Specific cytotoxicity of 16 alpha-[125I]iodoestradiol for estrogen receptor-containing breast cancer cells.

We attempted to induce specific killing of estrogen receptor-containing breast cancer cells using estradiol coupled to a high specific activity gamma emitting isotope of iodine. MCF-7 human breast cancer cells were incubated with 16 alpha-[125I]iodoestradiol alone ([125I]E2), or with 16 alpha-[125I]iodoestradiol plus 100-fold excess 17 beta-estradiol (E2), and then viably frozen. After 8 weeks, the [125I]E2 exposed cells and the [125 I]E2 plus E2 exposed cells were 10% and 77% of controls, respectively. When the breast cancer cell line MDA-MB-231 which does not contain estrogen receptors was used, the rate of cell death was similar to the competed MCF-7 cells. When specific cytotoxicity was compared using a cloning technique, nearly a 5 log reduction in surviving cell fraction was seen with [125I]E2, as compared to identical cells treated with [125I]E2 plus competitor. This technique shows promise for selecting a population of cells with defects in their estrogen receptor and in studying subcellular hormone interactions.