Development of plasmid and oligonucleotide nanometric particles

Nucleic acids delivery vectors have shown promising therapeutic potential in model systems. However, comparable clinical success is delayed essentially because of their poor biodistribution and of their ineffective intracellular trafficking. The size of condensed DNA particles is a key determinant for in vivo diffusion, as well as for gene delivery to the cell nucleus. Towards this goal, we have developed cationic thiol-detergents that individually compact plasmid DNA molecules into anionic particles. These particles are then ‘stabilized’ by air-induced dimerization of the detergent into a disulfide lipid on the template DNA. The particles all measure approximately 30 nm, which corresponds to the volume of a single molecule of plasmid DNA. The gel electrophoretic mobility of the anionic particles was found to be higher than that of the plasmid DNA itself. Similarly, particles formed with a 31-mer oligonucleotide measured 19 nm. Improved in vivo diffusion, as well as improved intracellular trafficking may be inferred from the faster migration of the complexes. Moreover, the size of the particles remains compatible with nuclear pore crossing. Finally, in an attempt to improve the biodistribution of these particles, we have coated the monomolecular particles with a poly(ethylene glycol) corona

Dimerizable Cationic Detergents with a Low cmc Condense Plasmid DNA into Nanometric Particles and Transfect Cells in Culture

The size of condensed DNA particles is a key determinant for in vivo diffusion and gene delivery to cells. Gene molecules can be individually compacted by cationic thiol detergents into nanometric particles that are stabilized by oxidative conversion of the detergent into a gemini lipid. To reach the other goal, gene delivery, a series of cationic thiol detergents with various chain lengths (C12−C16) and headgroups (ornithine or spermine) was prepared, using a versatile polymer-supported synthetic strategy. Critical micelle concentrations and thiol oxidation rates of the detergents were measured. The formation and stability of complexes formed with plasmid DNA, as well as the size, ξ-potential, morphology, and transfection efficiency of the particles were investigated. Using the tetradecane/ornithine detergent, a solution of 5.5 Kpb plasmid DNA molecules was converted into a homogeneous population of 35 nm particles. The same detergent, once oxidized, exhibited a typical lipid phase internal structure and was capable of effective cell transfection. The particle size did not increase with time. Surprisingly, the gel electrophoretic mobility of the DNA complexes was found to be higher than that of plasmid DNA itself. Favorable in vivo diffusion and intracellular trafficking properties may thus be expected for these complexes

Intracellular Delivery of Nanometric DNA Particles via the Folate Receptor

The size of condensed DNA particles is a key determinant for both diffusion to target cells in vivo and intracellular trafficking. The smallest complexes are obtained when each DNA molecule collapses individually. This was achieved using a designed cationic thiol-detergent, tetradecyl-cysteinyl-ornithine (C14COrn). The resulting particles were subsequently stabilized by air-induced dimerization of the detergent into a disulfide lipid on the DNA template. Particles are anionic (zeta potential = −45 mV), and their size (30 nm) corresponds to the volume of a single plasmid DNA molecule. The electrophoretic mobility of the condensed DNA, though quasi-neutralized, was found higher than that of the extended DNA. Moreover, the dimerized (C14COrn)2 lipid was found to be an efficient transfection reagent for various cell lines. In an attempt to achieve extended circulation times and to target tumors by systemic delivery, we have coated the particles with PEG−folate residues. Plasmid DNA was condensed into monomolecular particles as described above and coated by simple mixing with DPPE−PEG−folate. Physicochemical measurements showed particles coated with 2% of DPPE−PEG3400−folate remain monomolecular and are stable in the cell-culture medium. Caveolae-mediated cell entry was demonstrated by ligand-dependence, by competition with excess folic acid as well as by confocal microscopy

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 µg 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).β‐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

Oligonucleotide−Oligospermine Conjugates (Zip Nucleic Acids): A Convenient Means of Finely Tuning Hybridization Temperatures

Synthesis of oligonucleotide probes and control of their hybridization temperature are key aspects of polymerase chain reaction (PCR)-based detection of genetic sequences. A straightforward means to approach the last goal is to decrease the repulsion between the polyanionic probe and target strands. To this end, we have developed a versatile automated synthesis of oligonucleotide−oligospermine derivatives that gave fast access to a large variety of compounds. Plots of their hybridization temperatures Tm vs overall charge provided a measure of the impact of interstrand phosphate repulsion (and of spermine-mediated attraction) on the main driving force of duplex formation, i.e., base pairing. It showed that stabilization brought about by excess cationic charges can be of larger absolute magnitude than interstrand repulsion, even in high salt media. Base sequence and conjugation site (3′ or 5′) hardly influenced the effect of spermine on Tm. In typical PCR probe conditions, the Tm increased linearly with the number of grafted spermines (e.g., 6.2 °C per spermine for a decanucleotide probe). The large data set of Tm vs number of spermines and oligonucleotide length allowed us to empirically derive a simple mathematical relation that is accurately predicting the Tm of any oligonucleotide−oligospermine derivative. Zip nucleic acids (ZNA) are thus providing an interesting alternative to locked nucleic acids (LNA) or minor groove binders (MGB) for raising the stability of 8−12-mer oligonucleotides up to ca. 70 °C, the level required for quantitative PCR experiments

Cationic siRNAs Provide Carrier-Free Gene Silencing in Animal Cells

siRNA-mediated gene silencing requires intracellular delivery of the nucleic acid. We have developed a carrierless molecular approach that follows the same cell entry route as cationic supramolecular complexes, yet should avoid the extracellular barriers encountered by nanoparticles. Cationic oligospermine−oligonucleotide conjugates (ZNAs, for Zip Nucleic Acids) were synthesized stepwise on an oligonucleotide synthesizer using a DMT-spermine phosphoramidite derivative. They were shown to enter cells and have access to the cytoplasm, provided their formal charge ratio N/P was >1.5. Cationic siRNAs that fulfilled this condition were shown to achieve selective inhibition of luciferase gene expression in the submicromolar concentration range in constitutively luciferase-expressing cells

Effective polyethylenimine-mediated gene transfer into human endothelial cells

Background The major advantage in choosing non‐viral vectors such as cationic polymers for in vitro and in vivo transfection is their higher biosafety than viral ones. Among the cationic polymers, polyethylenimines (PEIs) are promising molecules for gene delivery to a variety of cells. Efficient transfection of primary endothelial cells using PEIs could be regarded as an interesting strategy of treatment in some ischemic cardiovascular diseases. Methods Efficacies of a 22‐kDa linear PEI (L‐PEI) and its glucose‐grafted derivative (L‐PEI‐Glc4) were compared for gene transfer into human umbilical vein endothelial cells (HUVEC) using the reporter gene luciferase. Cells were incubated for 2, 4 and 24 h with PEI/DNA complexes made in 150 mM sodium chloride (NaCl) or in 5% glucose solution. Luciferase activity was measured 24 h after the onset of transfection. The effects of low (2%) and high (30%) concentrations of serum on transfection efficacy were assessed as well. We then studied the intracellular fate of the PEI/DNA complexes labelled with the DNA intercalator YOYO‐1 using flow cytometry analysis (FACS) and confocal microscopy. Results PEI/DNA complexes formed in NaCl led to a higher transfection efficacy than those made in glucose. The optimal formulation, depending on the incubation time and the presence of serum in the medium, was obtained using DNA complexed to L‐PEI‐Glc4 and incubated for 4 h with the cells. This condition led to 50% fluorescent cells after GFP transfection. A high serum concentration diminished the L‐PEI associated toxicity but decreased L‐PEI‐Glc4 transfection efficiency. FACS analysis using both vectors showed that almost 90% of the cells had internalized the DNA complexes. Confocal microscopic observations showed a fast attachment of the complexes to the cell surface followed by inclusion into vesicles that migrated to the perinuclear region. Conclusions In this work, we defined the optimal conditions for gene delivery in HUVEC. These conditions were obtained when using derivatives L‐PEI and L‐PEI‐Glc4 complexed with DNA in 150 mM NaCl and added to cells for 2 and 4 h, respectively. Cellular trafficking of the complexes suggested that cell entry was not a limiting factor for gene delivery using PEI. This study underlined the interest in PEIs as efficient vectors for gene transfer into human endothelial cells

Genuine DNA/polyethylenimine (PEI) Complexes Improve Transfection Properties and Cell Survival

Polyethylenimine (PEI) has been described as one of the most efficient cationic polymers for in vitro gene delivery. Systemic delivery of PEI/DNA polyplexes leads to a lung-expression tropism. Selective in vivo gene transfer would require targeting and stealth particles. Here, we describe two strategies for chemically coupling polyethylene glycol (PEG) to PEI, to form protected ligand-bearing particles. Pre-grafted PEG–PEI polymers lost their DNA condensing property, hence their poor performances. Coupling PEG to pre-formed PEI/DNA particles led to the expected physical properties. However, low transfection efficacies raised the question of the fate of excess free polymer in solution. We have developed a straightforward a purification assay, which uses centrifugation-based ultrafiltration. Crude polyplexes were purified, with up to 60% of the initial PEI dose being removed. The resulting purified and unshielded PEI/DNA polyplexes are more efficient for transfection and less toxic to cells in culture than the crude ones. Moreover, the in vivo toxicity of the polyplexes was greatly reduced, without affecting their efficacy

Polyethylenimine-mediated gene transfer into pancreatic tumor dissemination in the murine peritoneal cavity

Although peritoneal dissemination of cancer cells often occurs at the advanced stages of pancreatic, gastric or ovarian cancers, no effective therapy has been established. Cationic lipid-mediated gene transfer into peritoneal dissemination may offer a prospect of safe therapies, but vector improvements are needed with regard to the efficiency and specificity of the gene transfer. In this study, the intraperitoneal injection of plasmid DNA:polyethylenimine (PEI) complexes into mice was evaluated as a gene delivery system for the peritoneal disseminations. The luciferase and β-galactosidase genes were used as marker genes. PEI was more efficient than the cationic lipids examined in this study in vivo, and the transgene was preferentially expressed in the tumors. Although PCR analysis showed that the injected DNA was delivered to various organs, the distributed DNA became undetectable by 6 months after the gene transfer. Blood chemistry and histological analysis showed no significant toxicity in the injected mice. This study demonstrated that the intraperitoneal injection of DNA:PEI is a promising delivery method to transduce a gene into disseminated cancer nodules in the peritoneal cavity

Inhibition of hepadnaviral replication by polyethylenimine-based intravenous delivery of antisense phosphodiester oligodeoxynucleotides to the liver

Antisense oligodeoxynucleotides (ODNs) appear as attractive anti-hepatitis B virus (HBV) agents. We investigated in vivo, in the duck HBV (DHBV) infection model, whether linear polyethylenimine (lPEI)-based intravenous delivery of the natural antisense phosphodiester ODNs (O-ODNs) can prevent their degradation and allow viral replication inhibition in the liver. DHBV-infected Pekin ducklings were injected with antisense O-ODNs covering the initiation codon of the DHBV large envelope protein, either in free form (O-ODN-AS2) or coupled to lPEI (lPEI/O-ODN-AS2). Following optimization of lPEI/O-ODN complex formulation, complete O-ODN condensation into a homogenous population of small (20–60 nm) spherical particles was achieved. Flow cytometry analysis showed that lPEI-mediated transfer allowed the intrahepatic delivery of lPEI/O-ODN-AS2 to increase three-fold as compared with the O-ODN-AS2. Following 9-day therapy the intrahepatic levels of both DHBV DNA and RNA were significantly decreased in the lPEI/O-ODN-AS2-treated group as compared with the O-ODN-AS2-treated, control lPEI/O-ODN-treated, and untreated controls. In addition, inhibition of intrahepatic viral replication by lPEI/O-ODN-AS2 was not associated with toxicity and was comparable with that induced by the phosphorothioate S-ODN-AS2 at a five-fold higher dose. Taken together, our results demonstrate that phosphodiester antisense lPEI/O-ODN complexes specifically inhibit hepadnaviral replication. Therefore we provide here the first in vivo evidence that intravenous treatment with antisense phosphodiester ODNs coupled to lPEI can selectively block a viral disease-causing gene in the liver