Curcumin Effectively Depletes Hepatic Cancer Stem-Like Cells

The cancer stem cells (CSCs) have important therapeutic implications for multi-resistant cancers including hepatocellular carcinoma (HCC). Among the key pathways frequently activated in liver CSCs is NF-kB signaling. Here we evaluated the CSCs-depleting potential of NF-kB inhibition in liver cancer achieved by IKK inhibitor curcumin and specific peptide SN50 . The effects on CSCs were assessed by analysis of Side Population (SP) and expression levels of CSC-related genes as determined by RT-qPCR, gene expression microarray, EMSA, and Western blotting. Curcumin caused anti-proliferative and pro-apoptotic responses directly related to the extent of NF-kB inhibition. In curcumin-sensitive tumor cells, the treatment led to a selective CSC depletion as evidenced by a reduced SP size, decreased sphere formation, down-regulation of CSC markers and suppressed tumorigenicity. Similarly, NF-kB inhibition by SN50 caused a general suppression of cell growth accompanied by a reduced SP fraction. In contrast, curcumin-resistant cells exhibited a paradoxical increase in proliferation and expression of CSC markers. Mechanistically, CSC-depleting activity of curcumin was exerted by the NF-kB-mediated HDAC inhibition causing down-regulation of c-MYC and other key oncogenic targets. Co-administration of the class I/II HDAC inhibitor trichostatine sensitized resistant cells to curcumin. Further, integration of a predictive signature of curcumin sensitity with our HCC database indicated that HCC patients with poor prognosis and progenitor features are most likely to benefit from NF-kB inhibition. These results demonstrate that NF-kB inhibition can specifically target CSC populations and suggest a potential for combined inhibition of NF-kB and HDAC signaling for treatment of liver cancer patients with poor prognosis. Five human hepatoma cell lines with and without curcumin