Effect of conjugated linoleic acid isomers on growth factor-induced proliferation of human breast cancer cells

We evaluated the effect of conjugated linoleic acid (CLA) isomers on the growth factor-induced proliferation of human breast cancer MCF-7 cells. When MCF-7 cells were cultured in RPMI 1640 medium supplemented with 1% fetal bovine serum (FBS), CLA inhibited the proliferation and notably cis9, trans11 (c9,t11)-CLA showed the strongest effect. However, cells barely grew when cultured with 1% charcoal-treated FBS (cFBS). Proliferation was promoted in cFBS cultured cells by the addition of 17β-estradiol (E2), insulin, and epidermal growth factor (EGF). Trans10, cis12 (T10,c12)-CLA inhibited cell proliferation induced by E2 and insulin, but not by EGF. T10,c12-CLA also exhibited cell-killing activity when cells were induced with insulin. On the other hand, c9,t11-CLA was shown to have no effect on MCF-7 cell proliferation induced by and of these three growth factors. In conclusion, although both c9, t11 and t10, c12-CLA can inhibit the proliferation of MCF-7 cells, our results suggested that they have separate mechanisms and different targets of actions.