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- All codes are written down: an improved genomic editor will help in the treatment of rare diseases
All codes are written down: an improved genomic editor will help in the treatment of rare diseases
Russian scientists have managed to significantly improve the efficiency of primed genomic editing. They developed and tested a new approach and were able to make this technique safer and more accurate. The specialists worked with the most common pathogenic variant of the CFTR gene in the European population, which leads to cystic fibrosis. But the new approach is universal and can be used in the future to correct thousands of hereditary pathologies, experts interviewed by Izvestia said.
How scientists improved the genomic editor
A team of Russian scientists has developed and demonstrated the effectiveness of a new approach in primed genomic editing. This was reported in the press service of the Ministry of Education and Science. It allows you to adjust specific sections of DNA quite accurately and is safer than the classic editor, since it acts precisely and cuts only one strand of DNA, not both. The work was performed by scientists from the N.P. Bochkov Medical and Genetic Research Center (MGNC) of the Ministry of Science and Higher Education and the Federal Medical Biophysical Center named after A.I. Burnazyan of the FMBA.
The specialists worked with the most common pathogenic variant of the CFTR — F508del gene in the European population, which leads to cystic fibrosis and is characterized by the "loss" of three nucleotides.
As the scientists explained, targeted therapy drugs have now been developed for patients with this disease, which significantly improve their health. However, they are prescribed strictly depending on the genotype, not for every pathogenic variant such treatment will be effective. Another problem is that medications must be taken throughout life, so the search for approaches that can directly correct the cause of the disease, that is, the variant in the gene itself, remains relevant.
The genome is a kind of huge instruction for the assembly and operation of the human body, written in letters-nucleotides. A typo in one word (gene) can lead to serious illness. Cystic fibrosis is just such a "typo". Scientists have been working on the molecular technology of "pencil and eraser" for a long time to correct this error right in the text-genome. This is genomic editing.
Recent research by the MGNC Genome Editing laboratory has shown that the primed editing system is more efficient than others. Unlike them, it breaks only one strand of DNA, which makes it safer. Another advantage is the absence of an off-target effect, when DNA breaks in an off-target area.
However, the effectiveness of the method itself is unstable, it can vary depending on many factors. As MGNC experts explained to Izvestia, the natural DNA repair system manages to intervene and patch up the gap that the editor made using the previous pathogenic version of the nucleotide sequence, rather than a new one that is synthesized at the site of the gap.
The MGNC scientists have modified the editing system so that the pathogenic variant of the sequence is immediately removed, then the repair system will use the new, correct variant.
The specialists developed and tested 12 modification options for this system to correct the pathogenic variant of CFTR F508del in the basal cells of the respiratory tract obtained from patients. The effectiveness of one of them turned out to be up to 2.13 times higher compared to the standard editor.
— Today, many scientific groups are working to improve the efficiency of primed editing, for example, using different proteins involved in DNA repair in the repair system. However, this is the first time we have used this approach with the removal of an unnecessary nucleotide sequence," Svetlana Smirnikhina, head of the genome editing laboratory, PhD, told Izvestia.
As the experts explained to Izvestia, the standard primed editor approached the desired section of DNA (the double helix), made a neat incision in only one strand and "slipped" the corrected sample to the cell. But the cell repair system can ignore the new sample, sewing up the gap with the help of an old, erroneous copy, so the effectiveness may vary.
The scientists decided that the old, cut—out DNA fragment was interfering with the "tail". They attached an additional tool to their editor, the protein exonuclease FEN, which cuts off this interfering "tail". This makes it much easier for the cell to use the synthesized correct template to close the gap. This has significantly improved the effectiveness of correcting the most common mutation in the European population that leads to cystic fibrosis.
Gene therapy of cystic fibrosis
The classic CRISPR-Cas9 method often causes inappropriate editing, that is, it makes changes in those areas of the genome that should not be affected, said Mikhail Bolkov, a researcher at the Institute for the Study of Aging at the Russian State Scientific and Clinical Center of the Pirogov Russian National Research Medical University of the Russian Ministry of Health. Moreover, previous methods could edit certain sections of DNA from the point of view of structure and chemistry, and the prime editing method potentially allows correcting up to 89% of human genetic diseases.
— But this method also has its limitations. One of the most pressing problems is that we have our own DNA repair systems, and they are faster. At the moment when the wrong area is edited and cut out, the repair system can overtake our enzyme and patch up the gap not according to our delivered sample, but according to the old one, with an error, that is, it returns everything as it was. This is exactly what the domestic improvement of the prime editing system is aimed at. In this case, inappropriate editing turned out to be minimal," the specialist said.
This achievement is an important step towards gene therapy for cystic fibrosis, but the clinic is still far away, Albert Rizvanov, head of the Personalized Medicine Center of Excellence at Kazan (Volga Region) Federal University, told Izvestia.
"Doubling the efficiency of editing is a breakthrough in the laboratory, but for real treatment, it is necessary to ensure that a mutation in almost 100% of cells is corrected with very high accuracy. The developed approach may be one of the solutions to the problem of low efficiency of primed editing. It is universal and in the future can be used to correct thousands of other hereditary diseases, which is the main importance of this work," the expert said.
The results of a joint study by Russian scientists have been published in the International Journal of Molecular Sciences.
Cystic fibrosis is a systemic hereditary disease caused by a mutation of the gene for the transmembrane regulator of cystic fibrosis and characterized by damage to the endocrine glands and severe respiratory disorders.
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