Development of novel anti-influenza A virus (IAV) drugs with high efficiency and low toxicity is critical for preparedness against influenza outbreaks. Herein, we investigated the anti-IAV activities and mechanisms of fucoidan in vitro and in vivo. The results showed that a fucoidan KW derived from brown algae Kjellmaniella crassifolia effectively blocked IAV infection in vitro with low toxicity. KW possessed broad anti-IAV spectrum and low tendency of induction of viral resistance, superior to the anti-IAV drug amantadine. KW was capable of inactivating virus particles before infection and blocked some stages after adsorption. KW could bind to viral neuraminidase (NA) and inhibit the activity of NA to block the release of IAV. KW also interfered with the activation of EGFR, PKCα, NF-κB, and Akt, and inhibited both IAV endocytosis and EGFR internalization in IAV-infected cells, suggesting that KW may also inhibit cellular EGFR pathway. Moreover, intranasal administration of KW markedly improved survival and decreased viral titers in IAV-infected mice. Therefore, fucoidan KW has the potential to be developed into a novel nasal drop or spray for prevention and treatment of influenza in the future.

Significance: Although heparan sulfate (HS) modified by a 3- O -sulfate (3-OS) has been implicated in many biological processes, there is only a rudimentary understanding of ligand requirements of HS-binding proteins requiring this type of modification. We developed a modular synthetic approach that provided a structurally diverse collection of HS oligosaccharides with and without 3-OS. The compounds were printed as a glycan microarray to determine ligand requirements of HS-binding proteins, which revealed specific HS sequons for binding, and led to the discovery of proteins needing 3-OS for binding. The compounds made it possible to determine receptor requirements of herpes simplex virus, and substrate specificities of heparin lyases. The platform provides an important means to examine the biology of 3-OS−modified HS.