Production of SARS-CoV-2 Omicron Variant Main Protease for Screening Approved Drugs as Its Potential Inhibitors

OBJECTIVE To develop a high-throughput screening assay for the discovery of Omicron variant main protease(OM-Mpro) inhibitors based on the principle of fluorescence resonance energy transfer(FRET).

METHODS The recombinant OM-Mpro enzyme was expressed in Escherichia coli Rosetta(DE3) cells, and further purified by a HisTrap^TM chelating column. Subsequently, the enzymatic activity of OM-Mpro and wild type main protease(WT-Mpro) enzymes and inhibition of nirmatrelvir against both proteases were measured using FERT assay. With the FRET assay, OM-Mpro inhibitors were identified via high-throughput screening of an approved drug library.

RESULTS The active OM-Mpro enzyme was successfully prepared from E. coli cells. OM-Mpro and WT-Mpro enzymes possessed the same enzymatic activity, and OM-Mpro remained susceptible to nirmatrelvir in vitro. Through high-throughput screening of the marketed drug library, it was found that cetylpyridinium chloride(CPC) is a mixed-type OM-Mpro inhibitor in vitro with an IC₅₀ value of 8.76 μmol·L⁻¹.

CONCLUSION A robust FRET assay has been successfully developed based on the production of active OM-Mpro enzyme for screening of its inhibitors, and CPC is identified as a potential lead compound against OM-Mpro in vitro. This study provides a promising avenue for rapid discovery of broad-spectrum antivirals against coronavirus protease.