The synthesis of 11 beta-methoxy-[16 alpha-123I] iodoestradiol and its interaction with the estrogen receptor in vivo and in vitro

In order to produce an estrogen receptor mediated imaging agent, we have synthesized 11 beta-methoxy-16 alpha-iodoestradiol labeled with 123I, and have studied its interaction with the estrogen receptor and its distribution in rats and rabbits. This 123I-labeled steroid, 11 beta-methoxy-16 alpha-[123I]iodoestradiol, binds with high affinity, Ka = 6 x 10(9) M-1, and specificity to the estrogen receptor in uterine cytosol. When tested in vivo, this radiolabeled steroid concentrates by a receptor mediated mechanism, in the estrogen target tissue, the uterus, producing very high target to nontarget tissue ratios. The results of these experiments indicate that 11 beta-methoxy-16 alpha-[123I]iodoestradiol may be a useful imaging agent for clinically monitoring and detecting estrogen receptor containing tumors.