Screening of potential cancer preventing chemicals as antioxidants in an in vitro assay.

We used an azo-initiated fluorescence assay to rank a series of antioxidants, with the objective of selecting compounds for further evaluation as chemopreventive agents. Trolox was the positive control for the assay and, with an IC50 of 0.50 microM, was more active than any of the other 16 compounds examined. Three compounds, U83836E, glutathione, and purpurgallin, were only slightly less active with IC50's in the 1-3 microM range. Four other compounds were almost as active: protochatechuic acid, N-acetyl-L-cysteine, U74389G, and lipoic acid (reduced). This fluorescence-based assay for antioxidant activity is a rapid, economical way of ranking antioxidants for further development in the National Cancer Institute's chemoprevention program.