Abstract Number: PB1147
Meeting: ISTH 2020 Congress
Background: Haemophilia A (HA) is a bleeding disorder resulting from deficient Factor VIII (FVIII), which is a cofactor facilitating activation of Factor X (FX) via Factor IXa (FIXa). Here, we have developed a next generation anti-FIXa/anti-FX bispecific antibody, Mim8, which has demonstrated haemostatic properties in vitro as well as in bleeding models in HA mice1. In preclinical models, Mim8 shows 15-fold increased potency as compared to the marketed bispecific antibody emicizumab (Hemlibra®).
Aims: The aim of the present study was to investigate the mode of action of Mim8 using a biochemical in vitro set-up.
Methods: Biochemical and biological assays were used. FX activation assays, using various recombinant variants of FX, were employed to investigate the mode of action for Mim8 in the presence of FIXa and synthetic phospholipid vesicles.
Results: The enhanced activity of Mim8 was demonstrated to primarily derive from a strong stimulation of FIXa’s proteolytic activity by the anti-FIXa arm, which increased the turnover of FX by FIXa approximately 18×103-fold (Fig 1).
Furthermore, Mim8 targets unique epitopes on FIXa and FX allowing for their simultaneous engagement with the procoagulant membrane surface. This results in an efficient assembly of the FIXa/Mim8/FX complex on phosphatidyl serine-containing vesicles with an apparent dissociation constant (KD) of 12 nM despite binding FIXa and FX in solution with KD-values in the low micromolar range.
Conclusions: Mim8 is a next-generation FVIII-mimetic with a potent and efficacious haemostatic effect in preclinical studies. The activity of Mim8 is derived from efficient assembly with FIXa and FX on the procoagulant membrane surface and a strong stimulation of FIXa’s proteolytic activity.
1Kjellev et al. Blood (2019) 134 (S1): 96.
To cite this abstract in AMA style:Lund J, Østergaard H, Greisen PJ, Bonde AC, Gandhi PS, Lorenzen N, Johansson E, Andersen LM, Rasch MG, Lund S, Zhou R, Bjelke JR, Røder G, Johnsen LB, Stavenuiter F, Egebjerg T, Henriksen A, Hansen BG, Thorn K, Hilden I. A Novel FVIIIa-Mimetic Bispecific Antibody, Mim8, Enhances FIXa Proteolytic Activity While Allowing for Efficient, Lipid-Dependent Assembly with FX [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/a-novel-fviiia-mimetic-bispecific-antibody-mim8-enhances-fixa-proteolytic-activity-while-allowing-for-efficient-lipid-dependent-assembly-with-fx/. Accessed May 16, 2021.
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