Artemisia annuaL. extracts inhibit thein vitroreplication of SARS-CoV-2 and two of its variants
Authors: Nair M.S. , Huang Y. , Fidock D.A. , Polyak S.J. , Wagoner J. , Towler M.J. , Weathers P.J. 
Published: January 2021

ABSTRACTEthnopharmacological relevanceArtemisia annuaL. has been used for millennia in Southeast Asia to treat “fever”. Many infectious microbial and viral diseases have been shown to respond toA. annuaand communities around the world use the plant as a medicinal tea, especially for treating malaria.Aim of the StudySARS-CoV-2 (the cause of Covid-19) globally has infected and killed millions of people. Because of the broad-spectrum antiviral activity of artemisinin that includes blockade of SARS-CoV-1, we queried whetherA. annuasuppressed SARS-CoV-2.Materials and MethodsUsing Vero E6 and Calu-3 cells, we measured anti viral activity SARS-CoV-2 activity against fully infectious virusof dried leaf extracts of seven cultivars ofA. annuasourced from four continents. IC50s were calculated and defined as (the concentrations that inhibited viral replication by 50%.) and CC50s (the concentrations that kill 50% of cells) were calculated.ResultsHot-water leaf extracts based on artemisinin, total flavonoids, or dry leaf mass showed antiviral activity with IC50values of 0.1-8.7 μM, 0.01-0.14 μg, and 23.4-57.4 μg, respectively. Antiviral efficacy did not correlate with artemisinin or total flavonoid contents of the extracts. One dried leaf sample was >12 years old, yet the hot-water extract was still found to be active. The UK and South African variants, B1.1.7 and B1.351, were similarly inhibited. While all hot water extracts were effective, concentrations of artemisinin and total flavonoids varied by nearly 100-fold in the extracts. Artemisinin alone showed an estimated IC50of about 70 μM, and the clinically used 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. 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 above the antiviral IC90values.ConclusionsA. annuaextracts inhibit SARS-CoV-2 infection, and the active component(s) in the extracts is likely something besides artemisinin or a combination of components that block virus infection at a step downstream of virus entry. Further studies will determine in vivo efficacy to assess whetherA. annuamight provide a cost-effective therapeutic to treat SARS-CoV-2 infections.List of compounds studiedAmodiaquineArtemisininArtesunateArtemetherDeoxyartemisininDihydroartemisininHighlightsArtemisia annuais effective in stopping replication of SARS-CoV-2 including 2 new variants.The anti-viral effect does not correlate to artemisinin, nor to the total flavonoid content.The anti-viral mechanism does not appear to involve blockade virus entry into cell.The plant offers two additional benefits: a decreased inflammatory response and blunting of fibrosis.A. annuamay provide a safe, low-cost alternative for treating patients infected with SARS-CoV-2.