Virus World

An oral antiviral drug that targets a key part of the respiratory syncytial virus (RSV) polymerase has been identified, a finding that could provide an effective treatment against RSV disease, according to researchers in the Center for Translational Antiviral Research at Georgia State University.  The findings, published in the journal Science Advances, identify AVG-388 as the lead drug candidate, which effectively blocks the activity of the viral RNA polymerase, an enzyme responsible for replication of the viral genome. RSV is a leading cause of lower respiratory infections in infants and immunocompromised individuals, but no efficient therapeutic exists. The virus caused an estimated 33.1 million cases worldwide in 2015 that required 3.2 million hospitalizations and resulted in 59,800 deaths. Finding effective drugs to fight RSV has been challenging. Through mutations, RSV has escaped advanced candidate classes that prevent the virus from entering a cell. To overcome this issue, recent drug development efforts have focused on the viral RNA-dependent RNA polymerase complex of RSV because of the possible broader window of opportunity to fight the virus during viral genome replication and transcription.

"We have identified the AVG class of inhibitors of RSV RNA synthesis. Through chemical optimization, we have developed the clinical candidate AVG-388, which is orally efficacious against RSV in animal models of infection." Dr. Richard K. Plemper, senior author of the study, Distinguished University Professor and director of the Center for Translational Antiviral Research in the Institute for Biomedical Sciences at Georgia State

In addition, the researchers demonstrated potent antiviral activity in human airway epithelium organoid cultures. "In this study, we have mapped an exciting druggable target in the RSV RNA-dependent RNA-polymerase and established the clinical potential of the AVG inhibitor class against RSV disease," said Dr. Julien Sourimant, first author of the study and a postdoctoral fellow in the Center for Translational Antiviral Research in the Institute for Biomedical Sciences at Georgia State. The research team investigated the effect of treatment on viral replication at different oral doses intended to prevent or cure disease. They demonstrated that treatment reduced virus load by several orders of magnitude in the different disease models. "Our results lay the foundation for formal development of the AVG class and the structure-guided identification of companion drugs with overlapping target sites but distinct resistance profiles," Plemper said. Co-authors of the study include Julien Sourimant (first author), Carolin M. Lieber, Jeong-Joong Yoon, Mart Toots and Richard K. Plemper of the Center for Translational Antiviral Research in the Institute for Biomedical Sciences at Georgia State; Mugunthan Govindarajan, Venkata Udumula and Michael G. Natchus of Emory Institute for Drug Development at Emory University; Kaori Sakamoto of the College of Veterinary Medicine at the University of Georgia; Joseph Patti of Aviragen Therapeutics Inc. (now at JP Biotech Advisors Inc.); and John Vernachio of Aviragen Therapeutics Inc. The study was funded by the National Institutes of Health.

SARS-CoV-2 mortality has been extensively studied in relationship to a patient’s predisposition to the disease. However, how sequence variations in the SARS-CoV-2 genome affect mortality is not understood. To address this issue, we used a whole-genome sequencing (WGS) association study to directly link death of SARS-CoV-2 patients with sequence variation in the viral genome. Specifically, we analyzed 3,626 single stranded RNA-genomes of SARS-CoV-2 patients in the GISAID database (Elbe and Buckland-Merrett, 2017; Shu and McCauley, 2017) with reported patient’s health status from COVID-19, i.e. deceased versus non-deceased. In total, evaluating 28,492 loci of the viral genome for association with patient/host mortality, two loci, 12,053bp and 25,088bp, achieved genome-wide significance (p-values of 1.24e-12, and 1.24e-26, respectively).

Mutations at 25,088bp occur in the S2 subunit of the SARS-CoV-2 spike protein, which plays a key role in viral entry of target host cells. Additionally, mutations at 12,053bp are within the ORF1ab gene, in a region encoding for the protein nsp7, which is necessary to form the RNA polymerase complex responsible for viral replication and transcription. Both mutations altered amino acid coding sequences, potentially imposing structural changes that could enhance viral infectivity and symptom severity, and may be important to consider as targets for therapeutic development.

Preprint available at bioRxiv (Nov. 24, 2020):

https://doi.org/10.1101/2020.11.17.386714

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