A common drug, already approved by the US Food and Drug Administration (FDA), may also be a powerful tool in fighting COVID-19, according to research.
SARS-CoV-2, the virus that causes COVID-19, uses a surface spike protein to latch onto human cells and initiate infection. But heparin, a blood thinner also available in non-anticoagulant varieties, binds tightly with the surface spike protein, potentially blocking the infection from happening. This makes it a decoy, which might be introduced into the body using a nasal spray or nebulizer and run interference to lower the odds of infection. Similar decoy strategies have already shown promise in curbing other viruses, including influenza A, Zika, and dengue.
"This approach could be used as an early intervention to reduce the infection among people who have tested positive, but aren't yet suffering symptoms. But we also see this as part of a larger antiviral strategy," said Robert Dr Linhardt, lead author and a professor of chemistry and chemical biology at Rensselaer Polytechnic Institute. "Ultimately, we want a vaccine, but there are many ways to combat a virus, and as we've seen with HIV, with the right combination of therapies, we can control the disease until a vaccine is found."
To infect a cell, a virus must first latch onto a specific target on the cell surface, slice through the cell membrane, and insert its own genetic instructions, hijacking the cellular machinery within to produce replicas of the virus. But the virus could just as easily be persuaded to lock onto a decoy molecule, provided that molecule offers the same fit as the cellular target. Once bound to a decoy, the virus would be neutralized, unable to infect a cell or free itself, and would eventually degrade.
In humans, SARS-CoV-2 binds to an ACE2 receptor, and the researchers hypothesised that heparin would offer an equally attractive target. In a binding assay, the researchers found that heparin bound to the trimeric SARS-CoV-2 spike protein at 73 picomoles, a measure of the interaction between the two molecules.
"That's exceptional, extremely tight binding," said Dr Jonathan Dordick, a chemical and biological engineering professor at Rensselaer who is collaborating with Linhardt to develop the decoy strategy. "It's hundreds of thousands of times tighter than a typical antibody antigen. Once it binds, it's not going to come off."
Internationally recognised for his creation of synthetic heparin, Linhardt said that, in reviewing sequencing data for SARS-CoV-2, the team recognised certain motifs on the spike protein and strongly suspected it would bind to heparin. In addition to the direct binding assay, the team tested how strongly three heparin variants – including a non-anticoagulant low molecular weight heparin – bind to SARS-CoV-2, and used computational modelling to determine the specific sites where the compounds bind to the virus. All the results confirm heparin as a promising candidate for the decoy strategy. The researchers have subsequently initiated work on assessments of antiviral activity and cytotoxicity in mammalian cells.
"This isn't the only virus that we're going to confront in a pandemic," Dordick said. "We don't really have great antivirals, but this is a pathway forward. We need to be in a position where we understand how things like heparin and related compounds can block virus entry."
In previous work, a team led by Linhardt and Dordick demonstrated the decoy strategy on viruses with a mechanism similar to SARS-CoV-2. In 2019, the team created a trap for dengue virus, attaching specific aptamers – molecules the viral latches will bind to – precisely to the tips and vertices of a five-pointed star made of folded DNA. Floating in the bloodstream, the trap lights up when sprung, creating the world's most sensitive test for mosquito-borne diseases. In work prior to that, they created a synthetic polymer configured to match the sialic acid latch points on influenza virus, reducing influenza A mortality in mice from 100% to 25% over 14 days.
"This innovative approach to effectively trapping viruses is a prime example of how biotechnology approaches developed at Rensselaer are being brought forward to address challenging global health problems," said Deepak Vashishth, the director of the Centre for Biotechnology and Interdisciplinary Studies at Rensselaer, of which both Dordick and Linhardt are a part. "Professors Dordick and Linhardt have worked collaboratively across disciplines, and their research shows promise even beyond this current pandemic."
At Rensselaer, Linhardt and Dordick were joined on the research by Fuming Zhang, and also by researchers at the University of California – San Diego, Duke University, and the University of George-Athens with support from the National Institutes of Health.
Abstract
Severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) has resulted in a pandemic and continues to spread around the globe at an unprecedented rate. To date, no effective therapeutic is available to fight its associated disease, COVID-19. Our discovery of a novel insertion of glycosaminoglycan (GAG)-binding motif at S1/S2 proteolytic cleavage site (681–686 (PRRARS)) and two other GAG-binding-like motifs within SARS-CoV-2 spike glycoprotein (SGP) led us to hypothesize that host cell surface GAGs may interact SARS-CoV-2 SGPs to facilitate host cell entry. Using a surface plasmon resonance direct binding assay, we found that both monomeric and trimeric SARS-CoV-2 SGP bind more tightly to immobilized heparin (KD = 40 pM and 73 pM, respectively) than the SARS-CoV and MERS-CoV SGPs (500 nM and 1 nM, respectively). In competitive binding studies, the IC50 of heparin, tri-sulfated non-anticoagulant heparan sulfate, and non-anticoagulant low molecular weight heparin against SARS-CoV-2 SGP binding to immobilized heparin were 0.056 μM, 0.12 μM, and 26.4 μM, respectively. Finally, unbiased computational ligand docking indicates that heparan sulfate interacts with the GAG-binding motif at the S1/S2 site on each monomer interface in the trimeric SARS-CoV-2 SGP, and at another site (453–459 (YRLFRKS)) when the receptor-binding domain is in an open conformation. The current study serves a foundation to further investigate biological roles of GAGs in SARS-CoV-2 pathogenesis. Furthermore, our findings may provide additional basis for further heparin-based interventions for COVID-19 patients exhibiting thrombotic complications.
Authors
So Young Kim, Weihua Jin, Amika Sood, David W Montgomery, Oliver C Grant, Mark M Fuster, Li Fu, Jonathan S Dordick, Robert J Woods, Fuming Zhang, Robert J Linhardt
[link url="https://news.rpi.edu/content/2020/07/15/common-fda-approved-drug-may-effectively-neutralize-virus-causes-covid-19"]Rensselaer Polytechnic Institute material[/link]
[link url="https://www.sciencedirect.com/science/article/pii/S0166354220302874?via%3Dihub"]Antiviral Research abstract[/link]