Antibody-recruiting molecules: an emerging paradigm for engaging immune function in treating human disease

A platform for mapping reactive cysteines within the immunopeptidome

The major histocompatibility complex class I antigen presentation pathways play pivotal roles in orchestrating immune responses. Recent studies have begun to explore the therapeutic potential of cysteines within the immunopeptidome, such as the use of covalent ligands to generate haptenated peptide neoepitopes for immunotherapy. In this work, we report a platform for mapping reactive cysteines on MHC-I-bound peptide antigens. We develop cell-impermeable sulfonated maleimide probes capable of capturing reactive cysteines on these antigens. Using these probes in chemoproteomic experiments, we discover that cysteines on MHC-I-bound antigens exhibit various degrees of reactivity. Moreover, interferon-gamma stimulation enhances the reactivity of cysteines at position 8 of 9-mer MHC-I-bound antigens. Finally, we demonstrate that targeting reactive cysteines on MHC-I-bound antigens with a maleimide-conjugated Fc-binding cyclic peptide contributes to the induction of antibody-dependent cellular phagocytosis.

In Situ Self-Assembly of Antibody-Rhamnose Complex as a Pre-Targeting Strategy for Enhanced Cancer Immunotherapy

Enhancing the Fc effector functions of monoclonal antibodies (mAbs) is a proven strategy for improving cancer immunotherapy. In this study, we present a novel pre-targeting approach that integrates host-guest chemistry with an antibody-recruiting concept to create mAbs with superior effector functions. Using rituximab (RTX), a clinically approved anti-CD20 mAb, as our model, we modified RTX by conjugating it with adamantane (Ada) derivatives and various polyethylene glycol (PEG) linkers to produce RTX-Ada conjugates. These conjugates effectively formed RTX-rhamnose (Rha) complexes in situ through self-assembly, driven by host-guest interactions with Rha-modified β-cyclodextrin. This mechanism successfully redirected endogenous anti-Rha antibodies to target cells, enhancing the availability of Fc domains for improved effector functions, including complement-dependent cytotoxicity (CDC). A structure-activity relationship study indicated that the potency of these in situ complexes was significantly influenced by the length of the PEG linker used; shorter PEG linkers correlated with higher CDC activity. Given the variability in endogenous antibody levels among individuals, this strategy presents a flexible and promising platform for enhancing the efficacy of mAb-based cancer immunotherapy.

Leveraging Covalency to Stabilize Ternary Complex Formation For Cell-Cell "Induced Proximity"

Recent advances in the field of translational chemical biology use diverse "proximity-inducing" synthetic modalities to elicit new modes of "event driven" pharmacology. These include mechanisms of targeted protein degradation and immune clearance of pathogenic cells. Heterobifunctional "chimeric" compounds like Proteolysis TArgeting Chimeras (PROTACs) and Antibody Recruiting Molecules (ARMs) leverage these mechanisms, respectively. Both systems function through the formation of reversible "ternary" or higher-order biomolecular complexes. Critical to function are key parameters, such as bifunctional molecule affinity for endogenous proteins, target residence time, and turnover. To probe the mechanism and enhance function, covalent chemical approaches have been developed to kinetically stabilize ternary complexes. These include electrophilic PROTACs and Covalent Immune Recruiters (CIRs), the latter designed to uniquely enforce cell-cell induced proximity. Inducing cell-cell proximity is associated with key challenges arising from a combination of steric and/or mechanical based destabilizing forces on the ternary complex. These factors can attenuate the formation of ternary complexes driven by high affinity bifunctional/proximity inducing molecules. This Account describes initial efforts in our lab to address these challenges using the CIR strategy in antibody recruitment or receptor engineered T cell model systems of cell-cell induced proximity. ARMs form ternary complexes with serum antibodies and surface protein antigens on tumor cells that subsequently engage immune cells via Fc receptors. Binding and clustering of Fc receptors trigger immune cell killing of the tumor cell. We applied the CIR strategy to convert ARMs to covalent chimeras, which "irreversibly" recruit serum antibodies to tumor cells. These covalent chimeras leverage electrophile preorganization and kinetic effective molarity to achieve fast and selective covalent engagement of the target ternary complex protein, e.g., serum antibody. Importantly, covalent engagement can proceed via diverse binding site amino acids beyond cysteine. Covalent chimeras demonstrated striking functional enhancements compared to noncovalent ARM analogs in functional immune assays. We revealed this enhancement was in fact due to the increased kinetic stability and not concentration, of ternary complexes. This finding was recapitulated using analogous CIR modalities that integrate peptidic or carbohydrate binding ligands with Sulfur(VI) Fluoride Exchange (SuFEx) electrophiles to induce cell-cell proximity. Mechanistic studies in a distinct model system that uses T cells engineered with receptors that recognize covalent chimeras or ARMs, revealed covalent receptor engagement uniquely enforces downstream activation signaling. Finally, this Account discusses potential challenges and future directions for adapting and optimizing covalent chimeric/bifunctional molecules for diverse applications in cell-cell induced proximity.

Targeted recruitment of immune effector cells for rapid eradication of influenza virus infections

Despite much research, considerable data suggest that influenza virus remains a serious health problem because i) the effectiveness of current vaccines ranges only from 19% to 60%, ii) available therapies remain ineffective in advanced stages of disease, iii) death rates vary between 25,000 and 72,000/year in the United States, and iv) avian influenza strains are now being transmitted to dairy cattle that in turn are infecting humans. To address these concerns, we have developed zanDR, a bispecific small molecule that binds and inhibits viral neuraminidase expressed on both free virus and virus-infected cells and recruits naturally occurring anti-rhamnose and anti-dinitrophenyl (DNP) antibodies with rhamnose and DNP haptens. Because the neuraminidase inhibition replicates the chemotherapeutic mechanism of zanamivir and oseltamivir, while rhamnose and DNP recruit endogenous antibodies much like an anti-influenza vaccine, zanDR reproduces most of the functions of current methods of protection against influenza virus infections. Importantly, studies on cells in culture demonstrate that both of the above protective mechanisms remain highly functional in the zanDR conjugate, while studies in lethally infected mice with advanced-stage disease establish that a single intranasal dose of zanDR not only yields 100% protection but also reduces lung viral loads faster and ~1,000× more thoroughly than current antiviral therapies. Since zanDR also lowers secretion of proinflammatory cytokines and protects against virus-induced damage to the lungs better than current therapies, we suggest that combining an immunotherapy with a chemotherapy in single pharmacological agent constitutes a promising approach for treating the more challenging forms of influenza.

The effect of Fc region affinity of protein-based antibody-recruiting molecules on antibody-dependent cellular cytotoxicity

Previously, we reported anticancer molecules, Fc-binding antibody-recruiting molecules (Fc-ARMs), which crosslink proteins on cancer cells with endogenous immunoglobulin Gs (IgGs) via their Fc region. The mobilized IgGs on cancer cells can accommodate natural killer cells to induce antibody-dependent cellular cytotoxicity (ADCC). Because previous Fc-ARMs utilized Fc-binding peptides, their affinity to IgGs is weak, which resulted in the limited induction capability of ADCC. Previous Fc-ARMs also unitized small molecular ligands to cancer cells, which limited their universal applicability to any cancer cells. A recent study reported that protein-based Fc-ARMs might overcome the issues associated with non-proteinous Fc-ARMs. Here, we examined the universality of a protein-based Fc-ARM by replacing its tumor-binding domain with a human epidermal growth factor receptor 2 (HER2)-specific affibody (ZHER2:342). We also examined the requirement of its Fc-binding domain affinity. We found that the Fc-ARMs accepted an affibody as a tumor-binding domain to induce ADCC. Furthermore, the required residence time of the complex between Fc-ARM and IgG was ∼102 min, which was comparable to that when monoclonal antibodies bind to their specific antigens. However, we found that the extent of ADCC induced by Fc-ARM was lower than that of conventional IgG-mediated ADCC, indicating that further enhancement of the affinity of the antibody-binding terminus and tumor-binding terminus of Fc-ARM may be needed to achieve ADCC equivalent to that of conventional IgG-mediated ADCC.

Chemical immunology: Recent advances in tool development and applications

Immunology was one of the first biological fields to embrace chemical approaches. The development of new chemical approaches and techniques has provided immunologists with an impressive arsenal of tools to address challenges once considered insurmountable. This review focuses on advances at the interface of chemistry and immunobiology over the past two decades that have not only opened new avenues in basic immunological research, but also revolutionized drug development for the treatment of cancer and autoimmune diseases. These include chemical approaches to understand and manipulate antigen presentation and the T cell priming process, to facilitate immune cell trafficking and regulate immune cell functions, and therapeutic applications of chemical approaches to disease control and treatment.

Rhamnose modified antibodies show improved immune killing towards EGFR-positive solid tumor cells

Therapeutic monoclonal antibodies (mAbs) against the epidermal growth factor receptor (EGFR) have shown clinical efficacy in colorectal cancer and other solid cancers. Enhancing the effector functions of these anti-EGFR mAbs is believed to be a valuable approach to achieve improved efficacy in clinical setting. Here, we report the development of an effector function-enhanced antibody by rhamnose (Rha) functionalization. Cetuximab, a human/mouse chimeric anti-EGFR mAb, was selected and site-specifically conjugated with Rha haptens. The obtained cetuximab-Rha conjugate was shown to be able to selectively redirect amounts of endogenous anti-Rha antibodies onto EGFR-positive solid tumor cells and thereby provide more Fc domains to achieve enhancement of effector functions including complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated phagocytosis (ADCP). Particularly, CDC, one powerful cell killing mechanism which is inactive in cetuximab, was dramatically improved. This study demonstrates the potential of rhamnose-modified antibody for EGFR-positive solid tumor immunotherapy.

Defining the Cell Surface Cysteinome Using Two-Step Enrichment Proteomics

The plasma membrane proteome is a rich resource of functionally important and therapeutically relevant protein targets. Distinguished by high hydrophobicity, heavy glycosylation, disulfide-rich sequences, and low overall abundance, the cell surface proteome remains undersampled in established proteomic pipelines, including our own cysteine chemoproteomics platforms. Here, we paired cell surface glycoprotein capture with cysteine chemoproteomics to establish a two-stage enrichment method that enables chemoproteomic profiling of cell Surface Cysteinome. Our "Cys-Surf" platform captures >2,800 total membrane protein cysteines in 1,046 proteins, including 1,907 residues not previously captured by bulk proteomic analysis. By pairing Cys-Surf with an isotopic chemoproteomic readout, we uncovered 821 total ligandable cysteines, including known and novel sites. Cys-Surf also robustly delineates redox-sensitive cysteines, including cysteines prone to activation-dependent changes to cysteine oxidation state and residues sensitive to addition of exogenous reductants. Exemplifying the capacity of Cys-Surf to delineate functionally important cysteines, we identified a redox sensitive cysteine in the low-density lipoprotein receptor (LDLR) that impacts both the protein localization and uptake of low-density lipoprotein (LDL) particles. Taken together, the Cys-Surf platform, distinguished by its two-stage enrichment paradigm, represents a tailored approach to delineate the functional and therapeutic potential of the plasma membrane cysteinome.

Hapten/Myristoyl Functionalized Poly(propyleneimine) Dendrimers as Potent Cell Surface Recruiters of Antibodies for Mediating Innate Immune Killing

Recruiting endogenous antibodies to the surface of cancer cells using antibody-recruiting molecules has the potential to unleash innate immune effector killing mechanisms against antibody-bound cancer cells. The affinity of endogenous antibodies is relatively low, and many currently explored antibody-recruiting strategies rely on targeting over-expressed receptors, which have not yet been identified in most solid tumors. Here, both challenges are addressed by functionalizing poly(propyleneimine) (PPI) dendrimers with both multiple dinitrophenyl (DNP) motifs, as anti-hapten antibody-recruiting motifs, and myristoyl motifs, as universal phospholipid cell membrane anchoring motifs, to recruit anti-hapten antibodies to cell surfaces. By exploiting the multivalency of the ligand exposure on the dendrimer scaffold, it is demonstrated that dendrimers featuring ten myristoyl and six DNP motifs exhibit the highest antibody-recruiting capacity in vitro. Furthermore, it is shown that treating cancer cells with these dendrimers in vitro marks them for phagocytosis by macrophages in the presence of anti-hapten antibodies. As a proof-of-concept, it is shown that intratumoral injection of these dendrimers in vivo in tumor-bearing mice results in the recruitment of anti-DNP antibodies to the cell surface in the tumor microenvironment. These findings highlight the potential of dendrimers as a promising class of novel antibody-recruiting molecules for use in cancer immunotherapy.

Defining the Cell Surface Cysteinome using Two-step Enrichment Proteomics

The plasma membrane proteome is a rich resource of functional and therapeutically relevant protein targets. Distinguished by high hydrophobicity, heavy glycosylation, disulfide-rich sequences, and low overall abundance, the cell surface proteome remains undersampled in established proteomic pipelines, including our own cysteine chemoproteomics platforms. Here we paired cell surface glycoprotein capture with cysteine chemoproteomics to establish a two-stage enrichment method that enables chemoproteomic profiling of cell Surface Cysteinome. Our "Cys-Surf" platform captures >2,800 total membrane protein cysteines in 1,046 proteins, including 1,907 residues not previously captured by bulk proteomic analysis. By pairing Cys-Surf with an isotopic chemoproteomic readout, we uncovered 821 total ligandable cysteines, including known and novel sites. Cys-Surf also robustly delineates redox-sensitive cysteines, including cysteines prone to activation-dependent changes to cysteine oxidation state and residues sensitive to addition of exogenous reductants. Exemplifying the capacity of Cys-Surf to delineate functionally important cysteines, we identified a redox sensitive cysteine in the low-density lipoprotein receptor (LDLR) that impacts both the protein localization and uptake of LDL particles. Taken together, the Cys-Surf platform, distinguished by its two-stage enrichment paradigm, represents a tailored approach to delineate the functional and therapeutic potential of the plasma membrane cysteinome.

Chemoenzymatic Tagging of Tn/TF/STF Antigens in Living Systems

Truncated mucin-type O-glycans, such as Tn-associated antigens, are aberrantly expressed biomarkers of cancer, but remain challenging to target. Reactive antibodies to these antigens either lack high-affinity or are prone to antigen escape. Here, we have developed a robust chemoenzymatic strategy for the global labeling of Tn-associated antigens, i.e. Tn (GalNAcα-O-Ser/Thr), Thomsen-Friedenreich (Galβ1-3GalNAcα-O-Ser/Thr, TF) and STF (Neu5Acα2-3Galβ1-3GalNAcα-O-Ser/Thr, STF) antigens, in human whole blood with high efficiency and selectivity. This method relies on the use of the O-glycan sialyltransferase ST6GalNAc1 to transfer a sialic acid-functionalized adaptor to the GalNAc residue of these antigens. By tagging, the adaptor functionalized antigens can be easily targeted by customized strategies such as, but not limited to, chimeric antigen receptor T-Cells (CAR-T). We expect this tagging system to find broad applications in cancer diagnostics and targeting in combination with established strategies.

Merging Solid-Phase Peptide Synthesis and Automated Glycan Assembly to Prepare Lipid-Peptide-Glycan Chimeras

Biomaterials with improved biological features can be obtained by conjugating glycans to nanostructured peptides. Creating peptide-glycan chimeras requires superb chemoselectivity. We expedite access to such chimeras by merging peptide and glycan solid-phase syntheses employing a bifunctional monosaccharide. The concept was explored in the context of the on-resin generation of a model α(1→6)tetramannoside linked to peptides, lipids, steroids, and adamantane. Chimeras containing a β(1→6)tetraglucoside and self-assembling peptides such as FF, FFKLVFF, and the amphiphile palmitoyl-VVVAAAKKK were prepared in a fully automated manner. The robust synthetic protocol requires a single purification step to obtain overall yields of about 20 %. The β(1→6)tetraglucoside FFKLVFF chimera produces micelles rather than nanofibers formed by the peptide alone as judged by microscopy and circular dichroism. The peptide amphiphile-glycan chimera forms a disperse fiber network, creating opportunities for new glycan-based nanomaterials.

Proximity-inducing modalities: the past, present, and future

Living systems use proximity to regulate biochemical processes. Inspired by this phenomenon, bifunctional modalities that induce proximity have been developed to redirect cellular processes. An emerging example of this class is molecules that induce ubiquitin-dependent proteasomal degradation of a protein of interest, and their initial development sparked a flurry of discovery for other bifunctional modalities. Recent advances in this area include modalities that can change protein phosphorylation, glycosylation, and acetylation states, modulate gene expression, and recruit components of the immune system. In this review, we highlight bifunctional modalities that perform functions other than degradation and have great potential to revolutionize disease treatment, while also serving as important tools in basic research to explore new aspects of biology.

Immune Targeting of Mycobacteria through Cell Surface Glycan Engineering

Mycobacteria and other organisms in the order Mycobacteriales cause a range of significant human diseases, including tuberculosis, leprosy, diphtheria, Buruli ulcer, and non-tuberculous mycobacterial (NTM) disease. However, the intrinsic drug tolerance engendered by the mycobacterial cell envelope undermines conventional antibiotic treatment and contributes to acquired drug resistance. Motivated by the need to augment antibiotics with novel therapeutic approaches, we developed a strategy to specifically decorate mycobacterial cell surface glycans with antibody-recruiting molecules (ARMs), which flag bacteria for binding to human-endogenous antibodies that enhance macrophage effector functions. Mycobacterium-specific ARMs consisting of a trehalose targeting moiety and a dinitrophenyl hapten (Tre-DNPs) were synthesized and shown to specifically incorporate into outer-membrane glycolipids of Mycobacterium smegmatis via trehalose metabolism, enabling recruitment of anti-DNP antibodies to the mycobacterial cell surface. Phagocytosis of Tre-DNP-modified M. smegmatis by macrophages was significantly enhanced in the presence of anti-DNP antibodies, demonstrating proof-of-concept that our strategy can augment the host immune response. Because the metabolic pathways responsible for cell surface incorporation of Tre-DNPs are conserved in all Mycobacteriales organisms but absent from other bacteria and humans, the reported tools may be enlisted to interrogate host-pathogen interactions and develop immune-targeting strategies for diverse mycobacterial pathogens.

Sequence-defined antibody-recruiting macromolecules

Antibody-recruiting molecules represent a novel class of therapeutic agents that mediate the recruitment of endogenous antibodies to target cells, leading to their elimination by the immune system. Compared to single-ligand copies, macromolecular scaffolds presenting multiple copies of an antibody-binding ligand offer advantages in terms of increased complex avidity. In this study, we describe the synthesis of sequence-defined macromolecules designed for antibody recruitment, utilising dinitrophenol (DNP) as a model antibody-recruiting motif. The use of discrete macromolecules gives access to varying the spacing between DNP motifs while maintaining the same chain length. This characteristic enables the investigation of structure-dependent binding interactions with anti-DNP antibodies. Through solid-phase thiolactone chemistry, we synthesised a series of oligomers with precisely localised DNP motifs along the backbone and a terminal biotin motif for surface immobilisation. Utilising biolayer interferometry analysis, we observed that oligomers with adjacent DNP motifs exhibited enhanced avidity for anti-DNP antibodies. Molecular modelling provided insights into the structures and dynamics of the various macromolecules, shedding light on the accessibility of the ligands to the antibodies. Overall, our findings highlight that the use of sequence-defined macromolecules can contribute to our understanding of structure-activity relationships and provide insights for the design of novel antibody-recruiting therapeutic agents.

Practical Antibody Recruiting by Metabolic Labeling with Caged Glycans

We propose a de novo glycan display approach that combines metabolic labeling and a glycan-caging strategy as a facile editing method for cell-surface glycans. This method enables the introduction of antigen glycans onto cancer cells to induce immune responses through antibody recruiting. The caging strategy prevents the capture of α-rhamnose (an antigen glycan) by endogenous antibodies during the introduction of the glycan to the targeted cell surface, and subsequent uncaging successfully induces immune responses. Therefore, this study proposes a practical method for editing the cell-surface glycocalyx under promiscuous conditions, such as those in vivo, which paves the way for the development of glycan function analysis and regulation.

Multivalent glycocyclopeptides: conjugation methods and biological applications

Click chemistry was extensively used to decorate synthetic multivalent scaffolds with glycans to mimic the cell surface glycocalyx and to develop applications in glycosciences. Conjugation methods such as oxime ligation, copper(I)-catalyzed alkyne-azide cycloaddition, thiol-ene coupling, squaramide coupling or Lansbury aspartylation proved particularly suitable to achieve this purpose. This review summarizes the synthetic strategies that can be used either in a stepwise manner or in an orthogonal one-pot approach, to conjugate multiple copies of identical or different glycans to cyclopeptide scaffolds (namely multivalent glycocyclopeptides) having different size, valency, geometry and molecular composition. The second part of this review will describe the potential of these structures to interact with various carbohydrate binding proteins or to stimulate immunity against tumor cells.

A covalent inhibitor of K-Ras(G12C) induces MHC class I presentation of haptenated peptide neoepitopes targetable by immunotherapy

Immunotargeting of tumor-specific antigens is a powerful therapeutic strategy. Immunotherapies directed at MHC-I complexes have expanded the scope of antigens and enabled the direct targeting of intracellular oncoproteins at the cell surface. We asked whether covalent drugs that alkylate mutated residues on oncoproteins could act as haptens to generate unique MHC-I-restricted neoantigens. Here, we report that KRAS G12C mutant cells treated with the covalent inhibitor ARS1620 present ARS1620-modified peptides in MHC-I complexes. Using ARS1620-specific antibodies identified by phage display, we show that these haptenated MHC-I complexes can serve as tumor-specific neoantigens and that a bispecific T cell engager construct based on a hapten-specific antibody elicits a cytotoxic T cell response against KRAS G12C cells, including those resistant to direct KRAS G12C inhibition. With multiple K-RAS G12C inhibitors in clinical use or undergoing clinical trials, our results present a strategy to enhance their efficacy and overcome the rapidly arising tumor resistance.

Chemical Reporters for Bacterial Glycans: Development and Applications

Bacteria possess an extraordinary repertoire of cell envelope glycans that have critical physiological functions. Pathogenic bacteria have glycans that are essential for growth and virulence but are absent from humans, making them high-priority targets for antibiotic, vaccine, and diagnostic development. The advent of metabolic labeling with bioorthogonal chemical reporters and small-molecule fluorescent reporters has enabled the investigation and targeting of specific bacterial glycans in their native environments. These tools have opened the door to imaging glycan dynamics, assaying and inhibiting glycan biosynthesis, profiling glycoproteins and glycan-binding proteins, and targeting pathogens with diagnostic and therapeutic payload. These capabilities have been wielded in diverse commensal and pathogenic Gram-positive, Gram-negative, and mycobacterial species─including within live host organisms. Here, we review the development and applications of chemical reporters for bacterial glycans, including peptidoglycan, lipopolysaccharide, glycoproteins, teichoic acids, and capsular polysaccharides, as well as mycobacterial glycans, including trehalose glycolipids and arabinan-containing glycoconjugates. We cover in detail how bacteria-targeting chemical reporters are designed, synthesized, and evaluated, how they operate from a mechanistic standpoint, and how this information informs their judicious and innovative application. We also provide a perspective on the current state and future directions of the field, underscoring the need for interdisciplinary teams to create novel tools and extend existing tools to support fundamental and translational research on bacterial glycans.

Metabolic labelling of cancer cells with glycodendrimers stimulate immune-mediated cytotoxicity

The recruitment of antibody naturally present in human blood stream at the surface of cancer cells have been proved a promising immunotherapeutic strategy to fight cancer. Antibody recruiting molecules (ARMs) combining tumor and antibody binding modules have been developed for this purpose, however the formation of the interacting complex with both antibody and cell is difficult to optimize to stimulate immune-mediated cytotoxicity. To circumvent this limitation, we report herein a more direct approach combining cell metabolism of azido-sugar and bio-orthogonal click chemistry to conjugate at the cell glycocalyx structurally well-defined glycodendrimers as antibody binding module (ABM). We demonstrate that this strategy allows not only the recruitment of natural antibody at the surface of isolated cells or solid tumor models but also activate a cytotoxic response with human serum as unique source of immune effectors.

Epitope alteration by small molecules and applications in drug discovery

Small molecules and antibodies are normally considered separately in drug discovery, except in the case of covalent conjugates. We unexpectedly discovered several small molecules that could inhibit or enhance antibody–epitope interactions which opens new possibilities in drug discovery and therapeutic modulation of auto-antibodies. We first discovered a small molecule, CRANAD-17, that enhanced the binding of an antibody to amyloid beta (Aβ), one of the major hallmarks of Alzheimer's disease, by stable triplex formation. Next, we found several small molecules that altered antibody–epitope interactions of tau and PD-L1 proteins, demonstrating the generality of this phenomenon. We report a new screening technology for ligand discovery, screening platform based on epitope alteration for drug discovery (SPEED), which is label-free for both the antibody and small molecule. SPEED, applied to an Aβ antibody, led to the discovery of a small molecule, GNF5837, that inhibits Aβ aggregation and another, obatoclax, that binds Aβ plaques and can serve as a fluorescent reporter in brain slices of AD mice. We also found a small molecule that altered the binding between Aβ and auto-antibodies from AD patient serum. SPEED reveals the sensitivity of antibody–epitope interactions to perturbation by small molecules and will have multiple applications in biotechnology and drug discovery.

A screening platform based on epitope alteration for drug discovery (SPEED).

Chemical Synthesis of Antibody-Hapten Conjugates Capable of Recruiting the Endogenous Antibody to Magnify the Fc Effector Immunity of Antibody for Cancer Immunotherapy

Monoclonal antibodies (mAbs) with enhanced effector functions in cancer immunotherapy, such as complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC), could improve the clinical performance. Here, we develop an mAb-hapten conjugate strategy to augment the mAb effector functions with the engagement of endogenous antibodies. An "off-the-shelf" mAb, rituximab, is site-specifically conjugated with the rhamnose (Rha) hapten to generate rituximab-Rha conjugates. The octopus-like conjugates could recruit anti-Rha antibodies onto the cancer cell surface and further form an immune complex that is able to provide multivalent Fc domains to interact with immune cells or complement protein C1q, leading to magnified ADCC and CDC simultaneously. One optimal conjugate R2 with PEG2 as a linker exhibits the most potent in vitro cancer cell killing activity and significant in vivo antitumor efficacy in a xenograft model. This is a general and cost-effective approach to generate mAb with improved effector functions that may have broad applications.

Interaction with 2,4-dinitrophenol correlates with polyreactivity, self-binding, and stability of clinical-stage therapeutic antibodies

Therapeutic antibodies should cover particular physicochemical and functional requirements for successful entry into clinical practice. Numerous experimental and computational approaches have been developed for early identification of different unfavourable features of antibodies. Immune repertoires of healthy humans contain a fraction of antibodies that recognize nitroarenes. These antibodies have been demonstrated to manifest antigen-binding polyreactivity. Here we observed that >20 % of 112 clinical stage therapeutic antibodies show pronounced binding to 2,4-dinitrophenol conjugated to albumin. This interaction predicts a number of unfavourable functional and physicochemical features of antibodies such as polyreactivity, tendency for self-association, stability and expression yields. Based on these findings we proposed a simple approach that may add to the armamentarium of assays for early identification of developability liabilities of antibodies intended for therapeutic use.

Targeted Protein Acetylation in Cells Using Heterobifunctional Molecules

Protein acetylation is a central event in orchestrating diverse cellular processes. However, current strategies to investigate protein acetylation in cells are often nonspecific or lack temporal and magnitude control. Here, we developed an acetylation tagging system, AceTAG, to induce acetylation of targeted proteins. The AceTAG system utilizes bifunctional molecules to direct the lysine acetyltransferase p300/CBP to proteins fused with the small protein tag FKBP12F36V, resulting in their induced acetylation. Using AceTAG, we induced targeted acetylation of a diverse array of proteins in cells, specifically histone H3.3, the NF-κB subunit p65/RelA, and the tumor suppressor p53. We demonstrate that targeted acetylation with the AceTAG system is rapid, selective, reversible and can be controlled in a dose-dependent fashion. AceTAG represents a useful strategy to modulate protein acetylation and should enable the exploration of targeted acetylation in basic biological and therapeutic contexts.

Dinitrophenol-Hyaluronan Conjugates as Multivalent Antibody-Recruiting Glycopolymers for Targeted Cancer Immunotherapy

Multivalent antibody-recruiting glycopolymers (MARGs) composed of hyaluronic acid (HA) grafted with multiple copies of dinitrophenol (DNP) were developed for targeted cancer immunotherapy. Structure-activity studies demonstrated that the MARGs were able to specifically recognize CD44-positive cancer cells and displayed remarkable antibody-recruiting capacities and tumor cell killing activities dependent on the introduced multivalent effect and the length of PEG linker. One of the MARGs, HA-[PEG₃ -DNP]₈ , showed the best capacity for clustering anti-DNP antibodies onto CD44-positive cancer cells and displayed potent in vitro anti-cancer activity by triggering complement dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC). Moreover, we found that HA-[PEG₃ -DNP]₈ significantly inhibited the xenograft tumor growth of Babl/c nude mice bearing triple negative breast cancer cells, while it did not cause detectable histological cytotoxicity. Given the easy access of this type of natural glycopolymer and the practical synthesis approach, these MARGs provide promising immunotherapeutics for cancer immunotherapy.

A Versatile Platform for the Development of Radiolabeled Antibody-Recruiting Small Molecules

Building on clinical case reports of the abscopal effect, there has been considerable interest in the synergistic effects of radiation and immunotherapies for the treatment of cancer. Here, the first radiolabeled antibody-recruiting small molecule that can chelate a variety of cytotoxic radionuclides is described. The platform consists of a tunable antibody-binding domain against a serum antibody of interest (e.g., dinitrophenyl hapten) to recruit endogenous antibodies that activate effector cell function, a chelate capable of binding diagnostic and therapeutic radiometals, and a tetrazine for bioorthogonal coupling with trans-cyclooctene-modified targeting vectors. The dinitrophenyl-tetrazine ligand was shown to both affect dose-dependent antibody recruitment and immune cell function (phagocytosis) in vitro, and the bisphosphonate ¹⁷⁷Lu-complex was shown to accumulate at sites of calcium accretion in vivo, which was achieved using both active and pretargeting strategies.

Structural influence of antibody recruiting glycodendrimers (ARGs) on antitumoral cytotoxicity

The recruitment of endogenous antibodies against cancer cells has become a reliable antitumoral immunotherapeutic alternative over the last decade. The covalent attachment of antibody and tumor binding modules (ABM and TBM) within a single, well-defined synthetic molecule was indeed demonstrated to promote the formation of an interacting ternary complex between both the antibodies and the targeted cell, which usually results in the simultaneous immune-mediated cellular destruction. In a preliminary study, we have described the first Antibody Recruiting Glycodendrimers (ARGs), combining cRGD as ligands for the αVβ3-expressing melanoma cell line M21 and Rha as ligand for natural IgM, and demonstrated that multivalency is an essential requirement to form this complex. In the present study, we synthesized a new series of ARGs composed of ABMs, i.e. self-condensed rhamnosylated cyclopeptide and polylysine dendrimer, which have been conjugated to the TBM with or without spacer. Flow cytometry and confocal microscopy experiments with human serum and different cell lines revealed that the ABM geometry significantly influences the ternary complex formation in M21, whereas no significant binding occurs in BT 549 having low integrin expression. In addition, we demonstrate with a cellular viability assay that ARGs induce high level of cytotoxicity against M21 which is also in close correlation with the ABM structure. In particular, we have shown that ARG combining cyclopeptide core and branches, with or without spacer, induce 40-57% of selective cytotoxicity against M21 cells in the presence of human serum as the unique source of immunity effectors. Finally, we also highlight that the spacer between ABM and TBM enables an increase of the immune-mediate cytotoxicity even with ABM of lower valency.

Cancer cell death using metabolic glycan labelling techniques

Herein we describe a method for inducing cancer cell death, which relies on the use of a H2O2-responsive glycan metabolic precursor in conjunction with antibody-dependent cellular cytotoxicity (ADCC) or photodynamic therapy (PDT).

Exendin 4-Hapten Conjugate Capable of Binding with Endogenous Antibodies for Peptide Half-life Extension and Exerting Long-Acting Hypoglycemic Activity

Hapten-specific endogenous antibodies are naturally occurring antibodies present in human blood. Herein, we investigated a new strategy in which small-molecule haptens were utilized as naturally occurring antibody binders for peptide half-life extension. The glucagon-like peptide 1 receptor agonist exendin 4 was site-specifically functionalized with the dinitrophenyl (DNP) hapten at the C-terminus via sortase A-mediated ligation. The resulting Ex4-DNP conjugates retained GLP-1 receptor activation potency in vitro and had a similar in vivo acute glucose-lowering effect comparable to that of native Ex4. Pharmacokinetic studies and hypoglycemic duration tests demonstrated that the Ex4-DNP conjugates displayed significantly elongated half-lives and improved long-acting antidiabetic activity in the presence of endogenous anti-DNP antibodies. In chronic treatment studies, once-daily administration of optimal conjugate 7 demonstrated more beneficial effects without prominent toxicity compared with Ex4. This strategy provides a new approach and represents an alternative to the well-established peptide-Fc fusion strategy to improve the peptide half-life and the therapeutic efficacy.

Interaction of clinical-stage antibodies with heme predicts their physiochemical and binding qualities

Immunoglobulin repertoires contain a fraction of antibodies that recognize low molecular weight compounds, including some enzymes' cofactors, such as heme. Here, by using a set of 113 samples with variable region sequences matching clinical-stage antibodies, we demonstrated that a considerable number of these antibodies interact with heme. Antibodies that interact with heme possess specific sequence traits of their antigen-binding regions. Moreover they manifest particular physicochemical and functional qualities i.e. increased hydrophobicity, higher propensity of self-binding, higher intrinsic polyreactivity and reduced expression yields. Thus, interaction with heme is a strong predictor of different molecular and functional qualities of antibodies. Notably, these qualities are of high importance for therapeutic antibodies, as their presence was associated with failure of drug candidates to reach clinic. Our study reveled an important facet of information about relationship sequence-function in antibodies. It also offers a convenient tool for detection of liabilities of therapeutic antibodies.

Antibody recruiting molecules (ARMs): synthetic immunotherapeutics to fight cancer

Antibody-recruiting molecules (ARMs) are one of the most promising tools to redirect the immune response towards cancer cells. In this review, we aim to highlight the recent advances in the field. We will illustrate the advantages of different ARM approaches and emphasize the importance of a multivalent presentation of the binding units.

Antibody-recruiting molecules (ARMs) are one of the most promising tools to redirect the immune response towards cancer cells.

Synthesis and biological evaluation of a monocyclic Fc-binding antibody-recruiting molecule for cancer immunotherapy

Antibody-recruiting molecules (ARMs) are bispecific molecules composed of an antibody-binding motif and a target-binding motif that redirect endogenous antibodies to target cells to elicit immune responses. To enhance the translational potential of ARMs, it is crucial to design antibody/target-binding motifs that have strong affinity and are easy to synthesize. Here, we synthesized a novel Fc-binding ARM (Fc-ARM) that targets folate receptor (FR)-positive cancer cells, Reo-3, using a recently developed monocyclic peptide 15-Lys8Leu, which binds strongly to the Fc region of an antibody. Reo-3 bound to the Fc region of the antibody with a K d of 5.8 nM, and recruited a clinically used antibody mixture to attack FR-positive IGROV-1 cells as efficiently as Fc-ARM2, in which a bicyclic Fc-binding peptide was used. These results indicate that 15-Lys8Leu, which can be synthesized readily, is suitable for various applications including the development of Fc-ARMs.

Synthetic chemical ligands and cognate antibodies for biorthogonal drug targeting and cell engineering

A vast range of biomedical applications relies on the specificity of interactions between an antigen and its cognate receptor or antibody. This specificity can be highest when said antigen is a non-natural (synthetic) molecule introduced into a biological setting as a bio-orthogonal ligand. This review aims to present the development of this methodology from the early discovery of haptens a century ago to the recent clinical trials. We discuss such methodologies as antibody recruitment, artificial internalizing receptors and chemically induced dimerization, present the use of chimeric receptors and/or bispecific antibodies to achieve drug targeting and transcytosis, and illustrate how these platforms most impressively found use in the engineering of therapeutic cells such as the chimeric antigen receptor cells. This review aims to be of interest to a broad scientific audience and to spur the development of synthetic artificial ligands for biomedical applications.

Universal endogenous antibody recruiting nanobodies capable of triggering immune effectors for targeted cancer immunotherapy

Developing monoclonal antibodies (mAbs) for cancer immunotherapy is expensive and complicated. Nanobodies are small antibodies possessing favorable pharmacological properties compared with mAbs, but have limited anticancer efficacy due to the lack of an Fc region and poor pharmacokinetics. In this context, engineered universal endogenous antibody-recruiting nanobodies (UEAR Nbs), as a general and cost-effective approach, were developed to generate functional antibody-like nanobodies that could recapitulate the Fc biological functions for cancer immunotherapy. The UEAR Nbs, composed of the IgG binding domain and nanobody, were recombinantly expressed in E. coli and could recruit endogenous IgGs onto the cancer cell surface and trigger potent immune responses to kill cancer cells in vitro. Moreover, it was proved that UEAR Nbs displayed significantly improved half-lives in vivo. The in vivo antitumor efficacy of UEAR Nbs was demonstrated in a murine model using EGFR positive triple-negative breast cancer (TNBC).

Synthesis and Biopharmaceutical Applications of Sugar-Based Polymers: New Advances and Future Prospects

The rapid rise in research interest in carbohydrate-based polymers is undoubtedly due to the nontoxic nature of such materials in an in vivo environment and the versatile roles that the polymers can play in cellular functions. Such polymers have served as therapeutic tools for drug delivery, including antigens, proteins, and genes, as well as diagnostic devices. Our focus in the first half of this Review is on synthetic methods based on ring-opening polymerization and enzyme-catalyzed polymerization, along with controlled radical polymerization. In the second half of this Review, sugar-based polymers are discussed on the basis of their remarkable success in competitive receptor binding, as multifunctional nanocarriers of targeting inhibitors for cancer treatment, in genome-editing delivery, in immunotherapy based on endogenous antibody recruitment, and in treatment of respiratory diseases, including influenza A. Particular emphasis is put on the synthesis and biopharmaceutical applications of sugar-based polymers published in the most recent 5 years. A noticeable attribute of carbohydrate-based polymers is that the sugar-receptor interactions can be facilitated by the cooperative effect of multiple sugar units. Their diversified topology and structures will drive the development of new synthetic strategies and bring about important applications, including coronavirus-related drug therapy.

Fc-Binding Antibody-Recruiting Molecules Targeting Prostate-Specific Membrane Antigen: Defucosylation of Antibody for Efficacy Improvement*

Synthetic small molecules that redirect endogenous antibodies to target cells are promising drug candidates because they overcome the potential shortcomings of therapeutic antibodies, such as immunogenicity and the need for intravenous delivery. Previously, we reported a novel class of bispecific molecules targeting the antibody Fc region and folate receptor, named Fc-binding antibody-recruiting molecules (Fc-ARMs). Fc-ARMs can theoretically recruit most endogenous antibodies, inducing antibody-dependent cell-mediated cytotoxicity (ADCC) to eliminate cancer cells. Herein, we describe new Fc-ARMs that target prostate cancer (Fc-ARM-Ps). Fc-ARM-Ps recruited antibodies to cancer cells expressing prostate-specific membrane antigen but did so with lower efficiency compared with Fc-ARMs targeting the folate receptor. Upon recruitment by Fc-ARM-P, defucosylated antibodies efficiently activated natural killer cells and induced ADCC, whereas antibodies with intact N-glycans did not. The results suggest that the affinity between recruited antibodies and CD16a, a type of Fc receptor expressed on immune cells, could be a key factor controlling immune activation in the Fc-ARM strategy.

Multivalent Antibody-Recruiting Macromolecules: Linking Increased Binding Affinity with Enhanced Innate Immune Killing

Antibody-recruiting molecules (ARMs) are a novel class of immunotherapeutics. They are capable of introducing antibodies onto disease-relevant targets such as cancer cells, bacterial cells or viruses. This can induce antibody-mediated immune responses such as antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC) and antibody-dependent phagocytosis (ADCP), which can kill the pathogen. In contrast to the classic ARMs, multivalent ARMs could offer the advantage of increasing the efficiency of antibody recruitment and subsequent innate immune killing. Such compounds consist of multiple target-binding termini (TBT) and/or antibody-binding termini (ABT). Those multivalent interactions are able to convert low binding affinities into increased binding avidities. This minireview summarizes the current status of multivalent ARMs and gives insight into possible benefits, hurdles still to be overcome and future perspectives.

Bacterial Lectin-Targeting Glycoconjugates for Selective Elimination of Pathogenic Bacteria

Herein we report a strategy to eradicate pathogenic bacteria selectively, which utilizes bacterial lectin-targeting glycoconjugates that contain an epitope or a photosensitizer to promote antibody-dependent cellular cytotoxicity (ADCC) or photodynamic therapy (PDT), respectively. Our results show that death promoted by using the designed synthetic glycoconjugates coupled with ADCC or PDT takes place selectively in pathogenic bacteria expressing lectins on their surfaces.

A Universal CAR-NK Cell Targeting Various Epitopes of HIV-1 gp160

Engineering T cells and natural killer (NK) cells with anti-HIV chimeric antigen receptors (CAR) has emerged as a promising strategy to eradicate HIV-infected cells. However, current anti-HIV CARs are limited by targeting a single epitope of the HIV envelope glycoprotein gp160, which cannot counter the enormous diversity and mutability of viruses. Here, we report the development of a universal CAR-NK cell, which recognizes 2,4-dinitrophenyl (DNP) and can subsequently be redirected to target various epitopes of gp160 using DNP-conjugated antibodies as adaptor molecules. We show that this CAR-NK cell can recognize and kill mimic HIV-infected cell lines expressing subtypes B and C gp160. We additionally find that anti-gp160 antibodies targeting membrane-distal epitopes (including V1/V2, V3, and CD4bs) are more likely to activate universal CAR-NK cells against gp160⁺ target cells, compared with those targeting membrane-proximal epitopes located in the gp41 MPER. Finally, we confirm that HIV-infected primary human CD4⁺ T cells can be effectively killed using the same approach. Given that numerous anti-gp160 antibodies with different antigen specificities are readily available, this modular universal CAR-NK cell platform can potentially overcome HIV diversity, thus providing a promising strategy to eradicate HIV-infected cells.

Disparities between Antibody Occupancy, Orientation, and Cytotoxicity in Immunotherapy

We report fusion proteins designed to bind spatially distinct epitopes on the extracellular portion of HER2, a breast cancer biomarker and established therapeutic target, and recruit IgG (either anti-His₆ or serum IgG) to the cell surface. When the proteins were incubated with anti-His₆ antibody and various concentrations of a single HER2-binding protein His₆ fusion, we observed interference and a decrease in antibody recruitment at HER2-binding protein concentrations exceeding ∼30 nM. In contrast, concomitant treatment with two or three distinct HER2-binding protein His₆ fusions, and anti-His₆ , results in increased antibody recruitment, even at relatively high HER2-binding protein concentration. In some instances, increased antibody recruitment leads to increased antibody-dependent cellular cytotoxicity (ADCC) activity. While a fusion protein consisting of a HER2-binding nanobody and Sac7d, a protein evolved to recognize the Fc domain of IgG, binds IgG from serum, antibody recruitment does not lead to ADCC activity. Rationales for these disparities are provided. Collectively, our findings have implications for the design of efficacious targeted immunotherapeutic biologics, and ensembles thereof.

Side chain effect in the modulation of αvβ3/α5β1 integrin activity via clickable isoxazoline-RGD-mimetics: development of molecular delivery systems

Construction of small molecule ligand (SML) based delivery systems has been performed starting from a polyfunctionalized isoxazoline scaffold, whose αvβ3 and α5β1 integrins' potency has been already established. The synthesis of this novel class of ligands was obtained by conjugation of linkers to the heterocyclic core via Huisgen-click reaction, with the aim to use them as "shuttles" for selective delivery of diagnostic agents to cancer cells, exploring the effects of the side chains in the interaction with the target. Compounds 17b and 24 showed excellent potency towards α5β1 integrin acting as selective antagonist and agonist respectively. Further investigations confirmed their effects on target receptor through the analysis of fibronectin-induced ERK1/2 phosphorylation. In addition, confocal microscopy analysis allowed us to follow the fate of EGFP conjugated α5β1 integrin and 17b FITC-conjugated (compound 31) inside the cells. Moreover, the stability in water solution at different values of pH and in bovine serum confirmed the possible exploitation of these peptidomimetic molecules for pharmaceutical application.

Unifying principles of bifunctional, proximity-inducing small molecules

Nature uses a variety of tools to mediate the flow of information in cells, many of which control distances between key biomacromolecules. Researchers have thus generated compounds whose activities stem from interactions with two (or more) proteins simultaneously. In this Perspective, we describe how these 'bifunctional' small molecules facilitate the study of an increasingly wide range of complex biological phenomena and enable the drugging of otherwise challenging therapeutic targets and processes. Despite their structural and functional differences, all bifunctional molecules employ Nature's strategy of altering interactomes and inducing proximity to modulate biology. They therefore exhibit a shared set of chemical and biophysical principles that have not yet been appreciated fully. By highlighting these commonalities-and their wide-ranging consequences-we hope to chip away at the artificial barriers that threaten to constrain this interdisciplinary field. Doing so promises to yield remarkable benefits for biological research and therapeutics discovery.

Fc-binding antibody-recruiting molecules exploit endogenous antibodies for anti-tumor immune responses

Redirecting endogenous antibodies in the bloodstream to tumor cells using synthetic molecules is a promising approach to trigger anti-tumor immune responses. However, current molecular designs only enable the use of a small fraction of endogenous antibodies, limiting the therapeutic potential. Here, we report Fc-binding antibody-recruiting molecules (Fc-ARMs) as the first example addressing this issue. Fc-ARMs are composed of an Fc-binding peptide and a targeting ligand, enabling the exploitation of endogenous antibodies through constant affinity to the Fc region of antibodies, whose sequence is conserved in contrast to the Fab region. We show that Fc-ARM targeting folate receptor-α (FR-α) redirects a clinically used antibody mixture to FR-α⁺ cancer cells, resulting in cancer cell lysis by natural killer cells in vitro. Fc-ARMs successfully interacted with antibodies in vivo and accumulated in tumors. Furthermore, Fc-ARMs recruited antibodies to suppress tumor growth in a mouse model. Thus, Fc-ARMs have the potential to be a novel class of cancer immunotherapeutic agents.

Fc-binding antibody-recruiting molecules provide robust and sufficient opportunities to employ endogenous antibodies for anti-tumor immune responses.

Antibody-recruiting protein-catalyzed capture agents to combat antibiotic-resistant bacteria

Antibiotic resistant infections are projected to cause over 10 million deaths by 2050, yet the development of new antibiotics has slowed. This points to an urgent need for methodologies for the rapid development of antibiotics against emerging drug resistant pathogens. We report on a generalizable combined computational and synthetic approach, called antibody-recruiting protein-catalyzed capture agents (AR-PCCs), to address this challenge. We applied the combinatorial protein catalyzed capture agent (PCC) technology to identify macrocyclic peptide ligands against highly conserved surface protein epitopes of carbapenem-resistant Klebsiella pneumoniae, an opportunistic Gram-negative pathogen with drug resistant strains. Multi-omic data combined with bioinformatic analyses identified epitopes of the highly expressed MrkA surface protein of K. pneumoniae for targeting in PCC screens. The top-performing ligand exhibited high-affinity (EC₅₀ ∼50 nM) to full-length MrkA, and selectively bound to MrkA-expressing K. pneumoniae, but not to other pathogenic bacterial species. AR-PCCs that bear a hapten moiety promoted antibody recruitment to K. pneumoniae, leading to enhanced phagocytosis and phagocytic killing by macrophages. The rapid development of this highly targeted antibiotic implies that the integrated computational and synthetic toolkit described here can be used for the accelerated production of antibiotics against drug resistant bacteria.