In May 2020, during the height of the COVID-19 lockdown, Michelle Werner learned that her son had been diagnosed with Duchenne muscular dystrophy, a rare genetic disorder that causes the muscles to weaken over time. The diagnosis came on his tenth birthday.  

Werner, then a pharmaceutical executive at AstraZeneca, immediately began looking into clinical programs for the disease, but she was disheartened to find that her son was not eligible for any of the available clinical trials. “His diagnosis really cast a spotlight on the real inadequacies with innovation and development across not just Duchenne muscular dystrophy, but rare diseases in general,” she said. 

This experience led to a career shift for Werner. In April 2022, she became the Chief Executive Officer of Alltrna, a biotech startup founded in 2018 with the goal of developing therapies based on tRNA for a wide range of rare genetic diseases caused by similar or identical mutations.

Unlike mRNA, which encodes the instructions for building proteins, tRNA serves as a bridge for protein translation. At the ribosome, tRNA molecules match the three-letter codons in mRNA to the corresponding amino acids, and they transfer the amino acids in the proper sequence to the growing polypeptide chain that will form a protein. Sometimes, a mutation in the mRNA can change a protein-coding codon into a stop codon — called premature termination codons (PTCs). These kinds of mutations are also called nonsense mutations because they result in incomplete and nonfunctional proteins. PTCs lead to multiple rare genetic disorders, collectively referred to as “stop codon disease,” and these account for ten to 15 percent of all inherited diseases (1). 

The team at Alltrna has developed a tRNA oligonucleotide called AP003, which they reported was capable of overwriting PTCs in a preclinical proof-of-concept report. Because the same PTCs underlie several stop codon diseases, Werner hopes that AP003 could serve as a single treatment for multiple diseases.

How do tRNA medicines differ from other genetic therapeutics, like gene editing or mRNA-based medicines?  

Gene replacement therapy replaces faulty genes with healthy copies of the same gene. In gene editing a cut is made with a pair of molecular scissors to correct the mutation at the source. mRNA-based therapeutics give a version of the protein back to the cell. However, all of these technologies are specific to a gene or a protein. There would need to be many different types of these therapies to address all patients across all genetic diseases. With a tRNA approach, we can completely turn that paradigm on its head. The first way we’re thinking of applying tRNAs in a therapeutic modality is in targeting nonsense mutations. It’s important to recognize that the same nonsense mutations occur across thousands of different diseases, so we can use tRNAs as a tool to treat various diseases caused by the same mutations.

Why have tRNA therapies not been widely pursued given that nonsense mutations are implicated in several inherited diseases?

When Alltrna was founded in 2018, we wanted to know if we could leverage tRNAs to restore the protein translation process in genetic diseases. But back then, the foundational tools to do that just didn’t exist. For example, we didn’t know if we could chemically synthesize a tRNA molecule, which is about 76 nucleotides long. We didn’t have the tools to quantify and characterize tRNAs or differentiate an engineered tRNA from an endogenous one. We couldn’t yet reliably measure how much of the tRNA got delivered to the site of action. We needed to do all of the foundational work in the same way that others did for mRNAs and siRNAs about ten to 15 years ago. We now have a suite of proprietary tools that allow us to characterize, quantify, and synthesize tRNA molecules that we didn’t have back in 2018.

What is AP003 and how does it work? 

AP003 is Alltrna’s first development candidate. It is an engineered tRNA formulated in a lipid nanoparticle delivery vehicle. We have a robust amount of preclinical data in animal models that gives us reason to believe that we can use this technology to read through nonsense mutations in a variety of rare genetic liver diseases. Our data also suggests that it has the safety and efficacy profile needed to justify testing the platform in a clinical trial. In our preclinical data, we saw that the tRNA used in AP003 was effective in animal models of two different genetic liver diseases: methylmalonic acidemia and phenylketonuria. These are rare metabolic disorders that prevent the body from breaking down certain amino acids, proteins, and fats. It has been really encouraging for us to see that we can restore protein levels in fundamentally different genetic diseases using the exact same engineered tRNA.

What challenges has Alltrna faced in developing AP003, and how did you overcome them?

Every day is a different challenge — that’s biotech. We're doing things that have never been done before. But one of the key challenges with any oligonucleotide-based therapy is figuring out how to deliver the medicine. We knew that lipid nanoparticles were available and used in different therapeutics, including the COVID-19 vaccines. We didn't know if they were going to be an effective vehicle to get the engineered tRNAs to the hepatocytes. Fortunately, we found that lipid nanoparticles are very good for delivering AP003 to the liver, but the big challenge that we’ll be tackling next is to go beyond the liver. We believe that a tRNA is uniquely suited for treating different types of diseases, including muscle and central nervous system conditions. That’s going to require a different delivery vehicle. The good news is that this is an industry-wide problem, and many companies are actively looking to solve it. A tRNA should be very amenable to different delivery technologies, and that's what we’ll be looking at in the not-too-distant future.

What’s next for Alltrna? 

We are currently progressing AP003 into Investigational New Drug (IND)-enabling work, to hopefully get an IND to begin testing it in patients. This is a top priority for us, and we're excited about its potential. Looking ahead, we also have other tRNA candidates in the pipeline that could target different mutations in rare genetic liver diseases, so there's a lot of exciting work ahead. When we started this company a few years ago, we weren’t sure if this approach would work. Now, seeing positive results in preclinical models gives us hope that it will translate to humans, and we’re committed to proving that it can.

This interview has been condensed and edited for clarity. 

Reference

1. Lueck, J.D. et al.  Engineered transfer RNAs for suppression of premature termination codons. Nat Commun  10, 822 (2019).