Great, thanks so much. It's my pleasure to be hosting a panel with Kirk Brown, who runs CNS Research at Alnylam. We just made this joke offline, but I'll say it online: this panel will not include 10 nuanced statistical questions on HELIOS-B. I am doing a dinner with Alnylam with Pushkal soon, so contact me if you're interested in that. Anyways, I'm really excited to talk about CNS because you guys have done some super cool stuff here. This APP program is really under the radar, but it's kind of coming to a head soon with, you know, some longer-term data and some maybe some downstream biomarkers that I want to talk about. So, Kirk, thank you.
Do you want to just give, like, a brief background on sort of your, you know, what you oversee at Alnylam and the overarching efforts in CNS?
Absolutely, yeah. First, thanks for the invitation to participate in this call. I really appreciate it, and I'm really happy to be here. So yeah, so my role here, I oversee the CNS Research Group, which focuses on target biology as well as siRNA delivery approaches, which we published some of that work back in Nature Biotechnology in 2022. And essentially, that work applies the lessons that we learned from delivering to the liver. So that foundation of innovation that brought us chemical modifications that improved stability, potency, and specificity, and give us that durable potent pharmacology that we see in liver, we've now incorporated into our C16 conjugates for the delivery to the CNS, which, as we've shown, very nicely delivers up through the spinal cord and into the brain and even deep reaches into the brain following a lumbar puncture, intrathecal administration.
And importantly, as it gets to the brain, we also see good distribution to a wide variety of cell types, including neurons, microglia, astrocytes, and oligodendrocytes, which gives us somewhat of an agnostic approach and delivery approach, excuse me, to all the different cell types with this initial distribution delivery enhancer that we've got. And so we're very excited about that. And so my team then, in partnership with Regeneron, has been growing a CNS portfolio which leverages this C16 conjugate platform for delivery. And then you didn't mention about the ALN-APP program. I also serve as a research lead on that program and oversee quite a bit of the ongoing research in that space. And it is our lead program in CNS and targets amyloid precursor protein, or APP, for the potential treatment of Alzheimer's disease as well as cerebral amyloid angiopathy, or CAA.
It's currently in phase I in early AD, and we reported positive interim results last year in 2023, which, you know, as far as, as a research focus, to see that clinical translation last year where we saw a deep and durable knockdown of APP as well as the amyloid biomarkers, amyloid beta 42 and 40, which are the ones implicated in Alzheimer's disease and CAA, to see that movements, relatively rapidly, consistently with what we had seen in preclinical species, was particularly exciting to us.
Yep. Yep. Go ahead. Sorry.
Yep. And we've now initiated the multi-dose Part B. This is ongoing in Canada, where the majority of our Part A patients are enrolled, and in addition to the Netherlands and UK, we've actually now received clearance from the FDA to proceed with multiple dosing dose levels that include and exceed those that we have planned to evaluate in the Part B. And so with that in totality, we believe these positive results do de-risk our C16 conjugate technology in humans and provide us additional confidence as we move to enable many more CNS or preclinical targets for CNS. A couple of those would be HTT. It's another target of high interest to us for the treatment of Huntington's disease. This program's currently in IND-enabling studies, as well as pursuing SOD1, targeting SOD1-specific subset of ALS, also currently in IND. And then.
Great.
Yeah. So last couple of targets I'll mention, on the preclinical space is, you know, we have programs that are ongoing, which I think I shared some of that data back at R&D Day in December, targeting MAPT for, or tau for various tauopathies, as well as alpha-synuclein for Parkinson's. And there we shared, in my mind, extremely exciting data where we were able to treat and lower tau aggregates with a single dose targeting MAPT, and those enabled improvements both in clearance as well as phenotypic benefit in those animals. And, and also likely in the synuclein model disease, whether we treat it pre or post-treatment with alpha-synuclein aggregates, we're able to clear those aggregates and also produce phenotypic benefit in that model.
So what we find here is we've got essentially a modular platform very consistent in line with what we see in the liver, now just focused on CNS and CNS implications. We couldn't really be more excited with what we're seeing so far.
Yeah. Awesome. It's a great overview. So let's, let's talk about APP as a target because I feel like the, the clinical data you've shown and the knockdown data you've shown, like, there's, there's not much to dig into. It's, it's, it's pretty, for better or worse, uncontroversial, which is great. So APP, I mean, the main question we've had, especially for Alzheimer's, is, you know, why isn't this too far upstream? And why isn't this functionally a retest of the BACE inhibitor hypothesis that ultimately didn't really show much on PET? And I know BACE might have its own idiosyncratic tox issues, but at least from an efficacy perspective, like, it wasn't even really close. What, why is that kind of a misunderstanding, at least in your view?
Yeah. Yeah. I mean, it's a great, it's a great question. I mean, the answer is, you know, we don't know because no one has ever really tried this specific approach before, right? No one has ever used an RNAi therapeutic to knock down messenger mRNA of APP in AD models. And then what we can take away from the amyloid work, amyloid antibody work, excuse me, is that, they have moved the needle some, but haven't really been able to halt the disease progression. So, we're trying this unique approach, which is targeting APP at the messenger RNA level, which is importantly, in our minds, upstream of all of those downstream events. And in so doing, we actually reduce all AD amyloid isoforms as well as APP-derived peptides, in particular peptides that work intracellularly, like the beta-C- terminal fragments.
And so I, I will add we've gained confidence in the potential of this approach with preclinical models, one of which some of that data we shared, I believe, in our Nature Biotechnology paper in 2022, where a mouse model of AD where we showed reductions in amyloid deposition with APP knockdown. Importantly, the single dose, which was importantly durable in that study as well, reduced amyloid deposits in the brain, reduced inflammation, and resulted in corrections in certain behavioral phenotypes. So we've seen that, with the APP messenger mRNA targeting approach, we are still clearing extracellular amyloid in a more natural manner, but also addressing the intracellular manifestations of the disease, some of which include endosomal lysosomal complications, trafficking issues within the cell.
And so we're able to address all of those upstream amyloid fragments that are driving some of those intracellular manifestations of disease, which the antibodies certainly would not be able to touch, right? So.
Right.
We believe we have a unique and differentiated approach here. I would put a plug in, so Lan Deng from my group is a talented scientist who works in the patient-derived stem cell space, recently shared a poster at AD/PD, and I would think we have that now up on our company site if those are interested in looking in more detail. Here she used APP targeting siRNA in a presenilin patient-derived neuron. To your question of what else are we doing outside of amyloid clearance, we see a correction of RAB5-positive endosome enlargement, which is common in AD lines, and in patients' brain samples. Importantly, in addition to the RAB5, we see also RAB7 reductions.
Actually, which is one remarkable piece of data that came out of that, we see that using a multi-electrode array following treatment with APP messenger RNA, we're able to, when compared to healthy controls and a control siRNA, we restored neuronal connectivity and synchronicity following siRNA treatment, which is essentially a functional correction of neuronal health roughly three weeks after a single administration of siRNA. So we're doing something functionally different and unique within the cell in addition to what would likely be an outcome of natural clearance of amyloid plaques in the brain. So that's one of the many reasons why we're very excited. So I would definitely recommend those who are interested take a look at that poster that was just shared at AD/PD for more details around that work. It's pretty exciting.
Okay. Great. So as it relates to progressing forward in the phase I study and looking at multiple ascending doses in Alzheimer's patients, do you want to talk about where you are there? And I guess our view has been that in a MAD study, you can look at things like pTau. I'm not sure if you're doing PET scans, but maybe tell me if you are. But at the very least, you can look at some downstream pharmacodynamic biomarkers and have a better sense if you're having at least a preliminary impact on the more pathogenic amyloid species. Is that a fair characterization? Maybe, maybe you can expound upon that.
Yeah. No, that's, that is a fair question. Yeah. So, this is a reminder. Part B is our open-label multi-dose portion of the phase I. We're evaluating patients previously enrolled in Part A. And so, we're still obviously still looking at safety, tolerability, and pharmacology. Our hope is, as you mentioned, with multiple doses, we will be able to maintain this robust soluble APP alpha and beta reduction or target engagement biomarkers throughout a full 12-month period and a follow-up period. But in addition to our standard target engagement biomarkers and safety evaluations, we are embedding a comprehensive set of exploratory fluid, cognitive, and neuroimaging biomarkers in that part B of the study. So we believe this will allow us to explore how reducing APP protein production and prolonged APP pharmacology, with multi-doses will give us some glimpse into what might be happening in that disease progression biomarkers.
Just as a reminder, with 50 mg and 75 mg single doses, we saw really robust target engagements in the range of 84% and 90% knockdown of soluble APP alpha and beta, which we shared last summer. Remarkably, even with a single dose, we see sustained pharmacology to the degree of 30%-40% knockdown of those biomarkers out to 10 months post-dose. So we have the expectation that a second dose at six-month time will provide that even more robust in-patientt pharmacology. To speak to some of these questions that you're asking, what is going on with the fluid biomarkers that are more exploratory? What's going on with cognitive assessments as well as the neuroimaging biomarkers, which are particularly important to us?
I mean, as I said, we do have confidence in the cell and the body's natural ability to clear. We have seen that in AD models of disease. Just with single doses, we were able to reduce amyloid burden in the animals after several months of treatment. So.
Yeah.
Yeah. There is some expectation that we would see some clearance occur.
Okay. So when might we get that data, Kirk?
Yeah. So the plan is to continue to report out data throughout this year, and at various conferences and updates. I don't have confirmed dates to share.
Okay. But that's, like, that's the MAD data, and that's some of this downstream biomarker data that we should be getting in the next 12 months or so. Is that fair?
Yeah. Yes. That is fair. Yep.
Okay. Okay. Do you think, like, what's your view on, so I think, like, pTau-181 makes a lot of sense. Do you have a view on, on neurofilament and whether that is something we could expect to move in, in Alzheimer's?
Yeah. I mean, it's a great question. We are evaluating neurofilament and others as safety biomarkers, but also as important biomarkers of disease impact and neuronal health. And so it is something we are keeping an eye on here. It is on our list as a longitudinal .
Okay. And just in terms of pursuing Alzheimer's, like, I think you guys have talked about, you know, all-comers Alzheimer's for this approach versus familial versus this kind of early-onset population. Like, to what degree are these, like, overlapping, and what is your sort of how would you kind of tier your focus here?
Yeah. It's a great question. I mean, the mechanism of action is likely to be successful in many AD patient populations. We started with the early-onset patient population as a starting point. But you're right. Numerous other AD populations certainly would be amenable to this type of treatment depending on how the results come from this first study.
Okay. Okay. And sorry, the first set is early-onset Alzheimer's?
That's what we're looking at now. Yeah. Early-onset.
And who is that? Like, is that a more genetic population, or is it, like, a little bit kind of grayer, right? I'm assuming these patients are probably more likely than not a carrier for at least one APOE4 allele. But, like, what else sort of differentiates them from your run-of-the-mill Alzheimer's patient?
Yeah. They're patients that are showing signs of AD at a much earlier age. And so we're going after them. But as a distinction, this is not an ADAD patient population. We're not going after APP direct mutation carriers or.
Understood. Okay. But is the thought that this population is, like, more enriched than a later-onset or a typical-onset population?
More enriched for.
More enriched for the drug to work?
I think our expectation is that the drug would be likely to work in early-onset AD, autosomal dominant AD, and potentially sporadically.
Okay. Okay. Okay. Got it. Do you want to talk a little bit about CAA? I mean, my thought has been that, you know, although Alzheimer's is hard, right, we'll have to kind of see how these questions related to knocking down APP and then the downstream impact on oligomers and plaques plays out. Everything you say sounds promising, right? But in the meantime, for CAA, like, you know, knocking down APP, like, you're much more proximal to the biology given that monomers themselves are toxic. Like, is that is that the right way to think about it? And I guess maybe just can you speak a little bit more about CAA, the biology, and the phenotype there?
Absolutely. Yes. Yeah. I mean, in some ways, you can think of CAA as somewhat analogous to ATTR amyloidosis in that the accumulation of amyloid deposits themselves are directly implicated in disease pathophysiology. The difference here is that while TTR amyloid deposits can cause damage in the peripheral nerves in the heart, here, CAA deposits in the cerebral vasculature cause vascular damage and lead to increased risk of strokes and other bleeding events. And given the potential of our approach to just shut the faucet off way upstream, we're moving aggressively here with ALN-APP to develop into CAA. So we do plan to initiate phase II in CAA on the first half of this year. I believe we shared that recent call.
Okay. Great. Maybe just CAA a little bit more on that as, like, a disease and the phenotype and natural history?
I mean, similar to AD, APP is a genetically validated target for CAA. For example, there are well-characterized autosomal dominant forms known as HCAA or hereditary CAA, most notable in the Dutch type CAA where mutations result in amyloid deposits in the vessels, which occurs at quite a young age, 30s, 40s, and 50s. Here, again, the accumulation of amyloid deposits can drive wild-type CAA. Speaking generally, it's thought to affect a larger group of patients much relative to this age of the patient population. Biomarkers here, which we report in clinical development, include measures of target engagement similar to what we have before, but also measures of vascular reactivity to assess disease progression. We do believe this represents an important complementary disease opportunity for ALN-APP, our mechanism of action to serve as potentially disease-modifying therapy for this particularly high-need patients.
Yep. Okay. How do you plan on selecting patients with this? And, you know, in Alzheimer's, right, there's been kind of a longstanding establishment of at least where we think the window intervention is, right? You have to go early. Like, with APP, you know, what might the ideal trial population look like?
Yeah. No, it's a great question. I mean, it is, I would say, somewhat underdiagnosed. It's an under-recognized cause of stroke. I mean, CAA pathology is actually quite common, especially in older individuals. Moderate to severe CAA pathology is seen in upwards of 20% of the population, maybe 5% of those who have Alzheimer's disease. So only a subset will have the imaging abnormalities that would enable the clinical diagnosis of CAA. I mean, we believe the most significant on that need here is patients with CAAs to reduce the risk of strokes. It's the second most common cause of ICH or intracerebral hemorrhage after hypertension. Patients with CAA and ICH have significant increased risk of recurrence. And so diagnosis of CAAs typically accomplished through neuroimaging, to your question, which has been increasing with obviously with disease awareness.
However, CAA includes, yeah, underdiagnosed, but just a small fraction of them formally diagnosed. But underlying inclusive CAA includes hemorrhages and microbleeds, which can be seen via neuroimaging. So neuroimaging includes.
Yeah. Okay. Makes sense. On the stroke side, so do you have a benchmark of, like, can you run a phase II study that is powered for showing a difference on the rate of strokes? Like, how regularly are these events happening?
Yeah. That's a good question. I'd have to defer to some of my clinical colleagues for more specifics around stroke occurrence.
Okay. Okay. Yeah. No worries. It's just.
I would make the comments we are confident in. I can speak to my preclinical experience in models of CAA where a single administration of APP targeting siRNA in a rat model of CAA did reduce both parenchymal plaques to this question of clearance, but also importantly, vascular accumulation of amyloid around the vessels. Importantly, what we learned from that study six months after a single dose is that we saw a clear difference in the amount of microbleeds in those same animals with robust clearance of amyloid around the vasculature.
This gives us an incredible amount of confidence then in that our mechanism of action on targeting APP upstream, reducing the amyloid production, also reduces the amount that will impact the vessels, but also allow the vessels to clear those compared to control animals, which had a much more significant amyloid beta 40 burden on the vasculature and less healthy vessels in that study and more microbleeds.
Got it. Okay. On the safety side, you know, where are things at with resolving the clinical holds in the U.S.? And do you expect, you know, as you do CAA phase II, MAD, to be generating data in the U.S.?
Yeah. No, it's a great question. So just to remind everyone that FDA did place a partial clinical hold on the Part B multidose portion of our phase I last year. This was due to findings observed in prior non-clinical chronic tox studies, which were done at very high, very frequent doses, much higher and more frequent than the doses we're actually using in clinic. However, as announced at our recent Q4 call, the FDA has confirmed that multiple dosing can proceed at doses up to 180 mg given every six months. This covers all the dose regimens planned to be explored in Part B.
But I would say, however, given the robust and durable efficacy seen with our 75 mg single dose in Part A, we think it's very unlikely we'll need to dose higher than the levels we've cleared for or certainly more frequently given the durability we're seeing in clinic. So, you know, we couldn't be more thrilled with this outcome as it means we'll be able to proceed with our phase 1 multiple dose studies at levels up to and exceeding what we've dosed previously in Part A. And we've seen great target engagement with as little as 50 and 75 mg. We're confident we'll be able to get our full appreciation for what durable GalNAc science and we'll see with multiple doses. And just as a reminder, this has already been approved.
Proceed with multiple doses in Canada, the U.K., and the Netherlands, which are the other three countries for this study.
Great. Okay. Maybe to round things out, on a technology perspective, you guys have this collaboration with PeptiDream. There's a lot of buzz in the CNS space around the use of transferrin receptor. You know, with Alnylam, right, I mean, you guys have been at the forefront of conjugation. You know, where do your efforts here stand with the peptides and any view on, like, looking at antibody conjugates or things like that?
Yeah. No, I think you're absolutely right. I mean, we've been thrilled with our C16 platform today demonstrating the potency and durable silencing both through preclinical species and now a clinical translation. This quite unprecedented potency does bode well for exploring systemic delivery doses across the blood-brain barrier. It's very little drug goes a very long way in the CNS, right? So that bar is relatively low with the amount of percent of injected dose that actually needs to get to the brain to see this amount of silence. And my colleague Vasant Jadhav at R&D Day in December did present some initial data with antibody- siRNA conjugate, which I believe we showed up to 50% silencing across various brain regions with a single administration in the mouse.
So I do think it's highly likely we'll be able to apply this technology to some of our CNS pipeline programs. We've got quite a bit of work ongoing, a whole list of exciting targets and approaches here, including and not limited to antibody conjugates, peptides, and inhalers. Yeah. I think it's an exciting space and an incredible opportunity given what we've learned so far with our pharmacology safety profile with siRNA antibody conjugates and.
Yeah. Okay. Great. Well, we're up against time. Anything that we didn't cover that you'd like to add, Kirk?
No. I'm thrilled with what we've seen so far being part of this program. It's research from the earliest days. Happy to see it progress as much as it has and excited for what potential RNAi therapeutics for patients with neurodegenerative diseases. It's just extremely exciting time.
Yeah. Okay. Very good. Well, thank you for taking the time this morning. We appreciate it and look forward to more data.
Thanks so much. Thanks again for having me, Paul.
Okay. Awesome.