Proliferative responses of normal human mammary and MCF-7 breast cancer cells to linoleic acid, conjugated linoleic acid and eicosanoid synthesis inhibitors in culture

Potential mechanisms for the stimulation or inhibition of cell growth by linoleic acid (LA) and conjugated linoleic acid (CLA) were investigated by using eicosanoid synthesis inhibitors. Normal human mammary epithelial cells (HMEC) and MCF-7 breast cancer cells were incubated in serum-free medium supplemented with LA and CLA and cyclooxygenase (indomethacin; INDO) or lipoxygenase (nordihydroguaiaretic acid; NDGA) inhibitors. Linoleic acid stimulated the growth and [H-3]thymidine incorporation of normal HMEC and MCF-7 cancer cells, while CLA was inhibitory. Supplementation with LA increased intracellular lipid peroxide concentrations in normal HMEC and MCF-7 cancer cells, whereas CLA did not affect lipid peroxide formation. Normal HMEC and MCF-7 cells supplemented with LA and INDO or NDGA resulted in growth inhibition. The treatment of normal HMEC with CLA and INDO or NDGA, and MCF-7 cells with CLA and INDO stimulated cell growth. However, the addition of CLA and NDGA to MCF-7 cells resulted in synergistic growth suppression suggesting that CLA effects were mediated through lipoxygenase inhibition. Although NDGA was more inhibitory of cell growth in the presence of LA or CLA than INDO, growth was associated with both prostaglandin and leukotriene production. Additional studies are warranted to elucidate the mechanism(s) whereby LA or CLA affect breast cell growth.