A novel antiviral strategy targeting human metapneumovirus through pH modulation in human airway epithelial cells

Human metapneumovirus (hMPV) is a major cause of respiratory infections, particularly among infants, older adults, and immunocompromised individuals, yet no approved vaccines or targeted antiviral therapies are currently available. pH-regulated processes, including airway epithelial physiology, endosomal acidification, and viral fusion mediated by the fusion (F) protein, are critical for hMPV infection. This study evaluates PHOH-001, an inhaled alkaline buffer, as a potential therapeutic strategy to modulate airway epithelial pH and inhibit hMPV infection. Using a recombinant hMPV expressing green fluorescent protein (rhMPV-GFP), viral replication was assessed in primary human airway epithelial cells (HAECs). PHOH-001 significantly reduced GFP expression at 72 hours post-infection in both submerged and air-liquid interface (ALI) cultures, with effects comparable to those of the endosomal acidification inhibitor bafilomycin A1. In Vero E6 cells, used as a mechanistic <i>in vitro</i> model, PHOH-001 increased extracellular and intracellular pH in a concentration-dependent manner and correspondingly reduced hMPV infection. In HAECs, PHOH-001 reduced viral replication, as measured by TCID ₅₀ assays of infectious virus, and inhibited syncytium formation, a key step in viral spread. Furthermore, PHOH-001 altered F protein localization and was associated with changes in actin organization, consistent with impaired viral spread. Collectively, these findings demonstrate that PHOH-001 alters multiple pH-dependent steps in hMPV infection <i>in vitro</i> and support airway pH modulation as a potential antiviral strategy against hMPV.