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Corporate Presentation June 5, 2025
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© 2025 Enanta Pharmaceuticals, Inc. | This presentation contains forward-looking statements concerning our business, operations and financial performance and condition, as well as our plans, objectives and expectations for our research and development programs, our business and the industry in which we operate. Any statements contained herein that are not statements of historical facts may be deemed to be forward-looking statements. In some cases, you can identify forward-looking statements by terminology such as “aim,” “anticipate,” “assume,” “believe,” “contemplate,” “continue,” “could,” “due,” “estimate,” “expect,” “goal,” “intend,” “may,” “objective,” “plan,” “predict,” “potential,” “positioned,” “seek,” “should,” “target,” “will,” “would,” and other similar expressions that are predictions of or indicate future events and future trends, as well as other comparable terminology. These forward-looking statements include, but are not limited to, statements about overall trends, royalty revenue trends, research and clinical development plans and prospects, liquidity and capital needs and other statements of expectations, beliefs, future plans and strategies, anticipated events or trends, and similar expressions. These forward-looking statements are based on our management’s current expectations, estimates, forecasts and projections about our business and the industry in which we operate and our management’s beliefs and assumptions. These forward-looking statements are not guarantees of future performance or results and involve known and unknown risks, uncertainties and other factors that are in some cases beyond our control. As a result, any or all of our forward-looking statements in this presentation may turn out to be inaccurate. Please refer to the risk factors described or referred to in “Risk Factors” in Enanta’s most recent Annual Report on Form 10-K, and other periodic reports filed with the Securities and Exchange Commission. Enanta cautions investors not to place undue reliance on the forward-looking statements contained in this presentation. These statements speak only as of the date of this presentation, and Enanta undertakes no obligation to update or revise these statements, except as may be required by law. Forward Looking Statements Disclaimer 2
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© 2025 Enanta Pharmaceuticals, Inc. | Leveraging our core strength in small molecule drug discovery to develop treatments for high unmet medical needs A Proven Approach to Drug Discovery 3 Proven Track Record of Success Robust Pipeline Strong balance sheet and ongoing royalties to support robust pipeline $193.4M in cash at March 31, 2025* Glecaprevir: HCV protease inhibitor in MAVYRET®/MAVIRET® Strong Balance Sheet Virology: Phase 2 in pediatric patients with RSV complete Phase 2 in high-risk adults with RSV ongoing Phase 2 challenge study with second RSV candidate complete Phase 2 in COVID-19 complete Immunology: Preclinical KIT inhibitor (mast cell driven diseases, e.g., CSU) Preclinical STAT6 inhibitor (type 2 immune diseases, e.g., atopic dermatitis) * An additional $33.8M in cash was received in April 2025 via a federal income tax refund
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© 2025 Enanta Pharmaceuticals, Inc. | DISEASE TARGET DISCOVERY PRECLINICAL PHASE 1 PHASE 2 PHASE 3 MARKET Virology: Liver Hepatitis C Virus Protease Hepatitis B Virus Core Virology: Respiratory Respiratory Syncytial Virus N-Protein L-Protein COVID-19 3CL Protease Immunology: Type 2 Immune Diseases Chronic Spontaneous Urticaria*** KIT Atopic Dermatitis*** STAT6 Zelicapavir (EDP-938) High-Risk Adults EDP-323 (challenge study) Zelicapavir (EDP-938) Pediatrics Glecaprevir* EDP-235** SPRINT Enanta Pipeline 4 EDP-514** *Fixed-dose antiviral combination contains glecaprevir and AbbVie's NS5A inhibitor, pibrentasvir. Marketed by AbbVie as MAVYRET® (U.S.) and MAVIRET® (ex-U.S.). **Continued development dependent on a future collaboration. ***Initial indications. Potential future indications include asthma, chronic inducible urticaria (CIndU), eosinophilic esophagitis (EoE), prurigo nodularis (PN), and others.
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Virology: Respiratory Syncytial Virus
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© 2025 Enanta Pharmaceuticals, Inc. | Populations at higher risk for severe illness: • Pediatrics (infants and children) • High-risk adults (>65 yrs, COPD, asthma, CHF) • Immunocompromised (e.g. HIV, transplant) Respiratory Syncytial Virus (RSV) 6 RSV at a Glance Children < 5 years2 Adults > 65 years3 33M global cases 3M global hospitalizations 177K U.S. hospitalizations 101K global deaths 14K U.S. deaths Causes severe lung infections, including bronchiolitis (infection of small airways in the lungs) and pneumonia. Leading cause of hospitalization in infants1. No safe and effective treatments are currently approved. Sources: 1. CDC RSV In Infants and Young Children. 2. Li P et al. The Lancet. 2022 3. Falsey AR et al. NEJM. 2005. 4. Terlizzi EP et al. NCHS Data Brief. 2020; Age 60+ 5. CDC Influenza Vaccination Coverage, Adults 65+ 6. FDA-approved labels: Pfizer; GSK & Moderna 7. June 2024 ACIP recommendation Significant unmet need for antiviral treatment despite availability of prophylaxis: • Adoption of adult vaccines is sub-optimal and not recommended for all FDA-approved patient groups* – Peak adoption of vaccines for elderly range from ~35% (shingles4) to ~55% (flu5) • Pediatric prophylaxis approaches provide passive immunity; will shift first infection to next season – Antibody approach has a low barrier to resistance • Even with adoption, breakthrough infections will still occur *FDA-approved for adults age ≥60 & 50-59 years who are at increased risk for LRTD caused by RSV6, but ACIP-recommended for adults age ≥75 years and age 60-74 years at increased risk of severe RSV7
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© 2025 Enanta Pharmaceuticals, Inc. | • Zelicapavir is currently the only N-inhibitor in clinical development for RSV – Replication inhibitor: shuts down the production of new virions (vs. fusion inhibitors which block viral entry) • Granted Fast Track designation by the FDA • Strong preclinical profile – Nanomolar potency against RSV-A and RSV-B – Antiviral potency across all clinical isolates tested – High-barrier to resistance – Synergistic activity and no cross-resistance with other drug mechanisms (e.g. L-inhibitors) • Favorable safety and efficacy profile in clinical studies – Challenge study showed statistically significant (p<0.001) reduction in viral load and clinical symptoms Zelicapavir (EDP-938): N-Protein Inhibitor for RSV 7 RSV
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© 2025 Enanta Pharmaceuticals, Inc. | Goal: Treat patients at high-risk for developing severe infection leading to hospitalization or death, populations with the most significant unmet need Infants and young children Age ≥65 years Chronic heart or lung disease (e.g. COPD, CHF, asthma) Zelicapavir Development Plans: Treatment for Patients at High-Risk for Severe RSV Infection 8 High-risk populations have reduced RSV immunity, resulting in a higher and longer duration of viral load and greater disease severity, allowing a bigger window to observe benefit
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© 2025 Enanta Pharmaceuticals, Inc. | • First zelicapavir pediatric study: safety and dose selection • Signal finding in different patient populations to inform a potential registration-enabling trial – Age: ≥28 days to <6 months and ≥6 months to ≤36 months – Time from symptom onset to treatment – Hospitalized or outpatient Zelicapavir Phase 2 Pediatric Study: Design & Objectives 9 ~90 patients Dosed in 2 age cohorts: ≥28 days to <6 months ≥6 months to ≤36 months Double-Blind Treatment Phase 5 days Part 1: MAD vs Placebo Part 2: Selected dose from Part 1 vs Placebo Day 1 Day 5 Day 28 23 Day Follow-up Primary Objectives of Study • Overall: Antiviral activity of zelicapavir across all patients • Part 1: Safety and PK • Part 2: Antiviral activity
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© 2025 Enanta Pharmaceuticals, Inc. | • Viral load decline of 0.88 log at Day 3 and 1.18 log at Day 5 Zelicapavir Phase 2 Pediatric Study: Prespecified mITT-3 Population: RSV PCR Viral Load 10 1 3 5 9 14 -6 -5 -4 -3 -2 -1 0 Placebo N=(10) EDP-938 N=(28) LS Mean Viral Load Change from Baseline (+/-SE) (log10 copies/mL) Study Day Zelicapavir (n=28) Placebo (n=10) Δ = -0.88 Δ = -1.18 Δ = -0.57 Δ = -0.20 mITT-3: patients randomized within 3 days of symptom onset
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© 2025 Enanta Pharmaceuticals, Inc. | • Well-tolerated, with favorable safety profile – No adverse events leading to treatment discontinuation or study withdrawal • Antiviral effect observed for the primary and secondary virology endpoints in overall population • Viral load decline of 1.4 log at the end of treatment in Part 2 • Viral load decline of 1.2 log at Day 5 observed in prespecified subset of patients randomized within 3 days of symptom onset • RSV Signs/Symptoms – ReSViNET: No difference in signs/symptoms between groups – RESOLVE-P: Trend toward greater signs/symptom reduction with zelicapavir in a small dataset • Data support further clinical development of zelicapavir Zelicapavir Phase 2 Pediatric Study: Summary 11 Primary Objectives of Study Overall: Antiviral activity of zelicapavir across all patients Part 1: Safety and PK Part 2: Antiviral activity
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© 2025 Enanta Pharmaceuticals, Inc. | Zelicapavir Phase 2 High-Risk Adult Study: Design & Objectives 12 • Primary Objective: Time to resolution of RSV LRTD symptoms (RiiQ symptom scale) – Shortness of breath, wheezing, coughing, coughing up phlegm • Secondary Objectives: PROs, MAVs, virology, antibiotic use, bronchodilator use, corticosteroid use, hospitalization, ICU, mechanical ventilation, all cause mortality, PK and safety Double-Blinded Treatment Phase 5 days Placebo (QD) 800mg (QD)** Day 1 Day 33Day 5 ~180 adults with at least one of the following: • COPD • Congestive heart failure • Asthma* • Age ≥65* 28 Day Follow-up *The total proportion of subjects either 65-74 years of age or patients with asthma combined will be capped at 20%. **Equivalent to 600mg suspension dosage form used in challenge study PK: pharmacokinetics; LRTD: lower respiratory tract disease; PROs: patient reported outcomes; MAVs: medically attended visits First proof-of-concept Phase 2 high-risk adult study designed to give initial indication of treatment effect on time to symptom resolution
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© 2025 Enanta Pharmaceuticals, Inc. | Clinically Meaningful Reduction in Symptom Duration of ~1 Day Demonstrated by Multiple Approved Antivirals 13 7.3 5.1 3.3 8.06.3 4.1 2.2 7.0 0.0 2.0 4.0 6.0 8.0 Ph3 Age 65+ Meta-analysis Age >12 Ph3 Age 12-64 Ph3 Age 12-70 Median days to alleviation of symptoms Placebo Active 1. Dobson J Lancet 2015 2. Hayden FG NEJM 2018 3. https://www.kegg.jp/medicus-bin/japic_med?japic_code=00070668 n = intent-to-treat infected 1d (14%) SARS-CoV-2Influenza 1d (21%) 1.1d (33%) 1d (13%) oseltamivir1 ensitrelvir3baloxavir marboxil2 n 477 2860 685 657
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© 2025 Enanta Pharmaceuticals, Inc. | RSVHR: Zelicapavir Proof-of-Concept High-Risk Adult Study 14 • RSVHR is a proof-of-concept study (n~180) expected to show a clinically meaningful reduction in symptom duration of at least ~1 day • Totality of data, including numerous secondary endpoints, will provide additional support – All symptoms (upper respiratory, lower respiratory, systemic) – Predefined subsets of specific symptoms – Additional PROs – Virology – Antibiotic, bronchodilator, corticosteroid use • Treatment effect to be confirmed with statistical significance in a larger Phase 3 study (n~500-700) PROs: patient reported outcomes
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© 2025 Enanta Pharmaceuticals, Inc. | • Direct-acting antiviral targeting the L-protein – Replication inhibitor: shuts down the production of new virions (vs. fusion inhibitors which block viral entry) • Granted Fast Track designation by the FDA • Potential to be used alone or in combination – Additive to synergistic activity with zelicapavir – No cross resistance expected with other mechanisms • Sub-nanomolar potency against RSV-A and B • Protects mice in a dose-dependent manner from RSV infection • Phase 1 indicated 200mg or 600mg once-daily as potential safe and efficacious doses EDP-323: RSV L-Protein Inhibitor 15 . RSV
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© 2025 Enanta Pharmaceuticals, Inc. | • Highly statistically significant reductions in Viral Load AUC measured by qRT-PCR compared to placebo – No statistically significant difference between the two EDP-323 dosing regimens; 600mg and 200mg (with 600mg loading dose) EDP-323: Robust Antiviral Effect in Human Challenge Model Primary Efficacy Endpoint: 85-87% ↓ in Viral Load AUC by qRT-PCR 16 Viral Load (Log10 copies/mL) Mean (±SE) 26 26 26 26 26 26 26 26 26 26 26 26 26 26 15 12 10 6 4 1 23 23 23 23 23 23 23 23 23 23 23 23 23 23 17 16 10 5 4 2 30 30 30 30 30 30 30 30 30 30 30 30 30 30 19 18 11 8 6 4 Number of Subjects EDP-323 High dose EDP-323 Low dose Placebo Time (days) EDP-323 High Dose EDP-323 Low Dose % AUC Reduction (vs pbo) 84.93% 87.48% P-value <0.0001 <0.0001 VL AUC: viral load area under the curve (hours x log10 copies/mL); qRT-PCR: quantitative reverse transcriptase polymerase chain reaction; SE: standard error
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© 2025 Enanta Pharmaceuticals, Inc. | • Well-tolerated with safety profile similar to placebo • Primary and key secondary efficacy endpoints achieved with high statistical significance at both dose levels compared to placebo: – Reduction in viral load of 85-87% – Reduction in viral culture of 97-98% – Alleviation of clinical symptoms by 66-78% • Data support further clinical evaluation of EDP-323 EDP-323 Phase 2a RSV Challenge Study: Conclusions 17
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Immunology
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© 2025 Enanta Pharmaceuticals, Inc. | Immunology Portfolio: Advancing Multiple Targets in Pipeline 19 KIT inhibition blocks cell survival signal resulting in apoptosis and mast cell death STAT6 inhibition impedes type 2 inflammation KIT STAT6 Atopic Dermatitis Asthma CSU CIndU COPD EoE PN CRSwNP Others Potential Indications CSU: Chronic Spontaneous Urticaria; CIndU: Cold Inducible Urticaria; COPD: Chronic Obstructive Pulmonary Disease; CRSwNP: Chronic Rhinosinusitis with Nasal Polyps; EoE: Eosinophilic Esophagitis; PN: Prurigo Nodularis
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© 2025 Enanta Pharmaceuticals, Inc. | • Type 2 inflammation is characterized by overproduction of IL-4, IL-5, IL-13, and IgE which recruits and activates Th2 CD4 T cells, B cells, mast cells, eosinophils, and basophils • Potential to treat broad patient populations across numerous disease areas Immunology Portfolio: Multiple Targets Addressing Type 2 Immune Diseases 20 Indications / 2030F Market Potential1 Enduring unmet need in multiple diseases driven by Type 2 immune phenotype Source: 1. Evaluate Pharma, © Evaluate Ltd, September 2024, www.evaluate.com Explore Expansion Fast PoC Urticaria AD Asthma, COPD CRSwNP, EoE, PN TBD Total $50B $>100B AD: Atopic Dermatitis; COPD: Chronic Obstructive Pulmonary Disease; CRSwNP: Chronic Rhinosinusitis with Nasal Polyps; EoE: Eosinophilic Esophagitis; PN: Prurigo Nodularis
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Immunology: KIT Inhibitor
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© 2025 Enanta Pharmaceuticals, Inc. | • Mast cells: primary driver of inflammation in skin, and implicated in multiple allergic diseases – Urticaria, asthma, eosinophilic esophagitis (EoE), and prurigo nodularis (PN) • KIT: well-characterized receptor tyrosine kinase critical for regulating mast cell activity • KIT inhibitors: potential for best-in-disease efficacy – Directly reduces quantity of mast cells through apoptosis and depletion, addressing key disease driver – Current therapy reduces mast cell activator levels or downstream mediators, but not mast cells directly – Positive proof-of-concept in urticaria and PN with anti-KIT mAb KIT Inhibitors Offer Potential for Differentiated Efficacy 22
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© 2025 Enanta Pharmaceuticals, Inc. | • Severely debilitating, chronic inflammatory skin disease – Driven by mast cell activation, triggering release of inflammatory mediators1 – Quality of life impacts beyond the skin: sleep disturbances, fatigue, irritability, anxiety and depression 2 • Affects ~0.5-1% of the global population1 • Substantial unmet need for efficacious oral agent – ~50% not controlled with antihistamines1,3 – Minority treated with one indicated biologic (~10%)4 Chronic Spontaneous Urticaria (CSU): KIT Inhibitor Initial Focus for Clinical Proof of Concept 23 Angioedema Sources: 1. Kaplan A et al. Allergy. 2023; 78(2): 389–401. 2. Yosipovitch et al. Dermatol Ther. 2023; 13(8): 1647–1660. 3. H1 antihistamines up to 4x standard dose. 4. Reidel MA et al. Ann Allergy, Asthma Immunol. 2024; S1081-1206(24)01731-9. Hives Itch Erythema
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© 2025 Enanta Pharmaceuticals, Inc. | • EPS-1421 selected as development candidate – Inhibits KIT with nanomolar potency in both binding and cellular assays – Demonstrates sub-nanomolar activity in vivo – Highly selective for KIT versus other kinases – Good in vitro and in vivo ADME properties • Good PK profile across multiple preclinical species • No GSH adducts (or reactive metabolites) detected in vitro or in vivo • Low drug-drug interaction potential via CYP inhibition Goal of Oral KIT Inhibitor Program: Develop Best-in-Class Treatment for Mast Cell Mediated Diseases 24
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© 2025 Enanta Pharmaceuticals, Inc. | • Prevents KIT mediated cellular proliferation with EC50 of 2-11nM EPS-1421 Exhibits Potent Inhibition of KIT In Vitro and In Vivo 25 *M-07e and UT-7 cells endogenously express KIT; Ba/F3 cells are engineered to express KIT Binding or Cellular Assay* EC50 (nM) KINOMEscan Kd 0.8 M-07e phosphorylated KIT 2 M-07e Cell Proliferation 11 UT-7 Cell Proliferation 3 KIT Ba/F3 Proliferation 2 CD34+ Derived Mast Cell Degranulation 4 • Inhibits SCF-mediated histamine release in mice with an EC50 (free drug) of 0.25nM **KIT binding to its ligand SCF (Stem Cell Factor) in vivo triggers mast cell degranulation with histamine release 0 .1 1 10 100 1000 0 20 40 60 80 100 EPS- 1421 ( ng/ m L) H i st am i ne ( % Vehi cl e) ** Histamine (% vehicle) EPS-1421 (ng/mL)
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© 2025 Enanta Pharmaceuticals, Inc. | • Greater than 500-fold selectivity for KIT over other KIT family members EPS-1421 Demonstrates Good Selectivity for KIT 26 Selectivity EPS-1421 S(10) @ 1 µM 0.015 CSF1R* >500x PDGFRα* >1300x PDGFRβ* >1100x FLT3 Kd >1800x *Cellular selectivity calculated as ratio of EC50 in kinase dependent Ba/F3 cells CSF1R: colony stimulating factor 1 receptor; FLT3: FMS-like tyrosine kinase 3; PDGFRA/B: platelet-derived growth factor receptor alpha/beta; S(10) @ 1 μM: selectivity score at a concentration of 1 μM
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Immunology: STAT6 Inhibitor
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© 2025 Enanta Pharmaceuticals, Inc. | • Th2 dysregulation drives allergic and autoimmune diseases including atopic dermatitis and asthma – Characterized by IL-4 & IL-13 overproduction • STAT6: transcription factor responsible for IL-4/IL-13 signaling, which drives a Th2 dominant phenotype – STAT6 gain-of-function variants result in severe atopic dermatitis1 – STAT6 loss-of-function protects against type 2 high asthma2 – Inhibition of the IL-4/13 pathway is clinically validated • STAT6 inhibitors: potential for an “oral DUPIXENT” – Blocks IL-4/13 signaling pathway – Reduces inflammation in Th2 driven preclinical models – No oral therapy selectively targeting IL-4/13 pathway available STAT6 Inhibitors Offer Potential for an “Oral DUPIXENT®” 28 Sources: 1. Suratannon et al. Journal of Allergy and Clinical Immunology 2023. 2. Kristjansdottir et al. Journal of Allergy and Clinical Immunology 2024.
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© 2025 Enanta Pharmaceuticals, Inc. | • Chronic dermatological disease characterized by dry, red, inflamed, irritated and itchy skin – Driven by Th2 immune dysregulation1 – Quality of life impacts beyond the skin: limited lifestyle, avoidance of social interaction and impacted activities1 • 7.3% of U.S. adults, ~40% have moderate-severe symptoms2 • Significant need for efficacious and safe oral agents – Market dominated by mAb (IL-4/13) – Oral JAKi use <10%3 • Boxed warning: serious infections, mortality, malignancy, major adverse cardiac events, thrombosis4 Atopic Dermatitis (AD): STAT6 Inhibitor Initial Focus for Clinical Proof of Concept 29 Sources: 1. Silverberg JI et al. Annals of Allergy, Asthma & Immunol. 2018. 2. Asthma and Allergy Foundation of America: https://aafa.org/asthma-allergy-research/our-research/atopic- dermatitis-in-america/. 3. Market share ($) from Evaluate Pharma, © Evaluate Ltd, 9/2024, www.evaluate.com 4.Prescribing Information for RINVOQ & CIBINQO
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© 2025 Enanta Pharmaceuticals, Inc. | • Novel, orally active prototype compounds with good potency and selectivity discovered – Favorable in vitro and in vivo ADME properties – Inhibit STAT6 with nanomolar potency in both binding and cellular assays – Highly selective for STAT6 versus other STATs – Demonstrate STAT6 target engagement in vivo – Suppress type 2 inflammatory profile in an acute OVA asthma model • Prototypes being optimized with goal of selecting development candidate in 2H 25 Goal of Oral STAT6 Inhibitor Program: Discover Novel, Potent and Selective Oral STAT6 Inhibitors 30
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© 2025 Enanta Pharmaceuticals, Inc. | • Good intrinsic permeability • High metabolic stability with low clearance • Good target tissue distribution to the skin and lung – No off-target distribution to brain • Oral bioavailability with once-daily dosing potential – Low DDI potential via inhibitions of CYPs, hepatic or intestinal transporters 31 Prototypes Display Favorable In Vitro and In vivo ADME Properties
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© 2025 Enanta Pharmaceuticals, Inc. | Prototype STAT6 Inhibitor Demonstrates Potent Activity 32 Cellular Assay Prototype EC50 (nM) Upadacitinib EC50 (nM) TF-1 Proliferation 23 15 IL-4 induced pSTAT6 (hPBMC) 19 28 IL-4 induced TARC (hPBMC) 6 13 • Prototype inhibitors exhibit nanomolar inhibition in biochemical and cellular assays – Inhibit phosphorylation of STAT6 in human PBMCs after IL-4 stimulation – Prevent production of TARC, a STAT6 driven biomarker of type 2 inflammation TF-1: human erythroleukemic cell line, dependent on STAT6 signaling for cell growth Upadacitinib: JAK Inhibitor 0.01 1 100 10000 0 50 100 hPBMC IL-4 Induced TARC [Inhibitor] nM % Inhibition hPBMC: human peripheral blood mononuclear cells ; pSTAT6: phosphorylated STAT6; TARC: thymus and activation-regulated chemokine
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© 2025 Enanta Pharmaceuticals, Inc. | Prototype STAT6 Inhibitor Displays Good Selectivity 33 • No inhibition of other STATs observed in human PBMCs • Greater than 1000x biochemical selectivity for STAT6 over other STATs • Selectivity much improved compared to JAK inhibitors pSTAT1 pSTAT2 pSTAT3 pSTAT4 pSTAT5 pSTAT6 Prototype STAT6 Inhibitor >5000 >5000 >5000 >5000 >5000 19 Upadacitinib (JAK Inhibitor) 1 8 24 195 16 28 Selectivity in hPBMCs EC50 (nM) pSTAT: phosphorylated STAT; hPBMCs: human peripheral blood mononuclear cells
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© 2025 Enanta Pharmaceuticals, Inc. | Prototype STAT6 Oral Inhibitor Results in Complete Inhibition of pSTAT6 in Mouse Model 34 • In vivo STAT6 target engagement after a single dose • Rapid, complete inhibition of phosphorylated STAT6 STAT6 Inhibitor Oral Delivery in Mouse pSTAT6 Detection Ex Vivo Stimulation + IL-4 Vehicle Prototype 0 20 40 60 80 100 IL-4 Induced Blood pSTAT6% pSTAT6 Induction pSTAT6: phosphorylated STAT6
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© 2025 Enanta Pharmaceuticals, Inc. | • Asthma challenge model triggers an allergic airway inflammation response that mimics key aspects of human allergic asthma – e.g.; eosinophil infiltration and Th2 cytokine production Prototype STAT6 Inhibitor Reduces STAT6 Activation in Ovalbumin (OVA) Asthma Model 35 Study Day 1 2 3 4 5 6 7 8 9 IP Sensitization Oral Prototype Inhibitor IN Challenge • Dose-dependent pSTAT6 inhibition observed in lung at trough drug concentrations (Cmin) No OVA - Low Medium High 0 20 40 60 80 100 120 Lung pSTAT6 @ Cmin % Activation * * Prototype Dose *p<0.05 vs OVA-Vehicle IP: Intraperitoneal ; IN: Intranasal ; pSTAT6: phosphorylated STAT6
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© 2025 Enanta Pharmaceuticals, Inc. | Prototype STAT6 Inhibitor Suppresses Type 2 Inflammatory Profile in Ovalbumin (OVA) Asthma Model 36 No OVA - Low Medium High 0 10 20 30 40 Eosinophils Cell Number (X10^4) * * Prototype Dose * No OVA - Low Medium High 0 100 200 300 400 500 TARC pg/ml ** Prototype Dose * No OVA - Low Medium High 0 20 40 60 80 Eotaxin pg/ml * * Prototype Dose * No OVA - Low Medium High 0 200 400 600 800 1000 IL-4 pg/ml Prototype Dose * BALF: bronchioalveolar lavage fluid Inhibition of Eosinophil Infiltration in BALF Attenuation of OVA-induced Cytokines and Chemokines in BALF • Deep suppression of type 2 inflammatory profile observed at trough drug concentrations (Cmin)
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© 2025 Enanta Pharmaceuticals, Inc. | Respiratory Syncytial Virus Report Phase 2 data of zelicapavir in high-risk adults in late 3Q 25 2025 Key Catalysts 37 KIT Inhibition Perform scale-up and IND enabling activities of EPS-1421 STAT6 Inhibition Select development candidate in 2H 25 New Program Announce third immunology program Virology Immunology Business Development Respiratory Syncytial Virus Pursue partnerships for zelicapavir and/or EDP-323
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