Combining cold physical plasma with pulsed electrical fields for cancer treatment

Pallation of end-stage melanoma and breast cancer patients is a challenge. Despite the generally successful use of electrochemotherapy (ECT) in these patients, response rates can still be improved. Previous studies demonstrated the anticancer potential of nano-second PEFs (nsPEFs), which are able to induce apoptosis [1] or nanopore formation when using different settings [2]. Likewise, the anticancer capacity of cold physical plasma has been demonstrated in various studies in cell lines and in xenograft tumors in mice [3-7]. The apoptotic effect of cold plasmas is mediated by a variety of reactive species being released onto the cells, where the species trigger redox signaling, and subsequent cell death in some instances [8, 9]. By contrast, PEFs act by a mechanism much less dependent on the newly generated reactive species. Our idea was to combine both treatments to improve palliative cancer treatment in the future.

Malignant suspension cell lines were tested to investigate the proof of concept of additive or possible even synergistic cytotoxic effects. Plasma treatment time (kINPen) and PEF intensity as well as pulse length were varied to retrieve sublethal dosage regimens for each treatment. The sequence of combination (first plasma, then PEF or vice versa) was also modulated. To investigate the mode of action of both therapies, a number of cellular parameters were investigated. This included oxidation at cytosolic and membrane compartments, thiol content, mitochondrial depolarization, caspase activation and phosphatidylserine exposure, metabolic activity, cell membrane permeabilization, cell growth and morphology, and protection by antioxidants. Furthermore, we identified a synergistic effect of plasma and PEFs using tumorigenic adherent cells in preliminary tests.