Related Experiment Video
Updated: Jun 25, 2026
Rapid, Seamless Generation of Recombinant Poxviruses using Host Range and Visual Selection
Published on: May 24, 2020
Specific targeting of the F13L protein by ST-246 affects orthopoxvirus production differently
Sophie Duraffour1, Solenne Vigne, Kurt Vermeire
1Rega Institute for Medical Research, KU Leuven, Leuven, Belgium.
Background:
ST-246 is a potent anti-orthopoxviral molecule targeting the F13L protein of vaccinia virus, which is involved in the wrapping of viruses. The discrepancy in sensitivities of several orthopoxviruses to ST-246 has raised questions about potential differences in their replicative cycles and/or the presence of another drug target.
Methods:
Density gradients were used to evaluate the differences between the viral cycles of vaccinia, cowpox and camelpox viruses. Also, to investigate if ST-246 inhibits a single target, we compared its activity to that of small interfering RNAs designed to silence the F13L gene (siF13Ls).
Results:
We showed that the spread of vaccinia virus involved both intracellular and extracellular enveloped viruses, whereas both cowpox and camelpox viruses seemed to propagate via non-enveloped intracellular forms and cell-associated viral particles. Although ST-246 exerted a clear antiviral activity by interfering with the egress of the virus from infected cells, we observed that cowpox and camelpox viruses, in contrast to vaccinia virus, could be directed towards a lytic cycle under ST-246 treatment. We specifically knocked down the F13L transcripts of vaccinia and camelpox viruses by > 85%, reduced virus progeny by 90% and showed that siF13Ls affect camelpox and vaccinia virus propagation differently. Flow cytometry data validated that ST-246 interfered with the activity of the F13L protein, whereas siF13Ls silenced the F13L gene.
Conclusions:
Our observations support that vaccinia, cowpox and camelpox viruses exhibit different levels of sensitivity to ST-246 because of dissimilarities between their ways of propagation, and provide a better understanding of the mode of action of ST-246.
Insights
Differences in orthopoxvirus replication cycles explain varying sensitivities to ST-246, an antiviral targeting the F13L protein. This study clarifies the drug's mechanism and viral propagation differences.
Area of Science:
- Virology
- Molecular Biology
- Drug Discovery
Background:
- ST-246 is an anti-orthopoxviral drug targeting the vaccinia virus F13L protein involved in viral wrapping.
- Varied sensitivities of orthopoxviruses to ST-246 suggest differences in replication or drug targets.
Purpose of the Study:
- To investigate differences in the viral replication cycles of vaccinia, cowpox, and camelpox viruses.
- To determine if ST-246 targets a single molecule by comparing its activity with F13L gene silencing.
Main Methods:
- Density gradients were used to analyze viral cycle differences.
- Small interfering RNAs (siF13Ls) were employed to silence the F13L gene.
- Flow cytometry validated drug and gene silencing effects.
Main Results:
- Vaccinia virus spread involved enveloped forms; cowpox and camelpox utilized non-enveloped intracellular and cell-associated forms.
- ST-246 inhibited viral egress, but cowpox and camelpox viruses could enter a lytic cycle under treatment.
- siF13Ls affected vaccinia and camelpox virus propagation differently, confirming F13L as a target.
Conclusions:
- Orthopoxvirus sensitivity to ST-246 varies due to distinct propagation mechanisms.
- This research enhances understanding of ST-246's mode of action and orthopoxviral replication.
