Targeted therapy against cancer stem cells.

Research into cancer stem cells (CSCs), which have the ability to self-renew and give rise to more mature (differentiated) cancer cells, and which may be the cells responsible for the overall organization of a tumor, has progressed rapidly and concomitantly with recent advances in studies of normal tissue stem cells. CSCs have been reported in a wide spectrum of human tumors. Like normal tissue stem cells, CSCs similarly exhibit significant phenotypic and functional heterogeneity. The ability of CSCs to self-renew results in the immortality of malignant cells at the population level, whereas the ability of CSCs to differentiate, either fully or partially, generates the cellular hierarchy and heterogeneity commonly observed in solid tumors. CSCs also appear to have maximized their pro-survival mechanisms leading to their relative resistance to anti-cancer therapies and subsequent relapse. Studies in animal models of human cancers have also provided insight into the heterogeneity and characteristics of CSCs, helping to establish a platform for the development of novel targeted therapies against specific CSCs. In the present study, we briefly review the most recent progress in dissecting CSC heterogeneity and targeting CSCs in various human tumor systems. We also highlight a few examples of CSC-targeted drug development and clinical trials, with the ultimate aim of developing more effective therapeutic regimens that are capable of preventing tumor recurrence and metastasis.