The previous year’s noble prize in chemistry went to a revolutionary technology, CRISPR/Cas9. The amusing discoveries in the field of gene editing from the discovery of DNA, molecular scissors, recombinant DNA discovery, generation of Insulin in-vitro, discovery of ZFNs and TALEN’s. In 2011, Emmanuelle Charpentier found a type of tracrRNA in Streptococcus pyrogenes, where the bacteria immune system cleaves the viral genetic material and disarms the viruses. Later in a 2012 paper published in Science, Dr. Charpentier, and Dr. Jennifer Doudna isolated components of CRISPR-Cas9 systems and discovered bacteria’s genetic scissors in a tube. Naturally, bacteria detect the viral DNA. Scientists used this strategy to manipulate the DNA as they can cut any predetermined site on DNA using these CRISPR-Cas9 scissors and edit the DNA code. This strategy paved the way in many basic and applications based studies in agriculture, Medicine, Bioenergy, etc.
One such application is shown by a study presented by Intelia Therapeutics and Regeneron Pharmaceuticals. They dramatically decreased the level of misfolded protein that causes a disease known as transthyretin amyloidosis or ATTR. It is a progressive disease caused by the accumulation of amyloid deposits of transthyretin protein (TTR) in body organs and tissues. This disease seems fatal if untreated, and early identification and treatment are essential for the patient. The symptoms in each patient differ from numbness to limbs and toes (polyneuropathy), heart diseases to loss of motor activities, etc. The symptoms worsen over time. There was only a generic drug named diflunisal or tafamidis that acts by stabilizing the tetrameric form of the protein or inhibiting protein synthesis by degrading its mRNA, and this kind of treatment has a better survival rate but has to administer for the long term to maintain the TTR protein knockdown. Since 2018, the Food and Drug Administration (FDA) has cleared three drugs to treat this disease, such as Onpattro (from Alnylam Pharmaceuticals), infused medicine that will improve nerve function but consists of side effects preexposure to glucocorticoids and antihistamines. The second one is from Akcea Therapeutics, known as Tegsedi (intotersen) has some side effects such as glomerulonephritis and decrease platelet count and the third is from Pfizer known as Vyndamax for patients with a heart problem. But each of these drugs is costly or has side effects and must be taken for their whole lives. So, a better treatment is required. And what could be better than permanently halt or reverse the disease course?
To accomplish this, Intellia Therapeutics has used the gene-editing approach. They used the approach already well studied by Alnylam, where they deliver their medicine in the liver cells using lipid nanoparticles. Intellia also uses lipid nanoparticles to deliver the CRISPR tools. Once absorbed, these nanoparticles are absorbed by the liver cells; they cut precisely the DNA segment that codes for TTR protein hence halt the production of misfolded protein at the genetic level. This study was first conducted in vitro and in vivo and then evaluated for safety and pharmacodynamics effect for a single dose of the NTLA-2001 in six polyneuropathy patients and is currently under Phase 1 trial. The results published in NEJM showed that after four weeks, the patients administered with low dosage showed a decrease in the protein level of TTR by 52%, while with the high dosage, the reductions go in between 80-90%, which seems remarkable as Onpattro also have such a percentage decrease in the level of TTR protein. So, it is as effective as the current treatment.
This study seems to be a landmark for modern medicine as this will open the door for new therapies based on gene editing. This appears to be good news for the patients, and there is hope for a cure in the future. But there are some unanswered questions, such as how long the effect will last? Is it permanent? What are the consequences of gene-editing in the long term? With CRISPR/Cas-9 system, there are off-targets involved, what is the percentage of off-targets? Because it will be difficult if this will hamper any vital gene in the liver. The study also performed off-target analysis using primary human hepatocytes, and low off-target was observed. But still, there are a lot of safety questions that are out there. The FDA applies strict rules for genetic medicines, and Scientists hope to improve this discovery further for the patient’s benefit.