title: Preclinical development of cancer stem cell drugs.
abstract: BACKGROUND
  Despite recent progress in cancer treatment, the current cancer chemotherapy can mainly produce remission but often fails to cure cancer due to the existence of cancer stem cells. The emerging cancer stem cell hypothesis offers new insight into the failure of current cancer drugs and suggests new approaches for improved understanding of cancer biology and cancer drug development.
  
  
  OBJECTIVE
  In this review, we discuss the concept of cancer stem cells, origin of cancer stem cells and different approaches for isolating or enriching cancer stem cells. We also review the resistance of cancer stem cells to standard chemotherapy and radiation therapy and potential mechanisms for the resistance. Finally, based on the current knowledge on cancer stem cells, we discuss potential approaches for developing new drugs that target cancer stem cells and propose new methods for evaluation of cancer stem cell drugs.
  
  
  CONCLUSIONS
  Improved cancer treatment is likely to be achieved by a combination of drugs that kill both replicating cancer cells and more quiescent cancer stem cells.
authors.affiliation: Yale University, Department of Biomedical Engineering, New Haven, CT 06511, USA.
authors.forename: Jiangbing
authors.initials: J
authors.lastname: Zhou
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhang