To evaluate the effects of the different tested compounds and DETA-NO on viability of MDA-MB-231 cells, the cells were cultured at a density of 25,000 cells/well in 48 multiwell plates for 24 hours. Next, the media were exchanged with FBS-free RPMI containing one concentration of the tested compounds or DETA-NO and the cells were cultured for 72 hours. To measure the metabolic activity of cells after 24, 48 and 72 hours of culture, the media were removed and kept at -20 o C. Each well was then washed with PBS, and 200 μL of fresh 10% AlamarBlue Reagent in PBS was added to each one, followed by incubation for 3 hours. Using the microplate reader, the fluorescence intensity was measured at an excitation of 550 nm and emission of 590 nm, and the percentage of metabolic activity was calculated by normalizing the fluorescence at each treatment to that of untreated cells. Three samples were tested for each concentration at each time point. For nitrite measurements, the frozen media were allowed to thaw and the nitrite concentration was measured using the Griess assay in accordance with the manufacturer's protocol. This was performed after 15, 24 and 40 hours of cell culture with the different treatments.