Engineering CD3/CD137 Dual Specificity into a DLL3-Targeted T-Cell Engager Enhances T-Cell Infiltration and Efficacy against Small-Cell Lung Cancer

Small-cell lung cancer (SCLC) is an aggressive cancer for which immune checkpoint inhibitors (ICI) have had only limited success. Bispecific T-cell engagers are promising therapeutic alternatives for ICI-resistant tumors, but not all patients with SCLC are responsive. Herein, to integrate CD137 costimulatory function into a T-cell engager format and thereby augment therapeutic efficacy, we generated a CD3/CD137 dual-specific Fab and engineered a DLL3-targeted trispecific antibody (DLL3 trispecific). The CD3/CD137 dual-specific Fab was generated to competitively bind to CD3 and CD137 to prevent DLL3-independent cross-linking of CD3 and CD137, which could lead to systemic T-cell activation. We demonstrated that DLL3 trispecific induced better tumor growth control and a marked increase in the number of intratumoral T cells compared with a conventional DLL3-targeted bispecific T-cell engager. These findings suggest that DLL3 trispecific can exert potent efficacy by inducing concurrent CD137 costimulation and provide a promising therapeutic option for SCLC.

Molecular subtypes of lung adenocarcinoma present distinct immune tumor microenvironments

Overcoming resistance to immune checkpoint inhibitors is an important issue in patients with non-small-cell lung cancer (NSCLC). Transcriptome analysis shows that adenocarcinoma can be divided into three molecular subtypes: terminal respiratory unit (TRU), proximal proliferative (PP), and proximal inflammatory (PI), and squamous cell carcinoma (LUSQ) into four. However, the immunological characteristics of these subtypes are not fully understood. In this study, we investigated the immune landscape of NSCLC tissues in molecular subtypes using a multi-omics dataset, including tumor-infiltrating leukocytes (TILs) analyzed using flow cytometry, RNA sequences, whole exome sequences, metabolomic analysis, and clinicopathologic findings. In the PI subtype, the number of TILs increased and the immune response in the tumor microenvironment (TME) was activated, as indicated by high levels of tertiary lymphoid structures, and high cytotoxic marker levels. Patient prognosis was worse in the PP subtype than in other adenocarcinoma subtypes. Glucose transporter 1 (GLUT1) expression levels were upregulated and lactate accumulated in the TME of the PP subtype. This could lead to the formation of an immunosuppressive TME, including the inactivation of antigen-presenting cells. The TRU subtype had low biological malignancy and "cold" tumor-immune phenotypes. Squamous cell carcinoma (LUSQ) did not show distinct immunological characteristics in its respective subtypes. Elucidation of the immune characteristics of molecular subtypes could lead to the development of personalized immune therapy for lung cancer. Immune checkpoint inhibitors could be an effective treatment for the PI subtype. Glycolysis is a potential target for converting an immunosuppressive TME into an antitumorigenic TME in the PP subtype.

Emicizumab-mediated hemostatic function assessed by thrombin generation assay in an in vitro model of factor VIII-depleted thrombophilia plasma

Patients with hemophilia A (PwHA) may have concurrent deficiency of representative anticoagulant proteins, protein (P)C, PS, and antithrombin (AT), which reduces bleeding frequency. However, emicizumab-driven hemostasis in PwHA with such thrombophilic potential remains unclarified. This study investigated the influence of natural anticoagulants on emicizumab-driven coagulation in HA model plasma. Various concentrations of PS and AT were added to PS-deficient plasma and AT-deficient plasma in the presence of anti-FVIII antibody (FVIIIAb; 10BU/mL). PC-deficient plasma was mixed with normal plasma at various concentrations in the presence of FVIIIAb. Emicizumab (50 µg/mL) was added to these thrombophilic HA model plasmas, prior to tissue factor/ellagic acid-triggered thrombin generation assays. Co-presence of emicizumab increased peak thrombin values (PeakTh) dependent on PS, AT, and PC concentrations. Maximum coagulation potentials in the PS-reduced HA model plasmas remained normal in the presence of emicizumab. PeakTh were close to normal in the presence of 50%AT irrespective of emicizumab, but were higher than normal in the presence of 25%AT. Addition of recombinant FVIIa (corresponding to an administered dose of 90 μg/kg) enhanced coagulation potential to normal levels. Our findings provide novel information on hemostatic regulation in emicizumab-treated PwHA with a possible thrombophilic disposition.

A bispecific antibody NXT007 exerts a hemostatic activity in hemophilia A monkeys enough to keep a nonhemophilic state

BACKGROUND

Emicizumab, a factor (F) VIIIa-function mimetic bispecific antibody (BsAb) to FIXa and FX, has become an indispensable treatment option for people with hemophilia A (PwHA). However, a small proportion of PwHA still experience bleeds even under emicizumab prophylaxis, as observed in the long-term outcomes of clinical studies. A more potent BsAb may be desirable for such patients.

OBJECTIVES

To identify a potent BsAb to FIXa and FX, NXT007, surpassing emicizumab by in vitro and in vivo evaluation.

METHODS

New pairs of light chains for emicizumab's heavy chains were screened from phage libraries, and subsequent antibody optimization was performed. For in vitro evaluation, thrombin generation assays were performed with hemophilia A plasma. In vivo hemostatic activity was evaluated in a nonhuman primate model of acquired hemophilia A.

RESULTS

NXT007 exhibited an in vitro thrombin generation activity comparable to the international standard activity of FVIII (100 IU/dL), much higher than emicizumab, when triggered by tissue factor. NXT007 also demonstrated a potent in vivo hemostatic activity at approximately 30-fold lower plasma concentrations than emicizumab's historical data. In terms of dose shift between NXT007 and emicizumab, the in vitro and in vivo results were concordant. Regarding pharmacokinetics, NXT007 showed lower in vivo clearance than those shown by typical monoclonal antibodies, suggesting that the Fc engineering to enhance FcRn binding worked well.

CONCLUSION

NXT007, a potent BsAb, was successfully created. Nonclinical results suggest that NXT007 would have a potential to keep a nonhemophilic range of coagulation potential in PwHA or to realize more convenient dosing regimens than emicizumab.

NXT007-mediated hemostatic potential is suppressed by activated protein C-catalyzed inactivation of activated factor V

Background

Activated protein C (APC) inactivates activated factor (F) V (FVa) and FVIIIa. NXT007, an emicizumab-based engineered therapeutic bispecific antibody, enhances the coagulation potential of FVIII-deficient plasma (FVIIIdef-plasma) to near normal levels. However, little is known about the effect of APC-induced inactivation in NXT007-mediated hemostatic function.

Objectives

To investigate the contribution of APC-mediated reactions to NXT007-driven hemostasis.

Methods

In pooled normal plasma (PNP) or FVIIIdef-plasma spiked with NXT007 (10 μg/mL), effects of APC (0-16 nM) were measured using a thrombin generation assay (TGA). The direct effects of APC on cofactor activity of NXT007 or FVIIIa in a FXa generation assay were also measured. The FVdef-plasma and FV Leiden plasma (FVLeiden plasma) were preincubated with 2 anti-FVIII monoclonal antibodies (termed FVIII-depleted), and the APC effect in the presence of NXT007 in FVIII-depleted FVdef-plasma with the addition of exogenous FV (7.5-30 nM) or FVIII-depleted FVLeiden plasma was investigated.

Results

The APC dose-dependent suppression effect in TGA of FVIIIdef-plasma spiked with NXT007 was similar to that of PNP. FXa generation with NXT007 was not impaired by the addition of APC, suggesting that the APC-induced reaction in TGA with NXT007 was attributed to the direct inactivation of FVa. The addition of APC to FVIII-depleted FVdef-plasma, along with NXT007 and various FV concentrations, showed a similar attenuation to PNP. The NXT007-driven thrombin generation in FVIII-depleted FVLeiden plasma was suppressed by APC, similar to the reaction in native FVLeiden plasma.

Conclusion

NXT007 did not impair APC-mediated downregulation of FVa in FVIIIdef-plasmas, regardless of the presence of FV mutation with APC resistance.

Characterizations of a neutralizing antibody broadly reactive to multiple gluten peptide:HLA-DQ2.5 complexes in the context of celiac disease

In human celiac disease (CeD) HLA-DQ2.5 presents gluten peptides to antigen-specific CD4+ T cells, thereby instigating immune activation and enteropathy. Targeting HLA-DQ2.5 with neutralizing antibody for treating CeD may be plausible, yet using pan-HLA-DQ antibody risks affecting systemic immunity, while targeting selected gluten peptide:HLA-DQ2.5 complex (pHLA-DQ2.5) may be insufficient. Here we generate a TCR-like, neutralizing antibody (DONQ52) that broadly recognizes more than twenty-five distinct gluten pHLA-DQ2.5 through rabbit immunization with multi-epitope gluten pHLA-DQ2.5 and multidimensional optimization. Structural analyses show that the proline-rich and glutamine-rich motif of gluten epitopes critical for pathogenesis is flexibly recognized by multiple tyrosine residues present in the antibody paratope, implicating the mechanisms for the broad reactivity. In HLA-DQ2.5 transgenic mice, DONQ52 demonstrates favorable pharmacokinetics with high subcutaneous bioavailability, and blocks immunity to gluten while not affecting systemic immunity. Our results thus provide a rationale for clinical testing of DONQ52 in CeD.

Tumor-infiltrating Leukocyte Profiling Defines Three Immune Subtypes of NSCLC with Distinct Signaling Pathways and Genetic Alterations

Resistance to immune checkpoint blockade remains challenging in patients with non-small cell lung cancer (NSCLC). Tumor-infiltrating leukocyte (TIL) quantity, composition, and activation status profoundly influence responsiveness to cancer immunotherapy. This study examined the immune landscape in the NSCLC tumor microenvironment by analyzing TIL profiles of 281 fresh resected NSCLC tissues. Unsupervised clustering based on numbers and percentages of 30 TIL types classified adenocarcinoma (LUAD) and squamous cell carcinoma (LUSQ) into the cold, myeloid cell-dominant, and CD8⁺ T cell-dominant subtypes. These were significantly correlated with patient prognosis; the myeloid cell subtype had worse outcomes than the others. Integrated genomic and transcriptomic analyses, including RNA sequencing, whole-exome sequencing, T-cell receptor repertoire, and metabolomics of tumor tissue, revealed that immune reaction-related signaling pathways were inactivated, while the glycolysis and K-ras signaling pathways activated in LUAD and LUSQ myeloid cell subtypes. Cases with ALK and ROS1 fusion genes were enriched in the LUAD myeloid subtype, and the frequency of TERT copy-number variations was higher in LUSQ myeloid subtype than in the others. These classifications of NSCLC based on TIL status may be useful for developing personalized immune therapies for NSCLC.

Significance

The precise TIL profiling classified NSCLC into novel three immune subtypes that correlates with patient outcome, identifying subtype-specific molecular pathways and genomic alterations that should play important roles in constructing subtype-specific immune tumor microenvironments. These classifications of NSCLC based on TIL status are useful for developing personalized immune therapies for NSCLC.

Abstract 1872: A DLL3/CD3/CD137 trispecific T cell engager shows potent antitumor activity in small cell lung cancer models

Background: Despite the approval of immune checkpoint inhibitors (ICIs), prognosis of small cell lung cancer (SCLC) remains poor. DLL3 is upregulated in SCLC whereas expression in normal tissues is minimal, representing the favorable profile as a therapeutic target. T cell engager (TCE) is a potent immunotherapy that redirects T cells to tumors expressing a specific antigen. Unlike ICIs, TCEs do not require the recognition of tumor antigens by T cells and thus could be an alternative approach to target tumors where the benefit of ICIs is limited such as SCLC. CD137 (4-1BB) is a costimulatory molecule that promotes T cell activation, proliferation, and survival. Since CD137 agonists synergize with CD3-mediated T cell activation, inducing concurrent CD137 costimulation is a promising strategy to unleash the potential of TCEs. We therefore developed a DLL3/CD3/CD137 trispecific T cell engager composed of two CD3/CD137 dual specific Fabs and one extra DLL3 Fab (DLL3 trispecific, RG6524).

Results: We initially investigated the CD3 and CD137 signal transduction in Jurkat cells harboring NFAT or NF-κB reporter cocultured with DLL3 positive cells. DLL3 trispecific showed dose-dependent increase in NFAT and NF-κB activity, indicating that target engagement successfully activated CD3 and CD137 signaling. In the in vitro assay using human PBMC, DLL3 trispecific induced cytotoxicity against SCLC cell lines with EC50s in the two-digit pM range.

In vivo efficacy was evaluated in SCLC xenograft models established by engrafting SCLC cell lines into immune humanized NOG mice. DLL3 trispecific showed greater tumor growth inhibition compared to a traditional bispecific T cell engager. Furthermore, flow cytometry-based immunophenotyping revealed that DLL3 trispecific increased T cell number in tumors and improved IFN-γ production from CD8 T cells. We also explored the combination with platinum-based drugs, which are widely used for SCLC, and showed that DLL3 trispecific enhanced the efficacy of platinum-based drugs. These data demonstrated that DLL3 trispecific has the potent in vivo efficacy and the potential for clinical use.

We next evaluated whether cytokine release syndrome (CRS) mitigating approaches affect antitumor efficacy. Although prophylactic use of a steroid significantly reduced cytokine production, tumor growth inhibition by DLL3 trispecific remained unchanged. Likewise, tocilizumab treatment did not reduce the efficacy, suggesting that CRS mitigation did not abrogate the therapeutic benefit.

We finally assessed the tolerability in non-human primates. DLL3 trispecific did not reach the maximum tolerated dose and was well tolerated up to 16 mg/kg Q2D, the highest dose tested.

Conclusion: Our data showed that DLL3 trispecific has potent activity and is well suited for clinical application in SCLC. These findings provide a rationale for the clinical testing of DLL3 trispecific.

Citation Format: Hirofumi Mikami, Shu Feng, Sotaro Naoi, Yumiko Azuma, Yoko Kayukawa, Toshiaki Tsunenari, Kentaro Asanuma, Ryutaro Iwabuchi, Hiroaki Nagano, Junko Shinozuka, Masaki Yamazaki, Haruka Kuroi, Siok Wan Gan, Priyanka Chichili, Shun Shimizu, Yutaka Matsuda, Shinya Ishii, Shogo Kamikawaji, Yasuko Kinoshita, Yuichiro Shimizu, Akihisa Sakamoto, Masaru Muraoka, Noriyuki Takahashi, Tatsuya Kawa, Hirotake Shiraiwa, Kenji Kashima, Futa Mimoto, Mika Kamata-Sakurai, Takehisa Kitazawa, Tomoyuki Igawa. A DLL3/CD3/CD137 trispecific T cell engager shows potent antitumor activity in small cell lung cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1872.

Efficient production of bispecific antibody by FAST-IgTM and its application to NXT007 for the treatment of hemophilia A

Efficient production of bispecific antibodies (BsAbs) in single mammalian cells is essential for basic research and industrial manufacturing. However, preventing unwanted pairing of heavy chains (HCs) and light chains (LCs) is a challenging task. To address this, we created an engineering technology for preferential cognate HC/LC and HC/HC paring called FAST-Ig (Four-chain Assembly by electrostatic Steering Technology - Immunoglobulin), and applied it to NXT007, a BsAb for the treatment of hemophilia A. We introduced charged amino-acid substitutions at the HC/LC interface to facilitate the proper assembly for manufacturing a standard IgG-type BsAb. We generated CH1/CL interface-engineered antibody variants that achieved > 95% correct HC/LC pairing efficiency with favorable pharmacological properties and developability. Among these, we selected a design (C3) that allowed us to separate the mis-paired species with an unintended pharmacological profile using ion-exchange chromatography. Crystal structure analysis demonstrated that the C3 design did not affect the overall structure of both Fabs. To determine the final design for HCs-heterodimerization, we compared the stability of charge-based and knobs into hole-based Fc formats in acidic conditions and selected the more stable charge-based format. FAST-Ig was also applicable to stable CHO cell lines for industrial production and demonstrated robust chain pairing with different subclasses of parent BsAbs. Thus, it can be applied to a wide variety of BsAbs both preclinically and clinically.

Emicizumab enhances thrombus formation in vitro under high shear flow conditions in whole blood from patients with type 1 and type 3 von Willebrand disease

INTRODUCTION

Type 1 and type 3 von Willebrand disease (VWD) are caused by partial and complete, quantitative deficiency of von Willebrand factor (VWF), respectively, and factor (F)VIII/VWF complex concentrates are used for haemostatic treatment. Emicizumab, mimics activated FVIII, reduces bleeding in haemophilia A patients. The effects of emicizumab on haemostasis in both types of VWD remain to be fully established, however.

AIM

To examine the effects of emicizumab on thrombogenesis in type 1 and type 3 VWD.

PATIENTS/METHODS

Perfusion chamber experiments under high shear conditions (2500 s^-1 ) combined with immunostaining were performed using whole blood samples from patients with type 1 (VWF:Ag 25 U/dl) and type 3 VWD (<1.0 U/dl).

RESULTS

The addition of FVIII (1 U/ml) to type 1 blood did not affect thrombus formation, whilst supplementation with VWF (1.6 U/ml) or FVIII/VWF (1 U/ml/1.6 U/ml) enhanced thrombogenesis to a similar extent. FVIII/VWF promoted thrombus formation significantly more than VWF alone, however, in type 3 blood. Emicizumab (100 μg/ml) augmented thrombus formation in type 3 blood compared to FVIII, and this potency seemed to be somewhat greater than that of VWF. Surface coverage of formed thrombus in type 3 VWD was less than that in type 1 VWD, but thrombus height was comparable in both. The addition of emicizumab to type 3 blood enhanced thrombin generation and fibrin formation compared to control IgG.

CONCLUSION

Emicizumab promoted mechanisms of thrombus formation in vitro in type 3 and type 1 VWD, suggesting the possibility of alternative therapeutic protocols in these patients.

Emicizumab improves thrombus formation of type 2A von willebrand disease under high shear condition

INTRODUCTION

Type 2A von Willebrand disease (VWD) is common in type-2 group caused by qualitative deficiency of von Willebrand factor (VWF). Emicizumab is a bispecific antibody that mimics activated factor VIII (FVIIIa) cofactor function, and emicizumab prophylaxis substantially reduces bleeding in patients with haemophilia A. It is unknown whether emicizumab affects thrombus formation in type 2A VWD characterized by not only low FVIII levels but also the impaired platelet adhesion and aggregation.

AIM

To examine the coagulant potential of emicizumab in type 2A VWD.

PATIENTS/METHODS

Perfusion chamber experiments combined with immunostaining were performed using whole blood from 5 patients with type 2A VWD under high shear condition (2500 s^-1 ).

RESULTS

The addition of FVIII to type 2A VWD whole blood did not augment thrombus formation, whilst supplementation with VWF or FVIII/VWF enhanced. FVIII appeared to contribute to thrombus height rather than surface coverage. The addition of emicizumab enhanced thrombus formation in type 2A VWD compared with FVIII, but this potency was less than the presence of VWF. The effect on thrombus formation mediated by emicizumab appeared to be more rapid than that by FVIII for non-requirement of activation step of FVIII, whilst that by FVIII showed more impact on thrombus formation at the late phase.

CONCLUSION

Emicizumab-induced enhancing effects of thrombus formation, independent on VWF, may be useful as an alternative therapy for type 2A VWD patients. These results supported a critical role for the FVIII-VWF complex facilitating thrombus formation under high shear.

Novel myostatin-specific antibody enhances muscle strength in muscle disease models

Myostatin, a member of the transforming growth factor-β superfamily, is an attractive target for muscle disease therapy because of its role as a negative regulator of muscle growth and strength. Here, we describe a novel antibody therapeutic approach that maximizes the potential of myostatin-targeted therapy. We generated an antibody, GYM329, that specifically binds the latent form of myostatin and inhibits its activation. Additionally, via "sweeping antibody technology", GYM329 reduces or "sweeps" myostatin in the muscle and plasma. Compared with conventional anti-myostatin agents, GYM329 and its surrogate antibody exhibit superior muscle strength-improvement effects in three different mouse disease models. We also demonstrate that the superior efficacy of GYM329 is due to its myostatin specificity and sweeping capability. Furthermore, we show that a GYM329 surrogate increases muscle mass in normal cynomolgus monkeys without any obvious toxicity. Our findings indicate the potential of GYM329 to improve muscle strength in patients with muscular disorders.

Activated factor VIII-mimicking effect by emicizumab on thrombus formation in type 2N von Willebrand disease under high shear flow conditions

INTRODUCTION

Type 2N von Willebrand disease (2NVWD) is characterized by a mild to moderate reduction in plasma levels of factor (F)VIII associated with defective binding of von Willebrand factor (VWF) to FVIII and accelerated proteolysis and clearance of FVIII. The clinical phenotype in 2NVWD is often indistinguishable from mild/moderate hemophilia (H)A. Emicizumab is a bispecific antibody to FIX/FIXa and FX/FXa that mimics FVIIIa cofactor function, and emicizumab prophylaxis significantly reduces bleeding events in patients with severe HA.

AIM

We investigated the potential benefits of emicizumab in the hemostatic management of 2NVWD.

PATIENTS/METHODS

Perfusion chamber experiments were performed using whole blood from three 2NVWD patients with different clinical phenotypes (bleeding scores: 0, 6 and 20; mutations: p.R816W, p.R816W, and p.R365X/p.T791M, respectively). Furthermore, the impact of specific FVIII-VWF interactions on thrombus formation was investigated.

RESULTS

Defective thrombus formation that correlated with bleeding phenotype was evident in these 2NVWD patients. Emicizumab improved surface coverage and thrombus height in all cases. Multi-color immunostaining of thrombi further demonstrated that emicizumab enhanced thrombin generation and fibrin formation. The addition of FVIII alone to 2NVWD whole blood did not augment thrombus formation, while supplementation with FVIII/VWF complex enhanced platelet-fibrin interactions. Furthermore, an anti-FVIII monoclonal antibody known to interrupt the release of FVIIIa from VWF depressed these effects.

CONCLUSIONS

Emicizumab-induced enhancing effects of thrombus formation, independent on VWF, might be useful as an alternative therapy for 2NVWD patients. The extent of FVIII-VWF interaction should be optimal to deliver and release FVIII/FVIIIa on the activated platelet surface.

Emicizumab Augments Thrombus Formation in Whole Blood from Patients with Hemophilia A under High Shear Flow Conditions

BACKGROUND

 Emicizumab is a bispecific antibody to factor (F) IXa and FX that mimics the FVIIIa cofactor function. Emicizumab prophylaxis markedly decreases bleeding episodes in patients with hemophilia A (PwHAs), irrespective of the presence of FVIII inhibitors. However, thrombotic microangiopathy (TMA) was reported when repeated high doses of activated prothrombin complex concentrates (aPCC) were concomitantly used with emicizumab. Although bypassing agents (BPAs) are vital in the hemostatic treatment for PwHAs with inhibitors, the mechanism of emicizumab-related TMA remains unclear.

AIM

 To assess the risk of excessive thrombus formation associated with BPAs and emicizumab under high shear conditions.

METHODS

 Perfusion flow-chamber experiments under high shear conditions were performed using whole blood from PwHAs in the presence of emicizumab without or together with FVIII or BPAs ex vivo.

RESULTS

 Emicizumab (100 μg/mL) added ex vivo to whole blood from PwHAs improved defective thrombus formation in a similar manner to that observed with the addition of recombinant FVIII at the early phase, while FVIII continued to be important at the later stages. aPCC (1.2 U/mL equivalent to 100 U/kg) or recombinant FVIIa (1.1 µg/mL; equivalent to 90 µg/kg) together with emicizumab further promoted platelet interactions and fibrin formation ex vivo but did not induce excessive thrombus formation.

CONCLUSION

 Emicizumab enhanced thrombin generation at local sites and improved defective hemostasis in whole blood from PwHAs under high shear conditions. Simple concomitant use of BPAs with emicizumab did not mediate excessive thrombus formation and remains an option for hemostatic management of emicizumab-treated PwHAs with inhibitors.

Antibody to CD137 Activated by Extracellular Adenosine Triphosphate Is Tumor Selective and Broadly Effective In Vivo without Systemic Immune Activation

Agonistic antibodies targeting CD137 have been clinically unsuccessful due to systemic toxicity. Because conferring tumor selectivity through tumor-associated antigen limits its clinical use to cancers that highly express such antigens, we exploited extracellular adenosine triphosphate (exATP), which is a hallmark of the tumor microenvironment and highly elevated in solid tumors, as a broadly tumor-selective switch. We generated a novel anti-CD137 switch antibody, STA551, which exerts agonistic activity only in the presence of exATP. STA551 demonstrated potent and broad antitumor efficacy against all mouse and human tumors tested and a wide therapeutic window without systemic immune activation in mice. STA551 was well tolerated even at 150 mg/kg/week in cynomolgus monkeys. These results provide a strong rationale for the clinical testing of STA551 against a broad variety of cancers regardless of antigen expression, and for the further application of this novel platform to other targets in cancer therapy. SIGNIFICANCE: Reported CD137 agonists suffer from either systemic toxicity or limited efficacy against antigen-specific cancers. STA551, an antibody designed to agonize CD137 only in the presence of extracellular ATP, inhibited tumor growth in a broad variety of cancer models without any systemic toxicity or dependence on antigen expression.See related commentary by Keenan and Fong, p. 20.This article is highlighted in the In This Issue feature, p. 1.

An anti-factor IXa/factor X bispecific antibody, emicizumab, improves ex vivo coagulant potentials in plasma from patients with acquired hemophilia A

INTRODUCTION

Acquired hemophilia A (AHA) is caused by autoantibodies against factor (F)VIII, and is characterized by severe, spontaneous bleeding, which can be life-threatening. Emicizumab, an anti-FIXa/FX bispecific antibody, significantly reduces bleeding events in congenital hemophilia A (HA) with and without inhibitors. The known pathophysiological mechanisms and current preclinical data in HA suggest that emicizumab could provide effective treatment for AHA, but the coagulation activities of emicizumab in these patients remain unknown.

AIM

To evaluate the coagulant effects of emicizumab in plasma from AHA patients.

METHODS AND RESULTS

Tissue factor-triggered thrombin generation assays using normal plasma preincubated with anti-FVIII monoclonal antibodies recognizing different epitopes demonstrated that 20 µg/mL emicizumab recovered the depressed peak levels of thrombin generation to 46% to 72%. Further studies were devised, therefore, to simulate the clinical course in AHA patients, including during the acute phase for severe bleeding requiring FVIII-bypassing therapy, and during the subacute/chronic phase with less bleeding. Various concentrations of emicizumab were used to represent the potential changes in plasma levels based on the half-life of the antibody (~30 days). The ex vivo addition of emicizumab to plasma samples from AHA patients (n = 16) increased peak thrombin in all cases, irrespective of the inhibitor epitope specificity. Thrombin generation at 20 and 100 µg/mL emicizumab was restored to (median) 43.9% and 92.2%, respectively. Differences were evident in some cases, however, and recovery rates appeared likely to be greater in patients with type 2 inhibitor than those with type 1.

CONCLUSION

Emicizumab improved ex vivo coagulation potential in plasma from AHA patients.

Emicizumab, the bispecific antibody to factors IX/IXa and X/Xa, potentiates coagulation function in factor XI-deficient plasma in vitro

Essentials Emicizumab mimics factor (F)VIIIa cofactor function, augments the intrinsic tenase activity. We assessed the emicizumab-driven hemostatic function in FXI-deficient plasmas. Emicizumab improved the coagulation potentials in severe FXI-deficient plasma. Emicizumab may provide a possibility for clinical application in patients with FXI deficiency. SUMMARY: Background Patients with factor (F)XI deficiency commonly present with markedly prolonged activated partial thromboplastin times (APTT), although bleeding phenotypes are heterogeneous. Emicizumab, a bispecific monoclonal antibody to FIX/FIXa and FX/FXa, mimics FVIIIa cofactor function on phospholipid (PL) surfaces. Antibody reactions were designed, therefore, to augment mechanisms during the propagation phase of blood coagulation. Aim To assess emicizumab-driven hemostatic function in FXI-deficient plasmas. Methods and Results Standard ellagic acid (Elg)/PL-based APTTs of different FXI-deficient plasmas (n = 13; FXI activity, < 1 IU dl-1 ) were markedly shortened dose dependently by the presence of emicizumab. To further analyze the effects of emicizumab, clot waveform analysis (CWA) in FXI-deficient plasmas with emicizumab, triggered by tissue factor (TF)/Elg demonstrated improvements in both clot times, reflecting the initiation phase, and coagulation velocity, which represents the propagation phase. Emicizumab also enhanced the TF/Elg-triggered thrombin generation in FXI-deficient plasmas dose-dependently although the degree of enhancement varied in individual cases. Thrombin generation with either FVII-deficient plasma or FIX-deficient plasma treated with anti-FXI antibody showed little or no increase by the co-presence of emicizumab, suggesting that the accelerated thrombin generation in FXI-deficient plasmas by emicizumab should depend on the FIXa-involved coagulation propagation initially triggered by FVIIa/TF. The ex vivo addition of emicizumab to whole blood from three patients with severe FXI deficiency demonstrated modest, dose-dependent improvements in Ca2+ -triggered thromboelastograms (NATEM mode). Conclusion Emicizumab appeared to improve coagulation function in severe FXI-deficient plasma, and might provide possibilities for clinical application in patients with FXI deficiency.

Antibody engineering to generate SKY59, a long-acting anti-C5 recycling antibody

Modulating the complement system is a promising strategy in drug discovery for disorders with uncontrolled complement activation. Although some of these disorders can be effectively treated with an antibody that inhibits complement C5, the high plasma concentration of C5 requires a huge dosage and frequent intravenous administration. Moreover, a conventional anti-C5 antibody can cause C5 to accumulate in plasma by reducing C5 clearance when C5 forms an immune complex (IC) with the antibody, which can be salvaged from endosomal vesicles by neonatal Fc receptor (FcRn)-mediated recycling. In order to neutralize the increased C5, an even higher dosage of the antibody would be required. This antigen accumulation can be suppressed by giving the antibody a pH-dependent C5-binding property so that C5 is released from the antibody in the acidic endosome and then trafficked to the lysosome for degradation, while the C5-free antibody returns back to plasma. We recently demonstrated that a pH-dependent C5-binding antibody, SKY59, exhibited long-lasting neutralization of C5 in cynomolgus monkeys, showing potential for subcutaneous delivery or less frequent administration. Here we report the details of the antibody engineering involved in generating SKY59, from humanizing a rabbit antibody to improving the C5-binding property. Moreover, because the pH-dependent C5-binding antibodies that we first generated still accumulated C5, we hypothesized that the surface charges of the ICs partially contributed to a slow uptake rate of the C5–antibody ICs. This idea motivated us to engineer the surface charges of the antibody. Our surface-charge engineered antibody consequently exhibited a high capacity to sweep C5 and suppressed the C5 accumulation in vivo by accelerating the cycle of sweeping: uptake of ICs into cells, release of C5 from the antibody in endosomes, and salvage of the antigen-free antibody. Thus, our engineered anti-C5 antibody, SKY59, is expected to provide significant benefits for patients with complement-mediated disorders.

Routine measurements of factor VIII activity and inhibitor titer in the presence of emicizumab utilizing anti-idiotype monoclonal antibodies

Essentials Emicizumab (Emi) affects the APTT-based assays of factor (F)VIII activity and inhibitor titer. A mixture of two anti-Emi monoclonal antibodies (mAb) effectively neutralized the Emi activity. Anti-Emi mAbs completely eliminated the influence of Emi on FVIII activity and inhibitor titer. The inclusion of anti-Emi mAbs in routine FVIII assays would be useful for Emi-treated patients.

SUMMARY

Background Emicizumab is an anti-factor (F)IXa/X bispecific monoclonal antibody (mAb), mimicking the factor (F)VIIIa cofactor activity. Emicizumab does not require activation by thrombin and its shortening effect on the activated partial prothrombin time (APTT) is more pronounced than that of factor (F)VIII. APTT-based FVIII activity (FVIII:C) and FVIII inhibiter titer measurements are influenced by the presence of emicizumab. Aim To establish a reliable APTT-based assay to measure FVIII in the presence of emicizumab. Methods Plasmas from hemophilia A (HA) patients without or with inhibitors were studied using one-stage FVIII:C and Bethesda inhibitor assays. Two recombinant anti-idiotype mAbs to emicizumab (anti-emicizumab mAbs) were prepared, rcAQ8 to anti-FIXa-Fab and rcAJ540 to anti-FX-Fab. Results The combined anti-idiotype mAbs (2000 nm each) eliminated the effects of emicizumab on APTTs of HA plasmas without or with inhibitor by competitive inhibition of antibody binding to FIX(a)/FX(a). Measurements of FVIII coagulation activity in HA plasmas without inhibitor were overestimated in the presence of emicizumab (1 μm = ~150 μg mL-1 ) at all reference levels of FVIII. The addition of anti-emicizumab mAbs to the assay mixtures completely neutralized the emicizumab and facilitated accurate determination of FVIII:C. Anti-FVIII inhibitor titers were undetectable in the presence of emicizumab in HA plasmas with inhibitor or normal plasmas mixed with anti-FVIII neutralizing antibodies. These effects of emicizumab were completely counteracted by the addition of the anti-idiotype mAbs, allowing accurate assessment of inhibitor titers. Conclusion The in vitro inclusion of anti-emicizumab mAbs in the standard one-stage coagulation assays prevented interference by emicizumab and enabled accurate measurements of FVIII:C and inhibitor titers.

Modified clot waveform analysis to measure plasma coagulation potential in the presence of the anti-factor IXa/factor X bispecific antibody emicizumab

Essentials The activated partial prothrombin time (aPTT) cannot predict the activity of emicizumab (Emi). Adjusted clot waveform analyses using a prothrombin time (PT)/aPTT initiator were developed. Activity of Emi in the co-presence of factor VIII or bypassing agents was quantified. This assay is useful for assessing coagulation potential in Emi-treated hemophilia A.

SUMMARY

Background Emicizumab is an anti-activated factor IX/FX bispecific antibody that mimics activated FVIII cofactor function. Emicizumab does not require activation by thrombin, and its effect on shortening the activated partial thromboplastin time (APTT) is much greater than that of FVIII. Therefore, the APTT has limited utility in hemophilia A (HA) patients treated with emicizumab. Aim To evaluate the global coagulation potential of emicizumab. Methods Clot waveform analysis (CWA) with prothrombin time (PT)/APTT mixed reagents was used to define hemostatic monitoring protocols in HA patients. A modified parameter, adjusted-|min1| (Ad|min1|), was developed. Maximum and minimum percentage transmittance were defined as 100% and 0% in the precoagulation and postcoagulation phases, respectively. Ad|min1| was calculated as an index of the maximum velocity of the coagulation process. Results Ad|min1| obtained with mixed-trigger reagent (PT/APTT/buffer, 1 : 15 : 135) in the presence of emicizumab optimally corresponded to the conversion rate estimated in animals; 0.2-0.4 IU dL-1 equivalent FVIII per 1 μg mL-1 emicizumab). Ex vivo addition of emicizumab to HA plasma with or without inhibitors resulted in concentration-dependent increases in Ad|min1|, with some individual variations. The addition of various concentrations of FVIII to HA plasma mixed with emicizumab resulted in dose-dependent increases in Ad|min1|. Similarly, mixtures of activated prothrombin complex concentrate and emicizumab added to HA plasma resulted in dose-dependent increases in Ad|min1|. In contrast, enhanced coagulation potential appeared to be better defined by the clot time than by Ad|min1| in experiments using recombinant activated FVII. Conclusion The PT/APTT reagent-triggered adjusted CWA could provide a useful means of assessing global coagulation potential in emicizumab-treated HA patients, with enhanced activity neither masking nor being masked by FVIII or bypassing agents.

Catheter-related bloodstream infection due to Rhodotorula mucilaginosa with normal serum (1→3)-β-D-glucan level

Rhodotorula species are environmental basidiomycete yeasts that have emerged as a cause of fungemia in immunocompromised hosts. The insertion of a central venous catheter was identified as a major risk factor for Rhodotorula fungemia. Few cases reports have reported (1→3)-β-D-glucan testing at the onset of Rhodotorula mucilaginosa fungemia. We report a case of catheter-related bloodstream infection due to R. mucilaginosa. Serum β-D-glucan level was normal at the onset of the bloodstream infection. It took 5 days to culture the isolate. The patient's fever persisted after empiric treatment with micafungin, and a switch to oral voriconazole immediately resolved the fungemia.

Emicizumab, A Bispecific Antibody to Factors IX/IXa and X/Xa, Does Not Interfere with Antithrombin or TFPI Activity In Vitro

Emicizumab is a humanized bispecific antibody that binds simultaneously to factor (F) IXa and FX replacing the cofactor function of FVIIIa. Because emicizumab recognizes FIX/FIXa and FX/FXa, a question may arise whether emicizumab competes with antithrombin (AT) and/or tissue factor pathway inhibitor (TFPI), thereby enhancing overall hemostatic potential by blocking their antihemostatic effects. To address this question, we performed enzymatic assays using purified coagulation factors to confirm whether emicizumab interferes with the action of AT on FIXa or FXa, or with the action of TFPI on FXa. In those assays, we found no interference of emicizumab on the actions of AT and TFPI. We next assessed emicizumab's influences on the anticoagulation actions of AT or TFPI in thrombin generation assays triggered with FXIa or tissue factor (TF) in AT-depleted or TFPI-depleted plasma supplemented with AT or TFPI in vitro. In those assays, we employed anti-FIXa and anti-FX monospecific one-armed antibodies derived from emicizumab instead of emicizumab itself so as to prevent emicizumab's FVIIIa cofactor activity from boosting thrombin generation. Consequently, we found that neither anti-FIXa, anti-FX monospecific antibody, nor the mixture of the two interfered with the anticoagulation actions of AT or TFPI in plasma. Although emicizumab can bind to FIXa and FXa, our results showed no interference of emicizumab with the action of AT or TFPI on FIXa or FXa. This indicates that the presence of emicizumab is irrelevant to the action of AT and TFPI, and thus should not alter the coagulant/anticoagulant balance related to AT and TFPI.

Neuropeptide Y (NPY) inhibits spontaneous contraction of the mouse atrium by possible activation of the NPY1 receptor

Neuropeptide Y (NPY) causes various central and peripheral actions through activation of G-protein-coupled NPY receptors. Although a species-dependent difference in cardiac actions of NPY has been reported, the responses to NPY have not been examined in mice, widely used experimental animals. This study aimed to clarify the responses to NPY and the receptor subtype involved in the responses in mouse atrium. Neuropeptide Y caused negative inotropic and negative chronotropic actions in spontaneous beating right atria. Negative inotropic actions were more marked than negative chronotropic actions. Therefore, negative inotropic actions were studied in detail for evaluation of the NPY-induced cardiac actions in mouse atrium. Neuropeptide Y-induced negative inotropic actions were not affected by atropine but were abolished in the atria from pertussis toxin-treated mice. In isolated atrial preparations from reserpine-treated mice, NPY-induced negative inotropic actions were significantly attenuated. [Leu31, Pro34]-NPY, but not peptide YY, was effective in decreasing spontaneous contraction in atrial preparations. Although Y₁ , Y₂ , Y₄ and Y₅ receptor mRNAs were expressed almost equally in the brain, NPY₁ receptor mRNA was dominantly expressed in the atrium. In conclusion, NPY caused negative inotropic and chronotropic actions through activation of the Y₁ receptor in the mouse atrium. A high expression level of Y₁ mRNA in the atrium suggests a functional role of NPY in the regulation of mouse cardiac contraction.

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

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.

Long lasting neutralization of C5 by SKY59, a novel recycling antibody, is a potential therapy for complement-mediated diseases

Dysregulation of the complement system is linked to the pathogenesis of a variety of hematological disorders. Eculizumab, an anti-complement C5 monoclonal antibody, is the current standard of care for paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS). However, because of high levels of C5 in plasma, eculizumab has to be administered biweekly by intravenous infusion. By applying recycling technology through pH-dependent binding to C5, we generated a novel humanized antibody against C5, SKY59, which has long-lasting neutralization of C5. In cynomolgus monkeys, SKY59 suppressed C5 function and complement activity for a significantly longer duration compared to a conventional antibody. Furthermore, epitope mapping by X-ray crystal structure analysis showed that a histidine cluster located on C5 is crucial for the pH-dependent interaction with SKY59. This indicates that the recycling effect of SKY59 is driven by a novel mechanism of interaction with its antigen and is distinct from other known pH-dependent antibodies. Finally, SKY59 showed neutralizing effect on C5 variant p.Arg885His, while eculizumab does not inhibit complement activity in patients carrying this mutation. Collectively, these results suggest that SKY59 is a promising new anti-C5 agent for patients with PNH and other complement-mediated disorders.

Inhibition of MEK1 Signaling Pathway in the Liver Ameliorates Insulin Resistance

Although mitogen-activated protein kinase kinase (MEK) is a key signaling molecule and a negative regulator of insulin action, it is still uncertain whether MEK can be a therapeutic target for amelioration of insulin resistance (IR) in type 2 diabetes (T2D) in vivo. To clarify whether MEK inhibition improves T2D, we examined the effect of continuous MEK inhibition with two structurally different MEK inhibitors, RO5126766 and RO4987655, in mouse models of T2D. RO5126766 and RO4987655 were administered via dietary admixture. Both compounds decreased blood glucose and improved glucose tolerance in doses sufficient to sustain inhibition of extracellular signal-regulated kinase (ERK)1/2 phosphorylation downstream of MEK in insulin-responsive tissues in db/db mice. A hyperinsulinemic-euglycemic clamp test showed increased glucose infusion rate (GIR) in db/db mice treated with these compounds, and about 60% of the increase was attributed to the inhibition of endogenous glucose production, suggesting that the liver is responsible for the improvement of IR. By means of adenovirus-mediated Mek1 shRNA expression, we confirmed that blood glucose levels are reduced by suppression of MEK1 expression in the liver of db/db mice. Taken together, these results suggested that the MEK signaling pathway could be a novel therapeutic target for novel antidiabetic agents.

Non-antigen-contacting region of an asymmetric bispecific antibody to factors IXa/X significantly affects factor VIII-mimetic activity

While antibody engineering improves the properties of therapeutic antibodies, optimization of regions that do not contact antigens has been mainly focused on modifying the effector functions and pharmacokinetics of antibodies. We recently reported an asymmetric anti-FIXa/FX bispecific IgG₄ antibody, ACE910, which mimics the cofactor function of FVIII by placing the two factors into spatial proximity for the treatment of hemophilia A. During the optimization process, we found that the activity was significantly affected by IgG subclass and by modifications to the inter-chain disulfide bonds, upper hinge region, elbow hinge region, and Fc glycan, even though these regions were unlikely to come into direct contact with the antigens. Of these non–antigen-contacting regions, the tertiary structure determined by the inter-chain disulfide bonds was found to strongly affect the FVIII-mimetic activity. Interestingly, IgG₄-like disulfide bonds between Cys131 in the heavy chain and Cys114 in the light chain, and disulfide bonds between the two heavy chains at the hinge region were indispensable for the high FVIII-mimetic activity. Moreover, proline mutations in the upper hinge region and removal of the Fc glycan enhanced the FVIII-mimetic activity, suggesting that flexibility of the upper hinge region and the Fc portion structure are important for the FVIII-mimetic activity. This study suggests that these non–antigen-contacting regions can be engineered to improve the biological activity of IgG antibodies with functions similar to ACE910, such as placing two antigens into spatial proximity, retargeting effector cells to target cells, or co-ligating two identical or different antigens on the same cell.

Anti-factor IXa/X bispecific antibody (ACE910): hemostatic potency against ongoing bleeds in a hemophilia A model and the possibility of routine supplementation

BACKGROUND

We previously reported that a humanized anti-factor IXa/X bispecific antibody, hBS23, mimics the function of FVIII even in the presence of FVIII inhibitors, and has preventive hemostatic activity against bleeding in an animal model of acquired hemophilia A. After further molecular engineering of hBS23, we recently identified an improved humanized bispecific antibody, ACE910, for clinical investigation.

OBJECTIVES

To elucidate the in vivo hemostatic potency of ACE910 by examining its effect against ongoing bleeds, and to determine its pharmacokinetic parameters for discussion of its potency for prophylactic use.

METHODS

A non-human primate model of acquired hemophilia A was established by injecting anti-primate FVIII neutralizing antibody. When bleeds emerged following an artificial bleed-inducing procedure, either ACE910 or recombinant porcine FVIII (rpoFVIII) was intravenously administered. rpoFVIII was additionally administered twice daily on the following 2 days. Bleeding symptoms were monitored for 3 days. A pharmacokinetic study and multiple-dosing simulations of ACE910 were also performed.

RESULTS

A single bolus of 1 or 3 mg kg-1 ACE910 showed hemostatic activity comparable to that of 10 U kg-1 (twice daily) rpoFVIII against ongoing bleeds. The determined ACE910 pharmacokinetic parameters included a long half-life (3 weeks) and high subcutaneous bioavailability (nearly 100%). The simulation results based on pharmacokinetic parameters indicated that the above hemostatic level could be maintained with once-weekly subcutaneous administration of ACE910, suggesting the possibility of more effective prophylaxis.

CONCLUSIONS

ACE910 may offer an alternative on-demand treatment option for patients with hemophilia A, as well as user-friendly and aggressive routine supplementation.

Anti-factor IXa/X bispecific antibody (ACE910): hemostatic potency against ongoing bleeds in a hemophilia A model and the possibility of routine supplementation

BACKGROUND

We previously reported that a humanized anti-factor IXa/X bispecific antibody, hBS23, mimics the function of FVIII even in the presence of FVIII inhibitors, and has preventive hemostatic activity against bleeding in an animal model of acquired hemophilia A. After further molecular engineering of hBS23, we recently identified an improved humanized bispecific antibody, ACE910, for clinical investigation.

OBJECTIVES

To elucidate the in vivo hemostatic potency of ACE910 by examining its effect against ongoing bleeds, and to determine its pharmacokinetic parameters for discussion of its potency for prophylactic use.

METHODS

A nonhuman primate model of acquired hemophilia A was established by injecting anti-primate FVIII neutralizing antibody. When bleeds emerged following an artificial bleed-inducing procedure, either ACE910 or recombinant porcine FVIII (rpoFVIII) was intravenously administered. rpoFVIII was additionally administered twice daily on the following 2 days. Bleeding symptoms were monitored for 3 days. A pharmacokinetic study and multiple-dosing simulations of ACE910 were also performed.

RESULTS

A single bolus of 1 or 3 mg kg⁻¹ ACE910 showed hemostatic activity comparable to that of 10 U kg⁻¹ (twice daily) rpoFVIII against ongoing bleeds. The determined ACE910 pharmacokinetic parameters included a long half-life (3 weeks) and high subcutaneous bioavailability (nearly 100%). The simulation results based on pharmacokinetic parameters indicated that the above hemostatic level could be maintained with once-weekly subcutaneous administration of ACE910, suggesting the possibility of more effective prophylaxis.

CONCLUSIONS

ACE910 may offer an alternative on-demand treatment option for patients with hemophilia A, as well as user-friendly and aggressive routine supplementation.

Roles of M2 and M3 muscarinic receptors in the generation of rhythmic motor activity in mouse small intestine

BACKGROUND

The roles of M2 and M3 muscarinic receptor subtypes in the regulation of gut motor activity were investigated.

METHODS

We simultaneously recorded changes in the intraluminal pressure (IP) and longitudinal tension (LT) in small intestinal segments from M2 or M3 receptor knockout (KO) and wild-type (WT) mice.

KEY RESULTS

In the WT preparations, luminal distension induced a continuous rhythmic contractile activity that was characterized by synchronous rises in IP and LT, occurring periodically at a constant interval. Tetrodotoxin completely abolished the response, whereas atropine either abolished or attenuated it. In the majority of the M2 KO preparations, however, no rhythmic activity was observed in response to the luminal distention, even though networks of enteric neurons and interstitial cells of Cajal (ICC) seemed to be intact. Where rhythmic activity did occur in M2 KO preparations, it was atropine resistant. In the M3 KO preparations, the IP and LT were synchronously changed by the luminal distention, but the changes occurred at irregular intervals. The W/W(v) mutant preparations, which lack ICC in the myenteric plexus (ICC-MY), showed results similar to those of the M3 KO preparations. In some of the M2 /M3 double-KO preparations, rhythmic activity was not observed, but in the others, an atropine-resistant rhythmicity appeared.

CONCLUSIONS & INFERENCES

These results suggest that M2 and M3 muscarinic receptors differentially regulate the intestinal motor activity: M2 receptors play an essential role in the generation of rhythmic motor activity, and M3 receptors have a modulatory role in controlling the periodicity of the rhythmic activity together with the ICC-MY.

Elevated plasma factor VIII enhances venous thrombus formation in rabbits: contribution of factor XI, von Willebrand factor and tissue factor

Elevated plasma levels of factor VIII (FVIII) are associated with increased risk of deep venous thrombosis. The aim of this study is to elucidate how elevated FVIII levels affect venous thrombus formation and propagation in vivo. We examined rabbit plasma FVIII activity, plasma thrombin generation, whole blood coagulation, platelet aggregation and venous wall thrombogenicity before and one hour after an intravenous infusion of recombinant human FVIII (rFVIII). Venous thrombus induced by the endothelial denudation of rabbit jugular veins was histologically assessed. Thrombus propagation was evaluated as indocyanine green fluorescence intensity. Argatroban, a thrombin inhibitor, and neutralised antibodies for tissue factor (TF), factor XI (FXI), and von Willebrand factor (VWF) were infused before or after thrombus induction to investigate their effects on venous thrombus formation or propagation. Recombinant FVIII (100 IU/kg) increased rabbit plasma FVIII activity two-fold and significantly enhanced whole blood coagulation and total plasma thrombin generation, but did not affect initial thrombin generation time, platelet aggregation and venous wall thrombogenicity. The rFVIII infusion also increased the size of venous thrombus 1 hour after thrombus induction. Argatroban and the antibodies for TF, FXI or VWF inhibited such enhanced thrombus formation and all except TF suppressed thrombus propagation. In conclusion, elevated plasma FVIII levels enhance venous thrombus formation and propagation. Excess thrombin generation by FXI and VWF-mediated FVIII recruitment appear to contribute to the growth of FVIII-driven venous thrombus.

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.

Colon-specific contractile responses to tetrodotoxin in the isolated mouse gastrointestinal tract

1 Tetrodotoxin (TTX) is a useful pharmacological tool for distinguishing neural and myogenic responses of isolated visceral organs to drugs. Although TTX does not generally affect smooth muscle tonus, in this study, we have found that TTX causes contraction of the mouse colon. The aim of this study was to characterize this TTX-induced contraction in the mouse gastrointestinal tract. 2 Longitudinal and circular muscle strips from the stomach and small intestine were less sensitive to TTX. However, TTX contracted both smooth muscle strips from the proximal colon and distal colon. 3 Pretreatment with TTX, Nω -nitro-L-arginine methyl ester (L-NAME), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and apamin inhibited the TTX-induced contraction. L-NAME, ODQ or apamin itself caused contraction in the colon but not in the gastric and small intestinal strips. Region dependency of L-NAME, ODQ and apamin-induced contraction correlated with that of TTX-induced contraction. 4 L-arginine but not D-arginine inhibited contractility of the colonic strips without affecting the contractility of muscle strips from other regions. Sodium nitroprusside caused strong relaxation of the colonic strips. 5 1,1-dimethyl-4-phenylpiperazinium (DMPP) caused relaxation of proximal and distal colons, which was significantly decreased by L-NAME or apamin. 6 In conclusion, among mouse gastrointestinal preparations, TTX induces contraction of colonic strips preferentially through blockade of potent tonic inhibitory neural outflow, which involves nitrergic and apamin-sensitive pathways. Colon-specific responses to L-arginine, L-NAME, ODQ and apamin support the hypothesis that there is a continuous suppression of colonic motility by enteric inhibitory neurons.

Ghrelin stimulates gastric motility of the guinea pig through activation of a capsaicin-sensitive neural pathway: in vivo and in vitro functional studies

BACKGROUND

Ghrelin stimulates gastric motility in rats, mice and humans. Although ghrelin and the ghrelin receptor are known to be expressed in the guinea-pig gastrointestinal tract, the effects of ghrelin on gastric motility have not been examined. Aim of the present study was to clarify the motor-stimulating action of ghrelin in the guinea-pig stomach.

METHODS

Gastric motility was measured as intraluminal pressure changes using a balloon inserted in the stomach of urethane-anaesthetized guinea pigs. The effects of ghrelin on gastric muscle contraction and [(3)H]-efflux from [(3)H]-choline-loaded strips were investigated in vitro.

KEY RESULTS

Ghrelin (0.3-30 microg kg(-1), i.v.) increased gastric motility in a dose-dependent manner but des-acyl ghrelin was ineffective. The action of ghrelin was completely inhibited by hexamethonium and D-Lys(3)-growth-hormone releasing peptide-6. Atropine partially decreased the stimulatory action of ghrelin. In capsaicin-pretreated guinea pigs, the ghrelin-induced response was markedly decreased. Ghrelin (1 micromol L(-1)) did not affect [(3)H]-efflux in non-stimulated preparations but significantly decreased electrical field stimulation (EFS)-induced [(3)H]-efflux. L-Nitro arginine methylester (L-NAME) attenuated the inhibition of [(3)H]-efflux by ghrelin. Ghrelin did not cause any mechanical changes in gastric strips. Electrical field stimulation caused relaxation of gastric strips, which changed to atropine-sensitive contraction in the presence of L-NAME. Relaxation induced by EFS was slightly potentiated, but the EFS-induced contraction was not affected by ghrelin.

CONCLUSIONS & INFERENCES

Ghrelin stimulates gastric motility of the guinea pig through activation of capsaicin-sensitive vago-vagal reflex pathway including efferent cholinergic neurons. Peripheral ghrelin receptors on enteric nitrergic nerves might affect the ghrelin-induced gastric action by releasing nitric oxide.

Design and synthesis of peptidomimetic factor VIIa inhibitors

Selective factor VIIa-tissue factor complex (FVIIa/TF) inhibition is regarded as a promising target for developing new anticoagulant drugs. In previous reports, we described a S3 subsite found in the X-ray crystal structure of compound 2 that bound to FVIIa/soluble tissue factor (sTF). Based on the X-ray crystal structure information and with the aim of improving the inhibition activity for FVIIa/TF and selectivity against other serine proteases, we synthesized derivatives by introducing substituents at position 5 of the indole ring of compound 2. Among them, compound 16 showed high selectivity against other serine proteases. Contrary to our expectations, compound 16 did not occupy the S3-subsite; X-ray structure analysis revealed that compound 16 improved selectivity by forming hydrogen bonds with Gln217, Thr99 and Asn100.