CC BY-NC-ND 4.0 · Thromb Haemost 2017; 117(07): 1348-1357
DOI: 10.1160/TH17-01-0030
Coagulation and Fibrinolysis
Schattauer GmbH

Factor VIIIa-mimetic cofactor activity of a bispecific antibody to factors IX/IXa and X/Xa, emicizumab, depends on its ability to bridge the antigens

Takehisa Kitazawa
1  Research Division, Chugai Pharmaceutical Co., Ltd., Kamakura, Kanagawa, Japan
,
Keiko Esaki
2  Research Division, Chugai Pharmaceutical Co., Ltd., Gotemba, Shizuoka, Japan
,
Tatsuhiko Tachibana
1  Research Division, Chugai Pharmaceutical Co., Ltd., Kamakura, Kanagawa, Japan
,
Shinya Ishii
2  Research Division, Chugai Pharmaceutical Co., Ltd., Gotemba, Shizuoka, Japan
,
Tetsuhiro Soeda
2  Research Division, Chugai Pharmaceutical Co., Ltd., Gotemba, Shizuoka, Japan
,
Atsushi Muto
2  Research Division, Chugai Pharmaceutical Co., Ltd., Gotemba, Shizuoka, Japan
,
Yoshiki Kawabe
2  Research Division, Chugai Pharmaceutical Co., Ltd., Gotemba, Shizuoka, Japan
,
Tomoyuki Igawa
2  Research Division, Chugai Pharmaceutical Co., Ltd., Gotemba, Shizuoka, Japan
,
Hiroyuki Tsunoda
1  Research Division, Chugai Pharmaceutical Co., Ltd., Kamakura, Kanagawa, Japan
,
Keiji Nogami
3  Department of Pediatrics, Nara Medical University, Kashihara, Nara, Japan
,
Midori Shima
3  Department of Pediatrics, Nara Medical University, Kashihara, Nara, Japan
,
Kunihiro Hattori
1  Research Division, Chugai Pharmaceutical Co., Ltd., Kamakura, Kanagawa, Japan
› Author Affiliations
Financial Support: This study was supported by Chugai Pharmaceutical Co., Ltd.
Further Information

Publication History

Received: 15 January 2017

Accepted after minor revision: 25 March 2017

Publication Date:
28 November 2017 (online)

Summary

Emicizumab, a humanised bispecific antibody recognising factors (F) IX/IXa and X/Xa, can accelerate FIXa-catalysed FX activation by bridging FIXa and FX in a manner similar to FVIIIa. However, details of the emicizumab–antigen interactions have not been reported so far. In this study, we first showed by surface plasmon resonance analysis that emicizumab bound FIX, FIXa, FX, and FXa with moderate affinities (K D = 1.58, 1.52, 1.85, and 0.978 μM, respectively). We next showed by immunoblotting analysis that emicizumab recognised the antigens’ epidermal growth factor (EGF)-like domains. We then performed K D-based simulation of equilibrium states in plasma for quantitatively predicting the ways that emicizumab would interact with the antigens. The simulation predicted that only a small part of plasma FIX, FX, and emicizumab would form antigen-bridging FIX–emicizumab–FX ternary complex, of which concentration would form a bell-shaped relationship with emicizumab concentration. The bell-shaped concentration dependency was reproduced by plasma thrombin generation assays, suggesting that the plasma concentration of the ternary complex would correlate with emicizumab’s cofactor activity. The simulation also predicted that at 10.0–100 μg/ml of emicizumab–levels shown in a previous study to be clinically effective–the majority of plasma FIX, FX, and emicizumab would exist as monomers. In conclusion, emicizumab binds FIX/FIXa and FX/FXa with micromolar affinities at their EGF-like domains. The K D-based simulation predicted that the antigen-bridging ternary complex formed in circulating plasma would correlate with emicizumab’s cofactor activity, and the majority of FIX and FX would be free and available for other coagulation reactions.

Institution where the work was carried out: Research Division, Chugai Pharmaceutical Co., Ltd.

Supplementary Material to this article is available online at www.thrombosis-online.com.