Trypstatin as a Novel TMPRSS2 Inhibitor with Broad‐Spectrum Efficacy against Corona and Influenza Viruses

Respiratory viruses, such as SARS‐CoV‐2 and influenza, exploit host proteases like TMPRSS2 for entry, making TMPRSS2 a prime antiviral target. Here, the identification and characterization of Trypstatin, a 61‐amino acid Kunitz‐type protease inhibitor derived from human hemofiltrate are reported. Trypstatin inhibits TMPRSS2 and related proteases with high potency, exhibiting half‐maximal inhibitory concentration values in the nanomolar range, comparable to the small molecule inhibitor camostat mesylate. In vitro assays demonstrate that Trypstatin effectively blocks spike‐driven entry of SARS‐CoV‐2, SARS‐CoV‐1, MERS‐CoV, and hCoV‐NL63, as well as hemagglutinin‐mediated entry of influenza A and B viruses. In primary human airway epithelial cultures, Trypstatin significantly reduces SARS‐CoV‐2 replication and retained activity in the presence of airway mucus. In vivo, intranasal administration of Trypstatin to SARS‐CoV‐2‐infected Syrian hamsters reduces viral titers and alleviates clinical symptoms. These findings highlight Trypstatin's potential as a broad‐spectrum antiviral agent against TMPRSS2‐dependent respiratory viruses.