Peptide-guided nanoparticles deliver mRNA to neurons

in a new paper nanolettersThe researchers showed how peptides (short chains of amino acids) act as precise targeting molecules, allowing LNPs to specifically deliver mRNA to the endothelial cells that line the brain’s blood vessels and neurons.

This represents an important advance in delivering mRNA to cell types, which is critical for treating neurodegenerative diseases; any such treatment needs to ensure that the mRNA gets to the right place. Previous work by the same researchers demonstrated that LNP could cross the BBB and deliver mRNA to the brain, but no attempt was made to control the cells targeted by LNP.

“Our first paper is a proof-of-concept for lipid nanoparticle design,” said Michael J. Mitchell, associate professor of bioengineering (BE) and the paper’s senior author. “It’s like showing we can send a package from Pennsylvania to California, but we don’t know where in California it will end up. Now, with peptides, we can send packages to specific destinations with sharing capabilities Land, like every house has a red mailbox.

Entering the Brain Challenge

Crossing the blood-brain barrier is difficult because its structure has evolved to block almost any dangerous or foreign molecule, including most drugs; like most drugs, the mRNA molecule is too large to penetrate the barrier. The BBB also actively removes materials it deems hazardous.

“You can inject treatments directly into the brain or spine, but these are highly invasive procedures,” said Emily Han, a doctoral student in Mitchell’s lab and first author of the paper.

Because the blood-brain barrier allows fat-soluble molecules to pass through (such as alcohol and THC, which is why these substances affect the brain), certain LNP formulas (composed in part of the same fatty compounds found in everyday oils) can sneak into the brain.

Peptides and Antibodies

So far, most research into targeting LNPs to specific organs has focused on conjugating them to antibodies, large proteins that function similarly to biological tags. “When you put antibodies on LNPs, they can become unstable and larger in size, which makes it difficult to squeeze through the barrier,” Han said.

In contrast to antibodies, which can be hundreds of amino acids long, peptides are only tens of amino acids long. Their smaller size means they are not only easier to place on LNPs in large quantities, but also cheaper to manufacture. Peptides are also much less likely than antibodies to aggregate or trigger unintended immune responses during LNP formulation.

The choice to use peptides began when Han had an unexpected encounter with a bat that flew into her room, possibly exposing her to rabies. While researching the vaccine she received against the disease, Han learned that one of the ways the rabies virus crosses the blood-brain barrier is through the rabies virus glycoprotein. “Then I stumbled upon one of our most promising targeting peptides,” Han said. The molecule is called RVG29, a 29-amino-acid fragment of the protein.

Test concept

To confirm that the peptides worked as expected, the researchers first needed to verify that they adhered to the LNPs. “Our LNPs are complex mixtures of nucleic acids, lipids and peptides,” Han said. “We have to optimize our quantification methods to single out peptides based on all the other signals.”

Once they know that the peptide has adhered to the LNP, researchers must determine whether the peptide-functionalized LNP (pLNP) actually achieves its intended goals in animal models. “This was really difficult to set up,” Han said, “because in the brain, there are so many different cell types and a lot of fat, which can interfere with the measurements.” Over more than six months, Han painstakingly developed a A plan to carefully break down brain tissue, like a mechanic taking apart an engine.

future direction

Next, the team aims to determine which parts of neurons must be treated with pLNPs to effectively relieve symptoms or potentially cure neurological diseases. “Going back to the same analogy, do we need to send these messages to every house with a red mailbox, or just 10 percent? Would 10 percent of the neurons be enough?” Mitchell asked.

Answering this question will guide the development of more effective delivery strategies, bringing the promise of mRNA-based treatments for Alzheimer’s, Parkinson’s and other brain diseases closer to reality.

This research was conducted in the Penn State College of Engineering and Applied Science and was supported by the National Institutes of Health (DP2 TR002776), the Burroughs Wellcome Foundation, the National Science Foundation (CBET-2145491), and the American Cancer Society (RSG-22-122-01-ET).

Other co-authors include Sophia Tang, Dongyoon Kim, Amanda M. Murray, Kelsey L. Swingle, Alex G. Hamilton, Kaitlin Mrksich, Marshall S. Padilla and Jacqueline Li of Penn Engineering, as well as Penn Engineering and Children’s Rohan Palanki of the Hospital of Philadelphia.