7 alpha-Methyl-17 alpha-(E-2'-[125I]iodovinyl)-19-nortestosterone: a new radioligand for the detection of androgen receptor

Bromine- and Iodine-Substituted 16α,17α-Dioxolane Progestins for Breast Tumor Imaging and Radiotherapy: Synthesis and Receptor Binding Affinity

Progesterone receptors (PRs) are present in many breast tumors, and their levels are increased by certain endocrine therapies. We describe the synthesis and PR binding affinities of a series of bromine- and iodine-substituted 16alpha,17alpha-dioxolane progestins, some of which, when appropriately radiolabeled, are potential agents for diagnostic imaging of PR-positive breast tumors using positron emission tomography (PET) and for radiotherapy. These compounds were synthesized from halogenated furanyl, phenyl, and thiophenyl aldehydes and a progestin 16alpha,17alpha,21-triol (5) in the presence of HClO4 or Sc(OTf)3 in high yields under optimized conditions. A new reagent, perfluoro-1-butanesulfonyl fluoride (PBSF), was used to convert the C-21 OH to F in high yields. The relative binding affinities (RBAs) of the most promising compounds for the PR (RBA of R5020 = 100) were 16alpha,17alpha-[(R)-1'-alpha-(5-bromofurylmethylidene)dioxyl]-21-hydroxy-19-norpregn-4-ene-3,20-dione (endo-6; RBA = 65 and moderate lipophilicity), 21-fluoro-16alpha,17alpha-[(R)-1'-alpha-(5-iodofurylmethylidene)dioxyl]-19-norpregn-4-ene-3,20-dione (endo-14; RBA = 40) and 21-fluoro-16alpha,17alpha-[(S)-1'-beta-(4-iodophenylmethylidene)dioxyl]-19-norpregn-4-ene-3,20-dione (exo-16; RBA = 34).

Synthesis of the 7alpha-cyano-(17alpha,20E/Z)-[125I]iodovinyl-19-nortestosterones: potential radioligands for androgen and progesterone receptors

We report the preparation of the 7alpha-cyano derivative of the isomeric (17alpha,20E/Z)-[125I]iodovinyl-19-nortestosterones (IVNT) together with their binding affinity for the androgen receptor (AR) and their biodistribution in two different animal models. The cyano group was introduced at the 7alpha-position by hydrocyanation of 4,6-estradien-17beta-ol-3-one with diethylaluminum cyanide. Selective protection of the A-ring enone system as the dienol ether followed by ethynylation and deprotection under base and acid hydrolysis condition gave 7alpha-cyano-17alpha-ethynyl-19-nortestosterone. The stannyl derivatives were prepared by addition of tri-n-butylstannyl hydride and converted stereospecifically to the corresponding [125I]iodovinyl analog using [125I]NaI and H2O2. The [125I]iodovinylsteroids were intravenously administered to male rats and estrogen-primed immature female rats and tissue uptake was measured up to 6h post-injection. Co-administration of NLP-004 or ORG-2058, highly selective ligands for the progesterone receptor, to the female rats did not affect uterus uptake of the 125I-ligands. However co-injection of testosterone to DES-primed male rats induced a marked increase in prostate uptake of the 20Z-isomer of 7alpha-cyano-[125I]-IVNT. The relative binding affinity (RBA) of either 7alpha-cyano-(17alpha,20E/Z)-IVNT isomer for the AR is low (RBA=4 and 3, respectively, versus 100 for 5alpha-dihydrotestosterone (DHT)), suggesting the absence of a possible role of the AR in the localization process. These findings contrast previously reported data for the analogous 7alpha-methyl-[125I]-IVNT where co-administration of testosterone was shown to result in a 50% drop in prostate uptake. These data indicate that the addition of an electron withdrawing 7alpha-cyano group to 123I-labeled nortestosterone derivatives does not improve their potential to serve as SPECT agents for the imaging of AR densities in the prostate.

7alpha-Iodo and 7alpha-fluoro steroids as androgen receptor-mediated imaging agents

We have synthesized several 7alpha-fluoro (F) and 7alpha-iodo (I) analogues of 5alpha-dihydrotestosterone (5alpha-DHT) and 19-nor-5alpha-dihydrotestosterone (5alpha-NDHT) and tested them for binding to the androgen receptor and for their biological activity in an in vitro assay with cells that have been engineered to respond to androgens. The relative binding affinity to the androgen receptor determined in competition assays showed that in the androstane series the fluoro steroids have the highest affinity and that F-17alpha-CH3-DHT (4) has a higher affinity than 5alpha-DHT. All other steroids were somewhat less potent than 5alpha-DHT with F-DHT (2) = I-17alpha-CH3-DHT (3) >/= F-NDHT (6) > F-17alpha-CH3-NDHT (8) = I-DHT (1) >/= I-NDHT (5) > I-17alpha-CH3-NDHT (7). The relative biological activity in cells transfected with the androgen receptor and an androgen responsive reporter gene is 4 >> 5alpha-DHT > 2 > 6 > 3 >/= 1 >/= 8 >/= 5 > 7. The iodinated compound, I-17alpha-CH3-DHT (3), with the highest binding activity was synthesized labeled with 125I and was shown to bind with high affinity, Ka = 1.9 x 10(10) L/mol, and low nonspecific binding to the androgen receptor in rat prostatic cytosol. However, when radiolabeled [125I]-17alpha-CH3-DHT ([125I]3) was injected into castrated male rats, it showed very poor androgen receptor-mediated uptake into the rat prostate. This was unexpected in light of its superior receptor binding properties and its protection by the 17alpha-methyl group from metabolic oxidation at C-17. However, the biological potency of I-17alpha-CH3-DHT (3) was not as high as would have been expected. When I-DHT (1) and I-17alpha-CH3-DHT (3) were incubated in aqueous media at 37 degrees C they rapidly decomposed, but they were stable at 0 degrees C. The fluorinated analogue 4 treated similarly at 37 degrees C was completely stable. The products of the decomposition reaction of I-DHT (1) at 37 degrees C were identified as iodide and principally 17beta-hydroxy-5alpha-androst-7-en-3-one. The temperature dependence of this elimination reaction explains the inconsistency between the high binding to the androgen receptor (measured at 0 degrees C) and the low biological activity, as well as the poor androgen receptor mediated concentration in vivo. The fluorinated analogue F-17alpha-CH3-DHT (4) has both high affinity for the androgen receptor and high stability in aqueous media. Of the compounds tested, 4 has the highest affinity for the androgen receptor as well as the highest androgenic activity. Thus it is likely that F-17alpha-CH3-DHT 4 labeled with 18F will be an excellent receptor-mediated diagnostic imaging agent.

Iodinated and fluorinated steroid 2'-aryl-[3,2-c] pyrazoles as potential glucocorticoid receptor imaging agents

We have synthesized several halogenated steroids as potential glucocorticoid receptor mediated imaging agents. These compounds are analogs of aryl-pyrazolo steroids, similar to the potent glucocorticoid, cortivazol. Compounds containing the halogens, iodine, bromine, and fluorine, as well as the E- and Z-iodovinyl side chain at the para position of 2'-phenyl-11 beta,17,21-trihydroxy-16 alpha-methyl-20-oxo-pregn-4-eno[3,2-c] pyrazole were prepared. They were tested as ligands for the glucocorticoid receptor by competition for the binding of [3H]dexamethasone and for glucocorticoid potency by the induction of alkaline phosphatase in HeLa cells. None of the iodinated steroids were good ligands for the glucocorticoid receptor or potent glucocorticoids. The bromo analog was only slightly better than the iodinated steroids as a ligand, and it had a potency in the HeLa cell assay about half that of dexamethasone. The fluoro analog good binding to the glucocorticoid receptor and was a very potent glucocorticoid, approximately seven times that of dexamethasone. Consequently, it appears that the fluoro steroid, 2'-(4-fluorophenyl)-11 beta,17,21-trihydroxy-16 alpha-methyl-20-oxo-pregn-4-eno[3,2-c] pyrazole, when labeled with 18F, would make an excellent glucocorticoid receptor-mediated imaging agent for positron emission tomography.

In vitro labeling of gonadal steroid hormone receptors in brain tissue sections

Autoradiographic methods have been developed for measurement of gonadal steroid receptors in situ in brain tissue sections. Based on principles established previously for estrogen receptors in the rat brain using a 125I-labeled ligand, procedures have been developed for in vitro labeling of estrogen, androgen, and progestin receptors with commercially available tritiated ligands. Addition of protamine sulfate to the incubation buffer precipitates the receptors in situ in the tissue sections, allowing them to be detected autoradiographically after incubation with labeled steroid and subsequent washing to remove unbound and nonspecifically bound ligand. Occupied and unoccupied estrogen receptors can be measured selectively using appropriately modified incubation conditions. In the case of androgen and progestin receptors, unoccupied receptors are readily detected by in vitro labeling of tissue sections, but occupied receptors do not appear to label efficiently. Preliminary data suggest that these methods should be equally applicable to a variety of laboratory animals, including the rat, mouse, guinea pig, and monkey.

Localization and measurement of occupied androgen receptors in thaw-mounted rat and human prostate tissue sections by in vitro autoradiography

In this paper we present an in vitro exchange binding assay procedure for measurement of androgen receptors in slide-mounted tissue sections. This method allows quantitative autoradiographic determinations with an anatomical resolution approaching the cellular level. Tissue sections are incubated with the synthetic androgen [3H]R1881 in the presence of triamcinolone acetonide to suppress possible binding of the radioligand to the progestin receptor. Adjacent tissue sections are incubated with [3H]R1881 in the presence of excess unlabeled 5 alpha- dihydrotestosterone or R1881 to assess nonspecific binding. Following incubation, the tissue sections are washed to remove unbound radioligand and either scraped for immediate determination of androgen receptor binding or placed against emulsion-coated film for the production of an autoradiographic image. In validation experiments with rat prostate sections from castrated, gonad-intact, and androgen-supplemented animals, maximum levels of androgen binding were observed with incubation at 4 degrees C or 72 h. Markedly less binding was detected with shorter incubations or with incubations at even slightly elevated temperatures. Very little androgen receptor binding was detected in castrated animals whereas receptor levels in intact and androgen-supplemented animals were 79.3 fmol/mg and 143.6 fmol/mg protein, respectively, suggesting that the method is selective for occupied receptors. Saturation binding analysis revealed binding to a single class binding site with high affinity (kd = 1.475 +/- 0.12 nM). Autoradiographic images of androgen binding in the prostate reflected the findings with the scraped sections: essentially no specific binding was present in sections from castrated animals whereas much heavier labeling was present in sections from intact animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of ALVA-41 cells, a new human prostatic cancer cell line

The ALVA-41 cell line was derived from a bony metastasis from a human prostatic carcinoma. The line has a number of distinct, advantageous properties that should make it useful as a tool for the study of prostate cancer. It grows rapidly and is easy to work with. It has receptors for androgens and glucocorticoids but not for estrogens. Its growth is enhanced by physiological concentrations of dihydrotestosterone. It does not secrete prostate specific antigen, but does secrete prostatic acid phosphatase. Further, the secretion of prostatic acid phosphatase is enhanced by dihydrotestosterone.

Synthesis of (17 alpha,20E/Z)iodovinyl testosterone and 19-nortestosterone derivatives as potential radioligands for androgen and progesterone receptors

To develop androgen and progesterone receptor-based radioligands for SPECT imaging we synthesized several radioiodinated 17 alpha-iodovinyl testosterone and 19-nortestosterone analogs and evaluated their biological properties. The synthesis of these compounds proceeds via the (17 alpha,20E/Z)stannyl intermediates and involves addition of tri-n-butyltin hydride to the 17 alpha-ethynyl group of the steroid using either azobisiso butyronitrile or triethylborane as a catalyst. The stannyl derivatives are stereospecifically converted to the corresponding (17 alpha,20E/Z)iodovinyl derivatives using molecular iodine, or to the [125I]iodovinyl analogs using [125I]NaI and H2O2. Androgen and progesterone receptor (AR and PgR) binding affinities were measured via a competitive in vitro binding assay. In general 19-nortestosterone derivatives showed higher receptor affinities as compared to the testosterone derivatives. In the latter series the highest PgR binding affinities were observed with the (17 alpha,20Z)iodovinyl-19-nortestosterone (IVNT) (92 vs 100 for R5020) followed by the 7 alpha-methyl analog, whereas the highest AR binding affinity was observed with the 7 alpha-Me-(17 alpha,20Z)IVNT (54 vs 100 for 5 alpha-dihydrotestosterone). These derivatives were also labeled with 125I and evaluated for their in vivo target organ uptake (prostate and estrogen-primed uterus). The highest PgR-mediated target tissue uptake was observed with the (17 alpha,20Z)-[125I]IVNT and its 7 alpha-methyl derivatives whereas only one derivative, the 7 alpha-Me-(17 alpha,20Z)-[125I]IVNT, showed AR-mediated dorsal prostate retention. Although some of the IVNT derivatives have interesting binding properties, the lack of in vivo selectivity does suggest that the 123I-labeled analogs are unlikely to be suitable for imaging of AR and PgR-rich tissues.