Multifunctional Glycoconjugates for Recruiting Natural Antibodies against Cancer Cells

Lysosomal Trafficking and Degradation of Extracellular Proteins via Multivalent Small Molecule Ligand Display on Dextran Scaffolds

Targeted protein degradation (TPD) marks a shift in drug development from conventional inhibition to the complete removal of pathological proteins. Traditional TPD technologies target intracellular proteins of interest (POIs) for degradation but are ineffective against extracellular cell surface and soluble proteins, a significant portion of the human proteome. Recent advances involve the formation of ternary complexes between a POI and a cell surface lysosomal trafficking receptor, directing POIs to lysosomes for degradation. We report on DEXtran TRAfficking Chimeras (DEXTRACs) comprising multiple copies of synthetic small molecule ligands for a model POI and the cation-independent mannose-6-phosphate receptor (CI-M6PR) lysosomal trafficking receptor. These ligands are arranged along the dextran backbones. We demonstrate that DEXTRACs leverage multivalency with their efficacy dependent on the dextran chain length and ligand density to form high-avidity ternary complexes. Our in vitro studies confirmed that DEXTRACs traffic the target POI to lysosomes and facilitate its degradation.

Exploration of Solid Phase Peptoid Synthesis for the Design of Trifunctional Hapten-Lipid-TLR7/8 Agonist Antibody-Recruiting Oligomers That Combine Innate Effector with Innate Activation Function

The strategic engagement of innate immunity is a promising avenue for cancer treatment. Antibody-recruiting molecules (ARMs) direct endogenous antibodies to target tumor sites, eliciting innate immune effector killing responses. In this study, we report the synthesis of ARMs by employing solid-phase peptoid synthesis to construct three libraries of antibody-recruiting oligomers. Using dinitrophenyl (DNP) as a model hapten and alkyl lipid chains for cell surface anchoring, we tailored oligomers with variations in valency and spatial configuration. Among these, an oligomer design featuring DNP connected to the oligomer backbone through an extended PEG linker and flanked by two lipid motifs emerged as the most effective in antibody recruitment in vitro. This oligomer was further functionalized to include an imidazoquinoline, creating a trifunctional hapten-lipid-TLR7/8 agonist oligomer, and a parallel variant was conjugated with rhodamine, resulting in a trifunctional hapten-lipid-dye oligomer. Upon intratumorally administration in a murine model, these oligomers induced localized immune activation within tumors. Subsequent ex vivo analysis of single-cell suspensions from excised tumors confirmed the enhanced binding of anti-DNP antibodies. These findings underscore the potential of custom-designed ARMs in orchestrating precise immune-mediated tumor targeting and highlight the adaptability of solid-phase synthesis in oligomer design for the design of multifunctional antibody recruiting molecules.

Monophosphoryl Lipid A-Rhamnose Conjugates as a New Class of Vaccine Adjuvants

Adjuvant is an integral part of all vaccine formulations but only a few adjuvants with limited efficacies or application scopes are available. Thus, developing more robust and diverse adjuvants is necessary. To this end, a new class of adjuvants having α- and β-rhamnose (Rha) attached to the 1- and 6'-positions of monophosphoryl lipid A (MPLA) was designed, synthesized, and immunologically evaluated in mice. The results indicated a synergistic effect of MPLA and Rha, two immunostimulators that function via interacting with toll-like receptor 4 and recruiting endogenous anti-Rha antibodies, respectively. All the tested MPLA-Rha conjugates exhibited potent adjuvant activities to promote antibody production against both protein and carbohydrate antigens. Overall, MPLA-α-Rha exhibited better activities than MPLA-β-Rha, and 6'-linked conjugates were slightly better than 1-linked ones. Particularly, MPLA-1-α-Rha and MPLA-6'-α-Rha were the most effective adjuvants in promoting IgG antibody responses against protein antigen keyhole limpet hemocyanin and carbohydrate antigen sTn, respectively.

Multivalent Rhamnose-Modified EGFR-Targeting Nanobody Gains Enhanced Innate Fc Effector Immunity and Overcomes Cetuximab Resistance via Recruitment of Endogenous Antibodies

Cetuximab resistance is a significant challenge in cancer treatment, requiring the development of novel therapeutic strategies. In this study, a series of multivalent rhamnose (Rha)-modified nanobody conjugates are synthesized and their antitumor activities and their potential to overcome cetuximab resistance are investigated. Structure-activity relationship studies reveal that the multivalent conjugate D5, bearing sixteen Rha haptens, elicits the most potent innate fragment crystallizable (Fc) effector immunity in vitro and exhibits an excellent in vivo pharmacokinetics by recruiting endogenous antibodies. Notably, it is found that the optimal conjugate D5 represents a novel entity capable of reversing cetuximab-resistance induced by serine protease (PRSS). Moreover, in a xenograft mouse model, conjugate D5 exhibits significantly improved antitumor efficacy compared to unmodified nanobodies and cetuximab. The findings suggest that Rha-Nanobody (Nb) conjugates hold promise as a novel therapeutic strategy for the treatment of cetuximab-resistant tumors by enhancing the innate Fc effector immunity and enhancing the recruitment of endogenous antibodies to promote cancer cell clearance by innate immune cells.

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.

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.

Tunable Multivalent Platform for Immune Recruitment to Lower Antigen Expressing Cancers

Chemical immunotherapeutic strategies including Antibody Recruiting Molecules (ARMs - bivalent small molecules containing an antibody-binding domain (ABD) and a target-binding domain (TBD)) direct immune-mediated clearance of diseased cells. Anti-cancer ARM function relies on high tumor antigen valency, limiting function against lower antigen expressing tumors. To address this limitation, we report a tunable multivalent immune recruitment (MIR) platform to amplify/stabilize antibody recruitment to cells with lower antigen valencies. An initial set of polymeric ARMs (pARMs) were synthesized and screened to evaluate ABD/TBD copy number, ratio, and steric occlusion on specific immune induction. Most pARMs demonstrated simultaneous high avidity binding to anti-dinitrophenyl antibodies and prostate-specific membrane antigens on prostate cancer. Optimized pARMs mediated enhanced anti-cancer immune function against lower antigen expressing target cells compared to an analogous ARM.

Multimeric RGD-Based Strategies for Selective Drug Delivery to Tumor Tissues

RGD peptides have received a lot of attention over the two last decades, in particular to improve tumor therapy through the targeting of the αVβ3 integrin receptor. This review focuses on the molecular design of multimeric RGD compounds, as well as the design of suitable linkers for drug delivery. Many examples of RGD-drug conjugates have been developed, and we show the importance of RGD constructs to enhance binding affinity to tumor cells, as well as their drug uptake. Further, we also highlight the use of RGD peptides as theranostic systems, promising tools offering dual modality, such as tumor diagnosis and therapy. In conclusion, we address the challenging issues, as well as ongoing and future development, in comparison with large molecules, such as monoclonal antibodies.

Aza-Michael promoted glycoconjugation of PETIM dendrimers and selectivity in mycobacterial growth inhibitions

The benign nature of aza-Michael addition reaction in aqueous solutions is demonstrated herein to conduct a direct glycoconjugation of amine-terminated poly(ether imine) (PETIM) dendrimers. Zero to three generations of dendrimers, possessing up to 16 amine functionalities at their peripheries, undergo aza-Michael reaction with unsaturated sugar vinyl sulfoxide in aq. MeOH solutions and afford the corresponding dendrimers modified with multiple glycosyl moieties at the periphery. First order kinetics of the glycoconjugation is monitored at varying temperatures and the rate constants are observed to be 60-508 s-1, for zero and first generation dendrimers. The antibacterial effects of amine-terminated dendrimers and the corresponding glycoconjugates are studied across Gram-positive, Gram-negative and acid-fast bacteria. Among the species, M. smegmatis and M. tuberculosis showed the greatest growth inhibition effect at micromolar concentrations, for the native amine-terminated and the corresponding glycoconjugated dendrimers. Quantitative assays are performed to adjudge the inhibition efficacies of dendrimers and the glycoconjugates. Selectivity to inhibit M. smegmatis and M. tuberculosis growth, and minimal effects on other bacterial species by dendrimers and glycoconjugates are emphasized.

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.

Repurposing the Pentameric B-subunit of Shiga Toxin for Gb3-targeted Immunotherapy of Colorectal Cancer by Rhamnose Conjugation

Globotriaosylceramide (Gb3 or CD77) is a tumor-associated carbohydrate antigen implicated in several types of cancer that serves as a potential cancer marker for developing target-specific diagnosis and therapy. However, the development of Gb3-targeted therapeutics has been challenging due to its carbohydrate nature. In the present work, taking advantage of its natural pentamer architecture and Gb3-specific targeting of shiga toxin B subunit (StxB), we constructed a pentameric antibody recruiting chimera by site-specifically conjugating StxB with the rhamnose hapten for immunotherapy of colorectal cancer. The Sortase A-catalyzed enzymatic tethering of rhamnose moieties to the C terminus of Stx1B and Stx2B had very moderate effect on their pentamer architectures and thus the resultant conjugates maintained the potent ability to bind to Gb3 antigen both immobilized on an assay plate and expressed on colorectal cancer cells. All StxB-rhamnose constructs were capable of efficiently mediating the binding of rhamnose antibodies onto HT29 colorectal cancer cells, which was further shown to be able to induce cancer cell lysis by eliciting potent antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) in vitro. Finally, the best StxB-rhamnose conjugate, i.e. 1B-3R, was confirmed to be able to inhibit the colorectal tumor growth using a HT29-derived xenograft murine model. Taken together, our data demonstrated the potential of repurposing StxB as an excellent multivalent scaffold for developing Gb3-targeted biotherapeutics and StxB-rhamnose conjugates might be promising candidates for targeted immunotherapy of Gb3-related colorectal cancer.

Pioglitazone-Loaded PLGA Nanoparticles: Towards the Most Reliable Synthesis Method

Recent findings have proved the benefits of Pioglitazone (PGZ) against atherosclerosis and type 2 diabetes. Since the systematic and controllable release of this drug is of significant importance, encapsulation of this drug in nanoparticles (NPs) can minimize uncontrolled issues. In this context, drug delivery approaches based on several poly(lactic-co-glycolic acid) (PLGA) nanoparticles have been rising in popularity due to their promising capabilities. However, a fully reliable and reproducible synthetic methodology is still lacking. In this work, we present a rational optimization of the most critical formulation parameters for the production of PGZ-loaded PLGA NPs by the single emulsification-solvent evaporation or nanoprecipitation methods. We examined the influence of several variables (e.g., component concentrations, phases ratio, injection flux rate) on the synthesis of the PGZ-NPs. In addition, a comparison of these synthetic methodologies in terms of nanoparticle size, polydispersity index (PDI), zeta potential (ζp), drug loading (DL%), entrapment efficiency (EE%), and stability is offered. According to the higher entrapment efficiency content, enhanced storage time and suitable particle size, the nanoprecipitation approach appears to be the simplest, most rapid and most reliable synthetic pathway for these drug nanocarriers, and we demonstrated a very slow drug release in PBS for the best formulation obtained by this synthesis.

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.

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.

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.

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.

One pot synthesis of thio-glycosides via aziridine opening reactions

thio-Glycosides with a pseudo-disaccharide structure are synthesized via aziridine opening reactions starting from glycosyl thioacetates with a one-pot protocol, which affords glycomimetics equipped for easy and stable conjugation to aglycones.

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.

Multimeric Presentation of RGD Peptidomimetics Enhances Integrin Binding and Tumor Cell Uptake

The use of multimeric ligands is considered as a promising strategy to improve tumor targeting for diagnosis and therapy. Herein, tetrameric RGD (Arg-Gly-Asp) peptidomimetics were designed to target α_v β₃ integrin-expressing tumor cells. These compounds were prepared by an oxime chemoselective assembly of cyclo(DKP-RGD) ligands and a cyclodecapeptide scaffold, which allows a tetrameric presentation. The resulting tetrameric RGD peptidomimetics were shown to improve α_v β₃ integrin binding compared with the monomeric form. Interestingly, these compounds were also able to enhance tumor cell endocytosis in the same way as tetrameric RGD peptides. Altogether, the results show the potential of the tetrameric cyclo(DKP-RGD) ligands for in vivo imaging and drug delivery.

Multifunctional Glycoconjugates for Recruiting Natural Antibodies against Cancer Cells

We have developed a fully synthetic and multifunctional antibody-recruiting molecule (ARM) to guide natural antibodies already present in the blood stream against cancer cells without pre-immunization. Our ARM is composed of antibody and tumor binding modules (i.e., ABM and TBM) displaying clustered rhamnose and cyclo-RGD, respectively. By using a stepwise approach, we have first demonstrated the importance of multivalency for efficient recognition with naturel IgM and αv β3 integrin expressing M21 tumor cell line. Once covalently conjugated by click chemistry, we confirmed by flow cytometry and confocal microscopy that the recognition properties of both the ABM and TBM are conserved, and more importantly, that the resulting ARM promotes the formation of a ternary complex between natural IgM and cancer cells, which is required for the stimulation of the cytotoxic immune response in vivo. Due to the efficiency of the synthetic process, a larger diversity of heterovalent ligands could be easily explored by using the same multivalent approach and could open new perspectives in this field.