Hepatocyte-targeted gene transfer by combination of vascularly delivered plasmid DNA and in vivo electroporation

CRISPR somatic genome engineering and cancer modeling in the mouse pancreas and liver

Genetically engineered mouse models (GEMMs) transformed the study of organismal disease phenotypes but are limited by their lengthy generation in embryonic stem cells. Here, we describe methods for rapid and scalable genome engineering in somatic cells of the liver and pancreas through delivery of CRISPR components into living mice. We introduce the spectrum of genetic tools, delineate viral and nonviral CRISPR delivery strategies and describe a series of applications, ranging from gene editing and cancer modeling to chromosome engineering or CRISPR multiplexing and its spatio-temporal control. Beyond experimental design and execution, the protocol describes quantification of genetic and functional editing outcomes, including sequencing approaches, data analysis and interpretation. Compared to traditional knockout mice, somatic GEMMs face an increased risk for mouse-to-mouse variability because of the higher experimental demands of the procedures. The robust protocols described here will help unleash the full potential of somatic genome manipulation. Depending on the delivery method and envisaged application, the protocol takes 3-5 weeks.

Understanding In Vivo Fate of Nucleic Acid and Gene Medicines for the Rational Design of Drugs

Nucleic acid and genetic medicines are increasingly being developed, owing to their potential to treat a variety of intractable diseases. A comprehensive understanding of the in vivo fate of these agents is vital for the rational design, discovery, and fast and straightforward development of the drugs. In case of intravascular administration of nucleic acids and genetic medicines, interaction with blood components, especially plasma proteins, is unavoidable. However, on the flip side, such interaction can be utilized wisely to manipulate the pharmacokinetics of the agents. In other words, plasma protein binding can help in suppressing the elimination of nucleic acids from the blood stream and deliver naked oligonucleotides and gene carriers into target cells. To control the distribution of these agents in the body, the ligand conjugation method is widely applied. It is also important to understand intracellular localization. In this context, endocytosis pathway, endosomal escape, and nuclear transport should be considered and discussed. Encapsulated nucleic acids and genes must be dissociated from the carriers to exert their activity. In this review, we summarize the in vivo fate of nucleic acid and gene medicines and provide guidelines for the rational design of drugs.

In Vivo Electroporation-Mediated, Intrahepatic Alpha1 Antitrypsin Gene Transfer Reduces Pulmonary Emphysema in Pallid Mice

Rationale: Mutation in the alpha1 antitrypsin (AAT) gene leads to low circulating levels of AAT, which is associated with several disease processes including pulmonary emphysema. The standard of care relies on substitution with plasma-purified AAT. We studied a novel approach to obtain sustained therapeutic levels of circulating AAT using nonviral in vivo electroporation-mediated gene transfer to the liver. Methods: In vivo intrahepatic electroporation-mediated human AAT gene transfer was performed in C57 Bl/6J mice carrying a genetic deficiency of murine AAT (pallid mice) and suffering from pulmonary emphysema. The animals were evaluated for lung function using flexiVent and detailed stereological assessments. Lung neutrophilic burden was assessed. Results: Pallid mice showed morphologically detectable pulmonary emphysema. Thirty days after in vivo electroporation-mediated gene transfer directly aimed at the liver, circulating human AAT was elevated and lung function was significantly improved compared to non-treated pallid mice. Stereological analysis revealed a reduction in pulmonary emphysema. Conclusion: Our data indicate that in vivo intrahepatic electroporation-mediated gene transfer of AAT is a safe and efficient procedure resulting in reduction of pulmonary emphysema in pallid mice.

Gene electrotransfer clinical trials

Plasmid or non-viral gene therapy offers an alternative to classic viral gene delivery that negates the need for a biological vector. In this case, delivery is enhanced by a variety of approaches including lipid or polymer conjugation, particle-mediated delivery, hydrodynamic delivery, ultrasound or electroporation. Electroporation was originally used as a laboratory tool to deliver DNA to bacterial and mammalian cells in culture. Electrode development allowed this technique to be modified for in vivo use. After preclinical therapeutic studies, clinical delivery of cell impermeant chemotherapeutic agents progressed to clinical delivery of plasmid DNA. One huge benefit of this delivery technique is its malleability. The pulse protocol used for plasmid delivery can be fine-tuned to control the levels and duration of subsequent transgene expression. This fine-tuning allows transgene expression to be tailored to each therapeutic application. Effective and appropriate expression induces the desired clinical response that is a critical component for any gene therapy. This chapter focuses on clinical trials using in vivo electroporation or electrotransfer as a plasmid delivery method. The first clinical trial was initiated in 2004, and now more than fifty trials use electric fields for gene delivery. Safety and tolerability has been demonstrated by several groups, and early clinical efficacy results are promising in both cancer therapeutic and infectious disease vaccine applications.

Nonviral vectors: we have come a long way

Gene therapy, once thought to be the future of medicine, has reached the beginning stages of exponential growth. Many types of diseases are now being studied and treated in clinical trials through various gene delivery vectors. It appears that the future is here, and gene therapy is just beginning to revolutionize the way patients are treated. However, as promising as these ongoing treatments and clinical trials are, there are many more barriers and challenges that need to be addressed and understood in order to continue this positive growth. Our knowledge of these challenging factors such as gene uptake and expression should be expanded in order to improve existing delivery systems. This chapter will provide a brief overview on recent advances in the field of nonviral vectors for gene therapy as well as point out some novel vectors that have assisted in the extraordinary growth of nonviral gene therapy as we know it today.

Therapeutic delivery opportunities, obstacles and applications for cell-penetrating peptides

Advancements in the development of large bioactive molecules as therapeutic agents have made drug delivery an active and important field of research. Cell-penetrating peptides (CPPs) have the ability to deliver an array of molecules and even nano-size particles into cells in an efficient and non-toxic manner, both in vitro and in vivo. This review aims to give a perspective on the obstacles that CPP-mediated drug delivery is currently facing as well as the great opportunities for improvements that lie ahead. Strategies for delivery of novel gene-modulating agents and enhancing efficacy of classical drugs will be discussed, as well as methods for increasing bioavailability and tissue specificity of CPPs. The usefulness and potential of CPPs as therapeutic drug-delivery vectors will be exemplified by their use in the treatment of cancer, viral infection and muscular dystrophy.

Nonviral gene therapy targeting cardiovascular system

The goal of gene therapy is either to introduce a therapeutic gene into or replace a defective gene in an individual's cells and tissues. Gene therapy has been urged as a potential method to induce therapeutic angiogenesis in ischemic myocardium and peripheral tissues after extensive investigation in recent preclinical and clinical studies. A successful gene therapy mainly relies on the development of the gene delivery vector. Developments in viral and nonviral vector technology including cell-based gene transfer will further improve transgene delivery and expression efficiency. Nonviral approaches as alternative gene delivery vehicles to viral vectors have received significant attention. Recently, a simple and safe approach of gene delivery into target cells using naked DNA has been improved by combining several techniques. Among the physical approaches, ultrasonic microbubble gene delivery, with its high safety profile, low costs, and repeatable applicability, can increase the permeability of cell membrane to macromolecules such as plasmid DNA by its bioeffects and can provide as a feasible tool in gene delivery. On the other hand, among the promising areas for gene therapy in acquired diseases, ischemic cardiovascular diseases have been widely studied. As a result, gene therapy using advanced technology may play an important role in this regard. The aims of this review focus on understanding the cellular and in vivo barriers in gene transfer and provide an overview of currently used chemical vectors and physical tools that are applied in nonviral cardiovascular gene transfer.

Efficient in vivo gene transfer by intraperitoneal injection of plasmid DNA and calcium carbonate microflowers in mice

Gene transfer to intraperitoneal organs is thought to be a promising approach to treat such conditions as peritoneal fibrosis and peritoneal dissemination of cancers. We previously discovered that simple instillation of naked plasmid DNA (pDNA) onto intraperitoneal organs such as the liver and stomach could effectively transfer foreign genes in mice. In this study, we developed a novel nonviral method to enhance transfection efficiency of naked pDNA to intraperitoneal organs using a calcium carbonate suspension containing pDNA. Using commercially available calcium carbonate, we successfully transfected pDNA to the stomach. Handling of commercially available calcium carbonate, however, was troublesome owing to rapid precipitation and caking. To obtain slowly settling particles of calcium carbonate, we tried to synthesize novel versions of such particles and succeeded in creating flower-shaped particles, named calcium carbonate microflowers. Sedimentation of calcium carbonate microflowers was sufficiently slow for in vivo experiments. Moreover, the transfection efficiency of the suspension of calcium carbonate microflowers to the stomach was more effective than that of commercially available calcium carbonate, especially at low concentrations. Intraperitoneal injection of the suspension of calcium carbonate microflowers containing pDNA greatly enhanced naked pDNA transfer to whole intraperitoneal organs in mice. Furthermore, lactate dehydrogenase activities in intraperitoneal fluid and plasma were not raised by the suspension of calcium carbonate microflowers.

Efficacy and safety of Sleeping Beauty transposon-mediated gene transfer in preclinical animal studies

Sleeping Beauty (SB) transposons have been effective in delivering therapeutic genes to treat certain diseases in mice. Hydrodynamic gene delivery of integrating transposons to 5-20% of the hepatocytes in a mouse results in persistent elevated expression of the therapeutic polypeptides that can be secreted into the blood for activity throughout the animal. An alternative route of delivery is ex vivo transformation with SB transposons of hematopoietic cells, which then can be reintroduced into the animal for treatment of cancer. We discuss issues associated with the scale-up of hydrodynamic delivery to the liver of larger animals as well as ex vivo delivery. Based on our and others' experience with inefficient delivery to larger animals, we hypothesize that impulse, rather than pressure, is a critical determinant of the effectiveness of hydrodynamic delivery. Accordingly, we propose some alterations in delivery strategies that may yield efficacious levels of gene delivery in dogs and swine that will be applicable to humans. To ready hydrodynamic delivery for human application we address a second issue facing transposons used for gene delivery regarding their potential to "re-hop" from one site to another and thereby destabilize the genome. The ability to correct genetic diseases through the infusion of DNA plasmids remains an appealing goal.

Biotin-directed assembly of targeted modular lipoplexes and their transfection of human hepatoma cells in vitro

The asialoglycoprotein receptor, which is abundantly and near exclusively expressed on hepatocytes, has received much attention in the design of non-viral hepatotropic DNA delivery systems. Thus, asialoglycoproteins and hexopyranosyl ligands have been coupled to DNA-binding cationic polymers and liposomes in the assembly of complexes intended for uptake by liver parenchymal cells. The aim of the study was to construct a hepatocyte-targeted multimodular liposome-based transfecting complex, in which the biotin-streptavidin interaction provides the cohesive force between the ligand asialorosomucoid and the liposome bilayer, and to evaluate its transfection capabilities in the hepatocyte-derived human transformed cell line HepG2. Dibiotinylated asialoorosomucoid was attached to cationic liposomes constructed from 3beta[N-(N',N'-dimethylaminopropane)-carbamoyl] cholesterol (Chol-T):dioleoylphosphatidylethanolamine:biotinylcholesterylformylhydrazide (MSB1) (48:50:2 mole ratio) through streptavidin interposition. Liposome-pGL3 DNA interactions were studied by gel band shift and ethidium displacement assays. The cytotoxicity of assemblies was evaluated in the HepG2 cell line and transfection capabilities determined by measuring the activity of the transgene luciferase. Binding assays showed that all DNA was liposome associated at a DNA (negative):liposome (positive) charge ratio of 1:1. Accommodation of a streptavidin dibiotinylated asialoorosomucoid assembly was achieved at a DNA:liposome:streptavidin dibiotinylated asialoorosomucoid ratio of 1:4:9 (weight basis). Complexes showed optimal transfection activity at this ratio, which was reduced 10-fold by the presence of the competing ligand asialofetuin. The streptavidin-biotin interaction has been applied for the first time to the assembly of hepatocyte-targeted lipoplexes that display asialoorosomucoid and that are well tolerated by a human hepatoma cell line in which transfection is demonstrably achieved by receptor mediation. Favorable size and charge ratio characteristics suggest that this system may be suitable for in vivo application.

Discovery of metabolically stabilized electronegative polyacridine-PEG peptide DNA open polyplexes

Cationic condensing peptides and polymers bind electrostatically to DNA to form cationic polyplexes. While many cationic polyplexes are able to achieve in vitro transfection mediated through electrostatic interactions, few have been able to mediate gene transfer in vivo. The present study describes the development and testing of polyacridine PEG-peptides that bind to plasmid DNA by intercalation resulting in electronegative open polyplex DNA. Polyacridine PEG-peptides were prepared by chemically conjugating 6-(9-acridinylamino) hexanoic acid onto side chains of Lys in PEG-Cys-Trp-(Lys)(3, 4, or 5). The resulting PEG-Cys-Trp-(Lys-(Acr))(3, 4, or 5) peptides bound tightly to DNA by polyintercalation, rather than electrostatic binding. Unlike polycationic polyplexes, polyacridine PEG-peptide polyplexes were anionic and open coiled, as revealed by zeta potential and atomic force microscopy. PEG-Cys-Trp-(Lys-(Acr))(5) showed the highest DNA binding affinity and the greatest ability to protect DNA from metabolism by DNase. Polyacridine PEG-peptide DNA open polyplexes were dosed intramuscularly and electroporated in mice to demonstrate their functional activity in gene transfer. These results establish polyacridine PEG-peptide DNA open polyplexes as a novel gene delivery method for in vivo use.

Electroporation and ultrasound enhanced non-viral gene delivery in vitro and in vivo

Non-viral vectors are less efficient than the use of viral vectors for delivery of genetic material to cells in vitro and especially in vivo. However, viral vectors involve the use of foreign proteins that can stimulate both the innate and acquired immune response. In contrast, plasmid DNA can be delivered without carrier proteins and is non-immunogenic. Plasmid gene delivery can be enhanced by the use of physical methods that aid the passage of the plasmid through the cell membrane. Electroporation and microbubble-enhanced ultrasound are two of the most effective physical delivery methods and these can be applied to a range of different cell types in vitro and a broad range of tissues in vivo. Both techniques also have the advantage that, unlike viral vectors, they can be used to target specific tissues with systemic delivery. Although electroporation is often the more efficient of the two, microbubble-enhanced ultrasound causes less damage and is less invasive. This review provides an introduction to the methodology and summarises the range of cells and tissues that have been genetically modified using these techniques.

Targeted RNA interference for hepatic fibrosis

Hepatic fibrosis is a common consequence in patients with chronic liver damage. To date, no agent has been approved for the treatment of hepatic fibrosis. RNA interference (RNAi) is known to be a powerful tool for post-transcriptional gene silencing and has opened new avenues in gene therapy. The problems of lack of cell specificity in vivo and subsequently the occurrence of side effects has hampered the development of hepatic fibrosis treatment. To overcome these shortcomings, several targeted strategies have been developed, such as hydrodynamics-based approaches, local administration, cell-type-selective ligands and cell-type-specific promoters or enhancers, etc. Here, we provide an overview of targeted strategies for the treatment of hepatic fibrosis, and particularly, targeted RNAi for hepatic fibrosis.

Nonviral gene delivery: principle, limitations, and recent progress

Gene therapy is becoming a promising therapeutic modality for the treatment of genetic and acquired disorders. Nonviral approaches as alternative gene transfer vehicles to the popular viral vectors have received significant attention because of their favorable properties, including lack of immunogenicity, low toxicity, and potential for tissue specificity. Such approaches have been tested in preclinical studies and human clinical trials over the last decade. Although therapeutic benefit has been demonstrated in animal models, gene delivery efficiency of the nonviral approaches remains to be a key obstacle for clinical applications. This review focuses on existing and emerging concepts of chemical and physical methods for delivery of therapeutic nucleic acid molecules in vivo. The emphasis is placed on discussion about problems associated with current nonviral methods and recent efforts toward refinement of nonviral approaches.

Liver- and lobe-specific gene transfer following the continuous microinstillation of Plasmid DNA onto the liver surface in mice: effect of instillation speed

Development of technology to deliver foreign gene(s) to a specific organ/tissue is one of the major challenges in gene therapy. Here, we show liver- and lobe-specific gene transfer following the continuous microinstillation of plasmid DNA (pDNA) onto the liver surface in mice. Naked pDNA was continuously instilled onto the right medial liver lobe using syringe pump in male ddY mice. Our previous studies showed liver- and lobe-selective gene expression after instillation of 30 mul of pDNA solution onto the liver surface, but gene expression was also found in the other liver lobe, kidney and spleen. To improve target site selectivity of gene expression, the instillation volume was decreased; however, non-specific gene expression in the other liver lobe and diaphragm was still detected. To prevent immediate diffusion of the pDNA solution, we performed continuous microinstillation of pDNA using a syringe pump; as a result, target site selectivity was greatly improved. As for instillation speed, 5 min infusion was enough to prevent diffusion of pDNA solution. Furthermore, transfection efficiency in the target site was maintained when instillation speed was slowed. Wiping off residual pDNA solution from the applied liver lobe resulted in a further improvement in selectivity, suggesting not only immediate diffusion, but also gradual diffusion, are important factors for successful target site-specific gene transfer. Information in this study will be useful for further development of an effective gene delivery system targeted to a specific organ/tissue by use of other non-viral or viral vectors.

Reactivation of silenced transgene expression in mouse liver by rapid, large-volume injection of isotonic solution

Rapid, large-volume injection, or so-called hydrodynamic injection, of naked plasmid DNA gives high transgene expression in mouse liver, and this method has been applied to liver-directed gene transfer in humans with slight modifications. To prove that injection-induced biological changes are involved in hydrodynamic injection-induced, high-level transgene expression in mouse liver, isotonic solutions were injected into mice that had received a hydrodynamic injection of plasmid DNA. Transgene expression in the liver was increased by such injections irrespective of the cDNA, promoter, and type of solution. This reactivation was repeatable and detectable even 3 months after gene transfer. Parameters required for reactivation were similar to those required for the hydrodynamic injection of plasmid DNA. Plasmid DNA-polyethyleneimine complex-based transgene expression in mouse liver was also reactivated by the same treatment. DNA microarray and quantitative RT-PCR analyses revealed that the expression of immediate-early response genes c-fos and c-jun was increased 70 and 100-fold, respectively. Activator protein (AP)-1- or nuclear factor (NF)-kappa B-dependent transgene expression was increased by an injection of isotonic solutions. These findings indicate for the first time that a rapid, large-volume injection of isotonic solution activates the transcription factors AP-1 and NF-kappa B in the liver, which in turn increases the transcription of genes delivered by hydrodynamic injection or other methods.

Physical approaches for nucleic acid delivery to liver

The liver is a key organ for numerous metabolic pathways and involves many inherited diseases that, although being different in their pathology, are often caused by lack or overproduction of a critical gene product in the diseased cells. In principle, a straightforward method to fix such problem is to introduce into these cells with a gene-coding sequence to provide the missing gene product or with the nucleic acid sequence to inhibit production of the excessive gene product. Practically, however, success of nucleic acid-based pharmaceutics is dependent on the availability of a method capable of delivering nucleic acid sequence in the form of DNA or RNA to liver cells. In this review, we will summarize the progress toward the development of physical methods for nucleic acid delivery to the liver. Emphasis is placed on the mechanism of action, pros, and cons of each method developed so far. We hope the information provided will encourage new endeavor to improve the current methodologies or develop new strategies that will lead to safe and effective delivery of nucleic acids to the liver.

Adenovirus serotype 35 vector-mediated transduction following direct administration into organs of nonhuman primates

Adenovirus (Ad) serotype 35 (Ad35) vectors have attracted remarkable attention as alternatives to conventional Ad serotype 5 (Ad5) vectors. In a previous study, we showed that intravenously administered Ad35 vectors exhibited a safer profile than Ad5 vectors in cynomolgus monkeys, which ubiquitously express CD46, an Ad35 receptor, in a pattern similar to that in humans. However, the Ad35 vectors poorly transduced the organs. In this study, we examined the transduction properties of Ad35 vectors after local administration into organs of cynomolgus monkeys. The vectors transduced different types of cells depending on the organ. Hepatocytes and microglia were mainly transduced after the vectors were injected into the liver and cerebrum, respectively. Injection of the vectors into the femoral muscle resulted in the transduction of cells that appeared to be fibroblasts and/or macrophages. Conjunctival epithelial cells showed transgene expression following infusion into the vitreous body of the eyeball. Transgene expression was limited to areas around the injection points in most of the organs. In contrast, Ad35 vector-mediated transgene expression was not detected in any of the organs not injected with Ad35 vectors. These results suggest that Ad35 vectors are suitable for gene delivery by direct administration to organs.

Pharmacokinetic considerations regarding non-viral cancer gene therapy

Cancer gene therapy, in which pharmacologically active compounds are administered to cancer patients in a genetic form, has been examined not only in animals but also in cancer patients. Viral vector-induced severe side effects in patients have greatly underscored the importance of non-viral gene transfer methods. Even though the importance of pharmacokinetics is undoubtedly understood in the development of anticancer therapies, its importance has been less well recognized in non-viral cancer gene therapy. When transgene products express their activity within transduced cells, such as herpes simplex virus type 1 thymidine kinase and short hairpin RNA, the pharmacokinetics of the vectors and the expression profiles of the transgenes will determine the efficacy of gene transfer. The percentage of cells transduced is highly important if few by-stander effects are expected. If transgene products are secreted from cells into the blood circulation, such as interferons and interleukins, the pharmacokinetics of transgenes becomes a matter of significant importance. Then, any approach to increasing the level and duration of transgene expression will increase the therapeutic effects of cancer gene therapy. Here we review the pharmacokinetics of both non-viral vectors and transgene products, and discuss what should be done to achieve safer and more effective non-viral cancer gene therapy.

Nonviral approaches for targeted delivery of plasmid DNA and oligonucleotide

Successful gene therapy depends on the development of efficient delivery systems. Although pDNA and ODN are novel candidates for nonviral gene therapy, their clinical applications are generally limited owing to their rapid degradation by nucleases in serum and rapid clearance. A great deal of effort had been devoted to developing gene delivery systems, including physical methods and carrier-mediated methods. Both methods could improve transfection efficacy and achieve high gene expression in vitro and in vivo. As for carrier-mediated delivery in vivo, since gene expression depends on the particle size, charge ratio, and interaction with blood components, these factors must be optimized. Furthermore, a lack of cell-selectivity limits the wide application to gene therapy; therefore, the use of ligand-modified carriers is a promising strategy to achieve well-controlled gene expression in target cells. In this review, we will focus on the in vivo targeted delivery of pDNA and ODN using nonviral carriers.

[In vivo siRNA delivery to tumor cells and its application to cancer gene therapy]

RNA interference (RNAi) is a posttranscriptional gene-silencing event in which short double-stranded RNA (siRNA) degrades target mRNA. Because of its potent and highly specific gene-silencing effect, RNAi is expected to be used in the treatment of various diseases. Cancer is one of the major targets of RNAi-based therapy, because silencing oncogenes or other genes contributing to tumor progression can be target genes for RNAi. The delivery of RNAi effector to target cells is one of the key factors determining therapeutic efficacy, because gene silencing is limited to cells reached by RNAi effectors. Tumor cell lines stably expressing reporter genes were confirmed to be effective in sensitively and quantitatively evaluating RNAi effects in tumor cells in vitro and in vivo. Quantitative analyses of the gene-silencing effect revealed that short-hairpin RNA expressing plasmid DNA (pshRNA) has more durable effects than siRNA. Intratumoral injection of RNAi effectors was effective in suppressing target gene expression in tumor cells, and silencing of beta-catenin or hypoxia-inducible factor-1alpha (HIF-1alpha) significantly inhibited tumor growth. RNAi effectors were successfully delivered to tumor cells colonizing the liver through the vascular route. We found that tumor-bearing liver showed elevated HIF-1alpha expression in the cells, and the silencing of the expression in normal liver cells is also effective in inhibiting metastatic tumor growth. These results indicate the possibility of RNAi-based cancer therapy.

Design of PCR-amplified DNA fragments for in vivo gene delivery: size-dependency on stability and transgene expression

PCR-amplified DNA fragments can be more efficient and safer vectors than conventional plasmid DNA because of their smaller size and fewer numbers of immunostimulatory cytosine-phosphate-guanine (CpG) motifs. In the present study, the expression unit of plasmid DNA encoding farnesylated enhanced green fluorescent protein (EGFPF; pEGFP-F) or firefly luciferase (pLuc) was amplified by polymerase chain reaction (PCR) to obtain DNA fragments (EGFPF-mini, Luc-mini). EGFPF-mini was as effective as pEGFP-F on the basis of the number of EGFPF-expressing cells after intravenous injection into mice by the hydrodynamics-based procedure. Then, the effects of the length of DNA fragments on transgene expression were examined using luciferase-expressing DNA preparations. Luc-mini preparations showed high levels of luciferase activity in cultured cells as well as in mouse liver, even although the levels did not exceed that of pLuc. An elongation of the DNA fragment on either side of the minimal expression unit was effective in increasing the transgene expression and the stability against nucleases. PCR-amplified DNA fragments showed a sustained luciferase activity in mouse liver compared with pLuc, indicating that they are effective in achieving a prolonged expression. Their stabilization against nucleases will further increase the potential of such short, structure-controlled and synthetic DNA fragments for in vivo gene delivery.

Electroporation-mediated gene therapy

Non-viral gene transfer is markedly enhanced by the application of in vivo electroporation. Electroporation is a safe and efficient system to introduce genes to a wide variety of tissues, including skeletal muscle, tumors, kidney, liver and skin. Electroporation has been demonstrated to be effective in numerous disease models. This review focuses on the principles of electroporation and the target tissues employed for gene therapy. Based on the accumulation of positive results, the first clinical study for the treatment of malignant melanoma is now underway, and preclinical studies have suggested that electroporation is useful as a gene therapy protocol.

Sine-wave current for efficient and safe in vivo gene transfer

Recently, electro-gene transfer has become a powerful tool to enhance the efficiency of gene expression in different organs and particularly in muscle, which provides efficient secretion of therapeutic proteins into the circulation. However, its toxicity, owing to the high field strengths of conventional direct current (DC) square-waves, should be taken into account and should be minimized if electroporation is to be used routinely for the treatment of human diseases. In this study, we demonstrate that efficient in vivo gene transfer could be safely achieved using pulses of alternating current sine-waves (ACSWs) with a frequency of 60 Hz. Importantly, the field strength was decreased to as low as 20 V/cm and the efficiency of muscle gene transfer increased more than tenfold and showed less toxicity than with conventional DC square-wave pulses. Using ACSW pulses to transfer human clotting factor IX (hFIX) plasmid into muscle, we observed significant phenotypic correction in mice with hemophilia B.

Nonviral gene delivery: what we know and what is next

Gene delivery using nonviral approaches has been extensively studied as a basic tool for intracellular gene transfer and gene therapy. In the past, the primary focus has been on application of physical, chemical, and biological principles to development of a safe and efficient method that delivers a transgene into target cells for appropriate expression. This review summarizes the current status of the most commonly used nonviral methods, with an emphasis on their mechanism of action for gene delivery, and their advantages and limitations for gene therapy applications. The technical aspects of each delivery system are also reviewed, with a focus on how to achieve optimal delivery efficiency. A brief discussion of future development and further improvement of the current systems is intended to stimulate new ideas and encourage rapid advancement in this new and promising field.

Therapeutic protein production in vivo after electroporation-assisted intramuscular gene delivery

Gene delivery to skeletal muscles assisted by electroporation(EP) is a promising strategy for in vivo production of the therapeutic proteins. But the commonly used procedure required the application of electric pulses with voltages at above 200V/cm and durations at least 40ms, which would result in several damages in the muscle and limited surviving cells expressing transgene. We reported here an optimization study of the various electric pulse parameters to reduce toxicity while maintain transgene expression. In addition, we also found that the secreted transgene product level detected in serum samples may not correlate with the total gene expression level in muscles. Based on our data, we'd propose some less damaging electroporation parameters that may be useful for intramuscular gene delivery and therapeutic protein production.

Enhancement of an electroporation system for gene delivery using electrophoresis with a planar electrode

In this paper a new electroporation (EP) system is developed, which includes an EP microchip and a logic circuit, which combined with electrophoresis (ES), can provide site-specific enhancement of gene concentration. In this ES-EP microchip, an arc planar electrode provides the ES function for DNA attraction, and interdigitated array electrodes provide appropriate electric fields for the EP on the chip surface. In addition, the adherent cells can be manipulated in situ without detachment of the ES-EP microchip, which performs the "Lab on a chip". Experimental results have shown that the efficiency of gene transfection with an attracting-electric field (35.89%) becomes much higher than that without an attracting-electric field (16.62%). Cell numbers as low as 10(4) cells, and DNA as little as 4 microg are sufficient for evaluating the phenotypic effects following the over-expression of the introduced genes on the ES-EP microchip. The proposed system has the advantages of portability, cost-effectiveness, a high transfection rate and ease of operation.

Mechanism of in vivo DNA transport into cells by electroporation: electrophoresis across the plasma membrane may not be involved

BACKGROUND

Recently, in vivo gene transfer with electroporation (electro-gene transfer) has emerged as a leading technology for developing nonviral gene therapies and nucleic acid vaccines. The widely hypothesized mechanism is that electroporation induces structural defects in the membrane and provides an electrophoretic force to facilitate DNA crossing the permeabilized membrane. In this study, we have designed a device and experiments to test the hypothesis.

METHODS

In this study, we have designed a device that alternates the polarity of the applied electric field to elucidate the mechanism of in vivo electro-gene transfer. We also designed experiments to challenge the theory that the low-voltage (LV) pulses cannot permeabilize the membrane and are only involved in DNA electrophoresis, and answer the arguments that (1) the reversed polarity pulses can cause opposing sides of the cell membrane to become permeabilized and provide the electrophoresis for DNA entry; or (2) once DNA enters cytoplasmic/endosomal compartments after electroporation, it may bind to cellular entities and might not be reversibly extracted. Thus a gradual buildup of the DNA in the cell still seems quite possible even under the condition of the rapid reversal of polarity.

RESULTS

Our results indicate that electrophoresis does not play an important role in in vivo electro-gene transfer.

CONCLUSIONS

This study provides new insights into the mechanism of electro-gene transfer, and may allow the definition of newer and more efficient conditions for in vivo electroporation.

Adenovirus serotype 35 vector-mediated transduction into human CD46-transgenic mice

We previously demonstrated that systemic administration of adenovirus serotype 35 (Ad35) vectors to mice does not mediate efficient transduction in organs, probably because expression of the mouse analog of the subgroup B Ad receptor, human CD46 (membrane cofactor protein), is limited to the testis. Here, we describe the in vitro and in vivo transduction characteristics of Ad35 vectors by using homozygous and hemizygous human CD46-transgenic (CD46TG) mice, which ubiquitously express human CD46. An Ad35 vector more efficiently transduced the primary dendritic cells and macrophages prepared from CD46TG mice than those from wild-type mice. In vivo transduction experiments demonstrated that CD46TG mice are more susceptible to Ad35 vector-mediated in vivo transduction than are wild-type mice. In particular, homozygous CD46TG mice, which express higher levels of CD46 in the organs than hemizygous CD46TG mice, tend to exhibit higher transduction efficiencies after intraperitoneal administration than hemizygous CD46TG mice. Intraperitoneal administration of Ad35 vectors resulted in efficient transduction into the mesothelial cells of the peritoneal organs in homozygous CD46TG mice. These results indicate that an Ad35 vector recognizes human CD46 as a cellular receptor in CD46TG mice. However, the in vivo transduction efficiencies of Ad35 vectors in CD46TG mice are much lower than those of conventional Ad5 vectors in wild-type mice.

In Vivo Liver Electroporation: Optimization and Demonstration of Therapeutic Efficacy

Adverse effects (death and leukemogenesis) from viral vector-mediated gene therapy have renewed interest in plasmids as safer, more scalable, simple, and cost-effective vectors. Electroporation and hydrodynamic delivery are two techniques that improve the efficiency of plasmid-mediated gene transfer. The liver is a good tissue platform for targeted transfer of therapeutically relevant genes for correction of metabolic disorders, for example, hemophilia A. However, in vivo electroporation of liver has not yet been shown to achieve therapeutic efficacy of systemically active, secreted transgenic proteins. We have investigated the effect of field strength, pulse duration, pulse number, electrical waveforms, electrode contact area, plasmid administration routes, and injection technique on the efficiency of in vivo electrotransfer of naked plasmid to liver. Plasmid injection into a systemic vein was superior to intrahepatic injection. Unlike in vivo muscle electroporation, high-voltage pulses and microsecond pulses offered no advantage. Optimal electroporation conditions were 8-10 uni- or bipolar pulses of 20 msec, each at 250 V/cm. Using a nonhydrodynamic technique that greatly enhanced electrotransfer efficiency with minimal tissue injury, we demonstrate for the first time that liverdirected in vivo electroporation of factor VIII cDNA achieved significant phenotypic correction in hemophilic mice.

Stabilizing of plasmid DNA in vivo by PEG-modified cationic gold nanoparticles and the gene expression assisted with electrical pulses

This study aimed to investigate the benefits of combining the use of PEG-modified cationic gold nanoparticles with electroporation for in vivo gene delivery. PEG-modified cationic gold nanoparticles were prepared by NaBH(4) reduction of HAuCl(4) in the presence of 2-aminoethanethiol and mPEG-SH. Zeta-potential of the particles was nearly neutral (+0.1 mV). After forming complexes with plasmid DNA at a w/w ratio of 8.4, nanoparticle complexes were 90 nm for at least 60 min and showed a negative zeta-potential. After intravenous injection of DNA-nanoparticle complexes, 20% of gold were detected in blood at 120 min after injection and 5% of DNA were observed in blood after 5 min, suggesting that PEG-modified nanoparticles were stably circulating in the blood flow, but some of the DNA bound to particles degraded during circulation. When electroporation was applied to a lobe of the liver following injection of DNA-nanoparticle complexes, significant gene expression was specifically observed in the pulsed lobe. We concluded that PEG-modified nanoparticles maintained DNA more stably in the blood flow than in the case of naked DNA and electroporation assisted in restricted gene expression of circulating DNA in limited areas of the liver.

Tissue-Specific Characteristics of in Vivo Electric Gene: Transfer by Tissue and Intravenous Injection of Plasmid DNA

PURPOSE

To evaluate the tissue-specific characteristics of electric gene transfer after tissue and intravenous injection of naked plasmid DNA (pDNA).

METHODS

pDNA encoding firefly luciferase was injected directly into the liver, kidney, spleen, skin and muscle, or into the tail vein of mice, and electric pulses were then applied to one of these organs. The distribution of transgene expressing cells was evaluated using pDNA encoding beta-galactosidase.

RESULTS

Tissue injection of pDNA produced a significant degree of transgene expression in any tissue with the greatest amount in the liver, followed by kidney and spleen. The expression in these organs decreased quickly with time, and muscle showed the greatest expression at 7 days. Electroporation significantly increased the expression, and the expression level was comparable among the organs. Intravenous injection of pDNA followed by electroporation resulted in a significant expression in the liver, spleen, and kidney but not in the skin or muscle.

CONCLUSIONS

Electric gene transfer to the liver, kidney, and spleen can be an effective approach to obtain significant amounts of transgene expression by either tissue or intravenous injection of pDNA, whereas it is only effective after tissue injection as far as skin- or muscle-targeted gene transfer is concerned.