Lethal Mutagenesis of RNA Viruses and Approved Drugs with Antiviral Mutagenic Activity.

In RNA viruses, a small increase in their mutation rates can be sufficient to exceed their threshold of viability. Lethal mutagenesis is a therapeutic strategy based on the use of mutagens, driving viral populations to extinction. Extinction catastrophe can be experimentally induced by promutagenic nucleosides in cell culture models. The loss of HIV infectivity has been observed after passage in 5-hydroxydeoxycytidine or 5,6-dihydro-5-aza-2'-deoxycytidine while producing a two-fold increase in the viral mutation frequency. Among approved nucleoside analogs, experiments with polioviruses and other RNA viruses suggested that ribavirin can be mutagenic, although its mechanism of action is not clear. Favipiravir and molnupiravir exert an antiviral effect through lethal mutagenesis. Both drugs are broad-spectrum antiviral agents active against RNA viruses. Favipiravir incorporates into viral RNA, affecting the G→A and C→U transition rates. Molnupiravir (a prodrug of ß-d-N4-hydroxycytidine) has been recently approved for the treatment of SARS-CoV-2 infection. Its triphosphate derivative can be incorporated into viral RNA and extended by the coronavirus RNA polymerase. Incorrect base pairing and inefficient extension by the polymerase promote mutagenesis by increasing the G→A and C→U transition frequencies. Despite having remarkable antiviral action and resilience to drug resistance, carcinogenic risks and genotoxicity are important concerns limiting their extended use in antiviral therapy.

Nucleotide sequences of IRES domains IV and V of natural ECHO virus type 11 isolates with different replicative capacity phenotypes.

ECHO viruses (ECV) belong to the enterovirus genus of the Picornaviridae family and are the most frequently isolated from clinical and environmental samples. They are responsible for a wide variety of clinical syndromes involving most organs of the human body. We previously postulated that some of the variations in the recognition of ECHO virus type 11 (ECV 11) strains by a group specific monoclonal antibody (Mab) which we have studied could be explained by variations in their replicative capacity in cell culture and variations within the 5' nontranslated region (5' NTR) of their genomes. To support this hypothesis, the replicative capacity in cell culture and the nucleotide sequences of domains IV and V of the IRES of the genome of five ECV11 strains (the Gregory reference strain and four wild isolates) were determined, and analysed. Our results indicate that the replicative capacity of wild ECV11 isolates studied by one-step growth cycle in both HEp-2 and Vero cell cultures showed variations among strains in comparison with the Gregory reference strain. The clinical ECV11 strains replicated as well as the reference strain, however environmental strains displayed a phenotype with a significant reduction of replication. The sequences of ECV 11 strains showed significant conservation with that of the poliovirus (PV1) Mahoney strain The comparative examination of the predicted secondary structures revealed, that the nucleotide variations did not affect the secondary structure of stem-loop structure IV and V in the IRES element, however differences were especially observed in the apical stem region (nucleotides 483 to 509) of the domain V of the ECV11 strains and resulted in modification of the central stem structure.