Alnylam Pharmaceuticals, Inc. (ALNY) Earnings Call Transcript & Summary

Hello, and welcome to the Alnylam Pharmaceuticals conference call to discuss interim results from the Phase I study of ALN-APP Conference Call. [Operator Instructions] 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 on Slide 2. 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 future of RNAi therapeutics, and we will then open the call to 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 quarterly recent earnings on filed with SEC. In addition, any forward-looking statements represent our views only 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. This 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 5 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 expressing other tissues like the CNS, eye, muscle, adipose tissue and even tumors. Achieving delivery of RNAi therapeutics for 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 for central nervous system in humans, Akshay will elaborate more on this and what it means to our future growth prospects. And these positive results with ALN-APP move us further along our path towards achieving our Alnylam P5x25 goals. 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 road map 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-kilodaltons membrane-associated protein. It goes through a variety of processing steps in enzymatic cleavage by alpha beta and gamma secretase to generate soluble APP alpha and soluble APP beta as well as amyloidogenic fragments, including Abeta 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, or amyloid plaque 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 5 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 Abeta 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 parent protein, APP can be harmful in 2 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 patisiran and vutrisiran in ATTR amyloidosis which has 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 within siRNA showed great promise with broad CNS distribution after a single intrathecal injection, as shown on the left. And with knockdown 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 nonhuman primates resulted in significant and sustained target knockdown with durability out to 6 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 2-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 dimension younger individuals. And unfortunately, their disease burden is high. They experienced progressive neurologic impairment and significant disability and have a shortened life expectancy of roughly 5 to 12 years after symptom onset. There are currently no available treatments that have been shown to halt to 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. And 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, measure 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 3 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 appears similar to placebo. And early data for neurofilament light chain, or NfL, which are currently available from 2 out of the 3 cohorts studied to date also looked comparable to placebo. Importantly, we've observed the 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. And at the highest dose tested, the median knockdown was greater than 70% for both biomarkers and sustained for at least 3 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 6 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 nonclinical 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 have 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 size 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 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 disorders confirmed. We believe this creates a significant opportunity for RNAi therapeutics to target these disease-causing CNS expressed genes. Today, we're pleased to report first ever clinical results with an RNAi therapeutic directive 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. The 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 angiography, we also plan to advance new RNAi therapeutic opportunities in the -- 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 and has 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 disease has entered the 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 HTT program on the Capella section of our website. The evidence in hand that suggests we can reach all major regions of the CNS and all key cell types in 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 Alan's leadership in RNAi therapeutics and our ability to hopefully bring RNAi to many orbits. We've had great success targeting disease-causing genes expressed in the liver. Today, we believe we've taken 1 major step forward in taking genes expressed in the CNS. And we also look forward to potentially addressing the 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 that those dialed in, we would like to emphasize that we 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 4. So any questions outside of scope of the content discussed in today's call can be addressed at that time. Operator, please go ahead.

[Operator Instructions] Our first question comes from the line of Paul Mattias with Stifel.

This is James on for Paul. 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 toxicology 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.

Look, thanks for the question. I think it's important to just reiterate how pleased we are with these results. I mean they're really groundbreaking in terms of providing evidence the first validation of human translation of our C16 platforms with CNS. And I think importantly, also the potential for patients' impact and these devastating neurologic conditions. And so we're thrilled with the data and Akshay, perhaps you could make a few remarks around your perspective on partial clinical hold in the U.S..

Yes. Thanks, Yvonne. 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 nonhuman primates that was well tolerated. In fact, in the nonhuman primate, single dose is giving 80-plus percent knockdown approximately out to 6 months and beyond almost to 9 months. So we're quite reassured by target knockdown and target engagement being well tolerated in nonhuman 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 higher than what we saw in the nonhuman 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're obviously done it to exaggerate doses and dosing frequency. 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 on 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.

And our next question comes from the line of David Lebowitz with Citi.

Again, regarding the partial clinical hold, is this something that's particular to ALN-APP or is the hold also indirectly affects the other programs that are currently being studied?

Yes. Thanks for that, Dave. This partial clinical hold relates to the multiple dose in 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 current point in time.

And our next question comes from the line of Ritu Baral with Cowen.

Akshay, I wanted to just confirm what I think you said in your previous answer that was this dose at a -- I'm sorry, 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?

Yes. Thanks, Ritu. So with respect to the 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. And we're quite confident by the safety that we see in Phase I so far and look forward to obviously engaging with the agency with the data in hand, both clinical and nonclinical and look forward to creating a path to move forward. What was your second question, Ritu?

It was just, does a partial hold mean that you're not dosing any more single dose patients in the U.S.?

Yes, we dose in the U.S. and the 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 the okay for Part B in Canada, et cetera. .

Our next question comes from the line of Maury Raycroft with Jefferies.

At a prior R&D Day, you provided some info on dose levels. Just wanted to confirm the first 3 doses are 25, 75 and 225 milligrams. 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 1,200 mg as well?

Yes, Maury, thanks for your question. The protocol did have some prespecified doses, but 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. The -- so yes, I think that was -- was there another part of your question?

I just wanted to check on the doses and the next steps for dosing up.

Yes. And what I would say is that the study is under the auspice of the 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.

Our next question comes from the line of Tazeen Ahmad with Bank of America.

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?

Yes. Maybe I can start off to lead, and then I'm sure Pushkal wants to talk about the Part B. We obviously -- we're not going to get into 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 available, the wonderful data that we've seen today, the rather encouraging safety data that we have in humans today. And we don't know what the frequency of the exposure will be in humans. Pushkal said earlier, maybe 6 months, maybe less frequently and we're seeing knockdown to a profound degree up to 90% at times. And 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. And then we can also discuss the findings about the exaggerated dosing exposures, and hopefully, we can work out a path ahead. And 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 in Canada?

Yes, absolutely. I agree with everything you said, Akshay. I think Tazeen, with regard to Part B, Part B really wasn't -- isn't designed and intended to really allow Part A patients to continue on into multiple dosing, right? So as we -- as I mentioned, the majority of the patients who are enrolled in Part A are in Canada. And so where, as Akshay mentioned, we do have a green light to move forward into Part B. And 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 and as Akshay said, we will be in active dialogue with the FDA to provide the information they need as well as the clinical data so that we can enable dosing in Part B in United States as well.

And our next question comes from the line of Salveen Richter with Goldman Sachs.

This is named [ Anomit ] on 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?

Yes. Thanks for that. I would refer you back to my response to Tazeen just now. You asked 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 a fully robust chronic toxicology study. 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 a very good knockdown and the associated effect 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.

And our next question comes from the line of Jessica Fye with JPMorgan.

This is [ Jay ] on for Jess. Yes. So a couple of clarifying questions from us on the partial clinical hold. First of all, have you disclosed like 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, the toxicity signal that you have seen, right, within the animals effect in any way, right, the harming of the animals or in another word, does it affect the movement of the animals? Yes.

Yes. Thanks for that. I mean in respect to 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 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 the 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. And again, just to reiterate, as would be expected, these are findings that are remarkably higher exposure than we anticipate in the clinical dosing realm. So issues like safety margin and those things will come in as well as we discussed with the FDA.

And our next question comes from the line of Mike Ulz with Morgan Stanley.

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.

Yes. 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 nonhuman primate study in humans, just as we have done many times before for the liver, we'll 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 a high unmet need.

And our next question comes from the line of Gena Wang with Barclays.

This is [ Harshita ] on for Gena. 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 second, on the dosing frequency, if I heard correctly, Pushkal, I think you mentioned at this point, you're -- 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.

Yes, I'll start and Pushkal will address your second question. So in terms of the dose and the dosing frequency, as I said, with chronic toxicology findings, they're both significantly higher then 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 3 months of knockdown up to 90% and still counting beyond 3 months. So that gets us into the issue of the frequency of administration and Pushkal, what would you like to say for that?

Yes. 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 Q 6-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 the human translation data now really encourage 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 the C16 platform and a path forward.

And our next question comes from the line of Luca Issi with RBC Capital Markets.

Great. This is Lisa on for Luca. A couple from us. First, I just want to clarify, have any other health authorities which participated in the Part A study like the Netherlands or the U.K. 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?

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 under -- for Part B and data are under review in the Netherlands and the U.K., so by the ethics committees and the regulatory authorities. So that's underway. So that's part 1. In terms of part 2 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 3 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...

Yes. I'd just add to what Pushkal said, that obviously, we're knocking down the APP transcripts at source so the reductions in all downstream products would be symmetrical biologically. The fact that you see this minor discrepancy is probably related. The turnover of the protein fragments being slightly different, could be assay differences in sensitivity, there could be fairly trivial explanations like that. But the issue at the heart is that we're going upstream and we're knocking down the APP transcripts. So all biologically relevant fragments downstream will be being similarly addressed.

And our next question comes from the line of Joseph Stringer with Needham & Company.

Just wanted to follow up on the median 70% knockdown that you're seeing for both the APP biomarkers, can you -- I realize that it is [indiscernible] dosing here, but can you comment on the importance of that medium 70%. Is that something that would be you think would be sufficient to translate into improvements in say, functional clinical measures? Or would you need to see much higher, say, 90-plus percent or extended time?

Yes, 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 time 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 knock down in both Alzheimer's disease and cerebral amyloid angiopathy. This really puts us in a great range to actually explore that hypothesis, evaluate the downstream clinical effects. As Akshay said, we're really targeting upstream and we'll expect to see then concordant reductions in all of these sort of amyloid proteins, beta amyloid proteins that are involved in these diseases.

And our next question comes from the line of Ellie Merle with UBS.

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?

Yes, 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, it's 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 will 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 the 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 other encouraging knockdown and safety findings that we have in hand, we're quite comfortable exploring the full range, including low 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 caller did 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 a modest elevation in and unfortunately, it 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.

And our next question comes from the line of David Hoang with SMBC.

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 wanted to just go back and touch a little bit on the safety and tolerability that you saw in the patient's dose 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?

Yes, David, 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 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 2 of the 3 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 3 cohorts, we'll continue to monitor these patients, but it's very encouraging and we'll share more at an upcoming medical congress.

Our next question comes from the line of Patrick Trucchio with H.C. Wainwright.

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 end points to share from this study?

Yes, Patrick. So thanks for your questions. In terms of NfL, you're right that certain times perturbation, for instance, through injection, et cetera, 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 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 are 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.

And our next question comes from the line of Michael King with E.F. Hutton Group.

Let me first congratulate you on the findings today. I just -- 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 are these sort of standard laboratory normal animals that didn't have any kind of plaque burden.

Yes. Mike, thanks for the congrats. These are indeed exciting data. With respect to your question about the chronic tox we use the typical rat nonhuman primary species. I'm not going to get into further details beyond that. And they were the standard issue CRO animals, not genetically modified or manipulated in anyway.

And our next question comes from the line of Myles Minter with William Blair.

Congratulations certainly looks impressive data on the clinical side here. So congrats on that. Just got to get back to the chronic nonclinical tox here. Have you seen any signs of drug accumulation specifically relative to a GalNAc conjugate? I 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 GalNAc, just given you've got so much history with the GalNAc conjugates here?

Yes. Thanks, Myles. So -- and thanks also congratulations noting these rather important data. With respect to the chronic tox findings and drug levels, we -- I don't have the data for the drug levels to hand in the relevant tissues. 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.

Yes, yes. 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're seeing single relatively low doses in humans given the 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 multi-dose studies like Part B will be significantly lower than the kind of dosing regimens that were used 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 answer the question.

And our next question comes from the line of Konstantinos Biliouris with BMO Capital Markets.

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 those? And the second one, can you disclose how long post dosing, you saw this adverse reaction in nonhuman primates because our recent discussion with KOLs, said -- the recent discussions say that the 6 to 12 months post dosing are very important for adverse events.

Thanks, Konstantinos. 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 timing and the kind of findings that -- we're not going to get into that here. I would emphasize, however, in the human setting, the rather and perhaps that ultimately is the species that matters in these sorts of things. But in the humans, the safety data are quite encouraging. As we've discussed today, the adverse events were marked moderate. All patients are retained on the study. We've had the green light for further multi dosing in Canada and all the safety biomarkers that Pushkal discussed, such us white cells, protein and the data we have on NfL are all supportive of the clinical observations. And this is out to multiple months of target suppression. So that really encourages us about the ultimate species, which is the human. Thank you.

And our next question comes from the line of Mani Foroohar with SVB Securities.

This is Jenny on 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 like different platforms or constructs that you consider in the U.S. versus OUS? Or would you go back to the drawing board across all geographies?

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 nonclinical 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.

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 potentially means for the future for 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, and you may now disconnect.