Jay Luly
Analyst · Jefferies
Thank you, Jennifer, and good afternoon, everyone. Throughout 2024, Enanta has remained squarely focused on advancing our virology and immunology pipeline to bring important oral therapeutics to market. Our commitment to developing treatments for areas of high unmet need is driven by our mission to transform patients' lives with curative therapies. And we are determined to achieve our milestones to drive near- and long-term shareholder value to fulfill this mission.
Our focus is critical as we approach meaningful inflection points with the potential to develop the first antiviral treatment for RSV. With that, today, I'll begin with an overview of our programs, beginning with our respiratory syncytial virus or RSV programs and then discuss our immunology program for chronic spontaneous urticaria or CSU.
As a reminder, RSV is a severe respiratory infection associated with significant morbidity and mortality that can cause serious disease in infants, children and other high-risk populations, including the elderly and individuals with congestive heart failure, chronic obstructive pulmonary disease, asthma or other high-risk conditions. Despite the availability of prophylactic options such as vaccines and monoclonal antibodies, there's a clear need for a safe and effective oral RSV antiviral treatment.
Adoption of vaccines has been suboptimal, and breakthrough infections still occur. Additionally, pediatric monoclonal antibodies only provide passive immunity for a few months and not long-term protection against the infection. With this clear need, we have developed a broad clinical program that has the potential to enable multiple opportunities to treat RSV.
RSV pipeline includes the most advanced clinical [ antiviral ] replication inhibitors: zelicapavir, formerly known as EDP-938, an N-protein inhibitor as well as EDP-323, an L-protein inhibitor. Zelicapavir is currently being studied in high-risk patient populations in two Phase II studies, RSVPEDs and RSVHR.
RSVPEDs is the first in pediatric's Phase II randomized, double-blind, placebo-controlled study in hospitalized and nonhospitalized RSV patients aged 28 days to 36 months. The study, which will enroll approximately 90 patients, is being conducted in two parts.
As this is a first in pediatric study, the objective of the first part is to evaluate the safety and pharmacokinetics of zelicapavir in multiple ascending doses to select the optimal dose for each age group. The second part of the study will evaluate the antiviral activity of zelicapavir at the selected dose. And virology and symptom scores will be assessed throughout the treatment duration.
This study was designed as a small proof of concept in pediatric patients to show a trend toward improved virology metrics for zelicapavir compared to placebo and to give confidence to move forward efficiently into larger registrational studies. A key objective of this study is to show improvement in virology endpoints in patients on zelicapavir compared to placebo, sufficient to allow us to advance into Phase III.
Currently, we have [ partially ] enrolled the last age cohort of 20 patients in part 2 of the study. As this cohort can only enroll patients 28 days to 6 months of age, the eligible population is narrower, and we will need to continue to recruit in the Southern Hemisphere. As we monitor the RSV season in the Southern Hemisphere, we anticipate reporting data from this study in the second half of 2024.
RSVHR is a Phase II randomized, double-blind, placebo-controlled study of approximately 180 adults with RSV infection, who are at high risk of complications, including the elderly, those with congestive heart failure, chronic obstructive pulmonary disease or asthma. The primary endpoint for RSVHR is time to resolution of RSV lower respiratory tract disease symptoms as assessed by the respiratory infection intensity and impact questionnaire symptom scale.
Secondary endpoints include additional clinical efficacy measures and antiviral activity compared to placebo, pharmacokinetics and safety of zelicapavir. The primary objective of this study is to show an improvement in time to symptom resolution.
Given the study was designed to be a small Phase II proof-of-concept study, it is powered based on a 50% reduction in symptom resolution. However, as there are no data showing a statistically significant effect on symptoms in community-acquired RSV adult population with which to benchmark, this reduction likely represents a high bar.
Therefore, directional efficacy data that is clinically meaningful would provide us with conviction to move directly into Phase III. Enrollment is progressing, and we will provide additional guidance on the RSVHR study as the Southern Hemisphere RSV season evolves.
Also ongoing in our RSV portfolio is the Phase IIa challenge study of EDP-323, which is in development as a once-daily oral treatment for RSV. In this randomized, double-blind, placebo-controlled study, up to 114 healthy adult subjects will be infected with RSV and then randomized 1:1:1 to receive once-daily dosing of either 600 milligrams of EDP-323, 200 milligrams of EDP-323 with a loading dose of 600 milligrams on the first day or placebo for 5 days.
Primary and secondary outcome measures include safety, changes in viral load measurements and changes in symptoms from baseline. The development of EDP-323 is supported by positive Phase I results in which the drug demonstrated favorable safety, tolerability and pharmacokinetics in healthy volunteers.
We anticipate reporting data from this challenge study in the third quarter of 2024. We believe either zelicapavir or EDP-323 would be effective as a monotherapy. Because they do not have cross resistance, we could also potentially use them in combination to broaden the treatment window or expand the eligible patient population to harder-to-treat patients.
Also in respiratory virology, data from SPRINT, our Phase II study of EDP-235, a 3CL protease inhibitor, was presented in April at the ESCMID Conference, formerly known as ECCMID. We are pleased to present this comprehensive data package in a scientific forum for the first time. As a reminder, we will conduct any future COVID-19 work in the context of the collaboration.
I'll now turn to our work in immunology, where we are concentrating on indications with a high unmet medical need and a clear clinical development path, including well-defined populations and biomarkers available for early signs of efficacy. Our first immunology indication is CSU, a severely debilitating chronic inflammatory skin disease, which can continue for years before remission.
Clinical manifestations include urticaria, commonly called hive, as well as angioedema, which is characterized by pronounced deep tissue swelling. The disease can be severely disabling, significantly impair quality of life and affect performance at work or school as patients with CSU can experience symptoms beyond the skin manifestations, including sleep disturbances, fatigue, irritability, anxiety and depression.
CSU is estimated to affect 0.5% to 1% of the global population at any given time. The standard of care for CSU is antihistamines. But in approximately half of patients, symptoms are not alleviated, and a minority of patients are treated with one indicated biologic.
Consequently, there is a substantial unmet need for a new efficacious drug that can be conveniently dosed as an oral agent. Mast cells are the primary driver for disease in CSU as well as being involved in multiple other allergic diseases.
In our first immunology program, we are seeking to develop a best-in-disease oral KIT inhibitor treatment that reduces the number of mast cells available to drive pathology in patients suffering from CSU. We are also encouraged by the potential to study KIT inhibition in additional indications.
Currently, our prototype KIT inhibitors in preclinical development demonstrate potent inhibition and are highly selective for KIT. We continue to optimize these leads around potency, selectivity and DMPK properties. And we are on track to select a development candidate in the fourth quarter of 2024 and plan to move into the clinic shortly thereafter.
We are excited about our pipeline growth into immunology and are confident in the team's ability to translate the learnings from our previous success with small molecule drugs to enable our development of a best-in-disease therapeutic for CSU. We are also pursuing additional immunology targets and look forward to introducing a second program this year.
Beyond our pipeline, I would also like to take a moment to welcome Matthew Kowalsky as our Chief Legal Officer, who joined last week. Matt is a strong addition to our team as he brings more than 20 years of experience in the life sciences industry, handling corporate governance, public company reporting, intellectual property, financing, business development and M&A activities. At Enanta, he will lead all legal and compliance activities for the company and provide strategic guidance and corporate governance oversight.
With that, I'd like to conclude by highlighting our upcoming milestones. We anticipate reporting data from the Phase IIa challenge study of EDP-323 in the third quarter and reporting data from the Phase II pediatric study of zelicapavir in the second half of this year. Further, we plan to identify a clinical candidate for our CSU program in the fourth quarter. And finally, we also plan to announce second immunology program this year.
Now I'll turn the call over to Paul to discuss our financials. Paul?