Monitoring of exosome dynamics in living organisms is essential to demonstrate the real functions of cancer-derived exosomes. Currently, these have been elucidated in vitro or under non-physiological conditions in vivo in most cases. To overcome these limitations, researchers from the Aichi Cancer Center Research Institute developed an imaging method using Antares2-mediated bioluminescence resonance energy transfer (BRET) for observing long-term accumulation of exosomes in vivo. Ectopic expression of CD63-Antares2 effectively labeled exosomes with Antares2, which emitted intense, long-wavelength luminescence suitable for in vivo monitoring. Transplantation of CD63-Antares2-expressing prostate cancer cells into mice allowed determining the amount of cancer-derived exosomes released from primary tumors into the bloodstream and visualizing the long-term homing behavior of exosomes to their target organs or tissues. Interestingly, secreted exosome was decreased upon administration of low dose of dasatinib, an approved tyrosine-kinase inhibitor. The CD63-Antares2 xenograft mouse model will be useful for elucidating the dynamics of cancer-derived exosomes in vivo and evaluating the therapeutic efficacy and mechanism of exosome production inhibitors.
CD63-Antares2 expression enables the detection of exosomes at long wavelength
(a) Schematic diagram of Antares2 and Antares2-fused CD63 (CD63-Antares2). (b) Western blot analysis of control (Mock), CD63-Antares2-, and Antares2-expressing PC3 cells. Total cell lysates were immunoblotted with antibodies against the indicated proteins. (c) BRET signal of culture media containing PC3/CD63-Antares2 cells that were treated with FRZ or DTZ (500, 50, 5, and 0.5 μM) and imaged using the in vivo imaging system (IVIS). The data are representative of at least three independent experiments. (d) Emission spectrum of CD63-Antares2 in culture medium containing PC3/CD63-Antares2 cells.