title: Non-thermal atmospheric plasma induces ROS-independent cell death in U373MG glioma cells and augments the cytotoxicity of temozolomide.
abstract: BACKGROUND
  Non-thermal atmospheric plasma (NTAP) is an ionised gas produced under high voltage that can generate short-lived chemically active species and induce a cytotoxic insult in cancer cells. Cell-specific resistance to NTAP-mediated cytotoxicity has been reported in the literature. The aim of this study was to determine whether resistance against NTAP could be overcome using the human glioma cell line U373MG.
  
  
  METHODS
  Non-thermal atmospheric plasma was generated using a Dielectric Barrier Device (DBD) system with a maximum voltage output of 120 kV at 50 Hz. The viability of U373MG GBM cells and HeLa cervical carcinoma cells was determined using morphology, flow cytometry and cytotoxicity assays. Fluorescent probes and inhibitors were used to determine the mechanisms of cytotoxicity of cells exposed to the plasma field. Combinational therapy with temozolomide (TMZ) and multi-dose treatments were explored as mechanisms to overcome resistance to NTAP.
  
  
  RESULTS
  Non-thermal atmospheric plasma decreased cell viability in a dose (time)-dependent manner. U373MG cells were shown to be resistant to NTAP treatment when compared with HeLa cells, and the levels of intracellular reactive oxygen species (ROS) quantified in U373MG cells were much lower than in HeLa cells following exposure to the plasma field. Reactive oxygen species inhibitor N-acetyl cysteine (NAC) only alleviated the cytotoxic effects in HeLa cells and not in the relatively NTAP-resistant cell line U373MG. Longer exposures to NTAP induced a cell death independent of ROS, JNK and caspases in U373MG. The relative resistance of U373MG cells to NTAP could be overcome when used in combination with low concentrations of the GBM chemotherapy TMZ or exposure to multiple doses.
  
  
  CONCLUSIONS
  For the very first time, we report that NTAP induces an ROS-, JNK- and caspase-independent mechanism of cell death in the U373MG GBM cell line that can be greatly enhanced when used in combination with low doses of TMZ. Further refinement of the technology may facilitate localised activation of cytotoxicity against GBM when used in combination with new and existing chemotherapeutic regimens.
authors.affiliation: BioPlasma Research Group, School of Food Science and Environmental Health, Dublin Institute of Technology, Dublin, Ireland.|Environmental Sustainability and Health Institute, Dublin Institute of Technology, Dublin, Ireland.|FOCAS Research Institute, Dublin Institute of Technology, Dublin, Ireland.
authors.forename: Gillian E
authors.initials: GE
authors.lastname: Conway
authors.affiliation: FOCAS Research Institute, Dublin Institute of Technology, Dublin, Ireland.
authors.forename: Alan
authors.initials: A
authors.lastname: Casey
authors.affiliation: BioPlasma Research Group, School of Food Science and Environmental Health, Dublin Institute of Technology, Dublin, Ireland.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Milosavljevic
authors.affiliation: School of Computing, Dublin Institute of Technology, Dublin, Ireland.
authors.forename: Yupeng
authors.initials: Y
authors.lastname: Liu
authors.affiliation: FOCAS Research Institute, Dublin Institute of Technology, Dublin, Ireland.|School of Biological Sciences, Dublin Institute of Technology, Dublin, Ireland.
authors.forename: Orla
authors.initials: O
authors.lastname: Howe
authors.affiliation: BioPlasma Research Group, School of Food Science and Environmental Health, Dublin Institute of Technology, Dublin, Ireland.|School of Chemical Engineering, UNSW, Sydney, Australia.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Cullen
authors.affiliation: BioPlasma Research Group, School of Food Science and Environmental Health, Dublin Institute of Technology, Dublin, Ireland.|Environmental Sustainability and Health Institute, Dublin Institute of Technology, Dublin, Ireland.
authors.forename: James F
authors.initials: JF
authors.lastname: Curtin
mesh_terms: D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D001932:Brain Neoplasms / Q000188:drug therapy* / Q000473:pathology*; D045744:Cell Line, Tumor; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004357:Drug Synergism; D005910:Glioma / Q000188:drug therapy* / Q000473:pathology*; D006367:HeLa Cells; D006801:Humans; D058626:Plasma Gases / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D000077204:Temozolomide
chemical_list: D018906:Antineoplastic Agents, Alkylating; D058626:Plasma Gases; D017382:Reactive Oxygen Species; D003606:Dacarbazine; D000077204:Temozolomide