Manufacturing Strategies for Chemically Modified tRNAs
William Kiesman, Ph.D., Chief Technology Officer, Alltrna
Correcting the misreading that underpins genetic diseases could yield drugs capable of treating multiple diseases, according tRNAs developer, Alltrna.
The Massachusetts startup made the case at TIDES USA, with CTO William Kiesman explaining the approach is to focus on one gene at a time.
Therapeutic tRNAs are the molecules responsible for matching genetic code to corresponding amino acids during protein synthesis.
“If you step back and look at disease in general, most genetically caused mutations fall into three basic categories: nonsense mutations in which you get a single snip that can turn a regular protein signal or a regular amino acid signal into a stop signal. And that way, you end up getting a truncated protein.
“You can have missense mutations in which you will actually switch the identity of your gene so that you put in a different amino acid and get a mutant protein. And then finally, frameshifts, in which you put in an extra nucleotide, and now you’re misreading the whole rest of the chain from that point on. So these are the very basic underpinnings for most monogenic genetic diseases,” Kiesman said.
There are around 6,000 mutation-driven conditions, and while all these conditions could potentially be treated by developing disease-specific oligonucleotide therapies, such efforts would take a long time, according to Kiesman.
“If you had to go at those diseases one at a time, as we do now, it will take you 6,000-plus new chemical entities to get there. And so that means that we will solve at least this set of genetic diseases sometime in the next 500 years.”
Kiesman contrasted this with Alltrna’s approach, explaining that the company is “trying to change that out and actually be able to look at the underlying mutation and correct that and be able to correct it in the read of the mRNA.”
The idea is to look at the genetic defects that are common to multiple diseases, and treat them as a shared mutation set with one drug, according to Kiesman.
“They’d be different genes, and they’d have that defect in a different spot in their DNA. But we should be able to read through that and provide the appropriate protein from that for all of us. And so that’s the idea. Many diseases, single agent.”
Enter the tRNA
In nature, tRNA functions by moving to the ribosome that is on the mRNA molecules, reads the appropriate codon, and then adds the appropriate amino acid to the elongating protein chain before leaving the ribosome and binding another amino acid.
Kiesman said, “We’re going after premature termination codons, in which there is a mutation in that mRNA that actually turns the amino acid codon into a stop codon so you will not get protein production past that point. So what we’ve been able to do is design tRNAs that actually read that stop at the correct spot and put the right amino acid in place. So you end up with a full-length protein at the end.
He contrasted this with gene editing, explaining that “we don’t do it upstream, we’re not changing the germline genetic code, we’re reading the mRNA the appropriate way to make the right protein in the right cell, and it will do it at the right level because all of the mRNA compensatory mechanisms are all still intact in that cell.”
Manufacturing
In parallel to its R&D efforts, Alltrna is developing manufacturing processes able to produce tRNAs at scale. And for a small firm such work can be challenging, according to Kiesman.
“In a very small company, things change quickly. You may have one lead that’s going in one area, and then now you’ve stopped that, and you move to another one. So what do you do? How do you platform things if it’s not consistent? You need to be able to stay on your toes, you need to outsource a lot and have good collaboration partners, people that can manage that flexibility and the risk with your pipeline. But also we’ll be able to stop on a dime when you learn something new
“And then you need to be able to scale appropriately,” Kiesman continued, adding, “We’re going after very rare genetic diseases. So we’re targeting 50-gram batches of material at the moment for our early clinical studies. That’s what we’re focused on. We’re not focused on multi kilogram, but you know, that will come as it does with everything if we’re successful.”
There are also regulatory considerations. Kiesman said, “You’ve got to be able to make sure you know what the regulator’s going to think when they now see something new come in. What bucket are they going to want to try to put it in? Is this an ASO? Or is this a guide strand or something else? And so that’s something that you have to be cognizant of while you’re working through it.”