Steroid hormone-receptor activity in the presence of a mycotoxic phomopsin toxin and the sesquiterpene ivalin toxin.

The influences of two toxins, phomopsin and ivalin, which are reported to exhibit carcinogenic and antitumor activities, respectively, were studied on steroid hormone receptor binding. A mycotoxic carcinogenic fraction A (phomopsin) was isolated from Phomopsis leptostromiformis. The antitumor sesquiterpene lactone ivalin was obtained from the "vomiting bush" Geigeria. Competitive binding analyses were conducted with radiolabeled steroid ligands and unlabeled toxins. No effect of these toxins was observed on either the binding capacity or on the rate of steroid association of [3H]-estradiol-17 beta, [3H]promegestone (R5020), and [3H]dexamethasone to their respective receptors in cytosol of human breast cancer and rat liver. The concentrations of phomopsin and ivalin varied between 0.85 nM to 14 micron in the competitive binding assays. These data suggest the carcinogenic and antitumor activities of these toxins do not involve association with steroid hormone receptors.