Effect of ribavirin on macromolecular synthesis in vesicular stomatitis virus-infected cells.

Ribavirin at 200 micrograms/ml inhibited vesicular stomatitis virus (VSV) growth in Chinese hamster ovary (CHO) cells by 2.5 logs. To determine the mechanism of this inhibition, viral macromolecular synthesis was examined. VSV primary transcription remained unaffected, but overall VSV RNA synthesis decreased by 40 to 60%. When ribavirin was added 1.5 h after infection, inhibition of progeny production was partially lost, indicating that the antiviral effect was on an early stage after primary transcription. Inhibition of RNA polymerization by premature chain termination was not evident. Viral translation, on the other hand, was reduced by 95% with an inhibition of every protein species. Furthermore, viral RNA synthesized in the presence of ribavirin did not translate well in an in vitro translation system. In contrast, uninfected CHO cells treated with ribavirin showed a greater sensitivity in RNA synthesis than in protein synthesis. This suggests that the cellular translational machinery was not directly affected. Short-term treatment of cells resulted in negligible toxicity, but after 24 h there was marked alteration of cellular integrity. These results, taken together with data on other viruses, suggest that in the presence of ribavirin, dysfunctional VSV mRNA was synthesized, resulting in its failure to be translated. The selective antiviral effects of ribavirin and its relative lack of toxicity for host cells may be predicted on the basis of mRNA turnover and the requirements for de novo functional mRNA.