Rabeprazole exhibits broad-spectrum fusion inhibition against Nipah pseudovirus and authentic HCoV-OC43 and RSV.

Rabeprazole was previously defined as a small-molecule fusion inhibitor that binds the conserved hydrophobic HR1 groove of the SARS-CoV-2 spike and blocks six-helix bundle assembly. Here, we expand its antiviral spectrum and demonstrate potent activity against Nipah virus pseudotype, HCoV-229E, and RSV. Using SPR, pseudovirus neutralization, docking, and 100-ns MD simulations, we validated binding of Rabeprazole to the HR1 domains of NiV F glycoprotein and HCoV-229E spike, with a conserved fusion-inhibitory mechanism. Systematic structure-activity relationship (SAR) profiling among clinically approved PPIs revealed that Ilaprazole and Lansoprazole exhibited stronger anti-NiV potency than Rabeprazole, while Rabeprazole sulfide showed enhanced antiviral activity relative to the parent compound. Rabeprazole also inhibited live RSV and HCoV-229E infection in a dose-dependent manner. Collectively, these findings establish the HR1 groove as a druggable pan-viral target and validate benzimidazole-based PPIs as a versatile scaffold for developing orally available, broad-spectrum antivirals against phylogenetically distinct enveloped viruses that rely on class I fusion machinery.