Harnessing the Body’s Natural RNA Machinery to Treat Diseases

RNA editing provides a way to address disease-causing mutations and modulate protein function. Korro Bio has developed platform technology that it says solves many of the challenges facing current gene therapy and gene editing approaches by harnessing the body’s natural RNA editing machinery to make precise, single-base RNA edits. We spoke to Ram Aiyar, president and CEO of Korro Bio, about the company’s RNA editing platform technology, how it works, and its initial focus on applying its approach to treat a rare liver disease.

Daniel Levine: Ram, thanks for joining us.

Ram Aiyar: Thank you for having me, Danny. It’s my pleasure.

Daniel Levine: We’re going to talk about RNA editing, Korro Bio, and its platform technology Opera. There’s been a lot of excitement around RNA targeted therapies like antisense oligonucleotides and mRNA.  RNA editing offers a new approach to targeting RNA. Where does RNA editing fit into the growing arsenal of genetic medicines and what can you do with that that provides advantages over existing approaches to RNA targeted medicines?

Ram Aiyar: Well, Danny, thank you for having me here. And also thank you for asking the question on RNA editing and the interest there. It’s been quite an exciting time. Just thinking about the genomic revolution, at least over the last decade or so, there have been numerous technologies that have come into play that have fundamentally changed the lives of patients. I started my career at a company called Centocor that was then acquired by J&J, and I saw the revolution where the drug that they developed, it’s called infliximab or Remicade, was utilized as an antibody therapy for patients with rheumatoid arthritis. And in that case, you saw patients who were not able to walk to start to walk. Since that time, there have been tremendous antibodies that have come on the market and it’s almost like antibodies are par for the course. They’re like small molecules. You can make them anytime and go and target pretty much any protein. I feel like we are in a similar revolution for RNA medicines. It’s taken a couple of companies over the last two decades or so to bring approved therapies. Specifically, when you think about knocking down a protein or silencing a gene or silencing RNA and providing that stop signal, from a protein standpoint, companies like Alnylam and Ionis have spent a lot of time on two separate constructs—one is an siRNA that is a double stranded RNA construct that’s chemically modified, and Ionis, that’s a single strand antisense oligonucleotide—both of them working fundamentally on proteins that are inside a cell that have an endogenous function to cut or silence a gene. And both of these companies have co-opted these RNA-binding proteins or endogenous enzymes to go and do what it naturally does. So, it’s really exciting to see. We’ve seen the approval of patisiran, we’ve seen the approval of which is a drug for ATTR therapy that targets the liver using a liver nanoparticle. We’ve seen a second generation or multiple second generation compounds that use what are called conjugates that target a specific receptor. Those are sub-q (subcutaneous) therapies. And then we’ve also seen an RNA therapy for spinal muscular atrophy that has been developed where it has been delivered intrathecally. So, over the last two years, there’s been a ton—10 years—there’s been a ton of development in RNA medicines, so it’s pretty exciting. The reason I was giving this background is much like the antibody therapies that have had this wave that have come, I feel like we are there from an RNA medicine standpoint. And so, the next wave of that, although we have technologies that can knock down a protein or a silenced gene on the RNA level, we haven’t seen anything that can activate the RNA or activate the protein or modulate the pathway in a very meaningful way. That’s where, at least our approach from a Korro standpoint, is where RNA editing fits. RNA editing is a technology where we deliver a synthetic oligonucleotide. We can co-opt another RNA binding protein called ADAR, or Adenosine Deaminase Acting on RNA, and we can redirect that enzyme to go make a specific change on an RNA by changing one of the alphabets on the RNA, which is an adenosine to another alphabet, which is called an inosine. And that inosine, usually, as it goes through a translation process as it gets converted to protein, gets converted to a guanosine. So think of it as a base edit. That doesn’t happen on DNA, that doesn’t touch your genomic material, but does it transiently on RNA as long as the medicine is present, and you can have tremendous biological impact through that pathway. I’ll stop there and see if you have any questions.

Daniel Levine: We’ve seen a lot of advances in both gene therapy and gene editing. How might this offer a way to overcome some of the challenges of existing approaches to gene therapy and gene editing?

Ram Aiyar: That’s a great question. I always go back to ask any parent who their favorite child is if they have two of them, right? Is it your younger one or older one? And usually the answer is, well, it depends. Each of them provide benefits in different ways and have characteristics and attributes that are very, very different. So, to apply that analogy, I think the DNA editing technologies, especially from the first generation of the CRISPR Cas9 systems, I guess the second generation of base editors and prime editors, and then beyond, you’re going to start to see many more nucleases that come into bear that can provide additional benefits, almost inserting whole genes. I think that those technologies have a role to play in areas where the causal impact of the disease. It’s usually restricted to a gene or a set of mutations within a gene, and you go in and have an impact by correcting them. That way you go after the fundamental source of that disease. Where it gets interesting is because when you start thinking about larger patient populations where you have an influence of the gene—not an impact or deleterious impact—where it has a confluence of impacts given epigenetic factors, environmental factors, other risk factors, you see genes play a role not at the genomic level, but more at the transcriptomic and protein level. And that’s where RNA editing sort of comes together. It plays a role in areas where you want to modulate protein function. You want to alter the function in a way that could be beneficial. And we do that again, specifically leveraging genetics, because if you see over the last decade, think about 23andMe, think about Ancestry, think about all the genetic screening that’s being done on a regular basis at hospitals in the Boston area and otherwise where people are starting to understand and build databases around entire, not just genomic material, but also transcriptomic material and understanding the genetic links to what the phenotypes are and how they manifest. That’s where RNA editing can really come in, learn from those genetic insights and create that single base edit to influence biology. So I wouldn’t treat it as is RNA editing better than DNA editing? I think both of them have a role in helping patients in meaningful ways. I would think about RNA editing as a space where we can go after common complex diseases and perturb the network, biological network, in meaningful ways to have clinical benefit.

Daniel Levine: You had referred to ADAR, an enzyme that’s critical in the editing of RNA. For listeners not familiar with this, can we just take a step back and have you explain what ADAR is and its function in RNA?

Ram Aiyar: It’s a very interesting question. I want to step back and tell you about the genesis of Korro. So, one of the founders of Korro is an investigator called Joshua Rosenthal, and he’s a professor at Woods Hole in the marine biology labs. And he studies cephalopods and through cephalopods, he studies ion channels and its impact. What he noticed during his discovery process was he identified and realized that there is this endogenous enzyme called AR in cephalopods, what happens is this enzyme is overactive in its neuronal system. It gives cephalopods or octopus or squids amazing plasticity around sensing its external environment and making changes to the proteins it produces. I don’t need to tell you about the plasticity that cephalopods and octopus and squid have to change color, to change temperature, and sense the environment. So, he took those learnings as the CRISPR Cas9 systems were coming into bear and thought about performing similar changes on RNA that you can do on DNA. And so, the enzyme that he was working on is this enzyme that you rightly called ADAR. This enzyme is present in every cell of our body. It’s conserved between lower species in worms all the way through humans. It has two real endogenous functions. The one aspect of it is to identify cells from non-cells, i.e., if you have a double stranded virus come in that is inside the cell, it sort of sends out alarm signals to destroy the cell and in the second half it provides the ability to create diversity in the proteins that are produced. So when you take a step back through the human genome project, the hope was that we would find a hundred thousand genes or so because there were a hundred thousand proteins. But in reality there were only about 23,000 genes or so. Somewhere between the 23,000 and a hundred thousand, there’s a lot of machinery that’s happening and it’s enzymes like ADAR that actually caused that diversity. And so this enzyme radar is essential. It’s important for development and the beauty, much like how the siRNAs and antisense oligonucleotides leverage an intracellular protein, ADAR is one such protein that we leverage.

Daniel Levine: Tell me about the Opera platform that Korro has developed. What is Opera and how does it work?

Ram Aiyar: So, Opera is a compendium of tools, is probably the easiest way to define it. It stands really on four pillars. The first pillar is an understanding of this enzyme ADAR and its impact on normal cells as well as how to leverage the enzyme to create potent drugs. So that’s the first pillar. I talked to you about Josh Rosenthal. And so, we have a slew of scientists that pulled together an understanding of how this enzyme reacts with normal function, what kind of RNA it binds and how it actually interacts with the RNA to make that specific adenosine to inosine edit. So that’s pillar number one. I don’t think you can design good drugs for patients without a good understanding of the enzyme and the tools that you are actually going to leverage to make those drugs. The second pillar in Opera is around chemistry. And I say chemistry in the context of RNA chemistry. There are, as you know, approved products that are on the market that have leveraged this chemistry on modifying RNA to make it more drug-like, more stable and have the ability to have its pharmacokinetic and pharmacodynamic properties that give it a drug-like ability. So, we leverage the second pillar that we have [that] is both an existing toolbox of chemistries that are utilized in approved products, but also building on a novel toolkit of chemistries that are specific for ADAR-mediated editing that we have developed. There are two more pillars I just want to touch on very, very quickly, and Opera really is a compendium of those four pillars. The third pillar is on delivery. As you know and having heard your other podcasts, delivery is a big component of oligonucleotide delivery to the right tissue at the right concentration so that you can have the benefit you need. And so, we view delivery as fit for purpose, i.e., for a patient population to solve a specific disease pathology, and we leverage existing delivery tools rather than reinventing the wheel on oligonucleotides. And then the last component is—we don’t talk much about it—but we design our compounds using a combination of computational tools as well as machine learning to really get to very potent compounds. This has been an empirical process since we started because nobody has really developed a rule book for RNA editing, and we’ve started to write the first few chapters on that by empirically understanding how you design these compounds. So those four components enable us to develop drugs, highly potent drugs specific for a patient population that we’ll go after. And so when you look at our pipeline, the first indication that we’re going after is a rare genetic liver disease that has manifestations across two tissue types and we transiently correct a pathogenic mutation. And that drug, the development candidate that we just nominated and presented data last week was developed through this Opera platform.

Daniel Levine: Before we talk about your experimental therapy, you used the term base editing earlier. That makes me think of your editor being able to make a very specific type of change. In this case adenosine to inosine. Is there the ability to make other changes and does that just require different enzymes or are you limited in what you can do at this point?

Ram Aiyar: It’s a fascinating question, Danny, because when you think about the transcriptome or the genome for that matter, and you comprise of these six alphabets that are between the two systems, that’s about 20 percent or so of your entire transcriptome that’s an adenosine. And so depending on the biology that you’re trying to go after and knowing that you can go after any adenosine using the system, we can make quite a few changes to impact biology. So although it may seem like a single change is what is being affected, there is a lot that we can do from a biological standpoint that’s going to be very, very meaningful. And so to give you a sense of what that looks like, I touched on areas where if you identify a rare genetic mutation that is a guanosine to an adenosine mutation and we want to repair that back to a guanosine, instead of touching the genetic material, you can actually do it transiently, which has some very specific benefits outside of safety. That’s something that we can do. But beyond that, just think about an adenosine in a coding region is present in multiple amino acid sequences. And so we have the ability to change 12 amino acid sequences from one to another. So just think about that. So amino acids are the building blocks of proteins. We have the ability to change the structure and function of proteins in very, very meaningful ways. And so that really opens up the possibilities of going after disease biology that has never been done before the advent of this technology. I think early on when Moderna was there, you would always hear Stephan talk about we’re going to make the cells create its own medicines, and it’s been outside of the vaccine space you’re starting to see more and more development in the mRNA space, but there are challenges around delivery and challenges around chronic dosing that are not yet solved. But using RNA editing we can create those designer proteins that can really change its function. So yes, we are limited by making a single adenosine to inosine change, but that doesn’t limit us in terms of the biology that we can go after in meaningful ways to impact the clinical pathology.

Daniel Levine: This technology has implications for both rare and common diseases. You talked a little bit about delivery. It’s not surprising to see you start with a disease of the liver. Was that selection in part because of delivery challenges or are you able to target other parts of the body as well?

Ram Aiyar: Danny, I’m an engineer by training. I work in very linear fashion. For better or worse, I’ve been in healthcare for a little over two decades. I think the most important thing is to deliver the right drug for patients that you can have a meaningful impact on. And so when you think about the possibilities of this technology, I’ve been part of many companies and I’ve seen many companies try to achieve too many things at the same time, changing too many variables. And so, for me keeping that mindset, alpha-1 antitrypsin deficiency, which is a—I will tell you a little bit more about the indication in a bit—but it’s a disease that is manifested by a gene that’s secreted, or a protein that’s secreted from the liver. It is a pathogenic mutation, so it’s a G to A variant. It’s a very heterogeneous patient population. You have mild patients all the way to very severe patients, and the severe patients have both liver cirrhosis where they may need a liver transplant, as well as lung damage that may need a lung transplant. So, when you think about this entire spectrum of heterogeneous disease, we wanted to focus on one aspect of it, which is changing that adenosine in the liver back to a guanosine transient. We know we can target the liver from a delivery standpoint with multiple modalities both from a lipid nanoparticle as well as through conjugates. We know that it’s a single point mutation that we need to reverse, and we know that the activity of this drug will be seen very quickly because the secretion of this biomarker of the protein in and of itself can be detected in serum. And so, you put all of those three together, you’ve now validated a novel technology that can have a vast benefit for a large number of patients, but you’re actually showing that the technology works by only changing one variable, which is converting that adenosine back to a guanosine from a protein standpoint. So the idea is to take as little risk as possible to provide a drug to patients that will meaningfully change their lives.

Daniel Levine: How is this condition generally treated today and what options exist for patients? What’s their prognosis?

Ram Aiyar: Yeah, it’s a great question. So I was at the education session. There is an alpha-1 foundation that looks after the benefit of the patients. They provide a lot of resources both from an education standpoint as well as connecting the dots in the context of therapies. So when I was there at this patient education session, you can see the spectrum of patients that show up and the physicians that show up. And so, when you think about the disease, just to step back for a second, this point mutation occurs in a gene called SERPINA 1. And that SERPINA 1 gene results in the secretion of a protein called alpha-1 antitrypsin deficiency. It’s primarily secreted in the liver and its benefit is really to stop overactivity of certain white blood cells. And so, when you have this point mutation, this protein starts to misfold and starts to aggregate within the liver. And when it starts to aggregate within the liver, it’s a little bit like plaque. It builds up and builds up and builds up over time and crystallizes. And the liver, as you know, is a regenerative organ. And so it’s fighting against these plaques to resolve itself. But over time these plaques lead to death of the liver cells and then leads to fibrosis. And because this protein aggregates within the liver cells, it’s not available to do its job outside, which primarily is manifested in the lung. So, if you have an attack in the lung, a viral attack or otherwise, you have this huge inflow of white blood cells, it comes and eats up this pathogen, but then it needs a signal to say stop. And this protein is the one that tells the signal to stop. So, when it’s not present, the white blood cells don’t know any better and start eating lung tissue. Because of that, now you end up with two issues both in the liver as well as in the lung. If you drink a lot, you end up with worse outcomes. If you end up smoking, you end up having worse outcomes in the lung. And so the entire spectrum is very heterogeneous. And so, you have some patients, even though the genetic mutation exists, with liver disease, some patients that exist with lung disease, and some patients with both, and the current standard of care really is a band-aid, which is a once a week fusion of this protein in and of itself. So, think about blood donations, those blood donations, you get plasma pool together. There are companies that extract this alpha-1 protein from pooled plasma, repackage it, and infuse it on a weekly basis. That is the current standard of care and that is specifically only to help with the lung manifestations so that you can tell the white blood cells to stop eating its own tissue. There is really nothing for preventing the liver manifestations and there is nothing that really helps both at the same time with one drug product, which is what we are trying to do.

Daniel Levine: Well, let’s talk about your experimental therapy, which is KRRO-110. What is it and how does it work?

Ram Aiyar: Thank you for asking that question. So as I mentioned, it’s a synthetic oligonucleotide that we’ve encapsulated in a lipid nanoparticle. We’re delivering it to the liver cells. Within the liver cells, this oligonucleotide binds the mRNA—that’s SERPINA 1—attracts the enzyme ADAR and changes that adenosine that is a mutation, and mutated version, to an inosine. And because of that inosine change, the protein gets corrected. The corrected protein, which is called the M protein, gets secreted. And we have shown in our preclinical animal models that we are able to correct that protein at very high levels, i.e., if you’ll look at these mouse models, we can show that greater than 80 percent of the circulating amount is the corrected protein and we’re also able to show a lot of the protein that gets stuck within the cells is actually not stuck anymore and is out in circulation and available for the lung to do its job. And so we hope over the next year to 18 months as we go to the clinic, we’re able to show that this investigational drug with a single dose is able to provide the same similar benefits that we’ve seen in preclinical models. So by giving this therapy as an IV infusion, somewhere between once in three weeks to once a month, we are able to functionally correct the RNA and provide the corrected protein in circulation that will help both the liver as well as the lung.

Daniel Levine: And what’s the development path forward?

Ram Aiyar: So, we publicly said—we are a public company, we got listed in November of last year, seems like a lifetime ago—and we’ve said publicly that we would have a regulatory filing in one jurisdiction at least by the end of this year, and we’ll initiate clinical studies and we’ll have or intend to have data in mid to the late half of 2025.

Daniel Levine: You mentioned Korro’s public, it went public through a reverse merger and was successful in raising $117 million concurrent with that. Given what public markets for biotech stocks were at the time, what was the thinking about going public?

Ram Aiyar: It’s a great question. I think when you think about the development needs for this drug, because you would imagine as we started to see the data come through, we started to see that this has the potential to be a best-in-class compound. We saw that it had in preclinical models an ability to resolve both the liver. Through histology experiments, we are able to show that the aggregates are not there and we are able to show that the amount in circulation is very, very high and better than anybody has ever shown—so much so that in one week we’re able to see approximately 50 micro molars of this protein in circulation that others have shown takes a very long time to get there. And so, our investors saw that, the internal folks as a management team we saw that, [and] we knew we needed to raise sufficient capital to get to the other side of clinical data. There were many ways to do it. We had multiple options at the table, but at the end, raising and having a strong balance sheet north of $170 million to get to that clinical endpoint as well as have other programs move forward, this was the best option at the table. I would say that in my prior companies, we’ve had fantastic data and we were in a situation where we needed a whole lot of capital to prosecute on it. Eventually we had good outcomes, we got bought out, but we didn’t want to be in a situation where that was the case knowing that we had a drug on our hand or a potential drug on our hand. And so that’s the reason why, as you know, money is the lifeblood for biotech companies, especially one with a novel technology. And so those are the reasons why we could gain sufficient capital to really focus on getting clinical data and show that we have one, a platform, and two, a potential therapy for these patients.

Daniel Levine: And how far would existing cash take you and what’s the plan for raising additional capital?

Ram Aiyar: This will take us into 2026. Additional capital raises is always an ongoing discussion internally as well as with our board. I think over the next two years, our fundamental focus is execution and showing that we can generate the data that we think we can and that will drive the next set of financing. There is multiple opportunities in the context of non-dilutive financing as we have a platform that can go after biology in a very unique way. I think we have options to think about partnerships with select individual companies that have the same mindset of developing therapeutics the way that we have. So a long-winded way of saying it will be evaluated on an ongoing basis, and depending on when our next product is announced, we’ll consider how that feeds into the capital needs to take the first program all the way through approval.

Daniel Levine: Ram Aiyer, president and CEO of Korro Bio. Ram, thanks so much for your time today,

Ram Aiyar: Really appreciate it, Danny. Thank you for the time and thank you for reaching out.

This transcript has been edited for clarity and readability.