Background We previously showed that fibrinogen is a major determinant of the growth of a murine model of colorectal cancer (CRC). Objective Our aim was to define the mechanisms coupling fibrin(ogen) to CRC growth. Results CRC tumors transplanted into the dorsal subcutis of Fib− mice were less proliferative and demonstrated increased senescence relative to those grown in Fib+ mice. RNA‐seq analyses of Fib+ and Fib− tumors revealed 213 differentially regulated genes. One gene highly upregulated in tumors from Fib− mice was stratifin, encoding 14‐3‐3σ, a master regulator of proliferation/senescence. In a separate cohort, we observed significantly increased protein levels of 14‐3‐3σ and its upstream and downstream targets (i.e., p53 and p21) in tumors from Fib− mice. In vitro analyses demonstrated increased tumor cell proliferation in a fibrin printed three‐dimensional environment compared with controls, suggesting that fibrin(ogen) in the tumor microenvironment promotes tumor growth in this context via a tumor cell intrinsic mechanism. In vivo analyses showed diminished activation of focal adhesion kinase (FAK), a key negative regulator of p53, in Fib− tumors. Furthermore, nuclear magnetic resonance–based metabolomics demonstrated significantly reduced metabolic activity in tumors from Fib− relative to Fib+ mice. Together, these findings suggest that fibrin(ogen)‐mediated engagement of colon cancer cells activates FAK, which inhibits p53 and its downstream targets including 14‐3‐3σ and p21, thereby promoting cellular proliferation and preventing senescence. Conclusions These studies suggest that fibrin(ogen) is an important component of the colon cancer microenvironment and may be exploited as a potential therapeutic target.

Fibrinogen plays a pathologic role in multiple diseases. It contributes to thrombosis and modifies inflammatory and immune responses, supported by studies in mice expressing fibrinogen variants with altered function or with a germline fibrinogen deficiency. However, therapeutic strategies to safely and effectively tailor plasma fibrinogen concentration are lacking. Here, we developed a strategy to tune fibrinogen expression by administering lipid nanoparticle (LNP)-encapsulated siRNA targeting the fibrinogen α chain (siFga). Three distinct LNP-siFga reagents reduced both hepatic Fga mRNA and fibrinogen levels in platelets and plasma, with plasma levels decreased to 42%, 16% and 4% of normal within one-week of administration. Using the most potent siFga, circulating fibrinogen was controllably decreased to 32%, 14%, and 5% of baseline with a 0.5, 1, and 2 mg/kg dose, respectively. Whole blood from mice treated with siFga formed clots with significantly decreased clot strength ex vivo, but siFga treatment did not compromise hemostasis following saphenous vein puncture or tail transection. In an endotoxemia model, siFga suppressed the acute phase response and decreased plasma fibrinogen, D-dimer, and proinflammatory cytokine levels. In a sterile peritonitis model, siFga restored normal macrophage migration in plasminogen-deficient mice. Finally, treatment of mice with siFga decreased the metastatic potential of tumour cells in a manner comparable to that observed in fibrinogen-deficient mice. The results indicate that siFga causes robust and controllable depletion of fibrinogen and provide the proof-of-concept that this strategy can modulate the pleiotropic effects of fibrinogen in relevant disease models.

No abstract