In vitro characterization of baloxavir acid, a first-in-class cap-dependent endonuclease inhibitor of the influenza virus polymerase PA subunit

Antiviral Res. 2018 Dec:160:109-117. doi: 10.1016/j.antiviral.2018.10.008. Epub 2018 Oct 11.

Abstract

Cap-dependent endonuclease (CEN) resides in the PA subunit of the influenza virus and mediates the critical "cap-snatching" step of viral RNA transcription, which is considered to be a promising anti-influenza target. Here, we describe in vitro characterization of a novel CEN inhibitor, baloxavir acid (BXA), the active form of baloxavir marboxil (BXM). BXA inhibits viral RNA transcription via selective inhibition of CEN activity in enzymatic assays, and inhibits viral replication in infected cells without cytotoxicity in cytopathic effect assays. The antiviral activity of BXA is also confirmed in yield reduction assays with seasonal type A and B viruses, including neuraminidase inhibitor-resistant strains. Furthermore, BXA shows broad potency against various subtypes of influenza A viruses (H1N2, H5N1, H5N2, H5N6, H7N9 and H9N2). Additionally, serial passages of the viruses in the presence of BXA result in isolation of PA/I38T variants with reduced BXA susceptibility. Phenotypic and genotypic analyses with reverse genetics demonstrate the mechanism of BXA action via CEN inhibition in infected cells. These results reveal the in vitro characteristics of BXA and support clinical use of BXM to treat influenza.

Keywords: Baloxavir acid; Baloxavir marboxil; Cap-dependent endonuclease; Influenza virus.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antiviral Agents / pharmacology*
  • Cytopathogenic Effect, Viral
  • DNA Mutational Analysis
  • Dibenzothiepins
  • Drug Resistance, Viral
  • Endonucleases / antagonists & inhibitors*
  • Endonucleases / genetics
  • Influenza A virus / drug effects*
  • Influenza A virus / enzymology
  • Influenza A virus / growth & development
  • Influenza B virus / drug effects*
  • Influenza B virus / enzymology
  • Influenza B virus / growth & development
  • Microbial Sensitivity Tests
  • Morpholines
  • Mutation, Missense
  • Oxazines / pharmacology*
  • Pyridines / pharmacology*
  • Pyridones
  • RNA-Dependent RNA Polymerase / antagonists & inhibitors*
  • RNA-Dependent RNA Polymerase / genetics
  • Reverse Genetics
  • Serial Passage
  • Thiepins / pharmacology*
  • Transcription, Genetic / drug effects
  • Triazines / pharmacology*
  • Viral Proteins / antagonists & inhibitors*
  • Viral Proteins / genetics
  • Virus Replication / drug effects

Substances

  • Antiviral Agents
  • Dibenzothiepins
  • Morpholines
  • Oxazines
  • PA protein, influenza viruses
  • Pyridines
  • Pyridones
  • Thiepins
  • Triazines
  • Viral Proteins
  • baloxavir
  • RNA-Dependent RNA Polymerase
  • Endonucleases