The Anticoagulant Nafamostat Potently Inhibits SARS-CoV-2 S Protein-Mediated Fusion in a Cell Fusion Assay System and Viral Infection In Vitro in a Cell-Type-Dependent Manner

Viruses. 2020 Jun 10;12(6):629. doi: 10.3390/v12060629.


Although infection by SARS-CoV-2, the causative agent of coronavirus pneumonia disease (COVID-19), is spreading rapidly worldwide, no drug has been shown to be sufficiently effective for treating COVID-19. We previously found that nafamostat mesylate, an existing drug used for disseminated intravascular coagulation (DIC), effectively blocked Middle East respiratory syndrome coronavirus (MERS-CoV) S protein-mediated cell fusion by targeting transmembrane serine protease 2 (TMPRSS2), and inhibited MERS-CoV infection of human lung epithelium-derived Calu-3 cells. Here we established a quantitative fusion assay dependent on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) S protein, angiotensin I converting enzyme 2 (ACE2) and TMPRSS2, and found that nafamostat mesylate potently inhibited the fusion while camostat mesylate was about 10-fold less active. Furthermore, nafamostat mesylate blocked SARS-CoV-2 infection of Calu-3 cells with an effective concentration (EC)50 around 10 nM, which is below its average blood concentration after intravenous administration through continuous infusion. On the other hand, a significantly higher dose (EC50 around 30 mM) was required for VeroE6/TMPRSS2 cells, where the TMPRSS2-independent but cathepsin-dependent endosomal infection pathway likely predominates. Together, our study shows that nafamostat mesylate potently inhibits SARS-CoV-2 S protein-mediated fusion in a cell fusion assay system and also inhibits SARS-CoV-2 infection in vitro in a cell-type-dependent manner. These findings, together with accumulated clinical data regarding nafamostat's safety, make it a likely candidate drug to treat COVID-19.

Keywords: SARS-CoV-2; TMPRSS2; fusion inhibitor.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Angiotensin-Converting Enzyme 2
  • Angiotensin-Converting Enzyme Inhibitors / pharmacology
  • Animals
  • Anticoagulants / pharmacology*
  • Benzamidines
  • Betacoronavirus / drug effects*
  • Betacoronavirus / metabolism
  • COVID-19
  • Cell Line
  • Chlorocebus aethiops
  • Coronavirus Infections / drug therapy*
  • Coronavirus Infections / virology
  • Esters
  • Gabexate / analogs & derivatives
  • Gabexate / pharmacology
  • Guanidines / pharmacology*
  • HEK293 Cells
  • Humans
  • Pandemics
  • Peptidyl-Dipeptidase A / metabolism
  • Pneumonia, Viral / drug therapy*
  • Pneumonia, Viral / virology
  • SARS-CoV-2
  • Serine Endopeptidases / metabolism
  • Spike Glycoprotein, Coronavirus / antagonists & inhibitors*
  • Spike Glycoprotein, Coronavirus / metabolism
  • Vero Cells
  • Virus Internalization / drug effects*


  • Angiotensin-Converting Enzyme Inhibitors
  • Anticoagulants
  • Benzamidines
  • Esters
  • Guanidines
  • Spike Glycoprotein, Coronavirus
  • spike protein, SARS-CoV-2
  • camostat
  • Gabexate
  • Peptidyl-Dipeptidase A
  • ACE2 protein, human
  • Angiotensin-Converting Enzyme 2
  • Serine Endopeptidases
  • TMPRSS2 protein, human
  • nafamostat