AT-527, a Double Prodrug of a Guanosine Nucleotide Analog, Is a Potent Inhibitor of SARS-CoV-2 In Vitro and a Promising Oral Antiviral for Treatment of COVID-19

Steven S. Good, Jonna Westover, Kie Hoon Jung, Xiao-Jian Zhou, Adel Moussa, Paolo La Colla, Gabriella Collu, Bruno Canard, Jean-Pierre Sommadossi

The impact of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative agent of COVID-19, is global and unprecedented. Although remdesivir has recently been approved by the FDA to treat SARS-CoV-2 infection, no oral antiviral is available for outpatient treatment. AT-527, an orally administered double prodrug of a guanosine nucleotide analog, was previously shown to be highly efficacious and well tolerated in hepatitis C virus (HCV)-infected subjects. Here, we report the potent in vitro activity of AT-511, the free base of AT-527, against several coronaviruses, including SARS-CoV-2. In normal human airway epithelial cells, the concentration of AT-511 required to inhibit replication of SARS-CoV-2 by 90% (EC90) was 0.47mM, very similar to its EC90 against human coronavirus (HCoV)-229E, HCoV-OC43, and SARS-CoV in Huh-7 cells. Little to no cytotoxicity was observed for AT-511 at concentrations up to 100mM. Substantial levels of the active triphosphate metabolite AT-9010 were formed in normal human bronchial and nasal epithelial cells incubated with 10mM AT-511 (698 6 15 and 236 6 14mM, respectively), with a half-life of at least 38 h. Results from steady-state pharmacokinetic and tissue distribution studies of nonhuman primates administered oral doses of AT-527, as well as pharmacokinetic data from subjects given daily oral doses of AT-527, predict that twice daily oral doses of 550 mg AT-527 will produce AT-9010 trough concentrations in human lung that exceed the EC90 observed for the prodrug against SARS-CoV-2 replication. This suggests that AT-527 may be an effective treatment option for COVID-19.


SARS-CoV-2 virus, COVID-19, (HCoV)-229E, HCoV-OC43, Huh-7, RD cells, infection, viral replication, EpiAirway (AIR-100), guanosine nucleotide analog, USA/WA1-2020, Infectious disease research, viral infection

Materials Tested

USA/WA1-2020, Molnupiravir, AT-511

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