Repurposing existing drugs: identification of SARS-CoV-2 3C-like protease inhibitors

J Enzyme Inhib Med Chem. 2021 Dec;36(1):147-153. doi: 10.1080/14756366.2020.1850710.


Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for coronavirus disease 2019 (COVID-19). Since its emergence, the COVID-19 pandemic has not only distressed medical services but also caused economic upheavals, marking urgent the need for effective therapeutics. The experience of combating SARS-CoV and MERS-CoV has shown that inhibiting the 3-chymotrypsin-like protease (3CLpro) blocks the replication of the virus. Given the well-studied properties of FDA-approved drugs, identification of SARS-CoV-2 3CLpro inhibitors in an FDA-approved drug library would be of great therapeutic value. Here, we screened a library consisting of 774 FDA-approved drugs for potent SARS-CoV-2 3CLpro inhibitors, using an intramolecularly quenched fluorescence (IQF) peptide substrate. Ethacrynic acid, naproxen, allopurinol, butenafine hydrochloride, raloxifene hydrochloride, tranylcypromine hydrochloride, and saquinavir mesylate have been found to block the proteolytic activity of SARS-CoV-2 3CLpro. The inhibitory activity of these repurposing drugs against SARS-CoV-2 3CLpro highlights their therapeutic potential for treating COVID-19 and other Betacoronavirus infections.

Keywords: 3CLpro inhibitors; FRET; SARS-CoV-2 3CL protease; antiviral; repurposing drugs.

MeSH terms

  • Antiviral Agents / pharmacology*
  • COVID-19 / virology*
  • COVID-19 Drug Treatment*
  • Catalytic Domain
  • Coronavirus 3C Proteases / antagonists & inhibitors*
  • Coronavirus 3C Proteases / chemistry
  • Cysteine Proteinase Inhibitors / pharmacology*
  • Drug Evaluation, Preclinical
  • Drug Repositioning*
  • Fluorescent Dyes
  • Humans
  • Molecular Docking Simulation
  • SARS-CoV-2 / drug effects*
  • SARS-CoV-2 / enzymology*
  • Substrate Specificity


  • Antiviral Agents
  • Cysteine Proteinase Inhibitors
  • Fluorescent Dyes
  • 3C-like proteinase, SARS-CoV-2
  • Coronavirus 3C Proteases

Grants and funding

This work was supported by research grant [MOST 109–2327-B-010–006] – from the Ministry of Science and Technology, Taiwan.