Cancer stem cells and chemosensitivity

Cancer lethality is mainly due to the onset of distant metastases and refractoriness to chemotherapy. Thus, the development of molecular targeted agents that can restore or increase chemosensitivity will provide valuable therapeutic options for cancer patients. Growing evidence indicates that a cellular subpopulation with stem cell-like features, commonly referred to as cancer stem cells (CSCs), is critical for tumor generation and maintenance. Recent advances in stem cell biology are revealing that this cellular fraction shares many properties with normal adult stem cells and is able to propagate the parental tumor in animal models. CSCs seem to be protected against widely used chemotherapeutic agents by means of different mechanisms, such as a marked proficiency in DNA damage repair, high expression of ATP-binding cassette drug transporters, and activation of PI3K/AKT and Wnt pathways. Moreover, microenvironmental stimuli such as those involved in the epithelial-mesenchymal transition and hypoxia indirectly contribute to chemoresistance by inducing in cancer cells a stem-like phenotype. Understanding how CSCs overcome chemotherapy-induced death stimuli, and integrating such knowledge into clinical research methodology, has become a priority in the process of identifying innovative therapeutic strategies aimed at improving the outcome of cancer patients.