Background The 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. Objectives This 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. Methods Dose 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. Results Here 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. Conclusions One 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.
Antiviral activity of molnupiravir precursor NHC against SARS-CoV-2 Variants of Concern (VOCs) and its therapeutic window in a human lung cell model