Cytotoxicity of Receptor-Mediated 16 [125I]Iodo-estradiol in Cultured MCF-7 Human Breast Cancer Cells

Abstract

Therapeutic strategies using ¹²⁵I-labeled steroid hormones are attractive in light of the estrogen dependence of many human breast cancers and the favorable microdosimetry resulting from ¹²⁵I decay. We determined the uptake, specific estrogen receptor (ER) binding, and cytotoxicity of 16α-[¹²⁵.I]iodoestradiol in cultured MCF-7 human breast cancer cells. The cytotoxicity of receptor-mediated ¹²⁵I appears to be sufficient in MCF-7 cells to warrant in vivo experimentation. Furthermore, cytotoxicity not specific to ERs is minimal within the dose range necessary for ER saturation and specific cell killing. Competitive toxicity studies using nonradioactive 17β-estradiol demonstrate an unequivocal relationship between ER binding and clonogenic viability. [J Natl Cancer Inst 81:437–440, 1989]