Printed Poster | Session 1

010 – Targeting the tumor extracellular matrix as an immune-boosting strategy for malignant gliomas

ROSHINI ARIVAZHAGAN (1) – NANDHU MS (1) – SHARON LONGO (1) – JOHN LONGO (1) – LAWRENCE CHIN (2) – MARIANO S VIAPIANO (1)
SUNY UPSTATE MEDICAL UNIVERSITY, NEUROSCIENCE AND PHYSIOLOGY, SYRACUSE, United States (1) – SUNY UPSTATE MEDICAL UNIVERSITY, DEPT OF NEUROSURGERY, SYRACUSE, United States (2)

Malignant gliomas are the most common primary tumors in the CNS and represent one of the most lethal forms of cancer. The most aggressive gliomas, glioblastomas (GBM) are heavily infiltrated by local microglia and circulation-derived macrophages, which acquire a tumor-promoting phenotype and contribute to GBM progression. These tumor-associated microglia/macrophages (TAMs) respond to immunosuppressive signals from GBM cells, which has prompted the search for strategies to disrupt this communication and restore an inflammatory, anti-tumor behavior of innate immune cells in GBM. Fibulin-3 is an extracellular matrix protein secreted by GBM cells that promotes tumor invasion, angiogenesis and survival of the GBM stem cell (GSC) population. We recently developed a function-blocking antibody against fibulin-3 (mAb428.2) that inhibits the molecular signaling initiated by this protein and reduces the growth of orthotopic GBMs. Although we expected that this antibody would have a tumor cell-intrinsic effect, we surprisingly observed that mAb428.2 treatment caused a significant increase in the presence of TAMs in the tumor parenchyma. Moreover, TAMs in tumors treated with mAb428.2 showed little histological and mRNA expression of markers typically associated with a “tumor promoting” (M2-like) TAM phenotype, such as Arginase-1 and CD206. On the other hand, these TAMs recovered from the tumors (and processed for qRT-PCR) exhibited a significant pro-inflammatory signature (IFNgamma, IL-1B, TNFα), suggesting that anti-fibulin-3 treatment had exacerbated their anti-tumor response, which was matched by presence of extensive necrosis in these tumors. Further analysis revealed that fibulin-3 regulated the cytokine CSF-1a and in an NFKB dependent manner. Anti-fibulin-3 approaches against GSCs (either mAb428.2 treatment or fibulin-3 knockdown) decreased the expression of CSF-1a in these tumor cells, thus removing this potent immunosuppressive signal from the tumor microenvironment. Accordingly, co-culture of GSCs with PMA-activated U937 macrophages resulted in significant cell death when mAb428.2 was added to the cultures, suggesting that the antibody potentiates ADCC at the same time that it contributes to reactivating macrophage inflammation. These results strongly suggest that anti-fibulin-3 and possibly other anti-ECM approaches may induce a marked inflammatory reaction driven by innate immune cells, potentiating anti-tumor effects against GBM.