Inhibition of the cancer stem cells-like properties by arsenic trioxide, involved in the attenuation of endogenous transforming growth factor beta signal.

The elevation of cancer stem cells (CSCs)-like properties is involved in the initiation and progression of various human cancers. Current standard practices for treatment of cancers are less than satisfactory because of CSCs-mediated recurrence. For this reason, targeting the CSCs or the cancer cells with CSCs-like properties has become the new approach for the cancer treatments. In addition to treating leukemia, arsenic trioxide (As₂O₃) also suppresses other solid tumors. However, the roles of As₂O₃ in the regulation of CSCs-like properties remain largely uninvestigated. Here by using sphere formation assay, luciferase reporter assay, and some other molecular biology approaches, we found that As₂O₃ attenuated the CSCs-like properties in human hepatocellular carcinoma (HCC). Briefly, in HCC cells and mice xenograft models, As₂O₃ improved the expression of miR-491 by DNA-demethylation. MiR-491, which targeted the SMAD3-3'-UTR, decreased the expressions of SMAD3, and inhibited the CSCs-like properties in HCC cells. Knockdown of either miR-491 or SMAD3 attenuated the As₂O₃-induced inhibition of endogenous transforming growth factor beta signal and the CSCs-like properties. Further, in HCC patients, miR-491 is inversely correlated with the expressions of SMAD3, CD133, and the metastasis/recurrence outcome. By understanding a novel mechanism whereby As₂O₃ inhibits the CSCs-like properties in HCC, our study would help in the design of future strategies of developing As₂O₃ as a potential HCC chemopreventive agent when used alone or in combination with other current drugs.