Size Dependence of Steric Shielding and Multivalency Effects for Globular Binding Inhibitors

Pathogen-binding nanoparticles to inhibit host cell infection by heparan sulfate and sialic acid dependent viruses and protozoan parasites

Global health faces an immense burden from infectious diseases caused by viruses and intracellular protozoan parasites such as the coronavirus disease (COVID-19) and malaria, respectively. These pathogens propagate through the infection of human host cells. The first stage of this host cell infection mechanism is cell attachment, which typically involves interactions between the infectious agent and surface components on the host cell membranes, specifically heparan sulfate (HS) and/or sialic acid (SA). Hence, nanoparticles (NPs) which contain or mimic HS/SA that can directly bind to the pathogen surface and inhibit cell infection are emerging as potential candidates for an alternative anti-infection therapeutic strategy. These NPs can be prepared from metals, soft matter (lipid, polymer, and dendrimer), DNA, and carbon-based materials among others and can be designed to include aspects of multivalency, broad-spectrum activity, biocidal mechanisms, and multifunctionality. This review provides an overview of such anti-pathogen nanomedicines beyond drug delivery. Nanoscale inhibitors acting against viruses and obligate intracellular protozoan parasites are discussed. In the future, the availability of broadly applicable nanotherapeutics would allow early tackling of existing and upcoming viral diseases. Invasion inhibitory NPs could also provide urgently needed effective treatments for protozoan parasitic infections.

Rationally Designing the Supramolecular Interfaces of Nanoparticle Superlattices with Multivalent Polymers

In supramolecular materials, multiple weak binding groups can act as a single collective unit when confined to a localized volume, thereby producing strong but dynamic bonds between material building blocks. This principle of multivalency provides a versatile means of controlling material assembly, as both the number and the type of supramolecular moieties become design handles to modulate the strength of intermolecular interactions. However, in materials with building blocks significantly larger than individual supramolecular moieties (e.g., polymer or nanoparticle scaffolds), the degree of multivalency is difficult to predict or control, as sufficiently large scaffolds inherently preclude separated supramolecular moieties from interacting. Because molecular models commonly used to examine supramolecular interactions are intrinsically unable to examine any trends or emergent behaviors that arise due to nanoscale scaffold geometry, our understanding of the thermodynamics of these massively multivalent systems remains limited. Here we address this challenge via the coassembly of polymer-grafted nanoparticles and multivalent polymers, systematically examining how multivalent scaffold size, shape, and spacing affect their collective thermodynamics. Investigating the interplay of polymer structure and supramolecular group stoichiometry reveals complicated but rationally describable trends that demonstrate how the supramolecular scaffold design can modulate the strength of multivalent interactions. This approach to self-assembled supramolecular materials thus allows for the manipulation of polymer-nanoparticle composites with controlled thermal stability, nanoparticle organization, and tailored meso- to microscopic structures. The sophisticated control of multivalent thermodynamics through precise modulation of the nanoscale scaffold geometry represents a significant advance in the ability to rationally design complex hierarchically structured materials via self-assembly.

Viral Attachment Blocking Chimera Composed of DNA Origami and Nanobody Inhibits Pseudorabies Virus Infection In Vitro

Antivirals are indispensable tools that can be targeted at viral domains directly or at cellular domains indirectly to obstruct viral infections and reduce pathogenicity. Despite their transformative use in healthcare, antivirals have been clinically approved to treat only 10 of the more than 200 known pathogenic human viruses. Additionally, many virus functions are intimately coupled with host cellular processes, which presents challenges in antiviral development due to the limited number of clear targets per virus, necessitating extensive insight into these molecular processes. Compounding this challenge, many viral pathogens have evolved to evade effective antivirals. We hypothesize that a viral attachment blocking chimera (VirABloC) composed of a viral binder and a bulky scaffold that sterically blocks interactions between a viral particle and a host cell may be suitable for the development of antivirals that are agnostic to the extravirion epitope that is being bound. We test this hypothesis by modifying a nanobody that specifically recognizes a nonessential epitope presented on the extravirion surface of pseudorabies virus strain 486 with a 3-dimensional wireframe DNA origami structure ∼100 nm in diameter. The nanobody switches from having no inhibitory properties to 4.2 ± 0.9 nM IC50 when conjugated with the DNA origami scaffold. Mechanistic studies support that inhibition is mediated by the noncovalent attachment of the DNA origami scaffold to the virus particle, which obstructs the attachment of the viruses onto host cells. These results support the potential of VirABloC as a generalizable approach to developing antivirals.

Emerging drug design strategies in anti-influenza drug discovery

Influenza is an acute respiratory infection caused by influenza viruses (IFV), According to the World Health Organization (WHO), seasonal IFV epidemics result in approximately 3-5 million cases of severe illness, leading to about half a million deaths worldwide, along with severe economic losses and social burdens. Unfortunately, frequent mutations in IFV lead to a certain lag in vaccine development as well as resistance to existing antiviral drugs. Therefore, it is of great importance to develop anti-IFV drugs with high efficiency against wild-type and resistant strains, needed in the fight against current and future outbreaks caused by different IFV strains. In this review, we summarize general strategies used for the discovery and development of antiviral agents targeting multiple IFV strains (including those resistant to available drugs). Structure-based drug design, mechanism-based drug design, multivalent interaction-based drug design and drug repurposing are amongst the most relevant strategies that provide a framework for the development of antiviral drugs targeting IFV.

Dual-Action Heteromultivalent Glycopolymers Stringently Block and Arrest Influenza A Virus Infection In Vitro and Ex Vivo

Here, we demonstrate the concerted inhibition of different influenza A virus (IAV) strains using a low-molecular-weight dual-action linear polymer. The 6'-sialyllactose and zanamivir conjugates of linear polyglycerol are optimized for simultaneous targeting of hemagglutinin and neuraminidase on the IAV surface. Independent of IAV subtypes, hemagglutination inhibition data suggest better adsorption of the heteromultivalent polymer than homomultivalent analogs onto the virus surface. Cryo-TEM images imply heteromultivalent compound-mediated virus aggregation. The optimized polymeric nanomaterial inhibits >99.9% propagation of various IAV strains 24 h postinfection in vitro at low nM concentrations and is up to 10000× more effective than the commercial zanamivir drug. In a human lung ex vivo multicyclic infection setup, the heteromultivalent polymer outperforms the commercial drug zanamivir and homomultivalent analogs or their physical mixtures. This study authenticates the translational potential of the dual-action targeting approach using small polymers for broad and high antiviral efficacy.

Iterative synthesis of 1,3-polyboronic esters with high stereocontrol and application to the synthesis of bahamaolide A

Polyketide natural products often contain common repeat motifs, for example, propionate, acetate and deoxypropionate, and so can be synthesized by iterative processes. We report here a highly efficient iterative strategy for the synthesis of polyacetates based on boronic ester homologation that does not require functional group manipulation between iterations. This process involves sequential asymmetric diboration of a terminal alkene, forming a 1,2-bis(boronic ester), followed by regio- and stereoselective homologation of the primary boronic ester with a butenyl metallated carbenoid to generate a 1,3-bis(boronic ester). Each transformation independently controls the stereochemical configuration, making the process highly versatile, and the sequence can be iterated prior to stereospecific oxidation of the 1,3-polyboronic ester to yield the 1,3-polyol. This methodology has been applied to a 14-step synthesis of the oxopolyene macrolide bahamaolide A, and the versatility of the 1,3-polyboronic esters has been demonstrated in various stereospecific transformations, leading to polyalkenes, -alkynes, -ketones and -aromatics with full stereocontrol.

Endothelial Cell Adhesion Molecules- (un)Attainable Targets for Nanomedicines

Endothelial cell adhesion molecules have long been proposed as promising targets in many pathologies. Despite promising preclinical data, several efforts to develop small molecule inhibitors or monoclonal antibodies (mAbs) against cell adhesion molecules (CAMs) ended in clinical-stage failure. In parallel, many well-validated approaches for targeting CAMs with nanomedicine (NM) were reported over the years. A wide range of potential applications has been demonstrated in various preclinical studies, from drug delivery to the tumor vasculature, imaging of the inflamed endothelium, or blocking immune cells infiltration. However, no NM drug candidate emerged further into clinical development. In this review, we will summarize the most advanced examples of CAM-targeted NMs and juxtapose them with known traditional drugs against CAMs, in an attempt to identify important translational hurdles. Most importantly, we will summarize the proposed strategies to enhance endothelial CAM targeting by NMs, in an attempt to offer a catalog of tools for further development.

Bioactive Synthetic Polymers

Synthetic polymers are omnipresent in society as textiles and packaging materials, in construction and medicine, among many other important applications. Alternatively, natural polymers play a crucial role in sustaining life and allowing organisms to adapt to their environments by performing key biological functions such as molecular recognition and transmission of genetic information. In general, the synthetic and natural polymer worlds are completely separated due to the inability for synthetic polymers to perform specific biological functions; in some cases, synthetic polymers cause uncontrolled and unwanted biological responses. However, owing to the advancement of synthetic polymerization techniques in recent years, new synthetic polymers have emerged that provide specific biological functions such as targeted molecular recognition of peptides, or present antiviral, anticancer, and antimicrobial activities. In this review, the emergence of this generation of bioactive synthetic polymers and their bioapplications are summarized. Finally, the future opportunities in this area are discussed.

Influenza Virus Precision Diagnosis and Continuous Purification Enabled by Neuraminidase-Resistant Glycopolymer-Coated Microbeads

Rapid diagnosis and vaccine development are critical to prevent the threat posed by viruses. However, rapid tests, such as colloidal gold assays, yield false-negative results due to the low quantities of viruses; moreover, conventional virus purification, including ultracentrifugation and nanofiltration, is multistep and time-consuming, which limits laboratory research and commercial development of viral vaccines. A rapid virus enrichment and purification technique will improve clinical diagnosis sensitivity and simplify vaccine production. Hence, we developed the surface-glycosylated microbeads (glycobeads) featuring chemically synthetic glycoclusters and reversible linkers to selectively capture the influenza virus. The surface plasmon resonance (SPR) evaluation indicated broad spectrum affinity of S-linked glycosides to various influenza viruses. The magnetic glycobeads were integrated into clinical rapid diagnosis, leading to a 30-fold lower limit of detection. Additionally, the captured viruses can be released under physiological conditions, delivering purified viruses with >50% recovery and without decreasing their native infectivity. Notably, this glycobead platform will facilitate the sensitive detection and continuous one-step purification of the target virus that contributes to future vaccine production.

Evaluation of Multivalent Sialylated Polyglycerols for Resistance Induction in and Broad Antiviral Activity against Influenza A Viruses

The development of multivalent sialic acid-based inhibitors active against a variety of influenza A virus (IAV) strains has been hampered by high genetic and structural variability of the targeted viral hemagglutinin (HA). Here, we addressed this challenge by employing sialylated polyglycerols (PGs). Efficacy of prototypic PGs was restricted to a narrow spectrum of IAV strains. To understand this restriction, we selected IAV mutants resistant to a prototypic multivalent sialylated PG by serial passaging. Resistance mutations mapped to the receptor binding site of HA, which was accompanied by altered receptor binding profiles of mutant viruses as detected by glycan array analysis. Specifying the inhibitor functionalization to 2,6-α-sialyllactose (SL) and adjusting the linker yielded a rationally designed inhibitor covering an extended spectrum of inhibited IAV strains. These results highlight the importance of integrating virological data with chemical synthesis and structural data for the development of sialylated PGs toward broad anti-influenza compounds.

Nanotechnology for virus treatment

The continued emergence of novel viruses poses a significant threat to global health. Uncontrolled outbreaks can result in pandemics that have the potential to overburden our healthcare and economic systems. While vaccination is a conventional modality that can be employed to promote herd immunity, antiviral vaccines can only be applied prophylactically and do little to help patients who have already contracted viral infections. During the early stages of a disease outbreak when vaccines are unavailable, therapeutic antiviral drugs can be used as a stopgap solution. However, these treatments do not always work against emerging viral strains and can be accompanied by adverse effects that sometimes outweigh the benefits. Nanotechnology has the potential to overcome many of the challenges facing current antiviral therapies. For example, nanodelivery vehicles can be employed to drastically improve the pharmacokinetic profile of antiviral drugs while reducing their systemic toxicity. Other unique nanomaterials can be leveraged for their virucidal or virus-neutralizing properties. In this review, we discuss recent developments in antiviral nanotherapeutics and provide a perspective on the application of nanotechnology to the SARS-CoV-2 outbreak and future virus pandemics.

A quantitative view on multivalent nanomedicine targeting

Although the concept of selective delivery has been postulated over 100 years ago, no targeted nanomedicine has been clinically approved so far. Nanoparticles modified with targeting ligands to promote the selective delivery of therapeutics towards a specific cell population have been extensively reported. However, the rational design of selective particles is still challenging. One of the main reasons for this is the lack of quantitative theoretical and experimental understanding of the interactions involved in cell targeting. In this review, we discuss new theoretical models and experimental methods that provide a quantitative view of targeting. We show the new advancements in multivalency theory enabling the rational design of super-selective nanoparticles. Furthermore, we present the innovative approaches to obtain key targeting parameters at the single-cell and single molecule level and their role in the design of targeting nanoparticles. We believe that the combination of new theoretical multivalent design and experimental methods to quantify receptors and ligands aids in the rational design and clinical translation of targeted nanomedicines.

Filamentous anti-influenza agents wrapping around viruses

Owing to the emerging resistance to current anti-influenza therapies, strategies for blocking virus-cell interaction with agents that mimic interactions with host cell receptors are garnering interest. In this context, a multivalent presentation of sialyl groups on various types of scaffold materials such as dendrimers, liposomes, nanoparticles, and natural/synthetic polymers has been investigated for the inhibition of influenza A virus infection. However, the development of versatile antiviral agents based on monodisperse scaffolds capable of precise molecular design remains challenging. Whether an anisotropically extended filamentous nanostructure can serve as an effective scaffold for maximum inhibition of viral cell attachment has not been investigated. In this study, the preparation of a series of sialyllactose-conjugated filamentous bacteriophages (SLPhages), with controlled loading levels, ligand valencies, and two types of sialyllactose (α2,3' and α2,6'), is demonstrated. With optimal ligand loading and valency, SLPhages showed inhibitory activity (in vitro) against influenza A viruses at concentrations of tens of picomolar. This remarkable inhibition is due to the strong interaction between the SLPhage and the virus; this interaction is adequately potent to compensate for the cost of the bending and wrapping of the SLPhage around the influenza virus. Our study may open new avenues for the development of filamentous anti-viral agents, in which virus-wrapping or aggregation is the primary feature responsible for the blocking of cell entry.

Heteromultivalent topology-matched nanostructures as potent and broad-spectrum influenza A virus inhibitors

Here, we report the topology-matched design of heteromultivalent nanostructures as potent and broad-spectrum virus entry inhibitors based on the host cell membrane. Initially, we investigate the virus binding dynamics to validate the better binding performance of the heteromultivalent moieties as compared to homomultivalent ones. The heteromultivalent binding moieties are transferred to nanostructures with a bowl-like shape matching the viral spherical surface. Unlike the conventional homomultivalent inhibitors, the heteromultivalent ones exhibit a half maximal inhibitory concentration of 32.4 ± 13.7 μg/ml due to the synergistic multivalent effects and the topology-matched shape. At a dose without causing cellular toxicity, >99.99% reduction of virus propagation has been achieved. Since multiple binding sites have also been identified on the S protein of SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), we envision that the use of heteromultivalent nanostructures may also be applied to develop a potent inhibitor to prevent coronavirus infection.

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.

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.

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.

Topology-Matching Design of an Influenza-Neutralizing Spiky Nanoparticle-Based Inhibitor with a Dual Mode of Action

In this study, we demonstrate the concept of "topology-matching design" for virus inhibitors. With the current knowledge of influenza A virus (IAV), we designed a nanoparticle-based inhibitor (nano-inhibitor) that has a matched nanotopology to IAV virions and shows heteromultivalent inhibitory effects on hemagglutinin and neuraminidase. The synthesized nano-inhibitor can neutralize the viral particle extracellularly and block its attachment and entry to the host cells. The virus replication was significantly reduced by 6 orders of magnitude in the presence of the reverse designed nano-inhibitors. Even when used 24 hours after the infection, more than 99.999 % inhibition is still achieved, which indicates such a nano-inhibitor might be a potent antiviral for the treatment of influenza infection.

Topology-Matching Design of an Influenza-Neutralizing Spiky Nanoparticle-Based Inhibitor with a Dual Mode of Action

In this study, we demonstrate the concept of "topology-matching design" for virus inhibitors. With the current knowledge of influenza A virus (IAV), we designed a nanoparticle-based inhibitor (nano-inhibitor) that has a matched nanotopology to IAV virions and shows heteromultivalent inhibitory effects on hemagglutinin and neuraminidase. The synthesized nano-inhibitor can neutralize the viral particle extracellularly and block its attachment and entry to the host cells. The virus replication was significantly reduced by 6 orders of magnitude in the presence of the reverse designed nano-inhibitors. Even when used 24 hours after the infection, more than 99.999 % inhibition is still achieved, which indicates such a nano-inhibitor might be a potent antiviral for the treatment of influenza infection.

Spiky Nanostructures with Geometry-matching Topography for Virus Inhibition

Geometry-matching has been known to benefit the formation of stable biological interactions in natural systems. Herein, we report that the spiky nanostructures with matched topography to the influenza A virus (IAV) virions could be used to design next-generation advanced virus inhibitors. We demonstrated that nanostructures with spikes between 5 and 10 nm bind significantly better to virions than smooth nanoparticles, due to the short spikes inserting into the gaps of glycoproteins of the IAV virion. Furthermore, an erythrocyte membrane (EM) was coated to target the IAV, and the obtained EM-coated nanostructures could efficiently prevent IAV virion binding to the cells and inhibit subsequent infection. In a postinfection study, the EM-coated nanostructures reduced >99.9% virus replication at the cellular nontoxic dosage. We predict that such a combination of geometry-matching topography and cellular membrane coating will also push forward the development of nanoinhibitors for other virus strains, including SARS-CoV-2.

Quantification of Multivalent Interactions between Sialic Acid and Influenza A Virus Spike Proteins by Single-Molecule Force Spectroscopy

Multivalency is a key principle in reinforcing reversible molecular interactions through the formation of multiple bonds. The influenza A virus deploys this strategy to bind strongly to cell surface receptors. We performed single-molecule force spectroscopy (SMFS) to investigate the rupture force required to break individual and multiple bonds formed between synthetic sialic acid (SA) receptors and the two principal spike proteins of the influenza A virus (H3N2): hemagglutinin (H3) and neuraminidase (N2). Kinetic parameters such as the rupture length (χ_β) and dissociation rate (k_off) are extracted using the model by Friddle, De Yoreo, and Noy. We found that a monovalent SA receptor binds to N2 with a significantly higher bond lifetime (270 ms) compared to that for H3 (36 ms). By extending the single-bond rupture analysis to a multibond system of n protein-receptor pairs, we provide an unprecedented quantification of the mechanistic features of multivalency between H3 and N2 with SA receptors and show that the stability of the multivalent connection increases with the number of bonds from tens to hundreds of milliseconds. Association rates (k_on) are also provided, and an estimation of the dissociation constants (K_D) between the SA receptors to both proteins indicate a 17-fold higher binding affinity for the SA-N2 bond with respect to that of SA-H3. An optimal designed multivalent SA receptor showed a higher binding stability to the H3 protein of the influenza A virus than to the monovalent SA receptor. Our study emphasizes the influence of the scaffold on the presentation of receptors during multivalent binding.

First-order 'hyper-selective' binding transition of multivalent particles under force

Multivalent particles bind to targets via many independent ligand-receptor bonding interactions. This microscopic design spans length scales in both synthetic and biological systems. Classic examples include interactions between cells, virus binding, synthetic ligand-coated micrometer-scale vesicles or smaller nano-particles, functionalised polymers, and toxins. Equilibrium multivalent binding is a continuous yet super-selective transition with respect to the number of ligands and receptors involved in the interaction. Increasing the ligand or receptor density on the two particles leads to sharp growth in the number of bound particles at equilibrium. Here we present a theory and Monte Carlo simulations to show that applying mechanical force to multivalent particles causes their adsorption/desorption isotherm on a surface to become sharper and more selective, with respect to variation in the number of ligands and receptors on the two objects. When the force is only applied to particles bound to the surface by one or more ligands, then the transition can become infinitely sharp and first-order-a new binding regime which we term 'hyper-selective'. Force may be imposed by, e.g. flow of solvent around the particles, a magnetic field, chemical gradients, or triggered uncoiling of inert oligomers/polymers tethered to the particles to provide a steric repulsion to the surface. This physical principle is a step towards 'all or nothing' binding selectivity in the design of multivalent constructs.

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.

Cells Undergo Major Changes in the Quantity of Cytoplasmic Organelles after Uptake of Gold Nanoparticles with Biologically Relevant Surface Coatings

Here, we use cryo soft X-ray tomography (cryo-SXT), which delivers 3D ultrastructural volumes of intact cells without chemical fixation or staining, to gain insight about nanoparticle uptake for nanomedicine. We initially used dendritic polyglycerol sulfate (dPGS) with potential diagnostic and therapeutic applications in inflammation. Although dPGS-coated gold nanoparticle (dPGS-AuNP) uptake followed a conventional endocytic/degradative pathway in human lung epithelial cell lines (A549), with cryo-SXT, we detected ∼5% of dPGS-AuNPs in the cytoplasm, a level undetectable by confocal light microscopy. We also observed ∼5% of dPGS-AuNPs in a rarely identified subcellular site, namely, lipid droplets, which are important for cellular energy metabolism. Finally, we also found substantial changes in the quantity of cytoplasmic organelles upon dPGS-AuNP uptake over the 1-6 h incubation period; the number of small vesicles and mitochondria significantly increased, and the number of multivesicular bodies and the number and volume of lipid droplets significantly decreased. Although nearly all organelle numbers at 6 h were still significantly different from controls, most appeared to be returning to normal levels. To test for generality, we also examined cells after uptake of gold nanoparticles coated with a different agent, polyethylenimine (PEI), used for nucleic acid delivery. PEI nanoparticles did not enter lipid droplets, but they induced similar, albeit less pronounced, changes in the quantity of cytoplasmic organelles. We confirmed these changes in organelle quantities for both nanoparticle coatings by confocal fluorescence microscopy. We suggest this cytoplasmic remodeling could reflect a more common cellular response to coated gold nanoparticle uptake.

Analysis of Multivalent IDP Interactions: Stoichiometry, Affinity, and Local Concentration Effect Measurements

Nuclear magnetic resonance (NMR) titration and isothermal titration calorimetry can be combined to provide an assessment of how multivalent intrinsically disordered protein (IDP) interactions can involve enthalpy-entropy balance. Here, we describe the underlying technical details and additional methods, such as dynamic light scattering analysis, needed to assess these reactions. We apply this to a central interaction involving the disordered regions of phe-gly nucleoporins (FG-Nups) that contain multiple phenylalanine-glycine repeats which are of particular interest, as their interactions with nuclear transport factors (NTRs) underlie the paradoxically rapid yet also highly selective transport of macromolecules mediated by the nuclear pore complex (NPC). These analyses revealed that a combination of low per-FG motif affinity and the enthalpy-entropy balance prevents high-avidity interaction between FG-Nups and NTRs while the large number of FG motifs promotes frequent FG-NTR contacts, resulting in enhanced selectivity.

Multivalent Flexible Nanogels Exhibit Broad-Spectrum Antiviral Activity by Blocking Virus Entry

The entry process of viruses into host cells is complex and involves stable but transient multivalent interactions with different cell surface receptors. The initial contact of several viruses begins with attachment to heparan sulfate (HS) proteoglycans on the cell surface, which results in a cascade of events that end up with virus entry. The development of antiviral agents based on multivalent interactions to shield virus particles and block initial interactions with cellular receptors has attracted attention in antiviral research. Here, we designed nanogels with different degrees of flexibility based on dendritic polyglycerol sulfate to mimic cellular HS. The designed nanogels are nontoxic and broad-spectrum, can multivalently interact with viral glycoproteins, shield virus surfaces, and efficiently block infection. We also visualized virus-nanogel interactions as well as the uptake of nanogels by the cells through clathrin-mediated endocytosis using confocal microscopy. As many human viruses attach to the cells through HS moieties, we introduce our flexible nanogels as robust inhibitors for these viruses.

Combinatorial approaches in post-polymerization modification for rational development of therapeutic delivery systems

The combinatorial polymer library approach has been proven to be effective for the optimization of therapeutic delivery systems. The library of polymers with chemical diversity has been synthesized by (i) polymerization of functionalized monomers or (ii) post-polymerization modification of reactive polymers. Most scientists have followed the first approach so far, and the second method has emerged as a versatile approach for combinatorial biomaterials discovery. This review focuses on the second approach, especially discussing the post-modifications that employ reactive polymers as templates for combinatorial synthesis of a library of functional polymers with distinct structural diversity or a combination of different functionalities. In this way, the functional polymers have a consistent chain length and distribution, which allows for systematic optimization of therapeutic delivery polymers for the efficient delivery of genes, small-molecule drugs, and protein therapeutics. In this review, the modification of representative reactive polymers for the delivery of different therapeutic payloads are summarized. The recent advances in rational design and optimization of therapeutic delivery systems based on reactive polymers are highlighted. This review ends with a summary of the current achievements and the prospect on future directions in applying the approach of post-polymerization modification of polymers to accelerate the development of therapeutic delivery systems.

STATEMENT OF SIGNIFICANCE

A strategy to rationally design and systematically optimize polymers for the efficient delivery of specific therapeutics is highly needed. The combinatorial polymer library approach could be an effective way to this end. The post-polymerization modification of reactive polymer precursors is applicable for the combinatorial synthesis of a library of functional polymers with distinct structural diversity across a consistent degree of polymerization. This allows for parallel comparison and systematic evaluation/optimization of functional polymers for efficient therapeutic delivery. This review summarizes the key elements of this combinatorial polymer synthesis approach realized by post-polymerization modification of reactive polymer precursors towards the development and identification of optimal polymers for the efficient delivery of therapeutic agents.

Interactions of Fullerene-Polyglycerol Sulfates at Viral and Cellular Interfaces

Understanding the mechanism of interactions of nanomaterials at biointerfaces is a crucial issue to develop new antimicrobial vectors. In this work, a series of water-soluble fullerene-polyglycerol sulfates (FPS) with different fullerene/polymer weight ratios and varying numbers of polyglycerol sulfate branches are synthesized, characterized, and their interactions with two distinct surfaces displaying proteins involved in target cell recognition are investigated. The combination of polyanionic branches with a solvent exposed variable hydrophobic core in FPS proves to be superior to analogs possessing only one of these features in preventing interaction of vesicular stomatitis virus coat glycoprotein (VSV-G) with baby hamster kidney cells serving as a model of host cell. Interference with L-selectin-ligand binding is dominated by the negative charge, which is studied by two assays: a competitive surface plasmon resonance (SPR)-based inhibition assay and the leukocyte cell (NALM-6) rolling on ligands under flow conditions. Due to possible intrinsic hydrophobic and electrostatic effects of synthesized compounds, pico- to nanomolar half maximal inhibitory concentrations (IC₅₀ ) are achieved. With their highly antiviral and anti-inflammatory properties, together with good biocompatibility, FPS are promising candidates for the future development towards biomedical applications.

A Water-Processable and Bioactive Multivalent Graphene Nanoink for Highly Flexible Bioelectronic Films and Nanofibers

The capabilities of conductive nanomaterials to be produced in liquid form with well-defined chemical, physical, and biological properties are highly important for the construction of next-generation flexible bioelectronic devices. Although functional graphene nanomaterials can serve as attractive liquid nanoink platforms for the fabrication of bioelectronics, scalable synthesis of graphene nanoink with an integration of high colloidal stability, water processability, electrochemical activity, and especially bioactivity remains a major challenge. Here, a facile and scalable synthesis of supramolecular-functionalized multivalent graphene nanoink (mGN-ink) via [2+1] nitrene cycloaddition is reported. The mGN-ink unambiguously displays a well-defined and flat 2D morphology and shows good water processability and bioactivity. The uniquely chemical, physical, and biological properties of mGN-ink endow the constructed bioelectronic films and nanofibers with high flexibility and durability, suitable conductivity and electrochemical activity, and most importantly, good cellular compatibility and a highly efficient control of stem-cell spreading and orientation. Overall, for the first time, a water-processable and bioactive mGN-ink is developed for the design of flexible and electrochemically active bioelectronic composites and devices, which not only presents manifold possibilities for electronic-cellular applications but also establishes a new pathway for adapting macroscopic usages of graphene nanomaterials in bionic, biomedical, electronic, and even energy fields.

Multivalent Peptide-Nanoparticle Conjugates for Influenza-Virus Inhibition

To inhibit binding of the influenza A virus to the host cell glycocalyx, we generate multivalent peptide-polymer nanoparticles binding with nanomolar affinity to the virus via its spike protein hemagglutinin. The chosen dendritic polyglycerol scaffolds are highly biocompatible and well suited for a multivalent presentation. We could demonstrate in vitro that by increasing the size of the polymer scaffold and adjusting the peptide density, viral infection is drastically reduced. Such a peptide-polymer conjugate qualified also in an in vivo infection scenario. With this study we introduce the first non-carbohydrate-based, covalently linked, multivalent virus inhibitor in the nano- to picomolar range by ensuring low peptide-ligand density on a larger dendritic scaffold.

The influence of surface charge on serum protein interaction and cellular uptake: studies with dendritic polyglycerols and dendritic polyglycerol-coated gold nanoparticles

Nanoparticles (NPs) have gained huge interest in the medical field, in particular for drug delivery purposes. However, binding of proteins often leads to fast NP uptake and rapid clearance, thereby hampering medical applications. Thus, it is essential to determine and control the bio-nano interface. This study investigated the serum protein interactions of dendritic polyglycerols (dPGs), which are promising drug delivery candidates by means of two dimensional gel electrophoresis (2DE) in combination with mass spectrometry. In order to investigate the influence of surface charge, sulfated (sulfated dendritic polyglycerol [dPGS]) and non-sulfated (dPGOH) surfaces were applied, which were synthesized on a gold core allowing for easier separation from unbound biomolecules through centrifugation. Furthermore, two different sizes for dPGS were included. Although size had only a minor influence, considerable differences were detected in protein affinity for dPGS versus dPGOH surfaces, with dPGOH binding much less proteins. Cellular uptake into human CD14+ monocytes was analyzed by flow cytometry, and dPGOH was taken up to a much lower extent compared to dPGS. By using a pull-down approach, possible cellular interaction partners of serum pre-incubated dPGS-Au20 NPs from the membrane fraction of THP-1 cells could be identified such as for instance the transferrin receptor or an integrin. Clathrin-mediated endocytosis was further investigated using chlorpromazine as an inhibitor, which resulted in a 50% decrease of the cellular uptake of dPGS. This study could confirm the influence of surface charge on protein interactions and cellular uptake of dPGS. Furthermore, the approach allowed for the identification of possible uptake receptors and insights into the uptake mechanism.

Detecting the Formation and Transformation of Oligomers during Insulin Fibrillation by a Dendrimer Conjugated with Aggregation-Induced Emission Molecule

The fibrillation of protein is harmful and impedes the use of protein drugs. It also relates to various debilitating diseases such as Alzheimer's diseases. Thus, investigating the protein fibrillation process is necessary. In this study, poly(amido amine) dendrimers (PAMAM) of generation 3 (G3) and generation 4 (G4) were synthesized and conjugated with 4-aminobiphenyl, an aggregation-induced emission (AIE) moiety, at varied grafting ratios. Among them, one fluorescence probe named G3-biph-3 that was grafted average 3.25 4-aminobiphenyl to the G3, can detect the transformations both from native insulin to oligomers and from oligomers to fibrils. The size difference of native insulin, oligomers, and fibrils was proposed to be the main factor leading to the detection of the above transformations. Different molecular weights of sodium polyacrylate (PAAS) were also applied as a model to interact with G3-biph-3 to further reveal the mechanism. The results indicated that PAMAM with a certain generation and grafted with appropriate AIE groups can detect the oligomer formation and transformation during the insulin fibrillation process.

Functional Graphene Nanomaterials Based Architectures: Biointeractions, Fabrications, and Emerging Biological Applications

Functional graphene nanomaterials (FGNs) are fast emerging materials with extremely unique physical and chemical properties and physiological ability to interfere and/or interact with bioorganisms; as a result, FGNs present manifold possibilities for diverse biological applications. Beyond their use in drug/gene delivery, phototherapy, and bioimaging, recent studies have revealed that FGNs can significantly promote interfacial biointeractions, in particular, with proteins, mammalian cells/stem cells, and microbials. FGNs can adsorb and concentrate nutrition factors including proteins from physiological media. This accelerates the formation of extracellular matrix, which eventually promotes cell colonization by providing a more beneficial microenvironment for cell adhesion and growth. Furthermore, FGNs can also interact with cocultured cells by physical or chemical stimulation, which significantly mediate their cellular signaling and biological performance. In this review, we elucidate FGNs-bioorganism interactions and summarize recent advancements on designing FGN-based two-dimensional and three-dimensional architectures as multifunctional biological platforms. We have also discussed the representative biological applications regarding these FGN-based bioactive architectures. Furthermore, the future perspectives and emerging challenges will also be highlighted. Due to the lack of comprehensive reviews in this emerging field, this review may catch great interest and inspire many new opportunities across a broad range of disciplines.

Highly Efficient Multivalent 2D Nanosystems for Inhibition of Orthopoxvirus Particles

Efficient inhibition of cell-pathogen interaction to prevent subsequent infection is an urgent but yet unsolved problem. In this study, the synthesis and functionalization of novel multivalent 2D carbon nanosystems as well as their antiviral efficacy in vitro are shown. For this reason, a new multivalent 2D flexible carbon architecture is developed in this study, functionalized with sulfated dendritic polyglycerol, to enable virus interaction. A simple "graft from" approach enhances the solubility of thermally reduced graphene oxide and provides a suitable 2D surface for multivalent ligand presentation. Polysulfation is used to mimic the heparan sulfate-containing surface of cells and to compete with this natural binding site of viruses. In correlation with the degree of sulfation and the grafted polymer density, the interaction efficiency of these systems can be varied. In here, orthopoxvirus strains are used as model viruses as they use heparan sulfate for cell entry as other viruses, e.g., herpes simplex virus, dengue virus, or cytomegalovirus. The characterization results of the newly designed graphene derivatives demonstrate excellent binding as well as efficient inhibition of orthopoxvirus infection. Overall, these new multivalent 2D polymer nanosystems are promising candidates to develop potent inhibitors for viruses, which possess a heparan sulfate-dependent cell entry mechanism.

The Role of Galectin-1 in Cancer Progression, and Synthetic Multivalent Systems for the Study of Galectin-1

This review discusses the role of galectin-1 in the tumor microenvironment. First, the structure and function of galectin-1 are discussed. Galectin-1, a member of the galectin family of lectins, is a functionally dimeric galactoside-binding protein. Although galectin-1 has both intracellular and extracellular functions, the defining carbohydrate-binding role occurs extracellularly. In this review, the extracellular roles of galectin-1 in cancer processes are discussed. In particular, the importance of multivalent interactions in galectin-1 mediated cellular processes is reviewed. Multivalent interactions involving galectin-1 in cellular adhesion, mobility and invasion, tumor-induced angiogenesis, and apoptosis are presented. Although the mechanisms of action of galectin-1 in these processes are still not well understood, the overexpression of galectin-1 in cancer progression indicates that the role of galectin-1 is significant. To conclude this review, synthetic frameworks that have been used to modulate galectin-1 processes are reviewed. Small molecule oligomers of carbohydrates, carbohydrate-functionalized pseudopolyrotaxanes, cyclodextrins, calixarenes, and glycodendrimers are presented. These synthetic multivalent systems serve as important tools for studying galectin-1 mediated cancer cellular functions.

Affinity-controlled protein encapsulation into sub-30 nm telodendrimer nanocarriers by multivalent and synergistic interactions

Novel nanocarriers are highly demanded for the delivery of heterogeneous protein therapeutics for disease treatments. Conventional nanoparticles for protein delivery are mostly based on the diffusion-limiting mechanisms, e.g., physical trapping and entanglement. We develop herein a novel linear-dendritic copolymer (named telodendrimer) nanocarrier for efficient protein delivery by affinitive coating. This affinity-controlled encapsulation strategy provides nanoformulations with a small particle size (<30 nm), superior loading capacity (>50% w/w) and maintained protein bioactivity. We integrate multivalent electrostatic and hydrophobic functionalities synergistically into the well-defined telodendrimer scaffold to fine-tune protein binding affinity and delivery properties. The ion strength and density of the charged groups as well as the structure of the hydrophobic segments are important and their combinations in telodendrimers are crucial for efficient protein encapsulation. We have conducted a series of studies to understand the mechanism and kinetic process of the protein loading and release, utilizing electrophoresis, isothermal titration calorimetry, Förster resonance energy transfer spectroscopy, bio-layer interferometry and computational methods. The optimized nanocarriers are able to deliver cell-impermeable therapeutic protein intracellularly to kill cancer cells efficiently. In vivo imaging studies revealed cargo proteins preferentially accumulate in subcutaneous tumors and retention of peptide therapeutics is improved in an orthotopic brain tumor, these properties are evidence of the improved pharmacokinetics and biodistributions of protein therapeutics delivered by telodendrimer nanoparticles. This study presents a bottom-up strategy to rationally design and fabricate versatile nanocarriers for encapsulation and delivery of proteins for numerous applications.

ECBS & ICBS 2015 Joint Meeting: Bringing Chemistry to Life

The European Chemical Biology Society (ECBS) and the International Chemical Biology Society (ICBS) recently organized a joint meeting in Berlin. This meeting had more than 250 participants. Four keynote lectures were given by Timothy Mitchison, David Tirrell, Carolyn Bertozzi and Jason Chin; in addition there were 13 invited speakers, 20 selected oral talks and 30 talks selected from 90 posters. The meeting was divided into six topics: chemoproteomics, epigenetics, conjugates for target delivering, anti-infectives, molecular imaging and probing the structure, and function of post-translational modifications. The highlights of the meeting are presented in this report.