An orally bioavailable antipoxvirus compound (ST-246) inhibits extracellular virus formation and protects mice from lethal orthopoxvirus Challenge.

ST-246 is a low-molecular-weight compound (molecular weight = 376), that is potent (concentration that inhibited virus replication by 50% = 0.010 microM), selective (concentration of compound that inhibited cell viability by 50% = >40 microM), and active against multiple orthopoxviruses, including vaccinia, monkeypox, camelpox, cowpox, ectromelia (mousepox), and variola viruses. Cowpox virus variants selected in cell culture for resistance to ST-246 were found to have a single amino acid change in the V061 gene. Reengineering this change back into the wild-type cowpox virus genome conferred resistance to ST-246, suggesting that V061 is the target of ST-246 antiviral activity. The cowpox virus V061 gene is homologous to vaccinia virus F13L, which encodes a major envelope protein (p37) required for production of extracellular virus. In cell culture, ST-246 inhibited plaque formation and virus-induced cytopathic effects. In single-cycle growth assays, ST-246 reduced extracellular virus formation by 10 fold relative to untreated controls, while having little effect on the production of intracellular virus. In vivo oral administration of ST-246 protected BALB/c mice from lethal infection, following intranasal inoculation with 10x 50% lethal dose (LD(50)) of vaccinia virus strain IHD-J. ST-246-treated mice that survived infection acquired protective immunity and were resistant to subsequent challenge with a lethal dose (10x LD(50)) of vaccinia virus. Orally administered ST-246 also protected A/NCr mice from lethal infection, following intranasal inoculation with 40,000x LD(50) of ectromelia virus. Infectious virus titers at day 8 postinfection in liver, spleen, and lung from ST-246-treated animals were below the limits of detection (<10 PFU/ml). In contrast, mean virus titers in liver, spleen, and lung tissues from placebo-treated mice were 6.2 x 10(7), 5.2 x 10(7), and 1.8 x 10(5) PFU/ml, respectively. Finally, oral administration of ST-246 inhibited vaccinia virus-induced tail lesions in Naval Medical Research Institute mice inoculated via the tail vein. Taken together, these results validate F13L as an antiviral target and demonstrate that an inhibitor of extracellular virus formation can protect mice from orthopoxvirus-induced disease.
AuthorsGuang Yang, Daniel C Pevear, Marc H Davies, Marc S Collett, Tom Bailey, Susan Rippen, Linda Barone, Chris Burns, Gerry Rhodes, Sanjeev Tohan, John W Huggins, Robert O Baker, R L Mark Buller, Erin Touchette, Kem Waller, Jill Schriewer, Johan Neyts, Erik DeClercq, Kevin Jones, Dennis Hruby, Robert Jordan
JournalJournal of virology (J Virol) Vol. 79 Issue 20 Pg. 13139-49 (Oct 2005) ISSN: 0022-538X [Print] United States
PMID16189015 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, U.S. Gov't, P.H.S.)
Chemical References
  • Antiviral Agents
  • Benzamides
  • Indoles
  • Isoindoles
  • Membrane Proteins
  • ST-246
  • Viral Envelope Proteins
  • p37 protein, Vaccinia virus
  • Administration, Oral
  • Amino Acid Sequence
  • Animals
  • Antiviral Agents (adverse effects, chemistry, pharmacology)
  • Benzamides (adverse effects, chemistry, pharmacology)
  • Cytopathogenic Effect, Viral (drug effects)
  • Drug Evaluation, Preclinical
  • Ectromelia virus (isolation & purification)
  • Ectromelia, Infectious (prevention & control)
  • Female
  • Indoles (adverse effects, chemistry, pharmacology)
  • Isoindoles
  • Liver (virology)
  • Lung (virology)
  • Membrane Proteins (drug effects, genetics)
  • Mice
  • Mice, Inbred BALB C
  • Molecular Sequence Data
  • Molecular Weight
  • Orthopoxvirus (drug effects, isolation & purification, physiology)
  • Poxviridae Infections (prevention & control, virology)
  • Sequence Alignment
  • Spleen (virology)
  • Vaccinia (prevention & control)
  • Viral Envelope Proteins (drug effects, genetics)
  • Viral Plaque Assay
  • Virus Assembly (drug effects)

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