Improving the pharmacokinetic properties of biologics by fusion to an anti-HSA shark VNAR domain

Isolation and Characterization of the First Antigen-Specific EGFRvIII vNAR from Freshwater Stingray (Potamotrygon spp.) as a Drug Carrier in Glioblastoma Cancer Cells

Glioblastoma is the most common and highly malignant brain tumor in adults. New targeted therapeutic approaches are imperative. EGFRvIII has appealing therapeutic targets using monoclonal antibodies. Thus, endeavors toward developing new mAbs therapies for GBM capable of targeting the tumor EGFRvIII biomarker must prevail to improve the patient's prognosis. Here, we isolated and characterized an anti-EGFRvIII vNAR from a non-immune freshwater stingray mixed library, termed vNAR R426. The vNAR R426 and pEGFRvIII interaction was demonstrated by molecular docking and molecular dynamics, and the recognition of EGFRvIII in vitro was further confirmed by cell immunofluorescence staining. Moreover, the vNAR R426 was shown to be an effective cisplatin drug carrier in the U87-MG glioma cell line. The cisplatin-coupled vNAR demonstrated highly significant differences when compared to free CDDP at 72 h. Notably, the cisplatin-vNAR carrier achieved better efficacy in the U87-MG cell line. Thus, we described the vNAR R426 internalization by receptor-mediated endocytosis and the subsequent COPI-mediated nuclear translocation of EGFRvIII and highlighted the importance of this shuttle mechanism to enhance the targeted delivery of cisplatin within the glioma cell's nucleus and improved cytotoxic effect. In conclusion, vNAR R426 could be a potential therapeutic carrier for EGFRvIII-targeted glioblastoma and cancer therapies.

Translational pharmacokinetic and pharmacodynamic modelling of the anti-ADAMTS-5 NANOBODY® (M6495) using the neo-epitope ARGS as a biomarker

M6495 is a first-in-class NANOBODY® molecule and an inhibitor of ADAMTS-5, with the potential to be a disease modifying osteoarthritis drug. In order to investigate the PK/PD (pharmacokinetic and pharmacodynamic) properties of M6495, a single dose study was performed in cynomolgus monkeys with doses up to 6 mg/kg, with the goal of understanding the PK/PD properties of M6495. The neo-epitope ARGS (Alanine-Arginine-Glycine-Serine) generated by cleavage of aggrecan by ADAMTS-5 was used as a target-engagement biomarker. A long-lasting dose-dependent decrease in serum ARGS could be observed after a single dose of M6495 in cynomolgus monkeys. The serum biomarker ARGS decreased to levels below the limit of quantification of the assay in animals which received doses of M6495 of 6 mg/kg and higher, indicating a strong inhibition of ADAMTS-5. Data from the single-dose PK/PD study was combined with data from a multiple dose study, and a non-linear mixed effects model was used to explore the relationship between plasma concentrations of M6495 and the reduction of serum ARGS. The model was subsequently used to inform the clinical phase 1 study design and was successful in predicting the human clinical pharmacokinetics and pharmacodynamics of M6495. In addition to having enabled a Phase 1 trial with M6495, this is the first PK/PD model describing the pharmacodynamics of the neo-epitope ARGS after ADAMTS5 inhibition. It is expected that in the future, this model can be used or adapted to explore the PK/PD relationship between M6495 serum concentrations and the ARGS serum biomarker.

Nanobodies in the fight against infectious diseases: repurposing nature's tiny weapons

Nanobodies are the smallest known antigen-binding molecules to date. Their small size, good tissue penetration, high stability and solubility, ease of expression, refolding ability, and negligible immunogenicity in the human body have granted them excellence over conventional antibodies. Those exceptional attributes of nanobodies make them promising candidates for various applications in biotechnology, medicine, protein engineering, structural biology, food, and agriculture. This review presents an overview of their structure, development methods, advantages, possible challenges, and applications with special emphasis on infectious diseases-related ones. A showcase of how nanobodies can be harnessed for applications including neutralization of viruses and combating antibiotic-resistant bacteria is detailed. Overall, the impact of nanobodies in vaccine design, rapid diagnostics, and targeted therapies, besides exploring their role in deciphering microbial structures and virulence mechanisms are highlighted. Indeed, nanobodies are reshaping the future of infectious disease prevention and treatment.

Modular design of bi- and multi-specific knob domain fusions

Introduction

The therapeutic potential of bispecific antibodies is becoming widely recognised, with over a hundred formats already described. For many applications, enhanced tissue penetration is sought, so bispecifics with low molecular weight may offer a route to enhanced potency. Here we report the design of bi- and tri-specific antibody-based constructs with molecular weights as low as 14.5 and 22 kDa respectively.

Methods

Autonomous bovine ultra-long CDR H3 (knob domain peptide) modules have been engineered with artificial coiled-coil stalks derived from Sin Nombre orthohantavirus nucleocapsid protein and human Beclin-1, and joined in series to produce bi- and tri-specific antibody-based constructs with exceptionally low molecular weights.

Results

Knob domain peptides with coiled-coil stalks retain high, independent antigen binding affinity, exhibit exceptional levels of thermal stability, and can be readily joined head-to-tail yielding the smallest described multi-specific antibody format. The resulting constructs are able to bind simultaneously to all their targets with no interference.

Discussion

Compared to existing bispecific formats, the reduced molecular weight of the knob domain fusions may enable enhanced tissue penetration and facilitate binding to cryptic epitopes that are inaccessible to conventional antibodies. Furthermore, they can be easily produced at high yield as recombinant products and are free from the heavy-light chain mispairing issue. Taken together, our approach offers an efficient route to modular construction of minimalistic bi- and multi-specifics, thereby further broadening the therapeutic scope for knob domain peptides.

vNARs as Neutralizing Intracellular Therapeutic Agents: Glioblastoma as a Target

Glioblastoma is the most prevalent and fatal form of primary brain tumors. New targeted therapeutic strategies for this type of tumor are imperative given the dire prognosis for glioblastoma patients and the poor results of current multimodal therapy. Previously reported drawbacks of antibody-based therapeutics include the inability to translocate across the blood-brain barrier and reach intracellular targets due to their molecular weight. These disadvantages translate into poor target neutralization and cancer maintenance. Unlike conventional antibodies, vNARs can permeate tissues and recognize conformational or cryptic epitopes due to their stability, CDR3 amino acid sequence, and smaller molecular weight. Thus, vNARs represent a potential antibody format to use as intrabodies or soluble immunocarriers. This review comprehensively summarizes key intracellular pathways in glioblastoma cells that induce proliferation, progression, and cancer survival to determine a new potential targeted glioblastoma therapy based on previously reported vNARs. The results seek to support the next application of vNARs as single-domain antibody drug-conjugated therapies, which could overcome the disadvantages of conventional monoclonal antibodies and provide an innovative approach for glioblastoma treatment.

Development of Shark Single Domain Antibodies Specific for Human α-Fetoprotein and the Multimerization Strategy in Serum Detection

Sensitive detection of cancer biomarkers can contribute to the timely diagnosis and treatment of diseases. In this study, the whitespotted bamboo sharks were immunized with human α-fetoprotein (AFP), and a phage-displayed variable new antigen receptor (VNAR) single domain antibody library was constructed. Then four unique VNARs (VNAR1, VNAR11, VNAR21, and VNAR25) against AFP were isolated from the library by biopanning for the first time. All of the sequences belong to type II of VNAR, and the VNAR11 was much different from the rest of the three sequences. Then VNAR1 and VNAR11 were selected to fuse with the C4-binding protein α chain (C4bpα) sequence and efficiently expressed in the Escherichia coli system. Furthermore, a VNAR-C4bpα-mediated sandwich chemiluminescence immunoassay (VSCLIA) was developed for the detection of AFP in human serum samples. After optimization, the VSCLIA showed a limit of detection of 0.74 ng/mL with good selectivity and accuracy. Moreover, the results of clinical serum samples detected by the VSCLIA were confirmed by an automatic immunoanalyzer in the hospital, indicating its practical application in actual samples. In conclusion, the novel antibody element VNAR exhibits great potential for immunodiagnosis, and this study also provides a new direction and experimental basis for AFP detection.

Design and Construction of Antibody Fusion Proteins Incorporating Variable New Antigen Receptor (VNAR) Domains

Antibody therapeutics have become a cornerstone of the pharmaceutical market due to their precise molecular targeting, favorable pharmacokinetic properties, and multitiered mechanisms of action. Since the first monoclonal antibody was clinically approved 35 years ago, there have been considerable advances in antibody technology. A major breakthrough has been the design of multispecific antibodies and antibody fusion proteins, which introduce the possibility of recognizing two or more targets with a single molecule. However, despite tremendous progress in the antibody engineering field, challenges in formulation, stability, and tissue penetration necessitate the design of novel antibody formats with improved pharmaceutical properties. There is a growing interest in development of single-domain antibodies, which harbor advantages such as high solubility, robust thermostability, and unique geometries that allow for access to cryptic epitopes. Chondrichthyes such as sharks and rays provide a source of single-domain antibody fragments known as variable new antigen receptors (VNARs), which have been exploited as molecular targeting agents. Here, we describe methods to engineer antibody fusion proteins that incorporate VNARs. We present multiple fusion topologies, and detail the design, expression, and purification for each format. These novel antibody fusion proteins hold great promise for a range of applications in biomedical research and therapeutic design.

Evaluation of variable new antigen receptors (vNARs) as a novel cathepsin S (CTSS) targeting strategy

Aberrant activity of the cysteine protease Cathepsin S (CTSS) has been implicated across a wide range of pathologies. Notably in cancer, CTSS has been shown to promote tumour progression, primarily through facilitating invasion and migration of tumour cells and augmenting angiogenesis. Whilst an attractive therapeutic target, more efficacious CTSS inhibitors are required. Here, we investigated the potential application of Variable New Antigen Receptors (vNARs) as a novel inhibitory strategy. A panel of potential vNAR binders were identified following a phage display panning process against human recombinant proCTSS. These were subsequently expressed, purified and binding affinity confirmed by ELISA and SPR based approaches. Selected lead clones were taken forward and were shown to inhibit CTSS activity in recombinant enzyme activity assays. Further assessment demonstrated that our lead clones functioned by a novel inhibitory mechanism, by preventing the activation of proCTSS to the mature enzyme. Moreover, using an intrabody approach, we exhibited the ability to express these clones intracellularly and inhibit CTSS activity whilst lead clones were also noted to impede cell invasion in a tumour cell invasion assay. Collectively, these findings illustrate a novel mechanistic approach for inhibiting CTSS activity, with anti-CTSS vNAR clones possessing therapeutic potential in combating deleterious CTSS activity. Furthermore, this study exemplifies the potential of vNARs in targeting intracellular proteins, opening a range of previously "undruggable" targets for biologic-based therapy.

Development of a cationic polyethyleneimine-poly(lactic-co-glycolic acid) nanoparticle system for enhanced intracellular delivery of biologics

Intracellular delivery of proteins, peptides and biologics is an emerging field which has the potential to provide novel opportunities to target intracellular proteins, previously deemed 'undruggable'. However, the delivery of proteins intracellularly remains a challenge. Here, we present a cationic nanoparticle delivery system for enhanced cellular delivery of proteins through use of a polyethyleneimine and poly-(lactic-co-glycolic acid) polymer blend. Cationic nanoparticles were shown to provide increased cellular uptake compared to anionic and neutral nanoparticles, successfully delivering Variable New Antigen Receptors (vNARs), entrapped within the nanoparticle core, to the cell interior. vNARs were identified as ideal candidates for nanoparticle entrapment due to their remarkable stability. The optimised 10% PEI-PLGA nanoparticle formulation displayed low toxicity, was uniform in size and possessed appropriate cationic charge to limit cellular toxicity, whilst being capable of escaping the endo/lysosomal system and delivering their cargo to the cytosol. This work demonstrates the ability of cationic nanoparticles to facilitate intracellular delivery of vNARs, novel biologic agents with potential utility towards intracellular targets.

Designing and computational analyzing of chimeric long-lasting GLP-1 receptor agonists for type 2 diabetes

Glucagon-like peptide-1 (GLP-1) is an intestinally derived incretin that plays a vital role in engineering the biological circuit involved in treating type 2 diabetes. Exceedingly short half-life (1-2 min) of GLP-1 limits its therapeutic applicability, and the implication of its new variants is under question. Since albumin-binding DARPin as a mimetic molecule has been reported to increase the serum half-life of therapeutic compounds, the interaction of new variants of GLP-1 in fusion with DARPin needs to be examined against the GLP-1 receptor. This study was aimed to design stable and functional fusion proteins consisting of new protease-resistant GLP-1 mutants (mGLP1) genetically fused to DARPin as a critical step toward developing long-acting GLP-1 receptor agonists. The stability and solubility of the engineered fusion proteins were analyzed, and their secondary and tertiary structures were predicted and satisfactorily validated. Molecular dynamics simulation studies revealed that the predicted structures of engineered fusion proteins remained stable throughout the simulation. The relative binding affinity of the engineered fusion proteins' complex with human serum albumin and the GLP-1 receptor individually was assessed using molecular docking analyses. It revealed a higher affinity compared to the interaction of the individual GLP-1 and HSA-binding DARPin with the GLP-1 receptor and human serum albumin, respectively. The present study suggests that engineered fusion proteins can be used as a potential molecule in the treatment of type 2 diabetes, and this study provides insight into further experimental use of mimetic complexes as alternative molecules to be evaluated as new bio-breaks in the engineering of biological circuits in the treatment of type 2 diabetes.

Human serum albumin binders: A piggyback ride for long-acting therapeutics

Human serum albumin (HSA) is the most abundant protein in the blood and has desirable properties as a drug carrier. One of the most promising ways to exploit HSA as a carrier is to append an albumin-binding moiety (ABM) to a drug for in situ HSA binding upon administration. Nature- and library-derived ABMs vary in size, affinity, and epitope, differentially improving the pharmacokinetics of an appended drug. In this review, we evaluate the current state of knowledge regarding various aspects of ABMs and the unique advantages of ABM-mediated drug delivery. Furthermore, we discuss how ABMs can be specifically modulated to maximize potential benefits in clinical development.

Shark IgNAR: The Next Broad Application Antibody in Clinical Diagnoses and Tumor Therapies?

Antibodies represent a relatively mature detection means and serve as therapeutic drug carriers in the clinical diagnosis and treatment of cancer-among which monoclonal antibodies (mAbs) currently occupy a dominant position. However, the emergence and development of small-molecule monodomain antibodies are inevitable due to the many limitations of mAbs, such as their large size, complex structure, and sensitivity to extreme temperature, and tumor microenvironments. Thus, since first discovered in Chondroid fish in 1995, IgNAR has become an alternative therapeutic strategy through which to replace monoclonal antibodies, thus entailing that this novel type of immunoglobulin has received wide attention with respect to clinical diagnoses and tumor therapies. The variable new antigen receptor (VNAR) of IgNAR provides an advantage for the development of new antitumor drugs due to its small size, high stability, high affinity, as well as other structural and functional characteristics. In that respect, a better understanding of the unique characteristics and therapeutic potential of IgNAR/VNAR in clinical and anti-tumor treatment is needed. This article reviews the advantages of its unique biochemical conditions and molecular structure for clinical diagnoses and novel anti-tumor drugs. At the same time, the main advantages of the existing conjugated drugs, which are based on single-domain antibodies, are introduced here, thereby providing new ideas and methods for the development of clinical diagnoses and anti-tumor therapies in the future.

First pan-specific vNAR against human TGF-β as a potential therapeutic application: in silico modeling assessment

Immunotherapies based on antibody fragments have been developed and applied to human diseases, describing novel antibody formats. The vNAR domains have a potential therapeutic use related to their unique properties. This work used a non-immunized Heterodontus francisci shark library to obtain a vNAR with recognition of TGF-β isoforms. The isolated vNAR T1 selected by phage display demonstrated binding of the vNAR T1 to TGF-β isoforms (-β1, -β2, -β3) by direct ELISA assay. These results are supported by using for the first time the Single-Cycle kinetics (SCK) method for Surface plasmon resonance (SPR) analysis for a vNAR. Also, the vNAR T1 shows an equilibrium dissociation constant (K_D) of 9.61 × 10^-8 M against rhTGF-β1. Furthermore, the molecular docking analysis revealed that the vNAR T1 interacts with amino acid residues of TGF-β1, which are essential for interaction with type I and II TGF-β receptors. The vNAR T1 is the first pan-specific shark domain reported against the three hTGF-β isoforms and a potential alternative to overcome the challenges related to the modulation of TGF-β levels implicated in several human diseases such as fibrosis, cancer, and COVID-19.

IgNAR characterization and gene loci identification in whitespotted bamboo shark (Chiloscyllium plagiosum) genome

Single domain antibodies (sdAb) are promising candidates in cancer and anti-virus biotherapies for their unique structure characters. Though VHH and IgNAR have been discovered in camelidae and nurse shark (Ginlymostoma cirratum) respectively serval decades ago, expense of these large animals still limits the studies and applications of sdAb. Recently, IgNAR has been found in whitespotted bamboo shark (Chiloscyllium plagiosum), a small-sized sharks, while how to characterize and achieved the IgNAR of whitespotted bamboo shark is still unclear. In our research, we identified four IgNAR coding gene loci in whitespotted bamboo shark chromosome 44 (NC_057753.1), and primers were designed for single domain variable regions of IgNAR (VNAR) libraries preparation. Following sequencing results revealed that all plasmids constructed with our predicted VNAR libraries contained VNAR coding sequences, which confirmed the specificities of our primers in VNAR amplification. To our surprise, ≥90% VNAR sequences were encoded by IgNAR1, which suggests IgNAR1 is the most active IgNAR transcription locus in whitespotted bamboo shark. Interestingly, we found IgNAR(ΔC2-C3) were encoded by IgNAR3. Our findings gave a new sight of whitespotted bamboo shark IgNAR, which would broad the way of IgNAR studies and applications in biotherapies.

“Human and Mouse Cross-Reactive” Albumin-Binding Helix–Loop–Helix Peptide Tag for Prolonged Bioactivity of Therapeutic Proteins

The effectiveness of protein and peptide pharmaceuticals depends essentially on their intrinsic pharmacokinetics. Small-sized pharmaceuticals in particular often suffer from short serum half-lives due to rapid renal clearance. To improve the pharmacokinetics by association with serum albumin (SA) in vivo, we generated an SA-binding tag of a helix–loop–helix (HLH) peptide to be linked with protein pharmaceuticals. For use in future preclinical studies, screening of yeast-displayed HLH peptide libraries against human SA (HSA) and mouse SA (MSA) was alternately repeated to give the SA-binding peptide AY-VE, which exhibited cross-binding activities to HSA and MSA with K_D of 65 and 20 nM, respectively. As a proof of concept, we site-specifically conjugated peptide AY-VE with insulin to examine its bioactivity in vivo. In mouse bioassay monitoring the blood glucose level, the AY-VE conjugate was found to have a prolonged hypoglycemic effect for 12 h. The HLH peptide tag is a general platform for extending the bioactivity of therapeutic peptides or proteins.

Identification of Anti-TNFα VNAR Single Domain Antibodies from Whitespotted Bambooshark (Chiloscyllium plagiosum)

Tumor necrosis factor α (TNFα), an important clinical testing factor and drug target, can trigger serious autoimmune diseases and inflammation. Thus, the TNFα antibodies have great potential application in diagnostics and therapy fields. The variable binding domain of IgNAR (VNAR), the shark single domain antibody, has some excellent advantages in terms of size, solubility, and thermal and chemical stability, making them an ideal alternative to conventional antibodies. This study aims to obtain VNARs that are specific for mouse TNF (mTNF) from whitespotted bamboosharks. After immunization of whitespotted bamboosharks, the peripheral blood leukocytes (PBLs) were isolated from the sharks, then the VNAR phage display library was constructed. Through phage display panning against mTNFα, positive clones were validated through ELISA assay. The affinity of the VNAR and mTNFα was measured using ELISA and Bio-Layer Interferometry. The binding affinity of 3B11 VNAR reached 16.7 nM. Interestingly, one new type of VNAR targeting mTNF was identified that does not belong to any known VNAR type. To understand the binding mechanism of VNARs to mTNFα, the models of VNARs-mTNFα complexes were predicted by computational modeling combining HawkDock and RosettaDock. Our results showed that four VNARs’ epitopes overlapped in part with that of mTNFR. Furthermore, the ELISA assay shows that the 3B11 potently inhibited mTNFα binding to mTNFR. This study may provide the basis for the TNFα blockers and diagnostics applications.

A Modified Fibronectin Type III Domain-Conjugated, Long-Acting Pan-Coronavirus Fusion Inhibitor with Extended Half-Life

The coronavirus disease 2019 (COVID-19) pandemic caused by infection of SARS-CoV-2 and its variants has posed serious threats to global public health, thus calling for the development of potent and broad-spectrum antivirals. We previously designed and developed a peptide-based pan-coronavirus (CoV) fusion inhibitor, EK1, which is effective against all human CoVs (HCoV) tested by targeting the HCoV S protein HR1 domain. However, its relatively short half-life may limit its clinical use. Therefore, we designed, constructed, and expressed a recombinant protein, FL-EK1, which consists of a modified fibronectin type III domain (FN3) with albumin-binding capacity, a flexible linker, and EK1. As with EK1, we found that FL-EK1 could also effectively inhibit infection of SARS-CoV-2 and its variants, as well as HCoV-OC43. Furthermore, it protected mice from infection by the SARS-CoV-2 Delta variant and HCoV-OC43. Importantly, the half-life of FL-EK1 (30 h) is about 15.7-fold longer than that of EK1 (1.8 h). These results suggest that FL-EK1 is a promising candidate for the development of a pan-CoV fusion inhibitor-based long-acting antiviral drug for preventing and treating infection by current and future SARS-CoV-2 variants, as well as other HCoVs.

Preparation of a Nanobody Specific to Dectin 1 and Its Anti-inflammatory Effects on Fungal Keratitis

Objective

To prepare a nanobody specific to dectin 1 and verify its specificity and anti-inflammatory effects on Aspergillus fumigatus keratitis.

Methods

The nanobody was selected from a high-quality shark-antibody library constructed with phage-display technology. The nanobody was developed in the expression systems of Escherichia coli. Indirect ELISA was used to determine the specificity of the nanobody to recombinant dectin 1 protein. The potential of the nanobody to be recognized and expressed on the surfaces of cells and corneas was detected by immunofluorescence, and its anti-inflammatory effect on A. fumigatus keratitis was further verified. After infection with A. fumigatus, eyes of C57B L/6 mice were treated with nanobodies. Human corneal epithelial cells (HCECs) were pretreated with nanobodies and then incubated with A. fumigatus. Clinical scores and slit-lamp photography were used to assess disease response in mouse corneas. RT-PCR and ELISA were used to evaluate mRNA and protein expression of IL1β and IL6 in both mouse corneas and HCECs.

Results

The nanobody was successfully expressed through microbial system and showed specific high-affinity binding to recombinant dectin 1. Furthermore, it exhibited specific binding to dectin 1 expressed on the surfaces of cells and recognized dectin 1 in mouse corneas. Importantly, it reduced clinical scores of A. fumigatus keratitis in mice compared with a PBS-treatment group. In addition, it decreased mRNA and protein expression of IL1β and IL6 in infected corneas and HCECs stimulated with A. fumigatus.

Conclusion

These results suggest that this nanobody can bring about anti-inflammatory effects. This highlights the potential of these nanobodies as innovative therapeutic agents in A. fumigatus.

Overview, Generation, and Significance of Variable New Antigen Receptors (VNARs) as a Platform for Drug and Diagnostic Development

The approval of the first VHH-based drug caplacizumab (anti-von Willebrand factor) has validated a two-decade long commitment in time and research effort to realize the clinical potential of single-domain antibodies. The variable domain (VNAR) of the immunoglobulin new antigen receptor (IgNAR) found in sharks provides an alternative small binding domain to conventional monoclonal antibodies and their fragments and heavy-chain antibody-derived VHHs. Evolutionarily distinct from mammalian antibody variable domains, VNARs have enhanced thermostability and unusual convex paratopes. This predisposition to bind cryptic and recessed epitopes has facilitated both the targeting of new antigens and new (neutralizing) epitopes on existing antigens. Together these unique properties position the VNAR platform as an alternative non-antibody binding domain for therapeutic drug, diagnostic and reagent development. In this introductory chapter, we highlight recent VNAR advancements that further underline the exciting potential of this discovery platform.

Central Nervous System Delivery of Antibodies and Their Single-Domain Antibodies and Variable Fragment Derivatives with Focus on Intranasal Nose to Brain Administration

IgG antibodies are some of the most important biopharmaceutical molecules with a high market volume. In spite of the fact that clinical therapies with antibodies are broadly utilized in oncology, immunology and hematology, their delivery strategies and biodistribution need improvement, their limitations being due to their size and poor ability to penetrate into tissues. In view of their small size, there is a rising interest in derivatives, such as single-domain antibodies and single-chain variable fragments, for clinical diagnostic but also therapeutic applications. Smaller antibody formats combine several benefits for clinical applications and can be manufactured at reduced production costs compared with full-length IgGs. Moreover, such formats have a relevant potential for targeted drug delivery that directs drug cargo to a specific tissue or across the blood–brain barrier. In this review, we give an overview of the challenges for antibody drug delivery in general and focus on intranasal delivery to the central nervous system with antibody formats of different sizes.

A resource of high-quality and versatile nanobodies for drug delivery

Therapeutic and diagnostic efficacies of small biomolecules and chemical compounds are hampered by suboptimal pharmacokinetics. Here, we developed a repertoire of robust and high-affinity antihuman serum albumin nanobodies (NbHSA) that can be readily fused to small biologics for half-life extension. We characterized the thermostability, binding kinetics, and cross-species reactivity of NbHSAs, mapped their epitopes, and structurally resolved a tetrameric HSA-Nb complex. We parallelly determined the half-lives of a cohort of selected NbHSAs in an HSA mouse model by quantitative proteomics. Compared to short-lived control nanobodies, the half-lives of NbHSAs were drastically prolonged by 771-fold. NbHSAs have distinct and diverse pharmacokinetics, positively correlating with their albumin binding affinities at the endosomal pH. We then generated stable and highly bioactive NbHSA-cytokine fusion constructs "Duraleukin" and demonstrated Duraleukin's high preclinical efficacy for cancer treatment in a melanoma model. This high-quality and versatile Nb toolkit will help tailor drug half-life to specific medical needs.

Production of monoclonal shark-derived immunoglobulin new antigen receptor antibodies using Chinese hamster ovary cell expression system

Cartilaginous fishes such as sharks have adaptive immune systems based on immunoglobulins similar to those in mammals. During their evolution, cartilaginous fishes individually have acquired their adaptive immune system called immunoglobulin new antigen receptor (IgNARs). IgNARs maintain their functions in the harsh environment of shark serum, which contains a high concentration of urea to prevent water loss in seawater. Therefore, IgNARs have high structural stability, and are expected to be used as next-generation antibodies in applications different from those of conventional IgG antibodies. However, no recombinant expression system for IgNAR, which has a molecular weight of approximately 147 kDa as a dimer and multiple N-glycosylation sites, has yet been constructed. This has stalled research into IgNAR development. Here, we constructed a recombinant expression system for IgNAR using Chinese hamster ovary (CHO) cells, widely used as hosts for IgG antibody production. Using this system, IgNAR was successfully expressed and purified as a human IgG Fc fusion protein and showed antigen-binding ability. After Protein A affinity purification, followed by specific cleavage and removal of the human Fc-region, the final yield of IgNAR was 1.07 mg/L-medium. Moreover, this CHO cell expression system modified IgNAR with various N-glycans, including high-mannose and complex types. This expression system will allow us to analyze the structure, physicochemical properties, and biological functions of IgNAR. This fundamental information will advance the development of IgNARs for industrial and biotechnological applications.

Shark New Antigen Receptor (IgNAR): Structure, Characteristics and Potential Biomedical Applications

Shark is a cartilaginous fish that produces new antigen receptor (IgNAR) antibodies. This antibody is identified with a similar human heavy chain but dissimilar sequences. The variable domain (VNAR) of IgNAR is stable and small in size, these features are desirable for drug discovery. Previous study results revealed the effectiveness of VNAR as a single molecule or a combination molecule to treat diseases both in vivo and in vitro with promising clinical applications. We showed the first evidence of IgNAR alternative splicing from spotted bamboo shark (Chiloscyllium plagiosum), broadening our understanding of the IgNARs characteristics. In this review, we summarize the discoveries on IgNAR with a focus on its advantages for therapeutic development based on its peculiar biochemistry and molecular structure. Proper applications of IgNAR will provide a novel avenue to understand its special presence in cartilaginous fishes as well as designing a number of drugs for undefeated diseases.

TriTACs, a Novel Class of T-Cell-Engaging Protein Constructs Designed for the Treatment of Solid Tumors

T cells have a unique capability to eliminate cancer cells and fight malignancies. Cancer cells have adopted multiple immune evasion mechanisms aimed at inhibiting T cells. Dramatically improved patient outcomes have been achieved with therapies genetically reprogramming T cells, blocking T-cell inhibition by cancer cells, or transiently connecting T cells with cancer cells for redirected lysis. This last modality is based on antibody constructs that bind a surface antigen on cancer cells and an invariant component of the T-cell receptor. Although high response rates were observed with T-cell engagers specific for CD19, CD20, or BCMA in patients with hematologic cancers, the treatment of solid tumors has been less successful. Here, we developed and characterized a novel T-cell engager format, called TriTAC (for Trispecific T-cell Activating Construct). TriTACs are engineered with features to improve patient safety and solid tumor activity, including high stability, small size, flexible linkers, long serum half-life, and highly specific and potent redirected lysis. The present study establishes the structure/activity relationship of TriTACs and describes the development of HPN424, a PSMA- (FOLH1-) targeting TriTAC in clinical development for patients with metastatic castration-resistant prostate cancer.

Anti-DLL4 VNAR targeted nanoparticles for targeting of both tumour and tumour associated vasculature

Whilst there is an extensive body of preclinical nanomedicine research, translation to clinical settings has been slow. Here we present a novel approach to the targeted nanoparticle (NP) concept: utilizing both a novel targeting ligand, VNAR (Variable New Antigen Receptor), a shark-derived single chain binding domain, and an under-investigated target in delta-like ligand 4 (DLL4). We describe the development of an anti-DLL4 VNAR and the site-specific conjugation of this to poly(lactic-co-glycolic) acid PEGylated NPs using surface maleimide functional groups. These nanoconjugates were shown to specifically bind DLL4 with high affinity and were preferentially internalized by DLL4-expressing pancreatic cancer cell lines and endothelial cells. Furthermore, a distinct anti-angiogenic effect endowed by the anti-DLL4 VNAR was evident in in vitro tubulogenic assays. Taken together these findings highlight the potential of anti-DLL4 targeted polymeric NPs as a novel therapeutic approach in pancreatic cancer.

Diagnostic and therapeutic potential of shark variable new antigen receptor (VNAR) single domain antibody

Conventional monoclonal antibodies (mAbs) have been widely used in research and diagnostic applications due to their high affinity and specificity. However, multiple limitations, such as large size, complex structure and sensitivity to extreme ambient temperature potentially weaken the performance of mAbs in certain applications. To address this problem, the exploration of new antigen binders is extensively required in relation to improve the quality of current diagnostic platforms. In recent years, a new immunoglobulin-based protein, namely variable domain of new antigen receptor (VNAR) was discovered in sharks. Unlike conventional mAbs, several advantages of VNARs, include small size, better thermostability and peculiar paratope structure have attracted interest of researchers to further explore on it. This article aims to first present an overview of the shark VNARs and outline the characteristics as an outstanding new reagent for diagnostic and therapeutic applications.

In Vitro ELISA and Cell-Based Assays Confirm the Low Immunogenicity of VNAR Therapeutic Constructs in a Mouse Model of Human RA: An Encouraging Milestone to Further Clinical Drug Development

Anti-drug antibodies (ADAs), specific for biotherapeutic drugs, are associated with reduced serum drug levels and compromised therapeutic response. The impact of ADA on the bioavailability and clinical efficacy of blockbuster anti-hTNF-α monoclonal antibodies is well recognised, especially for adalimumab and infliximab treatments, with the large and complex molecular architecture of classical immunoglobulin antibody drugs, in part, responsible for the immunogenicity seen in patients. The initial aim of this study was to develop solid-phase enzyme-linked immunosorbent assays (ELISA) and an in vitro cell-based method to accurately detect ADA and estimate its impact on the preclinical in vivo efficacy outcomes of two novel, nonimmunoglobulin VNAR fusion anti-hTNF-α biologics (Quad-X™ and D1-NDure™-C4) and Humira®, a brand of adalimumab. Serum drug levels and the presence of ADA were determined in a transgenic mouse model of polyarthritis (Tg197) when Quad-X™ and Humira® were dosed at 1 mg/kg and D1-NDure™-C4 was dosed at 30 mg/kg. The serum levels of the Quad-X™ and D1-NDure™-C4 modalities were consistently high and comparable across all mice within the same treatment groups. In 1 mg/kg and 3 mg/kg Quad-X™- and 30 mg/kg D1-NDure™-C4-treated mice, an average trough drug serum concentration of 8 μg/mL, 50 μg/mL, and 350 μg/mL, respectively, were estimated. In stark contrast, Humira® trough serum concentrations in the 1 mg/kg treatment group ranged from <0.008 μg/mL to 4 μg/mL with trace levels detected in 7 of the 8 animals treated. Trough serum Humira® and Quad-X™ concentrations in 3 mg/kg treatment samples were comparable; however, the functionality of the detected Humira® serum was significantly compromised due to neutralising ADA. The impact of ADA went beyond the simple and rapid clearance of Humira®, as 7/8 serum samples also showed no detectable capacity to neutralise hTNF-α-mediated cytotoxicity in a murine fibrosarcoma (L929) cell assay. The neutralisation capacity of all the VNAR constructs remained unchanged at the end of the experimental period (10 weeks). The data presented in this manuscript goes some way to explain the exciting outcomes of the previously published preclinical in vivo efficacy data, which showed complete control of disease at Quad-X™ concentrations of 0.5 mg/kg, equivalent to 10x the in vivo potency of Humira®. This independent corroboration also validates the robustness and reliability of the assay techniques reported in this current manuscript, and while it comes with the caveat of a mouse study, it does appear to suggest that these particular VNAR constructs, at least, are of low inherent immunogenicity.

Isolation of highly selective IgNAR variable single-domains against a human therapeutic Fc scaffold and their application as tailor-made bioprocessing reagents

The adaptive immune system of cartilaginous fish (Elasmobranchii), comprising of classical hetero-tetrameric antibodies, is enhanced through the presence of a naturally occurring homodimeric antibody-like immunoglobulin-the new antigen receptor (IgNAR). The binding site of the IgNAR variable single-domain (VNAR) offers advantages of reduced size (<1/10th of classical immunoglobulin) and extended binding topographies, making it an ideal candidate for accessing cryptic epitopes otherwise intractable to conventional antibodies. These attributes, coupled with high physicochemical stability and amenability to phage display, facilitate the selection of VNAR binders to challenging targets. Here, we explored the unique attributes of these single domains for potential application as bioprocessing reagents in the development of the SEED-Fc platform, designed to generate therapeutic bispecific antibodies. A panel of unique VNARs specific to the SEED homodimeric (monospecific) 'by-products' were isolated from a shark semi-synthetic VNAR library via phage display. The lead VNAR candidate exhibited low nanomolar affinity and superior selectivity to SEED homodimer, with functionality being retained upon exposure to extreme physicochemical conditions that mimic their applicability as purification agents. Ultimately, this work exemplifies the robustness of the semi-synthetic VNAR platform, the predisposition of the VNAR paratope to recognise novel epitopes and the potential for routine generation of tailor-made VNAR-based bioprocessing reagents.

Next-Generation Antibody Therapeutics: Discovery, Development and Beyond: highlights of the third annual conference of the Chinese Antibody Society

The Chinese Antibody Society (CAS) convened the third annual conference in Cambridge, Massachusetts, USA on April 7, 2019. More than 600 global members attended the meeting. The theme of this conference was Next-Generation Antibody Therapeutics: Discovery, Development and Beyond. The meeting covered a vast variety of topics including cancer immunotherapy, single-domain antibodies as well as bispecific antibodies, immunotoxins, transgenic mouse platforms for next-generation monoclonal antibody discovery and antibody chemistry, manufacturing and controls (CMCs). Two hot topics were comprehensively discussed by the prestigious panelists and hosts at the panel discussions during the conferences, i.e., bispecific antibodies and antibody CMC.

Statement of Significance: The Chinese Antibody Society convened the third annual conference in Cambridge, Massachusetts, USA on 7 April 2019. The meeting covered a variety of topics, including cancer immunotherapy, single-domain antibody, bispecific antibody, immunotoxin, transgenic mouse platforms for next-generation monoclonal antibody discovery and antibody CMC.

Site-specific C-terminal dinitrophenylation to reconstitute the antibody Fc functions for nanobodies

Nanobodies are a class of camelid-derived single-domain antibodies that have many potential advantages over conventional antibodies and have been utilized to develop new therapeutic strategies for cancer and other diseases. However, nanobodies lack the Fc region of a conventional antibody, which possesses many functions, e.g., eliciting antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC), essential for effective immunotherapy. The small molecular size of nanobodies also leads to poor pharmacokinetics, such as short in vivo half-life. To address these deficiencies, an endogenous antibody-based strategy to reconstitute the Fc functions for nanobodies was developed. As a proof-of-principle, an anti-human EGFR nanobody, 7D12, was selected to conduct C-terminal modification with the dinitrophenyl (DNP) hapten through Sortase A-mediated site-specific ligation. It was expected that the DNP motif would recruit endogenous human anti-DNP antibodies to indirectly reinstate the Fc functions. The resultant nanobody-DNP conjugates were shown to exhibit specific and high affinity binding to human EGFR expressed on target cancer cells. It was further proved that in the presence of anti-DNP antibody, these conjugates could mediate potent ADCC and CDC in vitro and exhibit significantly elongated half-life in vivo. Ultimately, it was proven in severe combined immunodeficiency (SCID) mice that treatment with the nanobody 7D12-DNP conjugate and anti-DNP mouse serum could inhibit xenograft tumor growth efficiently. In view of the abundance of anti-DNP and other endogenous antibodies in the human blood system, this could be a generally applicable approach employed to reconstitute the Fc functions for nanobodies and develop nanobody-based cancer immunotherapy and other therapies.

Uveitis Therapy With Shark Variable Novel Antigen Receptor Domains Targeting Tumor Necrosis Factor Alpha or Inducible T-Cell Costimulatory Ligand

PURPOSE

We assess the efficacy of two next-generation biologic therapies in treating experimental autoimmune uveitis.

METHODS

Variable binding domains from shark immunoglobulin novel antigen receptors (VNARs) were fused with a mouse IgG2a constant domain (Fc) to generate VNAR-Fc molecules with binding specificity to tumor necrosis factor alpha (TNFα) or inducible T-cell costimulatory ligand (ICOSL). Treatment with VNAR-Fc fusion proteins was compared to treatment with dexamethasone or vehicle in the Lewis rat model of experimental autoimmune uveitis (EAU). Inflammation control was determined by comparing OCT clinical and histologic scores, and aqueous humor protein concentration. The concentration of 27 inflammatory cytokines in the aqueous humor was measured using a multiplex enzyme-linked immunosorbent assay platform.

RESULTS

Administration of S17-Fc significantly decreased clinical, histologic, and aqueous protein levels when compared to vehicle treatment. Inflammation scores and aqueous protein levels in A5-Fc-treated animals were decreased compared to vehicle treatment, but not significantly. The concentration of vascular endothelial growth factor (VEGF), regulated on activation, normal T cell expressed and secreted (RANTES), macrophage inflammatory protein 1 alpha (MIP-1α), interleukin (IL)-1β, LPS-induced CXC chemokine (LIX), monocyte chemoattractant protein-1 (MCP-1), and interferon (IFN)-γ were significantly decreased in the eyes of animals treated with dexamethasone. VNAR treatment demonstrated a trend towards decreased cytokine concentrations, but only VEGF and RANTES were significantly decreased by S17-Fc.

CONCLUSIONS

Treatment with the anti-TNFα VNAR S17-Fc ameliorates EAU as effectively as treatment with corticosteroids.

TRANSLATIONAL RELEVANCE

VNAR-Fc molecules are a next-generation therapeutic biologic that overcome the limitations of classical biologic monoclonal antibodies, such as complex structure, large size, and limited tissue penetration. This is a novel drug modality that could result in the development of new therapy options for patients with noninfectious uveitis.

Fusion of Lysostaphin to an Albumin Binding Domain Prolongs Its Half-Life and Bactericidal Activity in the Systemic Circulation

Antibacterial lysins are promising proteins that are active against both antibiotic-susceptible and antibiotic-resistant bacterial strains. However, a major limitation of antibacterial lysins is their fast elimination from systemic circulation. PEGylation increases the plasma half-life of lysins but renders them inactive. Here we report the construction of a fusion protein of lysostaphin, a potent anti-staphylococcal lysin, and an albumin-binding domain from streptococcal protein G. The resulting fusion protein was less active than the parent enzyme lysostaphin, but it still retained significant antibacterial activity even when bound to serum albumin. The terminal half-life of the fusion protein in rats was five-fold greater than that of lysostaphin (7.4 vs. 1.5 h), and the area under the curve increased more than 115 times. Most importantly, this increase in systemic circulation time compensated for the decrease in activity. The plasma from rats that received an injection of the fusion protein retained bactericidal activity for up to 7 h, while plasma from rats that received plain lysostaphin lacked any detectable activity after 4 h. To the best of our knowledge, this is the first report of an antibacterial lysin with both improved pharmacokinetic parameters and prolonged bactericidal activity in the systemic circulation.

Fusion with an albumin-binding domain improves pharmacokinetics of an αvβ3-integrin binding fibronectin scaffold protein

Fusion with an albumin-binding domain (ABD) of streptococcal protein G represents a popular approach for half-life extension of small protein therapeutics in the organism. To increase the circulation time of engineered αvβ3-integrin-binding protein (JCL) based on the 10th human fibronectin type III domain (¹⁰ Fn3), we have constructed several fusions with ABD with different orientations of the partner proteins and linker length. The recombinant proteins were expressed in Escherichia coli cells and purified by nickel-affinity chromatography. All fusion proteins bound human serum albumin (HSA) in ELISA assay; however, fusions with longer linkers demonstrated better performance. Interaction of ABD-L₁₅ -JCL and JCL-L₁₄ -ABD with HSA was confirmed by analytical size exclusion chromatography and pull-down assays. Surprisingly, the thermal stability of ABD-L₁₅ -JCL was dramatically decreased in comparison with JCL and JCL-L₁₄ -ABD proteins. Pharmacokinetic studies revealed that JCL-L₁₄ -ABD circulated in murine blood about 10 times longer than ABD-L₁₅ -JCL and 960 times longer than JCL. Biodistribution studies of JCL-L₁₄ -ABD in mice revealed its increased level in blood and a decreased accumulation in liver and kidneys in comparison with JCL. Obtained results demonstrate the utility of the fusion with ABD for half-life extension of the binding proteins based on ¹⁰ Fn3.

Non-covalent albumin-binding ligands for extending the circulating half-life of small biotherapeutics

Peptides and small protein scaffolds are gaining increasing interest as therapeutics. Similarly to full-length antibodies, they can bind a target with a high binding affinity and specificity while remaining small enough to diffuse into tissues. However, despite their numerous advantages, small biotherapeutics often suffer from a relatively short circulating half-life, thus requiring frequent applications that ultimately restrict their ease of use and user compliance. To overcome this limitation, a large variety of half-life extension strategies have been developed in the last decades. Linkage to ligands that non-covalently bind to albumin, the most abundant serum protein with a circulating half-life of ∼19 days in humans, represents one of the most successful approaches for the generation of long-lasting biotherapeutics with improved pharmacokinetic properties and superior efficacy in the clinic.

Computer-assembled cross-species/cross-modalities two-pore physiologically based pharmacokinetic model for biologics in mice and rats

Two-pore physiologically-based pharmacokinetic (PBPK) models can be expected to describe the tissue distribution and elimination kinetics of soluble proteins, endogenous or dosed, as function of their size. In this work, we amalgamated our previous two-pore PBPK model for an inert domain antibody (dAb) in mice with the cross-species platform PBPK model for monoclonal antibodies described in literature into a unified two-pore platform that describes protein modalities of different sizes and includes neonatal Fc receptor (FcRn) mediated recycling. This unified PBPK model was parametrized for organ-specific lymph flow rates and the endosomal recycling rate constant using an extended tissue distribution time-course dataset that included an inert dAb, albumin and IgG in rats and mice. The model was evaluated by comparing the ab initio predictions for the tissue distribution and elimination properties of albumin-binding dAbs (AlbudAbs^TM) in mice and rats with the experimental observations. Due to the large number of molecular species and reactions involved in large-scale PBPK models, we have also developed and deployed a Matlab^TM script for automating the assembly of SimBiology^TM-based two-pore biologics PBPK models which drastically cuts the time and effort required for model building.

Single-Domain Antibodies as Therapeutic and Imaging Agents for the Treatment of CNS Diseases

Antibodies have become one of the most successful therapeutics for a number of oncology and inflammatory diseases. So far, central nervous system (CNS) indications have missed out on the antibody revolution, while they remain 'hidden' behind several hard to breach barriers. Among the various antibody modalities, single-domain antibodies (sdAbs) may hold the 'key' to unlocking the access of antibody therapies to CNS diseases. The unique structural features of sdAbs make them the smallest monomeric antibody fragments suitable for molecular targeting. These features are of particular importance when developing antibodies as modular building blocks for engineering CNS-targeting therapeutics and imaging agents. In this review, we first introduce the characteristic properties of sdAbs compared to traditional antibodies. We then present recent advances in the development of sdAbs as potential therapeutics across brain barriers, including their use for the delivery of biologics across the blood-brain and blood-cerebrospinal fluid (CSF) barriers, treatment of neurodegenerative diseases and molecular imaging of brain targets.

An Anti-hTNF-α Variable New Antigen Receptor Format Demonstrates Superior in vivo Preclinical Efficacy to Humira® in a Transgenic Mouse Autoimmune Polyarthritis Disease Model

Tumor necrosis factor-alpha (TNF-α), an established pro-inflammatory cytokine plays a central role in the induction and progression of several chronic inflammatory and autoimmune diseases. Targeting TNF-α as a treatment modality has shown tremendous success, however there are several limitations associated with the current anti-TNF-α biologic drugs including: immunogenicity, life-threatening infections, resistance to treatment, complexity of manufacture and cost of treatment. Here, we report the in vivo efficacy of novel anti-TNF-α formats generated from molecular engineering of variable new antigen receptors (VNARs), originally derived from the immune system of an immunized nurse shark. Two anti-TNF-α VNAR formats, a tandem multivalent trimer, D1-BA11-C4 and an Fc-fused quadrivalent D1-Fc-C4 (Quad-X™) construct were tested in a clinically relevant, preclinical mouse efficacy model of polyarthritis (Tg197) and compared to the commercial anti-TNF-α "best in class" therapy, Adalimumab (Humira®). Both VNAR formats bind and neutralize TNF-α through an epitope that appears to be different from those recognized by other anti-TNF biologics used clinically. All doses of Quad-X™, from 0.5 to 30 mg/kg, significantly blocked the development of polyarthritis. At 0.5 mg/kg Quad-X™, the arthritis score was improved by 76% and the histopathology score by 63%. At 3 mg/kg Quad-X™, control of disease was almost complete at 90% (arthritis) and 88% (histopathology). In marked contrast, 1 mg/kg Humira® saw profound disease breakthrough with scores of 39 and 16% respectively, increasing to a respectable 82 and 86% inhibition at 10 mg/kg Humira®. We have previously reported the superior potency of anti-TNF-α VNARs in vitro and in these studies translate this superiority into an in vivo setting and demonstrate the potential of VNAR formats to meet the requirements of next-generation anti-TNF-α therapies.

Next-generation flexible formats of VNAR domains expand the drug platform's utility and developability

Therapeutic mAbs have delivered several blockbuster drugs in oncology and autoimmune inflammatory disease. Revenue for mAbs continues to rise, even in the face of competition from a growing portfolio of biosimilars. Despite this success, there are still limitations associated with the use of mAbs as therapeutic molecules. With a molecular mass of 150 kDa, a two-chain structure and complex glycosylation these challenges include a high cost of goods, limited delivery options, and poor solid tumour penetration. There remains an urgency to create alternatives to antibody scaffolds in a bid to circumvent these limitations, while maintaining or improving the therapeutic success of conventional mAb formats. Smaller, less complex binders, with increased domain valency, multi-specific/paratopic targeting, tuneable serum half-life and low inherent immunogenicity are a few of the characteristics being explored by the next generation of biologic molecules. One novel 'antibody-like' binder that has naturally evolved over 450 million years is the variable new antigen receptor (VNAR) identified as a key component of the adaptive immune system of sharks. At only 11 kDa, these single-domain structures are the smallest IgG-like proteins in the animal kingdom and provide an excellent platform for molecular engineering and biologics drug discovery. VNAR attributes include high affinity for target, ease of expression, stability, solubility, multi-specificity, and increased potential for solid tissue penetration. This review article documents the recent drug developmental milestones achieved for therapeutic VNARs and highlights the first reported evidence of the efficacy of these domains in clinically relevant models of disease.

Anti-ICOSL New Antigen Receptor Domains Inhibit T Cell Proliferation and Reduce the Development of Inflammation in the Collagen-Induced Mouse Model of Rheumatoid Arthritis

Lymphocyte costimulation plays a central role in immunology, inflammation, and immunotherapy. The inducible T cell costimulator (ICOS) is expressed on T cells following peptide: MHC engagement with CD28 costimulation. The interaction of ICOS with its sole ligand, the inducible T cell costimulatory ligand (ICOSL; also known as B7-related protein-1), triggers a number of key activities of T cells including differentiation and cytokine production. Suppression of T cell activation can be achieved by blocking this interaction and has been shown to be an effective means of ameliorating disease in models of autoimmunity. In this study, we isolated specific anti-ICOSL new antigen receptor domains from a synthetic phage display library and demonstrated their ability to block the ICOS/ICOSL interaction and inhibit T cell proliferation. Anti-mouse ICOSL domains, considered here as surrogates for the use of anti-human ICOSL domains in patient therapy, were tested for efficacy in a collagen-induced mouse model of rheumatoid arthritis where they significantly decreased the inflammation of joints and delayed and reduced overall disease progression and severity.

Expanding the Boundaries of Biotherapeutics with Bispecific Antibodies

Bispecific antibodies have moved from being an academic curiosity with therapeutic promise to reality, with two molecules being currently commercialized (Hemlibra® and Blincyto®) and many more in clinical trials. The success of bispecific antibodies is mainly due to the continuously growing number of mechanisms of actions (MOA) they enable that are not accessible to monoclonal antibodies. One of the earliest MOA of bispecific antibodies and currently the one with the largest number of clinical trials is the redirecting of the cytotoxic activity of T-cells for oncology applications, now extending its use in infective diseases. The use of bispecific antibodies for crossing the blood-brain barrier is another important application because of its potential to advance the therapeutic options for neurological diseases. Another noteworthy application due to its growing trend is enabling a more tissue-specific delivery or activity of antibodies. The different molecular solutions to the initial hurdles that limited the development of bispecific antibodies have led to the current diverse set of bispecific or multispecific antibody formats that can be grouped into three main categories: IgG-like formats, antibody fragment-based formats, or appended IgG formats. The expanded applications of bispecific antibodies come at the price of additional challenges for clinical development. The rising complexity in their structure may increase the risk of immunogenicity and the multiple antigen specificity complicates the selection of relevant species for safety assessment.

In silico-designed mutations increase variable new-antigen receptor single-domain antibodies for VEGF165 neutralization

The stability, binding, and tissue penetration of variable new-antigen receptor (VNAR) single-domain antibodies have been tested as part of an investigation into their ability to serve as novel therapeutics. V13 is a VNAR that recognizes vascular endothelial growth factor 165 (VEGF₁₆₅). In the present study V13 was used as a parental molecule into which we introduced mutations designed in silico. Two of the designed VNAR mutants were expressed, and their ability to recognize VEGF₁₆₅ was assessed in vitro and in vivo. One mutation (Pro98Tyr) was designed to increase VEGF₁₆₅ recognition, while the other (Arg97Ala) was designed to inhibit VEGF₁₆₅ binding. Compared to parental V13, the Pro98Tyr mutant showed enhanced VEGF₁₆₅ recognition and neutralization, as indicated by inhibition of angiogenesis and tumor growth. This molecule thus appears to have therapeutic potential for neutralizing VEGF₁₆₅ in cancer treatment.

Intraocular Penetration of a vNAR: In Vivo and In Vitro VEGF165 Neutralization

Variable new antigen receptor domain (vNAR) antibodies are novel, naturally occurring antibodies that can be isolated from naïve, immune or synthetic shark libraries. These molecules are very interesting to the biotechnology and pharmaceutical industries because of their unique characteristics related to size and tissue penetrability. There have been some approved anti-angiogenic therapies for ophthalmic conditions, not related to vNAR. This includes biologics and chimeric proteins that neutralize vascular endothelial growth factor (VEGF)₁₆₅, which are injected intravitreal, causing discomfort and increasing the possibility of infection. In this paper, we present a vNAR antibody against human recombinant VEGF₁₆₅ (rhVEGF₁₆₅) that was isolated from an immunized Heterodontus francisci shark. A vNAR called V13, neutralizes VEGF₁₆₅ cytokine starting at 75 μg/mL in an in vitro assay based on co-culture of normal human dermal fibroblasts (NHDFs) and green fluorescence protein (GFP)-labeled human umbilical vein endothelial cells (HUVECs) cells. In the oxygen-induced retinopathy model in C57BL/6:Hsd mice, we demonstrate an endothelial cell count decrease. Further, we demonstrate the intraocular penetration after topical administration of 0.1 μg/mL of vNAR V13 by its detection in aqueous humor in New Zealand rabbits with healthy eyes after 3 h of application. These findings demonstrate the potential of topical application of vNAR V13 as a possible new drug candidate for vascular eye diseases.

Generation of Semi-Synthetic Shark IgNAR Single-Domain Antibody Libraries

Besides classical antibodies with the composition of heavy and light chains, sharks produce a unique heavy chain only isotype, termed Immunoglobulin New Antigen Receptor (IgNAR), in which antigen binding is solely mediated by a single domain, referred to as vNAR. Owing to their high affinity and specificity combined with their small size and high stability, vNAR domains emerged as promising target-binding scaffolds that can be tailor-made for biotechnological and biomedical applications. Herein, we describe protocols for the construction of semi-synthetic, CDR3-randomized vNAR libraries for the isolation of target-specific antibodies using yeast surface display or phage display as platform technology. Additionally, we provide information for affinity maturation of target-specific molecules through CDR1 diversification and sublibrary establishment.

Novel, Anti-hTNF-α Variable New Antigen Receptor Formats with Enhanced Neutralizing Potency and Multifunctionality, Generated for Therapeutic Development

The management of chronic inflammatory diseases, such as inflammatory bowel disease, psoriasis, and rheumatoid arthritis has significantly improved over the last decade with the clinical availability of anti-TNF-α biologics. Despite this undoubted treatment success, a combination of acquired resistance together with an increased risk of systemic complications, means that a significant number of patients either fail to find a suitable targeted therapy or frustratingly discover that an approach that did work is no longer efficacious. Here, we report the isolation and characterization of a new class of super-neutralizing anti-TNF-α biologics formats, the building blocks of which were originally derived as variable new antigen receptor (VNAR) domains from an immunized nurse shark. These parental small, stable VNAR monomers recognize and neutralize tumor necrosis factor (TNF)-α, in cell-based assays, at nanomolar concentrations. However, the simple, single-chain molecular architecture of VNARs allows for easy and multiple reformatting options. Through reformatting, we achieved a 50,000-fold enhancement in in vitro efficacy with super-neutralizing fusion proteins able to block TNF-α induced cytotoxicity in the 2–5 pM range while retaining other functionality through the addition of fusion proteins known to extend serum half-life in vivo. In an in vitro intestinal epithelial barrier dysfunction efficacy model, the lead VNAR domains, restored barrier function and prevented paracellular flux with comparable efficacy to adalimumab (Humira^®). In addition, all multivalent VNAR constructs restored trans-epithelial electrical resistance (TEER) to approximately 94% of the untreated control. Reformatted VNAR domains should be considered as a new class of biologic agents for the treatment of hTNF-α driven diseases; either used systemically with appropriate half-life extension or alternatively where site-specific delivery of small and stable neutralizers may provide improvements to current therapy options.

Half-life extension using serum albumin-binding DARPin® domains

A long systemic half-life is key for therapeutic proteins. To that end we have generated serum albumin-binding designed ankyrin repeat domains. These domains bind serum albumin of different species with nanomolar affinities, and have significantly improved pharmacokinetic properties both in mouse and cynomolgus monkey compared to non-serum albumin-binding DARPin® domains. In addition, they exhibit high thermal stability and long storage stability, which is an essential feature for their use in drug development. Covalently linking a serum albumin-binding DARPin® domain to domains with other target specificities results in improvements of multiple orders of magnitude in exposure and terminal half-life, both in mouse and cynomolgus monkey. Pharmacokinetic assessment of such constructs revealed terminal half-life values ranging from 27 h to 80 h in mouse, and from 2.6 days to 20 days in cynomolgus monkey. Extrapolation by allometric scaling on these findings suggests terminal half-life values of 5-50 days in human, indicating that pharmacokinetic properties in the range of monoclonal antibodies can be achieved with DARPin® drug candidates. Such serum albumin-binding DARPin® domains are thus valuable tools for the generation of multi-functional drugs with an extended in vivo half-life.

Allosteric inhibition of Aurora-A kinase by a synthetic vNAR domain

The vast majority of clinically approved protein kinase inhibitors target the ATP-binding pocket directly. Consequently, many inhibitors have broad selectivity profiles and most have significant off-target effects. Allosteric inhibitors are generally more selective, but are difficult to identify because allosteric binding sites are often unknown or poorly characterized. Aurora-A is activated through binding of TPX2 to an allosteric site on the kinase catalytic domain, and this knowledge could be exploited to generate an inhibitor. Here, we generated an allosteric inhibitor of Aurora-A kinase based on a synthetic, vNAR single domain scaffold, vNAR-D01. Biochemical studies and a crystal structure of the Aurora-A/vNAR-D01 complex show that the vNAR domain overlaps with the TPX2 binding site. In contrast with the binding of TPX2, which stabilizes an active conformation of the kinase, binding of the vNAR domain stabilizes an inactive conformation, in which the αC-helix is distorted, the canonical Lys-Glu salt bridge is broken and the regulatory (R-) spine is disrupted by an additional hydrophobic side chain from the activation loop. These studies illustrate how single domain antibodies can be used to characterize the regulatory mechanisms of kinases and provide a rational basis for structure-guided design of allosteric Aurora-A kinase inhibitors.

In Vitro Maturation of a Humanized Shark VNAR Domain to Improve Its Biophysical Properties to Facilitate Clinical Development

Molecular engineering to increase the percentage identity to common human immunoglobulin sequences of non-human therapeutic antibodies and scaffolds has become standard practice. This strategy is often used to reduce undesirable immunogenic responses, accelerating the clinical development of candidate domains. The first humanized shark variable domain (VNAR) was reported by Kovalenko and colleagues and used the anti-human serum albumin (HSA) domain, clone E06, as a model to construct a number of humanized versions including huE06v1.10. This study extends this work by using huE06v1.10 as a template to isolate domains with improved biophysical properties and reduced antigenicity. Random mutagenesis was conducted on huE06v1.10 followed by refinement of clones through an off-rate ranking-based selection on target antigen. Many of these next-generation binders retained high affinity for target, together with good species cross-reactivity. Lead domains were assessed for any tendency to dimerize, tolerance to N- and C-terminal fusions, affinity, stability, and relative antigenicity in human dendritic cell assays. Functionality of candidate clones was verified in vivo through the extension of serum half-life in a typical drug format. From these analyses the domain, BA11, exhibited negligible antigenicity, high stability and high affinity for mouse, rat, and HSA. When these attributes were combined with demonstrable functionality in a rat model of PK, the BA11 clone was established as our clinical candidate.

Therapeutic Potential of Shark Anti-ICOSL VNAR Domains is Exemplified in a Murine Model of Autoimmune Non-Infectious Uveitis

Induced costimulatory ligand (ICOSL) plays an important role in the activation of T cells through its interaction with the inducible costimulator, ICOS. Suppression of full T cell activation can be achieved by blocking this interaction and has been shown to be an effective means of ameliorating disease in models of autoimmunity and inflammation. In this study, we demonstrated the ability of a novel class of anti-ICOSL antigen-binding single domains derived from sharks (VNARs) to effectively reduce inflammation in a murine model of non-infectious uveitis. In initial selections, specific VNARs that recognized human ICOSL were isolated from an immunized nurse shark phage display library and lead domains were identified following their performance in a series of antigen selectivity and in vitro bioassay screens. High potency in cell-based blocking assays suggested their potential as novel binders suitable for further therapeutic development. To test this hypothesis, surrogate anti-mouse ICOSL VNAR domains were isolated from the same phage display library and the lead VNAR clone selected via screening in binding and ICOS/ICOSL blocking experiments. The VNAR domain with the highest potency in cell-based blocking of ICOS/ICOSL interaction was fused to the Fc portion of human IgG1 and was tested in vivo in a mouse model of interphotoreceptor retinoid-binding protein-induced uveitis. The anti-mICOSL VNAR Fc, injected systemically, resulted in a marked reduction of inflammation in treated mice when compared with untreated control animals. This approach inhibited disease progression to an equivalent extent to that seen for the positive corticosteroid control, cyclosporin A, reducing both clinical and histopathological scores. These results represent the first demonstration of efficacy of a VNAR binding domain in a relevant clinical model of disease and highlight the potential of VNARs for the treatment of auto-inflammatory conditions.