therapeutic utility. In this review, we cover three technologies based on nucleic acids--DNA microarrays, antisense technology, and gene therapy--that are especially promising and may make a substantial impact in the laboratory and in the clinic during the coming years. For each of these areas, an overview of the current status and applications is provided, followed by a discussion of critical issues and challenges to be faced for further advancement of the technology; an emphasis is placed on quantitative and engineering aspects.

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.

The nuclear pore complex is involved in nuclear transfer of plasmid DNA condensed with an oligolysine-RGD peptide containing nuclear localisation properties

One of the major barriers to efficient gene transfer and expression of nonviral vectors for gene therapy is passage across the nuclear envelope. We have previously shown that an oligolysine-RGD peptide that condenses plasmid DNA and binds to cell surface integrins can mediate increased internalisation of plasmid DNA into cells and synergistic enhancement of gene expression when complexed to a cationic lipid. In this report, we show that this enhancement is due to increased nuclear transfer of the plasmid DNA. We have applied the digitonin-permeabilised cell system that has been well established for the study of the nuclear transport of proteins to examine the nuclear transfer of plasmid DNA. Nuclear transfer of plasmid DNA complexed to an oligolysine-RGD peptide and lipofectamine appears to be an energy-dependent process involving the nuclear pore complex, since it is inhibited at 4 degrees C and by treatment with wheat germ agglutinin or with an antibody to the nuclear pore complex which all block nuclear protein import. In accordance with active nuclear transport, we have shown that all these treatments inhibit expression of a luciferase reporter plasmid in permeabilised cells. Nuclear transfer of pDNA is enhanced in mitotic cells, but cell division is not a prerequisite for transfer. We propose that the oligolysine-RGD peptide acts as a nuclear localisation signal and that the cationic lipid is more important for cell entry and endosome destabilisation than nuclear transfer.

Gene delivery with synthetic (non viral) carriers

Non-viral gene delivery involving the use of cationic polymer and cationic lipid based carriers still continues to enjoy a high profile due to the safety advantages offered by these systems when compared with viruses. However, there are still problems associated with the use of these agents, notably their comparatively low efficiency and the inability to target gene expression to the area of pathology. On intravenous administration gene expression is found predominantly in the first capillary bed encountered-the lung endothelium. The clinical use of non-viral gene delivery systems in cystic fibrosis or cancer has involved their direct application to the site of pathology due to the targeting difficulties experienced. For gene expression to occur genes must be transported to the interior of the cell nucleus and a number of biological barriers to effective gene delivery have been identified. These may be divided into extracellular such as the targeting barrier mentioned above and intracellular such as the need for endosomal escape after endocytosis and the inefficient trafficking of genes to the nucleus. Targeting ligands have been used with moderate success to overcome the targeting barrier while endosomal escape and nuclear targeting peptides are some of the strategies, which have been employed to overcome the problems of endosomal escape and nuclear trafficking. It is hoped that the next generation of carriers will incorporate mechanisms to overcome these barriers thus improving the efficacy of such materials.

Gene therapy of pain: emerging strategies and future directions

Gene therapy to alleviate pain could appear surprising and perhaps not appropriate when opioids and other active molecules are available. However, the possibility of introducing a therapeutic protein into some targeted structures, where it would be continuously synthesised and exert its biological effect in the near vicinity of, or inside the cells, might avoid some drawbacks of "classical" drugs. Moreover, the gene-transfer techniques might improve present therapies or lead to novel ones. The recent significant and constant advances in vector systems design suggest that these techniques will be available in the near future for safe application in humans. The first experimental protocols attempting the transfer of opioid precursors genes, leading to their overexpression at the spinal level, demonstrated the feasibility and the potential interest of these approaches. Indeed, overproduction of opioid peptides in primary sensory neurones or spinal cord induced antihyperalgesic effects in various animal models of persistent pain. However, numerous other molecules involved in pain processing or associated with chronic pain have been identified and the gene-based techniques might be particularly adapted for the evaluation of the possible therapeutic interest of these new potential targets.

Liver-targeted gene transfer into a human hepatoblastoma cell line and in vivo by sterylglucoside-containing cationic liposomes

We investigated the transfection efficiency of beta-sitosterol beta-D-glucoside (Sit-G)-containing liposome/DNA complex (Sit-G-liposome/DNA complex) for liver targeting. The Sit-G-liposome/DNA complex was composed of Tfx-20 reagent (Tfx), ie synthetic cationic lipid [N,N,N',N'-tetramethyl-N,N'-bis(2-hydroxyethyl)-2,3-di(oleoyloxy)-1,4-butanediammonium iodide] with L-dioleoylphosphatidylethanolamine (DOPE), 3 beta[N-(N',N'-dimethylaminoethane)-carbamoyl]cholesterol (DC-Chol) and Sit-G with plasmid DNA. The in vitro studies were performed in HepG2 cells in serum-containing medium and the in vivo studies were carried out in the mice following intravenous injection. The Sit-G-liposome produced a Sit-G-liposome/DNA complex of relatively small size (100--250 nm). Transfection efficiency of the luciferase marker gene by Sit-G-liposome/DNA complex was increased in the presence of 10% serum in vitro, and was selectively high in the mouse liver reaching expression values up to an average of 14.9 pg luciferase/mg tissue protein, compared with Tfx/DNA complex, which showed approximately three-fold higher gene expression than Sit-G-liposome/DNA complex in vitro. High in vitro transfection efficiency by Sit-G-liposome/DNA complex seemed to be possible even with large lipid precipitates, whereas high in vivo activity seemed to be related to small and dispersed complexes. The interaction of liposome/DNA complexes with serum may be a key point to predict the in vivo efficiency of a liposome vector.

DNA/polyethylenimine transfection particles: influence of ligands, polymer size, and PEGylation on internalization and gene expression

Receptor-binding ligands have been incorporated into DNA/polyethylenimine (PEI) complexes to enhance cell binding and cellular internalization. This study characterizes receptor-mediated uptake of DNA/PEI complexes on a cellular basis. A novel assay based on flow cytometry was applied, discriminating between total cell-associated and extracellularly bound DNA complexes. Receptor-mediated uptake of ligand-containing DNA/PEI (molecular weight, 800 kd) complexes was found to occur quickly (within 1 hour), whereas unspecific uptake through adsorptive endocytosis is less efficient or requires extended periods to reach the same degree of internalization. Rapid, receptor-mediated internalization requires a small complex size; however, large, aggregated complexes show higher gene expression. Using PEI 25 kd conjugated to large proteins such as transferrin or antibodies, improper condensation with DNA leads to suboptimal uptake and gene expression, whereas partial replacement of ligand-PEI with unconjugated PEI increases both uptake and transfection. In contrast, the 8 kd protein epidermal growth factor conjugated to PEI 25 kd properly condenses DNA and mediates specific uptake into human adenocarcinoma (KB) cells. Modification of the complex surface with appropriate amounts of poly(ethylene glycol) (PEG) does not block ligand-mediated internalization. A higher degree of PEGylation reduces the internalization of transferrin or antibody-containing complexes to a level similar to that of ligand-free complexes. In contrast, epidermal growth factor "mediated uptake is less effected by excessive PEGylation.