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The requirements for new technologies to serve as anticancer agents go far beyond their toxicity potential. Novel applications also need to be safe on a molecular and patient level. In a broader sense, this also relates to cancer metastasis and inflammation. In a previous study, the toxicity of an atmospheric pressure argon plasma jet in four human pancreatic cancer cell lines was confirmed and plasma treatment did not promote metastasis in vitro and in ovo. Here, these results are extended by additional types of analysis and new models to validate and define on a molecular level the changes related to metastatic processes in pancreatic cancer cells following plasma treatment in vitro and in ovo. In solid tumors that were grown on the chorion-allantois membrane of fertilized chicken eggs (TUM-CAM), plasma treatment induced modest to profound apoptosis in the tissues. This, however, was not associated with a change in the expression levels of adhesion molecules, as shown using immunofluorescence of ultrathin tissue sections. Culturing of the cells detached from these solid tumors for 6d revealed a similar or smaller total growth area and expression of ZEB1, a transcription factor associated with cancer metastasis, in the plasma-treated pancreatic cancer tissues. Analysis of in vitro and in ovo supernatants of 13 different cytokines and chemokines revealed cell line-specific effects of the plasma treatment but a noticeable increase of, e.g., growth-promoting interleukin 10 was not observed. Moreover, markers of epithelial-to-mesenchymal transition (EMT), a metastasis-promoting cellular program, were investigated. Plasma-treated pancreatic cancer cells did not present an EMT-profile. Finally, a realistic 3D tumor spheroid co-culture model with pancreatic stellate cells was employed, and the invasive properties in a gel-like cellular matrix were investigated. Tumor outgrowth and spread was similar or decreased in the plasma conditions. Altogether, these results provide valuable insights into the effect of plasma treatment on metastasis-related properties of cancer cells and did not suggest EMT-promoting effects of this novel cancer therapy.
Molecular Mechanisms of the Efficacy of Cold Atmospheric Pressure Plasma (CAP) in Cancer Treatment
(2020)
Background: Cold atmospheric plasma (CAP) is increasingly used in the field of oncology.
Many of the mechanisms of action of CAP, such as inhibiting proliferation, DNA breakage, or the
destruction of cell membrane integrity, have been investigated in many different types of tumors.
In this regard, data are available from both in vivo and in vitro studies. Not only the direct treatment
of a tumor but also the influence on its blood supply play a decisive role in the success of the therapy
and the patient’s further prognosis. Whether the CAP influences this process is unknown, and the
first indications in this regard are addressed in this study. Methods: Two different devices, kINPen
and MiniJet, were used as CAP sources. Human endothelial cell line HDMEC were treated directly
and indirectly with CAP, and growth kinetics were performed. To indicate apoptotic processes,
caspase-3/7 assay and TUNEL assay were used. The influence of CAP on cellular metabolism
was examined using the MTT and glucose assay. After CAP exposure, tube formation assay was
performed to examine the capillary tube formation abilities of HDMEC and their migration was
messured in separate assays. To investigate in a possible mutagenic effect of CAP treatment,
a hypoxanthine-guanine-phosphoribosyl-transferase assay with non malignant cell (CCL-93) line was
performed. Results: The direct CAP treatment of the HDMEC showed a robust growth-inhibiting
effect, but the indirect one did not. The MMT assay showed an apparent reduction in cell metabolism
in the first 24 h after CAP treatment, which appeared to normalize 48 h and 72 h after CAP application.
These results were also confirmed by the glucose assay. The caspase 3/7 assay and TUNEL assay
showed a significant increase in apoptotic processes in the HDMEC after CAP treatment. These results
were independent of the CAP device. Both the migration and tube formation of HDMEC were
significant inhibited after CAP-treatment. No malignant effects could be demonstrated by the CAP
treatment on a non-malignant cell line.
Despite continuous advances in therapy, malignant melanoma is still among the deadliest
types of cancer. At the same time, owing to its high plasticity and immunogenicity, melanoma is
regarded as a model tumor entity when testing new treatment approaches. Cold physical plasma is a
novel anticancer tool that utilizes a plethora of reactive oxygen species (ROS) being deposited on the
target cells and tissues. To test whether plasma treatment would enhance the toxicity of an established
antitumor therapy, ionizing radiation, we combined both physical treatment modalities targeting
B16F10 murine melanoma cell in vitro. Repeated rather than single radiotherapy, in combination
with gas plasma-introduced ROS, induced apoptosis and cell cycle arrest in an additive fashion. In
tendency, gas plasma treatment sensitized the cells to subsequent radiotherapy rather than the other
way around. This was concomitant with increased levels of TNFα, IL6, and GM-CSF in supernatants.
Murine JAWS dendritic cells cultured in these supernatants showed an increased expression of cell
surface activation markers, such as MHCII and CD83. For PD-L1 and PD-L2, increased expression
was observed. Our results are the first to suggest an additive therapeutic effect of gas plasma and
radiotherapy, and translational tumor models are needed to develop this concept further.
Chondrosarcoma is the second most common malign bone tumor in adults. Surgical
resection of the tumor is recommended because of its resistance to clinical treatment such as
chemotherapy and radiation therapy. Thus, the prognosis for patients mainly depends on sufficient
surgical resection. Due to this, research on alternative therapies is needed. Cold atmospheric plasma
(CAP) is an ionized gas that contains various reactive species. Previous studies have shown an
anti-oncogenic potential of CAP on different cancer cell types. The current study examined the effects
of treatment with CAP on two chondrosarcoma cell lines (CAL-78, SW1353). Through proliferation
assay, the cell growth after CAP-treatment was determined. A strong antiproliferative effect for
both cell lines was detected. By fluorescein diacetate (FDA) assay and ATP release assay, alterations
in the cell membrane and associated translocation of low molecular weight particles through the
cytoplasmic membrane were observed. In supernatant, the non-membrane-permeable FDA and
endogenously synthesized ATP detected suggest an increased membrane permeability after CAP
treatment. Similar results were shown by the dextran-uptake assay. Furthermore, fluorescence
microscopic G-/F-actin assay was performed. G- and F-actin were selectively dyed, and the ratio
was measured. The presented results indicate CAP-induced changes in cell membrane function and
possible alterations in actin-cytoskeleton, which may contribute to the antiproliferative effects of CAP.
Osteosarcoma and Ewing’s sarcoma are the most common malignant bone tumors.Conventional therapies such as polychemotherapy, local surgery, and radiotherapy improve theclinical outcome for patients. However, they are accompanied by acute and chronic side effectsthat affect the quality of life of patients, motivating novel research lines on therapeutic optionsfor the treatment of sarcomas. Previous experimental work with physical plasma operated atbody temperature (cold atmospheric plasma, CAP) demonstrated anti-oncogenic effects on differentcancer cell types. This study investigated the anti-cancer effect of CAP on two bone sarcomaentities, osteosarcoma and Ewing’s sarcoma, which were represented by four cell lines (U2-OS,MNNG/HOS, A673, and RD-ES). A time-dependent anti-proliferative effect of CAP on all cell lineswas observed. CAP-induced alterations in cell membrane functionality were detected by performinga fluorescein diacetate (FDA) release assay and an ATP release assay. Additionally, modifications ofthe cell membrane and modifications in the actin cytoskeleton composition were examined usingfluorescence microscopy monitoring dextran-uptake assay and G-/F-actin distribution. Furthermore,the CAP-induced induction of apoptosis was determined by TUNEL and active caspases assays.The observations suggest that a single CAP treatment of bone sarcoma cells may have significantanti-oncogenic effects and thus may be a promising extension to existing applications.