ABSTRACT: We characterized an endocrine disruptor from ground corncob bedding material that interferes with male and female sexual behavior and ovarian cyclicity in rats and stimulates estrogen receptor (ER)-positive and ER-negative breast cancer cell proliferation. The agents were identified as an isomeric mixture of tetrahydrofurandiols (THF-diols; 9,12-oxy-10,13-dihydroxy-octadecanoic acid and 10,13-oxy-9,12-dihydroxyoctadecanoic acid). Synthetic THF-diols inhibited rat male and female sexual behavior at oral concentrations of 0.5-1 ppm, and stimulated MCF-7 human breast cancer cell proliferation in vitro.Because THF-diols are derived from lipoxygenase and cyclooxygenase pathways, we suspected that these compounds may regulate cell proliferation by modulating specific enzymatic sites involved in linoleic acid metabolism including phospholipase A(2) (PLA2), lipoxygenases (LOX-5 and LOX-12), cyclooxygenases (COX-1 and COX-2), and closely coupled enzymes including aromatase (AROM).MCF-7 human breast cancer cells were treated with inhibitors for PLA2 (quinacrine), lipoxygenases (LOX-5 and LOX-12; baicalein, REV-5091, nordihydroguaiaretic acid), cyclooxygenases (COX-1, COX-2, indomethacin), and AROM (formestane). The effects of these enzyme inhibitors on cell proliferation in response to THF-diols or estradiol (E(2)) were assessed. THF-diol modulation of the expression (RNA and protein) of these enzymes was also evaluated by quantitative real-time PCR (QPCR) and Western blot analyses.The enzyme inhibition and gene expression (RNA and protein) studies identified PLA2, LOX-5, LOX-12, COX-2, and perhaps AROM as likely sites of THF-diol regulation in MCF-7 cells. COX-1 was not affected by THF-diol treatment.THF-diol stimulation of MCF-7 cell proliferation is mediated through effects on the expression of the PLA2, COX-2, LOX-5, and LOX-12 genes and/or their respective enzyme activities. The products of these enzymes, including prostaglandins, hydroxyeicosatetraenoic acids (HETEs) and hydroxyoctadecenoic acids (HODEs), are well-established mitogens in normal and malignant cells. Therefore, it is likely that these compounds are involved in the mechanism of action of THF-diols in breast cancer cells. Although the formestane inhibition studies suggested that AROM activity might be modulated by THF-diols, this was not confirmed by the gene expression studies.
