Dual-Site Inhibition of SARS-CoV-2 RNA-Dependent RNA Polymerase by Small Molecules Able to Block Viral Replication Identified through a Computer-Aided Drug Discovery Approach.

Since its emergence in late 2019, SARS-CoV-2, the causative agent of COVID-19, has continued to spread globally, with more than 7 million reported deaths as of March 2025. Among the viral nonstructural proteins, nsp12 serves as the RNA-dependent RNA polymerase (RdRp), mediating viral genome replication and transcription in concert with its cofactors nsp7 and nsp8. To date, only two nucleoside analogs specifically targeting SARS-CoV-2 nsp12, remdesivir and molnupiravir, have been authorized by the FDA for COVID-19 treatment. In response to the need for additional safe and effective antiviral agents, we screened two extensive in silico libraries of safe-in-man compounds (>9,000) and natural compounds (>249,000), against the SARS-CoV-2 nsp12/7/8 complex, targeting the orthosteric and two allosteric nsp12 sites, using the EXSCALATE (EXaSCale smArt pLatform Against paThogEns) platform. Compounds were then selected based on docking score significance, novelty for the target, and clinical safety profiles. The top 119 candidates were subsequently evaluated in a biochemical assay to assess their potential to inhibit SARS-CoV-2 nsp12/7/8 polymerase activity, identifying 42 compounds able to block it, among which four showed IC