IMPS-10: BRAF^V600E-MUTANT IMMUNOCOMPETENT GLIOMA MODEL EXHIBITS TYPICAL HISTOPATHOLOGICAL FEATURES OF HUMAN GLIOBLASTOMA MULTIFORME

INTRODUCTION: Targeted monotherapy against BRAF^V600E displays efficacy in preclinical models of BRAF^V600E-mutant gliomas, however xenograft tumors adapt rapidly and escape from the growth-inhibitory effects. The question emerges whether a more durable anti-tumor effect will be achieved by combining BRAF inhibitors with immune-modulatory agents such as anti-CTLA-4 and anti-PD-L1. The lack of an immunocompetent preclinical model of BRAF^V600E-mutant astrocytoma however has been prohibitive to addressing this question. METHODS: A BRAF^V600E-mutant murine tumor cell line (2341) was isolated from tumors developed in transgenic mice with Cre-conditional alleles of BRAF^V600E and CDKN2A. Multiple cohorts of syngeneic FVBN mice, as well as athymic mice were injected orthotopically with the BRAF^V600E-mutant tumor cell line and evaluated for the occurrence of neurological symptoms. Symptomatic animals were sacrificed and brains were harvested and subjected to a detailed immunohistopathological characterization. Tumor growth was studied employing bioluminescence (BLI). The presence of tumor fluorescence following in vivo injection of 5-aminolevulinic acid (5-ALA) was investigated as well. RESULTS: Injected animals developed tumors in the right striatum exhibiting all histopathological diagnostic features of human glioblastomas. Neurological free survival was significantly longer in immunocompetent FVBN mice (mean 56 days) compared to similarly treated athymic mice (mean 15 days). Additionally, 5-ALA injected mice exhibited strong fluorescence of tumor cells, when exposed to ultraviolet light compared to normal brain tissue. Results from ongoing work regarding T-cell regulation in the immunocompetent glioma model will be presented and discussed at the meeting. CONCLUSIONS: A BRAF^V600E-mutant glioma model that recapitulates the typical genetical, histopathological and behavioral features of human glioblastoma multiforme can be established in fully immunocompetent FVBN mice. These tumors also exhibit 5-ALA induced tumor fluorescence, a typical feature of human malignant astrocytomas. Further studies will reveal this modelś ability to reliably test the anti-glioma efficacy of immune-modulatory drugs in combination with BRAF^V600E inhibition.