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Cantor Fitzgerald’s Virtual Muscular Dystrophy Symposium

Apr 2, 2024

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

Hey, good morning. This is Charles Duncan. I'm a senior biotech analyst with Cantor, and it's a pleasure to kick off the muscular dystrophy conference that we're hosting today. With me, the first company that is presenting is Solid Biosciences, and I have Bo Cumbo, the company's President and CEO, and Dr. Gabriel Brooks, the company's Chief Medical Officer. Bo and Gabriel, good morning to you. Thank you for joining us.

Bo Cumbo
President and CEO, Solid Biosciences

Yeah, thank you, Charles, and thank you, Cantor, for hosting this.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

Yeah, it's, it's an exciting time in muscular dystrophy, and there is, yeah, many, many different programs in the clinic. But you have a program that is, in the clinic now and starting to dose patients, and we wanna talk about that. But before we do, Bo, I wanted to get, a broader overview on Solid Biosciences and what it is and, and why you do the, the things that you do.

Bo Cumbo
President and CEO, Solid Biosciences

Yeah, no, thank you very much. I really do appreciate it. You know, we're really trying hard to bring, you know, unique and innovative and next-generation medicines to a host of different diseases for patients that are needed. As you know, Solid Biosciences bought a little company called AavantiBio in 2022, and that really led to the transformation of the company as we see it today. A new management team, one of our latest additions here, but he's been here for an extended period of time now, Dr. Gabriel Brooks, who came most recently came from Pfizer. He's a cardiologist by background. The management team really has a great deal of experience in precision genetic medicine.

We've now diversified our pipeline completely, and so obviously our lead program, and we're gonna talk about it today with Duchenne muscular dystrophy as a next-generation microdystrophin program, we'll be in the clinic. We'll be dosing patients very, very shortly. This month. MYBPC3 and for TNNT2. Obviously we're working with Dr. Chamberlain and others for our Duchenne program with our two sites that are gonna be opening up at Nationwide Children's Hospital as well as UCLA. Very, very optimistic, you know, very happy about where we're at and excited about the future for Solid Biosciences.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

It seems like the balance sheet is solid as well.

Bo Cumbo
President and CEO, Solid Biosciences

Well, it's doing well. We raised $109 million in early January, and we have over $200 million. It's trading. We should have cash into 2026. We haven't guided past that, but very excited about the position we're in right now, not only with cash for an extended period of time, but also a pipeline and multiple hits on target, you know. So it would, you know, CPVT, which we'll talk a little bit about. It's our next program, catecholaminergic polymorphic ventricular tachycardia, highly fatal, young disease, high unmet need. And that'll be in the clinic in about 12 months. So we're very excited about that program as well. So really diversified and changed the whole, the face of the company.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

Yeah, congratulations on this last year. Very productive in terms of, as you mentioned, transforming the company with regard to, not only balance sheet but also focus. And so I do wanna get to the neuromuscular programs in a minute, but I wanna dive back into, or you just mentioned the cardiac programs, and you mentioned Gabriel's being a cardiologist. And so perhaps before we get into the Duchenne's program, one of the things that I see as being differentiated about Solid is the cardiac pipeline. Now, this is a preclinical pipeline, so we won't spend as much time perhaps than as we do on the Duchenne's candidate. But tell us a little bit about why you see there being an opportunity for precision gene therapy or precision gene genetic medicines in cardiac diseases. You, Bo, as well as perhaps Gabriel.

Bo Cumbo
President and CEO, Solid Biosciences

Yeah, I'm gonna turn it over to Gabriel in a minute to talk about CPVT, because we're extremely excited about that. It's high unmet need. When we were building the company and looking at sort of the commercial landscape and, really where the highest unmet needs are, we looked at obviously CNS, neuromuscular, and but really cardiac was the next frontier. There's a lot of dilated cardiomyopathies, hypertrophic cardiomyopathies, as well as arrhythmogenic, cardiac programs such as CPVT that really high unmet needs, not a lot of drugs, not a lot of companies in the space, monogenic can use gene therapy replacement, to where you can hopefully mitigate the disease.

And, you know, these are fatal diseases that need drugs, and they don't have anything there. And so we really built out a pretty strategic and thoughtful commercial pipeline, RBM20, TNNT2, BAG3, Myosin-binding protein C . We work with Duke on heart, heart transplant. And then our lead drug for in the cardiac space is gonna be for CPVT. So very, very excited about that. You know, Gabriel's an expert on CPVT. So why don't I just, you know, have Gabriel just talk a little bit about CPVT, and then we can dive into Duchenne.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

It sounds good.

Gabriel Brooks
Chief Medical Officer, Solid Biosciences

Thanks, Charles, for the question. I think, as Bo alluded, I think this is a really compelling portfolio that's addressing a very high unmet medical need in terms of cardiac indications. Catecholaminergic polymorphic ventricular tachycardia is an inherited arrhythmia syndrome. It's a channelopathy that really strikes patients starting at the age of 7 with the manifestation of a potentially fatal arrhythmia. And it's, I think, a gene therapy for this disease is especially fit for purpose, because we're able to provide a transgenic therapy that we think we believe can protect those patients durably and continuously. And really the unmet need in CPVT is, you know, a really constant threat of having that arrhythmic episode with exercise, with an adrenergic surge, with an adrenaline surge.

So being able to prevent that child having a near-fatal or potentially fatal event when they run out onto the soccer pitch or when they get nervous about a math test or giving a speech, that's really what the patients need, and I think what the families are so desperate for. Turning our attention to the cardiomyopathies, you know, Charles, we have to remember that, you know, those manifest as heart failure, and patients with advanced heart failure have a prognosis that is as bad as poor as metastatic cancer. So, you know, we often neglect heart failure as a significant cause of morbidity and mortality in the United States.

When we look at heart failure in general, half of that is non-ischemic heart failure, and 40% of that is caused by genetic mutations, so monogenic disease gene cardiomyopathies. So this is really an area that has been orphaned for precision medicines, and now we have the molecular genetic tools to address these specific and highly, highly mortal diseases, and we're really eager to do so. I think our portfolio is actually very well positioned to address some of the more pathogenic forms of monogenic dilated cardiomyopathy.

Bo Cumbo
President and CEO, Solid Biosciences

Yeah, and CPVT, by the way, is 20,000 patients in the United States. Even if you took the hardest commercial cut possible, it's almost as big as all of Duchenne. And as I mentioned before, you know, 40% mortality in 10 years, and, you know, it's diagnosis somewhere between 7 and 12 years of age. So it's a very severe disease state that we need to address. The other aspect of our cardiac pipeline that I think is important for this conference, Duchenne, is that we're so focused on cardiac.

But realistically, when you think about Duchenne, most of these kids, unfortunately, pass away due to cardiac and pulmonary failure. And we're gonna have a lot of the expertise in the space, and we're gonna be diving in on these non-ambulatory boys or boys with cardiomyopathies in Duchenne and how we can solve that problem as well. So, they really, the pipeline goes really hand in hand with each other and very synergistic.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

Yeah, seems to do. One last question on CPVT. There seems to be a couple of different genes that are mutated, monogenic forms of this disease. I guess the question that I have for you is, how is this diagnosed, and is there genetic testing now upfront, or is this something that, you know, perhaps can expand as there is a good drug, such as your SGT-501 that comes to light that, you know, patients can or caregivers can access?

Gabriel Brooks
Chief Medical Officer, Solid Biosciences

Thank you. Thank you, Charles. So there are a number of diseases, many diseases that etiologies of CPVT, and our specific therapy is really geared towards the most prevalent that causes 70%-80% of CPVT, which is CPVT1 caused by abnormalities in the ryanodine receptor. And we also believe that our gene therapy can also address CPVT2, which is the second most prevalent that which is a loss of the calsequestrin gene. So those are the genes. Yes, there are genetic tests. There are genetic panels for patients that have arrhythmia syndromes and certainly the ryanodine receptor and calsequestrin are part of those panels.

Actually, we're engaged in trying to make sure that we can have as much robust testing as possible, and hopefully we can contribute it to the medical space in that way. Your question about how are patients diagnosed? Usually, sadly, Charles, they are initially usually misdiagnosed with having epilepsy or fainting, because this is a I think a under-recognized disease. And so it I think you're right. I think this is going to be a case like I saw with tafamidis, where, you know, we under-recognize this in cardiology and medical care in general, with the emergence of effective more effective therapies.

I think that that will increase our awareness of this disease problem in our society, and I think that'll militate for better testing. We're definitely engaged in that endeavor, because we think that's really, frankly, the right thing to do for the patients.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

Okay, very good. That's helpful, Gabriel. Bo, one last, I guess, final point on this. When will this become a more visible program to investors?

Bo Cumbo
President and CEO, Solid Biosciences

Yeah, so, we're completing all the proof of concept, the pilot studies now. We've already done some work on non-human primates. Then we're gonna be heading later on this year into our GLP tox studies, writing the IND, hopefully filing the IND first quarter of next year, end of the first quarter of next year. And we should be in the clinic sometime next year. I'm very excited about it because I think it's a great follow-on to Duchenne. So we have a next-generation Duchenne drug that will be going into the clinic this year, hopefully heading into registrational trials next year. Then we'll be in the clinic with CPVT and then followed by multiple cardiac programs right behind that. So it should be a nice little one-two punch in 2024 and 2025.

I think investors, once they really start understanding the severity of this disease and how, you know, it's young and fatal and how many patients there really are in this disease state, I think that this can be a great opportunity for investors to get behind a company that I believe is gonna be undervalued significantly when you have two drugs in the clinic and with two fatal disease states, as DMD and CPVT.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

Yeah, I agree with you, Bo. And clearly this is an area of precision genetic medicine that is not, I think, focused on and therefore not well valued by investors at this point. This program, as well as your Duchenne program, SGT-003, really come out of, I think, a differentiated platform. So why don't we talk a little bit about this? You have a nice slide in your January deck talking about the platform generally as being potentially differentiated. So why don't we touch on that? So for SGT-003, the Duchenne program, which is now in the clinic, and we'll get to that, help us understand why you think that is different than other approaches for gene therapy in Duchenne.

Bo Cumbo
President and CEO, Solid Biosciences

Yeah, yeah, I think it comes down to three items, really. The next-gen transgene, the capsid, and the manufacturing process. Obviously, we did keep the transgene from Solid's original program called 001 that we discontinued, or stopped dosing patients. That's why we kept the transgene because it is considered by the KOLs globally and many patients as a truly next-generation transgene. It has unique binding domain in R16, R17. And when you have this binding domain, it's the only one of its kind. You do recruit protein called alpha-syntrophin. And when you have alpha-syntrophin in the R16, R17 binding spot, it gives a landing spot for nNOS. And when you have nNOS, we do see increased vasodilation. Obviously, hopefully that increases blood flow.

And then that should help with endurance and longevity of the muscle as the children are walking or being active on a daily basis. We also have a unique hinge structure that adds flexibility to the microdystrophin construct. So as children are running around and being little boys and hopefully, you know, enjoying life, the construct, the protein that we're making is flexible in structure so it can move with the muscle. Then we have this capsid. This capsid is extremely unique. We create the capsid ourselves by adding peptides for endocytic receptors on skeletal and cardiac muscle. So we took AAV9 and we modified it. AAV9 is already a very good capsid, especially when you're thinking about transduction and then ultimately expression when you get to skeletal muscle, cardiac muscle.

But we've enhanced it, and it's significantly enhanced when you whether you look at biodistribution, expression, binding capacity, and speed of transduction, very, very different than AAV9. We believe that this capsid will help increase microdystrophin expression over time. The other really important thing is the CMC process. Originally, Solid was using an HSV manufacturing platform many, many years ago. That platform has completely been shut down, and we've transitioned to a triple transfection manufacturing process. We've made multiple changes within this process and created what I believe is probably one of the most robust or at least purest manufacturing platforms in the industry. We work with a lot of CDMOs. We work with a lot of companies.

When you go head to head from not only a yield perspective but also an empty to full ratio, it's one of the purest that we've seen when we partner with people. On every single batch, 77%-81% true-fulls. That's true-fulls. We do not include partials. We do not include empties. We lump partials with empties. It's roughly 18% partials, 1% empties. We push those aside, and that's, so we roughly have 81%. Now, why is that important? Well, we're dosing these kids at VG/kg. So, you know, if you were at 50% full at 2E14, you're actually going 4E14. You're doubling the dose to get them to that true-full ratio.

When your product is already at 80%, you're not having to overwhelm the body with extra capsids to get up to the VG/kg from a safety standpoint. We've also done work, and I think this is extremely important. It's not just important for Duchenne. It's important for everybody that's in Duchenne gene therapy. We've done work, and we've been able to show that as you lower your empty to full ratio, you do have lower expression. And because these partials and these empty capsids are blocking transduction of the true-fulls. And so as you see an increase of empties and partials, you should expect lower expression. And we think that that's really gonna matter and play a role in this. So really, those three things have changed this program pretty dramatically.

We see transduction very, very quickly because of the capsid. We see transduction and expression in as low as 4 days. We've repeated the experiment and looked at expression all the way down to 2 days, and you can see it. You don't see this with the other capsids that are out there. We also measured it at 90 days to make sure that we're not looking and dropping off, microdystrophin expression after 90 days because we're gonna take biopsies in these children at 90 days. And, and it holds at 100%. And we go all the way down to 3E13, which is at 100%. Now we're dosing our patients at 1E14 because we wanna put our best foot forward and really transform these kids. So hopefully, we're gonna see that.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

It's a great overview, Bo, not to be dismissive of the manufacturing piece because I understand it's very important. But you have some data, some preclinical data that really informs the clinical design and conduct of the clinical study. And I wanna get to that. But before we do, let's talk a little bit about the transgene and the capsid and what you've seen preclinically that you think has predictive value for success in the human clinical studies. So first of all, with regard to, really, you know, I guess the capsid, you have data both in murine as well as non-human primates that show you have very good expression across different muscle groups. So can you describe that?

Bo Cumbo
President and CEO, Solid Biosciences

Yeah, and I'll turn it over to Gabriel as well. And we'll just sort of, you know, go back and forth. We've done a ton of preclinical work on this transgene, this capsid, with our manufacturing process. And across the board, it's acting very differently than AAV9. You know, we didn't even find a dose curve all the way down to 3E13. It was 100% across the board in microdystrophin expression when you look at the diaphragm, the quad, the heart, the gastroc. So very, very pleased with the expression that we were seeing in the mice. We had to go all the way down to 2E12 and 6E12 to get that dose curve.

We also noticed that, when you get to that 3E13, when you're getting to that sort of 100% microdystrophin expression, you're really seeing robust nNOS activity in the muscles, the diaphragm, the quad. I think it's also extremely important when you think of these older non-ambulatory kids, right? AAV9 already gets to the heart very, very well, but the diaphragm, it's extremely hard to dose. And what you're seeing from a distribution standpoint in non-human primates compared to AAV9, it's roughly 5-10 times greater in the diaphragm. And so you're getting like 2-5 times greater depending on the muscle, in the quad, the gastroc, etc. But in the diaphragm, it's 5-10 times greater. And so it's great. I'll just turn it over to Gabriel on some of his thoughts as well.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

Do mention the liver expression as well because that's notable in that it goes in the opposite direction.

Gabriel Brooks
Chief Medical Officer, Solid Biosciences

Absolutely, Charles. So, you know, I think adding on to that prompt from you and Bo's comments, you know, from a medical translational standpoint, we're really excited to be coming into the clinic where we have liver detargeting. We're seeing, you know, less than twofold transduction of the liver, compared to AAV9. And as Bo indicated, you know, we're really coming in with a dose that is, I think, far higher than the minimal dose we could have justified in coming into the clinic, because we had such an early plateau of transduction and expression in the preclinical models. And we're well beyond what we believe that plateau would be. So this means that, you know, from our very first boys, we feel confident that we're giving them the best possible chance at robust transduction.

So it's not we're skating in here, and bumping up against maximum tolerated dose. No, we believe that we're, you know, multiple-fold higher than what we saw in the preclinical models, that plateau. So that, that's very exciting for us. Detargeting the liver and having also this only scant amount of empty particles means that we're reducing the total antigenic load that the patient is facing. And hopefully, that means that we're gonna reduce the risk of, you know, something that we see in the field, which is antigen-antibody complex-mediated immune manifestations. Of course, we're gonna have to see with all of this safety and efficacy. We need to remain humble. But we're coming in here, I think, really well poised from both sides here. You know, safety, reducing the antigen load, threefold lower than our NOAEL, No Observed Adverse Effect Level in non-human primates.

So we're not even bumping up against that. We're well below that, and we're well above where we saw this plateau. And then one final thing I'd like to add, which is very important, is that we saw this really robust transduction in the diaphragm, in skeletal muscles. And so we're proud to be able to, I think, meet these boys where they are in their disease. We're, of course, going to focus on the, you know, a certain population, probably the ambulatory population. But we want to expand and also address the boys that are non-ambulatory because there is a significant amount of morbidity in those boys that their families face that we really wanna be able to address.

Bo Cumbo
President and CEO, Solid Biosciences

Yeah, Charles, I just wanna add on the safety, because, you know, Gabriel touched on it, you know, but I wanna make sure I just bring this home. This is a very different program than originally at 001.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

Sure.

Bo Cumbo
President and CEO, Solid Biosciences

This is the non-human primate study was well tolerated at all groups. There were no mortality events. There were no unscheduled takedowns. There were no all interventions of any kind, no pathology findings, or no organ weight changes. Liver enzymes were comparable to vehicle. We dosed at three times higher than what we're going into the clinic with. And there was not one single question from the FDA on our safety, in our IND. So, you know, that gives us a lot of comfort, that we're doing the right thing from a safety standpoint. And so, you know, I think that should be driven home. Now we're gonna be dosing patients very soon, site initiations are this month and screening patients, you know, very, very quickly and then going into the clinic. So we're gonna find out what it looks like in humans.

We'll be presenting that data later on this year.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

Well, let's talk about that. Let's talk about the INSPIRE study. So the SGT-003, clearly, it sounds like you have the prospects for greater safety tolerability than in the past but also enhanced efficacy for several different reasons, including distribution but also the nNOS component. Why don't we talk a little bit about the INSPIRE study? You mentioned that you just got the IRB approvals and that site initiations will happen soon. What are the clinical sites that you're working with, and how quickly do you think we can get to see the first, call it, dosing of patients?

Gabriel Brooks
Chief Medical Officer, Solid Biosciences

Thank you, Charles. So, you know, we are starting with 2 really, I think we feel very experienced sites for gene therapy from a clinical aspect in terms of integration into their clinical practice, as well as from experience doing clinical trials. And so that's Nationwide, with Kevin Flanigan and UCLA with Perry Shieh. We're very proud to collaborate with those 2 sites. And we are, you know, we're starting with, I think, a fairly modest initial study, looking at 2 cohorts of 3 patients each, 4- to 5-year-old and 6- to 7-year-old, where we're looking, obviously, at safety. And then we're looking at muscle transduction expression, in that first, you know, 3 months, and then a year's time.

In so doing, we are carefully interrogating safety and our you know initial pharmacodynamic marker here, but it's very important, which is microdystrophin expression, which of course was an accelerated approval endpoint for Elevidys. In terms of the overall prospect for benefit in these patients, we think that proper localization of nNOS is going to be important for these boys, because it means with muscle use that there will be we believe more appropriate vasodilation. So we're not gonna see the ischemic injury that we believe that if you don't have proper nNOS localization that is a potential liability. And so that's endurance over time and retention we believe of more retention of the muscles.

and also another critical piece here is that we avoid the inclusion of some of the hinge regions that we know in microdystrophin can lead to smaller muscle caliber and also potential muscle breakdown. So we're avoiding that liability. All of this purpose is to give these boys the best possible chance of having resilient muscles, which is our goal.

Bo Cumbo
President and CEO, Solid Biosciences

Charles, just to give you some timing, obviously, doing site initiation visits in the next couple of weeks and then screening patients. We will be dosing. We have two cohorts that'll be open, cohort one and cohort two, basically 4 years of age all the way to under 8, so 4 through 7. We're gonna be dosing 3 - 4 patients and then pausing and then taking a look at their microdystrophin expression. Obviously, look at CK. We have patient videos. Look at titin, a couple other markers as well as, you know, rise time and everything else, NSAA. But it'll be an asterisk because it'll only be 3 months post-dose, but we'll have all that data. So what do you what should investors look for?

If we dose our 3-4 patients in a every 30-day staggered manner as the FDA would like, that means that we should have safety data for 3-4 patients in late summer, right around September-ish. We can tell everybody, "Okay, we've dosed our 3-4 patients. Now we're gonna take our biopsies of these kids, 90 days post dosing." We can look at expression data, and we'll announce all the data at the end of the year, Q4. We might hold it to JP Morgan, but you know, we also might release it in December, depending on when we get the data and you know, our thought process on how quickly we'll be moving into registration trial. We are filing CTAs right now. So we've already started that process, filing CTAs in Canada as well as the U.K.

We'll have multiple sites up and running in Europe. We are already speaking with some of the world's leading KOLs, not only in the United States but ex-U.S., to get these sites up and running.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

Now, one point of clarification. Are those two cohorts open? And can you enroll patients in them in parallel or in sequence? And if the latter, which do you start with?

Gabriel Brooks
Chief Medical Officer, Solid Biosciences

In parallel.

Bo Cumbo
President and CEO, Solid Biosciences

Yeah, but you still have to wait the 30 days in between dosing any patient. So they are open in parallel. But, you know, for investors out there, if we enroll a six-year-old and we have a four-year-old waiting, we still have to wait that 30 days before we can dose that four-year-old.

Gabriel Brooks
Chief Medical Officer, Solid Biosciences

Which is really a standard, you know, mandate by the agency with a novel AAV gene therapy. So we'll continue as the safety database evolves. We'll continue to have discussions with the agency around that, to make sure that we can appropriately enroll patients in the most expeditious but safe manner.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

Now, that makes sense to me, Gabriel, for sure. You mentioned a couple of pretty interesting measures of efficacy, if you will. These are not classic measures. They're but when you think about function, you've first of all, microdystrophin or dystrophin expression, right? So that's gonna have a short-run impact on activity. But over time, you may actually see more durable muscle or stronger muscle. And so what will you be looking at as a physician to really start to evaluate, you know, the target product profile?

Gabriel Brooks
Chief Medical Officer, Solid Biosciences

That absolutely. I think, you know, Charles, when we think about these boys and the prospects we hope of being able to offer them a product that can lead to increased durability of muscle. That would mean we hope, you know, a improvement or a sustained things like time to rise, timed function tests over time, certainly something like the 10-meter walk run. But also some of the more activities that require a longer endurance. So that would be, you know, the 100-meter walk run as well. But I think it's not just saying, not just looking to those endurance measures, but also it's the over time sustaining, or, you know, we will see, but maybe even improvement in those ambulatory measures.

When we talk about ambulatory measures, let's please not forget also those non-ambulatory boys. So, I think there, it's keeping respiratory function, keeping boys off of the ventilator. These are, of course, longer-term measures that take a longer study. But we're committed, I think, over time to being able to interrogate that as well and having, I think, again, that compensatory vasodilation that nNOS allows for; we believe gives our these boys the best shot at having a more durable muscle.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

Now, let me ask you about a recently read-out competitor program that showed activity that seemed to be different. It was based on age. And I guess my question is, when you think about your transgene, do you anticipate that there's going to be a difference in terms of signal to noise with regard to efficacy measures in different age patients? If the younger patients are gonna respond better, or do you anticipate there to be clinical impact across board?

Bo Cumbo
President and CEO, Solid Biosciences

Yeah, I'll start there. I don't know which program you're talking about, but I will tell you, you know, look, this is a terrible disease. You know, time is muscle.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

Yeah.

Bo Cumbo
President and CEO, Solid Biosciences

Over time, these kids, you know, they lose their muscle pretty pretty dramatically.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

Yeah.

Bo Cumbo
President and CEO, Solid Biosciences

By the time they're non-ambulatory, which averages somewhere right around age 12, they have 80% fat fraction. So 80% of their body is fat. So, you know, it's unfortunate that these drugs that we're all trying to create can't start immediately in children, because and hopefully to, you know, slow the decline over time. Because you should expect differences in outcomes in these kids as they age and lose ambulation or lose the ability for upper arm function. So, you know, time is muscle. It's important to get to these kids as fast as possible. That's just my comments, and then I'll turn it over to Dr. Brooks.

Gabriel Brooks
Chief Medical Officer, Solid Biosciences

Yeah, I think that's right. I think that we want to be able to engage, ultimately, you know, as we progress, we wanna be able to engage these boys as early as we can in their disease process because we believe that, you know, that's gonna give them the best possible chance at retaining the quality of life they have. But Charles, you know, for those boys that are non-ambulatory, that are older, there's still really important things for them. Upper arm strength is really important.

Being able to have hand-to-mouth strength is incredibly important. And those boys that maybe do not have hand-to-mouth and are using, you know, joysticks, that's important too. And staying off the respirators is important as well. So I think as we think about the older boys, we certainly want to be able to address the musculature that they have. And we hope to do so.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

Now, in the last minute or so that we have, let's talk about a potentially registrational program. So I'm gonna assume success in this particular phase I/II, and that you may move to a capital-efficient registrational program in a year. Can you describe that, briefly?

Bo Cumbo
President and CEO, Solid Biosciences

Yeah, I think I'll turn it over to Dr. Brooks for a second. But I think what you know, we're gonna do two things. One, we're gonna go after accelerated approval. I think that door has been open in the United States. And so, then the trial will be looking very differently than the trial that's the confirmatory trial. So we're gonna open up a trial in a success scenario, as you described. We're gonna look at their data. We're gonna move forward with a trial, whether it's open label or using natural history, looking at microdystrophin expression and as a surrogate marker for accelerated approval and aggressively go after that in the United States. Then we're also gonna look for a confirmatory trial, mainly ex-U.S., where we can provide a clinical benefit.

It'll be multiple sites, multiple patients to be determined on the number and on the clinical endpoint. So we can get not only registration, ex-U.S., but also reimbursement, because many of these healthcare authorities, these reimbursement authorities want to see P values and, for reimbursement of very expensive precision genetic medicine drugs. And you can see it in multiple drugs that are already on the market. And there's tens of thousands. We talk about the U.S., and we think that, you know, we focus on the U.S. And I understand why. But there's tens of thousands. Unfortunately, there's hundreds of thousands of kids ex-U.S. that we've gotta get to, not just us, but other companies. And so, you need a clinical endpoint. And we're gonna try to hit that. Gabe, do you want?

Gabriel Brooks
Chief Medical Officer, Solid Biosciences

Yeah, very briefly, you know, there's an advantage in coming and being the next generation gene therapy. We've learned a lot in terms of biology to have a better fit-for-purpose capsid, a better fit-for-purpose process, for the manufacturer that puts us in a great position. We talked a lot about from the clinical side, you know, we believe that we can take the learnings of the others in the field here and take up, I think, the agency on a more streamlined process of approval, using markers like a microdystrophin.

So we will plan on engaging the agency in that for accelerated approval as well as all of the learnings that we have had from some of the programs that have read out here in terms of the clinical for something that has a clinical endpoint of time to rise in other function tests. We are incorporating those learnings so we can have an efficient other trial that has, you know, more clinical endpoints than microdystrophin.

Charles Duncan
Managing Director of Biotechnology Equity Research, Cantor Fitzgerald

This is very helpful, Gabriel and Bo. Thank you for sharing the Solid Biosciences story for us. We are pulling for you. We're pulling for the Duchenne community and others. So thank you very much for your efforts and thoughts today.

Bo Cumbo
President and CEO, Solid Biosciences

Yeah, thanks, Charles. Thanks, Cantor, for hosting this.

Gabriel Brooks
Chief Medical Officer, Solid Biosciences

A real privilege. Thank you.

Bo Cumbo
President and CEO, Solid Biosciences

Thank you.

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