Iodohexestrols. II. Characterization of the binding and estrogenic activity of iodinated hexestrol derivatives, in vitro and in vivo

Abstract

The affinity of ortho-iodinated hexestrols for the estrogen binding protein from rat uterus, determined by competitive binding assay, decreases with progressive iodine substitution; 3-iodohexestrol (I-Hex) has a binding affinity 42% that of estradiol. Analysis of [3-H]-I-Hex binding in rat uterine cytosol by sucrose density gradient centrifugation shows both an estrogen-specific binding component (8 S) and a more abundant component (4 S) that is not estrogen specific. Scatchard analysis indicates that this latter binding is of high affinity (Kd equals to 3.7-8.3 times 10- minus-9 M) but is not uterine specific. Polyacrylamide gel electrophoresis shows that most of the [3-H]-I-Hex binding activity in serum and uterine cytosol is distinct from and anodic to the principal protein component (albumin), and that is comigrates with [14-C]thyroxine binding activity. In in vitro incubation of rat uteri, I-Hex can block the specific uptake of [3-H]estradiol into the nuclear fraction; it itself causes a translocation of estrogen-specific binding capacity (as measured by exchange) from cytoplasm to nuclei, and can induce the synthesis of an estrogen-specific uterine protein, all under conditions where it is not metabolically deiodinated to hexestrol. The uterotrophic activities of the iodohexestrols are in most cases comparable to that expected on the basis of their competitive binding affinities. However, selective, estrogen-specific uptake of [3-H]-I-Hex into rat uterus, either in vitro or in vivo, cannot be demonstrated.

Iodine-125—Labeled Estradiol: a Gamma-Emitting Analog of Estradiol That Binds to the Estrogen Receptor

“…12 February 1979; revised 2 April 1979 tained complete polyoma genomes which were infectious when enzymatically excised from the recombinant molecules, E. coli carrying these molecules consistently failed to induce polyoma infection, even when massive numbers were fed or injected into mice, a highly sensitive indicator system for productive polyoma infection. Similar results were recently reported by Fried et al (3). As a further step in evaluating the biologic activity of the polyoma-plasmid and polyoma-lambda recombinant DNA host-vector systems, we have tested their ability to induce tumors in suckling SCIENCE, VOL.…”

“…As emphasized by Katzenellenbogen et al (3), there are three criteria for an iodinated steroid to be useful for recep- Table 1. Uptake of 125I-labeled estradiol in vivo.…”

Interaction of 16 alpha-[125I]iodo-estradiol with estrogen receptor and other steroid-binding proteins.

“…The entire procedure was described previously (9) but we have made some modifications. After synthesis of the brominated steroid (9), 5 mg of it was dissolved in 500 ,l of CH2Cl2 and subjected to high-pressure liquid chromatography on a column of Lichrosorb Diol (250 X 4.6 mm, Merck) which was eluted at 1 ml/min with CH2Gl2. The brominated steroid eluted in a sharp peak in 8 min.…”

“…These advantages of y-emitting isotopes are well known and the search for an estrogen containing such an isotope (3), which could bind specifically to estrogen receptors, has not been neglected (4)(5)(6)(7)(8). Until recently, attempts to synthesize appropriate compounds were unsuccessful.…”

Tumor Receptor Imaging

“…In this situation, the choices of radionuclide and labeling position for imaging may be relatively limited, such as for ER imaging agents (14). Considerable work has been done with both singlephoton-emitting and positron-emitting halides for ER imaging (49)(50)(51), but studies have suggested that 18 F is the most attractive label for PET ER imaging (14). Fluorine is a small halogen in which substitutions can be made at several positions of the estrogen while preserving binding affinities for both ER and SHBG (52,53).…”