Abstract 505: Plasma treatment induces apoptosis in U87 cells in vitro and in vivo

Abstract

Abstract Background Over the past few years, nonthermal atmospheric pressure plasma has emerged as a novel promising tool in medicine. Plasma is a partially ionized gas sustained by a supply of energy in various forms (electric, thermal, radiative . . .). Plasma contains free charges (electrons, ions), free radicals, excited molecules, energetic photons (UV) and generates transient electric fields. Studies have demonstrated an antitumor effect of plasma treatment on melanoma cells lines and our group has recently demonstrated an antitumor effect of plasma treatment on U87 glioma bearing mice. The aim of this work was to better understand the mechanisms involved in the antitumor effect of plasma treatment observed on U87 glioma cells in vitro and in vivo. Methods The experiments were performed using a floating electrode DBD plasma reactor. For in vitro experiments, 24-well plate were seeded with U87 cells previously transfected by the luciferase gene (U87-Luc). Cells were treated by a single fraction of plasma. Effects of treatment on proliferation and viability were assessed by bioluminescence imaging (BLI), MTT assay and by trypan blue assay. For in vivo experiments, malignant glioma U87 model was heterotopically implanted in nude mice. When tumors reached 150 mm3, mice were randomly assigned into two groups: CTRL and Plasma. Plasma was delivered as a daily fraction of 6 min at 200Hz for five consecutive days and tumors were imaged by bioluminescence before treatment and 24h after the first and the last fraction. Treatment effects on tumor cells proliferation and apoptosis were assessed 24h after the last fraction by determination of cell cycle distribution and detection of annexin V positive cells, respectively. Results and Discussion Plasma treatment showed a significant antitumoral effect on U87 glioma in vitro and in vivo. In vitro plasma induced a decrease of BLI resulting from a massive cell death. Moreover, in vivo experiments, plasma treated tumors presented an important BLI decrease of ∼70% associated with a ∼60% reduction of tumor volume as compared to CTRL. Such results are particularly encouraging in this high chemo and radioresistant model. Cell cycle distribution and annexin V analysis showed a marked apoptosis induction in the treated group. To our knowledge, only in vitro experiments have reported an apoptosis induction of plasma treatment on melanoma cell lines. DNA double strand break and ROS formation have been reported in vitro during plasma treatment and these mechanisms may participate in the induction of apoptosis observed in vivo. Our data highlight a major antitumor effect of plasma treatment both in vitro and in vivo and this effect may be linked to an apoptosis induction. Further studies are ongoing to elucidate mechanism of action of plasma in apoptosis induction and to understand the implication of the different plasma components in the cytotoxic effect. These results will allow us to develop more efficient plasma types. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 505.