A week after China notified the first cases of severe pneumonia of unknown origin to WHO, the causative agent – the new SARS-CoV-2 coronavirus – was identified. A few days later his genome was already available. In just under three months we have more than 970 scientific articles in the PubMed database.
Knowing the biology of the virus facilitates the design of therapeutic (antiviral) and preventive (vaccines) strategies. We know that its genome is 79% similar to that of SARS. We know that the key of entry of the virus to the cell is protein S, and the lock in the cell is the ACE2 receptor.
The SARS-CoV-2 protein S has a 76% similarity with that of its relative SARS, and a higher affinity for the ACE2 receptor. This could explain why the new coronavirus is more contagious and communicable than SARS. The entry of the virus is also facilitated by a protease from the cell itself, which is called TMPRSS211.
There are other important SARS-CoV-2 genes that work when the virus is already inside the cell. They are that of RNA polymerase (RdRp), an enzyme that replicates the virus genome, and those of the C3CLpro and PLpro proteases, which are involved in the processing of viral proteins. These genes have a similarity to SARS of 95, 95 and 83%, respectively.
In these scarce three months, there are already several therapeutic proposals and vaccines against the new coronavirus. Science has never advanced so far in such a short time to combat an epidemic. Many of the proposals come from research groups that have spent years working against other viruses, especially against SARS and MERS. All that accumulated knowledge has now allowed you to go at a speed never seen before.
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Knowing in detail the genome of the virus and how it multiplies within cells allows us to propose antivirals that block it and inhibit its multiplication.
Inhibit the entry of the virus.
Chloroquine has been used for years against malaria. This cheap and available drug is also known to be a powerful antiviral because it blocks the virus from entering the cell. For this reason, there are several research groups interested in seeing if it is effective in reducing viral load in patients with SARS-CoV-2.
Some of the enveloped viruses, such as SARS-CoV-2, enter the cell by endocytosis, forming a small vesicle. Once inside, a drop in pH promotes the fusion of the virus envelope with the membrane of the gallbladder that contains it, in order to be free in the cytoplasm.
Chloroquine prevents this drop in pH, which would inhibit the fusion of the membranes to prevent the entry of the virus into the cell cytoplasm. Hydroxychloroquine, a less toxic derivative, has so far been found to inhibit the replication of SARS-CoV-2 in vitro in cell culture.
It is not the only proposal that is being tested. Barcitinib, an anti-inflammatory approved to treat rheumatoid arthritis, may inhibit endocytosis of the virus. Camostat mesylate, a drug approved in Japan for use in inflammation of the pancreas, inhibits the cellular protease TMPRSS2 necessary for virus entry. This compound has been shown to block the virus from entering lung cells.
- Inhibit viral RNA polymerase.
One of the most promising antivirals against SARS-CoV-2 is redelivered, a nucleotide analog that inhibits viral RNA polymerase, which prevents the virus from multiplying within the cell.
It has already been used against SARS and MERS and has been successfully tested in the latest Ebola epidemics, and against other viruses with the RNA genome. It is, therefore, a broad-spectrum antiviral. At least twelve-phase II clinical trials are already underway in China and the US. The USA, and another phase III has started with 1,000 patients in Asia.
Another wide-spectrum viral RNA polymerase inhibitor that has already started clinical trials is favipiravir: the first results with 340 Chinese patients have been satisfactory. The drug has been approved to inhibit the influenza virus and tested against other RNA viruses.
- Protease inhibitors.
The combination of ritonavir and lopinavir has been suggested that it may inhibit SARS-CoV-2 proteases. These compounds are already used to treat HIV infection.
Lopinavir is a virus protease inhibitor, which breaks down easily in the patient’s blood. Ritonavir acts as a protector and prevents the breakdown of lopinavir, which is why they are administered together.
However, the good news is that there are at least 27 clinical trials with different combinations of antiviral treatments such as interferon alfa-2b, ribavirin, methylprednisolone, and Azzedine.
At the moment they are experimental treatments, but they are a hope for the most severe and severe cases.
Vaccines for the future
The other strategy to control the virus is vaccines. Remember that they are preventive: they are developed now to protect us from the next wave of the virus, if it ever comes back. The WHO has a list of at least 41 candidates.
Perhaps one of the most advanced is the Chinese proposal, a recombinant adenovirus vector-based vaccine with the SARS-CoV-2 S gene, which has already been tested in monkeys and is known to produce immunity. A phase I clinical trial will be started with 108 healthy volunteers, between 18 and 60 years of age, in which three different doses will be tested. The goal is to check the safety of the vaccine (if there are any side effects) and to test which dose induces an increased antibody response.
Other proposals are being promoted by CEPI, an international association in which public, private, civil and philanthropic organizations collaborate to develop vaccines against future epidemics. It is currently funding eight SARS-CoV-2 vaccine projects that include recombinant, protein, and nucleic acid vaccines.
Let’s see what they are:
- Recombinant measles virus vaccine (Pasteur Institute, Themis Bioscience and the University of Pittsburg).
It is a vaccine built on a live attenuated or defective measles virus, which is used as a vehicle and that contains a gene that encodes a protein of the SARS-CoV-2 virus.
In this way, the vector virus directly presents the SARS-CoV-2 antigen to the immune system to induce a protective response. This consortium already has experience with similar vaccines against MERS, HIV, yellow fever, West Nile virus, dengue and other emerging diseases. It is in the preclinical phase.
- Recombinant influenza virus vaccine (University of Hong Kong).
It is also a live vaccine that uses an attenuated influenza virus as a vector, which has had the virulence gene NS1 removed, and is therefore not virulent.
A virus SARS-CoV-2 is added to this vector virus. This proposal has some advantages: it could be combined with any strain of seasonal influenza virus and thus serve as a flu vaccine, it can be quickly manufactured in the same production systems that already exist for influenza vaccines, and they could be used as intranasal vaccines via spray. It is in the preclinical phase.
- Recombinant vaccine using the Oxford chimpanzee adenovirus, ChAdOx1 (Jenner Institute, University of Oxford) as a vector.
This attenuated vector is capable of carrying another gene that encodes a viral antigen. Models for MERS, influenza, chikungunya and other pathogens such as malaria and tuberculosis have been tested in volunteers.
This vaccine can be manufactured on a large scale in bird embryo cell lines. The recombinant adenovirus carries the SARS-CoV-2 glycoprotein S gene. It is in the preclinical phase.
- Recombinant protein vaccine obtained by nanoparticle technology (Novavax).
This company already has vaccines against other respiratory infections such as adult flu (Nano-Flu) and respiratory syncytial virus (RSV-F) in clinical phase III and has manufactured vaccines against SARS and MERS.
Its technology is based on producing recombinant proteins that are assembled into nanoparticles and that is administered with its own adjuvant, Matrix-M. This compound (a mixture of plant-based saponins, cholesterol and phospholipids) is a well-tolerated immunogen capable of stimulating a powerful and long-lasting nonspecific immune response. The advantage is that in this way the number of necessary doses would be reduced (thus avoiding revaccination). It is in the preclinical phase.
- Recombinant Protein Vaccine (University of Queensland).
It consists of creating chimeric molecules capable of maintaining the original three-dimensional structure of the viral antigen. They use the technique called “molecular clamp”, which allows vaccines to be produced using the virus genome in record time. It is in the preclinical phase.
- Vaccine mRNA-1273 (Modern).
It is a vaccine made up of a small fragment of messenger RNA with the instructions to synthesize part of the SARS-Co-V protein S. The idea is that once introduced into our cells, it is these cells that make this protein, which would act as an antigen and stimulate the production of antibodies. It is already in the clinical phase and it has begun to be tested in healthy volunteers.
- Messenger RNA Vaccine (CureVac).
This is a similar proposal, with recombinant messenger RNA molecules that are easily recognized by the cellular machinery and produce large amounts of antigen. They are packaged in lipid nanoparticles or other vectors. In the preclinical phase.
- DNA INO-4800 vaccine (Inovio Pharmaceuticals).
It is a platform that manufactures synthetic vaccines with DNA of the S gene from the surface of the virus. They had already developed a prototype against MERS (the INO-4700 vaccine) that is in phase II.
They recently published the Phase I results with this INO-4700 vaccine and found that it was well tolerated and produced a good immune response (high antibody levels and good T-cell response, maintained for at least 60 weeks after vaccination). In the preclinical phase.
There is still more
The Spanish proposal has just received express financing from the Spanish Government. It is the vaccine of the group of Luis Enjuanes and Isabel Sola, a live attenuated vaccine that may be easier to manufacture and be much more immunogenic (greater capacity to stimulate the immune system).
In this case, the idea is, from the virus RNA genome, to rewrite it to DNA, and on this replica to build mutants that are not virulent. In short, making an altered copy of the virus that is incapable of producing the disease, but that serves to activate our defenses.
There is still no approved antiviral or specific SARS-Cov-2 vaccine. All of these antiviral and vaccine proposals are in the experimental phase. Some will not work, but the chances of hitting are many.
In addition, a review of the entire therapeutic arsenal and vaccines under investigation and development against other human coronaviruses, such as SARS and MERS, has just been published.
There are more than 2,000 patents related to the SARS and MERS coronaviruses. 80% on therapeutic agents, 35% on vaccines and 28% on diagnostic techniques (a patent can cover various aspects, so the total amounts to more than 100%).
On that list are several hundred patents for antibodies, cytokines, RNA interference therapies, and other interferons that are under investigation and development for the SARS and MERS coronaviruses, and that could very well work against the new SARS-CoV-2.
There are also several dozen patents on possible SARS and MERS vaccines that we can benefit from to combat SARS-CoV-2. They are vaccines of all kinds: inactive, live attenuated, dead vaccines, DNA, messenger RNA and VLP vaccines. All this shows that there is an immense amount of scientific knowledge that will speed up clinical and experimental trials to combat this virus.
Science and solidarity
The WHO has released an international consortium called Solidarity, whose goal is to seek effective treatment with COVID-19. At the moment Argentina, Bahrain, Canada, France, Iran, Norway, South Africa, Spain, Switzerland and Thailand are participating, and it is expected that more and more nations will join this great global clinical trial project.
There is no doubt: it is the moment of science and solidarity.