Base Editing Could Cure a Host of Genetic Diseases

Picture the familiar double helix of human DNA — a long, twisted ladder with 3 billion rungs on it, each made of a pair of genetic bases (A, T, C, and G). A mistake in just one base along that ladderan A where there should be a G — can be enough to cause a disease. In fact, researchers have linked over 31,000 different mistakes, known as “point mutations,” to human diseases. Now, an advanced form of gene therapy — called base editing — could make it possible to safely correct them.

Base editing is a type of gene editing technology, just like CRISPR. However, while CRISPR cuts through both strands of the DNA ladder to swap in different genes, a base editor makes precise changes to individual letters along the genome — a much less invasive kind of DNA surgery.

It’s like your spell-checker,” neuroscientist Jeffrey Holt said. “If you type the wrong letter, spell checker fixes it for you.” Base editing was first developed by Broad Institute researcher David Liu in 2016, and it’s not perfect — the best base editors still make off-target edits and aren’t 100%  efficient. However, the technique is more efficient than CRISPR and causes fewer errors, which has made it the focus of considerable research into correcting disease-causing point mutations.

Base editing is like your spell-checker. If you type the wrong letter, it fixes it for you,” explained Jeffrey Holt. Holt was part of a team that used base editing to partially restore the hearing of mice with a point mutation that causes deafness in people. Earlier in 2020, University of Illinois researchers used base editing to slow the progression of ALS in mice. More recently, Liu was part of a group that used base editing to correct the point mutation that causes progeria, a premature-aging syndrome, in mice. By changing a T to a C in a single gene, they were able to more than double the lifespan of mice with the disease.

There’s no guarantee that a therapy that works in mice will translate to humans (although gene editing is conceptually much simpler than drugs that rely on complex chemistry). To find out whether base editing can live up to its promise as a disease-curing technology, we need human studies — and now, one is just on the horizon.

On January 12, Massachusetts-based biotech company Verve Therapeutics announced the promising results of a study testing a base editing treatment for heterozygous familial hypercholesterolemia (HeFH), a genetic heart diseaseHeFH is fairly common, affecting about one in 500 people, and it causes consistently high levels of “badcholesterol (LDL-C) — that makes people with the disease susceptible to heart attacks or strokes at a relatively young age. In primates with HeFH, Verve used base editing to change an A to a G in a single gene. Within two weeks, the animals’ blood LDL-C levels had dropped by 59%. Six months later, they were still just as low.The treatment, dubbed “VERVE-101,” was well-tolerated, with no adverse effects reported.

When we started, we had no idea this would work,” Verve CEO Sekar Kathiresan said in a press release, adding, “It works, and we expect this to be durable for the lifetime of the animals.” Now, Verve wants to find out if VERVE-101 works in humans.

Source: https://www.freethink.com/

Human Brain Cells Gene-edited To reduce The Risk Of Developing Alzheimer’s Disease

Cells in the human brain could one day be edited by scientists to prevent the development of Alzheimer’s disease, a new study suggests. The causes of Alzheimer’s are still not well understood, but a leading theory is that it is triggered by the build-up of a protein called beta-amyloid outside the brain cells. Researchers from Laval University in Canada have been investigating how a key gene in human nerve cells could reduce the formation of this protein. Many variants of this gene increases beta-amyloid production, but one variant, called A673T, instead reduces it.

A673T was first discovered in 2012, and is only active in one in 150 people in Scandinavia, but those that have it are four times less likely to get Alzheimer’s. The researchers believe that switching on this gene variant in brain cells could reduce the production of beta-amyloid and thereby reduce Alzheimer’s risk. As the A673T variant doesn’t become relevant until later in life, it isn’t selected for by evolution, according to the study authors. It differs from other variants of the gene by a single DNA letter. Researchers showed that, by editing this one DNA letter, they were able to activate the A673T variant in brain cells growing in a culture dish. Jacques Tremblay and colleagues say this is the first step to proving that engineering the variant into brains could have the same benefits as inheriting it.

The team are still refining the technique before they try it on animals. The researchers initially used a CRISPR technique called base editing, which allows the direct, irreversible conversion of a DNA base into another, targeted base. However, they have now switched to a relatively new method called prime editing – a ‘search and replace‘ technique for editing genomes that directly writes new genetic information into a targeted DNA site using a fusion protein.  Working with cells in a dish they managed to edit about 40 per cent of the cells, but they think a higher proportion might be needed for it to work in a human brain.

The researchers  worked with a process known as base editing, a relatively new method that allows the direct, irreversible conversion of a DNA base into another, targeted base
Source: https://www.dailymail.co.uk/

How To Substantially Lower LDL Cholesterol Levels

Verve Therapeutics, a next-generation cardiovascular company, today announced the presentation of new preclinical proof-of-concept data in non-human primates that demonstrate the successful use of base editing to turn off a gene in the liver and thereby lower blood levels of either LDL cholesterol or triglyceride-rich lipoproteins, two factors leading to coronary atherosclerosis. Verve is developing one-time gene editing medicines that safely edit the adult human genome and mimic naturally-occurring cardioprotective variants to permanently knock out cholesterol-raising genes in the liver and treat coronary heart disease. The data were presented at the International Society for Stem Cell Research (ISSCR) 2020 Virtual Annual Meeting.

In a keynote address titled, “From reading the genome for risk to rewriting it for health,” Sekar Kathiresan, M.D., co-founder and chief executive officer of Verve Therapeutics, presented the results of recent studies utilizing adenine base editing (ABE) technology, licensed from Beam Therapeutics, in which substantial lowering of plasma LDL cholesterol or triglycerides was successfully demonstrated in non-human primates. Base editing is a gene editing technology developed to enable precise and permanent rewriting of a single DNA letter in the genome.

At Verve, our goal is to develop medicines, given once in life, that precisely edit targeted genes in the liver to permanently reduce LDL cholesterol and triglyceride levels in adults with coronary heart disease, the leading cause of death in the U.S. and worldwide,” said Dr. Kathiresan. “These proof-of-concept data, which to the best of our knowledge represent the first successful application of the base editing technology in non-human primates, show that we can safely edit the primate genome at highly efficacious levels to significantly lower blood LDL cholesterol and triglycerides. The findings are very encouraging and add to our growing body of evidence in using both base editing and CRISPR-Cas9 in vivo against various gene targets. We expect to choose a lead program by year-end 2020 with the goal of initiating human clinical studies within the next three years.”

The studies were conducted in a total of 14 non-human primates and evaluated in vivo liver base editing to turn off proprotein convertase subtilisin/kexin type 9 (PCSK9), a gene whose protein product elevates blood LDL cholesterol or angiopoietin-like protein 3 (ANGPTL3), a gene whose protein product elevates blood triglyceride-rich lipoproteins. Verve’s proprietary drug product consisting of the ABE mRNA and an optimized guide RNA packaged in an engineered lipid nanoparticle was delivered through a single intravenous infusion. Across two separate studies, seven animals were treated with the drug product targeting the PCSK9 gene and seven additional animals with the drug product targeting the ANGPTL3 gene.

Whole liver editing, blood protein and lipid levels were measured at two weeks and compared to baseline. The program targeting PCSK9 showed an average of 67% whole liver PCSK9 editing, which translated into an 89% reduction in plasma PCSK9 protein and resulted in a 59% reduction in blood LDL cholesterol levels. The program targeting ANGPTL3 showed an average of 60% whole liver ANGPTL3 editing, which translated into a 95% reduction in plasma ANGPTL3 protein and resulted in a 64% reduction in blood triglyceride levels and 19% reduction in LDL cholesterol levels.

Source: https://www.vervetx.com/