Thymoquinone-loaded mesenchymal stem cell-derived exosome as an efficient nano-system against breast cancer cells

Exosomes became the subject of extensive research in drug delivery approach due to their potential applicability as therapeutic tools for cancer therapy. Thymoquinone (Tq) is an anti-cancer agent due to its great anti-proliferative effect. However, poor solubility and weak bioavailability restrict its therapeutic applications. In this study, exosomes secreted from human adipocyte-derived mesenchymal stem cells (AdMSCs) were isolated and the efficacy of a novel encapsulation method for loading of Tq was investigated. Finally, the cytotoxic effect of Tq incorporated exosomes against cancer cells was evaluated. Exosomes secreted from AdMSCs were isolated via ultracentrifugation and characterized by electron microscopy and western blotting. Then, through a novel encapsulation approach, Tq was loaded into exosomes by the combination of three methods including incubation, freeze-thawing, and surfactant treatment. Then, the encapsulation efficiency, in vitro cellular uptake, and cytotoxicity of Tq incorporated exosomes (Tq@EXOs) in MCF7 and L929 cells were estimated.  Tq loading into exosomes through our novel method caused a significant improvement in encapsulation efficiency of about 60%. The fluorescent microscopy and flow cytometry outcomes indicated the efficient uptake of Tq@EXOs-FITC by cells throughout 4 hr. Furthermore, MTT results displayed the ability of Tq@EXOs in effectively decreasing the cell viability of MCF7 without causing any obvious cytotoxicity on L929 as normal cells. The results suggest that our approach provides effective loading of Tq into exosomes which offer a valuable and safe platform for drug delivery to cancer cells thus having a great potential for clinical studies.