Considerations for the discovery and development of 3-chymotrypsin-like cysteine protease inhibitors targeting SARS-CoV-2 infection

Curr Opin Virol. 2021 Aug;49:36-40. doi: 10.1016/j.coviro.2021.04.006. Epub 2021 Apr 27.


Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of the COVID-19 pandemic. The coronavirus 3-chymotrypsin-like protease (3CLpro) controls virus replication and is therefore considered a major target and promising opportunity for rational-based antiviral discovery with direct acting agents. Here we review first-generation SARS-CoV-2 3CLpro inhibitors PF-07304814, GC-376, and CDI-45205 that are being delivered either by injection or inhalation due to their low intrinsic oral bioavailability. In addition, PF-07321332 is now emerging as a promising second-generation clinical candidate for oral delivery. A key challenge to the development of novel 3CLpro inhibitors is the poor understanding of the predictive value of in vitro potency toward clinical efficacy, an issue complicated by the involvement of host proteases in virus entry. Further preclinical and clinical validation will be key to establishing 3CLpro inhibitors as a bona fide class for future SARS-CoV-2 therapeutics for both hospitalized and outpatient populations.

Publication types

  • Review

MeSH terms

  • Animals
  • Antiviral Agents / chemistry
  • Antiviral Agents / pharmacology*
  • Antiviral Agents / therapeutic use
  • COVID-19 Drug Treatment*
  • Coronavirus 3C Proteases / antagonists & inhibitors*
  • Cysteine Proteinase Inhibitors / chemistry
  • Cysteine Proteinase Inhibitors / pharmacology*
  • Cysteine Proteinase Inhibitors / therapeutic use
  • Drug Administration Routes
  • Drug Development
  • Drug Discovery
  • Humans
  • SARS-CoV-2 / drug effects*
  • SARS-CoV-2 / enzymology


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