Juglone Inhibits Tumor Metastasis by Regulating Stemness Characteristics and the Epithelial-to-Mesenchymal Transition in Cancer Cells both in Vitro and in Vivo

Background: The stemness characteristics of cancer cells, such as self-renewal and tumorigenicity, are considered to be responsible, in part, for tumor metastasis. Epithelial-to-mesenchymal transition (EMT) plays an important role in promoting both stemness and tumor metastasis. Although the traditional medicine juglone is thought to play an anticancer role by affecting cell cycle arrest, induction of apoptosis, and immune regulation, a potential function of juglone in regulating cancer cell stemness characteristics remains unknown. Methods: In the present study, tumor sphere formation assay and limiting dilution cell transplantation assays were performed to assess the function of juglone in regulating maintenance of cancer cell stemness characteristics. EMT of cancer cells was assessed by western blot and transwell assay in vitro, and a liver metastasis model was also performed to demonstrate the effect of juglone on colorectal cancer cells in vivo. Results: Data gathered indicates juglone inhibits stemness characteristics and EMT in cancer cells. Furthermore, we verified that metastasis was suppressed by juglone treatment. We also observed that these effects were, in part, achieved by inhibiting Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1). Conclusions: These results indicate that juglone inhibits maintenance of stemness characteristics and metastasis in cancer cells.