Table 2.

Characteristics of preclinical studies.

Authors	Level (In Vitro/In Vivo/Ex Vivo)	Models	Cell Type(s)	Plasma Device	Direct/ Indirect Treatment	Condition of Use	Analyses	Results
Choi B.B. et al., 2012 [37]	In vitro	Cell lines	Normal: WI-38 Tumor: SCC-25	air-NTP	Direct	4 × 104 cells incubated on cover slip (12 mm diameter) for 24 h with the GNP-EGFR, washed with serum free media, and then cover slips placed 2 mm from the plasma source and exposed to treatment. During plasma treatment, cells humidified by 5 μL serum free media.	Biological: -Cell viability; -Protein expression; -Cell morphology.	BIOLOGICAL Cell Viability (Trypan blue): -Plasma death rate 3.61% in WI-38 and 15.7% in SCC-25; -Plasma plus GNP-EGFR death rate 34% in WI-38 and 92% in SCC-25. Protein expression (Western blot): -Basal EGFR more expressed in SCC-25 cells than in WI-38. Cell morphology (SEM): -SCC-25 morphology, after plasma plus GNP-EGFR changed from spindle to round shape, and cell shrinkage and membrane rupture were observed.
Han X. et al., 2013 [23]	In vitro	Cell line	Tumor: SCC-25	N2-APPJ	Direct	Before plasma irradiation, SCC-25 were grown on a grid slide with a marked dot at the center placed inside a P35 cultural dish (3 mm thickness). 2.4 mL PBS was added instead of a culture medium to prevent cell desiccation. Control 1: treated with N2 gas without plasma. Control 2: untreated neither plasma nor gas flow.	Biological: -Identification and quantification of cells with DNA damage. Chemical: -Determination of reactive species.	BIOLOGICAL DNA damage (Immunofluorescence): -60% DSB damage after 30 s irradiation; -Nearly 80% at 2 min. CHEMICAL Determination of reactive species (Optical emission spectroscopy): -Nitrogen oxide bands (NO-ƴ) detected between 200 and 300 nm; -The bands of the second positive system of molecular nitrogen recorded in the range of 300–420 nm; -The dominant peak around 557 nm represents an excimer of ON2 (O(1D)N2).
Chang J.W. et al., 2014 [36]	In vitro	Cell lines	Tumor: MSK QLL1 SCC-1483 SCC-15 SCC-25	He + O2− NTP spray type	Direct	Cells were treated in complete medium. Control: cells treated with He + O2 gas without plasma.	Biological: -Apoptosis; -Cell cycle -DNA damage; -Cell morphology; -Protein expression.	BIOLOGICAL Apoptosis and cell morphology (FACS, fluorescence microscopy): -Rounding, shrinkage, detachment and increase in annexin V, PI and TUNEL positive cells. Cell cycle (FACS): -Sub-G1 cell cycle arrest in wild-type p53 OSCCs (SCC-25), not in mutated p53; -Decrease in sub-G1 phase cells in the ATM siRNA-transfected compared with the control siRNA-transfected. DNA damage (COMET assay, immunocytochemistry): -Intensity-dependent increase in the number of typical comets with elongated tails; -Increased ƴH2AX foci in the nuclei of SCC-25 cells. Protein expression (Western blot): -NTP increased p-ATM, p-p53, p21, cyclin D1, and ƴH2AX expression in wild-type p53, but not mutated p53 cells.
Guerrero-Preston R. et al., 2014 [5]	In vitro	Cell lines	Normal: NOKsi OKF-6 Tumor: JHU-022 JHU-028 JHU-029 SCC-25	He CAP	Direct	Cells were treated in complete medium. Control: cells treated with He gas without plasma.	Biological: -Cell viability; -Colony formation; -Protein expression.	BIOLOGICAL Cell viability (MTT): -Dose-response decrease in SCC-25 and JHU-O28; -Decreased in JHU-O22 and JHU-O29 after 30 and 45 s treatment; -Not affected in OKF-2; -SCC-25 and OKF-6 formed colonies after 10 s treatment; -NOKsi cells formed colonies. Protein expression (Western blot): -No occurrence of PARP cleavage.
Kang S.U. et al., 2014 [73]	In vitro	Cell lines	Tumor: FaDu HN-9 SNU-1041 SNU-899	He + O2-NTP spray type	Direct	3 mL of cell suspension with a concentration of 1 × 105 cells/mL on the petri dish (diameter 60 mm) treated in complete medium (depth 10 mm). Control: cells treated with He + O2 gas without plasma.	Biological: -Apoptosis; -Protein expression; -Mitochondrial damage. Chemical: -ROS production.	BIOLOGICAL Apoptosis (FACS, TUNEL): -Significant increased apoptosis of treated FaDu, HN-9, SNU-899, and SNU-1041 compared with the control and gas-only groups; -In FaDu, NTP induced apoptosis by MAPK-mediated mitochondrial ROS. Protein expression (Western blot): -Increased expression of p-p38, p-c-JUN N-terminal kinase (JNK), and p-ERK after NTP treatment in FaDu. Mitochondrial damage (FACS—MMP measurement): -Loss of MMP and mitochondrial damage. CHEMICAL ROS production (FACS and confocal microscopy) -Mitochondrial superoxide levels increase in NTP-treated cells.
Kang S.U. et al., 2014 [73]	In vivo	FaDu-derived xenograft in 16 male BALB/c nu/nu mice.	Tumor: FaDu	He + O2-NTP spray type	Direct	Daily single treatment, 1 cm apart from the upper margin of tumor for 20 days. Control: untreated BALB/c nu/nu mice	Biological: -Protein expression; -Apoptosis; -Tumor mass measurement.	BIOLOGICAL Protein expression (IHC): -Increased caspase-3 and Nox-3 levels. Apoptosis (TUNEL assay): -Increased TUNEL staining, compared with control. Tumor mass measurement (Sliding caliper): -Inhibition of tumor growth after 11 days of treatments.
Kim S.Y. et al., 2015 [74]	In vitro	Cell lines	Normal: MRC-5 HNLF Tumor: AMC-HN6 Human derived cancer cell lines: FaDu SCC-15 SCC-QLL1 SCC-1483 SNU-1041 Murine derived cancer cell line: SCC-7	LTP produced by He + O2-NTP spray type	Indirect	LTP was applied to HNC cells in the absence of serum. Control Media (CM): air-treated media.	Biological: -Cell viability; -Apoptosis; -Protein expression; -Colony forming assay; -Gene expression; -Detection of AKT ubiquitination. Chemical: -ROS production.	BIOLOGICAL after NTP treatment. Cell Viability (MTT on SCC-15 and SCC-QLL1): -Significant reduction of HNC viability. Apoptosis (TUNEL assay on SCC-15 and SCC-QLL1): -Apoptotic cell death. Detection of AKT ubiquitination (SCC-15): -AKT degradation via lysine 48-linked ubiquitination. RT-PCR (SCC-15) and proximity ligation assay (SCC-15, SCC-QLL1): -Increased level of MUL1 mRNA; -Cellular ROS increase MUL1/AKT binding and cytotoxicity. BIOLOGICAL after LTP treatment. -Decreased SCC-15 viability; -Greater inhibition of colony-forming growth in LTP-treated SCC-15 compared with CM; -LTP reduced AKT or p-AKT levels and increased the level of MUL1; -CM did not change the levels of AKT, p-AKT, or MUL1; -LTP reduced AKT and p-AKT levels, which was prevented by MUL1 knockdown. CHEMICAL Measurement of ROS (FACS): -NTP induced ROS production in human HNC cells.
Kim S.Y. et al., 2015 [74]	In vivo	SCC-7-derived syngeneic tumor model in 10 female C3H/HeJ mice. SCC-15-derived xenograft in BALB/c nu/nu mice.	Tumor: SCC-7 SCC-15	LTP produced by He + O2-NTP spray type	Indirect by injection	Daily treatment of 200 μL of medium or LTP for 6 days by intra-tumoral injection.	Biological: -IHC; -Protein expression.	BIOLOGICAL -Inhibitory effect of tumor development after the fourth treatment and reduction in tumor weight; -Inhibition in tumor volume after the ninth treatment; -Reduction of p-AKT levels and increase in MUL1.
Welz C. et al., 2015 [82]	In vitro	Cell lines	Tumor: FaDu OSC-19	air-CAP (SMD)	Direct	Cell culture medium was removed before the CAP treatment and was added immediately after treatment. Control: cells not exposed to CAP.	Biological: -Cell viability; -DNA damage; -Apoptosis.	BIOLOGICAL Cell viability (MTT): -Time-dependent reduction in OSC-19 and FaDu cells compared to control. DNA damage (COMET assay): -Time-dependent DNA fragmentation. Apoptosis (FACS): -No dose-dependent apoptosis in both cell lines.
Lee J.H. et al., 2016 [75]	In vitro	Cell lines	Normal: HGF-1 Tumor: HSC-2 SCC-15	N2-CAP jet	Direct	Cells were treated in complete medium (concentration of 1 × 104 cells/100 μL). Control: cells not exposed to CAP.	Biological: -Cell viability; -Apoptosis; -Cell cycle; -Protein expression. Chemical: -Intracellular ROS detection; -Thiol detection.	BIOLOGICAL Cell Viability (Tetrazolium salt assay): -Significant decrease in HSC-2 and SCC-15 compared to HGF-1. Apoptosis (FACS): -More apoptotic death in HSC-2 compared to HGF-1. Cell Cycle (FACS): -HSC-2 killed via sub-G1 arrest; -HGF-1 did not show changes in cell cycle components. Protein expression (Immunoblot assay): -Degradation and dephosphorylation of EGFR in HSC-2 cells; ->deactivation of the EGFR pathway. CHEMICAL -ROS measurement by OES.
Chauvin J. et al., 2018 [6]	In vitro	Cell lines	Tumor: FaDu monolayer culture FaDu spheroids (MCTS)	PAM produced by He-CAP jet (DBD)	Indirect	PAM was applied to FaDu and FaDu MCTS. Control: cells treated with He gas without plasma.	Biological: -Cell viability.	BIOLOGICAL Cell viability (PrestoBlue®): -PAM exposure dependent cell detachment from MCTS due to the presence of H2O2; -A rapid spheroids regrowth due to a resistance of FaDu cells to H2O2; -Inhibition of cell growth after multiple treatments of MCTS with PAM; -MCTS are brought out when comparing PAM effect on 2D versus MCTS. Inversely, PAM induces cell death in the case of 2D cell culture.
Hasse S. et al., 2019 [72]	In vitro Ex vivo	Cell lines	Normal: HaCaT Tumor: HNO-97 -10 patients (6 M/4 F); age range: 43–75 years affected by maxillofacial cancer.	PAM produced by Ar-CAP Ar-CAP	Indirect for cell lines. Direct on tissue samples.	PAM was applied to cells. Tissue samples were directly exposed. Control: untreated tissue sample and human non-malignant mucosa.	Biological: -Cell viability; -Cell cycle; -Protein expression; -Cell motility. -Apoptosis; -DNA fragmentation; -Cytochrome C measurement; -Cytokine detection.	BIOLOGICAL Cell viability (Resazurin-based assay): -After plasma treatment, time-dependent reduction in HaCaT and HNO-97. Cell cycle (FACS): -19.3% of HNO-97 cells in G2/M vs. 30% of HaCaT cells. Global protein expression (Spectrometry): -Time dependent activation of caspase 3/7 in both cell types; -Several protein expression changes. Cell motility (Wound Healing): -Reduction in HNO-97; -Normal cells not affected. Apoptosis/DNA fragmentation (TUNEL assay): -Stronger induction of apoptosis in tumor tissue in situ compared to healthy tissue. Cytochrome C measurement (ELISA): -Three-fold increase in tumor tissue. Cytokine detection (Flow cytometer): -IL-22 increased in healthy tissue; -INF-γ TNF-α and IL-10 found predominantly in tumor tissue compared to non-cancerous tissue.
Sato K. et al., 2019 [80]	In vitro	Cell lines	Normal: HS-K IMR-90-SV Tumor: Ca9-22 Ho-1-u-1 HSC-2 HCS-3 HSC-4 Sa-3 SAS	Ar-NTP	Direct	Cells were treated in complete medium with NTP. Control: cells treated with Ar gas without plasma.	Biological: -Cell viability; -Apoptosis; -Quantification and localization of catalytic Fe(II); -Migration and Invasion; -Protein expression; -Colony formation. Chemical -ROS detection.	BIOLOGICAL Cell viability (WST-8 assay): -Time and treatment-dependent decrease in SCC; -Decrease in SAS e CA9-22 viability as the concentration of FAC increased; -Increase as the concentration of DFO increased in co-treatment with NTP. Quantification and localization of Fe(II) (Flow cytometer): -The Fe level in IMR-SV-90 was lower than SAS and CA9-22; -No difference in the Fe levels between SAS and Ca9-22 cells. Apoptosis (FACS, TUNEL): -Apoptotic cells in SAS and treated Ca9-22. Migration and invasion (Wound Healing and transwell) -Suppressed migratory and invasive ability of SAS and Ca9-22 compared with control. Protein expression (Western blot): -Decrease in MMP-2 SCC cells compared to control. Colony formation (Soft agar): -Decreased colony formation in treated SAS cells compared with control. CHEMICAL ROS detection (Flow cytometer): -Increased ROS levels in treated SCC.
Han X. et al., 2020 [71]	In vitro	Cell lines	Normal: OKF-6/T Tumor: SCC-25	N2-APPJ	Direct	Cells were treated in 2.4 mL of PBS (3 mm depth) with N2-APPJ. Control: cells treated with N2 gas without plasma and no treatment. Control: untreated cells	Biological: -DNA double strand breaks	BIOLOGICAL DNA double strand breaks (Immunofluorescence): -DNA damage in cancer cells was maximized at the plasma jet treatment region and declined radially outward; -In cancer cells DNA damage decreased slightly over the first 4 h and rapidly decreasing by approximately 60% at 8 h post-treatment; -Damage observed 2 h after treatment in non-malignant cells; -S phase cells were more susceptible to DNA damage than either G1 or G2 phase cells.
Lee C.M. et al., 2020 [38]	In vitro	Cell lines	Normal: HGF-1 Tumor: SCC-15	Ar-CAP jet	Direct	Cells (1 × 105 cells/100 μL) in medium were treated. Group 1: 1 µM cisplatin + 3 min CAP. Group 2: 3 µM cisplatin + 1 min CAP.	Biological: -Cell viability; -Apoptosis; -Protein expression. Chemical: -ROS generation; -CAP jet measurement.	BIOLOGICAL Cell Viability (MTT) and Apoptosis (fluorescence microscopy/FACS): -Decrease in cell viability by increasing cisplatin concentration and CAP exposure. Protein expression (Western blot): -Increased expression of PTEN and p53 in both cell lines; -Increased expression of cleaved Cas-9 in SCC-15. CHEMICAL ROS generation (Fluorimetric assay): -Group 1 and group 2 reported 300% and 500% increase in SCC-15 vs. 130% and 170% in HGF-1. CAP jet measurement (OES analysis): -Peaks of Ar+, OH and O− ions observed in the UV range (200 nm–400 nm) and visible range (690 nm–950 nm).
Ramireddy L. et al., 2020 [79]	In vitro	Cell line	Tumor: SCC-4	He-CAPP jet	Direct	He-CAPP jet was applied to SCC-4 cells in cell medium. Control: cells treated with He gas without plasma.	Biological: -Cell viability; -Cell cycle; -Protein expression. Chemical: -ROS/RNS detection.	BIOLOGICAL Cell viability (MTT): -Significantly greater cell death (dose-dependent) compared to controls. Cell cycle (FACS): -Dose-dependent increase G1 cell cycle. Protein expression (Western blot): -Downregulation of ATM protein, Bax increase, and Bcl-2 decrease compared to controls. CHEMICAL ROS/RNS detection (Fluorimetric assay): -He-CAPP time-dependent increase in intracellular ROS and RNS levels; -H2O2 increased immediately after He plasma treatment but reached basal level after 3 h.
Lin A. et al., 2021 [76]	In vitro	Cell lines	Tumor: A-375 CAL-27 U-87	Air-microsecond pulsed DBD	Direct	Cells (15 × 104) were treated with DBD after removing the medium. Control: untreated cells.	Biological: -Cell viability. Chemical: -H2O2, NO2− and NO3− measurements	BIOLOGICAL Cell survival (Trypan Blue Assay): -Reduced survival for all cell lines; -No significant difference between the different treatment times and pulse frequencies. CHEMICAL H2O2 (Fluorimetric assay) and NO2− /NO3− (Colorimetric assay) measurement: -H2O2, NO2− and NO3− concentrations linearly increased with pulse frequency and time of application; -The generation of H2O2, NO2− and NO3− depends on the total delivered energy during treatment.
Oh C. et al., 2021 [77]	In vitro	Cell lines	Normal: Primary normal human fibroblasts Tumor: SCC-25 SNU-1041 SNU-1076	NTPAM produced by He-O2-PlasmaJet	Indirect	NTPAM preparation: NTP was exposed to the culture media for various activation times.	Biological: -Cell viability; -Apoptosis; -Gene expression; -Protein expression; -Mitochondrial damage; -Cells morphology. Chemical: -ROS detection	BIOLOGICAL Cell viability (WST-1): -Significantly reduced in all HNC cell lines in a manner dependent on NTP activation time compared to normal control cells. Apoptosis (FACS): -Selectively induced apoptosis in HNC cells. Gene expression by qRT-PCR analysis: -NTPAM treatment regulated mechanisms related to cell death and cell cycle; -Significant association with the regulation of PERK, closely related to an altered cell stress response; -ATF4 and CHOP are key regulators of NTPAM induced HNC cell death. Protein expression (Western blot): -Increase in cleaved PARP levels, -Decrease in pro-Caspase 3 and Bcl-2. Mitochondrial damage (OCR, SEM): -Induction of mitochondrial dysfunction in HNC cells through mitochondrial damage. CHEMICAL ROS detection (Fluorescent assay): -Significant increase in mitochondrial peroxide levels.
Oh C. et al., 2021 [77]	In vivo	Xenograft Animal Model: 10 healthy male BALB/c nude mice (5 control group, 5 NTPAM treatment group).	Tumor: SNU-1041	NTPAM	Indirect	SNU1041 cells (5 × 106 cells/mL) were injected subcutaneously into each mouse. Tumor formation was confirmed on the 10th day after injection. 100 μL intra-tumoral injections of medium in the control group and NTPAM in the experimental group was administered once daily for 11 days.	Biological: -Protein expression; -Tumor weight measurement.	BIOLOGICAL Protein expression (Histological and Immunohistochemical analysis): -In tumor tissues, low expression levels of Ki-67 and high expression levels of ATF4 and CHOP were observed in the NTPAM-treated group, compared with the normal control group. Tumor weight measurement: -After NTPAM treatment, the tumor weight was significantly lower than in control tumors.
Park J. et al., 2021 [78]	In vitro	Cell lines	Normal: HaCaT Tumor: SCC-25	Ar-NTP	Direct	A day prior, cells were cultivated in a growth medium with or without PD-L1 Ab + GNP. Immediately prior to treatment, the dishes were rinsed with PBS and later positioned under the end of the plasma jet.	Biological: -Cell viability; -Apoptosis; -Protein expression.	BIOLOGICAL Cell viability (SRB assay, Fluorescent dyes): -The treatment with PD-L1 ab + GNP + NTP significantly increased the number of dead cells in SCC-25 compared to the other treatments. Apoptosis (Western blot, Immunocytochemistry): -Elevated expression levels of cleaved caspase-3 and cleaved PARP in the PD-L1 ab + GNP + NTP group; -AIF and cyt C in the control were clustered in punctuate distribution forms whilst they were disseminated in treated cells.
Sklias K. et al., 2021 [81]	In vitro	Cell lines	Normal: 1BR3 hTERT RPE1 (immortalized with hTERT) Tumor: CAL-27 FaDu	He + O2-DBD micro plasma jet	Indirect Direct	Indirect: -PBS in empty well was treated with He/O2 PAP. -Tumor or normal cells were then incubated for 1 h with PAP. Reconstituted buffer (RB): PBS adjusted with plasma-induced concentrations of H2O2, NO2−, NO3− and pH Direct: Cell culture medium was removed, and the cells were washed with PBS. Then, PBS was added to cells and exposed to plasma for 1 h.	Biological: -Cell viability; -Apoptosis. Chemical: -ROS detection; -Lipid peroxidation measurement.	INDIRECT TREATMENT Cell viability (MTT, trypan-blue and CellTiterGlo®): -Lower in FaDu compared to CAL-27; -The strongest cytotoxic effect at a higher concentration of RONS and acidic pH. Apoptosis: Caspase-Glo® 3/7 Assay System. ROS detection (OES): -The highest concentration of H2O2, NO2−, NO3− is obtained after 12 min plasma treatment, at a gas flow of 0.5 slm and at a treatment distance of 8 mm; -These conditions induced the strongest reduction in pH; -H2O2 is a master player in PAP-induced cancer cell death since the addition of catalase during PAP treatment prevents the toxicity of PAP. RECONSTITUTED BUFFER RB is as efficient as PAP to induce lipid peroxidation, intracellular ROS formation, caspase 3/7 activity and cell death in FaDu and CAL-27 cell lines. DIRECT TREATMENT OF CAL27 AND FADU CELL LINES -Greater CAL-27 and FaDu death in direct than indirect plasma treatment DIRECT TREATMENT OF NORMAL CELLS Strong reduction of 1Br3 and RPE-hTERT metabolic activity of normal cell lines direct plasma treatment, while no change after indirect and reconstituted buffer from 6 h up to 72 h post treatment.
Wu C.Y. et al., 2021 [83]	In vitro	Cell lines	Tumor: SAS CAL-27 FaDu Detroit 562	N2+He-NT micro plasma jet	Direct	After cells exposure to plasma, the medium was changed with a new fresh one and incubated for further 24 h.	Biological: -Cell viability; -Apoptosis. Chemical: -ROS and RNS detection	BIOLOGICAL Cell viability (MTS): -Significant decrease with plasma exposure time in SAS, CAL-27 and FaDu; -Significant less decrease in Detroit 562 cells between 30 and 60 s. Apoptosis (FACS/TUNEL): -After plasma exposure for 5 min, 7.8-fold increase in the apoptotic percentage compared to non-treatment group. CHEMICAL ROS and RNS detection (OxiSelect Intracellular Assay kits): -ROS and RNS concentration in medium increased with plasma exposure time.

1BR-3: human normal skin; A-375: human melanoma; Ab: antibody; AIF: apoptosis-inducing factor; AMC-HN6: human floor of the mouth squamous cell carcinoma; AMC-HN-9: human undifferentiated carcinoma of the parotid gland; APPJ: atmospheric pressure plasma jet; Ar: argon; ATF4: activating transcription factor 4; ATM: ataxia telangiectasia mutated; BAX: BCL2 associated X; BCL-2: B-cell lymphoma-2; BR3: human primary skin fibroblasts; Ca9-22: Human gingival squamous cell carcinoma; CAL-27: human tongue squamous cell carcinoma; CAP: cold atmospheric plasma; CAPP: cold atmospheric pressure plasma; Cas-9: caspase-9; CHOP: C/EBP homologous protein; cyt C: cytochrome C; DBD: dielectric barrier discharge; DFO: desferrioxamine; Detroit-562: human pharyngeal squamous cell carcinoma; DSB: DNA double-strand break; ep: energy per pulse; FAC: ferric ammonium citrate; FACS: fluorescence activated cell sorting; FaDu: human hypopharynx squamous cell carcinoma; Fe: iron; GNP: gold nanoparticles; GNP-EGFR: anti-epidermal growth factor (EGFR) antibody conjugated gold nanoparticle (GNP); GNP: gold nanoparticles; HaCaT: human nonmalignant keratinocytes; He: helium; HGF-1: human gingival fibroblasts; HNLF: human normal lung fibroblast; HN-9: human tongue squamous cell carcinoma; HNO-97: human tongue squamous cell carcinoma; HNC: squamous cell carcinoma of the head and neck; Ho-1-u-1: human floor of the mouth squamous cell carcinoma; HSC-2: human oral cavity squamous cell carcinoma; HSC-3: human tongue squamous cell carcinoma; HSC-4: human tongue squamous cell carcinoma; HS-K: human kidney fibroblasts; hTERT RPE1: human retinal pigment epithelial cells; IHC: immunohistochemistry; JHU-022: human laryngeal squamous cell carcinoma; JHU-028: human lung adenocarcinoma; JHU-029: human laryngeal squamous cell carcinoma; ICC: immunocytochemistry; IMR-90-SV: human lung fibroblasts; LTP: liquid-type NTP; MMP: mitochondrial membrane potential; MRC-5: human lung fibroblast; MSK-QLL1: human head and neck squamous cell carcinoma; MCTS: multi cellular tumor spheroids; N: nitrogen; N/A: not applicable; NOKsi: human normal oral keratinocytes; NTP: non-thermal atmospheric pressure plasma; NTPAM: non-thermal atmospheric plasma-activated media; O₂: oxygen; OCR: oxygen consumption rate; OES: optical emission spectroscopy; OKF6/T: human normal floor of the mouth keratinocytes; OSC-19: human low graded tongue squamous cell carcinoma; PAM: plasma activated medium; PAP: plasma activated PBS; PARP: poly adenosine diphosphate-ribose polymerase; PBS: phosphate buffered saline; PD-L1: programmed death-ligand 1; PERK: protein kinase R-like endoplasmic reticulum kinase; PI: propidium iodide; PTEN: phosphatase and tensin homolog; RNS: reactive nitrogen species; ROS: reactive oxygen species; SAS: human tongue squamous cell carcinoma; SCC-1483: human oral retromolar trigone cavity squamous cell carcinoma; SCC-15: human tongue squamous cell carcinoma; SCC-25: human tongue squamous cell carcinoma; SCC-4: human tongue squamous cell carcinoma; SCC-7: murine squamous carcinoma cells; SCC-QLL1: human oral cavity cancer; SEM: scanning electron microscope; SMD: surface micro discharge; SNU-1041: human hypopharynx squamous cell carcinoma; SNU-1076: human laryngeal squamous cell carcinoma; SNU-899: human laryngeal squamous cell carcinoma; SRB: sulforhodamine B; td: treatment distance; tt: treatment time; TUNEL: terminal deoxynucleotidyl transferase dUTP nick end labeling; U-87: human glioblastoma; WB: western Blotting; WI-38: human normal lung fibroblasts; WST-1: water-soluble tetrazolium salt-1.