Targeted cancer therapy using engineered exosome as a natural drug delivery vehicle

Exosomes are small 30-100 nm vesicles secreted by various cell types. They are released by most cell types, indicating their important role in physiological and pathological processes, including signaling pathways, cell-to-cell communication, tumor progression, and molecule transferring. As natural nanovesicles, exosomes can be a good candidate for drug delivery due to low immunogenicity and ability to enter tissues and even cross the blood-brain barrier. In an effort to improve the efficiency of exosomes for targeted drug delivery with minimal effect on normal cells, we expressed ligands against HER2+ cells.

To purify exosomes, transduced mesenchymal stromal cells were cultured to reach 80% confluency. Next, the cells were cultured in serum-free media for 48 hours and the supernatant was harvested to purify exosomes. These exosomes were then labeled with PKH67 and added to BT-474, SKBR3 (HER2+), and MDA-MB231 (HER2-), cell lines and their binding to HER2+ was evaluated by flow cytometry. Exosomes were loaded with doxorubicin and quantified using intrinsic fluorescence of doxorubicin at 594 nm.

Targeted exosomes were preferably uptaken by HER2+ cells. Therefore, untargeted exosomes showed lower binding to HER2+ cells compared to their targeted counterparts. MTT assay was performed to analyze cytotoxic effect of exo-DOX (exosome encapsulated with doxorubicin). Efficiency of exo-DOX and free DOX (doxorubicin) delivery with different concentrations, to the BT-474 cell line, was compared, and no significant difference was observed.

Our results imply that targeted exosomes are preferentially uptaken by HER2+ cells relative to HER2- cells and have the potential to be used as an efficient drug delivery system.