2-Thiouridine is a Broad-spectrum Antiviral Ribonucleoside Analogue Against Positive-strand RNA Viruses

Emerging and reemerging viral infections, such as the dengue virus (DENV), continue to cause public health concerns, affecting millions of people worldwide annually. The recent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak resulted in significant morbidity and mortality worldwide, seriously impacting human health and the global economy. Given the lack of effective and specific therapeutics against most emerging or reemerging viruses, the development of effective therapeutic measures against such viruses is urgently needed. Most RNA viruses have RNA-dependent RNA polymerase (RdRp), which is indispensable for the replication and transcription of viral genomes. Moreover, the core structural features of viral RdRps are functionally essential and conserved across a wide range of viruses. Thus, viral RdRp serves as a promising target for broad-spectrum antivirals. In this study, we screened nucleoside analogues from a compound library of Hokkaido University, identifying 2-thiouridine (s2U) as a broad-spectrum antiviral ribonucleoside analogue. In particular, s2U exhibited potent antiviral activity against several positive-strand RNA [ssRNA(+)] viruses, including orthoflaviviruses such as DENV and coronaviruses such as SARS-CoV-2. s2U inhibited RNA synthesis catalyzed by viral RdRp, thereby reducing viral RNA replication and improving the survival rate of mice challenged with lethal DENV2 or SARS-CoV-2 in our animal models. In addition to the potent antiviral activities in vitro and in vivo, s2U exhibited no significant toxicity, suggesting its potential as a broad-spectrum antiviral agent against ssRNA(+) viruses, including orthoflaviviruses and coronaviruses.