GENISTEIN AND BIOCHANIN-A INHIBIT THE GROWTH OF HUMAN PROSTATE-CANCER CELLS BUT NOT EPIDERMAL GROWTH-FACTOR RECEPTOR TYROSINE AUTOPHOSPHORYLATION

The effect of the isoflavones, genistein, daidzein, and biochanin A on the growth of the LNCaP and DU-145 human prostate cancer cell lines has been examined. Genistein and biochanin A, but not daidzein, inhibit both serum and EGF-stimulated growth of LNCaP and DU-145 cells (IC50 values from 8.0 to 27 mug/ml for serum and 4.3 to 15 mug/ml for EGF), but have no significant effect of the EGF receptor tyrosine autophosphorylation. In contrast, tyrphostin 25, a specific EGF receptor tyrosine kinase inhibitor, inhibits EGF-stimulated growth and EGF receptor tyrosine autophosphorylation in these whole cells, but does not inhibit serum-stimulated growth. These data suggest that the mechanism of action of genistein and biochanin A does not depend on inhibition of EGF receptor tyrosine autophosphorylation, but on a more distal event in the EGF receptor-mediated signal transduction cascade. (C) 1993 Wiley-Liss, Inc.