Researchers at the University of Toronto have demonstrated that chemically modified suppressor transfer RNAs combined with lipid nanoparticles can restore cystic fibrosis transmembrane conductance regulator protein production in cell, mouse, and patient-derived organoid models, offering a potential new therapeutic approach for genetic disorders caused by nonsense mutations.
Scientists have long sought ways to correct genetic diseases at the protein stage rather than editing the underlying genome. A team led by biomedical engineer Bowen Li has now shown that suppressor transfer RNAs can successfully restore production of a critical protein associated with cystic fibrosis in multiple model systems, according to research published in Science.
The Problem of Nonsense Mutations in Cystic Fibrosis
Genes contain the instructions cells use to make proteins, which are first copied into messenger RNA and then read by cellular machinery. A nonsense mutation introduces a premature stop signal, or premature termination codon, into that messenger RNA.
Instead of continuing to build the full-length protein, the cell halts translation too early. The resulting protein is often shortened and unable to perform its normal function.
In cystic fibrosis, these nonsense mutations occur in the cystic fibrosis transmembrane conductance regulator gene. When functional CFTR protein is absent or severely reduced, thick mucus accumulates in the lungs and contributes to chronic respiratory disease.
Engineering Suppressor tRNAs and Modifying Lipid Nanoparticles
Transfer RNAs normally help translate messenger RNA into proteins by carrying specific amino acids and recognizing corresponding three-letter codons. Suppressor tRNAs are engineered with altered anticodons designed to recognize premature stop codons instead.
By changing these anticodons, researchers can make them insert an amino acid at the premature stop signal, allowing translation to continue. However, laboratory-made tRNAs traditionally struggle because they lack the chemical modifications present on natural tRNAs.
To overcome this, Li’s team tested various modifications and discovered that adding a single methyladenosine marker at the 57 or 58 position greatly enhanced performance.
“If you put that M1A modification at the 57 or 58 position of the tRNA, it can very efficiently increase the read-through activity, prolong its functional persistence, and reduce its innate immune activation.”
Bowen Li, University of Toronto, via C&EN
Delivering those fragile RNA molecules into cells requires specialized transport vehicles.
Combining Therapies and Testing in Patient Organoids
When the research team tested the combination of modified suppressor tRNAs and TTP-3-based lipid nanoparticles in bronchial epithelial cells and mouse models, they observed successful restoration of the CFTR protein. In patient-derived intestinal organoids, however, optimal success required combining the suppressor tRNA therapy with Trikafta, an FDA-approved therapy marketed by Vertex Pharmaceuticals. The combined treatment outperformed either approach used alone.
Furthermore, the therapeutic effect demonstrated remarkable durability in patient cells.
“When we treat patient cells with the CFTR mutation with our modified tRNA, the CFTR protein can be restored for more than 7 weeks . . . longer than unmodified tRNA and also much longer than mRNA.”
Bowen Li, University of Toronto, via C&EN
Expert Perspectives and Preclinical Safety Hurdles
Because the approach relies on RNA delivery rather than DNA alteration, it does not permanently change the genome.
“It doesn’t permanently change or affect the genome. . . . If you observe any abnormal phenomena in the patient, you can just easily stop it.”
Bowen Li, University of Toronto, via C&EN
Jeff Coller, an RNA scientist at Johns Hopkins University who was not involved in the study, observed that these tRNA approaches, are really going to be transformative for genetic disorders
and called the development of a suppressor tRNA–specific LNP that can facilitate passage through the mucosa a very important game changer.
Despite the promising laboratory results, researchers emphasize that the work remains preclinical. In a related Perspective published alongside the study, Jacob Myerson and Drew Weissman cautioned that establishing the safety of repeated delivery remains an essential hurdle, pointing out that dose-dependent inflammation was observed in mice and prior animal studies involving inhaled lipid nanoparticle delivery.
Broad Implications and Next Steps for Clinical Translation
Developing a separate gene therapy for every rare individual mutation remains exceptionally challenging due to the sheer diversity of disease-causing variants. By establishing a common therapeutic strategy that addresses the same type of mutation across multiple genes and rare conditions, the platform aims to fill a critical treatment gap.
