Duchenne muscular dystrophy is caused by genetic mutations in the dystrophin gene that result in loss of dystrophin expression in muscle cells. Nonsense mutations arising from the conversion of a sense codon to a stop codon within the dystrophin gene account for 10-15% of cases, and over 800 unique nonsense mutations have been reported in Duchenne muscular dystrophy patients. Transfer RNAs (tRNAs) engineered to read through the premature termination codon (PTC) created by a nonsense mutation have the potential to restore expression of full-length dystrophin in these patients. This therapeutic approach is not in principle affected by the immense size of the dystrophin gene, nor the large number of distinct nonsense mutations observed in Duchenne muscular dystrophy patients. This would overcome limitations of gene replacement, mRNA therapeutic, and gene editing approaches, and more generally could potentially unify the treatment of thousands of rare and ultrarare stop codon diseases.
To develop tRNAs with desired therapeutic features, such as high activity, specificity, durability, and low immunogenicity, Alltrna has built a unique platform based on (i) high-throughput screening of engineered tRNA oligonucleotides combining optimized sequence and chemical modification patterns and (ii) rational and machine learning-guided design principles. Preclinical data demonstrate productive PTC readthrough in vitro in a wide range of clinically relevant disease models spanning more than 15 different genes, and in vivo in PTC-containing mouse models across different stop codons.
These preclinical proof-of-concept results are promising and provide an attractive programmable design framework for tRNAs as a novel class of medicines to restore disrupted protein production, regardless of target, for thousands of diseases with the same underlying genetic mutation. Recent preclinical data and rationale for therapeutic application in muscle stop codon diseases such as Duchenne muscular dystrophy will be presented at the meeting.