JS-K, but not JS-43-126, increases nitric oxide production in breast cancer cells. Conditioned medium supernatant was collected from MDA-MB-231, F10, and MCF-7/COX-2 cells treated in the absence or presence of JS-K or JS-43-126 for 72 hours. Total nitric oxide (NO) was determined by quantifying nitrite, the stable end product of NO oxidation, spectrophotometrically using a colorimetric nonenzymatic nitric oxide assay kit. Nitrite values were normalized for total cell counts and expressed as picomoles per 106 cells. Columns indicate the mean of triplicate wells ± standard deviation. *Significant increase in NO levels relative to untreated cells, P < 0.05.