Chrysin 7-O-ß-D-glucuronide, a dual inhibitor of SARS-CoV-2 3CLpro and PLpro, for the prevention and treatment of COVID-19.

The emergence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) resulted in the coronavirus disease 2019 (COVID-19) pandemic. Given the advent of subvariants, there is an urgent need to develop novel drugs. The aim of this study was to find SARS-CoV-2 inhibitors from Scutellaria baicalensis Georgi targeting the proteases 3CLpro and PLpro. After screening 25 flavonoids, chrysin 7-O-ß-D-glucuronide was found to be a potent inhibitor of SARS-CoV-2 on Vero E6 cells, with half-maximal effective concentration of 8.72 µM. Surface plasmon resonance assay, site-directed mutagenesis and enzymatic activity measurements indicated that chrysin-7-O-ß-D-glucuronide inhibits SARS-CoV-2 by binding to H41 of 3CLpro, and K157 and E167 of PLpro. Hydrogen-deuterium exchange mass spectrometry analysis showed that chrysin-7-O-ß-D-glucuronide changes the conformation of PLpro. Finally, chrysin 7-O-ß-D-glucuronide was shown to have anti-inflammatory activity, mainly due to reduction of the levels of the pro-inflammatory cytokines interleukin (IL)-1ß and IL-6.

Flavonols as potential antiviral drugs targeting SARS-CoV-2 proteases (3CLpro and PLpro), spike protein, RNA-dependent RNA polymerase (RdRp) and angiotensin-converting enzyme II receptor (ACE2).

The novel coronavirus outbreak (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) represents the actual greatest global public health crisis. The lack of efficacious drugs and vaccines against this viral infection created a challenge for scientific researchers in order to find effective solutions. One of the promising therapeutic approaches is the search for bioactive molecules with few side effects that display antiviral properties in natural sources like medicinal plants and vegetables. Several computational and experimental studies indicated that flavonoids especially flavonols and their derivatives constitute effective viral enzyme inhibitors and possess interesting antiviral activities. In this context, the present study reviews the efficacy of many dietary flavonols as potential antiviral drugs targeting the SARS-CoV-2 enzymes and proteins including Chymotrypsin-Like Protease (3CLpro), Papain Like protease (PLpro), Spike protein (S protein) and RNA-dependent RNA polymerase (RdRp), and also their ability to interact with the angiotensin-converting enzyme II (ACE2) receptor. The relationship between flavonol structures and their SARS-CoV-2 antiviral effects were discussed. On the other hand, the immunomodulatory, the anti-inflammatory and the antiviral effects of secondary metabolites from this class of flavonoids were reported. Also, their bioavailability limitations and toxicity were predicted.