ABSTRACT
Epidemiological data demonstrate that SARS-CoV-2 variants of concern (VOC) B.1.1.7 and B.1.617.2 are more transmissible and infections are associated with a higher mortality than non-VOC virus infections. Phenotypic properties underlying their enhanced spread in the human population remain unknown. B.1.1.7 virus isolates displayed inferior or equivalent spread in most cell lines and primary cells compared to an ancestral B.1 SARS-CoV-2, and were outcompeted by the latter. Lower infectivity and delayed entry kinetics of B.1.1.7 viruses were accompanied by inefficient proteolytic processing of spike. B.1.1.7 viruses failed to escape from neutralizing antibodies, but slightly dampened induction of innate immunity. The bronchial cell line NCI-H1299 supported 24- and 595-fold increased growth of B.1.1.7 and B.1.617.2 viruses, respectively, in the absence of detectable ACE2 expression and in a spike-determined fashion. Superior spread in NCI-H1299 cells suggests that VOCs employ a distinct set of cellular cofactors that may be unavailable in standard cell lines.
ABSTRACT
Effective and affordable treatments for patients suffering from coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), are needed. We report in vitro efficacy of Artemisia annua extracts as well as artemisinin, artesunate, and artemether against SARS-CoV-2. The latter two are approved active pharmaceutical ingredients of anti-malarial drugs. Proof-of-concept for prophylactic efficacy of the extracts was obtained using a plaque-reduction assay in VeroE6 cells. Subsequent concentration-response studies using a high-throughput antiviral assay, based on immunostaining of SARS-CoV-2 spike glycoprotein, revealed that pretreatment and treatment with extracts, artemisinin, and artesunate inhibited SARS-CoV-2 infection of VeroE6 cells. In treatment assays, artesunate (50% effective concentration (EC50): 7 g/mL) was more potent than the tested plant extracts (128-260 g/mL) or artemisinin (151 g/mL) and artemether (>179 g/mL), while generally EC50 in pretreatment assays were slightly higher. The selectivity index (SI), calculated based on treatment and cell viability assays, was highest for artemisinin (54), and roughly equal for the extracts (5-10), artesunate (6) and artemether (<7). Similar results were obtained in human hepatoma Huh7.5 cells. Peak plasma concentrations of artesunate exceeding EC50 values can be achieved. Clinical studies are required to further evaluate the utility of these compounds as COVID-19 treatment.
