An orally bioavailable broad-spectrum antiviral inhibits SARS-CoV-2 in human airway epithelial cell cultures and multiple coronaviruses in mice

Original Article: Sheahan TP, Sims AC, Zhou S, Graham RL, Pruijssers AJ, Agostini ML, Leist SR, Schäfer A, Dinnon KH 3rd, Stevens LJ, Chappell JD, Lu X, Hughes TM, George AS, Hill CS, Montgomery SA, Brown AJ, Bluemling GR, Natchus MG, Saindane M, Kolykhalov AA, Painter G, Harcourt J, Tamin A, Thornburg NJ, Swanstrom R, Denison MR, Baric RS. An orally bioavailable broad-spectrum antiviral inhibits SARS-CoV-2 in human airway epithelial cell cultures and multiple coronaviruses in mice. Sci Transl Med. 2020 Apr 29;12(541).

Author of Summary: Bárbara Oliveira; Revision and translation: Giulia Poggi, Agnese Loda

Original Article Published on April 29th, 2020

Application of the broad-spectrum antiviral β-D-N4-hydroxycytidine (NHC, EIDD-1931) in MERS-CoV, SARS-CoV and SARS-CoV-2 infection. Evidence from in vitro and in vivo studies. 

In the past 20 years, three novel human coronaviruses (CoV) have emerged: MERS-CoV, SARS-CoV and, recently the SARS-CoV-2. Currently, there are no approved therapies specific for any human CoV. β-D-N4-hydroxycytidine (NHC, EIDD-1931) is an orally bioavailable ribonucleoside analog with broad-spectrum antiviral activity against various RNA viruses including influenza, Ebola, CoV, and Venezuelan equine encephalitis virus (VEEV). For VEEV, the mechanism of action (MOA) for NHC has been shown to be through lethal mutagenesis where deleterious transition mutations accumulate in viral RNA. Sheahan et al., used different human cell cultures and mouse models to assess the range of NHC antiviral activity against the novel human CoV, its mechanism of action and in vivo efficacy in models of CoV pathogenesis.

Their main findings include:

• Potential inhibitory effect of NHC on MERS-CoV and SARS-CoV-2 replication: Dose range of NHC for 48h on human lung epithelial cell line Calu-3 2B4 or the African green monkey kidney (Vero) cells leads to a dose-dependent reduction in viral genomic RNA, detected via MERS-luciferase approach. Additionally, NHC induces dose dependent reduction in virus production (without cytotoxic effects) in human airway epithelial cell cultures (HAE) exposed to MERS-CoV and SARS-CoV-2.

• NHC is effective against remdesivir (RDV)-resistant virus: There is high sequence conservation in the RNA-dependent RNA polymerase (RdRp, nsp12) across CoV. Mutations in RdRp residues F480L and V557L have been previously linked to CoV resistance to RDV, another broad-spectrum nucleoside analog. However, the two RDV resistance mutations, alone or together, conferred increased sensitivity to inhibition by NHC suggesting that NHC and RDV may select for exclusive and mutually sensitizing resistance pathways.

• NHC antiviral activity is associated with increased viral mutation rates in MERS-CoV: Highly-sensitive high-fidelity deep sequencing approach (Primer ID NGS) revealed an enrichment for A:G and C:U transitions in MERS-CoV RNA in HAE cell cultures after NHC treatment. Moreover, the magnitude of the error rate in NHC-treated cultures correlated with virus titer reduction.

• Therapeutic EIDD-2801 reduces SARS-CoV replication and pathogenesis: In vivo studies were conducted using EIDD-2801, a NHC prodrug with improved in vivo pharmacokinetics and oral bioavailability in humans and non-human primates. Therapeutic EIDD-2801 showed antiviral activity against SARS-CoV in vivo, especially when treatment was initiated until up to 12h post-infection. In mouse-adapted SARS-CoV or MERS-CoV infection, EIDD-2801 significantly reduced body weight loss and lung hemorrhage when initiated up to 24h after infection and improved bronchoconstriction or pulmonary obstruction if treatment was initiated up to 12h after infection. Moreover, nucleotide transitions observed in MERS-CoV genomes in vitro, were also observed in vivo when treatment was initiated prior to and up to 12 hours post infection. EIDD-2801-driven mutagenesis correlated well with the reductions in viral load, suggesting an error catastrophe-driven mechanism of action under therapeutic conditions.

Although the results of this study are encouraging, two main limitations should be considered: the lack of in vivo efficacy testing with SARS-CoV-2 and the lack of drug efficacy testing in CoV aged mouse models. These studies along with studies in primate models of human disease will be of great relevance to address the therapeutic potential of EIDD-2801 in treating SARS-CoV, SARS-CoV-2 or MERS-CoV infection.