1 June 2023
New, promising approaches in gene therapyTricking Harmful Mutations
Photo: Pixabay
In protein synthesis, different vital proteins are produced in the cells of the human body according to a blueprint stored in deoxyribonucleic acid (DNA). The first step is transcription, whereby a messenger RNA (mRNA) reads the information for the respective protein in the cell. The RNA, like the DNA, is a nucleic acid but unlike DNA, it can leave the cell’s nucleus and transport the genetic blueprints for creating the protein to the ribosomes—the machines that perform biological protein synthesis in cells.
Then it is time for the second step: translation. With the help of the tRNAs, the mRNAs are “translated” into the respective protein by the ribosomes. When this happens, the operative units of tRNA, the so-called anticodons, accumulate according to the operative units of mRNA, the so-called codons. To mark where the protein to be synthesized begins and ends, the mRNA blueprint has special start-and-stop markings, the START and STOP codons.
Hereditary nonsense mutations turn a normal codon on the mRNA into a STOP codon, which, like the tearing off of part of a blueprint, has dramatic consequences because protein synthesis then stops prematurely, resulting in an incomplete protein. Because the necessary protein cannot be produced, the associated biological function is also missing in the person affected. The results are catastrophic and incurable diseases such as spinal muscular atrophy, cystic fibrosis, and muscular dystrophy, as well as growth hormone deficiencies. An estimated 11 percent of all hereditary diseases are caused by nonsense mutations.
A few microorganisms counter these mutations using so-called “suppressor tRNAs” that arise through the mutations in the tRNA and enable the cell to completely read the mRNA despite the new STOP codon resulting from mutation. Human cells, however, do not have these kinds of repair mechanisms. Now, however, the international research team headed by biochemist and last author Prof. Dr. Zoya Ignatova (Department of Chemistry, Universität Hamburg) has exploited this mechanism and developed an innovative strategy to transform tRNAs into efficient suppressors of nonsense mutations.
First, the researchers generated different suppressor tRNAs on a computer; they then synthesized these and extensively tested them. This ultimately resulted in suppressor tRNAs that work on the ribosomes and effectively suppressed the mutation-generated STOP codons—the process of synthesis was not disrupted and the protein was created in full. “Our goal is to trick the premature STOP codon caused by the mutation and to influence the STOP signals as little as possible with our suppressor tRNAs,” says first author Dr. Suki Albers (Department of Chemistry, Universität Hamburg).
The researchers’ biggest problem, however, is transport, because during transport, tRNAs in our bodies but also in our individual cells break down. “That’s why we cooperated with the US company Arcturus Therapeutics, a leading corporation in the field of gene therapies and RNA-based vaccines,” explains Ignatova. Arcturus developed lipid nanoparticles in which the tRNAs can be encapsulated and thus protected while also retaining their full efficacy. Similar lipid nanoparticles were used in the anti-covid vaccines developed by BioNtech/Pfizer and Moderna.
“In the current study, we were able to show that our suppressor tRNAs encapsulated in lipid nanoparticles provided highly useful in clinical trials in mice and patient cells and restored the function of the diseased proteins,” says Ignatova “Thus, we have an innovative gene therapy that corrects genetic diseases at mRNA level and opened a path to a new type of treatments with high levels of safety and no side effects.”
For the developed tRNA technology, the researchers at Universität Hamburg have already been granted 2 patents and they have applied for 3 more, 2 of which Arcturus has already licensed.
Original publication:
Suki Albers, Elizabeth C. Allen, Nikhil Bharti, Marcos Davyt, Disha Joshi,, Carlos G. Perez-Garcia, Leonardo Santos, Rajesh Mukthavaram, Miguel Angel Delgado-Toscano, Brandon Molina, Kristen Kuakini, Maher Alayyoubi, Kyoung-Joo Jenny Park, Grishma Acharya, Jose A. Gonzalez, Amit Sagi, Susan E. Birket, Guillermo J. Tearney, Steven M. Rowe, Candela Manfredi,, Jeong S. Hong,, Kiyoshi Tachikawa, Priya Karmali, Daiki Matsuda, Eric J. Sorscher, Pad Chivukula, Zoya Ignatova: Engineered tRNAs suppress nonsense mutations in cells and in vivo. Nature (2023): https://doi.org/10.1038/s41586-023-06133-1