TNFa inhibitor C87 sensitizes EGFRvIII transfected glioblastoma cells to gefitinib by a concurrent blockade of TNFa signaling

Abstract

Objective: More than half of human glioblastomas show EGFR gene amplification and mutation, but EGFR inhibitors have not been effective in treating EGFR-positive glioblastoma patients. The mechanism behind this type of primary resistance is not well understood. The aim of this study was to investigate gefitinib resistance in glioblastoma, and explore ways to circumvent this significant clinical problem. Methods: MTT method was used to test the cell viability after EGFR-positive glioblastoma cells were treated with indicated drugs; real-time quantitative PCR method was included to detect the TNFa mRNA levels in glioma tissues and cell lines. ELISA was introduced to measure the TNFa protein levels in cell culture supernatant of glioblastoma cells treated with gefitinib. Western blot was used to detect the activity change of intracellular kinases in drug-treated glioblastoma cells. Two mouse xenograft tumor models were carried out to evaluate the in vivo effects of a combination of EGFR and TNFa inhibitors. Results: We found that glioblastoma resistance to gefitinib may be mediated by an adaptive pro-survival TNFa-JNK-Axl signaling axis, and that high TNFa levels in the glioblastoma microenvironment may further intensify primary resistance. A combination of the TNFa-specific small-molecule inhibitor C87 and gefitinib significantly enhanced the sensitivity of glioblastoma cells to gefitinib in vitro and in vivo. Conclusions: Our findings provide a possible explanation for the primary resistance of glioblastoma to EGFR inhibitors and suggest that dual blockade of TNFa and EGFR may be a viable therapeutic strategy for the treatment of patients with chemotherapy-refractory advanced glioblastoma.