Metastatic cancer is a major clinical challenge that accounts for numerous deaths annually in the United States, particularly in women with triple-negative breast cancer (TNBC). Many tumors develop within a microenvironment (TME) characterized by altered/stiffened extracellular matrix (ECM) and compromised immunity. These alterations play a causal role in malignancy and metastasis. Recently tumor-derived exosomes have drawn tremendous interest as they are implicated in modulating the TME, suppressing anti-tumor immunity, and preparing the metastatic site for progression. A hallmark of cancer cells is their ability to evade the immune system. Exosomes play a pivotal role in the suppression of anti-tumor immunity. In this project, focusing on TNBC, we explore how ECM stiffness and cytoskeletal tension (collectively referred to as tissue tension) regulate exosome production and cargo composition, and how these exosomes contribute to the suppression of anti- tumor immunity and promote metastasis. We pursue a unique set of hypotheses linking tissue tension to exosome production and defining the role of tumor-derived exosomes in immune surveillance and metastatic progression. To test our hypotheses, we have assembled a strong team from UPENN and UCSF, integrating expertise in bioengineering, cancer mechanobiology, and cancer immunology. In Aim 1, we address whether and how the tissue tension affects exosome production and alters exosome cargo in vitro in TNBC cells. We will also delineate a molecular pathway linking ECM stiffness to intracellular signaling and exosome trafficking, using experimental and subcellular biophysical modeling methods. In Aim 2, we address how tissue tension promotes metastatic progression via exosomes in vivo. In this aim we test the hypothesis that the tension of the primary tumor tissue enhances exosome production and alters exosome cargo to promote the dissemination of primary tumor cells and foster their survival and outgrowth at the metastatic site. We will use unique genetically engineered mouse models (GEMMs) and syngeneic TNBC models, and TNBC patient PDXs, combined with multiscale pharmacokinetic modeling. In Aim 3, we address how tissue tension contributes to the suppression of anti-tumor immunity. In this aim, we will investigate the role of exosomes derived from tumors with high tension in stiff ECM TMEs in suppressing anti-tumor immunity through (1) reprogramming macrophages against T cells; and (2) the engagement of PD-1/PD-L1 checkpoint axis in T cells. We will use a combination of in vitro cell culture experiments, in vivo genetically engineered mouse models and syngeneic transplant manipulations and tissue-scale agent-based modeling. The expected results will shed light on the roles of exosomes in immune regulation and metastatic tumor progression; these are important and timely questions in cancer research. The results will lay the foundation for future therapeutic intervention of metastatic disease through the identification of actionable biomarkers, development of new immune checkpoint inhibitor (ICB)-based therapies, and ultimately reduce patient mortality.

PROJECT NARRATIVE We focus on understanding fundamental mechanisms governing immune modulation and progression of disseminated tumor cells at the metastatic sites, both of which carry immense clinical relevance in treating metastatic disease in women with triple negative breast cancer, for which there currently is no cure. Moreover, the proposed studies focusing on tumor-derived exosomes carry a high translational potential in the development of liquid biopsy-based biomarkers for noninvasive detection, and discovery of new targets for immunotherapy and prevention of metastasis.