Electrically-assisted nucleic acids delivery to tissues in vivo: where do we stand?

Electropulsation (electroporation) is a physical method for delivery of various molecules into the cells in vitro and in vivo. It is an expanding field due to its applicability in cancer therapy, where combined application of electric pulses and chemotherapeutic drugs is used for treatment of cutaneous and subcutaneous nodules of different malignancies. Another application of electropulsation in vivo is electrogene therapy, where after injection of naked plasmid DNA and delivery of electric pulses directly to the tissue the expression of gene of interest can be obtained. However, the transfection efficiency of this methodology in vivo is still lower than with viral vectors. Nevertheless, due to the lack of immunogenicity of the method, easiness of the preparation of large quantities of endotoxin free plasmid DNA, control and reproducibility of the method and the development of electropulsators approved for the clinical use, electrically-assisted nucleic-acid delivery holds a great potential for the clinical application. This aim of this minireview is to critically discuss the main limitations and obstacles associated with electrogene therapy and the failures and problems as well as the successes. Topics on electric field distribution in the tissue, electrode geometries, construction of plasmid, modulation of extracellular space, tissue damage, pro-inflammatory and immune response as well as blood flow modification associated with application of electric pulses and injection of naked DNA are presented with possible directions how to overcome these limitations. Furthermore, for successful electrogene therapy in clinical setting it is of utmost importance to elucidate the mechanisms of DNA transfer into the cells of tissues in vivo. This will enable appropriate selection of electric pulse parameters and plasmid DNA constructs for each particular intended use. In the long run, this review should encourage other scientists to consider electrically assisted gene delivery for gene therapy as it matures.