Targeting molecular pathways in cancer stem cells by natural bioactive compounds

Cancer Stem Cells (CSCs) or Tumor-Initiating Cells (TICs) are a small sub-population of cells within the tumor, able to give chemio- and radio-resistance and cause the onset of metastasis and the presence of relapses; for these reasons, they are recently becoming a potential target for anticancer therapy. One of the main characteristics of these cells is the self-renewal through the capability of modulating different molecular signalling pathways, including Wnt/β-Catenin, Sonic Hedgehog and Notch pathways. Natural bioactive compounds such as resveratrol, epigallocatechin, curcumin, quercetin, ellagic acid, anthocyanins and other compounds and extracts can have a direct or indirect effect on these molecular pathways, decreasing the pathological activities of CSCs. This review aims to report and summarize the in vitro and in vivo studies about the preventive, therapeutic and chemosensitizing effects of these natural bioactive compounds on CSCs deriving from different types of tumors.