Although messenger RNA (mRNA) was used successfully in the COVID-19 vaccine, for it to have broader therapeutic uses it needs to last longer in the body. Toward that goal, researchers from the Broad Institute and MIT have engineered a new mRNA structure with multiple "tails" that significantly increases mRNA activity levels in cells and extends its duration in animals. This development, reported in Nature Biotechnology, could lead to mRNA-based treatments for diseases requiring long-lasting therapies that edit genes or replace faulty proteins.
“The use of mRNA in COVID vaccines is fantastic, which prompted us to explore how we could expand the possible therapeutic applications for mRNA,” said Xiao Wang, senior author of the new paper. “We’ve shown that non-natural structures can function so much better than naturally occurring ones. This research has given us a lot of confidence in our ability to modify mRNA molecules chemically and topologically.”
The mRNA in today’s COVID vaccines is so effective because very little is needed—once injected into the body, it stimulates the production of proteins that resemble parts of the COVID virus. “The immune system is very robust, so it’s able to create many antibodies in response to transient expression of a foreign protein,” explained Hongyu Chen, first author of the paper. But for that same type of mRNA to produce enough proteins to treat diseases that disrupt normal production of essential proteins, a much larger dose would be needed, which could cause toxic side effects.
Based on previous research, Wang and Chen knew that one part of mRNA’s structure, a branch called the poly(A) tail, plays an important role in protecting mRNA from degradation inside cells. In 2022, they showed that chemically modifying the poly(A) tail slows down the natural decay of mRNA, rendering it more useful for a wider range of therapies. They named those modified molecules “mRNA-oligo conjugates” or mocRNAs.
To build on this work, Wang and Chen hypothesized that engineering an even more complex shape of mRNA, containing multiple modified tails of poly(A), would enhance therapeutic effects of mRNA even more. In their latest effort, the team made their multi-tailed mRNAs, tested them in human cells, and found that they sustained mRNA translation much longer than both natural mRNA and mocRNA, producing up to 20 times more proteins per dose over time.
In mouse experiments, the researchers discovered that just one dose of multi-tailed mRNA led to protein production that lasted as long as 14 days—nearly double the lifetime demonstrated by previous mRNA technologies.
They also used their multi-tailed mRNA to encode the DNA-cutting Cas9 protein as part of the CRISPR-Cas9 gene-editing system and tested that in mice to edit genes linked to high cholesterol, Pcsk9 and Angptl3. They found that just a single dose of multi-tailed Cas9 mRNA could induce higher levels of gene editing, resulting in decreased cholesterol circulating in the bloodstream, compared to animals treated with control Cas9 mRNA.
Wang and Chen are now focused on making their multi-tailed mRNA synthesis and purification process more scalable. They are also taking a closer look at how mRNA modifications affect the interplay between its therapeutic stability and activity.