Electroporation: theory and methods, perspectives for drug delivery, gene therapy and research

Optimization of electroporation parameters for the intramuscular delivery of plasmids in pigs

Increased transgene expression after plasmid transfer to the skeletal muscle is obtained with electroporation in many species, but optimum conditions are not well defined. Using a plasmid with a muscle-specific secreted embryonic alkaline phosphatase (SEAP) gene, we have optimized the electroporation conditions in a large mammal (pig). Parameters tested included electric field intensity, number of pulses, lag time between plasmid injection and electroporation, and plasmid delivery volume. Electric pulses, between 0.4 and 0.6 Amp constant current, applied 80 sec after the injection of 0.5 mg SEAP-expressing plasmid in a total volume of 2 mL produced the highest levels of expression. Further testing demonstrated that electroporation of a nondelineated injection site reduces the levels of SEAP expression. These results demonstrate that electroporation parameters such as amperage, lag time, and the number of pulses are able to regulate the levels of reporter gene expression in pigs.

Detection of integration of plasmid DNA into host genomic DNA following intramuscular injection and electroporation

Plasmid vectors have been widely used for DNA vaccines and gene therapy. Following intramuscular injection, the plasmid that persists is extrachromosomal and integration into host DNA, if it occurs at all, is negligible. However, new technologies for improving DNA delivery could increase the frequency of integration. In the present study, we tested the effect of electroporation on plasmid uptake and potential integration following intramuscular injection in mice, using a plasmid containing the mouse erythropoietin gene. Electroporation increased plasmid tissue levels by approximately six- to 34-fold. Using a quantitative gel-purification assay for integration, electroporation was found to markedly increase the level of plasmid associated with high-molecular-weight genomic DNA. To confirm integration and identify the insertion sites, we developed a new assay - referred to as repeat-anchored integration capture (RAIC) PCR - that is capable of detecting rare integration events in a complex mixture in vivo. Using this assay, we identified four independent integration events. Sequencing of the insertion sites suggested a random integration process, but with short segments of homology between the vector breakpoint and the insertion site in three of the four cases. This is the first definitive demonstration of integration of plasmid DNA into genomic DNA following injection in vivo.

Enhanced biotransformations and product recovery in a membrane bioreactor through application of a direct electric current

The simultaneous enhancement of biotransformation coupled to product recovery, purification and concentration is presented. The nitrilase of Rhodococcus rhodochrous LL100-21 catalyses the single-step hydrolytic biotransformation of benzonitrile to benzoic acid and ammonia. When a direct electric current is applied across a bioreactor containing the bacterium and benzonitrile, the charged product (benzoic acid) can be removed in situ across an anion exchange membrane and recovered in a separate compartment. Over the course of a 24-hour biotransformation, benzonitrile was converted to benzoic acid which was completely removed from the bioreactor chamber and concentrated 3-fold in a separate chamber. The rate of production of benzoic acid increased by 42% when the current was applied (0.044 mmol/min/g dry cell weight in the presence of current as compared to 0.03 mmol/min/g dry cell weight in its absence). The enhanced reaction rate was achieved irrespective of product separation and therefore appears to be a direct effect upon the bacterial cells. This process has potential for enhanced productivity from biotransformations through a simultaneous increase in metabolic activity and in situ product recovery.

Cell and Animal Imaging of Electrically Mediated Gene Transfer

Electropermeabilization is a nonviral method successfully used to transfer genes into cells in vitro as in vivo. Although it shows promise in field of gene therapy, very little is known on the basic processes supporting the DNA transfer. The aim of the present investigation is to visualize gene electrotransfer and expression both in vitro and in vivo. In vitro studies have been performed by using digitized fluorescence microscopy. Membrane permeabilization occurs at the sides of the cell membrane facing the two electrodes. A free diffusion of propidium iodide across the membrane to the cytoplasm is observed in the seconds following electric pulses. Fluorescently labeled plasmids only interact with the electropermeabilized side of the cell facing the cathode. The plasmid interaction with the electropermeabilized cell surface is stable over a few minutes. Changing the polarity and the orientation of the pulses lead to an increase in gene expression. In vivo experiments have been performed in Tibialis Cranialis mice muscle. Electric field application lead to the in vivo expression of plasmid DNA. We directly visualize gene expression of the Green Fluorescent Protein (GFP) on live animals. GFP expression is shown to be increased by applying electric field pulses with different polarities and orientations.

Effects of Electrogenetherapy with p53wt Combined with Cisplatin on Survival of Human Tumor Cell Lines with Different p53 Status

The aim of our study was to evaluate electrogenetherapy with p53wt alone or combined with cisplatin on two colorectal (HT-29 and LoVo) and two prostatic (PC-3 and Du145) carcinoma cell lines with different p53 status. In addition, the feasibility of electrogenetherapy with p53wt was tested also in vivo on PC-3 prostatic cancer xenografts. Electrogenetherapy with p53wt was dependent on the p53 status of the cell lines used. Electrogenetherapy was the most effective on the PC-3 (p53 null) and Du145 (p53mt) cells, and to the much lesser extent in LoVo cells (p53wt). The exception was the HT-29 cell line with overexpressed mutated p53, where electrogenetherapy with p53wt was the least effective. Sensitivity of the cell lines to cisplatin was independent of the p53 status. Furthermore, the presence of exogenous p53 due to electrogenetherapy did not enhance cisplatin cytotoxicity, since the combination of these therapies resulted in additive cytotoxic effect. The effectiveness of electrogenetherapy with p53wt was also demonstrated in vivo by successful treatment of subcutaneous PC-3 tumors in mice. In conclusion, our study shows that electrogenetherapy with p53wt is feasible, and resulted in comparable cytotoxic and antitumor effectiveness to viral-mediated p53wt gene therapy. This therapy was effective and dependent on the p53 status of the tumor cell lines. Combination of electrogenetherapy and cisplatin resulted in additional cell kill by cisplatin, and was not dependent on the p53 status.

Primer on medical genomics. Part X: Gene therapy

Gene therapy is defined as any therapeutic procedure in which genes are intentionally introduced into human somatic cells. Both preclinical and clinical gene therapy research have been progressing rapidly during the past 15 years; gene therapy is now a highly promising new modality for the treatment of numerous human disorders. Since the first clinical test of gene therapy in 1989, more than 600 gene therapy protocols have been approved, and more than 3000 patients have received gene therapy. However, at the time of writing this article, no gene therapy products have been approved for clinical use. This article explains the potential clinical scope of gene therapy and the underlying pharmacological principles, describes some of the major gene transfer systems (or vectors) that are used to deliver genes to their target sites, and discusses the various strategies for controlling expression of therapeutic transgenes. Safety issues regarding clinical use of gene therapy are explored, and the most important technical challenges facing this field of research are highlighted. This review should serve as an introduction to the subject of gene therapy for clinician investigators, physicians and medical scientists in training, practicing clinicians, and other students of medicine.

Target discovery

Target discovery, which involves the identification and early validation of disease-modifying targets, is an essential first step in the drug discovery pipeline. Indeed, the drive to determine protein function has been stimulated, both in industry and academia, by the completion of the human genome project. In this article, we critically examine the strategies and methodologies used for both the identification and validation of disease-relevant proteins. In particular, we will examine the likely impact of recent technological advances, including genomics, proteomics, small interfering RNA and mouse knockout models, and conclude by speculating on future trends.