S-337308

S-337308 (formerly known as S-336) is an investigational, orally bioavailable small molecule antiviral agent developed by Shionogi for the treatment of Respiratory Syncytial Virus (RSV) infection. It functions as a potent and selective inhibitor of the RSV polymerase, specifically targeting the L protein (large protein) which is essential for viral RNA transcription and replication. By binding to the polymerase complex, S-337308 effectively prevents the synthesis of viral mRNA and the replication of the viral genome, thereby halting the production of new viral progeny. Preclinical studies have demonstrated that S-337308 possesses broad-spectrum antiviral activity against various RSV strains, including both A and B subtypes, and exhibits a high genetic barrier to the development of resistance. The drug is currently in clinical development, with trials focusing on its safety, tolerability, and efficacy in healthy volunteers and patients with RSV infection, aiming to address the significant unmet medical need in pediatric, elderly, and immunocompromised populations.