In Vitro and In Vivo Enhancement of Temozolomide Effect in Human Glioblastoma by Non-Invasive Application of Cold Atmospheric Plasma

SIMPLE SUMMARY: Glioblastoma (GBM) is an aggressive type of brain cancer, with which only 25% of patients survive for more than one year. Treatment of GBM has remained a challenge due to its resistance to chemotherapy. Here, we aimed to assess the potential for a combination therapy of cold atmospheric plasma (CAP) and Temozolomide (TMZ) to treat GBM. We confirmed the effect of co-treatment on different GBM cell lines in vitro and determined the enhancement of the effect of TMZ and the potential sensitization of GBM to CAP + TMZ in murine models in vivo. We found that co-treatment with CAP + TMZ inhibited GBM significantly compared to single treatment with CAP or TMZ alone. We provided further evidence related to the bone penetration of reactive oxygen and nitrogen species, as well as electromagnetic waves generated by CAP. RNA sequencing further indicated an effect of CAP + TMZ on cell cycle pathways. Collectively, these findings point to potential non-invasive translational approaches to target GBM in the future. ABSTRACT: Glioblastoma (GBM) is one of the most aggressive forms of adult brain cancers and is highly resistant to treatment, with a median survival of 12–18 months after diagnosis. The poor survival is due to its infiltrative pattern of invasion into the normal brain parenchyma, the diffuse nature of its growth, and its ability to quickly grow, spread, and relapse. Temozolomide is a well-known FDA-approved alkylating chemotherapy agent used for the treatment of high-grade malignant gliomas, and it has been shown to improve overall survival. However, in most cases, the tumor relapses. In recent years, CAP has been used as an emerging technology for cancer therapy. The purpose of this study was to implement a combination therapy of CAP and TMZ to enhance the effect of TMZ and apparently sensitize GBMs. In vitro evaluations in TMZ-sensitive and resistant GBM cell lines established a CAP chemotherapy enhancement and potential sensitization effect across various ranges of CAP jet application. This was further supported with in vivo findings demonstrating that a single CAP jet applied non-invasively through the skull potentially sensitizes GBM to subsequent treatment with TMZ. Gene functional enrichment analysis further demonstrated that co-treatment with CAP and TMZ resulted in a downregulation of cell cycle pathway genes. These observations indicate that CAP can be potentially useful in sensitizing GBM to chemotherapy and for the treatment of glioblastoma as a non-invasive translational therapy.