A powerful nonviral vector for in vivo gene transfer into the adult mammalian brain: polyethylenimine

Uptake and intracellular fate of polyethylenimine in vivo

Branched polyamines are extensively used as nonviral vectors for plasmid DNA in transfection experiments. Moreover, recently it has been shown that these compounds are able to eliminate prions from infected cells in cultures. It has been proposed that in both cases endosomes or lysosomes are the site of action. This raises the question of how these molecules are taken up by the cells and what is their intracellular fate. In the work presented here, the question has been addressed by investigating the uptake and the intracellular distribution of branched polyethyleneimine (25 kD) by centrifugation methods. The polyamine was labelled with (125)I-tyramine cellobiose and injected to the rat. The radioactive polymer is taken up after injection into the liver, kidney, spleen, and lungs and remains in these organs for many days. In the liver, it is found mainly in the hepatocytes. Intracellular distribution of radioactivity present in that organ was investigated by differential and isopycnic centrifugations. Early after injection, radioactivity exhibits a distribution pattern similar to that of alkaline phosphodiesterase, a plasma membrane marker. Later, the distribution pattern becomes similar to that of cathepsin C, a lysosomal enzyme. Radioactivity and hydrolase distributions in a sucrose gradient are similarly modified by a pretreatment of the rat with Triton-WR1339, a specific density perturbant of lysosomes. These results indicate that polyethyleneimine is endocytosed and reaches lysosomes. For many days it persists in these organelles probably due to its resistance to lysosomal hydrolases.

Characterization of commercially available and synthesized polyethylenimines for gene delivery

Five new polyethylenimines (PEI) were synthesized by polymerization of aziridine in aqueous solution and compared to several commercially available PEI used for gene transfer. Polymers were characterized by 13C NMR spectroscopy, capillary viscosimetry, potentiometric titration and Cu(II) complex formation to gain insight into structural and functional properties. 13C NMR analysis revealed differences in the extent of branching based on the ratio of primary, secondary and tertiary amino groups. An amino group ratio 1 degrees :2 degrees :3 degrees =1:2:1 was obtained for the synthesized PEI, whereas commercially available PEI generally showed a higher degree of branching (1:1:1). Capillary viscosimetry of aqueous PEI solutions with a sufficient amount of salt gave Mark-Houwink parameters of alpha=0.26 and K(V)=1.00 cm(3)/g for the commercially available polymers. In case of the synthesized polymers, variation of reaction conditions yielded viscosity average molar masses (M(v)) in the range of 8000-24000 g/mol. PEI solutions were investigated by potentiometric titration analysis showing that their buffer capacity was not significantly influenced by molar mass or polymer structure. The pK(a) values (8.18-9.94) and the buffer capacity beta (0.08-0.014 mol/l) were of comparable magnitude. This study highlights the necessity of more detailed characterization methods for PEI used in gene transfer protocols since physico-chemical properties do not reflect the vast differences found in transfection efficiencies.

Translocating peptides and proteins and their use for gene delivery

A dramatic surge in the development of peptides for gene delivery in vitro and in vivo has been witnessed in the past decade. A better understanding of the structural and mechanistic properties of peptides has been an important step for the rational design of optimal peptide-based gene delivery systems. Research has focused on the design of short synthetic peptides that overcome both extracellular and intracellular limitations of other gene delivery systems by binding reversibly and condensing DNA, specifically targeting cells and/or tissues, rapidly releasing plasmids into the cytoplasm and mediating efficient nuclear translocation.

Development of biomaterials for gene therapy

Novel biocompatible polymeric gene carriers have been examined for their potential in treating various genetic and acquired diseases. The use of polymeric gene carriers may overcome the current problems associated with viral vectors in safety, immunogenicity, and mutagenesis. However, effective polymer-based gene therapy requires the control of cellular access and uptake, intracellular trafficking, and nuclear retention of plasmid DNA. Inefficient endosomal release, cytoplasmic transport, and nuclear entry of plasmids are currently limiting factors in the use of polymers for effective plasmid-based gene therapy. Therefore, several different polymeric gene carriers have been designed recently in an attempt to overcome these problems. This review explores the conceptual and experimental aspects of polymer-based gene delivery and presents an overview on the recent use of polymers to enhance the effectiveness of plasmid-based systems. Despite their current limitations, polymeric carriers have significant potential as commercially viable gene medicines.

Use of polyethylenimine-adenovirus complexes to examine triplex formation in intact cells

Triplex-forming oligonucleotides (TFOs) show potential for sequence-specific DNA binding and inhibition of gene expression. We have applied this antigene strategy using a TFO incorporating an Auger-emitting radionucleotide, 125I, to study the production of double-strand breaks (dsb) in the rat aquaporin 5 (rAQP5) cDNA. 125I-TFO bound to the pCMVrAQP5 plasmid in vitro in a dose-dependent manner and formed stable triplexes up to 65 degrees C and in the presence of 140 mM KCl. Further, 125I-TFO resulted in a predictable dsb when analyzed by Southern hybridization. To deliver TFOs to epithelial cells, we employed 125I-TFO-polyethyleneimine-adenovirus (125I-TFO-PEI-Ad) complexes. We hypothesized that these complexes would take advantage of adenoviral characteristics to transfer 125I-TFO to the cell nucleus. Adenovirus-containing complexes brought about greater uptake and nuclear localization of TFOs compared with delivery with 125I-TFO-PEI complexes alone. No significant degradation of 125I-TFO was found after delivery into cells using PEI-Ad complexes and freezing and thawing. We next used PEI-Ad complexes to deliver 125I-TFO and pCMVrAQP5 separately to epithelial cells to determine if triplexes can form de novo within cells, resulting in the specific dsb in the rAQP5 cDNA. After delivery, cell pellets were stored at -80 degrees C for more than 60 days. Thereafter, plasmid DNA was isolated from cells and analyzed for dsb by Southern hybridization. However, none were detected. We conclude that under the experimental conditions employed, effective triplexes, with 125I-TFO and pCMVrAQP5, do not form de novo inside cells.

Homeostatic regulation of serotonergic function by the serotonin transporter as revealed by nonviral gene transfer

With the aim of exploring the relationship between the serotonin transporter (5-HTT or SERT) and the activity level of serotonin (5-HT) neurotransmission, in vivo expression of this protein was specifically altered using a nonviral DNA transfer method. Plasmids containing the entire coding sequence or a partial antisense sequence of the 5-HTT gene were complexed with the cationic polymer polyethylenimine and injected into the dorsal raphe nucleus of adult male rats. Significant increase or decrease in both [(3)H]citalopram binding and [(3)H]5-HT synaptosomal uptake were observed in various brain areas up to 2 weeks after a single administration of the sense plasmid or 7 d after injection of the short antisense plasmid, respectively. Such changes in 5-HTT expression were associated with functional alterations in 5-HT neurotransmission, as shown by the increased capacity of 5-HT(1A) receptor stimulation to enhance [(35)S]GTP-gamma-S binding onto the dorsal raphe nucleus in sections from rats injected with the sense plasmid. Conversely, both a decrease in 5-HT(1A)-mediated [(35)S]GTP-gamma-S binding and a reduced potency of the 5-HT(1A) receptor agonist ipsapirone to inhibit neuronal firing were observed in the dorsal raphe nucleus of antisense plasmid-injected rats. Furthermore, changes in brain 5-HT and/or 5-HIAA levels, and sleep wakefulness circadian rhythm in the latter animals demonstrated that altered expression of 5-HTT by recombinant plasmids has important functional consequences on central 5-HT neurotransmission in adult rats.

Enhanced gene expression in mouse lung after PEI-DNA aerosol delivery

Aerosol gene delivery to the pulmonary system has vast potential for many diseases, including cystic fibrosis and lung cancer. We recently reported that polyethyleneimine (PEI), a cationic polymer, holds promise as a gene delivery vector for transfection in lung by aerosol. To further optimize the gene expression in the lung by aerosol, we utilized 5% CO(2) in air for the nebulization of PEI-DNA complexes. Five percent CO(2)-in-air gave a threefold higher gene expression compared to normal air using the chloramphenicol acetyl transferase (CAT) reporter gene delivered by Aerotech II nebulizer. The delivery of DNA by PEI was dose dependent with the highest expression obtained when 2 mg of DNA in 10 ml was nebulized at a PEI nitrogen:DNA phosphate (N:P) ratio of 10:1. The optimal N:P ratio for lung transfection was found to be between 10:1 and 20:1 using the CAT and luciferase reporter genes. The time-course studies showed the highest expression at 24 h after aerosol delivery and 40-50% of peak level was detectable even after a week. Tissue distribution indicates the expression to be specific to the lung with no detectable expression in any other tissue examined. Histological and biochemical analysis of lungs revealed no evidence of acute inflammation.

Polycation liposomes, a novel nonviral gene transfer system, constructed from cetylated polyethylenimine

A novel gene transfer system was developed by using liposomes modified with cetylated polyethylenimine (PEI, MW 600). This polycation liposome, PCL, showed remarkable transfection efficiency as monitored by the expression of the GFP reporter gene. Most conventional cationic liposomes require phosphatidylethanolamine or cholesterol as a component, although PCLs did not. Egg yolk phosphatidylcholine- and dipalmitoylphosphatidylcholine-based PCL were as effective as dioleoylphosphatidylethanolamine-based PCLs for gene transfer. Concerning the cytotoxicity against COS-1 cells and hemolytic activity, the PCL was superior to conventional cationic liposome preparations. Furthermore, the transfection efficacy of PCLs was enhanced, instead of being diminished, in the presence of serum. Effective gene transfer was observed in all eight malignant and two normal cells line tested, as well as in COS-1 cells. We also examined the effect of the molecular weight of PEI on PCL-mediated gene transfer, and observed that PEI with a MW of 1800 Da was as effective as that with one of 600, but that PEI of 25,000 was far less effective. Finally, an in vivo study was done in which GFP was effectively expressed in mouse liver after injection of PCL via the portal vein. Thus, PCL represents a new system useful for transfection and gene therapy.

Targeted transfer of polyethylenimine-avidin-DNA bioconjugates to hematopoietic cells using biotinylated monoclonal antibodies

Here we examine whether attachment of biotinylated antibodies to proteins on the cell surface increases the transfection efficiency of polyethylenimine-avidin-DNA bioconjugate gene transfer. Preliminary experiments were performed to compare avidin endocytosis into cells incubated with biotinylated antibodies. Antibody biotinylation resulted in the endocytosis of avidin-FITC into nearly 100% of cells compared with no detectable binding or entry into unbiotinylated cells. Gene transfer was accomplished with avidin conjugated to polyethylenimine (PEI) at a molar ratio of 4:1 (PA4). Plasmid DNA encoding the green fluorescent protein (GFP) gene was condensed on the PA4, and transfection efficiencies were measured by flow cytometry as the percentage of cells that fluoresced at levels greater than two standard deviations above the negative control. Gene transfer efficiencies were compared among K562, HEL, and Jurkat leukemia cell lines. Control transfections with DNA alone or untargeted PEI-DNA resulted in </=2% GFP positive cells. Targeting PEI-avidin-DNA to antibody biotinylated cells increased transfection efficiency several fold over untargeted PEI. For each cell type, the increase in transfection efficiency was not significantly different among four biotinylated antibodies tested (antiCD55, antiCD59, antiCD71, and antiCD98). These data suggest biotinylated antibodies may be useful for targeting polyethylenimine-avidin mediated gene transfer.

Targeted gene delivery to pulmonary endothelium by anti-PECAM antibody

To achieve efficient systemic gene delivery to the lung with minimal toxicity, a vector was developed by chemically conjugating a cationic polymer, polyethylenimine (PEI), with anti-platelet endothelial cell adhesion molecule (PECAM) antibody (Ab). Transfection of mouse lung endothelial cells with a plasmid expression vector with cDNA to luciferase (pCMVL) complexed with anti-PECAM Ab-PEI conjugate was more efficient than that with PEI-pCMVL complexes. Furthermore, the anti-PECAM Ab-PEI conjugate mediated efficient transfection at lower charge plus-to-minus ratios. Conjugation of PEI with a control IgG (hamster IgG) did not enhance transfection of mouse lung endothelial cells, suggesting that the cellular uptake of anti-PECAM Ab-PEI-DNA complexes and subsequent gene expression were governed by a receptor-mediated process rather than by a nonspecific charge interaction. Conjugation of PEI with anti-PECAM Ab also led to significant improvement in lung gene transfer to intact mice after intravenous administration. The increase in lung transfection was associated with a decrease compared with PEI-pCMVL with respect to circulating proinflammatory cytokine (tumor necrosis factor-alpha) levels. These results indicate that targeted gene delivery to the lung endothelium is an effective strategy to enhance gene delivery to the pulmonary circulation while simultaneously reducing toxicity.

Systemic linear polyethylenimine (L-PEI)-mediated gene delivery in the mouse

BACKGROUND

Several nonviral vectors including linear polyethylenimine (L-PEI) confer a pronounced lung tropism to plasmid DNA when injected into the mouse tail vein in a nonionic solution.

METHODS

and results We have optimized this route by injecting 50 microg DNA with excess L-PEI (PEI nitrogen/DNA phosphate = 10) in a large volume of 5% glucose (0.4 ml). In these conditions, 1-5% of lung cells were transfected (corresponding to 2 ng luciferase/mg protein), the other organs remaining essentially refractory to transfection (1-10 pg luciferase/mg protein). beta-Galactosidase histochemistry confirmed alveolar cells, including pneumocytes, to be the main target, thus leading to the puzzling observation that the lung microvasculature must be permeable to cationic L-PEI/DNA particles of ca 60 nm. A smaller injected volume, premixing of the complexes with autologous mouse serum, as well as removal of excess free L-PEI, all severely decreased transgene expression in the lung. Arterial or portal vein delivery did not increase transgene expression in other organs.

CONCLUSIONS

These observations suggest that effective lung transfection primarily depends on the injection conditions: the large nonionic glucose bolus prevents aggregation as well as mixing of the cationic complexes and excess free L-PEI with blood. This may favour vascular leakage in the region where the vasculature is dense and fragile, i.e. around the lung alveoli. Cationic particles can thus reach the epithelium from the basolateral side where their receptors (heparan sulphate proteoglycans) are abundant.

Comparison between cationic polymers and lipids in mediating systemic gene delivery to the lungs

Airway inflammation frequently found in congenital and acquired lung diseases may interfere with gene delivery by direct administration through either instillation or aerosol. Systemic delivery by the intravenous administration represents an alternative route of delivery that might bypass this barrier. A nonviral approach for transfecting various airway-derived cell lines in vitro showed that cationic polymers (PEI 22K and 25K) and lipids (DOTAP, GL-67/DOPE) are able to transfect with high efficiency the reporter genes firefly luciferase and E. coli lacZ. Notably, two properties predicted that cationic vectors would be useful for a systemic gene delivery approach to the lung: (1) transfection was not inhibited or increased when cells were incubated with cationic lipids or polymers in the presence of serum; and (2) cationic vectors protected plasmid DNA from DNase degradation. A single injection of DNA complexed to the cationic polymer PEI 22K into the tail vein of adult mice efficiently transfected primarily the lungs and to a lesser extent, heart, spleen, kidney and liver. The other vectors mediated lower to undetectable levels of luciferase expression in the lungs, with DOTAP > GL67/DOPE > PEI 25K > DOTMA/DOPE. A double injection protocol with a 15-min interval between the two doses of DOTAP/DNA complexes was investigated and showed a relevant role of the first injection in transfecting the lungs. A two log increase in luciferase expression was obtained either when the two doses were comprised of luciferase plasmid or when an irrelevant plasmid was used in the first injection. The double injection of luciferase/PEI 22K complexes determined higher transgene levels than a single dose, but a clear difference using an irrelevant plasmid as first dose was not observed. Using lacZ as a reporter gene, it was shown that only cells in the alveolar region, including type II penumocytes, stained positively for the transgene product.

Optimisation of polyethylenimine-based gene delivery to mouse brain

Polyethylenimine (PEI) is proving to be an efficient and versatile vector for gene delivery in vivo. However, a limiting factor is the relatively short duration of gene expression in some sites. Given the particularly high levels of expression seen in the short term we postulated that loss of expression could result from overloading the nucleus with foreign DNA. To address this problem we first followed DNA delivery and localisation with digoxin-labelled plasmid DNA complexed with 22 kD linear PEI and used these complexes for intraventricular injection into brains of anaesthetised newborn mice. At 24 h post-injection, labelled DNA was found exclusively in the nuclear and perinuclear regions. We next carried out a dose response curve using decreasing amounts of DNA, either in a constant volume (2 microl) or at a constant concentration (500 ng/microl). In both conditions, transgene expression yield was maximum at 100 ng DNA per injection. Using this optimal amount of DNA increased yield of transgene expression significantly at 24 h and one week post-injection as compared to 1 microg DNA. A final point addressed was whether co-expressing an anti-apoptotic gene could enhance gene expression in the longer term. Co-expressing bcl-X(L) with luciferase or LacZ significantly increased expression of both these genes at one week post-injection.

Polyethylenimine but not cationic lipid improves antisense activity of 3'-capped phosphodiester oligonucleotides

Lipofectin, which is a mixture of neutral lipid with a cationic lipid, has been widely used to enhance cellular delivery of phosphorothioate, 2'-sugar-modified, and chimeric antisense oligonucleotides. Phosphodiester oligonucleotides delivered with Lipofectin usually do not elicit antisense activity probably because cationic lipid formulations do not sufficiently protect unmodified oligonucleotides from nuclease degradation. We show that a cationic polymer, polyethylenimine (PEI), improves the uptake and antisense activity of 3'-capped 20-mer and 12-mer antisense phosphodiester oligonucleotides (PO-ODN) targeted to different regions of Ha-ras mRNA and to the 3'-untranslated region (3'-UTR) of C-raf kinase. In contrast, PEI, which forms a very stable complex with the 20-mer phosphorothioate oligonucleotide (PS-ODN), does not enhance its antisense activity. Using fluorescently labeled carriers and ODN, we show that PEI-PS-ODN particles are very efficiently taken up by cells but PS-ODN is not dissociated from the carrier. Our results indicate that carrier-ODN particle size and stability and ODN release kinetics vary with the chemical nature of the ODN and the carrier being transfected into the cells. The very low cost of PEI compared with cytofectins and the increased affinity for target mRNA and decreased affinity for proteins of PO-ODN compared with PS-ODN make the use of PEI-PO-ODN very attractive.

Development of transferrin-polycation/DNA based vectors for gene delivery to melanoma cells

We describe the comparison of non-viral polycation transfection reagents, adenovirus-enhanced transferrinfection (AVET), polyethylenimine (PEI800) and transferrin-conjugated PEI800 (Tf-PEI800) in their ability to transfect murine and primary human melanoma cell lines. Expression of a reporter gene, cell surface marker and secreted protein (interleukin-2) was assessed for each vector system. Testing for luciferase reporter gene expression in murine and primary human cell lines, AVET and Tf-PEI800, both showed high levels of expression and comparable activity. Furthermore, when the melanoma cell line B16F10 was transfected with a cell surface marker up to approximately 97% of the cells expressed the protein on the cell surface. Assessing the levels of secreted IL-2 in murine cell lines, AVET/IL-2, Tf-PEI800/IL-2 and PEI800/IL-2 all expressed high levels of the cytokine (up to 20 microg IL-2/10(6) cells/24 h). In primary human melanoma cell lines, AVET/IL-2 transfected cells secreted more IL-2 than cells transfected with either Tf-PEI800/IL-2 or PEI800/IL-2. In murine melanoma cell culture experiments, positively charged PEI800/DNA and Tf-PEI800/DNA complexes gave similar transfection efficiencies. However, when subcutaneous tumors in mice were injected with the luciferase reporter gene complexed with either Tf-PEI800 or AVET, higher transfection activity was measured in the tumors as compared to ligand free PEI800/DNA complexes.

Polyplex-mediated gene transfer into human retinal pigment epithelial cells in vitro

The human retinal pigment epithelium (RPE) is a potential target tissue for directed transfer of candidate genes to treat age-related macular degeneration (AMD). The RPE is uniquely suited to gene therapy protocols that use liposome-mediated DNA transfer because of its high intrinsic phagocytic function in vivo. In these studies, we examined the efficacy of human RPE cell uptake and expression of the green fluorescent protein (GFP) and neomycin resistance marker genes by polyplex-mediated gene transfer in vitro. The effects of varying DNA and polyplex concentration and ratios on GFP transgene expression were examined. A narrow range of experimental conditions were found to maximize transgene expression; most important were the DNA concentration and the DNA:polyplex ratio. The transfection efficiency for human RPE cells was reproducibly 20% in vitro by this method and reached a maximum level of expression after 48 h. There was a rapid decline in gene expression over 2 weeks following polyplex-mediated gene transfer, but stable integration does occur at low frequencies with and without selection.

Pharmaceutical perspectives of nonviral gene therapy

The use of nonviral plasmid-based gene medicines represents an attractive in vivo gene transfer strategy that is simple and lacks many risks that are inherent to viral systems. Commercialization of gene medicines requires a thorough analysis of business opportunities, unmet clinical needs, competitive products under development, and issues related to intellectual property. Synthetic gene delivery systems are designed to control the location of a gene within the body by affecting distribution and access of a gene expression system to the target cell, and/or recognition by a cell surface receptor and uptake followed by intracellular and nuclear translocation. Plasmid-based gene expression systems are designed to control the level, fidelity, and duration of in vivo production of a therapeutic gene product. This review will provide insights into the potentials of plasmid-based gene therapy and critical evaluation of gene delivery sciences and clinical applications of gene medicines.

Correction of the UDP-glucuronosyltransferase gene defect in the gunn rat model of crigler-najjar syndrome type I with a chimeric oligonucleotide

Crigler-Najjar syndrome type I is characterized by unconjugated hyperbilirubinemia resulting from an autosomal recessive inherited deficiency of hepatic UDP-glucuronosyltransferase (UGT) 1A1 activity. The enzyme is essential for glucuronidation and biliary excretion of bilirubin, and its absence can be fatal. The Gunn rat is an excellent animal model of this disease, exhibiting a single guanosine (G) base deletion within the UGT1A1 gene. The defect results in a frameshift and a premature stop codon, absence of enzyme activity, and hyperbilirubinemia. Here, we show permanent correction of the UGT1A1 genetic defect in Gunn rat liver with site-specific replacement of the absent G residue at nucleotide 1206 by using an RNA/DNA oligonucleotide designed to promote endogenous repair of genomic DNA. The chimeric oligonucleotide was either complexed with polyethylenimine or encapsulated in anionic liposomes, administered i.v., and targeted to the hepatocyte via the asialoglycoprotein receptor. G insertion was determined by PCR amplification, colony lift hybridizations, restriction endonuclease digestion, and DNA sequencing, and confirmed by genomic Southern blot analysis. DNA repair was specific, efficient, stable throughout the 6-month observation period, and associated with reduction of serum bilirubin levels. Our results indicate that correction of the UGT1A1 genetic lesion in the Gunn rat restores enzyme expression and bilirubin conjugating activity, with consequent improvement in the metabolic abnormality.

Cytosolic drug delivery using pH- and light-sensitive liposomes

A growing body of literature describes the development and applications of novel targeting and/or contents release triggering schemes to improve the therapeutic index of drugs encapsulated within liposomes. This review focuses on literature appearing between January 1995-December 1997 that report 1) antibody and receptor-mediated targeting approaches for improving drug localization and 2) acid, enzymatic, thermal or photochemical triggering processes that destabilize membranes and improve drug bioavailability via cytoplasmic delivery of liposomal contents.

Poly(ethylenimine) and its role in gene delivery

Since the first published examination of poly(ethylenimine) (PEI) as a gene delivery vehicle, there has been a flurry of research aimed at this polycation and its role in gene therapy. Here we will briefly review PEI chemistry and the characterization of PEI/DNA complexes used for gene delivery. Additionally, we will note various PEI transfection considerations and examine findings involving other polycationic gene delivery vehicles used with cellular targeting ligands. The current state of our knowledge regarding the mechanism of PEI/DNA transfection will also be discussed. Finally, we will survey toxicity issues related to PEI transfection.

A novel non-viral vector for DNA delivery based on low molecular weight, branched polyethylenimine: effect of molecular weight on transfection efficiency and cytotoxicity

PURPOSE

Low molecular weight branched polyethylenimine (LMW-PEI) was synthesized and studied as a DNA carrier for gene delivery with regard to physico-chemical properties, cytotoxicity, and transfection efficiency.

METHODS

The architecture of LMW-PEI, synthesized by acid catalyzed ring-opening polymerization of aziridine was characterized by size exclusion chromatography in combination with laser light scattering and 13C-NMR-spectroscopy. In vitro cytotoxic effects were quantified by LDH and MTT assay and visualized by transmission electron microscopy. The potential for transgene expression was monitored in ECV304 cells using luciferase driven by a SV40 promotor as reporter gene system.

RESULTS

LMW-PEI (Mw 11'900 D) with a low degree of branching was synthesized as a DNA carrier for gene delivery. In contrast to high molecular weight polyethylenimines (HMW-PEI; Mw 1'616'000 D), the polymer described here showed a different degree of branching and was less cytotoxic in a broad range of concentrations. As demonstrated by transmission electron microscopy the LMW-PEI formed only small aggregates which were efficiently taken up by different cells in the presence of serum, most likely by an endocytic pathway. LMW-PEI yielded transfection efficiencies measured via expression of the reporter gene luciferase which were up to two orders of magnitude higher than those obtained with HMW-PEI. The reporter gene expression was concentration dependent, but in contrast to lipofection independent of serum addition.

CONCLUSIONS

The LMW-PEI described here is a new, highly efficient, and non-cytotoxic vector with a favorable efficiency/toxicity profile for gene therapeutic applications.

Improved packing of poly(ethylenimine)/DNA complexes increases transfection efficiency

We have developed a modified poly(ethylenimine) (PEI) transfection procedure that significantly increases PEI's transfection efficiency. While the basic transfection procedure had a transfection efficiency of 37%, our modified procedure yielded a 53% transfection efficiency. The altered procedure gives improved results because of two simultaneous actions: free polycations are removed from the transfecting solutions, and the composition of the PEI complexes that are administered to cells has been modified. The reduction in the amount of free polycations in transfecting solutions reduced the toxicity sometimes associated with the administration of polycations to cellular environments. The structural modification of PEI/DNA transfecting complexes involves improved PEI packing around the delivered plasmid to yield a greater buffering capacity without a change in the complex's surface charge concentration. These structural properties were confirmed by titration and zeta potential analyses. Whether the modified PEI/DNA complexes are more effective because of increased cellular uptake or an enhanced ability to escape from endolysosomes has been addressed. The increase in transfection efficiency was obtained when the buffering capacity of the PEI/DNA was increased without a change in surface charge concentration, which implies that it is the property of enhanced lysosomal buffering that is responsible for successful PEI transfection.

Mannose polyethylenimine conjugates for targeted DNA delivery into dendritic cells

Cell surface-bound receptors represent suitable entry sites for gene delivery into cells by receptor-mediated endocytosis. Here we have taken advantage of the mannose receptor that is highly expressed on antigen-presenting dendritic cells for targeted gene transfer by employing mannosylpolyethylenimine (ManPEI) conjugates. Several ManPEI conjugates were synthesized and used for formation of ManPEI/DNA transfection complexes. Conjugates differed in the linker between mannose and polyethylenimine (PEI) and in the size of the PEI moiety. We demonstrate that ManPEI transfection is effective in delivering DNA into mannose receptor-expressing cells. Uptake of ManPEI/DNA complexes is receptor-specific, since DNA delivery can be competed with mannosylated albumin. Additionally, incorporation of adenovirus particles into transfection complexes effectively enhances transgene expression. This is particularly important for primary immunocompetent dendritic cells. It is demonstrated here that dendritic cells transfected with ManPEI/DNA complexes containing adenovirus particles are effective in activating T cells of T cell receptor transgenic mice in an antigen-specific fashion.

In vivo delivery to tumors of DNA complexed with linear polyethylenimine

Synthetic gene delivery vectors have shown promise in several organs, including brain and lung. Tumor cell targeting, however, is still hindered by their low efficacy. A linear polyethylenimine (L-PEI, Exgen 500) was found to be effective in vivo. Our first attempts to use L-PEI for intratumoral gene delivery were not successful, presumably because of poor diffusion of the complexes within the tumor mass after injection with a syringe. Here we show that L-PEI-mediated transfection can be strongly enhanced when the complexes are delivered slowly into a solid tumor mass, using a micropump. Furthermore, L-PE/DNA complexes actively transfect pseudocystic tumor cells when injected into the cyst cavity. In both cases L-PEI induced a significant and long-lasting (> or =15 days) expression of the reporter gene. Finally, even though systemic delivery of L-PEI/DNA complexes leads to high levels of expression in the lung, this method is not adapted for transfection of subcutaneous tumors implanted in the thigh nor for transfection of lung metastases. Altogether, these results show that L-PEI has promising features for transfection of tumor cells, provided that the mode of delivery is adapted.

Reversible immortalization of human myogenic cells by site-specific excision of a retrovirally transferred oncogene

Myogenic cells have a limited life span in culture, which prevents expansion at clinically relevant levels, and seriously limits any potential use in cell replacement or ex vivo gene therapy. We developed a strategy for reversibly immortalizing human primary myogenic cells, based on retrovirus-mediated integration of a wild-type SV40 large-T antigen (Tag), excisable by means of the Cre-Lox recombination system. Myogenic cells were transduced with a vector (LTTN-LoxP) expressing the SV40 Tag under the control of an LTR modified by the insertion of a LoxP site in the U3 region. Clonal isolates of Tag-positive cells showed modified growth characteristics and a significantly extended life span, while maintaining a full myogenic potential. Transient expression of Cre recombinase, delivered by transfection or adenoviral vector transduction, allowed excision of the entire provirus with up to >90% efficiency. Cultures of Cre-treated (Tag-) or untreated (Tag+) myogenic cells were genetically labeled with a lacZ retroviral vector, and injected into the regenerating muscle of SCID/bg immunodeficient mice. Tag- cells underwent terminal differentiation in vivo, giving rise to clusters of beta-Gal+ hybrid fibers with an efficiency comparable to that of control untransduced cells. Tag+ cells could not be detected after injection. Neither Tag+ nor Tag- cells formed tumor in this xenotransplantation model. Reversible immortalization by Tag therefore allows the expansion of primary myogenic cells in culture without compromising their ability to differentiate in vivo, and could represent a safe method by which to increase the availability of these cells for clinical application.

Use of triplex-forming oligonucleotides and adenoviral constructs for studying the regulation of gene expression

Short synthetic homopyrimidine- or homopurine-rich oligonucleotides can form sequence-specific triplexes with corresponding homopurine-homopyrimidine sites on duplex DNA and block transcription of a target gene in vitro. Such triplex-forming oligonucleotides (TFOs) can be rationally designed to target homopurine/homopyrimidine sequences that are often found in eukaryotic genes and thus used to modulate the expression of these genes. The antigene strategy using TFOs has been successfully applied to a number of genes in vitro. In this article we describe methods used in applying this antigene approach to the rat aquaporin 5 (rAQP5) gene. We specifically focus on the selection of TFOs based on the sequence of the target gene and on a novel method employing adenoviruses for delivery of TFOs to cells in vitro.

Size matters: molecular weight affects the efficiency of poly(ethylenimine) as a gene delivery vehicle

Poly(ethylenimine) (PEI) samples of various molecular weights and pHs were used to transfect endothelial cells to achieve levels of gene expression for comparison. PEIs with nominal molecular weights of 600, 1200, 1800, 10,000, and 70,000 Da were examined at pHs of 5. 0, 6.0, 7.0, and 8.0, and the results were recorded in terms of transfection efficiencies at 24, 48, 68, 92, and 120 h post-transfection. Trials were performed on the human endothelial cell-derived cell line EA.hy 926. We found that, for the polymers tested, transfection efficiency increased as the molecular weight of PEI increased. Representative values of PEIs at pH 6 and molecular weight 70,000 produced average transfection efficiencies of 25.6 +/- 7.9% (n = 8) at the greatest average expression levels, while PEI of molecular weight 10,000 yielded efficiencies of only 11.4 +/- 1.7% (n = 6). Transfection efficiencies for molecular weight 1,800 PEI were essentially zero, and PEIs of lower molecular weights produced no transfection at all. In contrast, the pH of the PEI solutions had no discernible effect on transfection. Optimal expression of the green fluorescent protein reporter occurred between 2 and 3 days post-transfection. The amount of reporter expression also was noted, as determined by the brightness of fluorescing cells under UV. The data obtained demonstrate that the molecular weight of the PEI carrier has an effect on transfection efficiency while the pH of the PEI solutions prior to DNA complexation has no such effect.

Transfection and physical properties of various saccharide, poly(ethylene glycol), and antibody-derivatized polyethylenimines (PEI)

BACKGROUND

The ideal non-viral vector should be cell-type directed and form complexes with DNA that are physically stable, small and electrically neutral.

METHODS

We have synthesized several PEI derivatives that coat the PEI/DNA complexes with water-soluble residues able to stabilize the particles, to mask their surface charge and eventually to direct them to a particular tissue. The morphologies and sizes of the complexes were observed by TEM and DLS techniques, and their apparent surface charge was quantitated by zeta potential measurements; in vitro transfection efficacies were determined in serum-containing cell culture medium.

RESULTS

When compared to DNA complexes formed with the unmodified PEI, extensive grafting with maltose (15-25% of the amine functions) led to beneficial electrostatic shielding of the particle surface, but was unable to prevent aggregation in physiological salt concentration. More extended hydrophilic residues were therefore explored as a mean of physical repulsion between the particles. Low grafting (2.7%) with a linear dextran non-asaccharide led to small and stable toroids having no apparent surface charge, yet still reaching effective transfection levels. Electron microscopy of complexes with a higher extent of grafting showed worm-like structures unsuited for cell entry. Conjugation of PEI with as little as 0.5% of a terminally galactose-derivatized polyethyleneglycol (PEG)-3400 also gave neutral complexes of another worm-like structure that failed to transfect receptor-expressing hepatocytes.

CONCLUSION

These results show that conjugation of large and flexible hydrophilic residues to PEI, while protecting the complexes from parasitic interactions also interfere with DNA condensation. PEG conjugation after PEI/DNA complex formation may avoid this problem, provided intracomplex reorganization is slow. Finally an anti-GD2 antibody (mAb) grafted with PEI was synthesized. The corresponding protein-coated DNA complexes were compact and small (50-60 nm), yet did not enhance transfection of GD2 ganglioside-expressing cells.

Cationic lipids and polymers are able to enhance adenoviral infection of cultured mouse myotubes

Adenovirus-mediated gene transfer has been used to promote efficient expression of various reporter and therapeutic transgenes such as minidystrophin in skeletal muscle tissue. However, down-regulation of the adenovirus internalisation receptors, alpha(v)/beta3 and alpha(v)beta5, in adult myofibres and in mature cultured myotubes makes them less susceptible to infection than neonatal muscle or cultured myoblasts. It has been reported elsewhere that adenoviral transduction of cells that are normally refractory to infection can be enhanced by complexing virus particles with cationic lipids or cationic polymers. In this study we describe increased levels of adenovirus-mediated transduction of cultured C2C12 myotubes, when the vector is complexed with either of the cationic lipids Lipofectamine or 1,3-dioleoyloxy-2-(6-carboxyspermyl)propylamide (DOSPER) or the cationic polymer polyethylenimine. The presence of polycations allowed a smaller dose of adenovirus vector to be used to attain the same level of infection seen with adenovirus alone, which has important relevance to future in vivo studies. Electron microscopic analysis of adenovirus/polycation complexes showed large aggregates as opposed to single adenovirus particles in the absence of polycations. Finally, by complexing adenovirus particles with polycations, partial protection against the neutralising effect of adenovirus antiserum was observed.

Tracking the intracellular path of poly(ethylenimine)/DNA complexes for gene delivery

Poly(ethylenimine) (PEI) is one of a number of polycations that has been used successfully to transfer genes into living cells. Although PEI shows promise in the field of gene therapy, to date no rigorous proof of mechanism has been published regarding the fate of PEI/DNA administered for transfection. Here we show, by using fluorescent labeling and confocal microscopy, the paths of PEI/DNA complexes from endocytosis to gene expression. We found that complexes attach to cell surfaces and migrate into clumps that are endocytosed. The endocytotic vesicles grow in number and size and are occasionally seen to lyse. Most interesting is the fact that endocytosed PEI, whether administered with or without DNA, undergoes nuclear localization in the form of ordered structures.

Nucleotide exchange in genomic DNA of rat hepatocytes using RNA/DNA oligonucleotides. Targeted delivery of liposomes and polyethyleneimine to the asialoglycoprotein receptor

Chimeric RNA/DNA oligonucleotides have been shown to promote single nucleotide exchange in genomic DNA. A chimeric molecule was designed to introduce an A to C nucleotide conversion at the Ser365 position of the rat factor IX gene. The oligonucleotides were encapsulated in positive, neutral, and negatively charged liposomes containing galactocerebroside or complexed with lactosylated polyethyleneimine. The formulations were evaluated for stability and efficiency in targeting hepatocytes via the asialoglycoprotein receptor. Physical characterization and electron microscopy revealed that the oligonucleotides were efficiently encapsulated within the liposomes, with the positive and negative formulations remaining stable for at least 1 month. Transfection efficiencies in isolated rat hepatocytes approached 100% with each of the formulations. However, the negative liposomes and 25-kDa lactosylated polyethyleneimine provided the most intense nuclear fluorescence with the fluorescein-labeled oligonucleotides. The lactosylated polyethyleneimine and the three different liposomal formulations resulted in A to C conversion efficiencies of 19-24%. In addition, lactosylated polyethyleneimine was also highly effective in transfecting plasmid DNA into isolated hepatocytes. The results suggest that both the liposomal and polyethyleneimine formulations are simple to prepare and stable and give reliable, reproducible results. They provide efficient delivery systems to hepatocytes for the introduction or repair of genetic mutations by the chimeric RNA/DNA oligonucleotides.

PEGylated DNA/transferrin-PEI complexes: reduced interaction with blood components, extended circulation in blood and potential for systemic gene delivery

We investigated the in vitro and in vivo properties of DNA/transferrin-polyethylenimine (800 kDa) complexes before and after covalent coupling of poly(ethylene glycol) (PEG). Upon incubation with plasma, the positively charged non-PEGylated DNA complexes form aggregates. Plasma proteins such as IgM, fibrinogen, fibronectin and complement C3 were found to bind to non-PEGylated DNA complexes. At DNA concentrations relevant for in vivo gene delivery a strong aggregation of erythrocytes was also observed. PEGylation of the complexes strongly reduces plasma protein binding and erythrocyte aggregation. Furthermore, PEGylated complex size was stabilized and had a reduced surface charge. Prolonged circulation in the blood of the PEGylated complexes was also observed when injected intravenously. In tumor bearing mice, application of non-PEGylated complexes through the tail vein resulted in reporter gene expression in tail and lung, but severe toxicity was observed in some mice. In contrast, PEGylated complexes mediated reporter gene transfer to the tumor without significant toxicity.

Efficient gene delivery into human dendritic cells by adenovirus polyethylenimine and mannose polyethylenimine transfection

Gene-modified human dendritic cells (DCs) were generated by transfection with adenovirus polyethylenimine DNA (Ad/PEI/DNA) and mannose polyethylenimine DNA (ManPEI/DNA) complexes. Ad/PEI/DNA complexes have plasmid DNA bound to adenovirus particles by PEI and deliver DNA into cells via the adenovirus infection route. Such transfection complexes yield high transduction levels and sustained expression of luciferase and green fluorescent protein reporter genes and were almost as effective as recombinant adenovirus vectors. ManPEI/DNA complexes rely on uptake by receptor-mediated endocytosis via mannose receptor, which is highly expressed on DCs. While gene delivery by ManPEI/DNA complexes was less efficient than by Ad/PEI transfection, incorporation of adenovirus particles in ManPEI/DNA transfection complexes further enhanced transduction efficiencies and transgene expression. We also demonstrate that Ad/PEI-transfected DCs are competent in stimulating T cell proliferation in allogeneic and autologous mixed lymphocyte reactions, and in activating T cells from T cell receptor (TCR)-transgenic mice in an antigen-specific manner. Thus, the present study establishes the following relative order of transduction efficiencies of viral and nonviral gene delivery systems for primary human DCs: recombinant adenovirus > Ad/PEI = Ad/ManPEI > ManPEI > PEI. Ad/PEI and ManPEI transfection modes represent particularly versatile transduction systems for DCs, with ManPEI being built up exclusively of synthetic compounds.

The role of immunophilins in mutant superoxide dismutase-1linked familial amyotrophic lateral sclerosis

It has been reported that expression of familial amyotrophic lateral sclerosis (FALS)-associated mutant Cu/Zn superoxide dismutase-1 (SOD) induces apoptosis of neuronal cells in culture associated with an increase in reactive oxygen species. SOD recently has been shown to prevent calcineurin inactivation, initiating the present investigations examining the role of calcineurin in mutant SOD-induced cell death. Wild-type or mutant SOD was expressed in neuronal cells by infection with replication-deficient adenoviruses. PC12 cells overexpressing human wild-type SOD exhibited higher calcineurin activity than cells expressing FALS-related mutant SOD (SODV148G); however, cells expressing SODV148G had calcineurin activity equal to mock-infected cells, suggesting that cell death induced by mutant SOD was not related to a decrease in calcineurin activity. Calcineurin antagonists such as cyclosporin A and FK506, as well as nonimmunosuppressant analogs of cyclosporin A, significantly enhanced SODV148G- and SODA4V-induced cell death. Because both groups of drugs inhibit the rotamase activity of cyclophilins (CyP), but only the immunosuppressant analogs inhibit calcineurin activity, these data suggest that rotamase inhibition underlies the enhanced cell death after SODV148G expression. The importance of rotamase activity in mutant SOD-mediated apoptosis was supported by experiments showing that overexpressed wild-type cyclophilin A (CyPA), but not CyPA with a rotamase active site point mutation, protected cells from death after SODV148G expression. These data suggest that mutant SOD produces a greater need for rotamase and, also, highlights possible new therapeutic strategies in FALS.

Polycation-based DNA complexes for tumor-targeted gene delivery in vivo

BACKGROUND

Efficient and target-specific in vivo gene delivery is a major challenge in gene therapy. Compared to cell culture application, in vivo gene delivery faces a variety of additional obstacles such as anatomical size constraints, interactions with biological fluids and extracellular matrix, and binding to a broad variety of non-target cell types.

METHODS

Polycation-based vectors, including adenovirus-enhanced transferrinfection (AVET) and transferrin-polyethylenimine (Tf-PEI), were tested for gene delivery into subcutaneously growing tumors after local and systemic application. DNA biodistribution and reporter gene expression was measured in the major organs and in the tumor.

RESULTS

Gene transfer after intratumoral application was 10-100 fold more efficient with Tf-PEI/DNA or AVET complexes in comparison to naked DNA. Targeted gene delivery into subcutaneously growing tumors after systemic application was achieved using electroneutral AVET complexes and sterically stabilized PEGylated Tf-PEI/DNA complexes, whereas application of positively charged polycation/DNA complexes resulted in predominant gene expression in the lungs and was associated by considerable toxicity.

CONCLUSION

For systemic application, the physical and colloidal parameters of the transfection complexes, such as particle size, stability, and surface charge, determine DNA biodistribution, toxicity, and transfection efficacy. By controlling these parameters, DNA biodistribution and gene expression can be targeted to different organs.

Thyroid hormone effects on Krox-24 transcription in the post-natal mouse brain are developmentally regulated but are not correlated with mitosis

Krox-24 (NGFI-A, Egr-1) is an immediate-early gene encoding a zinc finger transcription factor. As Krox-24 is expressed in brain areas showing post-natal neurogenesis during a thyroid hormone (T3)-sensitive period, we followed T3 effects on Krox-24 expression in newborn mice. We analysed whether regulation was associated with changes in mitotic activity in the subventricular zone and the cerebellum. In vivo T3-dependent Krox-24 transcription was studied by polyethylenimine-based gene transfer. T3 increased transcription from the Krox-24 promoter in both areas studied at post-natal day 2, but was without effect at day 6. An intact thyroid hormone response element (TRE) in the Krox-24 promoter was necessary for these inductions. These stage-dependent effects were also seen in endogenous Krox-24 mRNA levels: activation at day 2 and no effect at day 6. Moreover, similar results were obtained by examining beta-galactosidase expression in heterozygous mice in which one allele of the Krox-24 gene was disrupted with an inframe Lac-Z insertion. However, bromodeoxyuridine incorporation showed mitosis to continue through to day 6. We conclude first, that T3 activates Krox-24 transcription during early post-natal mitosis but that this effect is extinguished as development proceeds and second, loss of T3-dependent Krox-24 expression is not correlated with loss of mitotic activity.

Interactions of polymeric and liposomal gene delivery systems with extracellular glycosaminoglycans: physicochemical and transfection studies

Complexes of DNA with cationic lipids and cationic polymers are frequently used for gene transfer. Extracellular interactions of the complexes with anionic glycosaminoglycans (GAGs) may interfere with gene transfer. Interactions of GAGs with the carrier-DNA complexes were studied using tests for DNA relaxation (ethidium bromide intercalation), DNA release (electrophoresis), and transfection (pCMVbetaGal transfer into RAA smooth muscle cells). Several cationic lipid formulations (DOTAP, DOTAP/Chol, DOTAP/DOPE, DOTMA/DOPE, DOGS) and cationic polymers (fractured dendrimer, polyethylene imines 25 kDa and 800 kDa, polylysines 20 kDa and 200 kDa) were tested. Polycations condensed DNA more effectively than the monovalent lipids. Hyaluronic acid did not release or relax DNA in any complex, but it inhibited the transfection by some polyvalent systems (PEI, dendrimers, DOGS). Gene transfer by the other carriers was not affected by hyaluronic acid. Sulfated GAGs (heparan sulfate, chondroitin sulfates B and C) completely blocked transfection, except in the case of the liposomes with DOPE. Sulfated GAGs relaxed and released DNA from some complexes, but these events were not prerequisites for the inhibition of transfection. In conclusion, polyvalent delivery systems with endosomal buffering capacity (DOGS, PEI, dendrimer) were most sensitive to the inhibitory effects of GAGs on gene transfer, while fusogenic liposomes (with DOPE) were the most resistant systems.

Efficient gene delivery by a peptide derived from a monoclonal anti-DNA antibody

We recently reported that translocating murine polyreactive anti-DNA antibodies can be used as vectors for the transfer of macromolecules into cells growing in culture. We show here that two such monoclonal antibodies (J20.8 and F4.1) conjugated to polylysine with a high (93) but not a low (19) number of lysine residues can transfer genes in the presence of serum. A 30 amino acid long peptide, VAYISRGGVSTYYSDTVKGRFTRQKYNKRA (peptide P3), corresponding to joined heavy-chain complementary-determining regions 2 and 3 of F4.1 antibody and carrying 19 lysine residues at its N-terminal, was found to be an efficient vector for the transfection of the luciferase gene into 3T3 and CCL39 cells in the presence of serum. Addition of 0.23 M glycerol during transfection considerably enhanced gene delivery. These results show that conjugation of a short polylysine tail converted a spontaneously internalizing peptide into a potent nontoxic plasmid vector.

Inhibition of glycogen synthase kinase 3beta activity regulates proliferation of cultured cerebellar granule cells

Insulin-like growth factor I (IGF-I) is mitogenic for several types of neuronal progenitors including cerebellar granule neuron progenitors. The present study confirms that IGF-I can function as a mitogen in purified cultures of cerebellar granule cells and identifies intracellular signal transduction molecules that mediate this mitogenesis. In cultured granule cells, IGF-I inhibits GSK-3 activity and leads to phosphorylation of serine9 an inhibitory site on GSK-3beta. Phosphoinositide 3-kinase (PI3-K) activation by IGF-I can lead to phosphorylation and inactivation of GSK-3. A PI3-K inhibitor, LY294002, completely inhibited IGF-I-induced proliferation with half-maximal inhibition occurring at a concentration (1.5 micrograms) close to its reported IC50 value for inhibition of PI3-K. Lithium chloride (LiCl), a direct inhibitor of GSK-3beta, can alone stimulate granule cell proliferation and enhance proliferation induced by IGF-I. LiCl can reverse the inhibitory effect of LY294002 on granule cell proliferation suggesting that GSK-3 inhibition may be downstream of PI3-K activation in IGF-I's mitogenic pathway. Experiments further show that the expression of a dominant active form of GSK-3beta antagonizes IGF-I-induced mitogenesis. These studies support a role for inhibition of GSK-3beta activity in the signal transduction pathway by which IGF-I regulates granule neuron progenitor proliferation.

Up- and down-expression of the dopamine transporter by plasmid DNA transfer in the rat brain

The functional role of the dopamine transporter (DAT) in central dopaminergic neurotransmission was assessed further by investigating the consequences on dopamine (DA) turn-over of up- and down-regulation of this protein induced by a non-viral gene transfer approach. For this purpose, expression plasmids containing the sense or antisense coding sequence of DAT complexed with the cationic polymer, polyethylenimine (PEI), were injected into the rat substantia nigra, the brain region containing the majority of DA cell bodies. Before in vivo injection, the efficacies of the different DNA constructs were assessed by transfection studies into LLC-PK1 cells. Stereotaxic administration of the sense plasmid complexed to PEI induced, 3 days later, a significant increase in the immunoautoradiographic labelling by anti-DAT antibodies of the substantia nigra and various DA projection areas. These effects were associated with a significantly enhanced capacity of striatal synaptosomes to take up [3H]-DA and lasted up to 14 days postinjection. In contrast, 7 days after intranigral administration of the antisense plasmid complexed to PEI, we observed a significant decrease of DAT immunolabelling in the substantia nigra and [3H]-DA uptake by striatal synaptosomes. Whereas DA turnover in the striatum was unaltered 3 days after intranigral administration of the sense plasmid, it was increased 7 days after intranigral administration of the antisense construct. These data indicate that non-viral transfer of the sense or antisense coding sequence of DAT can be used as a novel approach to induce long-term changes in central DA neurotransmission.

Liver-directed gene transfer: a linear polyethlenimine derivative mediates highly efficient DNA delivery to primary hepatocytes in vitro and in vivo

Efficient DNA delivery is a prerequisite for the successful implementation of molecular antiviral strategies against chronic viral hepatitis and gene therapy in general. The cationic polymer polyethylenimine (PEI) has recently been explored as a gene transfer vector in various cell types in vitro and in vivo. In this study, we evaluated a linear PEI derivative (lPEI) as a vector for gene and oligodeoxynucleotide transfer into hepatocytes in vitro and in vivo. A simple protocol was developed that allowed transfection of up to 50% of primary hepatocytes in vitro. In addition, fluorescent oligodeoxynucleotides were efficiently delivered to the liver in vivo after intravenous injection into Pekin ducks. Thus, lPEI mediates highly efficient gene and oligodeoxynucleotide transfer into primary hepatocytes and is potentially useful for DNA delivery in vivo.

Polyethylenimine but not cationic lipids promotes transgene delivery to the nucleus in mammalian cells

The beta-galactosidase reporter gene, either free or complexed with various cationic vectors, was microinjected into mammalian cells. Cationic lipids but not polyethylenimine or polylysine prevent transgene expression when complexes are injected in the nucleus. Polyethylenimine and to a lesser extent polylysine, but not cationic lipids, enhance transgene expression when complexes are injected into the cytoplasm. This latter effect was independent of the polymer vector/cDNA ionic charge ratio, suggesting that nucleic acid compaction rather than surface charge was critical for efficient nuclear trafficking. Cell division was not required for nuclear entry. Finally, comparative transfection and microinjection experiments with various cell lines confirm that barriers to gene transfer vary with cell type. We conclude that polymers but not cationic lipids promote gene delivery from the cytoplasm to the nucleus and that transgene expression in the nucleus is prevented by complexation with cationic lipids but not with cationic polymers.

Gene transfer with lipospermines and polyethylenimines

It is an obvious and basic principle that to be efficient, gene therapy requires effective gene transfer followed by adequate gene expression. However, getting DNA, a pro-drug, into the cell and into the nucleus, remains a crucially limiting factor. Even recombinant viral methods still show poor performances in clinical situations and non-viral methods are considered classically to be of yet lower efficiency. Here, we consider the mode of action, the nature of the complexes formed with DNA and the transfection potentials of two categories of inert, cationic vectors, the lipospermines and polyethylenimine. Both are among the best vectors currently available for in vitro work. Moreover, polyethylenimine is proving to be a versatile and effective carrier for different in vivo situations, especially for delivering genes into the mammalian brain.

In vivo site-directed mutagenesis of the factor IX gene by chimeric RNA/DNA oligonucleotides

A chimeric RNA/DNA oligonucleotide was constructed to induce a sequence mutation in the rat factor IX gene, resulting in prolonged coagulation. Oligonucleotides were targeted to hepatocytes in cell culture or in vivo by intravenous injection. Nucleotide conversion was both site-specific and dose-dependent. The mutated gene was associated in vivo with significantly reduced factor IX coagulant activity and a marked prolongation of the activated partial thromboplastin time. The results demonstrate that single base-pair alterations can be introduced in hepatocytes in situ by RNA/DNA oligonucleotides, suggesting a potentially powerful strategy for hepatic gene repair without the use of viral vectors.