Tumor Endothelial Cell Regulation of Pro-Metastatic Fibrin Matrices

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Project Summary Lung and triple-negative breast cancers (TNBCs) are leading causes of cancer-related deaths in the U.S. This high mortality rate is largely due to their propensity to rapidly progress and metastasize. While targeted therapies for lung adenocarcinoma have improved overall survival, similar advances in lung squamous carcinoma (LUSC) and TNBC have been stagnant. However, for both cancer types, immune checkpoint blockade and/or angiogenesis inhibitors improves disease control. Thus, a more complete understanding of how vascular/immune niches within the tumor microenvironment (TME) promotes LUSC and TNBC will allow us to build upon these advances. Our teams have recently demonstrated that LUSC and TNBC promote tumor growth and metastases through a convergence on fibrin remodeling (Nature Communications, 2018; J Clinical Investigation, 2019) and activation of endothelial cell wound-healing programs (Oncogene, 2019). Fibrin(ogen) that escapes leaky tumor endothelial cells (TECs) acts as a scaffold for tumor cell motility and creates a provisional matrix for tumor progression. Using highly integrated bioinformatics and novel LUSC models, we recently found that CCL2- mediated recruitment of Factor XIIIA (FXIIIA)-expressing inflammatory monocytes (IMs) promotes fibrin cross- linking, metastases and poor survival in LUSC. We also found that TEC heterogeneity (TECH) directs fibrin accumulation through a TGFβ/miR-30c/PAI-1 signaling axis - TECs with high levels of the fibrinolysis inhibitor, PAI-1, increase perivascular fibrin networks that support sprouting angiogenesis and tumor progression. We have also uncovered a secondary connection between fibrin remodeling and the RNA-binding protein Quaking (QKI) which is enriched in TECs and drives tumor angiogenesis. Silencing QKI in TECs inhibits sprouting angiogenesis and metastases, but micro-vessel density (MVD) paradoxically increases; which we posit is due to CXCL12-mediated sequestering of CXCR4+ IMs that initiate fibrin cross-linking. Based on these collective new insights from our groups, we hypothesize that (i) inhibition of TEC QKI initially blocks tumor angiogenesis and metastasis, however, a CXCL12-mediated retention of FXIIIA+ IMs promotes fibrin remodeling and rebound angiogenesis. Additionally, we propose (ii) that TECH drives the formation of aberrant and persistent perivascular fibrin scaffolds in LUSC and TNBC via a spectrum of TGFβ/miR-30c/PAI-1 expression. The objective of this proposal is to elucidate how fibrin remodeling and tumor progression depend on the heterotypic relationships between TECs and IMs, and the heterogeneity amongst TECs within the TME.