SYNTHESIS, STRUCTURE AND BIOLOGICAL PROPERTIES OF Z-17-ALPHA-(2-IODOVINYL)-11-BETA-CHLOROMETHYL ESTRADIOL-17-BETA (Z-CMIV), A HIGH-AFFINITYLIGAND FOR THE CHARACTERIZATION OF ESTROGEN RECEPTOR-POSITIVE TUMORS

Linkage of a 11 beta-chloromethyl group to estradiol-17 beta (E(2)) dr amatically increases the binding affinity of the steroid for the estro gen receptor (ER) with the formation of a quasi-irreversible steroid-r eceptor complex. We have synthesized the two isomers of 11 beta-chloro methyl-17 alpha-iodovinyl-estradiol (E-CMIV and Z-CMIV) by a novel rou te. Both derivatives demonstrated high binding affinitJ; and selectivi ty for ER (RBAs: ER=820 and 1008; SHBG=1.2 and 0.25, respectively; E(2 )=100). On the basis of X-ray crystallographic data for Z-CMIV and its precursor, we have postulated that Z-CMIV might interact strongly wit h aromatic amino-acids within a hydrophobic groove of the ER hormone b inding domain (HBD) that incorporates pockets corresponding to the 11 beta and 17 alpha steroid substituents. The binding properties of Z-CM IV labeled with I-125 were investigated, especially its ability to det ect and quantify altered ER forms with low binding affinity for E(2). Sucrose density gradient analysis revealed that Z-CMIV has a higher ac tivation potency than E(2) as it converts a higher proportion of non-a ctivated monomers in the cytosol into activated monomers with the pote ntial to dimerize. In in vitro (MCF-7 cells) and in vive (rat uterus) determinations of estrogenic activity, Z-CMIV was as potent as E(2) in increasing progesterone receptor (PgR) concentrations and decreasing ER levels and in stimulating uterine growth. [I-125]-Z-CMIV could open the way to new applications in the diagnosis and therapy of ER-positi ve breast cancers, especially those containing altered (variant) ERs. Copyright (C) 1996 Elsevier Science Ltd.