Plant-derived exosomes from black soybeans for combatting pancreatic and colon cancer cells

Background: Plant-derived dietary exosomes are biocompatible granular vesicles that are considered safe and have been increasingly reported to exert beneficial effects on the human body. We independently developed a novel method for isolating food-derived exosomes from black soybeans and demonstrated their therapeutic efficacy against pancreatic and colon cancer cells. Materials and methods: We developed a technique to efficiently isolate exosomes from freshly harvested black soybean pods. The size and morphology of the exosomes were evaluated using nanoparticle tracking analysis and transmission electron microscopy (TEM). The antitumor effects were evaluated by assessing the cell proliferation inhibitory effects using WST/MTT assays with human pancreatic cancer MIAPaca-2 and human colon cancer HCT116 cells. The efficacies of different exosome conditioning methods, such as freezing, boiling, boiling in salt, or immediate extraction, were compared in terms of their cell proliferation inhibitory effects. The radiosensitizing effects were also investigated using a colony-forming assay. The extent and frequency of DNA damage were determined using gammaH2AX staining, a marker for DNA damage, between four groups: control, black soybean exosomes alone, radiation alone, and a combination of both. Results: The mean size of the exosomes was less than 200 nm. Absorption of the exosome were observed in very high frequency in MIApaca-2 cells. The exosomes obtained from approximately 20 black soybeans exhibited much higher tumor growth inhibitory effects than the solution of black soybeans without exosomes. The exosomes also showed radiosensitizing effect in response to 6 Gy of ionizing radiation. Conclusions: These findings together represent that the plant-derived dietary exosomes from black soybeans may have potential to be a novel strategy for cancer cell growth inhibition and radiosensitization.