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

Electrodes for in vivo localised subcutaneous electropulsation and associated drug and nucleic acid delivery

BACKGROUND

Drug and nucleic acids can be delivered in vivo by an injection of the product followed by the application of a train of electric pulses.

OBJECTIVE

The success of the method is linked to the proper distribution of the electric field in the target tissue. This is under the control of the design of the electrodes.

METHODS

The field distribution can be obtained by computer simulation mainly by using numerical methods and simplifying hypothesis. The conclusions are validated by comparing the computed current and its experimental values on phantoms. A good agreement is obtained.

RESULTS/CONCLUSION

Targeting the delivery to the skin can be obtained by using an array of very short needle electrodes, by pinching the skin between two parallel plate electrodes, or by using contact wire electrodes.

Mitf silencing cooperates with IL-12 gene transfer to inhibit melanoma in mice

Malignant melanoma is a malignant neoplasm originating from the melanocyte lineage. Microphthalmia-associated transcription factor (Mitf) is crucially involved in the melanin synthesis as well as proliferation and survival of melanocyte and melanoma. We previously showed that short interfering RNA (siRNA) that is specific for the Mitf gene (Mitf-siRNA) significantly inhibited growth of B16 melanoma after electro-transfected in vivo into preestablished tumor in mice. Here we assessed efficacy of electroporation-mediated co-transfection of Mitf-siRNA and IL-12 gene in the treatment of murine melanoma. As results, the tumor growth was more strongly inhibited by intratumor co-transfection with Mitf-siRNA and IL-12-encoding plasmid DNA than by transfection with either of the molecules alone. The co-transfection induced intratumor infiltration of CD4+ and CD8+ T cells, and hampered neoangiogenesis in the tumor. The findings suggest that the RNAi/cytokine gene combination therapy by means of electroporation may become a novel and efficacious therapeutic modality to treat neoplasms including melanoma.

Mild hyperthermia prior to electroporation increases transfection efficiency in HCT 116, HeLa S3 and SGC 7901 cells

The change in transfection efficiency of electroporation by the combined treatment with mild preheating (40 degrees C for 30 min) was investigated. HCT 116, HeLa S3 and SGC 7901 cells were treated with electroporation in medium containing pBKCMV-Luc plasmid with or without preheating. After 24 h, luciferase activity was increased by 36, 28 and 77%; luciferase mRNA transcription was increased by 45, 50 and 68%; and fluorescein isothiocyanate-dextran accumulation was increased by 9, 35 and 15% in preheated groups, respectively. These results demonstrate that the transfection efficiency was enhanced by mild preheating. The mechanism partially involves increased macromolecular particle accumulation.

Accelerated adhesion of grafted skin by laser-induced stress wave-based gene transfer of hepatocyte growth factor

Gene therapy using wound healing-associated growth factor gene has received much attention as a new strategy for improving the outcome of tissue transplantation. We delivered plasmid DNA coding for human hepatocyte growth factor (hHGF) to rat free skin grafts by the use of laser-induced stress waves (LISWs); autografting was performed with the grafts. Systematic analysis was conducted to evaluate the adhesion properties of the grafted tissue; angiogenesis, cell proliferation, and reepithelialization were assessed by immunohistochemistry, and reperfusion was measured by laser Doppler imaging as a function of time after grafting. Both the level of angiogenesis on day 3 after grafting and the increased ratio of blood flow on day 4 to that on day 3 were significantly higher than those in five control groups: grafting with hHGF gene injection alone, grafting with control plasmid vector injection alone, grafting with LISW application alone, grafting with LISW application after control plasmid vector injection, and normal grafting. Reepithelialization was almost completed on day 7 even at the center of the graft with LISW application after hHGF gene injection, while it was not for the grafts of the five control groups. These findings demonstrate the validity of our LISW-based HGF gene transfection to accelerate the adhesion of grafted skins.

Nonviral gene delivery: principle, limitations, and recent progress

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

The Role of Plasmalemmal-Cortical Anchoring on the Stability of Transmembrane Electropores

The structure of eukaryotic cells is maintained by a network of filamentous actin anchored subjacently to the plasma membrane. This structure is referred to as the actin cortex. We present a locally constrained surface tension model for electroporation in order to address the influence of plasmalemmal-cortical anchoring on electropore dynamics. This model predicts that stable electropores are possible under certain conditions. The existence of stable electropores has been suggested in several experimental studies. The electropore radius at which stability is achieved is a function of the characteristic radii of locally constrained regions about the plasma membrane. This model opens the possibility of using actin-modifying compounds to physically manipulate cortical density, thereby manipulating electroporation dynamics. It also underscores the need to improve electroporation models further by incorporating the influence of trans-electropore ionic and aqueous flow, cortical flexibility, transmembrane protein mobility, and active cellular wound healing mechanisms.

Increased in vivo immunological potency of HB-110, a novel therapeutic HBV DNA vaccine, by electroporation

Pulse-induced permeabilization of cellular membranes, generally referred to as electroporation (EP), has been used for years as a tool to increase macromolecule uptake in tissues, including nucleic acids, for gene therapeutic applications, and this technique has been shown to result in improved immunogenicity. In this study, we assessed the utility of EP as a tool to improve the efficacy of HB-110, a novel therapeutic DNA vaccine against chronic hepatitis B, now in phase 1 of clinical study in South Korea. The potency of HB-110 in mice was shown to be improved by EP. The rapid onset of antigen expression and higher magnitude of humoral and cellular responses in electric pulse-treated mice revealed that EP may enable a substantial reduction in the dosage of DNA vaccine required to elicit a response similar in magnitude to that achievable via conventional administration. This study also showed that EP-based vaccination at 4-week-intervals elicited a cellular immune response which was about two-fold higher than the response elicited by conventional vaccination at 2-week intervals. These results may provide a rationale to reduce the clinical dose and increase the interval between the doses in the multidose vaccination schedule. Electric pulsing also elicited a more balanced immune response against four antigens expressed by HB-110: S, preS, Core, and Pol.

Physical methods of nucleic acid transfer: general concepts and applications

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

Molecular-targeted therapy for Duchenne muscular dystrophy: progress and potential

Duchenne muscular dystrophy (DMD) is a lethal heritable childhood myodegenerative condition caused by a mutation within the gene encoding the dystrophin protein within the X chromosome. While, historically, patients with this condition rarely lived into their thirties, they are now living substantially longer as a result of new treatments based on multi-disciplinary care. Despite these advances, the prognosis for DMD patients is limited, and a progressive reduction in quality of life and early death in adulthood cannot be prevented using currently available treatment regimens. The best hopes for a cure lies with cellular and gene therapy approaches that target the underlying genetic defect. In the past several years, viral and nonviral gene therapy methodologies based on adeno-associated viruses, naked plasmid delivery, antisense oligonucleotides, and oligonucleotide-mediated gene editing have advanced to a high degree of sophistication, to the extent that research has moved from the laboratory setting to the clinic. Notwithstanding these accomplishments, shortcomings with each therapy remain, so more work is required to devise an appropriate therapeutic strategy for the management and eventual cure of this debilitating disease.

Muscle and fat mass modulation in different clinical models

Studies described in the recent literature support the idea that gene therapy can lead to genuine clinical benefits when mediated by plasmid delivery in conjunction with electroporation. Plasmid-mediated muscle-targeted gene transfer offers the potential of a cost-effective pharmaceutical-grade therapy delivered by simple intramuscular injection. This approach is particularly appropriate for modulating muscle and fat mass and their intrinsic properties, from treatment of conditions such as cachexia associated with chronic diseases, autoimmune diseases, e.g., myasthenia gravis, to stimulation or suppression of appetite, and further to in vivo manipulation of glucose metabolism and fat deposition in patients with diabetes, or to basic studies of muscle-specific transcription factors and their impact in development. Recent innovations, including in situ electroporation, enabling sustained systemic protein delivery within the therapeutic range, are reviewed. Translation of these advances to human clinical trials will enable muscle- and fat-targeted gene therapy to become a viable therapeutic alternative.

Quantification of electroporative uptake kinetics and electric field heterogeneity effects in cells

We have conducted experiments quantitatively investigating electroporative uptake kinetics of a fluorescent plasma membrane integrity indicator, propidium iodide (PI), in HL60 human leukemia cells resulting from exposure to 40 mus pulsed electric fields (PEFs). These experiments were possible through the use of calibrated, real-time fluorescence microscopy and the development of a microcuvette: a specialized device designed for exposing cell cultures to intense PEFs while carrying out real-time microscopy. A finite-element electrostatic simulation was carried out to assess the degree of electric field heterogeneity between the microcuvette's electrodes allowing us to correlate trends in electroporative response to electric field distribution. Analysis of experimental data identified two distinctive electroporative uptake signatures: one characterized by low-level, decelerating uptake beginning immediately after PEF exposure and the other by high-level, accelerating fluorescence that is manifested sometimes hundreds of seconds after PEF exposure. The qualitative nature of these fluorescence signatures was used to isolate the conditions required to induce exclusively transient electroporation and to discuss electropore stability and persistence. A range of electric field strengths resulting in transient electroporation was identified for HL60s under our experimental conditions existing between 1.6 and 2 kV/cm. Quantitative analysis was used to determine that HL60s experiencing transient electroporation internalized between 50 and 125 million nucleic acid-bound PI molecules per cell. Finally, we show that electric field heterogeneity may be used to elicit asymmetric electroporative PI uptake within cell cultures and within individual cells.

Vascular growth in ischemic limbs: a review of mechanisms and possible therapeutic stimulation

Stimulation of vascular growth to treat limb ischemia is promising, and early results obtained from uncontrolled clinical trials using angiogenic agents, e.g., vascular endothelial growth factor, led to high expectations. However, negative results from recent placebo-controlled trials warrant further research. Here, current insights into mechanisms of vascular growth in the adult, in particular the role of angiogenic factors, the immune system, and bone marrow, were reviewed, together with modes of its therapeutic stimulation and results from recent clinical trials. Three concepts of vascular growth have been described to date-angiogenesis, vasculogenesis, and arteriogenesis (collateral artery growth)-which represent different aspects of an integrated process. Stimulation of arteriogenesis seems clinically most relevant and has most recently been attempted using autologous bone marrow transplantation with some beneficial results, although the mechanism of action is not completely understood. Better understanding of the highly complex molecular and cellular mechanisms of vascular growth may yet lead to meaningful clinical applications.

Efficient electrotransfection into canine muscle

Two different types of electroporation protocols have been developed for efficient electrotransfer of plasmid DNA into skeletal muscle of experimental animals. At first, only low voltage electric pulses have been used, but lately, a combination of high and low voltage pulses has been suggested as more efficient. Up to date, in dogs, this type of electroporation protocol has never been used for muscle targeted plasmid DNA electrotransfection. In this study, we used two different DNA plasmids, one encoding green fluorescent protein and one encoding human interleukin-12. Five different electroporation protocols were evaluated. Three of them featured different combinations of high and low voltage pulses, and two were performed with delivery of low voltage pulses only. Our study shows that combination of 1 high voltage pulse (600 V/cm, 100 mus), followed by 4 low voltage pulses (80 V/cm, 100 ms, 1 Hz) yielded in the same transfection efficiency as the standard trains of low voltage pulses. However, this protocol is performed quicker and, thus, more suitable for potential use in clinical practice. In addition, it yielded in detectable systemic expression of human interleukin-12. Electrotransfer of either of the plasmids was associated with only mild and transitory local side effects, without clinically detectable systemic side effects. The results indicate that electrotransfection is a feasible, effective, and safe method for muscle targeted gene therapy in dogs, which could have potential for clinical applications in veterinary medicine of small animals.

Field distribution and DNA transport in solid tumors during electric field-mediated gene delivery

Gene therapy has a great potential in cancer treatment. However, the efficacy of cancer gene therapy is currently limited by the lack of a safe and efficient means to deliver therapeutic genes into the nucleus of tumor cells. One method under investigation for improving local gene delivery is based on the use of pulsed electric field. Despite repeated demonstration of its effectiveness in vivo, the underlying mechanisms behind electric field-mediated gene delivery remain largely unknown. Without a thorough understanding of these mechanisms, it will be difficult to further advance the gene delivery. In this review, the electric field-mediated gene delivery in solid tumors will be examined by following individual transport processes that must occur in vivo for a successful gene transfer. The topics of examination include: (i) major barriers for gene delivery in the body, (ii) distribution of electric fields at both cell and tissue levels during the application of external fields, and (iii) electric field-induced transport of genes across each of the barriers. Through this approach, the review summarizes what is known about the mechanisms behind electric field-mediated gene delivery and what require further investigations in future studies.

Transfection by electroporation

Electroporation--the use of high-voltage electric shocks to introduce DNA into cells--can be used with most cell types, yields a high frequency of both stable transformation and transient gene expression, and, because it requires fewer steps, can be easier than alternate techniques. In this unit, the describes the electroporation of mammalian cells and an outlines modifications for preparation and transfection of plant protoplasts.

Nonviral vector gene modification of stem cells for myocardial repair

Therapeutic angiogenesis and myogenesis restore perfusion of ischemic myocardium and improve left ventricular contractility. These therapeutic modalities must be considered as complementary rather than competing to exploit their advantages for optimal beneficial effects. The resistant nature of cardiomyocytes to gene transfection can be overcome by ex vivo delivery of therapeutic genes to the heart using genetically modified stem cells. This review article gives an overview of different vectors and delivery systems in general used for therapeutic gene delivery to the heart and provides a critical appreciation of the ex vivo gene delivery approach using genetically modified stem cells to achieve angiomyogenesis for the treatment of infarcted heart.

Application of electroporation gene therapy: past, current, and future

Twenty-five years after the publication of the first report on gene transfer in vitro in cultured cells by the means of electric pulse delivery, reversible cell electroporation for gene transfer and gene therapy (DNA electrotransfer) is at a crossroad in its development. Present knowledge on the effects of cell exposure to appropriate electric field pulses, particularly at the level of the cell membrane, is reported here as an introduction to the large range of applications described in this book. The importance of the models of electric field distribution in tissues and of the correct choice of electrodes and applied voltages is highlighted. The mechanisms involved in DNA electrotransfer, which include cell electropermeabilization and DNA electrophoresis, are also surveyed. The feasibility of electric pulse for gene transfer in humans is discussed taking into account that electric pulse delivery is already regularly used for localized drug delivery in the treatment of cutaneous and subcutaneous solid tumors by electrochemotherapy. Because recent technological developments have made DNA electrotransfer more efficient and safer, this nonviral gene therapy approach is now ready to reach the clinical stage. A good understanding of DNA electrotransfer principles and a respect for safe procedures will be key elements for the successful future transition of DNA electrotransfer to the clinics.

Ultrasound-based nonviral gene delivery induces bone formation in vivo

Nonviral gene delivery is a promising, safe, therapeutic tool in regenerative medicine. This study is the first to achieve nonviral, ultrasound-based, osteogenic gene delivery that leads to bone tissue formation, in vivo. We hypothesized that direct in vivo sonoporation of naked DNA encoding for the osteogenic gene, recombinant human bone morphogenetic protein-9 (rhBMP-9) would induce bone formation. A luciferase plasmid (Luc), encoding rhBMP-9 or empty pcDNA3 vector mixed with microbubbles, was injected into the thigh muscles of mice. After injection, noninvasive sonoporation was applied. Luc activity was monitored noninvasively, and quantitatively using bioluminescence imaging in vivo, and found for 14 days with a peak expression on day 7. To examine osteogenesis in vivo, rhBMP-9 plasmid was sonoporated into the thigh muscles of transgenic mice that express the Luc gene under the control of a human osteocalcin promoter. Following rhBMP-9 sonoporation, osteocalcin-dependent Luc expression lasted for 24 days and peaked on day 10. Bone tissue was formed in the site of rhBMP-9 delivery, as was shown by micro-computerized tomography and histology. The sonoporation method was also compared with previously developed electrotransfer-based gene delivery and was found significantly inferior in its efficiency of gene delivery. We conclude that ultrasound-mediated osteogenic gene delivery could serve as a therapeutic solution in conditions requiring bone tissue regeneration after further development that will increase the transfection efficiency.

Prolonged in vivo gene silencing by electroporation-mediated plasmid delivery of small interfering RNA

For the successful application of RNA interference in vivo, it is desired to achieve (local) delivery of small interfering RNAs (siRNAs) and long-term gene silencing. Nonviral electrodelivery is suitable to obtain local and prolonged expression of transgenes. By intramuscular electrodelivery of a plasmid in which two opposing human polymerase III promoters (H1 and U6) drive the expression of siRNA constructs that form functional double-stranded siRNAs, in combination with in vivo bioluminescence imaging, we were able to knock down exogenous delivered luciferase for at least 100 days in murine calf muscles. This effect was sequence specific, because scrambled siRNA had no effect. Moreover, we were able to demonstrate in vivo reduction of endogenous TLR4 expression for at least 1 week, using a similar vector expressing an siRNA for TLR4 in the muscle. In this study, we demonstrate that in vivo suppression of both endogenous (for at least 1 week) and introduced genes (>100 days) is feasible via plasmid-driven siRNA expression after electroporation-mediated intramuscular gene transfer. With this approach the short-term effect of oligonucleotides and the drawbacks of viral gene delivery, like immunological responses, could be circumvented. Therefore, this application of RNA interference is a useful tool with which to investigate gene function and might be promising as a therapeutic tool for locally acting diseases such as restenosis or tumors.

Tumor ablation with irreversible electroporation

We report the first successful use of irreversible electroporation for the minimally invasive treatment of aggressive cutaneous tumors implanted in mice. Irreversible electroporation is a newly developed non-thermal tissue ablation technique in which certain short duration electrical fields are used to permanently permeabilize the cell membrane, presumably through the formation of nanoscale defects in the cell membrane. Mathematical models of the electrical and thermal fields that develop during the application of the pulses were used to design an efficient treatment protocol with minimal heating of the tissue. Tumor regression was confirmed by histological studies which also revealed that it occurred as a direct result of irreversible cell membrane permeabilization. Parametric studies show that the successful outcome of the procedure is related to the applied electric field strength, the total pulse duration as well as the temporal mode of delivery of the pulses. Our best results were obtained using plate electrodes to deliver across the tumor 80 pulses of 100 µs at 0.3 Hz with an electrical field magnitude of 2500 V/cm. These conditions induced complete regression in 12 out of 13 treated tumors, (92%), in the absence of tissue heating. Irreversible electroporation is thus a new effective modality for non-thermal tumor ablation.

An electroporation microchip system for the transfection of zebrafish embryos using quantum dots and GFP genes for evaluation

This study focuses on the design and experimental verification of an electroporation (EP) microchip system for the transfection of zebrafish (Danio rerio). For generating suitable pulses, a circuit is used to provide voltages between 0 and 700 V, with nearly 0-3,500 V/cm electric field. In addition, a proposed EP microchip, designed in a modular fashion, is fabricated using micro electromechanical system (MEMS) technology to allow for rapid and convenient replacement of each component. A numerical simulation is carried out to analyze the uniformity and strength of the EP electric fields generated in the microchip. Trypan blue dye, water-soluble quantum dots (MUA-QDs) and genes coding for green fluorescence protein (pEGFP-N1 plasmids) were employed to verify the successful delivery and transfection of zebrafish embryos. The experimental results show that the optimum delivery rate of trypan blue dyes and MUA-QDs were respectively up to 62 and 36% by using the proposed EP system. The successfully transfected embryos with the pEGFP-N1 plasmid used exhibit green fluorescence in the zebrafish embryos. The approach in the transfection of zebrafish embryos will provide many potential usages for cellular imaging areas, gene therapy research and medical applications.

A study of the immunological response to tumor ablation with irreversible electroporation

Immune cell recruitment during the treatment of sarcoma tumors in mice with irreversible electroporation was studied by immunohistochemistry. Irreversible electroporation is a non-thermal tissue ablation technique in which certain short duration electrical fields are used to permanently permeabilize the cell membrane, presumably through the formation of nanoscale defects in the membrane. Employing irreversible electroporation parameters known to completely ablate the tumors without thermal effects we did not find infiltration of immune cells probably because of the destruction of infiltration routes. We confirm here that immune response is not instrumental in irreversible electroporation efficacy, and we propose that irreversible electroporation may be, therefore, a treatment modality of interest to immunodepressed cancer patients.

Improvement of in vivo transfer of plasmid DNA in muscle: comparison of electroporation versus ultrasound

Plasmid-based gene delivery to muscle is a treatment strategy for many diseases with potential advantages above viral-based gene delivery methods, however, with a relative low transfection efficiency. We compared two physical methods - electroporation and ultrasound - that facilitate DNA uptake into cells. Mice (C57Bl/6) were injected intramuscular using plasmid DNA encoding an intracellular protein (p53) followed by electroporation or ultrasound. Then 48 hr after the injections the mice were sacrificed. The parameter for transfection efficiency was the area of muscle expressing the transgene. The p53 expression plasmid showed a 36-fold increase (p = 0.015) in transfection efficiency with electroporation compared to ultrasound. Compared with ultrasound, electroporation significantly improves transfection efficiency of naked plasmid DNA transfer into skeletal muscle.

Nucleocytoplasmic transport of DNA: enhancing non-viral gene transfer

Gene therapy, the correction of dysfunctional or deleted genes by supplying the lacking component, has long been awaited as a means to permanently treat or reverse many genetic disorders. To achieve this, therapeutic DNA must be delivered to the nucleus of cells using a safe and efficient delivery vector. Although viral-based vectors have been utilized extensively due to their innate ability to deliver DNA to intact cells, safety considerations, such as pathogenicity, oncogenicity and the stimulation of an immunological response in the host, remain problematical. There has, however, been much progress in the development of safe non-viral gene-delivery vectors, although they remain less efficient than the viral counterparts. The major limitations of non-viral gene transfer reside in the fact that it must be tailored to overcome the intracellular barriers to DNA delivery that viruses already master, including the cellular and nuclear membranes. In particular, nuclear transport of the therapeutic DNA is known to be the rate-limiting step in the gene-delivery process. Despite this, much progress had been made in recent years in developing novel means to overcome these barriers and efficiently deliver DNA to the nuclei of intact cells. This review focuses on the nucleocytoplasmic delivery of DNA and mechanisms to enhance to non-viral-mediated gene transfer.

Electroporation enhances reporter gene expression following delivery of naked plasmid DNA to the lung

BACKGROUND

Existing methods of non-viral airway gene transfer suffer from low levels of efficiency. Electroporation has been used to enhance gene transfer in a range of tissues. Here we assess the usefulness of electroporation for enhancing gene transfer in the lungs of mice and sheep.

METHODS

Naked plasmid DNA (pDNA) expressing either luciferase or green fluorescent protein (GFP) was delivered to mouse lungs by instillation. Following surgical visualisation, the lungs were directly electroporated and the level and duration of luciferase activity was assessed and cell types that were positive for GFP were identified in lung cryosections. Naked pDNA was nebulised to the sheep lung and electrodes attached to the tip of a bronchoscope were used to electroporate airway segment bifurcations, Luciferase activity was assessed in electroporated and control non-electroporated regions, after 24 h.

RESULTS

Following delivery of naked pDNA to the mouse lung, electroporation resulted in up to 400-fold higher luciferase activity than naked pDNA alone when luciferase was under the control of a cytomegalovirus (CMV) promoter. Following delivery of a plasmid containing the human polyubiquitin C (UbC) promoter, electroporation resulted in elevated luciferase activity for at least 28 days. Visualisation of GFP indicated that electroporation resulted in increased GFP detection compared with non-electroporated controls. In the sheep lung electroporation of defined sites in the airways resulted in luciferase activity 100-fold greater than naked pDNA alone.

CONCLUSIONS

These results indicate that electroporation can be used to enhance gene transfer in the lungs of mice and sheep without compromising the duration of expression.

Electric field-mediated transport of plasmid DNA in tumor interstitium in vivo

Local pulsed electric field application is a method for improving non-viral gene delivery. Mechanisms of the improvement include electroporation and electrophoresis. To understand how electrophoresis affects pDNA delivery in vivo, we quantified the magnitude of electric field-induced interstitial transport of pDNA in 4T1 and B16.F10 tumors implanted in mouse dorsal skin-fold chambers. Four different electric pulse sequences were used in this study, each consisted of 10 identical pulses that were 100 or 400 V/cm in strength and 20 or 50 ms in duration. The interval between consecutive pulses was 1 s. The largest distance of transport was obtained with the 400 V/cm and 50 ms pulse, and was 0.23 and 0.22 microm/pulse in 4T1 and B16.F10 tumors, respectively. There were no significant differences in transport distances between 4T1 and B16.F10 tumors. Results from in vivo mapping and numerical simulations revealed an approximately uniform intratumoral electric field that was predominantly in the direction of the applied field. The data in the study suggested that interstitial transport of pDNA induced by a sequence of ten electric pulses was ineffective for macroscopic delivery of genes in tumors. However, the induced transport was more efficient than passive diffusion.

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.

Electrochemotherapy in treatment of tumours

AIM

Electrochemotherapy is a local drug delivery approach aimed at treatment with palliative intent of cutaneous and subcutaneous tumour nodules of different histologies. Electrochemotherapy, via cell membrane permeabilising electric pulses, potentiates the cytotoxicity of non-permeant or poorly permeant anticancer drugs with high intrinsic cytotoxicity, such as bleomycin or cisplatin, at the site of electric pulse application.

METHODS

An overview of preclinical and clinical studies is presented, and the treatment procedure is further critically evaluated.

RESULTS

In clinical studies electrochemotherapy has proved to be a highly efficient and safe approach for treating cutaneous and subcutaneous tumour nodules. The treatment response for various tumours (predominantly melanoma) was approximately 75% complete and 10% partial response of the treated nodules.

CONCLUSIONS

Electrochemotherapy is a new, clinically acknowledged method for the treatment of cutaneous and subcutaneous tumours. Its advantages are high effectiveness on tumours with different histologies, simple application, minimal side effects and the possibility of effective repetitive treatment.

Gene Transfection of Mammalian Cells Using Membrane Sandwich Electroporation

To avoid safety issues such as immune response and cytotoxicity associated with viruses and liposomes, physical methods have been widely used for either in vivo or ex vivo gene delivery. They are, however, very invasive and often provide limited efficiency. Using pEGFP and pSEAP plasmids and NIH 3T3 fibroblasts as models, we demonstrate a new electroporation-based gene delivery method, called membrane sandwich electroporation (MSE). The MSE method is able to provide better gene confinement near the cell surface to facilitate gene transport into the cells and thus shows significant improvement over transgene expression of mammalian cells compared to current electroporation techniques.

Type I interferon response against viral and non-viral gene transfer in human tumor and primary cell lines

BACKGROUND

Type I interferon (IFN-alpha/beta) response is one of the major host defence mechanisms against viruses. Some recent reports suggest that IFNs may interfere with the efficacy of both non-viral and virus-vector-mediated therapeutic gene transfer.

METHODS

The type I IFN response upon different gene transfer methods in human tumor and primary cell lines was studied by analysing IFN-beta mRNA expression, secretion of type I IFNs and accumulation of IFN-alpha/beta-induced MxA protein (myxovirus resistance protein A).

RESULTS

Infection with avirulent Semliki Forest virus A7[74] induced MxA protein accumulation and increased the IFN-beta mRNA level, whereas none of the studied virus vectors (adenovirus, CRAd, lentivirus or AAV) induced IFN response. However, plasmid DNA induced the accumulation of MxA protein when transfected with several commercial transfection reagents. RNA transfection appeared to be an efficient inducer of type I IFN response: replicating alphaviral RNA, eukaryotic total RNA, or mRNA all induced both MxA protein accumulation and IFN-beta expression. siRNA transfection failed to induce MxA response.

CONCLUSIONS

The non-viral gene transfer methods have gained more interest in recent years due to their better safety profiles when compared to their viral counterparts. However, the efficiency of non-viral gene transfer is well below those reached by viral vector systems. The type I interferon response induced by non-viral methods may in part contribute to this inefficiency, while most currently used viral gene transfer vectors fail to induce or are able to suppress type I IFN response.

Real time electroporation control for accurate and safe in vivo non-viral gene therapy

In vivo cell electroporation is the basis of DNA electrotransfer, an efficient method for non-viral gene therapy using naked DNA. The electric pulses have two roles, to permeabilize the target cell plasma membrane and to transport the DNA towards or across the permeabilized membrane by electrophoresis. For efficient electrotransfer, reversible undamaging target cell permeabilization is mandatory. We report the possibility to monitor in vivo cell electroporation during pulse delivery, and to adjust the electric field strength on real time, within a few microseconds after the beginning of the pulse, to ensure efficacy and safety of the procedure. A control algorithm was elaborated, implemented in a prototype device and tested in luciferase gene electrotransfer to mice muscles. Controlled pulses resulted in protection of the tissue and high levels of luciferase in gene transfer experiments where uncorrected excessive applied voltages lead to intense muscle damage and consecutive loss of luciferase gene expression.

Electric Fields around and within Single Cells during Electroporation—A Model Study

One of the key issues in electric field-mediated molecular delivery into cells is how the intracellular field is altered by electroporation. Therefore, we simulated the electric field in both the extracellular and intracellular domains of spherical cells during electroporation. The electroporated membrane was modeled macroscopically by assuming that its electric resistivity was smaller than that of the intact membrane. The size of the electroporated region on the membrane varied from zero to the entire surface of the cell. We observed that for a range of values of model constants, the intracellular current could vary several orders of magnitude whereas the maximum variations in the extracellular and total currents were less than 8% and 4%, respectively. A similar difference in the variations was observed when comparing the electric fields near the center of the cell and across the permeabilized membrane, respectively. Electroporation also caused redirection of the extracellular field that was significant only within a small volume in the vicinity of the permeabilized regions, suggesting that the electric field can only facilitate passive cellular uptake of charged molecules near the pores. Within the cell, the field was directed radially from the permeabilized regions, which may be important for improving intracellular distribution of charged molecules.

Electrically Assisted Ocular Gene Therapy

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

Electrogene therapy with p53 of murine sarcomas alone or combined with electrochemotherapy using cisplatin

The aim of our study was to evaluate feasibility and therapeutic potential of electrogene therapy with p53 alone or combined with electrochemotherapy using cisplatin on two murine sarcomas with different p53 status. Antitumor effectiveness of three consecutive electrogene treatments with p53 was more effective in wild-type LPB tumors than mutated SA-1 tumors, resulting in 21.4% of tumor cures in LPB tumors and 12.5% in SA-1 tumors. Pretreatment of tumors with electrogene therapy with p53 enhanced chemosensitivity of both tumor models treated by electrochemotherapy with cisplatin. After only one application of this treatment combination in the LPB tumor model, specific tumor growth delay was prolonged in the combined treatment group compared to electrogene therapy with p53 or electrochemotherapy with cisplatin alone, whereas in SA-1 tumors this treatment combination resulted in 31.6% of cured animals. Results of our study show that electrogene therapy with p53 alone or combined with electrochemotherapy is feasible and effective treatment of tumors. The combination of electrogene therapy and electrochemotherapy after only one application resulted in complete regression of tumors.

Plasmid-based gene therapy of diabetes mellitus

Type I diabetes mellitus (T1D) is due to a loss of immune tolerance to islet antigen and thus, there is intense interest in developing therapies that can re-establish it. Tolerance is maintained by complex mechanisms that include inhibitory molecules and several types of regulatory T cells (Tr). A major historical question is whether gene therapy can be employed to generate Tr cells. This review shows that gene transfer of immunoregulatory molecules can prevent T1D and other autoimmune diseases. In our studies, non-viral gene transfer is enhanced by in vivo electroporation (EP). This technique can be used to perform DNA vaccination against islet cell antigens and when combined with appropriate immune ligands results in the generation of Tr cells and protection against T1D. In vivo EP can also be applied for non-immune therapy of diabetes. It can be used to deliver protein drugs such as glucagon-like peptide 1 (GLP-1), leptin or transforming growth factor beta (TGF-beta). These act in T1D or type II diabetes (T2D) by restoring glucose homeostasis, promoting islet cell survival and growth or improving wound healing and other complications. Furthermore, we show that in large animals EP can deliver peptide hormones, such as growth hormone releasing hormone (GHRH). We conclude that the non-viral gene therapy and EP represent a safe and efficacious approach with clinical potential.

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

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

New anti angiogenesis developments through electro-immunization: Optimization by in vivo optical imaging of intradermal electrogenetransfer

Direct application of high voltage electric pulses of milliseconds duration to the skin of a mouse enhances in vivo intradermal delivery of injected therapeutic molecules such as DNA. The efficacy of gene transfer and expression is dependent on electrical parameters. DNA electrotransfer in tissues increases the associated DNA expression vaccine potency. This protocol is called "electro-immunization". In the present study, we report a new strategy for optimizing electro-immunization. In vivo fluorescence imaging was used to detect the expression of a fluorescent protein (DsRed) and therefore allowed rapid optimization of the protocol. In vivo electrogenetransfer in the skin was well tolerated and DsRed expression was followed for over 2 weeks. Expression was voltage dependent under our conditions. Parameters were selected giving the highest level of expression. Under these optimized conditions, electrotransfer of a plasmid encoding VEGF was evaluated for its immune response as a gene therapy of interest involved in anti-angiogenic strategies. Anti VEGF 165 antibodies in sera of mice were evaluated by ELISA and compared to those obtained after conventional immunization. Comparable titres of antibodies were obtained in both groups. An IgG2a predominance was found in mice immunized with the plasmid whereas a IgG1 predominance was observed in mice immunized classically. Skin electro-immunization is therefore shown as a good route for DNA immunization for anti-angiogenesis concern.

Electroporation of DNA, RNA, and morpholinos into zebrafish embryos

The combination of accessible embryology and forward genetic techniques has made zebrafish a powerful model system for the study of vertebrate development. One limitation of genetic analysis is that the study of gene function is usually limited to the first developmental event affected by a gene. In vivo electroporation has recently matured as a method for studying gene function at different developmental time points and in specific regions of the organism. The focal application of current allows macromolecules to be efficiently introduced into a targeted region at any time in the life cycle. Here we describe a rapid protocol by which DNA, RNA and morpholinos can all be precisely electroporated into zebrafish in a temporally and spatially controlled manner. This versatile technique allows gene function to be determined by both gain and loss of function analyses in specific regions at specific times. This is the first report that describes the electroporation of three different molecules into embryonic and larval zebrafish cells.

99mTc-DTPA Uptake and Electrical Impedance Measurements in Verification ofIn VivoElectropermeabilization Efficiency in Rat Muscle

OBJECTIVE

In vivo electropermeabilization of cell membranes in rat muscle tissue cause a significant decrease of the electrical impedance, in the frequency region of 1-10 kHz. We aimed to study how the 99mTc-DTPA uptake in the electropermeabilized region correlates to the change of admittance Y = 1/absZ, where Z is the measured impedance.

METHODS

The electropermeabilization was performed in vivo by applying high-voltage (0.5-2 kV) short (0.1-2 ms) pulses through gold-plated needle electrodes in skeletal muscle. The impedance was measured before and after each electropermeabilization pulse. The uptake of 99mTc-DTPA uptake in the electropermeabilized region was measured after 6 and 24 hours with a gamma camera.

RESULTS

The pulse shape (square and exponential), duration, and amplitude of the applied electric field were varied, and electropermeabilization efficiency was evaluated using the various measurement modalities. Good correlations were found (correlation coefficient approximately 0.9) between the 99mTc-DTPA uptake in the electropermeabilized and control "region of interest" the admittance ratio Y (post-treatment)/Y (pretreatment), and charge displacement parameter Q.

CONCLUSION

The electrical impedance measurements method can be utilized in clinical settings to verify the efficiency of electropermeabilization applied to chemotherapy and to power RNAi (RNA-interference) and DNA-plasmid transfection in vaccination, immunization, and gene-therapy.

The effect of interleukin-10 knock-out and overexpression on neointima formation in hypercholesterolemic APOE*3-Leiden mice

OBJECTIVE

Inflammatory factors are thought to play a regulatory role in restenosis. Interleukin-10 (IL10) is an important anti-inflammatory cytokine with anti-atherogenic potentials. The aim of this study was to assess the effects of IL10 modulation on cuff-induced neointima formation in hypercholesterolemic APOE*3-Leiden mice.

METHODS

The involvement of IL10 in neointima formation was studied in a hypercholesterolemic mouse model of cuff-induced stenosis of the femoral artery by IL10 knocking-out or overexpression procedures. IL10(+/-) mice were crossbred with APOE*3-Leiden mice to generate hypercholesterolemic APOE*3-LeidenIL10(-/-) mice. To achieve IL10 overexpression in APOE*3-Leiden mice, a single intramuscular injection of a murine IL10 overexpression plasmid was performed followed by electroporation.

RESULTS

Knocking-out IL10, in hypercholesterolemic APOE*3-Leiden mice, resulted in a significant 1.9-fold increase of neointima surface as compared to APOE*3-LeidenIL10(+/+) littermates (p=0.02). Conversely, a marked 45% inhibition on cuff-induced neointima formation was obtained after IL10 overexpression (p=0.02). Electrodelivery of IL10 vector leads to detectable IL10 serum levels, with a sustained expression over the experimental period of 3 weeks. IL10 overexpression reduced plasma cholesterol levels in APOE*3-Leiden mice, whereas IL10 deficiency in these mice did not lead to altered cholesterol levels as compared to the IL10(+/+) group. Finally, IL10 overexpression stimulated endogenous IL10 mRNA expression in the spleen and reduced the transcriptional responses of several pro-inflammatory cytokines.

CONCLUSION

Here, we clearly demonstrate the role of IL10 in the development of neointima formation in hypercholesterolemic mice and the potential therapeutic effect of non-viral electrodelivery of IL10 cDNA to inhibit post-angioplasty restenosis.