Abstract P6-03-01: Low dose exposure of non-malignant breast epithelial cells to the polyester and PET precursor, terephthalic acid, triggers broad-based dysfunctional changes

Abstract

Abstract BACKGROUND: Terephthalic acid (TPA) is the raw material for the production of polyester fiber and polyethylene terephthalate (PET) or #1 plastic. With steadily increasing levels of TPA in our environment, concerns for public health are foreseeable. We report the role of low dose TPA exposure in the induction of well-accepted endpoints of cancer progression within non-cancerous breast cells. METHODS: In our previous work with bisphenol-A (BPA) and methylparaben (MP), we employed human, benign, high-risk donor breast epithelial cells (HRBECs) to study functional response to chemical exposure. To measure the effects of TPA, 3 independent spontaneously immortalized ER-positive HRBEC lines were treated with concentrations ranging from 100pM to 100μM for 7 days. Changes in the levels of key signaling proteins encoded by genes associated with estrogenic stimulation, cell cycle, DNA replication, DNA repair, and apoptosis, were analyzed by Western blots. Fluorescence-activated cell sorting (FACS) was used to quantitate alterations in cell proliferation and programmed cell death. TPA-induced DNA double strand breaks were visualized as nuclear foci of activated gH2AX, and p53 by immunofluorescence microscopy. RESULTS: TPA exposure was estrogenic in HRBECs as evident by ERα activation. Similar to our findings with BPA and MP, prior exposure to TPA at 1 or more concentrations in the low dose range enabled programmed cell death evasion in 3/3 immortalized HRBEC lines (p<0.01), further confirmed in finite-life HRBECs (p<0.001) from 3/3 independent donors. Otherwise, effects of TPA were distinct from those induced by BPA and MP. Instead of an increase in the S-phase fraction of the cell cycle, TPA treatment led to a G1-arrest. These G1-arrested cells accumulated the DNA repair proteins – DNA-PK, ATM (pSer1981), RAD50, MRE11, p53 (pSer15) and H2AX (pSer139), indicating the occurrence of DNA damage. TPA removal released HRBECs from G1-arrest and restored proliferation. However, due to the propensity for apoptosis evasion conferred by TPA, unrepaired cells displaying DNA repair signals persisted even in its absence. Taken together, these findings demonstrate perpetuation of cells with evidence of DNA damage from prior TPA exposure, and suggest a scenario whereby potential DNA aberrations incurred from exposure to this and other DNA damaging agents might be transmitted to the cell progeny. CONCLUSION: Supporting the novel observation of mTOR activation in HRBECs by BPA in our previous work, TPA-induced pathway perturbations demonstrate that the common practice of screening for potential breast carcinogens simply based on increased cell proliferation, presumably stimulated by the mitogenic activity of estrogen mimics, is an oversimplification of possible sources of risk to target cells within the breast. Using such limited tests, TPA would be deemed inactive – ostensibly a false negative result. Effects of environmental chemicals must therefore be evaluated by multiple endpoints in independent biological programs within responsive human cell types. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P6-03-01.