Membrane Radiolabelling of Exosomes for Comparative Biodistribution Analysis in Immunocompetent and Immunodeficient Mice - A Novel and Universal Approach

• Published in: Theranostics Vol. 9; no. 6; pp. 1666 - 1682
• Main Authors: Faruqu, Farid N, Wang, Julie Tzu-Wen, Xu, Lizhou, McNickle, Luke, Chong, Eden Ming-Yiu, Walters, Adam, Gurney, Mark, Clayton, Aled, Smyth, Lesley A, Hider, Robert, Sosabowski, Jane, Al-Jamal, Khuloud T
• Format: Journal Article
• Language: English
• Published: Australia Ivyspring International Publisher 01.01.2019
• Subjects: Administration, Intravenous; Animals; Cell Line, Tumor; Cell Membrane - chemistry; Drug Carriers - administration & dosage; Drug Carriers - chemistry; Drug Carriers - pharmacokinetics; Drug Delivery Systems; Exosomes - chemistry; Isotope Labeling - methods; Mice, Inbred C57BL; Research Paper; Tissue Distribution; biodistribution; drug delivery; radiolabelling; exosomes
• ISSN: 1838-7640; 1838-7640
• DOI: 10.7150/thno.27891

Extracellular vesicles, in particular exosomes, have recently gained interest as novel drug delivery vectors due to their biological origin and inherent intercellular biomolecule delivery capability. An in-depth knowledge of their biodistribution is therefore essential. This work aimed to develop a novel, reliable and universal method to radiolabel exosomes to study their biodistribution. : Melanoma (B16F10) cells were cultured in bioreactor flasks to increase exosome yield. B16F10-derived exosomes (Exo ) were isolated using ultracentrfugation onto a single sucrose cushion, and were characterised for size, yield, purity, exosomal markers and morphology using Nanoparticle Tracking Analysis (NTA), protein measurements, flow cytometry and electron microscopy. Exo were radiolabelled using 2 different approaches - intraluminal labelling (entrapment of Indium tropolone shuttling); and membrane labelling (chelation of Indium covalently attached bifunctional chelator DTPA-anhydride). Labelling efficiency and stability was assessed using gel filtration and thin layer chromatography. Melanoma-bearing immunocompetent (C57BL/6) and immunodeficient (NSG) mice were injected intravenously with radiolabelled Exo (1x10 particles/mouse) followed by metabolic cages study, whole body SPECT-CT imaging and gamma counting at 1, 4 and 24 h post-injection. : Membrane-labelled Exo showed superior radiolabelling efficiency and radiochemical stability (19.2 ± 4.53 % and 80.4 ± 1.6 % respectively) compared to the intraluminal-labelled exosomes (4.73 ± 0.39 % and 14.21 ± 2.76 % respectively). Using the membrane-labelling approach, the biodistribution of Exo in melanoma-bearing C57Bl/6 mice was carried out, and was found to accumulate primarily in the liver and spleen (~56% and ~38% ID/gT respectively), followed by the kidneys (~3% ID/gT). Exo showed minimal tumour i.e. self-tissue accumulation (~0.7% ID/gT). The membrane-labelling approach was also used to study Exo biodistribution in melanoma-bearing immunocompromised (NSG) mice, to compare with that in the immunocompetent C57Bl/6 mice. Similar biodistribution profile was observed in both C57BL/6 and NSG mice, where prominent accumulation was seen in liver and spleen, apart from the significantly lower tumour accumulation observed in the NSG mice (~0.3% ID/gT). : Membrane radiolabelling of exosomes is a reliable approach that allows for accurate live imaging and quantitative biodistribution studies to be performed on potentially all exosome types without engineering parent cells.