Cytotoxic Activity of a Cold Atmospheric Plasma Jet in Relation to a 3D Cell Model of Human Breast Cancer

The treatment of solid tumors by a cold atmospheric plasma (CAP) jet is an innovative approach that has been actively developed only in the last decade. As a result, studies aimed at identifying the conditions for selective effect on tumor cells, including as parts of 3D models that mimic malignant neoplasms are pertinent. It is known that the main cytotoxic effects of a CAP are caused by reactive oxygen and nitrogen species in the plasma jet. Their availability for cells in classical 2D and 3D models of cell cultivation may be different. Here, we used multicellular spheroids of MCF7–EGFR cells with overexpression of the epidermal growth-factor receptor (EGFR), cells of parental breast adenocarcinoma MCF7 cell line, and nontransformed human breast cells MCF10A. Irradiation of MCF7–EGFR spheroids induced destruction of multicellular 3D structures into individual cells and activated cell death. It has been shown that the cells of irradiated spheroids undergo phagocytosis by activated macrophages. Comparison of a direct CAP irradiation of MCF7–EGFR spheroids and indirect treatment with plasma-activated medium (PAM) revealed a higher content of reactive oxygen and nitrogen species in spheroid cells cultivated in the irradiated medium. It produced a higher cytotoxic effect than direct irradiation. It has been shown that the cytotoxic properties of PAM are better preserved when such a medium is stored at 4° than at –20°C. Thus, the death of tumor cells in spheroids was more effective with addition of the culture medium irradiated with a CAP than direct irradiation of cells.