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At the surface of dendritic cells, C-type lectin receptors (CLRs) allow the recognition of carbohydrate-based PAMPS or DAMPS (pathogen- or danger-associated molecular patterns, respectively) and promote immune response regulation. However, some CLRs are hijacked by viral and bacterial pathogens. Thus, the design of ligands able to target specifically one CLR, to either modulate an immune response or to inhibit a given infection mechanism, has great potential value in therapeutic design. A case study is the selective blocking of DC-SIGN, involved notably in HIV trans-infection of T lymphocytes, without interfering with langerin-mediated HIV clearance. This is a challenging task due to their overlapping carbohydrate specificity. Toward the rational design of DC-SIGN selective ligands, we performed a comparative affinity study between DC-SIGN and langerin with natural ligands. We found that GlcNAc is recognized by both CLRs; however, selective sulfation are shown to increase the selectivity in favor of langerin. With the combination of site-directed mutagenesis and X-ray structural analysis of the langerin/GlcNS6S complex, we highlighted that 6-sulfation of the carbohydrate ligand induced langerin specificity. Additionally, the K313 residue from langerin was identified as a critical feature of its binding site. Using a rational and a differential approach in the study of CLR binding sites, we designed, synthesized, and characterized a new glycomimetic, which is highly specific for DC-SIGN vs langerin. STD NMR, SPR, and ITC characterizations show that compound 7 conserved the overall binding mode of the natural disaccharide while possessing an improved affinity and a strict specificity for DC-SIGN.

DC-SIGN antagonists were designed combining one selective monovalent glycomimetic ligand with trivalent dendrons separated by a rigid core of controlled length. The design combines multiple multivalency effects to achieve inhibitors of HIV infection, which are active in nanomolar concentration.

The development of new and effective adjuvants may play a fundamental role in improving HIV vaccine efficacy. New classes of vaccine adjuvants activate innate immunity receptors, notably toll like receptors (TLRs). Adjuvants targeting the C-Type lectin receptor DC-SIGN may be alternative or complementary to adjuvants based on TRL activation. Herein we evaluate the ability of the glycomimetic DC-SIGN ligand Polyman 19 (PM 19) to modulate innate immune responses. Results showed that PM 19 alone, or in combination with TLR agonists, induces the expression of cytokines, β chemokines and co-stimulatory molecules that may, in turn, modulate adaptive immunity and exert anti-viral effects. These results indicate that the suitability of this compound as a vaccine adjuvant should be further evaluated.

Dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN) and Langerin are C-type lectins of dendritic cells (DCs) that share a specificity for mannose and are involved in pathogen recognition. HIV is known to use DC-SIGN on DCs to facilitate transinfection of T-cells. Langerin, on the contrary, contributes to virus elimination; therefore, the inhibition of this latter receptor is undesired. Glycomimetic molecules targeting DC-SIGN have been reported as promising agents for the inhibition of viral infections and for the modulation of immune responses mediated by DC-SIGN. We show here for the first time that glycomimetics based on a mannose anchor can be tuned to selectively inhibit DC-SIGN over Langerin. Based on structural and binding studies of a mannobioside mimic previously described by us (2), a focused library of derivatives was designed. The optimized synthesis gave fast and efficient access to a group of bis(amides), decorated with an azide-terminated tether allowing further conjugation. SPR inhibition tests showed improvements over the parent pseudomannobioside by a factor of 3-4. A dimeric, macrocyclic structure (11) was also serendipitously obtained, which afforded a 30-fold gain over the starting compound (2). The same ligands were tested against Langerin and found to exhibit high selectivity towards DC-SIGN. Structural studies using saturation transfer difference NMR spectroscopy (STD-NMR) were performed to analyze the binding mode of one representative library member with DC-SIGN. Despite the overlap of some signals, it was established that the new ligand interacts with the protein in the same fashion as the parent pseudodisaccharide. The two aromatic amide moieties showed relatively high saturation in the STD spectrum, which suggests that the improved potency of the bis(amides) over the parent dimethyl ester can be attributed to lipophilic interactions between the aromatic groups of the ligand and the binding site of DC-SIGN., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In genital mucosa, different fates are described for HIV according to the subtype of dendritic cells (DCs) involved in its recognition. This notably depends on the C-type lectin receptor, langerin or DC-SIGN, involved in gp120 interaction. Langerin blocks HIV transmission by its internalization in specific organelles of Langerhans cells. On the contrary, DC-SIGN enhances HIV trans-infection of T lymphocytes. Thus, approaches aiming to inhibit DC-SIGN, without blocking langerin, represent attractive anti-HIV strategies. We previously demonstrated that dendrons bearing multiple copies of glycomimetic compounds were able to block DC-SIGN-dependent HIV infection in cervical explant models. Optimization of such ligand requires detailed characterization of its binding mode. In the present work, we determined the first high-resolution structure of a glycomimetic/DC-SIGN complex by X-ray crystallography. This glycomimetic, pseudo-1,2-mannobioside, shares shape and conformational properties with Manα1-2Man, its natural counterpart. However, it uses the binding epitope previously described for Lewis X, a ligand specific for DC-SIGN among the C-type lectin family. Thus, selectivity gain for DC-SIGN versus langerin is observed with pseudo-1,2-mannobioside as shown by surface plasmon resonance analysis. In parallel, ligand binding was also analyzed by TR-NOESY and STD NMR experiments, combined with the CORCEMA-ST protocol. These studies demonstrate that the complex, defined by X-ray crystallography, represents the unique binding mode of this ligand as opposed to the several binding orientations described for the natural ligand. This exclusive binding mode and its selective interaction properties position this glycomimetic as a good lead compound for rational improvement based on a structurally driven approach.