Identification and Multidimensional Optimization of an Asymmetric Bispecific IgG Antibody Mimicking the Function of Factor VIII Cofactor Activity

Abstract

In hemophilia A, routine prophylaxis with exogenous factor VIII (FVIII) requires frequent intravenous injections and can lead to the development of anti-FVIII alloantibodies (FVIII inhibitors). To overcome these drawbacks, we screened asymmetric bispecific IgG antibodies to factor IXa (FIXa) and factor X (FX), mimicking the FVIII cofactor function. Since the therapeutic potential of the lead bispecific antibody was marginal, FVIII-mimetic activity was improved by modifying its binding properties to FIXa and FX, and the pharmacokinetics was improved by engineering the charge properties of the variable region. Difficulties in manufacturing the bispecific antibody were overcome by identifying a common light chain for the anti-FIXa and anti-FX heavy chains through framework/complementarity determining region shuffling, and by pI engineering of the two heavy chains to facilitate ion exchange chromatographic purification of the bispecific antibody from the mixture of byproducts. Engineering to overcome low solubility and deamidation was also performed. The multidimensionally optimized bispecific antibody hBS910 exhibited potent FVIII-mimetic activity in human FVIII-deficient plasma, and had a half-life of 3 weeks and high subcutaneous bioavailability in cynomolgus monkeys. Importantly, the activity of hBS910 was not affected by FVIII inhibitors, while anti-hBS910 antibodies did not inhibit FVIII activity, allowing the use of hBS910 without considering the development or presence of FVIII inhibitors. Furthermore, hBS910 could be purified on a large manufacturing scale and formulated into a subcutaneously injectable liquid formulation for clinical use. These features of hBS910 enable routine prophylaxis by subcutaneous delivery at a long dosing interval without considering the development or presence of FVIII inhibitors. We expect that hBS910 (investigational drug name: ACE910) will provide significant benefit for severe hemophilia A patients.

A first-in-human phase 1 study of ACE910, a novel factor VIII–mimetic bispecific antibody, in healthy subjects

“…15 Although the pharmacological concept was clearly demonstrated by hBS23, further optimization to improve FVIII-mimetic cofactor activity, PK, immunogenicity, physicochemical stability, and manufacturability resulted in ACE910, a humanized bispecific antibody with multidimensionally optimized properties. 16 The hemostatic activity of ACE910 was demonstrated in a primate model of acquired hemophilia A, 17 and weekly subcutaneous doses of ACE910 at 1 mg/kg in a longterm primate model significantly reduced spontaneous joint bleeds, The online version of this article contains a data supplement.…”

Long-term safety and efficacy of emicizumab in a phase 1/2 study in patients with hemophilia A with or without inhibitors

“…Emicizumab is a recombinant humanized bispecific monoclonal antibody that acts as an FVIII mimetic by binding simultaneously to activated factor IX (FIXa) and factor X (FX). 18,19 Because of its unique structure, emicizumab is not expected to induce FVIII inhibitor development or be affected by existing FVIII inhibitors. Subcutaneously administered emicizumab showed high bioavailability in cynomolgus monkeys, 20 and once-weekly administration significantly reduced spontaneous bleeding symptoms in a primate model of acquired hemophilia A.…”

Production of recombinant coagulation factors: Are humans the best host cells?

“…24 The new therapeutic alternative for patients with inhibitor is a humanized bispecific antibody that binds to and bridges activated factor IX (factor IXa) and factor X, thereby acting as a factor VIII-mimetic agent. 25,26 Emicizumab has a unique structure and it is not affected by factor VIII inhibitors. Moreover, clinical trials results showed that this product is safe and a single weekly subcutaneous administration has the potential to reduce or prevent bleeding episodes in patients with severe hemophilia A with or without factor VIII inhibitors.…”