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An in-vitro and ex-vivo study is presented aimed at elucidating the role or Reactive Oxygen and Nitrogen Species (RONS) in promoting a selective killing of cancer cells by cold plasma treatment. The investigation is, in particular, dedicated to the possibility of emphasizing the selectivity towards cancer cells by combining the plasma treatment with the effect of a molecule known to enhance intracellular ROS production. Lung carcinoma cell lines and cultured primary cells isolated from surgical samples of laryngeal and lung cancers as well as healthy tissue counterparts were treated with an indirect plasma source, in which a helium flow mixed with ambient air in the region between two brass grids is ionized by means of a RF voltage[1]. The helium enriched with active chemical species is then sent to the substrate to be treated. As already reported, this kind of treatment induces an increase of endogenous Reactive Oxygen Species (ROS) in eukaryotic human cells [2]. In the present study, induced ROS generation was confirmed, but a markedly higher increase was found in cancer cells than in healthy ones. The same effect was observed for intracellular nitric oxide (NO). Moreover, incubating the cells with antimycin A (AMA), a molecule known to increase ROS production [3], an amplification of the effect, both for ROS and NO, could be obtained,. The selective increase in endogenous RONS was associated to increased expression of hypoxia-inducible factor (HIF)-a, an oxygen-sensitive transcriptional activator, and to a higher apoptosis in cancer cells than of their healthy counterparts. Incubation with AMA emphasizes these effects. Overall, these results confirm the importance of the role played by RONS in plasma-based cancer treatment, and indicate that the combination with chemotherapeutic drugs could represent a useful tool to enhance the selective effect induced by the plasma treatment.

Plasma medicine is an emerging application of low-temperature, atmospheric pressure plasmas to the treatment of several medical conditions. These plasmas are usually produced ionizing a noble gas flow with RF or pulsed high voltage. The presence in the flow of a fraction of air, or specific gases, causes the production of reactive chemical species which interact with the substrate to which the flow is applied. Metastable states of the noble gas also contribute to the interaction, through Penning ionization. The low power used in these plasma sources ensures that the flow remains at almost ambient temperature, so that no thermal effects are induced and living tissues can be treated in a harmless way. The most straightforward application is disinfection, thanks to the effect of the reactive species on the pathogens, especially bacteria, which lack the mechanisms of defense against oxidative stress which allow survival of the eukaryotic cells composing the substrate. Further applications rely on the ability of the activation of cellular processes, such as the intracellular generation of Reactive Oxygen Species (ROS), which can lead to therapeutic effects, including accelerated wound healing and cancer cell selective killing. In this contribution we present the advances made by our group in this field, showing experimental results concerning an indirect plasma treatment performed using a plasma source patented by our group. The targeted applications are the treatment of corneal infections (keratitis) and cancer treatment.