Increased anti-tumour activity by exosomes derived from doxorubicin-treated tumour cells via heat stress.

Purpose: Tumour-cell-derived exosomes (Exo) have been proposed as a new kind of drug carrier, and heat stress can promote release of exosomes from tumour cells. This study investigated the impact of heat stress on the quantity of doxorubicin in exosomes from the same number of doxorubicin-treated MFC-7 tumour cells and their anti-tumour effects.

Materials And Methods: Exosomes were isolated from phosphate-buffered saline (Exo), doxorubicin (Exo-Dox) or doxorubicin combined with heat-stress-treated (Exo-Dox-HS) MCF-7 cells. The content of doxorubicin in the exosomes was determined by flow cytometry. The effects of individual types of exosomes on the MCF-7 cell proliferation and apoptosis as well as the tumour growth were determined by MTT assay, flow cytometry and murine xenograft tumour modelling.

Results: We found that the amount of Exo-Dox-HS was higher than that of Exo-Dox from the same number of MCF-7 cells, and Exo-Dox-HS contained higher levels of doxorubicin than Exo-Dox from the same number of cells. Exo-Dox and Exo-Dox-HS, but not Exo or 10 µg/mL doxorubicin, significantly inhibited the MCF-7 cell proliferation and triggered MCF-7 cell apoptosis, associated with increased levels of cleaved caspase-3 and -8 and morphological changes in MCF-7 cells. Treatment with Exo-Dox and Exo-Dox-HS inhibited the growth of implanted breast tumours in mice.

Conclusions: Our study indicated that heat stress increased the quantity of doxorubicin-containing exosomes from tumour cells, and enhanced the anti-tumour effect of exosomes from the doxorubicin-treated tumour cells. Our findings may aid in designing new strategies for cancer therapy by combination of chemotherapy and hyperthermia.