Conjugated linoleic acid modulates the human breast microenvironment

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The breast local microenvironment is theorized to be crucial for the neoplastic transformation, promotion, and progression of breast epithelial cells leading to cancer. The breast microenvironment is greatly influenced by breast stromal cells which interact with breast epithelial cells and can promote or inhibit cancer promotion and progression. Conjugated linoleic acid (CLA), a naturally occurring compound, found in ruminant products has been shown to possess anti-cancer abilities in in vivo and in vitro models. In breast cancer patients, the presence of estrogen receptor α (ERα) has been associated with a better prognosis. ERβ is considered a tumor suppressor gene in ERβ knockout mice and it has been suggested that the loss of ERβ expression is a common step in estrogen-dependent tumor progression. Our study investigated (1) whether CLA exerts its chemopreventive and chemotherapeutic activities on the epithelial cells, or the stromal cells or both (2) whether CLA exerts these activities through modulating ERα and ERβ. Two CLA isomers, t10,c12-CLA and c9,t11-CLA were tested at doses from 0 to 40 μM. A two cell type co-culture system was used. For our normal human breast model, primary cultured normal breast epithelial cells and stromal cells from the same patient, were cultured alone or were co-cultured in the presence or absence of CLA. For our human breast cancer model, primary cultured normal and cancer human breast stromal cells were cultured alone or were co-cultured with the human breast cancer epithelial cell line MCF-7 in the presence or absence of CLA. c9,t11-CLA, but not t10,c12-CLA resulted in up-regulation of ERβ protein (0.6 fold) in normal co-cultured breast cells compared with down-regulation in those cultured alone. Interestingly, ERα protein was almost totally eliminated in normal breast epithelial cells co-cultured with stromal cells. t10,c12-CLA increased ERβ protein in co-cultured MCF-7 cells (2 fold) and normal stromal (32 fold) cells. Co-culture of MCF-7 and normal stromal cells resulted in a dramatic up-regulation of ERα in MCF-7 (>16 fold) and normal stromal cells (2.5 fold) in comparison with MCF-7 (8 fold) and normal stromal cells (1 fold) cultured alone. Therefore, this evidence implies that modulation of the breast microenvironment is critical for the chemopreventive and chemotherapeutic effects of CLA on 1.) increasing tumor suppressor gene, ERβ, expression in both normal and cancerous breast tissue; 2.) up-regulating ERα in breast cancer which may increase the efficacy of anti-estrogen therapy; and 3.) eliminating ERα in normal breast tissue which may be protective, although, the surrounding stromal cells are perhaps a more important target for CLA-mediated chemopreventive and chemotherapeutic effects.(Supported by NIH Grants CA94718 & CA95915 and DOD Breast Cancer Research Programs Grants DAMD 8140, 0319 & 9341).