Abstract
BACKGROUND: NXT007 is a factor (F)VIIIa-mimetic bispecific antibody (BsAb) for hemophilia A (HA), engineered from emicizumab. It is designed to achieve non-hemophiliac levels of plasma coagulation potential and is currently under clinical development. In the future, emicizumab users may switch to NXT007. OBJECTIVES: To investigate the effects of NXT007 in the coexistence of emicizumab on coagulation potential in vitro. METHODS: Coagulation potentials of HA plasma were determined by thrombin generation (TG) assays. NXT007 binding was analyzed by biolayer interferometry (BLI) and immunoblotting. Plasma levels of FIX-BsAb-FX ternary complexes were simulated using dissociation constant values for calculating theoretical coagulation potentials. RESULTS: In coexistence of emicizumab at 50 μg/mL (therapeutic concentration), NXT007 (0.1-100 μg/mL) dose-dependently increased TG capacity of HA plasma, similar to its effect without emicizumab. At 10-100 μg/mL of NXT007, TG capacity reached levels comparable to NXT007-only conditions. BLI analysis revealed that emicizumab and NXT007 could not simultaneously bind to the same antigens, indicating that only ternary complexes or lower stoichiometry can be formed from FIX(a), FX(a), emicizumab, and NXT007. Immunoblotting analyses confirmed both BsAbs recognized the same antigen domains. Therefore, plasma coagulation potential should be the sum of the contributions of both BsAbs. Our calculations in this manner were concordant with the TG results. CONCLUSION: NXT007 enhanced TG capacity of HA plasma in vitro in the coexistence of emicizumab without an abnormal synergistic increase or reduction in coagulation potential, consistent with their competitive antigen binding. These findings suggest that switching from emicizumab to NXT007 can be achieved without emicizumab washout.