Influence of estradiol and triiodothyronine on breast cancer cell lines proliferation and expression of estrogen and thyroid hormone receptors

Objective: To better understand the estrogen (E2) agonist action of triiodothyronine (T3) the effects of these hormones on ER negative MDA-MB-231 breast cancer cells were compared with those on S30, a clone of MDA-MB-231 stably transfected with ER alpha cDNA, in terms of proliferation and modulation of hormone receptors. Results: Growth experiments showed that MDA-MB-231 was not modulated by any hormone or tamoxifen (TAM). Treatment with E2, 10(-8)M or 10(-9)M had little effect on S30 proliferation. T3 at 10(-8)M significantly inhibited proliferation. This effect was not reverted by TAM. Treatments with 10(-8)M concentration of E2 or T3 reduced ER alpha. gene expression in S30, an effect partially blocked by association with TAM, with no effect on TR expression. These results suggest that, in S30, 10(-8)M T3 has a similar action to E2 relative to ER alpha gene modulation. Conclusions: Such results emphasize the need of determining T3 levels, before the introduction of antiestrogenic forms of treatment in breast cancer patients. Arq Bras Endocrinol Metab.2009;53(7):859-64.