Pharmacological Blockade of Group II Metabotropic Glutamate Receptors Reduces the Incidence of Brain Tumors Induced by Prenatal Exposure to N-ethyl-N-nitrosourea in Rats

Background: The study demonstrates that pharmacological blockade of type 3 metabotropic glutamate (mGlu3) receptors at the time of tumor induction significantly reduces the incidence of brain gliomas in rats. The overall survival of patients with high-grade brain gliomas is 14-20 months after current multimodal therapy, including surgery, radiotherapy, and adjuvant chemotherapy. Objective: To demonstrate in this experimental model that pharmacological blockade of group II metabotropic glutamate receptors reduces the incidence of brain tumors induced by prenatal exposure to N- ethyl-N-nitrosourea (ENU) in rats. Methods: Dams received a single injection of ENU (40 mg/kg, e.v.) at day 20 of pregnancy, combined with 5 daily injections of either saline or the mGlu2/3 receptor antagonist, LY341495 (10 mg/kg) (from day 15 to day 21 of pregnancy). Assessment of brain tumors in the offspring at 5 months of age showed the presence of mixed gliomas (astrocytomas/oligodendrogliomas) in 70% of the ENU + saline group of rats and only in 30% of the ENU + LY341495 group. Conclusion: Tumors in both groups of rats showed a moderate/high expression of the astrocyte marker, GFAP, and the oligodendrocyte marker, OLIG-2, and a low expression of the proliferation marker, Ki-67. However, tumors of the ENU + LY341495 group showed a reduced density of Iba-1+ cells, suggesting a lower extent of neuroinflammation in the tumor microenvironment. These findings strengthen the hypothesis that mGlu3 receptors are candidate drug targets for the treatment of malignant gliomas.