Therapy of estrogen receptor-positive micrometastases in the peritoneal cavity with Auger electron-emitting estrogens--theoretical and practical considerations

Previous studies have demonstrated that Auger electron-emitting estrogens, when associated with the estrogen receptor (ER), can effect breaks in DNA and ER-dependent radiotoxicity. To evaluate the potential of [123I]-iodoestrogens, ([123I]-IE) to treat ER-positive human cancer cells, we have studied the effect of incubation of [123I]-IE with ER-positive MCF-7 breast cancer cells on cell survival in vitro and found that subnanomolar concentrations of [123I]-IE effectively reduce survival, with a mean lethal dose of about 800 decays per cell. MCF-7 cells incubated 30 min with 2 nM [123I]-IE (13 MBq/ml) showed a 2 log reduction in the ability to form tumors in immunodeficient mice. Evaluation of a mathematical model for [123I]-IE therapy for intraperitoneal micrometases in vivo in the mouse, based on variables related to the (a) specific activity of [123I]-IE; (b) its affinity for ER; (c) the characteristics of the uptake and retention of [123I]-IE by the target cells; (d) the concentration of ER in the tumor cells and (e) the tumor weight suggest that such therapy may be feasible.

Radiotoxicity of Auger electron-emitting estrogens in MCF-7 spheroids: a potential treatment for estrogen receptor-positive tumors

To approach treatment of micrometastases of steroid receptor-rich cancers using estrogen receptor-directed therapy with Auger electrons, multicellular spheroids of the estrogen receptor-rich human breast cancer cell line, MCF-7, were prepared and exposed to a range of concentrations of an Auger electron-emitting estrogen, E-17alpha-[123I]-iodovinyl-11beta-methoxyestradiol, [123I]IVME2, in vitro. After washing, the treated spheroids were dissociated to single cells and plated for assay of colony survival, whereby we observed a dose-dependent reduction in survival that was inhibited by inclusion of an excess of unlabeled estradiol in the initial incubation with [123I]IVME2. Spheroids of a range of sizes from 40 to 280 microm showed similar sensitivity to the Auger electron-emitting estrogen. The mean lethal dose was approximately 700 decays per cell and corresponded to an initial [123I]IVME2 concentration of less than 0.5 nM. If the control and treated spheroids were not trypsinized but rather were allowed to grow intact, there was not only a significant reduction in the growth of the treated spheroids, but in 18 days nearly half became necrotic, while few control spheroids were necrotic. Considering the low concentrations of Auger electron-emitting estrogen required for a significant reduction in survival, we believe this approach has merit to pursue in vivo, especially in cases where it may be possible to target the steroid receptor-rich micrometastases directly, such as ovarian cancer.

Uptake and interconversion of the Z and E isomers of 17 alpha-iodovinyl-11 beta-methoxyestradiol in the immature female rat

This study compares the specific uptake and retention of the Z and E isomers of 17 alpha-iodovinyl-11 beta-methoxyestradiol (IVME2) in estrogen target tissues in immature female rats following intraperitoneal injection. Estrogen receptor binding studies in vitro showed that the Z-IVME2 had greater affinity than the E-IVME2, but our initial in vivo data, comparing 125I-labeled E- or Z-IVME2 in separate studies showed no difference between the two isomers in either uptake or retention. These results were confirmed when the two isomers, labeled either with 123I or 125I, were injected simultaneously, allowing direct comparison of uptake and retention patterns in the same animal. Analysis of the nature of the radioiodinated estrogens in estrogen target tissues showed that at all time points, the estrogen target tissues contained mainly the E isomer, even at short times after injection of Z isomer. Although the Z-IVME2 was reasonably stable in the injectant, analysis of a peritoneal lavage soon after intraperitoneal injection of Z-[125I]-IVME2 showed that mainly the E isomer was present, suggesting that the conversion occurred prior to uptake by the tissues. In vitro studies with intraperitoneal fluid and serum showed that denaturing by heating at 65 degrees C substantially reduced their ability to affect the conversion of Z to E isomer, suggesting a possible enzymatic conversion.

DNA and chromosome breaks induced by iodine-123-labeled estrogen in Chinese hamster ovary cells

The effects of the Auger electron-emitting isotope 123I, covalently bound to estrogen, on DNA single- and double-strand breakage and on chromosome breakage was determined in estrogen receptor-positive Chinese hamster ovary (CHO-ER) cells. Exposure to the 123I-labeled estrogen induced both single- and double-strand breaks with a ratio of single- to double-strand breaks of 2.8. The corresponding ratio with 60Co gamma rays was 15.6. The dose response was biphasic, suggesting either that receptor sites are saturated at high doses, or that there is a nonrandom distribution of breaks induced by the 123I-labeled estrogen. The 123I-labeled estrogen treatment induced chromosome aberrations with an efficiency of about 1 aberration for each 1000 disintegrations per cell. This corresponds to the mean lethal dose of 123I-labeled estrogen for these cells, suggesting that the lethal event induced by the Auger electron emitter bound to estrogen is a chromosome aberration. Most of the chromosome-type aberrations were dicentrics and rings, suggesting that 123I-labeled estrogen-induced chromosome breaks are rejoined. The F ratio, the ratio of dicentrics to centric rings, was 5.8 +/- 1.7, which is similar to that seen with high-LET radiations. Our results suggest that 123I bound to estrogen is an efficient clastogenic agent, the cytotoxic damage produced by 123I bound to estrogen is very like damage induced by high-LET radiation, and the 123I in the estrogen receptor-DNA complex is probably in proximity to the sugar-phosphate backbone of the DNA.

DNA damage induction by 125I-estrogen

DNA damage induced by the radioactive decay of 125I-estrogen (125I-VME2) in an estrogen receptor expressing CHO cell line, CHO-ER, was measured. 125I-VME2 targeted 125I atoms proximal to DNA estrogen response elements (EREs). 125I decays were accumulated at -135 degrees C, and thereafter assayed by alkaline and neutral filter elution techniques to measure DNA single strand break (ssb) and double strand break (dsb) induction respectively. Increasing DNA damage (both ssbs and dsbs) was detected after exposure of cells to increasing concentrations of 125I-VME2. DNA ssb and dsb dose-response curves for 125I-VME2 were multiphasic. The rates of DNA damage induction by the decay of 125I-VME2 was determined by comparing slopes of all data or by comparing initial slopes. DNA ssb induction per 125I-VME2 decay was approximately 2 times greater compared with DNA dsb induction. 125I-VME2 decay induced approximately 4-8 times more DNA dsbs than 125IUdR decay.

Cellular and subcellular studies of the radiation effects of Auger electron-emitting estrogens

We studied the effect of 123I-labeled estrogen (123I-E) in estrogen receptor (ER)-rich cells in culture and in cell free model systems in vitro to elucidate the nature of the radiotoxicity for ER + cells of estrogens containing nuclides which emit Auger electrons. In cells the 123I-E caused a dose-dependent, unlabeled estrogen-inhibitable induction of chromosome aberrations. A dose of about 1000 decays per cell, which is approximately the mean lethal dose for these cells, resulted in an average of 1 chromosome break per cell. This supports the hypothesis that the lethal lesion induced by 123I-E is a chromosome break. Incubation of 123I-E/ER complex, but not 123I-E alone, with 27-mer duplex estrogen response element (ERE) DNA produced a dose-dependent cleavage of the ERE. However, we were unable to detect any fragmentation of either the 66 kDa full length ER in cell extracts or a purified 31 kDa hormone binding domain when incubated with excess 123I-E. Thus it appears that 123I-E effects its radiotoxicity by binding to ER, associating with ERE DNA and, by directing high LET radiation to DNA, inducing lethal chromosome breaks.

Immunohistochemical localization of the oestrogen-responsive 110 kDa and 74 kDa polypeptides and complement component C3 in the rat genital tract after oestrogen treatment and during the oestrous cycle

In previous studies we showed that two oestrogen-responsive rat uterine secretory polypeptides of molecular mass 110 and 74 kDa share sequence similarities with the alpha and beta chains of rat complement component C3. Using polyclonal antibodies specific to the 110 kDa polypeptide, the 74 kDa polypeptide and rat serum C3, we studied the localization of these proteins in the rat genital tract using an indirect immunoperoxidase technique. The results showed that in oestradiol-treated rats immunostaining for the three antigens was heterogeneously distributed in the epithelia of the endometrium, cervix and vagina and that the intensity of staining was greater after oestrogen treatment than in controls. In oestradiol-treated immature rats, the immunoreactivity for the 110 kDa and 74 kDa polypeptides was greater in the endometrial and vaginal epithelia than in the cervical epithelium, whereas immunoreactivity for C3 was greatest in the vaginal epithelium. In cyclic rats, staining by all three antibodies was seen only during pro-oestrus and oestrus, during which stages the immunostaining for the 110 kDa and 74 kDa polypeptides was detected only in the endometrial epithelium, whereas immunostaining for C3 was also found in the epithelia of the cervix and vagina. In general, consecutive sections of these tissues revealed a close correlation between the immunostaining for the 110 kDa and 74 kDa polypeptides and C3. However, there were some sections that showed clear differences in staining, suggesting that more than one C3-related protein species was detected in the female rat reproductive tract.

Comparison of the distribution of radioiodinated-E-17 alpha-iodovinyl-11 beta-methoxyestradiol and 2-iodo-1,1-bis(4-hydroxyphenyl)-phenylethylene estrogens in the immature female rat

Current therapies for estrogen receptor-positive (ER+) cancers rely heavily on growth prevention by cytostatic agents rather than destruction of the cancer cells. In these studies, we compared the tissue distribution of two radioiodinated estrogens, one a triphenylethylene estrogen, IBHPE, the other steroidal, IVME2. The radioiodoestrogens were prepared using the halodestannylation reaction from the respective tributyltin precursors. The specificity of binding of these radioiodinated estrogens to the estrogen receptor (ER) was established by sucrose-density gradient analyses and their specific activities by comparison with the ER binding of 3H-estradiol of known specific activity. The time-dependent tissue distribution of the two radioiodoestrogens in immature female rats was studied to compare the relative uptake and specific retention of the two estrogens in ER target organs and assess their possible use for imaging ER positive tissues or for Auger electron-mediated ER-directed therapy. While the uterus showed only slightly poorer retention of the nonsteroidal estrogen (IBHPE) than the steroidal estrogen (IVME2), those target tissues that required blood-supplied ligand (e.g., vagina, pituitary) showed substantially higher uptake of the steroidal estrogen. IBHPE showed significantly higher blood levels at all time points. While the tissue-to-muscle ratios for IBHPE in the uterus and ovary were higher initially, the IVME2 showed higher tissue-to-muscle ratios, suggesting that the steroidal estrogen may be the more promising ligand for imaging purposes. However, IBHPE showed excellent uptake by peritoneal target tissues, with much lower concentrations in more distant target tissues (e.g., pituitary) so it might have distinct potential for therapy of intraperitoneal ER-containing cancers.

Estrogen receptor-directed radiotoxicity with Auger electrons: specificity and mean lethal dose

To assess the feasibility of using estrogen receptor-directed therapy with Auger electron-emitting ligands for therapy of estrogen receptor (ER)-containing cancers, we synthesized and evaluated the radiotoxicity of several 123I-labeled estrogens to specifically kill ER+ cells in culture. Auger electrons have been previously shown to be of short range, generally less than the dimensions of a cell, so that to use them therapeutically a mechanism is needed to deliver the Auger electron-emitting nuclide to the vicinity of the DNA. Since it is now well established that the estrogen receptor, when bound to estrogen, forms a high affinity association with distinct estrogen response elements in the DNA, we wished to test the hypothesis that a short exposure of cells to a 123I-labeled estrogen would be specifically radiotoxic to ER+ cells, and that the decays per cell needed for cell killing would be compatible with reasonable levels of receptor occupancy. Using the halodestannylation reaction with tributyl tin precursors of several estrogens and commercially available iodine-123, we prepared the iodoestrogens, E-17 alpha(-)[123I]-iodo-11 beta-methoxyestradiol and 2(-)[123I]iodo-1,1-bis(4-hydroxyphenyl)--2-phenylethylene, at high specific activities, in several cases at essentially the specific activity of 123I itself, 240,000 Ci/mmol. When various concentrations of either of the 123I-labeled estrogens were incubated for 1 h with a subline of ER+ Chinese hamster ovary cells and the washed cells plated for survival assays, a dose-dependent, unlabeled estradiol-inhibitable reduction in survival was observed. In contrast, Chinese hamster ovary cells not expressing estrogen receptor showed little sensitivity to the radiotoxicity of the 123I-labeled estrogens. Calculations based on the assayed residence time of the iodoestrogens in the cells indicate that several hundred decays per cell are sufficient to kill cells.

Comparison of the distribution of bromine-77-bromovinyl steroidal and triphenylethylene estrogens in the immature rat

The specific uptake and distribution of steroidal and non-steroidal [77Br]bromovinylestrogens were studied in immature female rats to assess the potential of these radioligands for imaging or therapy of estrogen receptor (ER) positive cancers. E-17 alpha [77Br]bromovinylestradiol, its 3 methyl ether and 11 beta-methoxy derivative, as well as the triphenylethylene estrogen, 1,1-bis[4-hydroxy-phenyl]-2-[77Br]bromo-2- phenylethylene all showed diethylstilbestrol inhibitable, specific uptake of radiobromine between 2 and 16 hr after i.p. administration. The highest concentrations in the estrogen target tissues and the highest target tissue-to-blood ratios were found with E-17 alpha-[Br]bromovinyl-11 beta-methoxyestradiol, but it also had rather high nonspecific uptake in all tissues. The triphenylethylene estrogen showed comparable specific uptake in estrogen target tissues to 17 alpha [77Br]bromovinylestradiol at 2 hr but better apparent retention, indicated by higher specific target tissue levels at the later time points. Thus, [77Br]bromovinyl-11 beta- methoxyestradiol and 1,1-bis[4-hydroxyphenyl]-2-[77Br]bromo-2-phenylethylene appear most favorable for these applications.

Comparison of the quantity of estrogen receptors in human endometrium and myometrium by steroid-binding assay and enzyme immunoassay based on monoclonal antibodies to human estrophilin

The recently developed enzyme immunoassay for estrogen receptors is more simple to perform with quality assurance than conventional steroid-binding assays with radioactive labeled estrogen. However, it is not known how well the results of the two assays agree for normal human uterine samples. We compared enzyme immunoassay (Abbott estrogen receptor enzyme immunoassay) and steroid-binding assay of normal human endometrium and myometrium. Low-salt, "cytosol" estrogen receptor determinations were performed by dextran-coated charcoal assay, and high-salt, "nuclear" estrogen receptors were measured by controlled pore glass bead assay. Results showed excellent correlation (p less than 0.0001) for cytosol estrogen receptor of endometrium (r = 0.95) and myometrium (r = 0.79) and also for a smaller number of nuclear estrogen receptors of myometrium (p less than 0.01, r = 0.69). Good agreement between steroid-binding assay and enzyme immunoassay was seen for estrogen receptors of both proliferative and secretory phase samples. Thus the data indicate that the simpler estrogen receptor enzyme immunoassay is useful to measure estrogen receptor in the normal uterus. Furthermore, with this sandwich assay, there is no evidence for the existence of significant quantities of receptor fragments that do not bind estrogen.

The estrogen-responsive 110K and 74K rat uterine secretory proteins are structurally related to complement component C3

Estrogens stimulate the synthesis of specific secretory proteins in the rat uterus. Here we show that two of these, polypeptides of relative molecular weight 110,000 (110K) and 74,000 (74K), are structurally related to C3, the third component of complement, a glycoprotein that plays a central role in regulating complement-mediated inflammatory and immune responses. The similarities were based on the observations that (1) NH2-terminal amino acid sequence of the 74K polypeptide showed sequence homology with the beta chain of mouse C3, (2) comparison of the electrophoretic mobilities of the 110K and 74K polypeptides in the presence and absence of reducing agents revealed that they were disulfide-linked subunits of a protein of Mr approximately 180,000, (3) the native protein was immunoreactive with antibodies specific for rat C3, and (4) both polypeptides were immunoprecipitated with antibodies to rat C3.

Bromine-80m radiotoxicity and the potential for estrogen receptor-directed therapy with auger electrons

While theoretically feasible, estrogen receptor (ER)-directed radiotherapy of hormone-dependent cancers has not been realized because no ER-seeking ligand with an appropriate radiotoxic potential has been identified. Since an appropriate nuclide is a key component we studied the 4.4-h half-life, Auger electron-emitting nuclide bromine-80m. When incorporated into DNA this nuclide was radiotoxic to cells in culture and caused substantial chromosomal damage, while similar concentrations of bromine-80m as bromide or bromoantipyrine were without effect. The mean lethal dose for bromine-80m was 45 atoms per nucleus which is consistent with use in receptor-positive cancers with limited numbers of ER.

Estrogen receptor binding affinity and uterotrophic activity of triphenylhaloethylenes

Radiohalogenated estrogens have considerable potential for estrogen receptor-directed imaging and therapy for cancers which contain such receptors. In an effort to evaluate the potential of the triphenyl ethylene structure for such purposes we have synthesized 3 series of 2-halosubstituted triphenylethylenes containing oxygen functions in the 4 position of both aromatic rings attached to carbon 1 of the ethylene and tested their uterotrophic activity and competition for rat uterine low salt extractable, "cytosol" estrogen receptor. Most active, both as competitors for estradiol binding to estrogen receptors and by their ability to stimulate uterine growth are the 1,1-bis-4-hydroxyphenyl derivatives although the 1,1-bis-4-acetoxyphenyl derivatives also show good receptor affinity and demonstrate uterotrophic activities. However, since uterine cytosol contains enzymes which hydrolyze the acetates to the free phenols even during the incubation in the cold used for the competitive binding studies, a significant portion of the competition shown by the diacetates is probably due to their hydrolysis products, the free phenols. The 1,1-bis-4-methoxyphenyl derivatives are weak competitive binders and demonstrate uterotrophic activity only when administered at the higher, 20 micrograms, doses. Comparing the relative activities of various halogens at the 2 position, in each series the bromo and chloro derivatives generally were of similar activity and significantly more active than the corresponding iodo derivative. The non-halogen substituted derivatives were very good competitors for estrogen receptor binding but less active with regard to uterine growth stimulation, providing evidence that in vivo the vinyl halides would appear to be relatively stable to simple dehalogenation. Since they show reasonably good apparent affinities for the estrogen receptor and apparent in vivo stability, reflected by estrogenic activity, these halogen substituted triphenylethylene derivatives appear to be promising substrates for investigations of estrogen receptor directed imaging and therapy.

Bromine-80m-labeled estrogens: Auger electron-emitting, estrogen receptor-directed ligands with potential for therapy of estrogen receptor-positive cancers

To assess their possible use for estrogen receptor (ER)-directed radiotherapy of estrogen receptor-containing cancers, two estrogens were synthesized with the Auger electron-emitting nuclide bromine-80m and administered to immature female rats. Both the triphenylethylene-based estrogen, [80mBr]-2-bromo-1,1-bis(4-hydroxyphenyl)phenylethylene (Br-BHPE) and the steroidal estrogen [80mBr]17 alpha-bromovinylestradiol, showed substantial diethylstilbestrol-inhibitable localization only in the estrogen target tissues, the uterus, pituitary, ovaries, and vagina and, except for the liver and intestines, generally lower concentrations in all other tissues at both 0.5 and 2 h. The [80mBr]Br-BHPE (specific activity, 8700 Ci/mmol), was shown to bind specifically to the low salt extractable ER of the rat uterus. Comparing i.p., i.v., and s.c. administration of [80mBr]BHPE the i.p. route was found to be particularly advantageous to effect maximum, DES-inhibitable concentrations of radiobromine in the ER-rich target organs in the peritoneal cavity. When the tissue distribution of the [80mBr]Br-BHPE was compared with that of sodium bromide-80m, it was apparent that no substantial amounts of radiobromine were released from the bromoestrogen prior to its target tissue localization. The substantial concentration of these bromine-80m-labeled estrogens in ER-rich tissues, combined with previously reported evidence for the effective radiotoxicity of Auger electron-emitting nuclides within cell nuclei suggest a good potential for such ligands for therapy of ER positive cancers.

Regulation of estrogen and progestin receptor concentrations in an experimental rat prostatic carcinoma by estrogen, antiestrogen, and progesterone

In order to assess prostatic tissue as a target for receptor-mediated estrogen action, we have examined the regulation of estrogen (ER) and progestin receptors (PgR) by estrogen, antiestrogen, and progesterone in cytosolic and nuclear fractions of the R3327H (Dunning) prostatic adenocarcinoma of the rat. Twenty micrograms diethylstilbestrol (DES) with or without 800 micrograms tamoxifen (Tam) were injected s.c. in oil 5 times weekly for 2 weeks. Controls were given oil only. Estrogen receptor assays were carried out using [3H]estradiol and a hydroxylapatite exchange method. Progestin receptors were assayed using [3H]R5020 and dextran-coated charcoal to separate free and bound steroid. All binding data were evaluated by using Scatchard analysis. Treatment with DES depleted cytosolic ER, promoted association of ER with the nuclear fraction, and concomitantly increased PgR concentrations in amounts proportional to nuclear ER. Treatment with Tam alone resulted in higher nuclear ER concentrations than treatment with DES, but induced only one-fifth the amount of PgR. Treatment with DES plus Tam resulted in similar nuclear ER concentrations as with Tam alone, but PgR concentrations were intermediate between those observed with DES alone and Tam alone. Thus Tam exhibited both estrogenic and antiestrogenic properties. In this experiment, the same cytosolic and nuclear extracts were also assayed for ER by using monoclonal antibodies to the receptor in an enzyme immunoassay. No significant differences were observed between the results obtained by the radioligand and enzyme immunoassay methods in the cytosol and nuclear fractions from the control and DES-treated tumors. However in both Tam-treated groups, the ER values obtained by the enzyme immunoassay method were significantly higher than those obtained by the radioligand method in both cytosolic and nuclear fractions. This confirms the observations made by others in female target organs, that monoclonal antibody to ER reacts differently with the Tam-bound ER complex than with the estradiol-bound ER complex. In a separate experiment, administration of progesterone with DES decreased the concentration of nuclear ER to less than one-half that observed after administration of DES alone, with proportional decreases in both cytosolic and nuclear PgR. All these observations indicate that the control of ER and PgR concentrations in this prostatic tumor is identical to that observed in female rat target organs. Use of an immunohistochemical method for the detection of ER in frozen sections indicated that the receptor was localized in the glandular epithelium in both control and DES-treated tumors.

Prognostic usefulness of estrogen receptor immunocytochemical assays for human breast cancer

Breast cancers of postmenopausal patients at high risk for recurrence participating in an adjuvant therapy protocol were independently assayed for estrogen receptor by conventional dextran-coated charcoal steroid binding assays and by immunocytochemistry (ER-ICA) to compare the two assays and to assess the prognostic usefulness of ER-ICA. The ER-ICA was based on a monoclonal antibody to the estrogen receptor and was applied to lightly fixed, frozen sections of the cancers. Excellent agreement was found between the two estrogen receptor methods. It was found that a combination of the distribution of ER-ICA stained cells and the overall staining intensity gave a statistically significant correlation with the quantitative estrogen receptor dextran-coated charcoal steroid binding assay value. In addition, the overall appraisal of the lesion as ER-ICA positive or negative as well as the ER-ICA staining intensity and proportion of ER-ICA stained cancer cells related to patient disease-free interval and survival, independent of patient lymph node involvement. This relationship of ER-ICA status to prognosis appeared not to relate only to responses to adjuvant tamoxifen treatment since it also was observed with patients who did not receive the antiestrogen.

The effects of sequential administration of 17 beta-estradiol on the synthesis and secretion of specific proteins in the immature rat uterus

We report here results of a study of the effect of sequential administration of 1 microgram 17 beta-estradiol in vivo on the incorporation of L-[35S]methionine into specific proteins in vitro in the immature rat uterus. One-dimensional SDS-PAGE analysis of labeled secreted uterine proteins and cellular proteins extracted from the luminal epithelial and from the stroma plus myometrial uterine fractions revealed that estradiol preferentially stimulated the synthesis of 110 K, 74 K and 66 K secreted proteins, 180 K and 110 K epithelial proteins and a 175 K stroma-myometrial protein among others, while it decreased the relative rate of synthesis of a 32.5 K secreted protein and a 70 K stroma-myometrial protein. The 110 K protein, a secreted luminal epithelial protein whose labeling in vitro dramatically increased greater than 60-fold per mg endometrial DNA after in vivo estrogen stimulation, may be a useful marker for studying estrogen action in the luminal epithelium of the immature rat uterus. Comparison of the secreted proteins labeled at 28 h (4 h after a second injection) and at 54 h (6 h after a third injection) revealed that estradiol effected a sequential change in the pattern of synthesis of secreted uterine proteins in vitro. Comparison of the number and magnitude of changes in the synthesis of specific proteins in the luminal epithelium and the stroma plus myometrium revealed that protein synthesis in the luminal epithelium is clearly more responsive to estradiol and readily distinguishable from the responsiveness of the stroma plus myometrium.

Progestin modulation of estrogen-dependent marker protein synthesis in the endometrium

While it is well known that progestins have significant effects on estrogen-dependent processes in the uterus, very little is known about the molecular details of these effects. To understand these processes we have developed an immunocytochemical staining technique to help clarify the progestin regulation of estrogen receptor (ER), and we have also studied the effects of progestins on estrogen-dependent specific protein synthesis and secretion in the immature rat uterus. The immunocytochemical method for identifying estrogen receptor in tissue sections uses biotinylated monoclonal antibody to the estrogen receptor protein and shows a largely nuclear localization of the receptor protein in the rat uterine endometrium and myometrium. This method can be used to explore changes in the intercellular and intracellular localization of the uterine ER during progestin action. In an effort to correlate these changes with specific biological responses in the uterus we have been studying the effects of the administration of estrogens and progestins in vivo on the synthesis of specific proteins in uterine target cells in vitro. We previously reported that one-dimensional SDS-PAGE analysis of labeled secreted uterine proteins and cellular proteins extracted from the luminal epithelium and from the stroma plus myometrial fractions of the uterus revealed that estradiol-17 beta preferentially stimulated the synthesis of 110,000, 74,000, and 66,000 dalton secreted proteins, and 180,000 and 110,000 dalton epithelial proteins. We found that while progestins administered alone in vivo did not have any stimulatory effect on the synthesis of these secreted or cellular uterine proteins, concomitant administration of either progesterone or megestrol acetate and estradiol in vivo substantially reduced the estrogen-stimulated increase in labeling of the 110,000, 74,000, and 66,000 dalton secreted uterine proteins in vitro. In animals first primed with the progestin prior to combined estrogen/progestin treatment, the progestins were even more effective antagonists of estrogen. In addition, progestins alone given 24 hours after estradiol substantially inhibited the estrogen-stimulated synthesis of these proteins. These results suggest that progestins can both modulate the initial level of estrogen stimulation of synthesis of specific proteins and selectively terminate their synthesis, by affecting the continued transcription of their estrogen-regulated genes, altering the processing, half-life, or translation of their mRNAs, or by modulating the translation or the posttranslational processing of the nascent peptide chains.

Comparison of immunocytochemical and steroid-binding assays for estrogen receptor in human breast tumors

An estrogen receptor immunocytochemical assay which uses monoclonal antibodies to the estrogen receptor protein [Nature (Lond.), 307: 745-747, 1984] was applied to several human tissues, including human breast tumors, and the results were compared to those of steroid-binding assays performed on cytosol extracts of the same tissues. Specific immunoperoxidase staining in fixed, frozen sections was confined to the nucleus of selected cell populations within each tissue examined. In 117 human breast cancers, the presence or absence of nuclear staining was significantly associated with the concentration of cytosolic estrogen receptor. Thirty-eight estrogen receptor immunocytochemical assay-positive tumors were further assessed for several quantifiable features of the staining, including intensity, cellularity, and the proportion of tumor cells stained. Of these, epithelial cellularity showed the highest degree of correlation with the results of steroid-binding assays.

Differences between estrogen- and antiestrogen-estrogen receptor complexes from human breast tumors identified with an antibody raised against the estrogen receptor

Radiolabeled estrogens 17 beta-[3H]estradiol and diethylstilbestrol ( [3H]DES) and the antiestrogen [3H]monohydroxytamoxifen ( [3H]MHT) all bind with high affinity to the extranuclear estrogen receptor (ER) from the MCF-7 human breast tumor cell line (Kd = 3 X 10(-10), 2 X 10(-10), and 0.63 X 10(-10) M, respectively). A polyclonal antibody raised in a goat to the calf nuclear ER selectively decreased the binding affinity and number of binding sites for 17 beta-[3H]estradiol, but did not appear to affect these binding parameters for [3H]MHT. In the presence of goat antibody, the binding of the nonsteroidal estrogen DES was so perturbed that it was not possible to quantitate the decreased number of binding sites or affinity of this compound as assessed by Scatchard saturation analysis. These results were confirmed in human breast tumor cytosols by sucrose density gradient analysis. The binding of 17 beta-[3H]-estradiol and [3H]DES to the ER was significantly reduced by preincubation with the polyclonal antibody, whereas the binding of [3H]MHT was reduced only when the tumor cytosol was preincubated with a very high concentration of antibody. At these concentrations of antibody, the binding of 17 beta-[3H]estradiol and [3H]DES to the receptor was prevented completely. In contrast, when the antibody was added to the tumor cytosol after the 3H-ligand had bound to the receptor, the binding properties of all 3H-ligands were unaffected. The [3H]MHT-ER antibody complex consistently sedimented as a higher-molecular-weight complex on sucrose density gradients than did the corresponding estrogenic complexes. The decrease in the affinity of estrogenic ligands can be explained in part by an increase in the dissociation rate at 4 degrees of these compounds from the ER. The dissociation rate of MHT was unaffected by the goat antibody. These results imply that there are important differences in the binding of antiestrogen and estrogens to the tumor cytosol ER. A ligand-binding model is proposed that may aid in the understanding of antiestrogen action.

Interaction of [3H] estradiol - and [3H] monohydroxytamoxifen-estrogen receptor complexes with a monoclonal antibody

The aim of this study was to compare and contrast the interaction of estrogen [( 3H]17 beta-estradiol)- or antiestrogen [( 3H]monohydroxytamoxifen)-receptor complexes from human breast tumor cytosols with monoclonal antibodies raised to the human breast tumor estrogen receptor. Breast tumor cytosols containing estrogen receptor which sedimented as radiolabeled peaks in either the 8S, 8S and 4S, or 4S regions of sucrose density gradients, interacted with the monoclonal antibody D547 to produce a broad 9-10S peak, a broad 8S-10S peak, or a more discrete 8S peak, respectively. On high salt (0.4M KC1) sucrose density gradients the 4S ligand-receptor complex plus antibody produced a binding peak at approximately the 8S region of the gradient. These sedimentation studies with the monoclonal antibody D547, and similar studies with the monoclonal antibody D58, could detect no differences in the cytosolic estrogen receptor whether complexed with [3H]estradiol or with [3H]monohydroxytamoxifen. These observations were confirmed by Scatchard equilibrium saturation analysis and sucrose density gradient analysis of cytosols from the MCF-7 human breast cancer cell line. The antibody D547 interacted with 8S ER from these cytosols to produce a broad 8S-10S peak, but the antibody produced no change in the affinity or number of binding sites present in these cytosols. It seems, therefore, that the antigenic determinants recognized by these particular antibodies on the breast tumor cytosolic receptor are not significantly altered by the binding of either an estrogen or an antiestrogen to the receptor.

Epithelial peroxidase and endometrial granulocytes in the normal cyclic human endometrium

Studies in animal models have clearly shown a relationship between the administration of estrogens and the appearance of peroxidase activity in growth-responsive estrogen target tissues (endometrium, cervix, vagina, breast, and DMBA rat mammary tumor). We have studied the ultrastructural localization of endogenous peroxidase activity in the normal cyclic human endometrium. Endogenous peroxidase activity was not identified in proliferative phase endometria, with the exception of one very late proliferative phase endometrium. Most secretory phase endometria showed at least some ultrastructurally identified peroxidase activity in glandular epithelial cells. The number of epithelial cells showing peroxidase activity varied from less than 10% to 85%. The peroxidase activity was present throughout the endoplasmic reticulum of these epithelial cells, extending from the perinuclear cistern to the most peripheral portions of the endoplasmic reticulum adjacent to the apical lumen. Biochemical assays of peroxidase activity in these endometria were compared with the ultrastructurally identified epithelial peroxidase and the endometrial granulocyte count. Uterine granulocyte peroxidase appeared to make a substantial contribution to the total peroxidase activity assayed by biochemical methods. Standard biochemical techniques alone, therefore were not considered to be adequate to evaluate epithelial peroxidase activity.

Calculating specific binding for prolactin receptor assays

Specific binding of [125I]iodo-prolactin and receptor is usually calculated by subtracting the amount of bound radioactivity of assays containing excess unlabeled hormone (competed) from that of noncompeted assays. A proportional method to calculate specific binding of prolactin-receptor or other hormone-receptor interactions is introduced as a replacement for the currently used subtraction method. The proportional method calculates specific binding by multiplying the ratio of free radioactivities of noncompeted and competed assays by the radioactivity retained in the competed assay and subtracting this value from the radioactivity retained by the noncompeted assay. In prolactin-receptor assays greater specific binding is seen when data is calculated by this proportional method rather than the subtraction method. The amount of this increase relates directly to the levels of specific and nonspecific binding. Additionally, the binding characteristics of prolactin and receptor in both equilibrium and kinetic studies are significantly different when specific binding is calculated by the proportional method rather than the subtraction method.

Characterization of [125I]-iodo-ovine prolactin and evaluation of prolactin receptor assay methods

In an attempt to establish more rigorous conditions for assay of prolactin receptor, a study of the preparation, recovery and specific binding of iodoprolactin was conducted. Averaging the results of 20 preparations starting with 5 micrograms prolactin preparation and iodinated by a lactoperoxidase method, an average of 0.62 +/- 0.12 micrograms of the iodinated prolactin was recovered in a form capable of binding to excess rat liver membrane preparations, corresponding to between 24 and 51% of the total recovered iodinated prolactin. Based on preliminary amino acid analysis and N-terminus determination, 53% of a weighed amount of ovine prolactin was determined to be protein with the N-terminal amino acid being consistent with homogeneity. The percent specific binding assay (single point assay) and Scatchard analysis were tested for their ability to give assay results in a direct relationship to sample receptor. Scatchard analyses were determined to be a superior method to the percent specific binding assay. Using commonly employed conditions for the percent specific binding assay, the relative amounts of receptor found in increasing amounts of sample were significantly less than that found by Scatchard analysis in all likelihood due to the use of subsaturating concentrations of iodohormone. As more hormone was added per assay tube, the relationship of sample receptor to the results of the single point assay improved, but the results never equaled those of Scatchard analyses. Thus, many workers who have used the percent specific binding assay under nonsaturating conditions have underestimated the relative receptor contents of samples.

Estrophilin assays in breast cancer: quantitative features and application to the mastectomy specimen

Knowledge of the tumor content of estrogen receptor, called estrophilin, has proved to be of significant clinical value in human breast cancer. Although most breast cancer tissues contain cytosol estrophilin, essentially only patients whose cancers have moderate to high levels of estrophilin, designated estrophilin-rich, are found to respond to endocrine therapy. About two-thirds of patients with estrophilin-rich cancers obtain objective benefit from endocrine therapy. Present results indicate that predictions of response to endocrine therapy at time of recurrence can be based on the estrophilin assay of the primary lesion. Nonetheless, changes in estrophilin content during the course of disease are not uncommon. Despite an occasional patient in whom multiple samples separated by a long time have unchanged estrophilin content, there is a general tendency toward decreased estrophilin content with time.

Peroxidase activity and iodide uptake in hormone-responsive and hormone-independent GR mouse mammary tumors

Transplanted mammary tumors growing in the inbred GR/AFib mouse were assayed for peroxidase activity and ability to concentrate injected 125I. Both tumor peroxidase activity and iodide uptake were about ten times greater in the hormone-resonsive (HR) tumors than in the hormone-independent tumors. However, although peroxidases are known for their ability to participate in the iodination of proteins, over 90% of the radioactive iodine found in the tumors was shown to be free iodide. This finding suggests that these two parameters may be independent of each other, but both are higher in HR tumors.

The immunoendocrinology of estrophilin

Immunoglobulin from the serum of rabbits immunized with highly purified estradiol-receptor complex from calf uterine nuclei has been shown to contain specific antibodies to estrophilin by five criteria. Antibodies to calf nuclear estrophilin cross react with nuclear estradiol-receptor complexes of rat, rabbit and sheep uterus, rat endometrial and pituitary tumor, and MCF-7 human breast cancer cell line. They also react with extranuclear receptor of calf, rat, mouse, rabbit, guinea pig, monkey and sheep uterus, rat mammary, endometrial and pituitary tumor, and human breast cancer. There is no interaction of the antibody with estradiol itself. The nuclear form of estrophilin appears to bind more immunoglobulin molecules than does the cytosol form. The antibodies do not react with either the nuclear or extranuclear dihydrotestosterone-receptor complexes of rat prostate, with the extranuclear progesterone-receptor complexes of rabbit uterus, chick oviduct or rat endometrial tumor, or with rat and mouse alpha-fetoprotein. These findings indicate an immunochemical similarity among estrophilins from several mammalian species, as well as between nuclear and extranuclear forms of the receptor, but not among receptor proteins for different steroid hormones. Immunoglobulin from the serum of a goat immunized with similar antigen shows a considerably higher titer of antibodies to estrophilin. These react with nuclear and extranuclear estradiol-receptor complexes of calf uterus to produce somewhat larger entities than those formed with the rabbit antibody. Unlike the rabbit antibody, interaction with the goat antibody causes a noticeable decrease in estradiol-binding affinity of the extranuclear estrophilin as well as an apparent decrease in the total hormone-binding capacity. Specific antibodies to estrophilin offer promise as valuable reagents for receptor analysis and purification, as well as for the elucidation of many still unresolved questions concerning receptor synthesis, localization and function.

Steroid hormone regulations of uterine peroxidase activity

Uterine peroxidase enzyme activity has been studied as a marker for estrogen action in the uterus to help clarify the mechanism of estrogen action and its modulation by antiestrogens and progestins. Estrogen-induced increases in peroxidase were found to closely parallel increases in uterine weight and DNA content in the castrate rat. In the cycling female rat, uterine peroxidase levels were highest during proestrus and estrus and the lower levels of metestrous and diestrous uteri could be raised to estrous levels by administration of estrogen. However, the estrous levels were not further increased by estrogen treatment. The antiestrogen, CI628, while a very weak inducer of uterine peroxidase, is an effective antagonist of the estrogen induction of the enzyme. The prolonged duration of this CI628-effected inhibition corresponds to the prolonged depletion of cytoplasmic estrogen receptor seen with CI628 treatment. Progesterone, R5020 and norethindrone were also found to be effective antagonists of estrogen-induced uterine peroxidase. Medrogestone and clogestrone, less potent progestins in the rat, were also less effective antagonists of peroxidase induction. Since progesterone was found to inhibit peroxidase induction due to both estrone and diethylstilbestrol, as well as estradiol, it is considered unlikely that this antagonism relates to progestin-induced increases in uterine 17 beta-hydroxysteroid dehydrogenase. Rather, it is proposed that progestins, acting through progestin receptor, may have a more direct role, possibly acting at the level of the genome to repress the expression of estrogen-induced products.

Isolation and purification of rat mammary tumor peroxidase

7,12-Dimethylbenz(a)anthracene-induced rat mammary tumors often contain high levels of the enzyme perioxidase, a putative marker of estrogen dependence. This enzyme can be effectively extracted with 0.5 M CaCl2, giving rise to a soluble peroxidase with a molecular weight of about 50,000 as determined by gel filtration. This is the same size as the estrogen-induced peroxidase of rat uterus but smaller than other mammalian peroxidases. Further purification of the rat mammary tumor peroxidase by concanavalin A-Sepharose chromatography and hydrophobic interaction chromatography on phenyl Sepharose provides a 640-fold purification of the enzyme.

Antibodies to estrogen receptor: immunochemical similarity of estrophilin from various mammalian species

Immunoglobulin obtained from the serum of rabbits immunized with a highly purified preparation of estradiol-receptor complex from calf uterine nuclei has been shown to contain specific antibodies to the receptor protein (estrophilin) by four criteria: (a) precipitation of the radioactive steroid upon addition of goat antibody against rabbit gamma globulin to a mixture of the tritiated estradiol-receptor complex and the immunoglobulin, (b) adsorption of the estradiol-receptor complex by the immunoglobulin linked to Sepharose, (c) adsorption of the estradiol-receptor complex in the presence of the immunoglobulin by Staphylococcus aureus protein-A linked to Sepharose, and (d) the ability of the immunoglobulin to increase the sedimentation rate of the estradiol-receptor complex. Antibodies to calf nuclear estrophilin were shown to crossreact with the nuclear receptor of rat uterus, as well as with the extranuclear receptor of calf, rat, mouse, and guinea pig uterus and of human breast cancer. The antibodies do not react with either the nuclear or extranuclear dihydrotestosterone-receptor complexes of rat prostate or with the extranuclear progesterone-receptor complex of chick oviduct. These findings indicate an immunochemical similarity among estrophilins from several mammalian species, as well as between extranuclear and nuclear forms of the receptor, but not among receptor proteins for different steroid hormones.

Uterine peroxidase as a marker for estrogen action

Administration of a single dose of estradiol to immature rats gives rise to the appearance of substantial amounts of peroxidase (donor:hydrogen-peroxide oxidoreductase, EC 1.11.1.7) enzyme activity in the uterus. This enzyme induction, which is inhibited by administration of actinomycin D and cycloheximide, can be detected at 4 hr after administration of estradiol, reaches a maximum level by 20 hr, and thereafter declines. The amount of uterine peroxidase seen at 20 hr after a single dose increases with dose from 0.1 to 100 microgram of estradiol. Estrone and estriol also show dose-dependent induction of peroxidase, and the quantitative peroxidase responses to these steroids follow their uterotropic capacities. The antiestrogen CI628, capable of low levels of enzyme induction by itself, can inhibit the induction due to estrogen. Solubilization of the uterine enzyme with divalent cations, especially calcium, results in a substantially increased yield of peroxidase. This extraction method provides an enzyme of about 50,000 molecular weight in distinction to the large aggregated form obtained by the usual extraction with sodium chloride.

Endocrine-dependent rat mammary tumor regression: use of a gonadotropin releasing hormone analog

Long-term administration of [D-Leu6, des-Gly-NH210, Pro-ethylamide9]-GnRH, an analog of gonadotropin releasing hormone, caused regression of neoplastic tissue in a rat bearing a spontaneous mammary adenocarcinoma and in rats in which tumors had been induced by treatment with dimethylbenzanthracene (DMBA). During two separate treatment periods with the analog, the tumor in the single animal regressed although it had previously grown spontaneously. After a third period of growth, ovariectomy also induced regression, suggesting endocrine dependency of the tumor. These observations were confirmed in the DMBA-induced tumor system, where tumor regression in the analog-treated rats was comparable to that observed in the ovariectomized rats, and in both cases the tumor regression was significant when compared to untreated controls.

Regression of rat mammary tumors effected by a gonadoliberin analog

A synthetic analog of gonadoliberin (gonadtropin-releasing factor of luteinizing hormone/follicle-stimulating hormone-releasing hormone), designated A-43818, was evaluated for its ability to effect regression of carcinogen-induced mammary tumors in the Sprague-Dawley rat. This analog, specifically (D-leuyl6, desglycyl-NH210, prolyl ethylamide9), gonadoliberin, is a potent synthetic luteinizing hormone/follicle-stimulating hormone-releasing hormone at low dose levels but, at the higher dose levels used in these studies, the effect appears to be that of a potent gonadoliberin antagonist. Administration of 5 or 20 mug of A-43818 per day to tumor-bearing rats was essentially as effective as ovariectomy in causing mammary tumor regression. At least 80% of the tumors in the A-43818-treated animals underwent regression; about one-half of the regressing tumors disappeared in the 6-week period of continuous treatment, and, unlike the 0.9% NaCl solution control group, no new tumors appeared during the treatment period. A subsequent 4-week period of drug withdrawal resulted in the regrowth of palpable tumors and the appearance of new tumors, most of which again regressed on further A-43818 administration.

Estrogen and prolactin receptor concentrations in rat mammary tumors and response to endocrine ablation

Estrogen and prolactin receptor concentrations were measured in 24 carcinogen-induced rat mammary tumors and correlated with the tumor response to host ovariectomy or hypophysectomy. It was found that essentially all of the tumors contained some specific estrogen receptor, and all but three contained prolactin receptor. The values for each receptor comprised a continuum from very low to relatively high concentrations, suggesting that previous considerations of hormone dependence on the basis of presence or absence of hormone receptors may be oversimplified. The concentration of each receptor tended to be lower in the hormone-independent than in the hormone-dependent tumors, but there were a number of hormone-independent tumors with higher receptor levels than some of the hormone-dependent tumors had. A better correlation of tumor response to endocrine ablation resulted from a combination of the 2 receptor levels than from either receptor concentration alone. These results suggest that there is a complex relationship between mammary tumor response to endocrine ablatin and levels of estrogen and prolactin receptors and that some tumors may be dependent upon 1 or both of these hormones for growth.

Endogenous peroxidase: specific marker enzyme for tissues displaying growth dependency on estrogen

Data derived from a correlated morphological and biochemical study suggest the following: (a) estradiol-17beta, diethylstilbestrol, the estrogen antagonists nafoxidine (Upjohn 11,000), and Parke Davis C1628 induce synthesis of an endogenous peroxidase in the epithelium of target tissues like the vagina, the cervix, the uterus, and in the acinar cells of the estrogen-dependent rat mammary tumor; (b) peroxidase is a "specific" secretory protein of the estrogen-sensitized uterine endometrium; (c) peroxidase synthesis is not a nonspecific response to steroid hormone action, since progesterone and testosterone do not induce its synthesis; (d) endogenous peroxidase is a possible diagnositc protein for the detection of estrogen-dependent growing tissues, including breast cancer; (e) movement of exogenous horseradish peroxidase from the interstitium to the uterine lumina is restricted by tight junctions located at the apices of epithelial cells. Estrogen and antagonists do not appear to influence the transepithelial movement of exogenous peroxidase into the lumen.

Modulation of uterine morphology and growth by estradiol-17beta and an estrogen antagonist

The estrogen antagonist C1628 maintains sustained hypertrophy of the uterine epithelium and the synthesis of many proteins including peroxidase. C1628 is a progestogen, inducing secretion of the protein by surface epithelial and glandular cells. C1628 is a connective tissue mitogen, inducing DNA synthesis in fibroblasts and the endothelium. C1628 and estrogen share these properties mentioned above. Estrogen, however, induced moderate growth of the mucosa within a 24-h period and massive hyperplasia of the mucosa within a 24-h period thereafter. C1628 alone, or in combination with estradiol, does not have mitogenic effect on the mucosa, and in fact blocks the mitotic response normally induced by estrogen alone.

Estrogen and antagonist-induced changes in endometrial topography of immature and cycling rats

The topographical changes of the luminal surface of the endometrium of immature and ovariectomized rats treated with estrogen, antagonists to estrogen, and progesterone. and during various stages of the estrous cycle and in pregnancy were examined by scanning electron microscopy. Massive increases in numbers and length of endometrial cell microvilli were observed at estrus, after injection of estradiol-17beta, diethylstilbestrol, estrogen plus progesterone. or the inhibitor C1628 to immature and ovariectomized rats. Withdrawal of the estrogen stimulus results in diminution of microvilli, producing a state identical to diestrus, during pregnancy, and after injection of progesterone, The estrogen antagonist appears to have both estrogenic and progestogenic properties, stimulating endometrial cell hypertrophy, secretion of protein, and production of numerous apical microvilli.