Cold Atmospheric Plasma: A New Strategy Based Primarily on Oxidative Stress for Osteosarcoma Therapy

Abstract

Osteosarcoma is the most common primary bone tumor, and its first line of treatment presents a high failure rate. The 5-year survival for children and teenagers with osteosarcoma is 70% (if diagnosed before it has metastasized) or 20% (if spread at the time of diagnosis), stressing the need for novel therapies. Recently, cold atmospheric plasmas (ionized gases consisting of UV-Vis radiation, electromagnetic fields and a great variety of reactive species) and plasma-treated liquids have been shown to have the potential to selectively eliminate cancer cells in different tumors through an oxidative stress-dependent mechanism. In this work, we review the current state of the art in cold plasma therapy for osteosarcoma. Specifically, we emphasize the mechanisms unveiled thus far regarding the action of plasmas on osteosarcoma. Finally, we review current and potential future approaches, emphasizing the most critical challenges for the development of osteosarcoma therapies based on this emerging technique.

Keywords: cancer stem cells; cold atmospheric plasma; osteosarcoma; oxidative stress; plasma treated liquids; reactive oxygen and nitrogen species; tumor microenvironment.

Figure 1

(A) Atmospheric pressure plasma jet (APPJ) in operation. (B) illustration of the principle of generation of plasma, where a power discharge is applied to two electrodes in between a gas (usually He or Ar) flows through a dielectric tube. This generates the plasma discharge that can then be applied directly to OS tumors in vivo, cells in vitro or used to produce plasma-treated liquids that can in turn be used to treat tumors or cells.

Figure 2

Strategies to apply Cold Atmospheric Plasma (CAP) in cell culture and tissues. In the direct CAP application to cancer cells and tissues, all plasma components (i.e., electromagnetic fields, ultraviolet (UV), total RONS and different particles) can interact with cells, but limitations include the limited depth of penetration. In the indirect treatment, based on plasma-treated liquids, only the most stable reactive species and ions have an effect, while they allow local delivery by injection.

Figure 3

Methods of application of CAP treatment in an OS clinical situation. (A) Schematic model of direct treatment of an OS tumor in the early stages of tumor progression or after surgical resection of the tumor. (B) Indirect treatment via injection of plasma-treated liquids in the early stages of OS or inside the defect generated after tumor resection.

Figure 4

Summary of the main in vitro mechanisms of CAP in OS. Green boxes indicate increase or upregulation, while red boxes indicate decrease or down-expression. CAP containing ultraviolet (UV) and electromagnetic fields produce RONS in liquids. In the cell, pyruvate scavenges hydrogen peroxide. CAP induces cell membrane disruption, which facilitates the transport of RONS into the cell, inducing an increase in intracellular RONS and oxidative stress, which can be attenuated by antioxidants. On the one hand, oxidative stress increases peroxiredoxin expression and modulates protein phosphorylation and transcription factor activation, which determines cell death or survival. CAP-derived RONS can also alter the expression pattern of cytokines, chemokines and growth factors related to OS progression. On the other hand, CAP produces DNA damage that is related to p53 activation and caspase-dependent apoptosis. CAP can also produce mitochondrial injury directly or cause it indirectly by increasing the RE-mitochondrial calcium influx. CAP is also reported to induce mitochondrial autophagy, which may decide between cell death and survival.

Figure 5

Possible involvement of CAP treatment in the OS microenvironment. (A) Schematic illustration of an OS tumor and the main characteristics enhanced by the OS microenvironment that may be affected by CAP. (B) Cellular components that are present in the OS microenvironment.