The RNA-dependent RNA polymerase of SARS-CoV-2 can serve as a pivot for developing the treatment of coronavirus disease 2019. Molnupiravir, a broad-spectrum antiviral and a prodrug of the nucleoside analogue β-D-N4-hydroxycytidine (NHC) have the potential to increase G to A and C to U transition mutations in reproducing coronaviruses. 

This rise in mutation frequencies tends to increase the antiviral effects; however, biochemical data of molnupiravir-induced mutagenesis is not available. 

A study investigated the effects of the active compound NHC 5’-triphosphate (NHC-TP) against the purified SARS-CoV-2 RNA-dependent RNA polymerase complex and made the following observations- 

• The efficiency of incorporation of natural nucleotides than NHC-TP into model RNA substrates was highest in GTP followed by ATP, UTP and CTP respectively.
• This highlighted the competition of NHC-TP predominantly with CTP for incorporation.
• Incorporation of monophosphate in the RNA primer strand did not inhibit the RNA synthesis significantly. 
• After infiltrating the template strand, NHC-monophosphate showed similar efficiencies in creating both NHC:G and NHC:A base pairs. 
• NHC:G product extension was fairly inhibited, but higher nucleotide concentrations could overpower this stoppage. 
• However, the NHC:A base pair caused G to A (G:NHC:A) or C to U (C:G:NHC:A:U) mutations. 

These biochemical data support the RNA mutagenesis mediated via the template strand mechanism of action of molnupiravir.

Source- Journal of Biological Chemistry,2021;297(1):100770. https://doi.org/10.1016/j.jbc.2021.100770.