ABSTRACT
BackgroundSARS-CoV-2 variants of concern (VOC) represent an alarming threat as they show altered biological behavior and may escape vaccination effectiveness. Some exhibit increased pathogenicity and transmissibility compared to the original wild type WUHAN (Hu-1). Broad-spectrum antivirals could complement and further enhance preventive benefits achieved through SARS-CoV-2 vaccination campaigns MethodsThe anti-coronavirus activity of Echinacea purpurea (Echinaforce(R) extract, EF) against (i) VOCs B1.1.7 (alpha), B.1.351.1 (beta), P.1 (gamma), B1.617.2 (delta), AV.1 (Scottish) and B1.525 (eta), (ii) SARS-CoV-2 spike (S) protein-pseudotyped viral particles and reference strain OC43 as well as (iii) wild-type SARS-CoV-2 (Hu-1) were analyzed. Molecular dynamics (MD) were applied to study interaction of Echinaceas phytochemical markers with known pharmacological viral and host cell targets. ResultsEF extract broadly inhibited propagation of all investigated SARS-CoV-2 VOCs as well as entry of SARS-CoV-2 pseudoparticles at EC50s ranging from 3.62 to 12.03 {micro}g/ml. Preventive addition of 20 {micro}g/ml EF to epithelial cells significantly reduced sequential infection with SARS-CoV-2 (Hu-1) as well as with the common human strain OC43. MD analyses showed constant binding affinities to Hu-1, B1.1.7, B.1.351, P.1 and B1.617.2-typic S protein variants for alkylamides, caftaric acidand feruoyl-tartaric acid in EF extract. They further indicated that the EF extract could possibly interact with TMPRSS-2, a serine protease required for virus endocytosis. ConclusionsEF extract demonstrated stable antiviral activity across 6 tested VOCs, which is likely due to the constant affinity of the contained phytochemical marker substances to all spike variants. A possible interaction of EF with TMPRSS-2 partially would explain cell protective benefits of the extract by inhibition of endocytosis. EF may therefore offer a supportive addition to vaccination endeavors in the control of existing and future SARS-CoV-2 virus mutations.
ABSTRACT
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a betacoronavirus in the subgenus Sarbecovirus causes a respiratory disease with varying symptoms referred to as coronavirus disease 2019 (COVID-19) and is responsible for a pandemic that started in early 2020. With no vaccines or effective antiviral treatments available, and infection and fatality numbers continuing to increase globally, the quest for novel therapeutic solutions remains an urgent priority. Rocaglates, a class of plant-derived cyclopenta[b]benzofurans, exhibit broad-spectrum antiviral activity against positive- and negative-sense RNA viruses. This compound class inhibits eukaryotic initiation factor 4A (eIF4A)-dependent mRNA translation initiation, resulting in strongly reduced viral RNA translation. The synthetic rocaglate CR-31-B (-) has previously been shown to inhibit the replication of human coronaviruses, such as HCoV-229E and MERS-CoV, as well as Zika-, Lassa-, Crimean Congo hemorrhagic fever virus in primary cells. Here, we assessed the antiviral activity of CR-31-B (-) against SARS-CoV-2 using both in vitro and ex vivo cell culture models. In African green monkey Vero E6 cells, CR-31-B (-) inhibited SARS-CoV-2 replication with an EC50 of ~1.8 nM. In line with this, viral protein accumulation and replication/transcription complex formation were found to be strongly reduced by this compound. In an ex vivo infection system using human airway epithelial cells, CR-31-B (-) was found to cause a massive reduction of SARS-CoV-2 titers by about 4 logs to nearly non-detectable levels. The data reveal a potent anti-SARS-CoV-2 activity by CR-31-B (-), corroborating previous results obtained for other coronaviruses and supporting the idea that rocaglates may be used in first-line antiviral intervention strategies against novel and emerging RNA virus outbreaks.
