Genes, be silent!
The first drug based on RNA interference has been approved in the USA
Polina Loseva, "The Attic"
While the world is thinking about the ethics and safety of genome editing using CRISPR-Cas, other technologies are already entering the market. The new leader of the molecular race is a drug that uses RNA interference to "jam" the expression of certain genes.
In search of the causes of diseases, modern medicine is digging deeper into the molecular soil. Previously, we worked with the symptoms of diseases, alleviating the condition of the sick organism, then switched to the causes, adding missing proteins or destroying excess ones, now we are trying to prevent the occurrence of these causes by manipulating the work of individual genes.
We already know how to create individual human cells that work the way we need – for example, the recently approved CAR-T cell therapy for leukemia patients or a boy cured of epidermolysis bullosa. In both cases, doctors took the wrong cells from the patients and replaced them with edited, correct ones.
But bringing RNA interference to the market for the first time allows us to radically change the work of genes in vivo, and this is a fundamentally new level of control over the work of our body.
All for the fight against amyloidosis
Imagine that packages from the store are piling up in your apartment. The package itself is a useful thing if you need to bring something somewhere. But when a lot of them accumulate, moving around the apartment turns into a difficult quest. According to this principle, amyloidosis develops – the accumulation and deposition of extracellular proteins. It can accompany a variety of diseases, from diabetes to Alzheimer's disease. But regardless of which protein fills the body, the reason is usually a mutation that prevents it from folding properly. Sloppily packed protein performs its basic functions worse, sticks together with other proteins, settles on the walls of organs and is poorly excreted by the kidneys.
Today on the agenda is a cure for ATTR – amyloidosis caused by the accumulation of the protein transtiretin (TTR). Normally, it just performs the function of a package, transferring thyroxine (thyroid hormone) and vitamin A through the blood. The result of the deposition of such protein packages is polyneuropathy – disruption of peripheral nerves, loss of sensitivity, tremor and pain syndromes.
What can we do to stop the growth of such a snowball? The easiest option is to transplant the liver so that it produces healthy protein. However, sometimes you want to do without surgical interventions. It is possible to prohibit the protein from changing its shape – this is how TTR stabilizers, drugs of the previous generation, worked. But it would be more effective to destroy the cause and stop the formation of protein in cells. Protein production consists of many stages: the rewriting of information from DNA to matrix RNA (mRNA), the release of RNA from the nucleus into the cytoplasm of the cell, binding to the ribosome and, in fact, protein synthesis – translation. New technologies suggest blocking mRNA in the cytoplasm so that synthesis becomes impossible.
A drug with developed amyloidosis. Photo: Michael Feldman, MD, PhD University of Pennsylvania School of Medicine / wikimedia commons
They'll kill everyone
The RNA in a human cell always consists of a single chain. And for any of its functions, it is critical that it remains single-stranded and can bind to DNA or other RNAs. Therefore, the easiest way to disrupt her work is to add a second chain to her. Antisense RNAs work according to this principle: they complementarily stick together with matrix RNA, a double-stranded molecule is obtained, which the ribosome can no longer recognize and, accordingly, use it as a blueprint for protein synthesis. This method can be used in medicine – for example, the drug fomivirsen worked against cytomegalovirus infection (now it is no longer used). The problem is that the binding of antisense RNA to mRNA is fragile, therefore reversible. In addition, one molecule of antisense RNA blocks only one mRNA molecule, and high concentrations of the drug are needed to achieve the effect.
Everything changed in 1998, when American scientists were looking for the optimal way to deliver antisense RNAs to the cells of the roundworm C. elegans. Unexpectedly, they discovered that if you make antisense RNA double-stranded, it blocks protein synthesis much more effectively. And after eight years they received The Nobel Prize in Physiology and Medicine for the discovery of RNA interference, and journalists wrote together that "stubs" for RNA promise mankind to get rid of all diseases associated with protein production.
What do we know about RNA interference 20 years later? Just like the CRISPR-Cas system, this mechanism is part of the virus protection system, only adopted not by bacteria, but by more complex organisms, eukaryotes. Let's say an RNA-containing virus appears in the cytoplasm of a cell. He came to multiply and capture the cell: to do this, he needs to copy his RNA and build shell proteins on its matrix. When the virus copies the RNA, it becomes double-stranded. At this moment, it is recognized by the Dicer protein and violently cuts into small fragments – small interfering RNAs (miRNAs). The massacre does not end there: single-stranded miRNAs are captured by the RISC protein complex. RISC floats in the cytoplasm, armed with miRNA, and waits for the appearance of mRNA complementary to it. As soon as one is nearby, the miRNA binds to it, and RISC cuts the mRNA into small fragments. In other words, the cell captures the double-stranded RNA of the virus and uses it as a tip to single-stranded RNAs to split them and prevent the virus from building its proteins.
Scheme: Polina Loseva, Anatoly Lapushko / Chrdk
RNA interference is used by our cells not only, however, in order to hunt and "jam" the activity of viruses. Its cells are also used to block the work of some of their genes. There are areas in our genome that do not encode proteins. Some of them instead encode miRNAs, which then help break down mRNAs, stopping the production of proteins. miRNAs work more efficiently than antisense RNAs, because one miRNA molecule can lead to the destruction of many mRNA molecules.
Everyone can RNA
The hero of today is the company Alnylam Pharmaceuticals and its drug patisiran, which is a miRNA against transtyretin mRNA enclosed in a lipid envelope. The drug is administered intravenously. It is worth noting here that ATTR is a very convenient disease for such treatment. The fact is that most liposomes, lipid bubbles with medications, when injected into the blood, settle in liver cells and do not spread to other tissues. But, by a happy coincidence, most of the transtiretin in the human body is also produced by liver cells. Therefore, the drug inevitably achieves its main goal and blocks the formation of a defective protein.
Side effects as a result of such therapy are minimized, since miRNAs selectively bind to the mRNA of the desired protein.
In the report on the third phase of clinical trials, the pharmaceutical company reports that side effects are mainly associated with the injection itself, i.e. the insertion of a needle into the patient's vein, and therefore their set does not differ in the experimental group from the placebo group.
Approval by American regulators of patisiran (and its inclusion in the British list of early access to medicines) – the culmination of a story about people who undertook to pave the way from a purely scientific discovery, fundamental knowledge – to a specific technology, in this case a medicine.
"I assure you, God did not create RNA interference in order to get medicines," John Maraganor, CEO of the company, joked two years ago in a conversation with STAT journalists. "We had to deal with it on our own."
According to STAT, the first biotech startups that planned to create drugs based on RNA interference began to appear en masse back in 2001. The investment bubble in the region grew, and then collapsed, because no one has learned how to deliver miRNA to the address. In 2006, Mello and Fire received the Nobel Prize for their discovery, grand pharma were already interested in the technology, which began to buy assets, writing checks for billions of dollars, and a few years later, having lost all faith in success, they sold what they had bought for a song. Alnylam, which overcame the last step in the race to bring the "Nobel" medicine to the market, went to this finish line for 16 (!) years.
Alnylam has several more drugs in its plans, which are currently at different stages of testing. They are supposed to be used to treat acute hepatic porphyria, hypercholesterolemia, hyperoxaluria and atypical hemolytic uremic syndrome. All of them are in some way accumulation diseases, that is, they develop as a result of an excess of certain substances outside or inside the cells. Therefore, they are a good target for RNA interference - you can block either the synthesis of the enzyme that produces them, or their own synthesis.
Alnylam is not the only participant in this molecular race. In parallel, other companies developing drugs with miRNA inside are also increasing their power. Still others continue to improve the technology of antisense RNAs. The official website of clinical research in America is full of the most unexpected technologies based on RNA: blockers of blood cell division in leukemia, immune cell stimulators, modulators of the immune response to cancer – what is not there. We can safely count on a rich harvest from these RNA fields.
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