P18.03.A EPIGENETIC INFLUENCE OF CANNABINOIDS IN GLIOBLASTOMA

Abstract BACKGROUND Glioblastoma (GBM) is the most malignant of primary brain tumors. Its fast and infiltrative growth limits the possibilities of early diagnostics and successful treatment. Standard therapies such as surgery, radiotherapy, and chemotherapy are rarely effective enough and tumor recurrence is usually expected. Therefore there is a continuous need for novel approaches for GBM. In recent years the potential use of cannabinoids gained a significant scientific interest. Cannabinoids, particularly tetrahydrocannabinol (THC) and cannabidiol (CBD), exhibit potential anti-tumor effects through multiple mechanisms, including apoptosis, autophagy, anti-proliferative actions, and modulation of the tumor microenvironment. Such various effects require explanation, leading to further clinical application. The epigenetic regulatory level gives such a possibility. The role of epigenetic events and oxidative stress in gliomagenesis is undoubtful. Epigenetics offers a connection between genetic and environmental factors that influence neoplasm development. The best-characterized epigenetic mark is 5-methylcytosine (m5C) in DNA. It was shown that loss in total DNA methylation correlates with oxidative DNA damage, as well as a higher tumor malignancy. The most sensitive marker of oxidative stress is the presence of 8-oxo-deoxyguanosine (8-oxo-dG). Taking that into account we decided to analyze the influence of cannabinoids’ administration on the total DNA methylation, as well as oxidative stress level in glioblastoma. MATERIAL AND METHODS Using the nucleotide post-labeling method, we analyzed the total amount of m5C in DNA of GBM (T98G, U118, U138), and normal (HaCaT) cell lines treated with cannabinoids (cannabis paste, THC, and CBD) alone and in combination with TMZ. The amount of 8-oxo-deoxyguanosine was established with electrochemical detection. RESULTS Cell viability in GBM cell lines was stable for THC and CBD at concentrations up to 1250 ng/ml. However, for Cannabis paste, it dropped significantly after the concentration of 20 ng/ml. We observed higher DNA methylation with shorter exposure times (24h) than with longer (120h) exposure periods. With increasing cannabinoids’ concentration we observed the rise of DNA methylation up to a certain point and then the decrease. The addition of TMZ caused demethylation for cannabis paste and THC, but increased methylation in the case of CBD. CONCLUSION Our results show the epigenetic mechanism of cannabinoid action in glioblastoma, and in the context of balancing the DNA methylation as a therapeutic target explain their observed positive effect in the clinical setting. The data also show the importance of adjusting the effective drug type and concentration. This work was supported by OPUS 19 (2020/37/B/NZ5/03249) from the National Science Center, Poland.