Transporting via Neutrophil as a Key Mechanism for Nanoparticle Redistribution to Tumor and Spleen

Elucidating nanoparticle (NP) tumor accumulation mechanisms is crucial for advancing chemotherapeutic nanomedicines. While the Enhanced Permeability and Retention (EPR) effect constitutes the cornerstone of passive tumor targeting, the efficacy of most EPR-driven nanomedicines is limited by low tumor accumulation (<1%). Recently, endothelial macropinocytosis has emerged as another major mechanism. Critically, both mechanisms depend on sustained plasma concentrations of NPs. However, we observed a paradoxical phenomenon unexplained by existing paradigms: persistent late-phase tumor accumulation occurring when plasma NPs decline to undetectable levels. Resolving this, we identified neutrophil hitchhiking as the dominant intermediate-to-late phase mechanism. Tumor burden substantially enhanced late-phase neutrophil-hitchhiked NPs. Intravital imaging directly visualized neutrophil-mediated NP delivery via adhesion, aggregation, and transendothelial transport during late-phase. Furthermore, we observed that neutrophil hitchhiking mechanism governs late-phase splenic accumulation as well. By modulating NP surface properties to achieve differential neutrophil-hitchhiking affinity, we demonstrated that enhanced neutrophil-hitchhiked NP delivery directly correlates with superior late-phase spleen-targeting efficiency. Thus, neutrophil hitchhiking drives sustained tumor and spleen redistribution of NPs amidst systemic NP clearance. These findings propose distinct design principles for nanomedicine leveraging peripheral blood immune cell interactions for organ-selective targeting.