Thank you. All right. Good afternoon, everyone. Thank you very much for joining us here for this afternoon session with Enanta Pharmaceuticals, Inc. and a fireside chat with President and Chief Executive Officer Jay R. Luly and Chief Product Strategy Officer Tara L. Kieffer. Jay, Tara, thanks very much for joining us. Jay, do you mind just, you know, providing an overview of Enanta?
Sure. Let me pull up the slides here. Before I begin, I want to remind you that I'll be making some forward-looking statements, and for a summary of the risks associated with these statements, please see our filings on sec.gov and on our website. Enanta, for those of you who are less familiar, has deep roots in virology. We began working in hepatitis C very early on and helped bring forward two products to market with our partner AbbVie. We discovered the protease inhibitors into the HCV combos that were sold sequentially as Viekira Pak and then ultimately MAVYRET, which is on the market today and is the only eight-week cure for both acute and chronic hepatitis C and the only eight-week cure for any hep C patient. With that, we moved into liver viruses.
We expanded into human respiratory viruses before the pandemic, and we became quite interested in respiratory syncytial virus, where there are currently very recently some vaccines that have come to market and monoclonal antibodies that are used prophylactically, but there are no approved therapeutics for RSV. We recognize that as a very large opportunity, not only for the pediatric population, but for the adult population. We have multiple different programs going on there. Our first program and most advanced is a drug called Zelekapivir. It's been through several different clinical trials, most recently having finished a pediatric trial in children aged 28 days to three years. We reported that late last year, and we're on the cusp of reporting later this month on the high-risk adult study, which we'll spend a few minutes talking about. Behind that, we have an L-protein inhibitor.
The L-protein is another replication inhibitor mechanism that is the viral polymerase. We have a non-nucleoside RSV inhibitor called EDP-323 that successfully completed a challenge study, providing some of the best challenge study data ever generated in that model. We have two assets in RSV moving ahead, both with phase 2 data and a data set in high-risk adults, again coming soon. The pandemic broke out. We had the experience in protease and other replication mechanisms, and we discovered and developed a molecule to phase 2 called EDP-235, which someday, you know, may result in a partnership down the line when people have a clearer path on the regulatory pathway to get a COVID-19 drug approved today. And then, having sort of mined liver viruses and respiratory viruses fairly completely, we turned our attention to immunology where we have two new programs.
One is in KIT inhibition, which is going after mast cell disease. The other is STAT6 inhibition, which is targeting a small molecule that could be a so-called oral Dupixent. Later this year, we expect to announce a third immunology program. Let's turn our attention to the high-risk adult study. This is, again, the data set that's coming. We targeted about 180 patients. We actually recruited a bit over that, 186. The high-risk adult population is defined as people who are 65 years of age or older, people who have asthma, congestive heart failure, or COPD. Having looked at that set, though, we defined it even further to enhance the high-risk nature of that patient population by capping the patient numbers for people who were 65 to 74 years of age. If they're otherwise healthy, they're at higher risk, but they're not at the highest of risk.
We enhanced the trial to be people 75 and older. We did the same with asthmatics. If you were otherwise, well, you know, sort of well-treated asthmatic, you're at higher risk, but maybe not at the highest risk if your asthma is well managed. The trial is really concentrated then on 80% of the study as people with COPD, congestive heart failure, or 75 years of age and older. You dose for five days, and then there's a follow-up period. A couple of other key things: one is that we are targeting to get the drug into patients at a reasonable, as reasonable as possible after symptom onset. We define that inclusion criteria at 72 hours. The idea, of course, is just treating earlier is always better. The objective, we're going to use a symptom endpoint.
We'll have symptom data on all the patients using an already established symptom tool called RIIQ. This is a patient-reported outcome tool. You can see the symptoms that we'll be cataloging. We'll have a number of other secondary measures in the study as well so that we can capture as much data as possible to help inform the best registration study we can. One might ask, what sort of time to symptom resolution improvement are you looking for? The answer is we're looking for something that would be clinically meaningful. For that definition, we've looked to earlier examples where acute respiratory virus drugs have been approved based on symptom endpoints and registration studies. What you can see on the left-hand side of this slide is influenza, and the right-hand side is SARS-CoV-2. If you drill down on influenza, you can see also Tamiflu, which is Tamiflu.
In the middle of the slide is baloxavir. That's Shionogi Xofluza. On the right-hand side is ensitrelvir, which is a SARS-CoV-2 protease that was approved on the basis of symptom endpoints in Japan. What's striking is you can see, regardless of the virus or regardless of the mechanism used to go after the virus, the shortening of duration of symptoms was about a day. You have in each instance about a day reduction in the time to resolution of symptoms. That was viewed to be clinically meaningful and ultimately led to the registration of these drugs. At the very bottom, you can see the N on these registration studies. Apart from the meta-analysis, which groups a whole bunch of studies, you can see that the registration studies were in the ballpark of 500 to almost 700 patients, sort of in that range. What are our expectations?
On this slide, our study is not quite as big as those registration studies. This is a proof of concept phase 2 study, but we have about 186 patients. We're aiming to have a symptom duration improvement of at least a day. We're also looking, as I mentioned, at a number of other endpoints that will be cataloged, looking at virology and other kinds of endpoints. In its totality, we would gain confidence to then move to a registration study, which again would be powered to show that, in a statistically significant improvement of about a day in a study that would roughly be in that 500 to 700 patient range. That's the study in a nutshell. We're tracking to report data later this month. Shifting gears briefly to our immunology program, we have two programs actually in immunology that we've announced.
The first was announced early last year and is going after mast cell-mediated diseases, things like chronic spontaneous urticaria, for example. We have selected a development candidate. It's a very potent molecule. It's potent both in vitro and in vivo. We've looked at it in terms of selectivity, high degree of selectivity for KIT versus other kinases, and have generated some very strong in vivo data. We like our program here. This year was about building up clinical trial supply and performing IND-enabling studies to get into the clinic as early as possible next year. Then shifting gears to STAT6, we're going after an oral Dupixent type of a molecule here. I mean, Dupixent is well validated in the commercial landscape. It's approved in many different indications. It goes through a signaling pathway that involves STAT6.
We think this is a highly targeted and selective approach to a small molecule opportunity. Once again, we do what we like to do. We make molecules that are highly selective for the target of interest, that are very potent in vitro and in vivo, have good DMPK properties. We'll be planning to announce later in the year a development candidate going after this really important target. With that, I'll just wrap up. In immunology, the catalyst is doing the IND-enabling work and basically to scale up to get our KIT molecule into the clinic as early next year as possible. STAT6, select the development candidate and start pushing that one toward the clinic. We also plan to announce a third immunology program that we've been working on and building up chemical matter and other things, so stay tuned on that front.
In virology, the big catalyst for us in virology is the high-risk data. Our plan is ultimately to, on the basis of having pediatric data, having high-risk adult data, both for Zelekapivir, and also some very nice challenge study data on EDP-323, is to explore BD opportunities to help team up and get these drugs to the first in market opportunity as quickly as we can. With that, I'll pause and we'll go into Q and A. Thank you.
Fantastic. Thanks very much, Jay. I guess just given that we are in September, I think there's no surprises in sort of where I'm going to start here. Thank you for the overview. You know, it's obviously a tremendously broad platform you have with a lot of very interesting programs going on. That said, I'm going to focus a lot on Zelekapivir. You put that slide up that's very helpful about the one-day symptom reduction. Can you maybe just talk about the confidence or the interactions you may have that influenza and COVID-19 translates across to respiratory syncytial virus in terms of a regulatory pathway? Wrapped up in that, how do we think about the totality of data in terms of your internal hurdle rate versus just seeing that one-day symptom reduction?
Sure. Yeah, absolutely. I think in terms of a regulatory path, that's been fairly clear in the other acute respiratory indications you mentioned. Tamiflu, Xofluza, both approved on reducing symptom duration, as well as ensitrelvir in Japan was approved for COVID-19 based on that symptom data, again, of about a day reduction. I think that would be the primary path forward. In the case of the adult population, we would be looking at using that tool that Jay mentioned, the RIIQ tool that's being used in this study. Once we get a sense of the treatment effect in this phase 2 proof of concept, that would then enable us to design and power a phase 3 study to show that with statistical significance.
To your question about kind of that primary endpoint where we're really looking at lower respiratory tract symptoms, we have a whole host of other secondary outcomes that we'll look at as well. Upper respiratory, lower respiratory, systemic symptoms like fatigue, fever. We also have predefined subsets of symptoms that we'll look at, as well as virology, of course, and things like antibiotic use, bronchodilator use, corticosteroids. It's really going to be that full data package that will give us confidence and conviction for moving forward into a larger phase 3 study.
Okay. Maybe using those analogs where we've seen the one-day reduction, how well has phase 2 translated into phase 3 in those indications in the past? How should we think about the translatability of phase 2 being replicated in a larger phase 3 study in that 500 to 700 patient range?
I think, you know, we would look to be able to just understand the treatment effect here and then translate that into a phase 3 by powering it around that. Obviously, with some variability in those numbers, but really being able to understand well what endpoints we can use and what, you know, powering design we'll need for the phase 3.
Okay. Maybe just sort of touching on safety, any off-target effects here we should, or any adverse events we should keep an eye out on when we see the data?
Zelekapivir has been in over 500 patients at this point, and very good safety profile similar to placebo. So well tolerated, good safety profile.
Which is really also important in peds, obviously. I think the peds market opportunity is sizable in RSV. Having gone in, done a pediatric study, and again, dose children down to very, very young age, done so safely, done so with good exposures and good antiviral effects, it's very, very helpful.
Okay. Fantastic. Jay, I remember the last slide at the bottom there, right? You highlighted the business development potential and sort of, I think it was partnering on Zelekapivir and/or 323. Tara, you just mentioned designing a phase 3 trial, right? Can you talk about if we see positive data here, what is your path forward or approach here? Is it a dual approach in terms of move forward as if you're going to run a phase 3, consider partnering at this stage, or run the phase 3 and then look for a partner?
I think, you know, we've been doing a lot on the pathway to enabling these next studies, not only the registration side of Zelekapivir, but also the next study for EDP-323 so that, you know, ideally it would be turnkey. I think I lost my microphone here. Ideally it would be turnkey enablement. We'll get the data and we'll do our exploration in terms of potential deal opportunities. Again, I think our plan A is to explore those different opportunities right now. It's a question of really being able to get out there, ideally with a partner who shares the vision of wanting to have the first ever therapeutic for this important virus. People have been working on this since the virus was basically first characterized back in 1956.
The chance to have a first-to-market opportunity with Zelekapivir, maybe a follow-on strategy with EDP-323, would be compelling, but we would have to make sure we saw the right sort of deal.
Fantastic. I'm just going to change gears here. Maybe just other things to watch out for in the second half of the year. You've got the STAT6 development candidate. Can you just help us think about sort of the gating factors from your side until you sort of let it be known to us what that is?
We have a little bit of work to finish up. The scientists at Enanta have done a wonderful job in terms of interrogating that target, honing selectivity, going through lots of different series of chemical matter, and building, I think, a very strong intellectual property portfolio. I think it's picking the final finalist amongst many good choices in our pipeline there. I think it's a question of when do you stop apple polishing and you pick it and move. We're at that final stage right now.
Fantastic. I think, isn't it apple picking season anyway? I have maybe just one more, just on this sort of third immunology program there. I'm sure I've asked you before, I'm sure a lot of people have asked you this, but how do you think about what that may be, the synergies with the current pipeline, the alignment with the current pipeline, any insights you can give at this stage or willing to give at this stage, or should we just be patient?
I think what I can say is, you know, we'd like targets where there's really good and well-understood biology, understood disease pathology, and where there's a straightforward clinical path and a large unmet need for these populations.
Fantastic. We are out of time, so I appreciate it from both of you, but best of luck with the Zelekapivir readout. I think, as you mentioned, it's a tremendous development to get to this stage in RSV when so many have tried. Best of luck for that. Hopefully it's positive and hopefully we'll be speaking soon to sort of ask you more questions about it.
Great. Thank you very much.