Respiratory viruses are amongst the leading cause of acute illness worldwide, with the influenza virus alone causing 650,000 annual deaths. The rise of antiviral resistance in influenza underscores the urgent need for new antiviral treatments. Natural products are a valuable source of antimicrobials, amongst which the spirotetronate polyketides have demonstrated potent bioactivity. The class II spirotetronate MM 46115 (renamed pellemicin) was previously reported to possess antiviral activity against parainfluenza, influenza and RSV, with the latter two at cytotoxic concentrations.    We investigated the antiviral properties and mechanism of action of pellemicin by isolating it from the Actinomadura pelletieri bacterial strain. Pellemicin demonstrated antiviral activity without toxicity against influenza A and B with an IC50 of 0.762 µM. Infections performed over 24 hours showed pellemicin activity lasted 6-8 hours, whilst time-of-addition assays indicated pellemicin was targeting an early stage of viral infection. Furthermore, mechanistic studies showed pellemicin does not affect viral haemagglutinin or neuraminidase activity nor disrupt viral replication. This suggested a host-targeted mechanism, which was supported by microscopy experiments that showed pellemicin inhibited internalisation via clathrin-mediated endocytosis (CME), a process used for virus uptake. Proteomic analysis further identified 4 host proteins associated with viral replication or immune regulation (IRAK4, GCLC, ITGB4, FLT4) which were altered by pellemicin, indicating it may have multiple targets.   Overall, these findings establish pellemicin as a host-targeting antiviral which inhibits CME and potentially modulates multiple host pathways. Pellemicin and its related structural compounds therefore represent promising candidates for the development of novel therapeutics against respiratory viral infections.