125I-ligand for progesterone receptor: 17 alpha-(6'-iodohex-1'-ynyl)-19-nortestosterone.
Progesterone receptor (PgR) is known to be a significant indicator of hormone dependency of a breast tumor and also an important prognostic factor for recurrence and survival. Relatively low specific activity of tritium-labeled ligands makes it difficult to detect the presence of PgR in very small specimens and in specimens with low PgR content. We therefore undertook the synthesis of a radioiodinated progestin. We have synthesized unlabeled 17 alpha-(omega-haloalk-1'-ynyl)-19-nortestosterones with 4, 6, and 8 carbon side chains; these have high affinity for PgR and clear potential for conversion to a 125I form. Since the six-carbon side chain analogue had the highest relative PgR affinity (38% of the affinity of R5020, using PgR from T47D human breast cancer cells), it was selected for preparation of the 125I form by radiohalogen exchange of a omega-bromoalkynyl precursor with carrier-free Na125I. This new ligand was found by Scatchard analysis to have a Kd of 0.47 nM, as compared with [3H]R5020 at 0.22 nM and [3H]progesterone at 2.0 nM. (For affinity studies, all ligands were diluted in dimethylformamide and added to PgR-containing T47D cytosol to give a final DMF concentration of 4%, in order to prevent R5020 and the test compounds from binding nonspecifically to proteins and glass/plasticware.) The new 125I-ligand showed very little instability when stored in ethanol at approximately 10 degrees C even for several months. Thus, 17 alpha-(6'-[125I]iodohex-1'-ynyl)-19-nortestosterone should prove to be a useful ligand for high sensitivity PgR assays.
Salman
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University of Texas Health Science Center, San Antonio Division of Medical Oncology 78284-7884.
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D001667:Binding, Competitive; D001943:Breast Neoplasms / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D005260:Female; D006801:Humans; D007202:Indicators and Reagents; D007457:Iodine Radioisotopes; D007700:Kinetics; D008024:Ligands; D013058:Mass Spectrometry; D009277:Nandrolone / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000378:metabolism; D011980:Receptors, Progesterone / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000378:metabolism*
D007202:Indicators and Reagents; D007457:Iodine Radioisotopes; D008024:Ligands; D011980:Receptors, Progesterone; C060677:17-(6'-iodohex-1'-ynyl)-19-nortestosterone; D009277:Nandrolone