The Discovery of a Novel Anticoagulant Mechanism: Factor XI Activation Inhibitors

Area of Science:

• Biochemistry
• Pharmacology
• Drug Discovery

Background:

• Factor Xa (FXa) inhibitors represent a standard in anticoagulant therapy but carry bleeding risks.
• Factor XI (FXI) plays a crucial role in coagulation, and FXI-based anticoagulants may offer improved safety.
• Novel therapeutic strategies are needed to mitigate bleeding risks associated with anticoagulation.

Purpose of the Study:

• To discover and characterize novel inhibitors of Factor XI (FXI) activation.
• To explore a new allosteric mechanism of action for inhibiting FXI activation.
• To evaluate the therapeutic potential of FXI activation inhibitors in preclinical models.

Main Methods:

• An activity-based, mass spectrometry (AS-MS) screen was employed to identify FXI zymogen inhibitors.
• Biochemical and biophysical methods were used to characterize inhibitor binding and mechanism of action.
• Co-complex structure determination provided insights into the inhibitor binding site.
• In vitro assays (aPTT) and in vivo thrombosis models (rabbit AV-shunt) were utilized for functional evaluation.

Main Results:

• A novel allosteric mechanism of inhibiting FXI activation was identified.
• Structurally diverse small molecules targeting FXI zymogen were characterized.
• Inhibitor binding was confirmed to be specific to the FXI zymogen at a site distal to the cleavage site.
• FXI activation inhibitors demonstrated efficacy in prolonging aPTT and reducing thrombosis in vivo.

Conclusions:

• FXI activation inhibitors represent a novel class of anticoagulants with a unique mechanism.
• These inhibitors show potential for comparable efficacy and superior safety compared to existing anticoagulants.
• Targeting FXI activation offers a promising new strategy for managing thrombotic disorders.