Tert-butyl-2(4,5-dihydrogen-4,4,5,5-tetramethyl-3-O-1H-imidazole-3-cationic-1-oxyl-2-pyrrolidine-1-carboxylic ester displays novel cytotoxicity through reactive oxygen species-mediated oxidative damage in MCF-7 and MDA-MB-231 cells

The cytotoxicity of a new nitroxyl nitroxide radical, tert-butyl-2 (4,5-dihydrogen-4,4,5,5-tetramethyl-3-O-1H-imidazole-3-cationic-1-oxyl-2-pyrrolidine-1-carboxylic ester (L-NNP) was examined in MCF-7 and MDA-MB-231 cells. L-NNP treatment resulted in a significant growth inhibition in MCF-7 and MDA-MB-231 cells. Compared with control, 10, 30, and 50 μg/ml L-NNP treatments for 48 h induced significant cell and nuclei swelling, and organelle distension. The marked cell death was seen in a concentration- and time-dependant manner in L-NNP treated groups. The L-NNP treated group displayed a concentration-dependant increase in DNA double strand damage compared to the control and the 1 Gy γ-rays exposure groups. These results suggest that L-NNP could result in more lethal genotoxicity than 1 Gy γ-radiation. Based on mitochondrial alteration (membrane potential loss and SDH activity descend), DNA damage, an increase in MDA production, and GSH-PX inactivation, we predicate that L-NNP induces lipid oxidation and oxidative damage in MCF-7 and MDA-MB-231 cells. Since L-NNP initiated a significant increase in reactive oxygen species, which could largely be inhibited by NAC pretreatment, the overall data strongly suggest that the mechanism of cytotoxicity of L-NNP was its ability to act as a strong free radical, and significantly increase intracellular reactive oxygen species production. This led to intracellular oxidative damage, and antioxidant enzyme inactivation, resulting in cell death. We hypothesize that the greater cytotoxicity of L-NNP in MDA-MB-231 cells than in MCF-7 cells might be due to more ROS production in MDA-MB-231 cells, leading to more oxidative damage.