In one of the first examples of gene-editing technology being effectively used to knock out the expression of a gene in non-human primates, researchers from the University of Pennsylvania have lowered the blood cholesterol in monkeys by disabling a single gene in the liver. The successful experiments pave the way for future human trials in five to 10 years.
The target of the research is a well-known protein called PCSK9. A great deal of prior study has established that PCSK9 is a protein that inhibits the liver's ability to remove harmful cholesterol. Several drugs have been developed to inhibit the activity of PCSK9 but they are expensive and not consistently effective.
So some scientists have been investigating ways of genetically inhibiting PCSK9. This new study is the first to show effective reduction of PCSK9 in the liver through gene editing in a non-human primate. Rather than the more popular and recent CRISPR gene-editing technique, the study used a slightly older and different technique called meganuclease-based gene-editing.
Identified in the 1990s, meganucleases are enzymes that can be engineered for precision gene editing. In the case of this experiment the enzyme was engineered to inactivate the PCSK9 gene and was delivered to the liver by a harmless adeno-associated virus. The results were impressive, with the rhesus macaque monkeys showing between 45 and 84 percent reductions in PCSK9 levels, and associated cholesterol levels dropping by up to 60 percent. Analysis of liver tissue found effective mutations in 40 to 65 percent of PCSK9 genes.
"Our initial work with several delivery and editing approaches produced the most impressive data in non-human primates when we paired AAV for delivery with the engineered meganuclease for editing," says James Wilson, senior author on the new study.
Several other research teams have also been working to switch off PCSK9 genes as a potential treatment for heart disease, and there have been successful experiments using the CRISPR gene-editing technique to silence PCSK9 in mouse models. The team at UPenn was unable to successfully replicate these results in primates, which led them to experimenting with the meganuclease gene-editing method.
The experiments were not without unwanted side effects, though. The researchers report the treatment triggering a rise in liver enzymes, suggesting a degree of immune response to the treatment. This is not entirely unexpected but may suggest multiple treatments could results in the body developing a more heightened immune response. Some off-target genetic cuts were also identified that have the potential to lead to the development of cancers.
It is obviously still very early in the development of these treatments and the researchers suggest further refinement certainly needs to be done before human trials are considered. Lili Wang, one of the authors on the study, thinks the work is about five to 10 years away from human testing.
"First, we have to make many improvements and thoroughly evaluate and characterize this technology in large animal models to ensure both safety and efficacy," says Wang.
However, the team is confident that this approach could lead to a promising treatment for patients suffering from more extreme and life-threatening forms of heart disease. Permanently editing out a gene to help reduce cholesterol levels seems to be a promising future treatment for cardiovascular disease, but it certainly looks to be at least 10 or 20 years away from real-world clinical use.
The study was published in the journal Nature Biotechnology.
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