Enanta Pharmaceuticals starts late-stage RSV trial with 2027 data due
RESOLVE will test symptom recovery and hospitalization in high-risk adults, starting with at least 200 patients in its Phase 2b portion.
Adrian Kessler
A late-stage test of oral RSV treatment zelicapavir has begun as Enanta Pharmaceuticals, Inc. NASDAQENTA dosed the first patient in RESOLVE, the company said on Monday. The Phase 2b portion will enroll at least 200 high-risk adults, with results expected in 2027.
The Oct. 26 announcement sets symptom recovery as the main measure of success, with hospitalization a key secondary endpoint. A subsequent Phase 3 portion is expected to enroll approximately 660 patients, but Enanta did not give an enrollment completion date.
Enanta is a small clinical-stage biotechnology company based in Watertown, Mass., developing oral medicines for viral infections and immunological diseases. Enanta shares NASDAQENTA closed at US$11.64 on Nasdaq at 4:00 p.m. EDT on Oct. 23, before Monday's announcement.
The next adult RSV data are due in 2027, alongside results from the pediatric LOTUS study. Enanta's Aug. 10 financial report projected funding into fiscal 2029, based on cash and investments plus retained future royalties.
RESOLVE Tests Recovery And Hospitalization
The randomized, double-blind trial compares zelicapavir with placebo in outpatients who test positive for RSV within three days of respiratory symptoms starting. Eligible adults must have congestive heart failure, chronic obstructive pulmonary disease or be at least 75 years old.
Participants will receive 800 milligrams of zelicapavir or placebo once daily for seven days, followed by another 28 days of evaluation. The primary endpoint is time to complete resolution of all 13 RSV symptoms measured with the RiiQ tool.
The initial portion is designed to confirm the treatment effect size in that selected population. It will also assess hospitalization, other clinical measures, antiviral activity and safety before the larger planned stage.
"The Phase 2b portion is designed to confirm the treatment effect size and generate an additional dataset with the goal of strengthening the clinical evidence supporting zelicapavir," Enanta chief medical officer Scott T. Rottinghaus said in Monday's release.
The selection follows an earlier adult trial in which Enanta reported a 6.7-day symptom-resolution benefit for the subgroup with those risk factors. Monday's release also cited RSV-related hospitalization rates of zero per cent with zelicapavir versus five per cent with placebo.
The announcement did not provide that subgroup's denominator, confidence interval or p value. Those earlier findings therefore leave RESOLVE to establish the size and reliability of the benefit in its prospectively selected population.
Enanta said zelicapavir had been well tolerated in more than 700 people across development, but Monday's announcement contained no new trial safety results. The drug inhibits the RSV N-protein, targeting viral replication.
Enanta announced the development plan on June 18 after an end-of-Phase 2 meeting with the FDA. The company describes the combined trial as registrational and says zelicapavir has Fast Track designation; neither amounts to approval.
RSV Vaccines Address Prevention
The commercial RSV peer group includes GSK plc LONGSK NYSEGSK, whose Arexvy vaccine addresses prevention. GSK announced expanded U.S. approval on March 13 for adults aged 18 to 49 at increased risk, extending its existing older-adult indications.
Read more: GSK wins FDA approval for Hibsago in chronic hepatitis B
Pfizer Inc. NYSEPFE also markets a preventive RSV vaccine. Its Oct. 22, 2024 announcement documented Abrysvo's U.S. approval for high-risk adults aged 18 to 59, alongside its older-adult indication.
Read more: Pfizer details 25-strain infant vaccine data as pivotal trials advance
Those preventive products serve a different clinical purpose from treating patients after infection. For broader sector context, the iShares Biotechnology ETF NASDAQIBB closed at US$207.74 at 4:00 p.m. EDT on Oct. 23.
Enanta held US$211.5 million in cash and marketable securities at June 30, according to its August report. The next RSV milestones are the adult RESOLVE Phase 2b and pediatric LOTUS readouts in 2027, which will test symptom recovery in their respective populations.
