Factor VIII in vitro bioequivalence of denecimig (Mim8) hemostatic effect by thrombin generation assays

Background: Denecimig (Mim8, Novo Nordisk A/S) is a next-generation bispecific antibody designed to mimic activated factor (F)VIII and restore hemostasis in persons with hemophilia A. The extent to which activated FVIII mimetics, such as denecimig and emicizumab, can correct clotting deficiency remains unclear. Objectives: FVIII bioequivalence of denecimig hemostatic activity using thrombin generation assays (TGAs). Methods: Thrombin generation was analyzed in severe hemophilia A platelet-poor plasma, spiked with various levels of FVIII or with clinical doses of denecimig (5 μg/mL) or emicizumab (50 μg/mL), using a sequence-identical analog (SIA). TGA used 4 trigger conditions: tissue factor (TF), activated FXI, a combination of TF and activated FXI, or activated FIX. Results: The average FVIII bioequivalence estimate using 1 pM TF trigger was 42 IU/dL (SD, 14) for 5 μg/mL denecimig and 14 IU/dL (SD, 5) for 50 μg/mL emicizumab-SIA using peak thrombin. The FVIII bioequivalence estimates of denecimig and emicizumab-SIA for hemostatic activity were generally highest for endogenous thrombin potential, followed by peak thrombin and velocity index across trigger concentrations. FVIII bioequivalence increased with decreasing trigger concentrations. Denecimig demonstrated a higher thrombin peak in conditions with limited activated FIX compared with emicizumab-SIA, suggesting differences in mechanisms of action. Conclusion: FVIII bioequivalence than emicizumab-SIA, indicating the potential for effective hemostatic coverage. Further studies are needed to fully understand the hemostatic effects of bispecific antibodies.