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

Abstract

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 uM in contrast to an IC50 of 28.3 uM 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 VSVdeltaG-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 uM) 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.

Immune Responses of a Novel Bi-Cistronic SARS-CoV-2 DNA Vaccine Following Intradermal Immunization With Suction Delivery

“…Sera collected from immunized animals were evaluated in a modified high-throughput surrogate neutralization assay that uses homogenous time resolved fluorescence (HTRF) technology, where SARS-CoV-2 spike RBD from WT (USA-WA1/2020), Beta (B.1.351), or Delta (B.1.617.2) variants were assessed for ability to interact with ACE2 protein. In this assay, initial experiments showed that 50% human control plasma (i.e., from individuals without SARS-CoV-2 exposure or COVID-19) had no effect on the HTRF signal, while the control inhibitory antibody REGN10933 (casirivimab) blocked HTRF signal due to WT, Beta, or Delta variant RBDs in the presence of human plasma with half-maximal inhibitory concentrations (IC50s) of 47.3, 937.5, and 35.4 ng/mL, consistent with previous reports (33,34). Serial dilutions of day 0 and 41 sera from hamsters were then evaluated for their ability to inhibit binding between ACE2 and the RBD variants of SARS-CoV-2.…”