Hello, and welcome to the Alnylam Pharmaceuticals Conference Call to discuss interim results from the phase I study of ALN-APP. At this time, all participants are in a listen-only mode. After the speaker presentation, there will be a question-and-answer session. To ask a question during this session, you will need to press star 11 on your telephone. You will then hear an automated message advising that your hand has been raised. To lower your hand, press star 11 again. Please be advised that today's conference is being recorded. I would now like to hand the conference over to the company. Please go ahead.
Good afternoon. I'm Christine Lindenboom, Senior Vice President of Investor Relations and Corporate Communications at Alnylam. With me today on the phone are Yvonne Greenstreet, our Chief Executive Officer; Pushkal Garg, our Chief Medical Officer; and Akshay Vaishnaw, our President. Also in the room and available for Q&A is Kevin Fitzgerald, our Chief Scientific Officer. For those of you participating via conference call, the slides we have made available via webcast can also be accessed by going to the investors page of our website, alnylam.com/events. Now, turning to today's call as outlined in slide two, Yvonne will provide some opening remarks, Pushkal will provide an overview of the ALN-APP program, and discuss the interim phase I results in more detail. Akshay will discuss the implications of the data set for Alnylam's product engine and potential impact on the future of RNAi therapeutics.
We will then open the call for your questions. Before we begin, I would like to remind you that this call will contain remarks concerning Alnylam's future expectations, plans, and prospects, which constitute forward-looking statements for the purposes of the Safe Harbor Provision under the Private Securities Litigation Reform Act of 1995. Actual results may differ materially from those indicated by these forward-looking statements as a result of various important factors, including those discussed in our most recent earnings release on file with the SEC. In addition, any forward-looking statements represent our views only as of the date of this recording and should not be relied upon as representing our views as of any subsequent date. We specifically disclaim any obligation to update such statements. With that, I'd like to turn the call over to Yvonne. Yvonne?
Thank you, Christine, and thanks to everyone for joining the call today. Today is a very exciting day for Alnylam and the field of RNAi therapeutics. As you saw in our press release, we're reporting interim results from the phase I study of ALN-APP, an investigational RNAi therapeutic in development for the treatment of Alzheimer's disease and cerebral amyloid angiopathy. Pushkal will review the clinical data in more detail, but first, I'd like to provide some additional context. We believe that these results establish human proof of concept for RNAi therapeutics in the central nervous system, and as a result, we now potentially have an opportunity to address a wide range of neurologic diseases with high unmet medical need.
In our view, this achievement is reminiscent of the initial human data that we obtained from our liver targeting programs over a decade ago, specifically data from our phase I study with patisiran, which today is marketed as Onpattro, which showed robust knockdown of the target gene, in that case, TTR, with an encouraging safety profile and thereby demonstrating the power of RNAi in silencing disease-causing genes that are expressed in the liver. Those data emboldened us in our efforts to develop other RNAi therapeutics against different liver targets in a wide range of diseases. As you know, we stand here today with five commercially approved products, including Onpattro, and a robust and high-yielding clinical pipeline of over a dozen programs that target liver-expressed genes.
While the strategy of targeting genetically validated genes expressed in the liver continues to be fruitful for us, that is, of course, just one organ system, and there are a myriad of opportunities to target genes expressed in other tissues like the CNS, eye, muscle, adipose tissue, and even tumors. Achieving delivery of RNAi therapeutics to tissues outside the liver is a key element of our sustainable innovation engine, and we believe it constitutes a major growth driver for the company. With the clinical results we're announcing today, it is our view that we have achieved delivery of RNAi therapeutics to the central nervous system in humans. Akshay will elaborate more on this and what it means for our future growth prospects, and these positive results with ALN-APP move us further along our path towards achieving our Alnylam P5x25 goals.
Our Alnylam P5x25 is aimed at bringing transformative medicines for rare and prevalent diseases to patients around the world while advancing a robust and high-yielding pipeline of first and/or best-in-class clinical programs from our organic product engine, as well as delivering exceptional financial performance. In our view, this is a compelling roadmap to build our company and also create value for our shareholders. And of course, there is much more to do in making this vision a reality for patients. And everyone here at Alnylam is focused and determined to achieve that goal. Indeed, today's results are a major step forward that further inspire us in our efforts. And with that, I'll now turn it over to Pushkal to review the ALN-APP phase I study in more detail. Pushkal?
Thanks, Yvonne. This is indeed an exciting day for us here at Alnylam as it ushers in an incredible opportunity for us to use RNAi therapeutics to potentially address a number of neurologic diseases for which we have far too few treatments. As you know, ALN-APP targets amyloid precursor protein or APP, which we are investigating as a potential treatment for both Alzheimer's disease and cerebral amyloid angiopathy. APP is an 87-kilodalton membrane-associated protein.
It goes through a variety of processing steps in enzymatic cleavage by alpha, beta, and gamma secretases to generate soluble APP alpha and soluble APP beta, as well as amyloidogenic fragments, including A beta 40 and 42. Human genetics teaches us that certain mutations in the APP gene or duplications in the gene can cause early-onset Alzheimer's disease, where amyloid plaques deposit in brain tissue and are associated with neurodegeneration.
I don't need to remind you of the terrible burden of Alzheimer's disease, which is estimated to affect five million people in the United States and over 30 million around the world. Other particular mutations in the same gene can cause cerebral amyloid angiopathy or CAA, where certain A beta fragments deposit within the walls of blood vessels in the brain and can result in bleeds or hemorrhages. CAA is, in fact, the second leading cause of intracerebral hemorrhage or stroke. So this one precursor protein, APP, can be harmful in two distinct pathophysiologic processes. Our therapeutic hypothesis is that by lowering APP protein production in the CNS with RNAi, we can reduce the downstream fragments that aggregate and deposit in tissues and also potentially enable natural clearance mechanisms, thereby halting or even improving the clinical manifestations of these diseases.
This therapeutic hypothesis probably looks pretty familiar to many of you because we pursued a very similar hypothesis with the TTR and vutrisiran in ATTR amyloidosis, where it's been shown that by silencing the amyloidogenic protein upstream, we can halt or reverse certain aspects of the disease. In animal studies, we've shown that targeting APP with an siRNA showed great promise with broad CNS distribution after a single intrathecal injection, as shown on the left, and with knockdown in all major CNS cell types, such as the neuron, oligodendrocyte, microglia, and astrocytes, and on the right, we can see that a single intrathecal injection in non-human primates resulted in significant and sustained target knockdown with durability out to six months. Based on these data, we have been excited to see whether a similar effect could be reproduced in humans.
Let me now turn to a review of the interim phase I results with ALN-APP. The phase I trial is designed as a two-part study: a single ascending dose, part A, followed by a multiple dose, Part B. The study is being conducted in patients with early-onset Alzheimer's disease. This population represents approximately 5% of the total Alzheimer's disease population who have onset of symptoms at less than 65 years of age. We selected this population for the phase I study for several reasons. First, EOAD is the leading cause of dementia in younger individuals, and unfortunately, their disease burden is high. They experience progressive neurologic impairment and significant disability and have a shortened life expectancy of roughly five to 12 years after symptom onset. There are currently no available treatments that have been shown to halt or reverse the progression of disease in this population.
Second, these patients have overproduction of amyloid beta as a key feature of disease pathogenesis, which strengthens the mechanistic fit for an RNAi therapeutic targeting APP. Finally, because these patients are younger, they have fewer CNS and non-CNS comorbidities, which make this population well-suited for a phase I study. The primary endpoint of the study is safety and tolerability. Secondary objectives are focused on characterizing the pharmacology of ALN-APP. Specifically, we want to assess the level of target knockdown we can achieve and the duration of effect.
The study also includes a variety of exploratory biomarkers, which will allow us to assess whether ALN-APP is showing any impact on measures of disease progression. These include fluid biomarkers of amyloid, tau, and neurodegeneration, measures of synaptic health, neuroimaging, and exploratory cognitive and functional measures.
While we're not sharing any of these exploratory assessments today, we expect that these measures will become more relevant as we move towards longer follow-up, multiple dosing, and larger numbers of patients. The data I'll share with you in a moment are from the initial single ascending dose cohorts, and we continue enrolling patients in part A as we explore further doses.
At the time of this interim look, 20 patients with early-onset Alzheimer's disease have been enrolled in three single-dose cohorts in part A of the ongoing phase I study. To date, single doses of ALN-APP have been well tolerated, with no study dropouts and all adverse events being mild or moderate in severity. Available CSF data for white blood cells and protein appear similar to placebo.
Early data for neurofilament light chain, or NfL, which are currently available from two out of the three cohorts studied to date, also looked comparable to placebo. Importantly, we've observed that ALN-APP treatment resulted in dose-dependent, rapid, and sustained reductions of both soluble APP alpha and soluble APP beta, biomarkers of target engagement in the CSF. We saw rapid knockdown as early as day 15 and observed maximum knockdown of 84% and 90%, respectively, for soluble APP alpha and beta.
At the highest dose tested, the median knockdown was greater than 70% for both biomarkers and sustained for at least three months. This durability of effect is important for ALN-APP, as well as our overall CNS efforts, as it suggests the potential for infrequent dosing. We look forward to seeing with longer follow-up how long this knockdown effect is sustained.
We believe these data demonstrate that this drug will be able to be dosed quarterly at most, and based on animal data and translation of our platform, we believe there's the potential to dose once every six months or even less frequently. Enrollment in the single ascending dose portion of the phase I study is ongoing in Canada, the Netherlands, the U.K. and the United States. Additional enrollment in part A will allow us to continue to explore single-dose PK and PD and characterize the durability of effect and longer-term safety. Results from part A will also inform the doses and regimens to bring forward into part B, the multiple dose portion of the study, which will include patients from part A. The FDA has currently placed a partial clinical hold on the multi-dose part B in the United States due to findings observed in prior non-clinical chronic toxicology studies.
We plan to share additional preclinical data as well as these interim phase I clinical data with the FDA to support initiation of part B in the United States. We've already received regulatory approval to begin part B in Canada, where, in fact, the majority of the part A patients have been enrolled to date. To close, I am incredibly excited about these remarkable human data that provide the first-ever evidence that we may be able to use RNAi to silence disease-causing transcripts in the CNS. I want to thank my R&D colleagues whose innovative spirit and tenacity have brought us here. We look forward to presenting the interim results from part A of the phase I study at an upcoming medical congress. And with that, I'll now turn it over to Akshay to provide some additional context on today's news. Akshay?
Thanks, Pushkal, and good afternoon, everybody. We're very excited by these initial clinical results with ALN-APP. Currently, therapies to alter the course of disease are lacking in numerous neurological disorders, and so we believe CNS disease represents an area of very high unmet medical need. As shown on this slide, there are many neurological disorders.
Many of these have genetically validated gain-of-function targets, where lowering the level of the pathogenic protein would be expected to lead to clinical benefit. Indeed, some of these diseases, for example, Alzheimer's, Parkinson's, and ALS, have multiple genetically validated targets. To date, however, almost all of these targets have proven undruggable, and there are no disease-modifying therapies available for the disorders concerned. We believe this creates a significant opportunity for RNAi therapeutics to target these disease-causing CNS expressed genes. Today, we're pleased to report the first-ever clinical results with an RNAi therapeutic directed to the CNS. As Pushkal described, the interim phase I data with ALN-APP show robust target engagement that appears durable in a clinically relevant fashion and has an encouraging safety profile.
This first demonstration of the human translation of our RNAi therapeutics in the CNS has further increased the confidence in our platform, resulting in the potential for Alnylam to now advance a series of differentiated product development opportunities across the CNS. As we continue advancing ALN-APP as a potential new therapeutic option for patients with Alzheimer's or cerebral amyloid angiopathy, we also plan to advance new RNAi therapeutic opportunities in other diseases of the central nervous system. As a reminder, we have an ongoing collaboration with Regeneron that is aimed at advancing RNAi therapeutics for CNS disease.
Beyond APP, we and Regeneron have named 10 targets for diseases of the CNS as part of this collaboration today. As shown, the potentially reproducible and modular nature of our platform with potent and durable knockdown across multiple targets after a single IT injection. ALN-SOD, an investigational RNAi therapeutic targeting superoxide dismutase or SOD1 for the potential treatment of SOD1 ALS, is currently in IND-enabling development and is being led by our partner Regeneron.
We're also announcing today that ALN-HTT, an investigational RNAi therapeutic targeting huntingtin for the potential treatment of Huntington's disease, has entered IND-enabling development. Just this week, we're participating in the CHDI conference in Dubrovnik, Croatia, where we presented our assessment of different approaches to HTT targeting and our view for how an RNAi approach could be used to address this very high unmet need disease area.
You can view this presentation on the ALN-HTT program on the Capella section of our website. With evidence in hand that suggests we can reach all major regions of the CNS and all key cell types and today's report of human translation from NHP to humans for our ALN-APP program, we look forward to continuous advancements in our efforts to bring RNAi therapeutics to patients with a wide range of neurological disorders. Today's clinical data further extend Alnylam's leadership in RNAi therapeutics and our ability to hopefully bring RNAi to many organs. We've had great success targeting disease-causing genes expressed in the liver.
Today, we believe we've taken one major step forward in targeting genes expressed in the CNS. And we also look forward to potentially addressing a vast landscape of therapeutic opportunities through targeting additional tissues with our ongoing delivery efforts to tissues such as muscle, heart, lung, adipose, kidney, and even tumors. I'll now hand it back to Christine to coordinate Q&A. Christine?
Thank you, Akshay. Operator, we will now open the call for questions. As a reminder to those dialed in, we would like to emphasize that if you will be fielding one question from each analyst, we ask that you please get back in the queue if you have any additional questions. Also, as a reminder, we'll be hosting our first quarter earnings call next Thursday, May 4th. So any questions outside the scope of the content discussed in today's call can be addressed at that time. Operator, please go ahead.
Thank you. And as a reminder, to ask a question, you will need to press star 11 on your telephone. One moment, please. Our first question comes from the line of Paul Matteis with Stifel.
Hi, this is James on for Paul. Thanks for taking our question. I guess the knockdown data are really interesting, but we have a couple of questions or one question on the clinical hold. And I guess, given that it stems from this chronic toxicology work, I guess, can you speak about whether or not it's due to the level of knockdown in these chronic tox studies that you're getting with APP? Or is it something more kind of idiosyncratic with just RNAi itself being the first time in humans? Anything there would be great. Thanks so much.
Look, thanks for the question. I think it's important to just illustrate how pleased we are with these results. I mean, they're really groundbreaking in terms of providing evidence of first validation of human translation of our C16 platforms for CNS. And I think, importantly, also the potential for patient impact in these devastating neurologic conditions. And so we're thrilled with the data. And Akshay, perhaps you could make a few remarks around your perspectives on the partial clinical hold in the U.S.
Yeah. Thanks, Paul. The first thing I want to say is that, of course, in the run-up to the toxicology studies, we had evidence from pharmacology studies showing APP knockdown both in rats and non-human primates that was well tolerated. In fact, in the non-human primate, single dose is giving 80+% knockdown approximately out to six months and beyond, almost to nine months, so we're quite reassured by target knockdown and target engagement being well tolerated in non-human primates. And of course, that put us in a position to do the toxicology studies where we have similar findings, and we don't believe this is primarily, therefore, APP target-related suppression. Obviously, there's more to learn.
We're delighted that today's data from the human setting showed that APP suppression, at least in the short term, out to a period of months, is well tolerated to degrees that are similar or higher than what we saw in the non-human primate. So more to discuss with the FDA. We need to bring these clinical data to their attention, obviously, and have further dialogue on the chronic toxicology data, which, as I would remind you, we've obviously done at exaggerated doses and dosing frequencies. So you would expect to see some toxicity at some elevated exposures like that. And so we'll discuss all of this. And we're delighted that from the discussions with the Canadians, we've got the green light to go ahead. And we hope to do so in the other territories concerned.
Thanks so much.
Thank you. Our next question comes from the line of David Lebowitz with Citi.
Thank you very much for taking my question. Again, regarding the partial clinical hold, is this something that's particular to ALN-APP, or is the hold also indirectly affecting the other CNS programs that are currently being studied?
Yeah, thanks for that, Dave. This partial clinical hold relates to the multiple dose of part B of the ALN-APP program. Part A is ongoing. These are the data we've discussed today and more data to come. And so it has no bearing on other programs at this present point in time.
Thanks for taking my question.
Thank you. And our next question comes from the line of Ritu Baral with Cowen.
Good afternoon, guys. Thanks for taking the question. Akshay, I wanted to just confirm what I think you said in your previous answer. Was this preclinical finding at a dose that would be higher than you planned on studying in the phase I? And then if you could just tell us the nature of the partial hold, does this mean you can still treat U.S. patients with a single dose, or is dosing in U.S. patients effectively ended even though you're going to higher doses in those other geographies? Thanks.
Yeah, thanks, Ritu. So with respect to the non-chronic toxicology findings, you'll all appreciate that we started the IND-enabling efforts with shorter single-dose studies, and that allowed us to get into the program and get into the clinic. Those findings were very encouraging. Now, at that time, of course, we don't know at what level we're going to see knockdown in humans. We've just started the phase I study. This is a little while back. And so we initiated the chronic toxicology studies in parallel to enable further dosing across the phase I and beyond for multiple doses.
So we naturally picked, as one is expected to do, higher doses and exaggerate the dosing frequency from that which was anticipated in humans. So yes, we're seeing the chronic toxicology findings at significant multiples of where we are in the clinic. So it's unsurprising that we've seen some findings. We're quite comforted by the safety that we've seen in phase I so far and look forward to, obviously, engaging with the agency with the data in hand, both clinical and non-clinical, and look forward to having a path to move forward. What was your second question, Ritu?
Oh, it was just [crosstalk], does the partial hold mean that you're not dosing any more single-dose patients in the U.S.?
Yeah. No, so we've dosed in the U.S., and part A continues across all territories. So the U.S. FDA partial hold just relates to multiple dosing for part B in the U.S. But we have okay for part B in Canada, etc. Yeah.
Great. Thank you.
Thanks, Ritu.
Our next question comes from the line of Maury Raycroft with Jefferies.
Hi. Thanks for taking my question. At a prior R&D day, you provided some info on dose levels. Just wanted to confirm the first three doses are 25, 75, and 225 mg. And can you say what the next steps are with dosing up with part A? Will that be the 600 mg dose? And have you decided whether to explore 900 and 1200 mg as well?
Yeah, Maury, thanks for your question. The protocol did have some pre-specified doses, but it also allowed flexibility based on what was observed in the clinic. So we're not speaking today about the specific doses that were studied. We'll share those doses as well as with the detailed data at an upcoming scientific congress. Again, just to reiterate, I think we're very pleased with the level of knockdown we're seeing, which is dose-dependent. We're seeing rapid knockdown, and it's quite durable. So yeah, I think that was there another part to your question?
That was it. Just wanted to check on the doses and the next steps for dosing up.
Yeah, and what I would say is that the study is under the auspices of a safety review committee. They've looked at the data, and further dose exploration is ongoing, and that's really to characterize pharmacokinetics, pharmacodynamics, the durability, as well as longer-term safety, so further dose exploration is ongoing.
Got it. Thanks for taking my question.
Thank you. And our next question comes from the line of Tazeen Ahmad with Bank of America.
Hi, guys. Good afternoon. Thanks for taking my questions. Can you just provide a little bit more color on what exactly the observation was that led to the partial clinical hold from FDA? And is it possible that your part B portion would also include all Canadian patients, if not most Canadian patients, the way that it was for part A? Thanks.
Yeah, maybe I can start off, Tazeen, and then I'm sure Pushkal wants to talk about the Part B. We obviously, we're not going to get into all the back and forth on the exact details of the chronic toxicology findings. I also want to just step back and just sort of set the scene a little bit for everybody. In drug development, you do chronic toxicology studies. Every sponsor has to do them. You exaggerate the dose. You exaggerate the exposures. Your job is to elicit findings. We elicited findings. So there's no kind of big shock or surprise about that. I think the agency took a look at them, and they want to discuss them, and we will have that discussion with them. They have not been availed of all the wonderful data that we've seen today, the rather encouraging safety data that we have in humans today.
We don't know what the frequency of the exposure will be in humans. Pushkal said earlier, maybe six months, maybe less frequently. We're seeing knockdown to a profound degree, up to 90% at times. So all of that, with the clinical safety and with safety biomarkers like NfL not showing any obvious differences, I think all has to be discussed with the FDA. Then we can also discuss the findings at the exaggerated dose and exposures, and hopefully, we can work out a path ahead. In that regard, as we've iterated before, we've had an application to Canada, of course, for part B, and they have looked at everything and allowed us to go ahead with the green light. I'll stop there. Pushkal, do you want to comment on part B and Canada?
Yeah, absolutely. I agree with everything you said, Akshay. I think, Tazeen, with regard to part B, part B is designed and intended to really allow part A patients to continue on into multiple dosing, right? So as I mentioned, the majority of the patients who are enrolled in part A are in Canada. And so, whereas Akshay mentioned, we do have a green light to move forward into part B.
The other interesting observation here is that with the prolonged pharmacology that we're seeing, the durability, it means that even in part A, we're going to get actual substantial amount of evidence in terms of the durability of effect as well as longer-term safety. And so it's an interesting opportunity here to actually explore the long-term effects of APP knockdown, even in part A. But we will move forward in Canada. As Akshay said, we will be in active dialogue with the FDA to provide the information they need, as well as this clinical data, so that we can enable dosing in part B in the United States as well.
Okay. Thank you.
Thank you. And our next question comes from the line of Salveen Richter with Goldman Sachs.
Good afternoon. This is [Anumidan] for Salveen. Again, just on the partial hold on part B, I guess what specifically from the preclinical chronic tox data could be driving the hold? And then what do you think the FDA would want to see to be able to move forward? Thank you.
Yeah, thanks for that. I would refer you back to my response to Tazeen just now, as you ask a very similar question about the findings and how to lift the partial hold. Just to reiterate briefly, we obviously, as is expected, exaggerated the exposures greatly to do a fully robust chronic toxicology studies. There are findings at the top dose. The FDA wants to understand those further. That obviously is their prerogative.
This is a new platform. They'll want to understand that. In the face of all of that, we have rather encouraging, we feel, human safety data and these phase I data showing very good knockdown and the associated safety that goes with that. So we need to take all of this back to the agency, discuss it with them, and craft a path ahead, just as we have done with the Canadians, where we have a green light to proceed to part B.
Thank you. And our next question comes from the line of Jessica Fye with J.P. Morgan.
Good afternoon. This is JL for Jess. Yeah, so a couple of clarifying questions from us on the partial clinical hold. First of all, have you disclosed when does the partial clinical hold happen, and when were you notified by the FDA? And then have you got a chance to communicate with the FDA yet since the notification of the partial clinical hold? And then secondly, does the toxicity signal that you have seen, right, in the animals affect in any way, right, the handling of the animals? Or in another word, does it affect the movement of the animals? Thank you.
Yeah. Yeah, thanks for that. I mean, in respect of the timing, obviously, whenever we get chronic toxicology data of note, we always inform regulatory agencies in a timely fashion. We've done that here. We're sharing with you today. Now, contemporaneous to all of that, these wonderful data that you see today from the phase I study have emerged, and so we will go and discuss all of those with them and look to create a path ahead, which we're confident we can do, especially in light of the fact that other agencies, for example, the Canadians, have given us the green light.
I think the other part of your question was about the exact findings of the toxicology study. We're not going to discuss those. I don't know if that's so relevant here today. Again, just to reiterate, as would be expected, these are findings that are remarkably higher exposure than we anticipate in the clinical dosing realm. Issues like safety margin and those things will come in as well as be discussed with the FDA.
Thank you. And our next question comes from the line of Mike Ulz with Morgan Stanley.
Hey, guys. Thanks for taking the question. And congrats on the strong knockdown here. Just curious, as we think about read-through to other CNS targets, you sort of highlighted some preclinical data for SOD1 and HTT, which looked good as well. But as we kind of move into humans, do you think you can get to a similar level of knockdown that we saw preclinically, also in the clinic for those targets as well? Or is there any reason why we should expect it to be noticeably different? Thanks.
Yeah, good question, Mike. And our anticipation would be that the APP data showing the potency and durability of the platform with this wonderful translation from the non-human primate setting into humans, just as we have done many times before for the liver, will now reproduce across multiple targets. And so we feel quite confident about that. And as you've seen, we've initiated a number of programs with Regeneron, and we're excited that we're going to address diseases like ALS, Parkinson's, Huntington's, and others that we highlighted today. So we feel very good about the observations today and their translatability, not just the further impact we hope to have with APP and Alzheimer's and CA, but also the vast array of other neurological disorders where there's such high unmet need.
Thank you. And our next question comes from the line of Gina Wang with Barclays.
Hi, good afternoon. This is Harshita on for Gina. Thank you for taking our questions. Just a couple of quick ones. On the chronic tox, are you able to disclose what dose led to the tox? And if you're not able to disclose and just at this time able to disclose that it's at an exaggerated dose, that's fine. And then quickly on the second, on the dosing frequency, if I heard correctly, Pushkal, I think you mentioned at this point it would be like a quarterly dosing frequency, or are you trying to get to a biannual dosing frequency? So any color you can give us on how you're thinking about dosing frequency for the asset, that would be helpful. Thank you very much.
Yeah, I'll start, and Pushkal will address your second question. So in terms of the dose and the dosing frequency associated with chronic toxicology findings, they're both significantly higher than we are seeing knockdown and duration in the clinic. So I mentioned this concept of safety margin that you'll all be familiar with. That obviously is important in any aspect of drug development. And so again, the exaggerated exposures and the chronic tox are associated with certain findings. Here, we have a single dose giving us at least three months of knockdown, up to 90%, and still counting beyond three months. So that gets us into the issue of the frequency of administration. And Pushkal, what would you like to say to that?
Yeah. I mean, I think, as you're saying, Akshay, I think what we're seeing is really durable knockdown. And we anticipate that this is likely to be a Q6-month drug or even less frequent than that. Obviously, we're going to get longer follow-up. That's what we're doing in part A. But the data here are incredibly encouraging. And I just want to reiterate what Akshay said. We designed the chronic tox studies without the knowledge of the human translation.
We had to cover a range of potential exposures in the clinic. And so they were done using higher doses and more frequent administration. And this human translation data now really encourages us to see that we actually have greater potency, greater knockdown, and durability. And that's very encouraging. So again, we'll engage in discussions with the regulators around this. But we're very optimistic about what we're seeing here, very encouraged about what we're seeing in terms of human translatability of this C16 platform and a path forward.
Thank you. And our next question comes from the line of Luca Issi with RBC Capital Markets.
Oh, great. Thanks for taking our question. This is Lisa on for Luca. A couple from us. First, just want to clarify. Have any other health authorities, which participated in a part A study, like the Netherlands or the UK, have they also seen this preclinical chronic tox data? And also, what has their reaction been to starting in part B in the multi-dose portion? And just curious, just wondering why the APP alpha and APP beta, the knockdown was slightly different, 84% versus 90%. Were you expecting these knockdown values to be more similar, or why or why not? Thanks for taking our questions.
Sure. So in terms of the health authorities, all the health authorities have been informed of the findings. That was communicated across to all the health authorities. We've talked about the FDA. Canada, as we've mentioned, has approved moving into part B. And the file of the applications for part B and data are under review in the Netherlands and the U.K., so by ethics committees and the regulatory authorities. So that's underway. So that's part one. In terms of part two of your question around the 84% versus 90%, I think, again, these are small numbers in early days. In terms of the data that we're collecting, I think what we're really encouraged about is by the level of knockdown that we're seeing. The fact that we're seeing with single doses up to 84% or 90% knockdown, we think is quite remarkable.
And the fact that we're seeing 70% average median knockdown after three months with a single dose is quite remarkable. And that we're seeing that reduction happening as early as day 15. And we think that provides a very differentiated profile that we hope will be a benefit across a range of diseases that we may choose to go after with RNAi therapeutics. So I would like to add something.
Yeah, I just add to what Pushkal said, that obviously, we're knocking down the APP transcript at source. So the reductions in all downstream products would be symmetrical biologically. The fact that you see this minor discrepancy is probably related to turnover of the protein fragments being slightly different. It could be assay differences in sensitivity. There could be fairly trivial explanations like that. But the issue at heart is that we're going upstream and we're knocking down the APP transcript. So all biologically relevant fragments downstream will be being similarly addressed.
Thank you. And our next question comes from the line of Joseph Stringer with Needham & Company.
Hi. Thanks for taking our questions. Just wanted to follow up on the median 70% knockdown that you're seeing for both the APP biomarkers. Can you realize that it is SAD dosing here, but can you comment on the importance of that median 70%? Is that something that you think would be sufficient to translate into improvements in, say, functional clinical measures, or would you need to see much higher, say, 90 + % or extended time?
Yeah, it's a great question. Look, when we again, I think we have to say, first of all, we're interrogating new biology here, right? And so no one knows the exact answer to your question. But when we were pursuing this as we've been pursuing this target, one of the what we've said in the past is that based on human genetic data, we think that getting to north of 50% or so puts us in a range where we can really evaluate this therapeutic hypothesis. So the fact that we're seeing median knockdown of 70% or so, I think, gives us a lot of confidence that we have the proper tool to really explore the importance and the benefits that we might see with APP knockdown in both Alzheimer's disease and cerebral amyloid angiopathy.
So this really puts us in a great range to actually explore that hypothesis and evaluate the downstream clinical effects. As Akshay said, we're really targeting upstream, and we'll expect to see then concordant reductions in all these sort of amyloid proteins and beta-amyloid proteins that are involved in these diseases.
Great. Thanks for taking our question.
Thank you. And our next question comes from the line of Ellie Merle with UBS.
Hey, guys. Thanks so much for taking the question. Just in terms of the dose optimization, when you say that dose exploration in part A is still continuing, you're already seeing some pretty deep knockdown in the CSF. Can you just elaborate on what you're looking to optimize and if you're looking at lower doses or higher doses in the further part A dose optimization and the latest thinking on sort of what the ideal degree of target knockdown of APP is? Thanks.
Yeah, Ellie. So I think, as I said, part of our obligation and what we want to do for any phase I study, and certainly as we're bringing in our first RNAi therapeutic in CNS, is really to characterize the dose response curve, and so we're going to look at a range of doses to really fully characterize what that looks like. It'll be important, as we said, to really understand pharmacokinetics, pharmacodynamics. We're going to want to look at durability across a range of doses, and we're also going to want to get long-term safety data, so all of those things are enabled in part A with the single dose, and particularly in light of the data that we're seeing here today, so we'll continue part A to do that.
In terms of the next steps, will then be to actually we can't say today exactly what doses we'll be taking into subsequent studies. As I said, we are in the therapeutic range that we were hoping to get to, to explore these hypotheses in patients with Alzheimer's disease and with CAA, and we'll provide further details as the data mature and as we develop our plans further.
And Pushkal, I think you'd agree that based on the rather encouraging knockdown and safety findings that we have in hand, we're quite comfortable exploring the full range, including lower and higher doses, exactly relative to where we have been to fully characterize this drug and enable the Part B. And I think, Ellie, you touched on the target knockdown and the previous call of it as well. And 50%, if you think about Down syndrome and trisomy 21, the patients have a triplication of APP. So that extra third copy gives them a modest elevation in APP and, unfortunately, gives a much heightened risk of Alzheimer's disease. So that tells us that we don't need to knock this down by 90%, 95%. And so 50 and above is a good zone to aim at. But it's a phase I study, and we'll characterize the full dose range.
Great. Thanks.
Thank you. And our next question comes from the line of David Hoang with SMBC.
Hey, thanks for taking my question and congrats on the robust knockdown that you guys are seeing. So I think a lot of my questions have been answered so far, but I just want to go back and touch a little bit on the safety and tolerability that you saw in the patients dosed so far. I know that you said it was mild, moderate AEs and nothing out of the ordinary or unexpected, but could you just maybe clarify as to any side effects that you did see in these patients?
Yeah, David, thank you. Thanks for your comments and your question. Overall, we've been really encouraged by the safety and tolerability we've seen to date. Obviously, it's early days in single-dose data, but what we're seeing across the range of cohorts is that the AEs have all been mild to moderate. You'll get more color in an upcoming scientific meeting, but I think we're very encouraged by what we're seeing here. And we're also doing a lot of monitoring of these patients, as you would expect. So they get CSF sampling, for instance, and we've looked at CSF white cells and CSF protein. And that all really looks quite comparable to placebo.
We also monitor biomarkers like neurofilament light chain, which is a marker of neuronal injury. We have more limited data on two of the three cohorts so far, but that also looks quite encouraging and comparable to placebo. So overall, we're really pleased with the safety and tolerability profile that we're seeing in these first three cohorts. We'll continue to monitor these patients, but it's very encouraging, and we'll share more at an upcoming medical congress.
Thank you. And our next question comes from the line of Patrick Trucchio with H.C. Wainwright.
Thanks. Good afternoon. Just a follow-up on that last comment. I'm just wondering if you can discuss further the implications of NfL looking comparable to placebo and if that data was comparable throughout or if it ever elevated, such as following administration of ALN-APP. And then secondly, if you could tell us, what are the expectations for the exploratory cognitive and functional measures, and when may you have more data on those endpoints to share from the study?
Yeah, Patrick. So thanks for your questions. In terms of NfL, you're right that certain times perturbation, for instance, through injection, etc., can affect NfL levels. We obviously think about that in the way that we've designed and sampled. And so we're quite comfortable as we've looked at the early data. Our safety review committee as well as they've looked at the early data that we're that the NfL levels, these early time points in these cohorts looks comparable to placebo. And in terms of additional assessments, you're right, these patients are undergoing a variety of assessments. And again, we're reassured by the safety that we're seeing, and we'll provide that data in due course. We don't have those data to share today, but those will be parts of subsequent presentations.
Thank you. And our next question comes from the line of Michael King with EF Hutton.
Good afternoon, guys. Let me first congratulate you on the findings today. I hate to come back to the chronic tox findings, but I'm just curious if you can say what species you found this in, or if you can't say that, can you just say if these were genetically modified animals? I'm thinking of the APP mouse, the Alzheimer's mouse model, or these sort of standard laboratory normal animals that didn't have any kind of plaque burden.
Yeah. Mike, thanks for the congrats. These are indeed exciting data. With respect to your question about the chronic tox, we used the typical rat non-human primate species. I'm not going to get into further details beyond that. And there were the standard issue CRO animals that are not genetically modified or manipulated in any way.
Okay. That's great. Thanks so much.
Thanks, Mike.
Thank you. And our next question comes from the line of Myles Minter with William Blair.
Thanks a lot, Mark. Congratulations. Certainly looks impressive data on the clinical side here. So congrats on that. Just got to get back to the chronic non-clinical tox here. Have you seen any signs of drug accumulation, specifically relative to a GalNAc conjugate? Just know that you're putting a fatty acid conjugate here, so curious about drug accumulation. And then also, is the safety margin based on the no adverse effect levels or no observed adverse effect levels? Are they materially different for a C16 conjugate versus a GalNAc, just given you've got so much history with the GalNAc conjugates here? Thanks.
Yeah. Thanks, Myles. And thanks also for the congratulations, noting these rather important data. With respect to the chronic tox findings and drug levels, I don't have the data for the drug levels to hand in the relevant issues, so I can't comment on the question of accumulation. But you raise an important point that these studies were done at significantly higher doses than we anticipate in humans and also significantly higher dosing frequencies. So that's all I can say to that at the moment. And the second part of your question was?
Just whether you're observing materially different safety margins based on no observed adverse effect levels between C16 and GalNAc because you know so much more about GalNAc.
Yeah. Yeah. This is obviously a new part of the platform, so there's much to be learned. But the interesting thing is, and what your question brings up, is that given that we did these chronic tox studies at significantly higher doses and dosing frequencies, and we've seen single, relatively low doses in humans give this sort of profound knockdown to a marked degree up to 90% and out to many months now, this is why I made the comment earlier about safety margins.
But that leads us to believe that both dose levels and dosing frequencies in humans, ultimately in multidose studies like part B, will be significantly lower than the kind of dose and regimens that we use in the chronic tox studies. And that gives rise to the concept of a safety margin, which we're all familiar with in drug development. And hence our optimism for moving ahead in the clinic with part B and reaching a satisfactory conclusion with the FDA, as we've done with the Canadians. I hope that answers that question.
Yep. Does. Thank you.
Thank you. And our next question comes from the line of Kostas Biliouris with BMO Capital Markets.
Hello, everyone. Thanks for taking my questions and congrats on the data. A couple of questions from us on the chronic tox study. Number one, did the repeated dosing drive a stronger APP lowering compared to the single dose or the knockdown levels were similar between the single dose and the repeated dose? And the second one, can you disclose how long post-dosing you saw this adverse reaction in non-human primates because our recent discussions with KOLs say that the 6-12-month post-dosing are very important for adverse events? Thank you.
Yeah. Thanks, Kostas. With respect to the APP knockdown, they're in a very similar range, single dose and multiple doses. We've obviously, both with the single-dose tox studies and the multiple doses, exaggerated the dose to really suppress the target hard. So that answers the first part of your question. With respect to the further details of the tox studies and the timings and the kind of findings, we're not going to get into that here. I would emphasize, however, in the human setting, the rodent and perhaps that ultimately is the species that matters in these sorts of things. But in the human setting, the safety data are quite encouraging, as we've discussed today. The adverse events were mild to moderate. All patients were retained on study.
We've had the green light for further multiple dosing in Canada, and all the safety biomarkers as Pushkal discussed, such as CSF, white cells, protein, and the data we have on NfL are all supportive of the clinical observations, and this is up to multiple months of target suppression, so that really encourages us about the ultimate species, which is the human. Thank you.
Thank you. Very helpful.
Thank you. And our next question comes from the line of Mani Foroohar with SVB Securities.
Hi. Thanks for taking our question. This is Jenny Goldstein for Mani. I was just wondering if you could give us an idea of how you would navigate a setting where OUS regulators are comfortable dosing patients with the platform as is while the U.S. remains on partial hold. Would there be different platforms or constructs that you would consider in the U.S. versus OUS, or would you go back to the drawing board across all geographies? Thank you.
I mean, I think that's a hypothetical that we don't need to discuss today. We haven't even had a chance to engage with the FDA with these clinical data and discuss the non-clinical data. And I think when we do that, we're confident that we can find a path ahead and have a harmonized protocol across all territories. So I'll leave it at that. Thank you.
Perfect [crosstalk] Thank you. .
Thanks, everyone, for joining us today. As you've heard on the call, we are really encouraged by these initial data, clinical data with ALN-APP. And we're very excited about what this essentially means for future RNAi therapeutics in the CNS. So thanks, everyone, and enjoy the rest of the day.
Thank you. This concludes today's conference call. Thank you for participating. Now, disconnect.