Scope of Multivalent Ligand Function: Lactose-Bearing Neoglycopolymers By Ring-Opening Metathesis Polymerization

Abstract

A lactose-bearing norbornene imide template was polymerized using (Cy 3 P) 2 Cl 2 Ru=CHPh to produce a lactose-substituted neoglycopolymer. The resulting polymer showed a 100-fold overall increase in inhibitory potency (5-fold increase on a per saccharide residue basis) compared to monomeric lactose in both a galectin-binding assay and an Erythrina corallodendrum hemagglutination assay.The relatively low affinity and specificity of individual carbohydrate-protein interactions is hard to reconcile with the diversity of oligosaccharide structures that are involved in specific recognition processes. Many scientists resolve this paradox with the assumption that multiple carbohydrate-protein interactions can cooperate in each recognition event to give the necessary functional affinity. 1,2 By changing the number of individual interactions as well as controlling their spatial arrangement, a multivalent ligand can become specific to a target or targets. Because protein-carbohydrate complexation is important in a wide range of medically significant interactions including inflammation and bacterial and viral pathogenesis, an understanding of multivalent recognition events is critical for designing therapeutics that target these processes. 3 Multivalent interactions are paramount in a variety of physiological processes, yet relatively little is known about these binding events. For example, much work has been done in elucidating the specific monovalent interactions between carbohydrate ligands with specific proteins such as the cell-surface selectins, 4 the galectins, 5 and various plant lectins, 6 yet an understanding of the contribution of polyvalent interactions to the functional affinity and specificity of these processes is only beginning to emerge. To build on our studies of multivalent saccharide derivatives, 7-10 we decided to explore the inhibitory properties of polymeric ligands that display a high local concentration of saccharide epitopes in assays with two different lectins.Several mechanisms may operate to enhance the functional affinity (i.e., the measured activity) of a particular multivalent ligand. Two such mechanisms include the chelate effect and the statistical effect due to high local concentration. In the chelate effect, a multidentate ligand occupies multiple binding sites within a protein (Figure 2A). The statistical effect we refer to is that in which ligands that present a high local concentration of saccharide epitopes to a single binding site exhibit slower off rates ( Figure 2B). To test the contributions of these effects to saccharide recognition, we chose to explore galectin-3 (Gal-3) and the lactose-binding lectin from Erythrina corallodendrum (EcorL). The galectins, like the selectins, have been implicated in the inflammatory response. Some of the naturally occurring ligands that bind the galectin family of proteins consist of polylactosamine units found in glycoconjugates such as fibronectin and laminin. 11 The structures of naturally occurring galectin ligands suggests multidentate inhi...

Smart Glycopolymeric Nanoparticles for Multivalent Lectin Binding and Stimuli-Controlled Guest Release

“…The ring-opening metathesis polymerization (ROMP) is a versatile and easy-to-handle method to prepare a variety of sophisticated polymers with different functionalities including multivalent carbohydrate systems. ,, Norbornene-based monomers can be easily modified with different functional groups and have been successfully polymerized by ROMP to accomplish biologically active materials. , In the present study, we decorated a norbornene anhydride with a GCP-zwitterion and a lactose unit (Scheme ). Both binding motifs were protected either by tert -butyloxycarbonyl (Boc) or by acetyl (OAc) groups to guarantee compatibility with ROMP using Grubbs catalysis and avoiding unwanted side reactions and assembly processes.…”

“…Many biological processes, including cell–cell recognition, cell adhesion, signaling, and infection of pathogens, are mediated via binding interactions between carbohydrates and carbohydrate binding proteins known as lectins. − Individual protein–carbohydrate interactions are unusually weak, when acting in a multivalent fashion; however, their affinity becomes significant when a phenomenon comes into play known as the “glycoside clustering effect” . Thus, synthetic multivalent glycoconjugates are of interest for the study of various multivalency effects related to carbohydrate recognition in biological systems. − In the light of this, synthetic glycopolymers containing pendant carbohydrate moieties have gained considerable attention to study their interaction with lectins. ,− Moreover, glycopolymers have been designed to prepare nanoparticles (NPs), which are more appealing models to investigate cell-related interactions, because of a multivalent array of carbohydrates on its surface and thus makes it attractive candidates in nanomedicine and other biological applications. − A common approach to achieve glycopolymer-based NPs is to design amphiphilic block copolymers attached with carbohydrate functionalities that undergo self-assembly in aqueous media. − Nevertheless, homoglycopolymers have also been used to form self-assembled NPs in which repeating units contains both hydrophilic and hydrophobic moieties. − Importantly, in most of these cases, polymeric NPs were formed via self-assembly based on mainly hydrophobic effects in aqueous media. On the other hand, polymers functionalized with supramolecular binding motifs would allow constructing an elegant class of polymeric nanomaterials that show diverse stimuli-responsive properties. − The self-complementary ureidopyrimidone quadruple AADD H-bonding motif has attracted a lot of attention. − However, this self-assembly process is based on purely H-bonding of self-complementary binding units, which limits their application in aqueous media.…”

“…Nuclear Magnetic Resonance. The 1 H NMR spectra were recorded at 300 MHz or 500 MHz and the 13 C NMR spectra at 75 and 150 MHz from Bruker at ambient temperature. The description of the fine structure is as follows: s = singlet, bs = broad singlet, d = doublet, t = triplet, and m = multiplet.…”

Glucose Single-Chain Polymer Nanoparticles for Cellular Targeting

“…17,21−23 Multivalency in such structures is a striking factor to achieve selective binding toward the target site. 2,24,25 One way to evaluate the selective recognition of glycomacromolecules is to test their binding affinity to lectins. Concanavalin A (ConA) from Canavalia ensiformis (Jack bean) is one of the most studied lectins for modeling receptor interactions of glycomacromolecules, as it is structurally similar to a large number of bacterial and animal lectins in cell communication events.…”

“…The carbohydrate recognition efficacy of transporters depends on the architecture of the glycomacromolecule and varies with the carbohydrate hydroxyl group substitutions and carbohydrate linker density and spacing. ,,, Not only in nature, but also synthetically, a variety of glycomacromolecule topologies is known, ranging from dendrimers to nanogels. ,− Multivalency in such structures is a striking factor to achieve selective binding toward the target site. ,, One way to evaluate the selective recognition of glycomacromolecules is to test their binding affinity to lectins. Concanavalin A (ConA) from Canavalia ensiformis (Jack bean) is one of the most studied lectins for modeling receptor interactions of glycomacromolecules, as it is structurally similar to a large number of bacterial and animal lectins in cell communication events. − Dendritic structures and micelles have shown superior binding as compared to linear polymer chains, as evaluated through ConA binding assays. − Whereas the complexity of the well-defined dendrimers increases with every generation, polymeric structures offer ease of synthesis, to certain extents at the cost of loss in structural control.…”