Multivalency as a Chemical Organization and Action Principle

Cooperative assembly of H-bonded rosettes inside a porphyrin nanoring

The melamine·barbiturate H-bonded rosette motif is of comparable dimensions and symmetry to the cavity of a butadiyne-linked 6-porphyrin nanoring. Functionalisation of each of the barbiturate components and the pyrimidine components of a H-bonded rosette with a pyridine ligand leads to a self-assembled hexapyridine ligand, which binds cooperatively to the zinc porphyrin nanoring. UV-vis-NIR and ¹H NMR experiments show that the 7-component assembly forms at concentrations at which neither the H-bonding interactions nor the zinc porphyrin–pyridine interactions are formed in the absence of one of the three components. The mean effective molarities of these rosette complexes are around 200 mM in chloroform at 298 K.

Mixing barbiturates and pyrimidines equipped with pyridine ligands to leads to self-assembly of a hexadentate rosette ligand, which is complementary to a hexameric zinc porphyrin macrocycle.

Selective recognition of ATP by multivalent nano-assemblies of bisimidazolium amphiphiles through "turn-on" fluorescence response

Bisimidazolium receptors, tagged with chromophoric pyrene at one end and linked to an n-alkyl chain at the other, underwent self-assembly in aqueous media depending on the length of the alkyl segment. The amphiphilic derivatives having n-decyl or longer chains, formed nano-assemblies with cyanic-green emission resulting from the stacked pyrene chromophores in the aggregates. The presence of positive surface charges on the multivalent aggregates led to ATP binding which was accompanied by a significant increase in the excimeric emission intensity. This provided a convenient way of monitoring ATP binding in a "turn-on" mode and an efficient detection of ATP was achieved in aqueous buffer and also in buffer containing 150 mM NaCl at physiological pH value. Furthermore, the multivalent aggregates demonstrated a significant selectivity in ATP detection over ADP, AMP and pyrophosphate.

Conjugation of biphenyl groups with poly(ethylene glycol) to enhance inhibitory effects on the PD-1/PD-L1 immune checkpoint interaction

Monoclonal antibodies have been developed as anticancer agents to block immune checkpoint pathways associated with programmed cell death 1 (PD-1) and its ligand PD-L1. However, the high cost of antibodies has encouraged researchers to develop other inhibitor types. Here, biphenyl compounds were conjugated with poly(ethylene glycol) (PEG) to enhance the activity of small molecular inhibitors. Immunoassay results revealed the decrease in the inhibition activity following conjugation with linear PEG, suggesting that the PEG moiety reduced the interaction between the biphenyl structure and PD-L1. However, the inhibitory effect on PD-1/PD-L1 interaction was further enhanced by using branched PEG conjugates. The increase in the number of conjugated biphenyl compounds resulted in increased inhibitory activity. The highest IC50 value was 0.33 μM, which was about 5 times higher than that observed for a non-conjugated monovalent compound. The inhibitory activity was more than 20 times the activity reported for the starting compound. Considering the increase in the inhibition activity, this multivalent strategy can be useful in the design of new immune checkpoint inhibitors.

Rational Design of a DNA-Scaffolded High-Affinity Binder for Langerin

Binders of langerin could target vaccines to Langerhans cells for improved therapeutic effect. Since langerin has low affinity for monovalent glycan ligands, highly multivalent presentation has previously been key for targeting. Aiming to reduce the amount of ligand required, we rationally designed molecularly defined high-affinity binders based on the precise display of glycomimetic ligands (Glc2NTs) on DNA-PNA scaffolds. Rather than mimicking langerin's homotrimeric structure with a C3-symmetric scaffold, we developed readily accessible, easy-to-design bivalent binders. The method considers the requirements for bridging sugar binding sites and statistical rebinding as a means to both strengthen the interactions at single binding sites and amplify the avidity enhancement provided by chelation. This gave a 1150-fold net improvement over the affinity of the free ligand and provided a nanomolar binder (IC50 =300 nM) for specific internalization by langerin-expressing cells.

Say no to drugs: Bioactive macromolecular therapeutics without conventional drugs

The vast majority of nanomedicines (NM) investigated today consists of a macromolecular carrier and a drug payload (conjugated or encapsulated), with a purpose of preferential delivery of the drug to the desired site of action, either through passive accumulation, or by active targeting via ligand-receptor interaction. Several drug delivery systems (DDS) have already been approved for clinical use. However, recent reports are corroborating the notion that NM do not necessarily need to include a drug payload, but can exert biological effects through specific binding/blocking of important target proteins at the site of action. The seminal work of Kopeček et al. on N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers containing biorecognition motifs (peptides or oligonucleotides) for crosslinking cell surface non-internalizing receptors of malignant cells and inducing their apoptosis, without containing any low molecular weight drug, led to the definition of a special group of NM, termed Drug-Free Macromolecular Therapeutics (DFMT). Systems utilizing this approach are typically designed to employ pendant targeting-ligands on the same macromolecule to facilitate multivalent interactions with receptors. The lack of conventional small molecule drugs reduces toxicity and adverse effects at off-target sites. In this review, we describe different types of DFMT that possess biological activity without attached low molecular weight drugs. We classified the relevant research into several groups by their mechanisms of action, and compare the advantages and disadvantages of these different approaches. We show that identification of target sites, specificity of attached targeting ligands, binding affinity and the synthesis of carriers of defined size and ligand spacing are crucial aspects of DFMT development. We further discuss how knowledge in the field of NM accumulated in the past few decades can help in the design of a successful DFMT to speed up the translation into clinical practice.

Dimeric and Multimeric DNA Aptamers for Highly Effective Protein Recognition

Multivalent interactions frequently occur in biological systems and typically provide higher binding affinity and selectivity in target recognition than when only monovalent interactions are operative. Thus, taking inspiration by nature, bivalent or multivalent nucleic acid aptamers recognizing a specific biological target have been extensively studied in the last decades. Indeed, oligonucleotide-based aptamers are suitable building blocks for the development of highly efficient multivalent systems since they can be easily modified and assembled exploiting proper connecting linkers of different nature. Thus, substantial research efforts have been put in the construction of dimeric/multimeric versions of effective aptamers with various degrees of success in target binding affinity or therapeutic activity enhancement. The present review summarizes recent advances in the design and development of dimeric and multimeric DNA-based aptamers, including those forming G-quadruplex (G4) structures, recognizing different key proteins in relevant pathological processes. Most of the designed constructs have shown improved performance in terms of binding affinity or therapeutic activity as anti-inflammatory, antiviral, anticoagulant, and anticancer agents and their number is certainly bound to grow in the next future.

Optical detection of di- and triphosphate anions with mixed monolayer-protected gold nanoparticles containing zinc(II)-dipicolylamine complexes

Gold nanoparticles covered with a mixture of ligands of which one type contains solubilizing triethylene glycol residues and the other peripheral zinc(II)–dipicolylamine (DPA) complexes allowed the optical detection of hydrogenphosphate, diphosphate, and triphosphate anions in water/methanol 1:2 (v/v). These anions caused the bright red solutions of the nanoparticles to change their color because of nanoparticle aggregation followed by precipitation, whereas halides or oxoanions such as sulfate, nitrate, or carbonate produced no effect. The sensitivity of phosphate sensing depended on the nature of the anion, with diphosphate and triphosphate inducing visual changes at significantly lower concentrations than hydrogenphosphate. In addition, the sensing sensitivity was also affected by the ratio of the ligands on the nanoparticle surface, decreasing as the number of immobilized zinc(II)–dipicolylamine groups increased. A nanoparticle containing a 9:1 ratio of the solubilizing and the anion-binding ligand showed a color change at diphosphate and triphosphate concentrations as low as 10 μmol/L, for example, and precipitated at slightly higher concentrations. Hydrogenphosphate induced a nanoparticle precipitation only at a concentration of ca. 400 μmol/L, at which the precipitates formed in the presence of diphosphates and triphosphates redissolved. A nanoparticle containing fewer binding sites was more sensitive, while increasing the relative number of zinc(II)–dipicolylamine complexes beyond 25% had a negative impact on the limit of detection and the optical response. Transmission electron microscopy provided evidence that the changes of the nanoparticle properties observed in the presence of the phosphates were due to a nanoparticle crosslinking, consistent with the preferred binding mode of zinc(II)–dipicolylamine complexes with phosphate anions which involves binding of the anion between two metal centers. This work thus provided information on how the behavior of mixed monolayer-protected gold nanoparticles is affected by multivalent interactions, at the same time introducing a method to assess whether certain biologically relevant anions are present in an aqueous solution within a specific concentration range.

Mucin-Inspired, High Molecular Weight Virus Binding Inhibitors Show Biphasic Binding Behavior to Influenza A Viruses

Multivalent binding inhibitors are a promising new class of antivirals that prevent virus infections by inhibiting virus binding to cell membranes. The design of these inhibitors is challenging as many properties, for example, inhibitor size and functionalization with virus attachment factors, strongly influence the inhibition efficiency. Here, virus binding inhibitors are synthesized, the size and functionalization of which are inspired by mucins, which are naturally occurring glycosylated proteins with high molecular weight (MDa range) and interact efficiently with various viruses. Hyperbranched polyglycerols (hPGs) with molecular weights ranging between 10 and 2600 kDa are synthesized, thereby hitting the size of mucins and allowing for determining the impact of inhibitor size on the inhibition efficiency. The hPGs are functionalized with sialic acids and sulfates, as suggested from the structure of mucins, and their inhibition efficiency is determined by probing the inhibition of influenza A virus (IAV) binding to membranes using various methods. The largest, mucin-sized inhibitor shows potent inhibition at pm concentrations, while the inhibition efficiency decreases with decreasing the molecular weight. Interestingly, the concentration-dependent IAV inhibition shows a biphasic behavior, which is attributed to differences in the binding affinity of the inhibitors to the two IAV envelope proteins, neuraminidase, and hemagglutinin.

Guanidinothiosialoside-Human Serum Albumin Conjugate Mimics mucin Barrier to Restrict Influenza Infection

A guanidinothiosialoside-human serum albumin conjugate as mucin mimic was prepared via a copper-free click reaction. Matrix-Assisted Laser Desorption/Ionization-Time of Flight-Mass Spectrometry (MALDI-TOF-MS) indicated that three sialoside groups were grafted onto the protein backbone. The synthetic glycoconjugate exhibited strong influenza virion capture and trapping capability. Further mechanistic studies showed that this neomucin bound tightly to neuraminidase on the surface of influenza virus with a dissociation constant (K_D) in the nanomolar range and had potent antiviral activity against a broad spectrum of virus strains. Most notably, the glycoconjugate acted as a biobarrier was able to protect Madin-Darby canine kidney (MDCK) cells from influenza viral infection with 50% effective concentrations (EC₅₀) in the nanomolar range and showed no cytotoxicity towards Human Umbilical Vein Endothelial Cells (HUVEC) at high concentrations. This research establishes an attractive strategy for the development of new multivalent antiviral agents based on mucin structure. Moreover, the method for the functionalization of the natural biological macromolecular scaffold with bioactive small molecules also lays the experimental foundation for potential biomedical and biomaterial applications.

Distance-Dependent Cellular Uptake of Oligoproline-Based Homobivalent Ligands Targeting GPCRs-An Experimental and Computational Analysis

Tumor targeting with bivalent radiolabeled ligands for GPCRs is an attractive means for cancer imaging and therapy. Here, we studied and compared the distance dependence of homobivalent ligands for the human gastrin-releasing peptide receptor (hGRP-R) and the somatostatin receptor subtype II (hSstR_2a). Oligoprolines were utilized as molecular scaffolds to enable distances of 10, 20, or 30 Å between two identical, agonistic recognition motifs. In vitro internalization assays revealed that ligands with a distance of 20 Å between the recognition motifs exhibit the highest cellular uptake in both ligand series. Structural modeling and molecular dynamics simulations support an optimal distance of 20 Å for accommodating ligand binding to both binding sites of a GPCR dimer. Translation of these findings to the significantly higher complexity in vivo proved difficult and showed only for the hGRP-R increased tumor uptake of the bivalent ligand.

Advances in the development of entry inhibitors for sialic-acid-targeting viruses

Over the past decades, several antiviral drugs have been developed to treat a range of infections. Yet the number of treatable viral infections is still limited, and resistance to current drug regimens is an ever-growing problem. Therefore, additional strategies are needed to provide a rapid cure for infected individuals. An interesting target for antiviral drugs is the process of viral attachment and entry into the cell. Although most viruses use distinct host receptors for attachment to the target cell, some viruses share receptors, of which sialic acids are a common example. This review aims to give an update on entry inhibitors for a range of sialic-acid-targeting viruses and provides insight into the prospects for those with broad-spectrum potential.

Effect of PEGylation on Receptor Anchoring and Steric Shielding at Interfaces: An Adhesion and Surface Plasmon Resonance Study with Precision Polymers

This study aims at quantifying the steric shielding effect of multivalent glycoconjugates targeting pathogens by blocking their carbohydrate binding sites. Specifically, PEGylated and non-PEGylated glycoconjugates are studied as inhibitors of lectins and bacterial adhesins evaluating the steric repulsion effect of the nonbinding PEG chains. We use the soft colloidal probe (SCP) adhesion assay to monitor the change in the adhesion energy of mannose (Man)-decorated hydrogel particles on a layer of concanavalin A (ConA) in the presence of sequence-defined multivalent glycoconjugate inhibitors over time. The results show that PEGylated glycoconjugates achieve a stronger adhesion inhibition when compared to non-PEGylated glycoconjugates although the dissociation constants (K_D) of the PEGgylated compounds to ConA were larger. These results appear in line with Escherichia coli adhesion inhibition assays showing a small increase of bacteria detachment by PEGgylated glycoconjugates compared to non-PEGylated compounds. This suggests that an increase of sterical shielding via PEGylation may help reduce the invasiveness of pathogens even after they have adhered. Adhesion studies based on electrostatic interactions using amine-linked PEG of varying molecular weight confirm that such sterical shielding effect is not limited to carbohydrate-mediated adhesion.

No small matter: a perspective on nanotechnology-enabled solutions to fight COVID-19

There is an urgent need for safe and effective approaches to combat COVID-19. Here, we asked whether lessons learned from nanotoxicology and nanomedicine could shed light on the current pandemic. SARS-CoV-2, the causative agent, may trigger a mild, self-limiting disease with respiratory symptoms, but patients may also succumb to a life-threatening systemic disease. The host response to the virus is equally complex and studies are now beginning to unravel the immunological correlates of COVID-19. Nanotechnology can be applied for the delivery of antiviral drugs or other repurposed drugs. Moreover, recent work has shown that synthetic nanoparticles wrapped with host-derived cellular membranes may prevent virus infection. We posit that nanoparticles decorated with ACE2, the receptor for SARS-CoV-2, could be exploited as decoys to intercept the virus before it infects cells in the respiratory tract. However, close attention should be paid to biocompatibility before such nano-decoys are deployed in the clinic.

A Remarkable Fluorescence Quenching Based Amplification in ATP Detection through Signal Transduction in Self-Assembled Multivalent Aggregates

Signal transduction is essential for the survival of living organisms, because it allows them to respond to the changes in external environments. In artificial systems, signal transduction has been exploited for the highly sensitive detection of analytes. Herein, a remarkable signal transduction, upon ATP binding, in the multivalent fibrillar nanoaggregates of anthracene conjugated imidazolium receptors is reported. The aggregates of one particular amphiphilic receptor sensed ATP in high pm concentrations with one ATP molecule essentially quenching the emission of thousands of receptors. A cooperative merging of the multivalent binding and signal transduction led to this superquenching and translated to an outstanding enhancement of more than a millionfold in the sensitivity of ATP detection by the nanoaggregates; in comparison to the "molecular" imidazolium receptors. Furthermore, an exceptional selectivity to ATP over other nucleotides was demonstrated.

Combinatorial entropy behaviour leads to range selective binding in ligand-receptor interactions

From viruses to nanoparticles, constructs functionalized with multiple ligands display peculiar binding properties that only arise from multivalent effects. Using statistical mechanical modelling, we describe here how multivalency can be exploited to achieve what we dub range selectivity, that is, binding only to targets bearing a number of receptors within a specified range. We use our model to characterise the region in parameter space where one can expect range selective targeting to occur, and provide experimental support for this phenomenon. Overall, range selectivity represents a potential path to increase the targeting selectivity of multivalent constructs.

Thermally Stable Nitrothiacalixarene Chromophores: Conformational Study and Aggregation Behavior

Achieving high thermal stability and control of supramolecular organization of functional dyes in sensors and nonlinear optics remains a demanding task. This study was aimed at the evaluation of thermal behavior and Langmuir monolayer characteristics of topologically varied nitrothiacalixarene multichromophores and phenol monomers. A nitration/azo coupling alkylation synthetic route towards partially O-substituted nitrothiacalixarenes and 4-nitrophenylazo-thiacalixarenes was proposed and realized. Nuclear magnetic resonance (NMR) spectroscopy and X-ray diffractometry of disubstituted nitrothiacalix[4]arene revealed a rare 1,2-alternate conformation. A synchronous thermal analysis indicated higher decomposition temperatures of nitrothiacalixarene macrocycles as compared with monomers. Through surface pressure/potential-molecular area measurements, nitrothiacalixarenes were shown to form Langmuir monolayers at the air–water interface and, through atomic force microscopy (AFM) technique, Langmuir–Blodgett (LB) films on solid substrates. Reflection-absorption spectroscopy of monolayers and electronic absorption spectroscopy of LB films of nitrothiacalixarenes recorded a red-shifted band (290 nm) with a transition from chloroform, indicative of solvatochromism. Additionally, shoulder band at 360 nm was attributed to aggregation and supported by gas-phase density functional theory (DFT) calculations and dynamic light scattering (DLS) analysis in chloroform–methanol solvent in the case of monoalkylated calixarene 3. Excellent thermal stability and monolayer formation of nitrothiacalixarenes suggest their potential as functional dyes.

Engineering anti-cancer nanovaccine based on antigen cross-presentation

Dendritic cells (DCs) present exogenous antigens on major histocompatibility complex (MHC) class I molecules, thereby activating CD8⁺ T cells, contributing to tumor elimination through a mechanism known as antigen cross-presentation. A variety of factors such as maturation state of DCs, co-stimulatory signals, T-cell microenvironment, antigen internalization routes and adjuvants regulate the process of DC-mediated antigen cross-presentation. Recently, the development of successful cancer immunotherapies may be attributed to the ability of DCs to cross-present tumor antigens. In this review article, we focus on the underlying mechanism of antigen cross-presentation and ways to improve antigen cross-presentation in different DC subsets. We have critically summarized the recent developments in the generation of novel nanovaccines for robust CD8⁺ T-cell response in cancer. In this context, we have reviewed nanocarriers that have been used for cancer immunotherapeutics based on antigen cross-presentation mechanism. Additionally, we have also expressed our views on the future applications of this mechanism in curing cancer.

Multivalency Beats Complexity: A Study on the Cell Uptake of Carbohydrate Functionalized Nanocarriers to Dendritic Cells

Herein, we report the synthesis of carbohydrate and glycodendron structures for dendritic cell targeting, which were subsequently bound to hydroxyethyl starch (HES) nanocapsules prepared by the inverse miniemulsion technique. The uptake of the carbohydrate-functionalized HES nanocapsules into immature human dendritic cells (hDCs) revealed a strong dependence on the used carbohydrate. A multivalent mannose-terminated dendron was found to be far superior in uptake compared to the structurally more complex oligosaccharides used.

Template-Controlled Synthesis of Polyimidazolium Salts by Multiple [2+2] Cycloaddition Reactions

The tetrakisimidazolium salt H4 -2(Br)4 , featuring a central benzene linker and 1,2,4,5-(nBu-imidazolium-Ph-CH=CH-) substituents reacts with Ag2 O in the presence of AgBF4 to yield the tetranuclear, oktakis-NHC assembly [3](BF4 )4 . Cation [3]4+ features four pairs of olefins from the two tetrakis-NHC ligands perfectly arranged for a subsequent [2+2] cycloaddition. Irradiation of [3](BF4 )4 with a high pressure Hg lamp connects the two tetra-NHC ligands through four cyclobutane linkers to give compound [4](BF4 )4 . Removal of the template metals yields the novel oktakisimidazolium salt H8 -5(BF4 )8 . The tetrakisimidazolium salt H4 -2(BF4 )4 and the oktakisimidazolium salt H8 -5(BF4 )8 have been used as multivalent anion receptors and their anion binding properties towards six different anions have been compared.

Click-Free Synthesis of a Multivalent Tricyclic Peptide as a Molecular Transporter

The cellular delivery of cell-impermeable and water-insoluble molecules remains an ongoing challenge to overcome. Previously, we reported amphipathic cyclic peptides c[WR]₄ and c[WR]₅ consisting of alternate arginine and tryptophan residues as nuclear-targeting molecular transporters. These peptides contain an optimal balance of positive charge and hydrophobicity, which is required for interactions with the phospholipid bilayer to facilitate their application as a drug delivery system. To further optimize them, we synthesized and evaluated a multivalent tricyclic peptide as an efficient molecular transporter. The monomeric cyclic peptide building blocks were synthesized using Fmoc/tBu solid-phase chemistry and cyclization in the solution and conjugated with each other through an amide bond to afford the tricyclic peptide, which demonstrated modest antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA), Klebsiella pneumoniae, Pseudomonas aeruginosa, and Escherichia coli (E. coli) with a minimum inhibitory concentration (MIC) of 64–128 µg/mL. The tricyclic peptide was found to be nontoxic up to 30 µM in the breast cancer cell lines (MDA-MB-231). The presence of tricyclic peptide enhanced cellular uptakes of fluorescently-labeled phosphopeptide (F’-GpYEEI, 18-fold), anti-HIV drugs (lamivudine (F’-3TC), emtricitabine (F’-FTC), and stavudine (F’-d4T), 1.7–12-fold), and siRNA (3.3-fold) in the MDA-MB-231 cell lines.

GE11 peptide-installed chimaeric polymersomes tailor-made for high-efficiency EGFR-targeted protein therapy of orthotopic hepatocellular carcinoma

Hepatocellular carcinoma (HCC) remains a leading malignancy with a high mortality and little improvement in treatments. Protein drugs though known for their extraordinary potency and specificity have rarely been investigated for HCC therapy owing to lack of appropriate delivery systems. Here, we designed GE11 peptide-installed chimaeric polymersomes (GE11-CPs) for high-efficiency EGFR-targeted protein therapy of orthotopic SMMC-7721 HCC-bearing nude mice. GE11-CPs were assembled from poly(ethylene glycol)-b-poly(trimethylene carbonate-co-dithiolane trimethylene carbonate)-b-poly(aspartic acid) (PEG-P(TMC-DTC)-PAsp) and GE11-functionalized PEG-P(TMC-DTC), which allowed efficient loading and protection of proteins in the watery interior and fine-tuning of GE11 densities at the surface. CPs with short PAsp segments (degree of polymerization (DP) = 5, 10 and 15) exhibited a protein loading efficiency of 60%-72% and glutathione-responsive protein release. Saporin-loaded GE11-CPs had a size of 36 - 62 nm depending on GE11 densities and DP of PAsp. Notably, GE11-CPs with 10% GE11 revealed greatly enhanced uptake in SMMC-7721 cells, boosting the anticancer potency of saporin for over 3-folds compared with non-targeted control (half-maximal inhibitory concentration (IC₅₀) = 11.0 versus 36.3 nM). The biodistribution studies using Cy5-labeled cytochrome C as a model protein demonstrated about 3-fold higher accumulation of GE11-CPs formulation than CPs counterpart in both subcutaneous and orthotopic SMMC-7721 tumor models. Notably, saporin-loaded GE11-CPs revealed low toxicity, effective tumor inhibition and significant improvement of survival rate compared with PBS and non-targeted groups (median survival time: 99 versus 37 and 42 days). EGFR-targeted chimaeric polymersomes carrying proteins appear an interesting HCC treatment modality.

Multivalent weak interactions enhance selectivity of interparticle binding

The selectivity of binding of colloidal particles is an important research topic for the field of targeted drug delivery. Extensive theoretical work has shown that high selectivity can be obtained by using multivalent weak interactions. Here we provide comprehensive experimental proof using DNA-coated particles. The ligand–receptor affinity is varied by changing the number of complementary bases, showing that fewer complementary bases yield a higher binding selectivity. The experimental data and corresponding numerical model simulations demonstrate the scaling behavior between molecular density, molecular affinity, and resulting density selectivity of interparticle binding. These results are important for the design of novel systems for targeted nanoparticle drug delivery.

Targeted drug delivery critically depends on the binding selectivity of cargo-transporting colloidal particles. Extensive theoretical work has shown that two factors are necessary to achieve high selectivity for a threshold receptor density: multivalency and weak interactions. Here, we study a model system of DNA-coated particles with multivalent and weak interactions that mimics ligand–receptor interactions between particles and cells. Using an optomagnetic cluster experiment, particle aggregation rates are measured as a function of ligand and receptor densities. The measured aggregation rates show that the binding becomes more selective for shorter DNA ligand–receptor pairs, proving that multivalent weak interactions lead to enhanced selectivity in interparticle binding. Simulations confirm the experimental findings and show the role of ligand–receptor dissociation in the selectivity of the weak multivalent binding.

Functional Nanoassemblies of Cyclic Polymers Show Amplified Responsiveness and Enhanced Protein-Binding Ability

The physicochemical properties of cyclic polymer adsorbates are significantly influenced by the steric and conformational constraints introduced during their cyclization. These translate into a marked difference in interfacial properties between cyclic polymers and their linear counterparts when they are grafted onto surfaces yielding nanoassemblies or polymer brushes. This difference is particularly clear in the case of cyclic polymer brushes that are designed to chemically interact with the surrounding environment, for instance, by associating with biological components present in the medium, or, alternatively, through a response to a chemical stimulus by a significant change in their properties. The intrinsic architecture characterizing cyclic poly(2-oxazoline)-based polyacid brushes leads to a broad variation in swelling and nanomechanical properties in response to pH change, in comparison with their linear analogues of identical composition and molecular weight. In addition, cyclic glycopolymer brushes derived from polyacids reveal an enhanced exposure of galactose units at the surface, due to their expanded topology, and thus display an increased lectin-binding ability with respect to their linear counterparts. This combination of amplified responsiveness and augmented protein-binding capacity renders cyclic brushes invaluable building blocks for the design of "smart" materials and functional biointerfaces.

Selective Promotion of Adhesion of Shewanella oneidensis on Mannose-Decorated Glycopolymer Surfaces

Using glycopolymer surfaces, we have stimulated Shewanella oneidensis bacterial colonization and induced where the bacteria attach on a molecular pattern. When adherent bacteria were rinsed with methyl α-d-mannopyranoside, the glycopolymer-functionalized surfaces retained more cells than self-assembled monolayers terminated by a single mannose unit. These results suggest that the three-dimensional multivalency of the glycopolymers both promotes and retains bacterial attachment. When the methyl α-d-mannopyranoside competitor was codeposited with the cell culture, however, the mannose-based polymer was not significantly different from bare gold surfaces. The necessity for equilibration between methyl α-d-mannopyranoside and the cell culture to remove the enhancement suggests that the retention of cells on glycopolymer surfaces is kinetically controlled and is not a thermodynamic result of the cluster glycoside effect. The MshA lectin appears to facilitate the improved adhesion observed. Our findings that the surfaces studied here can induce stable initial attachment and influence the ratio of bacterial strains on the surface may be applied to harness useful microbial communities.

Endosomal Organization of CpG Constructs Correlates with Enhanced Immune Activation

This Letter describes how the endosomal organization of immunostimulatory nanoconstructs can tune the in vitro activation of macrophages. Nanoconstructs composed of gold nanoparticles conjugated with unmethylated cytosine-phosphate-guanine (CpG) oligonucleotides have distinct endosomal distributions depending on the surface curvature. Mixed-curvature constructs produce a relatively high percentage of hollow endosomes, where constructs accumulated primarily along the interior edges. These constructs achieved a higher level of toll-like receptor (TLR) 9 activation along with the enhanced secretion of proinflammatory cytokines and chemokines compared to constant-curvature constructs that aggregated mostly in the center of the endosomes. Our results underscore the importance of intraendosomal interactions in regulating immune responses and targeted delivery.

On-Chip Neo-Glycopeptide Synthesis for Multivalent Glycan Presentation

Single glycan-protein interactions are often weak, such that glycan binding partners commonly utilize multiple, spatially defined binding sites to enhance binding avidity and specificity. Current array technologies usually neglect defined multivalent display. Laser-based array synthesis technology allows for flexible and rapid on-surface synthesis of different peptides. By combining this technique with click chemistry, neo-glycopeptides were produced directly on a functionalized glass slide in the microarray format. Density and spatial distribution of carbohydrates can be tuned, resulting in well-defined glycan structures for multivalent display. The two lectins concanavalin A and langerin were probed with different glycans on multivalent scaffolds, revealing strong spacing-, density-, and ligand-dependent binding. In addition, we could also measure the surface dissociation constant. This approach allows for a rapid generation, screening, and optimization of a multitude of multivalent scaffolds for glycan binding.

Accelerated trypsin autolysis by affinity polymer templates

Self-cleavage of proteins is an important natural process that is difficult to control externally. Recently a new mechanism for the accelerated autolysis of trypsin was discovered involving polyanionic template polymers; however it relies on unspecific interactions and is inactive at elevated salt loads. We have now developed affinity copolymers that bind to the surface of proteases by specific recognition of selected amino acid residues. These are highly efficient trypsin inhibitors with low nanomolar IC50 levels and operate at physiological conditions. In this manuscript we show how these affinity copolymers employ the new mechanism of polymer-assisted self-digest (PAS) and act as a template for multiple protease molecules. Their elevated local concentration leads to accelerated autolysis on the accessible surface area and shields complexed areas. The resulting extremely efficient trypsin inhibition was studied by SDS-PAGE, gel filtration, CD, CZE and ESI-MS. We also present a simple theoretical model that simulates most experimental findings and confirms them as a result of multivalency and efficient reversible templating. For the first time, mass spectrometric kinetic analysis of the released peptide fragments gives deeper insight into the underlying mechanism and reveals that polymer-bound trypsin cleaves much more rapidly with low specificity at predominantly uncomplexed surface areas.

The Convergence of Extracellular Vesicle and GPCR Biology

Transmembrane receptors, of which G protein-coupled receptors (GPCRs) constitute the largest group, typically act as cellular antennae that reside at the plasma membrane (PM) to collect and interpret information from the extracellular environment. The discovery of cell-released extracellular vesicles (EVs) has added a new dimension to intercellular communication. These unique nanocarriers reflect cellular topology and can systemically transport functionally competent transmembrane receptors, ligands, and a cargo of signal proteins. Recent developments hint at roles for GPCRs in the EV life cycle and, conversely, at roles for EVs in GPCR signal transduction. We highlight key points of convergence, discuss their relevance to current GPCR and EV paradigms, and speculate on how this intersection could lend itself to future therapeutic avenues.

Adaptive Flexible Sialylated Nanogels as Highly Potent Influenza A Virus Inhibitors

Flexible multivalent 3D nanosystems that can deform and adapt onto the virus surface via specific ligand-receptor multivalent interactions can efficiently block virus adhesion onto the cell. We here report on the synthesis of a 250 nm sized flexible sialylated nanogel that adapts onto the influenza A virus (IAV) surface via multivalent binding of its sialic acid (SA) residues with hemagglutinin spike proteins on the virus surface. We could demonstrate that the high flexibility of sialylated nanogel improves IAV inhibition by 400 times as compared to a rigid sialylated nanogel in the hemagglutination inhibition assay. The flexible sialylated nanogel efficiently inhibits the influenza A/X31 (H3N2) infection with IC50 values in low picomolar concentrations and also blocks the virus entry into MDCK-II cells.

Barcoded DNA origami structures for multiplexed optimization and enrichment of DNA-based protein-binding cavities

Simultaneous binding of molecules by multiple binding partners is known to strongly reduce the apparent dissociation constant of the corresponding molecular complexes, and can be used to achieve strong, non-covalent molecular interactions. Based on this principle, efficient binding of proteins to DNA nanostructures has been achieved previously by placing several aptamers in close proximity to each other onto DNA scaffolds. Here, we develop an approach for exploring design parameters, such as the geometric arrangement or the nanomechanical properties of the binding sites, that use two-dimensional DNA origami-based nanocavities that bear aptamers with known mechanical properties at defined distances and orientations. The origami structures are labelled with barcodes, which enables large numbers of binding cavities to be investigated in parallel and under identical conditions, and facilitates a direct and reliable quantitative comparison of their binding yields. We demonstrate that binding geometry and mechanical properties have a dramatic effect on origami-based multivalent binding sites, and that optimization of linker spacings and flexibilities can improve the effective binding strength of the sites substantially.

Toward Nanotechnology-Enabled Approaches against the COVID-19 Pandemic

The COVID-19 outbreak has fueled a global demand for effective diagnosis and treatment as well as mitigation of the spread of infection, all through large-scale approaches such as specific alternative antiviral methods and classical disinfection protocols. Based on an abundance of engineered materials identifiable by their useful physicochemical properties through versatile chemical functionalization, nanotechnology offers a number of approaches to cope with this emergency. Here, through a multidisciplinary Perspective encompassing diverse fields such as virology, biology, medicine, engineering, chemistry, materials science, and computational science, we outline how nanotechnology-based strategies can support the fight against COVID-19, as well as infectious diseases in general, including future pandemics. Considering what we know so far about the life cycle of the virus, we envision key steps where nanotechnology could counter the disease. First, nanoparticles (NPs) can offer alternative methods to classical disinfection protocols used in healthcare settings, thanks to their intrinsic antipathogenic properties and/or their ability to inactivate viruses, bacteria, fungi, or yeasts either photothermally or via photocatalysis-induced reactive oxygen species (ROS) generation. Nanotechnology tools to inactivate SARS-CoV-2 in patients could also be explored. In this case, nanomaterials could be used to deliver drugs to the pulmonary system to inhibit interaction between angiotensin-converting enzyme 2 (ACE2) receptors and viral S protein. Moreover, the concept of "nanoimmunity by design" can help us to design materials for immune modulation, either stimulating or suppressing the immune response, which would find applications in the context of vaccine development for SARS-CoV-2 or in counteracting the cytokine storm, respectively. In addition to disease prevention and therapeutic potential, nanotechnology has important roles in diagnostics, with potential to support the development of simple, fast, and cost-effective nanotechnology-based assays to monitor the presence of SARS-CoV-2 and related biomarkers. In summary, nanotechnology is critical in counteracting COVID-19 and will be vital when preparing for future pandemics.

Selectins-The Two Dr. Jekyll and Mr. Hyde Faces of Adhesion Molecules-A Review

Selectins belong to a group of adhesion molecules that fulfill an essential role in immune and inflammatory responses and tissue healing. Selectins are glycoproteins that decode the information carried by glycan structures, and non-covalent interactions of selectins with these glycan structures mediate biological processes. The sialylated and fucosylated tetrasaccharide sLe^x is an essential glycan recognized by selectins. Several glycosyltransferases are responsible for the biosynthesis of the sLe^x tetrasaccharide. Selectins are involved in a sequence of interactions of circulated leukocytes with endothelial cells in the blood called the adhesion cascade. Recently, it has become evident that cancer cells utilize a similar adhesion cascade to promote metastases. However, like Dr. Jekyll and Mr. Hyde’s two faces, selectins also contribute to tissue destruction during some infections and inflammatory diseases. The most prominent function of selectins is associated with the initial stage of the leukocyte adhesion cascade, in which selectin binding enables tethering and rolling. The first adhesive event occurs through specific non-covalent interactions between selectins and their ligands, with glycans functioning as an interface between leukocytes or cancer cells and the endothelium. Targeting these interactions remains a principal strategy aimed at developing new therapies for the treatment of immune and inflammatory disorders and cancer. In this review, we will survey the significant contributions to and the current status of the understanding of the structure of selectins and the role of selectins in various biological processes. The potential of selectins and their ligands as therapeutic targets in chronic and acute inflammatory diseases and cancer will also be discussed. We will emphasize the structural characteristic of selectins and the catalytic mechanisms of glycosyltransferases involved in the biosynthesis of glycan recognition determinants. Furthermore, recent achievements in the synthesis of selectin inhibitors will be reviewed with a focus on the various strategies used for the development of glycosyltransferase inhibitors, including substrate analog inhibitors and transition state analog inhibitors, which are based on knowledge of the catalytic mechanism.

Time-resolved luminescence spectroscopy for monitoring the stability and dissolution behaviour of upconverting nanocrystals with different surface coatings

We demonstrate the potential of time-resolved luminescence spectroscopy for the straightforward assessment and in situ monitoring of the stability of upconversion nanocrystals (UCNPs). Therefore, we prepared hexagonal NaYF4:Yb3+,Er3+ UCNPs with various coatings with a focus on phosphonate ligands of different valency, using different ligand exchange procedures, and studied their dissolution behaviour in phosphate-buffered saline (PBS) dispersions at 20 °C and 37 °C with various analytical methods. The amount of the released UCNPs constituting fluoride ions was quantified by potentiometry using a fluoride ion-sensitive electrode and particle disintegration was confirmed by transmission electron microscopy studies of the differently aged UCNPs. In parallel, the luminescence features of the UCNPs were measured with special emphasis on the lifetime of the sensitizer emission to demonstrate its suitability as screening parameter for UCNP stability and changes in particle composition. The excellent correlation between the changes in luminescence lifetime and fluoride concentration highlights the potential of our luminescence lifetime method for UCNP stability screening and thereby indirect monitoring of the release of potentially hazardous fluoride ions during uptake and dissolution in biological systems. Additionally, the developed in situ optical method was used to distinguish the dissolution dynamics of differently sized and differently coated UCNPs.

Multivalent glycan arrays

Glycan microarrays have become a powerful technology to study biological processes, such as cell-cell interaction, inflammation, and infections. Yet, several challenges, especially in multivalent display, remain. In this introductory lecture we discuss the state-of-the-art glycan microarray technology, with emphasis on novel approaches to access collections of pure glycans and their immobilization on surfaces. Future directions to mimic the natural glycan presentation on an array format, as well as in situ generation of combinatorial glycan collections, are discussed.

Tuning the Brightness and Photostability of Organic Dots for Multivalent Targeted Cancer Imaging and Surgery

Specific labeling of biomarkers with bright and high photostable fluorophores is vital in fluorescent imaging applications. Here, we report a general strategy to develop single-molecule dendritic nanodots with finely tunable optical properties for in vivo fluorescent imaging. The well-defined nanodots are based on the divergent growth of biodegradable polylysine dendrimers with a fluorophore as the core. By tuning the size and surface chemistry, we obtained fluorescent nanodots with excellent brightness and photostability, favorable pharmacokinetics, and multivalent tumor-targeting capability. The nanodots provided robust, stable, long-lasting, and specific fluorescence enhancement in tumor tissue with an in situ tumor-to-normal ratio (TNR) of ∼3 and lasting over 5 days and an ex vivo TNR up to ∼17, holding considerable promise for cancer imaging and image-guided surgery. This strategy significantly improves the in vivo performance of fluorophores and can be applied to other modality imaging probes.

Nanovesicles displaying functional linear and branched oligomannose self-assembled from sequence-defined Janus glycodendrimers

Synthetic macromolecules that mimic glycolipids, named Janus glycodendrimers (JGDs), have been shown to self-assemble into nanoscale vesicles displaying glycans on their outer surface, similar to the glycocalyx coating of eukaryotic cells, bacteria, and viruses. Specifically, both linear and branched oligosaccharides synthesized by automated glycan assembly, with hydrophobic linkers, have been used to create JGDs via an isothiocyanate–amine coupling reaction. Surprisingly, in spite of the hydrophobic linker, these JGDs self-organize into nanovesicles exhibiting lamellar surface morphologies, which mimic the recognition structures of cell-surface glycans and viral glycoproteins. Therefore, they are likely to be useful in helping elucidate mechanisms of significance for translational medicine such as the camouflage functionality employed by viruses to evade recognition.

Cell surfaces are often decorated with glycoconjugates that contain linear and more complex symmetrically and asymmetrically branched carbohydrates essential for cellular recognition and communication processes. Mannose is one of the fundamental building blocks of glycans in many biological membranes. Moreover, oligomannoses are commonly found on the surface of pathogens such as bacteria and viruses as both glycolipids and glycoproteins. However, their mechanism of action is not well understood, even though this is of great potential interest for translational medicine. Sequence-defined amphiphilic Janus glycodendrimers containing simple mono- and disaccharides that mimic glycolipids are known to self-assemble into glycodendrimersomes, which in turn resemble the surface of a cell by encoding carbohydrate activity via supramolecular multivalency. The synthetic challenge of preparing Janus glycodendrimers containing more complex linear and branched glycans has so far prevented access to more realistic cell mimics. However, the present work reports the use of an isothiocyanate-amine “click”-like reaction between isothiocyanate-containing sequence-defined amphiphilic Janus dendrimers and either linear or branched oligosaccharides containing up to six monosaccharide units attached to a hydrophobic amino-pentyl linker, a construct not expected to assemble into glycodendrimersomes. Unexpectedly, these oligoMan-containing dendrimers, which have their hydrophobic linker connected via a thiourea group to the amphiphilic part of Janus glycodendrimers, self-organize into nanoscale glycodendrimersomes. Specifically, the mannose-binding lectins that best agglutinate glycodendrimersomes are those displaying hexamannose. Lamellar “raft-like” nanomorphologies on the surface of glycodendrimersomes, self-organized from these sequence-defined glycans, endow these membrane mimics with high biological activity.

Pustulan Activates Chicken Bone Marrow-Derived Dendritic Cells In Vitro and Promotes Ex Vivo CD4+ T Cell Recall Response to Infectious Bronchitis Virus

Infectious bronchitis virus (IBV) is a highly contagious avian coronavirus. IBV causes substantial worldwide economic losses in the poultry industry. Vaccination with live-attenuated viral vaccines, therefore, are of critical importance. Live-attenuated viral vaccines, however, exhibit the potential for reversion to virulence and recombination with virulent field strains. Therefore, alternatives such as subunit vaccines are needed together with the identification of suitable adjuvants, as subunit vaccines are less immunogenic than live-attenuated vaccines. Several glycan-based adjuvants directly targeting mammalian C-type lectin receptors were assessed in vitro using chicken bone marrow-derived dendritic cells (BM-DCs). The β-1-6-glucan, pustulan, induced an up-regulation of MHC class II (MHCII) cell surface expression, potentiated a strong proinflammatory cytokine response, and increased endocytosis in a cation-dependent manner. Ex vivo co-culture of peripheral blood monocytes from IBV-immunised chickens, and BM-DCs pulsed with pustulan-adjuvanted recombinant IBV N protein (rN), induced a strong recall response. Pustulan-adjuvanted rN induced a significantly higher CD4⁺ blast percentage compared to either rN, pustulan or media. However, the CD8⁺ and TCRγδ⁺ blast percentage were significantly lower with pustulan-adjuvanted rN compared to pustulan or media. Thus, pustulan enhanced the efficacy of MHCII antigen presentation, but apparently not the cross-presentation on MHCI. In conclusion, we found an immunopotentiating effect of pustulan in vitro using chicken BM-DCs. Thus, future in vivo studies might show pustulan as a promising glycan-based adjuvant for use in the poultry industry to contain the spread of coronaviridiae as well as of other avian viral pathogens.

Mesoscale computational protocols for the design of highly cooperative bivalent macromolecules

The last decade has witnessed a swiftly increasing interest in the design and production of novel multivalent molecules as powerful alternatives for conventional antibodies in the fight against cancer and infectious diseases. However, while it is widely accepted that large-scale flexibility (10–100 nm) and free/constrained dynamics (100 ns -μs) control the activity of such novel molecules, computational strategies at the mesoscale still lag behind experiments in optimizing the design of crucial features, such as the binding cooperativity (a.k.a. avidity). In this study, we introduced different coarse-grained models of a polymer-linked, two-nanobody composite molecule, with the aim of laying down the physical bases of a thorough computational drug design protocol at the mesoscale. We show that the calculation of suitable potentials of mean force allows one to apprehend the nature, range and strength of the thermodynamic forces that govern the motion of free and wall-tethered molecules. Furthermore, we develop a simple computational strategy to quantify the encounter/dissociation dynamics between the free end of a wall-tethered molecule and the surface, at the roots of binding cooperativity. This procedure allows one to pinpoint the role of internal flexibility and weak non-specific interactions on the kinetic constants of the nanobody-wall encounter and dissociation. Finally, we quantify the role and weight of rare events, which are expected to play a major role in real-life situations, such as in the immune synapse, where the binding kinetics is likely dominated by fluctuations.

Searching for Antipneumococcal Targets: Choline-Binding Modules as Phagocytosis Enhancers

Choline-binding proteins (CBPs) from Streptococcus pneumoniae comprise a family of modular polypeptides involved in essential events of this pathogen. They recognize the choline residues present in the teichoic and lipoteichoic acids of the cell wall using the so-called choline-binding modules (CBMs). The importance of CBPs in pneumococcal physiology points to them as novel targets to combat antimicrobial resistances shown by this organism. In this work we have tested the ability of exogenously added CBMs to act as CBP inhibitors by competing with the latter for the binding to the choline molecules in the bacterial surface. First, we carried out a thorough physicochemical characterization of three native CBMs, namely C-LytA, C-Cpl1, and C-CbpD, and assessed their affinity for choline and macromolecular, pneumococcal cell-wall mimics. The interaction with these substrates was evaluated by molecular modeling, analytical ultracentrifugation, surface plasmon resonance, and fluorescence and circular dichroism spectroscopies. Van't Hoff thermal analyses unveiled the existence of one noncanonical choline binding site in each of the C-Cpl1 and C-CbpD proteins, leading in total to 5 ligand-binding sites per dimer and 4 sites per monomer, respectively. Remarkably, the binding affinities of the CBMs do not directly correlate with their native oligomeric state or with the number of choline-binding sites, suggesting that choline recognition by these modules is a complex phenomenon. On the other hand, the exogenous addition of CBMs to pneumococcal planktonic cultures caused extensive cell-chaining probably as a consequence of the inhibition of CBP attachment to the cell wall. This was accompanied by bacterial aggregation and sedimentation, causing an enhancement of bacterial phagocytosis by peritoneal macrophages. In addition, the rational design of an oligomeric variant of a native CBM led to a substantial increase in its antibacterial activity by multivalency effects. These results suggest that CBMs might constitute promising nonlytic antimicrobial candidates based on the natural induction of the host defense system.

Phage capsid nanoparticles with defined ligand arrangement block influenza virus entry

Multivalent interactions at biological interfaces occur frequently in nature and mediate recognition and interactions in essential physiological processes such as cell-to-cell adhesion. Multivalency is also a key principle that allows tight binding between pathogens and host cells during the initial stages of infection. One promising approach to prevent infection is the design of synthetic or semisynthetic multivalent binders that interfere with pathogen adhesion^1-4. Here, we present a multivalent binder that is based on a spatially defined arrangement of ligands for the viral spike protein haemagglutinin of the influenza A virus. Complementary experimental and theoretical approaches demonstrate that bacteriophage capsids, which carry host cell haemagglutinin ligands in an arrangement matching the geometry of binding sites of the spike protein, can bind to viruses in a defined multivalent mode. These capsids cover the entire virus envelope, thus preventing its binding to the host cell as visualized by cryo-electron tomography. As a consequence, virus infection can be inhibited in vitro, ex vivo and in vivo. Such highly functionalized capsids present an alternative to strategies that target virus entry by spike-inhibiting antibodies⁵ and peptides⁶ or that address late steps of the viral replication cycle⁷.

Precipitation-free high-affinity multivalent binding by inline lectin ligands

Multivalent ligand-protein interactions are a key concept in biology mediating, for example, signalling and adhesion. Multivalent ligands often have tremendously increased binding affinities. However, they also can cause crosslinking of receptor molecules leading to precipitation of ligand-receptor complexes. Plaque formation due to precipitation is a known characteristic of numerous fatal diseases limiting a potential medical application of multivalent ligands with a precipitating binding mode. Here, we present a new design of high-potency multivalent ligands featuring an inline arrangement of ligand epitopes with exceptionally high binding affinities in the low nanomolar range. At the same time, we show with a multi-methodological approach that precipitation of the receptor is prevented. We distinguish distinct binding modes of the ligands, in particular we elucidate a unique chelating binding mode, where four receptor binding sites are simultaneously bridged by one multivalent ligand molecule. The new design concept of inline multivalent ligands, which we established for the well-investigated model lectin wheat germ agglutinin, has great potential for the development of high-potency multivalent inhibitors as future therapeutics.