Lung cancer stem cells and implications for future therapeutics.

Lung cancer is the most dreaded of all cancers because of the higher mortality rates associated with it worldwide. The various subtypes of lung cancer respond differently to a particular treatment regime, which makes the therapeutic interventions all the more complicated. The concept of cancer stem cells (CSCs) is based primarily on the clinical and experimental observations that indicate the existence of a subpopulation of cells with the capacity to self-renew and differentiate as well as show increased resistance to radiation and chemotherapy. They are considered as the factors responsible for the cases of tumor relapse. The CSCs may have significant role in the development of lung tumorigenesis based on the identification of the CSCs which respond during injury. The properties of multi-potency and self-renewal are shared in common by the lung CSCs with the normal pluripotent stem cells which can be isolated using the similar markers. This review deals with the origin and characteristics of the lung cancer stem cells. The role of different markers used to isolate lung CSCs like CD44, ALDH (aldehyde dehydrogenase), CD133 and ABCG2 (ATP binding cassette sub family G member 2) have been discussed in detail. Analysis of the developmental signaling pathways such as Wnt/β-catenin, Notch, hedgehog in the regulation and maintenance of the lung CSCs have been done. Finally, before targeting the lung CSC biomarkers for potential therapeutics, challenges faced in lung cancer stem cell research need to be taken into account. With the accepted notion that the CSCs are to blame for cancer relapse and drug resistance, targeting them can be an important aspect of lung cancer therapy in the future.