Figure 1: The cellular antioxidant systems. Tumor progression induces increasing oxidative stress. Cells have several antioxidant systems to directly inactivate ROS (e.g., Trx peroxidases, GSH peroxidases, catalase, and SOD) as well as REDOX regulatory systems that recycle/reactivate the ROS scavenging proteins and other REDOX sensitive proteins (e.g., PTPs, PTEN, and transcription factors).