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

Abstract

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 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 0.47 μM, very similar to its EC90 against HCoV-229E, HCoV-OC43 and SARS-CoV in Huh-7 cells. Little to no cytotoxicity was observed for AT-511 at concentrations up to 100 μM. Substantial levels of the active triphosphate metabolite AT-9010 were formed in normal human bronchial and nasal epithelial cells incubated with 10 μM AT-511 (698 ± 15 and 236 ± 14 μM, respectively), with a half-life of at least 38 h. Results from steady-state pharmacokinetic and tissue distribution studies of non-human 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.

A robust SARS-CoV-2 replication model in primary human epithelial cells at the air liquid interface to assess antiviral agents

“…Anti-SARS-CoV-2 activity of AT-511, the free base form of AT-527, was not observed in VeroE6, Huh7 cells nor in the HAEC cultures. This is in contrast with a recent publication where sub-micromolar activities of AT-511 were observed in very similar assay systems ( Good et al, 2021 ). Currently, there is no data to reconcile this discrepancy.…”

“…Four nucleoside analogues that are known inhibitors of SARS-CoV-2 replication were selected as reference for studies in HAEC cultures. These included remdesivir, GS-441524 ( Li et al, 2021 ; Pruijssers et al, 2020 ; Shi et al, 2020 ; Xie et al, 2020 ; Zandi et al, 2020 ) (the parent nucleoside of remdesivir), EIDD-1931 ( Zandi et al, 2020 ; Good et al, 2021 ; Sheahan et al, 2020 ) (the parent nucleoside of molnupiravir) and AT-511 ( Good et al, 2021 ) [a guanosine nucleotide analogue with activity against hepatitis C virus (HCV)]. To select a suitable concentration range of these molecules, we first explored their effect in VeroE6 and Huh7 cell lines.…”

“…The effect of EIDD-1931, which is the parent nucleoside of the ester prodrug molnupiravir (EIDD-2801), was also investigated. EIDD-1931 has been reported to exert antiviral activity against various human coronaviruses and molnupiravir is currently in clinical trials for SARS-CoV-2 ( Good et al, 2021 ; Sheahan et al, 2020 ). Initial interim data from a phase II study provides first evidence for antiviral activity in COVID patients ( https://www.croiconference.org/abstract/reduction-in-infectious-sars-cov-2-in-treatment-study-of-covid-19-with-molnupiravir/ ).…”

Progress and pitfalls of a year of drug repurposing screens against COVID-19

“…AT-527, a 2’-fluoro-2’-methyl guanosine analog prodrug, is currently being evaluated to treat HCV and SARS-CoV-2 infections. It has returned promising results in differentiated human airway primary cells and shown favorable pharmacokinetics profile after oral delivery to human and non-human primates [ 36 ]. Likewise, an orally available prodrug of the cytidine analog ß-d-N 4 -hydroxycytidine, EIDD-2801 (molnupiravir) that was in development against influenza viruses [ 37 •• ], was found to be orally efficacious against SARS-CoV-2 in the ferret infection model, reducing both virus burden and direct contact transmission rates [ 38 •• ].…”

Time to ‘Mind the Gap’ in novel small molecule drug discovery for direct-acting antivirals for SARS-CoV-2

“…While IV administration is compatible for treatment of hospitalized patients, this requirement presents a significant challenge in treatment of exposures (prophylactic), asymptomatic or mild symptoms, as these individuals will not be admitted to overburdened hospitals and would benefit from an orally bioavailable drug that can be obtained from the local pharmacy. Repurposed, broad spectrum, nucleotide analog antivirals targeting replication that have advanced into clinical trials include favipiravir [ 25 ], MK-4482 (molnupiravir, EIDD-2801) and AT-527 [ 26 ]. Favipiravir inhibits by a combination of chain termination, slowed viral RNA synthesis, and lethal mutagenesis, while MK-4482 is a cytidine nucleoside analogue and acts as a mutagen like ribavirin [ 27 ].…”