Towards non thermal plasma endoscopy for cancer treatment

International audienceGREMI is involved from a few years in a Plasma Medicine program, PLASMED, in association with the TAAM CIPA laboratory for biology studies and in collaboration with medical doctors from both Orleans and Tours Hospital. The main goal of the project is the assessment of non thermal plasma for the treatment of cancerous targets. Three essential tasks are performed dealing with the development and characterization of two non thermal plasma sources, in vitro evaluation of non thermal plasma action on different cancer cell lines and in vivo trials with two main targets, lung and colorectal cancers. In vitro experiments are likely to allow for different treatment protocols, thus affording the opportunity to perform detailed biological analysis to try to determine the main agent in plasma for therapeutic action. In vivo experiment requires first preliminary plasma tolerance studies on mice and then, tumor induction through different modalities, plasma treatment and biological measurements of the tumor activity and volume evolutions during and after plasma treatment. The in vivo plasma treatment evaluation on small animals is mandatory but very challenging. Tumor induction, bio imaging diagnostics, and plasma delivery requires specific care and development to be performed routinely, with a good reproducibility and with accounting for their possible upgrading for larger animals or patients in a next step. Dealing with the plasma sources, a preliminary and very encouraging experiment was performed using FE-DBD plasma as an external applicator on mice subcutaneously grafted with human brain (U87) cancer tumors [1]. Tumor volume stabilization during a five day plasma treatment, daily plasma fraction being delivered as a 3 times 2 minute 200 Hz application, was measured together with a consecutive tumor growth rate reduction after plasma treatment. The combination of these two effects leads to a 60% mice lifespan increase, associated with neither systemic behavior alteration nor skin burns. In vitro experiments performed on U87 (brain), HCT 116 (colon), H460 (lung) cancer cell lines evidenced the crucial role of reactive species in the triggering of a biological process cascade, including DNA damage production, cell cycle distribution modification and apoptosis induction. Such cascade is usually encountered and “optimized” when using today’s conventional anticancer strategies based on radio and chemo therapies. Most questioning was the plasma action during in vivo experiments. Very comparable cell cycle modification and apoptosis induction were measured when analyzing excised tumors from plasma treated mice. This would suggest that reactive species could also be at the origin of the biological cascade associated with tumor growth rate reduction. The issue is then to explain the origin of the presence of these reactive species in the tumor environment. Two main assumptions are considered: on one hand diffusion, may be field enhanceddiffusion, processes may account for the penetration through the skin and tissues of the air plasma reactive species produced on the external surface on the mouse. On the other hand, charging processes, electric field applications and plasma reactive species leading to cutaneous and sub cutaneous pH modifications may be at the origin of intracellular reactive species release. In this latter case, the plasma would act as a trigger for intracellular signaling cascade. While being a simple indication, histological analyses performed through the plasma treated tumor volume, does not show any evidence for diffusion like process action but exhibit a rather homogenous distribution of apoptotic cells through the whole tumor volume. Recent experiments, reported by the Drexel Plasma Institute group [2], nevertheless demonstrate that active species, such as H2O2, may penetrate up to a few mm in tissues which is an argument for the plasma reactive species role in the tumor environment. Nevertheless, considering our selected colon and lung targets, two plasma delivery strategies are now under evaluation through PLASMED program. Whether FE-DBD or plasma jet are applied, following surgical act, directly on the targeted organ such as the colon (see Vandamme et al. in this proceedings) or plasma endoscopic protocol involving plasma jet source is processed. In both cases, the main idea is to deliver reactive species but also all other plasma ingredients in the very vicinity of the tumor to try to induce and optimize a strong antitumor action. The plasma source likely to allow for endoscopic treatment, probably the only path for lung treatment, is a kind of plasma jet developed in GREMI and labeled as the plasma gun. In the next section, a brief description of the plasma gun is proposed, then the optical and chemical diagnostics performed to measure the temperature and reactive species are documented. In the last two sections, the rather unique propagation properties of the plasma gun device and preliminary endoscopic plasma treatment are summarized