Addressing the Limits of Emx2 Therapy of Glioblastoma Multiforme by Transgene Insulation and Epigenetic...

Introduction/Objectives: Implicated in the regionalization of the anterior central nervous system (CNS) and the progression of pallial astrogliogenesis, the transcription factor gene EMX2 has been reported to be specifically silenced in several tumors, both non-neural and neural. Based on that, its overexpression has been proposed as a tool for the treatment of a subset of these malignancies, including glioblastoma. Here we tested this proposal. Methods/Results: We found that Emx2 overexpression in human glioblastoma cells transplanted into the striatum of immunotolerant mice significantly prolonged animals' survival, outperforming their treatment by temozolomide. However, this approach did not eradicate the tumor, because of in vivo silencing of the therapeutic Emx2 transgene. Notably, silencing of this transgene (or of a reporter designed to monitor its competence to be expressed) also occurred during long-term in vitro culture of GBM cells and was exacerbated by coculture with murine pallial glia under hypoxic conditions. Remarkably, partial insulation of the transgene and the use of a specific combination of epigenetic drugs substantially counteracted the progressive activatability decline undergone by the Emx2-transgene expression reporter, suggesting a promising strategy for overcoming a major limitation of Emx2-based therapy for GBM. Conclusions: An Emx2-encoding transgene, protected by insulation and appropriate epigenetic drugs, can provide a substantial benefit in experimental therapy for glioblastoma.