Production of a versatile SARS-CoV-2 main protease biosensor based on a dimerization-dependent red fluorescent protein

Invalidation of geraniin as a potential inhibitor against SARS-CoV-2 main protease

Recently, geraniin has been identified as a potent antiviral agent targeting SARS-CoV-2 main protease (Mpro). Considering the potential of geraniin in COVID-19 treatment, a stringent validation for its Mpro inhibition is necessary. Herein, we rigorously evaluated the in vitro inhibitory effect of geraniin on Mpro using the fluorescence resonance energy transfer (FRET), fluorescence polarization (FP), and dimerization-dependent red fluorescent protein (ddRFP) assays. Our data indicate that geraniin is not a potential inhibitor against Mpro based on the results from a set of in vitro assays. These results suggest a stringent in vitro validation with diverse biochemical assays is essential for the discovery of Mpro inhibitors, and the fluorescence quenching effect caused by natural products should be considered when evaluating Mpro inhibitors.

Improved fluorescence-based assay for rapid screening and evaluation of SARS-CoV-2 main protease inhibitors

The outbreak of coronavirus disease 2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a global threat to human health. In parallel with vaccines, efficacious antivirals are urgently needed. SARS-CoV-2 main protease (Mpro) is an attractive drug target for antiviral development owing to its key roles in virus replication and host immune evasion. Due to the limitations of currently available methods, the development of novel high-throughput screening assays is of the highest importance for the discovery of Mpro inhibitors. In this study, we first developed an improved fluorescence-based assay for rapid screening of Mpro inhibitors from an anti-infection compound library using a versatile dimerization-dependent red fluorescent protein (ddRFP) biosensor. Utilizing this assay, we identified MG-101 as a competitive Mpro inhibitor in vitro. Moreover, our results revealed that ensitrelvir is a potent Mpro inhibitor, but baicalein, chloroquine, ebselen, echinatin, and silibinin are not. Therefore, this robust ddRFP assay provides a faithful avenue for rapid screening and evaluation of Mpro inhibitors to fight against COVID-19.

Evaluation of natural products from virtual screenings as SARS-CoV-2 main protease inhibitors using combinational experiments

Recently, andrographolide, kaempferol, maslinic acid, rutin, and schaftoside have been identified as potent SARS-CoV-2 main protease (Mpro) inhibitors via molecular docking studies. However, no comprehensive in vitro testing of these compounds against Mpro has been conducted. In this study, we rigorously evaluated the in vitro inhibition of Mpro by these compounds using combinational experiments, including fluorescence resonance energy transfer (FRET), fluorescence polarization (FP), and dimerization-dependent red fluorescent protein (ddRFP) assays. Our data revealed that these compounds are not Mpro inhibitors based on the results from a set of in vitro assays. These results suggest that an efficient combination of a molecular docking approach and an experimental assay is essential for the discovery of Mpro inhibitors in the future.