The natural stilbenoid (–)-hopeaphenol inhibits cellular entry of SARS-CoV-2 USA-WA1/2020, B.1.1.7 and B.1.351 variants

Tietjen, Ian; Cassel, Joel; Register, Emery T.; Zhou, Xiang Yang; Messick, Troy E.; Keeney, Frederick; Lu, Lily D.; Beattie, Karren D.; Rali, Topul; Ertl, Hildegund C. J.; Salvino, Joseph M.; Davis, Rohan A.; Montaner, Luis J.

Antivirals are urgently needed to combat the global SARS-CoV-2/COVID-19 pandemic, supplement existing vaccine efforts, and target emerging SARS-CoV-2 variants of concern. Small molecules that interfere with binding of the viral spike receptor binding domain (RBD) to the host ACE2 receptor may be effective inhibitors of SARS-CoV-2 cell entry. Here we screened 512 pure compounds derived from natural products using a high-throughput RBD/ACE2 binding assay and identified (–)-hopeaphenol, a resveratrol tetramer, in addition to vatalbinoside A and vaticanol B, as potent and selective inhibitors of RBD/ACE2 binding and viral entry. For example, (–)-hopeaphenol disrupted RBD/ACE2 binding with a 50% inhibitory concentration (IC50) of 0.11 μM in contrast to an IC50 of 28.3 μM against the unrelated host ligand/receptor binding pair PD-1/PD-L1 (selectivity index = 257.3). When assessed against the USA-WA1/2020 variant, (–)-hopeaphenol also inhibited entry of a VSVΔG-GFP reporter pseudovirus expressing SARS-CoV-2 spike into ACE2-expressing Vero-E6 cells and in vitro replication of infectious virus in cytopathic effect assays (IC50 = 10.2 μM) without cytotoxicity. Notably, (–)- hopeaphenol also inhibited two emerging variants of concern originating from the United Kingdom (B.1.1.7) and South Africa (B.1.351) in both cytopathic effect and spike-containing pseudovirus assays with similar (B.1.1.7) or improved (B.1.351) efficacies over the USA- WA1/2020 variant. These results identify (–)-hopeaphenol and related stilbenoid analogues as potent and selective inhibitors of viral entry across multiple SARS-CoV-2 variants including those with increased infectivity and/or reduced susceptibility to existing vaccines. Importance SARS-CoV-2 antivirals are needed to supplement existing vaccine efforts and target emerging viral variants with increased infectivity or reduced susceptibility to existing vaccines. Here we show that (–)-hopeaphenol, a naturally-occurring stilbenoid compound, in addition to its analogues vatalbinoside A and vaticanol B, inhibit SARS-CoV-2 by blocking the interaction of the viral spike protein with the cellular ACE2 entry receptor. Importantly, in addition to inhibiting the early USA-WA1/2020 SARS-CoV-2 variant, hopeaphenol also inhibits emerging variants of concern including B.1.1.7 (“United Kingdom variant”) and B.1.351 (“South Africa variant”), with improved efficacy against B.1.351. (–)-Hopeaphenol therefore represents a new antiviral lead against infection from multiple SARS-CoV-2 variants.