Suppressor tRNAs and lipid nanoparticles offer new approach to nonsense mutation cystic fibrosis

Engineering Suppressor tRNAs to Read Through Premature Stop Signals

Genetic instructions are transcribed into messenger RNA before cellular machinery translates them into proteins. When a nonsense mutation introduces a premature stop signal into the mRNA transcript, protein assembly halts early, yielding a shortened molecule that cannot perform its normal biological duties. These genetic errors account for an estimated 11 percent of human genetic disorders.

In cystic fibrosis, such mutations strike the CFTR gene, preventing the proper regulation of salt and water across cell membranes and triggering the buildup of thick mucus in the respiratory tract. Rather than attempting to replace or permanently edit the underlying DNA, an interdisciplinary research team developed engineered suppressor transfer RNAs designed to coax cells into reading past those premature termination codons.

“There are so many types of disease-causing mutations – many affecting only a small number of people – that developing a separate gene therapy for every individual mutation is extremely challenging. With tRNA therapeutics, our goal is to develop a common therapeutic approach that could potentially address the same type of mutation across many different genes and diseases, including rare conditions that currently have few or no effective treatment options.”

Bowen Li, Leslie Dan Faculty of Pharmacy, University of Toronto

Chemical Modifications and Inhaled Lipid Nanoparticle Delivery

Natural tRNAs carry specific amino acids and match three-letter codons in mRNA. By altering their anticodons, researchers created suppressor tRNAs that insert an amino acid at premature stop signals, letting translation continue to the end of the protein. Unmodified tRNAs, however, are unstable and vulnerable to rapid immune clearance. To overcome this, the study team chemically modified the sup-tRNAs to boost aminoacylation, prolong functional stability, and suppress innate immune activation.

Co-senior author Haissi Cui noted that nature served as the primary design guide for the chemistry. We used nature as our design guide and found that adding one specific modification made the engineered tRNA more active and longer-lasting, Cui explained, adding that it shows what becomes possible when chemistry and RNA biology come together.

Delivering fragile RNA molecules to targeted tissues requires specialized carriers. The team packaged the engineered tRNAs into lipid nanoparticles designed for inhaled delivery directly to the lungs. Jingan Chen, a PhD candidate and co-lead author in the lab, emphasized that delivery remains paramount: No matter how powerful you make those tRNAs, without delivery, they cannot be a drug.

Preclinical Results Across Multiple Models

The research team tested the combined therapeutic strategy across a broad spectrum of experimental platforms, including bronchial epithelial cells, mouse models, and patient-derived cystic fibrosis organoids. Across all three platforms, the treatment successfully restored the production and function of full-length CFTR protein.

Furthermore, investigators observed that the tRNA therapy can be combined with existing pharmaceutical treatments for cystic fibrosis, opening the door to potential combination therapies. The findings were documented in the journal Science.

Safety Hurdles and Next Steps for Respiratory Function

Despite the restoration of protein function in laboratory models, independent experts caution that considerable preclinical work remains before human trials can begin. In a related Perspective published alongside the study, Jacob Myerson and Drew Weissman highlighted dose-dependent inflammation observed in treated mice and prior animal studies involving inhaled lipid nanoparticles.

Establishing the long-term safety of repeated LNP-based pulmonary administration stands as the primary obstacle on the path toward clinical translation, according to the accompanying analysis.