TMIC-54. OHSV-MEDIATED NOTCH BLOCKADE FOR BRAIN TUMORS

Abstract Primary brain tumors such as glioblastoma (GBM) are refractory to current standard-of-care, and so there is an urgent need to develop novel therapies to treat brain tumors. NOTCH is a cell-cell communication pathway that is exploited by GBM stem cells to bypass treatment. The role of NOTCH signaling in tumor growth and resistance is well studied, but the significance of this pathway for immunotherapy of GBM is not very well understood. We have recently shown that NOTCH activation with viro-immunotherapy contributes to tumor regrowth and induces recruitment of monocytic MDSC cells into the tumor, which limit optimal immune activation to kill tumor cells. Herein, we evaluated the impact of blocking NOTCH signaling using two different peptides: NIX1 and NIX2 that can interfere with NOTCH ligand binding with their receptors. Both NIX1 and NIX2 could effectively block the ligation of NOTCH ligands with Notch receptors in the tumor microenvironment. Secretion of both NIX1 and NIX2 was confirmed by western blot (WB) and ELISA. Functionality of NIX1 and NIX2 to block NOTCH signaling was assessed by western blot analysis for NOTCH cleaved intracellular domain (NICD). RNA sequencing and PCR based assays were utilized to evaluate the impact of NIX1 and NIX2 on global pathways that were enriched. Gene therapy using oncolytic immunotherapy vectors revealed that both NIX1 and NIX2 could suppress NOTCH signaling. In vitro, NIX1 and NIX2 did not increase the benefit of viro-immunotherapy. Treatment of mice bearing intracranial tumors with NIX1 or NIX2 armed viro-immunotherapy revealed a significant increase in therapeutic benefit with some long-term survivors. Both NIX1 and NIX2-expressing viruses induced macrophage migration relative to unarmed viro-immunotherapy in two different glioma models. Role of macrophages in guiding therapeutic benefit is currently being explored.