Gene transfer types: in vitro in cultured cells by the means of electric pulse delivery, reversible cell electroporation for gene transfer and DNA gene therapy. The mechanisms involved in DNA electrotransfer include cell electropermeability and DNA electrophoresis. The voltage applied to cells or tissues over a given distance is referred to as electroporation field strength and it has a strong influence on cell cytotoxicity and survival. When the field strength of the electroporation pulse is high enough, reversible permeability occurs in the cell membrane that allows outside molecules to enter the cell. In general, efficient transfection is achieved at higher voltages, but also associated with higher toxicity. The duration of the electrical field applied is referred to as pulse length. The best pulse length is largely dependent on cell diameter. Recent technological developments have made DNA electroporation more efficient and safer; this nonviral gene therapy approach is now ready to reach the clinical stage.
Delivery of DNA into Tumors – Delivery of plasmid DNA encoding therapeutic genes into tumors is one of the main applications of electroporation. The optimal volume for gene delivery into tumors via electroporation may vary greatly based on the tumor size and the electroporation parameters. Many efforts were done to define the optimal intratumoral injection volume for i.t. electroporation gene therapy for treating tumors.
Cyclophosphamide and Interleukin-12 (IL-12) have been successfully used in clinical trials for treating malignancies. Coadministration of cyclophosphamide and IL-12 plasmid DNA followed by electroporation was successfully used for treating SCCVII in mice – delays tumor growth and increases survival in mice. Cyclophosphamide (CTX) can stimulate delayed type hypersensitivity, and it induces a TH1 antitumor response in combination with interleukin-12 (IL-12)
Efficient electroporation delivery is controlled by the way the solution of the nucleic acids is injected in the tissue and by the electrical parameters. Expression level of the electroporated gene (or siRNA) is under the control of the electric field strength (voltage and geometry of electrodes), the electroporation pulse duration, and on the geometry of the field.
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