Polymeric gene carrier for insulin secreting cells: poly(L-lysine)-g-sulfonylurea for receptor mediated transfection

Tempo-spatial Activation of Sequential Quadruple Stimuli for High Gene Expression of Polymeric Gene Nanocomplexes

The clinical application of intracellular gene delivery via nanosized carriers is hindered by intracellular multistep barriers that limit high levels of gene expression. To solve these issues, four different intracellular or external stimuli that can efficiently activate a gene carrier, a gene, or a photosensitizer (pheophorbide A [PhA]) were assessed in this study. The designed nanosized polymeric gene complexes were composed of PhA-loaded thiol-degradable polycation (PhA@RPC) and cytomegalovirus (CMV) promoter-equipped pDNA. After cellular internalization of the resulting PhA@RPC/pDNA complexes, the complexes escaped endosomal sequestration, owing to the endosomal pH-induced endosomolytic activity of RPC in PhA@RPC. Subsequently, intracellular thiol-mediated polycation degradation triggered the release of PhA and pDNA from the complexes. Late exposure to light (for example, 12 h post-treatment) activated the released PhA and resulted in the production of reactive oxygen species (ROS). Intracellular ROS successively activated NF-κB, which then reactivated the CMV promoter in the pDNA. These sequential, stimuli-responsive chemical and biological reactions resulted in high gene expression. In particular, the time-point of light exposure was very significant to tune efficient gene expression as well as negligible cytotoxicity: early light treatment induced photochemical internalization but high cytotoxicity, whereas late light treatment influenced the reactivation of silent pDNA via PhA-generated ROS and activation of NF-κB. In conclusion, the quadruple triggers, such as pH, thiol, light, and ROS, successively influenced a gene carrier (RPC), a photosensitizer, and a genetic therapeutic, and the tempo-spatial activation of the designed quadruple stimuli-activatable nanosized gene complexes could be potential in gene delivery applications.

DNA Polyplexes as Combinatory Drug Carriers of Doxorubicin and Cisplatin: An in Vitro Study

Double helix nucleic acids were used as a combination drug carrier for doxorubicin (DOX), which physically intercalates with DNA double helices, and cisplatin (CDDP), which binds to DNA without an alkylation reaction. DNA interacting with DOX, CDDP, or both was complexed with positively charged, endosomolytic polymers. Compared with the free drug, the polyplexes (100-170 nm in size) delivered more drug into the cytosol and the nucleus and demonstrated similar or superior (up to a 7-fold increase) in vitro cell-killing activity. Additionally, the gene expression activities of most of the chemical drug-loaded plasmid DNA (pDNA) polyplexes were not impaired by the physical interactions between the nucleic acid and DOX/CDDP. When a model reporter pDNA (luciferase) was employed, it expressed luciferase protein at 0.7- to 1.4-fold the amount expressed by the polyplex with no bound drugs (a control), which indicated the fast translocation of the intercalated or bound drugs from the "carrier DNA" to the "nuclear DNA" of target cells. The proposed concept may offer the possibility of versatile combination therapies of genetic materials and small molecule drugs that bind to nucleic acids to treat various diseases.

Dexamethasone-loaded reconstitutable charged polymeric (PLGA)n -b-bPEI micelles for enhanced nuclear delivery of gene therapeutics

This study investigates the potential of dexamethasone (Dex) to enhance the nuclear accumulation and subsequent gene expression of plasmid DNA (pDNA) delivered using a charged polymeric micelle-based gene delivery system. (PLGA)n -b-bPEI25kDa block copolymers are synthesized and used to prepare Dex-loaded cationic micelles (DexCM). After preparing DexCM/pDNA complexes, bPEI1.8kDa is coated on the complexes using a Layer-by-Layer (LbL) technique to construct DexCM/pDNA/bPEI1.8kDa complexes (i.e., LbL-DexCM polyplexes) that are 100-180 nm in diameter and have a zeta potential of 30-40 mV. In MCF7 cells, LbL-DexCM polyplexes cause 3-13-fold higher transfection efficiencies compared to LbL-CM polyplexes and show negligible cytotoxicity. LbL-DexCM3 polyplexes induce much higher nuclear delivery of pDNA compared to LbL-CM3 polyplexes. These results suggest that Dex-loaded polyplexes could be used in gene and drug delivery applications to increase nuclear accumulation of therapeutic payloads, further leading to a decrease in the dose of the drug and gene necessary to achieve equivalent therapeutic effects.

Endosomolytic reducible polymeric electrolytes for cytosolic protein delivery

Despite the numerous vital functions of proteins in the cytosolic compartment, less attention has been paid to the delivery of protein drugs to the cytosol than to the plasma membrane. To address this issue and effectively deliver charged proteins into the cytoplasm, we used endosomolytic, thiol-triggered degradable polyelectrolytes as carriers. The cationic, reducible polyelectrolyte RPC-bPEI(0.8 kDa)2 was synthesized by the oxidative polymerization of thiolated branched polyethyleneimine (bPEI). The polymer was converted to the anionic, reducible polyelectrolyte RPA-bPEI(0.8 kDa)2 by introducing carboxylic acids. The two reducible polyelectrolytes (RPC-bPEI(0.8 kDa)2 and RPA-bPEI(0.8 kDa)2) were complexed with counter-charged model proteins (bovine serum albumin (BSA) and lysozyme (LYZ)), forming polyelectrolyte/protein complexes of less than 200 nm in size at weight ratios (WR) of ≥1. The resultant complexes maintained a proton buffering capacity nearly equivalent to that of the polyelectrolytes in the absence of protein complexation and were cytocompatible with MCF7 human breast carcinoma cells. Under cytosol-mimicking thiol-rich conditions, RPC-bPEI(0.8 kDa)2/BSA and RPA-bPEI(0.8 kDa)2/LYZ complexes increased significantly in size and released the loaded protein, unlike the protein complexes with nonreducible polyelectrolytes (bPEI(25 kDa) and bPEI(25 kDa)COOH). The polyelectrolyte/protein complexes showed cellular uptake similar to that of the corresponding proteins alone, but the former allowed more protein to escape into the cytosol from endolysosomes than the latter as a result of the endosomolytic function of the polyelectrolytes. In addition, the proteins in the polyelectrolyte/protein complexes kept their intrinsic secondary structures. In conclusion, the results show the potential of the designed endosomolytic, reducible polyelectrolytes for the delivery of proteins to the cytosol.

Nanoparticles for gene delivery

Nanocarriers are a new type of nonviral gene carriers, many of which have demonstrated a broad range of pharmacological and biological properties, such as being biodegradable in the body, stimulus-responsive towards the surrounding environment, and an ability to specifically targeting certain disease sites. By summarizing some main types of nanocarriers, this Concept considers the current status and possible future directions of the potential clinical applications of multifunctional nanocarriers, with primary attention on the combination of such properties as biodegradability, targetability, transfection ability, and stimuli sensitivity.

Effective antitumor gene therapy delivered by polyethylenimine-conjugated stearic acid-g-chitosan oligosaccharide micelles

Non-viral vesicle composing of low-molecular weight polyethylenimine-conjugated stearic acid-g-chitosan oligosaccharide (CSOSA-g-PEI) was synthesized for gene delivery and therapy. The synthesized CSOSA-g-PEI had good ion-buffer capabilities and DNA-binding capacity, which could form positively charged nano-sized particles (100-150 nm) with plasmid DNA; in vitro gene transfection tests demonstrated that CSOSA-g-PEI presented much lower cytotoxicity and corresponding transfection efficiency in comparison with Lipofectamine 2000 in both human cancer cells (Hela and MCF-7). The gene transfection of CSOSA-g-PEI/pDNA could be further enhanced in the presence of serum or by adding arginine during incubation of CSOSA-g-PEI micelles with plasmid DNA. The biodistribution experiments demonstrated CSOSA-g-PEI conjugate highly localized in the tumor tissue and indicated a persistently increased accumulation. In vivo antitumor activity results showed that CSOSA-g-PEI/plasmid pigment epithelium-derived factor formulation could effectively suppress the tumor growth (above 60% tumor inhibition) without systematic toxicity against animal body after intravenous injection.

The effect of environmental pH on polymeric transfection efficiency

Although polymers, polyplexes, and cells are exposed to various extracellular and intracellular pH environments during polyplex preparation and polymeric transfection, the impact of environmental pH on polymeric transfection has not yet been investigated. This study aims to understand the influence of environmental pH on polymeric transfection by modulating the pH of the transfection medium or the culture medium. Changes in the extracellular pH affected polymeric transfection by way of complex factors such as pH-induced changes in polymer characteristics (e.g., proton buffering capacity and ionization), polyplex characteristics (e.g., size, surface charge, and decomplexation), and cellular characteristics (e.g., cellular uptake, cell cycle phases, and intracellular pH environment). Notably, acidic medium delayed endocytosis, endosomal acidification, cytosolic release, and decomplexation of polyplexes, thereby negatively affecting gene expression. However, acidic medium inhibited mitosis and reduced dilution of gene expression, resulting in increased transfection efficiency. Compared to pH 7.4 medium, acidic transfection medium reduced gene expression 1.6-7.7-fold whereas acidic culture medium enhanced transfection efficiency 2.1-2.6-fold. Polymeric transfection was affected more by the culture medium than by the transfection medium. Understanding the effects of extracellular pH during polymeric transfection may stimulate new strategies for determining effective and safe polymeric gene carriers.

Co-delivery of small interfering RNA and plasmid DNA using a polymeric vector incorporating endosomolytic oligomeric sulfonamide

Cationic polymers are potential intracellular carriers for small interfering RNA (siRNA). The short and rigid nature of an siRNA chain often results in larger and more loosely packed particles compared to plasmid DNA (pDNA) after complexing with carrier polycations, and in turn, poor silencing effects are seen against the target mRNAs. A helper polyanion, pDNA, was incorporated along with siRNA to form compact nanosized polyplexes. At C/A (cation/anion) ratios of 2 and 5, poly(l-lysine) (PLL)/siRNA-pGFP and PLL/siRNA-pGFP-OSDZ (oligomeric sulfadiazine (OSDZ) for endosomolysis) complexes produced particles 90-150 nm in size with a 15-45 mV surface charge, while PLL/siRNA complexes yielded particles 1-2 μm in size at the same C/A ratios. The PLL/siRNA-pGFP (C/A 2) complexes showed significantly higher specific gene silencing (50-90% vs. 10-25%) than the complexes formed at C/A 5. PLL/siRNA-pGFP-OSDZ (C/A 2) complexes improved the specific gene silencing (90%) more dramatically than PLL/siRNA-pGFP (C/A 2) complexes (50%), demonstrating a potential role for OSDZ. PLL/siRNA-pGFP-OSDZ (C/A 2) complexes sustained higher specific gene silencing compared with PLL/siRNA-pGFP (C/A 2) complexes. Other oligomeric sulfonamides (OSA) with varying pK(a) used in PLL/siRNA-pGFP-OSA complexes also caused effective gene silencing. The pGFP in the PLL/siRNA-pGFP complexes successfully expressed GFP protein without interfering with the siRNA. In conclusion, this study demonstrates that long pDNA helps effectively form nanosized siRNA particles and that OSA enhances specific gene silencing. In a single nucleic acid carrier formulation, co-delivery of siRNA and pDNA is feasible to maximize therapeutic effects or to include therapeutic or diagnostic functionalities.

Reconstitutable charged polymeric (PLGA)(2)-b-PEI micelles for gene therapeutics delivery

This study investigated the potential of creating a charged polymeric micelle-based nucleic acid delivery system that could easily be reconstituted by the addition of water. (PLGA(36kDa))(2)-b-bPEI(25kDa) (PLGA MW 36 kDa, bPEI M(w) 25 kDa, PLGA:bPEI block ratio = 2) was synthesized and used to prepare cationic micelles. The copolymer retained proton-buffering capability from the bPEI block within the endosomal pH range. Micelle/pDNA complexes retained their particle size (100-150 nm) and surface charge (30-40 mV) following reconstitution. It was found that adding a small amount of low molecular weight bPEI (1.8 kDa) completely shielded pDNA in the micelle/pDNA complexes and enhanced transfection efficiency 50-100 fold for both fresh and reconstituted complexes without affecting complex size. Transfection efficiency for "reconstituted" micelle/pDNA/bPEI(1.8kDa) (WR 1) complexes was 16-fold higher than its "fresh" counterpart. Although transfection levels achieved using "reconstituted" micelle/pDNA/bPEI(1.8kDa) complexes were 3.6-fold lower than control "fresh" bPEI(25kDa)/pDNA (N/P 5) complexes, transfection levels were 39-fold higher than "reconstituted" bPEI(25kDa)/pDNA (N/P 5) complexes. The micelle/pDNA/bPEI(1.8kDa) system showed very low cytotoxicity in MCF7 cells even with pDNA doses up to 20 μg, and transfection levels increased linearly with increasing pDNA dose. These results indicate that this PLGA-b-bPEI polymeric micelle-based system is well suited as a reconstitutable gene delivery system, and has high potential for use as a delivery system for gene therapy applications.

A reducible polycationic gene vector derived from thiolated low molecular weight branched polyethyleneimine linked by 2-iminothiolane

To improve transfection efficiency and reduce the cytotoxicity of polymeric gene vectors, reducible polycations (RPC) were synthesized from low molecular weight (MW) branched polyethyleneimine (bPEI) via thiolation and oxidation. RPC (RPC-bPEI(0.8 kDa)) possessed MW of 5 kDa-80 kDa, and 50%-70% of the original proton buffering capacity of bPEI(0.8 kDa) was preserved in the final product. The cytotoxicity of RPC-bPEI(0.8 kDa) was 8-19 times less than that of the gold standard of polymeric transfection reagents, bPEI(25 kDa). Although bPEI(0.8 kDa) exhibited poor gene condensing capacities (∼2 μm at a weight ratio (WR) of 40), RPC-bPEI(0.8 kDa) effectively condensed plasmid DNA (pDNA) at a WR of 2. Moreover, RPC-bPEI(0.8 kDa)/pDNA (WR ≥2) formed 100-200 nm-sized particles with positively charged surfaces (20-35 mV). In addition, the results of the present study indicated that thiol/polyanions triggered the release of pDNA from RPC-bPEI(0.8 kDa)/pDNA via the fragmentation of RPC-bPEI(0.8 kDa) and ion-exchange. With negligible polyplex-mediated cytotoxicity, the transfection efficiencies of RPC-bPEI(0.8 kDa)/pDNA were approximately 1200-1500-fold greater than that of bPEI(0.8 kDa)/pDNA and were equivalent or superior (∼7-fold) to that of bPEI(25 kDa)/pDNA. Interestingly, the distribution of high MW RPC-bPEI(0.8 kDa)/pDNA in the nucleus of the cell was higher than that of low MW RPC-bPEI(0.8 kDa)/pDNA. Thus, the results of the present study suggest that RPC-bPEI(0.8 kDa) has the potential to effectively deliver genetic materials with lower levels of toxicity.

Trafficking microenvironmental pHs of polycationic gene vectors in drug-sensitive and multidrug-resistant MCF7 breast cancer cells

While multidrug resistance (MDR) has been a significant issue in cancer chemotherapy, delivery resistance to various anti-cancer biotherapeutics, including genes, has not been widely recognized as a property of MDR. This study aims to provide a better understanding of the transfection characteristics of drug-sensitive and drug-resistant cells by tracing microenvironmental pHs of two representative polymer vectors: poly(L-lysine) and polyethyleneimine. Drug-sensitive breast MCF7 cells had four- to seven-times higher polymeric transfection efficiencies than their counterpart drug-resistant MCF7/ADR-RES cells. Polyplexes in MCF7/ADR-RES cells after endocytosis were exposed to a more acidic microenvironment than those in MCF7 cells; the MDR cells show faster acidification rates in endosomes/lysosomes than the drug-sensitive cells after endocytosis (in the case of PLL/pDNA complexes, approximately pH 5.1 for MCF7/ADR-RES cells vs. approximately pH 6.8 for MCF7 cells at 0.5 h post-transfection). More polyplexes were identified trapped in acidic subcellular compartments of MCF7/ADR-RES cells than in MCF7 cells, suggesting that they lack endosomal escaping activity. These findings demonstrate that the design of polymer-based gene delivery therapeutics should take into account the pH of subcellular compartments.

Degradable poly(amino ester) based on poly(ethylene glycol) dimethacrylate and polyethylenimine as a gene carrier: molecular weight of PEI affects transfection efficiency

The aim of the research is to study the effect of polyethylenimine (PEI) molecular weight on the gene transfection efficiency of degradable poly(amino ester) based on poly(ethylene glycol) dimethacrylate (PEGDMA) and polyethylenimine (PEG-cr-PEI) as a gene carrier. Various low molecular weight (LMW) branched PEI based PEG-cr-PEI was synthesized via Michael addition. The degradation half-life of PEG-cr-PEI was longer at pH 5.6 than that at pH 7.4. The plasmid condensation and protection ability of the PEG-cr-PEI were confirmed by agarose gel electrophoresis assay. PEG-cr-PEI/DNA nanoparticles showed high positive zeta potential (>+20 mV), narrow size distribution, and spherical shapes with size below 250 nm when N/P ratios of PEG-cr-PEI to DNA were above 10, suggesting that they have endocytosis potential. The cytotoxicity of PEG-cr-PEI/DNA complexes was lower than that of PEI 25K/DNA complexes, and the transfections mediated by PEG-cr-PEI were checked in 293T, HeLa and HepG2 cell lines. The report gene expression was increased with increasing the molecular weight of LMW PEI. The "proton sponge effect" was proposed as the mechanism of PEG-cr-PEI mediated gene transfection.

In vitro assessment of a novel polyrotaxane-based drug delivery system integrated with a cell-penetrating peptide

In the development of anti-cancer drugs, it is important to yield selective cytotoxicity primarily against tumor tissues. To achieve this goal, the use of a polymer-drug conjugate appears to be appealing, simply because it can take the advantage of the so-called enhanced permeability and retention (EPR) effect due to vascular leak in tumors. Among various types of polymers, polyrotaxane (PR) is an interesting candidate and warrants further consideration. It is a self-assembled polymer made entirely of biocompatible components, by threading alpha-cyclodextrin (alpha-CD) molecules with the poly(ethylene glycol) (PEG) chain. The abundance in functional -OH groups on the CD residues renders PR the capability of carrying a large dose of small anti-tumor agents for delivery. Herein, we presented a novel PR-based delivery system using doxorubicin (DOX) as the model anti-cancer drug. Daunorubicin (DNR) was conjugated to the PR polymer via hydrolysable linkages, and upon hydrolysis, doxorubicin was released as the cytotoxic drug. To facilitate an intracellular uptake by the tumor cells of the PR-DOX conjugates, a cell-penetrating low molecular weight protamine (LMWP) peptide was further attached to the two termini of the PR chain. Using an innovative principle established in our laboratory, such as via the inhibition of the cell-penetrating activity by binding with heparin and reversal of this inhibition by subsequent addition of protamine, cellular uptake of the polymer-drug conjugates could be readily regulated. In this paper, we performed in vitro studies to demonstrate the feasibility of this delivery system. The LMWP-PR-DOX conjugates, which yielded a sustained release of DOX over a period of greater than 4 days, were successfully synthesized. Intracellular uptake of these conjugates by A2780 human ovarian cancer cells and regulation of such uptake by heparin and protamine were confirmed by using the MTT assay and also the confocal microscopy method.

Self-assembled polyethylenimine-graft-poly(epsilon-caprolactone) micelles as potential dual carriers of genes and anticancer drugs

A series of amphiphilic cationic graft polymers (PEC) were synthesized by coupling poly(epsilon-caprolactone) of differing molecular weights (MW) to low MW branched polyethylenimine via an amide group. IR, (1)H-NMR and GPC were employed to characterize the graft copolymers. The self-assembly characteristics of these copolymers in an aqueous solution were studied by fluorescence techniques. The critical micelle concentration (CMC) varied from 0.044 to 0.032g/L when the MW of poly(epsilon-caprolactone) increased from 1,800 to 5,500. The micelles formed electrostatic complexes with a reporter gene (pCMV-Luc) after an anticancer drug, Doxorubicin (DOX), was loaded by dialysis method. Gel retardation studies proved that micelles with or without DOX were able to complex with DNA completely at an equivalent N/P ratio of around 2.0, indicating that drug loading did not interfere in the interaction between the PEI shell and DNA. Particle size slightly decreased at higher N/P ratios of polyplexes, but increased with drug encapsulation. It was also noted that DNA/micelle complexes were significantly less toxic to HepG2 cells than blank PEC micelles, and improved gene transfection efficiency (about 3 orders of magnitude greater than PEI 25K alone at most) whether DOX was present in the system or not. These results suggest that this group of cationic graft polymers may be a potential candidate for the development of a drug delivery system that can examine the synergistic effects of combined drug and gene therapy.

An overview of condensing and noncondensing polymeric systems for gene delivery

INTRODUCTIONSelf-assembling synthetic vectors for DNA delivery are designed to fulfill several biological functions. They must be able to deliver their genetic payload specifically to the target tissue/cells in a site-specific manner, while protecting the genetic material from degradation by metabolic or immune pathways. Furthermore, they must exhibit minimal toxicity and be proven safe enough for therapeutic use. Ultimately, they must have the capability to express a therapeutic gene for a finite period of time in an appropriate, regulated fashion. The DNA encapsulated in these vectors may be in a condensed or noncondensed form, depending on the nature of the polymer and the technique used for formulating the vector system. The whole process presents many barriers at both tissue and cellular levels. Overcoming these hurdles is the principal objective for efficient polymer-based DNA therapeutics.

Nonviral delivery vehicles for use in short hairpin RNA-based cancer therapies

The use of DNA vector-based short hairpin (sh)RNA for RNA interference shows promise as a precise means for the disruption of gene expression to achieve a therapeutic effect. The in vivo usage of shRNA therapeutics in cancer is limited by obstacles related to effective delivery into the nuclei of target cancer cells. Nonviral delivery vehicles that are relevant for shRNA delivery into humans belong to a group of substances about which significant preclinical data has been amassed to show an acceptable safety profile, resistance to immune defenses and good transfection efficiency. Here, we review the most promising current nonviral gene delivery vehicles with a focus on their potential use in cancer shRNA therapeutics.

Polymeric gene transfection on insulin-secreting cells: sulfonylurea receptor-mediation and transfection medium effect

PURPOSE

In vitro transfection of secreting cells is regarded as one strategy for improved cell engineering/ transplantation. Insulin-secreting insulinoma cell lines or pancreatic beta-cells could be genetically engineered using designed polymeric vectors which are safer than viral vectors. This study investigates the effects of the constituents in transfection media on polymeric transfection.

METHODS

Polyplexes conjugated with sulfonylurea (SU) were evaluated under different transfection conditions for gene transfection and their effects on cytotoxicity and insulin secretion. Several components in transfection media specifically associated with the insulin secretion pathway were amino acids, vitamins, Ca2+ and K+. The interactions of the polyplexes with insulin were monitored by surface charge and particle size to monitor how insulin as a protein influences transfection.

RESULTS

For an insulin-secreting cell line (RINm5F), polyplexes in Ca2+--containing KRH medium (Ca2+(+)KRH) enhanced transfection and did not cause damage to biological functions. When adding amino acids, vitamins, or K+ or depleting Ca2+ from Ca2+(+)KRH, poly(L-lysine)/DNA complexes showed a greater reduction in transfection than SU receptor (SUR)-targeting polyplexes (SU-polyplex). Positively charged polyplexes interacted with insulin, developing a negative surface charge, and these interactions may cause a decrease in transfection.

CONCLUSION

The findings suggest that in vitro and ex vivo polymeric transfection of insulin-secreting cells can be modulated and enhanced by adjusting the transfection conditions.

Biodegradable cationic polyester as an efficient carrier for gene delivery to neonatal cardiomyocytes

Viral-mediated gene delivery has been explored for the treatment and protection of cardiomyocytes, but so far there is only one report using cationic polymer for gene delivery to cardiomyocytes in spite of many advantages of polymer-mediated gene delivery. In this study, a cationic poly(beta-amino ester) (PDMA) with a degradable backbone and cleavable side chains was synthesized by Michael addition reaction. The toxicity of PDMA to neonatal mouse cardiomyocytes (NMCMs) was significantly lower than that of polyethyleneimine (PEI). PDMA formed stable polyplexes with pEGFP. The dissociation of the polyplexes could be triggered by PDMA degradation, and the dissociation time was tunable via the polymer/pEGFP ratio. In vitro transfection showed that PDMA was an effective and low toxic gene delivery carrier for NMCMs. The PDMA/pEGFP polyplexes transfected EGFP gene to NMCMs with about 28% efficiency and caused little death. In contrast, a significant portion of cardiomyocytes cultured with PEI/pEGFP died.

Hypoxia-inducible gene expression system using the erythropoietin enhancer and 3′-untranslated region for the VEGF gene therapy

Gene therapy with the vascular endothelial growth factor (VEGF) gene is a potential treatment for many disorders or injuries with ischemia. However, unregulated expression of VEGF may induce pathological angiogenesis, promoting tumor growth, diabetic proliferative retinopathy and rupture of atherosclerotic plaque. Therefore, the effective regulation of the gene expression is one of the requirements for the VEGF gene therapy. In this research, we evaluated the hypoxia-inducible gene expression system with the erythropoietin (Epo) enhancer and the Epo 3'-untranslated region (UTR). The luciferase plasmids were constructed with the Epo enhancer (pEpo-SV-Luc), the Epo 3'-UTR (pSV-Luc-EpoUTR) or both (pEpo-SV-Luc-EpoUTR). The polyethylenimine/plasmid complexes were transfected to 293 or A7R5 cells and the cells were incubated under normoxia or hypoxia. The results showed that the Epo enhancer or Epo 3'-UTR increased the target gene expression under hypoxia. pEpo-SV-Luc-EpoUTR showed the highest luciferase expression. The VEGF expression plasmid with the Epo enhancer and 3'-UTR was also constructed. The VEGF expression by pEpo-SV-VEGF-EpoUTR showed the highest specificity of the gene expression in the hypoxic cells. The results suggest that the VEGF plasmid with the Epo enhancer and the Epo 3'-UTR may be useful for gene therapy for ischemic diseases.

The development and characterization of a glutathione-sensitive cross-linked polyethylenimine gene vector

A glutathione-sensitive cross-linked polyethylenimine gene vector CLPEI(50%) was specially designed via the cross-linking reaction between the low molecular weight polyethylenimine (PEI(1800)) and dimethyl 3.3'-dithiopropionimidate dihydrochloride (DTBP). The acid-base titration test indicated that CLPEI(50%) still possessed efficient proton sponge effect. The property of CLPEI(50%)-DNA complexes were investigated by atomic force microscopy (AFM) and dynamic light scattering (DLS). CLPEI(50%) induced DNA condensation and formed spherical nanoparticles. The diameter of polyplexes prepared at pH value of 6.0 and 7.4 was about 150 and 260 nm, respectively. It was interesting to find the polyplexes were sensitive to the reductive glutathione (GSH). The CLPEI(50%)-DNA polyplexes prepared at N/P ratio of 10 were unpacked at GSH concentration of 3mm, which was comparable to the intracellular environment. The in vitro cytotoxicity of CLPEI(50%) was also significantly reduced comparing with PEI(25k). The biomimetic CLPEI(50%)-DNA polyplexes with the low cytotoxicity and GSH-sensitive property could be a good candidate for gene delivery.

A novel chitosan oligosaccharide-stearic acid micelles for gene delivery: properties and in vitro transfection studies

Stearic acid (SA) grafted chitosan oligosaccharide (CSO) (CSO-SA), which was synthesized by an 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)-mediated coupling reaction, was demonstrated to form micelle like structure by self-aggregation in aqueous solution. The critical micelle concentration (CMC) of CSO-SA with 15.4% amino substituted degree of CSO was about 0.035 mg/ml. The micelles with 1mg/ml CSO-SA concentration had 70.6 nm volume average hydrodynamic diameter with a narrow size distribution and 46.4+/-0.1 mV surface potential. Due to the cationic property, the micelles could compact the plasmid DNA to form micelle/DNA complexes nanoparticles, which can efficiently protect the condensed DNA from enzymatic degradation by DNase I. The volume average hydrodynamic diameter of CSO-SA micelle/DNA complex increased from 203 nm to 318 nm and decreased to 102 nm due to the variation of zeta potential when the N/P ratio increased from 0.25 to 3.6 and from 3.6 to 58. The IC(50) value of the CSO-SA micelle against A549 cells was 543.16 microg/ml, while the IC(50) of Lipofectamine 2000 was about 6 microg/ml. The in vitro transfection efficiency of CSO-SA micelles was investigated by using plasmid DNA (pEGFP-C1). The transfection efficiency with CSO-SA/DNA (N/P ratio is 29) was increased with the post-transfection time (in 76h), while the optimal transfection of Lipofectamine 2000/DNA was obtained at 24h. The transfection of CSO-SA was not interfered in the presence of 10% fetal bovine serum, which showed remarkable enhancement effect. The optimal transfection efficiency of CSO-SA micelles in A549 cells was about 15%, which was higher than that of CSO (about 2%) and approach to that of Lipofectamine 2000 (about 20%). The low cytotoxic biodegradable CSO-SA micelles could be used as an effective DNA condensation carrier for gene delivery system.