P10.27.A THE INFLUENCE OF DEXAMETHASONE ON TOTAL DNA METHYLATION LEVEL IN GLIOBLASTOMA CELL LINES

Abstract

Abstract BACKGROUND Dexamethasone (DEX) is a first-line antiedematic drug for glioblastoma (GBM) patients. There is also some evidence it also inhibits GBM cell proliferation and migration, thus impacting patients’ outcomes. However, other studies show that the use of DEX is associated with poor treatment outcomes in GBM patients. The exact mechanism of DEX action is unclear, and no definitive conclusion has yet been reached on its benefits in neurooncological treatment. Temozolomide (TMZ) is a first-line chemotherapeutic in GBM. Epigenetics offers a connection between genetic and environmental factors that influence the development of the disease. The best-characterized epigenetic mark is 5-methylcytosine (m5C) in DNA. The aim of that project is to show the effects of DEX administration on the total DNA methylation level. MATERIAL AND METHODS Using the nucleotide post-labeling method, we analyzed the total amount of m5C in DNA of GBM (T98G, U118, U138), cancer (HeLa) and normal (HaCaT) cell lines treated with DEX, and a combination of DEX and with TMZ. RESULTS We adjusted the DEX doses to the ones achieved in the central nervous system during treatment. We observed dose-dependent increase in total DNA methylation in all cell lines. However, the exposition of GBM cells to the combination of DEX and TMZ caused an adverse synergistic effect resulting in DNA demethylation in high doses of both drugs. In lower concentrations of both drugs DEX kept the increased DNA methylation and attenuated the demethylating effect of TMZ. CONCLUSION Total DNA methylation changes in glioma cell lines under DEX treatment suggest the new mechanism of that drug action and promote clinical implications for adjusting DEX and TMZ therapy in GBM patients. Our results show the potential and possible obstacles of the combined therapy of TMZ with DEX. Our experiments show that combined therapy with both drugs leads to total DNA hypomethylation in high doses of both drugs. Therefore the conclusion would be to adjust DEX administration during TMZ chemotherapy.