tempo and Breast-Neoplasms

The limited application of traditional antioxidants to reducing elevated levels of reactive oxygen species (ROS) is potentially due to their lack of stability and biocompatibility when tested in a biological milieu. For instance, the poor biological antioxidant performance of small molecular nitroxides arises from their limited diffusion across cell membranes and their significant side effects when applied at high doses. Herein, we describe the use of nanostructured carriers to improve the antioxidant activity of a typical nitroxide derivative, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO). Polymers with star-shaped structures were synthesised and were further conjugated to TEMPO moieties

Topics: Antioxidants; Biocompatible Materials; Breast Neoplasms; Cell Line, Tumor; Cell Survival; Coculture Techniques; Cyclic N-Oxides; Female; Fibroblasts; Humans; Mitochondria; Nanostructures; Oxidative Stress; Polyethylene Glycols; Reactive Oxygen Species

Tempol and tempo are stable free radical nitroxides that possess antioxidant properties. In this study, we examined the effects of these compounds on components of the mitogen-activated protein kinase signal transduction cascade. Tempo treatment (15 min) of MDA-MB 231 human breast cancer cells resulted in significant levels of tyrosine phosphorylation of several as yet unidentified proteins compared with equimolar concentration of tempol (10 mM). Both compounds caused tyrosine phosphorylation and activation of Raf-1 protein kinase (30 min, 2-3-fold). Interestingly, however, only tempol caused increased extracellular signal-regulated kinase 1 activity (2 h, approximately 3-fold). On the other hand, tempo, but not tempol, potently activated stress-activated protein kinase (2 h, >3-fold). Consistent with these data, tempol was found to be noncytotoxic, whereas tempo induced apoptotic cell death (2 h, >50%). Tempo treatment also resulted in significant elevation of ceramide levels at 30 min (54% over control) and 1 h (71% over control) posttreatment, preceding stress-activated protein kinase activation and apoptosis. These data suggest that in the absence of an environmental oxidative stress, tempol and tempo elicit distinct cellular signaling pathways. The recognition of the molecular mechanisms of nitroxide action may have important implications for biological effectiveness of these compounds.

Topics: Antioxidants; Apoptosis; Breast Neoplasms; Calcium-Calmodulin-Dependent Protein Kinases; Ceramides; Cyclic N-Oxides; Enzyme Activation; Humans; JNK Mitogen-Activated Protein Kinases; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Phosphorylation; Protein Tyrosine Phosphatases; Proto-Oncogene Proteins c-raf; Signal Transduction; Spin Labels; Tumor Cells, Cultured