Kinetic Characterization of SARS-CoV-2 nsp13 ATPase Activity and Discovery of Small-Molecule Inhibitors.

SARS-CoV-2 non-structural protein 13 (nsp13) is a highly conserved helicase and RNA 5'-triphosphatase. It uses the energy derived from the hydrolysis of nucleoside triphosphates for directional movement along the nucleic acids and promotes the unwinding of double-stranded nucleic acids. Nsp13 is essential for replication and propagation of all human and non-human coronaviruses. Combined with its defined nucleotide binding site and druggability, nsp13 is one of the most promising candidates for the development of pan-coronavirus therapeutics. Here, we report the development and optimization of bioluminescence assays for kinetic characterization of nsp13 ATPase activity in the presence and absence of single-stranded DNA. Screening of a library of 5000 small molecules in the presence of single-stranded DNA resulted in the discovery of six nsp13 small-molecule inhibitors with IC50 values ranging from 6 ± 0.5 to 50 ± 6 μM. In addition to providing validated methods for high-throughput screening of nsp13 in drug discovery campaigns, the reproducible screening hits we present here could potentially be chemistry starting points toward the development of more potent and selective nsp13 inhibitors, enabling the discovery of antiviral therapeutics.