Polysialosides outperform sulfated analogs for the inhibition of SARS-CoV-2

Both polysialosides and polysulfates are known to interact with the receptor binding domain (RBD) of the SARS-CoV-2 spike protein. However, a comprehensive site by site analysis of their binding affinities and potential synergistic antiviral effects have not been performed. Here, we report on the synthesis of polysialosides with nanomolar binding affinities to spike proteins of SARS-CoV-2 in solution using microscale thermophoresis (MST). The dendritic polyglycerol based polysialosides dPG500(SA)0.55 and dPG500(SA)0.25, with a dissociation constant Kd of 4.78 nM and 10.85 nM, respectively, bind ~500 times stronger than the high density polysulfated analog dPG500(OSO3Na)0.55, to intact SARS-CoV-2 virus particles or isolated spike protein. In fact, the presence of sulfate groups in a heteromultivalent compound dPG500(SA)0.20(OSO3Na)0.20 weakens the binding to spike proteins. A polycarboxylated analog does not bind to SARS-CoV-2, ruling out that the interaction of polysialoside is simply driven by electrostatic interactions. Furthermore, we found potent nanomolar binding of dPG500(SA)0.55 to SARS-CoV-2 variant B.1.617 (Delta) and B.1.1.529 (Omicron) RBD. Using explicit-solvent all-atom molecular dynamics (MD) simulations and docking studies, we obtain atomistic details on the interaction of different functional groups with the SARS-CoV-2 RBD and their binding affinities. Our data support the conclusion that sialosides interact stronger with RBD than sulfates. Notably, our most affine binder dPG500(SA)0.55 inhibits SARS-CoV-2 (WT, D614G) replication up to 98.6% at low nanomolar concentrations.