Reagents for photoaffinity labeling of estrogen binding proteins. Synthesis of some azide and diazo derivatives of estradiol, estrone, and hexestrol

Synthesis and analgesic effects of kyotorphin-steroid linkers

Kyotorphin (KTP, H-Tyr-Arg-OH) was covalently bonded with hydrocortisone or estrone to form the corresponding hydrocortisone-21-O-yl-succinyl-Tyr-ArgOH or estrone-3-O-yl-acyl-Tyr-Arg-OH. Their analgesic activities were investigated using the tail flick test. The potency of the two linkers were significantly higher than that of KTP and the mixture of KTP and hydrocortisone or estrone in the CNS and/or the periphery administration.

Study of the rat liver S-adenosylmethionine synthetase active site with 8-azido ATP

The active site of rat liver S-adenosylmethionine synthetase was studied using 8-azido ATP, a photolabile analogue of ATP. Both forms of the enzyme, tetramer and dimer, could be labelled by using concentrations of the analogue similar to the KmATP values for each form, 350 microM and 1 mM respectively. Labelling of both S-adenosylmethionine synthetase forms with 8-azido [alpha-32P]ATP, followed by tryptic digestion and purification by HPLC, afforded one specifically labelled peptide in each case. Identification of the labelled peptide by amino acid analysis and peptide sequencing, and comparison with the enzyme sequence, indicated that the same peptide (267-286) was modified in both enzyme forms. The results are discussed on the basis of the high degree of similarity that this peptide shows in all the known S-adenosylmethionine synthetase sequences.

Nonsteroidal estrogens bearing acyl azide functions: potential electrophilic and photoaffinity labeling agents for the estrogen receptor

In an effort to develop novel affinity labeling agents for the estrogen receptor, we have synthesized two nonsteroidal ligands, a 1-aroyl-2-aryl tetralin system (1) and a 2-aryl-3-aroylbenzo[b]thiophene system (2). These agents, patterned after the Lilly antiestrogens trioxifene and LY 117018, respectively, embody acyl azide functions as part of a benzoyl chromophore. The acyl azide group has weak acylating activity, suitable for electrophilic affinity labeling, but this function is also photoreactive and, in its particular embodiment within these ligands, it could provide an efficient photochemical route to the highly reactive singlet acyl nitrene. The tetralin system (1) was prepared in nine steps from 6-methoxy-1-tetralone, and the benzothiophene system (2) was prepared in four steps from a known substituted benzo[b]thiophene precursor. In competitive binding assays, both compounds show reasonable binding affinity for the rat and lamb uterine estrogen receptor: estradiol = 100%, 1 = 3%, and 2 = 12%. When assayed by indirect receptor consumption assays, both compounds appear to have substantial capacity for irreversible binding (electrophilic reaction) with the receptor. This reactivity, which suggests that acylation of the receptor has occurred, is photoreversible. The nature of this ligand-receptor interaction is being investigated further.

Synthesis and evaluation for uterotrophic and antiimplantation activities of 2-substituted estradiol derivatives

Two novel series of 2-substituted estradiol derivatives have been synthesized and evaluated for uterotrophic and antiimplantation activities. Among the compounds tested in the rat, 2-acetylestradiol 17 beta-acetate (1), 2-(3'-dimethylamino-1'-propionyl)estradiol 3,17 beta-diacetate (7), 2-(3'-diethylamino-1'-propionyl)estradiol 3,17 beta-diacetate (8), 2-(3'-piperidino-1'-propionyl)estradiol 3,17 beta-diacetate (9), 1'-(2-estradiol 3,17 beta-diacetate-3'-diethylaminopropionyl thiosemicarbazone (12), and 1'-(2-estradiol 3,17 beta-diacetate)-3'-morpholinopropionyl thiosemicarbazone (14) displayed estrogenic activity. At dosages of 4 microliters/rat/day, none of the tested compounds elicited antiimplantation activity. All compounds shared a similar characteristic: nuclear substitution at the C-2 position of the steroid nucleus, a property previously thought to be markedly inhibitory for estrogenic activity.

Synthesis, receptor binding and target-tissue uptake of carbon-11-labeled carbamate derivatives of estradiol and hexestrol

Carbon-11-labeled estradiol and hexestrol derivatives were prepared via the reaction of [11C]ethylchloroformate with the 2- and 4-amino derivatives of estradiol, the 3'-amino derivatives of hexestrol, and the 1-aminophenoxy derivatives of hexestrol and 1-norhexestrol. The corresponding nonradioactive carbamates were prepared for chemical characterization and in vitro receptor binding assays. The positions of the substituents on the parent molecules were selected with a view to minimize interference with the receptor binding process. In spite of this, affinity for the estrogen receptor was strongly impaired for all carbamate derivatives. Likewise, in vivo, the [11C]carbamate analogs failed to localize in receptor rich tissue via an estrogen receptor mediated process.

Efficient and selective photoaffinity labeling of the estrogen receptor using two nonsteroidal ligands that embody aryl azide or tetrafluoroaryl azide photoreactive functions

3-(4-Azido-2,3,5,6-tetrafluorobenzoyl)-6-hydroxy-2-(4- hydroxyphenyl)benzo[b]thiophene 1 (tetrafluoroaryl azide, TFAA) and its protio analogue 3-(4-azidobenzoyl)-6- hydroxy-2-(4-hydroxyphenyl)benzo[b]thiophene 2 (protioaryl azide, PAA), photoaffinity labeling (PAL) reagents for the estrogen receptor (ER), have been prepared in high specific activity tritium-labeled form (19 Ci/mmol) and shown to undergo selective and efficient photocovalent attachment to ER from rat uterus. Both azides 1 and 2 demonstrate high binding affinity for ER as determined by both a competitive binding assay (relative binding affinities: estradiol = 100; TFAA = 9.3; PAA = 66) and a direct binding assay (Kd: estradiol = 0.24 nM; TFAA = 2.64 nM; PAA = 0.37 nM). When unlabeled TFAA and PAA are irradiated at greater than 315 nm, they demonstrate site-specific photoinactivation of ER that reaches 43% and 55%, respectively, by 30 min. Specific photocovalent attachment to ER can be effected by irradiation of the tritium-labeled azides; the covalent attachment efficiency is good (1 = 20-30%, 2 = ca. 25%) and the selectivity of ER labeling is high. Characterization of the photolabeled proteins by SDS-polyacrylamide gel electrophoresis shows specific labeling of a major component at Mr 60,000 and a minor species at Mr 46,000, the same two species that are labeled by [3H]tamoxifen aziridine, a well-characterized affinity label for ER. The ER-specific antibodies H222Sp gamma and D547Sp gamma show a clean precipitation of only these two species. In the MCF-7 human breast cancer cell line, PAA is a full estrogen agonist in terms of stimulation of cell proliferation and induction of progesterone receptor. These two azides provide the first system in which the photocovalent attachment efficiency of an aryl azide can be compared to its tetrafluorosubstituted aryl azide analogue in a complex biological receptor system. Azides 1 and 2 are the most efficient and selective PAL reagents prepared to date for ER, and they should be useful in further studies of the hormone-binding domain of this protein.

Desmethylnafoxidine aziridine: an electrophilic affinity label for the estrogen receptor with high efficiency and selectivity

Desmethylnafoxidine aziridine (Naf-Az), an affinity label for the estrogen receptor based structurally on the antiestrogen nafoxidine, has been prepared in unlabeled and in high specific activity, tritium-labeled form and has been evaluated for its apparent competitive binding, and time-dependent irreversible, covalent attachment to the estrogen receptor. Naf-Az was synthesized through a key 1,2-diaryl-3,4-dihydronaphthalene intermediate that was prepared from 6-methoxy-1-tetralone by two routes involving alternate strategies for arylation. Conversion of the diaryldihydronaphthalene to Naf-Az through a series of deprotection-activation reactions culminated in ethyleneimine displacement of a methanesulfonate. The tritium-labeled material was prepared by tritium-iodine exchange on an iodinated methanesulfonate precursor, followed by ethyleneimine displacement. Compared to our previously-prepared reagent tamoxifen aziridine (Tam-Az), Naf-Az has a higher apparent competitive binding affinity, and it reacts with the estrogen receptor in cytosol preparations and in intact MCF-7 breast cancer cells rapidly and with at least comparable efficiency and selectivity. SDS-polyacrylamide gel electrophoretic analysis confirms its selective labeling of the Mr 66,000 estrogen receptor. Naf-Az should prove to be useful in studies aimed at characterizing the properties and structure of estrogen receptors.

Synthesis of photoaffinity analogs of progesterone

A photoaffinity analog of progesterone, 11 alpha-diazoacetate progesterone, has been synthesized by a two step procedure. This has been made possible by a single reaction combining both esterification and diazotization. Numerous diazoacetate analogs of progesterone can be synthesized using these simple reaction conditions. Radioactive analogs can be produced that transfer the isotope covalently to the site of protein modification upon photolysis.

A photoaffinity inhibitor of aromatase

Several 7 alpha-substituted 4-androstene-3,17-diones are potent inhibitors of the biosynthesis of estrogens, with the most effective being 7 alpha-(4'-amino)phenylthio-4-androstene-3,17-dione. An azide derivative of this 7 alpha-thioether compound has been prepared as a potential photoaffinity inhibitor. The enzyme kinetics of the azide analog were examined under both dark conditions and UV irradiation. In the dark, the azide was a very potent competitive inhibitor, with an apparent Ki of 1.3 nM. Under UV-irradiation, a time-dependent loss of aromatase activity was also observed. These studies indicate that the 7 alpha-substituent enhances the affinity of the steroidal analogs for the enzyme site.

The synthesis and study of some potential affinity labeling reagents for estrogen receptors

The influence of the following affinity labeling reagents on the binding of tritiated estradiol-17 beta (E) by human and calf uterine cytosols was studied: 11 beta-chloromethylestradiol (ORG4333), 2-azidoestradiol (2A-E), 4-azidoestradiol (4A-E), 3-azidohexestrol (3A-H), estradiol-17 beta 17-bromoacetate (E-17BrAc), 6-[O-carbo-(2'-chloroethoxy)methyl] oximinoestradiol (6-CMOEtC1), 17-[O-carbo-(2'-chloroethoxy) methyl] oximinoestrone (17-CMOEtCl), 2-di (2'-hydroxy-3'-chloropropyl)aminoestradiol (E-Mustard). For the human uterine estrogen receptor the relative binding affinity decreased in the order E greater than ORG 4333 greater than E-17BrAc greater than 3A-H greater than 2A-E greater than 4A-E greater than 6-CMOEtCl greater than E-Mustard greater than 17-CMOEtCl. The binding characteristics of the calf uterine estrogen receptor were qualitatively similar, but quantitatively different. ORG 4333 appeared to form a highly stable association with the receptors, but alkylation of the protein could not be conclusively demonstrated.

Structural requirements for maximal inhibitory allosteric effect of estrogens and estrogen analogues on glutamate dehydrogenase

The inhibition of glutamate dehydrogenase by estrogens, estrogen analogues or polyphenylethylene derivatives (about one hundred molecules, most of them having estrogenic or antiestrogenic activities) was measured. The efficiency of these compounds in inducing allosteric inhibition of the enzyme was compared and correlated to their chemical structure: an aromatic ring A, a free phenolic group in the region of carbon 3 of the steroid nucleus and a lipophilic substitution in the region of C-12, C-13 or C-17 were found to be the main structural features required for maximal efficiency on glutamate dehydrogenase. A tentative model for the relative orientation of the main inhibitor families is proposed. It accounts for most of the kinetic results and can be used as a tool for the selection of affinity labels directed towards the estrogen binding site of glutamate dehydrogenase.

Ultraviolet photosensitivity of the estrogen binding protein from rat uterus. Wavelength and ligand dependence. Photocovalent attachment of estrogens to proteins

Ultraviolet irradiation of the estrogen binding protein in rat uterine cytosol results in a progressive photoinactivation which is rapid at 254 nm and slower at greater than 315 nm. Both unfilled and estradiol-filled sites are inactivated at approimately the same rates at 254 nm (t 1/2 equals 8 min and 11 min, respectively), but at 315 nm, empty sites are consumed much more rapidly (t 1/2 equals 3.4 hr) than filled ones (t 1/2 equals 24 hr). The protective effect of the estrogen ligand at this wavelength appears to depend on its binding to the estrogen-specific binding site, as inactivation rate studies at different concentrations of estrone, estradiol, and estriol show a good correlation between the extent of protection and the fractional saturation of the high affinity estrogen binding sites. Scatchard analysis indicates that inactivation is the result of a loss of binding sites and not a decrease in their affinity, and sedimentation analysis shows that increased heterogeneity and aggregation of the estrogen binding species accompanies the photoinactivation process. Photoinactivation appears to be the result of direct irradiative damage of the animo acid residues, as the inactivation rate is the same under air and nitrogen atmospheres, and is unaffected by nucleophiles, reductants, and radical scavengers. When photoinactivation is measureed by irradiation of cytosol containing [3-H]estradiol, a concurrent photocovalent attachment process is noted; the steroid becomes linked to protein in a solvent-extractable manner (boiling ethanol inextractable). This attachment, however, does not appear to be related to the steroid binding at the estrogen binding site. Its rate is affected by reductants and scavengers. A similar photocovalent attachment reaction occurs when bovine serum albumin or ovalbumin is irradiated in the presence of [3-H]estradiol or [3-H]diethylstilbestrol. The detailed reactions involved in this photocovalent attachment process have not been defined at present.

Iodohexestrols. I. Synthesis and photoreactivity of iodinated hexestrol derivatives

The five possible ortho-iodinated hexestrols, containing from 1-4 iodines per molecule, have been synthesized as potential iodine-containing estrogenic ligands. After chromatographic separation and purification, each derivative has been fully characterized by spectroscopic methods. [3-H]-3-Iodohexestrol, [131-I]- and [125-I]-3-iodohexestrol, and [125-IA1-3,5-diiodohexestrol have also been prepared. Photolysis of 3,5-diiodohexestrol in methanol results in rapid deiodination to 3-iodohexestrol; further reduction to hexestrol is slower. Photolysis of 3-iodohexestrol in benzene gives 3-phenylhexestrol.