Structural Basis for Activity and Specificity of an Anticoagulant Anti-FXIa Monoclonal Antibody and a Reversal Agent
Lauren K Ely1, Marco Lolicato2, Tovo David2
1Centers for Therapeutic Innovation, San Francisco, Pfizer Inc., 1700 Owens Street, San Francisco, CA 94158, USA.
Abstract:
Coagulation factor XIa is a candidate target for anticoagulants that better separate antithrombotic efficacy from bleeding risk. We report a co-crystal structure of the FXIa protease domain with DEF, a human monoclonal antibody that blocks FXIa function and prevents thrombosis in animal models without detectable increased bleeding. The light chain of DEF occludes the FXIa S1 subsite and active site, while the heavy chain provides electrostatic interactions with the surface of FXIa. The structure accounts for the specificity of DEF for FXIa over its zymogen and related proteases, its active-site-dependent binding, and its ability to inhibit substrate cleavage. The inactive FXIa protease domain used to obtain the DEF-FXIa crystal structure reversed anticoagulant activity of DEF in plasma and in vivo and the activity of a small-molecule FXIa active-site inhibitor in vitro. DEF and this reversal agent for FXIa active-site inhibitors may help support clinical development of FXIa-targeting anticoagulants.
Insights
A new antibody, DEF, targets coagulation factor XIa (FXIa) to prevent blood clots without increasing bleeding risk. Its structure reveals how it inhibits FXIa, offering insights for developing safer anticoagulants.
Area of Science:
- Biochemistry
- Structural Biology
- Pharmacology
Background:
- Coagulation factor XIa (FXIa) is a potential target for anticoagulants aiming to balance antithrombotic efficacy with reduced bleeding risk.
- Current anticoagulants often struggle to achieve this balance, necessitating novel therapeutic strategies.
Purpose of the Study:
- To elucidate the structural basis of inhibition of FXIa by the human monoclonal antibody DEF.
- To understand how DEF's structure contributes to its FXIa specificity and inhibitory function.
- To explore the implications of DEF's mechanism for the development of FXIa-targeting anticoagulants.
Main Methods:
- Co-crystal structure determination of the FXIa protease domain with the monoclonal antibody DEF.
- Analysis of the structural interactions between DEF and FXIa, including the role of light and heavy chains.
- In vitro and in vivo assays to assess the anticoagulant activity of DEF and the effect of an FXIa active-site inhibitor reversal agent.
Main Results:
- The co-crystal structure revealed that DEF's light chain occludes the FXIa active site (S1 subsite), while the heavy chain mediates surface electrostatic interactions.
- DEF demonstrates high specificity for FXIa over its zymogen and related proteases, consistent with its active-site-dependent binding and inhibition of substrate cleavage.
- An inactive FXIa protease domain reversed DEF's anticoagulant activity in plasma and in vivo, and also reversed the activity of a small-molecule FXIa inhibitor in vitro.
Conclusions:
- The structural insights into DEF-FXIa interaction provide a rationale for DEF's potent and specific inhibition of FXIa.
- The findings support the potential of DEF and FXIa active-site inhibitor reversal agents in the clinical development of FXIa-targeting anticoagulants.
- Understanding the structural mechanisms of antibody-mediated FXIa inhibition can guide the design of next-generation anticoagulants with improved safety profiles.
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