A single mutation in the chikungunya virus RNA polymerase causes resistance to Favipiravir (T-705)

T-705, also known as Favipiravir, is a small-molecule inhibitor that is currently in clinical development for the treatment of influenza virus infections. This molecule also inhibits the replication of a broad spectrum of other RNA viruses. In the host cell, T-705 is converted into its active metabolite, the ribonucleoside analogue T-705RTP. However, the precise molecular mechanism of action against influenza virus or any other virus remains to be elucidated. We here demonstrate that T-705 inhibits the replication of laboratory strains and clinical isolates of chikungunya virus (CHIKV) [EC50 = 2-25 µM]. When given orally to CHIKV-infected AG129 mice in a pre- or post-exposure scenario, T-705 reduced virus-induced mortality by 85% and 65%, respectively. T-705 resistant CHIKV variants all acquired a K291R mutation in motif F1 of the RNA-dependent RNA polymerase. Reverse-engineering of this mutation in an infectious clone of CHIKV corroborated the link between the mutant genotype and the compound-resistant phenotype. Interestingly, the lysine in motif F1 is also highly conserved in positive-stranded RNA viruses in general, again highlighting the importance of this amino acid. Although our observations do not exclude additional mechanisms of action against other viruses, this study lifts an important tip of the veil on the precise molecular mechanism of the antiviral activity of T-705 against (alpha)viruses and may help to design other potent broad-spectrum antivirals. Furthermore, this is the first report of resistance of any of the viruses that are susceptible to T-705.status: publishe