Transcription of plasmid DNA: Influence of plasmid DNA/polyethylenimine complex formation

Optimization of 25kDa linear polyethylenimine for efficient gene delivery

A 25-kDa linear polyethylenimine (25 kDa L-PEI) has proven to be efficient and versatile agent for gene delivery. Therefore, we determined the optimal transfection conditions of 25 kDa L-PEI and examined whether it has comparable transfection efficiency with other commercially available reagents, ExGen 500, LipofectAMINE 2000, and Effectene by using EGFP expression vector in different cell lines. Transfection efficiency and cytotoxicity were measured by flow cytometry. First of all, we determined the optimal ratio of nitrogen to phosphorous (N/P) and DNA concentration. With the increase of N/P ratio and DNA amounts, transfection efficiency increased with a slight variation in cell types. The optimal amounts of 25 kDa L-PEI were determined at N/P ratio 40 and DNA concentration varied among the cell types. In addition, 25 kDa L-PEI worked efficiently and was less toxic than other reagents. However, the efficiency and toxicity of all these reagents varied according to cell types as well as the ratio of DNA to reagents and the amounts of DNA. Our finding illustrates the importance of optimal transfection conditions of 25 kDa L-PEI to obtain maximal transgene expression with less cytotoxicity. Importantly, the optimization of those conditions may make possible to perform transfection cost-effectively and efficiently.

Influence of polyethylene glycol chain length on the physicochemical and biological properties of poly(ethylene imine)-graft-poly(ethylene glycol) block copolymer/SiRNA polyplexes

Polyplexes between siRNA and poly(ethylene imine) (PEI) derivatives are promising nonviral carriers for siRNA. The polyplex stability is of critical importance for efficient siRNA delivery to the cytoplasm. Here, we investigate the effect of PEGylation at a constant ratio ( approximately 50%) on the biophysical properties of the polyplexes. Particle size, zeta potential, and stability against heparin as well as RNase digestion and reporter gene knockdown under in vitro conditions of different siRNA polyplexes were characterized. Stability and size of siRNA polyplexes were clearly influenced by PEI-PEG structure, and high degrees of substitution such as PEI(25k)-g-PEG(550)(30) resulted in large (300-400 nm), diffuse complexes (AFM) which showed condensation behavior only at high N/P ratios. All other polyplexes and the PEI control showed similar sizes (150 nm) and compact structures in AFM, with complete condensation reached at N/P ratio of 3. Stability of siRNA polyplexes against heparin displacement and RNase digestion could be modified by PEGylation. Protection against RNase digestion was highest for PEI(25k)-g-PEG(5k)(4) and PEI(25k)-g-PEG(20k)(1), while siRNA/PEI provided insufficient protection. In knockdown experiments using NIH/3T3 fibroblasts stably expressing beta-galactosidase, it was shown that PEG chain length had a significant influence on biological activity of siRNA. Polyplexes with siRNA containing PEI(25k)-g-PEG(5k)(4) and PEI(25k)-g-PEG(20k)(1) yielded similar efficiencies of ca. 70% knockdown as lipofectamine controls. Confocal microscopy demonstrated enhanced cellular uptake of siRNA into cytosol by polyplexes formation with PEI copolymers. In conclusion, both the chain length and graft density of PEG were found to strongly influence siRNA condensation and stability and hence affect the knockdown efficiency of PEI-PEG/siRNA polyplexes.

Non-viral vector delivery from PEG-hyaluronic acid hydrogels

Hydrogels have been widely used in tissue engineering as a support for tissue formation or to deliver non-viral gene therapy vectors locally. Hydrogels that combine these functionalities can provide a fundamental tool to promote specific cellular processes leading to tissue formation. This report investigates controlled release of gene therapy vectors from hydrogels as a function of the physical properties for both the hydrogel and the vector. Hydrogels were formed by photocrosslinking acryl-modified hyaluronic acid (HA) with a 4-arm poly(ethylene glycol) (PEG) acryl. The polymer content, and relative composition of HA and PEG modulated the swelling ratio, water content, and degradation, which can influence transport of the vector through the hydrogel. All hydrogels had a water content of 94% or higher, though the water content and swelling ratio increased with a decrease in the PEG:HA ratio. Plasmids were stably incorporated into the hydrogel, with a majority of the release occurring during the initial 2 days. For incubation in buffer, the cumulative release increased with a decreasing PEG or increasing HA content, with approximately 20% to 80% released during the first week depending on the hydrogel composition. Hydrogels incubated in hyaluronidase, an enzyme that degrades HA, significantly increased plasmid release for hydrogels containing 4% PEG and 4% HA-Acryl. The encapsulation of plasmid complexed with polyethylenimine had less than 14% of the complexes released from the hydrogel both in the presence and absence of hyaluronidase. The limited release of the complexes likely results from the complex size and interactions between the vector and hydrogel. These studies demonstrate the dependence of non-viral vector release on the physical properties of the hydrogel and the vector, suggesting vector and hydrogel designs for maximizing localized delivery of non-viral vectors.

Crosslinked nanocarriers based upon poly(ethylene imine) for systemic plasmid delivery: In vitro characterization and in vivo studies in mice

Crosslinked poly(ethylene imine) (PEI) polyplexes for intracellular DNA release were generated using a low molecular weight crosslinking reagent, Dithiobis(succinimidyl propionate) (DSP). Disulfide bonds of the crosslinked polyplexes were susceptible to intracellular redox conditions and DNA release was observed using an ethidium bromide exclusion assay and dynamic light scattering. Transfection experiments were performed to elucidate the effect of extra- and intracellular redox conditions. Pharmacokinetics and organ accumulation of uncrosslinked and crosslinked polyplexes were compared and gene expression patterns were measured in mice 24 h after intravenous injection. Crosslinked PEI and plasmid DNA formed stable polyplexes in a size range of 100-300 nm, with zeta potentials between +16.4 and +26.1 mV. DNA release occurred after cleavage of the disulfide bonds. Cell culture experiments under reducing conditions as well as with glutathione loaded cells confirmed the proposed intracellular activation. A significant influence of the intracellular glutathione status on the transfection efficiency was observed. Pharmacokinetic profiles of crosslinked PEI/DNA polyplexes in mice after intravenous administration showed higher blood levels for crosslinked polyplexes. These polyplexes accumulated mainly in the liver and the lungs. In vivo transfection data revealed significantly reduced (unwanted) lung transfection while liver transfection predominated. These studies suggest that crosslinked polyplexes are more stable in circulation and retain their transfection efficiency after intravenous administration.

Ternary complex consisting of DNA, polycation, and a natural polysaccharide of schizophyllan to induce cellular uptake by antigen presenting cells

A natural polysaccharide called schizophyllan (SPG) can form a complex with polynucleotides, and the complex has been shown to deliver biofunctional short DNAs such as antisense DNAs and CpG-DNAs. Although it is a novel and efficient method, there is a drawback: attachment of homo-polynucleotide tails [for example, poly(dA) or poly(C)] to the end of DNA is necessary to stabilize the complex, because DNA heterosequences cannot bind to SPG. The aim of this paper is to present an alternative method in which SPG/DNA complexes can be made without using the tails. The basic strategy is as follows: since SPG can form hydrophobic domains in aqueous solutions, hydrophobic objects should be encapsulated by this domain. DNA alone is highly hydrophilic; however, once DNA/polycation complexes are made, they should be included by the SPG hydrophobic domain. The aim of this paper is to prove the formation of the polycation/DNA/SPG ternary complex. Gel electrophoresis showed that presence of SPG influenced the migration pattern of polycation+DNA mixtures. With increasing the SPG ratio, the zeta potential (zeta) of the polycation+DNA+SPG mixture decreased drastically to reach almost zeta = 0 and the particle size distributions were altered due to the ternary complex formation. Confocal laser scanning microscopy revealed that the polycation/DNA/SPG ternary complexes showed high uptake efficiency when the complexes were exposed to macrophage-like cells (J774.A1). IL-12 secretion was enhanced when CpG-DNA was added as the ternary complex. These features can be ascribed to the fact that J774.A1 has a SPG recognition site called Dectin-1 on the cellular surface and the ternary complex can be ingested by this pathway.

Polyplex-mediated gene transfer and cell cycle: effect of carrier on cellular uptake and intracellular kinetics, and significance of glycosaminoglycans

BACKGROUND

Here we report on studies that probe whether the intracellular kinetics of plasmid DNA (pDNA) and cell surface glycosaminoglycans (GAGs) are modified during the cell cycle in a way that can be correlated with changes in gene transfer efficiency with poly(ethyleneimine) (PEI) and poly-L-lysine (PLL) polyplexes.

METHODS

Synchronized D407 retinal cells were transfected with PEI and PLL polyplexes using a luciferase reporter. The free and/or loosely complexed nuclear pDNA was determined by real-time PCR, and compared with transgene expression, the rate of pinocytosis by FITC-dextran uptake and the content of cell surface GAGs.

RESULTS

The amount of free and/or loosely complexed nuclear pDNA between cell cycle phases varied approximately 4-20 times (G1 < S < G2/M). Both carriers delivered pDNA in a similar way into the nucleus (PLL vs. PEI < or = 3.5-fold), but PEI was approximately 10-100 times more efficient in gene expression than PLL (G1 < G2/M < S). The rate of pinocytosis increased up to 70-fold from G1 to middle S phase. Cell surface heparan and chondroitin sulfate increased 50-80%, and hyaluronan decreased 50% when the cells went from G1 through S to G2/M.

CONCLUSIONS

The data obtained indicates that no single parameter (pinocytosis, cell surface GAGs, nuclear uptake) solely accounts for the differential pDNA uptake or expression during cell cycle, and that the main difference in PLL- and PEI-mediated transfections seems to be at the nuclear level.

Which mechanism for nuclear import of plasmid DNA complexed with polyethylenimine derivatives?

BACKGROUND

To investigate the nuclear import mechanism of plasmid/polyethylenimine (PEI) derivative complexes and the putative nuclear targeting of therapeutic genes by the use of oligosaccharides, we have studied the nuclear import of plasmid DNA complexed either with PEI or with lactosylated PEI (Lac-PEI) in cystic fibrosis human airway epithelial cells ( summation operatorCFTE29o- cells).

METHODS AND RESULTS

Cells were synchronized by a double-thymidine block protocol and gene transfer efficiency was evaluated: Lac-PEI- and PEI-mediated gene transfer was greatly increased when cells have undergone mitosis during the course of transfection. However, both types of complexes were able to transfect some growth-arrested cells. When the nuclear import of plasmid/Lac-PEI or plasmid/unsubstituted PEI complexes was studied in digitonin-permeabilized cells, the nuclear uptake of both types of complexes did not follow the classic pathway of nuclear localization sequence (NLS)-containing proteins and lactose residues did not act as a nuclear localization signal.

CONCLUSIONS

Our results show that for complexes made with PEI derivatives, the major route for plasmid DNA nuclear entry is a passive nuclear importation during mitosis when the nuclear membrane temporarily breaks down. However, albeit to a lesser extent as that observed in dividing cells, a plasmid DNA importation also occurs in nondividing cells by a yet unknown mechanism.