Electroporation: A new interventional oncology paradigm
formation of nanometer-sized pores. The type of electroporation can be varied by the strength of the electrical field that has been applied to the cell. Starting from a very low field strength, if the field strength is elevated, it will pass an initial critical field strength threshold and reversible transmembrane nanopores form. If this electrical field is removed, the nanopores will close. However, if the field strength is elevated further, it will cross a higher critical
E
lectroporation is broadly defined as the application of short electrical fields to cell membranes, causing the
field strength threshold and pore formation will be irreversible, leading to cell death[1].
In 1982, French scientists carried out an experiment to examine DNA transfection in cells using this “electroporation” model. This model suggested that the interaction of an external electric field with lipid membrane of a cell could cause pore formation and could thus increase permeability in the cell membrane, allowing extracellular components, such as plasmids, to enter the cell. In their experiment, cells were co-cultured with DNA plasmids and exposed to electrical
fields. Their experiment demonstrated that electroporation methods lead to a significantly higher number of plasmid-transfected cells than with any other gene transfection method. This experiment proved electroporation’s simplicity, applicability and efficiency in gene transfection and would subsequently usher in a new era of genetic research[2].
While low field strength electroporation had found a use, use of higher applied electrical field strengths had not found utility. However, in 2005, American researchers took advantage of this phenomenon. Davalos et al developed electrodes capable of delivering high electrical fields to tumor cells, inducing permanent electroporation and cell death. This ablative method became known as irreversible electroporation (IRE)[3]. The first human experience with IRE was performed in the prostate. Of note, while there was uniform destruction of glandular cellular elements, sparing of normal structures was also demonstrated[4].
Since its advent, IRE has demonstrated several advantages over other percutaneous ablation methods. First, although it can cause tissue heating at very high applied electrical fields, cellular death is not dependent on reaching critical temperatures to induce cell death. Issues of heat sink that cause ablation failure adjacent to vasculature in radiofrequency ablation or cryoablation are not present in IRE. Secondly, IRE
18 IR QUARTERLY | SPRING 2016
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