Tumor metabolism, cancer cell transporters, and microenvironmental resistance.

Cancer cells reprogram their metabolic machineries to enter into permanent glycolytic pathways. The full reason for such reprogramming takes place is unclear. However, this metabolic switch is not made in vain for the lactate that is generated and exported outside cells is reused by other cells. This results in the generation of a pH gradient between the low extracellular pH that is acidic (pHe) and the higher cytosolic alkaline or near neutral pH (pHi) environments that are tightly regulated by the overexpression of several pumps and ion channels (e.g. NHE-1, MCT-1, V-ATPase, CA9, and CA12). The generation of this unique pH gradient serves as a determining factor in defining "tumor fitness". Tumor fitness is the capacity of the tumor to invade and metastasize due to its ability to reduce the efficiency of the immune system and confer resistance to chemotherapy. In this article, we highlight the importance of tumor microenvironment in mediating the failure of chemotherapeutic agents.