INHIBITION OF PROLIFERATION OF ESTROGEN RECEPTOR-POSITIVE MCF-7 HUMANBREAST-CANCER CELLS BY FLAVONOIDS IN THE PRESENCE AND ABSENCE OF EXCESS ESTROGEN

The flavonoids are a group of naturally-occurring, low molecular weigh t compounds that are widespread in plants. Representatives of several different classes of flavonoids were tested for their effects on the p roliferation of an estrogen receptor-positive human breast cancer cell line, MCF-7. The IC(50)s (concentration at which cell proliferation w as inhibited by 50%), based on [H-3]thymidine incorporation, ranged fr om 4.2 to 18.0 mu g/mL. The cells were viable at these concentrations. The possibility that flavonoids may block cell proliferation by bindi ng to the estrogen receptor was explored. The cells were depleted of e ndogenous steroids and incubated with individual flavonoids at their I C50 concentration. Half of the cells were exposed to an excess concent ration of 17 beta-estradiol to see if this affected antiproliferation by the flavonoids. Of the flavonoids tested, only the inhibition of ce ll proliferation by genistein was reversed with the addition of excess , competing estrogen. Baicalein, galangin, hesperetin, naringenin and quercetin apparently exert their antiproliferative activity via some o ther mechanism. (C) 1997 Elsevier Science Ireland Ltd.