Antiproliferative effects of synthetic and naturally occurring flavonoids on tumor cells of the human breast carcinoma cell line, ZR-75-1.

An examination was made of the effects of 21 synthetic and naturally occurring flavonoids on the in vitro growth of cells of the human breast carcinoma, ZR-75-1. In all cases, antiproliferative effects were noted, with an IC50 ranging from 2.7 to 33.5 micrograms/ml, except for the isoflavonoid, daidzin (IC50 greater than 50 micrograms/ml). No significant structure-activity relationship among the compounds could be found. Flavone, 6-hydroxyflavone and 4',5,7-trihydroxyflavone (apigenin) were the most potent with IC50 of 2.7, 3.4, and 3.5 micrograms/ml, respectively. The flavonoid effects observed here were not due to cytostatic action alone, since cell death was found to increase dose-dependently, according to the results of a dye exclusion test.