Cancer stem cell targeted agents: Therapeutic approaches and consequences

An increased understanding of stem-cell biology at the molecular level, as well as the isolation and characterization of a rare subset of cells with tumor-initiating properties from several human tumor types, have renewed interest in the exploitation of cancer stem cells (CSCs) as therapeutic targets. Although CSCs share various characteristics with normal stem cells, including self-renewal, asymmetric cell division, indefinite proliferative capacity, and self-protection mechanisms, they also contain unique and disease-specific features suitable for exploitation as therapeutic targets. Several existing anticancer agents and experimental therapeutics can inhibit pathways critical to CSC maintenance, and could, therefore, be utilized to eradicate CSCs. In this review, general and tumor-type specific cancer-stem-cell targets are highlighted. In addition, known inhibitors of these targets that could be utilized in the design of clinical protocols together with conventional cytotoxics as debulking agents are described.