Influence of phomopsin and ivalin on steroid-hormone binding and growth of MCF-7 human breast cancer cells.

Ivalin is a plant alkaloid that inhibits the induction of tumors in animals. Phomopsin is a mycotoxin known to be carcinogenic. To determine if these compounds influence endocrine responsiveness, their effect on steroid receptors was measured. Neither of these toxins had a direct effect on either the binding capacity or the rate of steroid association of [3H]estradiol-17 beta, [3H]R5020, or [3H]dexamethasone to their respective receptors in cytosol of human breast cancer and rat liver. However, steroid receptor levels of MCF-7 cells, grown in tissue culture, were altered by ivalin and phomopsin. Ivalin at 10(-6) M depressed estrogen receptor levels, while glucocorticoid receptor levels were increased. At 10(-6) M, phomopsin was inhibitory of both progestin and glucocorticoid binding capacities. Data obtained from the proliferation of MCF-7 cells indicated that ivalin and phomopsin at 10(-6) M decreased the number of cells grown in tissue culture. Phomopsin exhibited an inhibitory effect on both [3H]thymidine and [3H]glycine incorporation, while ivalin stimulated [3H]glycine incorporation.