Phase 2a Randomized Placebo-Controlled Human Challenge Trial of the Respiratory Syncytial Virus L-Protein Inhibitor S-337395 for Respiratory Syncytial Virus Infection.
Stuart Byrne, Takamichi Baba, Nao Kawaguchi et al.
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In 30 seconds
This phase 2a, randomized, double-blind, placebo-controlled, single-centre human challenge trial assessed oral S-337395 in healthy adults aged 18–55 years inoculated with RSV-A Memphis 37b. Among 60 participants with confirmed infection, the 30-mg and 300-mg doses significantly reduced viral-load area under the curve (VL-AUC) by qRT-PCR compared with placebo: 64.87% and 88.94%, respectively (both P < .05). The 300-mg dose also reduced total symptom-score AUC by 78.15% (P < .05). Treatment was reported as well tolerated, with no safety concerns.
Key findings
- qRT-PCR VL-AUC was reduced by 64.87% with 30 mg and 88.94% with 300 mg; both comparisons had P < .05.
- Viral-culture VL-AUC was reduced by 72.32% with 30 mg and 86.17% with 300 mg; both comparisons had P < .05.
- Total symptom-score AUC was 78.15% lower in the 300-mg group (P < .05).
- S-337395 was well tolerated, with no safety concerns reported.
Why it matters
The findings provide proof-of-concept evidence that inhibiting RSV L-protein can reduce viral measures and symptoms in a controlled human infection model. The observed effects at higher doses support further evaluation of S-337395 as an oral antiviral, while the challenge setting and selected healthy population mean the results do not establish effectiveness in naturally acquired RSV illness or in broader patient groups.
What to keep in mind
This was a single-centre human challenge study in healthy adults aged 18–55 years, with efficacy assessed in 60 participants with confirmed infection; applicability to naturally acquired RSV and other populations is uncertain.