Virus World

Researchers in Europe and the United States have demonstrated the potential of the influenza drug enisamium as a treatment for infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) – the agent that causes coronavirus disease 2019 (COVID-19).  Aartjan te Velthuis from the University of Cambridge in the UK and colleagues showed that enisamium prevented SARS-CoV-2 replication in human cell lines and stopped viral RNA synthesis in vitro. Furthermore, in a double-blind, randomized, placebo-controlled trial of adults hospitalized with COVID-19, enisamium significantly reduced recovery time among patients who required supplementary oxygen. The drug is already clinically approved for use against influenza in eleven different countries. Furthermore, enisamium does not require intravenous administration and could be used outside of the hospital setting. The researchers say the observations point to enisamium as a viable and accessible option for the treatment of SARS-CoV-2 infection and COVID-19. A pre-print version of the research paper is available on the bioRxiv* server, while the article undergoes peer review.

Vaccines are available, but antivirals are still needed

Since the COVID-19 outbreak first began in Wuhan, China, late last year (2020), vaccines have been developed to prevent the spread of SARS-CoV-2, and several antiviral agents such as remdesivir have been clinically approved for emergency use in COVID-19 cases. However, additional strategies are needed because vaccine roll-out is a slow process and the current antivirals can only be delivered intravenously within the hospital setting.

SARS-CoV-2 RNA polymerase transcribes the viral genome

Within the viral genome of SARS-CoV-2, two open reading frames (ORFs) – 1a and 1b  – encode two large polyproteins that are proteolytically cleaved to produce 16 non-structural proteins (nsps).  One of these proteins – nsp12 – is the RNA-dependent RNA polymerase that copies and transcribes the SARS-CoV-2 genome. Nsp12 requires nsp7 and nsp8 to perform this process in vitro, but te Velthuis and colleagues say Nsp12 likely requires other nsps such as nsp9 and nsp13, for in vivo processing. Cryogenic electron microscopy structures of nsp12/7/8 and nsp8/9/12/13 complexes from SARS-CoV-2 have already been determined, says the team. Furthermore, the antiviral remdesivir has previously been shown to inhibit the nsp12/7/8 complex and other small molecule inhibitors have been suggested as therapeutic candidates.

Where does enisamium come in?

One drug that has been highlighted by the World Health Organization as a potential candidate for treating SARS-CoV-2 infection is enisamium. This drug is an active inhibitor of influenza A and B viruses that have been licensed for use against influenza in 11 countries of the Commonwealth of Independent States. Research has recently shown that an enisamium metabolite called VR17-04 inhibits activity of the influenza virus RNA polymerase, reduces viral shedding and improves recovery among infected patients.

What did the researchers do?

The researchers showed that enisamium could inhibit the growth of SARS-CoV-2 in normal human bronchial epithelial cells (NHBE) cells and in a human colon epithelial cancer cell line called Caco-2. They also conducted an in vitro assay showing that the metabolite VR17-04 directly inhibits the RNA synthesis activity of the SARS-CoV-2 nsp12/7/8 complex. To confirm the anti-SARS-CoV-2 activity of enisamium, the team conducted a double-blind, randomized, placebo-controlled trial of 373 hospitalized COVID-19 patients who needed medical care either with or without supplementary oxygen. Participants received either enisamium (500 mg per dose) or placebo over the course of 7 days. An interim analysis showed that among those who required supplementary oxygen (n=77), enisamium significantly improved the meantime to recovery, compared with placebo (11.1 versus 13.9 days). No significant difference in recovery time was observed for all patients (n=373) or for those who required medical care without oxygen supplementation (n=296)....

Preprint available in bioRxiv (Jan. 12, 2021):

https://doi.org/10.1101/2021.01.05.21249237

Like an adjustable wrench that becomes the "go-to" tool because it is effective and can be used for a variety of purposes, an existing drug that can be adapted to halt the replication of different viruses would greatly expedite the treatment of different infectious diseases. Such a strategy would prevent thousands of deaths each year from diseases like dengue and Ebola, but whether it can be done has been unclear. Now, in new work, researchers at the Lewis Katz School of Medicine at Temple University (LKSOM) show that repurposing an existing drug to treat viral diseases is in fact possible - potentially bypassing the decades needed to develop such a broad-spectrum drug from scratch.

In a new study published in the journal Molecular Therapy, the Temple researchers report that a drug used in the treatment of HIV also suppresses Zika virus infection. In cell and animal models, they show that the drug, called rilpivirine, stops Zika virus by targeting enzymes that both HIV and Zika virus depend on for their replication. These enzymes occur in other viruses closely related to Zika, including the viruses that cause dengue, yellow fever, West Nile fever, and hepatitis C. Dr. Khalili, a senior investigator on the new study, attributed the breakthrough work to a productive collaboration with Temple University colleagues, including Dr. Michael L. Klein, FRS, Laura H. Carnell Professor of Science and Dean of the College of Science and Technology at Temple; and Ilker K. Sariyer, DVM, PhD, and Jennifer Gordon, PhD, Associate Professors of Neuroscience at Temple's Center for Neurovirology.

Historically rare and isolated to parts of Africa and Asia, Zika virus is now present throughout the Americas and occurs in multiple other regions of the world. It has attracted increasing attention in recent years, owing to its damaging effects to the brain and nervous system. The virus is transmitted to humans by mosquitoes. Once in the body, it infects cells and replicates, typically taking up residence in cells in neural tissues. In severe cases, Zika virus infection can cause an autoimmune condition known as Guillain-Barré syndrome, which culminates in muscle paralysis. Infants born to mothers infected during pregnancy may experience delays in neurological development and may be affected by microcephaly (abnormal smallness of the head).

To replicate inside cells, Zika virus requires an enzyme called non-structural protein 5 RNA-dependent RNA polymerase (NS5 RdRp). In the new study, Dr. Sariyer showed that rilpivirine suppresses Zika virus infection in cells by blocking viral replication. Using structural biology and computational studies, Eleonora Gianti, PhD, a research assistant professor in Dr. Klein's laboratory, was able to show that rilpivirine prevents viral replication by binding specifically to the NS5 domain. Dr. Gordon's team carried out experiments in mice, in which animals were infected with Zika virus through their footpads, similar to the way a person becomes infected through a mosquito bite. Mice that become infected with Zika virus normally become very sick within about a week and eventually die. "We found, however, that when treated with rilpivirine, the animals survived," Dr. Gordon said. "Our conclusion is that rilpivirine disrupted the virus's usual course of infection."

Rilpivirine is one of several non-nucleoside reverse transcriptase inhibitor (NNRTI) drugs that have been developed for the treatment of HIV infection. Experiments in which the Temple researchers tested two other NNRTIs in Zika-infected cells revealed similar effects on viral replication, with the drugs specifically inhibiting NS5 activity.

Published on Molecular Therapy (October 11, 2019):

https://doi.org/10.1016/j.ymthe.2019.10.006