Examining Downstream Effects of Concizumab in Hemophilia A with a Mathematical Modeling Approach.

Background: Tissue factor pathway inhibitor (TFPI) is an anticoagulant protein that inhibits FXa, the TF-FVIIa-FXa complex, and early forms of the prothrombinase complex. Concizumab is a monoclonal antibody that blocks FXa inhibition by TFPI and reduces bleeding in hemophilia.

Objectives: To examine how concizumab impacts various reactions of TFPI to restore thrombin generation in hemophilia A using mathematical models.

Methods: A compartment model was used to estimate plasma concentrations of free concizumab and its complexes with TFPIα and TFPIβ. Concizumab was integrated into a flow-mediated mathematical model of coagulation and a small injury was simulated under hemophilia A conditions. Simulations were then analyzed to determine how concizumab's blockade of TFPI anticoagulant activities, specifically the inhibition of FXa in plasma and on platelets, inhibition of TF:VIIa at the subendothelium, and prior sequestration of plasma TFPIα to the endothelium via TFPIβ, altered thrombin generation.

Results: Concizumab improved simulated thrombin generation in hemophilia A by simultaneously altering all three mechanisms of TFPI anticoagulant blockade examined. Concizumab sequesters ∼75% of plasma TFPIα through formation of ternary TFPIα-concizumab-TFPIβ-complexes. For all TF levels, reducing the TFPIα plasma concentration had the largest impact on the lag time followed by blocking TFPIα inhibition of TF:VIIa:FXa and subsequently followed by blocking TFPIα inhibition of FXa in plasma and on the platelet surface.

Conclusions: The effectiveness of concizumab is mediated through blockade of TFPI anticoagulant activities in plasma and on multiple physiological surfaces. An important and previously unrecognized function of concizumab was sequestration of plasma TFPIα to the endothelium.