Efficient virus extinction by combinations of a mutagen and antiviral inhibitors

The effect of combinations of the mutagenic base analog 5-fluorouracil (FU) and the antiviral inhibitors guanidine hydrochloride (G) and heparin (H) o n the infectivity of foot-and-mouth disease virus (FMDV) in cell culture ha s been investigated. Related FMDV clones differing up to 10(6)-fold in rela tive fitness in BHK-21 cells have been compared. Systematic extinction of i ntermediate fitness virus was attained with a combination of FU and G but n ot with the mutagen or the inhibitor alone. Systematic extinction of high-f itness FMDV required the combination of FU, G, and H. FMDV showing high rel ative fitness in BHK-21 cells but decreased replicative ability in CHO cell s behaved as a low-fitness virus with regard to extinction mutagenesis in C HO cells. This confirms that relative fitness, rather than a specific genom ic sequence, determines the FMDV response to enhanced mutagenesis. Mutant s pectrum analysis of several genomic regions from a preextinction population showed a statistically significant increase in the number of mutations com pared with virus passaged in parallel in the absence of FU and inhibitors. Also, in a preextinction population the types of mutations that can be attr ibuted to the mutagenic action of FU were significantly more frequent than other mutation types. The results suggest that combinations of mutagenic ag ents and antiviral inhibitors can effectively drive high-fitness virus into extinction.