Geometric Antibody Engineering Reveals the Spatial Factor on the Efficacy of Bispecific T Cell Engagers.

Bispecific antibodies (BsAbs) represent an emerging class of biologics that can recognize two different antigens or epitopes. T-cell engagers (TcEs) bind two targets in trans on the cell surface of the effector and target cell to induce proximal immune effects, opening exciting windows for immunotherapies. To date, the engineering of BsAbs has been mainly focused on tuning the molecular weight and valency. However, the effects of spatial factors on the biological functions of BsAbs have been less explored due to the lack of biochemical methods to precisely manipulate protein geometry. Here, we studied the geometric effects of the TcEs. First, by genetically inserting rigidly designed ankyrin repeat proteins into TcEs, we revealed that the efficacy progressively decreased as the spacer distance of the two binding domains increased. Then, we constructed 26 pairs of TcEs with the same size but varying orientations using click chemistry-mediated conjugation at different mutation sites. We found that linear ligation sites play a minor role in modulating cell-killing efficacy. Next, we rendered the TcEs' advanced topology by cyclization chemistry using the SpyTag/SpyCatcher pair or sortase ligation approaches. Cyclized TcEs were generally more potent than their linear counterparts. Particularly, sortase A cyclized TcEs, bearing a minimal tagging motif, exhibited better cell-killing efficacy in vitro and improved stability both in vitro and in vivo compared to the linear TcE. This work combines modern bioconjugation chemistry and protein engineering tools for antibody engineering, shedding light on the elusive spatial factors of BsAbs functionality.

How can we discover developable antibody-based biotherapeutics?

Antibody-based biotherapeutics have emerged as a successful class of pharmaceuticals despite significant challenges and risks to their discovery and development. This review discusses the most frequently encountered hurdles in the research and development (R&D) of antibody-based biotherapeutics and proposes a conceptual framework called biopharmaceutical informatics. Our vision advocates for the syncretic use of computation and experimentation at every stage of biologic drug discovery, considering developability (manufacturability, safety, efficacy, and pharmacology) of potential drug candidates from the earliest stages of the drug discovery phase. The computational advances in recent years allow for more precise formulation of disease concepts, rapid identification, and validation of targets suitable for therapeutic intervention and discovery of potential biotherapeutics that can agonize or antagonize them. Furthermore, computational methods for de novo and epitope-specific antibody design are increasingly being developed, opening novel computationally driven opportunities for biologic drug discovery. Here, we review the opportunities and limitations of emerging computational approaches for optimizing antigens to generate robust immune responses, in silico generation of antibody sequences, discovery of potential antibody binders through virtual screening, assessment of hits, identification of lead drug candidates and their affinity maturation, and optimization for developability. The adoption of biopharmaceutical informatics across all aspects of drug discovery and development cycles should help bring affordable and effective biotherapeutics to patients more quickly.

An adapted consensus protein design strategy for identifying globally optimal biotherapeutics.

Biotherapeutic optimization, whether to improve general properties or to engineer specific attributes, is a time-consuming process with uncertain outcomes. Conversely, Consensus Protein Design has been shown to be a viable approach to enhance protein stability while retaining function. In adapting this method for a more limited number of protein sequences, we studied 21 consensus single-point variants from eight publicly available CD3 binding sequences with high similarity but diverse biophysical and pharmacological properties. All single-point consensus variants retained CD3 binding and performed similarly in cell-based functional assays. Using Ridge regression analysis, we identified the variants and sequence positions with overall beneficial effects on developability attributes of the CD3 binders. A second round of sequence generation that combined these substitutions into a single molecule yielded a unique CD3 binder with globally optimized developability attributes. In this first application to therapeutic antibodies, adapted Consensus Protein Design was found to be highly beneficial within lead optimization, conserving resources and minimizing iterations. Future implementations of this general strategy may help accelerate drug discovery and improve success rates in bringing novel biotherapeutics to market.

Intrinsic physicochemical profile of marketed antibody-based biotherapeutics.

Feeding biopharma pipelines with biotherapeutic candidates that possess desirable developability profiles can help improve the productivity of biologic drug discovery and development. Here, we have derived an in silico profile by analyzing computed physicochemical descriptors for the variable regions (Fv) found in 77 marketed antibody-based biotherapeutics. Fv regions of these biotherapeutics demonstrate significant diversities in their germlines, complementarity determining region loop lengths, hydrophobicity, and charge distributions. Furthermore, an analysis of 24 physicochemical descriptors, calculated using homology-based molecular models, has yielded five nonredundant descriptors whose distributions represent stability, isoelectric point, and molecular surface characteristics of their Fv regions. Fv regions of candidates from our internal discovery campaigns, human next-generation sequencing repertoires, and those in clinical-stages (CST) were assessed for similarity with the physicochemical profile derived here. The Fv regions in 33% of CST antibodies show physicochemical properties that are dissimilar to currently marketed biotherapeutics. In comparison, physicochemical characteristics of ∼29% of the Fv regions in human antibodies and ∼27% of our internal hits deviated significantly from those of marketed biotherapeutics. The early availability of this information can help guide hit selection, lead identification, and optimization of biotherapeutic candidates. Insights from this work can also help support portfolio risk assessment, in-licensing, and biopharma collaborations.

Discovery Strategies to Maximize the Clinical Potential of T-Cell Engaging Antibodies for the Treatment of Solid Tumors.

T-cell Engaging bispecific antibodies (TcEs) that can re-direct cytotoxic T-cells to kill cancer cells have been validated in clinical studies. To date, the clinical success with these agents has mainly been seen in hematologic tumor indications. However, an increasing number of TcEs are currently being developed to exploit the potent mode-of-action to treat solid tumor indications, which is more challenging in terms of tumor-cell accessibility and the complexity of the tumor microenvironment (TME). Of particular interest is the potential of TcEs as an immunotherapeutic approach for the treatment of non-immunogenic (often referred to as cold) tumors that do not respond to checkpoint inhibitors such as programmed cell death protein 1 (PD-1) and programmed death ligand 1 (PD-L1) antibodies. This has led to considerable discovery efforts for, firstly, the identification of tumor selective targeting approaches that can safely re-direct cytotoxic T-cells to cancer cells, and, secondly, bispecific antibodies and their derivatives with drug-like properties that promote a potent cytolytic synapse between T-cells and tumor cells, and in the most advanced TcEs, have IgG-like pharmacokinetics for dosing convenience. Based on encouraging pre-clinical data, a growing number of TcEs against a broad range of targets, and using an array of different molecular structures have entered clinical studies for solid tumor indications, and the first clinical data is beginning to emerge. This review outlines the different approaches that have been taken to date in addressing the challenges of exploiting the TcE mode-of-action for a broad range of solid indications, as well as opportunities for future discovery potential.

A Bispecific DLL3/CD3 IgG-Like T-Cell Engaging Antibody Induces Antitumor Responses in Small Cell Lung Cancer.

PURPOSE: Small cell lung cancer (SCLC) is the most lethal and aggressive subtype of lung carcinoma characterized by highly chemotherapy-resistant recurrence in the majority of patients. To effectively treat SCLC, we have developed a unique and novel IgG-like T-cell engaging bispecific antibody (ITE) that potently redirects T-cells to specifically lyse SCLC cells expressing Delta-like ligand 3 (DLL3), an antigen that is frequently expressed on the cell surface of SCLC cells, with no to very little detectable expression in normal tissues. EXPERIMENTAL DESIGN: The antitumor activity and mode of action of DLL3/CD3 ITE was evaluated in vitro using SCLC cell lines and primary human effector cells and in vivo in an SCLC xenograft model reconstituted with human CD3+ T-cells. RESULTS: Selective binding of DLL3/CD3 ITE to DLL3-positive tumor cells and T-cells induces formation of an immunological synapse resulting in tumor cell lysis and activation of T-cells. In a human T-cell engrafted xenograft model, the DLL3/CD3 ITE leads to an increase in infiltration of T-cells into the tumor tissue resulting in apoptosis of the tumor cells and tumor regression. Consistent with the mode of action, the DLL3/CD3 ITE treatment led to upregulation of PD-1, PD-L1, and LAG-3. CONCLUSIONS: This study highlights the ability of the DLL3/CD3 ITE to induce strictly DLL3-dependent T-cell redirected lysis of tumor cells and recruitment of T-cells into noninflamed tumor tissues leading to tumor regression in a preclinical in vivo model. These data support clinical testing of the DLL3/CD3 ITE in patients with SCLC.

Choices of capture chromatography technology in antibody manufacturing processes.

The capture process employed in monoclonal antibody downstream purification is not only the most critically impacted process by increased antibody titer resulting from optimized mammalian cell culture expression systems, but also the most important purification step in determining overall process throughput, product quality, and economics. Advances in separation technology for capturing antibodies from complex feedstocks have been one focus of downstream purification process innovation for past 10 years. In this study, we evaluated new generation chromatography resins used in the antibody capture process including Protein A, cation exchange, and mixed mode chromatography to address the benefits and unique challenges posed by each chromatography approach. Our results demonstrate the benefit of improved binding capacity of new generation Protein A resins, address the concern of high concentration surge caused aggregation when using new generation cation exchange resins with over 100mg/mL binding capacity, and highlight the potential of multimodal cation exchange resins for capture process design. The new landscape of capture chromatography technologies provides options to achieve overall downstream purification outcome with high product quality and process efficiency.

Structural basis for pH-insensitive inhibition of immunoglobulin G recycling by an anti-neonatal Fc receptor antibody.

The neonatal Fc receptor FcRn plays a critical role in the trafficking of IgGs across tissue barriers and in retaining high circulating concentrations of both IgG and albumin. Although generally beneficial from an immunological perspective in maintaining IgG populations, FcRn can contribute to the pathogenesis of autoimmune disorders when an abnormal immune response targets normal biological components. We previously described a monoclonal antibody (DX-2507) that binds to FcRn with high affinity at both neutral and acidic pH, prevents the simultaneous binding of IgG, and reduces circulating IgG levels in preclinical animal models. Here, we report a 2.5 Å resolution X-ray crystal structure of an FcRn-DX-2507 Fab complex, revealing a nearly complete overlap of the IgG-Fc binding site in FcRn by complementarity-determining regions in DX-2507. This overlap explains how DX-2507 blocks IgG binding to FcRn and thereby shortens IgG half-life by preventing IgGs from recycling back into circulation. Moreover, the complex structure explains how the DX-2507 interaction is pH-insensitive unlike normal Fc interactions and how serum albumin levels are unaffected by DX-2507 binding. These structural studies could inform antibody-based therapeutic approaches for limiting the effects of IgG-mediated autoimmune disease.

Selective Inhibition of Membrane Type 1 Matrix Metalloproteinase Abrogates Progression of Experimental Inflammatory Arthritis: Synergy With Tumor Necrosis Factor Blockade.

OBJECTIVE: In rheumatoid arthritis (RA), destruction of articular cartilage by the inflamed synovium is considered to be driven by increased activities of proteolytic enzymes, including matrix metalloproteinases (MMPs). The purpose of this study was to investigate the therapeutic potential of selective inhibition of membrane type 1 MMP (MT1-MMP) and its combination with tumor necrosis factor (TNF) blockage in mice with collagen-induced arthritis (CIA). METHODS: CIA was induced in DBA/1 mice by immunization with bovine type II collagen. From the onset of clinical arthritis, mice were treated with MT1-MMP selective inhibitory antibody DX-2400 and/or TNFR-Fc fusion protein. Disease progression was monitored daily, and serum, lymph nodes, and affected paws were collected at the end of the study for cytokine and histologic analyses. For in vitro analysis, bone marrow-derived macrophages were stimulated with lipopolysaccharide for 24 hours in the presence of DX-2400 and/or TNFR-Fc to analyze cytokine production and phenotype. RESULTS: DX-2400 treatment significantly reduced cartilage degradation and disease progression in mice with CIA. Importantly, when combined with TNF blockade, DX-2400 acted synergistically, inducing long-term benefit. DX-2400 also inhibited the up-regulation of interleukin-12 (IL-12)/IL-23 p40 via polarization toward an M2 phenotype in bone marrow-derived macrophages. Increased production of IL-17 induced by anti-TNF, which correlated with an incomplete response to anti-TNF, was abrogated by combined treatment with DX-2400 in CIA. CONCLUSION: Targeting MT1-MMP provides a potential strategy for joint protection, and its combination with TNF blockade may be particularly beneficial in RA patients with an inadequate response to anti-TNF therapy.

Fully human monoclonal antibody inhibitors of the neonatal fc receptor reduce circulating IgG in non-human primates.

The therapeutic management of antibody-mediated autoimmune disease typically involves immunosuppressant and immunomodulatory strategies. However, perturbing the fundamental role of the neonatal Fc receptor (FcRn) in salvaging IgG from lysosomal degradation provides a novel approach - depleting the body of pathogenic immunoglobulin by preventing IgG binding to FcRn and thereby increasing the rate of IgG catabolism. Herein, we describe the discovery and preclinical evaluation of fully human monoclonal IgG antibody inhibitors of FcRn. Using phage display, we identified several potent inhibitors of human-FcRn in which binding to FcRn is pH-independent, with over 1000-fold higher affinity for human-FcRn than human IgG-Fc at pH 7.4. FcRn antagonism in vivo using a human-FcRn knock-in transgenic mouse model caused enhanced catabolism of exogenously administered human IgG. In non-human primates, we observed reductions in endogenous circulating IgG of >60% with no changes in albumin, IgM, or IgA. FcRn antagonism did not disrupt the ability of non-human primates to mount IgM/IgG primary and secondary immune responses. Interestingly, the therapeutic anti-FcRn antibodies had a short serum half-life but caused a prolonged reduction in IgG levels. This may be explained by the high affinity of the antibodies to FcRn at both acidic and neutral pH. These results provide important preclinical proof of concept data in support of FcRn antagonism as a novel approach to the treatment of antibody-mediated autoimmune diseases.

Inhibition of plasma kallikrein by a highly specific active site blocking antibody.

Plasma kallikrein (pKal) proteolytically cleaves high molecular weight kininogen to generate the potent vasodilator and the pro-inflammatory peptide, bradykinin. pKal activity is tightly regulated in healthy individuals by the serpin C1-inhibitor, but individuals with hereditary angioedema (HAE) are deficient in C1-inhibitor and consequently exhibit excessive bradykinin generation that in turn causes debilitating and potentially fatal swelling attacks. To develop a potential therapeutic agent for HAE and other pKal-mediated disorders, we used phage display to discover a fully human IgG1 monoclonal antibody (DX-2930) against pKal. In vitro experiments demonstrated that DX-2930 potently inhibits active pKal (Ki = 0.120 ± 0.005 nM) but does not target either the zymogen (prekallikrein) or any other serine protease tested. These findings are supported by a 2.1-Å resolution crystal structure of pKal complexed to a DX-2930 Fab construct, which establishes that the pKal active site is fully occluded by the antibody. DX-2930 injected subcutaneously into cynomolgus monkeys exhibited a long half-life (t½ ∼ 12.5 days) and blocked high molecular weight kininogen proteolysis in activated plasma in a dose- and time-dependent manner. Furthermore, subcutaneous DX-2930 reduced carrageenan-induced paw edema in rats. A potent and long acting inhibitor of pKal activity could be an effective treatment option for pKal-mediated diseases, such as HAE.

Drugs derived from phage display: from candidate identification to clinical practice.

Phage display, one of today's fundamental drug discovery technologies, allows identification of a broad range of biological drugs, including peptides, antibodies and other proteins, with the ability to tailor critical characteristics such as potency, specificity and cross-species binding. Further, unlike in vivo technologies, generating phage display-derived antibodies is not restricted by immunological tolerance. Although more than 20 phage display-derived antibody and peptides are currently in late-stage clinical trials or approved, there is little literature addressing the specific challenges and successes in the clinical development of phage-derived drugs. This review uses case studies, from candidate identification through clinical development, to illustrate the utility of phage display as a drug discovery tool, and offers a perspective for future developments of phage display technology.

A homogeneous fluorescence anisotropy assay for measuring transglutaminase 2 activity.

Transglutaminases catalyze the covalent linkage of protein polypeptides through their glutamine and lysine side chains. Tissue transglutaminase 2 (TG2) has been of particular interest given its potential role in several disorders, including a variety of cancers and neurodegenerative diseases. Here we report a biochemical assay that monitors TG2 activity by following an increase in the fluorescence anisotropy of a fluorescein-labeled substrate peptide as it conjugates to a bovine serum albumin (BSA) cosubstrate of larger hydrodynamic mass. The resulting homogeneous assay is sensitive to low TG2 concentrations (pM range) and is readily adapted to higher throughput formats.

Evaluation of protein engineering and process optimization approaches to enhance antibody drug manufacturability.

A potent single digit picomolar fully human monoclonal antibody (hMAb) inhibitor with a high degree of specificity to the antigen of interest was identified from a phage display library. The hMAb, however, exhibited a high degree of hydrophobicity and easily formed insoluble aggregates when purified using a Protein A based generic process. Strategies were designed using both protein engineering and process development approaches to optimize the molecule's amino acid sequence and its behavior in process conditions. The insoluble aggregation issue was brought under control by one single amino acid mutation in CDR region or by switching to non-ProA based purification process. Our study therefore presents the rational manufacturability design for future monoclonal antibody product and its purification process under the quality by design concept by either engineering the drug molecule to adapt existing platform process or optimizing the process to fit the specific properties of the drug product.

The distinctive separation attributes of mixed-mode resins and their application in monoclonal antibody downstream purification process.

Increased upstream productivity and the continuous pressure to deliver high quality drug product have resulted in the development of new separation technologies and platform strategies for downstream purification processes of monoclonal antibodies (mAb). In this study, the separation attributes of three mixed-mode resins, Mercapto-Ethyl-Pyridine (MEP) hydrophobic charge induction resin, Capto adhere multi-modal anion exchange resin, and ceramic hydroxyapatite/fluoroapatite (CHT/CFT) resins, were investigated to define their roles in monoclonal antibody purification processes. We demonstrated that the multi-modal nature of ligands on mixed-mode resins allows the separation resolution to be honed, either through a single dominant mechanism or through mix-modal balanced purification strategies. In addition, the three mixed-mode resins present different purification powers for different types of impurities. We also demonstrated that besides enhancing chromatography separation and improve product quality, especially for high molecular weight (HMW) aggregate reduction, mixed-mode resins can also help to improve process efficiency in industrial-scale mAb drug manufacturing. Our results underscore the importance of selecting appropriate chromatography resins during DSP design to obtain the best overall process outcome.

Specific inhibition of tissue kallikrein 1 with a human monoclonal antibody reveals a potential role in airway diseases.

KLK1 (tissue kallikrein 1) is a member of the tissue kallikrein family of serine proteases and is the primary kinin-generating enzyme in human airways. DX-2300 is a fully human antibody that inhibits KLK1 via a competitive inhibition mechanism (Ki=0.13 nM). No binding of DX-2300 to KLK1 was observed in a surface-plasmon-resonance biosensor assay when KLK1 was complexed to known active-site inhibitors, suggesting that DX-2300 recognizes the KLK1 active site. DX-2300 did not inhibit any of the 21 serine proteases that were each tested at a concentration of 1 microM. We validated the use of DX-2300 for specific KLK1 inhibition by measuring the inhibition of KLK1-like activity in human urine, saliva and bronchoalveolar lavage fluid, which are known to contain active KLK1. In human tracheobronchial epithelial cells grown at the air/liquid interface, DX-2300 blocked oxidative-stress-induced epidermal-growth-factor receptor activation and downstream mucus cell proliferation and hypersecretion, which have been previously shown to be mediated by KLK1. In an allergic sheep model of asthma, DX-2300 inhibited both allergen-induced late-phase bronchoconstriction and airway hyper-responsiveness to carbachol. These studies demonstrate that DX-2300 is a potent and specific inhibitor of KLK1 that is efficacious in in vitro and in vivo models of airway disease.

Selective inhibition of matrix metalloproteinase-14 blocks tumor growth, invasion, and angiogenesis.

Inhibition of specific matrix metalloproteinases (MMP) is an attractive noncytotoxic approach to cancer therapy. MMP-14, a membrane-bound zinc endopeptidase, has been proposed to play a central role in tumor growth, invasion, and neovascularization. Besides cleaving matrix proteins, MMP-14 activates proMMP-2 leading to an amplification of pericellular proteolytic activity. To examine the contribution of MMP-14 to tumor growth and angiogenesis, we used DX-2400, a highly selective fully human MMP-14 inhibitory antibody discovered using phage display technology. DX-2400 blocked proMMP-2 processing on tumor and endothelial cells, inhibited angiogenesis, and slowed tumor progression and formation of metastatic lesions. The combination of potency, selectivity, and robust in vivo activity shows the potential of a selective MMP-14 inhibitor for the treatment of solid tumors.

Discovery and characterization of human antibody inhibitors of pregnancy-associated plasma protein-A.

Pregnancy-associated plasma protein-A (PAPP-A) is a metalloprotease that cleaves insulin-like growth factor-binding proteins (IGFBPs) to release bioactive levels of free insulin-like growth factor. Specific and potent inhibitors of PAPP-A may further elucidate the biological functions of this protease and could prove to be of therapeutic value. Phage display was used to discover fully human antibody inhibitors of PAPP-A activity towards IGFBP4 cleavage. Estimates of the inhibition constants for these antibodies were subsequently determined using a novel continuous assay of PAPP-A protease activity that uses an internally quenched synthetic peptide substrate (DX-1655). DX-1655 was hydrolyzed by PAPP-A with a K(m) of 33 muM and a k(cat) of 0.3 s(-1) (k(cat)/K(m)=9.1x10(3) M(-1) s(-1)). PAPP-A activity towards DX-1655 displays a bell-shaped pH profile, with pK(a) values of 8.2 and 10.8 and a maximum rate at approximately pH 9.5. Using this continuous assay, we measured apparent K(i) values of 1.7+/-0.2 and 7.4+/-1.5 nM for the F2 and D9 antibodies, respectively.

Engineered protein inhibitors of proteases.

The control of proteolysis in an organism is achieved under normal circumstances through a balance of protease production, degradation and inactivation, via interaction with an endogenous inhibitor. When one of these mechanisms for control of proteolysis fails, it can result in the onset or progression of disease. Control of aberrant proteolysis is, therefore, a potetntial point of therapeutic intervention, and can be achieved either through the replacement of an absent endogenous inhibitor or by dosing with an inhibitor that is specific for a protease that is being over produced. Engineered protein inhibitors of proteases offer the potential to overcome the difficulties involved in identifying specific inhibitors via small-molecule-based approaches.

High-throughput affinity ranking of antibodies using surface plasmon resonance microarrays.

A method was developed to rapidly identify high-affinity human antibodies from phage display library selection outputs. It combines high-throughput Fab fragment expression and purification with surface plasmon resonance (SPR) microarrays to determine kinetic constants (kon and koff) for 96 different Fab fragments in a single experiment. Fabs against human tissue kallikrein 1 (hK1, KLK1 gene product) were discovered by phage display, expressed in Escherichia coli in batches of 96, and purified using protein A PhyTip columns. Kinetic constants were obtained for 191 unique anti-hK1 Fabs using the Flexchip SPR microarray device. The highest affinity Fabs discovered had dissociation constants of less than 1 nM. The described SPR method was also used to categorize Fabs according to their ability to recognize an apparent active site epitope. The ability to rapidly determine the affinities of hundreds of antibodies significantly accelerates the discovery of high-affinity antibody leads.