# Low-Dose Oxidant Toxicity and Oxidative Stress in Human Papillary Thyroid Carcinoma Cells K1
## 4 Discussion  
Exposure to excessive amounts of ROS/RNS causes oxidative distress and irreversible damage to cells, resulting in cell death. This concept is exploited by an array of approved and emerging redox-based therapies in oncology, including medical gas plasmas. The major drawback of this promising technology is its restricted use for treatment of superficially growing, localized cancers or intraoperatively, providing better accessibility of tumors. However, the applicability of medical gas plasmas is extended upon enriching carrier solutions with gas phase-derived ROS/RNS. Plasma-oxidized liquids contain fewer but stable oxidants, applicable for intratumoral injections or lavage. Pre-clinical investigation of such liquids in numerous tumor entities and models in vitro and in vivo provided evidence of their clinical relevance, broadening the range of patients that could benefit from medical gas plasma therapy in the future [27]. Figure 4: **Lipid peroxidation and total radical antioxidant potential. ** (**a**) Schematic overview of chemiluminescence based assessment of cellular membrane oxidation; (**b**) relative luminescence units indicative of lipid peroxidation 24 h after exposure to 60 s oxDMEM, 1800 uM H\({}_{2}\)O\({}_{2}\) and 400 uM SNP and (**c**) quantification of area under the curve; (**d**) assessment of the total radical antioxidant potential (**e**) measured 24 h after exposure to different dosages of oxDMEM, 1800 uM H\({}_{2}\)O\({}_{2}\) and 400 uM SNP. Bar graphs show mean \(\pm\) standard error of the mean (SEM). Box plots show median and min. to max. Mean is indicated as (+). Statistical analysis was performed using one-way analysis of variances (ANOVA) with [PERSON]’s post hoc testing (* \(p\) < 0.05, ** \(p\) < 0.01, and *** \(p\) < 0.001). C = control. ROS = reactive oxygen species. Research on the applicability of medical gas plasma in treating thyroid carcinoma is still incipient. The majority of studies focused on anaplastic and medullary thyroid carcinomas and found direct plasma treatment to induce oxidative stress and apoptosis abrogated after addition of ROS/RNS scavengers [28]. In a comparative study, SNU80 anaplastic thyroid carcinoma cells were, however, found to be more resistant compared to T89G glioblastoma and KB oral carcinoma cells, with only minimal changes in antioxidant consumption after treatment pointing to their capability to cope with high amounts of ROS/RNS [29]. In 2014, [PERSON] and colleagues provided evidence that direct application of medical gas plasmas reduces invasiveness of papillary thyroid carcinoma cells TPC-1 and BHP 10-3 via cytoskeletal alterations and decreased FAK, Src, and paxillin expression, as well as matrix metalloproteinase 2/9 and urokinase-type plasminogen activator activity [30]. [PERSON] and colleagues carried out pioneering research concerning the therapeutic efficacy of medical gas plasmas in the treatment of PTCs, showing enhanced toxicity and tumor immunogenicity after treatment of BCPAP PTC cells [31]. However, treatments performed in the mentioned studies were direct, which, from a clinical perspective, would only be applicable intraoperatively after thyroidectomy, to decrease recurrence rates due to micrometastases in the tumor margin. A recent study investigated transcriptional changes in a screening of five thyroid carcinoma cell lines after exposure to the plasma-oxidized medium and found plasma-induced toxicity to be associated with increased expression of GADD45, a regulator at the G2/M checkpoint playing a role in DNA damage response, cell-cycle arrest and apoptosis. The anti-tumor efficacy of the treatment was validated in a non-orthotopic model of anaplastic thyroid carcinoma in vivo [32], emphasizing the therapeutic efficacy of such an approach. The present study focused on anti-tumor effects of oxDMEM compared to H\({}_{2}\)O\({}_{2}\), and the RNS donor SNP on PTC K1 cells, carrying the BRAFV600E mutation, being of high clinical relevance.