Cookies on this website
We use cookies to ensure that we give you the best experience on our website. If you click 'Continue' we'll assume that you are happy to receive all cookies and you won't see this message again. Click 'Find out more' for information on how to change your cookie settings.

Authors: Walker et al.,

Link to paper:

Journal/ Pre-Print: BioRxiv

Tags: Drug discovery/Drug repurposing, Antiviral therapeutics, RNA viruses

Research Highlights 

1. Suggests that enisamium, an approved drug against influenza, is a potential therapeutic option against SARS-CoV-2 infection.

2. Identifies a putative hydroxylated metabolite of enisamium, VR17-04, which has a higher in vitro inhibitory activity against both influenza and SARS-CoV-2 RNA polymerase complexes


Using in vitro assays, the study confirms that enisamium, a clinically approved drug against influenza virus, possesses antiviral activity and inhibits the function of influenza polymerase. In vitro assays also show that enisamium can inhibit the activity of SARS-CoV-2 RNA polymerase complex, which could potentially lead to inhibition of viral growth. The study further demonstrates that a putative hydroxylated metabolite of enisamium, VR17-04, has a more potent inhibitory effect than enisamium in both influenza and SARS-CoV-2 RNA synthesis. The authors hence suggest the therapeutic importance of enisamium and its putative derivatives.

Impact for SARS-CoV2/COVID19 research efforts

Understand the virology and/or cell biology of SARS-CoV2/COVID19

Treat of SARS-CoV2/COVID19 positive individuals

Study Type

· In vitro study (cell culture and biochemical assays with purified proteins)

Strengths and limitations of the paper

Novelty: Shown for the first time that enisamium and its putative metabolite can inhibit RNA synthesis in SARS-CoV-2.

Standing in the field: The growth and RNA synthesis inhibitory effect of enisamium on influenza virus is in agreement with previous literature.

Appropriate statistics: No statistics are used. All quantification data are from n = 3 independent experiments.

Viral model used: No viruses were used. Recombinant proteins were generated from

- A/WSN/33 (H1N1) influenza virus

- SARS-CoV-2 (strain not given)


Early stage of translation. Enisamium is already a licensed drug and has been previously identified by the WHO as a candidate therapeutic against SARS-CoV2. However, it is essential to show that enisamium has antiviral activity against fully infectious SARS-CoV2 in vivo before it’s suitability as a treatment for SARS-CoV2 in the clinic is determined.

Main limitations:

- No cell culture data on SARS-CoV-2 viral inhibition. The data showing the inhibition of SARS-CoV2 RNA polymerase by enisamium are based on purified proteins from the virus used in an in vitro assay.

- There is no discussion about potential reasons why the putative metabolite, VR17-04, has a stronger inhibitory potency than enisamium and if it would be able to be used as a therapeutic.

- There is no discussion about the concentrations of the inhibitor used throughout this study, and whether these concentrations are physiologically relevant (e.g. toxicity etc.)

- The primer extension data would have benefitted from using a different concentration range.