Discovery of a nasal spray steroid, tixocortol, as an inhibitor of SARS-CoV-2 main protease and viral replication

  • RSC Med Chem. 2024 Sep 27;15(12):4193-4205. doi: 10.1039/d4md00454j.
David A Davis  1 ,  Ashwin Nair  1 ,  Yana Astter  1 ,  Emma Treco  1 ,  Brian Peyser  2 ,  Rick Gussio  3  4 ,  Tam Nguyen  2 ,  Brett Eaton  5 ,  Elena Postnikova  5 ,  Michael Murphy  5 ,  Prabha Shrestha  1 ,  Haydar Bulut  1 ,  Shin-Ichiro Hattorri  6 ,  Hiroaki Mitsuya  1  6 ,  Robert Yarchoan  1
Affiliations
  • 1. HIV and AIDS Malignancy Branch, Center for Cancer Research, National Cancer Institute Bethesda MD USA [email protected].
  • 2. Developmental Therapeutics Program, Division of Cancer Treatment and Diagnosis, National Cancer Institute, National Institutes of Health USA.
  • 3. Vaccine Branch, Center for Cancer Research, National Cancer Institute, Frederick National Laboratory for Cancer Research Frederick MD 21702 USA.
  • 4. Computational Institute for Health and Environmental Research, (CIFHER.ORG) Riverside 5, RM 4076, 8490 Progress Dr. Frederick MD 21701 USA.
  • 5. Integrated Research Facility at Fort Detrick 8200 Research Plaza Frederick MD 21702 USA.
  • 6. Department of Refractory Viral Infections, National Center for Global Health and Medicine Research Institute 1-21-1 Toyama Shinjuku-ku Tokyo 162-8655 Japan.
PMID: 39371432 DOI: 10.1039/d4md00454j
Abstract

Coronaviruses rely on the viral-encoded chymotrypsin-like main protease (Mpro or 3CLpro) for replication and assembly. Our previous research on Mpro of SARS-CoV-2 identified cysteine 300 (Cys300) as a potential allosteric site of Mpro inhibition. Here, we identified tixocortol (TX) as a covalent modifier of Cys300 which inhibits Mpro activity in vitro as well as in a cell-based Mpro expression assay. Most importantly TX inhibited SARS-CoV-2 replication in ACE2 expressing HeLa cells. Biochemical analysis and kinetic assays were consistent with TX acting as a non-competitive inhibitor. By contrast, TX was a weaker inhibitor and modifier of C300S Mpro, confirming a role for Cys300 in inhibition of WT Mpro but also providing evidence for an additional Cys target. TX pivalate (TP), a prodrug for TX that was previously marketed as a nasal spray, also inhibited SARS-CoV-2 replication in HeLa-ACE2 cells at low micromolar IC50s. These studies suggest that TX and/or TP could possibly be repurposed for the prevention and/or treatment of SARS-CoV-2 Infection.

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