Coagulation and Fibrinolysis Profiles in Mouse Breast Cancer 4T1 Tumor-Bearing Mice: A Characterization of Neutrophil-Associated Prothrombotic States

Cancer-associated thrombosis is the second leading cause of death in patients with cancer. The highly metastatic triple-negative mouse breast cancer cell line 4T1 induces thrombus formation that is dependent on neutrophil extracellular traps (NETs) in transplanted mice when exposed to certain stimuli, such as lipopolysaccharide (LPS) injection. These findings suggest that 4T1 transplantation into mice increases the susceptibility to NET release, followed by thrombus formation in response to external stimuli. However, the blood levels of coagulation-associated factors in 4T1-bearing mice that are in a primed state without any stimulation remain unknown. In this study, we analyzed coagulation and fibrinolytic factors in the plasma of mice orthotopically transplanted with 4T1 cells. In 4T1-bearing mice, a NET marker, citrullinated histone H3, was detected in the tumor tissues and lungs, but not in the plasma. The presence of fibrin(ogen)-containing Ly6G-positive cell clusters in the lung vasculature suggested that NET release and NET-induced microthrombus formation occurred in the lungs. In plasma, increased levels of tissue factor and active and total plasminogen activator inhibitor-1 (PAI-1) suggested enhanced procoagulant activity and suppressed fibrinolysis. However, plasma thrombin-antithrombin complex levels, which reflect overt thrombin activation that forms fibrin clots, were similar in 4T1-bearing and non-transplanted mice. These findings indicate that 4T1 cell growth and metastasis in mice establish a pre-thrombotic state characterized by NET release and procoagulant potential, which requires a secondary trigger, such as LPS, to develop into pathological thrombosis. Therefore, 4T1-bearing mice may be useful as an in vivo model for exploring secondary triggers of pathological thrombosis.