Effects of brilliant green on human erythroleukemic K562 and breast adenocarcinoma MCF7 cell growth and on inhibition of human topoisomerase IIα

780 Brilliant green (BG), ([4-[(4-diethylaminophenyl)-phenylmethylidene]-1-cyclohexa-2,5-dienylidene]-diethylazanium; hydrogen sulfate), is a pH indicator, a topical antiseptic and a selective bacteriostatic agent in culture media. It has also been used to dye silk and wool. In this study, we showed that BG strongly inhibited the growth of human erythroleukemia K562 and breast adenocarcinoma MCF7 cells with IC50 values in the nanomolar concentration range. BG also inhibited the DNA decatenation activity of human topoisomerase IIα (topo II) in the micromolar concentration range. BG stabilized the DNA-topo II covalent complex, and thus may act as a topo II poison. The growth inhibitory effects of BG on K562 and K/VP.5 cells (an etoposide-resistant cell line containing one-fifth the topo II content of the parental K562 cells) were not significantly different, a result which suggested that BG acted differently than etoposide. GB induced apoptosis in K562 cells as measured by flow cytometry using annexin V-FITC and PI staining. When K562 cells were treated with GB, the fraction of cells in S phase were increased. However, cells were not able to complete the G2/M phase. BG may directly react with DNA since it increased the DNA melting temperature of sonicated calf thymus DNA. In conclusion, our results indicate that BG may have potent antitumor activity. BG may exert its action by inhibiting the decatenation activity of topo II, by acting as a topo II poison and by directly reacting with DNA. Support: CIHR and a Canada Research Chair in Drug Development to BH, and NIH RO1 CA90787 to JCY.