Potent inhibition of breast cancer cell lines by the isoflavonoid kievitone: comparison with genistein.

The isoflavonoid kievitone potently inhibited the proliferation of the oestrogen receptor (ER)-positive breast cancer cell lines MCF-7 and T47D and the ER-negative breast cancer cell line SKBR3 (IC50 values 5-18 microM). DNA synthesis of MCF-7 cells stimulated by insulin-like growth factor 1, insulin-like growth factor 2, basic fibroblast growth factor or transforming growth factor alpha was inhibited by similar concentrations of kievitone (IC50 values 1-3 microM). DNA synthesis stimulated by 17, beta-oestradiol was also inhibited (IC50 = 6 microM). Compared with kievitone, genistein was 3-9 fold weaker as an inhibitor of the proliferation of the breast cancer cell lines and of growth factor-stimulated DNA synthesis. However, genistein was about 5-fold more potent than kievitone as an inhibitor of solubilised epidermal growth factor (EGF) receptor kinase activity and EGF receptor autophosphorylation.