P4-02-01: Bis(2-Ethylhexyl) Phthalate: A Potential Endocrine Disruptor Confer Letrozole Insensitivity and Induction of Aromatase Activity in Breast Cancer Cells.

Abstract

Abstract Exposure to endocrine disrupting compounds (EDC's) is an important determinant of mammary gland development and mammary tumor pathogenesis. The risk of breast cancer in adulthood is known to be influenced by environmental factors experienced as a fetus. Fetal exposure to dietary factors or certain pharmaceuticals and environmental chemicals that affect or mimic steroid hormones increase predisposition to breast cancer. The mechanisms by which EDC's alter epigenetic programming, differentiation and deregulation of ductal branching of mammary glands are poorly understood. A high ratio of estrogen receptor a (ERα) to ERβ has been recently found to be associated with poor prognosis and aggressive disease in breast cancer patients. Preliminary studies from our laboratory revealed that bis(2-ethylhexyl) phthalate (DEHP) is a possible EDC which induces cell proliferation in T47D, MCF7, MCF7/Aro breast cancer cells in vitro and confers insensitivity to letrozole, a third generation aromatase inhibitor. DEHP increased cell proliferation (MTT assay) in a dose dependent manner and was non toxic to T47D, MCF7 and MCF 7 Aro cells. 1, 10 and 100 nM concentrations of DEHP up regulated ERα and down regulated ERβ at the mRNA level. Hypermethylation in the estrogen receptor beta (ERβ) promoter was observed after treatment with 1nM DEHP for 24 h, suggesting that DEHP alter epigenetic programming through changes in the DNA methylation to modify the chromatin structure and change the accessibility of DNA to transcription factors. When breast cancer cells were treated with letrozole (200nM and DEHP (1nM) together, they survived, whereas those treated with letrozole alone did not survive. Aromatase mRNA and enzyme levels were higher in the DEHP treated cells by comparison with sham control MCF7/Aro cells. Nonmalignant MCF-10A breast epithelial cells showed a proliferation advantage (MTT assay) by up regulation of ERα as well as aromatase expression when treated with 1nM DEHP. Aromatase transgenic mice treated with 10mg/Kg b.wt of DEHP over a period of 30 days resulted in the excessive ductal branching density and epithelial outgrowth in the mammary gland. The present data suggest that dietary accumulation of DEHP through plastic food containers, water bottles, etc. may contribute to risk of hormone sensitive breast cancer in women and chemoinsensitivity and or drug resistance in breast cancer patients. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-02-01.