ADO (2-aminoethanethiol dioxygenase) is a thiol dioxygenase that catalyzes the oxidation of cysteamine to hypotaurine and sulfinylates amino-terminal cysteines in polypeptides, functioning as an oxidase that uses molecular oxygen as a cosubstrate 1. The enzyme oxidizes specific regulatory proteins including RGS4, RGS5, and IL-32 1. ADO plays a critical role in maintaining mitochondrial redox homeostasis by restraining polyamine accumulation; depletion of ADO leads to toxic polyamine levels that trigger proline dehydrogenase expression, resulting in mitochondrial hyperactivity, elevated reactive oxygen species production, and cell toxicity 1. In cancer biology, ADO depletion represents a therapeutic vulnerability—cancer cells require ADO for proliferation and survival, with ADO knockout reducing xenograft growth 1. Notably, the ADO knockout mouse demonstrates high tolerance for ADO loss in normal adult tissues, suggesting selectivity for cancer cell dependence 1. These findings identify ADO as a unique cancer cell vulnerability distinct from normal physiology. The enzyme's mechanistic importance centers on preventing polyamine-driven mitochondrial dysfunction and oxidative stress, making it a potential therapeutic target in oncology. However, clinical translation requires further investigation given the differential requirement between transformed and normal cells.