Efficient expression of naked dna delivered intraarterially to limb muscles of nonhuman primates

Hydrodynamic Delivery: Characteristics, Applications, and Technological Advances

The principle of hydrodynamic delivery was initially used to develop a method for the delivery of plasmids into mouse hepatocytes through tail vein injection and has been expanded for use in the delivery of various biologically active materials to cells in various organs in a variety of animal species through systemic or local injection, resulting in significant advances in new applications and technological development. The development of regional hydrodynamic delivery directly supports successful gene delivery in large animals, including humans. This review summarizes the fundamentals of hydrodynamic delivery and the progress that has been made in its application. Recent progress in this field offers tantalizing prospects for the development of a new generation of technologies for broader application of hydrodynamic delivery.

Nanomedicine for Gene Delivery and Drug Repurposing in the Treatment of Muscular Dystrophies

Muscular Dystrophies (MDs) are a group of rare inherited genetic muscular pathologies encompassing a variety of clinical phenotypes, gene mutations and mechanisms of disease. MDs undergo progressive skeletal muscle degeneration causing severe health problems that lead to poor life quality, disability and premature death. There are no available therapies to counteract the causes of these diseases and conventional treatments are administered only to mitigate symptoms. Recent understanding on the pathogenetic mechanisms allowed the development of novel therapeutic strategies based on gene therapy, genome editing CRISPR/Cas9 and drug repurposing approaches. Despite the therapeutic potential of these treatments, once the actives are administered, their instability, susceptibility to degradation and toxicity limit their applications. In this frame, the design of delivery strategies based on nanomedicines holds great promise for MD treatments. This review focuses on nanomedicine approaches able to encapsulate therapeutic agents such as small chemical molecules and oligonucleotides to target the most common MDs such as Duchenne Muscular Dystrophy and the Myotonic Dystrophies. The challenge related to in vitro and in vivo testing of nanosystems in appropriate animal models is also addressed. Finally, the most promising nanomedicine-based strategies are highlighted and a critical view in future developments of nanomedicine for neuromuscular diseases is provided.

Non-viral Gene Delivery Methods for Bone and Joints

Viral carrier transport efficiency of gene delivery is high, depending on the type of vector. However, viral delivery poses significant safety concerns such as inefficient/unpredictable reprogramming outcomes, genomic integration, as well as unwarranted immune responses and toxicity. Thus, non-viral gene delivery methods are more feasible for translation as these allow safer delivery of genes and can modulate gene expression transiently both in vivo, ex vivo, and in vitro. Based on current studies, the efficiency of these technologies appears to be more limited, but they are appealing for clinical translation. This review presents a summary of recent advancements in orthopedics, where primarily bone and joints from the musculoskeletal apparatus were targeted. In connective tissues, which are known to have a poor healing capacity, and have a relatively low cell-density, i.e., articular cartilage, bone, and the intervertebral disk (IVD) several approaches have recently been undertaken. We provide a brief overview of the existing technologies, using nano-spheres/engineered vesicles, lipofection, and in vivo electroporation. Here, delivery for microRNA (miRNA), and silencing RNA (siRNA) and DNA plasmids will be discussed. Recent studies will be summarized that aimed to improve regeneration of these tissues, involving the delivery of bone morphogenic proteins (BMPs), such as BMP2 for improvement of bone healing. For articular cartilage/osteochondral junction, non-viral methods concentrate on targeted delivery to chondrocytes or MSCs for tissue engineering-based approaches. For the IVD, growth factors such as GDF5 or GDF6 or developmental transcription factors such as Brachyury or FOXF1 seem to be of high clinical interest. However, the most efficient method of gene transfer is still elusive, as several preclinical studies have reported many different non-viral methods and clinical translation of these techniques still needs to be validated. Here we discuss the non-viral methods applied for bone and joint and propose methods that can be promising in clinical use.

piggyBac-Based Non-Viral In Vivo Gene Delivery Useful for Production of Genetically Modified Animals and Organs

In vivo gene delivery involves direct injection of nucleic acids (NAs) into tissues, organs, or tail-veins. It has been recognized as a useful tool for evaluating the function of a gene of interest (GOI), creating models for human disease and basic research targeting gene therapy. Cargo frequently used for gene delivery are largely divided into viral and non-viral vectors. Viral vectors have strong infectious activity and do not require the use of instruments or reagents helpful for gene delivery but bear immunological and tumorigenic problems. In contrast, non-viral vectors strictly require instruments (i.e., electroporator) or reagents (i.e., liposomes) for enhanced uptake of NAs by cells and are often accompanied by weak transfection activity, with less immunological and tumorigenic problems. Chromosomal integration of GOI-bearing transgenes would be ideal for achieving long-term expression of GOI. piggyBac (PB), one of three transposons (PB, Sleeping Beauty (SB), and Tol2) found thus far, has been used for efficient transfection of GOI in various mammalian cells in vitro and in vivo. In this review, we outline recent achievements of PB-based production of genetically modified animals and organs and will provide some experimental concepts using this system.

A Critical Review of Electroporation as A Plasmid Delivery System in Mouse Skeletal Muscle

The gene delivery to skeletal muscles is a promising strategy for the treatment of both muscular disorders (by silencing or overexpression of specific gene) and systemic secretion of therapeutic proteins. The use of a physical method like electroporation with plate or needle electrodes facilitates long-lasting gene silencing in situ. It has been reported that electroporation enhances the expression of the naked DNA gene in the skeletal muscle up to 100 times and decreases the changeability of the intramuscular expression. Coelectransfer of reporter genes such as green fluorescent protein (GFP), luciferase or beta-galactosidase allows the observation of correctly performed silencing in the muscles. Appropriate selection of plasmid injection volume and concentration, as well as electrotransfer parameters, such as the voltage, the length and the number of electrical pulses do not cause long-term damage to myocytes. In this review, we summarized the electroporation methodology as well as the procedure of electrotransfer to the gastrocnemius, tibialis, soleus and foot muscles and compare their advantages and disadvantages.

Translational Advances of Hydrofection by Hydrodynamic Injection

Hydrodynamic gene delivery has proven to be a safe and efficient procedure for gene transfer, able to mediate, in murine model, therapeutic levels of proteins encoded by the transfected gene. In different disease models and targeting distinct organs, it has been demonstrated to revert the pathologic symptoms and signs. The therapeutic potential of hydrofection led different groups to work on the clinical translation of the procedure. In order to prevent the hemodynamic side effects derived from the rapid injection of a large volume, the conditions had to be moderated to make them compatible with its use in mid-size animal models such as rat, hamster and rabbit and large animals as dog, pig and primates. Despite the different approaches performed to adapt the conditions of gene delivery, the results obtained in any of these mid-size and large animals have been poorer than those obtained in murine model. Among these different strategies to reduce the volume employed, the most effective one has been to exclude the vasculature of the target organ and inject the solution directly. This procedure has permitted, by catheterization and surgical procedures in large animals, achieving protein expression levels in tissue close to those achieved in gold standard models. These promising results and the possibility of employing these strategies to transfer gene constructs able to edit genes, such as CRISPR, have renewed the clinical interest of this procedure of gene transfer. In order to translate the hydrodynamic gene delivery to human use, it is demanding the standardization of the procedure conditions and the molecular parameters of evaluation in order to be able to compare the results and establish a homogeneous manner of expressing the data obtained, as ‘classic’ drugs.

Preclinical and clinical advances in transposon-based gene therapy

Transposons derived from Sleeping Beauty (SB), piggyBac (PB), or Tol2 typically require cotransfection of transposon DNA with a transposase either as an expression plasmid or mRNA. Consequently, this results in genomic integration of the potentially therapeutic gene into chromosomes of the desired target cells, and thus conferring stable expression. Non-viral transfection methods are typically preferred to deliver the transposon components into the target cells. However, these methods do not match the efficacy typically attained with viral vectors and are sometimes associated with cellular toxicity evoked by the DNA itself. In recent years, the overall transposition efficacy has gradually increased by codon optimization of the transposase, generation of hyperactive transposases, and/or introduction of specific mutations in the transposon terminal repeats. Their versatility enabled the stable genetic engineering in many different primary cell types, including stem/progenitor cells and differentiated cell types. This prompted numerous preclinical proof-of-concept studies in disease models that demonstrated the potential of DNA transposons for ex vivo and in vivo gene therapy. One of the merits of transposon systems relates to their ability to deliver relatively large therapeutic transgenes that cannot readily be accommodated in viral vectors such as full-length dystrophin cDNA. These emerging insights paved the way toward the first transposon-based phase I/II clinical trials to treat hematologic cancer and other diseases. Though encouraging results were obtained, controlled pivotal clinical trials are needed to corroborate the efficacy and safety of transposon-based therapies.

Delivery of Adeno-Associated Virus Gene Therapy by Intravascular Limb Infusion Methods

Recombinant adeno-associated virus (rAAV) can be delivered to the skeletal muscle of the limb (pelvic or thoracic) by means of regional intravascular delivery. This review summarizes the evolution of this technique to deliver rAAV either via the arterial blood supply or via the peripheral venous circulation. The focus of this review is on applications in large animal models, including preclinical studies. Based on this overview of past research, we aim to inform the design of preclinical and clinical studies.

Hydrodynamic delivery

Hydrodynamic delivery (HD) is a broadly used procedure for DNA and RNA delivery in rodents, serving as a powerful tool for gene/protein drug discovery, gene function analysis, target validation, and identification of elements in regulating gene expression in vivo. HD involves a pressurized injection of a large volume of solution into a vasculature. New procedures are being developed to satisfy the need for a safe and efficient gene delivery in clinic. Here, we summarize the fundamentals of HD, its applications, and future perspectives for clinical use.

Hemodynamics of a hydrodynamic injection

The hemodynamics during a hydrodynamic injection were evaluated using cone beam computed tomography (CBCT) and fluoroscopic imaging. The impacts of hydrodynamic (5 seconds) and slow (60 seconds) injections into the tail veins of mice were compared using 9% body weight of a phase-contrast medium. Hydrodynamically injected solution traveled to the heart and drew back to the hepatic veins (HV), which led to liver expansion and a trace amount of spillover into the portal vein (PV). The liver volumes peaked at 165.6 ± 13.3% and 165.5 ± 11.9% of the original liver volumes in the hydrodynamic and slow injections, respectively. Judging by the intensity of the CBCT images at the PV, HV, right atrium, liver parenchyma (LP), and the inferior vena cava (IVC) distal to the HV conjunction, the slow injection resulted in the higher intensity at PV than at LP. In contrast, a significantly higher intensity was observed in LP after hydrodynamic injection in comparison with that of PV, suggesting that the liver took up the iodine from the blood flow. These results suggest that the enlargement speed of the liver, rather than the expanded volume, primarily determines the efficiency of hydrodynamic delivery to the liver.

Hemodynamics of a hydrodynamic injection

The hemodynamics during a hydrodynamic injection were evaluated using cone beam computed tomography (CBCT) and fluoroscopic imaging. The impacts of hydrodynamic (5 seconds) and slow (60 seconds) injections into the tail veins of mice were compared using 9% body weight of a phase-contrast medium. Hydrodynamically injected solution traveled to the heart and drew back to the hepatic veins (HV), which led to liver expansion and a trace amount of spillover into the portal vein (PV). The liver volumes peaked at 165.6 ± 13.3% and 165.5 ± 11.9% of the original liver volumes in the hydrodynamic and slow injections, respectively. Judging by the intensity of the CBCT images at the PV, HV, right atrium, liver parenchyma (LP), and the inferior vena cava (IVC) distal to the HV conjunction, the slow injection resulted in the higher intensity at PV than at LP. In contrast, a significantly higher intensity was observed in LP after hydrodynamic injection in comparison with that of PV, suggesting that the liver took up the iodine from the blood flow. These results suggest that the enlargement speed of the liver, rather than the expanded volume, primarily determines the efficiency of hydrodynamic delivery to the liver.

Transfection efficiency along the regenerating soleus muscle of the rat

We investigated the efficiency of a single plasmid transfection along the longitudinal axis of the regenerating soleus of young rats. This also reflected transfection efficiency along the fibers because the soleus is a nearly fusiform muscle in young animals. The complete regeneration was induced by notexin and the transfection was made by intramuscular injection of enhanced green fluorescent protein- or Discosoma red-coding plasmids after 4 days. One week after transfection the number of transfected fibers was higher at the place of injection (i.e., in the muscle belly) and lower or absent at the ends of the muscle. The inspection of longitudinal sections and neuromuscular endplates indicated that one of the reasons of uneven transfection might be the shortness of transfected myotubes and the other reason might be the limit of diffusion of transgenic proteins from the expressing nuclei. As a result, the efficiency of transfection in the whole regenerating muscle was much lower than it could be estimated from the most successfully transfected part.

Dose response in rodents and nonhuman primates after hydrodynamic limb vein delivery of naked plasmid DNA

The efficacy of gene therapy mediated by plasmid DNA (pDNA) depends on the selection of suitable vectors and doses. Using hydrodynamic limb vein (HLV) injection to deliver naked pDNA to skeletal muscles of the limbs, we evaluated key parameters that affect expression in muscle from genes encoded in pDNA. Short-term and long-term promoter comparisons demonstrated that kinetics of expression differed between cytomegalovirus (CMV), muscle creatine kinase, and desmin promoters, but all gave stable expression from 2 to 49 weeks after delivery to mouse muscle. Expression from the CMV promoter was highest. For mice, rats, and rhesus monkeys, the linear range for pDNA dose response could be defined by the mass of pDNA relative to the mass of target muscle. Correlation between pDNA dose and expression was linear between a threshold dose of 75 μg/g and maximal expression at approximately 400 μg/g. One HLV injection into rats of a dose of CMV-LacZ yielding maximal expression resulted in an average transfection of 28% of all hind leg muscle and 40% of the gastrocnemius and soleus. Despite an immune reaction to the reporter gene in monkeys, a single injection transfected an average of 10% of all myofibers in the targeted muscle of the arms and legs and an average of 15% of myofibers in the gastrocnemius and soleus.

Hydrodynamic gene delivery and its applications in pharmaceutical research

Hydrodynamic delivery has emerged as the simplest and most effective method for intracellular delivery of membrane-impermeable substances in rodents. The system employs a physical force generated by a rapid injection of large volume of solution into a blood vessel to enhance the permeability of endothelium and the plasma membrane of the parenchyma cells to allow delivery of substance into cells. The procedure was initially established for gene delivery in mice, and its applications have been extended to the delivery of proteins, oligo nucleotides, genomic DNA and RNA sequences, and small molecules. The focus of this review is on applications of hydrodynamic delivery in pharmaceutical research. Examples are provided to highlight the use of hydrodynamic delivery for study of transcriptional regulation of CYP enzymes, for establishment of animal model for viral infections, and for gene drug discovery and gene function analysis.

Update on non-viral delivery methods for cancer therapy: possibilities of a drug delivery system with anticancer activities beyond delivery as a new therapeutic tool

IMPORTANCE OF THE FIELD

Cancer is the most formidable human disease. Owing to the heterogeneity of cancer, a single-treatment modality is insufficient for the complete elimination of cancer cells. Therapeutic strategies from various aspects are needed for cancer therapy. These therapeutic agents should be carefully selected to enhance multiple therapeutic pathways. Non-viral delivery methods have been utilized to enhance the tumor-selective delivery of therapeutic molecules, including proteins, synthetic oligonucleotides, small compounds and genes.

AREAS COVERED IN THIS REVIEW

As non-viral delivery methods, liposomes and polymer-based delivery materials to target tumors mainly by systemic delivery, physical methods including electroporation, sonoporation, and so on, to locally inject therapeutic molecules, and virosomes to use the viral infectious machinery for the delivery of therapeutic molecules are summarized.

WHAT THE READER WILL GAIN

This article aims to provide an overview of the characteristic properties of each non-viral vector. It will be beneficial to utilize appropriately the vector for cancer treatment.

TAKE HOME MESSAGE

Efficient and minimally invasive vectors are generally considered to be the ideal drug delivery system (DDS). However, against cancer, DDS equipped with antitumor activities may be a therapeutic choice. By combining therapeutic molecules with DDS having antitumor activities, enhancement of the multiple therapeutic pathways may be achieved.

Evaluation of hydrodynamic limb vein injections in nonhuman primates

The administration route is emerging as a critical aspect of nonviral and viral vector delivery to muscle, so as to enable gene therapy for disorders such as muscular dystrophy. Although direct intramuscular routes were used initially, intravascular routes are garnering interest because of their ability to target multiple muscles at once and to increase the efficiency of delivery and expression. For the delivery of naked plasmid DNA, our group has developed a hydrodynamic, limb vein procedure that entails placing a tourniquet over the proximal part of the target limb to block all blood flow and injecting the gene vector rapidly in a large volume so as to enable the gene vector to be extravasated and to access the myofibers. The present study was conducted in part to optimize the procedure in preparation for a human clinical study. Various injection parameters such as the effect of papaverine preinjection, tourniquet inflation pressure and duration, and rate of injection were evaluated in rats and nonhuman primates. In addition, the safety of the procedure was further established by determining the effect of the procedure on the neuromuscular and vascular systems. The results from these studies provide additional evidence that the procedure is well tolerated and they provide a foundation on which to formulate the procedure for a human clinical study.

Recent trends in non-viral vector-mediated gene delivery

Nucleic acids-based next generation biopharmaceuticals (i.e., pDNA, oligonucleotides, short interfering RNA) are potential pioneering materials to cope with various incurable diseases. However, several biological barriers present a challenge for efficient gene delivery. On the other hand, developments in nanotechnology now offer numerous non-viral vectors that have been fabricated and found capable of transmitting the biopharmaceuticals into the cell and even into specific subcellular compartments like mitochondria. This overview illustrates cellular barriers and current status of non-viral gene vectors, i.e., lipoplexes, liposomes, polyplexes, and nanoparticles, to relocate therapeutic DNA-based nanomedicine into the target cell. Despite the awesome impact of physical methods (i.e., ultrasound, electroporation), chemical methods have been shown to accomplish high-level and safe transgene expression. Further comprehension of barriers and the mechanism of cellular uptake will facilitate development of nucleic acids-based nanotherapy for alleviation of various disorders.

Genetics of athletic performance

Performance enhancing polymorphisms (PEPs) are examples of natural genetic variation that affect the outcome of athletic challenges. Elite athletes, and what separates them from the average competitor, have been the subjects of discussion and debate for decades. While training, diet, and mental fitness are all clearly important contributors to achieving athletic success, the fact that individuals reaching the pinnacle of their chosen sports often share both physical and physiological attributes suggests a role for genetics. That multiple members of a family often participate in highly competitive events, such as the Olympics, further supports this argument. In this review, we discuss what is known regarding the genes and gene families, including the mitochondrial genome, that are believed to play a role in human athletic performance. Where possible, we describe the physiological impact of the critical gene variants and consider predictions about other potentially important genes. Finally, we discuss the implications of these findings on the future for competitive athletics.

Image-guided, intravascular hydrodynamic gene delivery to skeletal muscle in pigs

Development of an effective, safe, and convenient method for gene delivery to muscle is a critical step toward gene therapy for muscle-associated diseases. Toward this end, we have explored the possibility of combining the image-guided catheter insertion technique with the principle of hydrodynamic delivery to achieve muscle-specific gene transfer in pigs. We demonstrate that gene transfer efficiency of the procedure is directly related to flow rate, injection pressure, and injection volume. The optimal gene delivery was achieved at a flow rate of 15 ml/second with injection pressure of 300 psi and injection volume equal to 1.5% of body weight. Under such a condition, hydrodynamic injection of saline containing pCMV-Luc (100 microg/ml) resulted in luciferase activity of 10(6) to 10(7) relative light units (RLU)/mg of proteins extracted from the targeted muscle 5 days after hydrodynamic gene delivery. Result from immunohistochemical analysis revealed 70-90% transfection efficiency of muscle groups in the hindlimb and persistent reporter gene expression for 2 months in transfected cells. With an exception of transient edema and elevation of creatine phosphokinase, no permanent tissue damage was observed. These results suggest that the image-guided, intravenous hydrodynamic delivery is an effective and safe method for gene delivery to skeletal muscle.

Effect of tissue-specific promoters and microRNA recognition elements on stability of transgene expression after hydrodynamic naked plasmid DNA delivery

Intravenous hydrodynamic injections into the liver and skeletal muscle have increased the efficacy of naked DNA delivery to a level that makes therapeutically relevant gene transfer attainable. Although there are no concerns about the immunogenicity of the delivered DNA itself, transgene products that are foreign to the host can trigger an immune response and hamper the therapeutic effect. Our goal was to determine whether and to what extent some known preventive measures are applicable to these delivery methods in order to achieve longterm expression of foreign proteins in immunocompetent mice. We designed plasmid DNA vectors that expressed a marker gene under the control of either a ubiquitous or a tissue-specific promoter. We also included microRNA (miR) target sites in the transcripts in order to silence expression in antigen-presenting cells (APCs). The constructs were delivered either into muscle or liver, using outbred ICR and inbred C57BL=6 mice. The data suggest that firefly luciferase, a potent immunogen, triggered a uniform immune response only in outbred ICR mice, and only when expressed from a ubiquitous promoter. This response could not be prevented by including APC-specific miR target sites in the transcript. In contrast, the probability of immune rejection in ICR mice could be significantly diminished by using tissue-specific promoters, and under these circumstances, the silencing of transgene expression in APCs did confer some benefits. After a single hydrodynamic injection, inbred mice did not reject luciferase under any of the tested conditions for at least 8 weeks. To test whether they became tolerized, they were challenged with a second boost of a cytomegalovirus promoter-driven luciferase construct. This triggered a strong immune response, suggesting that luciferase-reactive cells from the animals' T and B cell repertoire had not been eliminated. This secondary reaction could not be prevented by silencing expression in APCs. In conclusion, for the clinical application of hydrodynamic naked DNA delivery the use of tissue-specific promoters in combination with silencing expression in APCs will increase the probability of long-term expression, but the most desirable outcome, the establishment of transgene tolerance, appears unlikely to be achieved by any of these measures.

Therapeutic approaches for the sarcomeric protein diseases

No curative treatment currently exists for patients with skeletal myopathies caused by defects in sarcomeric proteins though symptomatic treatments including orthoses, night-time ventilation, or mechanical ventilation can provide major benefits. The molecular genetic discovery era has enabled many families to know which gene and precisely which gene defect their family, or in some cases only their affected child has. This knowledge has enormously increased the accuracy of genetic counselling and in some cases can enable prognosis, which helps families to make better-informed life decisions. However, symptomatic treatments and molecular genetics do not help the patient's skeletal muscle problems. The patients with skeletal muscle sarcomeric protein diseases, (from severely affected patients with shortened lifespan, through to the more mildly affected patients), would all benefit from more effective or curative treatments, as would their parents and families. This chapter outlines the experimental therapeutic strategies that have been investigated for other muscle diseases (predominantly the muscular dystrophies, towards which the majority of research emphasis has been focussed) and those that are beginning to be investigated for sarcomeric diseases. It analyses which of these approaches might be applicable to the different skeletal muscle sarcomeric protein diseases.

Physical methods of nucleic acid transfer: general concepts and applications

Physical methods of gene (and/or drug) transfer need to combine two effects to deliver the therapeutic material into cells. The physical methods must induce reversible alterations in the plasma membrane to allow the direct passage of the molecules of interest into the cell cytosol. They must also bring the nucleic acids in contact with the permeabilized plasma membrane or facilitate access to the inside of the cell. These two effects can be achieved in one or more steps, depending upon the methods employed. In this review, we describe and compare several physical methods: biolistics, jet injection, hydrodynamic injection, ultrasound, magnetic field and electric pulse mediated gene transfer. We describe the physical mechanisms underlying these approaches and discuss the advantages and limitations of each approach as well as its potential application in research or in preclinical and clinical trials. We also provide conclusions, comparisons, and projections for future developments. While some of these methods are already in use in man, some are still under development or are used only within clinical trials for gene transfer. The possibilities offered by these methods are, however, not restricted to the transfer of genes and the complementary uses of these technologies are also discussed. As these methods of gene transfer may bypass some of the side effects linked to viral or biochemical approaches, they may find their place in specific clinical applications in the future.

Intrathecal injection of naked plasmid DNA provides long-term expression of secreted proteins

Therapeutic benefit has been reported to result from intrathecal (i.t.) injection of transgene vectors, including naked DNA. However, most studies using naked DNA have measured only the transgene expression of intracellular proteins. Here we demonstrate that i.t. injection of naked DNA can result in long-term expression of secreted proteins. Plasmids expressing either secreted alkaline phosphatase (SEAP) or human interleukin-10 (hIL-10) were injected into the i.t. space in rats, and transgene products were repeatedly measured in the cerebrospinal fluid (CSF). Both SEAP and hIL-10 were maximal at 1 and 2 days after the injection and still detectable at 4 months. The utilization of a plasmid having two features that are hypothesized to increase gene expression (matrix attachment regions (MARs) and lack of CpG dinucleotides) resulted in a significant increase in gene expression. Reinjection of SEAP or hIL-10 plasmids after 4 months significantly increased protein levels at 1 and 14 days after the reinjection. SEAP was uniformly distributed between the DNA delivery site (approximately vertebral level T13) and the lumbar puncture site (L5/L6 inter-vertebral space), was reduced at the cisterna magna, and was detectable, though at much lower levels, in serum. These data suggest that naked DNA has the potential to be used as a therapeutic tool for applications that require long-term release of transgenes into the CSF.

Safety and efficacy of regional intravenous (r.i.) versus intramuscular (i.m.) delivery of rAAV1 and rAAV8 to nonhuman primate skeletal muscle

We developed a drug-free regional intravenous (r.i.) delivery protocol of recombinant adeno-associated virus (rAAV) 1 and 8 to an entire limb in the nonhuman primate (NHP), and compared the results with those produced by intramuscular (i.m.) delivery of the same dose of vector. We show that r.i. delivery of both serotypes was remarkably well tolerated with no adverse side-effects. After i.m., muscle transduction was restricted to the site of injection with a high number of vector copies per cell for rAAV1. In contrast, although r.i. delivery resulted in a lower vector copy per cell, it was detectable in the vast majority of muscles of the injected limb. The amounts of circulating infectious rAAV were similar for both serotypes and modes of delivery. At autopsy at up to 34 months after vector administration, similar biodistribution patterns were found for both vectors and for both modes of delivery, with numerous organs found to be positive for vector sequence when assayed using PCR and Southern blot. Altogether, we demonstrated that r.i. is a simple and efficient transduction protocol in NHPs, resulting in higher expression of the transgene with a lower number of vector genomes per cell. However, regardless of the mode of delivery, concerns continue to be raised by the presence of vector sequences detected at distant sites.

Non-viral gene transfection technologies for genetic engineering of stem cells

The recent rapid progress of molecular biology together with the steady progress of genome projects has given us some essential and revolutionary information about DNA and RNA to elucidate various biological phenomena at a genetic level. Under these circumstances, the technology and methodology of gene transfection have become more and more important to enhance the efficacy of gene therapy for several diseases. In addition, gene transfection is a fundamental technology indispensable to the further research development of basic biology and medicine regarding stem cells. Stem cells genetically manipulated will enhance the therapeutic efficacy of cell transplantation. In this paper, the carrier and technology of gene delivery are briefly overviewed while the applications to the basic researches of biology and medicine as well as regenerative medical therapy are introduced. A new non-viral carrier and the cell culture system are described to efficiently manipulate stem cells.

Hydrodynamic gene delivery: its principles and applications

Efficient and safe methods for delivering genetic materials into cells must be developed before the clinical potential of gene therapy can be fully realized. Recently, hydrodynamic gene delivery using a rapid injection of a relatively large volume of DNA solution has opened up a new avenue for gene therapy studies in vivo. This method is superior to the existing delivery systems because of its simplicity, efficiency, and versatility. Wide success in applying hydrodynamic principles to delivery of DNA, RNA, proteins, and synthetic compounds, into the cells in various tissues of small animals, has inspired the recent attempts at establishing a hydrodynamic procedure for clinical use. In this review, we provide an overview of the theory and practice of hydrodynamic gene delivery so as to aid researchers for the use of this method in their pre-clinical and translational gene therapy studies.

Systemic siRNA delivery via hydrodynamic intravascular injection

The main barrier to the use of RNAi in mammalian systems is the difficulty in delivering siRNA or shRNA to the appropriate tissues. Although progress has been made in this area, many of the technologies developed require specialized expertise and reagents that are beyond the reach of most investigators. In contrast, the hydrodynamic injection technique is simple to perform and enables highly efficient delivery of naked, unmodified siRNA to a number of tissues, especially the liver. This review describes the development of the technique and explores the possible mechanisms that enable uptake of siRNA to biological effect. Examples of the use of hydrodynamic injection in animal models of disease and for the study of gene function are presented and discussed.

Electrically Assisted Ocular Gene Therapy

Electrotransfer and iontophoresis are being developed as innovative non-viral gene delivery systems for the treatment of eye diseases. These two techniques rely on the use of electric current to allow for higher transfection yield of various ocular cell types in vivo. Short pulses of relatively high-intensity electric fields are used for electrotransfer delivery, whereas the iontophoresis technique is based on the application of low voltage electric current. The basic principles of these techniques and their potential therapeutic application for diseases of the anterior and posterior segments of the eye are reviewed. Iontophoresis has been found most efficient for the delivery of small nucleic acid fragments such as antisense oligonucleotides, siRNA, or ribozymes. Electrotransfer, on the other hand, is being developed for the delivery of oligonucleotides or custom designed plasmids. The wide range of strategies already validated and the potential for targeting specific types of cells confirm the promising early observations made using electrotransfer and iontophoresis. These two nonviral delivery systems are safe and can be used efficiently for targeted gene delivery to ocular tissues in vivo. At the present, their application for the treatment of ocular human diseases is nearing its final stages of adaptation and practical implementation at the bedside.

Optimization and delivery of plasmid DNA for vaccination

Vaccination with DNA is one of the most promising novel immunization techniques against a variety of pathogens and tumors, for which conventional vaccination regimens have failed. DNA vaccines are able to stimulate both arms of the immune system simultaneously, without carrying the safety risks associated with live vaccines, therefore representing not only an alternative to conventional vaccines but also significant progress in the prevention and treatment of fatal diseases and infections. However, translation of the excellent results achieved in small animals to similar success in primates or large animals has so far proved to be a major hurdle. Moreover, biosafety issues, such as the removal of antibiotic resistance genes present in plasmid DNA used for vaccination, remain to be addressed adequately. This review describes strategies to improve the design and production of conventional plasmid DNA, including an overview of safety and regulatory issues. It further focuses on novel systems for the optimization of plasmid DNA and the development of diverse plasmid DNA delivery systems for vaccination purposes.

Non-viral gene therapy for Duchenne muscular dystrophy: Progress and challenges

Duchenne muscular dystrophy (DMD) is one of the most common lethal, hereditary diseases of childhood. Since the identification of the genetic basis of this disorder, there has been the hope that a cure would be developed in the form of gene therapy. This has yet to be realized, but many different gene therapy approaches have seen dramatic advances in recent years. Although viral-mediated gene therapy has been at the forefront of the field, several non-viral gene therapy approaches have been applied to animal and cellular models of DMD. These include plasmid-mediated gene delivery, antisense-mediated exon skipping, and oligonucleotide-mediated gene editing. In the past several years, non-viral gene therapy has moved from the laboratory to the clinic. Advances in vector design, formulation, and delivery are likely to lead to even more rapid advances in the coming decade. Given the relative simplicity, safety, and cost-effectiveness of these methodologies, non-viral gene therapy continues to have great promise for future gene therapy approaches to the treatment of DMD.

Mechanism of plasmid delivery by hydrodynamic tail vein injection. I. Hepatocyte uptake of various molecules

BACKGROUND

The hydrodynamic tail vein (HTV) injection of naked plasmid DNA is a simple yet effective in vivo gene delivery method into hepatocytes. It is increasingly being used as a research tool to elucidate mechanisms of gene expression and the role of genes and their cognate proteins in the pathogenesis of disease in animal models. A greater understanding of its mechanism will aid these efforts and has relevance to macromolecular and nucleic acid delivery in general.

METHODS

In an attempt to explore how naked DNA enters hepatocytes the fate of a variety of molecules and particles was followed over a 24-h time frame using fluorescence microscopy. The uptake of some of these compounds was correlated with marker gene expression from a co-injected plasmid DNA. In addition, the uptake of the injected compounds was correlated with the histologic appearance of hepatocytes.

RESULTS

Out of the large number of nucleic acids, peptides, proteins, inert polymers and small molecules that we tested, most were efficiently delivered into hepatocytes independently of their size and charge. Even T7 phage and highly charged DNA/protein complexes of 60-100 nm in size were able to enter the cytoplasm. In animals co-injected with an enhanced yellow fluorescent protein (EYFP) expression vector and fluorescently labeled immunoglobulin (IgG), hepatocytes flooded with large amounts of IgG appeared permanently damaged and did not express EYFP-Nuc. Hepatocytes expressing EYFP had only slight IgG uptake. In contrast, when an EYFP expression vector was co-injected with a fluorescently labeled 200-bp linear DNA fragment, both were mostly (in 91% of the observed cells) co-localized to the same hepatocytes 24 h later.

CONCLUSIONS

The appearance of permanently damaged cells with increased uptake of some molecules such as endogenous IgG raised the possibility that a molecule could be present in a hepatocyte but its transport would not be indicative of the transport process that can lead to foreign gene expression. The HTV procedure enables the uptake of a variety of molecules (as previous studies also found), but the uptake process for some of these molecules may be associated with a more disruptive process to the hepatocytes that is not compatible with successful gene delivery.

A non-viral vector for targeting gene therapy to motoneurons in the CNS

Gene therapy vectors that can be targeted to motoneuronal cells are required in the field of neurodegenerative diseases. We propose the use of the atoxic fragment C of tetanus toxin (TTC) as biological activity carrier to the motoneurons. Naked DNA encoding beta-galactosidase-TTC hybrid protein was used to transfect muscle cells in vivo, resulting in a selective gene transfer of the enzymatic activity to the CNS. In the muscle, level expression of beta-galactosidase was readily detectable 24 h after injection, reaching a maximum after 4 days and gradually decreasing thereafter. Labelling in the hypoglossal motoneurons and motor cortex was observed from 4 days after injection. In this paper, we show that TTC works as an enzymatic activity carrier to the CNS when muscle cells are transfected in vivo. We have also shown that the presence of TTC does not have any influence on the expression of the transfected gene. Both these results warrant further studies of TTC as a means of treating motoneuron diseases in the field of gene therapy.

Naked plasmid DNA transfer to the porcine liver using rapid injection with large volume

The naked plasmid DNA transfer method of rapid injection with large volume has been useful for gene therapy in experimental study. However, only small animals like rodents have usually been reported on. In this study, the authors attempted to transfect naked plasmid DNA to the porcine liver by modified hydrodynamic method. We decided to transfer plasmid DNA to a part of the liver using the angio-catheter to reduce the liver damage. To discern the condition of injection, naked plasmid DNA-encoding green fluorescent protein (GFP) was transferred for use as a marker gene. The GFP gene expression was markedly observed in gene-transferred pig livers. In large animals, not only the naked gene quantity, the solution volume containing the plasmid DNA and the injection speed, but also the additional treatments of the portal vein and the hepatic artery preparation were crucial. We found that the following injection condition were needed: plasmid DNA, 3 mg; the solution volume, 150 ml and the injection speed, 5 ml/s. The portal vein and the hepatic artery were clamped during gene delivery and the blood flow of the portal vein was flushed out using normal saline. Cytotoxic T-lymphocyte antigen 4-immunoglobulin (CTLA4-Ig) gene was used to test for secretory protein. CTLA4-Ig gene was injected with a large volume of solution via the hepatic vein to the left outer lobe of the liver selectively. CTLA4-Ig was detected in the pig blood at a maximum serum level of 161.7 ng/ml 1 day after gene transfer, and the CTLA4-Ig was detected for several weeks. Our new technique of inserting a catheter into only a selected portion of the liver reduced liver toxicity and increased gene transfer efficiency. This is the first report of successful gene transfer, using a hydrodynamic method, to the segmental liver in pigs, and achieved more than enough secretory protein for the clinically therapeutic level in pigs.

Hydrodynamics-based gene delivery of naked DNA encoding fetal liver kinase-1 gene effectively suppresses the growth of pre-existing tumors

Antiangiogenic gene therapy is a promising strategy for cancer treatment, which generally requires highly efficient delivery systems. To date, success of this strategy has depended almost exclusively on the delivery of high titers of viral vectors, which can result in effective transgene expression. However, their cytotoxicity and immunogenicity are a major concern for clinical applications. Recent advances in delivery efficiency of naked DNA could potentially meet the requirement for both high transgene expression and minimal side effects. To investigate whether naked DNA can be used for antiangiogenic cancer therapy, an expression plasmid was generated that encodes a soluble form of fetal liver kinase-1 (Flk-1) gene, a receptor for vascular endothelial growth factor (VEGF). Hydrodynamic injection of this plasmid resulted in close to 0.1 mg/ml of soluble Flk-1 protein in mouse serum and blocked VEGF-driven angiogenesis in matrigel in vivo. The same delivery significantly suppressed the growth of two different pre-existing subcutaneous tumors, Renca renal cell carcinoma and 3LL lung carcinoma. CD31 immunohistochemistry revealed that the tumor-associated angiogenesis was also highly attenuated in soluble Flk-1-treated mice. Thus, expression of genes by hydrodynamics-based gene delivery of naked DNA appears to be a promising approach for antiangiogenic cancer gene therapy.

Recent advances in non-viral gene delivery

Gene therapy has been deemed the medicine of the future due to its potential to treat many types of diseases. However, many obstacles remain before gene delivery is optimized to specific target cells. Over the last several decades, many approaches to gene delivery have been closely examined. By understanding the factors that determine the efficiency of gene uptake and expression as well as those that influence the toxicity of the vector, we are better able to develop new vector systems. This chapter will provide a brief overview of recent advances in gene delivery, specifically on the development of novel non-viral vectors. The following chapters will provide additional details regarding the evolution of non-viral gene delivery systems.

Transthoracic direct current shock facilitates intramyocardial transfection of naked plasmid DNA infused via coronary vessels in canines

Catheter-mediated, percutaneous, transluminal delivery of naked plasmid DNA (pDNA) into myocardium may offer a valuable strategy to heart diseases. Here, we examined whether clinically available transthoracic direct current (DC) shock improves intracoronary naked DNA transfection into myocardium. Plasmid vector encoding the GL3 luciferase was infused retrogradely into the coronary veins of beagle dogs, whereas another pDNA solution was infused into the left coronary artery. During and after these procedures, the coronary venous sinus was occluded by balloon, and transthoracic DC shock of 200 J was applied immediately after the infusions. Without DC shock, no remarkable increase in luciferase activity was demonstrated in any part of the left ventricular myocardium. In the presence of DC pulsation, significant luciferase expression was detected in the regions that were supplied by left anterior descending coronary artery (LAD), whereas the gene expression in the right coronary artery (RCA) regions was much less drastic. X-gal (5-bromo-4-chloro-3-indolyl-beta-D-galactoside) staining of cardiac cross-sections also revealed regional expression of beta-galactosidase. Immunohistochemical examinations of heart cryosections revealed that cardiomyocytes in LAD regions successfully expressed transgene product. The present system may enable a new strategy for myocardial gene therapy, without any special device or technique other than cardiac catheterization and DC cardioversion that are generally performed in ordinary hospitals.

Angiogenic and antiangiogenic gene therapy

Gene therapy is thought to be a promising method for the treatment of various diseases. One gene therapy strategy involves the manipulations on a process of formation of new vessels, commonly defined as angiogenesis. Angiogenic and antiangiogenic gene therapy is a new therapeutic approach to the treatment of cardiovascular and cancer patients, respectively. So far, preclinical and clinical studies are successfully focused mainly on the treatment of coronary artery and peripheral artery diseases. Plasmid vectors are often used in preparations in angiogenic gene therapy trials. The naked plasmid DNA effectively transfects the skeletal muscles or heart and successfully expresses angiogenic genes that are the result of new vessel formation and the improvement of the clinical state of patients. The clinical preliminary data, although very encouraging, need to be well discussed and further study surely continued. It is really possible that further development of molecular biology methods and advances in gene delivery systems will cause therapeutic angiogenesis as well as antiangiogenic methods to become a supplemental or alternative option to the conventional methods of treatment of angiogenic diseases.

Rapid Intravascular Injection into Limb Skeletal Muscle: A Damage Assessment Study

We have recently developed a simple and highly efficient methodology for delivering plasmid DNA (pDNA) to skeletal muscle cells of mammalian limbs. The procedure involves the rapid intravascular injection of a large volume of saline (containing pDNA) into the vasculature of the distal limb. As a result of the robust delivery methodology involved, it is important to understand the effects of the injection procedure on the skeletal muscle tissue in the targeted limb. In previous studies, only modest and transient muscle damage was noted. In this study we quantitatively assessed the degree of muscle damage in rat limbs following intravascular injections using muscle histology (H&E staining), membrane integrity (Evans blue staining), and leukocyte infiltration (immunohistochemistry) assays. The rapid extravasation of fluid during the injection process resulted in edema of the muscle tissue of the targeted limb; however, the edema was transient and resolved within 24 h. Consistent with observations from previous studies, minimal levels of myofiber damage were detected. Immunohistochemical labeling indicated that increased numbers of neutrophils (CD43+) and macrophages (ED1+ and ED2+) were present in the muscle tissue interstitium shortly after injection but that elevations were relatively modest and resolved by 2 weeks postinjection.

Reducing the immunostimulatory activity of CpG-containing plasmid DNA vectors for non-viral gene therapy

The mammalian innate immune system has the ability to recognise and direct a response against incoming foreign DNA. The primary signal that triggers this response is unmethylated CpG motifs present in the DNA sequence of various disease-causing pathogens. These motifs are rare in vertebrate DNA, but abundant in bacterial and some viral DNAs. Because gene therapy generally involves the delivery of DNA from either plasmids of bacterial origin or recombinant viruses, an acute inflammatory response of variable severity inevitably results. The response is most serious for non-viral gene delivery vectors composed of cationic lipid-DNA complexes, producing adverse effects at lower doses and lethality at higher doses of complex. This review examines the role of immunostimulatory CpG motifs in the acute inflammatory response to non-viral gene therapy vectors. Strategies to neutralise or eliminate CpG motifs within plasmid DNA vectors, and the existing limitations of CpG reduction on improving the safety profile of non-viral vectors, will be discussed.

Plasmid electrotransfer of eye ciliary muscle: principles and therapeutic efficacy using hTNF‐α soluble receptor in uveitis

Due to its small size and particular isolating barriers, the eye is an ideal target for local therapy. Recombinant protein ocular delivery requires invasive and painful repeated injections. Alternatively, a transfected tissue might be used as a local producer of transgene-encoded therapeutic protein. We have developed a nondamaging electrically mediated plasmid delivery technique (electrotransfer) targeted to the ciliary muscle, which is used as a reservoir tissue for the long-lasting expression and secretion of therapeutic proteins. High and long-lasting reporter gene expression was observed, which was restricted to the ciliary muscle. Chimeric TNF-alpha soluble receptor (hTNFR-Is) electrotransfer led to elevated protein secretion in aqueous humor and to drastic inhibition of clinical and histological inflammation scores in rats with endotoxin-induced uveitis. No hTNFR-Is was detected in the serum, demonstrating the local delivery of proteins using this method. Plasmid electrotransfer to the ciliary muscle, as performed in this study, did not induce any ocular pathology or structural damage. Local and sustained therapeutic protein production through ciliary muscle electrotransfer is a promising alternative to repeated intraocular protein administration for a large number of inflammatory, degenerative, or angiogenic diseases.

Factors influencing the efficacy, longevity, and safety of electroporation-assisted plasmid-based gene transfer into mouse muscles

Intramuscular injection of plasmid is a potential alternative to viral vectors for the transfer of therapeutic genes into skeletal muscle fibers. The low efficiency of plasmid-based gene transfer can be enhanced by electroporation (EP) coupled with the intramuscular application of hyaluronidase. We have investigated several factors that can influence the efficiency of plasmid-based gene transfer. These factors include electrical parameters of EP, optimal use of hyaluronidase, age and strain of the host, and plasmid size. Muscles of very young and mature normal, mdx, and immunodeficient mice were injected with plasmids expressing beta-galactosidase, microdystrophin, full-length dystrophin, or full-length utrophin. Transfection efficiency, muscle fiber damage, and duration of transgene expression were analyzed. The best transfection level with the least collateral damage was attained at 175-200 V/cm. Pretreatment with hyaluronidase markedly increased transfection, which was also influenced by the plasmid size and the strain and the age of the mice. Even in immunodeficient mice, there was a significant late decline in transgene expression and plasmid DNA copies, although both still remained relatively high after 1 year. Thus, properly optimized EP-assisted plasmid-based gene transfer is a feasible, efficient, and safe method of gene replacement therapy for dystrophin deficiency of muscle but readministration may be necessary.