Estrogen receptor imaging with 17 alpha-[123I]iodovinyl-11 beta-methoxyestradiol (MIVE2)--Part I. Radiotracer preparation and characterization.

It is important to know the estrogen receptor rate in breast carcinoma management. Thus, an in vivo and atraumatic method would be very useful. Different ligands have been proposed for this. We present here the specific synthesis of 20E- and 20Z-17 alpha-iodovinyl-11 beta-methoxyestradiols and their biological characterization as estrogen receptor ligands. The two isomers were analysed by current chemical methods (NMR) and purified by HPLC. We carried out an in vivo study with 21-day-old Swiss mice to compare properties of the two ligands. The 20E-MIVE2 showed the best affinity for estrogen receptors, the uterus-to-blood ratio was 15-fold higher for the trans derivative. We enhanced the in vivo and in vitro properties of the 20E-MIVE2: the affinity constant was determined by Scatchard analysis, Kd = 16 x 10(-10) M, and biodistributions were performed with unlabelled estradiol pre-injection. We concluded that 20E-MIVE2 can be used for a feasibility study in patients with breast carcinoma.