New techniques show bright future in genetic disease care

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Genome editing is the technology that gives scientists the ability to change an organism’s DNA. It allows genetic material to be added, removed, or altered at particular locations in the genome. The most recent approach, which was discovered in 2012 by Jennifer Doudna, a Professor of molecular and cell biology and of chemistry at UC Berkeley, and colleague Emmanuelle Charpentier, of the Max Planck Institute for Infection Biology, is called CRISPR-Cas9. This is short for clustered regularly interspaced short palindromic repeats and CRISPR-associated protein 9. Cas-9 is an enzyme that can cut the two strands of DNA’s at a specific location in the genome, so that bits of DNA’s can be removed or added. It is currently the simplest, most precise and cheapest method of genome editing. However, Cas-9 is a set of proteins created by bacteria, and finding a way to deliver them has been a challenge as they cannot be isolated and injected into the system. Researchers used to employ viruses to deliver CRISPR-Cas9 components into the cells, but the technique introduced toxicity, amplifying the sides effects of Cas-9 and does not cure the original disease, only converts it to a milder one. To overcome these setbacks, the scientists at UC Berkeley have introduced a new delivery method, called CRISPR-Gold. They have tested CRISPR-Gold in mice with Duchenne muscular dystrophy and found that it led to an “18-times-higher correction rate and a two-fold increase in a strength and agility test” writes Berkley News Media relations writer Brett Israel. The new method is called CRISPR-Gold because of the heavy use of gold-nanoparticles to deliver all three components of the gene editing tool (Cas9 enzyme, guide RNA, and donor RNA) simultaneously. The Berkeley scientists invented a way to attach all three components into a package around a gold nanoparticle and bind them with a polymer. This package can be safely delivered into a wide variety of cell types. According to the publication of CRISPR-Gold, a single injection into muscle tissues of mice that model Duchenne muscular dystrophy restored 5.4 percent of the dystrophin gene to the normal sequence in two weeks. Unlike using viruses to deliver Cas9, CRISPR-Gold can also faithfully restore the normal sequence of dystrophin, reduce tissue fibrosis, and does not introduce any toxicity. The study shows that injecting CRISPR-Gold into the muscles of mice with DMD increased their muscle strength and agility by almost two times. In general, the editing tool efficiently corrected the DNA mutations that cause Duchenne muscular dystrophy. However, all is not successful for this new approach, as the fraction of mutant DNA that was repaired is still very low, only about 0.8%, and 5% is the needed amount to start therapeutics. Niren Murthy, a professor of bioengineering at the University of California, Berkeley and one of the authors of the study, speculates that CRISPR-Gold can reach this threshold with multiple injections. “CRISPR-Gold and, more broadly, CRISPR-nanoparticles open a new way for safer, accurately controlled delivery of gene-editing tools,” Irina Conboy, associate professor at Berkeley’s Department of Bioengineering and co-author of the study. “Ultimately, these techniques could be developed into a new medicine for Duchenne muscular dystrophy and a number of other genetic diseases.” Three of the study authors, Kunwoo Lee, Hyo Min Park and Niren Murthy have formed a start-up company called GenEdit, and are currently focusing on translating the CRISPR-Gold technology into humans. Recently, there have been a few attacks on the viability of CRISPR-Cas9, most notably the research “Unexpected mutations after CRISPR-Cas9 editing in vivo” carried out by Stephen Tsang and Wen-Hsuan Wu of Columbia University Medical Center and Kellie A.Schafer of Stanford University, which claims that while they achieved what they set out to do, most CRISPR modifications also unpredictably altered hundreds of other genetic functions. However, this paper is being vocally criticized by a large body of scientists, and is looking towards a full retraction. With that out of the way and with human trials on the horizon for the United States, and many have been carried out in China, we are looking at a very promising future for genome editing and for gene-disease treatments.

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