Pharmacological Depletion of Fibrinogen Suppresses the Growth of Primary Tumors and Metastasis of Pancreatic Ductal Adenocarcinoma (PDAC)

Abstract

PDAC is a highly metastatic disease often linked to the dysregulated activation of both coagulation and fibrinolytic systems. Clinically, patients show elevated plasma fibrinogen levels, particularly in those with distant metastasis. The presence of systemic fibrinogen plays a crucial role in shaping the complex tumor microenvironment characteristic of PDAC, evidenced by the excessive deposition of its active substrate, fibrin, in PDAC tumors. To investigate its contribution to disease progression, fibrinogen was significantly depleted from the TME in multiple PDAC patient-derived xenograft (PDX) models, and the impact on tumor growth and metastasis was followed. In an aggressive, metastatic orthotopic Pa03C model, Fib depletion using antisense oligonucleotide (ASO) treatment markedly decreased the size of primary pancreatic tumors and subsequent spontaneous metastasis to the liver. Following implantation of tumor chunks (PDX21) from a patient with high Fib staining, Fib ASO treatment significantly diminished growth of primary tumors. Using a third orthotopic model (PDX33) and lipid nanoparticle (LNP)-encapsulated-siRNA to deplete the fibrinogen--chain, tumor growth was significantly reduced compared to control. This confirms that Fib deposition within the tumor microenvironment (TME) is an important driver of disease progression. Mechanistically, global proteomics revealed a remarkable upregulation of matrisome and extracellular matrix (ECM)-associated proteins, indicating that the reduction in primary orthotopic Pa03C tumors was associated with fibrin-mediated TME remodeling. Loss of fibrin matrices led to enhanced collagen, laminin, fibronectin and emilin1 deposition, and increased recruitment of collagen-producing αSMA+ myofibroblasts. Notably, our data suggests that fibrinogen depletion altered the ECM composition, inducing TME remodeling which led to stiffer tumors that are less metastatic. To further interrogate the role of fibrinogen in mediating metastasis, we employed an experimental metastasis model to study the colonization of tumor cells in the liver in the absence of fibrinogen. In this model, fibrinogen depletion did not impede the colonization of Pa03C cells, suggesting that fibrinogen does not mediate the colonization of tumor cells in the cascade of events for liver metastasis and is likely involved in one of the other steps of metastasis. Collectively, our data showed that pharmacologically reducing systemic fibrinogen levels impeded tumor growth and metastasis by remodeling the TME.