Identification of Botanical Viral Entry Inhibitors for SARS-CoV-2.

The examination of biodiversity across the world has historically been a critical part of drug development and led to the discovery of common medications for many medical issues including pain management, cancer, heart disease, and infections. During the SARS-CoV-2 pandemic, the use of natural supplements in the United States has increased. The efficacy of these natural products to prevent SARS-CoV-2 infection and the safety of their use remains unexplored; therefore, more research must be done to determine which supplements have antiviral properties. The Quave Natural Product Library (QNPL) is a collection of over 2,000 botanical and fungal extracts and includes the 40 most used natural supplements in the United States. Collection of the biological samples for the library requires field expeditions to areas throughout the world with high levels of biodiversity. Each of these extracts were tested in a SARS-CoV-2 pseudotyped virus system to determine which extracts inhibit viral entry, specifically the virus spike protein binding to host cells ACE2 receptors. Mammalian cell cytotoxicity assays were run in parallel. Evaluation of 1,887 extracts and 18 single compounds from the QNPL against SARS-CoV-2 identified. 317 extracts derived from 134 species across 76 families (1 lichen, 2 fungi, 73 plant families) exhibited ≥50% inhibition activity in the wild type spike pseudotyped model at 20 µg/mL. Of these bioactive extracts, 129 extracts derived from 95 plant species exhibited ≥85% inhibition activity and ≤15% cytotoxicity in the wild-type model. Once these 129 extracts were identified, an interesting pattern emerged indicating many hits were from species that are known to be cardiotoxic due to rich composition of cardiac glycosides. For further selection and testing, we reviewed each extract and consulted the literature to eliminate extracts with those properties or similar compounds, which narrowed down our interest to 8 extracts. These extracts were further validated in a concentration-response assay in a pseudotyped virus model. The EC50 values of the top 3 extracts were all under 10 µg/mL. These 3 extracts all exhibited activity (≥85% inhibition activity) in the wildtype and variant pseudotyped models. Testing in live SARS-CoV-2 confirmed antiviral activity from 2 of 3 extracts, Plant Aflowers and Plant B roots. Further chemical characterization of the major metabolites of these two hits was performed using MS/MS fragmentation data compared with the literature, in silico prediction, and web-based databases. The results revealed phenylpropanoids, flavonoids, triterpenes, glycosidic terpenes, and fatty acids as the major chemical classes. The next steps of this study seek to identify and isolate purified bioactive compounds to further understand their role in SARS-CoV-2 inhibition.