Exploiting Reactive Oxygen Species in Cancer Therapy

Reactive oxygen species are compounds containing oxygen atoms with an unpaired electron, making them highly reactive. These substances are generated during the electron transport chain as a byproduct within the mitochondria, along with other cellular processes that involve proteins like NADPH oxidase. In the mitochondria, the electron transport chain is used to produce ATP through Complexes I-IV and the ATP synthase. About 0.2%-2% of electrons in the electron transport chain leak out and interact with oxygen, producing ROS. Most ROS produced in the electron transport chain are produced at Complex I, and Complexes II-IV produces negligible amounts compared to those at Complex I. It is crucial ROS are produced in proper concentrations at these complexes for cell survival because they serve as messengers within the cell and help manage various cellular functions, such as gene expression, cell division, cell differentiation, and the response to stress. They can influence pathways like growth-factor signaling pathways and mitogenic pathways, and both help stimulate cell division, growth differentiation, and survival. As a redox signaling messenger, ROS can cause reversible modifications to biomolecules in the cell but become dangerous when they bind to the cell's macromolecules, DNA, lipids, and proteins, and lead to the formation of cancer.