Prothena - Q4 2025

Transcript

Operator (participant)

Thank you for your patience. Prothena Biosciences fourth quarter and full year 2025 financial results call will begin in approximately five minutes. Again, thank you for standing by. Good day, ladies and gentlemen, and welcome to the Prothena Biosciences fourth quarter and full year 2025 financial results conference call. My name is Jeannie, and I will be your coordinator for today. At this time, all participants are in a listen-only mode. We will be facilitating a question-and-answer session at the end of today's call. If at any time during the call you require assistance, please press star followed by zero, and a coordinator will be happy to assist you. I would now like to turn the presentation over to Mark Johnson, Vice President and Head of Investor Relations at Prothena. Please proceed.

Mark Johnson (VP and Head of Investor Relations)

Thank you, operator. Good afternoon, everyone, and welcome to today's call to review Prothena's business progress, fourth quarter and full year 2025 financial results, and 2026 financial guidance. Please review the press release we issued earlier today, which is available on our website at prothena.com, and it's also attached to a Form 8-K filed today with the SEC. In addition, we are using supplemental slides, which are available on our investors website, Events and Presentations section. On today's call, Dr. Gene Kinney, our President and Executive Officer, will provide opening remarks, including an overview on Prothena's corporate strategy. Chad Swanson, our Chief Development Officer, will provide an update on our ongoing partnered clinical programs. Then Phil Dolan, our Vice President and Head of Discovery Research, will provide an update on our active preclinical programs.

Tran Nguyen, our Chief Strategy Officer and Chief Financial Officer, will then discuss our 2025 financial results and 2026 financial guidance before turning it back to Gene for closing remarks, at which point we will open up the call for a Q&A session. Brandon Smith, our Chief Operating Officer, will also be available during the Q&A session. Before we begin, I would like to remind you that during today's presentation, we will be making forward-looking statements that are subject to certain risks, uncertainties, and other factors that could cause actual results to differ materially from those referred to in any of the forward-looking statements.

For a discussion of these risks and uncertainties associated with our forward-looking statements, please see our press release issued today, as well as our most recent filings with the SEC and our annual report on Form 10-K to be filed with the SEC for our fiscal year 2025. We disclaim any obligation to update our forward-looking statement. With that, I'd like to turn the call over to Gene.

Gene Kinney (President and CEO)

Thank you, Mark, and thank you all for joining us today. Let's begin on slide five. In 2025, we saw significant progress with our clinical pipeline, where two of our partner programs, prasinezumab and coramitug, advanced into phase III clinical trials. Roche advanced prasinezumab into the phase III PARAISO trial, evaluating 900 participants with early Parkinson's disease. This decision was informed by results from two phase II clinical trials that both demonstrated consistent slowing of disease progression. Novo Nordisk advanced coramitug into the phase III CLEOPATRA trial, evaluating 1,280 patients with amyloid transthyretin cardiomyopathy, or ATTR-CM. This decision was informed by results from their phase II trial, demonstrating positive NT-proBNP and echocardiogram changes, as well as directional observation of benefit in the six-minute walk test.

Our collaborations with Bristol Myers Squibb also progressed in 2025, with several important advancements, including the phase II TargetTau-1 clinical trial, evaluating BMS-986446 in early Alzheimer's disease, which was fully enrolled in 2025, with completion expected in the first half of 2027. Bristol Myers Squibb also completed a phase I study evaluating a subcutaneous formulation of BMS-986446 in 2025, and BMS-986446 obtained Fast Track designation from the U.S. FDA for the treatment of Alzheimer's disease. Finally, we are conducting a phase I trial for PRX-019, which is on track for completion in 2026. We also shared important updates from our wholly-owned preclinical portfolio in 2025.

In the fourth quarter, we introduced our CYTOPE technology with presentations of our TDP-43 CYTOPE program for ALS at two scientific congresses. At a high level, these data demonstrated that our CYTOPE technology has the potential to enable precise targeting of intracellular disease pathways. We also reported results from our phase I ASCENT clinical program, evaluating PRX-012 in patients with early Alzheimer's disease. The results helped to elucidate the profile of this once-monthly subcutaneous anti-Aβ antibody. Based on significant scientific advances over the last several years, we believe we can further improve this profile with the addition of transferrin receptor technology and are actively advancing a PRX-012-TfR program in preclinical development. Turning to slide six, we have several key 2026 priorities that we believe meaningfully contribute to long-term value creation.

The first is to ensure we are best positioned to capture value embedded in our clinical partnerships. As a reminder, all of our partnerships with large pharma companies are programs that originated from Prothena's R&D engine. This year, we have the potential to earn up to $105 million in aggregate clinical milestone payments if coramitug achieves a pre-specified enrollment target in its ongoing phase III trial and if BMS decides to advance PRX-019 into phase II clinical development. In addition, we have now received all the necessary approvals from our extraordinary general meeting of shareholders and confirmed by the Irish High Court to support a share redemption program in 2026. Finally, we continue to advance our knowledge and understanding of our preclinical portfolio to support our business development team as they explore research collaborations and licensing agreements.

For example, we're engaged in a research collaboration with a large pharmaceutical company that explores multiple approaches for applying our CYTOPE technology to advance and elucidate intracellular targeting. We look forward to establishing additional research collaborations, which may lead to future licensing deals. Our strategic priorities are supported by our $308.4 million cash and restricted cash balance as of year-end 2025, and our prudent capital utilization to ensure that we are well positioned to receive future potential economics from our partner programs. Let's move to slide seven to review our upcoming catalysts from our partner portfolio. Looking ahead, we have two potential milestones in 2026 from coramitug and PRX-019, which could be worth up to $105 million.

In the first half of 2027, we expect Bristol Myers Squibb to complete their phase II TargetTau-1 trial for BMS-986446. In 2029, we expect primary completion from the two phase III trials evaluating Roche's prasinezumab and Novo Nordisk's coramitug. In total, when you look at our four partner clinical programs, they have the potential in aggregate to deliver up to approximately $3 billion in future milestone payments, which is in addition to any royalties. With that, I'll now turn the call over to Chad to discuss our partner programs in more detail.

Chad Swanson (Chief Development Officer)

Thanks, Gene. Let's start on slide nine. Prasinezumab is a humanized IgG1 monoclonal antibody designed to selectively bind aggregated forms of alpha-synuclein to reduce neurotoxicity and slow disease progression of Parkinson's disease by blocking further accumulation and propagation of these toxic aggregates.

Based on the consistent results from two phase II clinical trials, PADOVA and PASADENA, and our open-label extension, our partner, Roche, made the decision to advance prasinezumab to phase III, bringing this potential first disease-modifying therapy one step closer to patients. In fact, Roche made this decision based on a number of important questions. First, is there an unmet need? Yes, there are over 10 million Parkinson's patients globally, and it is the fastest growing neurodegenerative disease with no approved disease-modifying therapies to slow progression. Second, does it address a foundational target? Yes. Alpha-synuclein is a known biological driver of PD progression, and the clinical evidence demonstrates efficacy potential and supports a favorable safety and tolerability profile. Third, is there a meaningful therapeutic differentiation? Yes. The totality of data suggests clear evidence, delayed motor progression, even on top of the standard symptomatic treatment, levodopa.

Finally, is there a strong commercial rationale? Yes, Roche believes prasinezumab represents a global peak sales opportunity greater than $3.5 billion. For Prothena, our deal includes up to $620 million in potential future milestone payments and sales royalties tiered to high teen percentages. In the fourth quarter of 2025, Roche initiated the phase III PARAISO clinical trial, which will enroll approximately 900 participants with early Parkinson's disease, with primary completion expected in 2029. Moving on to slide 10. This is an important data set from phase II-B PADOVA trial, which Roche presented at ADPD 2025. Here they show progression on the MDS-UPDRS part three scale from baseline, which is used to measure disease progression on motor symptoms. This figure shows the results for an exploratory endpoint, looking at the subset of participants.

Approximately 75% of the trial population were on stable levodopa treatment, comparing 24 months of prasinezumab treatment versus placebo. What we see is a 40% relative reduction in progression, with a nominal P-value of 0.0177 on this exploratory endpoint. These were very important results as they were used to further optimize aspects of the phase III PARAISO trial design. On slide 11, let's review key aspects of the phase III protocol that were optimized to increase the relative probability of successful outcome. First, increased patient population. The phase III trial is evaluating 900 patients, whereas the phase II-B PADOVA trial enrolled 586 patients. Second, all patients in the phase III trial are required to be on stable symptomatic treatment with levodopa.

In the phase II-B PADOVA trial, approximately 75% of patients on levodopa treatment were nominally statistically significant on the primary outcome and exploratory endpoint shown on the previous slide. Third, the duration of the phase III trial is a minimum of 24 months versus 18 months in the phase II-B PADOVA trial. In the PADOVA trial, the patients who are on treatment for at least 24 months had greater separation from placebo on the exploratory endpoint shown on the previous slide. We believe Roche will continue to communicate clinical results from its completed phase II trials and ongoing open-label extensions at upcoming medical conferences. We look forward to the primary completion of the phase III PARAISO trial expected in 2029. Moving to coramitug on slide 12, potential first-in-class amyloid depleter antibody for the treatment of ATTR cardiomyopathy being developed by Novo Nordisk.

ATTR-CM is a rare, progressive, and potentially fatal disease characterized by deposition of abnormal, non-native forms of transthyretin amyloid in vital organs. Coramitug is thought to deplete both the positive amyloid and circulating non-native TTR to prevent further deposition and to improve organ function. This mechanism of action has the potential to provide benefit for all ATTR-CM patients, even those patients currently receiving treatment with a stabilizer or silencer. Novo Nordisk completed its phase II clinical trial, evaluating coramitug in ATTR-CM in 2025, and presented those positive results in a late-breaking session at the American Heart Association's 2025 Scientific Sessions, with a simultaneous publication in the journal Circulation. The results demonstrated reductions in NT-proBNP and echocardiogram improvements suggested a cardiac remodel, all with a favorable safety profile.

It's important to note that these results were demonstrated on top of standard of care, with over 80% of patients across coramitug and placebo control arms receiving concomitant TTR stabilizers. Based on these results, Novo Nordisk initiated a phase III CLEOPATRA trial, which is intended to enroll approximately 1,280 ATTR-CM patients, primary completion expected in 2029. Based on peak sales estimates for the currently approved ATTR-CM drugs, we believe that coramitug represents a multi-billion dollar market opportunity, allowing Prothena to potentially capture future milestone payments of up to an additional $1.13 billion. Let's review the phase II results on slide 13. This was a 12-month, 105 patient phase II trial, randomized to placebo, 10 mg/kg coramitug, or 60 mg/kg coramitug.

The co-primary endpoints were changed from baseline versus placebo in NT-proBNP in the six-minute walk test. The 60 mg per kg dose of coramitug resulted in a statistically significant reduction in NT-proBNP versus placebo, with a 48% difference and a P‑value equal to 0.0017. In addition, coramitug actually reduced NT-proBNP of the low baseline values in the 60 mg/kg dose. For the six-minute walk test, the 60 mg/kg coramitug group demonstrated an encouraging numerical improvement, but it was not statistically significant, likely due to small sample size and short study duration. Additional analyses included a wide range of echocardiogram parameters, including measure of left and right ventricular systolic function, diastolic function, and estimated pulmonary arterial pressures. Across these measures, coramitug at 60 mg/kg was associated with improvement compared to placebo, suggested a cardiac remodeling.

These results were the basis for advancing coramitug to phase III. As we see in slide 14, the phase III CLEOPATRA trial is anticipated to enroll approximately 1,280 ATTR-CM patients, randomized 1:1 to coramitug of standard of care, placebo of standard of care. The trial is available to New York Heart Association class one through four patients, with some additional inclusion/exclusion criteria. The primary endpoint is a composite endpoint of either the number of cardiovascular deaths or recurrent cardiovascular events, such as hospitalization or an urgent heart failure visit. We look forward to the primary completion of the phase III CLEOPATRA trial, expected in 2029. Moving on. Let's now discuss BMS-986446 in slide 15. This is our potential first-in-class anti-tau antibody being developed by Bristol Myers Squibb.

BMS-986446 was specifically designed to target a key epitope within the microtubule binding region or MTBR of tau protein implicated in the causal pathophysiology of Alzheimer's. Tau tangles, along with amyloid beta plaques, are core hallmarks of Alzheimer's pathology, and tau is strongly linked to clinical and cognitive decline. To date, BMS-986446 has completed its phase I MAD in cells, as well as an open-label, single-dose trial to assess the subcutaneous formulation. In addition, BMS-986446 was granted Fast Track designation by the U.S. FDA for the treatment of Alzheimer's. Bristol Myers Squibb completed enrollment in the ongoing phase II TargetTau-1 clinical trial in approximately 310 patients with early Alzheimer's in 2025, and we expect study completion in the first half of 2027.

Alzheimer's disease represents a multi-billion dollar market opportunity, and in our partnership with BMS, we have the potential to earn up to an additional $562.5 million future milestones, as well as tiered sales royalties up to high teens percentages on a weighted average basis. Slide 16 illustrates the various areas where antibodies have been developed to target tau. Tau is a large protein comprised of approximately 440 amino acids in some forms, with multiple phosphorylation sites, truncation sites, and multiple splice variants. One of the long-standing challenges in the field has been how to best target the tau protein in order to provide functional benefit in the context of disease. We took an approach called empirical epitope mapping in order to identify an antibody that delivered consistent, robust effects.

This work led us to target the MTBR domain, which was the only area that satisfied our internal requirements. The field has since clarified that MTBR domain is central to fiber formation, seeding, and cell-to-cell transmission of tau pathology. MTBR-tau 243 has been shown to be highly correlated tau PET and disease progression. In preclinical studies, MTBR targeting antibodies demonstrated blocking of internalization and spread of tau, leading to the reduction of tau pathology. Ongoing phase II clinical trials, including the phase II TargetTau-1 trial for our partner, BMS, are underway. A different anti-MTBR-tau antibody recently demonstrated positive trends on biomarkers, including MTBR-tau 243 and tau PET in a small number of patients.

Slide 17 highlights the phase II TargetTau-1 trial design, which enrolls approximately 310 patients with early Alzheimer's disease, randomized four to three, three in placebo, low-dose BMS-986446, and high-dose BMS-986446, respectively. The primary endpoint is change from baseline in brain tau deposition, measured by tau PET at 76 weeks, with secondary endpoints measuring functional and cognitive changes, including CDR sum of boxes and iADRS. We are excited to learn the results from the phase II trial, with primary completion expected in the first half of 2027.

Finally, I'll briefly review PRX-019 on slide 18. Per our agreement with Bristol Myers Squibb, we are conducting the phase I trial, both single ascending and multiple doses, evaluating safety, tolerability, immunogenicity, PK, and pharmacodynamic effects. We expect to complete the trial in 2026 and are eligible for a potential milestone should BMS decide to further develop PRX-019. In total, we have the potential to earn up to $617.5 million in future milestones, tiered sales royalties up to high teens percentage. With that, I'll now turn the call over to Phil Dolan to discuss our wholly owned preclinical portfolio.

Phil Dolan (VP and Head of Discovery Research)

Thanks, Chad. Please turn to slide 20 for an overview of our exciting new CYTOPE technology. Our CYTOPE technology is an innovative targeting technology invented by Prothena to reach virtually any cell type and enable precise targeting of intracellular disease pathways in the brain and periphery through an endosomal uptake and escape mechanism that preserves membrane and vesicle integrity following systemic administration. This technology potentially allows for targeting of previously undruggable intracellular disease targets. Each CYTOPE program is uniquely tailored to target a specific intracellular disease pathway and is comprised of a cell-internalizing technology, a targeting element derived from a macromolecule, such as an antibody, and may include optional elements, such as the addition of receptor-mediated technology, to enable delivery to specific cells or tissues. Our first disclosed program to utilize this technology is our TDP-43 CYTOPE program for Amyotrophic Lateral Sclerosis, or ALS. Let's discuss further on slide 21.

ALS is a progressive, fatal neurodegenerative disease characterized by the selective loss of upper and lower motor neurons, and in the majority of cases, by cytoplasmic aggregation and nuclear depletion of the RNA binding protein TDP-43. Current approved therapies used to treat ALS seek to affect disease progression by targeting broad mechanisms such as excitotoxicity and oxidative stress, rather than the core molecular pathology. These treatments do not stop or reverse motor neuron degeneration, and to date, provide limited clinical benefit. Consequently, there remains a major unmet need for disease-modifying therapies that directly address TDP-43-driven mechanisms. Using our internally discovered CYTOPE technology, we have developed an anti-phosphorylated TDP-43 CYTOPE that is designed to address the core molecular pathology associated with approximately 97% of ALS cases. Dysregulation of TDP-43 triggers both toxic gain-of-function and loss-of-function deficits in the context of disease.

The key challenge in the field has been how to effectively target intracellular phosphorylated TDP-43 aggregates, which are broadly deposited in the CNS and periphery, while preserving normal TDP-43 functions. As shown in the slide, neither conventional antibodies, small molecules, or oligonucleotides have all of the components needed to effectively target and eliminate intracellular phosphorylated TDP-43 aggregates. Enter TDP-43 CYTOPE on slide 22. TDP-43 CYTOPE was designed to specifically bind to and degrade intracellular phosphorylated TDP-43 aggregates that are central to ALS pathologies. In preclinical studies, our unique TDP-43 CYTOPE has been demonstrated to degrade phosphorylated TDP-43-associated aggregates located in the cytoplasm, addressing the toxic gain-of-function pathology. In addition, we have demonstrated that administration of our TDP-43 CYTOPE addresses the related loss-of-function pathology, potentially through restoration of TDP-43 trafficking and the function of normal TDP-43 in the nucleus.

Importantly, the unmatched targeting specificity suggests that we may effectively reduce the pathogenic phosphorylated TDP-43 aggregates while preserving normal TDP-43 activity throughout the body. Moving to slide 23, which highlights some of the key data presented at the Society for Neuroscience Congress in November of last year. On the left, we show supportive data on how TDP-43 CYTOPE addresses toxic gain-of-function by significantly reducing brain and muscle pathology in a highly aggressive ALS mouse model following systemic administration. These findings are particularly compelling, given rapid, persistent, and aggressive accumulation of pathogenic aggregates in the rNLS8 transgenic mouse model of ALS. On the right, we show supportive data demonstrating the TDP-43 CYTOPE also addresses the loss-of-function pathology. Here, TDP-43 CYTOPE attenuated RNA mis-splicing caused by cytoplasmic TDP-43 aggregation in both human neuronal cells and mice.

This is exciting data from our TDP-43 CYTOPE program and supports the potential of our CYTOPE technology more broadly. We look forward to continuing to elucidate the potential of this program and the technology. Let's move to slide 24 to provide an update on our PRX-012 transferrin receptor preclinical program, or PRX-012-TfR. Trontinemab is an anti-Aβ antibody developed from gantenerumab to also include transferrin receptor binding technology. So far, reported data indicate the addition of transferrin targeting in trontinemab has resulted in improvements over gantenerumab, including significantly decreased the time required to achieve meaningful amyloid reduction and substantially lower risk of ARIA-E associated with amyloid-targeting antibodies. Given the potential of our PRX-012 antibody, which is based in part on our demonstration of the activity of this antibody in the clinical setting, we believe the combination of transferrin receptor binding technology could be very exciting. Let's move to slide 25.

Last year, we reported interim results from the PRX-012 ASCENT phase I clinical program, including a mean reduction in amyloid PET to approximately 27.5 centiloids at month 12 for patients that received a monthly subcutaneous dose of 400 mg of PRX-012 from the start of the study. Preliminary results for patients reaching 18 months of treatment with a 400 mg dose showed a mean reduction in amyloid PET to approximately 60 centiloids, and nine of the 12 patients achieved amyloid negativity, defined as having a centiloid value less than 24.1.

But as we reported in August, the ARIA-E rates for PRX-012 were non-competitive relative to FDA-approved anti-Aβ antibodies. Based on these collective results, we believe a PRX-012-TfR approach is appropriate for further development. It is our desire to improve over PRX-012 while maintaining a convenient once-monthly subcutaneous administration. Currently, we are exploring partnership interest for PRX-012-TfR while advancing the program preclinically. With that, I'll turn it over to Tran to review our financial results.

Tran Nguyen (Chief Strategy Officer and CFO)

Thanks, Phil. Please turn to slide 27. Today, we reported financial results that were in line or favorable to our 2025 financial guidance. Please refer to our press release for a detailed breakdown of our financial results. In terms of our 2025 financial performance relative to guidance, we had net cash used in operating and investing activity of $163.7 million, which was favorable to our guidance range of $170 million-$178 million. Net loss was $244.1 million, which was in line with our guidance range of $240 million-$248 million.

As of December 31st, 2025, Prothena had $308.4 million in cash, cash equivalents, and restricted cash, which was favorable to our guidance of $298 million. As of February 12th, 2026, Prothena had 53.8 million ordinary shares outstanding. Additionally, we continue to have a simple capital structure with zero debt. Turning to our 2026 financial guidance on slide 28, we expect our full year 2026 net cash used in operating and investing activities to be between $50 million-$55 million. We expect to end the year with approximately $255 million in cash, cash equivalents, and restricted cash, which represents the midpoint of the range.

The estimated full year 2026 net cash used in operating and investing activities is primarily driven by an estimated net loss of $67 million-$72 million, which includes an estimated $24 million of non-cash share-based compensation expense. And as a reminder, our 2026 financial guidance does not include the up to $105 million of potential aggregate clinical milestone payments from strategic partners in 2026 related to the advancement of both coramitug for ATTR amyloidosis with cardiomyopathy by Novo Nordisk, and PRX-019 for neurodegenerative diseases by Bristol Myers Squibb. With that, I'll turn the call back to Gene for closing remarks.

Gene Kinney (President and CEO)

Thank you, Tran. Moving to slide 30. As we've shared today, we have a robust pipeline of programs that address significant unmet needs for potentially millions of patients, caregivers, and their families. It is our mission to continue to further develop our programs and elucidate the potential of our technology to address these needs. Let me end by recapping our 2026 strategic priorities, which are to capture the value embedded in our clinical partnerships, including up to $105 million in clinical milestones in 2026.

To implement a share redemption program and invest in our preclinical portfolio to support our ongoing partnering efforts in the form of research collaborations, especially on our CYTOPE technology, and drive future partnerships for our unpartnered programs. I'm proud of Prothena's execution and resilience in 2025, setting us up for an exciting future. We're well-capitalized with a robust cash position and remain focused on delivering long-term shareholder value by delivering on our mission to patients. With that, we will now open the call to Q&A. Operator?

Operator (participant)

Ladies and gentlemen, if you wish to ask a question, please press star followed by one on your touch-tone telephone. If your question has been answered, press star one again. Please limit yourself to one question. I repeat, please limit yourself to one question. Please stand by for your first question. Your first question comes from the line of Yasmeen Rahimi with Piper Sandler. Please go ahead.

Speaker 11

Hi, this is Shannon on for Yas Rahimi. Congrats on the great progress, guys, and thank you so much for taking our question. We just wanted to know, with the primary completion dates for the partnered program trials for PARAISO and CLEOPATRA not expected until 2029, could you maybe walk us through some of the key milestones to look out for in 2026 and 2027, and what those milestones might be contingent on?

Gene Kinney (President and CEO)

Yeah, thanks for the question, Shannon. So as we kind of laid out, we have a lot of things happening this year into next year, and for the next several years. So I think as we look to some of our emerging technologies, some of the CYTOPE activities that we talked about on the call, we certainly expect to share more of that information this year through scientific presentations, in particular around our TDP-43 CYTOPE program, and obviously the progress we're making there. We talked about in 2027, in the first half of 2027, starting to see the data coming from our partner's tau program with Bristol Myers Squibb.

So we think that phase II program would be very interesting, as it was outlined by Chad on the call. Clearly, the primary outcome measure there is tau PET. So, you know, we think this is gonna be a very interesting evaluation of our MTBR targeting tau approach. And then obviously, very much looking forward to the two phase III readouts with primary expected completion dates in 2029, as you outlined, for both coramitug and prasinezumab.

And clearly, as we indicated, not only do we think that those are well-positioned based on the phase II results to be you know tested in an adequate way in the phase III studies, but also represents the potential for significant medical advance in areas with pretty pretty high unmet need and also I think very interesting economic opportunities with respect to the commercial opportunity there. But so yeah. So I think it's actually gonna be a very busy time for us.

And the only other thing I would mention here, and maybe Tran if you want to speak to it further, as we look forward to instituting our share redemption program this year as well. So that's something that we needed to get approval for in an EGM, which took place at the end of last year. We needed Irish High Court approval for that. You know, I think this year we expect to implement that.

Tran Nguyen (Chief Strategy Officer and CFO)

Yeah, and we'll make further announcements with that closer to the filing of our 10-K. But that also being said, to repeat that this year we'll also have, you know, potentially up to $105 million worth of clinical milestones from our partners, which Gene covered in our prepared remarks from the coramitug and PRX-019. So exciting 2026 in view.

Speaker 11

Great, thank you so much.

Operator (participant)

Your next question comes from the line of Michael DiFiore with Evercore ISI. Please go ahead.

Michael DiFiore (Director and Equity Research Analyst)

Hey, guys. Thanks so much for taking my question. One on PRX-012, if you could just elaborate how you will try to keep the amyloid beta story alive versus much larger, more advanced competitors? And as a relative follow-up, there are many transferrin receptor tech platforms out there. Maybe you could describe what the ideal transferrin receptor platform would offer that would make one stand apart. Thank you.

Gene Kinney (President and CEO)

Yeah. So thank you for the question. You broke up a little bit, but I think I got most of it, and maybe I can, I'll ask Brandon to jump in just with respect to the BD space a little bit here. But just to answer the question, first in terms of why we're excited about our PRX-012 transferrin-based approach, you know, look, there are two elements to these types of molecules, right? And I think, you know, a lot of what we've learned about this space and the potential of adding transferrin technology or receptor technology to anti-beta antibodies comes from the gantenerumab/trontinemab approach.

You know, and there, I think we had a good understanding of what the activity rate on both, you know, the amyloid removal side, as well as the ARIA-E side for, again, trontinemab was, and then adding a transferrin receptor-based approach, that, you know, had certain characteristics to it. This is the Roche approach. I think, you know, gave us the results in trontinemab that we can directly compare to gantenerumab. You know, what we think we have here with PRX-012 is we've described now data for the parent molecule, PRX-012, and with a once monthly subcutaneous presentation, you know, showing what we think are very interesting and impressive results in terms of amyloid removal.

So, you know, at a flat dose, once a month subcutaneous administration, seeing the majority of patients be amyloid negative, seeing the average centiloid value being quite low, you know, we think positions us in a way that we can say this is a very convenient and very robust antibody with respect to amyloid removal. You know, what we thought was a little less competitive in those results were some of the ARIA-E rates.

And so here with this technology, provided that, you know, we follow the path with respect to transferrin, that, you know, others have seen success with, à la gantenerumab and trontinemab, that we have the opportunity to take advantage of that emerging biology and, you know, potentially see an improvement in the overall profile of PRX-012 with the PRX-012 transferrin program. So we're excited about that. We think that's something that we can move forward relatively quickly, and get a pretty definitive answer, you know, very early in phase I clinical testing, given that we know the characteristics of the parent PRX-012 so well. As you say, there's been a lot of interest in this space with respect to licensing, and we think that's a good thing.

You know, we're certainly happy to see that the momentum is not only continuing, but I think continuing to build around these types of approaches, which have the potential to decrease some of the AE profile limitations of the anti-beta antibodies, and potentially increase the primary mechanism of action, which is removal of amyloid. But maybe, Brandon, you can speak a little bit more to just some of the dynamics of what's happening in the business development space, particularly in this class.

Brandon Smith (COO)

Yeah, I appreciate that, Gene, so and appreciate the question. So, from the market's perspective, there is clearly a high level of interest for the approach that we're taking. And what we're building off of relative to what gantenerumab saw when they added transferrin and turned it into trontinemab, we think we're uniquely suited to build upon that story. And the market has begun to recognize that, and our dialogues are active. Probably the best I could say about the BD dialogue. What's really interesting about the space, though, is also the opportunity potentially to grow.

And what we're following very closely is that profile that Gene described, which is once a month subcu, leveraging a better ARIA profile that we expect to see and hope to see coming with the addition of transferrin, is uniquely suited for where the market is headed, not just early Alzheimer's disease, which we think we have a unique capability there, but really around the presymptomatic space. We're looking forward to what the field is seeing in the presymptomatic space. We expect readouts this year, and that opens up a unique opportunity for us because we are a paradigm that is much less frequent, much less cumbersome, and we're talking about those presymptomatic patients. That's exactly what they need.

They need something that is uniquely set up for them, something that is not cumbersome, and it potentially helps prevent the progression. That's recognized in the field and something that is very interesting. Obviously, we're also very interested in the data that we're generating internally to help build upon that program. We hope to talk about that, of course, this year, internally with you and with our potential partner.

Operator (participant)

Your next question comes from the line of Eric Schmidt with Cantor Fitzgerald. Please go ahead.

Alexa Deemer (Biotechnology Equity Research Associate)

Hi, guys. This is Alexa Deemer on for Eric. Congrats on the great year. So for the phase I study of PRX-019, which is expected to complete this year, do you plan to share data from the study this year, and what do you want to see for this program to advance? Thank you.

Gene Kinney (President and CEO)

Yeah, it's a great question. Thank you for the question. So with PRX-019, that is a program that we have a partnership with Bristol Myers Squibb on. We have not, for strategic reasons, talked about the target of that yet, except to say that it's broadly applicable to neurodegeneration. I think as Chad mentioned in his comments, that phase I study is being conducted by us. We expect that to complete this year. And what we would then do is share that information with our partners at Bristol Myers Squibb.

I think you heard, you know, both Tran earlier say, and I, I said in my remarks as well, that the potential to achieve up to $105 million this year through partnership programs, some of that is tied to decisions made around PRX-019. So what we expect is that we'll share that information with Bristol Myers Squibb. At the end of the day, it will be up to them to decide what and how much of that information to share publicly. But obviously, we'll be talking about, we'll be talking about that a little bit later this year. And with that said, maybe, Tran, you can add-

Tran Nguyen (Chief Strategy Officer and CFO)

Yes. Just, just a reminder, they have global rights to this program.

Gene Kinney (President and CEO)

Yeah.

Tran Nguyen (Chief Strategy Officer and CFO)

They exercised it, they paid us $80 million for it, so hence the data is theirs, and it's theirs to decide on how to disseminate that. So with that being said, what we would do is, of course, announce if we've earned and they've, they've taken that molecule forward, into further clinical development, and that's when we'll earn the clinical milestone associated with PRX-019.

Alexa Deemer (Biotechnology Equity Research Associate)

Got it. Thanks so much.

Operator (participant)

Your next question comes from the line of Jason Butler with Citizens. Please go ahead.

Jason Butler (Managing Director and Senior Biotechnology Equity Research Analyst)

Hi, thanks for taking the question. Can you maybe just from a broader level, speak to how you would think about the amount of data necessary to secure a partnership for the CYTOPE platform, or ultimately, if you made the decision to advance the program into the clinic yourselves from the CYTOPE platform, what data you'd want to see, to de-risk the initial clinical development? Thank you.

Gene Kinney (President and CEO)

Yeah, thanks, thanks for the question, Jason. So, maybe I can start with a little bit of the biology here, and then Brandon can speak a little bit to just the development strategy. But, I, I think from a, from a TDP-43 perspective, the data we shared, last year, I think was interesting, both with respect to the CYTOPE technology and also to the idea of targeting TDP-43 in the context of, of ALS.

Phil covered this in some of his remarks, but I think for the CYTOPE technology, you know, one of the things you clearly saw, in particular in those animal studies, the in-vivo animal studies, in the RNLS eight mice, is you saw that with systemic administration, you know, you were not only seeing active engagement with this intracellular target in a very disease or pathological specific way, but you were seeing actually removal of that target, and in the CNS, you were seeing that as well. So that's an important context here, which is systemic administration, you're seeing robust CNS activity. So not only does this platform appear to allow us to target things in the intracellular space, but also seems to allow us to do so in the central nervous system as well.

So we think that that's a really important lesson learned from the technology. Again, as was mentioned by Phil, we're not seeing any evidence that we're disrupting endosomes or causing problems that other forms of technology that have attempted to do these sorts of things have suffered from. I think in terms of ALS, it's particularly interesting. We know 97%, again, Phil covered, so this 97% of patients have TDP-43 dysfunction as a core element of their pathology. One of the challenges in targeting TDP-43 intracellularly directly is how to target the abnormal form of these proteins while leaving the normal form to do its day job, which is essential for cells to function properly.

And so by having a very specific targeting approach, you were able to see that specificity translate into not only kind of sorting out the toxic gain of function, which is the aggregates that you see in the cytosol, but also interestingly, in vitro setting in human cell types, correcting the loss of function, which is really the mis-splicing variants or the mis-splicing dysfunction that you see in the level of the nucleus. And so that seemed to be corrected as well. So that's very exciting. Targeting an abnormal form of TDP-43, which we know leads to both a loss of function and gain of function, and seeing indications that you can address both. So we're excited by those data.

You know, we think the mouse model, which is an extraordinarily aggressive mouse model, most folks in an unchanged way, if they don't change the mouse model in some way, really struggle to see any effect here. We saw some very robust clearing of the intracellular aggregates of TDP-43. So that said, in terms of what we need to see, we think we're very excited by what these data are telling us to date. And obviously, we are interested in continuing to move that program forward. In terms of just the strategy around this program and potentially other programs within our CYTOPE technology platform, maybe, Brandon, you can speak a little bit to that.

Brandon Smith (COO)

Yeah, I'll maybe the easiest thing to do is just to note that the technology itself didn't become publicly known until November of last year. Right? And so we are, you know, with that, that was the impetus for many subsequent conversations. And what we've been finding is that there really is a very broad set of applications for this technology. And what's unique is that set of applications goes well beyond neuroscience, which is our area of expertise, and it's essentially therapeutic area agnostic. So we can cast a very wide net from a BD standpoint and solve problems that some of our potential partners are looking to solve by utilizing this technology.

One of those specifics is that, and I think we alluded this in our call, is that we're already, you know, even in the three- to four-month timeframe that we're talking about, we've established specific research collaborations, but have others in process that are very focused on learning what we've learned from our TDP-43 program and applying it to a specific targeting area of their interest, and applying it in many ways. So that application, much more broadly, is uniquely suited for this technology, and we're excited about the progress we've made. In parallel, what happens when you have those discussions is those potential partners are actually spending their time and resources to get this in their own hands. So this is new, right? This is new and very exciting to them.

We wanna make sure that what we see is what they'll also see when they apply to their targets of interest. Doing that allows us to then see for the next step, which is a partnership around a target or on a set of targets, or maybe even more broad than that. We're very excited about where we are, and a lot more to go.

Operator (participant)

Your next question comes from the line of Brian Abrahams with RBC Capital Markets. Please go ahead.

Nevin Jacob (Associate in Equity Research)

Hi, everyone. This is Nevin on for Brian. Thank you so much for taking our questions. Just a couple from us. So I guess I'm curious to know, based on some of the preclinical experiments that you've done in-house, what you think might be maybe some of the mechanistic hypothesis for why the transferrin modification ends up reducing the ARIA risk? And, I guess, on, along with that, do you expect potential lower heme toxicities with this? And then, an additional clarification question on my end. Just wanted to see if the transferrin modification to PRX-012 would still enable PRX-012 to be subcutaneously delivered or if this would be IV administered. Thanks so much.

Gene Kinney (President and CEO)

Yeah. So good questions around PRX-012. So let me start and maybe Phil, if you have anything to add, you can do so. I think first, in terms of transferrin, and how that actually sorts out some of the ARIA events, you know, there are a lot of hypotheses out there. I think the one that both Roche and Eli Lilly have put forward as the more likely mechanism is really the location of transferrin and, you know, where that is in the vascular, in the cerebral vasculature. So this idea that potentially starting to get more penetration into the brain through capillary structures relative to arterial structures, may be providing some benefit.

It makes some face validity in as much as we know that when amyloid deposits in the cerebral vasculature, it tends to do so in the larger arterial structures, particularly in the perivascular space. And so obviously, you know, moving the route of entry into the capillary system could have some advantages in that respect. And so that's one possibility. Another possibility that I think, you know, folks talk about in the field from time to time is an idea of the amount of time that the antibody may sit on amyloid in the vasculature, and potentially with the transferrin-based approach, you get a transcytosis across the blood-brain barrier, which minimizes that dwell time, if you will. And of course, it could be a combination of things as well.

But I think what it points to, and it's a good question, is that, you know, we need to make sure that the transferrin-based approach, and obviously we're taking steps to do this with PRX-012, is something that has similar characteristics to those things that we know already work. So again, I think that is a pretty small sample set to date. You know, that's the gantenerumab, trontinemab, story that we've been talking about a little bit. So clearly, we're trying to stay as close to that down the fairway approach, so that we can be sure that whatever that mechanism is, that we're taking advantage of that as well. I think in terms of, you had some other parts of that question there.

Oh, yeah, so you know, some of the subcu part of that question, we have no reason to believe that the addition of transferrin at this point would cause us to change our route of entry. We think subcutaneous is still a viable approach for PRX-012 transferrin-based moieties. We think that in fact it's the potency of PRX-012 that provides us the ability to actually have a biological effect at a lower dose level setting, which obviously gives us the opportunity to have both the pharmacokinetic as well as potency advantage. And I think that's something that you can evidence, for example, in the dataset.

We talked about the impact of PRX-012, parent PRX-012, on amyloid reduction, and how that was quite robust, particularly at the 400 mg dose level. I think you could compare that back to some of the earlier gantenerumab data, you know, which maybe was less robust by comparison. So that really speaks to the potency of PRX-012, which we have always felt was a key element in terms of making sure that that is available to a subcutaneous route of administration, and obviously, we continue to believe that to be true. I don't know, Phil or Chad, if you have a comment that you'd like to make on this?

Phil Dolan (VP and Head of Discovery Research)

I might just say one thing, Gene. So you actually touched on the potency, right? So clearly, we see pretty comparable and robust levels of reduction at 18 months with an antibody that is dosed a flat dose of 400 mg, which is significantly less, I would say, than the 10 mg/kg that's in the clinic now. Because of that, and obviously, we don't know the answer to this, but I know you had a question about heme toxicity. And because of the potency, it's possible that we could dose at lower levels and see similar effects to what trontinemab saw, for instance. If that's the case, there is potential, perhaps, to minimize risk in terms of these non-ARIA AEs, i.e., you know, anemia or others. So I think there's potential there, and we just, you know, we have to do the study.

Nevin Jacob (Associate in Equity Research)

Thank you. That's very helpful.

Operator (participant)

Thank you, everyone. That completes our question and answer session. I'll now turn it over to Gene Kinney, CEO, for closing remarks.

Gene Kinney (President and CEO)

Thank you, Operator, and I want to thank you all for joining us on the call today. We appreciate your interest in Prothena and look forward to sharing further updates on our progress.

Phil Dolan (VP and Head of Discovery Research)

Thank you for your participation in today's conference call. This concludes the presentation. You may now disconnect. Good day.