New Lipids Dramatically Improve Gene Therapy and Vaccine Delivery

Every time a shuttle docks with the International Space Station (ISS), a highly precise process ensures a secure connection between the shuttle’s docking system and the station’s counterpart. These systems are universally designed for compatibility, allowing astronauts and cargo to transfer safely and seamlessly.

A similar process happens on a microscopic scale when lipid nanoparticles (LNPs)—the technology behind COVID-19 vaccines—deliver mRNA to cells. Just as a shuttle must dock correctly to function as intended, LNPs must effectively reach and release their cargo into cells. Improving the design of LNPs can enhance their ability to deliver mRNA, providing cells with vital disease-fighting instructions that could transform medicine.

Even when LNPs successfully reach their target cells, they often become trapped inside endosomes—small protective sacs within the cell. If they cannot escape, they fail to deliver their mRNA cargo, much like a shuttle getting stuck in the docking process and never making it safely aboard the space station.

If the endosomal escape process does not happen, LNPs become trapped and cannot deliver therapeutic cargo. They can make it all the way from a needle into the cell, but if they do not open that final barrier, they are useless.”

Michael J. Mitchell, Associate Professor, University of Pennsylvania

A New Approach

A few years ago, researchers at Carnegie Mellon University made a fascinating discovery: modifying the normally linear lipid tails of LNPs by adding a branch significantly improved mRNA delivery. This finding led Marshall Padilla, a Postdoctoral Fellow in the Mitchell Lab, to explore whether this approach could be the key to creating more effective lipids for mRNA delivery.

Every day, researchers are making new lipids to enhance the efficacy and safety of LNPs. But we lack a clear set of rules for designing better lipids.”

Marshall Padilla, Postdoctoral Fellow, University of Pennsylvania

Much of the research in this field resembles a guessing game. Scientists test extensive libraries of lipid variations without fully understanding why certain designs perform better than others.

Padilla, who holds a Ph.D. in Chemistry from the University of Wisconsin-Madison, believed it might be possible to move beyond trial-and-error methods and intentionally design lipids with branched tails to improve their ability to escape endosomes.

Introducing BEND Lipids

One significant obstacle in creating these improved lipids was synthesizing branched ionizable lipids, essential components of LNPs that alter their charge to facilitate endosomal escape. These lipids are not commercially available in branched form, so Padilla had to synthesize them himself.

The key issue was forming carbon-carbon bonds, which are notoriously difficult. I used a complex mix of lithium, copper, and magnesium to make the reaction work.”

Marshall Padilla, Postdoctoral Fellow, University of Pennsylvania

This effort resulted in a new class of lipids called branched endosomal disruptor (BEND) lipids. These specialized, branched molecules enable LNPs to penetrate the endosomal membrane more effectively, enhancing their ability to deliver mRNA and gene-editing tools.

Improving mRNA Delivery

In a recent study published in Nature Communications, Mitchell, Padilla, and their collaborators demonstrated that BEND lipids significantly improve the delivery of mRNA and gene-editing tools via LNPs, in some cases achieving up to a tenfold increase in effectiveness. Through a series of experiments, ranging from editing genes in liver cells to conducting advanced biochemical simulations, the researchers found that BEND lipids consistently outperformed even the LNPs used by Moderna and Pfizer/BioNTech, the developers of the COVID-19 vaccines. “

We found that our branching groups allow the lipids to help facilitate the escape of our payload from the endosome, where most cargo is destroyed, into the cytosol, where it can perform its intended therapeutic effect,” said Padilla.

Designing Better Therapeutics

The researchers hope that BEND lipids will not only enhance LNP delivery but also inspire a shift in how lipids are designed, moving away from trial-and-error approaches. With a deeper understanding of lipid functionality, scientists could develop more efficient delivery systems for advanced therapies.

Mitchell said, “Testing hundreds to thousands of LNPs and seeing which one works can be a major time, cost, and labor burden many labs are not capable of doing this. You want to know the rules so you can design solutions efficiently and cost-effectively.”