Keiko Esaki

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

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.

Factor XI contributes to thrombus propagation on injured neointima of the rabbit iliac artery

Summary.  Background: Thrombus formation through the activation of tissue factor (TF) and factor (F) XI is a critical event in the onset of cardiovascular disease. TF expressed in atherosclerotic plaques and circulating blood is an important determinant of thrombogenicity that contributes to fibrin‐rich thrombus formation after plaque disruption. However, the contribution of FXI to thrombus formation on disrupted plaques remains unclear. Methods: A mouse monoclonal antibody against FXI and activated FXI (FXIa) (XI‐5108) was generated by immunization with activated human FXI. Prothrombin time (PT), activated partial thromboplastin time (APTT), bleeding time, and ex vivo platelet aggregation in rabbits were measured before and after an intravenous bolus injection of XI‐5108. We investigated the role of FXI upon arterial thrombus growth in the rabbit iliac artery in the presence of repeated balloon injury. Results: The XI‐5108 antibody reacted to the light chain of human and rabbit FXI/FXIa, and inhibited FXIa‐initiated FXa and FXIa generation. Fibrin‐rich thrombi developed on the injured neointima that was obviously immunopositive for glycoprotein IIb‐IIIa, fibrin, TF, and FXI. Intravenous administration of XI‐5108 (3.0 mg kg−1) remarkably reduced thrombus growth, and the APTT was significantly prolonged. However, PT, bleeding time and platelet aggregation were not affected. Conclusions: These results indicate that plasma FXI plays a potent role in thrombus growth on the injured neointima. Inhibition of plasma FXI activity might help to reduce thrombus growth on ruptured plaques without prolonging bleeding time.

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

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.

IDENTIFICATION OF TUMOR VASCULAR ANTIGENS BY MONOCLONAL ANTIBODIES PREPARED FROM RAT-TUMOR-DERIVED ENDOTHELIAL CELLS

We have reported the isolation and specific in vitro properties of tumor‐derived endothelial cells (TEC) from rat KMT‐17 fibrosarcomas transplanted into rats. To develop antibody‐based tumor vascular targeting therapy for solid tumors, we have generated monoclonal antibodies (MAbs) using passive immunization of outside‐out membrane vesicles of rat epididymal‐fat‐pad‐derived capillary endothelial cells (FCEC) followed by active immunization of those of rat TEC. The MAbs produced were screened against TEC and FCEC. Of all cultured hybridomas, 75 (3.3%) of the secreted MAbs preferentially recognized TEC. We selected a total of 7 MAbs which detected antigens highly abundant in TEC, although 5 of the 7 MAbs were weakly positive for FCEC in cell‐ELISA and FACS analyses. The antigens recognized by these MAbs, with the exception of MAb TES‐7, were present on endothelial cells of tumor blood vessels in KMT‐17 fibrosarcoma tissues, as shown by immunohistochemical analysis. Antigens of 40‐ and 80‐kDa were recognized by MAbs TES‐1, 7, 17, 21 and 26 and by MAbs TES‐23 and 27 respectively. Although the function of these antigens, which are preferentially expressed on rat tumor‐derived endothelial cells, is still unknown, we believe that future studies of such antigens will help elucidate the role of endothelial cells in tumor vasculature. Our results indicate that MAbs may provide a novel tool for the development of antibody‐based therapy targeting tumor vasculature. Int. J. Cancer 77:561–566, 1998.

Factor VIIa inhibitors: target hopping in the serine protease family using X-ray structure determination.

Selective factor VIIa-tissue factor complex (FVIIa/TF) inhibition is regarded as a promising target for developing new anticoagulant drugs. Compound 1 was discovered from focused screening of serine protease-directed compounds from our internal collection. Using parallel synthesis supported by structure-based drug design, we identified peptidemimetic FVIIa/TF inhibitors (compounds 4-11) containing L-Gln or L-Met as the P2 moiety. However, these compounds lacked the selectivity of other serine proteases in the coagulation cascade, especially thrombin. Further optimization of these compounds was carried out with a focus on the P4 moiety. Among the optimized compounds, 12b-f showed improved selectivity.

Cynomolgus monkey model of interleukin-31-induced scratching depicts blockade of human interleukin-31 receptor A by a humanized monoclonal antibody

Scratching is an important factor exacerbating skin lesions through the so‐called itch‐scratch cycle in atopic dermatitis (AD). In mice, interleukin (IL)‐31 and its receptor IL‐31 receptor A (IL‐31RA) are known to play a critical role in pruritus and the pathogenesis of AD; however, study of their precise roles in primates is hindered by the low sequence homologies between primates and mice and the lack of direct evidence of itch sensation by IL‐31 in primates. We showed that administration of cynomolgus IL‐31 induces transient scratching behaviour in cynomolgus monkeys and by that were able to establish a monkey model of scratching. We then showed that a single subcutaneous injection of 1 mg/kg nemolizumab, a humanized anti‐human IL‐31RA monoclonal antibody that also neutralizes cynomolgus IL‐31 signalling and shows a good pharmacokinetic profile in cynomolgus monkeys, suppressed the IL‐31‐induced scratching for about 2 months. These results suggest that the IL‐31 axis and IL‐31RA axis play as critical a role in the induction of scratching in primates as in mice and that the blockade of IL‐31 signalling by an anti‐human IL‐31RA antibody is a promising therapeutic approach for treatment of AD. Nemolizumab is currently under investigation in clinical trials.

Identification of human IgG1 variant with enhanced FcRn binding and without increased binding to rheumatoid factor autoantibody

ABSTRACT Various studies have demonstrated that Fc engineering to enhance neonatal Fc receptor (FcRn) binding is effective for elongating half-life or increasing cellular uptake of IgG. A previous study has shown that a N434H mutation to enhance FcRn binding resulted in increased binding to rheumatoid factor (RF) autoantibody, which is not desirable for therapeutic use in autoimmune disease. In this study, we first showed that all the existing Fc variants with enhanced FcRn binding also show increased RF binding, and then identified specific mutations that could be introduced to those Fc variants to reduce the RF binding. Furthermore, we generated novel Fc variants that do not increase RF binding and show half-lives of 45 d in cynomolgus monkey, which is longer than those of previously reported Fc variants. In addition, we generated novel Fc variants with antigen sweeping activity that do not increase RF binding. We expect that these novel Fc variants will be useful as antibody therapeutics against autoimmune diseases.