Background: In recent years, cold physical plasma gained significant interest as a new anticancer 14 tool. Cold plasmas are versatile apparatuses in medicine and material processing. Among different 15 cold plasma devices, the argon plasma jet is an effective apparatus and favorite for researches in 16 plasma medicine science. 17 Methods: We developed an argon plasma jet for cancer treatments. Using optical emission 18 spectroscopy, the newly developed plasma jet produced a substantial amount of hydroxyl radicals 19 and other reactive oxygen and nitrogen species known to show cytotoxic effects at higher 20 concentrations. In this work, we studied the efficacy of the argon-based plasma jet treatment in 21 murine B16 melanoma cells in vitro and in vivo. In vitro, cell viability, apoptotic gene expression, 22 and cell death patterns were assessed at 24 h and compared against non-malignant murine dermal 23 fibroblasts (MDF). In vivo, B16 cells inoculated into the flank of the mice developed melanoma 24 tumors, which were plasma-treated for 5 min on days 1, 5, and 10 or were left untreated. 25 Results: Melanoma cells were significantly more sensitive to plasma treatment than MDF under the 26 same in vitro conditions (p= 0.00023). The results revealed that the argon-based plasma jet damaged 27 B16 melanoma cells in vitro selectively without a detrimental effect on non-malignant MDF cells. 28 In the animal model, the tumor volume was significantly reduced after three treatments 29 with the plasma jet(p< 0.01). 30 Conclusions: The argon plasma jet showed therapeutic anti-melanoma efficacy in vitro and in vivo, 31 which may spur new research lines in melanoma therapy.
