EXTH-111. Characterization of the cGAS-STING pathway as a novel approach to targeting glioblastoma

The glioblastoma (GBM) tumor microenvironment (TME) is characterized by its poor immune cell infiltration and high volume of abnormal vasculature. Treatment strategies to combat these features are needed to improve patient response to immunotherapies including immune checkpoint blockade which up until now have not shown efficacy in GBM. One focus of our lab is characterizing the cGAS-STING pathway, an innate anti-viral response pathway, as an approach to improve immune cell infiltration and vascular growth in tumors. Previous work in the field has demonstrated these beneficial effects which correlate to efficacy in preclinical mouse models upon STING agonist treatment. However, the role of endothelial cells which line the blood vessels and play a crucial role in angiogenesis, the formation of new blood vessels, has not yet been characterized as a potential mediator of STING-driven efficacy in GBM and is the focus of this work. By utilizing multiple human brain derived endothelial cell lines (hBECs), we have shown robust activation in response to STING agonist treatment through phosphorylation of downstream pathway mediators by Western blot and through quantification of canonical cytokines CXCL10 and CCL5 by ELISA and Luminex. Additionally, RNA sequencing revealed a strong signature of immune activation in response to STING agonism. Current experiments are aimed towards characterizing functional read-outs including migration, tube formation, and transendothelial electrical resistance (TEER) in response to STING activation. Lastly, we have recently shown that the combination of the STING agonist ADU-S100 and the MEK inhibitor Trametinib produces synergy through enhanced secretion of CXCL10 and increased phosphorylation of STAT1. This novel discovery may inform future combination treatment approaches and studies to validate this finding in vivo, using GBM preclinical mouse models, are currently underway.