Polyamine depletion inhibits murine and human norovirus infection.

UNLABELLED: Noroviruses are non-enveloped, positive-sense RNA viruses in the family Caliciviridae. Human noroviruses (HNoVs) are the leading cause of viral gastrointestinal disease. Despite their clinical relevance, therapeutic strategies for norovirus infections remain limited, partly due to challenges in cultivating HNoV and limited understanding of virus-host interactions. Polyamines (PAs) are small polycationic metabolites derived from amino acid metabolism that are essential for diverse cellular functions and serve as important host factors for many RNA viruses. However, their role in norovirus infection has remained elusive. Here, we demonstrate that PAs are critical for productive infection for both HNoV and murine norovirus (MNV), underscoring a conserved and functionally significant dependency across species. Functional analysis in MNV-infected cells showed that PA depletion resulted in a marked reduction in major capsid protein synthesis and reduced viral titers following the first replication cycle, coinciding with a loss of virus-induced cytopathic effect (CPE). In PA-depleted cells, viral titers and CPE could be restored by exogenous supplementation with spermine or spermidine (metabolites of the PA biosynthetic pathway), cholesterol, or a PI3-kinase inhibitor. In addition to MNV, depletion of PAs completely ablated HNoV infection in human intestinal enteroids, which was also partially rescued by adding exogenous PAs. Collectively, these findings identify PAs as a novel host dependency factor that facilitates norovirus infection and highlight PA metabolism as a potential therapeutic target for antiviral intervention against HNoV.

IMPORTANCE: Human noroviruses (HNoVs) are a major cause of acute viral gastroenteritis worldwide, yet the development of effective antivirals and vaccines has been hampered by the lack of small-animal models and robust in vitro systems to propagate the virus. Murine norovirus (MNV) shares key features with HNoV and serves as a valuable surrogate for studying norovirus biology. In this study, we identify host-derived polyamines (PAs) as essential and conserved metabolites required for productive infection for both HNoV and MNV. PAs exert multifactorial effects on norovirus infection, particularly by facilitating virus-induced apoptosis and promoting virion release in MNV-infected cells. Notably, PA depletion using difluoromethylornithine (DFMO), a well-established inhibitor of PA synthesis, effectively suppressed MNV and HNoV infection. Therefore, our results provide new insights into norovirus-host interactions and highlight the potential of a host-targeting antiviral approach to limit norovirus infection. Furthermore, our findings provide a rationale for further investigating DFMO, a licensed and well-tolerated drug, as a potential therapeutic option for chronic norovirus infections in immunocompromised patients.