Artemisia annuaL. extracts inhibit thein vitroreplication of SARS-CoV-2 and two of its variants

Abstract

SARS-CoV-2 (Covid-19) globally has infected and killed millions of people. Besides remdesivir, there are no approved small molecule-based therapeutics. Here we show that extracts of the medicinal plant, Artemisia annua L., which produces the antimalarial drug artemisinin, prevents SARS-CoV-2 replication in vitro. We measured antiviral activity of dried leaf extracts of seven cultivars of A. annua sourced from four continents. Hot-water leaf extracts based on artemisinin, total flavonoids, or dry leaf mass showed antiviral activity with IC₅₀ values of 0.1-8.7 μM, 0.01-0.14 μg, and 23.4-57.4 μg, respectively. One sample was >12 years old, but still active. While all hot water extracts were effective, concentrations of artemisinin and total flavonoids varied by nearly 100-fold in the extracts and antiviral efficacy was inversely correlated to artemisinin and total flavonoid contents. Artemisinin alone showed an estimated IC₅₀ of about 70 μM, and antimalarial artemisinin derivatives artesunate, artemether, and dihydroartemisinin were ineffective or cytotoxic at elevated micromolar concentrations. In contrast, the antimalarial drug amodiaquine had an IC₅₀ = 5.8 μM. The extracts had minimal effects on infection of Vero E6 or Calu-3 cells by a reporter virus pseudotyped by the SARS-CoV-2 spike protein. There was no cytotoxicity within an order of magnitude of the antiviral IC₉₀ values. Results suggest the active component in the extracts is likely something besides artemisinin or is a combination of components acting synergistically to block post-entry viral infection. Further studies will determine in vivo efficacy to assess whether A. annua might provide a cost-effective therapeutic to treat SARS-CoV-2 infections.