Effects of the 5′-Triphosphate Metabolites of Ribavirin, Sofosbuvir, Vidarabine, and Molnupiravir on CTP Synthase Catalysis and Filament Formation: Implications for Repurposing Antiviral Agents against SARS-CoV-2

Repurposing of antiviral drugs affords a rapid and effective strategy to develop therapies to counter pandemics such as COVID-19. SARS-CoV-2 replication is closely linked to the metabolism of cytosine-containing nucleotides, especially cytidine-5 '-triphosphate (CTP), such that the integrity of the viral genome is highly sensitive to intracellular CTP levels. CTP synthase (CTPS) catalyzes the rate-limiting step for the de novo biosynthesis of CTP. Hence, it is of interest to know the effects of the 5 '-triphosphate (TP) metabolites of repurposed antiviral agents on CTPS activity. Using E. coli CTPS as a model enzyme, we show that ribavirin-5 '-TP is a weak allosteric activator of CTPS, while sofosbuvir-5 '-TP and adenine-arabinofuranoside-5 '-TP are both substrates. beta-d-N-4-Hydroxycytidine-5 '-TP is a weak competitive inhibitor relative to CTP, but induces filament formation by CTPS. Alternatively, sofosbuvir-5 '-TP prevented CTP-induced filament formation. These results reveal the underlying potential for repurposed antivirals to affect the activity of a critical pyrimidine nucleotide biosynthetic enzyme.

Automated summary

Repurposed antiviral drugs have the potential to affect the activity of a critical pyrimidine nucleotide biosynthetic enzyme.