Specific targeting of the F13L protein by ST-246 affects orthopoxvirus production differently.
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.
Duraffour
Sophie
S
Rega Institute for Medical Research, KU Leuven, Leuven, Belgium.
Vigne
Solenne
S
Vermeire
Kurt
K
Garcel
Aude
A
Vanstreels
Els
E
Daelemans
Dirk
D
Yang
Guang
G
Jordan
Robert
R
Hruby
Dennis E
DE
Crance
Jean-Marc
JM
Garin
Daniel
D
Andrei
Graciela
G
Snoeck
Robert
R
D000998:Antiviral Agents / Q000494:pharmacology; D001549:Benzamides / Q000494:pharmacology*; D002460:Cell Line; D015608:Cowpox virus / Q000187:drug effects*; D020868:Gene Silencing; D006801:Humans; D054833:Isoindoles / Q000494:pharmacology*; D008565:Membrane Proteins / Q000378:metabolism*; D018155:Orthopoxvirus / Q000187:drug effects*; D034741:RNA, Small Interfering; D013045:Species Specificity; D014616:Vaccinia virus / Q000187:drug effects*; D014759:Viral Envelope Proteins / Q000378:metabolism*; D014779:Virus Replication / Q000187:drug effects; D010797:Phthalimides
D000998:Antiviral Agents; D001549:Benzamides; D054833:Isoindoles; D008565:Membrane Proteins; D034741:RNA, Small Interfering; D014759:Viral Envelope Proteins; C084759:p37 protein, Vaccinia virus; C505045:tecovirimat; D010797:Phthalimides