OPTIMIZED ISOLATION AND QUANTIFICATION OF IN VIVO DISTRIBUTION OF EXOSOMES FOR POTENTIAL TARGETED THERANOSTIC APPLICATION

Abstract

Exosomes are critical mediators of intercellular crosstalk and regulators of the cellular/tumor microenvironment. Exosomes have great prospects for clinical application as a theranostic and prognostic probe. Nevertheless, the advancement of exosome research has been thwarted by our limited knowledge of the most efficient isolation method and the in vivo trafficking. Here we have shown that a combination of two size-based methods using a 0.20 μm syringe filter and 100k centrifuge membrane filter followed by ultracentrifugation yields a greater number of uniform exosomes compared to other available methods. We demonstrated the visual representation and quantification of the differential in vivo distribution of radioisotope 131I-labeled exosomes from diverse cellular origins, e.g., tumor cells with or without treatments, myeloid-derived suppressor cells and endothelial progenitor cells. We also determined that the distribution was dependent on the exosomal protein/cytokine contents. Further, we also generated engineered exosomes expressing precision peptide for targeting CD206 positive M2-macrophages. M2-macrophages participate in immune suppression, epithelial to mesenchymal transition, invasion, angiogenesis, tumor progression and subsequent metastasis foci formation. Given their pro-tumorigenic function and prevalence in most malignant tumors with lower survival, early in vivo detection and intervention of M2-macrophages may boost the clinical outcome. To determine in vivo distribution of M2-macrophages, we adopted 111In-oxine based radiolabeling of the targeted exosomes and SPECT. When injected these radiolabeled targeted exosomes into 4T1 breast tumor-bearing mice, exosomes accumulated at the periphery of the primary tumor, metastatic foci in the lungs, in the spleen, and liver. Ex vivo quantification of radioactivity also showed similar distribution. Injected DiI dye-labeled exosomes into the same mice showed the adherence of exosomes to the CD206 positive macrophages on ex vivo fluorescent microscopy imaging, confirming the targeting efficacy of the exosomes. In addition, we utilized these engineered exosomes to carry the Fc portion of mouse IgG2b with the intention of augmenting antibody-dependent cell-mediated cytotoxicity. We have auspiciously demonstrated that M2-macrophage targeting therapeutic exosomes deplete M2-macrophages both in vitro and in vivo, and reduce tumor burden in a metastatic breast cancer model. The applied in vivo imaging modalities can be utilized to monitor disease progression, metastasis, and exosome-based targeted therapy.