In vivo gene delivery by electroporation

The Effect of Millisecond Pulsed Electric Fields (msPEF) on Intracellular Drug Transport with Negatively Charged Large Nanocarriers Made of Solid Lipid Nanoparticles (SLN): In Vitro Study

Drug delivery technology is still a dynamically developing field of medicine. The main direction in nanotechnology research (nanocarriers, nanovehicles, etc.) is efficient drug delivery to target cells with simultaneous drug reduction concentration. However, nanotechnology trends in reducing the carrier sizes to several nanometers limit the volume of the loaded substance and may pose a danger of uncontrolled access into the cells. On the other hand, nanoparticles larger than 200 nm in diameter have difficulties to undergo rapid diffusional transport through cell membranes. The main advantage of large nanoparticles is higher drug encapsulation efficiency and the ability to deliver a wider array of drugs. Our present study contributes a new approach with large Tween 80 solid lipid nanoparticles SLN (i.e., hydrodynamic GM-SLN-glycerol monostearate, GM, as the lipid and ATO5-SLNs-glyceryl palmitostearate, ATO5, as the lipid) with diameters DH of 379.4 nm and 547 nm, respectively. They are used as drug carriers alone and in combination with electroporation (EP) induced by millisecond pulsed electric fields. We evaluate if EP can support the transport of large nanocarriers into cells. The study was performed with two cell lines: human colon adenocarcinoma LoVo and hamster ovarian fibroblastoid CHO-K1 with coumarin 6 (C6) as a fluorescent marker for encapsulation. The biological safety of the potential treatment procedure was evaluated with cell viability after their exposure to nanoparticles and EP. The EP efficacy was evaluated by FACS method. The impact on intracellular structure organization of cytoskeleton was visualized by CLSM method with alpha-actin and beta-tubulin. The obtained results indicate low cytotoxicity of both carrier types, free and loaded with C6. The evaluation of cytoskeleton proteins indicated no intracellular structure damage. The intracellular uptake and accumulation show that SLNs do not support transport of C6 coumarin. Only application of electroporation improved the transport of encapsulated and free C6 into both treated cell lines.

A review of basic to clinical studies of irreversible electroporation therapy

The use of irreversible electroporation (IRE) for cancer treatment has increased sharply over the past decade. As a nonthermal therapy, IRE offers several potential benefits over other focal therapies, which include 1) short treatment delivery time, 2) reduced collateral thermal injury, and 3) the ability to treat tumors adjacent to major blood vessels. These advantages have stimulated widespread interest in basic through clinical studies of IRE. For instance, many in vitro and in vivo studies now identify treatment planning protocols (IRE threshold, pulse parameters, etc.), electrode delivery (electrode design, placement, intraoperative imaging methods, etc.), injury evaluation (methods and timing), and treatment efficacy in different cancer models. Therefore, this study reviews the in vitro, translational, and clinical studies of IRE cancer therapy based on major experimental studies particularly within the past decade. Further, this study provides organized data and facts to assist further research, optimization, and clinical applications of IRE.

Intradermal DNA Electroporation Induces Cellular and Humoral Immune Response and Confers Protection against HER2/neu Tumor

Skin represents an attractive target for DNA vaccine delivery because of its natural richness in APCs, whose targeting may potentiate the effect of vaccination. Nevertheless, intramuscular electroporation is the most common delivery method for ECTM vaccination. In this study we assessed whether intradermal administration could deliver the vaccine into different cell types and we analyzed the evolution of tissue infiltrate elicited by the vaccination protocol. Intradermal electroporation (EP) vaccination resulted in transfection of different skin layers, as well as mononuclear cells. Additionally, we observed a marked recruitment of reactive infiltrates mainly 6–24 hours after treatment and inflammatory cells included CD11c⁺. Moreover, we tested the efficacy of intradermal vaccination against Her2/neu antigen in cellular and humoral response induction and consequent protection from a Her2/neu tumor challenge in Her2/neu nontolerant and tolerant mice. A significant delay in transplantable tumor onset was observed in both BALB/c (p ≤ 0,0003) and BALB-neuT mice (p = 0,003). Moreover, BALB-neuT mice displayed slow tumor growth as compared to control group (p < 0,0016). In addition, while in vivo cytotoxic response was observed only in BALB/c mice, a significant antibody response was achieved in both mouse models. Our results identify intradermal EP vaccination as a promising method for delivering Her2/neu DNA vaccine.

Gene electrotransfer of plasmid AMEP, an integrin-targeted therapy, has antitumor and antiangiogenic action in murine B16 melanoma

Gene therapy with Plasmid AMEP (antiangiogenic metargidin peptide) has recently been studied as a potential targeted therapy for melanoma. This plasmid is designed to downregulate α5β1 and αvβ3 integrins. In our study, electroporation was used as a nonviral delivery system. We investigated the antiangiogenic and direct antitumor effectiveness of this gene therapy on low and highly metastatic B16 melanoma variants. In vitro, the antiangiogenic effectiveness as determined by tube formation assay on endothelial cells was predominantly dependent on AMEP expression levels. In vivo, antitumor effectiveness was mediated by the inhibition of proliferation, migration and invasion of melanoma cells and correlated with the expression of integrins on tumor cells after intratumor delivery. In addition, reduced metastatic potential was shown. Intramuscular gene electrotransfer of Plasmid AMEP, for AMEP systemic distribution, had no antitumor effect with this specific preventive treatment protocol, confirming that direct tumor delivery was more effective. This study confirms our previous in vitro data that the expression levels of integrins on melanoma cells could be used as a biomarker for antitumor effectiveness in integrin-targeted therapies, whereas the expression levels of AMEP peptide could be a predictive factor for antiangiogenic effectiveness of Plasmid AMEP in the treatment of melanoma.

Synthetic DNA vaccine strategies against persistent viral infections

The human body has developed an elaborate defense system against microbial pathogens and foreign antigens. However, particular microbes have evolved sophisticated mechanisms to evade immune surveillance, allowing persistence within the human host. In an effort to combat such infections, intensive research has focused on the development of effective prophylactic and therapeutic countermeasures to suppress or clear persistent viral infections. To date, popular therapeutic strategies have included the use of live-attenuated microbes, viral vectors and dendritic-cell vaccines aiming to help suppress or clear infection. In recent years, improved DNA vaccines have now re-emerged as a promising candidate for therapeutic intervention due to the development of advanced optimization and delivery technologies. For instance, genetic optimization of synthetic plasmid constructs and their encoded antigens, in vivo electroporation-mediated vaccine delivery, as well as codelivery with molecular adjuvants have collectively enhanced both transgene expression and the elicitation of vaccine-induced immunity. In addition, the development of potent heterologous prime-boost regimens has also provided significant contributions to DNA vaccine immunogenicity. Herein, the authors will focus on these recent improvements to this synthetic platform in relation to their application in combating persistent virus infection.

Cryosurgery with pulsed electric fields

This study explores the hypothesis that combining the minimally invasive surgical techniques of cryosurgery and pulsed electric fields will eliminate some of the major disadvantages of these techniques while retaining their advantages. Cryosurgery, tissue ablation by freezing, is a well-established minimally invasive surgical technique. One disadvantage of cryosurgery concerns the mechanism of cell death; cells at high subzero temperature on the outer rim of the frozen lesion can survive. Pulsed electric fields (PEF) are another minimally invasive surgical technique in which high strength and very rapid electric pulses are delivered across cells to permeabilize the cell membrane for applications such as gene delivery, electrochemotherapy and irreversible electroporation. The very short time scale of the electric pulses is disadvantageous because it does not facilitate real time control over the procedure. We hypothesize that applying the electric pulses during the cryosurgical procedure in such a way that the electric field vector is parallel to the heat flux vector will have the effect of confining the electric fields to the frozen/cold region of tissue, thereby ablating the cells that survive freezing while facilitating controlled use of the PEF in the cold confined region. A finite element analysis of the electric field and heat conduction equations during simultaneous tissue treatment with cryosurgery and PEF (cryosurgery/PEF) was used to study the effect of tissue freezing on electric fields. The study yielded motivating results. Because of decreased electrical conductivity in the frozen/cooled tissue, it experienced temperature induced magnified electric fields in comparison to PEF delivered to the unfrozen tissue control. This suggests that freezing/cooling confines and magnifies the electric fields to those regions; a targeting capability unattainable in traditional PEF. This analysis shows how temperature induced magnified and focused PEFs could be used to ablate cells in the high subzero freezing region of a cryosurgical lesion.

Temperature modulation of electric fields in biological matter

Pulsed electric fields (PEF) have become an important minimally invasive surgical technology for various applications including genetic engineering, electrochemotherapy and tissue ablation. This study explores the hypothesis that temperature dependent electrical parameters of tissue can be used to modulate the outcome of PEF protocols, providing a new means for controlling and optimizing this minimally invasive surgical procedure. This study investigates two different applications of cooling temperatures applied during PEF. The first case utilizes an electrode which simultaneously delivers pulsed electric fields and cooling temperatures. The subsequent results demonstrate that changes in electrical properties due to temperature produced by this configuration can substantially magnify and confine the electric fields in the cooled regions while almost eliminating electric fields in surrounding regions. This method can be used to increase precision in the PEF procedure, and eliminate muscle contractions and damage to adjacent tissues. The second configuration considered introduces a third probe that is not electrically active and only applies cooling boundary conditions. This second study demonstrates that in this probe configuration the temperature induced changes in electrical properties of tissue substantially reduce the electric fields in the cooled regions. This novel treatment can potentially be used to protect sensitive tissues from the effect of the PEF. Perhaps the most important conclusion of this investigation is that temperature is a powerful and accessible mechanism to modulate and control electric fields in biological tissues and can therefore be used to optimize and control PEF treatments.

Cellular apoptosis by nanosecond, high-intensity electric pulses: model evaluation of the pulsing threshold and extrinsic pathway

A simple, bistable rate-equation based model is used to predict trends of cellular apoptosis following electric pulsing. The caspase-8 extrinsic pathway with inherent delays in its activation, cytochrome c release, and an internal feedback mechanism between caspase-3 and cleavage of Bid are incorporated. Results obtained were roughly in keeping with the experimental cell-survival data and include an electrical pulse-number threshold followed by a near-exponential fall-off. The extrinsic caspase-8 mechanism is predicted to be more sensitive than the mitochondrial intrinsic pathway for electric pulse induced cell apoptosis. Also, delays of about an hour are predicted for detectable molecular concentration increases following electrical pulsing. Finally, our results suggest that multi-needle electrode systems with adjustable field orientations would likely enhance apoptosis in the context of pulsed voltage-induced inactivation of tumor cells.

Characterization of plasma mediated molecular delivery to cells in vitro

Ion-based strategies have recently emerged as a method to facilitate molecular delivery. These methods are attractive as they separate the applicator from the treatment site avoiding some issues encountered with other electrically driven methods. Current literature on plasma delivery has shown utility in vitro and in vivo for both drugs and genes. To advance this technology more information must become available on the mechanism responsible for delivery and the effects of ion exposure on eukaryotic cells. This in vitro investigation found that molecular delivery facilitated by a DC-based plasma follows a dose-response behavior, with optimum uptake of Sytox Green occurring in two cell lines after 600 s of exposure. In both cell lines exposure to the discharge caused no adverse effects in viability for exposure times up to 600 s. It was also found that membranes treated with ions remained permeabilized for several minutes following plasma treatment and that membrane resealing exhibited first order kinetics.

A matrix reservoir for improved control of non-viral gene delivery

Non-viral gene delivery suffers from a number of limitations including short transgene expression times and low transfection efficiency. Collagen scaffolds have previously been investigated as in vitro DNA reservoirs, which allow sustained release of genetic information. Efficient viral gene-transfer from these scaffolds has previously been demonstrated. However, due to concerns about the safety of viral gene therapy, the use of non-viral vectors may be preferable. In this study a DNA-dendrimer complex embedded in a cross-linked collagen scaffold was investigated as a reservoir for non-viral delivery. Elution from the scaffolds and transfection of seeded rat mesenchymal stem cells were used to evaluate the scaffold's ability to act as a reservoir for the complexes. Elution from the scaffolds was minimal after 2 days with a total of 25% of the complexes released after 7 days. Extended transgene expression after DNA-dendrimer complex delivery from the scaffolds in comparison to direct delivery to cells was observed. The elongated transfection period and relatively high levels of reporter gene expression are significant advantages over other non-viral gene therapy techniques. This platform has the potential to be an effective method of scaffold-mediated gene delivery suitable for in vitro and in vivo applications.

A time-dependent numerical model of transmembrane voltage inducement and electroporation of irregularly shaped cells

We describe a finite-element model of a realistic irregularly shaped biological cell in an external electric field that allows the calculation of time-dependent changes of the induced transmembrane voltage (Delta Psi) and simulation of cell membrane electroporation. The model was first tested by comparing its results to the time-dependent analytical solution for Delta Psi on a nonporated spherical cell, and a good agreement was obtained. To simulate electroporation, the model was extended by introducing a variable membrane conductivity. In the regions exposed to a sufficiently high Delta Psi, the membrane conductivity rapidly increased with time, leading to a modified spatial distribution of Delta Psi. We show that steady-state models are insufficient for accurate description of Delta Psi, as well as determination of electroporated regions of the membrane, and time-dependent models should be used instead. Our modeling approach also allows direct comparison of calculations and experiments. As an example, we show that calculated regions of electroporation correspond to the regions of molecular transport observed experimentally on the same cell from which the model was constructed. Both the time-dependent model of Delta Psi and the model of electroporation can be exploited further to study the behavior of more complicated cell systems, including those with cell-to-cell interactions.

A simple and reliable electroporation method for human bone marrow mesenchymal stem cells

Adult human mesenchymal stem cells (hMSCs) are able to differentiate into a range of specific cell types in vitro and in vivo, and thus hold tremendous potential for use in regenerative medicine. Despite this promise, deficient understanding of the mechanisms that regulate their differentiation has precluded their widespread use. Genetic manipulation of hMSCs by introduction of transgenes is an indispensable tool for gaining insight into these mechanisms. Like most primary cultures, hMSCs are difficult to transfect with conventional techniques, and although some viral transduction techniques are highly efficient, the protocols require extensive optimization and contain significant health risks. We were generally unable to achieve high transfection efficiencies with lipofection-based reagents that we found, in contrast to electroporation, adversely affected hMSC proliferation and differentiation. Here we report a simple and reliable electroporation protocol that results in transfection efficiencies up to 90% that are comparable to most viral methods while maintaining hMSC stemness. Most importantly, our protocol does not rely on a specific electroporator with preset programs and unique buffers, and is thus much simpler, cheaper, and easier to optimize. Furthermore, we show sustained transgene expression lasting several weeks that was useful for assessing the effects on hMSC function and in transient expression gene therapy.

Mass Transfer Model for Drug Delivery in Tissue Cells with Reversible Electroporation

Reversible electroporation is the temporary permeabilization of the cell membrane through the formation of nano-scale pores that are transient defects in the membrane. These pores are caused by short electrical pulses, typically on the order of a few to several hundred microseconds that are delivered by electroporation electrodes inserted around the treated tissue. Reversible electroporation has become an important technique in molecular medicine. It is used to introduce macromolecules such as genes or anti-cancer drugs, to which the cell membrane is normally not permeable, into the cytosol. For optimal application of molecular medicine, it is important to be able to predict precisely the mass transfer in tissue during reversible electroporation. In this study, we introduce a first attempt at developing a macroscopic mathematical model for analyzing the mass transfer into cells during reversible electroporation of tissue. The model combines a macroscopic model of the electrical fields around electroporation electrodes with a new cells-scale model of electroporation-driven mass transfer and with a macroscopic mass transfer model in tissue. The model is illustrated for a situation typical to that in electrochemotherapy in which cancer is treated with reversible electroporation and a non-cell membrane permeant drug such as bleomycin.

Gene transfer device utilizing micron-spiked electrodes produced by the self-organization phenomenon of Fe-alloy

In the diffusional phase transformation of two-phase alloys, the new phase precipitates form the matrix phase at specific temperatures, followed by the formation of a mixed microstructure comprising the precipitate and the matrix. It has been found that by specific chemical-etching treatment, the precipitate in Fe-25Cr-6Ni alloy projects substantially and clusters at the surface. The configuration of the precipitate has an extremely high aspect ratio: it is several microns in width and several tens of microns in length (known as micron-spiked). This study targets the development of a gene transfer device with a micro-spike produced based on the self-organization phenomenon of the Fe-25Cr-6Ni alloy. With this spike-projected device, we tried to efficiently transfer plasmid DNA into adherent cells by electric pulse-triggered gene transfer using a plasmid-loaded electrode (electroporation-based reverse transfection). The spiked structure was applied to a substrate of the device to allow efficient gene transfer into adherent cells, although the general substrate was flat and had a smooth surface. The results suggest that this unique spike-projected device has potential applications in gene transfer devices for the analysis of the human genome in the post-genome period.

Kinetics of transmembrane transport of small molecules into electropermeabilized cells

The transport of propidium iodide into electropermeabilized Chinese hamster ovary cells was monitored with a photomultiplier tube during and after the electric pulse. The influence of pulse amplitude and duration on the transport kinetics was investigated with time resolutions from 200 ns to 4 ms in intervals from 400 micros to 8 s. The transport became detectable as early as 60 micros after the start of the pulse, continued for tens of seconds after the pulse, and was faster and larger for higher pulse amplitudes and/or longer pulse durations. With fixed pulse parameters, transport into confluent monolayers of cells was slower than transport into suspended cells. Different time courses of fluorescence increase were observed during and at various times after the pulse, reflecting different transport mechanisms and ongoing membrane resealing. The data were compared to theoretical predictions of the Nernst-Planck equation. After a delay of 60 micros, the time course of fluorescence during the pulse was approximately linear, supporting a mainly electrophoretic solution of the Nernst-Planck equation. The time course after the pulse agreed with diffusional solution of the Nernst-Planck equation if the membrane resealing was assumed to consist of three distinct components, with time constants in the range of tens of microseconds, hundreds of microseconds, and tens of seconds, respectively.

In vivo silencing of a molecular target by short interfering RNA electroporation: tumor vascularization correlates to delivery efficiency

Screening for a molecular target for cancer therapy requires multiple steps, of which an important one is evaluation of the knockdown effect of the target molecule on pregrown xenograft tumors. However, methods currently used for local administration of knockdown reagents, such as short interfering RNA (siRNA), are not satisfactory as to simplicity and efficiency. We established an electroporation method involving a constant voltage and "plate and fork" type electrodes and used it for in vivo delivery of siRNA. The delivery efficiency correlated to the electric current. The electric current correlated to the microvascular density and vascular endothelial growth factor (VEGF) expression and exhibited a threshold that guaranteed efficient delivery. Consequently, we showed that the vascularization and VEGF expression in tumors determined the efficiency of delivery of siRNA by electroporation. VEGF was chosen as a model target. VEGF siRNA electroporation suppressed the growth of tumors exhibiting high VEGF expression to less than 10% of the control level, but it had no effect on low VEGF-expressing tumors. Notably, a long interval (20 days) of electroporation was enough to obtain a satisfactory effect. Systemically injected siRNA could also be delivered into tumors by this method. Our data will provide the technical basis for in vivo electroporation, and this simple and efficient siRNA delivery method is applicable to in vivo comprehensive screening for a molecular target.

Electroporation-induced cell lysis in SWLA-2 hybridomas

This paper describes experimental results involving the percentage cell lysis in SWLA-2 murine hybridomas produced by square wave electric field pulses of 100, 200, and 300 V across a 1 mm gap width in a standard cuvette. Pulse lengths were of 0.2 and 0.6 ms duration; 1, 2, or 3 pulses were applied with 100 ms time interval between pulses. Cells were cultured and separate samples examined at 48 hours to determine cell mortality. Nearly 90% cell mortality was produced by applying 3 pulses at of 0.6 ms duration at 300 V.

Feasibility of employing model-based optimization of pulse amplitude and electrode distance for effective tumor electropermeabilization

In electrochemotherapy (ECT) electropermeabilization, parameters (pulse amplitude, electrode setup) need to be customized in order to expose the whole tumor to electric field intensities above permeabilizing threshold to achieve effective ECT. In this paper, we present a model-based optimization approach toward determination of optimal electropermeabilization parameters for effective ECT. The optimization is carried out by minimizing the difference between the permeabilization threshold and electric field intensities computed by finite element model in selected points of tumor. We examined the feasibility of model-based optimization of electropermeabilization parameters on a model geometry generated from computer tomography images, representing brain tissue with tumor. Continuous parameter subject to optimization was pulse amplitude. The distance between electrode pairs was optimized as a discrete parameter. Optimization also considered the pulse generator constraints on voltage and current. During optimization the two constraints were reached preventing the exposure of the entire volume of the tumor to electric field intensities above permeabilizing threshold. However, despite the fact that with the particular needle array holder and pulse generator the entire volume of the tumor was not permeabilized, the maximal extent of permeabilization for the particular case (electrodes, tissue) was determined with the proposed approach. Model-based optimization approach could also be used for electro-gene transfer, where electric field intensities should be distributed between permeabilizing threshold and irreversible threshold-the latter causing tissue necrosis. This can be obtained by adding constraints on maximum electric field intensity in optimization procedure.

Gene therapy used for tissue engineering applications

This review highlights the advances at the interface between tissue engineering and gene therapy. There are a large number of reports on gene therapy in tissue engineering, and these cover a huge range of different engineered tissues, different vectors, scaffolds and methodology. The review considers separately in-vitro and in-vivo gene transfer methods. The in-vivo gene transfer method is described first, using either viral or non-viral vectors to repair various tissues with and without the use of scaffolds. The use of a scaffold can overcome some of the challenges associated with delivery by direct injection. The ex-vivo method is described in the second half of the review. Attempts have been made to use this therapy for bone, cartilage, wound, urothelial, nerve tissue regeneration and for treating diabetes using viral or non-viral vectors. Again porous polymers can be used as scaffolds for cell transplantation. There are as yet few comparisons between these many different variables to show which is the best for any particular application. With few exceptions, all of the results were positive in showing some gene expression and some consequent effect on tissue growth and remodelling. Some of the principal advantages and disadvantages of various methods are discussed.

Electrically Assisted Ocular Gene Therapy

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

Cell Lysis in SWLA-2 Hybridomas due to 1 kHz AC Electric Fields

This paper describes results involving the percentage cell lysis of SWLA-2 murine hybridomas produced by AC electric field pulses at 1 kHz with pulse widths ranging from 1 ms to 1 second. Cells that had been exposed to the electric fields were cultured and replicate samples were examined at 48 hours to determine the number of viable cells.

An examination of the effect of an AC pulsed electric field on cell mortality in SWLA-2 hybridomas

This work describes the initial experimental setup and results involving the percentage cell lysis in SWLA-2 murine hybridomas produced by AC electric field pulses of varying amplitudes and pulse widths. Cells were cultured and separate samples examined at 24 hours. The frequency, pulse width and peak-to-peak voltage were varied. AC electric fields producing at least 1 V across the cell membrane appear to be more effective in producing cell lysis than similar fields producing lower membrane voltages. Additionally, higher frequencies, in the 10 kHz range, appear to be more effective than lower frequencies at membrane voltages above 1 V in producing cell lysis.

An examination of the effect of decaying exponential pulse electric fields on cell mortality in murine spleenocytes, hybridomas, and human natural killer cells

This work describes the percentage cell lysis produced by exponentially decaying electric field pulses of varying amplitudes and time constants. Three different cell types were examined: murine spleenocytes, hybridomas, and human natural killer. Cells were cultured and separate samples examined at 24 hours and 48 hours. Two sets of experiments were performed for each cell type. At 0.3 kV, the spleenocytes exhibited a mortality of roughly 50% twenty-four hours after exposure to the pulse; while at forty-eight hours the spleenocyte cell count had reduced to roughly 25% viable cells. All other cell types showed mortality consistently in excess of 80% at field pulse strengths of about 0.3 V/m.

Complete regression of established subcutaneous B16 murine melanoma tumors after delivery of an HIV-1 Vpr-expressing plasmid by in vivo electroporation

Novel therapies and delivery methods directed against malignancies such as melanoma, and particularly metastatic melanoma, are needed. The HIV-1 accessory protein Vpr (viral protein R) has previously been demonstrated to induce G2 cell cycle arrest as well as in vitro growth inhibition/killing of a number of tumor cells by apoptosis. In vivo electroporation has been utilized as an effective delivery method for pharmacologic agents and DNA plasmids that express "therapeutic" proteins and has been targeted to various tissues, including malignant tumors. For the study reported here, we hypothesized that intratumoral delivery of a Vpr expression plasmid through in vivo electroporation would induce apoptosis and growth attenuation or regression of melanoma tumors. Established subcutaneous B16.F10 melanoma tumors were injected intratumorally with a Vpr-expressing (either 25 or 100 microg) plasmid, followed by electroporation, on day 0 (i.e., when tumors had attained an appropriate size) and day 4. Treatment with 25 or 100 microg of the Vpr-expressing plasmid resulted in complete tumor regression with long-term survival in 14.3 and 7.1% of the mice, respectively. In addition, electroporative delivery of the Vpr-expressing plasmid was shown to induce apoptosis in tumors after intratumoral injection. This is the first report demonstrating the ability of Vpr, when delivered as a DNA expression plasmid with in vivo electroporation, to attenuate melanoma lesion growth and induce complete tumor regression coupled with long-term survival of mice in a highly aggressive and metastatic solid tumor model.

Therapeutic antibody gene transfer: an active approach to passive immunity

Advances in gene transfer approaches are enabling the possibility of applying therapeutic antibodies using DNA. In particular gene transfer in combination with electroporation is promising and can result in generating in vivo antibody concentrations in the low therapeutic range. However, several important problems need to be dealt with before antibody gene transfer can become a valuable supplement to the current therapies. As antibody production following gene transfer is difficult to control, the danger of inducing autoimmune conditions or uncontrollable side effects occurs in cases in which autologous antigens are targeted. It is suggested that the most promising area of application therefore appears to be infectious disease in which heterologous antigens are targeted and concerns for long-term antibody exposure are minimal. Finally, genes encoding fully human antibodies will enhance long-term expression and decrease problems linked to immunogenicity.

Electroporation of transplantable tumour for the enhanced accumulation of photosensitizers

The aim of this study was to verify whether electroporation could increase the accumulation of the hydrophilic photosensitizers: aluminium phthalocyanine tetrasulphonate (AlPcS(4)) and chlorin e(6) (C e(6)) in tumour tissue. The experiment was performed in vivo using hybrid mice (C57Bl/CBA) bearing hepatoma A22 (MH-A22) tumours transplanted in the right haunch. The time dependence of the fluorescence intensity of administered photosensitizers was measured after the ordinary and electrically stimulated delivery. The obtained fluorescence spectroscopy results implied the tumour being affected by an electrical field in a way, which led to a higher accumulation of both photosensitizers (AlPcS(4) and C e(6)) in the periphery of the tumour and it superficial layer. Our pilot study suggests that electroporation could be considered as a useful procedure seeking for the more effective application of photodynamic tumour treatment.

Intraoviductal introduction of plasmid DNA and subsequent electroporation for efficient in vivo gene transfer to murine oviductal epithelium

Various growth factors and proteins produced by oviductal cells have been demonstrated to interact with developing embryos. However, little is known concerning the function of mammalian oviducts at the molecular biological level. This may be partly due to lack of efficient gene transfer to oviductal cells. In this study, we developed an efficient method for transfection of oviductal epithelium using in vivo electroporation (EP) in mice. One microliter of solution containing enhanced green fluorescent protein (EGFP) expression plasmid (0.5 microg) and 0.05% trypan blue (TB) were directly introduced into the ampulla of the eCG-hCG-treated B6C3F1 females at embryonic day (E) 0.6 of pregnancy (corresponding to 14:00-15:00 of the day the plug was recognized). The entire oviduct was then electroporated using tweezer-type electrodes attached to a T820 electroporator (BTX Genetronics, Inc., San Diego, CA) with eight square-wave pulses, 50 V in strength and 50 msec in duration. On E 3.4, embryos at morula/early blastocyst stages were collected and their number, morphology, and EGFP-derived fluorescence recorded. Fluorescence in oviducts was also examined. In some cases, these fluorescent oviducts were subjected to cryostat sectioning. Strong fluorescence was observed in some of the oviductal epithelia, with a maximum level of 36%. Neither the number nor morphology of the collected embryos was affected by EP. Some embryos possessed fluorescence in the blastocoel, but not cytoplasm, suggesting incorporation of EGFP present in the oviductal luminal fluid. This system may enable development of new factors regulating development of preimplantation embryos and offers the prospect of a new approach to understanding oviductal function.

Utilisation de facteurs de croissance pour la réparation osseuse

Osteoformation is induced by numerous growth factors that play an important role in bone repair such as fracture healing. They may serve as therapeutic agent in the treatment of squeletal injuries in the orthopeadic and maxillo-facial fields. Among these proteins, Bone Morphogenetic Proteins (BMP) are the only known osteoinductive growth factors. Unfortunately, they are highly susceptible to proteolysis in vivo and require a suitable delivery system to potentiate their biological activity in a local, controlled and durable manner. In this aim, three options are under investigations: (i) osteoinductive materials made of appropriate carrier to release the protein in situ, (ii) in vivo gene therapy in which the gene is directly transfected in cells of the patient or (iii) ex vivo gene therapy in which cells are harvested from the patient, transfected with DNA in culture and then implanted in the defect. These different kinds of BMP delivery will be discussed.

Nonviral gene transfer to surface skin of mid-gestational murine embryos by intraamniotic injection and subsequent electroporation

The surface epithelium of mid-gestational murine embryos is thought to be an attractive target for gene therapy in vivo, due to its visibility and accessibility from the external surface of the maternal uterus. Almost all studies of in utero gene transfer have adopted viral vectors for infection of fetal epithelium, and depended on intraamniotic introduction and simple incubation of vectors, leading to only infection of the surface layer (periderm) of fetal skin. Here we report a simple and convenient method of gene transfer of plasmid DNA into the deeper portion of surface skin of murine mid-gestational fetus. One to two microlitres of a solution containing a lacZ expression plasmid (0.5-1 microg) and trypan blue (0.05%) were placed onto the surface of a fetus (E 14.5) near the eye by a micropipette attached to a mouthpiece. This fetus was immediately electroporated by placing it between tweezer-type electrodes attached to a square-pulse generator. At 1 and 4 days after gene transfer, fetuses were subjected to histochemical staining for lacZ activity in the presence of X-Gal, a substrate for lacZ. Focal reactions were observed in the skin epidermal layers including periderm and basal layer 1 day after DNA introduction. However, lacZ-positive cells were limited to a skin surface layer, the stratum corneum, in the samples obtained 4 days after gene transfer. Similar observation was also made in the transgenic fetuses (carrying a lacZ gene placed immediately downstream of the loxP-flanked sequence) injected with Cre expression vector. These findings suggest rapid movement of fetal epidermal cells toward the surface during late developmental stages. This local gene transfer approach appears to be effective as a method for skin-targeted gene transfer, enabling study of the role of genes of interest and tracing of cell lineage during fetal skin development.

Visualization through Magnetic Resonance Imaging of DNA Internalized Following “In Vivo” Electroporation

The ability to visualize plasmid DNA entrapment in muscle cells undergoing an "in vivo" electroporation treatment was investigated on BALB/c mice using a 7-T magnetic resonance imaging (MRI) scanner using the paramagnetic Gd-DOTA-spd complex as imaging reporter. Gd-DOTA-spd bears a tripositively charged spermidine residue that yields a strong binding affinity toward the negatively charged DNA chain (6.4 kb, K(a) = 2.2 x 10(3) M(-1) for approximately 2500 +/- 500 binding sites). Cellular colocalization of Gd-DOTA-spd and plasmid DNA has been validated by histological analysis of excised treated muscle. In vivo MRI visualization of Gd-DOTA-spd distribution provides an excellent route to access the cellular entrapment of plasmid DNA upon applying an electroporation pulse.

Spatially and temporally controlled gene transfer by electroporation into adherent cells on plasmid DNA-loaded electrodes

Functional characterization of human genes is one of the most challenging tasks in current genomics. Owing to a large number of newly discovered genes, high-throughput methodologies are greatly needed to express in parallel each gene in living cells. To develop a method that allows efficient transfection of plasmids into adherent cells in spatial- and temporal-specific manners, we studied electric pulse-triggered gene transfer using a plasmid-loaded electrode. A plasmid was loaded on a gold electrode surface having an adsorbed layer of poly(ethyleneimine), and cells were then plated directly onto this modified surface. The plasmid was detached from the electrode by applying a short electric pulse and introduced into the cells cultured on the electrode, resulting in efficient gene expression, even in primary cultured cells. The location of transfected cells could be restricted within a small area on a micropatterned electrode, showing the versatility of the method for spatially controlled transfection. Plasmid transfection could also be performed in a temporally controlled manner without a marked loss of the efficiency when an electric pulse was applied within 3 days after cell plating. The method described here will provide an efficient means to transfer multiple genes, in parallel, into cultured mammalian cells for high-throughput reverse genetics research.

Tissue electroporation: quantification and analysis of heterogeneous transport in multicellular environments

Although electroporation is gaining increased attention as a technology to enhance clinical chemotherapy and gene therapy of tissues, direct measurements of electroporation-mediated transport in multicellular environments are lacking. In this study, we used multicellular tumor spheroids of DU145 prostate cancer cells as a model tissue to measure the levels and distribution of molecular uptake in a multicellular environment as a function of electrical and other parameters. These measurements, and subsequent analysis, were used to test the hypothesis that cells in a multicellular environment respond to electroporation in a heterogeneous manner that differs from isolated cells in suspension due to differences in cell state, local solute concentration, and local electric field. In support of the hypothesis, molecular uptake was consistently lower for cells within spheroids than cells in dilute suspension and was spatially heterogeneous, with progressively less uptake observed for cells located deeper within spheroid interiors. Reduced uptake and heterogeneity can be explained quantitatively by accounting for the effects of cell size on transmembrane voltage and cell volume, limited extracellular solute reservoir, heterogeneous field strength due to influence of neighboring cells, and diffusional lag times.

Gene delivery in bone tissue engineering: progress and prospects using viral and nonviral strategies

Bone tissue loss as a consequence of the natural aging process or as a result of trauma and degenerative disease has led to the need for procedures to generate cartilage and bone for a variety of orthopedic applications. The ability to transfer genes into multipotential mesenchymal stem cells, while still in its infancy, offers considerable therapeutic hope in a variety of musculoskeletal disorders. However, the choice of gene delivery method is key. This review examines the various techniques and methods currently available to enable gene transfer into a target population from viral methods (transduction) to nonviral (transfection) methods and the limitations associated with each method. The potential applications and current understanding of each method are presented. Given the demographic challenge of an aging population, the ultimate goal remains the development of simple, safe, and reproducible strategies for gene delivery that will address the pressing orthopedic clinical imperatives of many.

Electrotransfer of human IL-1Ra into skeletal muscles reduces the incidence of murine collagen-induced arthritis

BACKGROUND

It has previously been demonstrated that high levels of gene expression in skeletal muscles can be achieved after direct in vivo electrotransfer of naked plasmid DNA. The purpose of this study is to examine the potential of in vivo electroporation of plasmid DNA encoding human IL-1Ra for the prevention of murine collagen-induced arthritis (CIA).

METHODS

DBA/1 mice were injected in gastrocnemius muscles with plasmid DNA followed by in vivo electroporation. To uncover the optimum conditions of gene transfer, various electric field strengths and different amounts of plasmid DNA were applied. Calf muscles around the injected areas were investigated with histological methods for damage to muscle tissue. The levels of human IL-1Ra expression in the injected area and also in the serum were determined with ELISA for human IL-1Ra. Based on these data, the effects of electrotransfer of plasmid DNA were tested using the murine CIA model. DBA/1 mice were immunized with bovine collagen type II at the base of the tail. On day 21, mice were given a booster injection with the same antigen. Mice were divided into two groups on day 26. One group of mice received plasmid containing the IL-1Ra cDNA sequence, while control mice were given plasmid lacking the IL-1Ra coding sequence. The incidence of arthritis was evaluated by macroscopic analysis, histological analysis, and the levels of inflammatory cytokines.

RESULTS

IL-1Ra expression increased as a function of the electrical field strength and the amount of DNA. 200 V/cm (eight pulses; 20 ms per pulse; 1 Hz) and 15 microg of plasmid DNA per mouse were found to be optimum for gene transfer. After in vivo electroporation, gene expression in both muscle and serum increased gradually, reaching a peak value on day 10. Significant levels of human IL-1Ra expression were maintained for 20 days. Macroscopic analysis showed that the onset of CIA was significantly inhibited by direct electrotransfer of plasmid DNA encoding human IL-1Ra. Histological analysis of knee joints showed that the incidence of arthritis in knee joints was also prevented. The levels of mouse IL-1beta and IL-12 in paws were significantly lower in the group treated with IL-1Ra than those in the control group.

CONCLUSIONS

These results demonstrate that direct electrotransfer of plasmid containing the human IL-1Ra cDNA sequence to skeletal muscle can reduce the incidence of CIA in mice.

Electroporation-mediated and EBV LMP1-regulated gene therapy in a syngenic mouse tumor model

Latent membrane protein 1 (LMP1) is an Epstein-Barr virus (EBV)-encoded oncogene expressed in EBV-associated nasopharyngeal carcinoma (NPC). Previous studies indicate that a strategy combining LMP1-mediated NF-kappaB activation and the HSV thymidine kinase/Ganciclovir (HSVtk/GCV) prodrug system leads to regression of tumor growth in nude mice. To improve the efficacy of this strategy in immunocompetent hosts, we developed a therapeutic cassette, p6kappaB-EDL1E-tk, containing six copies of the NF-kappaB binding motif and an epithelial-specific EBV promoter, ED-L1E. The cassette was tested in a murine CT-26 carcinoma model in syngenic Balb/c mice. Coinjection of an LMP1-expressing vector and p6kappaB-EDL1E-tk by in vivo electroporation in mouse muscle revealed at least two-fold higher TK enzymatic activity than that of previously tested pLTR-tk. Furthermore, growth was attenuated in a group of mice containing LMP1-positive tumors that were intratumorally injected with the p6kappaB-EDL1E-tk cassette and GCV via in vivo electroporation, but not in mice treated with p6kappaB-EDL1E-tk or GCV alone. Similarly, no retardation of tumor growth was observed in mice containing LMP1-negative CT-26 tumors injected with both the p6kappaB-EDL1E-tk cassette and GCV. We propose that intratumoral injection of therapeutic agents, such as DNA of transcription-regulated cassette and GCV, via in vivo electroporation may be used as an alternative treatment for EBV LMP1-expressing cancers.

Gene packaging with lipids, peptides and viruses inhibits transfection by electroporation in vitro

To develop improved methods of gene delivery, packaging DNA in chemical or viral vectors could increase electroporation-mediated transfection. To test this hypothesis, electroporation was applied to DU145 prostate cancer cells incubated with green fluorescent protein-encoded DNA plasmid either naked or packaged with cationic lipid (Lipofectin), polycationic peptide (salmon protamine) or retroviral vectors (Moloney murine leukemia viruses) and then assayed for gene expression and cell viability. Cationic lipid or electroporation alone each significantly increased transfection, but their combination was less effective. Addition of protamine peptide during electroporation was also less effective than electroporation alone. The combination of retroviral vectors and electroporation transfected fewer cells than retrovirus alone. We conclude that the combination of electroporation with chemical or viral vectors does not improve gene transfection in vitro.

Somatic gene transfer into the lactating ovine mammary gland

BACKGROUND

Somatic gene therapy requires safe and efficient techniques for the gene transfer procedure. The ovine mammary gland is described as a model system for the evaluation of somatic gene transfer methods.

METHODS

Different gene delivery formulations were retrogradely injected into the mammary gland of lactating sheep. The efficiency of the gene transfer was subsequently measured by the detection of the secreted transgene products in the milk. To counteract the milk flow in the lactating gland caused by the permanent milk production, a newly developed pretreatment of the mammary gland with hyperosmotic solutions was applied. In addition, in vivo electroporation of DNA into the mammary gland is described.

RESULTS

Gene transfer using naked DNA or simple complexes of DNA with polycations did not result in traceable amounts of reporter gene products. However, utilizing the complex cationic lipid DOSPER, a peak expression of about 400 ng/ml was observed 6 days after transfection. Maximum expression rates of more than 1 microg/ml were obtained by combining hyperosmotic pretreatment and receptor-mediated gene transfer. For the in vivo electroporation, the proof of principle for this technique in the mammary gland is reported.

CONCLUSIONS

The ovine mammary gland turned out to be a very well suited as a model system for evaluation and optimization of various gene transfer protocols.

A syringe electrode device for simultaneous injection of DNA and electrotransfer

Electroporation for gene delivery has attracted considerable attention recently, because of both the site-specific nature of the delivery and the high efficiency of the method. Electrotransfer of genes involves the application of an electric field to cells to enhance their permeability, facilitating exogenous polynucleotide transit across the cytoplasmic membrane. However, the relatively high electric field strength required for electroporation induces tissue damage, thus limiting its widespread application. We describe here a syringe electrode of our design, with which the same transfection efficiency can be achieved by using much lower electric field strength than that of conventional electrodes, such that the tissue damage is minimized.

Intravenous delivery of naked plasmid DNA for in vivo cytokine expression

We previously demonstrated that electroporation-mediated cytokine gene delivery into muscle is an effective approach for long-term systemic delivery of cytokines. Here we show that hydrodynamics-based gene delivery into mice by intravenous administration of naked plasmid DNA is a more efficient procedure for expressing cytokines in vivo. A large volume of Ringer's solution containing an interleukin-10 (IL-10) expression plasmid pCAGGS-IL10 was rapidly injected into the tail vein of mice. Serum IL-10 levels increased in a dose-dependent manner with a saturation level (50.8 +/- 12.1 microg/ml) 10,000-fold higher than we obtained by the electroporation-mediated method. High levels of serum IL-10 were sustained for at least 2 weeks following a single injection. These results demonstrate that hydrodynamics-based gene delivery could induce sustained high-level expression of cytokines, which would be useful for further studies of cytokine function in vivo and the development of novel immunotherapeutic strategies for systemic cytokine gene therapy.

Prediction and optimization of gene transfection and drug delivery by electroporation

Although electroporation is widely used for laboratory gene transfection and gaining increased importance for nonviral gene therapy, it is generally employed using trial-and-error optimization schemes for lack of methods to predict electroporation's effects on cells. Therefore, we used a statistical approach to quantitatively predict molecular uptake and cell viability following electroporation and show that it predicts both in vitro and in vivo results for a wide range of molecules, including DNA, in 60 different cell types. Mechanistically, this broad predictive ability suggests that electroporation is mediated primarily by lipid bilayer structure and only secondarily by cell-specific characteristics. For gene therapy applications, this approach should facilitate rational design of electroporation protocols.

In vivo electroporation-mediated transfer of interleukin-12 and interleukin-18 genes induces significant antitumor effects against melanoma in mice

Direct intratumoral transfection of cytokine genes was performed by means of the in vivo electroporation as a novel therapeutic strategy for cancer. Plasmid vectors carrying the firefly luciferase, interleukin (IL)-12 and IL-18 genes were injected into established subcutaneous B16-derived melanomas followed by electric pulsation. When plasmid vectors with Epstein--Barr virus (EBV) nuclear antigen 1 (EBNA1) gene were employed, the expression levels of the transgenes were significantly higher in comparison with those obtained with conventional plasmid vectors. In consequence of the transfection with IL-12 and IL-18 genes, serum concentrations of the cytokines were significantly elevated, while interferon (IFN)-gamma also increased in the sera of the animals. The IL-12 gene transfection resulted in significant suppression of tumor growth, while the therapeutic effect was further improved by co-transfection with IL-12 and IL-18 genes. Repetitive co-transfection with IL-12 and IL-18 genes resulted in significant prolongation of survival of the animals. Natural killer (NK) and cytotoxic T lymphocyte (CTL) activities were markedly enhanced in the mice transfected with the cytokine genes. The present data suggest that the cytokine gene transfer can be successfully achieved by in vivo electroporation, leading to both specific and nonspecific antitumoral immune responses and significant therapeutic outcome.