Enanta Pharmaceuticals Announces Positive Topline Results from First-in-Pediatrics Phase 2 Study Evaluating Zelicapavir for the Treatment of Respiratory Syncytial Virus (RSV)
Enanta Pharmaceuticals announced positive topline results from its first-in-pediatrics Phase 2 study of zelicapavir for treating respiratory syncytial virus (RSV) in children aged 28 days to 36 months. The study demonstrated significant antiviral effects with a 1.4 log decline in viral load at Day 5 compared to placebo in Part 2. A prespecified analysis of patients treated within 3 days of symptom onset showed a 1.2 log decline in viral load.
The study involved 96 patients (70 receiving zelicapavir, 26 placebo) across two parts. Zelicapavir demonstrated a favorable safety profile with no adverse events leading to treatment discontinuation. The drug achieved target exposure levels across all age groups, with doses of 5 mg/kg for ages ≥28 days to <12 months and 7.5 mg/kg for ages ≥12 months to ≤36 months.
Enanta Pharmaceuticals ha annunciato risultati preliminari positivi dal suo studio di Fase 2, il primo in pediatria, su zelicapavir per il trattamento del virus respiratorio sinciziale (RSV) in bambini di età compresa tra 28 giorni e 36 mesi. Lo studio ha dimostrato effetti antivirali significativi con un declino di 1,4 log nella carica virale al Giorno 5 rispetto al placebo nella Parte 2. Un'analisi predefinita dei pazienti trattati entro 3 giorni dall'inizio dei sintomi ha mostrato un declino di 1,2 log nella carica virale.
Lo studio ha coinvolto 96 pazienti (70 trattati con zelicapavir, 26 con placebo) suddivisi in due parti. Zelicapavir ha dimostrato un profilo di sicurezza favorevole, senza eventi avversi che portassero a interruzioni del trattamento. Il farmaco ha raggiunto i livelli di esposizione target in tutte le fasce di età, con dosi di 5 mg/kg per età ≥28 giorni a <12 mesi e 7,5 mg/kg per età ≥12 mesi a ≤36 mesi.
Enanta Pharmaceuticals anunció resultados preliminares positivos de su estudio de Fase 2, el primero en pediatría, sobre zelicapavir para el tratamiento del virus sincitial respiratorio (VSR) en niños de 28 días a 36 meses. El estudio demostró efectos antivirales significativos con una disminución de 1.4 log en la carga viral al Día 5 en comparación con el placebo en la Parte 2. Un análisis preespecificado de pacientes tratados dentro de 3 días del inicio de los síntomas mostró una disminución de 1.2 log en la carga viral.
El estudio incluyó a 96 pacientes (70 recibiendo zelicapavir, 26 placebo) en dos partes. Zelicapavir mostró un perfil de seguridad favorable sin eventos adversos que llevaran a la interrupción del tratamiento. El fármaco logró niveles de exposición objetivo en todos los grupos de edad, con dosis de 5 mg/kg para edades de ≥28 días a <12 meses y 7.5 mg/kg para edades de ≥12 meses a ≤36 meses.
Enanta Pharmaceuticals는 28일에서 36개월 사이의 아동을 대상으로 실시한 zelicapavir의 호흡기 세포 융합 바이러스(RSV) 치료를 위한 1상 2단계 연구에서 긍정적인 최종 결과를 발표했습니다. 본 연구는 세제 2.Part에서 위약과 비교하여 5일째에 1.4 log 감소한 바이러스 부하에 관한 중요한 항바이러스 효과를 보여주었습니다. 증상 발현 후 3일 이내에 치료를 받은 환자에 대한 사전 지정된 분석 결과, 1.2 log 감소한 바이러스 부하를 나타냈습니다.
본 연구는 두 부분으로 나누어 96명의 환자가 참여하였으며 (70명이 zelicapavir 치료, 26명이 위약 치료), zelicapavir는 치료 중단으로 이어지는 부작용 없이 유리한 안전성 프로필을 보여주었습니다. 해당 약물은 모든 연령대에서 목표 노출 수치를 달성하였으며, 28일 ≥연령 <12개월인 경우에는 5mg/kg, 12개월 ≥연령 ≤36개월인 경우에는 7.5mg/kg의 용량을 투여했습니다.
Enanta Pharmaceuticals a annoncé des résultats préliminaires positifs de sa première étude de phase 2 chez les pédiatries pour zelicapavir dans le traitement du virus respiratoire syncytial (VRS) chez les enfants âgés de 28 jours à 36 mois. L'étude a démontré des effets antiviraux significatifs avec une baisse de 1,4 log de la charge virale au jour 5 par rapport au placebo dans la partie 2. Une analyse prédéfinie des patients traités dans les 3 jours suivant l'apparition des symptômes a montré une baisse de 1,2 log de la charge virale.
L'étude a inclus 96 patients (70 recevant zelicapavir, 26 placebo) répartis en deux parties. Zelicapavir a montré un profil de sécurité favorable sans événements indésirables entraînant une interruption du traitement. Le médicament a atteint des niveaux d'exposition cibles dans tous les groupes d'âge, avec des doses de 5 mg/kg pour les âges ≥28 jours à <12 mois et de 7,5 mg/kg pour les âges ≥12 mois à ≤36 mois.
Enanta Pharmaceuticals hat positive vorläufige Ergebnisse aus seiner ersten Phase-2-Studie bei Kindern zu zelicapavir zur Behandlung des Respiratorischen Synzytialvirus (RSV) bei Kindern im Alter von 28 Tagen bis 36 Monaten bekannt gegeben. Die Studie zeigte signifikante antivirale Effekte mit einem 1,4 log Rückgang der Viruslast am Tag 5 im Vergleich zu Placebo in Teil 2. Eine vordefinierte Analyse der Patienten, die innerhalb von 3 Tagen nach Symptombeginn behandelt wurden, zeigte einen 1,2 log Rückgang der Viruslast.
Die Studie umfasste 96 Patienten (70 erhielten zelicapavir, 26 Placebo) in zwei Teilen. Zelicapavir zeigte ein günstiges Sicherheitsprofil ohne unerwünschte Ereignisse, die zu einer Behandlungsunterbrechung führten. Das Medikament erreichte die angestrebten Expositionswerte in allen Altersgruppen, mit Dosen von 5 mg/kg für ≥28 Tage bis <12 Monate und 7,5 mg/kg für ≥12 Monate bis ≤36 Monate.
- Achieved primary endpoint with 1.4 log viral load decline at Day 5 in Part 2
- Demonstrated favorable safety profile with no treatment discontinuations
- Received FDA Fast Track designation
- Successfully achieved target drug exposure levels across all age groups
- Showed 1.2 log viral load reduction in early-treated patients
- No significant difference in symptoms between zelicapavir and placebo using ReSViNET assessment
- symptom data available from proprietary RESOLVE-P tool (only 15 patients)
Insights
The Phase 2 study results for zelicapavir represent a significant milestone in pediatric RSV treatment development. The 1.4 log viral load decline at Day 5 in Part 2 and 1.2 log decline in early-treated patients are clinically meaningful reductions. These results are particularly impressive given the challenging nature of pediatric drug development and the current lack of approved RSV antivirals.
The favorable safety profile in this vulnerable population aged 28 days to 36 months is crucial, as safety concerns often derail pediatric drug development. The achievement of consistent drug exposure across age groups and dosing cohorts indicates robust pharmacokinetics, which is essential for advancing to late-stage trials.
The study design, incorporating both hospitalized and non-hospitalized patients, provides valuable insights for positioning the drug in real-world clinical settings. However, the lack of clear symptom improvement using ReSViNET warrants careful consideration for future trial designs.
These positive results could significantly impact Enanta's market position in the competitive RSV therapeutics landscape. With RSV being a leading cause of infant hospitalizations, a successful oral antiviral could represent a substantial commercial opportunity. The FDA Fast Track designation further enhances the drug's market potential by potentially expediting the approval process.
For investors, key considerations include the drug's potential positioning against both existing and emerging RSV treatments, particularly given the recent approvals of preventive antibodies. The positive safety profile and once-daily oral administration could provide competitive advantages in terms of convenience and accessibility.
The stock may see increased interest as zelicapavir advances toward potential registration trials, though market response could be tempered by the mixed symptom reduction data.
- Observed an antiviral effect for the primary and secondary virology endpoints in the overall population, with a viral load decline of 1.4 log at the end of treatment in Part 2
- Demonstrated a viral load decline of 1.2 log compared to placebo at the end of treatment in prespecified analysis of patients randomized within 3 days of symptom onset
- Zelicapavir was well-tolerated with a favorable safety profile
- Conference call and webcast to discuss data at 8:30 a.m. ET today
“We are excited to share these positive results from our first-in-pediatric Phase 2 study of zelicapavir, which we believe confirm a strong profile for our lead RSV antiviral and strengthen Enanta’s position as a leader in developing treatments for RSV. Zelicapavir demonstrated an antiviral effect on both primary endpoints, as well as secondary virology endpoints. Furthermore, patients who joined the study within 3 days of symptom onset showed a robust 1.2 log reduction in viral load at Day 5. These data provide us with continued confidence in zelicapavir and valuable insights to inform the design of a potential registration enabling trial,” said Scott T. Rottinghaus, M.D., Chief Medical Officer of Enanta Pharmaceuticals. “There is a substantial need for safe and effective oral treatments for RSV, and we believe that these important antiviral data along with the favorable safety profile observed in this young, vulnerable population support further clinical evaluation of zelicapavir.”
“In my practice, I see many children requiring hospitalization for severe RSV infection during the RSV season. The impact of RSV is felt not only by patients and caregivers, but also broadly by public health. I believe that a safe and effective antiviral therapeutic is critical in addressing this significant and unmet need,” said Jaime Deville, MD, FAAP, a Principal Investigator in the Phase 2 pediatric clinical trial of zelicapavir and Professor of Clinical Infectious Diseases in the Department of Pediatrics at the David Geffen School of Medicine, University of
Zelicapavir Phase 2 Study Topline Results
This Phase 2 study was a randomized, double-blind, dose ranging, placebo-controlled study in hospitalized and non-hospitalized pediatric patients with RSV aged 28 days to 36 months. The primary objective of Part 1 of the study was to evaluate the safety and pharmacokinetics of zelicapavir and to determine the optimal dosing for Part 2 of the study. The primary objective of Part 2 of the study was to evaluate the antiviral activity of zelicapavir, with assessment of symptom severity as an exploratory objective. Because exposure was similar across all cohorts and doses, and all patients received a therapeutic dose, primary efficacy analyses were able to be performed across all dosed patients from Parts 1 and 2.
A total of 96 patients received zelicapavir (n=70) or placebo (n=26). Part 1 evaluated multiple doses and patients were treated with zelicapavir (n=36) or placebo (n=16) once-daily (QD) for 5 days. In Part 2, patients received the selected dose of zelicapavir (n=34) or placebo (n=10) QD for 5 days. Demographics and baseline characteristics were balanced across treatment groups, with the majority of patients being hospitalized at enrollment, and a mean duration of RSV symptoms prior to randomization of 4 days.
Zelicapavir demonstrated a favorable safety profile over the initial 5-day dosing period and through 23 days of follow-up. Adverse events (AEs) were similar between zelicapavir and placebo and there were no AEs leading to treatment discontinuation or study withdrawal. Furthermore, zelicapavir achieved target drug exposure levels across all age groups and dosing cohorts. Exposure was similar across cohorts and doses, and all patients received a therapeutic dose. A dose of 5 mg/kg was selected for age ≥ 28 days to <12 months, and a dose of 7.5 mg/kg was selected for age ≥12 months to ≤36 months.
An antiviral effect was observed for the primary and secondary virology endpoints in the overall pooled efficacy population, with the viral load decline peaking at 0.7 log on Day 9 compared to placebo. The primary endpoint for Part 2 of the study showed a more pronounced effect, with a viral load decline of 1.0 log at Day 3 and 1.4 log at Day 5 compared to placebo. Additionally, a rapid and robust antiviral effect was observed in the prespecified subset of patients who were randomized within 3 days of symptom onset, which represents about
As there are no validated symptom tools approved by regulatory agencies for pediatric RSV, multiple methods were used to assess symptoms. ReSViNET (REspiratory Syncytial VIrus NETwork), a publicly available pediatric tool with caregiver assessments, was used as an exploratory endpoint in all patients. This tool was originally designed primarily for prophylaxis studies to assess disease severity at a single timepoint. There was no difference in symptoms between zelicapavir and placebo using ReSViNET. RESOLVE-P (RESpiratory ObservabLE Reported Outcome-Pediatric), a proprietary tool being developed by Enanta in alignment with regulatory agency input, was specifically designed to assess the severity of pediatric RSV infection change over time based on observations by the child’s caregiver. As this tool was finalized and introduced late in the study, data are only available from a small number of patients (n=15). In this dataset, a trend toward greater symptom reduction in patients treated with zelicapavir was observed.
Full data from the study will be presented at a future medical conference or in a peer-reviewed publication.
Conference Call and Webcast Information
Enanta will host a conference call and webcast today at 8:30 a.m. ET. The live webcast can be accessed at "Events & Presentations" in the investors section of Enanta’s website. To participate by phone, please register for the call here. It is recommended that participants register a minimum of 15 minutes before the call. Once registered, participants will receive an email with the dial-in information. The archived webcast will be available on Enanta’s website for approximately 30 days following the event.
About Zelicapavir
Zelicapavir, Enanta’s lead N-protein inhibitor, is being developed for the treatment of RSV infection, and has been granted Fast Track designation by the
About Respiratory Syncytial Virus
RSV is the most common cause of bronchiolitis (inflammation of the small airways in the lung) and pneumonia in children under one year of age in
About Enanta Pharmaceuticals, Inc.
Enanta is using its robust, chemistry-driven approach and drug discovery capabilities to become a leader in the discovery and development of small molecule drugs with an emphasis on indications in virology and immunology. Enanta’s clinical programs are currently focused on respiratory syncytial virus (RSV) and its earlier-stage immunology pipeline aims to develop treatments for inflammatory diseases by targeting key drivers of the type 2 immune response, including KIT and STAT6 inhibition.
Glecaprevir, a protease inhibitor discovered by Enanta, is part of one of the leading treatment regimens for curing chronic hepatitis c virus (HCV) infection and is sold by AbbVie in numerous countries under the tradenames MAVYRET® (
Forward Looking Statements Disclaimer
This press release contains forward-looking statements, including with respect to the prospects for further development and advancement of zelicapavir for the treatment of RSV. Statements that are not historical facts are based on management’s current expectations, estimates, forecasts and projections about Enanta’s business and the industry in which it operates and management’s beliefs and assumptions. The statements contained in this release are not guarantees of future performance and involve certain risks, uncertainties and assumptions, which are difficult to predict. Therefore, actual outcomes and results may differ materially from what is expressed in such forward-looking statements. Important factors and risks that may affect actual results include: the development risks of early stage discovery efforts in the disease areas in Enanta’s research and development pipeline, such as RSV; the impact of development, regulatory and marketing efforts of others with respect to competitive treatments for RSV; Enanta’s limited clinical development experience; Enanta’s need to attract and retain senior management and key scientific personnel; Enanta’s need to obtain and maintain patent protection for its product candidates and avoid potential infringement of the intellectual property rights of others; and other risk factors described or referred to in “Risk Factors” in Enanta’s most recent Annual Report on Form 10-K for the fiscal year ended September 30, 2024 and other periodic reports filed more recently with the Securities and Exchange Commission. Enanta cautions investors not to place undue reliance on the forward-looking statements contained in this release. All forward-looking statements contained in this release speak only as of the date on which they were made and are based on management’s assumptions and estimates as of such date. Enanta undertakes no obligation to update such statements to reflect events that occur or circumstances that exist after the date on which they were made, except as required by law.
1. Centers for Disease Control & Prevention – Respiratory Syncytial Virus Last accessed: December 2024.
2. Centers for Disease Control & Prevention – RSV in Infants and Young Children Last accessed: December 2024.
3. Shi, Ting et al. “Global, regional, and national disease burden estimates of acute lower respiratory infections due to respiratory syncytial virus in young children in 2015: a systematic review and modelling study.” Lancet (
4. Falsey, Ann R et al. “Respiratory syncytial virus infection in elderly and high-risk adults.” The New England Journal of Medicine vol. 352,17 (2005): 1749-59. doi:10.1056/NEJMoa043951
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Source: Enanta Pharmaceuticals, Inc.
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