Madrigal Jamie, Monroe Dougald M, Sindi Suzanne S, Leiderman Karin
Mathematics Department, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA; UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
J Thromb Haemost. 2025 Oct;23(10):3111-3123. doi: 10.1016/j.jtha.2025.07.002. Epub 2025 Jul 16.
Emicizumab is a bispecific antibody that binds activated factor (F)IXa with 1-arm and FX with the other. Binding bridges FIXa and FX, replacing the function of FVIII in hemophilia A. Unlike FVIII, emicizumab does not bind directly to lipid surfaces.
This study aimed to investigate emicizumab's lipid-surface dependent mechanisms through mathematical modeling and biochemical assays.
We expanded our mathematical model of tissue factor (TF):VIIa activation of FX to incorporate emicizumab and FIXa interactions. We calibrated our model using experimental data.
High concentrations of emicizumab inhibit FX activation by TF:VIIa. Our mathematical model explains these observations only when FX bound to emicizumab is partially restricted from binding to lipid surfaces and to TF:VIIa. Lipid enhances FX activation of FIXa in the presence of emicizumab. In our 2-arm interaction model, we estimated kinetic rates for emicizumab-dependent activation of FX on the lipid surface. The model successfully predicted FIXa activation of FX with and without emicizumab across many experimental conditions. Ternary complexes (FIXa, FX, and emicizumab) in solution decreased when lipid increased while ternary complexes on lipid increased. Sensitivity analysis, which varied lipid, dissociation constants, and catalytic rates, highlighted the impact of binding-arm affinity on reaction velocities.
High concentrations of emicizumab decrease TF:VIIa activation of FX by reducing FX binding to both the lipid surface and TF:VIIa. Emicizumab enhances FIXa activation of FX on the lipid surface by preferentially binding to lipid-bound FX and subsequently to lipid-bound FIXa with an enhanced association rate due to colocalization on the lipid surface.
依美珠单抗是一种双特异性抗体，其一条臂结合活化因子（F）IXa，另一条臂结合FX。这种结合桥接了FIXa和FX，替代了A型血友病中FVIII的功能。与FVIII不同，依美珠单抗不直接结合脂质表面。
本研究旨在通过数学建模和生化测定研究依美珠单抗的脂质表面依赖性机制。
我们扩展了组织因子（TF）：VIIa激活FX的数学模型，以纳入依美珠单抗和FIXa的相互作用。我们使用实验数据校准了模型。
高浓度的依美珠单抗抑制TF：VIIa对FX的激活。仅当与依美珠单抗结合的FX与脂质表面和TF：VIIa的结合受到部分限制时，我们的数学模型才能解释这些观察结果。在存在依美珠单抗的情况下，脂质可增强FIXa对FX的激活。在我们的双臂相互作用模型中，我们估计了依美珠单抗依赖性激活脂质表面上FX的动力学速率。该模型成功预测了在许多实验条件下有无依美珠单抗时FIXa对FX的激活情况。当脂质增加时，溶液中的三元复合物（FIXa、FX和依美珠单抗）减少，而脂质上的三元复合物增加。通过改变脂质、解离常数和催化速率进行的敏感性分析突出了结合臂亲和力对反应速度的影响。
高浓度的依美珠单抗通过减少FX与脂质表面和TF：VIIa的结合来降低TF：VIIa对FX的激活。依美珠单抗通过优先结合脂质结合的FX，随后以增强的缔合速率结合脂质结合的FIXa，从而增强脂质表面上FIXa对FX的激活，这是由于在脂质表面上的共定位所致。
