Development of a highly selective glycomimetic ligand for L-SIGN: a new tool against SARS-CoV-2 and Ebola viruses

DC-SIGN (CD209) and L‑SIGN (CD209L) are two C-type lectin receptors (CLRs) structurally homologous, but functionally rather different. DC-SIGN, expressed by dendritic cells and dedicated to recognizing carbohydrate molecular patterns associated to pathogens, contributes to shaping the immune response; L‑SIGN is notably expressed in endothelial cells from airway epithelia and is not directly involved in immunity. Some viruses are able to manipulate CLRs during their infection. Indeed, SARS-CoV-2 utilizes both DC-SIGN and L-SIGN for enhanced infection through a trans-infection mechanism, sparking interest in the development of antagonists for these receptors. COVID‑19’s major threat is associated to hyperactivation of the immune system that might be reinforced if DC-SIGN is engaged by exogenous ligands. Thus L‐SIGN, co-localized with ACE2‐expressing cells in the respiratory tract, appears as a more appropriate target for anti-adhesion therapy. However, the Carbohydrate Recognition Domains (CRDs) of the two lectins share 72% sequence identity, making the creation of a selective ligand for L-SIGN a real challenge. We introduce here Man84, a mannose ring modified at position 2 with a methylene guanidine triazole, which binds L-SIGN with a KD of 12.7 μM ± 1 μM (ITC) and represents the first known L-SIGN selective ligand, showing a 50-fold selectivity over DC-SIGN (SPR). The X-ray structure of the L-SIGN CRD/Man84 complex reveals the role of the guanidinium group, which attains steric and electrostatic complementarity with L-SIGN, and allows to pinpoint the source of selectivity to a single amino acid difference between the two CRDs. NMR analysis confirms the binding mode in solution, highlighting a conformational selection of Man84 upon complex formation. Additional selectivity and avidity in the low nanomolar range have been reached with dimeric versions of Man84. These compounds selectively inhibit L-SIGN dependent trans infection by SARS-CoV-2 and by Ebola virus. Man84 and its dimeric constructs display the best affinity and avidity reported to date for low-valency glycomimetics targeting a CLRs. Their performance makes them viable tools for competing with SARS-CoV-2 anchoring in the respiratory tract and their potential extends to additional applications in other medical contexts.