正电子发射断层扫描 (PET) 是研究药物输送系统体内行为的强大工具。我们的目的是评估细胞外囊泡 (EV) 的生物分布，这是使用 PET 从各种人类细胞来源分离的细胞分泌的纳米大小的囊泡。通过离心从间充质基质细胞 (MSC) (MSC EV)、人巨噬细胞 (Mφ EV) 和黑色素瘤细胞系 (A375 EV) 中分离出 EV，并与去铁胺缀合，以用 Zr-89 进行放射性标记。使用共轭和放射性标记的 EV 进行 PET 评估其体内生物分布和组织向性。我们的研究还利用免疫功能正常和免疫功能低下的小鼠以及 A375 异种移植肿瘤模型研究了小鼠模型的差异。最后，我们研究了不同标记技术对观察到的 EV 生物分布的影响，包括共价表面修饰和膜掺入。 PET 显示，所有测试的 EV 均表现出体内循环延长，并且肝脏、脾脏和肺的摄取量普遍较低。然而，Mφ EVs 显示出较高的肝脏摄取量，这可能归因于这些 EVs 表面蛋白成分的内在组织向性。免疫功能正常的小鼠和免疫缺陷的小鼠之间的 MSC EV 生物分布不同，在后者中观察到脾脏摄取增加。使用 A375 异种移植物的 PET 证明肿瘤对 EV 的有效摄取，但没有发现 A375 EV 的优先组织特异性趋向性。标记技术之间的生物分布差异表明，与膜整合相比，表面缀合的 EV 具有优先的血液循环和较低的肝脏、脾脏和肺吸收。这项研究证明了 EV 作为各种疾病的有效药物载体的潜力，强调了选择适当的细胞来源用于基于 EV 的药物输送的重要性，并表明可以利用 EV 的趋向性来优化治疗效果。我们的研究结果表明，EV 的细胞来源、标记技术和动物模型可以影响观察到的生物分布。

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