Development and Applications of Electroporation in Biology

Fifty years ago, only aggressive chemical approaches were available to introduce genetic material into cells, or to fuse two or more cells. In 1982, three seminal papers — by Eberhard Neumann and colleagues in The EMBO Journal, Justin Teissié and colleagues in Science, and Ulrich Zimmermann in Biochimica et Biophysica Acta — demonstrated that biophysical approaches, namely delivering electric pulses, could facilitate gene transfer to cells or cell fusion. Interestingly, the procedures developed by these authors could (partly) maintain cell viability, therefore ameliorating a previous procedure known as membrane dielectric breakdown.

Two applications rapidly developed in the laboratories. From the article of Neumann et al., the very easy introduction of nucleic acids (basically, plasmids) into bacteria using electric pulses allowed the impressive development of the so-called gene therapy. Indeed, the procedure facilitated the production of plasmids in amounts convenient for their further in vitro modification or for their introduction into eukaryotic cells. On the other hand, from the papers of Teissié et al. and Zimmermann, the easy fusion of cells possessing (eventually) different properties through the delivery of short and intense electric pulses facilitated the production of monoclonal antibodies, an incredible tool in biological research as well as a still-developing diagnostic and therapeutic agent. All these applications were attributed to the “electroporation” of the cells, as the electroporated (or electropermeabilized) state is also an electrofusogenic state. Interestingly, since the beginning, these two applications used different types of electric pulses: exponentially decaying pulses for the transfer of genetic material in bacteria, and square-wave pulses (of a duration of microseconds or tens of microseconds) for the electrofusion approaches.

In parallel, research and applications were developed in the food and environmental sciences, in which the viability of the cells after the procedure was less critical. In biology laboratories, the search for electrical parameters allowing maximal preservation of cell viability (Mir et al. 1988) allowed the development of a pharmacology using “nonpermeant” agents, that is, molecules that do not enter the cells unless the cell membrane is transiently permeabilized. In the clinic, the first application, in 1991, was electrochemotherapy, which combines electropermeabilization with drugs such as bleomycin and cisplatin (Gehl et al. 2018). This combined treatment is regularly employed in oncology, but also for the treatment of benign lesions such as vascular anomalies, in particular in pediatric patients. Different types of electric pulses were also developed for the transfer of small molecules or large molecules (such as nucleic acids), the latter requiring in general longer pulses (Rols et al. 1998).

The loss of cell viability due to the delivery of electric pulses was also understood in the biology laboratories as a potential way for the localized and controlled destruction of cancerous and normal tissues (Davalos et al. 2005). This approach developed rapidly in the clinic to treat internal tumors and was termed “irreversible electroporation”. Later, it was found particularly efficient and safe to treat atrial fibrillation, in particular after the development in the biology laboratories of new types of pulses causing fewer side effects (contractions, pain) at the time of their delivery. The improvements were based on the application of shorter pulses, different repetition frequencies, the use of bipolar pulses instead of monopolar ones, and so on.

Thus, it is interesting to appreciate how, in the biology laboratories, the use of a variety of electric pulses not only facilitated the understanding of the mechanisms related to the effects of electric pulses, but also represented a crucial step before the technological and clinical development of the applications of electric pulse delivery.

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