Enanta Pharmaceuticals, Inc. (NASDAQ:ENTA), a clinical-stage biotechnology company dedicated to creating best-in-class small molecule drugs for virology and immunology indications, today announced positive topline results from a Phase 2a human challenge study of EDP-323 in healthy adults infected with respiratory syncytial virus (RSV). These data demonstrated that EDP-323 was generally safe and well-tolerated and achieved an 85-87% reduction in viral load area under the curve (AUC) by qRT-PCR (p<0.0001), a 97-98% reduction in infectious viral load AUC by viral culture (p<0.0001), and a 66-78% reduction of total clinical symptoms score AUC (p<0.0001) compared to placebo. EDP-323, which received Fast Track designation from the U.S. Food and Drug Administration (FDA), is a novel L-protein inhibitor in development as a once-daily oral treatment for RSV.
“We are excited about these impressive data that demonstrate a rapid and sustained reduction in viral load. These results are among the strongest ever reported in an RSV challenge study, raising the high bar set by zelicapavir. The significant antiviral activity and symptom alleviation observed in this study highlight EDP-323’s potential as a safe, highly effective, direct-acting antiviral for the treatment of RSV,” said Scott T. Rottinghaus, M.D., Chief Medical Officer of Enanta Pharmaceuticals.
“These EDP-323 results represent a meaningful advancement toward achieving our longstanding goal of developing new medicines to treat respiratory infections such as RSV, as there remains a substantial need for safe and effective oral treatments. Enanta has the leading portfolio of potent RSV replication inhibitors, with EDP-323, our L-protein inhibitor, and zelicapavir, our N-protein inhibitor, both in Phase 2 development. These distinct mechanisms have the potential to be developed as once-daily single agents or in combination for specific patient populations,” added Jay R. Luly, Ph.D., President and Chief Executive Officer of Enanta Pharmaceuticals.
EDP-323 Phase 2a Challenge Study Topline Results
This Phase 2a study was a randomized, double-blind, placebo-controlled, human challenge study of 142 healthy adult participants inoculated with RSV. Randomized participants (n=141) received either a once-daily (QD) 600 mg dose of EDP-323 for five days [high dose, n=47], a single 600 mg loading dose on day one followed by a 200 mg once-daily (QD) dose of EDP-323 for four days [low dose, n=47], or placebo for five days [n=47]. The intent-to-treat-infected population (ITT-I) was defined as all randomized participants receiving challenge virus and at least one dose of study drug with confirmed RSV infection.
EDP-323 demonstrated a rapid and sustained antiviral effect. A highly statistically significant reduction (p<0.0001) was observed for the primary efficacy endpoint of AUC for viral load as measured by qRT-PCR in the ITT-I population for each of the EDP-323 dosing groups as compared with placebo. Specifically, EDP-323 lowered viral load AUC by 85% in the high dose arm and 87% in the low dose arm compared to placebo. There was no statistically significant difference between the two EDP-323 dosing groups.
A highly statistically significant reduction (p<0.0001) was observed for the secondary efficacy endpoint of AUC for infectious viral load as measured by quantitative culture in the ITT-I population for each of the EDP-323 dosing groups, with a reduction in viral culture AUC by 98% in the high dose arm and 97% in the low dose arm compared to placebo. There was no statistically significant difference between the two EDP-323 dosing groups.
For the secondary efficacy endpoint of AUC for total symptom score, a highly statistically significant reduction (p<0.0001) was observed in the ITT-I population for each of the EDP-323 dosing groups, with a symptom reduction of 66% in the high dose arm and 78% in the low dose arm compared to placebo. There was no statistically significant difference between the two EDP-323 dosing groups.
EDP-323 demonstrated favorable pharmacokinetics, supportive of once-daily dosing. Mean trough plasma concentrations were maintained at 16-fold above the protein-adjusted EC90 with the low dose, and 35-fold above the protein-adjusted EC90 with the high dose, for both RSV A and B strains.
Overall, EDP-323 demonstrated a favorable safety profile over a 5-day dosing period and through 28 days of follow-up. Adverse events were similar between EDP-323 dosing groups and placebo. There were no serious adverse events, no severe adverse events, and no adverse events leading to treatment discontinuation or study withdrawal.
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.