Enanta Pharmaceuticals (NASDAQ:ENTA) used a presentation at the Citizens Life Sciences Conference to outline its evolving pipeline strategy, highlighting late-stage ambitions in respiratory syncytial virus (RSV) and a growing immunology and inflammation (I&I) portfolio built around small-molecule discovery.
Chief Executive Officer Jay Luly said Enanta is a Watertown, Massachusetts-based drug discovery and development company with a long-standing focus on small molecules. He reviewed the company’s history in hepatitis C, where Enanta-developed protease inhibitors partnered with AbbVie led to VIEKIRA PAK and MAVYRET. Luly said MAVYRET remains the only eight-week cure for chronic hepatitis C and acute hepatitis C, and that between 1 million and 2 million patients have been cured globally.
RSV: advancing zelicapavir toward Phase 3
Enanta has two RSV mechanisms in development: an N protein program (zelicapavir) and an L protein program (EDP-323, targeting the viral polymerase). Management said both candidates have completed Phase 1 studies in healthy volunteers and have generated results in human challenge studies. Luly noted that the first program’s challenge-study results have been published in The New England Journal of Medicine, and he described the second molecule’s challenge study as “very successful” as well.
Chief Product Strategy Officer Tara Kieffer said a Phase 3 adult study for zelicapavir would likely mirror the subgroup with the most robust Phase 2 results, which Enanta refers to as the “HR3” population. She described that population as including patients over 75 years of age and those with chronic obstructive pulmonary disease (COPD) or congestive heart failure.
Kieffer said the planned primary endpoint would likely be symptom-based, focused on time to complete symptom resolution measured by the RiiQ patient-reported outcome tool across 13 RSV symptoms. She estimated enrollment on the order of 600 to 700 patients and said the company is aligning with regulatory agencies, with additional communication expected in the second quarter.
On product profile, management said zelicapavir is being studied as a five-day regimen and has been safe and well-tolerated to date. Kieffer said the Phase 2 study showed about a seven-day reduction in symptom duration versus placebo—roughly three weeks on placebo compared with about two weeks for treated patients. She also said Enanta saw statistical significance on a second patient-reported outcome measure (PGIS) and observed about a 50% reduction in hospitalization rate in Phase 2, which the company expects to evaluate as a secondary endpoint in Phase 3.
EDP-323: a second RSV mechanism with rapid viral load reductions
Luly positioned EDP-323 as a highly potent polymerase inhibitor, describing it as a picomolar inhibitor with “outstanding” human pharmacokinetics. He emphasized the importance of sustained exposure over 24 hours for antiviral therapy.
In the RSV human challenge study, Luly said EDP-323 appeared to reduce viral loads more quickly than zelicapavir, with viral loads in culture “completely obliterated within 12 hours” after the first dose—nearly a day faster than what Enanta observed with zelicapavir. He added that Enanta recruits patients in its Phase 2 adult RSV study within 72 hours of symptom onset, and suggested that faster-acting antiviral effects could theoretically translate to improved efficacy, though the company noted that would require testing.
Management discussed several potential development and commercial strategies for the two RSV assets, including exploring comparative approaches, positioning EDP-323 as a next-generation lifecycle option, or evaluating whether two orthogonal mechanisms might benefit hard-to-treat, severely immunocompromised patients with longer dosing schedules. Luly also said Enanta observed a potential way to use EDP-323 in post-exposure prophylaxis in the challenge setting.
Partnering considerations and shifting virology priorities
On partnering, Luly said Enanta has seen the benefits of having a committed commercial partner, citing the company’s long-standing relationship with AbbVie. He said partnership timing for RSV could range “anytime between now and launch,” while acknowledging that Phase 3 data could represent a value inflection point that the company is currently weighing.
Luly also said Enanta is not as focused on expanding virology discovery as it once was, after having explored multiple viruses including hepatitis C, hepatitis E, human metapneumovirus, RSV, and SARS-CoV-2. He said the COVID-19 pandemic slowed Enanta’s entry into I&I because the company “couldn’t not work” on SARS-CoV-2, where it generated Phase 2 data and is seeking regulatory clarity on advancement given the current viral backdrop.
I&I portfolio: KIT, STAT6, and MRGPRX2
Enanta highlighted three disclosed I&I programs, all based on small-molecule approaches:
- KIT (EDP-978): Kieffer said KIT inhibition is intended to deplete mast cells, potentially benefiting mast cell-driven diseases. She referenced KIT-targeting antibodies in development, including a Celldex antibody currently in Phase 3, and said Enanta aims to replicate “best in disease” efficacy with an oral molecule, potentially with a dosing strategy that could mitigate certain on-target tolerability issues seen with antibodies. Enanta said it is on track for an IND in Q1 and Phase 1 data in Q4, with a typical SAD/MAD healthy-volunteer design including biomarkers such as serum tryptase. Kieffer said the program is targeting about 80% depletion as assessed by biomarkers and described preclinical potency in the 2–3 nanomolar range with high selectivity. The company anticipates once-daily dosing. Enanta said differentiation could come from oral administration and optimization across potency, selectivity, and ADME properties, while noting another oral KIT molecule in development by Blueprint Medicines. Enanta cited CSU, CIndU, and potential expansion into other mast cell-related diseases such as prurigo nodularis.
- STAT6 (EDP-3903): Luly described STAT6 as downstream of IL-4/IL-13 signaling targeted by Dupixent at the receptor level, and said STAT6 has historically been viewed as difficult to drug. Enanta is pursuing a “classic inhibitor,” non-degrader approach designed for complete and sustained inhibition, drawing on its antiviral drug-development mindset. Luly said Enanta has shown “Dupixent-like” activity in animal models of atopic dermatitis and asthma and is targeting an IND filing in the second half of the year.
- MRGPRX2: Kieffer said Enanta is optimizing prototypes and has shared early data showing good potency and selectivity, including potency across multiple agonists. The company is considering urticaria as an initial proof-of-concept indication, while also noting other potential areas such as migraine because the receptor is expressed on peripheral neurons as well as mast cells. Enanta said it is aiming to select a development candidate in the second half of the year.
Cash position and runway
On financing, management said Enanta ended the last quarter with $242 million in cash, providing runway into fiscal 2029. The company said all three I&I programs are funded through early clinical data sets, while the scope and funding of an RSV Phase 3 program will depend in part on whether it proceeds with or without a partnership.
About Enanta Pharmaceuticals (NASDAQ:ENTA)
Enanta Pharmaceuticals, Inc is a biotechnology company headquartered in Watertown, Massachusetts, specializing in the discovery and development of novel, small-molecule drugs targeting viral diseases. Leveraging a proprietary chemistry platform, Enanta has built extensive expertise in designing potent inhibitors of viral proteases and polymerases. The company initially gained recognition through partnerships focused on hepatitis C virus (HCV), where its protease inhibitors formed a key component of ABBVIE’s direct‐acting antiviral regimens.
Building on its HCV experience, Enanta has expanded its pipeline to address respiratory syncytial virus (RSV) and other viral infections.
