Fibrin-laden tumor stroma as a novel immunomodulatory factor in pancreatic ductal adenocarcinoma

Abstract public domain (NIH RePORTER)

Project Summary The efficacy of cancer immunotherapy depends on many vital factors, including the ability of the checkpoint inhibitor to perfuse and diffuse through the tumor microenvironment (TME), evade immunosuppressive microenvironment and finally, recognize cancer cells to kill. Pancreatic ductal adenocarcinomas (PDACs) are poorly responsive to both chemo- and immunotherapies, mainly because of the presence of dense stroma and absence of immunomodulatory T-cells and cytokines in the TME. However, the use of stroma-reducing agents has not been successful because of the fact that depletion of stroma-producing myofibroblasts did not correlate with immunosuppression and survival rate in pancreatic cancers. Thus, there is an unmet need to identify new strategies that can sensitize the TME of PDAC and increase the efficiency of immune checkpoint inhibitors. A largely overlooked, but potentially dominant immunosuppressive factor could be the cross-linked fibrin-stroma that could be an important feature of PDAC. Fibrin-laden tumor stroma (FibTS) is common in the most solid tumors, where PDACs exhibit extensive fibrinogen and insoluble crosslinked fibrin (x-fibrin) throughout the tumor cells and surrounding tumor stroma, respectively. However, the impact of FibTS in dampening the anti-tumor immunity has been immensely underestimated. We hypothesize that FibTS act as an immunomodulator and matrix-remodeling modulator in PDAC where x-fibrin deposition promotes the migration and polarization of macrophages by inducing stiff matrix. To test our hypothesis, we designed three specific aims: (1) To study the clinical and preclinical relevance of FibTS-induced stiffness gradient on regulating immunosuppressive microenvironment in PDAC, (2) To study mechanisms that PDAC-driven FibTS creates a niche for macrophage migration to differentiation by modulating matrix stiffness, and (3) To study how fibrin-laden stromal stiffness regulates immunosuppressive TME in PDAC. We will use human PDAC tissues, murine PDAC-organoids-on-Chip, and fibrin-graded soft-stiff gels to study the role of FibTS in TME immune landscape, macrophage migration and differentiation to pro-tumorigenic macrophages, and their activity to control T-cells. Thus, generating a new mouse line KPCFflox/flox to abrogate fibrinogen production from KPC derived cancer cells and using a fibrin-crosslinking inhibitor, we will demonstrate the role of fibrin-reduced stromal suppression of PDAC. Using two others newly developed FAKL994E KI and FGBfl/flLysMcre, we will study how stiff FibTS regulates macrophage migration and polarization via activating the mechnosensing pathways. Vertebrate animal models are essential for this project because they enable in vivo investigation of complex interactions among tumor, stromal, immune cells and circulatory system that closely recapitulate key features of human PDAC. Successful completion of this study will provide insight into the role of FibTS in the TME of PDAC and introduce x-fibrin cascade as a novel target to re-shape the immune landscape of the otherwise “cold” pancreatic tumors.

Public health relevance public domain (NIH RePORTER)

Project Narrative Pancreatic ductal adenocarcinomas are known to be highly thrombotic in nature where coagulation factors are activated early, produce high levels of fibrinogen and deposit crosslinked fibrin into the stroma. However, the role of crosslinked fibrin or fibrin-laden stroma in pancreatic ductal adenocarcinomas are largely unknown. This project will determine the effect of fibrin-laden stroma on tumor matrix stiffness and stiffness-induced changes in tumor microenvironment and immunity, and whether the use of a fibrin-crosslinking inhibitor can enhance the efficacy of immune checkpoint inhibitor in pancreatic cancer.