Enanta Pharma Reports Positive Phase 2a Results for EDP-323 in RSV Study

Enanta Pharmaceuticals, Inc., a clinical-stage biotechnology company based in Watertown, MA, has released promising results from a Phase 2a human challenge study of EDP-323, a novel treatment for respiratory syncytial virus (RSV). This study involved healthy adults infected with RSV, and the results indicate that EDP-323 is both safe and effective, showing significant reductions in viral load and symptom severity compared to a placebo.

The study's primary findings revealed that EDP-323 resulted in an 85-87% reduction in viral load area under the curve (AUC) as measured by quantitative reverse transcription PCR (qRT-PCR), and a 97-98% reduction in infectious viral load AUC as confirmed by viral culture. Additionally, the total clinical symptoms score AUC was reduced by 66-78% in those treated with EDP-323. These results are noteworthy for their statistical significance (p<0.0001) and align with Enanta's goal of providing a potent, once-daily oral treatment for RSV.

Scott T. Rottinghaus, M.D., Chief Medical Officer at Enanta Pharmaceuticals, expressed enthusiasm over these findings, emphasizing the rapid and sustained antiviral effects of EDP-323. He noted that these are among the most compelling data reported for an RSV challenge study, highlighting EDP-323's potential as a direct-acting antiviral agent.

Jay R. Luly, Ph.D., President and CEO of Enanta Pharmaceuticals, also commented on the meaningful progress represented by these results. He underscored the ongoing need for safe and effective oral treatments for respiratory infections like RSV. Enanta's portfolio includes potent RSV replication inhibitors, with both EDP-323 and another compound, zelicapavir, in Phase 2 development. These inhibitors work through distinct mechanisms and may be used as single agents or in combination for tailored patient treatments.

The Phase 2a study was designed as a randomized, double-blind, placebo-controlled challenge involving 142 participants who were inoculated with RSV. The study included three groups: one receiving a high dose of EDP-323 (600 mg daily for five days), another receiving a lower dose (600 mg on the first day followed by 200 mg daily for four days), and a placebo group.

The efficacy of EDP-323 was demonstrated through significant reductions in viral load and clinical symptoms compared to placebo. Both dosing regimens of EDP-323 showed similar results, suggesting no significant difference between the high and low dose groups. Moreover, the pharmacokinetics of EDP-323 supported once-daily dosing, with mean plasma concentrations remaining well above the effective concentration for both RSV A and B strains.

Safety-wise, EDP-323 was well-tolerated over the five-day dosing period and through the 28 days of follow-up. Adverse events were similar across the EDP-323 and placebo groups, with no serious or severe adverse events reported, nor any incidents leading to discontinuation or withdrawal from the study.

Future presentations at medical conferences or publications will provide more detailed data from this study. EDP-323, having received Fast Track designation from the U.S. Food and Drug Administration, has already shown promise in prior Phase 1 studies and in preclinical models, where it demonstrated significant reductions in RSV replication.

RSV is a major cause of respiratory illness, particularly in children under one year and older adults. It leads to millions of cases worldwide, with significant hospitalization and mortality rates. Enanta Pharmaceuticals aims to address this substantial health threat through its innovative treatments, leveraging its expertise in small molecule drug development for virology and immunology indications.