Plasma activated media and direct exposition can selectively ablate retinoblastoma cells

A new therapy based on atmospheric plasma, the fourth state of matter, has raised the medical community's attention by circumventing many undesirable effects of old anticancer treatments. This work aimed to evaluate the effect, selectivity, and mechanisms of action of cold atmospheric plasma (CAP) in human retinoblastoma cells. An electronic device was designed to generate CAP in the open air, 2 mm above seeded cell cultures. Three approaches were performed: direct use of CAP, plasma-activated media (PAM), and conditioned media (CM). Timely-resolved output voltage measurement, emission spectroscopy, and quantification of reactive species (RS) of PAM were performed. To evaluate cytotoxicity and selectivity, similarly treated Y79, fibroblasts HFF1, and retinal RPE-D407 cells were assessed. After 60 s of direct CAP treatment, the metabolic activity of retinoblastoma cells decreased more than 50%, mainly due to apoptosis, while HFF1 and RPE-D407 remained viable. Similar results were obtained with indirect treatment (PAM and CM). Cell survival was reduced, and cells accumulated in S and G2/M phases; however, no DNA strand breaks were detected. Regarding RS, plasma increased extracellular and intracellular concentrations of peroxides and nitric oxide, despite glutathione activation and lack of success in reverting cytotoxicity with some RS inhibitors. RS increase comes in two timely distant waves, the first one originating from the plasma itself with secondary solubilization and passive diffusion, the second wave deriving from the mitochondrion. The addition of low doses of carboplatin to CAP-treated cells resulted in a significant increase in cytotoxicity compared with either regimen alone. Additionally, maximal antiangiogenic effects were obtained with 60 s of plasma exposure. Direct and indirect treatment with CAP might be a selective therapy with the potential to target tumour cells and supporting the microenvironment.