NMDA receptor signaling induces the chemoresistance of temozolomide via upregulation of MGMT expression in glioblastoma cells.

PURPOSE: The alkylating agent temozolomide (TMZ) has a significant impact on the prognosis of glioblastoma (GBM) patients. Therefore, maximizing TMZ efficacy is important for GBM treatment. Many reports have shown that glutamate signaling promotes GBM progression via glutamate receptors, including N-methyl-D-aspartate receptors (NMDARs). Although NMDARs promote cell migration and invasion of GBM cells, their role in TMZ resistance remains unclear. Therefore, we focused on NMDAR signaling and investigated its effects on TMZ resistance. METHODS: We investigated the effect of NMDAR signaling on O6-methylguanine DNA methyltransferase (MGMT), a DNA repair enzyme that induces chemoresistance to TMZ, using quantitative real-time polymerase chain reaction and western blotting in human GBM T98G cells. In addition, we used memantine (MEM), an NMDAR antagonist, to investigate the cytotoxic effect of TMZ/MEM combination and its detailed mechanism. RESULTS: Activation of NMDAR by N-methyl-D-aspartate (NMDA) elevated MGMT expression and suppressed the effect of TMZ in T98G cells. In contrast, knockdown of NMDAR by NMDAR1 shRNA decreased MGMT expression and enhanced the effect of TMZ in T98G cells. The cytotoxic effect of TMZ was enhanced by MEM in T98G cells. Inhibition of NMDAR by MEM decreased MGMT expression and increased DNA alkylation by TMZ. CONCLUSION: NMDAR signaling induced chemoresistance of TMZ via the upregulation of MGMT expression in GBM cells. Furthermore, MEM inhibited TMZ-induced MGMT upregulation and increased the cytotoxic effect of TMZ on MGMT-positive cells. This study demonstrates that the combination of TMZ and MEM could be a new therapeutic strategy for MGMT-positive GBM. Overview of this study. NMDAR signaling controls the expression of MGMT and the cytotoxic effect of TMZ.