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 How far is RNA therapy from us?

 

39-year-old Carlos suffered from hereditary transthyretin amyloidosis (hATTR), a rare disease caused by the misfolding of the transthyretin protein, when he was approaching his innocent years. This genetic disease caused by genes can cause damage to the patient's organ function and ultimately lead to the death of the patient.

At that time (2004), patients diagnosed with this disease survived only 15 years at most, and the only effective treatment was organ transplantation. Fortunately, Carlos has the opportunity to participate in a clinical trial of RNA therapy, which controls symptoms by preventing the production of toxic proteins, greatly prolonging the life of patients and avoiding the waiting and rejection of organ transplants.

With the gradual approval of RNA therapy by the United States and the European Union in 2018, and the commercialization of RNA therapy technology, more and more patients are expected to be able to return to ordinary lives through RNA therapy like Carlos.

Post-it notes in "Life Restaurant"

Ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) can carry life information. Compared with DNA that is stable like a book, RNA is more like a post-it note in life: it is light, efficient but not very stable, and easy Is degraded. The new coronavirus pneumonia virus is a virus encoded by RNA, and it is precisely because of the unstable nature of RNA that mutations are very easy to occur. It is hard to imagine that every generation of our offspring will have uncontrollable mutations. One more eye or one less leg would be a terrible thing.

Also because RNA is unstable and easily degraded, RNA plays an important role in the execution of life functions. RNA can be used as a messenger to transmit genetic information, participate in protein synthesis, catalyze biochemical reactions, and regulate and control gene expression. It can also be used as a tool to mediate CRISPR gene editing, or as a vaccine to immunize the body.

One of the most important functions of RNA is to act as a messenger (mRNA) for gene expression. Gene is a string of nucleotides that can determine biological characteristics to encode life programs, and genes determine biological characteristics mainly through genes that produce corresponding proteins. And this process is not directly transformed into protein, but through a series of biochemical reactions of "transcription-translation-post-translational modification".

Suppose you follow the fragrance and come to a restaurant to sit down and pick up the menu written by DNA. The waiter RNA synthetase next to you will record your choice with mRNA, turn around and give it to the ribosome of the back kitchen. This process is called transcription. The back kitchen selects the appropriate amino acids contained in tRNA to make peptide chains according to your requirements. This process is called translation. If you need to add more material, the protein will be sent to the endoplasmic reticulum for further processing. This process is called post-translational modification. Of course, the takeaway service will also be handled by Golgi and other employees to ensure that your protein can be delivered to the place you want.

If the mRNA content of the post-it note in the hands of the waiter is modified, even a small change will cause the protein to be synthesized incorrectly. For example, just copy the sugar in braised pork into salt, and you will make a braised pork that is as salty as cured meat. Similarly, even one or two nucleic acid sequence changes may cause the production of wrong proteins and affect the normal function of life. For example, if the 12 or 13 position of the GTPase protein of ras is mutated, the transcription function of the cell will be disordered, which will induce the uncontrolled cell division and cause cancer.

The disease that Carlos suffered was precisely because of genetic errors that caused the misfolding of transthyretin, which in turn triggered the production of toxic proteins and their accumulation in the organs, eventually leading to organ failure. However, if we can destroy the wrong menu and introduce the correct menu according to the correct needs, the wrong protein can be corrected and the disease caused can be cured.

RNA therapy-save the "dark restaurant"

Many congenital genetic diseases are caused by the lack of key proteins or the presence of toxic proteins in the patient's body. The production of toxic proteins in cells is mostly due to the wrong coding of genes. Therefore, it is possible to prevent the production of the wrong protein or induce the production of the correct protein without modifying the gene, making it possible to cure genetic diseases.

Compared with the DNA editing therapy that is still under development, stable, reversible and safer RNA therapy has become an important choice for the treatment of genetic diseases.

Wrong post-it notes can be modified or destroyed directly, so that the chef will not receive the wrong menu and will not make unpalatable dishes.

RNA can pair with RNA or single-stranded DNA antisense to form double-stranded molecules, forming double-stranded molecules that are difficult to read by ribosomes. Such RNAs are called single-stranded antisense oligonucleotides (ASOs). It's like putting a layer of paper on a post-it note that just covers the writing completely, and the content inside is therefore invisible.

Alternatively, we can use small RNA molecules such as siRNA (small interfering RNA) or miRNA (microRNA) to prevent the translation of mRNA into protein. These small molecules are like a post-it note with "error" marks to prevent chefs from reading and executing mRNA instructions. . siRNA and miRNA are RNAs with only 20-27 base pairs (bp), which can inhibit gene expression. When the artificially designed small RNA vector containing target specificity is delivered to the target cell, the cell will recognize and start to execute the program in the vector to cut the RNA on the vector. After the small RNA is cut from the carrier to produce siRNA, it can form a RISC (RNA silencing complex) with other proteins in the cell. This complex will specifically bind to the target mRNA, causing the target mRNA to be degraded instead of being translated into protein, thereby preventing gene expression.

We can also regulate proteins directly through RNA. This simple and rude way is like crumpling post-it notes into a ball and throwing them directly on the plate to prevent guests from eating. A specially designed small RNA molecule called an RNA aptamer can bind to a specific site on a protein. For example, an RNA drug called Pegaptanib can bind to the vascular endothelial growth factor protein and prevent its function, allowing patients The growth rate and permeability of blood vessels in the eye are reduced, thereby treating the weakened vision caused by blood vessels penetrating the retina.

Of course, we can prevent the production of protein through RNA, and we can also produce the correct protein through mRNA. When mRNA is injected into the body and absorbed by the cell, the cell executes the corresponding protein synthesis program after recognizing the mRNA to produce the protein we need. For example, for patients who lack coagulation factor protein and suffer from coagulation disorders, we can deliver the correct mRNA encoding coagulation factor protein into the patient's body, and the patient can produce coagulation factor and coagulate normally.

If we deliver the characteristics of some pathogens, such as the spike protein mRNA of the new coronavirus, into the human body, some cells of the human body will also produce the characteristics of the new coronavirus and be recognized by the immune system, and finally form an immune memory. Compared with the cumbersome production process of inactivated vaccines and the longer development cycle of recombinant vector vaccines, mRNA vaccines are also regarded as future vaccines because they are relatively simple to synthesize and can quickly, efficiently and flexibly adapt to the virus pandemic.

The development process of RNA therapy-flying from the laboratory to ordinary people

In 1961, scientists discovered mRNA that can mediate the conversion of genes into proteins. But until 1990, 29 years later, after a research team injected mRNA directly into skeletal muscle, a protein compiled from this mRNA was found in the tissue, and this protein was not available in skeletal muscle. In other words, we can use mRNA as a small program to allow cells to produce the proteins we need. In 1993, scientists were surprised to find that mice injected with influenza virus mRNA showed an immune response. This means that we can use the pathogen's mRNA as a vaccine to easily produce safe antigens in the body instead of traditional attenuated or inactivated pathogens.

In 1998, American scientists Andrew and Craig discovered that RNA not only allows protein expression, but a small RNA called siRNA can prevent protein synthesis in C. elegans. Three years later, researchers discovered that this mechanism is also applicable in mammals, which makes siRNA possible as a medical method. With siRNA gene interference technology, the two scientists shared the 2006 Nobel Prize in Physiology and Medicine.

Also in 1998, the RNA therapy "fomivirsen", which inhibits retinal inflammation, was approved by the U.S. Food and Drug Administration (FDA), and for the first time, RNA therapy went from the laboratory to the clinical application. Since then, more exciting research advances in RNA therapy have been published, including RNAi (RNA activation) technology that inhibits HIV replication in macrophages and inhibits hepatitis C virus replication. These results have made it possible to cure a once difficult disease. In addition to rare diseases and viral infections, RNA therapy also has excellent curative effects on common chronic diseases. For example, siRNA drugs targeting PCSK9 gene can effectively and lastingly reduce low-density lipoprotein cholesterol levels, thereby achieving the purpose of treating or even preventing hyperlipidemia. .

Therapies based on RNA technology have sprung up like bamboo shoots after a rain in the 21st century. In August 2018, Alnylam's Onpattro was approved by the FDA and became the first RNAi therapeutic drug to be marketed. Moderna and Abbio's new crown vaccines based on mRNA immune technology have also achieved good clinical trial results. The RNA therapy products of Zhongmei Ruikang and Ruibo Biology are also getting closer and closer to clinical applications. Compared with traditional drugs, RNA therapy lasts longer after administration, has better specificity and stability, and the price is more acceptable. More importantly, RNA, as a new and innovative drug, marks A new pharmaceutical revolution is coming. We can foresee that in the near future, RNA therapy will change from an unfamiliar term to a common treatment plan. Hillhouse hopes that through investment in RNA therapy, RNA drugs of different types and used in various disease fields will enter the clinic as soon as possible, benefiting the majority of patients.