111In-radiolabeling of Mesenchymal Stem Cell-derived Extracellular Vesicles for Quantitative In Vivo Imaging

Purpose: Extracellular vesicles (EVs) serve as an important mode of cell-to-cell communication, and these vesicles are capable of horizontal transfer of protein, nucleic acids and lipids from parental cells to recipient cells. In order to assess the pharmacokinetics and biodistribution of EVs, the effective method to in vivo tracking EVs is needed. This study aims to label Wharton’s jelly MSC derived EVs (WJ-MSC-EVs) with 111In-oxine (8-hydroxyquinoline) for assessment of the biodistribution of the vesicles in vivo with small animal SPECT/CT imaging. Procedures: WJ-MSC-EVs were isolated from conditioned medium when the cells reached 90% confluence, then characterized using western blot, transmission electron microscopy (TEM), and nanoparticle tracking analysis (NTA). For in vivo tracking, WJ-MSC-EVs were labeled with 111In-oxine and injected to the C57BL/6 mice, followed by μSPECT/CT imaging. Organs and tissues were further assessed for quantitative analysis of ex vivo biodistribution. Results: The radiochemical purity of 111In-oxine-EVs was generally over 90% and remained stable up to 24 h. Further, WJ-MSC-EVs maintained their characteristics after radiolabeling with 111In-oxine. The results of μSPECT/CT imaging of the mice administrated with 111In-oxine-EVs showed accumulation of radiolabeled vesicles mainly in the liver, spleen, and kidney, whereas mice administrated with 111In-oxine exhibited high uptake of radiotracer in the lung and kidney. The ex vivo biodistribution of mice injected with 111In-oxine-EVs or 111In-oxine showed similar to the results of in vivo imaging. Conclusion: This study demonstrates that 111In-labeled EVs is able to reflect the in vivo behavior of WJ-MSC-EVs by μSPECT/CT imaging. The presented radiolabeling procedure is proved not to cause damages to the EVs but keep their original characteristics. Further, to chelate free 111Indium with EDTA is found necessary to decrease the nonspecific uptake. In conclusion, we have developed a simple, stable and potential radiolabeled probe for in vivo dynamic monitoring of exogenously administered WJ-MSC-EVs.