(Z)-17 beta-hydroxy-17 alpha-(2-[125I]iodovinyl)-4-estren-3-one: a new specific gamma-emitting ligand for determination of progesterone receptor.

An iodine-125 labeled ligand for progesterone receptor determination was synthesized: (Z)-17 beta-hydroxy-17 alpha-(2-[125I]iodovinyl)-4-estren-3-one ([125I]SH-D 510). The ligand is stable chemically as well as under the conditions of a receptor assay. The relative binding affinity of the nonradioactive compound towards human uterine progesterone receptor was 7.0 for the Z-isomer (promegestone (R5020) 1.0) and 0.95 for the E-isomer. 4 S and 8 S receptor forms were obtained on sucrose density gradient analysis. Progesterone receptors were assayed in 103 human mammary tumour cytosols, using either [3H]promegestone or [125I]SH-D 510. The coefficient of correlation was r = 0.951.