Study Shows Potential for Lipid Nanonparticles to Deliver Gene Editing Therapy to Liver

Rare Daily Staff

The genome editing technology CRISPR can be a powerful tool for treating diseases at the genetic level, but issues of safety and efficacy of this approach, and the ability to target specific tissues and organs remains a challenge.

Researchers at Tufts University and the Broad Institute of Harvard and MIT have developed a lipid nanoparticle (LNP) they say can package and deliver gene editing therapies to the liver. They report on their efforts in a study in mice published in the Proceedings of the National Academy of Sciences.

They said the study highlights the potential of LNP-mediated delivery as a specific, effective, and safe platform for Cas9-based therapeutics. Their approach, they said, is more efficient than the FDA-approved MC-3 LNP, the current gold standard. And, they found no evidence of toxicity or off-target mutagenesis where it was most likely to occur. The approach, they said, was effective and stable for at least 100 days.

In the study, the researchers used the LNPs to deliver CRISPR into the liver of mice to conduct targeting editing to reduce blood cholesterol levels. The were able to reduce cholesterol levels by as much as 57 percent—a reduction that can last for at least several months with just one injection.

More than 29 million Americans suffer from high cholesterol. In addition to life style and diet, multiple genes can be involved in causing the complex condition, which can make it difficult to treat. The researchers modified a single gene that could provide a protective effect against elevated cholesterol if it can be shut down by gene editing.

The researchers targeted angiopoietin-like 3 enzyme (Angptl3), which reduces the activity of other enzymes that help break down cholesterol. By knocking out the Angptl3 gene, other enzymes that reduce levels of cholesterol in the blood can operate unhindered. Some people have a natural mutation in their Angptl3 gene that results in low levels of triglycerides and low-density lipoprotein (LDL) cholesterol in their bloodstream without any known ill effects.

“If we can replicate that condition by knocking out the angptl3 gene in others, we have a good chance of having a safe and long-term solution to high cholesterol,” said Qiaobing Xu, associate professor of biomedical engineering at Tufts’ School of Engineering and corresponding author of the study. “We just have to make sure we deliver the gene editing package specifically to the liver so as not to create unwanted side effects.”

After a single injection of lipid nanoparticles packed with mRNA coding for CRISPR-Cas9 and a single-guide RNA targeting Angptl3, Xu’s team achieved as much as a 57 percent reduction in LDL cholesterol and about 29 percent in triglyceride levels, both of which remained at those lowered levels for at least 100 days. The researchers speculate that the effect may last much longer than that.

Because the reduction of cholesterol and triglycerides is dose dependent, levels could be adjusted by injecting fewer or more LNPs in the single shot, the researchers said.

By comparison, an existing, FDA-approved version of CRISPR mRNA-loaded LNPs could only reduce LDL cholesterol by at most 15.7 percent and triglycerides by 16.3 percent when it was tested in mice, according to the researchers.

The researchers found they could produce a better LNP by customizing the components. The LNPs are made up of long chain lipids that have a charged head that is attracted to water, a carbon chain tail that points toward the middle of the bubble containing the payload, and a chemical linker between them, among other components. The nature and relative ratio of these components appeared to have significant effects on the delivery of mRNA into the liver. By testing LNPs with many combinations of heads, tails, linkers and ratios among all components, the researchers were able to identify a design that was best able to target liver cells.

Because the in vitro potency of an LNP formulation rarely reflects its in vivo performance, they directly evaluated the delivery specificity and efficacy in mice that have a reporter gene in their cells that lights up red when genome editing occurs. Ultimately, they found a CRISPR mRNA-loaded LNP that lit up only the liver in mice, showing that it could deliver gene-editing tools into the liver to do their work.

“We envision that with this LNP platform in hand, we could now make CRISPR a practical and safe approach to treat a broad spectrum of liver diseases or disorders,” said Zachary Glass, graduate student in the Xu lab and co-first author of the study.

The work was supported by the National Institutes of Health’s Somatic Cell Genome Editing Program.

Thanks to Pfizer, Inc., Bluebird, and Novartis Gene Therapies for their support of this article, part of our Platforms of Hope: Advances in Gene Therapy and Gene Editing series.