Functional polymers for the inhibition of Mannose Binding Lectin, a potential new target for stroke therapy

Glycopolymers, synthetic sugar-containing macromolecules, are attracting ever-increasing interest from the chemistry community due to their role as biomimetic analogues and their potential for therapeutic applications. Indeed, most saccharides only weakly bind to their protein receptors, with dissociation constants normally in the millilmolar to micromolar range, which is not sufficient to effectively control the in vivo events mediated by protein–carbohydrate binding. In nature, both carbohydrate-binding proteins and the glycans they recognize are typically aggregated into higher-order oligomeric structures, which suggests that binding limitations can be circumvented through multivalency.



This project aims to create glycosylated and pseudo-glycosylated dendrimers capable of controlling the activity of Mannose Binding Lectin (MBL) in ischemic stroke. MBL is a trimeric C-type lectin, which binds to simple monosaccharides (D-mannose, N-acetylglucosamine). Recent studies suggest that MBL plays a major role in the pathophysiology of ischemia reperfusion and has emerged as a potential new target in the treatment of stroke.



We propose to inhibit MBL action in the ischemic brain by presenting multiple copies of MBL binding elements on dendritic cores. The binding units will be selected among known natural ligands of MBL and some unnatural mimics developed in the coordinating laboratory, which were found to effectively interact with mannose-specific lectins but are degraded by mannosidases several times slower than the corresponding oligosaccharides. Preliminary results recently obtained by Surface Plasmon Resonance (SPR) in the proponents’ laboratory show that a tetravalent dendron decorated with four copies of one of such mimics binds to MBL with a dissociation constant in the low micromolar range. Starting from this promising initial observation, the inhibitors can now be optimized by improving both the nature of the monovalent ligand units and the type of multivalent presentation, which can vary depending on the type and topology of the polymeric material used.



Polyvalent scaffolds of diverse structure, flexibility, and valency are gaining increasing biomedical importance as artificial multivalent ligands to inhibit sugar-protein interaction. Dendrimers, in particular, have been shown to provide promising adherence-inhibition for toxins and other relevant lectins and we will focus on this type of materials because they are well suited for applications in blood vessels, due to of their favorable hydrodynamic properties. Another notable characteristic of the materials we plan to develop is the use of unnatural, non-glycosidic linkages between the binding units and the dendrimer core. This feature is meant to stabilize the glycodendrimers against the action of glycosidases, which act in vivo to degrade glycoconjugates.



The affinity level which we will be able to achieve will depend both on improvement of the ligand unit and on the controlled level of presentation, which can be tuned based on the topology of the dendrimer. The affinity of the mono- and polyvalent ligands for MBL will be measured by Surface Plasmon Resonance techniques, which will provide the required feedback for the selection of the monovalent elements and will help to identify the most promising materials for in vivo studies.



The latter will allow to evaluate the ability of these novel materials to confer protection towards anatomical and functional brain damage after stroke, to determine the therapeutic window of the selected inhibitors and to characterize their biological interactions in the ischemic tissue and their functional consequences on complement activation.