Investigating\nthe In Vivo Biodistribution of Extracellular\nVesicles Isolated from Various Human Cell Sources Using Positron Emission\nTomography

Positron emission tomography (PET) is a powerful tool\nfor investigating\nthe in vivo behavior of drug delivery systems. We aimed to assess\nthe biodistribution of extracellular vesicles (EVs), nanosized vesicles\nsecreted by cells isolated from various human cell sources using PET.\nEVs were isolated from mesenchymal stromal cells (MSCs) (MSC EVs),\nhuman macrophages (Mϕ EVs), and a melanoma cell line (A375 EVs)\nby centrifugation and were conjugated with deferoxamine for radiolabeling\nwith Zr-89. PET using conjugated and radiolabeled EVs evaluated their\nin vivo biodistribution and tissue tropisms. Our study also investigated\ndifferences in mouse models, utilizing immunocompetent and immunocompromised\nmice and an A375 xenograft tumor model. Lastly, we investigated the\nimpact of different labeling techniques on the observed EV biodistribution,\nincluding covalent surface modification and membrane incorporation.\nPET showed that all tested EVs exhibited extended in vivo circulation\nand generally low uptake in the liver, spleen, and lungs. However,\nMϕ EVs showed high liver uptake, potentially attributable to\nthe intrinsic tissue tropism of these EVs from the surface protein\ncomposition. MSC EV biodistribution differed between immunocompetent\nand immunodeficient mice, with increased spleen uptake observed in\nthe latter. PET using A375 xenografts demonstrated efficient tumor\nuptake of EVs, but no preferential tissue-specific tropism of A375\nEVs was found. Biodistribution differences between labeling techniques\nshowed that surface-conjugated EVs had preferential blood circulation\nand low liver, spleen, and lung uptake compared to membrane integration.\nThis study demonstrates the potential of EVs as effective drug carriers\nfor various diseases, highlights the importance of selecting appropriate\ncell sources for EV-based drug delivery, and suggests that EV tropism\ncan be harnessed to optimize therapeutic efficacy. Our findings indicate\nthat the cellular source of EVs, labeling technique, and animal model\ncan influence the observed biodistribution.