Scientists in Canada find RNA therapy approach that acts like biological bypass

Professor Bowen Li said the main message is that tRNA can potentially be used as a new type of genetic medicine

University of Toronto scientists have found a novel RNA therapy approach that acts like a biological bypass, teaching cells to ignore faulty genetic “stop instructions” and produce missing, vital proteins naturally. The RNA mechanism, the scientists said, could bypass genetic stop signals across different inherited conditions, offering significant implications.

University of Toronto scientists said their clinical translation is limited by suboptimal activity and inefficient in vivo delivery.

Suppressor transfer RNAs (sup- tRNAs) can rescue disease-causing nonsense mutations by promoting readthrough of premature termination codons (PTC). Their clinical translation is limited by suboptimal activity and inefficient in vivo delivery, the scientists said in a paper. A codon is a sequence of three DNA or RNA nucleotides that codes for a specific amino acid or signals the start or end of protein synthesis.

Also, A nonsense mutation is a genetic change that turns a normal amino acid-coding codon into a premature stop codon, causing protein synthesis to end too early.

“The main message is that tRNA can potentially be used as a new type of genetic medicine. Unlike gene editing, which changes DNA, our approach works at the level of protein production and helps the cell read through a premature stop signal. Importantly, the same general strategy may apply to many different diseases caused by nonsense mutations, not just cystic fibrosis,” said Professor Bowen Li, the paper’s lead author.

Authors in the paper titled ‘Nonviral delivery of chemically modified tRNA rescues nonsense mutations in cystic fibrosis’, published in the journal Science, say that their work combines site-specific chemical modification of sup-tRNAs with cargo-tailored pulmonary lipid nanoparticle (LNP) engineering to overcome these barriers.

“Incorporation of N1-methyleadenosine in sup-tRNAs improved PTC readthrough, enhanced tRNA aminoacylation, prolonged functional persistence, and reduced innate immune activation. High throughput ionizable lipid screening and formulation optimisation identified a sup-tRNA-tailored LNP that efficiently delivered chemically modified sup-tRNA to the lung.”

This approach restored cystic fibrosis transmembrane conductance regulator (CFTR) expression and function in bronchial epithelial cells, mouse models, and patient-derived organoids. Thus, LNP-delivered, chemically engineered sup-tRNAs represent a potential therapeutic platform for treating nonsense mutations, scientists found and documented in the paper.

Nonsense mutations introduce premature termination codons into mRNAs, prematurely terminating mRNA translation and producing truncated non-functional proteins. These mutations mostly arise from single-neucleotide substitutions within coding regions and account for 11% of human genetic disorders, typically causing loss-of-function phenotypes. Pharmacological readthrough agents generally exhibit limited efficacy and dose-limiting toxicity, whereas gene-replacement and genome-editing strategies require careful evaluation of immunogenicity, off-target effects, and long-term safety.

“The immediate impact is that this creates a potential therapeutic route for patients whose mutations are not well addressed by existing treatments. Nonsense mutations occur in many inherited diseases, including cystic fibrosis, muscular dystrophy and some neurological disorders. The broader opportunity is to develop a platform in which the same type of engineered tRNA could potentially be adapted across multiple diseases that share the same kind of genetic error,” said Li.

Transfer RNAs (tRNAs), which decode mRNA codons by delivering amino acids to the ribosome, have emerged as a broadly applicable therapeutic modality. By replacing the anticodon to recognize PTCs, tRNAs can be engineered into suppressor tRNAs (sup- tRNAs), which are aminoacylated by endogenous aminoacyl- tRNA synthetases (ARSs) and restore full-length protein synthesis through translational readthrough.

Sup-tRNAs can also indirectly stabilise target transcripts by preventing nonsense-mediated decay while minimally perturbing normal translation termination, which makes them a potentially precise and safe strategy for treating nonsense mutations, said the authors.

The researchers used the technology for cystic fibrosis, where nearly 10% of the patients harbour nonsense mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene and cannot benefit from approved CFTR modulators.

“Sup- tRNAs offer a compelling RNA- level strategy for treating diseases caused by nonsense mutations by promoting PTC readthrough without altering the genome. Unlike-gene editing approaches, sup-tRNAs are reversible and avoid permanent genomic changes, thereby reducing concerns related to unintended off-target editing… sup-tRNA therapy offers distinctive advantages, including restoration of endogenous gene expression, prolonged functional persistence, and broad applicability across diseases, while circumventing side-effects from elevated protein levels,” the authors wrote.

In the long run, it means moving beyond RNA-based vaccines. “RNA therapeutics are expanding far beyond mRNA vaccines. Different forms of RNA can now be used to replace missing proteins, silence harmful genes, edit genomes or, as in our study, correct errors during protein production. I think the next major advance will come from combining better RNA design with better delivery systems so that these medicines can reach specific organs and cell types safely and efficiently. That could make RNA medicines applicable to a much broader range of genetic diseases, cancers and regenerative medicine,” said Li.