Electroporation for targeted gene transfer

Suppression of cancer growth by nonviral gene therapy based on a novel reactive oxygen species-responsive promoter

Increased reactive oxygen species (ROS) production has been reported as a distinctive feature of different pathologies including cancer. Therefore, we assessed whether increased ROS production in the cancer microenvironment could be selectively exploited to develop a selective anticancer therapy. For this purpose, we constructed a novel chimeric promoter, based on a ROS-response motif located in the VEGF gene promoter placed, in turn, downstream of a second ROS-response motif obtained from the early growth response 1 (Egr-1) gene promoter. The activity of the chimeric promoter was largely dependent on variations in intracellular ROS levels and showed a high inducible response to exogenous H(2)O(2). Transient expression of the thymidine kinase (TK) gene driven by the chimeric promoter, followed by gancyclovir (GCV) administration, inhibited human colorectal cancer and melanoma cell growth in vitro and in vivo. Moreover, electrotransfer of the TK gene followed by GCV administration exerted a potent therapeutic effect on established tumors. This response was improved when combined with chemotherapeutic drugs. Thus, we show for the first time that a distinctive pro-oxidant state can be used to develop new selective gene therapeutics for cancer.

Nonviral jet-injection technology for intratumoral in vivo gene transfer of naked DNA

The main challenges for application of gene therapy to patients are poor selectivity in vector targeting, insufficient gene transfer, and great difficulties in systemic treatment in association with safety concerns for particular vector systems. For success in gene therapy, safe, applicable, and efficient transfer technologies are required. Because of the complex nature of targeted vector delivery to the tumor, our strategy for gene therapy is focused on the development of local nonviral gene transfer. This approach of local interference with tumor growth and progression could contribute to better control of the disease. Transfer of naked DNA is an important alternative to liposomal or viral systems. Different physical procedures are used for improved delivery of naked DNA into the target cells or tissues in vitro and in vivo. Among the various nonviral gene delivery technologies, jet-injection is gaining increased attractiveness, because this technique allows gene transfer into different tissues with deep penetration of naked DNA by circumventing the disadvantages associated with, e.g., viral vectors. The jet-injection technology is based on jets of high velocity for penetration of the skin and underlaying tissues, associated with efficient transfection of the affected area. The jet-injection technology has been successfully applied for in vivo gene transfer in different tumor models. More importantly, the efficacy and safety of jet-injection gene transfer have recently been investigated in a phase I clinical trial.

Targeted gene silencing into solid tumors with electrically mediated siRNA delivery

Short interfering RNAs (siRNAs) represent new potential therapeutic tools, owing to their capacity to induce strong, sequence-specific gene silencing in cells. However, their clinical development requires new, safe, and efficient in vivo siRNA delivery methods. In this study, we report an efficient in vivo approach for targeting gene knockdown in solid tumors by the use of external electric field pulses. We show that gene silencing is efficiently obtained in vivo with chemically synthesized siRNA after targeted electrical delivery in the tumor-bearing mouse. The associated gene silencing was followed on the same animal by fluorescence imaging and confirmed by qPCR. Gene silencing obtained in tumors lasted from 2 to 4 days after a single treatment. Therefore, this method should allow gene function analysis or organ treatment by a localized delivery of siRNAs.

In vivo reversal of P-glycoprotein-mediated multidrug resistance by efficient delivery of stealth RNAi

P-Glycoprotein-mediated multidrug resistance (MDR) is a major hurdle in cancer therapy. P-Glycoprotein is a 170 KD protein encoded by the MDR1 gene. Over-expression of P-glycoprotein is considered one of the characteristics of the MDR phenotype, thus down-regulation of the MDR1 gene expression will circumvent MDR partly. RNA interference (RNAi) is a process that can result in sequence-specific gene silencing by cleavage target mRNA. Electroporation has been demonstrated to be a promising and efficient method for gene delivery and has been successfully applied in gene therapy. In our study, by using electric pulse to delivery Stealth RNAi into nude mice NCI-H460 tumour xenografts, we successfully inhibited MDR1 both at the mRNA level as determined by reverse transcription-polymerase chain reaction and at the protein level as determined by immunohistochemistry. Furthermore, by administration of navelbine after transfection with Stealth RNAi targeted on the MDR1 gene, its depression to tumour xenografts dramatically improved by nine times. These studies demonstrate that through electrotransfection of Stealth RNAi, P-glycoprotein-mediated MDR can be reversed.

Physical approaches for nucleic acid delivery to liver

The liver is a key organ for numerous metabolic pathways and involves many inherited diseases that, although being different in their pathology, are often caused by lack or overproduction of a critical gene product in the diseased cells. In principle, a straightforward method to fix such problem is to introduce into these cells with a gene-coding sequence to provide the missing gene product or with the nucleic acid sequence to inhibit production of the excessive gene product. Practically, however, success of nucleic acid-based pharmaceutics is dependent on the availability of a method capable of delivering nucleic acid sequence in the form of DNA or RNA to liver cells. In this review, we will summarize the progress toward the development of physical methods for nucleic acid delivery to the liver. Emphasis is placed on the mechanism of action, pros, and cons of each method developed so far. We hope the information provided will encourage new endeavor to improve the current methodologies or develop new strategies that will lead to safe and effective delivery of nucleic acids to the liver.

Relaxin treatment of solid tumors: effects on electric field-mediated gene delivery

Pulsed electric fields have been shown to enhance interstitial transport of plasmid DNA (pDNA) in solid tumors in vivo. However, the extent of enhancement is still limited partly due to the collagen component in extracellular matrix. To this end, effects of collagen remodeling on interstitial electrophoresis were investigated by pretreatment of tumor-bearing mice with a recombinant human relaxin (rh-Rlx). In the study, two tumor lines (4T1 and B16.F10) were examined and implanted s.c. to establish two murine models: dorsal skin-fold chamber (DSC) and hind leg. Effects of rh-Rlx on pDNA electrophoresis were measured either directly in the DSC model or indirectly in the hind leg model via reporter gene expression. It was observed that rh-Rlx treatment reduced collagen levels in the hind leg tumors but not in the DSC tumors. The observation correlated with the results from electromobility experiments, where rh-Rlx treatment enhanced transgene expression in 4T1 hind leg tumors but did not increase the electromobility of pDNA in the DSC tumors. In addition, it was observed that pDNA binding to collagen could block its diffusion in collagen gel in vitro. These observations showed that effects of rh-Rlx on the collagen content depended on microenvironment in solid tumors and that rh-Rlx treatment would enhance electric field-mediated gene delivery only if it could effectively reduce the collagen content in collagen-rich tumors.

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

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

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.

Current progress of DNA vaccine studies in humans

Despite remarkable progress in the field of DNA vaccine research since its discovery in the early 1990 s, the formal acceptance of this novel technology as a new modality of human vaccines depends on the successful demonstration of its safety and efficacy in advanced clinical trials. Although clinical trials conducted so far have provided overwhelming evidence that DNA vaccines are well tolerated and have an excellent safety profile, the early designs of DNA vaccines failed to demonstrate sufficient immunogenicity in humans. However, studies conducted over the last few years have led to promising results, particularly when DNA vaccines were used in combination with other forms of vaccines. Here, we provide a review of the data from reported DNA vaccine clinical studies with an emphasis on the ability of DNA vaccines to elicit antigen-specific, cell-mediated and antibody responses in humans. The majority of these trials are designed to test candidate vaccines against several major human pathogens and the remaining studies tested the immunogenicity of therapeutic vaccines against cancer.

Safety and immunogenicity of recombinant low-dosage HIV-1 A vaccine candidates vectored by plasmid pTHr DNA or modified vaccinia virus Ankara (MVA) in humans in East Africa

The safety and immunogenicity of plasmid pTHr DNA, modified vaccinia virus Ankara (MVA) human immunodeficiency virus type 1 (HIV-1) vaccine candidates were evaluated in four Phase I clinical trials in Kenya and Uganda. Both vaccines, expressing HIV-1 subtype A gag p24/p17 and a string of CD8 T-cell epitopes (HIVA), were generally safe and well-tolerated. At the dosage levels and intervals tested, the percentage of vaccine recipients with HIV-1-specific cell-mediated immune responses, assessed by a validated ex vivo interferon gamma (IFN-gamma) ELISPOT assay and Cytokine Flow Cytometry (CFC), did not significantly differ from placebo recipients. These trials demonstrated the feasibility of conducting high-quality Phase 1 trials in Africa.

Mechanistic analysis of electroporation-induced cellular uptake of macromolecules

Pulsed electric field has been widely used as a nonviral gene delivery platform. The delivery efficiency can be improved through quantitative analysis of pore dynamics and intracellular transport of plasmid DNA. To this end, we investigated mechanisms of cellular uptake of macromolecules during electroporation. In the study, fluorescein isothiocyanate-labeled dextran (FD) with molecular weight of 4,000 (FD-4) or 2,000,000 (FD-2000) was added into suspensions of a murine mammary carcinoma cell (4T1) either before or at different time points (ie, 1, 2, or 10 sec) after the application of different pulsed electric fields (in high-voltage mode: 1.2-2.0 kV in amplitude, 99 microsec in duration, and 1-5 pulses; in low-voltage mode: 100-300 V in amplitude, 5-20 msec in duration, and 1-5 pulses). The intracellular concentrations of FD were quantified using a confocal microscopy technique. To understand transport mechanisms, a mathematical model was developed for numerical simulation of cellular uptake. We observed that the maximum intracellular concentration of FD-2000 was less than 3% of that in the pulsing medium. The intracellular concentrations increased linearly with pulse number and amplitude. In addition, the intracellular concentration of FD-2000 was approximately 40% lower than that of FD-4 under identical pulsing conditions. The numerical simulations predicted that the pores larger than FD-4 lasted <10 msec after the application of pulsed fields if the simulated concentrations were on the same order of magnitude as the experimental data. In addition, the simulation results indicated that diffusion was negligible for cellular uptake of FD molecules. Taken together, the data suggested that large pores induced in the membrane by pulsed electric fields disappeared rapidly after pulse application and convection was likely to be the dominant mode of transport for cellular uptake of uncharged macromolecules.

The relative immunogenicity of DNA vaccines delivered by the intramuscular needle injection, electroporation and gene gun methods

Immunogenicity of DNA vaccines varies significantly due to many factors including the inherent immunogenicity of the protein antigen encoded in the DNA vaccine, the optimal immune responses that can be achieved in different animal models and in humans with different genetic backgrounds and, to a great degree, the delivery methods used to administer the DNA vaccines. Based on published results, only the gene gun-mediated delivery approach has been able to elicit protective levels of immune responses in healthy, adult volunteers by DNA immunization alone without the use of another vaccine modality as a boost. Recent results from animal studies suggest that electroporation is also effective in eliciting high level immune responses. However, there have been no reports to identify the similarities and differences between these two leading physical delivery methods for DNA vaccines against infectious disease targets. In the current study, we compared the relative immunogenicity of a DNA vaccine expressing a hemagglutinin (HA) antigen from an H5N1 influenza virus in two animal models (rabbit and mouse) when delivered by either intramuscular needle immunization (IM), gene gun (GG) or electroporation (EP). HA-specific antibody, T cell and B cell responses were analyzed. Our results indicate that, overall, both the GG and EP methods are more immunogenic than the IM method. However, EP and IM stimulated a Th-1 type antibody response and the antibody response to GG was Th-2 dominated. These findings provide important information for the further selection and optimization of DNA vaccine delivery methods for human applications.

Lipid-based nanoparticles for nucleic acid delivery

Lipid-based colloidal particles have been extensively studied as systemic gene delivery carriers. The topic that we would like to emphasize is the formulation/assembly of lipid-based nanoparticles (NP) with diameter under 100 nm for delivering nucleic acid in vivo. NP are different from cationic lipid-nucleic acid complexes (lipoplexes) and are vesicles composed of lipids and encapsulated nucleic acids with a diameter less than 100 nm. The diameter of the NP is an important attribute to enable NP to overcome the various in vivo barriers for systemic gene delivery such as: the blood components, reticuloendothelial system (RES) uptake, tumor access, extracellular matrix components, and intracellular barriers. The major formulation factors that impact the diameter and encapsulation efficiency of DNA-containing NP include the lipid composition, nucleic acid to lipid ratio and formulation method. The particle assembly step is a critical one to make NP suitable for in vivo gene delivery. NP are often prepared using a dialysis method either from an aqueous-detergent or aqueous-organic solvent mixture. The resulting particles have diameters about 100 nm and nucleic acid encapsulation ratios are >80%. Additional components can then be added to the particle after it is formed. This ordered assembly strategy enables one to optimize the particle physico-chemical attributes to devise a biocompatible particle with increased gene transfer efficacy in vivo. The components included in the sequentially assembled NP include: poly(ethylene glycol) (PEG)-shielding to improve the particle pharmacokinetic behavior, a targeting ligand to facilitate the particle-cell recognition and in some case a bioresponsive lipid or pH-triggered polymer to enhance nucleic acid release and intracellular trafficking. A number of groups have observed that a PEG-shielded NP is a robust and modestly effective system for systemic gene or small interfering RNA (siRNA) delivery.

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.

Nonviral gene delivery: what we know and what is next

Gene delivery using nonviral approaches has been extensively studied as a basic tool for intracellular gene transfer and gene therapy. In the past, the primary focus has been on application of physical, chemical, and biological principles to development of a safe and efficient method that delivers a transgene into target cells for appropriate expression. This review summarizes the current status of the most commonly used nonviral methods, with an emphasis on their mechanism of action for gene delivery, and their advantages and limitations for gene therapy applications. The technical aspects of each delivery system are also reviewed, with a focus on how to achieve optimal delivery efficiency. A brief discussion of future development and further improvement of the current systems is intended to stimulate new ideas and encourage rapid advancement in this new and promising field.

In vivo gene silencing in solid tumors by targeted electrically mediated siRNA delivery

RNA interference (RNAi)-mediated gene silencing approaches appear very promising for therapies based on the targeted inhibition of disease-relevant genes. The major hurdle to the therapeutic development of RNAi strategies remains, however, the efficient delivery of the RNAi-inducing molecules, the short interfering RNAs (siRNAs) and short hairpin RNAs (shRNAs), to the target tissue. With respect to cancer treatment the development of efficient delivery methods into solid tumors appears as a critical issue. However, very few studies have addressed this problem. In this study we have investigated the contribution of electrically mediated delivery of siRNA into murine tumors stably expressing an enhanced green fluorescent protein (EGFP) target reporter gene. The silencing of EGFP gene expression was quantified over time by fluorescence imaging in the living animal. Our study indicates that electric field can be used as an efficient method for siRNA delivery and associated gene silencing into cells of solid tumors in vivo.

Regenerative endodontics: a review of current status and a call for action

Millions of teeth are saved each year by root canal therapy. Although current treatment modalities offer high levels of success for many conditions, an ideal form of therapy might consist of regenerative approaches in which diseased or necrotic pulp tissues are removed and replaced with healthy pulp tissue to revitalize teeth. Researchers are working toward this objective. Regenerative endodontics is the creation and delivery of tissues to replace diseased, missing, and traumatized pulp. This review provides an overview of regenerative endodontics and its goals, and describes possible techniques that will allow regenerative endodontics to become a reality. These potential approaches include root-canal revascularization, postnatal (adult) stem cell therapy, pulp implant, scaffold implant, three-dimensional cell printing, injectable scaffolds, and gene therapy. These regenerative endodontic techniques will possibly involve some combination of disinfection or debridement of infected root canal systems with apical enlargement to permit revascularization and use of adult stem cells, scaffolds, and growth factors. Although the challenges of introducing endodontic tissue engineering therapies are substantial, the potential benefits to patients and the profession are equally ground breaking. Patient demand is staggering both in scope and cost, because tissue engineering therapy offers the possibility of restoring natural function instead of surgical placement of an artificial prosthesis. By providing an overview of the methodological issues required to develop potential regenerative endodontic therapies, we hope to present a call for action to develop these therapies for clinical use.

Therapeutic RNA interference of malignant melanoma by electrotransfer of small interfering RNA targeting Mitf

Microphthalmia-associated transcription factor (Mitf) is critically involved in melanin synthesis as well as differentiation of cells of the melanocytic lineage. Some earlier studies suggested that Mitf is also essential in the survival of melanoma cells, but this notion remains controversial. We synthesized short interfering RNA (siRNA) duplexes corresponding to the mitf sequence and transfected them into B16 melanoma. Lipid-mediated transfection in vitro of Mitf-specific siRNA resulted in specific downregulation of Mitf and of the tyrosinase that is a transcriptional target of Mitf. This treatment also remarkably reduced the viability of melanoma cells by inducing apoptosis. To examine the potential feasibility of RNAi therapy against melanoma, B16 cells were subcutaneously injected into syngenic mice and siRNA was transfected into the pre-established tumor by means of electroporation. The Mitf-specific siRNA drastically reduced outgrowth of subcutaneous melanoma, while nonspecific siRNA failed to affect tumor progression. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling-based analysis of tumor specimens demonstrated that the tumor cells transfected with Mitf-siRNA effectively underwent apoptosis in vivo. The present results indicate that Mitf plays important roles in melanoma survival. Intratumor electrotransfer of Mitf-specific siRNA may provide a powerful strategy for therapeutic intervention of malignant melanoma.

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.

Regression of subcutaneous B16 melanoma tumors after intratumoral delivery of an IL-15-expressing plasmid followed by in vivo electroporation

In vivo electroporation has been used to efficiently deliver drugs and 'therapeutic' genes to tumors, including melanoma lesions. This study reports on the effect of intratumoral delivery of an optimized DNA plasmid expressing interleukin-15 (pIL-15) on established murine melanoma tumors. IL-15 has been demonstrated to have a pivotal role in the function of memory CD8+ T cells and natural killer cells, which are critical for tumor immunosurveillance. In this study, C57BL/6 mice were injected with B16.F10 melanoma cells and randomized into different experimental groups: untreated (P-V-E-), treated with pIL-15 (P+) or backbone plasmid (V+), with or without electroporation (E+ or E-). Treatment was performed intratumorally with 50 microg of plasmid on days 0, 4 and 7 and tumor volume/size, tumor regression and long-term survival were measured. At day 100 after initiation of treatment, the percentage of mice surviving with complete tumor regression in the P-V+E+, P+V-E-, P+V-E+ and P-V-E- treatment groups were 0, 12.5, 37.5 and 0%, respectively. These results demonstrate the ability of pIL-15 to mediate B16 melanoma regression, with the effect being significantly enhanced by electroporative delivery. This is the first description of the ability of a naked DNA plasmid expressing IL-15 to alone mediate complete regression of B16 melanoma tumors and underscores the potential clinical use of these plasmids for the treatment of malignant tumors when delivered with in vivo electroporation.

Evaluation of toxicity following electrically mediated interleukin-12 gene delivery in a B16 mouse melanoma model

PURPOSE

Interleukin-12 (IL-12) has potential as an immunotherapeutic agent for the treatment of cancer but is unfortunately associated with toxicity. Delivery of a plasmid encoding IL-12 with electroporation induces an antitumor effect in the B16 mouse melanoma model without serious side effects. To translate this observation to the clinic, an evaluation of toxicity was done in the mouse model.

EXPERIMENTAL DESIGN

Weight change, tumor response, blood chemistry and hematology values, and serum IL-12 levels were evaluated. Multiple tissues were analyzed histopathologically.

RESULTS

A pronounced reduction in tumor volume, including a large percentage of complete regressions, was observed after electrically mediated gene therapy. No significant increases in serum IL-12 levels were detected. Tumor-bearing mice showed an increased number of atypical hematology values when compared with normal naive controls. Statistically significant differences in chemistry and hematology values were observed sporadically in most of the standard chemistry and hematology categories in all groups. The only histopathologic abnormality specific to the animals receiving both plasmid and electroporation was inflammation associated with the kidney at the last time point.

CONCLUSIONS

In general, mice that received both plasmid and electroporation showed the least abnormal histopathologic findings and were found to be in the best health, reflecting the reduced burden of disease. No significant toxic effects due to the IL-12 gene therapy were observed.

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

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