Modulation of TAFI function through different pathways--implications for the development of TAFI inhibitors

Area of Science:

• Coagulation and Fibrinolysis
• Immunology
• Drug Discovery

Background:

• Thrombin-activatable fibrinolysis inhibitor (TAFI) plays a crucial role in regulating clot lysis.
• Understanding how monoclonal antibodies (MA) interact with TAFI is essential for developing therapeutic strategies.
• TAFI activity is linked to thrombosis and bleeding disorders, necessitating targeted modulation.

Purpose of the Study:

• To investigate the mechanisms by which MA interfere with TAFI activation and TAFIa activity.
• To identify the specific binding regions of MA on TAFI.
• To explore potential molecular targets for pharmacologically modulating TAFIa activity.

Main Methods:

• Screening of 42 MA for interference with TAFI activation and TAFIa activity.
• Characterization of inhibition mechanisms, distinguishing between blocking activation and direct enzymatic inhibition.
• Affinity studies using human/murine TAFI chimeras to map MA binding sites.

Main Results:

• 19 out of 42 MA inhibited TAFI activation/TAFIa activity by up to 92%.
• 14 MA blocked TAFI activation by thrombin/thrombomodulin, while 5 MA inhibited TAFIa enzymatic activity.
• Binding regions were mapped to specific amino acid residues (AA1-67, Gly66, Val41) or the TAFIa moiety, correlating with distinct inhibition mechanisms.

Conclusions:

• The study identified at least three distinct molecular targets for modulating TAFIa activity.
• MA targeting TAFI activation significantly reduced clot lysis time, unlike those inhibiting enzymatic activity.
• These findings provide a basis for developing novel pharmacologically active compounds targeting TAFI.