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Oral Antiviral Candidate Shows Promise for Respiratory Syncytial Virus Treatment
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Key Takeaways
- S-337395 significantly reduces RSV viral load and improves clinical symptoms, achieving an 88.4% reduction in the highest dose group.
- The compound inhibits RNA-dependent RNA polymerase activity, differing from F protein inhibitors, and prevents viral proliferation.
S-337395 demonstrates an 88.4% reduction in viral load and had a statistically significant improvement in clinical symptoms scores.
New study findings show positive results from a phase 2 clinical trial, assessing S-337395 (Shionogi & Co Ltd and UBE Corporation), an oral antiviral candidate, for the treatment of respiratory syncytial virus (RSV). The randomized, placebo-controlled, double-blind human challenge study achieved its primary end point of significant reduction in viral load compared to the placebo group, according to study authors.1
S-337395 is a low-molecular-weight compound that contains a novel mechanism that inhibits the ribonucleic acid (RNA)-dependent RNA polymerase activity of the L protein controlled by RSV, which is crucial for virus replication. The study authors noted that S-337395 differs from the F protein inhibitors due to its role in preventing viral proliferation among infected cells, providing higher efficacy and a greater rapid reduction in the viral load.1
Further antiviral treatment options are needed for RSV as more than 3 million US individuals are infected each year. RSV infection leads to high rates of hospitalization and mortality amongst older adults, accounting for an estimated 159,000 hospitalizations in adults 65 years and older. Individuals with asthma, chronic obstructive pulmonary disease, and congestive heart failure are also considered high risk and could experience severe outcomes if infected with RSV.1,2
The phase 2 human challenge trial included a total of 114 healthy individuals that were intentionally infected with RSV and aimed to evaluate the onset of disease and the progression of symptoms after receiving S-337395 treatment or placebo for 5 days. The results displayed that the highest dose group of S-337395 demonstrated an 88.4% reduction in viral load and had a statistically significant improvement in clinical symptoms scores. Further results found that the antiviral treatment was safe and well tolerated and did not present any serious or severe adverse events, according to study authors.1
The positive study results follow the FDA fast track designation granted for S-337395 in October 2024, which aimed to review the potential new therapies that could treat RSV infection.3
Currently, ribavirin (Virazole; Bausch Health) is an FDA approved antiviral for RSV and is intended to treat high risk individuals, including older adults who are hospitalized due to infection. The role of ribavirin is to increase the mutation rate of the viral polymerase during RSV replication, which impacts the production of the virus. Additionally, nirsevimab (Beyfortus; AstraZeneca and Sanofi) was approved by the FDA in 2023, for the prevention of lower respiratory tract infection among infants 8 months or younger and children up to 24 months of age with an increased risk of RSV.4 However, S-337395 could offer further antiviral treatment to this patient population.1
