Antiviral activity of Molnupiravir precursor NHC against SARS-CoV-2 Variants of Concern (VOCs) and implications for the therapeutic window and resistance

Abstract

SynopsisBackgroundThe UK Medicines and Regulatory Healthcare Agency (MHRA) have recently licensed the anti-viral drug, molnupiravir, for use in patients with mild-moderate COVID-19 disease with one or more risk factors for serious illness. Treatment with anti-viral drugs is best initiated early to prevent progression to severe disease, although the therapeutic window for intervention has not yet been fully defined.ObjectivesThis study aimed to determine the activity of the molnupiravir (NHC) to different SARS-CoV-2 Variants of Concern (VoCs), and to establish the therapeutic window in human lung cell model.MethodsDose response assays were performed in parallel to determine the IC50 (the concentration of drug required to inhibit virus titre by 50%) of NHC against different variants. Human ACE-2 A549 cells were treated with NHC at different time points either before, during or after infection with SARS- CoV-2.ResultsHere we demonstrate that ß-D-N4-hydroxycytidine (NHC), the active metabolite of molnupiravir, has equivalent activity against four variants of SARS-CoV-2 in a human lung cell line ranging 0.04-0.16µM IC50. Furthermore, we demonstrate that in-vitro activity of the drug is reduced in cells exposed to drug 48 hours after infection.ConclusionsOne of the main advantages of molnupiravir is that it can be administered orally, and thus given to patients in an out-patient setting. These results support giving the drug early on after diagnosis or even in prophylaxis for individuals with high risk of developing severe disease.

SARS-CoV-2 variant of concern type and biological sex affect efficacy of molnupiravir in dwarf hamster model of severe COVID-19

“…Inhibitory values were similar for all VOC tested and ranged from 0.27 (omicron) to 0.62 (alpha) µM, which closely resembled that against the original SARS-CoV-2 isolate 18,24 . Consistent with other cell culture data 16 , also VOC delta was highly sensitive to treatment (EC50 0.33 µM).…”

“…In the absence of controlled clinical data assessing molnupiravir efficacy against omicron, it is currently unclear to what degree the dwarf hamster-derived results extend to human therapy. Our study demonstrates, however, that pharmacological mitigation of severe COVID-19 is complex and that attempts to predict drug efficacy based on unchanged ex vivo inhibitory concentrations alone 16 may be premature. The dwarf hamster-based results alert to the need to continuously reassess therapeutic benefit of approved antivirals for individual patient subgroups as SARS-CoV-2 evolves and potential future VOC may emerge.…”

“…Based on geographical location of trial participants and VOC prevalence in the earlier versus later phase of the trial, an advisory board to the FDA considered lower efficacy of molnupiravir against VOC delta as a possible explanation for the mixed results 15 . However, VOC delta was efficiently inhibited by the molnupiravir parent metabolite N 4 -hydroxycytidine (NHC) in ex vivo studies 16 , suggesting unchanged sensitivity to the drug.…”

Significance of Immune Status of SARS-CoV-2 Infected Patients in Determining the Efficacy of Therapeutic Interventions

“…As per the news reports, India-based enterprise Glenmark has secured government approval for the large-scale manufacturing and antiviral Favipiravir drug to treat SARS-CoV-2 infected patients [ 27 ]. Furthermore, molnupiravir parent drug (NHC) combination of drugs against SARS-CoV-2 viruses are recommended in a trial version of the treatment plan [ 28 ], including ritonavir/ralproveravir or ribavirin by intravenous injection in addition to the inhalation of alpha interferon [ 26 ]. Another example is the cheap and widely-available steroid drug called Dexamethasone, pushed by UK experts as a potential treatment of SARS-CoV-2 infection, with suggestions signifying great success in reducing deaths up to a third in patients showing severe symptoms, thus proving it to be a life-saving drug [ 29 ].…”

Inhibitors of dihydroorotate dehydrogenase cooperate with molnupiravir and N4-hydroxycytidine to suppress SARS-CoV-2 replication

“…NHC can base pair with guanosine, but also with adenosine, thus leading to multiple errors in the subsequently synthesized viral RNA genomes and resulting in replication-deficient virus particles. Molnupiravir is active against SARS-CoV-2 replication in vitro and in vivo (Rosenke et al, 2021;Sheahan et al, 2020;Wahl et al, 2021), and this includes the recently emerged Omicron variant (Prince et al, 2021;Vangeel et al, 2021). It also prevents SARS-CoV-2 transmission in the ferret model (Cox et al, 2021), and it was found clinically effective in large-scale clinical trials (Jayk Bernal et al, 2021;Painter et al, 2021), exemplified by the trials registered at clinicaltrials.gov with the numbers NCT04575584, NCT04575597 and NCT04405739, leading to approval in the UK.…”