Exosomal heterogeneity and functional zonation in cancer drug resistance

Exosomes are nanoscale extracellular vesicles that mediate critical intercellular communication within the tumor microenvironment (TME). Recent advancements reveal that exosome populations within tumors are not uniform but exhibit significant heterogeneity in their molecular cargo and functional output. This heterogeneity is particularly pronounced in spatially organized tumors, where distinct functional zones, driven by gradients in local stress, perfusion, and metabolic states, orchestrate the release of unique exosome subtypes. These functional zones include stromal, hypoxic, perivascular, quiescent, and immune-cold regions. The zone-specific exosomes deliver specialized molecular cargos, including nucleic acids, proteins, lipids, and metabolites, to recipient cells within the TME and at distant sites. This communication promotes tumor sustenance and contributes to drug resistance through diverse mechanisms, such as immune suppression, epithelial-mesenchymal transition (EMT), metabolic reprogramming, and the activation of prosurvival signaling pathways. Although bulk exosome analysis has enabled the development of biomarkers for personalized medicine, it often fails to capture these intricate, zone-specific influences. This review explores emerging techniques, including single-cell sequencing, microchip-based 3D tumor cultures, advanced spectroscopic methods, and spatial biology platforms, that are poised to elucidate the spatiotemporal communication networks mediated by zonal exosomes, thereby advancing the understanding of drug resistance mechanisms.