Estrogen receptor-mediated cytotoxicity using iodine-125.

Auger effects from 125I decay are singularly damaging if localized in DNA as the thymidine analogue 125I-iododeoxyuridine (125IUdR). Recent experience with steroid sex hormones extends these observations by demonstrating cytotoxicity in sites other than the DNA backbone. We have compared the cytotoxicity in human MCF-7 breast cancer cells of 125IUdR, 125I-iodotamoxifen, a nonsteroidal antiestrogen that is translocated from the cytoplasm to the nucleus of receptor containing cells, and 125I-iodoantipyrine, a biological indicator of the body water space. Cytotoxicity is critically dependent upon subcellular localization.