The effect of silibinin on CRC-CSCs from the HT29, SW480, and LoVo lines has been shown to be mediated by blocking IL-4/-6 protumorigenic signaling and is associated with decreased mRNA and protein levels of various CSC-associated transcription factors, signaling molecules, and surface markers (such as CD44, NANOG, TERT, SOX-2, SOX-9, and WT1). bone morphogenetic protein 4, Kindlin-1, tankyrases, and p21-activated kinase 1, are discussed. In addition, novel strategies aimed at inhibiting some crucial processes engaged in cancer progression regulated by the Wnt, transforming growth factor and Notch signaling pathways (pyrvinium pamoate, silibinin, PRI-724, P17, and P144 peptides) are also evaluated. Although the metabolic alterations in cancer were first described decades ago, it is 5′-Deoxyadenosine only recently that the concept of targeting key regulatory molecules of cell metabolism, such as sirtuin 1 (miR-34a) and AMPK (metformin), has emerged. In conclusion, the discovery of CSCs has resulted in the definition of novel therapeutic targets and the development of novel experimental therapies for CRC. However, further investigations are required in order to apply these novel drugs in human CRC. for as long as one year without any change in their phenotype, gaining the ability to form undifferentiated tumor spheres which maintain the ability to engraft (13). Moreover, it has been shown that even a single CD133+ cell is able to reproduce the tumor mass (23). Human CRCs resistant to a conventional 5-FU treatment have been found to be enriched in CD133+ cells; this is directly correlated with a worse outcome for patients (24). However, knockout of CD133 has been found not to affect the clonogenicity of cancer cells, suggesting that CD133 is a passive 5′-Deoxyadenosine marker, rather than a CSC-promoting factor (25C27). CD44 protein CD44 is a transmembrane glycoprotein, a receptor of hyaluronic acid that participates in many cellular processes, including growth, survival, differentiation and motility. CD44+ CD133? cells isolated from human CRC tumors have been shown to efficiently initiate a xenograft NT5E tumor that possesses similar properties to those of the primary tumor. Knockdown of CD44 strongly reduced proliferation of these cells and inhibited tumorigenicity in a mouse xenograft model (26,27). Aldehyde dehydrogenase 1 Aldehyde dehydrogenase 1 (ALDH-1) has been identified in both nonmalignant and malignant stem cells. In many neoplasms-such as colon, pancreas, breast, and urinary bladder cancers-this enzyme has been shown to be associated with disease progression (16,28C31). Generally, ALDH-1 is responsible for detoxification 5′-Deoxyadenosine and defending against free radicals, although it plays a crucial function in cancer recurrence due to the downregulation of CSCs’ metabolism during conventional chemotherapy (16,28C31). The activity of ALDH-1 may be pharmacologically blocked via the specific inhibitor DAEB (diethylaminobenzaldehyde) (30). A combination of DAEB with conventional chemotherapeutics, such as doxorubicin and paclitaxel, increases the level of oxidative stress in cells, enhancing their susceptibility to free radicals and apoptosis. The first promising results of such an approach were demonstrated for breast cancer cell lines (32). 3.?The characteristics of CRC-CSCs being considered for CSC-targeting therapeutic strategies The discovery of CSCs in various tumors has provided new opportunities to overcome chemoresistance and radioresistance of tumor cells through the targeting of this unique population (Fig. 1). To achieve this goal, diverse strategies have been used: the induction of CSC differentiation, the inhibition of the epithelial-mesenchymal transition (EMT), the reduction of angiogenesis, and the suppression of specific signaling or metabolic pathways. Significantly, our increasing understanding of the cellular and molecular mechanisms that regulate CSC quiescence, cell cycle progression, self-renewal, and resistance to proapoptotic signals and chemotherapeutics may provide new therapeutic modalities 5′-Deoxyadenosine that will reduce morbidity and increase the overall survival of CRC patients. Open in a separate window Figure 1. The features characteristic for CRC-CSCs and crucial signaling pathways which are under consideration in regards to CSC-targeting.