In vitro gene expression on smooth muscle cells using a terplex delivery system

Recent advances in the development of gene delivery systems

Background

Gene delivery systems are essentially necessary for the gene therapy of human genetic diseases. Gene therapy is the unique way that is able to use the adjustable gene to cure any disease. The gene therapy is one of promising therapies for a number of diseases such as inherited disorders, viral infection and cancers. The useful results of gene delivery systems depend open the adjustable targeting gene delivery systems. Some of successful gene delivery systems have recently reported for the practical application of gene therapy.

Main body

The recent developments of viral gene delivery systems and non-viral gene delivery systems for gene therapy have briefly reviewed. The viral gene delivery systems have discussed for the viral vectors based on DNA, RNA and oncolytic viral vectors. The non-viral gene delivery systems have also treated for the physicochemical approaches such as physical methods and chemical methods. Several kinds of successful gene delivery systems have briefly discussed on the bases of the gene delivery systems such as cationic polymers, poly(L-lysine), polysaccharides, and poly(ethylenimine)s.

Conclusion

The goal of the research for gene delivery system is to develop the clinically relevant vectors such as viral and non-viral vectors that use to combat elusive diseases such as AIDS, cancer, Alzheimer, etc. Next step research will focus on advancing DNA and RNA molecular technologies to become the standard treatment options in the clinical area of biomedical application.

Lipid-based drug carriers for prodrugs to enhance drug delivery

The combination of lipid drug delivery systems with prodrugs offers several advantages including improved pharmacokinetics, increased absorption, and facilitated targeting. Lipidization and use of lipid carriers can increase the pharmacological half-life of the drug, thus improving pharmacokinetics and allowing less frequent dosing. Lipids also offer advantages such as increased absorption through the intestines for oral drug absorption and to the CNS for brain delivery. Furthermore, the use of lipid delivery systems can enhance drug targeting. Endogenous proteins bind lipids in the blood and carry them to the liver to enable targeting of this organ. Drugs with significant side effects in the stomach can be specifically delivered to enterocytes by exploiting lipases for prodrug activation. Finally, lipids can be used to target the lymphatic system, thus bypassing the liver and avoiding first-pass metabolism. Lymphatic targeting is also important for antiviral drugs in the protection of B and T lymphocytes. In this review, both lipid-drug conjugates and lipid-based carriers will be discussed. An overview, including the chemistry and assembly of the systems, as well as examples from the clinic and in development, will be provided.

Recent trends of polymer mediated liposomal gene delivery system

Advancement in the gene delivery system have resulted in clinical successes in gene therapy for patients with several genetic diseases, such as immunodeficiency diseases, X-linked adrenoleukodystrophy (X-ALD) blindness, thalassemia, and many more. Among various delivery systems, liposomal mediated gene delivery route is offering great promises for gene therapy. This review is an attempt to depict a portrait about the polymer based liposomal gene delivery systems and their future applications. Herein, we have discussed in detail the characteristics of liposome, importance of polymer for liposome formulation, gene delivery, and future direction of liposome based gene delivery as a whole.

Polylysine copolymers for gene delivery

Polylysine and its copolymers have been extensively used as nonviral polymeric gene carriers. Although polylysine on its own is toxic to cells, when polyethylene glycol is covalently linked to polylysine, toxicity is reduced and DNA transfection efficiency is increased. A degradable polylysine analog, polyaminobutyl glycolic acid, has been synthesized. Stearyl polylysine shows strong hydrophobic interactions with low-density lipoprotein and these components can be combined with DNA to form a "terplex" system that allows delivery of DNA to targeted cells and significant levels of transfection both in vitro and in vivo.

Relationship between the extent of lipid substitution on poly(L-lysine) and the DNA delivery efficiency

Poly(L-lysine) (PLL) is a commonly used polymer for nonviral gene delivery. However, the polymer exhibits significant toxicity and is not very effective for transgene expression. To enhance the gene delivery efficiency of the polymer, we imparted an amphiphilic property to PLL by substituting approximately 10% of epsilon-NH2 with several endogenous lipids of variable chain lengths (lipid carbon chain ranging from 8 to 18). Lipid-modified PLL with high molecular weight (approximately 25 vs 4 kDa) was found to be more effective in delivering plasmid DNA intracellularly in clinically relevant bone marrow stromal cells (BMSC). For lipid-substituted 25 kDa PLL, a correlation between the extent of lipid substitution and the plasmid DNA delivery efficiency was obtained. Additionally, transgene expression by BMSC significantly increased (20-25%) when amphiphilic PLLs were used for plasmid delivery as compared to native PLL and the commercial transfection agent Lipofectamine-2000. The transfection efficiency of the polymers was positively correlated with the extent of lipid substitution. The amphiphilic polymers were able to modify the cells up to 7 days after transfection, after which the expression was decreased to background levels within 1 week. We conclude that lipid-substituted PLL can be used effectively as a nonviral carrier for DNA, and the extent of lipid substitution was an important determinant of gene delivery.

Cholesteryl Oligoarginine Delivering Vascular Endothelial Growth Factor siRNA Effectively Inhibits Tumor Growth in Colon Adenocarcinoma

Vascular endothelial growth factor (VEGF) is a multifunctional angiogenic growth factor that is a primary stimulant of the development and maintenance of a vascular network in the vascularization of solid tumors. It has been reported that a blockade of VEGF-mediated angiogenesis is a powerful method for tumor regression. RNA interference represents a naturally occurring biological strategy for inhibition of gene expression. In mammalian systems, however, the in vivo application of small interfering RNA (siRNA) is severely limited by the instability and poor bioavailability of unmodified siRNA molecules. In this study, we tested the hypothesis that a hydrophobically modified protein transduction domain, cholesteryl oligo-d-arginine (Chol-R9), may stabilize and enhance tumor regression efficacy of the VEGF-targeting siRNA. The noncovalent complexation of a synthetic siRNA with Chol-R9 efficiently delivered siRNA into cells in vitro. Moreover, in a mouse model bearing a subcutaneous tumor, the local administration of complexed VEGF-targeting siRNA, but not of scrambled siRNA, led to the regression of the tumor. Hence, we propose a novel and simple system for the local in vivo application of siRNA through Chol-R9 for cancer therapy.

Pluronic-grafted poly-(L)-lysine as a new synthetic gene carrier

Genes are attractive candidates as therapeutic agents, and the development of safe and effective gene carriers is essential for the success of human gene therapy. To develop a gene delivery vector that shows low cytotoxicity and high efficiency, we synthesized poly-L-lysine-g-pluronic by conjugating poly-L-lysine (PLL) to pluronic, which is partially functionalized with para-nitrophenyl carbonate groups, and evaluated for its efficiency as a possible nonviral gene carrier candidate. Structural analysis of synthesized polymer was performed by using 1H-NMR. Gel retardation assay, zeta potential and size measurement confirmed that the new gene carrier made a compact complex with plasmid DNA. pCMV-beta-gal was used as a reporter gene, and the in vitro transfection efficiency was measured in HeLa cells by using the o-nitrophenyl-beta-D-galactopyranoside assay. The highest transfection efficiency among those tested was achieved at the 1:1 weight ratio of polymer:DNA, and a 3-fold increase in transfection efficiency was achieved by treatment of a lysosomotropic agent, chloroquine. Compared with unmodified PLL, PLL-g-pluronic showed about 2-fold increase in transfection efficiency with similar cytotoxicity specifically at the 1:1 weight ratio of polymer:DNA.

Chitosan-based gastrointestinal delivery systems

Chitosan, a natural polymer obtained by alkaline deacetylation of chitin, is non-toxic, biocompatible, and biodegradable. These properties make chitosan a good candidate for the development of conventional and novel gastrointestinal (GI) drug and gene delivery systems. The objective of this review is to summarize the recent applications of chitosan in oral and/or buccal delivery, stomach-specific drug delivery, intestinal delivery, and colon-specific drug delivery. The use of chitosan for targeting of drugs to each of these sites in the GI tract is illustrated by examples supported by in vivo studies. Chitosan appears to be a promising material for GI drug and gene delivery applications as many derivatives and formulations are being examined.

Water-soluble lipopolymer as an efficient carrier for gene delivery to myocardium

Water-soluble lipopolymer (WSLP), which consisted of polyethylenimine (PEI, 1800 Da) and cholesterol, was characterized as a gene carrier to smooth muscle cells and myocardium. Acid-base titration showed that WSLP had a proton-buffering effect. The size of WSLP/plasmid DNA (pDNA) complex was around 70 nm. WSLP/pDNA complex was transfected to A7R5 cells, a smooth muscle cell line. WSLP showed the highest transfection at a 40/1 N/P ratio. WSLP has higher transfection efficiency than PEI (1800 and 25 000 Da), SuperFect, and lipofectamine. In addition, WSLP has less cytotoxicity than PEI (25 000 Da), SuperFect, and lipofectamine. Since WSLP has cholesterol moiety, it may utilize cellular cholesterol uptake pathway, in which low-density lipoprotein (LDL) is involved. An inhibition study with free cholesterol or low-density lipoprotein (LDL) showed that transfection was inhibited by cholesterol or LDL, suggesting that WSLP/pDNA complex is transfected to the cells through the cholesterol uptake pathway. To evaluate the transfection efficiency to myocardium, WSLP/pDNA complex was injected into the rabbit myocardium. WSLP showed higher transfection than PEI and naked pDNA. WSLP expressed the transgene for more than 2 weeks. In conclusion, WSLP is an efficient carrier for local gene transfection to myocardium, and useful in in vivo gene therapy.

Artery wall binding peptide-poly(ethylene glycol)-grafted-poly(L-lysine)-based gene delivery to artery wall cells

Artery wall binding peptide (AWBP; Cys-Gly-Arg-Ala-Leu-Val-Asp-Thr-Leu-Lys-Phe-Val-Thr-Gln-Ala-Glu-Gly-Ala-Lys), a specific targeting peptide, was conjugated to poly(ethylene glycol)-grafted-poly(L-lysine) (PEG-g-PLL) to enhance the gene transfer to artery wall cells. AWBP-PEG-PLL was synthesized by the reaction between the vinylsulfone group of PEG-g-PLL and the thiol group of cysteine in AWBP. 1H-NMR analysis confirmed the composition of the obtained polymer and indicated that four mol of AWBP were reacted to one mole of VS-PEG-PLL. The particles of AWBP-PEG-PLL/pDNA complexes were determined spherical with a size of approximately 100 nm by dynamic light scattering (DLS) and atomic force microscopy (AFM). Agarose gel retardation assay indicated that AWBP-PEG-PLL was able to condense plasmid DNA and reach complete complexation at and above a charge ratio 1/1 (+/-). Transfection efficiency of AWBP-PEG-PLL/pDNA complexes was 150-180 times higher than that of control systems, such as PEG-g-PLL/pDNA and PLL/pDNA, in both bovine aorta endothelial cells and smooth muscle cells. Luciferase activities of AWBP-PEG-PLL depended on the amount of free AWBP, while those of the control carriers such as PLL and PEG-g-PLL were not affected by free AWBP. These results supported that gene transfer of AWBP-PEG-PLL/pDNA complexes to bovine aorta wall cells was mediated by specific artery wall cell receptor-mediated endocytosis.

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.

Genetically engineered polymers for drug delivery

Genetic engineering methodology offers the ability to synthesize protein-based polymers with precisely controlled structures. Protein-based polymers synthesized by recombinant techniques have a well-defined monomer composition and sequence, stereochemistry, and a narrow molecular weight distribution. The structure of the polymeric carrier at the molecular level influences its biological disposition and drug release profile. Current methodologies of polymer synthesis (chemical polymerization) result in the production of polymers with heterogeneous molecular weights, and with monomer sequences and compositions defined in terms of statistical distributions. Genetic engineering methodologies can be used to design new polymeric drug carriers with improved properties, such as better-defined biorecognition, pharmacokinetic, biodegradation, and drug release profiles. In this review article the rationale and methodology of polymer synthesis using genetic engineering techniques, the status of such polymers in drug delivery to-date, and the potential of these polymers for the development of new systems in the future are discussed.

Optimization of folate-conjugated liposomal vectors for folate receptor-mediated gene therapy

A folate-targeted transfection complex that is internalized by certain cancer cells and displays several properties reminiscent of enveloped viruses has been developed. These liposomal vectors are comprised of a polycation-condensed DNA plasmid associated with a mixture of neutral and anionic lipids supplemented with folate-poly(ethylene glycol)-dioleylphosphatidylethanolamine for tumor cell-specific targeting. N-Citraconyl-dioleylphosphatidylethanolamine is also included for pH-dependent release of endosome-entrapped DNA into the cytoplasm, and a novel plasmid containing a 366-bp segment from SV40 DNA has been employed to facilitate transport of the plasmid into the nucleus. Because formation of the DNA core is an important step in the assembly of liposomal vectors, considerable effort was devoted to comparing the transfection efficiencies of various DNA condensing agents. It was found that complexation of plasmid DNA with high molecular weight polymers such as acylated-polylysine and cationic dendrimers leads to higher folate-mediated transfection efficiency than DNA complexed with unmodified polylysine. In contrast, compaction of plasmid DNA with small cationic molecules such as spermine, spermidine, or gramicidin S yields only weakly active folate-targeted liposomal vectors. Compared to analogous liposomal vector preparations lacking an optimally compacted DNA core, a cell-specific targeting ligand, a caged fusogenic lipid, and a nucleotide sequence that facilitates nuclear uptake, these modified liposomal vectors display greatly improved transfection efficiencies and target cell specificity.

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.

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.

Polyethylene glycol-grafted poly-L-lysine as polymeric gene carrier

A new series of gene carriers, polyethylene glycol (PEG)-grafted poly-L-lysine (PLL, mol. wt. = 25000) with three different PEG-grafted ratios (5, 10 and 25 mole%, which means 5, 10 and 25% of epsilon-amino group of PLL was modified by PEG), was synthesized. These new gene carriers, named comb-shaped PEG-g-PLL copolymer, showed a 5- to 30-fold increase in transfection efficiency compared to PLL alone on a human carcinoma cell line. It is likely that Hep G2 cells were transfected by plasmid DNA/PEG-g-PLL complexes through an endocytosis mechanism due to the fact that chloroquine increased transfection efficiency. Although Lipofectin, a cationic lipid formulation, showed slightly higher transfection efficiency than PEG-g-PLL in Hep G2 cells, our designed PEG-g-PLL demonstrated lower cytotoxicity, early gene expression and maintenance of gene expression for up to 96 h.

A new non-viral DNA delivery vector: the terplex system

A new DNA delivery vector (the terplex system) based on a balanced hydrophobicity and net surface charge between stearyl-poly(L-lysine), low density lipoprotein (LDL), and genetic material (i.e. plasmid DNA or antisense oligonucleotide) was developed. The pSV-beta-gal plasmid in terplex system showed a 2-5-fold increase in beta-galactosidase expression on murine smooth muscle cells (A7R5) compared to Lipofectin. Delivery of unmodified c-myb antisense oligonucleotide to A7R5 cells was also facilitated significantly by the terplex system, requiring as little as 5.4 nM of antisense oligonucleotide to achieve a 50% antiproliferative effect. Similar antiproliferative effect was observed when the c-myb antisense/terplex formulation was tested on CCD-32 Lu human lung fibroblasts. Characterization of the physical properties of the terplex system was performed using various techniques. Plasmid DNA was condensed by addition of stearyl-PLL and LDL, resulting in the terplex system of about 100 nm in diameter as shown by atomic force microscopy. A strong hydrophobic interaction between stearyl-poly(L-lysine) and LDL was registered by 1H-NMR spectrometry, showing a significant decrease in the epsilon-methylene signal of poly(L-lysine) backbone when stearyl-poly(L-lysine) was mixed with LDL; however, this phenomenon was not observed with unmodified poly(L-lysine). Agarose gel electrophoresis revealed that electrophoretic mobility of the terplex system decreased with increasing amounts of stearyl-poly(L-lysine), indicating that the surface charge of the terplex system became more positive by addition of stearyl-poly(L-lysine). Zeta-potential measurement showed that the terplex system exerted a slightly positive charge (+2 mV) at a 1:1:1 weight ratio of plasmid DNA:LDL:stearyl-poly(L-lysine). The obtained results will be utilized in the design of more efficient and safer DNA delivery vectors for in vivo gene therapy.

Preparation of chitosan self-aggregates as a gene delivery system

Hydrophobically modified chitosan containing 5.1 deoxycholic acid groups per 100 anhydroglucose units was synthesized by an EDC-mediated coupling reaction. Formation and characteristics of self-aggregates of hydrophobically modified chitosan were studied by fluorescence spectroscopy and dynamic light scattering method. The critical aggregation concentration (cac) of the self-aggregate was determined by measuring the fluorescence intensity of pyrene as a fluorescent probe. The cac value in PBS solution (pH 7.2) was 1.7x10(-2) mg/ml. Mean diameter of self-aggregates in PBS solution (pH 7.2) was 162 +/- 18 nm with an unimodal size distribution. Charge complex formation between self-aggregates and plasmid DNA was confirmed by electrophoresis on an agarose gel. Migration of DNA on an agarose gel was completely retarded above a charge ratio ( +/-) of 4/1 at pH 7.2. The free DNA dissociated from the complexes was observed by electrophoresis above pH 8.0 at a fixed charge ratio of 4/1. An efficient of COS-1 cells was achieved by self-aggregates/DNA complexes.