Mechanism of action and impact on thrombin generation of denecimig (Mim8), emicizumab, and zemocimig (NXT007): comparative analysis using sequence-identical analogs.

BACKGROUND

Activated factor VIII (FVIIIa) mimetic antibodies restore hemostasis in hemophilia A by bridging FIXa and FX. Next-generation mimetics such as denecimig and zemocimig have been optimized for improved hemostatic activity following the launch of emicizumab. However, direct comparisons of available mechanistic data are limited due to heterogeneous experimental conditions.

OBJECTIVES

This study employed FX activation and thrombin generation assays to assess how the distinct mechanistic properties of the 3 FVIIIa mimetics translate into differences in hemostatic potential.

METHODS

Sequence-identical analogs (SIAs) of zemocimig and emicizumab were produced recombinantly and purified. FX activation kinetics in the presence of FVIIIa mimetics were assessed across increasing FIXa concentrations, and apparent dissociation constants and specific activity were derived. Thrombin generation assays were performed in hemophilia A platelet-poor plasma triggered with tissue factor, FXIa, or both.

RESULTS

Complex assembly affinity was highest for zemocimig-SIA, intermediate for emicizumab-SIA, and lowest for denecimig. In contrast, denecimig demonstrated markedly higher specific activity than both comparators, indicating distinct kinetic behavior. However, the FX activation assay represents a simplified system, and its artificial nature limits broader conclusions regarding physiological coagulation. Thrombin generation assays showed comparable thrombin generation profiles for denecimig and zemocimig-SIA, both exceeding emicizumab-SIA in potency.

CONCLUSION

These data indicate distinct mechanistic strategies among the 3 FVIIIa mimetics, with efficient complex assembly for emicizumab-SIA and zemocimig-SIA versus lower-affinity assembly but higher catalytic activity for denecimig. Despite these differences, zemocimig-SIA and denecimig exhibit comparable thrombin generation potential, supporting similar improvement in hemostatic potential relative to emicizumab-SIA.