4-iodotamoxifen aziridine, a new affinity labeling agent for the rapid detection of estrogen receptor isoforms

We describe the simple and fast preparation of a new radioiodinated probe for the detection of the estrogen receptor (ER) and its isoforms. Iodotamoxifen aziridine was labeled with iodine 125 ([ 125I]TAZ) in position 4 of the α aromatic ring. The yield was high (>75%), the label was stable and the specific activity was near optimal (1900–2170 Ci/mmol). The apparent relative binding affinity of the probe to a recombinant human ER (hER) was high (RBA=35 vs estradiol=100). Electrophoretic studies (SDS–PAGE) with this hER indicated the high potency of [ 125I]TAZ at very low concentration (