Small molecule drug can block a wide range of influenza viruses in mice

Our body is capable of generating highly specific antibodies, targeting a single pathogen from a vertiginous mix of harmless bacteria and proteins made by our own cells. But in some cases, like the influenza virus, this specificity is limiting. These antibodies will usually choose a very specific strain of influenza virus, which makes us vulnerable to other strains and new variants that evolve each season.

In recent years, however, it has become apparent that the immune system is sometimes extremely lucky in generating a single antibody capable of neutralizing a wide range of viruses. These "largely neutralizing antibodies" provide significant protection against viruses against which the immune system normally struggles, such as HIV, Ebola and the flu virus. The mass production of these antibodies could be a useful therapy, and the hope is that we can incorporate what they tell us into the design of future vaccines against these pathogens.

However, some smart researchers have discovered how to use a largely neutralizing antibody as a tool to design a drug that can block the activity of a large number of influenza viruses.

Feel neutral

Why does the immune system not consistently generate such antibodies? It's a matter of evolution that stings us at the back. It is easier to generate an immune response against the most important characteristics of a pathogen, which usually helps to eliminate it quickly. But this creates a strong evolutionary selection for mutations that modify these characteristics. As a result, the immune response is primarily an evolutionary arms race opposing the immune system to the latest version of the virus and mutations producing even more recent versions.

But in rare cases, the immune system is lucky and makes an antibody against a smaller area of ​​the pathogen. Some of them are even more fortunate, and they attach to a portion of a protein that is absolutely essential to the pathogen and block its function. This type of blockade is very difficult to evolve. In addition, since different strains of a virus rely on the same functions to infect a cell, these antibodies can often block all strains.

In the case of the influenza virus, large neutralizing antibodies have been found which tend to bind to the virus hemagglutinin protein (H in the HA nomenclature of influenza). This protein becomes important when an influenza virus attaches to a cell and is introduced to it. The haemagglutinin detects this change in conditions and undergoes a rearrangement that allows the genetic material of the virus to enter the cell. Large neutralizing antibodies block this process, essentially capturing the genetic material of the virus where it ends up being safely digested. As a rule, they block all viruses belonging to one of the two classes of hemagglutinin protein, a wide range of viruses.

These antibodies alone could potentially be a therapy for those already infected. But the antibodies have problems. They must be refrigerated before use, must be injected (as they will not survive the digestive tract) and may cause the immune system to react. Thus, some people have tried to simplify the antibodies, creating much smaller proteins that have a structure similar to that of the antibody and can also block the hemagglutinin. And this is where new research comes into play: moving the antibody literally and figuratively.

Move an antibody

The researchers – a huge partnership between university labs and Johnson & Johnson – have come up with an extremely intelligent test for drug activity. They started with haemagglutinin and blocked the simplified and reduced version of the antibody. Then, the researchers launched a library at a time about half a million small molecules on hemagglutinin and looked for small molecules that would break down the small, simplified version of the hemagglutinin antibody. . This should only happen if the small molecule binds even better and thus has a good chance of blocking the virus even more efficiently.

About 9,000 molecules crossed the screen with a promising appearance and researchers looked for common features. Many of them had a specific structure (they had a benzylpiperazine group), so the researchers focused on one of them. Unfortunately, this chemical does not dissolve very well in water, and tests in mice showed that it was quickly removed from their system. The researchers made changes that added more oxygen to the structure to make it more soluble. Some additional changes increased the binding strength by 50 times.

To check if it works, the authors turned to an extreme and somewhat artificial situation: they started giving the medicine to the mouse. A day later, the researchers hit the mice with a lot of the flu virus – 25 times the dose that would normally kill half of them. With drugs, however, all rodents lived.

humans

Obviously, ethical considerations prevent us from doing a similar experiment in humans. The authors therefore developed a three-dimensional culture of human bronchial cells and infected it with the virus. Again, the drug effectively blocked the infection.

The research involves a lot more, including an exploration of what it would take to have a drug that blocks the second large class of hemagglutinin. But in reality, the important work will consist of experiments that are not reported here: elements such as toxicity and side effects, the ability to enter the blood when taken in tablet form and if the drug can block the consequences of infections started. These elements will determine whether the continuation of this activity (or any other associated chemical) as a potential treatment is of interest.

In either case, however, the basic idea here – using largely neutralizing antibodies as tools to identify virus blocking drugs – may work for many other viruses. So, even if this chemical does not work, the potential is there to identify other troublemakers, including even deadlier viruses.

Science, 2019. DOI: 10.1126 / science.aar6221 (About DOIs).