SPECIFIC CYTOTOXICITY OF 16α-[125I]IODOESTRADIOL FOR ESTROGEN RECEPTOR-CONTAINING BREAST CANCER CELLS

Abstract

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 16α-[¹²⁵l]iodoestradiol alone ([¹²⁵I]E₂), or with 16α-[¹²⁵I]iodoestradiol plus 100-fold excess 17 β-estradiol (E₂), and then viably frozen. After 8 weeks, the [¹²⁵I]E₂ exposed cells and the 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 techniq e shows promise for selecting a population of cells with defects in their estrogen receptor and in studying subcellular hormone interactions.