Targeting Genes: Delivery and Persistent Expression of a Foreign Gene Driven by Mammalian Regulatory Elements in Vivo

Surface functionalized nanoparticles: A boon to biomedical science

The rapid development of nanomedicine has increased the likelihood that manufactured nanoparticles will one day come into contact with people and the environment. A variety of academic fields, including engineering and the health sciences, have taken a keen interest in the development of nanotechnology. Any significant development in nanomaterial-based applications would depend on the production of functionalized nanoparticles, which are believed to have the potential to be used in fields like pharmaceutical and biomedical sciences. The functionalization of nanoparticles with particular recognition chemical moieties does result in multifunctional nanoparticles with greater efficacy while at the same time minimising adverse effects, according to early clinical studies. This is because of traits like aggressive cellular uptake and focused localization in tumours. To advance this field of inquiry, chemical procedures must be developed that reliably attach chemical moieties to nanoparticles. The structure-function relationship of these functionalized nanoparticles has been extensively studied as a result of the discovery of several chemical processes for the synthesis of functionalized nanoparticles specifically for drug delivery, cancer therapy, diagnostics, tissue engineering, and molecular biology. Because of the growing understanding of how to functionalize nanoparticles and the continued work of innovative scientists to expand this technology, it is anticipated that functionalized nanoparticles will play an important role in the aforementioned domains. As a result, the goal of this study is to familiarise readers with nanoparticles, to explain functionalization techniques that have already been developed, and to examine potential applications for nanoparticles in the biomedical sciences. This review's information is essential for the safe and broad use of functionalized nanoparticles, particularly in the biomedical sector.

Oligo-guanidyl targeted bioconjugates forming rod shaped polyplexes as a new nanoplatform for oligonucleotide delivery

Novel bioconjugates (Agm₆-M-PEG-FA) for active oligonucleotide (ON) delivery have been developed by conjugating a cationic oligo-guanidyl star-like shaped "head" (Agm₆-M) to a polymeric "tail" (PEG) terminating with folic acid (FA) as targeting agent or methoxy group (Agm₆-M-PEG-FA and Agm₆-M-PEG-OCH₃, respectively). Gel electrophoresis showed that the bioconjugates completely associated with ONs at 3 nitrogen/phosphate (N/P) ratio. Studies performed with folate receptor (FR)-overexpressing HeLa cells, showed that optimal cell up-take was obtained with the 75:25 w/w Agm₆-M-PEG-OCH₃:Agm₆-M-PEG-FA mixture. Dynamic light scattering and transmission electron microscopy showed that the polyplexes had size <80 nm with narrow polydispersity and rod-shaped morphology. The polyplexes were stable for several hours in plasma while ON was released in the presence of heparin concentration 16-times higher than the physiological one. The polyplexes displayed negligible cytotoxicity, hemolysis and low pro-inflammatory TNF-α release. Studies performed with FR-overexpressing HeLa and MDA-MB-231 cells using siRac1 revealed that the folated polyplexes caused significantly higher gene silencing (86.1 ± 9.6%) and inhibition of cell migration (40%) than the non-folated polyplexes obtained with Agm₆-M-PEG-OCH₃ only. Although cytofluorimetric analyses showed similar cell uptake for both folated and non-folated polyplexes, confocal, TEM and competition studies showed that the folated polyplexes were taken-up by lysosome escaping caveolin-mediated pathway with final polyplex localization within cytosol, while non-folated polyplexes were preferentially taken-up via clathrin-mediated pathway to localize in the lysosomes. Finally, preliminary in vivo studies carried out in mice revealed that the folated polyplexes dispose in the tumor mass.

Metabolically stabilized double-stranded mRNA polyplexes

The metabolic instability of mRNA currently limits its utility for gene therapy. Compared to plasmid DNA, mRNA is significantly more susceptible to digestion by RNase in the circulation following systemic dosing. To increase mRNA metabolic stability, we hybridized a complementary reverse mRNA with forward mRNA to generate double-stranded mRNA (dsmRNA). RNase A digestion of dsmRNA established a 3000-fold improved metabolic stability compared to single-stranded mRNA (ssmRNA). Formulation of a dsmRNA polyplex using a PEG-peptide further improved the stability by 3000-fold. Hydrodynamic dosing and quantitative bioluminescence imaging of luciferase expression in the liver of mice established the potent transfection efficiency of dsmRNA and dsmRNA polyplexes. However, hybridization of the reverse mRNA against the 5' and 3' UTR of forward mRNA resulted in UTR denaturation and a tenfold loss in expression. Repeat dosing of dsmRNA polyplexes produced an equivalent transient expression, suggesting the lack of an immune response in mice. Co-administration of excess uncapped dsmRNA with a dsmRNA polyplex failed to knock down expression, suggesting that dsmRNA is not a Dicer substrate. Maximal circulatory stability was achieved using a fully complementary dsmRNA polyplex. The results established dsmRNA as a novel metabolically stable and transfection-competent form of mRNA.

GalNAc-siRNA Conjugates: Leading the Way for Delivery of RNAi Therapeutics

Short-interfering RNA (siRNA)-induced RNAi responses have great potential to treat a wide variety of human diseases from cancer to pandemic viral outbreaks to Parkinson's Disease. However, before siRNAs can become drugs, they must overcome a billion years of evolutionary defenses designed to keep invading RNAs on the outside cells from getting to the inside of cells. Not surprisingly, significant effort has been placed in developing a wide array of delivery technologies. Foremost of these has been the development of N-acetylgalactosamine (GalNAc) siRNA conjugates for delivery to liver. Tris-GalNAc binds to the Asialoglycoprotein receptor that is highly expressed on hepatocytes resulting in rapid endocytosis. While the exact mechanism of escape across the endosomal lipid bilayer membrane remains unknown, sufficient amounts of siRNAs enter the cytoplasm to induce robust, target selective RNAi responses in vivo. Multiple GalNAc-siRNA conjugate clinical trials, including two phase III trials, are currently underway by three biotech companies to treat a wide variety of diseases. GalNAc-siRNA conjugates are a simple solution to the siRNA delivery problem for liver hepatocytes and have shown the RNAi (and antisense oligonucleotide) field the path forward for targeting other tissue types.

History of Polymeric Gene Delivery Systems

As an option for genetic disease treatment and an alternative for traditional cancer chemotherapy, gene therapy achieves significant attention. Nucleic acid delivery, however, remains a main challenge in human gene therapy. Polymer-based delivery systems offer a safer and promising route for therapeutic gene delivery. Over the past five decades, various cationic polymers have been optimized for increasingly effective nucleic acid transfer. This resulted in a chemical evolution of cationic polymers from the first-generation polycations towards bioinspired multifunctional sequence-defined polymers and nanocomposites. With the increasing of knowledge in molecular biological processes and rapid progress of macromolecular chemistry, further improvement of polymeric nucleic acid delivery systems will provide effective tool for gene-based therapy in the near future.

"Evolving nanoparticle gene delivery vectors for the liver: What has been learned in 30 years"

Nonviral gene delivery to the liver has been under evolution for nearly 30years. Early demonstrations established relatively simple nonviral vectors could mediate gene expression in HepG2 cells which understandably led to speculation that these same vectors would be immediately successful at transfecting primary hepatocytes in vivo. However, it was soon recognized that the properties of a nonviral vector resulting in efficient transfection in vitro were uncorrelated with those needed to achieve efficient nonviral transfection in vivo. The discovery of major barriers to liver gene transfer has set the field on a course to design biocompatible vectors that demonstrate increased DNA stability in the circulation with correlating expression in liver. The improved understanding of what limits nonviral vector gene transfer efficiency in vivo has resulted in more sophisticated, low molecular weight vectors that allow systematic optimization of nanoparticle size, charge and ligand presentation. While the field has evolved DNA nanoparticles that are stable in the circulation, target hepatocytes, and deliver DNA to the cytosol, breaching the nucleus remains the last major barrier to a fully successful nonviral gene transfer system for the liver. The lessons learned along the way are fundamentally important to the design of all systemically delivered nanoparticle nonviral gene delivery systems.

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.

NTS-Polyplex: a potential nanocarrier for neurotrophic therapy of Parkinson's disease

Nanomedicine has focused on targeted neurotrophic gene delivery to the brain as a strategy to stop and reverse neurodegeneration in Parkinson's disease. Because of improved transfection ability, synthetic nanocarriers have become candidates for neurotrophic therapy. Neurotensin (NTS)-polyplex is a "Trojan horse" synthetic nanocarrier system that enters dopaminergic neurons through NTS receptor internalization to deliver a genetic cargo. The success of preclinical studies with different neurotrophic genes supports the possibility of using NTS-polyplex in nanomedicine. In this review, we describe the mechanism of NTS-polyplex transfection. We discuss the concept that an effective neurotrophic therapy requires a simultaneous effect on the axon terminals and soma of the remaining dopaminergic neurons. We also discuss the future of this strategy for the treatment of Parkinson's disease.

FROM THE CLINICAL EDITOR

This review paper focuses on nanomedicine-based treatment of Parkinson's disease, a neurodegenerative condition with existing symptomatic but no curative treatment. Neurotensin-polyplex is a synthetic nanocarrier system that enables delivery of genetic cargo to dopaminergic neurons via NTS receptor internalization.

Polymer-based non-viral gene delivery as a concept for the treatment of cancer

Gene therapy has become a promising technique for the treatment of cancer. Nevertheless, the success of gene therapy depends on the effectiveness of the vector. The challenge of a gene carrier is to deliver exogenous DNA from the site of administration into the nucleus of the appropriate target cell. Polymer-based vectors are biologically safe, have low production costs and are efficient tools for gene therapy. Although non-degradable polyplexes exhibit high gene expression levels, their application potential is limited due to their inability to be effectively eliminated, which results in cytotoxicity. The development of biodegradable polymers has allowed for high levels of transfection without cytotoxicity. For site-specific targeting of polyplexes, further modifications, such as incorporation of ligands, can be performed. Most expectations have been addressed to polyplexes architecture according it dynamic response with the microenvironment.

The development of gene therapy: from monogenic recessive disorders to complex diseases such as cancer

During the last 4 decades, gene therapy has moved from preclinical to clinical studies for many diseases ranging from monogenic recessive disorders such as hemophilia to more complex diseases such as cancer, cardiovascular disorders, and human immunodeficiency virus (HIV). To date, more than 1,340 gene therapy clinical trials have been completed, are ongoing, or have been approved in 28 countries, using more than 100 genes. Most of those clinical trials (66.5%) were aimed at the treatment of cancer. Early hype, failures, and tragic events have now largely been replaced by the necessary stepwise progress needed to realize clinical benefits. We now understand better the strengths and weaknesses of various gene transfer vectors; this facilitates the choice of appropriate vectors for individual diseases. Continuous advances in our understanding of tumor biology have allowed the development of elegant, more efficient, and less toxic treatment strategies. In this introductory chapter, we review the history of gene therapy since the early 1960s and present in detail two major recurring themes in gene therapy: (1) the development of vector and delivery systems and (2) the design of strategies to fight or cure particular diseases. The field of cancer gene therapy experienced an "awkward adolescence." Although this field has certainly not yet reached maturity, it still holds the potential of alleviating the suffering of many individuals with cancer.

Gene therapy of neural cell injuries in vitro using the hypoxia-inducible GM-CSF expression plasmids and water-soluble lipopolymer (WSLP)

Non-viral polymeric gene carriers have been widely investigated but no promising biocompatible polymer was developed for the gene therapy of neural system injuries yet. This study evaluated the potential usage of water-soluble lipopolymer (WSLP) as a gene delivery vehicle in neural lineage cells of SK-N-BE(2)C, a neuroblastoma cell line and primary culture of mouse neural progenitor cells (mNPCs). When tested with the luciferase reporter (pSV-Luc), WSLP showed higher gene transfection efficiency by more than 8-10 folds yet with lower cytotoxicity than polyethylenimine of 1800 Da (PEI1800), a parental polymer, and Lipofectamine 2000. The optimum N/P ratios were 40:1 for WSLP and 10:1 for PEI1800, respectively. The transfection efficiency for both of WSLP and PEI1800 was higher overall in SK-N-BE(2)C cells than in mNPCs. WSLP was also used successfully for the delivery and hypoxia-inducible expression of luciferase reporter plasmid containing the erythropoietin (Epo) enhancer (pEpo-SV-Luc) or RTP801 promoter (pRTP801-Luc). The hypoxia-inducible system and WSLP were then successfully applied to the delivery of granulocyte macrophage colony-stimulating factor (GM-CSF) gene that was previously shown to have neuroprotective effect on neural cell death in vitro and in rat SCI model. The hypoxia-inducible GM-CSF plasmids (pEpo-SV-GM-CSF and pRTP801-GM-CSF) showed induced expression of GM-CSF under hypoxia and decrease in the hypoxia-induced cell death in SK-N-BE(2)C cells. In conclusion, this study demonstrated that WSLP could be an efficient gene delivery carrier for neural cells and gene therapy of GM-CSF using the hypoxia-inducible system could be a potential therapeutic intervention for neural injuries. Further studies are necessary to confirm the current findings in animal models of CNS injuries.

shRNA and siRNA delivery to the brain

The limiting factor in in vivo RNA interference (RNAi) is delivery. Drug delivery methods that are effective in cell culture may not be practical in vivo for intravenous RNAi applications. Nucleic acid drugs are highly charged and do not cross cell membranes by free diffusion. Therefore, the in vivo delivery of RNAi therapeutics must use targeting technology that enables the RNAi therapeutic to traverse biological membrane barriers in vivo. For RNAi of the brain, the nucleic acid-based drug must first cross the brain capillary endothelial wall, which forms the blood-brain barrier (BBB) in vivo, and then traverses the brain cell plasma membrane. Similar to the delivery of non-viral gene therapies, plasmid DNA encoding for short hairpin RNA (shRNA) may be delivered to the brain following intravenous administration with pegylated immunoliposomes (PILs). The plasmid DNA is encapsulated in a 100 nm liposome, which is pegylated, and conjugated with receptor specific targeting monoclonal antibodies (MAb). Weekly, intravenous RNAi with PILs enables a 90% knockdown of the human epidermal growth factor receptor, which results in a 90% increase in survival time in mice with intra-cranial brain cancer. Similar to the delivery of antisense agents, short interfering RNAi (siRNA) duplexes can be delivered with the combined use of targeting MAb's and avidin-biotin technology. The siRNA is mono-biotinylated in parallel with the production of a conjugate of the targeting MAb and streptavidin. Intravenous RNAi requires the combined use of RNAi technology and a drug targeting technology that is effective in vivo.

Vectors for airway gene delivery

Delivery of genes to the airway epithelium for therapeutic purposes seemed easy at first, because the epithelial cells interface with the environment and are therefore accessible. However, problems encountered were more substantial than were originally expected. Nonviral systems may be preferred for long-term gene expression, for they can be dosed repeatedly. Two nonviral gene transfer systems have been in clinical trials, lipid-mediated gene transfer and DNA nanoparticles. Both have sufficient efficiency to be candidates for correction of the cystic fibrosis defect, and both can be dosed repeatedly. However, lipid-mediated gene transfer in the first generation provokes significant inflammatory toxicity, which may be engineered out by adjustments of the lipids, the plasmid CpG content, or both. Both lipid-mediated gene transfer and DNA nanoparticles in the first generation have short duration of expression, but reengineering of the plasmid DNA to contain mostly eukaryotic sequences may address this problem. Considerable advances in the understanding of the cellular uptake and expression of these agents and in their practical utility have occurred in the last few years; these advances are reviewed here.

Complexes of DNA with cationic peptides: Conditions of formation and factors effecting internalization by mammalian cells

This work was devoted to the study of conditions of the formation of DNA/K8 complex and analysis of factors effecting the entry of DNA/K8 complex into mammalian cells in comparison with DNA complexes with arginine-rich fragment (47-57) of human immunodeficiency virus (type 1) transcription factor Tat (Tat peptide). The stoichiometry of positively charged DNA/K8 complexes has been studied for the first time. Non-cooperative character of DNA-K8 interaction was revealed. It has been shown that along with the positive charge of such complexes, the presence of an excess of free K8 peptide in the culture medium is a necessary condition for maximal efficiency of cell transfection with DNA/K8 complexes. A stimulatory effect of free K8 peptide on the efficiency of mammalian cell transfection by DNA/K8 complexes is likely to be mediated by the interactions of cationic peptide K8 with negatively charged proteoglycans on the cell surface, which leads to protection of DNA/K8 complexes from disruption by cellular heparan sulfates. However, the protective role of free cationic peptides depends not only on their positive charge, but also on the primary structure of the peptide. In contrast with the results obtained for DNA complexes with molecular conjugates based on poly-L-lysine, the aggregation of DNA/K8 complexes leads to a significant increase in the expression of transferred gene.

A multifunctional PEI-based cationic polyplex for enhanced systemic p53-mediated gene therapy

We recently reported a novel coupling strategy involving salicylhydroxamic acid and phenyl(di)boronic acid molecules to attach the CNGRC peptide to PEI/DNA for CD13 targeting in tumors. Here, we doubly coupled Simian Virus (SV) 40 peptide-(nuclear localization signal)) and oligonucleotide-based (DNA nuclear targeting signal) nuclear signals to the same vector using peptide nucleic acid chemistry. This vector, CNGRC/PEG/PEI/DNA-betagal/NLS/DNTS, was predominantly localized in the cell nucleus, yielding about 200-fold higher betagal gene expression in vitro, more than 20-fold increase in tumor-specific gene delivery, and a robust betagal gene expression as demonstrated in stained tumor sections. For gene therapy purposes, we further engineered a similar targeting polyplex, CNGRC/PEG/PEI/DNA-p53/NLS/DNTS, with EBV-based episomal vector for sustained p53 gene expression. A distribution of vector DNA and apoptosis in p53-containing tumors was observed, yielding a significant tumor regression and 95% animal survival after 60 days. This multicomponent vector also co-targeted tumor and tumor-associated endothelial cells but not normal cells, and had more efficient therapeutic index than each vector administered as a single modality. The use of an efficient coupling strategy without compromising the vector's integrity for DNA condensation and endosomal escape; nuclear import; tumor-specific and persistent p53 gene expression clearly provides a basis for developing a single combinatorial approach for non-viral gene therapy.

Strategies to improve non-viral vectors – potential applications in clinical transplantation

Prevention of acute rejection has been well controlled with immunosuppressive drugs. However, the long-term control of rejection is less satisfactory and the side effects of chronic usage of these drugs are far from acceptable. Thus, more imaginative options for therapy need to be explored. Gene therapy has potential promise in preserving allografts, preventing rejection and inducing tolerance. Despite this initial promise in many animal models, the translation of gene therapy to the clinical arena has been slow. This may be related in part to the deficiencies in vector development. Existing viral vectors are efficient at transducing allografts, but they induce inflammatory and pathogenic effects. Although the alternative non-viral systems are relatively innocuous, they are less efficient at gene delivery. This review systematically analyses the limitations of non-viral vector technology and the strategies that have been developed to overcome these limitations. Future development of non-viral vectors may have potential application in clinical transplantation.

The importance of valency in enhancing the import and cell routing potential of protein transduction domain-containing molecules

Protein transduction domains (PTDs) are peptides that afford the internalization of cargo macromolecules (including plasmid DNA, proteins, liposomes, and nanoparticles). In the case of polycationic peptides, the efficiency of PTDs to promote cellular uptake is directly related to their molecular mass or their polyvalent presentation. Similarly, the efficiency of routing to the nucleus increases with the number of nuclear localization signals (NLS) associated with a cargo. The quantitative enhancement, however, depends on the identity of the PTD sequence as well as the targeted cell type. Thus the choice and multivalent presentation of PTD and NLS sequences are important criteria guiding the design of macromolecules intended for specific intracellular localization. This review outlines synthetic and recombinant strategies whereby PTDs and signal sequences can be assembled into multivalent peptide dendrimers and promote the uptake and routing of their cargoes. In particular, the tetramerization domain of the tumour suppressor p53 (p53tet) is emerging as a useful scaffold to present multiple routing and targeting moieties. Short cationic peptides fused to the 31-residue long p53tet sequence resulted in tetramers displaying a significant enhancement (up to 1000 fold) in terms of their ability to be imported into cells and delivered to the cell nucleus in relation to their monomeric analogues. The design of future polycationic peptide dendrimers as effective delivering vehicles will need to incorporate selective cell targeting functions and provide solutions to the issue of endosomal entrapment.

Regulatable gene expression systems for gene therapy applications: progress and future challenges

Gene therapy aims to revert diseased phenotypes by the use of both viral and nonviral gene delivery systems. Substantial progress has been made in making gene transfer vehicles more efficient, less toxic, and nonimmunogenic and in allowing long-term transgene expression. One of the key issues in successfully implementing gene therapies in the clinical setting is to be able to regulate gene expression very tightly and consistently as and when it is needed. The regulation ought to be achievable using a compound that should be nontoxic, be able to penetrate into the desired target tissue or organ, and have a half-life of a few hours (as opposed to minutes or days) so that when withdrawn or added (depending on the regulatable system used) gene expression can be turned "on" or "off" quickly and effectively. Also, the genetic switches employed should ideally be nonimmunogenic in the host. The ability to switch transgenes on and off would be of paramount importance not only when the therapy is no longer needed, but also in the case of the development of adverse side effects to the therapy. Many regulatable systems are currently under development and some, i.e., the tetracycline-dependent transcriptional switch, have been used successfully for in vivo preclinical applications. Despite this, there are no examples of switches that have been employed in a human clinical trial. In this review, we aim to highlight the main regulatable systems currently under development, the gene transfer systems employed for their expression, and also the preclinical models in which they have been used successfully. We also discuss the substantial challenges that still remain before these regulatable switches can be employed in the clinical setting.

Synergistic effect of poly(ethylenimine) on the transfection efficiency of galactosylated chitosan/DNA complexes

The use of chitosan for gene delivery is limited due to the low transfection efficiency and difficulty in transfecting into a variety of cell types, especially the hepatoma cells. In order to solve this problem, lactobionic acid (LA) bearing galactose group was coupled with water-soluble chitosan (WSC) for liver specificity and poly(ethylenimine) (PEI) was combined to galactosylated chitosan (GC)/DNA complexes to enhance the transfection efficiency. For initial study, the effect of PEI on the transfection efficiency of WSC/DNA complex was studied in HeLa, A549 and 293 T cells, and bafilomycin A1 was used to ascertain the mechanism of synergistic effect. Transfection efficiency, cytotoxicity, and physicochemical properties of GC/DNA complex combined with PEI were investigated to determine the potential for the hepatocyte-targeting. The combination of PEI with WSC/DNA and GC/DNA complex dramatically increased the luciferase expression 10- to 1000-fold in various cell lines, and the synergistic effect was proved to be induced by proton sponge effect of PEI. The transfection of GC/DNA complex in HepG2 was much higher than that of WSC/DNA even after combination with PEI, and was highly inhibited in the presence of galactose. Cytotoxicity of PEI was much decreased by combination with GC/DNA complex. And PEI was proved to be coated on the surface of GC/DNA complex through the ionic interaction.

Design and development of polymers for gene delivery

The lack of safe and efficient gene-delivery methods is a limiting obstacle to human gene therapy. Synthetic gene-delivery agents, although safer than recombinant viruses, generally do not possess the required efficacy. In recent years, a variety of effective polymers have been designed specifically for gene delivery, and much has been learned about their structure-function relationships. With the growing understanding of polymer gene-delivery mechanisms and continued efforts of creative polymer chemists, it is likely that polymer-based gene-delivery systems will become an important tool for human gene therapy.

Tumor-specific gene delivery mediated by a novel peptide-polyethylenimine-DNA polyplex targeting aminopeptidase N/CD13

We have developed a novel polyethylenimine (PEI)-DNA vector formulation that is capable of efficient tumor-specific delivery after intravenous administration to nude mice. To further increase the specificity of delivery, we have attached the peptide CNGRC to the vector, which is specific for aminopeptidase N (CD13). The strategy for coupling this peptide to PEI was based on a novel method involving the strong affinity between phenyl(di)boronic acid (PDBA) and salicylhydroxamic acid (SHA) as well as a polyethylene glycol (PEG) linker to reduce steric hindrance between the vector and the peptide. In vitro assessment of targeting by the CNGRC/PEG/PEI/DNA vector carrying a beta-galactosidase (beta-Gal)-expressing plasmid showed as much as a 5-fold increase in transduction, relative to the untargeted PEG/PEI/DNA-betagal vector, of CD13-positive lung cancer, fibrosarcoma, bladder cancer, and human umbilical vein endothelial cells. Competition with free peptide resulted in up to a 90% reduction in delivery, indicating that gene delivery was specific for CD13-positive cells. Intravenous administration of the CNGRC/PEG/PEI/DNA-betagal vector to nude mice bearing subcutaneous tumors resulted in as much as a 12-fold increase in beta-Gal expression in tumors as compared with expression in either lungs or tumors from animals treated with the original PEI/DNA-betagal vector. In vivo transduction analysis using the CNGRC/PEG/PEI/DNA vector to target the intravenous delivery of a yellow fluorescence protein (YFP)-expressing plasmid to subcutaneous H1299 tumors confirmed delivery of YFP to both tumor cells and tumor endothelial cells. The use of this peptide to further increase tumor-specific delivery mediated by our novel PEI/DNA vector now provides a basis for developing tumor-targeted gene therapies for use in the clinical treatment of cancer.

Transgene vaccination using Ulex europaeus agglutinin I (UEA-1) for targeted mucosal immunization against HIV-1 envelope

Receptor-mediated gene transfer using an M cell ligand has been shown to be an efficient method for mucosal DNA immunization. To investigate further into alternative M cell ligands, the plant lectin, Ulex europaeus agglutinin I (UEA-1), was tested. UEA-1 binds to human intestinal Caco-2 cells, and these cells can be transfected with poly-l-lysine (PL)-conjugated UEA-1 for expression of reporter cDNAs. When tested in vivo, mice nasally immunized with UEA-1-PL complexed to plasmid encoding HIV-1 envelope showed elevated systemic and mucosal antibody responses, and these were supported by tissue antibody-forming cells. Likewise, elevated envelope-specific CTLs were induced. Thus, UEA-1 mediated DNA delivery represents an alternative mucosal formulation for inducing humoral and cellular immunity against HIV-1.

Cyclodextrin-polyethylenimine conjugates for targeted in vitro gene delivery

Many human gene therapies will require cell-specific targeting. Though recombinant viruses are much more efficient than nonviral vectors, the latter, especially polymers, have the advantage of being targetable via conjugation of cell-specific ligands, including sugars, peptides, and antibodies, which can be covalently attached to the polymer using a variety of chemistries. Cyclodextrin, which forms inclusion complexes with small hydrophobic molecules, has been incorporated into a gene-delivery polymer and may provide a facile and versatile attachment site for targeting ligands. Polyethylenimine (PEI) was derivatized with beta-cyclodextrin on approximately 10% of the polymer's amines (termed CD-PEI). Human insulin was also derivatized with a hydrophobic palmitate group (pal-HI), which could anchor the protein to CD-PEI/DNA polyplexes. CD-PEI was essentially nontoxic to HEK293 cells at concentrations optimal for gene delivery and mediated nearly 4-fold higher gene expression than unmodified PEI, which is relatively toxic to these cells. More importantly, addition of the pal-HI to CD-PEI enhanced gene expression by more than an order of magnitude compared to unmodified PEI, either with or without the pal-HI. Because of the relative ease with which CD-binding moieties may be attached to various types of ligands, CD-PEI may be a generally useful material for testing novel cell-specific targeting compounds.

Galactosylated chitosan/DNA nanoparticles prepared using water-soluble chitosan as a gene carrier

Water-soluble chitosan (WSC) was used to increase the stability of chitosan in water and decrease the cytotoxicity induced by acetic acid. Lactobionic acid (LA) bearing galactose group was coupled with WSC for hepatocytes specificity. The composition of galactose in galactosylated chitosan (GC) was determined by NMR spectroscopy. The GC was complexed with plasmid DNA in various GC/DNA (N/P) charge ratios and the resulting complex was characterized by dynamic light scattering, gel retardation, and turbidity to determine the particle sizes, complex formation, and complex stability, respectively. Cytotoxicity and transfection efficiency of GC were also studied in cultured HepG2 human hepatoblastoma cell line and HeLa human cervix epithelial carcinoma cells. The complete GC/DNA complex was formed at the charge ratio of 5 and the GC/DNA complex to DNase I resistance was obtained. Particle sizes decreased with increasing charge ratio of GC to DNA and had a minimum value around 120 nm at the charge ratio of 5. And no significant difference in particle sizes from the charge ratio of 5-20 was found. The suspension of GC/DNA complexes exhibited no significant change in turbidity at the charge ratios of 10, indicating the complete shielding of DNA charge. Cytotoxicity study showed that GC prepared by the water-soluble chitosan had no cytotoxic effects on cells. And transfection efficiency into HepG2, which has asialoglycoprotein receptors (ASGP-R), was higher than that into HeLa without ASGP-R.

Hepatocyte targeting of 111In-labeled oligo-DNA with avidin or avidin-dendrimer complex

To establish an effective nonviral gene transfer vector to hepatocytes, various oligo-carrier complexes were developed employing dendrimer (G4) and avidin-biotin systems (Av-bt), and their biodistribution were evaluated. In-111-labeled-oligo, without any carriers, showed low uptake in normal organs other than the kidney (21.48% ID/g at 15 min, 18.48% ID/g at 60 min). In contrast, 111In-oligo coupled with avidin through biotin (111In-oligo-bt-Av) showed very high accumulation in the liver (50.95% at 15 min, 47.88% at 60 min). 111In-oligo complexed with G4 showed high uptake in the kidney and spleen, but its hepatic uptake was relatively low (13.12% at 15 min, 10.67% at 60 min). When both G4 and Av-bt systems were employed, 111In-oligo/G4-bt-Av showed extremely high uptake in the lung (182.33% at 15 min, 125.54% at 60 min), probably due to the formation of large molecular weight complex and aggregates which are trapped in the lung, and its hepatic uptake was lower than 111In-oligo-bt-Av. 111In-oligo-bt-Av, which exhibited the highest hepatic uptake in vivo, also showed high and rapid internalization into hepatocytes. The avidin-biotin system seems to have potential as a carrier of oligo-DNA to the liver.

Lectin-mediated drug targeting: history and applications

The purpose of this paper is to review the history of using lectins to target and deliver drugs to their site of action. The hour of birth of "lectinology" may be defined as the description of the agglutinating properties of ricin, by Herrmann Stillmark in 1888, however, the modern era of lectinology began almost 100 years later in 1972 with the purification of different plant lectins by Sharon and Lis. The idea to use lectins for drug delivery came in 1988 from Woodley and Naisbett, who proposed the use of tomato lectin (TL) to target the luminal surface of the small intestine. Besides the targeting to specific cells, the lectin-sugar interaction can also been used to trigger vesicular transport into or across epithelial cells. The concept of bioadhesion via lectins may be applied not only for the GI tract but also for other biological barriers like the nasal mucosa, the lung, the buccal cavity, the eye and the blood-brain barrier.

Stable polyplexes based on arginine-containing oligopeptides for in vivo gene delivery

In this study, we investigated to what extent the stability and transduction capacity of polyplexed DNA can be improved by optimizing the condensing peptide sequence. We have synthesized a small library of cationic peptides, at which the lysine/arginine ratio and the cation charge were varied. All peptides were able to compact DNA, at which polyplexes of short lysine-rich sequences were considerably larger than those of elongated or arginine-rich peptides (GM102 and GM202). In addition, the arginine-rich peptides GM102 and GM202 rendered the polyplexes resistant to plasma incubation or DNase I-mediated digestion. While all peptides were found to improve the transfection efficiency in HepG2 cells, only the GM102- and GM202-derived polyplexes could be specifically targeted to HepG2 cells by incorporation of a ligand-derivatized YKAK(8)WK peptide. We propose that GM102 and GM202 combine the advantage of small condensing peptides to give small-sized polyplexes with the superior stability of condensing polymers, which makes GM102 and GM202 excellent candidates for future in vivo gene therapy studies.

M cell DNA vaccination for CTL immunity to HIV

To facilitate invasion, reovirus has evolved to attach to M cells, a specialized epithelium residing within the follicle-associated epithelium that covers mucosal inductive tissues. Thus, we questioned adapting reovirus protein sigma1 to ferry DNA vaccines to the mucosa to immunize against HIV. Three expression plasmids encoding HIV(Ba-L) gp160, cytoplasmic gp140, and secreted gp140 were tested in mice as protein sigma1-poly-L-lysine-DNA complexes (formulated vaccine) via the intranasal route. Evaluation of cell-mediated immunity showed that the formulated gp160 DNA vaccine was more effective for stimulating envelope (Env)-specific CTL responses in lungs, lower respiratory lymph nodes (LN), cervical LN, submaxillary gland LN, and spleens. Three doses of vaccine were required for CTL responses, and intranasal naked DNA immunizations were ineffective. The greatest CTL activity was observed between weeks 8 and 10 for gp160-vaccinated mice, and activity remained detectable by week 16. These Env-specific CTL responses were perforin dependent in peripheral tissues, but mostly Fas dependent in the lungs. These Env-specific CTLs also produced IFN-gamma. Mice vaccinated with the formulated gp160 DNA vaccine showed potent antiviral immunity against vaccinia virus-env replication in ovaries. Thus, compared with live vectors, protein sigma1-mediated DNA delivery represents an alternative mucosal formulation for inducing cellular immunity against HIV-1.

Strategies for cancer gene therapy

Gene therapy offers new opportunities for cancer treatment and prevention through the use of targeted, relatively nontoxic treatments that can identify, disable, and destroy malignant cells. This article reviews the principles behind oncogene inactivation, tumor suppressor gene replacement, inhibition of angiogenesis, immunopotentiation, molecular chemotherapy, and addition of drug resistance genes. The adcantages and limitations of viral and nonviral vectors for delivery of the therapeutic genes are presented.

Systemic genetic transfer of p21WAF-1 and GM-CSF utilizing of a novel oligopeptide-based EGF receptor targeting polyplex

Based on the fact that aberrant overexpression of some growth factor receptors was observed in a variety of human cancer cells, a novel nonviral gene delivery system GE7, which contains a 16-amino-acid ligand for identifying EGF receptor was constructed for tumor-targeted gene therapy. Intravenous administration of GE7 system revealed that it has the ability to target beta-galactosidase (beta-gal) reporter gene into murine hepatoma (Hepa) cells. Owing to the limited antitumor effects elicited by a single-gene transfer, recent efforts to treat malignancy using combined gene therapy have been accomplished with varying degrees of success. In this study, the human cyclin-dependent kinase inhibitor gene p21(WAF-1) and the murine cytokine gene granulocyte-macrophage colony-stimulating factor (GM-CSF) were used simultaneously for in vivo gene therapy through systemic injection of the EGF R targeted GE7/DNA complex into murine hepatoma-bearing mice. The results demonstrated that combined administration of p21(WAF-1) and GM-CSF could remarkably inhibit the growth of subcutaneously transplanted hepatoma Hepa cells, and significantly increase the survival rate of tumor-bearing mice. The activities of natural killer (NK) cells and specific cytotoxic T lymphocytes (CTL) were clearly enhanced after combined gene therapy. In vitro experiments showed that p21(WAF-1) gene transfer exhibited a suppressive function on the growth of Hepa cells and the expression of H-2K(b) and B7-1 molecules on Hepa cells increased significantly after combined genes delivery. All these results suggested that the GE7 system was able to target therapeutic genes efficiently to cancer cells, which showed high EGF R expression. The cotransfer of p21(WAF-1) and GM-CSF genes apparently inhibited the growth of tumors through (a) the arrest of tumor cell growth and (b) the enhancement of systemic antitumor immunity.

Distribution and anti-HBV effects of antisense oligodeoxynucleotides conjugated to galactosylated poly-L-lysine

AIM

To describe distribution of the phosphorothioated antisense oligodeoxynucleotides (PS-asODNs) conjugated to galactosylated poly-L-lysine (Gal-PLL) in mice, and to observe their effects on expression of HBV gene in the 2.2.15 cells and transgenic mice.

METHODS

According to the result of direct sequencing of PCR amplified products, a 16 mer phosphorothioate analogue of the antisense oligodeoxynucleotides (PS-asODNs) directed against the HBV U(5)-like region was conjugated to the hepatotropic Gal-PLL molecules. Its distribution was demonstrated using asODNs labeled with (32)P at the 5' terminus with a T4-polynucleotide Kinase. Its inhibition effect on HBV expression was observed in the transfected 2.2.15 cells and transgenic mice.

RESULTS

The Gal-PLL and asODNs could form stable complex at a molar ratio of 2:1. As shown in the HBV-transfected 2.2.15 cells, the inhibition effects of asODNs alone and asODNs conjugated to Gal-PLL, at 10 micromol/L for both, on HBsAg and HBeAg production were different,the former being 70 % and 58 %, respectively, and the latter being 96 % and 82 %, respectively. A more pronounced reduction was also observed in viral DNA load in the culture supernatant for the test with Gal-PLL-asODNs. Among many mouse organs, livers retained more asODNs molecules after administration. The preferential concentration in liver was found to be 52.14 % for Gal-PLL-asODNs, as high as 2.38-fold of that for asODNs (21.9 %). Both elements decreased gradually in liver, with 2.9 % of the former, 5.99 % of the latter retained 24 hours after the administration. The injection interval, therefore, was recommended to be 24 hours. In the transgenic mice, serum HBsAg decreased significantly (P<0.01) at the 12th day after administrating Gal-PLL- asODNs, the serum HBV DNA turned negative in 4 of the 6 mice.

CONCLUSION

Antisense oligodeoxynucleotides conjugated to Gal-PLL can be concentrated in liver and intaked by hepatocytic cells. This may result in specific inhibition of expression and replication of HBV in vitro and in vivo.

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.

Increased receptor-mediated gene delivery to the liver by protamine-enhanced-asialofetuin-lipoplexes

A novel lipidic vector composed of DOTAP/Chol liposomes, asialofetuin (AF), protamine sulfate and DNA has been developed. The resulting protamine-AF-lipoplexes improved significantly the levels of gene expression in cultured cells and in the liver upon i.v. administration. Lipoplexes containing the optimal amount of AF (1 microg/microg DNA) showed a 16-fold higher transfection activity in HepG2 cells than non-targeted (plain) complexes. The uptake by cells having asialoglycoprotein receptors (ASGPr) on their plasma membrane was decreased by the addition of free AF, indicating that AF-lipoplexes were taken up specifically by cells via ASGPr-mediated endocytosis. Results from transfections performed in cells defective in ASGPr, ie HeLa cells, confirmed this mechanism. By addition of the condensing peptide, protamine sulfate, smaller complexes were obtained, which enhanced even more the uptake of AF-complexes in HepG2 cells and in the liver. The optimal amount of protamine was 0.4 microg/mcirog DNA, and gene expression was about 5-fold over that obtained with AF-lipoplexes in the absence of the peptide, and 75-fold higher than that with plain conventional lipoplexes. Protamine-AF-lipoplexes increased by a factor of 12 luciferase gene expression in the liver of mice administered systemically via the tail vein, compared to plain complexes. In summary, our findings extend the scope of previous studies where AF-lipoplexes were used to introduce DNA into hepatocytes. The combination of targeting and protamine condensation obviated the need for partial hepatectomy, commonly required to obtain efficient gene delivery in this organ. Since protamine sulfate has been proven to be non-toxic in humans, the novel liver-specific vector described here may be useful for the delivery of clinically important genes to this organ.

Improved neurotensin-vector-mediated gene transfer by the coupling of hemagglutinin HA2 fusogenic peptide and Vp1 SV40 nuclear localization signal

Recently we reported that neurotensin-SPDP-poly-L-lysine (NT-vector) is able to bind plasmid DNA (NT-polyplex) and polyfect cells expressing the high-affinity neurotensin receptor (NTRH) although with low transfecting efficiency: in vitro, 6.5+/-1.5%, and in vivo, 5+/-4%. In this work, we attempted to increase the transfecting efficiency by integrating the hemagglutinin HA2 fusogenic peptide and the Vp1 nuclear localization signal of SV40 to the NT-polyplex (fusogenic-karyophilic-NT-polyplex). Confocal microscopy and flow cytometry analysis showed that the fusogenic-karyophilic-NT-polyplex produced mostly nuclear localization of the plasmid DNA in NTRH-bearing N1E-115 cells. About 50% of N1E-115 cells internalized and expressed the reporter gene when the plasmid DNA was transferred by the fusogenic-karyophilic-NT-polyplex. Although to a less extent, the addition of each viral peptide separately to NT-polyplex (fusogenic-NT-polyplex or karyophilic-NT-polyplex) improved polyfection. Fusogenic-NT-polyplex produced 22.41+/-5.96% of internalization and 20.35+/-0.82% of expression in N1E-115 cells, whereas karyophilic-NT-polyplex yielded 13.75+/-3.88% and 10.94+/-2.04%, respectively. Basal internalization and expression were detected in N1E-115 cells in the presence of 100 nM SR-48692 and in NTRH-lacking cells. The fusogenic-karyophilic-NT-polyplex was microinjected into the substantia nigra to test its ability for gene transfer in vivo. Fusogenic-karyophilic-NT-polyplex internalization was observed within dopamine neurons only. Reporter gene expression was observed in a high proportion of dopamine neurons up to 60 days after NT-polyfection. Both internalization and expression were prevented by SR-48692. Our results show that the fusogenic-karyophilic-NT-polyplex is a highly efficient and specific gene vector and encourage its use to transfer gene of physiological interest to NTRH-bearing neurons.

Protein/DNA polyplexes for gene therapy

The development of molecular conjugates as components of Protein/DNA polyplexes has resulted in the creation of a simple, non-virus vector for the targeted delivery of nucleic acids into specific cell types. This vector has many of the positive attributes of viruses, on without the limitations that continue to plague recombinant viruses. The simplicity of this vector allows for quick analysis of nucleic acids, expression vectors, and therapeutic genes in vitro and potentially in vivo, because the time that would be involved in the generation of recombinant viral vectors is not present. Essentially, the development of this delivery vector has resulted in the creation of a "synthetic virus" that has the capability of targeted delivery without the negative attributes of viruses.

Extrachromosomal recombinant adeno-associated virus vector genomes are primarily responsible for stable liver transduction in vivo

Recombinant adeno-associated virus (rAAV) vectors stably transduce hepatocytes in experimental animals. Although the vector genomes are found both as extrachromosomes and as chromosomally integrated forms in hepatocytes, the relative proportion of each has not yet been clearly established. Using an in vivo assay based on the induction of hepatocellular regeneration via a surgical two-thirds partial hepatectomy, we have determined the proportion of integrated and extrachromosomal rAAV genomes in mouse livers and their relative contribution to stable gene expression in vivo. Plasma human coagulation factor IX (hF.IX) levels in mice originating from a chromosomally integrated hF.IX-expressing transposon vector remained unchanged with hepatectomy. This was in sharp contrast to what was observed when a surgical partial hepatectomy was performed in mice 6 weeks to 12 months after portal vein injection of a series of hF.IX-expressing rAAV vectors. At doses of 2.4 x 10(11) to 3.0 x 10(11) vector genomes per mouse (n = 12), hF.IX levels and the average number of stably transduced vector genomes per cell decreased by 92 and 86%, respectively, after hepatectomy. In a separate study, one of three mice injected with a higher dose of rAAV had a higher proportion (67%) of integrated genomes, the significance of which is not known. Nevertheless, in general, these results indicate that, in most cases, no more than approximately 10% of stably transduced genomes integrated into host chromosomes in vivo. Additionally, the results demonstrate that extrachromosomal, not integrated, genomes are the major form of rAAV in the liver and are the primary source of rAAV-mediated gene expression. This small fraction of integrated genomes greatly decreases the potential risk of vector-related insertional mutagenesis associated with all integrating vectors but also raises uncertainties as to whether rAAV-mediated hepatic gene expression can persist lifelong after a single vector administration.

Gene delivery using a receptor-mediated gene transfer system targeted to hepatocellular carcinoma cells

For gene therapy to be effective in cancers, it is necessary to deliver therapeutic genes into cells with high specificity and efficiency. In this study, we examined the in vitro and in vivo gene delivery efficiency of a new, growth receptor-mediated gene transfer system in hepatocellular carcinoma (HCC). The effects of transfection of wild-type p53 using this system were also studied. The system consisted of a ligand oligopeptide for epidermal growth factor receptor (EGFR) recognition, a polypeptide for DNA binding, and an endosome-releasing oligopeptide for endosomolysis. Two human HCC cell lines and a normal liver cell line were used, and pCMV-beta-galactosidase (beta-gal) was used as a reporter gene. Both HCC cell lines had strong expression of EGFR and the in vitro transfer efficiency peaked at day 5 at about 50%. This finding was in contrast to the normal liver cell line, which had weak EGFR expression and less than 1% transfer efficiency throughout. For in vivo gene transfer in tumors produced by inoculating HCC cells in nude mice and with the vector-beta-gal gene complex injected peritumorally, beta-gal expression was detected within the tumors at 12 hr, peaked at day 5 involving about 50% of the tumor cells and persisted at 2 weeks. Using this vector system, transfection of wild-type p53 into Huh-7 cells that had mutated p53 resulted in significant growth inhibition of cancer cells accompanied by a decreased G2/M phase and increased p53 protein. In conclusion, this receptor-mediated gene transfer system appears to work specifically in HCC cells with high efficiency, and may be promising in delivering apoptotic and other genes into HCC cells.

Immunization of livestock with DNA vaccines: current studies and future prospects

Early studies using DNA immunization suggest the potential benefits of this form of immunization including: long-lived immunity, a broad spectrum of immune responses (both cell-mediated immunity and humoral responses) and the simultaneous induction of immunity to a variety of pathogens through the use of multivalent vaccines. Using marine and cow models, we studied methods to enhance and direct the immune response to polynucleotide vaccines. We demonstrated the ability to modulate the magnitude and direction of the immune response by co-administration of plasmid encoded cytokines and antigen. Also, we clearly demonstrated that the cellular components (cytosolic, membrane-anchored, or extracellular) to which the expressed antigen is delivered determines the types of immune responses induced. Since induction of immunity at mucosal surfaces (route of entry for many pathogens) is critical to prevent infection, various methods of delivering polynucleotide vaccines to animals including mucosal surfaces have been attempted and are described as future prospects for improving immune responses by DNA vaccination.