Antivirals and vaccines: help to stop coronavirus is on the way

In these three short months there are already several therapeutic proposals and vaccines against the new coronavirus. Never before has science made so much progress in such a short time to combat an epidemic.

A week after China notified the WHO of the first cases of severe pneumonia of unknown origin, the causative agent was identified: the new coronavirus SARS-CoV-2. A few days later its genome was available. In a little less than 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 (vaccine) strategies. We know that its genome is 79% similar to that of SARS. We know that the key of entry of the virus into the cell is the S protein, and the lock in the cell is the ACE2 receptor.

The SARS-CoV-2 S protein has a 76% similarity to that of its relative SARS, and a greater affinity for the ACE2 receptor. This may explain why the new coronavirus is more contagious and transmissible than SARS. The entry of the virus is also facilitated by a protease in the cell itself, called TMPRSS211.

There are other important SARS-CoV-2 genes that act when the virus is already inside the cell. These are RNA polymerase (RoRp), an enzyme that replicates the virus genome, and C3CLpro and PLpro proteases, which are involved in the processing of viral proteins. These genes have a similarity to SARS genes of 95, 95 and 83 % respectively.

In these three short months there are already several therapeutic proposals and vaccines against the new coronavirus. Never before has science made so much progress in such a short time to combat an epidemic. Many of the proposals come from research groups that have been working for years against other viruses, especially SARS and MERS. All that accumulated knowledge has now allowed us to advance at a speed never seen before.
 

Knowing in detail the genome of the virus and how it multiplies inside the cells allows us to propose antivirals that block it and inhibit its multiplication.

Inhibiting the entry of the virus

Chloroquine has been used for years against malaria. This drug (available and cheap) is also known to be a powerful antiviral because it blocks the entry of the virus into the cell. For that 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 viruses that are surrounded by an envelope, such as SARS-CoV-2, enter the cell through endocytosis, forming a small vesicle. Once inside, a drop in pH promotes the fusion of the virus envelope with the vesicle membrane that contains it, so that it becomes free in the cytoplasm.

Chloroquine prevents this drop in pH, which would inhibit the fusion of the membranes to prevent the virus from entering the cell cytoplasm. So far, hydroxychloroquine, a less toxic derivative, has been shown to inhibit the replication of SARS-CoV-2 in vitro in cell cultures.

It is not the only proposal being tested. Barcitinib, an anti-inflammatory approved for treating rheumatoid arthritis, may inhibit endocytosis of the virus. Camostat mesylate, a drug approved in Japan for use in pancreatic inflammation, inhibits the cell protease TMPRSS2 needed for virus entry. This compound has been shown to block the entry of the virus into lung cells.

Inhibiting viral RNA polymerase

One of the most promising antivirals against SARS-CoV-2 is remdesivir, a viral RNA polymerase inhibitor nucleotide analogue, which prevents the virus from multiplying inside the cell.

It has already been used against SARS and MERS and was successfully tested in recent Ebola epidemics, and against other viruses with RNA genomes. It is therefore a broad-spectrum antiviral. At least twelve Phase II clinical trials are already under way in China and the US, and another Phase III trial has begun with 1,000 patients in Asia.

Another broad-spectrum viral RNA polymerase inhibitor that has already begun clinical trials is favipiravir: initial 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 to inhibit SARS-CoV-2 proteases. These compounds are already used to treat HIV infection.

Lopinavir is a protease inhibitor of the virus, which is easily degraded in the patient's blood. Ritonavir acts as a protector and prevents lopinavir from breaking down, so they are given together.

Unfortunately, an article has just been published with 199 patients showing that treatment with ritonavir/lopinavir is not effective against coronavirus.

However, the good news is that there are at least 27 clinical trials with different combinations of antiviral treatments such as interferon alpha-2b, ribavirin, methylprednisolone and azvudine.

These are experimental treatments at the moment, but they offer hope for the most severe and severe cases.

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 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 is to begin with 108 healthy volunteers, aged 18-60 years, testing three different doses. The aim is to test the safety of the vaccine (if there are any side effects), and to test which dose induces the strongest antibody response.

Other proposals are being promoted by CEPI, an international partnership 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 University of Pittsburgh).

This is a vaccine built on a live attenuated or defective measles virus, used as a vehicle and containing a gene that encodes a SARS-CoV-2 virus protein.

In this way, the vector virus directly delivers 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).

This is also a live vaccine that uses an attenuated flu virus as a vector, which has had its NS1 virulence gene removed, and is therefore not virulent.

A SARS-CoV-2 gene 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 an influenza vaccine, it can be manufactured quickly in the same production systems already in place for influenza vaccines, and it could be used as an intranasal spray vaccine. It is in the pre-clinical phase.

Recombinant vaccine using as vector the chimpanzee adenovirus Oxford, ChAdOx1 (Jenner Institute, University of Oxford)

This attenuated vector is capable of carrying another gene that codes for a viral antigen. It has been tested in volunteers with models for MERS, influenza, chikungunya and other pathogens such as malaria and tuberculosis.
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 in clinical phase III against other respiratory infections such as adult flu (Nano-Flu) and respiratory syncytial virus (RSV-F) and has manufactured vaccines against SARS and MERS.

Its technology is based on producing recombinant proteins that are assembled into nanoparticles and administered with a proprietary adjuvant, Matrix-M. This compound (a mixture of plant saponins, cholesterol and phospholipids) is a well-tolerated immunogen capable of stimulating a potent and long-lasting non-specific immune response. The advantage is that this would reduce the number of doses required (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 a technique known as "molecular clamp", which makes it possible to produce vaccines using the virus genome in record time. It is in the preclinical phase.
mRNA-1273 vaccine (Modern).

This is a vaccine formed by a small fragment of messenger RNA with the instructions to synthesize part of the SARS-Co-V S protein. The idea is that once introduced into our cells, these same cells would manufacture that protein, which would act as an antigen and stimulate the production of antibodies. It is already in the clinical phase and has begun to be tested on 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 lipidic nanoparticles or other vectors. In preclinical phase.

DNA vaccine INO-4800 (Inovio Pharmaceuticals).

This is a platform that manufactures synthetic vaccines with DNA from the S gene on the surface of the virus. They had already developed a prototype against MERS (the INO-4700 vaccine) which is in phase II.

They recently published the results of phase I with this INO-4700 vaccine and proved that it was well tolerated and produced a good immune response (high levels of antibodies and good T-cell response, maintained for at least 60 weeks after vaccination). In preclinical phase.

The Spanish proposal has just received express funding from the Spanish government. It is the vaccine of Luis Enjuanes and Isabel Sola's group, a live attenuated vaccine that may be easier to manufacture and much more immunogenic (greater capacity to stimulate the immune system).

In this case, the idea is, from the virus RNA genome, to retro-transcribe it to DNA, and on this replica to build mutants that are not virulent. In short, to manufacture an altered copy of the virus that is incapable of producing the disease, but which serves to activate our defences.

There is no antiviral or specific SARS-Cov-2 vaccine approved yet. All of these antiviral and vaccine proposals are in the experimental phase. Some will not work, but the chances of success are high.

In addition, a review of the entire therapeutic arsenal and vaccines in research and development against other human coronaviruses, such as SARS and MERS, has just been published.

There are more than 2 000 patents related to SARS and MERS coronaviruses. Eighty percent on therapeutic agents, 35% on vaccines and 28% on diagnostic techniques (one patent can cover several aspects, so the total adds up to more than 100%).
In that list there are several hundred patents on antibodies, cytokines, RNA interference therapies and other interferons that are in the research and development phase for the SARS and MERS coronaviruses, and that may well work against the new SARS-CoV-2.

There are also several dozen patents on potential SARS and MERS vaccines that we could benefit from to combat SARS-CoV-2. These are vaccines of all kinds: inactivated killed vaccines, live attenuated vaccines, DNA, messenger RNA and PVL vaccines. All this shows that there is an immense amount of scientific knowledge that will allow to speed up clinical and experimental trials to fight this virus.

The WHO has announced an international consortium, called Solidarity, whose objective is to seek effective treatment with COVID-19. So far, Argentina, Bahrain, Canada, France, Iran, Norway, South Africa, Spain, Switzerland and Thailand are participating, and more and more nations are expected to join in this major global clinical trial project.

There is no doubt: it is time for science and solidarity.

Ignacio López-Goñi is Professor of Microbiology at the University of Navarra

Ignacio López-Goñi does not receive a salary, nor does he do consulting work, nor does he own shares, nor does he receive funding from any company or organization that could benefit from this article, and he has stated that he has no relevant links beyond the academic position cited.