Cnidii fructus and Sophorae Flavescentis Radix polysaccharides inhibit SARS-CoV-2 entry by interfering with Spike protein-mediated membrane fusion.

Polysaccharides derived from Traditional Chinese Medicine (TCM) show potential as therapeutic agents in the treatment of viral infections. In this study, seventeen polysaccharides extracted from TCM were screened for their inhibitory effects on SARS-CoV-2 pseudovirus (PsV) infection in ACE2-overexpressing HEK293T cells. The results revealed that Cnidii fructus polysaccharides (CFPs) and Sophorae Flavescentis Radix polysaccharides (SFPs) significantly inhibited PsV entry. Then, the effects of CFPs and SFPs on the authentic SARS-CoV-2 virus were studied. We found that CFPs and SFPs significantly inhibited cellular damage and virus invasion induced by both the Original SARS-CoV-2 strain and the Omicron variant in Vero E6 cells, without causing obvious cytotoxicity. In vivo studies demonstrated that CFPs and SFPs significantly protect mice against SARS-CoV-2 virus-induced mortality, along with reductions in viral load and lung injury. Time of addition (TOA) experiments indicated that CFPs and SFPs exert inhibitory effects during the pseudoviral pre-attachment and cell entry stages, with no substantial impacts after the PsV has entered the cells. Further mechanism studies showed that CFPs and SFPs inhibited syncytial formation primarily by suppressing the host cell surface membrane fusion process mediated by the Spike protein, without significantly affecting the endosome-mediated viral entry.