Reactive oxygen species (ROS) are constantly generated and eliminated in the
biological system, and play important roles in a variety of normal biochemical functions and abnormal
pathological processes. Growing evidence suggests that
cancer cells exhibit increased intrinsic ROS stress, due in part to oncogenic stimulation, increased metabolic activity, and mitochondrial malfunction. Since the mitochondrial respiratory chain (electron transport complexes) is a major source of ROS generation in the cells, the vulnerability of the
mitochondrial DNA to ROS-mediated damage appears to be a mechanism to amplify ROS stress in
cancer cells. The escalated ROS generation in
cancer cells serves as an endogenous source of
DNA-damaging agents that promote genetic instability and development of drug resistance. Malfunction of mitochondria also alters cellular apoptotic response to
anticancer agents. Despite the negative impacts of increased ROS in
cancer cells, it is possible to exploit this biochemical feature and develop novel therapeutic strategies to preferentially kill
cancer cells through ROS-mediated mechanisms. This article reviews ROS stress in
cancer cells, its underlying mechanisms and relationship with mitochondrial malfunction and alteration in
drug sensitivity, and suggests new therapeutic strategies that take advantage of increased ROS in
cancer cells to enhance therapeutic activity and selectivity.