A heterodimeric Fc-based bispecific antibody simultaneously targeting VEGFR-2 and Met exhibits potent antitumor activity

Clinical Progresses and Challenges of Bispecific Antibodies for the Treatment of Solid Tumors

In recent years, bispecific antibodies (BsAbs) have emerged as a promising therapeutic strategy against tumors. BsAbs can recruit and activate immune cells, block multiple signaling pathways, and deliver therapeutic payloads directly to tumor sites. This review provides a comprehensive overview of the recent advances in the development and clinical application of BsAbs for the treatment of solid tumors. We discuss the different formats, the unique mechanisms of action, and the clinical outcomes of the most advanced BsAbs in solid tumor therapy. Several studies have also analyzed the clinical progress of bispecific antibodies. However, this review distinguishes itself by exploring the challenges associated with bispecific antibodies and proposing potential solutions. As the field progresses, BsAbs hold promise to redefine cancer treatment paradigms and offer new hope to patients with solid tumors.

Design and engineering of bispecific antibodies: insights and practical considerations

Bispecific antibodies (bsAbs) have attracted significant attention due to their dual binding activity, which permits simultaneous targeting of antigens and synergistic binding effects beyond what can be obtained even with combinations of conventional monospecific antibodies. Despite the tremendous therapeutic potential, the design and construction of bsAbs are often hampered by practical issues arising from the increased structural complexity as compared to conventional monospecific antibodies. The issues are diverse in nature, spanning from decreased biophysical stability from fusion of exogenous antigen-binding domains to antibody chain mispairing leading to formation of antibody-related impurities that are very difficult to remove. The added complexity requires judicious design considerations as well as extensive molecular engineering to ensure formation of high quality bsAbs with the intended mode of action and favorable drug-like qualities. In this review, we highlight and summarize some of the key considerations in design of bsAbs as well as state-of-the-art engineering principles that can be applied in efficient construction of bsAbs with diverse molecular formats.

Engineering bispecific T-cell engagers to deplete eosinophils for the treatment of severe eosinophilic asthma

Severe eosinophilic asthma (SEA) is characterized by elevated eosinophil counts in the blood and airway mucosa. While monoclonal antibody therapies targeting interleukin-5 (IL-5) and its receptor (IL-5Rα) have improved treatment, some patients remain unresponsive. We propose an alternative approach to eliminate eosinophils using T cells by engineering IL-5Rα × CD3 bispecific T-cell engagers (bsTCEs) that target both IL-5Rα on eosinophils and CD3 on T cells. We designed different formats of IL-5Rα × CD3 bsTCEs, incorporating variations in valency, geometry, and affinity for the target antigen binding. We identified the single-chain variable fragment (scFv)-Fc format with the highest affinity toward the membrane-proximal domain of IL-5Rα in the IL-5Rα-binding arm showed the most potent cytotoxicity against IL-5Rα-expressing peripheral eosinophils by activating autologous primary T cells from healthy donors. This study proposes IL-5Rα × CD3 bsTCEs as potential alternatives for SEA treatment. Importantly, it demonstrates the first application of bsTCEs in eliminating disease-associated cells, including eosinophils, beyond cancer cells.

Design of an alternate antibody fragment format that can be produced in the cytoplasm of Escherichia coli

With increased accessibility and tissue penetration, smaller antibody formats such as antibody fragments (Fab) and single chain variable fragments (scFv) show potential as effective and low-cost choices to full-length antibodies. These formats derived from the modular architecture of antibodies could prove to be game changers for certain therapeutic and diagnostic applications. Microbial hosts have shown tremendous promise as production hosts for antibody fragment formats. However, low target protein yields coupled with the complexity of protein folding result in production limitations. Here, we report an alternative antibody fragment format 'FabH3' designed to overcome some key bottlenecks associated with the folding and production of Fabs. The FabH3 molecule is based on the Fab format with the constant domains replaced by engineered immunoglobulin G1 (IgG1) CH3 domains capable of heterodimerization based on the electrostatic steering approach. We show that this alternative antibody fragment format can be efficiently produced in the cytoplasm of E. coli using the catalyzed disulfide-bond formation system (CyDisCo) in a natively folded state with higher soluble yields than its Fab counterpart and a comparable binding affinity against the target antigen.

Improved intratumoral penetration of IL12 immunocytokine enhances the antitumor efficacy

Tumor-targeting antibody (Ab)-fused cytokines, referred to as immunocytokines, are designed to increase antitumor efficacy and reduce toxicity through the tumor-directed delivery of cytokines. However, the poor localization and intratumoral penetration of immunocytokines, especially in solid tumors, pose a challenge to effectively stimulate antitumor immune cells to kill tumor cells within the tumor microenvironment. Here, we investigated the influence of the tumor antigen-binding kinetics of a murine interleukin 12 (mIL12)-based immunocytokine on tumor localization and diffusive intratumoral penetration, and hence the consequent antitumor activity, by activating effector T cells in immunocompetent mice bearing syngeneic colon tumors. Based on tumor-associated antigen HER2-specific Ab Herceptin (HCT)-fused mIL12 carrying one molecule of mIL12 (HCT-mono-mIL12 immunocytokine), we generated a panel of HCT-mono-mIL12 variants with different affinities (K D) mainly varying in their dissociation rates (k off) for HER2. Systemic administration of HCT-mono-mIL12 required an anti-HER2 affinity above a threshold (K D = 130 nM) for selective localization and antitumor activity to HER2-expressing tumors versus HER2-negative tumors. However, the high affinity (K D = 0.54 or 46 nM) due to the slow k off from HER2 antigen limited the depth of intratumoral penetration of HCT-mono-mIL12 and the consequent tumor infiltration of T cells, resulting in inferior antitumor activity compared with that of HCT-mono-mIL12 with moderate affinity of (K D = 130 nM) and a faster k off. The extent of intratumoral penetration of HCT-mono-mIL12 variants was strongly correlated with their tumor infiltration and intratumoral activation of CD4+ and CD8+ T cells to kill tumor cells. Collectively, our results demonstrate that when developing antitumor immunocytokines, tumor antigen-binding kinetics and affinity of the Ab moiety should be optimized to achieve maximal antitumor efficacy.

Therapeutic bispecific antibodies against intracellular tumor antigens

Bispecific antibodies (BsAbs)-based therapeutics have been identified to be one of the most promising immunotherapy strategies. However, their target repertoire is mainly restricted to cell surface antigens rather than intracellular antigens, resulting in a relatively limited scope of applications. Intracellular tumor antigens are identified to account for a large proportion of tumor antigen profiles. Recently, bsAbs that target intracellular oncoproteins have raised much attention, broadening the targeting scope of tumor antigens and improving the efficacy of traditional antibody-based therapeutics. Consequently, this review will focus on this emerging field and discuss related research advances. We introduce the classification, characteristics, and clinical applications of bsAbs, the theoretical basis for targeting intracellular antigens, delivery systems of bsAbs, and the latest preclinical and clinical advances of bsAbs targeting several intracellular oncotargets, including those of cancer-testis antigens, differentiation antigens, neoantigens, and other antigens. Moreover, we summarize the limitations of current bsAbs, and propose several potential strategies against immune escape and T cell exhaustion as well as some future perspectives.

Bispecific antibodies-effects of point mutations on CH3-CH3 interface stability

A new format of therapeutic proteins is bispecific antibodies, in which two different heavy chains heterodimerize to obtain two different binding sites. Therefore, it is crucial to understand and optimize the third constant domain (CH3-CH3) interface to favor heterodimerization over homodimerization, and to preserve the physicochemical properties, as thermal stability. Here, we use molecular dynamics simulations to investigate the dissociation process of 19 CH3-CH3 crystal structures that differ from each other in few point mutations. We describe the dissociation of the dimeric interface as a two-steps mechanism. As confirmed by a Markov state model, apart from the bound and the dissociated state, we observe an additional intermediate state, which corresponds to an encounter complex. The analysis of the interdomain contacts reveals key residues that stabilize the interface. We expect that our results will improve the understanding of the CH3-CH3 interface interactions and thus advance the developability and design of new antibodies formats.

Antibody-Drug Conjugate PCMC1D3-Duocarmycin SA as a Novel Therapeutic Entity for Targeted Treatment of Cancers Aberrantly Expressing MET Receptor Tyrosine Kinase

BACKGROUND

Aberrant expression of the MET receptor tyrosine kinase is an oncogenic determinant and a drug target for cancer therapy. Currently, antibody-based biotherapeutics targeting MET are under clinical trials.

OBJECTIVE

Here we report the preclinical and therapeutic evaluation of a novel anti-MET antibody-drug conjugate PCMC1D3-duocarmycin SA (PCMC1D3-DCM) for targeted cancer therapy.

METHODS

The monoclonal antibody PCMC1D3 (IgG1a/κ), generated by a hybridoma technique and specific to one of the MET extracellular domains, was selected based on its high specificity to human MET with a binding affinity of 1.60 nM. PCMC1D3 was conjugated to DCM via a cleavable valine-citrulline dipeptide linker to form an antibody-drug conjugate with a drug-to-antibody ratio of 3.6:1. PCMC1D3-DCM in vitro rapidly induced MET internalization with an internalization efficacy ranging from 6.5 to 17.2h dependent on individual cell lines.

RESULTS

Studies using different types of cancer cell lines showed that PCMC1D3-DCM disrupted cell cycle, reduced cell viability, and caused massive cell death within 96h after treatment initiation. The calculated IC50 values for cell viability reduction were 1.5 to 15.3 nM. Results from mouse xenograft tumor models demonstrated that PCMC1D3-DCM in a single dose injection at 10 mg/kg body weight effectively delayed xenograft tumor growth up to two weeks without signs of tumor regrowth. The calculated tumoristatic concentration, a minimal dose required to balance tumor growth and inhibition, was around 2 mg/kg bodyweight. Taken together, PCMC1D3-DCM was effective in targeting inhibition of tumor growth in xenograft models.

CONCLUSION

This work provides the basis for the development of humanized PCMC1D3-DCM for MET-targeted cancer therapy in the future.

Bioassay Development for Bispecific Antibodies-Challenges and Opportunities

Antibody therapeutics are expanding with promising clinical outcomes, and diverse formats of antibodies are further developed and available for patients of the most challenging disease areas. Bispecific antibodies (BsAbs) have several significant advantages over monospecific antibodies by engaging two antigen targets. Due to the complicated mechanism of action, diverse structural variations, and dual-target binding, developing bioassays and other types of assays to characterize BsAbs is challenging. Developing bioassays for BsAbs requires a good understanding of the mechanism of action of the molecule, principles and applications of different bioanalytical methods, and phase-appropriate considerations per regulatory guidelines. Here, we review recent advances and case studies to provide strategies and insights for bioassay development for different types of bispecific molecules.

Oncogenic mechanism-based pharmaceutical validation of therapeutics targeting MET receptor tyrosine kinase

Aberrant expression and/or activation of the MET receptor tyrosine kinase is characterized by genomic recombination, gene amplification, activating mutation, alternative exon-splicing, increased transcription, and their different combinations. These dysregulations serve as oncogenic determinants contributing to cancerous initiation, progression, malignancy, and stemness. Moreover, integration of the MET pathway into the cellular signaling network as an addiction mechanism for survival has made this receptor an attractive pharmaceutical target for oncological intervention. For the last 20 years, MET-targeting small-molecule kinase inhibitors (SMKIs), conventional therapeutic monoclonal antibodies (TMABs), and antibody-based biotherapeutics such as bispecific antibodies, antibody–drug conjugates (ADC), and dual-targeting ADCs have been under intensive investigation. Outcomes from preclinical studies and clinical trials are mixed with certain successes but also various setbacks. Due to the complex nature of MET dysregulation with multiple facets and underlying mechanisms, mechanism-based validation of MET-targeting therapeutics is crucial for the selection and validation of lead candidates for clinical trials. In this review, we discuss the importance of various types of mechanism-based pharmaceutical models in evaluation of different types of MET-targeting therapeutics. The advantages and disadvantages of these mechanism-based strategies for SMKIs, conventional TMABs, and antibody-based biotherapeutics are analyzed. The demand for establishing new strategies suitable for validating novel biotherapeutics is also discussed. The information summarized should provide a pharmaceutical guideline for selection and validation of MET-targeting therapeutics for clinical application in the future.

Recent Advances in the Molecular Design and Applications of Multispecific Biotherapeutics

Recombinant protein-based biotherapeutics drugs have transformed clinical pipelines of the biopharmaceutical industry since the launch of recombinant insulin nearly four decades ago. These biologic drugs are structurally more complex than small molecules, and yet share a similar principle for rational drug discovery and development: That is to start with a pre-defined target and follow with the functional modulation with a therapeutic agent. Despite these tremendous successes, this "one target one drug" paradigm has been challenged by complex disease mechanisms that involve multiple pathways and demand new therapeutic routes. A rapidly evolving wave of multispecific biotherapeutics is coming into focus. These new therapeutic drugs are able to engage two or more protein targets via distinct binding interfaces with or without the chemical conjugation to large or small molecules. They possess the potential to not only address disease intricacy but also exploit new therapeutic mechanisms and assess undruggable targets for conventional monospecific biologics. This review focuses on the recent advances in molecular design and applications of major classes of multispecific biotherapeutics drugs, which include immune cells engagers, antibody-drug conjugates, multispecific tetherbodies, biologic matchmakers, and small-scaffold multispecific modalities. Challenges posed by the multispecific biotherapeutics drugs and their future outlooks are also discussed.

Pharmaceutical strategies in the emerging era of antibody-based biotherapeutics for the treatment of cancers overexpressing MET receptor tyrosine kinase

Pharmaceutical innovation in the development of novel antibody-based biotherapeutics with increased therapeutic indexes makes MET-targeted cancer therapy a clinical reality.

MET and RON receptor tyrosine kinases in colorectal adenocarcinoma: molecular features as drug targets and antibody-drug conjugates for therapy

Advanced colorectal adenocarcinoma (CRAC), featured by distinctive histopathological appearance, distant organ metastasis, acquired chemoresistance, and tumorigenic stemness is a group of heterogeneous cancers with unique genetic signatures and malignant phenotypes. Treatment of CRAC is a daunting task for oncologists. Currently, various strategies including molecular targeting using therapeutic monoclonal antibodies, small molecule kinase inhibitors and immunoregulatory checkpoint therapy have been applied to combat this deadly disease. However, these therapeutic modalities and approaches achieve only limited success. Thus, there is a pharmaceutical need to discover new targets and develop novel therapeutics for CRAC therapy. MET and RON receptor tyrosine kinases have been implicated in CRAC pathogenesis. Clinical studies have revealed that aberrant MET and/or RON expression and signaling are critical in regulating CRAC progression and malignant phenotypes. Increased MET and/or RON expression also has prognostic value for CRAC progression and patient survival. These features provide the rationale to target MET and RON for clinical CRAC intervention. At present, the use of small molecule kinase inhibitors targeting MET for CRAC treatment has achieved significant progress with several approvals for clinical application. Nevertheless, antibody-based biotherapeutics, although under clinical trials for more than 8 years, have made very little progress. In this review, we discuss the importance of MET and/or RON in CRAC tumorigenesis and development of anti-MET, anti-RON, and MET and RON-dual targeting antibody-drug conjugates for clinical application. The findings from both preclinical studies and clinical trials highlight the potential of this novel type of biotherapeutics for CRAC therapy in the future.

Progress and challenge in development of biotherapeutics targeting MET receptor for treatment of advanced cancer

Advanced epithelial cancers such as gastric, lung, and pancreatic tumors are featured by invasive proliferation, distant metastasis, acquired chemoresistance, and tumorigenic stemness. For the last decade, molecular-targeted therapies using therapeutic antibodies, small molecule kinase inhibitors and immune-checkpoint blockades have been applied for these diseases with significant clinical benefits. Nevertheless, there is still a large gap to achieve curative outcomes. MET (mesenchymal-epithelial transition protein), a receptor tyrosine kinase, is a tumorigenic determinant that regulates epithelial cancer initiation, progression, and malignancy. Increased MET expression also has prognostic value for cancer progression and patient survival. These features provide the rationale to target MET for cancer treatment. In this review, we discuss the importance of MET in epithelial tumorigenesis and the development of antibody-based biotherapeutics, including bispecific antibodies and antibody-drug conjugates, for clinical application. The findings from both preclinical and clinical studies highlight the potential of MET-targeted biotherapeutics for cancer therapy in the future.

A Novel T Cell-Engaging Bispecific Antibody for Treating Mesothelin-Positive Solid Tumors

As mesothelin is overexpressed in various types of cancer, it is an attractive target for therapeutic antibodies. T-cell bispecific antibodies bind to target cells and engage T cells via binding to CD3, resulting in target cell killing by T-cell activation. However, the affinity of the CD3-binding arm may influence CD3-mediated plasma clearance or antibody trapping in T-cell-containing tissues. This may then affect the biodistribution of bispecific antibodies. In this study, we used scFab and knob-into-hole technologies to construct novel IgG-based 1 + 1 MG1122-A and 2 + 1 MG1122-B bispecific antibodies against mesothelin and CD3ε. MG1122-B was designed to be bivalent to mesothelin and monovalent to CD3ε, using a 2 + 1 head-to-tail format. Activities of the two antibodies were evaluated in mesothelin-positive tumor cells in vitro and xenograft models in vivo. Although both antibodies exhibited target cell killing efficacy and produced regression of xenograft tumors with CD8+ T-cell infiltration, the antitumor efficacy of MG1122-B was significantly higher. MG1122-B may improve tumor targeting because of its bivalency for tumor antigen. It may also reduce systemic toxicity by limiting the activation of circulating T cells. Thus, MG1122-B may be useful for treating mesothelin-positive solid tumors.

Bispecific Antibodies and Antibody-Drug Conjugates for Cancer Therapy: Technological Considerations

The ability of monoclonal antibodies to specifically bind a target antigen and neutralize or stimulate its activity is the basis for the rapid growth and development of the therapeutic antibody field. In recent years, traditional immunoglobulin antibodies have been further engineered for better efficacy and safety, and technological developments in the field enabled the design and production of engineered antibodies capable of mediating therapeutic functions hitherto unattainable by conventional antibody formats. Representative of this newer generation of therapeutic antibody formats are bispecific antibodies and antibody–drug conjugates, each with several approved drugs and dozens more in the clinical development phase. In this review, the technological principles and challenges of bispecific antibodies and antibody–drug conjugates are discussed, with emphasis on clinically validated formats but also including recent developments in the fields, many of which are expected to significantly augment the current therapeutic arsenal against cancer and other diseases with unmet medical needs.

Diabody-Ig: a novel platform for the generation of multivalent and multispecific antibody molecules

Multivalent mono- or bispecific antibodies are of increasing interest for therapeutic applications, such as efficient receptor clustering and activation, or dual targeting approaches. Here, we present a novel platform for the generation of Ig-like molecules, designated diabody-Ig (Db-Ig). The antigen-binding site of Db-Ig is composed of a diabody in the V_H-V_L orientation stabilized by fusion to antibody-derived homo- or heterodimerization domains, e.g., C_H1/C_L or the heavy chain domain 2 of IgE (EHD2) or IgM (MHD2), further fused to an Fc region. In this study, we applied the Db-Ig format for the generation of tetravalent bispecific antibodies (2 + 2) directed against EGFR and HER3 and utilizing different dimerization domains. These Db-Ig antibodies retained the binding properties of the parental antibodies and demonstrated unhindered simultaneous binding of both antigens. The Db-Ig antibodies could be purified by a single affinity chromatography resulting in a homogenous preparation. Furthermore, the Db-Igs were highly stable in human plasma. Importantly, only one short peptide linker (5 aa) per chain is required to generate a Db-Ig molecule, reducing the potential risk of immunogenicity. The presence of a fully functional Fc resulted in IgG-like pharmacokinetic profiles of the Db-Ig molecules. Besides tetravalent bispecific molecules, this modular platform technology further allows for the generation of other multivalent molecules of varying specificity and valency, including mono-, bi-, tri- and tetra-specific molecules, and thus should be suitable for numerous applications.

MM-131, a bispecific anti-Met/EpCAM mAb, inhibits HGF-dependent and HGF-independent Met signaling through concurrent binding to EpCAM

Activation of the Met receptor tyrosine kinase, either by its ligand, hepatocyte growth factor (HGF), or via ligand-independent mechanisms, such as MET amplification or receptor overexpression, has been implicated in driving tumor proliferation, metastasis, and resistance to therapy. Clinical development of Met-targeted antibodies has been challenging, however, as bivalent antibodies exhibit agonistic properties, whereas monovalent antibodies lack potency and the capacity to down-regulate Met. Through computational modeling, we found that the potency of a monovalent antibody targeting Met could be dramatically improved by introducing a second binding site that recognizes an unrelated, highly expressed antigen on the tumor cell surface. Guided by this prediction, we engineered MM-131, a bispecific antibody that is monovalent for both Met and epithelial cell adhesion molecule (EpCAM). MM-131 is a purely antagonistic antibody that blocks ligand-dependent and ligand-independent Met signaling by inhibiting HGF binding to Met and inducing receptor down-regulation. Together, these mechanisms lead to inhibition of proliferation in Met-driven cancer cells, inhibition of HGF-mediated cancer cell migration, and inhibition of tumor growth in HGF-dependent and -independent mouse xenograft models. Consistent with its design, MM-131 is more potent in EpCAM-high cells than in EpCAM-low cells, and its potency decreases when EpCAM levels are reduced by RNAi. Evaluation of Met, EpCAM, and HGF levels in human tumor samples reveals that EpCAM is expressed at high levels in a wide range of Met-positive tumor types, suggesting a broad opportunity for clinical development of MM-131.

A Glycoengineered Interferon-β Mutein (R27T) Generates Prolonged Signaling by an Altered Receptor-Binding Kinetics

The glycoengineering approach is used to improve biophysical properties of protein-based drugs, but its direct impact on binding affinity and kinetic properties for the glycoengineered protein and its binding partner interaction is unclear. Type I interferon (IFN) receptors, composed of IFNAR1 and IFNAR2, have different binding strengths, and sequentially bind to IFN in the dominant direction, leading to activation of signals and induces a variety of biological effects. Here, we evaluated receptor-binding kinetics for each state of binary and ternary complex formation between recombinant human IFN-β-1a and the glycoengineered IFN-β mutein (R27T) using the heterodimeric Fc-fusion technology, and compared biological responses between them. Our results have provided evidence that the additional glycan of R27T, located at the binding interface of IFNAR2, destabilizes the interaction with IFNAR2 via steric hindrance, and simultaneously enhances the interaction with IFNAR1 by restricting the conformational freedom of R27T. Consequentially, altered receptor-binding kinetics of R27T in the ternary complex formation led to a substantial increase in strength and duration of biological responses such as prolonged signal activation and gene expression, contributing to enhanced anti-proliferative activity. In conclusion, our findings reveal N-glycan at residue 25 of R27T is a crucial regulator of receptor-binding kinetics that changes biological activities such as long-lasting activation. Thus, we believe that R27T may be clinically beneficial for patients with multiple sclerosis.

A robust heterodimeric Fc platform engineered for efficient development of bispecific antibodies of multiple formats

Bispecific monoclonal antibodies can bind two protein targets simultaneously and enable therapeutic modalities inaccessible by traditional mAbs. Bispecific formats containing a heterodimeric Fc region are of particular interest, as a heterodimeric Fc empowers both bispecificity and altered valencies while retaining the developability and druggability of a monoclonal antibody. We present a robust heterodimeric Fc platform, called the XmAb® bispecific platform, engineered for efficient development of bispecific antibodies and Fc fusions of multiple formats. First, we engineer a purification solution for proteins containing a heterodimeric Fc using engineered isoelectric point differences in the Fc region that enable straightforward purification of the heterodimeric species. Then, we combine this purification solution with a novel set of Fc substitutions capable of achieving heterodimer yields over 95% with little change in thermostability. Next, we illustrate the flexibility of our heterodimeric Fc with a case study in which a wide range of tumor-associated antigen × CD3 bispecifics are generated, differing in choice of tumor antigen, affinities for both tumor antigen and CD3, and tumor antigen valency. Finally, we present manufacturing data reinforcing the robustness of the heterodimeric Fc platform at scale.

Heterodimeric Fc-fused IL12 shows potent antitumor activity by generating memory CD8+ T cells

Interleukin-12 (IL12) (p35/p40 complex) is a heterodimeric cytokine with potent anti-tumor activity. However, its short serum half-life and high dose-related toxicities limit its clinical efficacy. Here, we constructed heterodimeric immunoglobulin Fc-fused mouse IL12 (mIL12) in a monovalent binding format (mono-mIL12-Fc) to generate long-acting mIL12 in the naturally occurring heterodimeric form. Mono-mIL12-Fc exhibited a much longer plasma half-life than recombinant mIL12, enabling twice-weekly systemic injections to remove established tumors in syngeneic mouse models. Mono-mIL12-Fc was more potent than wild-type Fc-based bivalent-binding IL12-Fc (bi-mIL12-Fc) for eradicating large established immunogenic tumors without noticeable toxicities by enhancing interferon-γ production and the proliferation of immune effector cells in tumors. More importantly, mono-mIL12-Fc triggered weaker IL12 signaling than bi-mIL12-Fc, favoring the generation of functional and protective memory CD8⁺ T cells. Our results demonstrate that heterodimeric-Fc-fused IL12 is a suitable format for augmenting adaptive CD8⁺ T cell immune responses, providing a practical alternative to the systemic administration of IL12 for antitumor therapy.

The making of bispecific antibodies

During the past two decades we have seen a phenomenal evolution of bispecific antibodies for therapeutic applications. The 'zoo' of bispecific antibodies is populated by many different species, comprising around 100 different formats, including small molecules composed solely of the antigen-binding sites of two antibodies, molecules with an IgG structure, and large complex molecules composed of different antigen-binding moieties often combined with dimerization modules. The application of sophisticated molecular design and genetic engineering has solved many of the technical problems associated with the formation of bispecific antibodies such as stability, solubility and other parameters that confer drug properties. These parameters may be summarized under the term 'developability'. In addition, different 'target product profiles', i.e., desired features of the bispecific antibody to be generated, mandates the need for access to a diverse panel of formats. These may vary in size, arrangement, valencies, flexibility and geometry of their binding modules, as well as in their distribution and pharmacokinetic properties. There is not 'one best format' for generating bispecific antibodies, and no single format is suitable for all, or even most of, the desired applications. Instead, the bispecific formats collectively serve as a valuable source of diversity that can be applied to the development of therapeutics for various indications. Here, a comprehensive overview of the different bispecific antibody formats is provided.

Structural basis of a novel heterodimeric Fc for bispecific antibody production

Bispecific antibodies provide an efficient tool for combinational clinical therapy. Here we have engineered a heterodimeric Fc for bispecific antibodies production by combining the knob-into-hole and electrostatic steering strategies where a bulky hydrophobic residue Phe405 of the IgG CH3 interface is mutated to a charged residue Lys and Lys409 of the corresponding CH3 domain is mutated to Ala. The crystal structure of this Fc heterodimer solved here at 2.7Å resolution revealed how these two mutations resulted a complementary binding interface and explained why F405K mutation could effectively inhibit Fc homodimer formation during protein expression. An anti-HER2 bispecific antibody derived from trastuzumab and pertuzumab was generated by this heterodimeric Fc. It showed comparable or improved efficacy than the combination of trastuzumab and pertuzumab in inhibiting proliferation of cancer cells in vitro and in vivo. Overall this study shows that the heterodimeric Fc engineered here provides an efficient platform for generating active bispecific antibody for cancer treatment.

Fc Engineering for Developing Therapeutic Bispecific Antibodies and Novel Scaffolds

Therapeutic monoclonal antibodies have become molecules of choice to treat autoimmune disorders, inflammatory diseases, and cancer. Moreover, bispecific/multispecific antibodies that target more than one antigen or epitope on a target cell or recruit effector cells (T cell, natural killer cell, or macrophage cell) toward target cells have shown great potential to maximize the benefits of antibody therapy. In the past decade, many novel concepts to generate bispecific and multispecific antibodies have evolved successfully into a range of formats from full bispecific immunoglobulin gammas to antibody fragments. Impressively, antibody fragments such as bispecific T-cell engager, bispecific killer cell engager, trispecific killer cell engager, tandem diabody, and dual-affinity-retargeting are showing exciting results in terms of recruiting and activating self-immune effector cells to target and lyse tumor cells. Promisingly, crystallizable fragment (Fc) antigen-binding fragment and monomeric antibody or half antibody may be particularly advantageous to target solid tumors owing to their small size and thus good tissue penetration potential while, on the other hand, keeping Fc-related effector functions such as antibody-dependent cellular cytotoxicity, complement-dependent cytotoxicity, antibody-dependent cell-mediated phagocytosis, and extended serum half-life via interaction with neonatal Fc receptor. This review, therefore, focuses on the progress of Fc engineering in generating bispecific molecules and on the use of small antibody fragment as scaffolds for therapeutic development.

Anti-metastatic effect of the TM4SF5-specific peptide vaccine and humanized monoclonal antibody on colon cancer in a mouse lung metastasis model

Transmembrane 4 superfamily member 5 protein (TM4SF5) is a potential therapeutic target for hepatocellular carcinoma (HCC) and colon cancer. In a previous study, we demonstrated the prophylactic and therapeutic effects of a TM4SF5-specific peptide vaccine and monoclonal antibody in HCC and colon cancer in a mouse model. Here, we designed a cyclic peptide targeting TM4SF5. Cyclic peptide-specific antibodies were produced in mice after immunization with a complex of the peptide, CpG-DNA, and liposomes. Intravenous injection of the CT-26 mouse colon cancer cell line into mice induced tumors in the lung. Immunization with the peptide vaccine improved the survival rate and reduced the growth of lung tumors. We established a monoclonal antibody specific to the cyclic TM4SF5-based peptide and humanized the antibody sequence by complementarity determining region-grafting. The humanized antibody was reactive to the cyclic peptide and TM4SF5 protein. Treatment of CT-26 cells with the humanized antibody reduced cell motility in vitro. Furthermore, direct injection of the humanized anti-TM4SF5 antibody in vivo reduced growth of lung tumors in mouse metastasis model. Therefore, we conclude that the immunization with the cyclic peptide vaccine and injection of the TM4SF5-specifc humanized antibody have an anti-metastatic effect against colon cancer in mice. Importantly, the humanized antibody may serve as a starting platf.

Engineered IgG1-Fc--one fragment to bind them all

The crystallizable fragment (Fc) of the immunoglobulin class G (IgG) is a very attractive scaffold for the design of novel therapeutics due to its quality of uniting all essential antibody functions. This article reviews the functionalization of this homodimeric glycoprotein by diversification of structural loops of CH3 domains for the design of Fcabs, i.e. antigen-binding Fc proteins. It reports the design of libraries for the selection of nanomolar binders with wildtype-like in vivo half-life and correlation of Fc receptor binding and ADCC. The in vitro and preclinical biological activity of selected Fcabs is compared with that of clinically approved antibodies. Recently, the great potential of the scaffold for the development of therapeutics for clinical use has been shown when the HER2-binding Fcab FS102 entered clinical phase I. Furthermore, methods for the engineering of biophysical properties of Fcabs applicable to proteins in general are presented as well as the different approaches in the design of heterodimeric Fc-based scaffolds used in the generation of bispecific monoclonal antibodies. Finally, this work critically analyzes and compares the various efforts in the design of highly diverse and functional libraries that have been made in the engineering of IgG1-Fc and structurally similar scaffolds.

Co-targeting of EGF receptor and neuropilin-1 overcomes cetuximab resistance in pancreatic ductal adenocarcinoma with integrin β1-driven Src-Akt bypass signaling

Pancreatic ductal adenocarcinoma (PDAC) cells usually overexpress the epidermal growth factor receptor (EGFR); however, most are resistant to the anti-EGFR monoclonal antibody, cetuximab. In this study, we report that the molecular mechanism of resistance to cetuximab in PDAC cells is mediated by the overexpression of active integrin β1 with downstream Src-Akt activation; this triggers an EGFR ligand-independent proliferation signaling, bypassing EGFR-blocking effect. Knockdown of integrin β1 or inhibition of Src or Akt sensitized cetuximab-resistant (Ctx^R) PDAC cells to cetuximab. We found that neuropilin-1 (NRP1) physically interacts with active integrin β1, but not inactive one, on the cell surface. To inhibit active integrin β1-driven signaling by targeting NRP1, while suppressing EGFR signaling, we generated an EGFR and NRP1 dual targeting antibody, Ctx-TPP11, by genetic fusion of the NRP1-targeting peptide, TPP11, to the C terminus of the cetuximab heavy chain (Ctx-TPP11). We demonstrate that Ctx-TPP11 efficiently inhibited the growth of Ctx^R PDAC cells, in vitro and in vivo. The sensitization mechanism involved downregulating active integrin β1 levels through NRP1-coupled internalization mediated by the TPP11 moiety, leading to the inhibition of active integrin β1-driven bypass signaling. Our findings identify aberrant active integrin β1-driven Src-Akt hyperactivation as a primary resistance mechanism to cetuximab in PDAC cells and offer an effective therapeutic strategy to overcome this resistance using an EGFR and NRP1 dual targeting antibody.

Immunoglobulin Fc Heterodimer Platform Technology: From Design to Applications in Therapeutic Antibodies and Proteins

The monospecific and bivalent characteristics of naturally occurring immunoglobulin G (IgG) antibodies depend on homodimerization of the fragment crystallizable (Fc) regions of two identical heavy chains (HCs) and the subsequent assembly of two identical light chains (LCs) via disulfide linkages between each HC and LC. Immunoglobulin Fc heterodimers have been engineered through modifications to the CH3 domain interface, with different mutations on each domain such that the engineered Fc fragments, carrying the CH3 variant pair, preferentially form heterodimers rather than homodimers. Many research groups have adopted different strategies to generate Fc heterodimers, with the goal of high heterodimerization yield, while retaining biophysical and biological properties of the wild-type Fc. Based on their ability to enforce heterodimerization between the two different HCs, the established Fc heterodimers have been extensively exploited as a scaffold to generate bispecific antibodies (bsAbs) in full-length IgG and IgG-like formats. These have many of the favorable properties of natural IgG antibodies, such as high stability, long serum half-life, low immunogenicity, and immune effector functions. As of July 2016, more than seven heterodimeric Fc-based IgG-format bsAbs are being evaluated in clinical trials. In addition to bsAbs, heterodimeric Fc technology is very promising for the generation of Fc-fused proteins and peptides, as well as cytokines (immunocytokines), which can present the fusion partners in the natural monomeric or heterodimeric form rather than the artificial homodimeric form with wild-type Fc. Here, we present relevant concepts and strategies for the generation of heterodimeric Fc proteins, and their application in the development of bsAbs in diverse formats for optimal biological activity. In addition, we describe wild-type Fc-fused monomeric and heterodimeric proteins, along with the difficulties associated with their preparations, and discuss the use of heterodimeric Fc as an alternative scaffold of wild-type Fc for naturally monomeric or heterodimeric proteins, to create Fc-fusion proteins with novel therapeutic modality.

Generation and characterization of a human nanobody against VEGFR-2

AIM

Nanobody is an antibody fragment consisting of a single monomeric variable antibody domain, which can be used for a variety of biotechnological and therapeutic purposes. The aim of this work was to isolate and characterize a human signal domain antibody against VEGFR-2 domain3 (VEGFR D3) from a phage display library.

METHODS

To produce antigen-specific recombinant nanobodies with high affinity to VEGFR2 D3, a liquid phase panning strategy was used for all rounds of panning. For nanobody expression and purification, four VEGFR2 D3-blocking clones were subcloned into a pETduet-biotin-MBP expression vector. The recombinant proteins carried an MBP tag to facilitate purification by affinity chromatography. Recombinant NTV(1-4) was obtained after an additional gel filtration chromatography step. The interactions between VEGFR2 D3 and NTV(1-4) were assessed with luminescence-based AlphaScreen assay and SPR assay. Anti-angiogenesis effects were examined in human umbilical vein endothelial cells (HUVECs).

RESULTS

In the AlphaScreen assay, NTV1 (100 and 200 nmol/L) elicited the highest binding signal with VEGFR2 D3; NTV2 showed moderate interactions with VEGFR2 D3; NTV3 and NTV4 exhibited little or no interaction with VEGFR2 D3. In the SPR assay, NTV1 displayed a high affinity for VEGFR2 D3 with an equilibrium dissociation constant (KD) of 49±1.8 nmol/L. NTV1 (1-1000 nmol/L) dose-dependently inhibited the proliferation of HUVECs and the endothelial tube formation by the HUVECs.

CONCLUSION

The nanobody NTV1 is a potential therapeutic candidate for blocking VEGFR2. This study provides a novel and promising strategy for development of VEGFR2-targeted nanobody-based cancer therapeutics.

Computationally Designed Bispecific Antibodies using Negative State Repertoires

A challenge in the structure-based design of specificity is modeling the negative states, i.e., the complexes that you do not want to form. This is a difficult problem because mutations predicted to destabilize the negative state might be accommodated by small conformational rearrangements. To overcome this challenge, we employ an iterative strategy that cycles between sequence design and protein docking in order to build up an ensemble of alternative negative state conformations for use in specificity prediction. We have applied our technique to the design of heterodimeric CH3 interfaces in the Fc region of antibodies. Combining computationally and rationally designed mutations produced unique designs with heterodimer purities greater than 90%. Asymmetric Fc crystallization was able to resolve the interface mutations; the heterodimer structures confirmed that the interfaces formed as designed. With these CH3 mutations, and those made at the heavy-/light-chain interface, we demonstrate one-step synthesis of four fully IgG-bispecific antibodies.

Engineering of Immunoglobulin Fc Heterodimers Using Yeast Surface-Displayed Combinatorial Fc Library Screening

Immunoglobulin Fc heterodimers, which are useful scaffolds for the generation of bispecific antibodies, have been mostly generated through structure-based rational design methods that introduce asymmetric mutations into the CH3 homodimeric interface to favor heterodimeric Fc formation. Here, we report an approach to generate heterodimeric Fc variants through directed evolution combined with yeast surface display. We developed a combinatorial heterodimeric Fc library display system by mating two haploid yeast cell lines, one haploid cell line displayed an Fc chain library (displayed FcCH3A) with mutations in one CH3 domain (CH3A) on the yeast cell surface, and the other cell line secreted an Fc chain library (secreted FcCH3B) with mutations in the other CH3 domain (CH3B). In the mated cells, secreted FcCH3B is displayed on the cell surface through heterodimerization with the displayed FcCH3A, the detection of which enabled us to screen the library for heterodimeric Fc variants. We constructed combinatorial heterodimeric Fc libraries with simultaneous mutations in the homodimer-favoring electrostatic interaction pairs K370-E357/S364 or D399-K392/K409 at the CH3 domain interface. High-throughput screening of the libraries using flow cytometry yielded heterodimeric Fc variants with heterodimer-favoring CH3 domain interface mutation pairs, some of them showed high heterodimerization yields (~80-90%) with previously unidentified CH3 domain interface mutation pairs, such as hydrogen bonds and cation-π interactions. Our study provides a new approach for engineering Fc heterodimers that could be used to engineer other heterodimeric protein-protein interactions through directed evolution combined with yeast surface display.

Design of liposomal formulations for cell targeting

Liposomes have gained extensive attention as carriers for a wide range of drugs due to being both nontoxic and biodegradable as they are composed of substances naturally occurring in biological membranes. Active targeting for cells has explored specific modification of the liposome surface by functionalizing it with specific targeting ligands in order to increase accumulation and intracellular uptake into target cells. None of the Food and Drug Administration-licensed liposomes or lipid nanoparticles are coated with ligands or target moieties to delivery for homing drugs to target tissues, cells or subcellular organelles. Targeted therapies (with or without controlled drug release) are an emerging and relevant research area. Despite of the numerous liposomes reviews published in the last decades, this area is in constant development. Updates urgently needed to integrate new advances in targeted liposomes research. This review highlights the evolution of liposomes from passive to active targeting and challenges in the development of targeted liposomes for specific therapies.

Immunoglobulin Fc-fused, neuropilin-1-specific peptide shows efficient tumor tissue penetration and inhibits tumor growth via anti-angiogenesis

Neuropilin-1 (NRP1) receptor, involved in vascular endothelial growth factor (VEGF)-mediated vascular permeability and tumor angiogenesis, is targeted by peptides that bind to its VEGF-binding site. However, these peptides also cross-react with the structurally related receptor, NRP2. Here, we describe an immunoglobulin Fc-fused peptide, Fc-TPP11, which specifically binds to the VEGF-binding site of NRP1 with approximately 2nM affinity, but negligibly to that of NRP2. Fc-TPP11 triggered NRP1-dependent signaling, enhanced vascular permeability via vascular endothelial (VE)-cadherin downregulation, and increased paracellular permeability via E-cadherin downregulation in tumor tissues. Fc-TPP11 also significantly enhanced the tumor penetration of co-injected anti-cancer drug, doxorubicin, leading to the improved in vivo anti-tumor efficacy. Fc-TPP11 was easily adapted to the full-length anti-epidermal growth factor receptor (EGFR) monoclonal antibody (mAb) cetuximab (Erbitux), cetuximab-TPP11, exhibiting more than 2-fold improved tumor penetration than the parent cetuximab. Fc-TPP11 exhibited a similar whole-body half-life to that of intact Fc in tumor bearing mice. In addition to the tumor-penetrating activity, Fc-TPP11 suppressed VEGF-dependent angiogenesis by blocking VEGF binding to NRP1, thereby inhibiting tumor growth without promoting metastasis in the mouse model. Our results show that NRP1-specific, high-affinity binding of Fc-TPP11, is useful to validate NRP1 signaling, independent of NRP2. Thus, Fc-TPP11 can be used as a tumor penetration-promoting agent with anti-angiogenic activity or directly adapted to mAb-TPP11 format for more potent anti-cancer antibody therapy.

Crystal structures of immunoglobulin Fc heterodimers reveal the molecular basis for heterodimer formation

We determined the X-ray crystal structure of an immunoglobulin fragment crystallizable (Fc) heterodimer, EW-RVT, at a resolution of 2.5Å and found that the designed asymmetric interaction residues located in the heterodimeric CH3 interface favor Fc heterodimer formation. We further generated an inter-CH3 disulfide-bonded heterodimeric Fc variant, EW-RVT(S-S), which exhibited improved heterodimer formation and thermodynamic stability compared with the parent EW-RVT variant. The crystal structure of EW-RVTS-S superimposed very closely with the wild-type Fc structure. Our results provide the detailed structure of heterodimeric Fc scaffolds, which will be useful for the generation of immunoglobulin G (IgG)-like bispecific antibodies.

Vascular endothelial growth factor a inhibition in gastric cancer

Angiogenesis is a vital process in the progression and metastasis of solids tumors including gastric adenocarcinoma. Tumors induce angiogenesis by secreting proangiogenic molecules such as vascular endothelial growth factor A (VEGF-A), and VEGF-A inhibition has become a common therapeutic strategy for many cancers. Several drugs targeting the VEGF-A pathway have been approved for clinical use in selected solid tumors, and several anti-VEGF-A strategies have been examined for gastric cancer. Phase II studies suggested that bevacizumab, an anti-VEGF antibody, can increase the efficacy of chemotherapy for advanced gastric cancer, but two international phase III trials failed to show an overall survival benefit. Two more recent international phase III trials have examined ramucirumab, an antibody targeting the primary receptor for VEGF-A, as second-line therapy for advanced gastric cancer and found a survival benefit both as single agent therapy and when combined with chemotherapy. Finally, correlative science studies suggest that the VEGF-A pathway may have varying importance in gastric cancer progression depending on ethnicity or race. This article will review the preclinical and clinical studies on the role of the VEGF-A pathway inhibition in gastric cancer.

Simultaneous targeting of two ligand-binding sites on VEGFR2 using biparatopic Affibody molecules results in dramatically improved affinity

Angiogenesis plays an important role in cancer and ophthalmic disorders such as age-related macular degeneration and diabetic retinopathy. The vascular endothelial growth factor (VEGF) family and corresponding receptors are regulators of angiogenesis and have been much investigated as therapeutic targets. The aim of this work was to generate antagonistic VEGFR2-specific affinity proteins having adjustable pharmacokinetic properties allowing for either therapy or molecular imaging. Two antagonistic Affibody molecules that were cross-reactive for human and murine VEGFR2 were selected by phage and bacterial display. Surprisingly, although both binders independently blocked VEGF-A binding, competition assays revealed interaction with non-overlapping epitopes on the receptor. Biparatopic molecules, comprising the two Affibody domains, were hence engineered to potentially increase affinity even further through avidity. Moreover, an albumin-binding domain was included for half-life extension in future in vivo experiments. The best-performing of the biparatopic constructs demonstrated up to 180-fold slower dissociation than the monomers. The new Affibody constructs were also able to specifically target VEGFR2 on human cells, while simultaneously binding to albumin, as well as inhibit VEGF-induced signaling. In summary, we have generated small antagonistic biparatopic Affibody molecules with high affinity for VEGFR2, which have potential for both future therapeutic and diagnostic purposes in angiogenesis-related diseases.

Design and applications of bispecific heterodimers: molecular imaging and beyond

Ligand-based molecular imaging probes have been designed with high affinity and specificity for monitoring biological process and responses. Single-target recognition by traditional probes can limit their applicability for disease detection and therapy because synergistic action between disease mediators and different receptors is often involved in disease progression. Consequently, probes that can recognize multiple targets should demonstrate higher targeting efficacy and specificity than their monospecific peers. This concept has been validated by multiple bispecific heterodimer-based imaging probes that have demonstrated promising results in several animal models. This review summarizes the design strategies for bispecific peptide- and antibody-based heterodimers and their applications in molecular targeting and imaging. The design and application of bispecific heterodimer-conjugated nanomaterials are also discussed.

Enhancement of the tumor penetration of monoclonal antibody by fusion of a neuropilin-targeting peptide improves the antitumor efficacy

The limited localization and penetration of monoclonal antibodies (mAb) into solid tumors restricts their antitumor efficacy. Here, we describe a solid tumor-targeting antibody with enhanced tumor penetration activity. We designed a 22-residue peptide (A22p), which was extracted from the C-terminal basic region of semaphorin 3A (Sema3A) but modified to have higher affinity with neuropilin receptors (NRP), and genetically fused it to the C-terminus of Fc of human immunoglobulin G1 via a 15-residue (G4S)3 linker, generating Fc-A22p, for the bivalent binding to NRPs. In contrast to Fc or the monovalent A22p peptide alone, Fc-A22p homed to tumor vessels and induced vascular permeability through VE-cadherin downregulation and penetrated tumor tissues by interacting with NRPs in mice bearing human tumor xenografts. We extended the Fc-A22p platform by generating mAb-A22p antibodies of two clinically approved solid tumor-targeting mAbs, the anti-EGF receptor mAb cetuximab (erbitux), and the anti-Her2 mAb trastuzumab (herceptin). The mAb-A22p antibodies retained the intrinsic antigen binding, natural Fc-like biophysical properties, and productivity in mammalian cell cultures, comparable with those of the parent mAbs. In mouse xenograft tumor models, the mAb-A22p antibodies more efficiently homed to tumor vessels and spread into the extravascular tumor parenchyma, which significantly enhanced antitumor efficacy compared with the parent mAbs. Our results suggest that mAb-A22p is a superior format for solid tumor-targeting antibodies due to its enhanced tumor tissue penetration and greater antitumor efficacy compared with conventional mAbs.