Downregulation of Cancer Stemness by Novel Diterpenoid Ovatodiolide Inhibits Hepatic Cancer Stem Cell-Like Traits by Repressing Wnt/β-Catenin Signaling

The hierarchical tumor propagation or cancer stem cells (CSCs) model of carcinogenesis postulates that like physiologic adult stem cell (ASC), the CSCs positioned at the apex of any tumor population form the crux of tumor evolution with a constitutive regenerative capacity and differentiation potential. The propagation and recurrence of the characteristically heterogeneous and therapy-resistant hepatocellular carcinoma (HCC), adds to accumulating evidence to support this CSCs model. Based on the multi-etiologic basis of HCC formation which among others, focuses on the disruption of the canonical Wnt signaling pathway, this study evaluated the role of cembrane-type phytochemical, Ovatodiolide, in the modulation of the Wnt/β-catenin pathway, and its subsequent effect on liver CSCs' activities. Our fluorescence-activated cell sorting (FACS) and quantitative RT-PCR analyses of side population (SP) indicated that CD133+ cells were β-catenin-overexpressing, more aggressive, and resistant to the conventional anticancer agents, Cisplatin and Doxorubicin, when compared to β-catenin-downregulated group. We demonstrated that marked upregulation of β-catenin and its downstream targets effectively enhanced hepatosphere formation, with an associated induction of CD133, OCT4 and Sox2 expression and also caused an significant enhancement of HCC proliferation. However, treatment with Ovatodiolide induced downregulation of β-catenin and its downstream effector genes, abolished hepatosphere formation and reversed the β-catenin-associated enhancement of HCC growth. In summary, we demonstrated for the first time that Ovatodiolide suppressed the canonical Wnt signaling pathway, and inhibited the generation of liver CSCs; Thus, projecting Ovatodiolide as a putatively effective therapeutic agent for anti-HCC target therapy.