| The present study characterizes the anti-estrogenic/apoptotic activities of phytochemicals (flavonoids), a group of chemicals naturally produced by plants. Initial studies using the Yeast Estrogen Screen (YES) allowed for the identification and characterization of estrogenic and anti-estrogenic activities establishing the basis for the further characterization of these chemicals in a human breast cancer cell line (MCF-7). The phytochemicals tested were organized into classes based on their anti-estrogenic activities and ER binding. The first and second classes displayed strong and weak anti-estrogenic activity, respectively, compared to the anti-estrogen 4-hydroxy tamoxifen; the anti-estrogenic activity of both classes appeared to correlate directly with ER binding. A third class kaempferide, apigenin and flavone also displayed potent anti-estrogenic activity; however they were distinct from chemicals in the first class since their anti-estrogenic activity did not appear to correlate with binding to ER. Our results suggest that phytochemicals can function as anti estrogens through hER-dependent and -independent mechanisms in MCF-7 cells.; Further investigation of the hER-independent mechanisms demonstrated the ability of selected anti-estrogenic flavonoids to stimulate a stress activated mitogen activated protein kinase (MAPK) pathway which is required for the anti-estrogenic activity of these compounds. The use of dominant negative mutants established a role of specific isoforms of the stress activated MAPKs in negative regulation of the ER. Specifically, chalcone and flavone required an intact JNK1 and JNK2 pathways respectively, while the antiestrogenic activity of both tamoxifen and the flavonoid kaempferide were unaffected by blockade of these pathways. This study implicates members of the stress activated MAPK family in the negative regulation of ER receptor function.; Apoptotic studies were initialized to characterize the ability of certain phytochemicals to inhibit estradiol induced cell proliferation. The cytotoxic effect of these chemicals was due to induction of apoptosis as determined by DNA fragmentation analysis and fluorescent microscopy. Those flavonoids which possessed the greatest induction of apoptosis including chalcone, kaempferide, flavone and apigenin, were further examined for Poly-ADP Ribose polymerase cleavage demonstrating that caspase activation may mediated flavonoid-induced apoptosis. Our results demonstrate that certain anti-estrogenic phytochemicals possess the ability to induce apoptosis in an ER positive breast carcinoma cell line that is correlated with increased caspase activity. |
