Hyaluronidase enhances recombinant adeno-associated virus (rAAV)-mediated gene transfer in the rat skeletal muscle

Enhancing In Vivo Electroporation Efficiency through Hyaluronidase: Insights into Plasmid Distribution and Optimization Strategies

Electroporation (EP) stands out as a promising non-viral plasmid delivery strategy, although achieving optimal transfection efficiency in vivo remains a challenge. A noteworthy advancement in the field of in vivo EP is the application of hyaluronidase, an enzyme with the capacity to degrade hyaluronic acid in the extracellular matrix, which thereby enhances DNA transfer efficiency by 2- to 3-fold. This paper focuses on elucidating the mechanism of hyaluronidase's impact on transfection efficiency. We demonstrate that hyaluronidase promotes a more uniform distribution of plasmid DNA (pDNA) within skeletal muscle. Additionally, our study investigates the effect of the timing of hyaluronidase pretreatment on EP efficiency by including time intervals of 0, 5, and 30 min between hyaluronidase treatment and the application of pulses. Serum levels of the pDNA-encoded transgene reveal a minimal influence of the hyaluronidase pretreatment time on the final serum protein levels following delivery in both mice and rabbit models. Leveraging bioimpedance measurements, we capture morphological changes in muscle induced by hyaluronidase treatment, which result in a varied pDNA distribution. Subsequently, these findings are employed to optimize EP electrical parameters following hyaluronidase treatment in animal models. This paper offers novel insights into the potential of hyaluronidase in enhancing the effectiveness of in vivo EP, as well as guides optimized electroporation strategies following hyaluronidase use.

CORP: Gene delivery into murine skeletal muscle using in vivo electroporation

The strategy of gene delivery into skeletal muscles has provided exciting avenues in identifying new potential therapeutics towards muscular disorders and addressing basic research questions in muscle physiology through overexpression and knockdown studies. In vivo electroporation methodology offers a simple, rapidly effective technique for the delivery of plasmid DNA into post-mitotic skeletal muscle fibers and the ability to easily explore the molecular mechanisms of skeletal muscle plasticity. The purpose of this review is to describe how to robustly electroporate plasmid DNA into different hindlimb muscles of rodent models. Further, key parameters (e.g., voltage, hyaluronidase, plasmid concentration) which contribute to the successful introduction of plasmid DNA into skeletal muscle fibers will be discussed. In addition, details on processing tissue for immunohistochemistry and fiber cross-sectional area (CSA) analysis will be outlined. The overall goal of this review is to provide the basic and necessary information needed for successful implementation of in vivo electroporation of plasmid DNA and thus open new avenues of discovery research in skeletal muscle physiology.

Induction of a local muscular dystrophy using electroporation in vivo: an easy tool for screening therapeutics

Intramuscular injection and electroporation of naked plasmid DNA (IMEP) has emerged as a potential alternative to viral vector injection for transgene expression into skeletal muscles. In this study, IMEP was used to express the DUX4 gene into mouse tibialis anterior muscle. DUX4 is normally expressed in germ cells and early embryo, and silenced in adult muscle cells where its pathological reactivation leads to Facioscapulohumeral muscular dystrophy. DUX4 encodes a potent transcription factor causing a large deregulation cascade. Its high toxicity but sporadic expression constitutes major issues for testing emerging therapeutics. The IMEP method appeared as a convenient technique to locally express DUX4 in mouse muscles. Histological analyses revealed well delineated muscle lesions 1-week after DUX4 IMEP. We have therefore developed a convenient outcome measure by quantification of the damaged muscle area using color thresholding. This method was used to characterize lesion distribution and to assess plasmid recirculation and dose–response. DUX4 expression and activity were confirmed at the mRNA and protein levels and through a quantification of target gene expression. Finally, this study gives a proof of concept of IMEP model usefulness for the rapid screening of therapeutic strategies, as demonstrated using antisense oligonucleotides against DUX4 mRNA.

Viral-Mediated Optogenetic Stimulation of Peripheral Motor Nerves in Non-human Primates

Objective: Reanimation of muscles paralyzed by disease states such as spinal cord injury remains a highly sought therapeutic goal of neuroprosthetic research. Optogenetic stimulation of peripheral motor nerves expressing light-sensitive opsins is a promising approach to muscle reanimation that may overcome several drawbacks of traditional methods such as functional electrical stimulation (FES). However, the utility of these methods has only been demonstrated in rodents to date, while translation to clinical practice will likely first require demonstration and refinement of these gene therapy techniques in non-human primates. Approach: Three rhesus macaques were injected intramuscularly with either one or both of two optogenetic constructs (AAV6-hSyn-ChR2-eYFP and/or AAV6-hSyn-Chronos-eYFP) to transduce opsin expression in the corresponding nerves. Neuromuscular junctions were targeted for virus delivery using an electrical stimulating injection technique. Functional opsin expression was periodically evaluated up to 13 weeks post-injection by optically stimulating targeted nerves with a 472 nm fiber-coupled laser while recording electromyographic (EMG) responses. Main Results: One monkey demonstrated functional expression of ChR2 at 8 weeks post-injection in each of two injected muscles, while the second monkey briefly exhibited contractions coupled to optical stimulation in a muscle injected with the Chronos construct at 10 weeks. A third monkey injected only in one muscle with the ChR2 construct showed strong optically coupled contractions at 5 ½ weeks which then disappeared by 9 weeks. EMG responses to optical stimulation of ChR2-transduced nerves demonstrated graded recruitment relative to both stimulus pulse-width and light intensity, and followed stimulus trains up to 16 Hz. In addition, the EMG response to prolonged stimulation showed delayed fatigue over several minutes. Significance: These results demonstrate the feasibility of viral transduction of peripheral motor nerves for functional optical stimulation of motor activity in non-human primates, a variable timeline of opsin expression in a animal model closer to humans, and fundamental EMG response characteristics to optical nerve stimulation. Together, they represent an important step in translating these optogenetic techniques as a clinically viable gene therapy.

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.

Selection and Identification of Skeletal-Muscle-Targeted RNA Aptamers

Oligonucleotide gene therapy has shown great promise for the treatment of muscular dystrophies. Nevertheless, the selective delivery to affected muscles has shown to be challenging because of their high representation in the body and the high complexity of their cell membranes. Current trials show loss of therapeutic molecules to non-target tissues leading to lower target efficacy. Therefore, strategies that increase uptake efficiency would be particularly compelling. To address this need, we applied a cell-internalization SELEX (Systematic Evolution of Ligands by Exponential Enrichment) approach and identified a skeletal muscle-specific RNA aptamer. A01B RNA aptamer preferentially internalizes in skeletal muscle cells and exhibits decreased affinity for off-target cells. Moreover, this in vitro selected aptamer retained its functionality in vivo, suggesting a potential new approach for targeting skeletal muscles. Ultimately, this will aid in the development of targeted oligonucleotide therapies against muscular dystrophies.

Gene therapy for the nervous system: challenges and new strategies

Current clinical treatments for central nervous system (CNS) diseases, such as Parkinson's disease and glioblastoma do not halt disease progression and have significant treatment morbidities. Gene therapy has the potential to "permanently" correct disease by bringing in a normal gene to correct a mutant gene deficiency, knocking down mRNA of mutant alleles, and inducing cell-death in cancer cells using transgenes encoding apoptosis-inducing proteins. Promising results in clinical trials of eye disease (Leber's congenital aumorosis) and Parkinson's disease have shown that gene-based neurotherapeutics have great potential. The recent development of genome editing technology, such as zinc finger nucleases, TALENS, and CRISPR, has made the ultimate goal of gene correction a step closer. This review summarizes the challenges faced by gene-based neurotherapeutics and the current and recent strategies designed to overcome these barriers. We have chosen the following challenges to focus on in this review: (1) delivery vehicles (both virus and nonviral), (2) use of promoters for vector-mediated gene expression in CNS, and (3) delivery across the blood-brain barrier. The final section (4) focuses on promising pre-clinical/clinical studies of neurotherapeutics.

Intramuscular DNA vaccination protocols mediated by electric fields

Vaccination is historically one of the most important methods for preventing infectious diseases in humans and animals. New insights in the biology of the immune system allow a more rational design of vaccines, and new vaccination strategies are emerging. DNA vaccines have been proposed as a promising approach for introducing foreign antigens into the host for inducing protective immunity against infectious and cancer diseases. Nevertheless, because of their poor immunogenicity, plasmid DNA vaccination strategies need further implementations. Recent data suggest electrotransfer as a useful tool to improve DNA-based vaccination protocols, being able to stimulate both the humoral and cellular immune responses. In preclinical trials, gene electrotransfer is successfully used in prime-boost combination protocols and its tolerability and safety has been demonstrated also in Phase I clinical trials. In this chapter, we report a short comment supporting electrotransfer as an effective strategy to improve DNA-based vaccination protocols and describe the vaccination procedures by plasmid DNA in combination with electrotransfer and hyaluronidase pretreatment in use in our laboratory.

Tackling obstacles for gene therapy targeting neurons: disrupting perineural nets with hyaluronidase improves transduction

Gene therapy has been proposed for many diseases in the nervous system. In most cases for successful treatment, therapeutic vectors must be able to transduce mature neurons. However, both in vivo, and in vitro, where preliminary characterisation of viral particles takes place, transduction of neurons is typically inefficient. One possible explanation is that the extracellular matrix (ECM), forming dense perineural nets (PNNs) around neurons, physically blocks access to the cell surface. We asked whether co-administration of lentiviral vectors with an enzyme that disrupts the ECM could improve transduction efficiency. Using hyaluronidase, an enzyme which degrades hyaluronic acid, a high molecular weight molecule of the ECM with mainly a scaffolding function, we show that in vitro in mixed primary cortical cultures, and also in vivo in rat cortex, hyaluronidase co-administration increased the percentage of transduced mature, NeuN-positive neurons. Moreover, hyaluronidase was effective at doses that showed no toxicity in vitro based on propidium iodide staining of treated cultures. Our data suggest that limited efficacy of neuronal transduction is partly due to PNNs surrounding neurons, and further that co-applying hyaluronidase may benefit applications where efficient transduction of neurons in vitro or in vivo is required.

Restrictions that control herpes simplex virus type 1 infection in mouse brain ex vivo

Elucidating the cellular and molecular factors governing herpes simplex virus type 1 (HSV-1) neurotropism is a prerequisite for understanding HSV-1 encephalitis and for targeting HSV-1-derived vectors for gene transfer to the brain. Earlier we had described an ex vivo system of mouse brain slices and demonstrated a selective and unique infection pattern, mostly around the ventricles. Here, we examined tissue factors controlling HSV-1 infection of brain slices. We demonstrated that heparan sulphate, while an important factor, does not determine the infection pattern. Hyaluronic acid, but not collagen, appears to enhance HSV-1 brain infection. To investigate whether tissue distribution of viral receptors determines the infection pattern, we examined transcription of herpes virus entry mediator and nectin-1 receptor genes in infected and uninfected brain regions. Both the infected and the uninfected regions express the receptors. We also explored the influence of intra-cellular factors. HSV-1 does not preferentially infect proliferating cells in the brain slices, despite its predilection to the ventricular zones. To delineate the step at which the HSV-1 infection cascade is restricted, mRNA was isolated following tissue infection, and transcription of the immediate-early and late viral genes was evaluated. The results indicated that HSV-1 genes are not expressed in regions that do not express a viral reporter gene. Therefore, we conclude that tissue resistance to infection is associated with a block at or prior to the immediate-early mRNA synthesis. Taken together, using the ex vivo system of organotypic culture we describe here extra-cellular and intra-cellular restriction levels of HSV-1 brain infection.

Design and testing of regulatory cassettes for optimal activity in skeletal and cardiac muscles

Gene therapy for muscular dystrophies requires efficient gene delivery to the striated musculature and specific, high-level expression of the therapeutic gene in a physiologically diverse array of muscles. This can be achieved by the use of recombinant adeno-associated virus vectors in conjunction with muscle-specific regulatory cassettes. We have constructed several generations of regulatory cassettes based on the enhancer and promoter of the muscle creatine kinase gene, some of which include heterologous enhancers and individual elements from other muscle genes. Since the relative importance of many control elements varies among different anatomical muscles, we are aiming to tailor these cassettes for high-level expression in cardiac muscle, and in fast and slow skeletal muscles. With the achievement of efficient intravascular gene delivery to isolated limbs, selected muscle groups, and heart in large animal models, the design of cassettes optimized for activity in different muscle types is now a practical goal. In this protocol, we outline the key steps involved in the design of regulatory cassettes for optimal activity in skeletal and cardiac muscle, and testing in mature muscle fiber cultures. The basic principles described here can also be applied to engineering tissue-specific regulatory cassettes for other cell types.

Therapeutic potential of replication-selective oncolytic adenoviruses on cells from familial and sporadic desmoid tumors

PURPOSE

Constitutive activation of the Wnt signaling pathway is a hallmark of many cancers and has been associated with familial and sporadic desmoid tumors. The aim of the present study is to assess the therapeutic potential of oncolytic adenoviruses selectively replicating in cells in which the Wnt signaling pathway is active on primary cells from desmoid tumors.

EXPERIMENTAL DESIGN

Primary cells extracted from familial (n = 3) or sporadic (n = 3) desmoid tumors were cultured short term. Cancer cell survival and viral replication were measured in vitro upon infection with two different oncolytic adenoviruses targeting a constitutive activation of the Wnt signaling pathway. Adenoviral infectivity was also assessed.

RESULTS

Although cells extracted from one sporadic desmoid tumor responded very well to the oncolytic action of the adenoviruses (<20% of viable cells upon infection at a multiplicity of infection of 10), cells from two tumor samples were totally resistant to the viral action. Cells from the remaining samples showed intermediate sensitivity to the oncolytic viruses. These effects were correlated to the level of infectivity of the cells. Finally, in responder cells, evidences of viral replication was observed.

CONCLUSIONS

Our experimental data suggest that the response of desmoid tumor cells to oncolytic adenovirus is neither correlated to the type of mutation activating the Wnt signaling pathway nor to the familial or sporadic nature of the tumor. In addition, they highlight the variability of infectivity of individual tumors and predict a great variability in the response to oncolytic adenoviruses.

Delivery of DNA into muscle for treating systemic diseases: advantages and challenges

An efficient and safe method to deliver DNA in vivo is a requirement for several purposes, such as the study of gene function and gene therapy applications. Among the different nonviral delivery methods currently under investigation, in vivo DNA electrotransfer has proven to be one of the most efficient and simple methods. This technique is a physical method of gene delivery consisting of a local application of electric pulses after injection of DNA. This technique can be applied to almost any tissue of a living animal, including tumors, skin, liver, kidney, artery, retina, cornea, or even brain, but the focus of this review will be on electrotransfer of plasmid DNA into skeletal muscle and its possible therapeutic uses for systemic diseases. Skeletal muscle is a good target for electrotransfer of DNA because of the following features: a large volume of easily accessible tissue, an endocrine organ capable of expressing several local and systemic factors, and muscle fibers as postmitotic cells have a long lifespan, which allows long-term gene expression. In this review, we will describe the main characteristics of DNA electrotransfer, including toxicity and safety issues related to this technique. We will focus on the important possible therapeutic applications of electrotransfer for systemic diseases demonstrated in animal models in the recent years, in the fields of monogenic diseases, tissue-specific diseases, metabolic disorders, immune-system-related diseases, and cancer. Finally, we will discuss the advantages and challenges of this technique.

Formulations for DNA delivery via electroporation in vivo

The importance of DNA formulation in safe and efficient electrogene transfer is increasingly recognized as electroporation technology enters into clinical development. A phenomenal increase in naked DNA delivery by electroporation offers new opportunities for nonviral gene therapies previously considered difficult because of insufficient delivery. However, significant tissue damage related to harsh electroporation conditions raises serious safety concerns with the use of electroporation in healthy tissues, which limits its current applications to only nonhealthy tissues such as tumors. DNA formulations designed to minimize tissue damage or enhance expression at weaker electric pulses have been examined to address these concerns. These include formulations fortified with the addition of transfection reagent(s), membrane-permeating agents, tissue matrix modifiers, targeted ligands, or agents modifying electrical conductivity or membrane stability to enhance delivery efficiency or reduce tissue damage. These advancements in DNA formulation could prove to be useful in improving the safety of electroporation protocols for human applications.

Proteolytic surface functionalization enhances in vitro magnetic nanoparticle mobility through extracellular matrix

Steric barriers such as collagen I sharply limit interstitial delivery of macromolecular and nanoparticle (NP) based therapeutic agents. Collagenase-linked superparamagnetic NPs overcame these barriers and moved through in vitro extracellular matrix (ECM) at 90 microm h(-1), a rate similar to invasive cells, under the influence of a magnetic field. NP migration in ECM diminished linearly over 5 days. The collagenase-NP construct overcame two of the most significant barriers to nano- and microscale therapeutics deployment: proteolytic enzyme stability was maintained during a clinically useful time frame by immobilization on the NP surface and degradation of interstitial barriers to tissue biodistribution was enabled by the conjugated microbial protease.

Quantitative evaluation of mammalian skeletal muscle as a heterologous protein expression system

The production of mammalian proteins in sufficient quantity and quality for structural and functional studies is a major challenge in biology. Intrinsic limitations of yeast and bacterial expression systems preclude their use for the synthesis of a significant number of mammalian proteins. This creates the necessity of well-identified expression systems based on mammalian cells. In this paper, we demonstrate that adult mammalian skeletal muscle, transfected in vivo by electroporation with DNA plasmids, is an excellent heterologous mammalian protein expression system. By using the fluorescent protein EGFP as a model, it is shown that muscle fibers express, during the course of a few days, large amounts of authentic replicas of transgenic proteins. Yields of approximately 1mg/g of tissue were obtained, comparable to those of other expression systems. The involvement of adult mammalian cells assures an optimal environment for proper protein folding and processing. All these advantages complement a methodology that is universally accessible to biomedical investigators and simple to implement.

RISUG (reversible inhibition of sperm under guidance)--an antimicrobial as male vas deferens implant for HIV free semen

HIV transmission from the male to the female is a major health problem. A hypothesis proposing an intra vas deferens implant of an antimicrobial compound to prevent the infection spread is presented. Mechanisms of action for the inhibition could include inactivating HIV in sperms passing through the vas deferens; drug release from the implant to destroy HIV entering into semen from genital structures distal to the vas deferens; and sperm acrosome released hyaluronidase mediated reabsorption of HIV. A subcomponent of the implant flowing along sperm pathway may have a role in reducing the entry of HIV from a positive female into penile tissue. A new drug RISUG (reversible inhibition of sperm under guidance) presently undergoing clinical trials for its contraceptive effect in the male (because it disrupts the sperm acrosome by an electrical charge and pH lowering effects) has also antimicrobial action. The drug being a combination of styrene maleic anhydride (SMA) and dimethyl sulfoxide (DMSO) on being injected into the lumen of the vas deferens produces styrene maleic acid thereby lowering pH; induces electrochemical action leading to a stable electrical charge generation; releases mandelic acid; and induces acrosome reaction in sperms with consequent release of hyaluronidase and sperm inactivation. Moreover, one time administration into the lumen of the vas gives long term action. All these phenomena very well match with the needs for HIV clearance of semen and hence RISUG is here proposed as a possible candidate material for the HIV inhibiting vas deferens implant when delivered in below contraceptive threshold dosage. For experimental validation, after obtaining data on the semen HIV load under control conditions in the HIV positive males inducted into the study, 30 mg of SMA in 120 microl of DMSO (contraceptive dose being 60 mg SMA+120 microl DMSO) is to be injected into vasa deferens bilaterally. Thereafter at intervals of one month the viral load needs to be determined in semen obtained either by masturbation or in lubricant free condom at intercourse - the method of collection remaining the same throughout for a particular subject. A significant reduction in the semen viral load following RISUG administration will validate the hypothesis. Speculated reduced female to male HIV transmission is more difficult to test. Nonspecific indications will come from a population study of the incidence of RISUG treated men becoming HIV positive as compared to that in the general population.

Targeted exon skipping in transgenic hDMD mice: A model for direct preclinical screening of human-specific antisense oligonucleotides

The therapeutic potential of frame-restoring exon skipping by antisense oligonucleotides (AONs) has recently been demonstrated in cultured muscle cells from a series of Duchenne muscular dystrophy (DMD) patients. To facilitate clinical application, in vivo studies in animal models are required to develop safe and efficient AON-delivery methods. However, since exon skipping is a sequence-specific therapy, it is desirable to target the human DMD gene directly. We therefore set up human sequence-specific exon skipping in transgenic mice carrying the full-size human gene (hDMD). We initially compared the efficiency and toxicity of intramuscular AON injections using different delivery reagents in wild-type mice. At a dose of 3.6 nmol AON and using polyethylenimine, the skipping levels accumulated up to 3% in the second week postinjection and lasted for 4 weeks. We observed a correlation of this long-term effect with the intramuscular persistence of the AON. In regenerating myofibers higher efficiencies (up to 9%) could be obtained. Finally, using the optimized protocols in hDMD mice, we were able to induce the specific skipping of human DMD exons without affecting the endogenous mouse gene. These data highlight the high sequence specificity of this therapy and present the hDMD mouse as a unique model to optimize human-specific exon skipping in vivo.

Cytotoxic immune response after retroviral-mediated hepatic gene transfer in rat does not preclude expression from adeno-associated virus 1 transduced muscles

Intravenous delivery of nls-lacZ retroviral vectors to the regenerating liver triggers a cytotoxic immune response directed against transduced hepatocytes. We sought to determine whether prior immunization with retroviral vectors impacted on adeno-associated virus (AAV)-mediated muscular expression of the same transgene. The first group of rats first received nls-lacZ retroviral vectors intravenously after a partial hepatectomy. Thirty days later they received AAV vectors intramuscularly in both legs. In the second group, animals received the same vectors in the opposite sequence (i.e., AAV first and retroviruses 20 days later). In the first group, immune response occurred after retrovirus delivery with appearance of anti-beta-galactosidase antibodies and elimination of transduced hepatocytes. However, the immune response did not prevent sustained (9-month) beta-galactosidase expression in AAV-injected muscles. In the second group, AAV injections did not induce immune response and resulted in beta-galactosidase expression in myofibers. In this group, subsequent delivery of retroviral vectors triggered appearance of immune response and elimination of transduced hepatocytes. However, the immune response did not modify beta-galactosidase expression in AAV-transduced myofibers for up to 9 months. These results demonstrate a differential susceptibility between retrovirally transduced liver and AAV-transduced muscles to immune response against the transgene product.

Non-viral gene delivery in skeletal muscle: a protein factory

Ever since the publication of the first reports in 1990 using skeletal muscle as a direct target for expressing foreign transgenes, an avalanche of papers has identified a variety of proteins that can be synthesized and correctly processed by skeletal muscle. The impetus to the development of such applications is not only amelioration of muscle diseases, but also a range of therapeutic applications, from immunization to delivery of therapeutic proteins, such as clotting factors and hormones. Although the most efficient way of introducing transgenes into muscle fibres has been by a variety of recombinant viral vectors, there are potential benefits in the use of non-viral vectors. In this review we assess the recent advances in construction and delivery of naked plasmid DNA to skeletal muscle and highlight the options available for further improvements to raise efficiency to therapeutic levels.

A versatile and scalable two-step ion-exchange chromatography process for the purification of recombinant adeno-associated virus serotypes-2 and -5

Here we describe the development of a two-step chromatography process based on the use of ion-exchange resins for the purification of recombinant adeno-associated virus (rAAV) serotypes-2 and-5. In vitro and in vivo results demonstrate that this method, which does not require any prepurification step of the cell lysate, can be applied to obtain highly pure rAAV2 and rAAV5 stocks. As such,this procedure can be easily transferred in vector cores and also scaled up, allowing the direct comparison of these two, and potentially other, AAV serotypes in large animal models.

A nonionic amphiphile agent promotes gene delivery in vivo to skeletal and cardiac muscles

Direct injection of naked DNA into skeletal or cardiac muscle induces detectable gene expression. Although this provides a practical system for transgene expression, the reported efficacy is too low to confer a therapeutic benefit. By following a rational strategy based on the supramolecular structures adopted by active complexes, we have discovered a novel nonionic amphiphile synthetic agent [poly(ethyleneoxide)(13)-poly(propyleneoxide)(30)-poly(ethyleneoxide)(13) block copolymer; PE6400] that enables gene expression in up to 35% of muscle fibers from mouse tibial cranial muscle. PE6400 abolishes the ceiling effect on transgene expression of increasing amounts of naked DNA and permits long-term expression of the beta-galactosidase reporter gene in immunologically tolerant transgenic rats. This improvement in gene expression over naked DNA was observed irrespective of the reporter gene, ranging from 0.7 to 3.4 kb, and of the animal model used. In skeletal muscle, the PE6400 formulation led to a level of transfection efficiency similar to that obtained by electrotransfer. PE6400 also promotes high transgene expression in cardiac muscle. In contrast, PE6400-DNA formulations were inefficient in vitro in established cell lines and in isolated cardiomyocytes. When microinjected into the cell cytoplasm, PE6400 promotes DNA trafficking into the nucleus and induces gene expression. PE6400 provides a simple gene delivery system for skeletal and myocardial gene transfer. We propose that the PE6400 formulation could serve for the treatment of diseases primarily affecting muscle or for the expression of therapeutic proteins for local or systemic benefit.

Recombinant adeno-associated virus type 2 mediates highly efficient gene transfer in regenerating rat skeletal muscle

The recent identification of genes responsible for several muscle diseases, particularly inherited myopathies, has made gene transfer to pathologic muscle tissue an attractive research field. As early pathologic changes in myopathic muscle involve repeated necrosis-regeneration cycles, leading to the coexistence of myofibers at different stages of maturity, a delivery system for efficient, durable gene therapy of inherited muscle diseases should allow gene transfer into myofibers at any stage of maturity. Experiments with rat skeletal muscles showed that recombinant adeno-associated virus (rAAV) type 2 can be highly efficient and even improve gene transfer in regenerating as compared with mature muscle, provided that vector injection is performed during the myotube growth period of the regenerative process. At this early period of muscle regeneration, young regenerating myotubes strongly express heparan sulfate proteoglycan AAV type 2 receptor. Improvement was associated with a greater number of transduced myofibers in muscle samples and an increase in viral genomic copies in transduced muscle. No significant deleterious effects on muscle phenotype or any evident alterations in the regenerative process were observed in transduced muscles. Unlike other available viral vectors, whose transduction efficiencies are highly maturation-dependent, rAAV type 2-based vectors provide efficient in vivo gene transfer in myofibers at various stages of maturity, making AAV a promising delivery system for pathological muscle tissue.

Tetracycline-inducible interleukin-10 gene transfer mediated by an adeno-associated virus: application to experimental arthritis

The adeno-associated viruses (AAV) offer new perspectives for cytokine gene transfer in rheumatoid arthritis (RA) because they are nonpathogenic and allow long-term transgene expression in vivo. Moreover, the use of a tetracycline-inducible promoter allows regulation of therapeutic gene expression. This study assessed the potential long-term gene regulation of a recombinant AAV vector expressing viral interleukin-10 (vIL-10) in human rheumatoid synovium and the therapeutic efficiency in a mouse model of RA. We constructed a recombinant AAV vector in which the transcription of vIL-10 cDNA is controlled by the TetON system. Transduction of human primary RA synovial cells with AAV-tetON-vIL10 conferred in vitro controlled vIL-10 expression. After intramuscular injection, both incidence and severity of collagen-induced arthritis were significantly reduced at macroscopic, radiological, and histological levels in the group of DBA1 mice treated with AAV-TetON-vIL10 vector plus doxycycline after immunization and boosting compared to control groups. When coinjecting two separate AAV vectors, one encoding the inducible vIL-10 and the other the transcriptional activator, a 10 times excess of the transactivator vector dose allowed efficient control of vIL-10 secretion by doxycycline administration or withdrawal, over an 8-week period. Our results supported, for the first time, the utility of AAV-tetON-vIL10 as a therapeutic tool for gene therapy in RA.

Nonviral approaches satisfying various requirements for effective in vivo gene therapy

Development of an efficient method of gene introduction to target cells is the key issue in treating genetic and acquired diseases by in vivo gene therapy. Although various nonviral approaches have been developed, any method needs to be optimized in terms of the target disease and transgene product. The most important information required is (i) target cell-specificity of gene transfer, (ii) efficiency, (iii) duration of transgene expression, and (iv) the number of transfected cells following in vivo application of a vector. These characteristics are determined by the properties of the vector used, as well as the route of its administration, biodistribution, interaction with biological components and the nature of the target cells. Cell-specific gene transfer can be achieved by controlling the tissue disposition of plasmid DNA (pDNA), although the interaction of the pDNA complex with biological components might limit the specificity. Various approaches have been reported to increase the efficiency of transgene expression, from cationic lipids/polymers to physical stimuli, but some of those are ineffective under in vivo conditions. The duration of transgene expression is a complex function involving variables including the cell type, transfection method, and plasmid construct. Immune response often reduces the level and duration of transgene expression. In addition, the number of transfected cells is important, especially in cases in which the therapeutic protein localizes within the target cells. Successful clinical application of nonviral gene delivery methods rely on the development of such methods optimized for a particular target disease.

Hyaluronidase increases electrogene transfer efficiency in skeletal muscle

Electrogene transfer (EGT) of plasmid DNA into skeletal muscle is a promising strategy for the treatment of muscle disorders and for the systemic secretion of therapeutic proteins. We report here that preinjecting hyaluronidase (HYAse) significantly increases the gene transfer efficiency of muscle EGT. Three constructs encoding mouse erythropoietin (pCMV/mEPO), secreted alkaline phosphatase (pCMV/SeAP), and luciferase (pGGluc) were electroinjected intramuscularly in BALB/c mice and rabbits with and without HYAse pretreatment. Preinjection 1 or 4 hr before EGT increased EPO gene expression by about 5-fold in mice and maintained higher gene expression than plasmid EGT alone. A similar increment in gene expression was observed on pretreatment with HYAse and electroinjection of pCMV/mEPO into rabbit tibialis muscle. The increment of gene expression in rabbits reached 17-fold on injection of plasmid pCMV/SeAP and 24-fold with plasmid pGGluc. Injection of a plasmid encoding beta-galactosidase (pCMV/beta gal/NLS) and subsequent staining with 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside indicated that HYAse increased the tissue area involved in gene expression. No irreversible tissue damage was observed on histological analysis of treated muscles. HYAse is used in a variety of clinical applications, and thus the combination of HYAse pretreatment and muscle EGT may constitute an efficient gene transfer method to achieve therapeutic levels of gene expression.

Immediate and long-term safety of recombinant adeno-associated virus injection into the nonhuman primate muscle

Previous studies on distribution and toxicity of viral vectors administered in monkeys indicated that the nonhuman primate model has a reasonable predictive value for clinical applications. In this study, eight macaques were injected intramuscularly with recombinant adeno-associated virus (rAAV) at doses similar to those administered to hemophilia B patients, and followed to analyze the dissemination and shedding in biological samples and long-term persistence in distant organs. Following rAAV delivery, we found vector genome in various biological fluids for up to 6 days and infectious particles exclusively in the serum during the first 48-72 hours. rAAV sequences were detected in peripheral blood mononuclear cells (PBMC) for up to 10 months. At necropsy, 8 to 18 months after rAAV delivery, rAAV sequences were found in lymph nodes and livers but never in the gonads. Tissue examination, of liver in particular, showed no abnormalities. We concluded that during our experimental time frame, rAAV-mediated gene transfer into skeletal muscle of macaques seemed to be safe with respect to the recipient and the environment. However, it was associated with a transient viremia and the persistence of rAAV sequences in PBMC, lymph nodes, and liver, the long-term consequences of which remain unknown.

Molecular pathophysiology and targeted therapeutics for muscular dystrophy

Experimental therapeutics of the muscular dystrophies has made impressive advances on several fronts. Adeno-associated virus has emerged as the clear 'vector of choice' for muscle gene delivery, with successful functional rescue of dystrophic muscle in rodent models. Correction of the dystrophin gene mutation in a dog model has been reported, and several reports of progress on myogenic stem cell characterization are resurrecting cell transplantation as a possible therapeutic approach. The downstream consequences of dystrophin deficiency are being defined quickly using microarray experiments, and drugs targeting specific biochemical pathways are being tested rapidly in animal models. Such targeted drug discoveries, which are discussed in this article, have begun to be implemented in human clinical trials.

Optimisation of electrotransfer of plasmid into skeletal muscle by pretreatment with hyaluronidase -- increased expression with reduced muscle damage

The efficiency of plasmid gene transfer to skeletal muscle can be significantly improved by the application of an electrical field to the muscle following injection of plasmid DNA. However, this electrotransfer is associated with significant muscle damage which may result in substantial loss of transfected muscle fibres. Reduction of the voltage used in the technique can result in a decrease in muscle damage, with a concomitant reduction in expression, but without a significant decrease in the number of transfected fibres. Pre-treatment of the muscle with a solution of bovine hyaluronidase greatly increases the efficiency of plasmid gene transfer when used in conjunction with electrotransfer, but not when used alone. This combination treatment results in greatly enhanced levels of transfected muscle fibres without the increases in muscle damage associated with the electrotransfer process.

Adeno-associated virus and lentivirus vectors mediate efficient and sustained transduction of cultured mouse and human dorsal root ganglia sensory neurons

Peripheral nervous system (PNS) sensory neurons are directly involved in the pathophysiology of numerous inherited and acquired neurological conditions. Therefore, efficient and stable gene delivery to these postmitotic cells has significant therapeutic potential. Among contemporary vector systems capable of neuronal transduction, only those based on herpes simplex virus have been extensively evaluated in PNS neurons. We therefore investigated the transduction performance of recombinant adeno-associated virus type 2 (AAV) and VSV-G-pseudotyped lentivirus vectors derived from human immunodeficiency virus (HIV-1) in newborn mouse and fetal human dorsal root ganglia (DRG) sensory neurons. In dissociated mouse DRG cultures both vectors achieved efficient transduction of sensory neurons at low multiplicities of infection (MOIs) and sustained transgene expression within a 28-day culture period. Interestingly, the lentivirus vector selectively transduced neurons in murine cultures, in contrast to human cultures, in which Schwann and fibroblast-like cells were also transduced. Recombinant AAV transduced all three cell types in both mouse and human cultures. After direct microinjection of murine DRG explants, maximal transduction efficiencies of 20 and 200 transducing units per neuronal transductant were achieved with AAV and lentivirus vectors, respectively. Most importantly, both vectors achieved efficient and sustained transduction of human sensory neurons in dissociated cultures, thereby directly demonstrating the exciting potential of these vectors for gene therapy applications in the PNS.