Biochemical screening for SARS-CoV-2 main protease inhibitors

The Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2) pandemic represents a global challenge. SARS-CoV-2's ability to replicate in host cells relies on the action of its non-structural proteins, like its main protease (M(pro)). This cysteine protease acts by processing the viruses' precursor polyproteins. As proteases, together with polymerases, are main targets of antiviral drug design, we here have performed biochemical high throughput screening (HTS) with recombinantly expressed SARS-CoV-2 M(pro). A fluorescent assay was used to identify inhibitors in a compound library containing known drugs, bioactive molecules and natural products. These screens led to the identification of 13 inhibitors with IC(50) values ranging from 0.2 μM to 23 μM. The screens confirmed several known SARS-CoV M(pro) inhibitors as inhibitors of SARS-CoV-2 M(pro), such as the organo-mercuric compounds thimerosal and phenylmercuric acetate. Benzophenone derivatives could also be identified among the most potent screening hits. Additionally, Evans blue, a sulfonic acid-containing dye, could be identified as an M(pro) inhibitor. The obtained compounds could be of interest as lead compounds for the development of future SARS-CoV-2 drugs.