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Protein Mapping Study Reveals Valuable Clues for COVID-19 Drug Development

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One way to fight COVID-19 is with drugs that directly target SARS-CoV-2, the novel coronavirus that causes the disease. That’s the strategy employed by remdesivir, the only antiviral drug currently authorized by the U.S. Food and Drug Administration to treat COVID-19. Another promising strategy is drugs that target the proteins within human cells that the virus needs to infect, multiply, and spread.

With the aim of developing such protein-targeted antiviral drugs, a large, international team of researchers, funded in part by the NIH, has precisely and exhaustively mapped all of the interactions that take place between SARS-CoV-2 proteins and the human proteins found within infected host cells. They did the same for the related coronaviruses: SARS-CoV-1, the virus responsible for outbreaks of Severe Acute Respiratory Syndrome (SARS), which ended in 2004; and MERS-CoV, the virus that causes the now-rare Middle East Respiratory Syndrome (MERS).

The goal, as reported in the journal Science, was to use these protein “interactomes” to uncover vulnerabilities shared by all three coronaviruses. The hope is that the newfound knowledge about these shared proteins—and the pathways to which they belong—will inform efforts to develop new kinds of broad-spectrum antiviral therapeutics for use in the current and future coronavirus outbreaks.

Facilitated by the Quantitative Biosciences Institute Research Group, the team, which included David E. Gordon and Nevan Krogan, University of California, San Francisco, and hundreds of other scientists from around the world, successfully mapped nearly 400 protein-protein interactions between SARS-CoV-2 and human proteins.

You can see one of these interactions in the video above. The video starts out with an image of the Orf9b protein of SARS-CoV-2, which normally consists of two linked molecules (blue and orange). But researchers discovered that Orf9b dissociates into a single molecule (orange) when it interacts with the human protein TOM70 (teal). Through detailed structural analysis using cryo-electron microscopy (cryo-EM), the team went on to predict that this interaction may disrupt a key interaction between TOM70 and another human protein called HSP90.

While further study is needed to understand all the details and their implications, it suggests that this interaction may alter important aspects of the human immune response, including blocking interferon signals that are crucial for sounding the alarm to prevent serious illness. While there is no drug immediately available to target Orf9b or TOM70, the findings point to this interaction as a potentially valuable target for treating COVID-19 and other diseases caused by coronaviruses.

This is just one intriguing example out of 389 interactions between SARS-CoV-2 and human proteins uncovered in the new study. The researchers also identified 366 interactions between human and SARS-CoV-1 proteins and 296 for MERS-CoV. They were especially interested in shared interactions that take place between certain human proteins and the corresponding proteins in all three coronaviruses.

To learn more about the significance of these protein-protein interactions, the researchers conducted a series of studies to find out how disrupting each of the human proteins influences SARS-CoV-2’s ability to infect human cells. These studies narrowed the list to 73 human proteins that the virus depends on to replicate.

Among them were the receptor for an inflammatory signaling molecule called IL-17, which has been suggested as an indicator of COVID-19 severity. Two other human proteins—PGES-2 and SIGMAR1—were of particular interest because they are targets of existing drugs, including the anti-inflammatory indomethacin for PGES-2 and antipsychotics like haloperidol for SIGMAR1.

To connect the molecular-level data to existing clinical information for people with COVID-19, the researchers looked to medical billing data for nearly 740,000 Americans treated for COVID-19. They then zeroed in on those individuals who also happened to have been treated with drugs targeting PGES-2 or SIGMAR1. And the results were quite striking.

They found that COVID-19 patients taking indomethacin were less likely than those taking an anti-inflammatory that doesn’t target PGES-2 to require treatment at a hospital. Similarly, COVID-19 patients taking antipsychotic drugs like haloperidol that target SIGMAR1 were half as likely as those taking other types of antipsychotic drugs to require mechanical ventilation.

More research is needed before we can think of testing these or similar drugs against COVID-19 in human clinical trials. Yet these findings provide a remarkable demonstration of how basic molecular and structural biological findings can be combined with clinical data to yield valuable new clues for treating COVID-19 and other viral illnesses, perhaps by repurposing existing drugs. Not only is NIH-supported basic science essential for addressing the challenges of the current pandemic, it is building a strong foundation of fundamental knowledge that will make us better prepared to deal with infectious disease threats in the future.

Reference:

[1] Comparative host-coronavirus protein interaction networks reveal pan-viral disease mechanisms. Gordon DE et al. Science. 2020 Oct 15:eabe9403.

Links:

Coronavirus (COVID-19) (NIH)

Krogan Lab (University of California, San Francisco)

NIH Support: National Institute of Allergy and Infectious Diseases; National Institute of Neurological Disorders and Stroke; National Institute of General Medical Sciences


Exploring Drug Repurposing for COVID-19 Treatment

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Drug screening-High throughput robot
Caption: Robotic technology screening existing drugs for new purposes. Credit: Scripps Research

It usually takes more than a decade to develop a safe, effective anti-viral therapy. But, when it comes to coronavirus disease 2019 (COVID-19), we don’t have that kind of time. One way to speed the process may be to put some old drugs to work against this new disease threat. This is generally referred to as “drug repurposing.”

NIH has been doing everything possible to encourage screens of existing drugs that have been shown safe for human use. In a recent NIH-funded study in the journal Nature, researchers screened a chemical “library” that contained nearly 12,000 existing drug compounds for their potential activity against SARS-CoV-2, the novel coronavirus that causes COVID-19 [1]. The results? In tests in both non-human primate and human cell lines grown in laboratory conditions, 21 of these existing drugs showed potential for repurposing to thwart the novel coronavirus—13 of them at doses that likely could be safely given to people. The majority of these drugs have been tested in clinical trials for use in HIV, autoimmune diseases, osteoporosis, and other conditions.

These latest findings come from an international team led by Sumit Chanda, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA. The researchers took advantage of a small-molecule drug library called ReFRAME [2], which was created in 2018 by Calibr, a non-profit drug discovery division of Scripps Research, La Jolla, CA.

In collaboration with Yuen Kwok-Yung’s team at the University of Hong Kong, the researchers first developed a high-throughput method that enabled them to screen rapidly each of the 11,987 drug compounds in the ReFRAME library for their potential to block SARS-CoV-2 in cells grown in the lab. The first round of testing narrowed the list of possible COVID-19 drugs to about 300. Next, using lower concentrations of the drugs in cells exposed to a second strain of SARS-CoV-2, they further narrowed the list to 100 compounds that could reliably limit growth of the coronavirus by at least 40 percent.

Generally speaking, an effective anti-viral drug is expected to show greater activity as its concentration is increased. So, Chanda’s team then tested those 100 drugs for evidence of such a dose-response relationship. Twenty-one of them passed this test. This group included remdesivir, a drug originally developed for Ebola virus disease and recently authorized by the U.S. Food and Drug Administration (FDA) for emergency use in the treatment of COVID-19. Remdesivir could now be considered a positive control.

These findings raised another intriguing question: Could any of the other drugs with a dose-response relationship work well in combination with remdesivir to block SARS-CoV-2 infection? Indeed, the researchers found that four of them could.

Further study showed that some of the most promising drugs on the list reduced the number of SARS-CoV-2 infected cells by 65 to 85 percent. The most potent of these was apilimod, a drug that has been evaluated in clinical trials for treating Crohn’s disease, rheumatoid arthritis, and other autoimmune conditions. Apilimod is now being evaluated in the clinic for its ability to prevent the progression of COVID-19. Another potential antiviral to emerge from the study is clofazimine, a 70-year old FDA-approved drug that is on the World Health Organization’s list of essential medicines for the treatment of leprosy.

Overall, the findings suggest that there may be quite a few existing drugs and/or experimental drugs fairly far along in the development pipeline that have potential to be repurposed for treating COVID-19. What’s more, some of them might also work well in combination with remdesivir, or perhaps other drugs, as treatment “cocktails,” such as those used to successfully treat HIV and hepatitis C.

This is just one of a wide variety of drug screening efforts that are underway, using different libraries and different assays to detect activity against SARS-CoV-2. The NIH’s National Center for Advancing Translational Sciences has established an open data portal to collect all of these data as quickly and openly as possible. As NIH continues its efforts to use the power of science to end the COVID-19 pandemic, it is critically important that we explore as many avenues as possible for developing diagnostics, treatments, and vaccines.

References:

[1] Discovery of SARS-CoV-2 antiviral drugs through large-scale compound repurposing. Riva L, Yuan S, Yin X, et al. Nature. 2020 Jul 24 [published online ahead of print]

[2] The ReFRAME library as a comprehensive drug repurposing library and its application to the treatment of cryptosporidiosis. Janes J, Young ME, Chen E, et al. Proc Natl Acad Sci USA. 2018;115(42):10750-10755.

Links:

Coronavirus (COVID-19) (NIH)

ReFRAMEdb (Scripps Research, La Jolla, CA)

The Chanda Lab (Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA)

Yuen Kwok-Yung (University of Hong Kong)

OpenData|Covid-19 (National Center for Advancing Translational Sciences/NIH)

NIH Support: National Institute of Allergy and Infectious Diseases; National Institute of General Medical Sciences


Pursuing Safe and Effective Anti-Viral Drugs for COVID-19

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Senior hospital patient on a ventilator
Stock photo/SoumenNath

Right now, the world is utterly focused on the coronavirus outbreak known as COVID-19. That’s certainly true for those of us at NIH. Though I am working from home to adhere rigorously to physical distancing, I can’t remember ever working harder, trying to do everything I can to assist in the development of safe and effective treatments and vaccines.

Over the past several weeks, a mind-boggling array of possible therapies have been considered. None have yet been proven to be effective in rigorously controlled trials, but for one of them, it’s been a busy week. So let’s focus on an experimental anti-viral drug, called remdesivir, that was originally developed for the deadly Ebola virus. Though remdesivir failed to help people with Ebola virus disease, encouraging results from studies of coronavirus-infected animals have prompted the launch of human clinical trials to see if this drug might fight SARS-CoV-2, the novel coronavirus that causes COVID-19.

You may wonder how a drug could possibly work for Ebola and SARS-CoV-2, since they are very different viruses that produce dramatically different symptoms in humans. The commonality is that both viruses have genomes made of ribonucleic acid (RNA), which must be copied by an enzyme called RNA-dependent RNA polymerase for the virus to replicate.

Remdesivir has an affinity for attaching to this kind of polymerase because its structure is very similar to one of the RNA letters that make up the viral genome [1]. Due to this similarity, when an RNA virus attempts to replicate, its polymerase is tricked into incorporating remdesivir into its genome as a foreign nucleotide, or anomalous letter. That undecipherable, extra letter brings the replication process to a crashing halt—and, without the ability to replicate, viruses can’t infect human cells.

Would this work on a SARS-CoV-2 infection in a living organism? An important step was just posted as a preprint yesterday—a small study showed infusion of remdesivir was effective in limiting the severity of lung disease in rhesus macaques [2]. That’s encouraging news. But the only sure way to find out if remdesivir will actually help humans who are infected with SARS-CoV-2 is to conduct a randomized, controlled clinical trial.

In late February, NIH’s National Institute of Allergy and Infectious Diseases (NIAID) did just that, when it launched a randomized, controlled clinical trial to test remdesivir in people with COVID-19. The study, led by NIAID’s Division of Microbiology and Infectious Diseases, has already enrolled 805 patients at 67 testing sites. Most sites are in the United States, but there are also some in Singapore, Japan, South Korea, Mexico, Spain, the United Kingdom, Denmark, Greece, and Germany.

All trial participants must have laboratory-confirmed COVID-19 infections and evidence of lung involvement, such as abnormal chest X-rays, rattling sounds when breathing (rales) with a need for supplemental oxygen, or a need for mechanical ventilation. They are randomly assigned to receive either a round of treatment with remdesivir or a harmless placebo with no therapeutic effect. To avoid bias from creeping into patient care, the study is double-blind, meaning neither the medical staff nor the participants know who is receiving remdesivir.

There is also an early hint from another publication that remdesivir may benefit some people with COVID-19. Since the end of January 2020, Gilead Sciences, Foster City, CA, which makes remdesivir, has provided daily, intravenous infusions of the drug on a compassionate basis to more than 1,800 people hospitalized with advanced COVID-19 around the world. In a study of a subgroup of 53 compassionate-use patients with advanced complications of COVID-19, nearly two-thirds improved when given remdesivir for up to 10 days [3]. Most of the participants were men over age 60 with preexisting conditions that included hypertension, diabetes, high cholesterol, and asthma.

This may sound exciting, but these preliminary results, published in the New England Journal of Medicine, come with major caveats. There were no controls, participants were not randomized, and the study lacked other key features of the more rigorously designed NIH clinical trial. We can all look forward to the results from the NIH trial, which are are expected within a matter of weeks. Hopefully these will provide much-needed scientific evidence on remdesivir’s safety and efficacy in people with COVID-19.

In the meantime, basic researchers continue to learn more about remdesivir and its interaction with the novel coronavirus that causes COVID-19. In a recent study in the journal Science, a research team, led by Quan Wang, Shanghai Tech University, China, mapped the 3D atomic structure of the novel coronavirus’s polymerase while it was complexed with two other vital parts of the viral replication machinery [4]. This was accomplished using a high-resolution imaging approach called cryo-electron microscopy (cryo-EM), which involves flash-freezing molecules in liquid nitrogen and bombarding them with electrons to capture their images with a special camera.

With these atomic structures in hand, the researchers then modeled exactly how remdesivir binds to the polymerase of the novel coronavirus. The model will help inform future efforts to tweak the structure of the drug and optimize its ability to disrupt viral replication. Such detailed biochemical information will be vital in the weeks ahead, especially if data generated by the NIH clinical trial indicate that remdesivir is a worthwhile lead to pursue in our ongoing search for anti-viral drugs to combat the global COVID-19 pandemic.

References:

[1] Nucleoside analogues for the treatment of coronavirus infections. Pruijssers AJ, Denison MR. Curr Opin Virol. 2019 Apr;35:57-62.

[2] Clinical benefit of remdesivir in rhesus macaques infected with SARS-CoV-2. Williamson B, Feldmann F, Schwarz B, Scott D, Munster V, de Wit E et. al. BioRxiv. Preprint posted 15 April 2020.

[3] Compassionate use of remdesivir for patients with severe Covid-19. Grein J, Ohmagari N, Shin D, Brainard DM, Childs R, Flanigan T. et. al. N Engl J Med. 2020 Apr 10. [Epub ahead of publication]

[4] Structure of the RNA-dependent RNA polymerase from COVID-19 virus. Gao Y, Yan L, Liu F, Wang Q, Lou Z, Rao A, et al. Science. 10 April 2020. [Epub ahead of publication]

Links:

Coronavirus (COVID-19) (NIH)

Accelerating COVID-19 Therapeutic Interventions and Vaccines (NIH)

NIH Clinical Trial of Remdesivir to Treat COVID-19 Begins (National Institute of Allergy and Infectious Diseases/NIH)

Developing Therapeutics and Vaccines for Coronaviruses (NIAID)

COVID-19, MERS & SARS (NIAID)

NIH Support: National Institute of Allergy and Infectious Diseases


Structural Biology Points Way to Coronavirus Vaccine

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Spike Protein on Novel Coronavirus
Caption: Atomic-level structure of the spike protein of the virus that causes COVID-19.
Credit: McLellan Lab, University of Texas at Austin

The recent COVID-19 outbreak of a novel type of coronavirus that began in China has prompted a massive global effort to contain and slow its spread. Despite those efforts, over the last month the virus has begun circulating outside of China in multiple countries and territories.

Cases have now appeared in the United States involving some affected individuals who haven’t traveled recently outside the country. They also have had no known contact with others who have recently arrived from China or other countries where the virus is spreading. The NIH and other U.S. public health agencies stand on high alert and have mobilized needed resources to help not only in its containment, but in the development of life-saving interventions.

On the treatment and prevention front, some encouraging news was recently reported. In record time, an NIH-funded team of researchers has created the first atomic-scale map of a promising protein target for vaccine development [1]. This is the so-called spike protein on the new coronavirus that causes COVID-19. As shown above, a portion of this spiky surface appendage (green) allows the virus to bind a receptor on human cells, causing other portions of the spike to fuse the viral and human cell membranes. This process is needed for the virus to gain entry into cells and infect them.

Preclinical studies in mice of a candidate vaccine based on this spike protein are already underway at NIH’s Vaccine Research Center (VRC), part of the National Institute of Allergy and Infectious Diseases (NIAID). An early-stage phase I clinical trial of this vaccine in people is expected to begin within weeks. But there will be many more steps after that to test safety and efficacy, and then to scale up to produce millions of doses. Even though this timetable will potentially break all previous speed records, a safe and effective vaccine will take at least another year to be ready for widespread deployment.

Coronaviruses are a large family of viruses, including some that cause “the common cold” in healthy humans. In fact, these viruses are found throughout the world and account for up to 30 percent of upper respiratory tract infections in adults.

This outbreak of COVID-19 marks the third time in recent years that a coronavirus has emerged to cause severe disease and death in some people. Earlier coronavirus outbreaks included SARS (severe acute respiratory syndrome), which emerged in late 2002 and disappeared two years later, and MERS (Middle East respiratory syndrome), which emerged in 2012 and continues to affect people in small numbers.

Soon after COVID-19 emerged, the new coronavirus, which is closely related to SARS, was recognized as its cause. NIH-funded researchers including Jason McLellan, an alumnus of the VRC and now at The University of Texas at Austin, were ready. They’d been studying coronaviruses in collaboration with NIAID investigators for years, with special attention to the spike proteins.

Just two weeks after Chinese scientists reported the first genome sequence of the virus [2], McLellan and his colleagues designed and produced samples of its spike protein. Importantly, his team had earlier developed a method to lock coronavirus spike proteins into a shape that makes them both easier to analyze structurally via the high-resolution imaging tool cryo-electron microscopy and to use in vaccine development efforts.

After locking the spike protein in the shape it takes before fusing with a human cell to infect it, the researchers reconstructed its atomic-scale 3D structural map in just 12 days. Their results, published in Science, confirm that the spike protein on the virus that causes COVID-19 is quite similar to that of its close relative, the SARS virus. It also appears to bind human cells more tightly than the SARS virus, which may help to explain why the new coronavirus appears to spread more easily from person to person, mainly by respiratory transmission.

McLellan’s team and his NIAID VRC counterparts also plan to use the stabilized spike protein as a probe to isolate naturally produced antibodies from people who’ve recovered from COVID-19. Such antibodies might form the basis of a treatment for people who’ve been exposed to the virus, such as health care workers.

The NIAID is now working with the biotechnology company Moderna, Cambridge, MA, to use the latest findings to develop a vaccine candidate using messenger RNA (mRNA), molecules that serve as templates for making proteins. The goal is to direct the body to produce a spike protein in such a way to elicit an immune response and the production of antibodies. An early clinical trial of the vaccine in people is expected to begin in the coming weeks. Other vaccine candidates are also in preclinical development.

Meanwhile, the first clinical trial in the U.S. to evaluate an experimental treatment for COVID-19 is already underway at the University of Nebraska Medical Center’s biocontainment unit [3]. The NIH-sponsored trial will evaluate the safety and efficacy of the experimental antiviral drug remdesivir in hospitalized adults diagnosed with COVID-19. The first participant is an American who was repatriated after being quarantined on the Diamond Princess cruise ship in Japan.

As noted, the risk of contracting COVID-19 in the United States is currently low, but the situation is changing rapidly. One of the features that makes the virus so challenging to stay in front of is its long latency period before the characteristic flu-like fever, cough, and shortness of breath manifest. In fact, people infected with the virus may not show any symptoms for up to two weeks, allowing them to pass it on to others in the meantime. You can track the reported cases in the United States on the Centers for Disease Control and Prevention’s website.

As the outbreak continues over the coming weeks and months, you can be certain that NIH and other U.S. public health organizations are working at full speed to understand this virus and to develop better diagnostics, treatments, and vaccines.

References:

[1] Cryo-EM structure of the 2019-nCoV spike in the prefusion conformation. Wrapp D, Wang N, Corbett KS, Goldsmith JA, Hsieh CL, Abiona O, Graham BS, McLellan JS. Science. 2020 Feb 19.

[2] A new coronavirus associated with human respiratory disease in China. Wu F, Zhao S, Yu B, Chen YM, Wang W, Song ZG, Hu Y, Tao ZW, Tian JH, Pei YY, Yuan ML, Zhang YL, Dai FH, Liu Y, Wang QM, Zheng JJ, Xu L, Holmes EC, Zhang YZ. Nature. 2020 Feb 3.

[3] NIH clinical trial of remdesivir to treat COVID-19 begins. NIH News Release. Feb 25, 2020.

Links:

Coronaviruses (National Institute of Allergy and Infectious Diseases/NIH)

Coronavirus (COVID-19) (NIAID)

Coronavirus Disease 2019 (Centers for Disease Control and Prevention, Atlanta)

NIH Support: National Institute of Allergy and Infectious Diseases