Radioiodine labeling and in vivo trafficking of extracellular vesicles

Biodistribution and role of extracellular vesicles (EVs) are still largely unknown. Reliable tracking methods for EVs are needed. In this study, nuclear imaging using radioiodine were developed and applied for tracking EVs derived from cell lines. EVs were obtained from supernatant of thyroid cancer cell (Cal62) and natural killer cells (NK92-MI) using sequential ultracentrifuges. Sulfosuccinimidyl-3-(4-hydroxypheynyl) propionate were labeled to membrane of Cal62 and NK92-MI cell derived EVs, then the EVs were labeled with radioiodine (I-131 and I-125) using pre-coated iodination tubes (RI-EVs). In vivo gamma camera images were obtained after intravenous injection of the RI-EVs, and ex vivo biodistribution study was also performed. EVs were labeled with radioiodine and radiochemical purity of the RI-EV was more than 98%. Results of nanoparticle tracking analysis and electron microscopy showed that there was no significant difference in EVs before and after the radioiodine labeling. After intravenous injection of RI-EVs to mice, gamma camera imaging well visualized the real-time biodistribution of the RI-EVs. RI-EVs were mainly visualized at liver, spleen, and lung. Nuclear imaging system of EVs derived from thyroid cancer and NK cells using radioiodine labeling of the EVs was established. Thus, this system might be helpful for in vivo tracking of EVs.