Identifying SARS-CoV-2 antiviral compounds by screening for small molecule inhibitors of nsp12/7/8 RNA-dependent RNA polymerase

Biochem J. 2021 Jul 16;478(13):2425-2443. doi: 10.1042/BCJ20210200.

Abstract

The coronavirus disease 2019 (COVID-19) global pandemic has turned into the largest public health and economic crisis in recent history impacting virtually all sectors of society. There is a need for effective therapeutics to battle the ongoing pandemic. Repurposing existing drugs with known pharmacological safety profiles is a fast and cost-effective approach to identify novel treatments. The COVID-19 etiologic agent is the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a single-stranded positive-sense RNA virus. Coronaviruses rely on the enzymatic activity of the replication-transcription complex (RTC) to multiply inside host cells. The RTC core catalytic component is the RNA-dependent RNA polymerase (RdRp) holoenzyme. The RdRp is one of the key druggable targets for CoVs due to its essential role in viral replication, high degree of sequence and structural conservation and the lack of homologues in human cells. Here, we have expressed, purified and biochemically characterised active SARS-CoV-2 RdRp complexes. We developed a novel fluorescence resonance energy transfer-based strand displacement assay for monitoring SARS-CoV-2 RdRp activity suitable for a high-throughput format. As part of a larger research project to identify inhibitors for all the enzymatic activities encoded by SARS-CoV-2, we used this assay to screen a custom chemical library of over 5000 approved and investigational compounds for novel SARS-CoV-2 RdRp inhibitors. We identified three novel compounds (GSK-650394, C646 and BH3I-1) and confirmed suramin and suramin-like compounds as in vitro SARS-CoV-2 RdRp activity inhibitors. We also characterised the antiviral efficacy of these drugs in cell-based assays that we developed to monitor SARS-CoV-2 growth.

Keywords: COVID-19; RNA-dependent RNA polymerase; coronavirus; nsp12.

MeSH terms

  • Animals
  • Antiviral Agents / chemistry*
  • Antiviral Agents / pharmacology*
  • Benzoates / pharmacology
  • Bridged Bicyclo Compounds, Heterocyclic / pharmacology
  • Chlorocebus aethiops
  • Coronavirus RNA-Dependent RNA Polymerase / antagonists & inhibitors*
  • Coronavirus RNA-Dependent RNA Polymerase / metabolism
  • Drug Evaluation, Preclinical*
  • Enzyme Assays
  • Fluorescence Resonance Energy Transfer
  • High-Throughput Screening Assays
  • Holoenzymes / metabolism
  • Reproducibility of Results
  • SARS-CoV-2 / drug effects
  • SARS-CoV-2 / enzymology*
  • Small Molecule Libraries / chemistry
  • Small Molecule Libraries / pharmacology*
  • Suramin / pharmacology
  • Vero Cells
  • Viral Nonstructural Proteins / antagonists & inhibitors
  • Viral Nonstructural Proteins / metabolism

Substances

  • Antiviral Agents
  • Benzoates
  • Bridged Bicyclo Compounds, Heterocyclic
  • Holoenzymes
  • NS8 protein, SARS-CoV-2
  • Small Molecule Libraries
  • Viral Nonstructural Proteins
  • 2-cyclopentyl-4-(5-phenyl-1H-pyrrolo(2,3-b)pyridin-3-yl)-benzoic acid
  • Suramin
  • Coronavirus RNA-Dependent RNA Polymerase
  • NSP12 protein, SARS-CoV-2
  • NSP7 protein, SARS-CoV-2