A team of researchers from the Spanish National Research Council (CSIC) is leading a project to use the CRISPR genetic editing tool with the aim of destroying the RNA genome of the coronavirus SARS-CoV-2, which has caused the Covid-19 pandemic.
"It's about using the CRISPR molecular 'scissors' to directly attack the heart of the coronavirus, its RNA genome, to destroy it. And it's also about doing it cleanly, without disturbing any of the other RNA molecules in the cell, which are necessary for it to continue functioning" explains geneticist Lluis Montoliu, from the Centro Nacional de Biotecnología (CNB-CSIC).
The project will test the functionality and non-toxicity of CRISPR reagents in zebrafish embryos, then they will be tested against RNA viruses and finally they will be tested against cells infected with the current coronavirus. If the therapeutic strategy is successful, the next step would be to test it on mice.
The project brings together researchers from the CNB-CSIC, the Centro Andaluz de Biología del Desarrollo (CABD-CSIC-UPO) and the CIBER-ISCIII. It is funded by the CSIC through the Global Health Platform.
Revolutionary genetic editing
"CRISPR's gene editing tools have proven their versatility on numerous occasions, over the course of just seven years that we researchers have been using them, after billions of years of bacteria using them to defend themselves against viruses that attack them", explains Montoliu, principal investigator of the project together with Dolores Rodríguez Aguirre (CNB-CSIC), Miguel Ángel Moreno Mateos (CABD-CSIC-UPO) and Almudena Fernández, CIBER-ISCIII.
"There are many types of CRISPR tools. Most are capable of cutting DNA through a protein that acts like a scissor, called Cas, which cuts the genome of any species simply by being guided by a small RNA molecule, the intermediary nucleic acid that usually transports the genetic information from the nucleus to the cytoplasm of the cell, where the proteins will be produced", says Montoliu. "This is why they are known as programmable scissors. Because they cut DNA at specific targets, thanks to RNA guidance, which we can change to make it cut at another site in the genome," he adds.
Scissors for cutting the heart of the coronavirus
A few years ago, a new type of Cas proteins were discovered that were capable of directly cutting RNA, and not DNA. And they did it in a very specific way. They only cut the RNA that was indicated, again, by another small complementary RNA molecule, which again acted as a guide. This protein was called Cas13d.
"This project pursues an apparently simple goal," Montoliu says. "If the CRISPR variant called Cas13d can cut RNA molecules in a specific way, and if the genome of the SARS-CoV-2 coronavirus, which causes COVID-19, is an RNA molecule: Why not 'programming' one of these Cas13d proteins, with a guide of RNA complementary to the coronavirus genome, so that it cuts it and promotes its destruction by the cell?".
Multidisciplinary team
Montoliu sums it up with a clear image: "It's about attacking the heart of the coronavirus directly, its RNA genome, to destroy it". To carry it out, the project brings together four researchers with different but complementary profiles: Dolores Rodríguez, virologist expert in the management and characterisation of different types of viruses; Miguel Ángel Moreno Mateos, development biologist, expert in the new Cas proteins and in CRISPR in vivo systems; and Almudena Fernández and Lluís Montoliu, geneticists, experts in the use of CRISPR genetic editing tools for the generation of animal models of rare diseases.
"During the project we will design the CRISPR-Cas13d reagents at the CABD, where their functionality and non-toxicity will first be evaluated using zebrafish embryos. These reagents will then be tested at the CNB-CSIC, using various RNA viruses, similar to the coronavirus, but less dangerous than the SARS-CoV-2, to establish the optimal conditions of attack and destruction of the viruses. Finally, with the protocol already established, we will test our strategy on cells infected with the current coronavirus, which causes Covid-19, in a laboratory with the appropriate biosafety."
"If our therapeutic strategy is successful, the next steps would be to test it in an animal model, in mice susceptible to being infected with the coronavirus, and finally, if the results are encouraging, in clinical trials with patients," Montoliu concludes.
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