FIG. 5.

The interplay between concentrations and functions of H₂O₂ in cancer cells. H₂O₂ is a potential candidate for a key molecule that decides the fate of cancer survival. Based on 3-AT-mediated inactivation of CAT assay, the steady state of H₂O₂ in selected cancer cells ranges from 5 to 50 pM (4, 69, 85, 253, 348). This range is associated with the following cancer responses: redox sensor on proteins, growth stimulation, and activation of transcription factors. In contrast, influxes that increase H₂O₂ concentrations more than 1.5-fold of its steady state via treatment of ROS-generating drugs, such as doxorubicin, AA, and MnP, lead to oxidatively damaged proteins, activation of proteolysis, mediation of apoptosis, and cancer cell death. 3-AT, 3-aminotriazole; AA, ascorbic acid; MnP, Mn(III) meso-tetrakis (N-n-butoxyethyl-pyridinium-2yl) porphyrin; pM, picomolar. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars