The unusual mRNA molecule and its possible applications
What is mRNA and what is its role in our body?
MRNA, or messenger RNA, is a molecule that is a recipe for building proteins in the body. In the classic gene expression scheme, DNA is converted into mRNA, which is then translated into proteins. This means that mRNA is an intermediary molecule between DNA and a protein. Due to its role, it is short-lived and appears in the body only when there is a need for a specific protein. These natural properties have intrigued scientists for years in the context of therapeutic use. MRNA seems to be the “ideal” molecule here. It is administered externally, but it stays in the body only for a while. It does not integrate into our genome, so it does not change the genome of cells. At the same time, the protein is produced on the mRNA matrix by our own cells, i.e. it is treated by the body as its own – and this is the greatest potential advantage of mRNA.
What is the difference between mRNA found in our body and therapeutic mRNA?
We try to ensure that the mRNA we use as a medicine resembles the natural one as much as possible. Natural mRNA has several structural elements. In their description, we use the numbering: 5’ (prim) and 3’ (prim) – these are the two ends of the mRNA chain. There is a “cap” at the 5’ end that protects the mRNA from degradation and additionally enables the initiation of protein synthesis. Next, we have the RNA sequence, which contains the recipe for the protein, and there are also regulatory sequences. And, finally, at the other end, 3’, we have the so-called “polyadenylate tail”, i.e. a sequence of several dozen to several hundred adenines. We construct therapeutic RNA in a similar way – but of course we introduce the recipe for the protein we want. Moreover, we modify the mRNA in such a way that it does not induce a strong antiviral response in the cell. It is known that the introduction of mRNA from the outside into our cells closely resembles a viral infection. Our own mRNA does not cause such a reaction because it is produced in the cell nucleus, so it does not have to cross the cell membrane.
Returning to mRNA coming from outside, it must be prepared in such a way that it does not resemble viral RNA. How? Katalin Karikό and Drew Weissman received the Nobel Prize last year for answering this question. They found that to make mRNA resemble viral RNA as little as possible, the nucleotides had to be modified. Scientists have proven that the introduction of modified uridines into the RNA structure makes the RNA entering the cell through the cell membrane less recognizable as viral RNA, and therefore less reactogenic. This means that it induces the production of cytokines by cells to a lesser extent (some authors use the incorrect term “immunogenicity” to describe reactogenicity).
Is such a modified mRNA a complete medicine?
No. Due to the fact that RNA is quite a long nucleic acid, it is not a compound that could freely penetrate the cell membrane. Therefore, it must be “pushed” into this cell. For this purpose, it is packaged in lipids. We create a so-called “lipid nanoparticle” and this is the complete drug that enters the cell. This happens by endocytosis, which means that the cell takes in lipids along with mRNA, just like other substances from the outside. Then the mRNA “gets out” from the endosome into the cytoplasm and protein synthesis occurs. Therefore, an important part of mRNA as a drug is lipids. It is worth recalling that therapeutic RNA was first administered to humans in 2004 (16 years before the CoViD-19 vaccine). And then it was administered in complexes with a protein: protamine. Lipids are the standard “wrapper” today.
How is therapeutic mRNA produced? is it a very complicated process?
On the contrary, the production of therapeutic RNA is very simple. We take a laboratory vessel, add the matrix (this is the piece of DNA that exactly reflects the structure of our therapeutic mRNA), add nucleotides, a “cap”, an enzyme and... it “cooks itself”. This is a very simple procedure and a simple synthesis mechanism. Then the finished mRNA is packaged in lipids and the drug is ready for administration.
And what happens when such therapeutic RNA enters our body?
We know from the hitherto studies, some completed by our team, that the main cells that take up mRNA packaged in the lipids used today are macrophages and, to a lesser extent, dendritic cells. Macrophages are found in every tissue – muscles, liver, spleen, brain, etc. These are cells of the immune system – cell cleaners. Depending on where we administer the drug, macrophages from that place will take it up and produce the protein that is programmed in the RNA. In the case of mRNA vaccines against CoViD-19, these will be macrophages from the muscle, because the vaccine is administered intramuscularly. However, if we administer mRNA intravenously, which is what is being done in oncology, it will be captured by macrophages in the liver and spleen. There is also data that shows that mRNA can be taken up by hepatocytes – cells of the liver parenchyma.
It must be admitted, however, that for now mRNA technology only works well in the case of vaccines. In other applications it is slightly worse. There are few diseases in which the uptake of mRNA by hepatocytes or macrophages and the production of protein into the blood is sufficient. Most often we need proteins intracellularly in specific locations for treatment. Therefore, the biggest challenge now is to develop methods of packaging RNA so that it can be delivered precisely where we want, and not only to macrophages or hepatocytes.
Why does this technology work so well in vaccines?
For vaccine RNA, the fact that it reaches macrophages and dendritic cells is like a winning lottery ticket. It must reach these cells for the immune response to develop. It is worth emphasizing that mRNA vaccines are unique. Thanks to them, both arms of immunity develop: both antibody-dependent immunity (so-called “humoral immunity”) and cellular immunity, i.e. T lymphocytes that destroy virus-infected cells. This is really unique because most of the vaccines we’ve had so far have primarily induced a humoral response.
MRNA vaccines against CoViD-19 were introduced for use during the pandemic but it is worth emphasizing that they are now 100% registered, i.e. they have passed all phases of full drug registration.
Can mRNA technology be used to treat cancer?
The first attempts to use mRNA were vaccines intended to treat cancer patients. The treatment would involve introducing a cancer antigen into the body using mRNA, thereby activating the patient’s immune system to treat the cancer as an “intruder” and destroy its cells. Unfortunately, these vaccines do not work yet. Cancer is a too complex disease. Not all of its cells are identical in a given patient. There are many different clones of them. It is a very complicated system that inhibits the development of the immune response. Therefore, although work on anticancer vaccines has been going on for over 50 years, unfortunately there has been no spectacular success.
Does mRNA have any use in inflammatory diseases?
In diseases such as rheumatoid arthritis, Crohn’s disease or ulcerative colitis, we have spectacular therapies using monoclonal antibodies that remove tumor necrosis factor alpha (anti-TNF alpha antibodies). Therefore, they have a strong anti-inflammatory effect. Now we want to achieve the same therapeutic effect using mRNA. There are attempts to administer mRNA for this antibody to the patient instead of a monoclonal antibody, i.e. a protein prepared outside the body. Then the patient’s body will produce the necessary antibody on its own. What is the advantage of doing this? The patient produces the needed antibody as their own. This is crucial. We know from many years of observations of patients with rheumatoid arthritis treated with monoclonal antibodies that after many years the body may develop an immune response against these antibodies and the therapy becomes less effective. We hope that if we deliver the antibodies in the form of mRNA and the patient produces them as his own, this immune response will not develop.
In what other areas of medicine can mRNA be used?
Research is being conducted on the use of mRNA in replacement therapies. Then we introduce mRNA for the protein that is missing in the body. The necessary protein begins to be produced by the patient’s own cells and, as a result, the person recovers or has no symptoms of the disease. The results of the 1st and 2nd phases of the clinical trial, in which mRNA for the missing enzymes was administered to patients with propionic acidosis, were recently published in “Nature”. Relatively good mRNA tolerance was achieved and the necessary protein, which is a drug, was also produced.
You mentioned three areas in which the possibility of using therapeutic mRNA is being investigated (in anticancer vaccines, as a recipe for monoclonal antibodies and in substitution therapies). In which of them can we count on success the fastest?
Should I play fairy? It seems to me that the greatest chance of success is to use mRNA as a recipe for monoclonal antibodies. This is a very good idea and we have everything to make it happen. We have the right RNA structure. We also know the delivery method, which is sufficient for this technology to work, i.e. we administer mRNA into the blood and it is captured by liver cells which produce antibodies according to the “recipe” and release them into the blood. Such therapy could benefit primarily patients suffering from the autoimmune diseases I mentioned earlier, but also people with cancer, because we also administer monoclonal antibodies to them. However, for a substitution therapy to work, we need to have a better way of targeted delivery. And when it comes to cancer vaccines, a better understanding of cancer biology is needed.
Is there currently research being conducted at our university on the potential therapeutic use of mRNA?
The Medical University of Warsaw participates in a consortium that deals with the development of therapeutic mRNA in oncology. This is a project implemented as part of the Virtual Research Institute financed by the Polish Center for Technology Development. The grant amounts to almost PLN 70 million for 5 years of research. The leader of the project is the International Institute of Molecular and Cell Biology with Prof. Andrzej Dziembowski who is one of the most recognized scientists in the world when it comes to RNA biology. Another consortium member is the University of Warsaw – the team of Prof. Jacek Jemielity and habilitated doctor Joanna Kowalska (who has been dealing with chemical modifications of RNA with great success for years). The consortium also includes the team of Prof. Robert Hołyst from the Institute of Physical Chemistry of the Polish Academy of Sciences. The Medical University of Warsaw is represented by Prof. Jakub Gołąb and me. Our independent teams examine RNA biologically. The participation in this consortium is a huge success of our university. This project is so far the only Virtual Research Institute that works. No team was awarded funding in the two subsequent competitions, which also shows that the scientific quality of our consortium was rated very highly. We already have patent applications and the first joint publication sent for review. I cannot say much about it now but I hope that, if it is accepted for publication, you will see how interesting and important research we conduct in our consortium.
Interviewed by Iwona Kołakowska
Fot. Michał Teperek
Communication and Promotion Office