Reply to Troth et al

We thank Troth et al. for the opportunity to extend the discussion of our data on the mutagenicity of N4-hydroxycytidine (rNHC) [1]. We view our work as providing the proof-of-concept showing that as rNHC is phosphorylated to its active ribonucleoside 5’-triphosphate, the ribonucleoside 5’-diphosphate intermediate that is the immediate precursor to the ribonucleoside 5’-triphosphate also plays the equivalent role of an intermediate precursor for the synthesis of 2’-deoxyribonucleoside 5’-diphosphate (by the activity of ribonucleotide reductase). This is the normal pathway for the synthesis of DNA precursors used from bacteria to humans; thus, it should not be a question of whether the mutagenic form of dNHC as a precursor to DNA is formed, but rather what the impact is. On this point we have unpublished cell-based data supporting conversion of rNHC to dNHC, albeit at low intracellular levels. Also, the near identity of rNHC to cytidine (the addition of a single oxygen atom) makes it likely that rNHC and cytidine undergo similar metabolism in the cell

β-D-N4-hydroxycytidine (NHC) Inhibits SARS-CoV-2 Through Lethal Mutagenesis But Is Also Mutagenic To Mammalian Cells

Mutagenic ribonucleosides can act as broad-based antiviral agents. They are metabolized to the active ribonucleoside triphosphate form and concentrate in the genomes of RNA viruses during viral replication. β-D-N 4-hydroxycytidine (NHC, the initial metabolite of molnupiravir) is more than 100-fold more active than ribavirin or favipiravir against SARS-CoV-2, with antiviral activity correlated to the level of mutagenesis in virion RNA. However, NHC also displays host mutational activity in an animal cell culture assay, consistent with RNA and DNA precursors sharing a common intermediate of a ribonucleoside diphosphate. These results indicate that highly active mutagenic ribonucleosides may hold risk for the host