Advertisement

Advances in Therapy

, Volume 33, Issue 6, pp 894–909 | Cite as

Clinical and Biological Principles of Cold Atmospheric Plasma Application in Skin Cancer

  • Jesús Gay-Mimbrera
  • Maria Carmen García
  • Beatriz Isla-Tejera
  • Antonio Rodero-Serrano
  • Antonio Vélez García-Nieto
  • Juan Ruano
Open Access
Review

Abstract

Plasma-based electrosurgical devices have long been employed for tissue coagulation, cutting, desiccation, and cauterizing. Despite their clinical benefits, these technologies involve tissue heating and their effects are primarily heat-mediated. Recently, there have been significant developments in cold atmospheric pressure plasma (CAP) science and engineering. New sources of CAP with well-controlled temperatures below 40 °C have been designed, permitting safe plasma application on animal and human bodies. In the last decade, a new innovative field, often referred to as plasma medicine, which combines plasma physics, life science, and clinical medicine has emerged. This field aims to exploit effects of mild plasma by controlling the interactions between plasma components (and other secondary species that can be formed from these components) with specific structural elements and functionalities of living cells. Recent studies showed that CAP can exert beneficial effects when applied selectively in certain pathologies with minimal toxicity to normal tissues. The rapid increase in new investigations and development of various devices for CAP application suggest early adoption of cold plasma as a new tool in the biomedical field. This review explores the latest major achievements in the field, focusing on the biological effects, mechanisms of action, and clinical evidence of CAP applications in areas such as skin disinfection, tissue regeneration, chronic wounds, and cancer treatment. This information may serve as a foundation for the design of future clinical trials to assess the efficacy and safety of CAP as an adjuvant therapy for skin cancer.

Keywords

Apoptosis Cold atmospheric plasma Dermatology Keratinocytes Melanoma Non-melanoma skin cancer Oncology 

Characteristics of Cold Atmospheric Plasma

Plasma is an ionized gas that is composed of ions, electrons, photons, and neutrals (radicals as well as excited atoms and molecules). All are active species capable of inducing different physical phenomena and chemical reactions. There are many examples of plasma in nature, such as plasmas that are generated in stars and the polar aurora. Plasmas can also be created in the laboratory setting; here, plasmas are maintained by applying an external source of energy, generally an electromagnetic field, to a gas. Plasma technology has gained much interest in recent years owing to its various applications in fields such as microelectronics, waste elimination, lighting, and textile. Several nonthermal plasma sources have been recently developed. These plasma sources can be well controlled and open to the air, allowing for the maintenance of CAPs with temperatures below 40 °C. These developments have encouraged therapeutic application of CAPs and the emergence of plasma medicine technology.

Nonetheless, plasma application on the human body for medical purposes has a significant history. In the mid-nineteenth century, electrotherapy was introduced as a therapeutic approach, and spark and flash discharges were employed to treat several diseases. Later, electrosurgical techniques based on the use of plasmas were developed. In electrosurgery, selective coagulation or tissue cutting is achieved by tissue heating which results in desiccation of cells, denaturation of proteins, or devitalization of tissues [1]. Argon plasma coagulation (APC) is a well-established method in the field and commonly employed today for tissue coagulation during endoscopy (in gastroenterology, general and visceral surgery, urology, or gynecology) [2]. APC is a monopolar technique introduced in the 1970s, in which electrical energy is transferred to target tissue as current by means of argon plasma. This technique competes with traditional laser ablation. Comparative studies have shown that APC is more effective for tissue destruction owing to its superior energy concentration. Furthermore, PlasmaJet®, another electrosurgical technique, possesses activity that is mostly mediated by thermal (thus destructive) interaction with living tissues. It consists of a bipolar electrode system with low-flow argon as the process gas. This technique is typically employed to cut or coagulate tissues in a well-defined and localized manner. These direct plasma applications on living tissues in electrosurgery are based on extreme interactions of plasma with cells or tissue, which may lead to cellular destruction and local “sealing” of tissue.

In the last decade, with the development of CAPs, modern plasma medicine has emerged. This branch of medicine aims to exploit the effects of mild plasma by utilizing the distinct interaction of plasma components (and other secondary species than can be formed from these) with specific structural elements as well as functionalities of living cells [1]. These interactions may lead to either stimulation or inhibition of cellular function; thus, this technique may be employed for various therapeutic purposes [3]. While most clinical studies have been conducted in the area of dermatology, interests in CAP technology have also emerged from other disciplines, such as oncology, surgery, otolaryngology, gastroenterology, and odontology [4, 5].

Sources of Cold Atmospheric Plasma

New CAP sources used in plasma medicine can be classified into three types [6]:
  1. 1.

    Direct plasma sources These plasmas use the human body (such as the skin, internal tissues, etc.) as an electrode; thus, the current produced by plasmas has to pass through the body. The most utilized technology in this category is the dielectric barrier discharge (DBD) plasma source.

     
  2. 2.

    Indirect plasma sources These plasmas are generated between two electrodes. Active species that are created by the plasmas are subsequently transported to target application areas. Several devices are available, ranging from very narrow plasma needles or jets to larger plasma torches such as the kINPen® MED, Atmospheric Pressure MicroPlasma Jet (APMPJ), and MicroPlaSter® α and β.

     
  3. 3.

    Hybrid plasma sources These plasmas combine the benefits of the two aforementioned plasma source types (e.g., using the plasma production technique of direct plasma sources and the essentially current-free property of indirect plasma sources). This is achieved by introducing a grounded wire mesh electrode, which has a significantly smaller electrical resistance than that of the tissue; thus, in principle, all current can pass through the wire mesh. The MiniFlatPlaSter is an example of a hybrid plasma source.

     
Nevertheless, plasmas can also be generated by discharges in air, noble gases, or any desired mixture. They can be excited by various means, including radio frequency, microwave frequencies, and high voltage AC or DC, in continuous or pulsed mode in order to produce a chemical cocktail of active species for biomedical applications. Table 1 summarizes the properties of various types of plasma reactors that have been employed for dermatological purposes. In cold atmospheric pressure plasma sources, the main reactive components are reactive neutral species (including free radicals and few ground state molecules such as peroxides and ozone) and UV radiation. Because CAP sources operate at atmospheric pressure while in contact with air, they generate copious quantities of reactive oxygen species (ROS) and reactive nitrogen species (RNS), collectively referred to as RONS. A list of RONS was provided in a recent review, which also highlighted the role of these species in redox biology and their implications for therapeutic applications of plasma [7]. RONS can strongly influence cellular biochemistry and are known to be important in animal and plant immune systems, supporting the notion that they are indeed key mediators in CAP therapeutics.
Table 1

Summary of plasma sources used in dermatology

Type of plasma source

Plasma source

Device

Gas

Frequency

Flow

Power/discharge voltage

Treatment

Direct plasma source

DBD

PlasmaDerm®, CINOGY GmbH

Ar

DC

Pulsed 100–400 Hz

8 slm

0.17–0.24 W/14 kV

Melanoma [36]

Chronic ulcer [42]

Skin moisture [47]

Custom design

Ar + O2

DC

Pulsed 60 Hz

No flow

0.9 W/20 kV

Keratinocytes effect [15]

Custom design

Air

DC

Pulsed 255–518 Hz

No flow

0.2–0.4 W/5–6 kV

Wound healing [49]

Custom design (point to plane arrangement)

Air

100 kHz

Pulsed 300 Hz

No flow

14 kV

Skin treatment (physical model) [50]

DBD, INP Greifswald

Air

31 kHz

No flow

0.4–1.6 W/13 kV

Study of skin irritation [51]

DBD plasma strip

Air

6.6 kHz

No flow

0.7 W/3.5 kV

Infected wound [52]

Direct DBD-Bioplasma cell modulation

Air

15–20 kHz

Pulsed 10–110 Hz

No flow

40 W/6–7 kV

Acne and aesthetic treatment [53]

Surface DBD

Air/Ar

20–21 kHz

No flow/0.5 slm

0.14–0.3 W/3.5–10 kV

Wound healing [54]

Volumen DBD

Ar

33 kHz

0.5 slm

6 W/9–10 kV

Wound healing [54]

Indirect plasma source

Jets

kINPen® MED, neoplas tools GmbH

Ar

1–1.5 MHz

3–8 slm

1–6 kV

Skin decontamination [55]

Psoriasis [43]

Melanoma [50]

Skin moisture [31]

Plasma effect in stratum corneum [56]

Wound healing [4, 18, 57, 58]

Custom design

Ar/He

10 kHz

2 slm

8/10 kV

Human mesenchymal stromal cells [30]

Custom design

He

230–270 kHz

2 slm

1.1–1.8 kV

Melanoma [35, 57]

APMPJ

He

60 kHz

1 slm

5–5.5 kV

Endoscopic sterilization [4]

Custom design

He

RF 25 kHz

Pulsed 400 Hz

16.5 slm

25 kV

Wounds healing [58]

HF plasma jet

Ar

1.82 MHz

Continuous/pulsed 10 kHz

2 slm

2–3 W/0.4–0.6 W

Study of plasma irritation [51]

RF APPJ

Ar

13.56 MHz

1.5 slm

1.7 W

Antibacterial [59]

Infected wound [51]

Torches

MicroPlaSter®, terraplasma GmbH

Ar

2.45 GHz

2.2–4 slm

86–110 W

Wound healing [9, 24, 40, 41]

Keratinocytes effect [19]

Pruritus [45]

Hybrid plasma source

SMD technology

Custom design

Air

12.5 kHz

No flow

0.5 W m−2/18 kV

Nosocomial infections [60]

MiniFlatPlaSter

Air

Pulsed 6.75 kHz

No flow

7 kV

In vivo skin disinfection (bacteria) [61]

Ex vivo nasal and pharyngeal

mucosa [48]

Melanoma [13]

SMD surface micro discharge, RF radio frequency, HF high frequency, APMPJ atmospheric pressure microplasma jet, APPJ atmospheric pressure plasma jet, DBD dielectric barrier discharge, Ar argon, slm standard liter per minute

Here, we review the latest evidence of the biological effects, mechanisms of action, and clinical benefits of CAP application in dermatology. This review also highlights the potential application of CAP as co-adjuvant therapy for the treatment of skin tumor. Analyses described in this review article were based on previously conducted studies. No studies involving human subjects or animals were performed for the publication of this review.

Biological Effects and Mechanisms of Action of Cold Atmospheric Plasma

CAP is a gas composed of multiple chemically active species. It induces physical and chemical changes on biological surfaces upon application. In recent years, several studies have demonstrated biological effects of these changes. Elucidation of the key mechanism behind the effects of CAP in cancerous cells will be crucial to determine the optimal dose of CAP for clinical use.

Oxidative Stress

The level of intracellular ROS and RNS (RONS) is tightly regulated by small antioxidant molecules and scavenging enzymes. At low concentrations, RONS are involved in various biological processes such as bacterial destruction by macrophages and endothelial nitric oxide-mediated vasodilatation. However, when their levels exceed the capacity of the redox balance control system, a state referred to as oxidative stress, they can be cytotoxic and cause cell death. Oxidative stress is involved in the development of various diseases such as psoriasis, chronic ulcers, and cancer.

Cancer cells display weaker antioxidant mechanisms when compared to normal cells. This property can facilitate selective attack of cancer cells by CAP mediated by the extracellular RONS, resulting in severe oxidative damage and cell death. Schmidt et al. observed that alterations in redox state due to CAP treatment caused changes in cellular morphology and mobility, but not cell viability [8]. The authors also found that oxidative stress induced by CAP can modify the expression of nearly 3000 genes encoding structural proteins and inflammatory mediators, such as growth factors and cytokines.

Gene Expression and Epigenetic Changes

Numerous studies have assessed the effects of CAP on gene expression and epigenetics in several cells lines. Application of CAP for 2 min with the MicroPlaSter β® device on a fibroblast culture and in a wound healing mouse model increased the expression of type I collagen and genes encoding proteins involved in wound healing processes (interleukin 6 [IL-6], IL-8, chemokine [C–C motif] ligand 2 [CCL2], transforming growth factor beta 1 [TGF-β1], TGF-β2, CD40 ligand, chemokine [C–X–C motif] ligand 1 [CXCL1], interleukin 1 receptor antagonist [IL-1RA], and plasminogen activator inhibitor-1 [PAI-1]) without affecting cellular migration, proliferation, and apoptosis [9]. Zhong et al. demonstrated the downregulation of IL-12 and upregulation of IL-1β, IL-6, IL-8, IL-10, tumor necrosis factor α (TNFα), interferon gamma (IFNγ), and vascular endothelial growth factor (VEGF) mRNAs when CAP was applied to keratinocyte cultures [10]. Park et al. demonstrated for the first time changes in DNA methylation pattern following CAP application in a breast cancer cell line expressing the estrogen receptor (MCF-7) and one that does not express it (MDA-MB-231). Epigenetic modifications were more extensive in MCF-7 cells, affecting the promoter region of genes related to “cell mobility”, “connective tissue function and development”, “motility development”, “cell–cell communication and cell–cell interaction”, and “cell survival and cell death” [11].

Mitochondria, Cell Cycle, and Apoptosis

Apoptosis is a type of programmed cell death, and mitochondria act as the major regulator of apoptosis. Various intracellular and extracellular signals induced by CAP-mediated oxidative stress converge in mitochondria, increasing their transmembrane potential and promoting the release of pro-apoptotic factors including cytochrome c. This process is regulated by the Bcl-2 protein family and ultimately leads to the activation of the caspase cascade [12]. Arndt et al. showed that when CAP was applied for 2 min to a melanoma cell line, pro-apoptotic changes such as Rad17 and tumor suppressor p53 phosphorylations, cytochrome c release, and caspase-3 activation were initiated [13].

The cell cycle is a series of events leading to cell replacement in tissues. RONS produced following high dose application of CAP can alter the cell cycle, which typically leads to apoptosis. However, lower doses of CAP can also inhibit cell proliferation by inducing cell senescence, especially when most cells in the tissue are in the proliferative phase, as observed in most tumors [13]. Typically, normal tissues differ from tumor in the proportion of cells in each cell cycle phase at a given time. In fact, this could be the biological mechanism behind the high selectivity of CAP to induce apoptosis of these cells while preserving viability of non-tumor cells. Yan et al. demonstrated that CAP increased the percentage of apoptotic tumor cells by blocking the cell cycle at the G2/M checkpoint, and this effect was mediated by reduced intracellular cyclin B1 and cyclin-dependent kinase 1 (Cdc2), increased p53 and cyclin-dependent kinase inhibitor 1 (p21), and increased Bcl-2-like protein 4 (Bax)/B cell lymphoma 2 (Bcl-2) ratio [14]. However, it is important to mention that the viability of non-tumor cells can also be altered if cells are exposed to CAP for a longer period of time [15].

Effects of Cold Atmospheric Plasma on Normal Skin Cells

In a laboratory setting, several studies have been performed to determine the effect of CAP applied to cells that are part of the epidermal (i.e., keratinocytes and melanocytes) or dermal (fibroblasts) cytoarchitecture. In these studies, dose-dependent effects of CAP on cells were observed. CAP application for less than 2 min on keratinocytes and fibroblasts was not associated with increased cell toxicity or apoptosis. However, lower or higher doses may stimulate or inhibit cell migration (fibroblasts) and proliferation (fibroblasts and keratinocytes), respectively. Most of these studies utilized normal melanocytes as a control for melanoma cells. The latest evidence of the effects of CAP on skin cells is summarized in this review.

The antiproliferative effects of CAP have been associated with increased numbers of keratinocytes in the G2/M1 phase [16]. Wende et al. evaluated 40-s CAP application on an in vitro model of wound healing based on culture of human keratinocytes colonized by Staphylococcus epidermidis [17]. Bacterial load reduction and closure of artificial wound were improved following CAP application when compared to the control. Hasse et al. investigated the ex vivo effects of CAP applied to healthy human skin samples for a longer period of time. In this study, while epidermis integrity and expression pattern of various keratins remained unchanged, basal proliferation of keratinocytes was found to be increased after 1–3 min of CAP exposure. Apoptosis was induced only when CAP was applied for 3–5 min [18]. This proliferative effect achieved using short exposure time may be beneficial to expedite healing processes. Other studies have demonstrated increased expression of IL-8, TGB-1β/TGB-β2, and β-defensin mRNA 24–48 h following keratinocytes exposure to CAP for 2 min, with no observable modification of cell proliferation, migration, or apoptosis [19].

Wound healing is a complex and dynamic biological process that requires the sequential coordination of cells, cytokines, chemokines, and proteins of the renin–angiotensin system. The time when resident fibroblasts achieve the capacity to produce growth factors and generate a collagen network is a critical point in the tissue restoration process [20]. Shashurin et al. observed that fibroblast adhesion and migration were halved following 5-min CAP application, which appeared concurrently with the downregulation of α and β integrins (10% and 22%, respectively) [21]. A subsequent study, in which CAP was applied on a human skin-derived fibroblast culture for less than 1 min, showed absence of cell proliferation and apoptosis changes [22]. However, opposing effects were observed in other studies. Tipa and Kroesen applied CAP on a cell culture-based wound model for 5–15 s and found that fibroblasts were able to cover the artificial wound more rapidly without any observable cytotoxic effects [23]. The observed increase in the proliferative and migration capacities of fibroblasts may be linked to peroxisome proliferator-activated receptor gamma (PPARγ) activation mediated by elevated intracellular ROS [19].

Standardization of Procedures and Safety Assessment

Several factors can influence the interpretation of the effects of CAP on cells and tissues, making it challenging to compare results obtained by different researchers. A standardized system of procedures related to plasma sources, devices, and treatment doses used in each study is necessary. Currently, only the DIN General Requirements of Plasma Sources in Medicine (DIN SPEC 91315, 2014), which was presented at the 5th International Conference on Plasma Medicine (ICPM5), has been published.

While most studies conducted in human subjects have described the short-term safety profile of the plasma device, there is currently no consensus on which strategy should be used to address this issue. In several studies, a tissue tolerable plasma (TTP) was determined. For example, Isbary et al. evaluated the tolerability and safety of CAP applied using the FlatPlaSter 2.0 and MiniFlatPlaSter devices through histology, electron microscopy, and DNA damage evaluations [24]. Ma et al. determined that the intracellular mechanisms were the most effective in protecting cells from oxidative stress induced by plasma by reducing cell death [25]. Lademann et al. focused on assessing the effects of UV radiation and temperature on the skin following CAP applications in several patients and healthy volunteers. They showed that UV radiation emitted by CAP was an order of magnitude lower than the minimal erythemal dose (the minimum dose needed to produce sunburn in the skin in vivo) and no thermal damage was observed in the CAP-treated areas [26]. Wende et al. recently used standardized procedures to evaluate the mutagenic potential of kIN-Pen® MED plasma in the clinic [27]. They demonstrated that RONS generated by the plasma were not able to interact directly with DNA or were found in low concentrations, which should allow for DNA damage repair by cellular mechanisms. Thus, plasma was determined to be non-genotoxic to human cells in vitro. Lastly, it should be highlighted that despite these attempts, in vivo studies evaluating potential long-term side effects of CAP have yet to be conducted.

Antitumor Effects of CAPs and Their Potential Application in Dermatology

CAP has shown a significant anticancer capacity over a wide range of cancer types. Several studies have found that tumor cells are more sensitive to CAP compared to normal cells; thus, this technology should be considered for an ideal cancer treatment.

As described previously, CAP can selectively induce apoptosis of tumor cells [28]. This feature supports CAP as a new therapeutic tool that complements the clinical benefits obtained with conventional treatments, as the latter may result in the damage of surrounding healthy tissues and are associated with greater treatment costs and/or risk of adverse effects. In contrast to chemotherapy and radiotherapy, the most attractive feature of CAP is its selective capacity for killing cancer cells. To date, several studies have demonstrated the benefit of CAP jet application on culture of cells obtained from human tumors or in immortal cell lines and animal models (Table 2). The selectivity of CAP was not only observed in cancer cells but also in various cancer cell lines. The killing capacity of CAP is dose-dependent and inversely proportional to the growth speed of cancer cells. Different studies have examined the effects of CAP on cell adhesion, migration, and invasive capacities. CAP can decrease cell adhesion without causing necrosis. In fact, CAP was able to induce detachment of certain cells through the action of ROS on the outer cell membrane without necessarily causing any intracellular changes [29]. This effect appeared to be reversible; thus, it can serve as the basis of future CAP applications in tumor microsurgery.
Table 2

Biological effects of cold plasma in preclinical models of various cancers

Non-skin tumors

Plasma

Exposure time

Model

Explored features

Lymphoma [62]

DBD plasma

Various, from 30 to 480 s

Human monocytic lymphoma cell line (U937)

Metabolic activity, cell viability, and apoptosis

Breast cancer [63]

Custom design

30, 60, and 120 s

Human metastatic cell line (MDA-MB-231)

Cell proliferation and migration

Ovarian cancer [64]

NEAPP

Various, from 2 to 600 s

Ovarian cancer cell lines (SKOV3 and HRA)

Cell proliferation and apoptosis

Colorectal cancer [65]

Torch with spray

1 s

Colorectal cancer cell lines

Migration and invasion

Lung cancer [66]

Plasma plume

10 s

Human lung adenocarcinoma cell line (A549)

DNA damage and cell viability

Liver cancer [67]

Microsize jet-type plasma

2 min

Human liver cancer cell line (SK- HEP-1)

Cell adhesion

Lung carcinoma [68]

Custom design (CU)

20 s

TC-1 mouse lung carcinoma cells

Apoptosis

Pancreatic cancer [69]

Plasma jet kINPen 09

5, 10, and 20 s

Human pancreatic cancer cell line (Colo-357 and PaTu8988T)/murine cell line (6606PDA)

Cell viability and apoptosis

Non-cutaneous squamous cell carcinoma [70]

Custom design (GWU)

10, 30, and 45 s

Head and neck squamous cell carcinoma cell lines

Cell viability and colony formation

Prostate cancer [71]

Custom design

Human and cell lines

Cell viability, gene expression, and apoptosis

Prostate cancer [72]

μ-APPJ

Various, from 2 min to 20 min

PC-3 prostate cancer cells

Cell viability, protein expression, and nitric oxide quantitation

Prostate cancer [73]

kIN-Pen Med

10 s

Human epithelial PC cell lines (LNCaP and PC-3)

Cell proliferation and apoptosis

Glioma [74]

DBD plasma

Human glioma cell line (U373MG)

Cell viability

Glioblastoma [75]

DBD plasma

20 s/day × 3 days

U87-Luc glioma tumor on athymic BALB/c nude and C57bl6 mice

Temperature and antitumor effects

Glioblastoma [76]

SMD plasma

30, 60, and 120 s

Human glioblastoma cancer cell lines

Cell viability, DNA damage, and cell cycle

Glioblastoma [77, 78]

Custom design (GWU)

Various, from 60 to 180 s

Human glioblastoma cancer cell line (U87)

Cell viability, cell cycle, and apoptosis

Glioblastoma [79]

DBD plasma

30, 60, 90, and 180 s

Glioma cell lines (U87, U373, A172), human normal astrocytes E6/E7, and HUVEC

Cell viability, cell cycle, and apoptosis

Neuroblastoma [80]

Helium-based plasma

0, 30, 60, and 120 s

Neuro2a cells murine neuroblastoma

Metabolic activity and apoptosis

HUVEC human umbilical vein endothelial cells, μ-APPJ micro-scaled atmospheric pressure plasma jet, GWU George Washington University, NEAPP non-equilibrium atmospheric pressure plasma, DBD dielectric barrier discharge, CU Clemson University, SMD surface micro discharge

Data related to the percentage or timing of the improvement achieved after CAP treatment vary widely among studies. There are many methodological differences (type of CAP, exposure time, and distance to cells) that make it difficult to compare the results (i.e., cell apoptosis after CAP application varies from 20% to 40% of melanoma cells and <10% of melanocytes) [13]. Related to the time needed to achieve the improvement, most of the reviewed studies were performed after aplying CAP for 1–180 s on cell cultures (Table 2). Short-time effects were assessed after 1–3 days in most of the cases; longer periods are needed to explore chronic effects, but in that case is not possible to use cell cultures because of confluency of cells; thus, animal models should be used for that purpose.

In most studies, CAP was applied directly to cells or tissues. However, over the past 4 years, CAP-irradiated media have also been found to effectively kill cancer cells. These media were used on mesenchymal stroma and LP-1 myeloma cell lines, and the majority of the observed effects were mediated by H2O2 and O2 species [30]. Yan et al. recently determined H2O2 as the main reactive species and cysteine as the central target molecule of CAP-irradiated media used on glioblastoma and breast cancer cells [31]. Plasma-activated water (PAW), an example of a CAP-irradiated media, is a promising anticancer therapeutic that has several advantages over the direct CAP application. These advantages should be accounted for if PAW implementation in the clinic is considered. PAW can be stored in a refrigerator for 1 week without losing its anticancer properties [32]. This feature will permit the central production of PAW in hospitals using a single plasma generator. PAW can then be packaged and distributed to various operating rooms as needed for cancer treatments within the same day. Moreover, PAW can be applied topically on tumor surfaces or injected into the tumor [33]. This feature is significant in dermatology because skin tumors are easily accessible using these approaches. However, basic principles to guide PAW application in cancer, specifically to treat skin cancer, remain undefined.

Oxidative stress may play various roles in the pathogenesis of human skin cancers. The most clinically relevant dermatological tumors are the basal cell carcinoma, cutaneous squamous cell carcinoma, and malignant melanoma. Melanoma cells exhibit increased oxidative stress, which could damage surrounding tissue, thereby supporting the progression of metastasis [34]. When CAP was applied on an immortal melanoma cell line for 2 min, apoptosis was induced in cancer cells, but not in non-neoplastic melanocytes [13]. CAP treatment for 1 min did not induce apoptosis, although a prolonged inhibition of cell proliferation was observed, promoting cell senescence. Importantly, this demonstrated the ability of CAP application to remove tumor cells from the proliferative phase of the cell cycle. Ishaq et al. also observed a similar effect by comparing a line of melanoma cells to melanocytes in culture [35]. Elevated intracellular ROS induced the expression of genes involved in cellular apoptosis mediated by TNFα and apoptosis signal-regulating kinase (ASK). When cells were pretreated with N-acetylcysteine and an antibody against TNFα, the apoptosis signal was inhibited. Recently, Daeschlein et al. evaluated the antitumor efficacy of CAP administered in conjunction with a bleomycin-based electrochemotherapy in a mouse model of melanoma. The combinational therapy improved mice survival significantly when compared to the electrochemotherapy alone [36].

To date, experimental and/or clinical studies of CAP use in non-melanoma skin cancer (such as basal cell carcinoma and squamous cell carcinoma) have yet to be conducted. In non-melanoma skin cancer, diminished antioxidant defense caused by chronic UV exposure may contribute to carcinogenesis [34]. A related study, assessing the use of CAP in cultured explants of human low-degree non-cutaneous epidermoid carcinoma of the head and neck, demonstrated that plasma can decrease cell viability and increase DNA fragmentation and cell apoptosis [37].

Clinical Use of CAP in Human Skin

Few studies have addressed the effects of CAP in humans, and studies related to skin cancer have not been performed. Most clinical trials evaluated the efficacy and safety of cold plasma application, mainly as adjuvant treatment of chronic cutaneous ulcers. This is due to the frequent bacterial colonization or wound infection in chronic cutaneous ulcers that may affect adequate restitution of tissue structure and function. Furthermore, development of bacterial resistance is unlikely based on CAP mechanism of action [38, 39]. Study design and information obtained on CAP efficacy and safety can serve as a foundation to develop future clinical trials to assess CAP as a treatment option for skin cancer [40, 41, 42]. Virtually all clinical studies of CAP have been performed using medical devices designed for topical application (MicroPlaSter® α, MicroPlaSter® β, and PlasmaDerm® VU 2010), following a phase I or II clinical trial design using small numbers of healthy volunteers or patients (from 14 to 70). In all cases, treatment was well tolerated and no significant differences in adverse effect frequency were observed in the CAP group as compared to the controls. Results obtained from other studies on CAP application in human subjects are circumstantial; most were communicated as case reports or small series of cases, and all studies were performed in non-cancerous skin diseases. In most studies, CAP treatment was not more effective than the placebo; however, it was well tolerated with no relevant adverse events [43, 44, 45]. Recently, Metelmann et al. published a retrospective review of 12 patients with head and neck non-cutaneous advanced squamous cell carcinoma that were treated with CAP to decontaminate infected cancer ulcerations. When they evaluated anticancer effects, superficial partial remission of tumor was observed in some cases following CAP exposure [46].

Conclusion

The recent development of new plasma sources and devices for simple CAP application on the skin paralleled numerous studies performed in vitro, ex vivo, and in human subjects. When applied directly or indirectly on cell cultures or disease models (in vitro or in vivo using animal models), CAP has been shown to reduce cell proliferation, adhesion, and migration, and induce selective apoptosis of neoplastic cells without damaging normal cells. These selective effects may be due to differences in the intracellular oxidative status and cell cycle phase between normal and tumor tissues. Furthermore, excessive levels of oxidative radicals induced by CAP can induce DNA damage and cell cycle exit into senescence, apoptosis, or necrosis. The antitumor capacity of CAP treatment can been regulated by controlling treatment time, gas source composition, gas flow rate, and supply voltage. When CAP is utilized to irradiate a medium or water to obtain WAS, the distance between CAP source and the liquid, and the final volume should be taken into consideration. Despite mounting evidence supporting its use, studies of CAP in human subjects are still limited. In the majority of these studies, CAP was shown to be well tolerated without any observable short-term adverse effects. Therefore, we suggest further investigation of CAP, including the use of PAW, as potential adjuvant therapies for skin tumors such as basal cell carcinoma, squamous cell carcinoma, and malignant melanoma.

Notes

Acknowledgments

No funding or sponsorship was received for this study or publication of this article. All authors meet the International Committee of Medical Journal Editors (ICMJE) criteria for authorship, take responsibility for the integrity of the work as a whole, and have given final approval for the version to be published. The authors would like to thank Editage (http://www.editage.com) for English-language editing.

Disclosures

Jesús Gay-Mimbrera, Maria Carmen García, Beatriz Isla-Tejera, Antonio Rodero-Serrano, Antonio Vélez García-Nieto, and Juan Ruano have nothing to disclose.

Compliance with Ethics Guidelines

Analyses described in this review article were based on previously conducted studies. No studies involving human subjects or animals were performed for the publication of this review.

Open Access

This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (http://creativecommons.org/licenses/by-nc/4.0/), which permits any noncommercial use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

References

  1. 1.
    von Woedtke Th, Reuter S, Masur K, Weltmann KD. Plasmas for medicine. Phys Rep. 2013;530:291–320.CrossRefGoogle Scholar
  2. 2.
    Raiser J, Zenker M. M. Argon plasma coagulation for open surgical and endoscopic applications: state of the art. J Phys D Appl Phys. 2006;39:3520–3.CrossRefGoogle Scholar
  3. 3.
    Heslin C, Boehm D, Milosavljevic V, Laycock M, Cullen PJ, Bourke P. Quantitative assessment of blood coagulation by cold atmospheric plasma. Plasma Med. 2014;4:153–63.CrossRefGoogle Scholar
  4. 4.
    Zuo X, Wei Y, Wei Chen L, Dong Meng Y. Non-equilibrium atmospheric pressure microplasma jet: an approach to endoscopic therapies. Phys Plasmas. 2013;20:083507.CrossRefGoogle Scholar
  5. 5.
    Kong MG, Kroesen G, Morfill G, et al. Plasma medicine: an introductory review. New J Phys. 2009;11:115012.CrossRefGoogle Scholar
  6. 6.
    Isbary G, Zimmermann JL, Shimizu T, et al. Non-thermal plasma-more than five years of clinical experience. Clin Plasma Med. 2013;1:19–23.CrossRefGoogle Scholar
  7. 7.
    Graves DB. The emerging role of reactive oxygen and nitrogen species in redox biology and some implications for plasma applications to medicine and biology. J Phys D Appl Phys. 2012;45:263001.CrossRefGoogle Scholar
  8. 8.
    Schmidt A, von Woedtke T, Bekeschus S. Periodic exposure of keratinocytes to cold physical plasma–an in vitro model for redox-related diseases of the skin. Oxid Med Cell Longev. 2016;2016:9816072.Google Scholar
  9. 9.
    Arndt S, Unger P, Wacker E, et al. Cold atmospheric plasma (CAP) changes gene expression of key molecules of the wound healing machinery and improves wound healing in vitro and in vivo. PLoS one. 2013;8:e79325.CrossRefPubMedPubMedCentralGoogle Scholar
  10. 10.
    Zhong S, Dong Y, Liu D, et al. Surface air plasma induced cell death and cytokines release of human keratinocytes in the context of psoriasis. Br J Dermatol. 2016;174:542–52.Google Scholar
  11. 11.
    Park S-B, Kim B, Bae H, et al. Differential epigenetic effects of atmospheric cold plasma on MCF-7 and MDA-MB-231 breast cancer cells. PLoS One. 2015;10:e0129931.CrossRefPubMedPubMedCentralGoogle Scholar
  12. 12.
    Ahn HJ, Kim KI, Kim G, Moon E, Yang SS, Lee JS. Atmospheric-pressure plasma jet induces apoptosis involving mitochondria via generation of free radicals. PLoS One. 2011;6:e28154.Google Scholar
  13. 13.
    Arndt S, Wacker E, Li YF, et al. Cold atmospheric plasma, a new strategy to induce senescence in melanoma cells. Exp Dermatol. 2013;22:284–9.CrossRefPubMedGoogle Scholar
  14. 14.
    Yan X, Zou F, Zhao S, et al. On the mechanism of plasma inducing cell apoptosis. IEEE Trans Plasma Sci. 2010;38:2451–7.CrossRefGoogle Scholar
  15. 15.
    Kim KC, Piao MJ, Madduma Hewage SRK, et al. Non-thermal dielectric-barrier discharge plasma damages human keratinocytes by inducing oxidative stress. Int J Mol Med. 2016;37:29–38.PubMedGoogle Scholar
  16. 16.
    Blackert S, Haertel B, Wende K, von Woedtke T, Lindequist U. Influence of non-thermal atmospheric pressure plasma on cellular structures and processes in human keratinocytes (HaCaT). J Dermatol Sci. 2013;70:173–81.CrossRefPubMedGoogle Scholar
  17. 17.
    Wende K, Landsberg K, Lindequist U, Weltmann K-D, von Woedtke T. Distinctive activity of a nonthermal atmospheric-pressure plasma jet on eukaryotic and prokaryotic cells in a cocultivation approach of keratinocytes and microorganisms. IEEE Trans Plasma Sci. 2010;38:2479–85.CrossRefGoogle Scholar
  18. 18.
    Hasse S, Duong Tran T, et al. Induction of proliferation of basal epidermal keratinocytes by cold atmospheric-pressure plasma. Clin Exp Dermatol. 2016;41(2):202–9.CrossRefPubMedGoogle Scholar
  19. 19.
    Arndt S, Landthaler M, Zimmermann JL, et al. Effects of cold atmospheric plasma (CAP) on β-defensins, inflammatory cytokines, and apoptosis-related molecules in keratinocytes in vitro and in vivo. PLoS One. 2015;10:e0120041.CrossRefPubMedPubMedCentralGoogle Scholar
  20. 20.
    Brun P, Pathak S, Castagliuolo I, et al. Helium generated cold plasma finely regulates activation of human fibroblast-like primary cells. PLoS One. 2014;9:e104397.CrossRefPubMedPubMedCentralGoogle Scholar
  21. 21.
    Shashurin A, Stepp MA, Hawley TS, et al. Influence of cold plasma atmospheric jet on surface integrin expression of living cells. Plasma Process Polym. 2010;7:294–300.CrossRefGoogle Scholar
  22. 22.
    Lopes BB, De Paula Leite Kraft MB, Rehder J, Batista FRX, Puzzi MB. The interactions between non-thermal atmospheric pressure plasma and ex vivo dermal fibroblasts. Proc Eng. 2013;59:92–100.Google Scholar
  23. 23.
    Tipa RS, Kroesen GMW. Plasma-stimulated wound healing. IEEE Trans Plasma Sci. 2011;39:2978–9.CrossRefGoogle Scholar
  24. 24.
    Isbary G, Köritzer J, Mitra A, et al. Ex vivo human skin experiments for the evaluation of safety of new cold atmospheric plasma devices. Clin Plasma Med. 2013;1:36–44.CrossRefGoogle Scholar
  25. 25.
    Ma R, Feng H, Li F, et al. An evaluation of anti-oxidative protection for cells against atmospheric pressure cold plasma treatment. Appl Phys Lett. 2012;100:3–7.Google Scholar
  26. 26.
    Lademann J, Richter H, Alborova A, et al. Risk assessment of the application of a plasma jet in dermatology. J Biomed Opt. 2009;14:054025.CrossRefPubMedGoogle Scholar
  27. 27.
    Wende K, Bekeschus S, Schmidt A, et al. Risk assessment of a cold argon plasma jet in respect to its mutagenicity. Mutat Res Genet Toxicol Environ Mutagen. 2016;798–799:48–54.CrossRefPubMedGoogle Scholar
  28. 28.
    Keidar M. Plasma for cancer treatment. Plasma Sour Sci Technol. 2015;24:033001.CrossRefGoogle Scholar
  29. 29.
    Kieft IE, Kurdi M, Stoffels E. Reattachment and apoptosis after plasma-needle treatment of cultured cells. IEEE Trans Plasma Sci. 2006;34:1331–6.CrossRefGoogle Scholar
  30. 30.
    Xu D, Liu D, Wang B, et al. In situ OH generation from O2 and H2O2 plays a critical role in plasma-induced cell death. PLoS One. 2015;10:e0128205.CrossRefPubMedPubMedCentralGoogle Scholar
  31. 31.
    Yan D, Talbot A, Nourmohammadi N, et al. Principles of using cold atmospheric plasma stimulated media for cancer treatment. Sci Rep. 2015;17(5):18339.CrossRefGoogle Scholar
  32. 32.
    Adachi T, Tanaka H, Nonomura S, et al. Plasma-activated medium induces A549 cell injury via a spiral apoptotic cascade involving the mitochondrial-nuclear network. Free Radic Biol Med. 2015;79:28–44.CrossRefPubMedGoogle Scholar
  33. 33.
    Utsumi F, Kajiyama H, Nakamura K, et al. Effect of indirect nonequilibrium atmospheric pressure plasma on anti-proliferative activity against chronic chemo-resistant ovarian cancer cells in vitro and in vivo. PLoS One. 2013;8(12):e81576.CrossRefPubMedPubMedCentralGoogle Scholar
  34. 34.
    Sander CS, Hamm F, Elsner P, Thiele JJ. Oxidative stress in malignant melanoma and non-melanoma skin cancer. Br J Dermatol. 2003;148(5):913–22.CrossRefPubMedGoogle Scholar
  35. 35.
    Ishaq M, Kumar S, Varinli H, et al. Atmospheric gas plasma-induced ROS production activates TNF-ASK1 pathway for the induction of melanoma cancer cell apoptosis. Mol Biol Cell. 2014;25:1523–31.CrossRefPubMedPubMedCentralGoogle Scholar
  36. 36.
    Daeschlein G, Scholz S, Lutze S, et al. Comparison between cold plasma, electrochemotherapy and combined therapy in a melanoma mouse model. Exp Dermatol. 2013;22:582–6.CrossRefPubMedGoogle Scholar
  37. 37.
    Welz C, Emmert S, Canis M, et al. Cold atmospheric plasma: a promising complementary therapy for squamous head and neck cancer. PLoS One. 2015;10:e0141827.CrossRefPubMedPubMedCentralGoogle Scholar
  38. 38.
    Maisch T, Shimizu T, Li Y-F, et al. Decolonisation of MRSA, S. aureus and E. coli by cold-atmospheric plasma using a porcine skin model in vitro. PLoS One. 2012;7:e34610.CrossRefPubMedPubMedCentralGoogle Scholar
  39. 39.
    Klampfl TG, Isbary G, Shimizu T, et al. Cold atmospheric air plasma sterilization against spores and other microorganisms of clinical interest. Appl Environ Microbiol. 2012;78:5077–82.CrossRefPubMedPubMedCentralGoogle Scholar
  40. 40.
    Isbary G, Morfill G, Schmidt HU, et al. A first prospective randomized controlled trial to decrease bacterial load using cold atmospheric argon plasma on chronic wounds in patients. Br J Dermatol. 2010;163:78–82.PubMedGoogle Scholar
  41. 41.
    Isbary G, Heinlin J, Shimizu T, et al. Successful and safe use of 2 min cold atmospheric argon plasma in chronic wounds: results of a randomized controlled trial. Br J Dermatol. 2012;167:404–10.CrossRefPubMedGoogle Scholar
  42. 42.
    Brehmer F, Haenssle HA, Daeschlein G, et al. Alleviation of chronic venous leg ulcers with a hand-held dielectric barrier discharge plasma generator (PlasmaDerm(®) VU-2010): results of a monocentric, two-armed, open, prospective, randomized and controlled trial (NCT01415622). J Eur Acad Dermatol Venereol. 2015;29:148–55.CrossRefPubMedGoogle Scholar
  43. 43.
    Klebes M, Lademann J, Philipp S, et al. Effects of tissue-tolerable plasma on psoriasis vulgaris treatment compared to conventional local treatment: a pilot study. Clin Plasma Med. 2014;2:22–7.CrossRefGoogle Scholar
  44. 44.
    Isbary G, Morfill G, Zimmermann J, Shimizu T, Stolz W. Cold atmospheric plasma: a successful treatment of lesions in Hailey-Hailey disease. Arch Dermatol. 2011;147:388–90.CrossRefPubMedGoogle Scholar
  45. 45.
    Heinlin J, Isbary G, Stolz W, et al. A randomized two-sided placebo-controlled study on the efficacy and safety of atmospheric non-thermal argon plasma for pruritus. J Eur Acad Dermatol Venereol. 2013;27:324–31.CrossRefPubMedGoogle Scholar
  46. 46.
    Metelmann HR, Nedrelow DS, Seebauer C, et al. Head and neck cancer treatment and physical plasma. Clin Plasma Med. 2015;3:17–23.CrossRefGoogle Scholar
  47. 47.
    Daeschlein G, Scholz S, Ahmed R, et al. Cold plasma is well-tolerated and does not disturb skin barrier or reduce skin moisture. J Dtsch Dermatol Ges. 2012;10:509–15.PubMedGoogle Scholar
  48. 48.
    Welz C, Becker S, Li Y-F, et al. Effects of cold atmospheric plasma on mucosal tissue culture. J Phys D Appl Phys. 2013;46:045401.CrossRefGoogle Scholar
  49. 49.
    Tiede R, Hirschberg J, Daeschlein G, von Woedtke T, Vioel W, Emmert S. Plasma applications: a dermatological view. Contrib Plasma Phys. 2014;2:118–30.CrossRefGoogle Scholar
  50. 50.
    Rajasekaran P, Mertmann P, Bibinov N, Wandke D, Viöl W, Awakowicz P. DBD plasma source operated in single-filamentary mode for therapeutic use in dermatology. J Phys D Appl Phys. 2009;42:225201.CrossRefGoogle Scholar
  51. 51.
    Bender C, Matthes R, Kindel E, et al. The irritation potential of nonthermal atmospheric pressure plasma in the het-CAM. Plasma Process Polym. 2010;7:318–26.CrossRefGoogle Scholar
  52. 52.
    Boekema BKHL, Vlig M, Guijt D, et al. A new flexible DBD device for treating infected wounds: in vitro and ex vivo evaluation and comparison with a RF argon plasma jet. J Phys D Appl Phys. 2016;49:044001.CrossRefGoogle Scholar
  53. 53.
    Chutsirimongkol C, Boonyawan D, Polnikorn N, Techawatthanawisan W, Kundilokchai T. Non-thermal plasma for acne treatment and aesthetic skin improvement. Plasma Med. 2014;4:79–88.CrossRefGoogle Scholar
  54. 54.
    Haertel B, von Woedtke T, Weltmann K-D, Lindequist U. Non-thermal atmospheric-pressure plasma possible application in wound healing. Biomol Ther 2014;22:477–90.CrossRefGoogle Scholar
  55. 55.
    Daeschleia G, Scholza S, Ahmed R, et al. Skin decontamination by low-temperature atmospheric pressure plasma jet and dielectric barrier discharge plasma. J Hosp Infect. 2012;81:177–83.CrossRefGoogle Scholar
  56. 56.
    Fluhr JW, Sassning S, Lademann O, et al. In vivo skin treatment with tissue-tolerable plasma influences skin physiology and antioxidant profile in human stratum corneum. Exp Dermatol. 2011;21:130–4.CrossRefPubMedGoogle Scholar
  57. 57.
    Ishaq M, Bazaka K, Ostrikov K. Pro-apoptotic NOXA is implicated in atmospheric-pressure plasma-induced melanoma cell death. J Phys D Appl Phys. 2015;48:464002.CrossRefGoogle Scholar
  58. 58.
    Jacofsky MC, Lubahn C, McDonnell C, et al. Spatially resolved optical emission spectroscopy of a helium plasma jet and its effects on wound healing rate in a diabetic murine model. Plasma Med. 2014;4:177–91.CrossRefGoogle Scholar
  59. 59.
    Boekema BKHL, Hofmann SS, van Ham BJT, Bruggeman PJ, Middelkoop E. Antibacterial plasma at safe levels for skin cells. J Phys D Appl Phys. 2013;46:422001.Google Scholar
  60. 60.
    Morfill G, Shimizu T, Steffes B, Schmidt H-U. Nosocomical infections-a new approach towards preventive medicine using plasmas. New J Phys. 2009;11:115019.CrossRefGoogle Scholar
  61. 61.
    Li YF, Taylor D, Zimmermann JL, et al. In vivo skin treatment using two portable plasma devices: comparison of a direct and an indirect cold atmospheric plasma treatment. Clin Plasma Med. 2013;1:35–9.CrossRefGoogle Scholar
  62. 62.
    Kaushik N, Kumar N, Kim CH, Kaushik NK, Choi EH. Dielectric barrier discharge plasma efficiently delivers an apoptotic response in human monocytic lymphoma. Plasma Process Polym. 2014;11:1175–87.CrossRefGoogle Scholar
  63. 63.
    Wang M, Holmes B, Cheng X, Zhu W, Keidar M, Zhang LG. Cold atmospheric plasma for selectively ablating metastatic breast cancer cells. PLoS One. 2013;8:e73741.CrossRefPubMedPubMedCentralGoogle Scholar
  64. 64.
    Iseki S, Nakamura K, Hayashi M, et al. Selective killing of ovarian cancer cells through induction of apoptosis by nonequilibrium atmospheric pressure plasma. Appl Phys Lett. 2012;100:113702.CrossRefGoogle Scholar
  65. 65.
    Kim CH, Kwon S, Bahn JH, et al. Effects of atmospheric nonthermal plasma on invasion of colorectal cancer cells. Appl Phys Lett. 2010;96.Google Scholar
  66. 66.
    Joh HM, Choi JY, Kim SJ, Chung TH, Kang T-H. Effect of additive oxygen gas on cellular response of lung cancer cells induced by atmospheric pressure helium plasma jet. Sci Rep. 2014;4:6638.CrossRefPubMedPubMedCentralGoogle Scholar
  67. 67.
    Gweon B, Kim M, Bee Kim D, et al. Differential responses of human liver cancer and normal cells to atmospheric pressure plasma. Appl Phys Lett. 2011;99:063701.CrossRefGoogle Scholar
  68. 68.
    Kim JY, Ballato J, Foy P, et al. Apoptosis of lung carcinoma cells induced by a flexible optical fiber-based cold microplasma. Biosens Bioelectron. 2011;28:530–8.CrossRefGoogle Scholar
  69. 69.
    Partecke LI, Evert K, Haugk J, et al. Tissue tolerable plasma (TTP) induces apoptosis in pancreatic cancer cells in vitro and in vivo. BMC Cancer. 2012;12:1–10.CrossRefGoogle Scholar
  70. 70.
    Guerrero-Preston R, Ogawa T, Uemura M, et al. Cold atmospheric plasma treatment selectively targets head and neck squamous cell carcinoma cells. Int J Mol Med. 2014;34:941–6.PubMedPubMedCentralGoogle Scholar
  71. 71.
    Hirst AM, Frame FM, Maitland NJ, Connell DO. Low temperature plasma: a novel focal therapy for localized prostate cancer. Biomed Res Int. 2014;2014:878319.CrossRefPubMedPubMedCentralGoogle Scholar
  72. 72.
    Gibson AR, McCarthy HO, Ali A, O’Connell D, Graham WG. Interactions of a non-thermal atmospheric pressure plasma effluent with PC-3 prostate cancer cells. Plasma Process Polym. 2014;11:1142–9.CrossRefGoogle Scholar
  73. 73.
    Weiss M, Gümbel D, Hanschmann E-M, et al. Cold atmospheric plasma treatment induces anti-proliferative effects in prostate cancer cells by redox and apoptotic signaling pathways. PLoS One. 2015;10:e0130350.CrossRefPubMedPubMedCentralGoogle Scholar
  74. 74.
    Conway GE, Casey A, Milosavljevic V, Liu Y, Howe O, Cullen PJ, et al. Non-thermal atmospheric plasma induces ROS-independent cell death in U373MG glioma cells and augments the cytotoxicity of temozolomide. Br J Cancer. 2016;114(4):435–43.CrossRefPubMedGoogle Scholar
  75. 75.
    Vandamme M, Robert E, Pesnel S, et al. Antitumor effect of plasma treatment on U87 glioma xenografts: preliminary results. Plasma Process Polym. 2010;7:264–73.Google Scholar
  76. 76.
    Köritzer J, Boxhammer V, Al E. Restoration of sensitivity in chemo-resistant glioma cells by cold atmospheric plasma. PLoS One. 2013;8:1–10.CrossRefGoogle Scholar
  77. 77.
    Cheng X, Murphy W, Recek N, et al. Synergistic effect of gold nanoparticles and cold plasma on glioblastoma cancer therapy. J Phys D Appl Phys. 2014;47:335402.CrossRefGoogle Scholar
  78. 78.
    Cheng X, Sherman J, Murphy W, Ratovitski E, Canady J, Keidar M. The effect of tuning cold plasma composition on glioblastoma cell viability. PLoS One. 2014;9:1–9.CrossRefGoogle Scholar
  79. 79.
    Siu A, Volotskova O, Cheng X, et al. Differential effects of cold atmospheric plasma in the treatment of malignant glioma. PLoS One. 2015;10:e0126313.CrossRefPubMedPubMedCentralGoogle Scholar
  80. 80.
    Walk RM, Snyder J, Srinivasan P, et al. Cold atmospheric plasma for the ablative treatment of neuroblastoma. J Pediatr Surg. 2013;48:67–73.CrossRefPubMedGoogle Scholar

Copyright information

© The Author(s) 2016

Authors and Affiliations

  • Jesús Gay-Mimbrera
    • 1
  • Maria Carmen García
    • 2
  • Beatriz Isla-Tejera
    • 1
    • 3
  • Antonio Rodero-Serrano
    • 4
  • Antonio Vélez García-Nieto
    • 1
    • 5
  • Juan Ruano
    • 1
    • 5
  1. 1.Instituto Maimónides de Investigación Biomédica de Córdoba (IMIBIC), Hospital Universitario Reina SofíaUniversity of CórdobaCórdobaSpain
  2. 2.Department of Applied PhysicsUniversity of CórdobaCórdobaSpain
  3. 3.Department of PharmacyHospital Universitario Reina SofíaCórdobaSpain
  4. 4.Department of Physics, School of Engineering Science of BelmezUniversity of CórdobaCórdobaSpain
  5. 5.Department of DermatologyHospital Universitario Reina SofíaCórdobaSpain

Personalised recommendations