Electrotransfer of naked DNA in the skeletal muscles of animal models of muscular dystrophies

The DUX4-HIF1α Axis in Murine and Human Muscle Cells: A Link More Complex Than Expected

FacioScapuloHumeral muscular Dystrophy (FSHD) is one of the most prevalent inherited muscle disorders and is linked to the inappropriate expression of the DUX4 transcription factor in skeletal muscles. The deregulated molecular network causing FSHD muscle dysfunction and pathology is not well understood. It has been shown that the hypoxia response factor HIF1α is critically disturbed in FSHD and has a major role in DUX4-induced cell death. In this study, we further explored the relationship between DUX4 and HIF1α. We found that the DUX4 and HIF1α link differed according to the stage of myogenic differentiation and was conserved between human and mouse muscle. Furthermore, we found that HIF1α knockdown in a mouse model of DUX4 local expression exacerbated DUX4-mediated muscle fibrosis. Our data indicate that the suggested role of HIF1α in DUX4 toxicity is complex and that targeting HIF1α might be challenging in the context of FSHD therapeutic approaches.

The use of electroporation to deliver DNA-based vaccines

INTRODUCTION

Nucleic acids represent a promising platform for creating vaccines. One disadvantage of this approach is its relatively low immunogenicity. Electroporation (EP) is an effective way to increase the DNA vaccines immunogenicity. However, due to the different configurations of devices used for EP, EP protocols optimization is required not only to enhance immunogenicity, but also to ensure greater safety and tolerability of the EP procedure.

AREA COVERED

An data analysis for recent years on the DNA vaccines delivery against viral and parasitic infections using EP was carried out. The study of various EP physical characteristics, such as frequency, pulse duration, pulse interval, should be considered along with the immunogenic construct design and the site of delivery of the vaccine, through the study of the immunogenic and protective characteristics of the latter.

EXPERT OPINION

Future research should focus on regulating the humoral and cellular response required for protection against infectious agents by modifying the EP protocol. Significant efforts will be directed to establishing the possibility of redirecting the immune response toward the Th1 or Th2 response by changing the EP physical parameters. It will allow for an individual selective approach during EP, depending on the pathogen type of an infectious disease.

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.

Contactless delivery of plasmid encoding EGFP in vivo by high-intensity pulsed electromagnetic field

High-Intensity Pulsed Electromagnetic Fields (HI-PEMF) treatment is an emerging noninvasive and contactless alternative to conventional electroporation, since the electric field inside the tissue is induced remotely by external pulsed magnetic field. Recently, HI-PEMF was applied for delivering siRNA molecules to silence enhanced green fluorescent protein (EGFP) in tumors in vivo. Still, delivered siRNA molecules were 21 base pairs long, which is 200-times smaller compared to nucleic acids such as plasmid DNA (pDNA) that are delivered in gene therapies to various targets to generate therapeutic effect. In our study, we demonstrate the use HI-PEMF treatment as a feasible noninvasive approach to achieve in vivo transfection by enabling the transport of larger molecules such as pDNA encoding EGFP into muscle and skin. We obtained a long-term expression of EGFP in the muscle and skin after HI-PEMF, in some mice even up to 230 days and up to 190 days, respectively. Histological analysis showed significantly less infiltration of inflammatory mononuclear cells in muscle tissue after the delivery of pEGFP using HI-PEMF compared to conventional gene electrotransfer. Furthermore, the antitumor effectiveness using HI-PEMF for electrotransfer of therapeutic plasmid, i.e., silencing MCAM was demonstrated. In conclusion, feasibility of HI-PEMF was demonstrated for transfection of different tissues (muscle, skin, tumor) and could have great potential in gene therapy and in DNA vaccination.

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.

Current understanding and treatment of cardiac and skeletal muscle pathology in laminin-α2 chain-deficient congenital muscular dystrophy

Congenital muscular dystrophy (CMD) is a class of severe early-onset muscular dystrophies affecting skeletal/cardiac muscles as well as the central nervous system (CNS). Laminin-α2 chain-deficient congenital muscular dystrophy (LAMA2 MD), also known as merosin-deficient congenital muscular dystrophy type 1A (MDC1A), is an autosomal recessive CMD characterized by severe muscle weakness and degeneration apparent at birth or in the first 6 months of life. LAMA2 MD is the most common congenital muscular dystrophy, affecting approximately 4 in 500,000 children. The most common cause of death in early-onset LAMA2 MD is respiratory tract infection, with 30% of them dying within the first decade of life. LAMA2 MD is caused by loss-of-function mutations in the LAMA2 gene encoding for the laminin-α2 chain, one of the subunits of laminin-211. Laminin-211 is an extracellular matrix protein that functions to stabilize the basement membrane and muscle fibers during contraction. Since laminin-α2 is expressed in many tissue types including skeletal muscle, cardiac muscle, Schwann cells, and trophoblasts, patients with LAMA2 MD experience a multi-systemic clinical presentation depending on the extent of laminin-α2 chain deficiency. Cardiac manifestations are typically associated with a complete absence of laminin-α2; however, recent case reports highlight cardiac involvement in partial laminin-α2 chain deficiency. Laminin-211 is also expressed in the brain, and many patients have abnormalities on brain imaging; however, mental retardation and/or seizures are rarely seen. Currently, there is no cure for LAMA2 MD, but various therapies are being investigated in an effort to lessen the severity of LAMA2 MD. For example, antisense oligonucleotide-mediated exon skipping and CRISPR-Cas9 genome editing have efficiently restored the laminin-α2 chain in mouse models in vivo. This review consolidates information on the clinical presentation, genetic basis, pathology, and current treatment approaches for LAMA2 MD.

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.

The effects of pprI gene of Deinococcus radiodurans R1 on acute radiation injury of mice exposed to 60Co γ-ray radiation

The role of the pprI gene from Deinococcus radiodurans R1 in therapy of acute radiation injury of a mammalian host was investigated. We injected a plasmid containing the pprI gene into the muscle of mice exposed to total 6Gy of ⁶⁰Co γ-ray radiation. After injection, we used in vivo gene electroporation technology to transfer the pprI gene into the cell. We found the PprI protein was expressed significantly at 1 d after irradiation, but there was no expression of pprI gene 7 d post-irradiation. The expression of pprI gene evidently decreased the death rate of mice exposed to lethal dose radiation, significantly relieved effects on blood cells in the acute stage, shortened the persistence time of the decrease of lymphocytes, and decreased the apoptotic rates of spleen cells, thymocytes and bone marrow cells. The expression of Rad51 protein in the lungs, livers, and kidneys was significantly higher in the mice treated with the pprI plasmid after irradiation. However, there were no obvious differences for Rad52 protein expression. We conclude that the prokaryotic pprI gene of D. radiodurans R1 first was expressed in mammalian cells. The expressed prokaryotic PprI protein has distinct effects of the prevention and treatment on acute radiation injury of mammal. The effects of radio-resistance may relate to expression of Rad51 protein which is homologous with RecA from D. radiodurans.

A synthetic erectile optogenetic stimulator enabling blue-light-inducible penile erection

Precise spatiotemporal control of physiological processes by optogenetic devices inspired by synthetic biology may provide novel treatment opportunities for gene- and cell-based therapies. An erectile optogenetic stimulator (EROS), a synthetic designer guanylate cyclase producing a blue-light-inducible surge of the second messenger cyclic guanosine monophosphate (cGMP) in mammalian cells, enabled blue-light-dependent penile erection associated with occasional ejaculation after illumination of EROS-transfected corpus cavernosum in male rats. Photostimulated short-circuiting of complex psychological, neural, vascular, and endocrine factors to stimulate penile erection in the absence of sexual arousal may foster novel advances in the treatment of erectile dysfunction.

Cell-matrix interactions in muscle disease

The extracellular matrix (ECM) provides a solid scaffold and signals to cells through ECM receptors. The cell-matrix interactions are crucial for normal biological processes and when disrupted they may lead to pathological processes. In particular, the biological importance of ECM-cell membrane-cytoskeleton interactions in skeletal muscle is accentuated by the number of inherited muscle diseases caused by mutations in proteins conferring these interactions. In this review we introduce laminins, collagens, dystroglycan, integrins, dystrophin and sarcoglycans. Mutations in corresponding genes cause various forms of muscular dystrophy. The muscle disorders are presented as well as advances toward the development of treatment.

Construction of porcine growth hormone eukaryotic expression vector and its transfection mediated by cationic liposome in mice

The present study was designed to construct the eukaryotic expression vector for pGH mature peptide (mpGH) and to investigate its transfection mediated by cationic liposome (CLs) in COS-7 cells and mice. The cDNA of mpGH ORF was successfully cloned by reverse transcription-PCR (RT-PCR) using the adult pig pituitary gland RNA. The recombinant eukaryotic expression vector, VmpGH, was constructed by ligating the cDNA fragment to the vector VR1020. The successful construction was confirmed by restriction enzyme digestion, and the expression of mpGH was confirmed by RT-PCR, immunofluorescence analyses (IFA), and ELISA in COS-7 cells. The VmpGH and VR1020 plasmids were entrapped with CLs, and four experimental groups of male Kunming mice were administrated with VmpGH / lipoplex or naked VmpGH plasmids at two dosages (0.5 and 1.0 mg/kg), while the mice injected with VR1020-lipoplex at the dosage of 0.5 mg/kg body weight (BW) were used as control. The BWs of the mice administrated with VmpGH-lipoplex at both dosages were significantly higher than not only those of the control (P < 0.01) but also those of mice injected with naked plasmids (P < 0.01), from 30 to 60 days post-transfection. The transcription of VmpGH was detected by RT-PCR in six tissues, including the liver, kidney, spleen, heart, muscle, and blood, of the mice injected with VmpGH-lipoplex, but not in the same tissues of control mice. Furthermore, the mice injected with VmpGH-lipoplex showed higher plasma GH contents than the control mice (P < 0.05), although their IgG contents did not show much difference. Our study demonstrates that the VmpGH plasmids' transfection mediated by CLs can significantly promote the growth of mice, which may be used to improve the livestock production.

Skeletal muscle regeneration in mice is stimulated by local overexpression of V1a-vasopressin receptor

Skeletal muscle has a remarkable capacity to regenerate after mechanical or pathological injury. We show that the V1a receptor (V1aR) for vasopressin, a potent myogenic-promoting factor that stimulates differentiation and hypertrophy in vitro, is expressed in mouse skeletal muscle and modulated during regeneration after experimental injury. We used gene delivery by electroporation to overexpress the myc-tagged vasopressin V1aR in specific muscles, thus sensitizing them to circulating vasopressin. The correct localization on the surface of the fibers of the recombinant product was demonstrated by confocal immunofluorescence directed against the myc tag. V1aR overexpression dramatically enhanced regeneration. When compared with mock-transfected controls, V1aR overexpressing muscles exhibited significantly accelerated activation of satellite cells and increased expression of differentiation markers. Downstream of V1aR activation, calcineurin was strongly up-regulated and stimulated the expression of IL-4, a potent mediator of myogenic cell fusion. The central role of calcineurin in mediating V1aR-dependent myogenesis was also demonstrated by using its specific inhibitor, cyclosporine A. This study identifies skeletal muscle as a physiological target of hormones of the vasopressin family and reveals a novel in vivo role for vasopressin-dependent pathways. These findings unveil several steps, along a complex signaling pathway, that may be exploited as potential targets for the therapy of diseases characterized by altered muscle homeostasis and regeneration.

Current status of pharmaceutical and genetic therapeutic approaches to treat DMD

Duchenne muscular dystrophy (DMD) is a genetic disease affecting about one in every 3,500 boys. This X-linked pathology is due to the absence of dystrophin in muscle fibers. This lack of dystrophin leads to the progressive muscle degeneration that is often responsible for the death of the DMD patients during the third decade of their life. There are currently no curative treatments for this disease but different therapeutic approaches are being studied. Gene therapy consists of introducing a transgene coding for full-length or a truncated version of dystrophin complementary DNA (cDNA) in muscles, whereas pharmaceutical therapy includes the use of chemical/biochemical substances to restore dystrophin expression or alleviate the DMD phenotype. Over the past years, many potential drugs were explored. This led to several clinical trials for gentamicin and ataluren (PTC124) allowing stop codon read-through. An alternative approach is to induce the expression of an internally deleted, partially functional dystrophin protein through exon skipping. The vectors and the methods used in gene therapy have been continually improving in order to obtain greater encapsidation capacity and better transduction efficiency. The most promising experimental approaches using pharmaceutical and gene therapies are reviewed in this article.

Electrotransfer of the full-length dog dystrophin into mouse and dystrophic dog muscles

Duchenne muscular dystrophy (DMD) is an X-linked genetic disease characterized by the absence of dystrophin (427 kDa). An approach to eventually restore this protein in patients with DMD is to introduce into their muscles a plasmid encoding dystrophin cDNA. Because the phenotype of the dystrophic dog is closer to the human phenotype than is the mdx mouse phenotype, we have studied the electrotransfer of a plasmid carrying the full-length dog dystrophin (FLDYS(dog)) in dystrophic dog muscle. To achieve this nonviral delivery, the FLDYS(dog) cDNA was cloned in two plasmids containing either a cytomegalovirus or a muscle creatine kinase promoter. In both cases, our results showed that the electrotransfer of these large plasmids (∼17 kb) into mouse muscle allowed FLDYS(dog) expression in the treated muscle. The electrotransfer of pCMV.FLDYS(dog) in a dystrophic dog muscle also led to the expression of dystrophin. In conclusion, introduction of the full-length dog dystrophin cDNA by electrotransfer into dystrophic dog muscle is a potential approach to restore dystrophin in patients with DMD. However, the electrotransfer procedure should be improved before applying it to humans.

Gene therapy for muscular dystrophies: progress and challenges

Muscular dystrophies are groups of inherited progressive diseases of the muscle caused by mutations of diverse genes related to normal muscle function. Although there is no current effective treatment for these devastating diseases, various molecular strategies have been developed to restore the expressions of the associated defective proteins. In preclinical animal models, both viral and nonviral vectors have been shown to deliver recombinant versions of defective genes. Antisense oligonucleotides have been shown to modify the splicing mechanism of mesenger ribonucleic acid to produce an internally deleted but partially functional dystrophin in an experimental model of Duchenne muscular dystrophy. In addition, chemicals can induce readthrough of the premature stop codon in nonsense mutations of the dystrophin gene. On the basis of these preclinical data, several experimental clinical trials are underway that aim to demonstrate efficacy in treating these devastating diseases.

Electroporation of corrective nucleic acids (CNA) in vivo to promote gene correction in dystrophic muscle

Non-viral gene transfer into skeletal muscle in vivo is enhanced by electroporation (EP) to efficiencies far beyond any other (non-EP) method reported to date. Electroporation consistently delivers high levels of transgene to muscle and has been used extensively for the delivery of therapeutic transgenes to dystrophic mouse muscle such as the mdx mouse model of human Duchenne muscular dystrophy (DMD). Since the earliest applications, electroporation has consistently and reproducibly achieved highly efficient DNA delivery to a high proportion (greater than 70%) of fibres in treated muscles. This manuscript describes a methodology for introduction of corrective nucleic acids (CNAs) for the purpose of correcting the dystrophin gene (DMD ( mdx )) mutation responsible for muscular dystrophy in the mdx mouse model of human DMD by targeted corrective gene conversion (TCGC).

Systemic IL-12 gene therapy for treating malignancy via intramuscular electroporation

Interleukin 12 (IL-12) is effective in treating systemic microscopic malignancies by inducing T helper 1 (T(H)1) response, inhibiting angiogenesis, and triggering secondary cytokine production. Unfortunately, daily systemic administration of an acute dose of IL-12 protein is very costly and severely toxic. Here, a simple, economic, and less toxic approach, intramuscular administration of IL-12 gene, is provided for treating tumors in three tumor models. The results indicate that intramuscular administration of IL-12 encoding plasmid DNA via electroporation is a promising technology for treating systemic residual malignancies (less than 3-5 mm in diameter), as illustrated by the inhibition of tumor growth and lung metastases as well as the extension of survival rate. This approach is not effective in treating tumors larger than 3-5 mm in diameter.

Gene delivery to dystrophic muscle

Electroporation is a powerful method for gene delivery to dystrophic muscle in the mdx mouse model of Duchenne muscular dystrophy. Successful transfer of reporter and therapeutic plasmids and antisense oligonucleotides has been demonstrated. However, the efficiency falls with increasing plasmid size. Although it is unlikely that the electrotransfer approach will be useful clinically, it is an important experimental tool, particularly in testing potential immune responses to gene transfer in the absence of vector proteins.

Long term expression of bicistronic vector driven by the FGF-1 IRES in mouse muscle

Background

Electrotransfer of plasmid DNA into skeletal muscle is a promising strategy for the delivery of therapeutic molecules targeting various muscular diseases, cancer and lower-limb ischemia. Internal Ribosome Entry Sites (IRESs) allow co-expression of proteins of interest from a single transcriptional unit. IRESs are RNA elements that have been found in viral RNAs as well as a variety of cellular mRNAs with long 5' untranslated regions. While the encephalomyocarditis virus (EMCV) IRES is often used in expression vectors, we have shown that the FGF-1 IRES is equally active to drive short term transgene expression in mouse muscle. To compare the ability of the FGF-1 IRES to drive long term expression against the EMCV and FGF-2 IRESs, we performed analyses of expression kinetics using bicistronic vectors that express the bioluminescent renilla and firefly luciferase reporter genes. Long term expression of bicistronic vectors was also compared to that of monocistronic vectors. Bioluminescence was quantified ex vivo using a luminometer and in vivo using a CCD camera that monitors luminescence within live animals.

Results

Our data demonstrate that the efficiency of the FGF-1 IRES is comparable to that of the EMCV IRES for long term expression of bicistronic transgenes in mouse muscle, whereas the FGF-2 IRES has a very poor activity. Interestingly, we show that despite the global decrease of vector expression over time, the ratio of firefly to renilla luciferase remains stable with bicistronic vectors containing the FGF-1 or FGF-2 IRES and is slightly affected with the EMCV IRES, whereas it is clearly unstable for mixed monocistronic vectors. In addition, long term expression more drastically decreases with monocistronic vectors, and is different for single or mixed vector injection.

Conclusion

These data validate the use of bicistronic vectors rather than mixed monocistronic vectors for long term expression, and support the use of the FGF-1 IRES. The use of a cellular IRES over one of viral origin is of particular interest in the goal of eliminating viral sequences from transgenic vectors. In addition, the FGF-1 IRES, compared to the EMCV IRES, has a more stable activity, is shorter in length and more flexible in terms of downstream cloning of second cistrons. Finally, the FGF-1 IRES is very attractive to develop multicistronic expression cassettes for gene transfer in mouse muscle.

Enhancement of antibody and cellular immune responses to malaria DNA vaccines by in vivo electroporation

We evaluated the effectiveness of in vivo electroporation (EP) for the enhancement of immune responses induced by DNA plasmids encoding the pre-erythrocytic Plasmodium yoelii antigens PyCSP and PyHEP17 administered intramuscularly and intradermally to mice. EP resulted in a 16- and 2-fold enhancement of antibody responses to PyCSP and PyHEP17, respectively. Immunization with 5 microg of DNA via EP was equivalent to 50 microg of DNA via conventional needle, thus reducing by 10-fold the required dose to produce a given effect. Moreover, IFN-gamma responses were increased by approximately 2-fold. Data demonstrate the potential of EP to enhance immune responses to DNA vaccines against infectious agents.

Ca(2+) sparks operated by membrane depolarization require isoform 3 ryanodine receptor channels in skeletal muscle

Stimuli are translated to intracellular calcium signals via opening of inositol trisphosphate receptor and ryanodine receptor (RyR) channels of the sarcoplasmic reticulum or endoplasmic reticulum. In cardiac and skeletal muscle of amphibians the stimulus is depolarization of the transverse tubular membrane, transduced by voltage sensors at tubular-sarcoplasmic reticulum junctions, and the unit signal is the Ca(2+) spark, caused by concerted opening of multiple RyR channels. Mammalian muscles instead lose postnatally the ability to produce sparks, and they also lose RyR3, an isoform abundant in spark-producing skeletal muscles. What does it take for cells to respond to membrane depolarization with Ca(2+) sparks? To answer this question we made skeletal muscles of adult mice expressing exogenous RyR3, demonstrated as immunoreactivity at triad junctions. These muscles showed abundant sparks upon depolarization. Sparks produced thusly were found to amplify the response to depolarization in a manner characteristic of Ca(2+)-induced Ca(2+) release processes. The amplification was particularly effective in responses to brief depolarizations, as in action potentials. We also induced expression of exogenous RyR1 or yellow fluorescent protein-tagged RyR1 in muscles of adult mice. In these, tag fluorescence was present at triad junctions. RyR1-transfected muscle lacked voltage-operated sparks. Therefore, the voltage-operated sparks phenotype is specific to the RyR3 isoform. Because RyR3 does not contact voltage sensors, their opening was probably activated by Ca(2+), secondarily to Ca(2+) release through junctional RyR1. Physiologically voltage-controlled Ca(2+) sparks thus require a voltage sensor, a master junctional RyR1 channel that provides trigger Ca(2+), and a slave parajunctional RyR3 cohort.

Electroporation for targeted gene transfer

The utilisation of nonviral gene delivery methods has been increasing steadily, however, a drawback has been the relative low efficiency of gene transfer with naked DNA compared with viral delivery methods. In vivo electroporation, which has previously been used clinically to deliver chemotherapeutic agents, also enhances the delivery of plasmid DNA and has been used to deliver plasmids to several tissue types, particularly muscle and tumour. Recently, a large number of preclinical studies for a variety of therapeutic modalities have demonstrated the potential of electrically mediated gene transfer. Although clinical trials using gene transfer with in vivo electroporation have not as yet been realised, the tremendous growth of this technology suggests that the first trials will soon be initiated.

Therapeutic restoration of dystrophin expression in Duchenne muscular dystrophy

It is 20 years since the discovery of the genetic defect causing Duchenne muscular dystrophy (DMD). This X-linked progressive and fatal myopathy is due to the absence of a functional version of a critical sub-sarcolemmal protein called dystrophin that appears to act both as a structural and as a signalling molecule in the muscle fibre. A number of molecular approaches have been developed to restore the expression of dystrophin in DMD patients. Pre-clinical experiments have demonstrated the potential of delivery of recombinant versions of the DMD gene using viral or non-viral vectors and importantly several of these systems are compatible with vascular delivery, an essential feature as all muscles are affected in this condition. Other studies have shown that antisense oligonucleotides can modify the splicing of the primary transcript to provide an internally truncated but still functional protein. Alternatively, in approximately 10-20% of cases it is possible to chemically persuade the translational machinery to read-through a pre-mature stop codon. The pre-clinical results of the last 4 years have encouraged the development of clinical trials for all of the above.

Identifying putative contraceptive targets by dissecting signal transduction networks in the epididymis using an in vivo electroporation (electrotransfer) approach

Our studies have focused on understanding how the initial segment is regulated, in particular, by testicular luminal fluid factor(s). Our working hypothesis is that testicular luminal fluid growth factors, e.g. FGFs, regulate initial segment function via activation of signal transduction pathways and PEA3 family transcription factors. These, in turn, regulate downstream genes that are important for providing an appropriate fluid milieu for the protection and survival of sperm and the initial segment. To test this hypothesis and to look for potential contraceptive targets, we used an in vivo electroporation technique to introduce dominant-negative plasmids of FGF Receptor 1 and ERM into the initial segment of the rat epididymis. The levels of several putative downstream genes were estimated using quantitative-PCR (q-PCR). Data suggests that initial segment genes are regulated by 5alpha-reductase-dependent and -independent pathways and that multiple growth factor pathways are activated to coordinate the expression of these genes.

IGF-I increases bone marrow contribution to adult skeletal muscle and enhances the fusion of myelomonocytic precursors

Muscle damage has been shown to enhance the contribution of bone marrow-derived cells (BMDCs) to regenerating skeletal muscle. One responsible cell type involved in this process is a hematopoietic stem cell derivative, the myelomonocytic precursor (MMC). However, the molecular components responsible for this injury-related response remain largely unknown. In this paper, we show that delivery of insulin-like growth factor I (IGF-I) to adult skeletal muscle by three different methods-plasmid electroporation, injection of genetically engineered myoblasts, and recombinant protein injection-increases the integration of BMDCs up to fourfold. To investigate the underlying mechanism, we developed an in vitro fusion assay in which co-cultures of MMCs and myotubes were exposed to IGF-I. The number of fusion events was substantially augmented by IGF-I, independent of its effect on cell survival. These results provide novel evidence that a single factor, IGF-I, is sufficient to enhance the fusion of bone marrow derivatives with adult skeletal muscle.

Amphiphilic block copolymers promote gene delivery in vivo to pathological skeletal muscles

We reported that amphiphilic block copolymers hold promise as nonviral vectors for the delivery of plasmid DNA, ranging from 4.7 to 6.2 kb, to healthy muscle for the production of local or secreted proteins. To evaluate the efficiency of these vectors to deliver large plasmid DNA molecules to pathological muscles, plasmid DNAs of various lengths were complexed with Lutrol or poloxamine 304 and injected intramuscularly into dystrophic muscles. Lutrol-DNA and poloxamine 304-DNA complexes promoted gene transfer into muscles of the naturally occurring mouse model for DMD (mdx) in a dose- and plasmid DNA size-dependent manner. For small plasmid DNAs encoding reporter genes, this improvement over naked DNA was smaller in mdx than in the wild-type control strain. By contrast, Lutrol enabled us to deliver the large plasmid (16.1 kb) encoding the rod-deleted dystrophin in mdx mouse muscle, whereas the same amount of naked DNA did not lead to dystrophin expression, under the same experimental conditions. Lutrol-treated mdx mice showed the production of dystrophin in large numbers of muscle fibers. More importantly, we also found that expressing dystrophin with Lutrol led to restoration of the dystrophin-associated protein complex. Thus, we conclude that block copolymers constitute a novel class of vectors for the delivery of large plasmid DNA not only to healthy muscles but also to pathological muscle tissues.

In vivo NMR imaging evaluation of efficiency and toxicity of gene electrotransfer in rat muscle

In vivo gene electrotransfer (ET) is a simple method of gene delivery in various tissues relying on the injection of plasmid DNA followed by application of electric pulses. Noninvasive tools are needed to evaluate the ET efficiency and the resulting tissue damages. In this study, we performed ET of rat tibialis muscle after injection of either a plasmid coding for luciferase or a contrast agent (CA) detected by using magnetic resonance imaging (MRI). Plasmid expression and CA intracellular trapped quantity were compared throughout the electric field intensity range 0-300 V/cm. Although the CA trapped quantity reflects only the electropermeabilization step, both measurements were correlated. MRI measurements gave easy access to tridimensional visualization of the labelled zones where the CA has been injected and the applied electric field had a value allowing permeabilization. We also performed MRI measurements of the water transverse relaxation time T2 as an indicator of tissue modification, and tested whether another CA specific for necrosis could be used to detect muscle necrosis at high electric field intensity. In conclusion, MRI measurements may bring multiparametric information upon the efficiency and tissue toxicity of an ET protocol by using a simple and safe CA.

Highly Efficient Constant-Current Electroporation IncreasesIn VivoPlasmid Expression

Electroporation has been demonstrated as an effective technique for enhancing the delivery of plasmids coding for DNA vaccines and therapeutic proteins into skeletal muscle. Nevertheless, constant-voltage techniques do not take into account the resistance of the tissue and result in tissue damage, inflammation, and loss of plasmid expression. In the present study, we have used a software-driven constant-current electroporator to deliver plasmids to mice and small and large pigs. The voltage, amperage, and resistance of the tissue during pulses were recorded and analyzed. Optimal conditions of electroporation were identified in both species, and found to be highly dependent on the individual tissue resistance. Six- to 10-week-old pigs had higher muscle resistance compared to 1- to 2-year-old pigs, but both values were four to five times lower than the resistance of the mouse muscle. In mice, optimum amperage, pulse length, and lag time between plasmid injection and electroporation were identified to be 0.1 Amps, 20 msec and 0 sec. The electroporation pulse pattern among the electrodes also affected plasmid expression. These results indicate that age- and tissue-specific resistance, pulse pattern, and other variables associated with the electroporation need to be optimized for each separate species to achieve maximum plasmid expression.

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.

Kinetic of transgene expression after electrotransfer into skeletal muscle: Importance of promoter origin/strength

We determined over a 3-week period some of the factors that may influence the kinetic of gene expression following in vivo gene electrotransfer. Histochemical analysis of beta-galactosidase and biochemical analysis of luciferase expressions were used to determine reporter gene activity in the Tibialis anterior muscles of young Sprague-Dawley male rats. Transfection efficiency peaked 5 days after gene electrotransfer and then exponentially decreased to reach non-detectable levels at day 28. Reduction of muscle damage by decreasing the amount of DNA injected or the cumulated pulse duration did not improve the kinetic of gene expression. Electrotransfer of luciferase expression plasmids driven either by viral or mammalian promoters rather show that most of the decrease in transgene expression was related to promoter origin/strength. By regulating the amount of transgene expression, the promoter origin/strength could modulate the immune response triggered against the foreign protein and ultimately the kinetic of transgene expression.

Acute bidirectional manipulation of muscle glucose uptake by in vivo electrotransfer of constructs targeting glucose transporter genes

Analysis of conventional germ-line or tissue-specific gene manipulation in vivo is potentially confounded by developmental adaptation of animal physiology. We aimed to adapt the technique of in vivo electrotransfer (IVE) to alter local gene expression in skeletal muscle of rodents as a means of investigating the role of specific proteins in glucose metabolism in vivo. We utilized a square-wave electroporator to induce intracellular electrotransfer of DNA constructs injected into rat or mouse muscles and investigated the downstream effects. In initial studies, expression of green fluorescent protein reporter was induced in 53 +/- 10% of muscle fibers peaking at 7 days, and importantly, the electrotransfer procedure itself did not impact upon the expression of stress proteins or our ability to detect a reduction in 2-deoxyglucose tracer uptake by electroporated muscle of high-fat-fed rats during hyperinsulinemic-euglycemic clamp. To demonstrate functional effects of electrotransfer of constructs targeting glucose transporters, we administered vectors encoding GLUT-1 cDNA and GLUT-4 short hairpin RNAs (shRNAs) to rodent muscles. IVE of the GLUT-1 gene resulted in a 57% increase in GLUT-1 protein, accompanied by a proportionate increase in basal 2-deoxyglucose tracer uptake into muscles of starved rats. IVE of vectors expressing two shRNAs for GLUT-4 demonstrated to reduce specific protein expression and 2-deoxyglucose tracer uptake in 3T3-L1 adipocytes into mouse muscle caused a 51% reduction in GLUT-4 protein, associated with attenuated clearance of tracer to muscle after a glucose load. These results confirm that glucose transporter expression is largely rate limiting for glucose uptake in vivo and highlight the utility of IVE for the acute manipulation of muscle gene expression in the study of the role of specific proteins in glucose metabolism.

Intraarterial delivery of naked plasmid DNA expressing full-length mouse dystrophin in the mdx mouse model of duchenne muscular dystrophy

Our previous studies have demonstrated that the intraarterial delivery of naked plasmid DNA leads to high levels of foreign gene expression throughout the muscles of the targeted limb. Although the procedure was first developed in rats and then extended to nonhuman primates, the present study has successfully implemented the procedure in normal mice and the mdx mouse model for Duchenne muscular dystrophy. After intraarterial delivery of plasmid DNA expressing the normal, full-length mouse dystrophin from either the cytomegalovirus promoter or a muscle-specific human desmin gene control region, mdx mouse muscle stably expressed dystrophin in 1-5% of the myofibers of the injected hind limb for at least 6 months. This expression generated an antibody response but no apparent cellular response.

Electric pulse-mediated gene delivery to various animal tissues

Electroporation designates the use of electric pulses to transiently permeabilize the cell membrane. It has been shown that DNA can be transferred to cells through a combined effect of electric pulses causing (1) permeabilization of the cell membrane and (2) an electrophoretic effect on DNA, leading the polyanionic molecule to move toward or across the destabilized membrane. This process is now referred to as DNA electrotransfer or electro gene transfer (EGT). Several studies have shown that EGT can be highly efficient, with low variability both in vitro and in vivo. Furthermore, the area transfected is restricted by the placement of the electrodes, and is thus highly controllable. This has led to an increasing use of the technology to transfer reporter or therapeutic genes to various tissues, as evidenced from the large amount of data accumulated on this new approach for non-viral gene therapy, termed electrogenetherapy (EGT as well). By transfecting cells with a long lifetime, such as muscle fibers, a very long-term expression of genes can be obtained. A great variety of tissues have been transfected successfully, from muscle as the most extensively used, to both soft (e.g., spleen) and hard tissue (e.g., cartilage). It has been shown that therapeutic levels of systemically circulating proteins can be obtained, opening possibilities for using EGT therapeutically. This chapter describes the various aspects of in vivo gene delivery by means of electric pulses, from important issues in methodology to updated results concerning the electrotransfer of reporter and therapeutic genes to different tissues.

Femoral intra-arterial injection: a tool to deliver and assess recombinant AAV constructs in rodents whole hind limb

With the aim of simplifying recombinant-adeno-associated virus (rAAV) delivery in muscle, a new femoral intra-arterial technique was designed and tested in rodents (rats and mice). Two serotypes, several promoters and transgenes (reporter or therapeutic) were tested using this administration route. The new route is both easy to perform and efficient. Its usefulness as a tool to assess gene delivery constructs in the muscle was established in the context of recombinant AAV serotypes 1 and 2, and with the ubiquitous CMV and two muscle-specific (C5-12 and CK6) promoters. Both serum monitoring of a secreted protein (murine alkaline phosphatase: muSEAP) and slide staining were used to compare the different constructs. Significantly different patterns of expression in kinetics of expression (muSEAP) and homogeneity of fiber transduction (staining) were evidenced with the different promoters tested, and compared with intra-muscular expression patterns. Detailed studies of differential transduction in leg and thigh muscles showed equivalent efficacy, except in rectus femoris, and to a lesser extent in soleus. In light of these results and prior data, intra-arterially mediated gene transfer mechanism is discussed.

DNA electrotransfer: its principles and an updated review of its therapeutic applications

The use of electric pulses to transfect all types of cells is well known and regularly used in vitro for bacteria and eukaryotic cells transformation. Electric pulses can also be delivered in vivo either transcutaneously or with electrodes in direct contact with the tissues. After injection of naked DNA in a tissue, appropriate local electric pulses can result in a very high expression of the transferred genes. This manuscript describes the evolution in the concepts and the various optimization steps that have led to the use of combinations of pulses that fit with the known roles of the electric pulses in DNA electrotransfer, namely cell electropermeabilization and DNA electrophoresis. A summary of the main applications published until now is also reported, restricted to the in vivo preclinical trials using therapeutic genes.

Electroporation for gene transfer to skeletal muscles: current status

Naked plasmid DNA can be used to introduce genetic material into a variety of cell types in vivo. However, such gene transfer and expression is generally very low compared with that achieved with viral vectors and so is unsuitable for clinical therapeutic application in most cases. This difference in efficiency has been substantially reduced by the introduction of in vivo electroporation to enhance plasmid delivery to a wide range of tissues including muscle, skin, liver, lung, artery, kidney, retina, cornea, spinal cord, brain, synovium, and tumors. The precise mechanism of in vivo electroporation is uncertain, but appears to involve both electropore formation and an electrophoretic movement of the plasmid DNA. Skeletal muscle is a favored target tissue for three reasons: there is a pressing need to develop effective therapies for muscular dystrophies; skeletal muscle can act as an effective platform for the long-term secretion of therapeutic proteins for systemic distribution; and introduction of DNA vaccines into skeletal muscle promotes strong humoral and cellular immune responses. All of these applications are significantly improved by the application of in vivo electroporation. Importantly, the increased efficiency of plasmid delivery following electroporation is seen in larger species as well as rodents, in contrast to the decreasing efficiencies with increasing body size for simple intramuscular injection of naked plasmid DNA. As this electroporation-enhanced non-viral gene delivery system works well in larger species and avoids the vector-specific immune responses associated with recombinant viruses, the prospects for clinical application are promising.

Long-term expression of full-length human dystrophin in transgenic mdx mice expressing internally deleted human dystrophins

One of the possible therapies for Duchenne muscular dystrophy (DMD) is the introduction of a functional copy of the dystrophin gene into the patient. For this approach to be effective, therapeutic levels and long-term expression of the protein need to be achieved. However, immune responses to the newly expressed dystrophin have been predicted, particularly in DMD patients who express no dystrophin or only very truncated versions. In a previous study, we demonstrated a strong humoral and cytotoxic immune response to human dystrophin in the mdx mouse. However, the mdx mouse was tolerant to murine dystrophin, possibly due to the endogenous expression of dystrophin in revertant fibres or the other nonmuscle dystrophin isoforms. In the present study, we delivered human and murine dystrophin plasmids by electrotransfer after hyaluronidase pretreatment to increase gene transfer efficiencies. Tolerance to murine dystrophin was still seen with this improved gene delivery. Tolerance to exogenous recombinant full-length human dystrophin was seen in mdx transgenic lines expressing internally deleted versions of human dystrophin. These results suggest that the presence of revertant fibres may prevent the development of serious immune responses in patients undergoing dystrophin gene therapy.

Increased gene expression and inflammatory cell infiltration caused by electroporation are both important for improving the efficacy of DNA vaccines

One potential reason for the enhancement of immune responses to DNA vaccines following electroporation is increased gene expression. However, the inflammatory response and accompanying cellular infiltration stimulated by electroporation may also be essential for enhancing immune responses to DNA vaccines. These parameters were investigated in pigs, using different electroporation conditions to induce different levels of gene expression and inflammation. Results indicated that the least effective strategy was conventional intramuscular injection where there was low gene expression and low inflammatory cell infiltration. The most efficacious strategy was plasmid administration immediately followed by electroporation. This latter set of conditions elicited a combination of high gene expression and high cellular infiltration. This indicates that electroporation enhances immune responses to DNA vaccines through increased gene expression and inflammatory cell infiltration.

Functional in vivo gene transfer into the myofibers of adult skeletal muscle

The postmitotic nature and longevity of skeletal muscle fibers permit stable expression of any transfected gene. Direct in vivo injection of plasmid DNA, in both adult and regenerating muscles, is a safe, inexpensive, and easy approach. Here we present an optimized electroporation protocol based on the use of spatula electrodes to transfer cDNA in vivo into the adult myofibers of an anatomically defined muscle, which could be functionally characterized. In our hands, about 80% of adult myofibers were transfected in vivo by different plasmids for GFP fusion proteins or for beta-galactosidase. The luciferase activity increased several orders of magnitude when compared to standard DNA delivery. In an anatomical defined muscle, the wide gene transfer was comparable to or better than that of retrovirus delivery, that recently has been shown to be prone to severe side-effects in human clinical studies. Furthermore, with our method the tissue damage was greatly decreased. Thus, the present work describes in vivo functional electrotransfer of genes in adult skeletal muscle fibers by a protocol that is of great potential for gene therapy, as well as for basic research.

Gene Therapy of Collagen-Induced Arthritis by Electrotransfer of Human Tumor Necrosis Factor-αSoluble Receptor I Variants

Electrotransfer is a simple and efficient strategy of nonviral gene delivery. We have used this method to deliver plasmids encoding three human tumor necrosis factor-alpha soluble receptor I variants (hTNFR-Is) a monomeric hTNFR-Is, a chimeric hTNFR-Is/mIgG1, and a dimeric (hTNFR-Is)(2) form. Electrotransfer parameters were studied and because anti-TNF strategies have proven efficient for the treatment of rheumatoid arthritis in clinics, we used a collagen-induced arthritis (CIA) mouse model to assess the efficacy of our constructs in the treatment of the disease. All proteins were proven bioactive, both in vitro and ex vivo. Plasmid intramuscular electrotransfer in mice resulted in a local expression of the three variants for at least 6 months; systemic expression lasted also more than 6 months for the hTNFR-Is/mIgG1 form, while it was shorter for the two other forms. This expression was plasmid dose-dependent. Electrotransfer of 50 microg of hTNFR-Is/mIgG1 at the onset of a CIA induced a clear-cut decrease in both clinical and histologic signs of the disease; the dimeric form also showed some efficacy. Moreover, the long-lasting protective effect was observed for more than 5 weeks. Comparison of this electrotransfer approach with repeated recombinant protein (etanercept) injections highlighted the potential practical interest of gene therapy approach for CIA, which leads to sustained therapeutic effect after single treatment. These results show that electrotransfer may be a useful method to deliver cytokine or anticytokine therapy in rheumatoid arthritis and also illustrate the potentiality of plasmid intramuscular electrotransfer for the rapid screening and assessment of different variant forms of secreted proteins.

Therapeutic Strategies for Duchenne and Becker Dystrophies

Duchenne muscular dystrophy (DMD), a severe X-linked genetic disease affecting one in 3500 boys, is the most common myopathy in children. DMD is due to a lack of dystrophin, a submembrane protein of the cytoskeleton, which leads to the progressive degeneration of skeletal, cardiac, and smooth muscle tissue. A milder form of the disease, Becker muscular dystrophy (BMD), is characterized by the presence of a semifunctional truncated dystrophin, or reduced levels of full-length dystrophin. DMD is the focus of three different supportive or therapeutic approaches: gene therapy, cell therapy, and drug therapy. Here we consider these approaches in terms of three potential goals: improvement of dystrophic phenotype, expression of dystrophin, and overexpression of utrophin. Utrophin exhibits 80% homology with dystrophin and is able to perform similar functions. Pharmacological strategies designed to overexpress utrophin appear promising and may circumvent many obstacles to gene and cell-based therapies.

A novel gene therapy to the graft organ by a rapid injection of naked DNA I: long-lasting gene expression in a rat model of limb transplantation

BACKGROUND

It is important to develop a nontoxic gene transfer method for immunosuppressed patients. In this study, the authors applied a nonviral gene transfer method using rapid injection of naked DNA into the graft limb in rats.

METHODS

Naked DNA (beta-galactosidase, luciferase, or green fluorescent protein expressing plasmid) was used to test an intravascular gene transfer approach in various conditions on the Lewis rat limb. Then, in a rat limb transplantation model, these marker genes were administered preoperatively (day -2) or perioperatively (day 0) to the graft limb by the authors' "venous protocol." The expression level of luciferase was observed over a long period using a noninvasive living image acquisition IVIS system.

RESULTS

Effective intravascular delivery of gene to the rat limb was achieved by a rapid bolus injection of naked DNA through the femoral caudal epigastric vein. Using this procedure, the limb graft with the marker gene perioperatively in place was safely transplanted. After limb transplantation, sustained marker gene expression was observed for more than 2 months.

CONCLUSIONS

This is the first report showing that the method of rapid injection of naked DNA into the limb can be applied to gene modification for organ transplantation.

Muscle electrotransfer as a tool for studying muscle fiber-specific and nerve-dependent activity of promoters

Muscle electrotransfer has recently become a promising tool for efficient delivery of plasmids and transgene expression in skeletal muscle. This technology has been mainly applied to use of muscle as a bioreactor for production of therapeutic proteins. However, it remains to be determined whether muscle electrotransfer may also be accurately used as an alternative tool to transgenesis for studying aspects of muscle-specific gene control that must be explored in fully mature muscle fibers in vivo, such as fiber specificity and nerve dependence. It was also not known to what extent the initial electrical stimulations alter muscle physiology and gene expression. Therefore, optimized conditions of skeletal muscle electroporation were first tested for their effects on muscles of transgenic mice harboring a pM310-CAT transgene in which the CAT reporter gene was under control of the fast IIB fiber-specific and nerve-dependent aldolase A pM promoter. Surprisingly, electrostimulation led to a drastic but transient shutdown of pM310-CAT transgene expression concomitant with very transient activation of MyoD and, mostly, with activation of myogenin, suggesting profound alterations in transcriptional status of the electroporated muscle. Return to a normal transcriptional state was observed 7-10 days after electroporation. Therefore, we investigated whether a reporter construct placed under control of pM could exhibit fiber-specific expression 10 days after electrotransfer in either fast tibialis anterior or slow soleus muscle. We show that not only fiber specificity, but also nerve dependence, of a pM-driven construct can be reproduced. However, after electrotransfer, pM displayed a less tight control than previously observed for the same promoter when integrated in a chromatin context.

Effects of plasmid-mediated growth hormone releasing hormone supplementation in young, healthy Beagle dogs

Our study focused on the evaluation of the pharmacological and toxicological effects of plasmid-mediated GHRH supplementation with electroporation in normal adult dogs over a 180-d period. Twenty-eight dogs (< 2 yr of age) were randomized to four groups. Three groups (four dogs/sex for each group) were treated with ascending doses of GHRH-expressing plasmid: 0.2, 0.6, and 1 mg. One group (two dogs of each sex) served as the control. Clinical observations and body weights were recorded. Hematological, serum biochemical, and urine analyses were performed. Serum IGF-I, ACTH, and insulin were determined. Necropsies were performed on d 93 and 180; organs were weighed and tissues were fixed and processed for light microscopy. Selected tissues were used to assess plasmid biodistribution on d 93. At all doses, plasmid GHRH caused increased weight gain (P < 0.001), without organomegaly. Serum glucose and insulin in fasted dogs remained within normal ranges at all time points. Adrenocorticotropic hormone was normal in all groups. Significant increases in number of red blood cells, hematocrit, and hemoglobin (P < 0.01) were observed. In conclusion, our study shows that plasmid-mediated GHRH supplementation is safe in electroporated doses up to 1.0 mg in young healthy dogs.

Electrotransfer at MR imaging: tool for optimization of gene transfer protocols--feasibility study in mice

PURPOSE

To test, by using an electrotransfer protocol for the transfection of skeletal muscle with naked plasmid complementary DNA, whether in vivo magnetic resonance (MR) imaging can help delineate either the spatial extent of the electric field when contrast agent is injected intraperitoneally or the transfection area when contrast agent is injected locally.

MATERIALS AND METHODS

Three groups of five mice each were examined at 4 T. Gadopentetate dimeglumine was injected intraperitoneally before electroporation in group 1 and after electroporation in group 2. In group 3, gadopentetate dimeglumine was coinjected in situ with plasmid pCMV-beta Gal in the gastrocnemius muscle before electroporation. MR imaging and muscle preparation for histologic examination were performed 3 days later. On T1-weighted images, increase of muscle signal intensity was determined in regions of interest (ROIs) of treated legs and compared with contralateral ROIs. Comparison of signal intensity increase between groups 1 and 2 was performed with Kruskal-Wallis test.

RESULTS

In groups 1 and 3, T1-weighted images of treated muscle showed zones of strongly increased signal intensity. In corresponding ROIs of groups 1, 2, and 3, the mean T1-weighted signal intensity increase at day 3 was 1.64 +/- 0.20 (SD), 1.16 +/- 0.06, and 1.58 +/- 0.17, respectively. The difference between groups 1 and 2 (ie, gadopentetate dimeglumine injected before and after electrotransfer) was significant (P <.001) both without and with correction for T2 variation (1.47 +/- 0.19 and 1.04 +/- 0.09, respectively). In group 3, after in situ coinjection of gadopentetate dimeglumine and plasmid, the area of increased signal intensity revealed at ex vivo MR imaging of the muscle showed a reasonable concordance with the transfected area revealed with beta-galactosidase on histologic sections.

CONCLUSION

In vivo and ex vivo results indicate that atraumatic visualization of the permeabilized and transfected area is possible.

Transcriptional activation of the metallothionein I gene by electric pulses in vivo: basis for the development of a new gene switch system

BACKGROUND

In vivo gene transfer to skeletal muscle is a promising strategy for the treatment of muscular disorders and for the systemic delivery of therapeutic proteins. Nevertheless, for a safe and effective protein production, the spatial and temporal control of gene expression is critical. The existing regulating systems rely on the use of an exogenously regulatory protein and/or an inducer drug whose pharmacological properties are of major concerns for therapeutic applications in humans. Therefore, new strategies based on endogenous regulatable elements have been explored.

METHODS

Gene expression profiles of skeletal muscle submitted or not to electrical pulses and harvested at different times were compared using the Affymetrix GeneChip technology. The endogenous metallothionein promoter was studied by Northern blot and semiquantitative and quantitative RT-PCR. The inducibility of the metallothionein I promoter placed in a plasmid exogenous context was studied using the murine SEAP reporter gene.

RESULTS

The expression of metallothionein I mRNA is significantly increased 6 h after electric pulses delivery. This induction is transient. Identical MT-I expression level is observed after several sequential series of pulses delivery. We demonstrated as well that the MT-II promoter was sensitive to electric pulses delivery. Moreover, the metallothionein I promoter, placed in a plasmid context in front of a reporter gene, was also activated by the application of transient electric field.

CONCLUSIONS

We identified a promoter highly inducible by the controlled electric stimuli applied for electrotransfer experiments. The use of the metallothionein promoter is promising for the time-control by physical stimuli of the expression of a therapeutic gene.