Steroid hormone receptors in human breast cancer

Molecular Imaging of Steroid Receptors in Breast Cancer

ABSTRACT

Steroid receptors regulate gene expression for many important physiologic functions and pathologic processes. Receptors for estrogen, progesterone, and androgen have been extensively studied in breast cancer, and their expression provides prognostic information as well as targets for therapy. Noninvasive imaging utilizing positron emission tomography and radiolabeled ligands targeting these receptors can provide valuable insight into predicting treatment efficacy, staging whole-body disease burden, and identifying heterogeneity in receptor expression across different metastatic sites. This review provides an overview of steroid receptor imaging with a focus on breast cancer and radioligands for estrogen, progesterone, and androgen receptors.

Metabolic Footprints and Molecular Subtypes in Breast Cancer

Cancer treatment options are increasing. However, even among the same tumor histotype, interpatient tumor heterogeneity should be considered for best therapeutic result. Metabolomics represents the last addition to promising “omic” sciences such as genomics, transcriptomics, and proteomics. Biochemical transformation processes underlying energy production and biosynthetic processes have been recognized as a hallmark of the cancer cell and hold a promise to build a bridge between genotype and phenotype. Since breast tumors represent a collection of different diseases, understanding metabolic differences between molecular subtypes offers a way to identify new subtype-specific treatment strategies, especially if metabolite changes are evaluated in the broader context of the network of enzymatic reactions and pathways. Here, after a brief overview of the literature, original metabolomics data in a series of 92 primary breast cancer patients undergoing surgery at the Istituto Nazionale dei Tumori of Milano are reported highlighting a series of metabolic differences across various molecular subtypes. In particular, the difficult-to-treat luminal B subgroup represents a tumor type which preferentially relies on fatty acids for energy, whereas HER2 and basal-like ones show prevalently alterations in glucose/glutamine metabolism.

Progesterone receptor targeting with radiolabelled steroids: an approach in predicting breast cancer response to therapy

Steroid receptors have demonstrated to be potentially useful biological targets for the diagnosis and therapy follow-up of hormonally responsive cancers. The over-expression of these proteins in human cancer cells as well as their binding characteristics provides a favourable mechanism for the localization of malignant tumours. The need for newer and more selective probes to non-invasively assess steroid receptor expression in hormone-responsive tumours has encouraged the synthesis and the biological evaluation of several steroidal derivatives labelled with positron and gamma emitters. The physiological effects of the steroid hormone progesterone are mediated by the progesterone receptor (PR). Since PR expression is stimulated by the oestrogen receptor (ER), PR status has been considered as a biomarker of ER activity and its value for predicting and monitoring therapeutic efficacy of hormonal therapy has been studied. Imaging of PR-expressing breast cancer patients under hormonal therapy may be advantageous, since the response to therapy can be more accurately predicted after quantification of both ER and PR status. Thus, ligands for PR targeting, although much less explored than ER ligands, have gained some importance lately as potential PET and SPECT tumour imaging agents. In this review, we present a brief survey of explored approaches for progesterone targeting using radiolabelled progestins as potential clinical probes to predict responsiveness to breast cancer therapy. This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

Radiotracer breast cancer imaging: Beyond FDG and MIBI

Radiotracer imaging with MIBI and FDG have shown the benefit of the functional imaging of breast cancer. Newer radiopharmaceuticals targeted to particular aspects of breast cancer biology will likely play an important role in directing more specific and individualized breast cancer treatment. Future studies will need to test the ability of SPECT and PET imaging to detect breast cancer, but also to assess target expression, identify resistance factors, and measure early response to treatment. This will require protocols designed to test the predictive capability of imaging in the setting of a therapy trial, a new paradigm for breast cancer imaging, for which radiotracer imaging is ideally suited.

Tumor receptor imaging

Tumor receptors play an important role in carcinogenesis and tumor growth and have been some of the earliest targets for tumor-specific therapy, for example, the estrogen receptor in breast cancer. Knowledge of receptor expression is key for therapy directed at tumor receptors and traditionally has been obtained by assay of biopsy material. Tumor receptor imaging offers complementary information that includes evaluation of the entire tumor burden and characterization of the heterogeneity of tumor receptor expression. The nature of the ligand-receptor interaction poses a challenge for imaging--notably, the requirement for a low molecular concentration of the imaging probe to avoid saturating the receptor and increasing the background because of nonspecific uptake. For this reason, much of the work to date in tumor receptor imaging has been done with radionuclide probes. In this overview of tumor receptor imaging, aspects of receptor biochemistry and biology that underlie tumor receptor imaging are reviewed, with the estrogen-estrogen receptor system in breast cancer as an illustrative example. Examples of progress in radionuclide receptor imaging for 3 receptor systems--steroid receptors, somatostatin receptors, and growth factor receptors-are highlighted, and recent investigations of receptor imaging with other molecular imaging modalities are reviewed.

Breast Cancer Treatment in the Era of Molecular Imaging

Molecular imaging employs molecularly targeted probes to visualize and often quantify distinct disease-specific markers and pathways. Modalities like intravital confocal or multiphoton microscopy, near-infrared fluorescence combined with endoscopy, surface reflectance imaging, or fluorescence-mediated tomography, and radionuclide imaging with positron emission tomography (PET) and single-photon emission computed tomography (SPECT) are increasingly used for small animal high-throughput screening, drug development and testing, and monitoring gene therapy experiments. In the clinical treatment of breast cancer, PET and SPECT as well as magnetic resonance-based molecular imaging are already established for the staging of distant disease and intrathoracic nodal status, for patient selection regarding receptor-directed treatments, and to gain early information about treatment efficacy. In the near future, reporter gene imaging during gene therapy and further spatial and qualitative characterization of the disease can become clinically possible with radionuclide and optical methods. Ultimately, it may be expected that every level of breast cancer treatment will be affected by molecular imaging, including screening.

Tumor-specific positron emission tomography imaging in patients: [18F] fluorodeoxyglucose and beyond

Biochemical and molecular imaging of cancer using positron emission tomography (PET) plays an increasing role in the care of cancer patients. Most clinical work to date uses the glucose analogue [(18)F]fluorodeoxyglucose (FDG) to detect accelerated and aberrant glycolysis present in most tumors. Although clinical FDG PET has been used largely to detect and localize cancer, more detailed studies have yielded biological insights and showed the utility of FDG as a prognostic marker and as a tool for therapeutic response evaluation. As cancer therapy becomes more targeted and individualized, it is likely that PET radiopharmaceuticals other than FDG, aimed at more specific aspects of cancer biology, will also play a role in guiding cancer therapy. Clinical trials designed to test and validate new PET agents will need to incorporate rigorous quantitative image analysis and adapt to the evolving use of imaging as a biomarker and will need to incorporate cancer outcomes, such as survival into study design.

Imaging readouts as biomarkers or surrogate parameters for the assessment of therapeutic interventions

Surrogate markers and biomarkers based on imaging readouts providing predictive information on clinical outcome are of increasing importance in the preclinical and clinical evaluation of novel therapies. They are primarily used in studies designed to establish evidence that the therapeutic principle is valid in a representative patient population or in an individual. A critical step in the development of (imaging) surrogates is validation: correlation with established clinical endpoints must be demonstrated. Biomarkers must not fulfill such stringent validation criteria; however, they should provide insight into mechanistic aspects of the therapeutic intervention (proof-of-mechanism) or document therapy efficacy with prognostic quality with regard to the long-term clinical outcome (proof of concept). Currently used imaging biomarkers provide structural, physiological and metabolic information. Novel imaging approaches annotate structure with molecular signatures that are tightly linked to the pathophysiology or to the therapeutic principle. These cellular and molecular imaging methods yield information on drug biodistribution, receptor expression and occupancy, and/or intra- and intercellular signaling. The design of novel target-specific imaging probes is closely related to the development of the therapeutic agents and should be considered early in the discovery phase. Significant technical and regulatory hurdles have to be overcome to foster the use of imaging biomarkers for clinical drug evaluation.

Molecular imaging research in the outcomes era: measuring outcomes for individualized cancer therapy

Advances in molecular imaging, combined with the goal of personalized cancer therapy, call for new approaches to clinical study design for trials testing imaging to guide therapy. The role of cancer imaging must expand and move beyond tumor detection and localization to incorporate quantitative evaluation of regional tumor phenotype. Imaging study design and outcome analysis must move beyond metrics designed to measure the performance for detection to include measures of prognosis, prediction of therapeutic success, and early therapy response. This implies changes in how studies are carried and out, and importantly in the regulatory oversight of cancer imaging. Demonstration that a biochemical or molecular imaging method correctly and accurately measures a specific biologic feature should be sufficient for approval for clinical trials. It may be possible that a combination of imaging procedures known to accurately depict tumor phenotype may be prognostic, even if the individual study cannot be directly validated against patient outcomes. Therefore, it will be important to be able to apply a range of possible imaging studies to different targeted cancer therapy trials. Academia and industry must work together with regulatory agencies and payers to facilitate well designed clinical studies, with appropriate outcome measures, to test the effectiveness of imaging in helping to direct cancer therapy. These will assure the appropriate use of imaging to direct treatment and make an important step towards individualized cancer therapy.

Current and future use of positron emission tomography (PET) in breast cancer

Positron emission tomography (PET) is a radiotracer imaging method that is increasingly used in both the clinical care of breast cancer patients and in translational breast cancer research. This review emphasizes current and future clinical applications of PET to breast cancer, and highlights some translational research using PET to elucidate the clinical biology of breast cancer. PET principles are reviewed, followed by a review of current applications of (18)F-fluorodeoxyglucose (FDG) to clinical breast cancer care. Finally we review work done with other radiopharmaceuticals beyond FDG designed to image a number of aspects of breast cancer biology, emphasizing those most likely to enter clinical trials in the near future.

The progress and promise of molecular imaging probes in oncologic drug development

As addressed by the recent Food and Drug Administration Critical Path Initiative, tools are urgently needed to increase the speed, efficiency, and cost-effectiveness of drug development for cancer and other diseases. Molecular imaging probes developed based on recent scientific advances have great potential as oncologic drug development tools. Basic science studies using molecular imaging probes can help to identify and characterize disease-specific targets for oncologic drug therapy. Imaging end points, based on these disease-specific biomarkers, hold great promise to better define, stratify, and enrich study groups and to provide direct biological measures of response. Imaging-based biomarkers also have promise for speeding drug evaluation by supplementing or replacing preclinical and clinical pharmacokinetic and pharmacodynamic evaluations, including target interaction and modulation. Such analyses may be particularly valuable in early comparative studies among candidates designed to interact with the same molecular target. Finally, as response biomarkers, imaging end points that characterize tumor vitality, growth, or apoptosis can also serve as early surrogates of therapy success. This article outlines the scientific basis of oncology imaging probes and presents examples of probes that could facilitate progress. The current regulatory opportunities for new and existing probe development and testing are also reviewed, with a focus on recent Food and Drug Administration guidance to facilitate early clinical development of promising probes.

Evolving role of positron emission tomography in breast cancer imaging

18F-fluorodeoxyglucose positron emission tomography (FDG-PET) has been used for detection, staging, and response monitoring in breast cancer patients. Although studies have proven its accuracy in detection of the primary tumor and axillary staging, its most important current clinical application is in detection and defining the extent of recurrent or metastatic breast cancer and for monitoring response to therapy. PET is complementary to conventional methods of staging in that it provides better sensitivity in detecting nodal and lytic bone metastases; however, it should not be considered a substitute for conventional staging studies, including computed tomography and bone scintigraphy. FDG uptake in the primary tumor carries prognostic information, but the underlying biochemical mechanisms responsible for enhanced glucose metabolism have not been completely elucidated. Future work using other PET tracers besides FDG will undoubtedly help our understanding of tumor biology and help tailor therapy to individual patient by improving our ability to quantify the therapeutic target, identify drug resistance factors, and measure and predict early response.

Current imaging paradigms in radiation oncology

The technological revolution in imaging during recent decades has transformed the way image-guided radiation therapy is performed. Anatomical imaging (plain radiography, computed tomography, magnetic resonance imaging) greatly improved the accuracy of delineating target structures and has formed the foundation of 3D-based radiation treatment. However, the treatment planning paradigm in radiation oncology is beginning to shift toward a more biological and molecular approach as advances in biochemistry, molecular biology, and technology have made functional imaging (positron emission tomography, nuclear magnetic resonance spectroscopy, optical imaging) of physiological processes in tumors more feasible and practical. This review provides an overview of the role of current imaging strategies in radiation oncology, with a focus on functional imaging modalities, as it relates to staging and molecular profiling (cellular proliferation, apoptosis, angiogenesis, hypoxia, receptor status) of tumors, defining radiation target volumes, and assessing therapeutic response. In addition, obstacles such as imaging-pathological validation, optimal timing of post-therapy scans, spatial and temporal evolution of tumors, and lack of clinical outcome studies are discussed that must be overcome before a new era of functional imaging-guided therapy becomes a clinical reality.

Current and future uses of positron emission tomography in breast cancer imaging

Positron emission tomography using (18)F-fluorodeoxyglucose (FDG-PET) has been used for the detection, staging, and response monitoring in breast cancer patients. Although studies have proven its accuracy in detection of the primary tumor and axillary staging, its most important current clinical application is in detection and defining the extent of recurrent or metastatic breast cancer and for monitoring response to therapy. PET is complementary to conventional methods of staging in that it provides better sensitivity in detecting nodal and lytic bone metastases; however, it should not be considered a substitute for conventional staging studies, including computed tomography and bone scintigraphy. FDG uptake in the primary tumor carries prognostic information, but the underlying biochemical mechanisms that are responsible for enhanced glucose metabolism have not been completely elucidated. Future work using other PET tracers besides FDG will undoubtedly help our understanding of tumor biology, improve our ability to measure and predict response and help tailor therapy to individual patients.

Distribution of 16alpha-[18F]fluoro-estradiol-3,17beta-disulfamate in rats, tumour-bearing mice and piglets

Based on a high affinity to the enzyme estrone sulfatase (ES), 16alpha-[18F]fluoroestradiol-3,17beta-disulfamate ([18F]FESDS) has been suggested as a potential PET radiotracer for imaging steroid-dependent breast tumours. The distribution of [18F]FESDS was studied in rats, tumour-bearing nude mice and piglets. In all species evidence for binding to a second target, the enzyme carbonic anhydrase (CA), was obtained. ES and CA inhibitors significantly reduced the radiotracer uptake in various organs but not in tumours. It is concluded that [18F]FESDS binds to ES and CA in vivo but this binding is not strong enough to allow tumour imaging with positron emission tomography (PET).

Characterizing tumors using metabolic imaging: PET imaging of cellular proliferation and steroid receptors

Treatment decisions in oncology are increasingly guided by information on the biologic characteristics of tumors. Currently, patient-specific information on tumor biology is obtained from the analysis of biopsy material. Positron emission tomography (PET) provides quantitative estimates of regional biochemistry and receptor status and can overcome the sampling error and difficulty in performing serial studies inherent with biopsy. Imaging using the glucose metabolism tracer, 2 -deoxy-2- fluoro-D-glucose (FDG), has demonstrated PET's ability to guide therapy in clinical oncology. In this review, we highlight PET approaches to imaging two other aspects of tumor biology: cellular proliferation and tumor steroid receptors. We review the biochemical and biologic processes underlying the imaging, positron-emitting radiopharmaceuticals that have been developed, quantitative image-analysis considerations, and clinical studies to date. This provides a basis for evaluating future developments in these promising applications of PET metabolic imaging.

New iodinated progestins as potential ligands for progesterone receptor imaging in breast cancer. Part 1: Synthesis and in vitro pharmacological characterization

Five putative iodinated progesterone receptor (PR) binding ligands were synthesized and evaluated as potential imaging agents for PR-positive human breast tumours. Two compounds (E- and Z-17-hydroxy-21-iodo-19-nor-17alpha-pregna-4,20-dien-3-one; E- and Z-IPG1) were previously described, but are re-evaluated. The other three were novel compounds: two nortestosterone analogues derived from ORG 3236 (E- and Z-13-ethyl-17-hydroxy-21-iodo-11-methylene-18,19-dinor-17alpha-pre gna-4,20-diene-3-one; E- and Z-IPG2) and one norprogesterone analogue derived from ORG 2058 (21-[4-iodophenoxy]-16alpha-ethyl-19-norpregn-4-ene-3, 20-dione; IPG3). The E-iodovinyl nortestosterone compounds were obtained by a new route of synthesis. Competitive binding studies were performed to determine their binding affinities for the PR in three types of tissue (human MCF-7 breast tumour cells and rat uterine and mammary tumour tissue) and for the androgen receptor (AR) in human MCF-7 breast tumour cells, as well as for the sex hormone-binding globulin (SHBG) and corticosteroid-binding globulin (CBG) in human plasma. All four 17alpha-iodovinyl nortestosterone derivatives displayed high binding affinity for the human PR, that of Z-IPG1 and E- and Z-IPG2 being even higher than that of ORG2058. Their affinities for the rat PR were somewhat lower, especially those of both E-isomers. The affinity of IPG3 was lower for both the human and rat PR. The nortestosterone derivatives also showed AR binding, the relative binding affinities ranging from 4.3 to 17.0% as compared with 5alphaDHT. Additionally, neither of these steroids displayed any significant binding to either SHBG or CBG in human plasma. We conclude that the in vitro binding properties of all four 17alpha-iodovinyl nortestosterone derivatives warrant evaluation of the distribution characteristics of their 123I-labelled analogues to determine their usefulness as PR imaging agents.

6 alpha-[18F]fluoroprogesterone: synthesis via halofluorination-oxidation, receptor binding and tissue distribution

We have evaluated 6 alpha-[18F]fluoroprogesterone as a potential imaging agent for progesterone receptor (PgR)-positive breast cancer. 6 alpha-Fluoroprogesterone (1) was obtained via halofluorination of the C-5 double bond in pregnenolone, followed by oxidation of the 3 beta-OH group, elimination of HBr from C-4,5, and epimerization at the C-6 center. The relative binding affinity (RBA) of 6 alpha-fluoroprogesterone (1) to PgR is 11 (R5020 = 100), and its binding selectivity index (BSI, i.e. the ratio of the RBA to the non-specific binding, NSB) is 14.4; these values are similar to those of progesterone. 17 alpha-Acetoxy-6 alpha-fluoroprogesterone (2) was also prepared by the same method, but was not used for fluorine-18 labeling studies because its binding affinity for PgR is very low (0.9). The synthesis of 1 was adapted to fluorine-18 labeling and although the overall radiochemical yield was low (decay-corrected, 0.3%), progestin [18F]1 was obtained in moderately high effective specific activity (147 Ci/mmol). In vivo distribution studies using estrogen-primed immature female rats showed that 6 alpha-fluoroprogesterone ([18F]1) has low uterine uptake, low target tissue selectivity, and high fat uptake, presumably due to its low RBA and BSI. High uptake in bone, which indicates extensive metabolic defluorination, suggests that the C-6 position of steroids may not be a good site for fluorine-18 labeling.

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.

Controlled release low dose medroxyprogesterone acetate (MPA) inhibits the development of mammary tumors induced by dimethyl-benz(a) anthracene in the rat

Medroxyprogesterone acetate (MPA) is well recognized to have beneficial effects for the treatment of advanced breast cancer which are comparable to those achieved with other forms of endocrine therapy. Using mammary tumors induced in the rat by dimethylbenz(a)anthracene (DMBA) as a model, we have studied the possibility that low dose MPA could prevent the development of these tumors. Single subcutaneous injection of Depo-Provera (crystalline suspension of MPA) or MPA encapsulated in biodegradable microspheres of 50:50 poly[DL-lactide-co-glycolide] was given 7 days before oral DMBA. While 63% of intact animals developed palpable mammary tumors within 85 days after DMBA administration, tumor incidence decreased to 28% and 23% in animals who had received 30 mg and 100 mg of Depo-Provera, respectively. The same amounts of MPA delivered in microspheres caused a further decrease in tumor incidence to respective values of 7% and 6%. Average tumor area, on the other hand, decreased from 4.89 cm2 in intact rats to about 0.75 (0.57-0.88) cm2 and approximately 0.20 (0.14-0.22) cm2 in the Depo-Provera and microsphere-treated groups, respectively. Using the 50:50 formulation of poly[DL-lactide-co-glycolide] designed to release MPA at a constant rate for a 4-month period, the serum MPA concentration at 3 months was measured at 4.99 +/- 0.43 ng/ml. Such data suggest that administration of a low dose controlled-release formulation of MPA in 50:50 poly[DL-lactide-co-glycolide] microspheres could well be an efficient and well tolerated approach for the prevention of breast cancer in women.

Interactions between estrogens, androgens, progestins, and glucocorticoids in ZR-75-1 human breast cancer cells

The human breast cancer cell line ZR-75-1 possesses androgen, estrogen, progesterone, and glucocorticoid receptors, thus offering a good model to study the specific role of each class of steroids in the control of breast cancer growth. Although the stimulatory action of classical estrogens (E2 and estrone) is well known, we have found a potent mitogenic effect of the adrenal estrogen androst-5-ene-3 beta,17 beta-diol (delta 5-diol) at concentrations within the range of those found in the serum of adult women, thus suggesting that delta 5-diol might be the most important estrogen in women. Androgens, on the other hand, exert a potent inhibitory effect on basal ZR-75-1 cell growth and completely reverse the stimulatory effect of estrogens on the same parameter. The antiproliferative effect of androgens was completely prevented by the antiandrogen OH-FLU, thus suggesting an action mediated by the androgen receptor. Part of the effect of androgens can be explained by the marked inhibition of estrogen receptor binding and mRNA levels by androgens. The antiproliferative effect of androgens is additive to that exerted by antiestrogens. Progestins, on the other hand, exert a specific antiproliferative effect in the presence of estrogens, the effect of progestins being antagonized by the stimulatory action of insulin on cell growth. Medroxyprogesterone acetate (MPA), a compound frequently used in the treatment of breast cancer in women, exerts its main inhibitory action through an androgen receptor-mediated action, whereas its glucocorticoid-like activity could play an additional role at high concentrations. All four classes of steroids are present, to various extents, as lipophilic esters of long-chain fatty acids. It is of interest to mention that all steroids that inhibit ZR-75-1 breast cancer cell growth (androgens, progestins, and glucocorticoids) stimulate the secretion and mRNA levels of gross cystic disease fluid protein-15 (GCDFP-15), whereas estrogens have the opposite effects, thus suggesting that GCDFP-15 could well be a good marker for monitoring the response to androgens, progestins, and antiestrogens during the course of breast cancer therapy.

Radioiodinated ligands for the estrogen receptor: tissue distribution of 17 alpha-[125I]iodovinylestradiol derivatives in normal and tumor-bearing adult female rats

A series of three 125I-labeled 17 alpha-iodovinylestradiol derivatives previously demonstrated to have a selectivity for estrogen receptor tissues in immature female rats were selected for further evaluation in adult female rats. In normal adult female rats, the iodovinyl analogs of moxestrol (IV beta ME2), and moxestrol-3-O methyl ether (IV beta ME2-3-OMe) demonstrated high uterine uptake (0.296-0.437 and 0.135-0.199%ID-kg/g) and selectivity (10-18:1) over the 6 h time period. Subsequent evaluation in two tumor models indicated that [125I]V beta ME2 also possessed the highest tumor uptake and selectivity in the adult female rats bearing the estrogen responsive 9,10-dimethyl-1,2-benzanthracene(DMBA)-induced mammary tumors and that this was receptor mediated. An estrogen independent tumor, the transplanted Walker 256 mammary adenocarcinoma, showed no selectivity of radioligand uptake compared with nontarget tissues. The results suggest the applicability of this agent to the in vivo detection and characterization of estrogen responsive tumors in man.

Target tissue uptake selectivity of three fluorine-substituted progestins: potential imaging agents for receptor-positive breast tumors

We have studied three new fluorine-substituted progestins (1-3) as potential imaging agents for progesterone receptor (PgR)-positive human breast tumors. Two of these are fluorine-substituted analogs of the potent progestin R5020 (promegestone), derived from (21S)-hydroxy R 5020 (RU 27987) and (21R)-hydroxy R 5020 (RU 27988), known metabolites of R 5020, which have affinities for PgR that are 116 and 4%, respectively (relative to R 5020 = 100%). These precursors were protected as their 3,3-dioxolane derivatives and converted to the 21-trifluoromethanesulfonate derivatives. Fluoride ion displacement, followed by acid-catalyzed deprotection, furnished in good yield the epimeric fluoroanalogs, (21S)- and (21R)-fluro R 5020 (1 and 2, affinities for PgR, 11 and 45%, respectively). These compounds were also prepared in 18F labeled form by the same route, in 14-32% overall radiochemical yield (decay corrected; synthesis time 90 min; sp. act. 370-1060 Ci/mmol). In tissue distribution studies in estrogen-primed immature rats, uterus-to-muscle ratios were 4.3 at 1 h for the 21S-epimer and 1.1 for the 21R-epimer, paralleling their relative binding affinities. Considerable metabolic defluorination was observed. The third fluorine-substituted progestin, DU 41165, has a novel retroprogesterone (9 beta, 10 alpha) structure, substituted with fluorine at C-6; its binding affinity is 145% relative to R 5020, and it was prepared in tritium-labeled form by acetylation of DU 41231, the 17 alpha-hydroxy precursor, with [3H]acetic anhydride. In estrogen-primed immature rats, this compound shows uterus-to-muscle ratios of 15 at 1 h, and 18-71 between 2 and 6 h, suggesting that compounds in this retroprogesterone series may be very promising candidates for selective imaging of PgR-positive tissues and tumors.

The relationship of steroid receptor expression to nuclear DNA distribution and clinicopathological characteristics in epithelial ovarian tumors

Tumor specimens from 92 patients with ovarian carcinoma were analyzed for estrogen receptor (ER), progesterone receptor (PR), proliferative fraction, and ploidy. Seventy-one percent of tumors were either ER+ (greater than 5 fmole/mg protein) or PR+ (greater than 10 fmole/mg protein) with 27% of tumors overall being both ER+ and PR+. There was no significant relationship between receptor expression and stage, grade, or histological subtype. Thirteen percent of diploid tumors were receptor negative in contrast to 38% of aneuploid tumors (P less than 0.01). There was no significant association between ER status and ploidy, but 60% of diploid tumors were PR+ in contrast to 33% of aneuploid tumors (P less than 0.02). Eleven percent of tumors overall were both ER rich and PR rich and comprised 23% of diploid and 5% of aneuploid tumors (P less than 0.01). Receptor-negative tumors had a median S phase of 18.8% which was significantly higher than the median S phase of 12% in receptor-positive tumors (P less than 0.02). A similar analysis was also performed on specimens from 9 patients with borderline epithelial ovarian tumors and 12 with benign epithelial ovarian tumors. Up to 50% of benign and borderline epithelial tumors had measurable receptors, but all were diploid with a relatively low S phase fraction. The functional significance of steroid receptor expression in ovarian cancer is unclear, but the association with ploidy and proliferative activity particularly in patients with malignant ovarian tumors may allow better identification of prognostic subsets and aid in selection of patients for hormonal therapy.

Androstenedione and androst-5-ene-3 beta,17 beta-diol stimulate DMBA-induced rat mammary tumors--role of aromatase

The effect of the adrenal steroids androst-5-ene-3 beta,17 beta-diol (delta 5-diol) and androstenedione (delta 4-dione) was studied on the growth of mammary carcinoma induced in the rat by dimethylbenz[a]anthracene (DMBA). The plasma levels of the two steroids were maintained at values within the range of those found in the circulation of post-menopausal women by constant release from osmotic pumps in ovariectomized animals. delta 5-diol and delta 4-dione, at the daily release rate of 500 micrograms, led to plasma levels of 1.26 +/- 0.19 and 1.72 +/- 0.75 ng/ml, respectively. At these physiologically relevant plasma concentrations, both delta 5-diol and delta 4-dione caused a marked stimulation of tumor growth while having minimal or no effect on uterine weight or on plasma prolactin and LH levels. Concomitant treatment with the aromatase inhibitor aminoglutethimide completely blocked the stimulatory effect of delta 4-dione released from silastic implants on tumor growth, while simultaneous administration of the antiandrogen flutamide had no significant effect. On the other hand, when aminoglutethimide was administered with delta 5-diol, the stimulatory effect of the adrenal steroid on tumor growth was not affected. Such data indicate that, under the present experimental conditions, transformation of delta 4-dione into androgens plays a minor role, the predominant effect of the adrenal steroid being stimulation of tumor growth through conversion into estrogens, while delta 5-diol exerts a direct estrogenic effect independent from aromatase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and evaluation of (17 alpha,20E)21-[125I]iodo-11-substituted-19-norpregna-1,3,5(10), 20-tetraene-3,17 beta-diols: the influence of 11-stereochemistry on tissue distribution of radioiodinated estrogens

The 21-tri-n-butylstannyl derivatives of (17 alpha,20E)-11 alpha and beta-methoxy-19-norpregna-1,3,5(10),20-tetraene-3,17 beta-diol were synthesized and characterized. These compounds, as well as the 11-unsubstituted compound were converted via electrophilic ipso radioiododestannylation to the corresponding 21[125I]iodo analogs at the no-carrier-added level in 73-90% isolated radiochemical yields. The radiochemical 4c [IV alpha ME2, (17,20E)-21[125I]iodo-11 alpha-methoxy-19-norpregna-1,3, 5(10),20-tetraene-3,17 beta-diol] was evaluated in immature female rats and the results compared to those previously reported for 4a (IVE2) and 4b (IV beta ME2) to determine the influence of 11-substitution on the ability of the compounds to function as estrogen receptor-seeking agents in vivo. The results indicated that the uptake of 11 alpha-methoxy derivative in the target organ was substantially lower, of shorter duration, with a much smaller specific receptor binding component than the other two radioligands. The distribution profile of the three 17 alpha-iodovinyl estrogens paralleled that previously reported for the corresponding 17 alpha-ethynyl estrogens and this study suggests that the in vivo pharmacological results reported for the 17 alpha-ethynyl estrogens may be used to predict the in vivo behavior of the corresponding 17 alpha-iodovinyl analogs.

The steroid and thyroid hormone receptor superfamily

Analyses of steroid receptors are important for understanding molecular details of transcriptional control, as well as providing insight as to how an individual transacting factor contributes to cell identity and function. These studies have led to the identification of a superfamily of regulatory proteins that include receptors for thyroid hormone and the vertebrate morphogen retinoic acid. Although animals employ complex and often distinct ways to control their physiology and development, the discovery of receptor-related molecules in a wide range of species suggests that mechanisms underlying morphogenesis and homeostasis may be more ubiquitous than previously expected.

Uptake of three [3H]progestins by target tissues in vivo: implications for the design of diagnostic imaging agents

We have investigated the tissue distribution of radioactivity for 0.5-4 h following the i.v. injection of three tritium-labeled progestins in estrogen-primed, immature rats. Whereas [3H]progesterone shows minimal uterine uptake (less than 0.7% injected dose per gram; %ID/g), the two higher affinity, synthetic progestins [3H]R 5020 (promegestrone) and [3H]ORG 2058 show highly selective uptake that reaches 4-5% ID/g by 1-3 h. The uterus to non-target tissue activity ratio at 2-4 h is approximately 12-20 for R 5020 and ORG 2058, but less than 2 for progesterone; the uterus to blood activity ratio for R 5020 is also high (approximately 15), but is lower for ORG 2058, possibly due to the accumulation of radiolabeled metabolites in the blood. The uterine uptake is selectively blocked by simultaneous injection of a large dose of unlabeled steroid, indicating that the uptake is mediated by a high affinity, low capacity binding system, presumably the progesterone receptor. Pronounced uptake is also observed by the liver and into fat, but is not receptor-mediated. The highly selective target tissue uptake by the two synthetic steroids, but not by progesterone, indicates that one must have ligands with sufficiently high affinity for the target tissue receptor, as well as low affinity for certain non-receptor binding proteins, in order to obtain adequate contrast between target and non-target tissues in dynamic uptake studies. These guidelines will be important in the development of suitable in vivo imaging agents based on the progesterone receptor.

Colocalization of DNA-binding and transcriptional activation functions in the human glucocorticoid receptor

Using a combination of a transient expression assay and in vitro mutagenesis, we showed previously that the human glucocorticoid receptor (hGR) is composed of a series of discrete functional domains. Here we report the effects of selective deletion of each of these domains on hGR ability to activate transcription of the MTV-CAT fusion gene. Deletion of the immunogenic domain or the entire amino-terminal half of the protein reduces but does not abolish the ability of the hGR to induce transcriptional activation. Somewhat surprisingly, deletion of the steroid-binding domain engenders a constitutively active receptor, revealing that this domain normally represses receptor function. However, the central, cysteine-rich region contains all the information required for both DNA binding and trans-activation. Taken together, these data delineate a core domain in the hGR spanning 88 amino acids that determines both DNA-binding and transcriptional activation functions. This physical linkage distinguishes the glucocorticoid receptor from other described eukaryotic regulatory proteins, where these two functions have been shown to be separable.

The effect of estradiol on human myelomonocytic cells. II. Mechanism of enhancing activity of colony formation

Elevated proportions of monocytes have previously been found in the blood of healthy women during the ovulation period as well as in other conditions associated with increased blood estradiol (E2). This phenomenon was explained, in part, by an augmenting effect which physiological concentrations of E2 may have on the development of granulocyte-macrophage (GM) colonies derived from normal peripheral blood mononuclear cells. To analyze this effect, we tested possible alternatives for the interaction between E2, colony-stimulating factor (CSF) and GM colony progenitor cells. E2 was found not to interact synergistically with CSF, but pre-treatment of the progenitor cells with E2 resulted in higher numbers of colonies in response to CSF. Moreover, E2 did not induce higher secretion of CSF but treatment with anti-CSF antibodies abolished the enhancing effect of E2. Based on these results, we suggest that the augmenting effect of E2 on GM colony formation is mediated by inducing the colony precursor cells to be more responsive to CSF. These findings may help to elucidate some of the complex relationships between estrogens, immune responses and hemopoiesis.

Recognition with a monoclonal antibody of a cytoplasmic mammary carcinoma antigen, correlated to the estrogen receptor status

Immunohistochemical reactivity of mammary carcinomas with monoclonal antibodies (MAbs) to human milk fat globule (HMFG) membrane antigens was compared with the estrogen (ER) and progesterone receptor (PR) status of the tumors. Antibody III D 5 stained 55 of the 74 tumors studied, the reaction being of borderline intensity in 19 cases and unequivocally positive in 36 cases. The staining was always cytoplasmic; in addition occasional extracellular III D 5-positive secretory material was observed. Positive reactivity of the tumor with antibody III D 5 was significantly correlated with ER and/or PR content of the tumors. The presence of extracellular, III D 5-positive secretory material correlated to the ER but not to the PR status of the tumors.

Dexamethasone modulation of in vitro growth pattern and of lung colonization ability in clones of a metastatic BALB/c mammary carcinoma cell line

The expression of steroid receptors and the in vitro responsiveness to steroids were used to investigate the cell heterogeneity of a BALB/c mammary carcinoma cell line (TS/A) by means of its high- and low-metastatic clones previously selected in vitro. All the clones studied contained appreciable levels of receptors for oestrogens and for glucocorticoids. The in vitro responses of clones to 17 beta-oestradiol were very poor and comparable; conversely, a heterogeneous pattern of responsiveness to glucocorticoids was observed. In the presence of dexamethasone, the in vitro growth of high-metastatic clones was either unaffected or stimulated and dome formation was significantly increased. Dexamethasone treatment of low-metastatic clones caused inhibition of in vitro proliferation and a morphological shift from a fibroblast-like growth pattern towards the epithelial phenotype. One out of the three low-metastatic clones tested acquired the ability to form domes in the presence of dexamethasone, albeit sporadically. The in vitro treatment with dexamethasone significantly increased the lung colonization ability of the two low-metastatic clones studied, whereas no significant effect was observed with high-metastatic clones. Data presented here suggest that TS/A cell line consists of heterogeneous populations with peculiar proliferative and differentiative responses to glucocorticoids.

Expression and modulation of estrogen receptors in human breast cancer

Estrogen receptors have been traced at the tissue level in premalignant and malignant changes of human mammary gland by an immunoperoxidase technique using a monoclonal antibody against the receptor protein. Proliferative premalignant cells show an increased and homogeneous expression of the estrogen receptor by this technique; it seems that a constitutive expression of the receptor may play a role in the promotional carcinogenetic process. Moreover, infiltrating tumors show a striking heterogeneity in the cellular expression of estrogen receptor, which seems related to differentiation level.

The effect of estradiol on human myelomonocytic cells. 1. Enhancement of colony formation

Cyclic changes were observed in the content of blood monocytes during the menstrual cycle of normal women. Elevated blood monocytes were found during the ovulation period as well as in other conditions which are associated with increased blood estradiol (E2). To understand the possible association between E2 and monocytosis, we analysed the in vitro effect of E2 on the development of myelomonocytic colonies in culture. E2 in physiological concentrations was found to increase the number of colonies developed from peripheral blood mononuclear cells (PBM) of both females and males. The optimal concentration for the augmenting effect on males' PBM was lower than that for females. Mononuclear cells derived from cord blood, which yielded much higher numbers of colonies than adult PBM, also responded to the stimulatory effect of E2. Estrone and estriol were less effective than E2 in adult PBM. In contrast, progesterone, diethylstilbestrol and testosterone did not affect the number of colonies at the range of physiological concentrations tested. The anti-estrogen Tamoxifen did not inhibit the stimulatory effect of E2. The augmenting effect of E2 on monomyelocytic colony formation may explain at least in part the increase in blood monocyte content of women with high E2 as well as other phenomena of macrophage and granulocyte changes associated with the menstrual cycle.

Estrogen response of MCF-7 cells grown on diverse substrates and in suspension culture: promotion of morphological heterogeneity, modulation of progestin receptor induction; cell-substrate interactions on collagen gels

In this study we observed the incidence of hormone sensitivity in the response of MCF-7 cells to estrogen stimulation when the cells were cultured in different contact environments (hydrophilic plastic, bovine corneal extracellular matrix, type I collagen and in suspension culture). The major purpose was to describe the influence of cell to cell and cell to substrate contacts on the morphological response to estrogen treatment. However, other parameters including growth and induction of progestin receptor were also explored, keeping in mind that the MCF-7 cell line, although representative of normal mammary epithelium in that it contains a similar hormone receptivity, was selected in vitro from a metastatic population in a pleural effusion. Although substrate conditions did not modify growth enhancement by estrogens, progestin receptor levels were significantly higher in three-dimensional spheroid cultures in which cell to cell contacts were optimal due to elimination of basal contact. A careful morphological survey of large surfaces lead to an objective opinion of the overall effect of the hormone treatment on the non-cloned cell line in which a marked heterogeneity in the response of individual cells was observed. In terms of morphofunctional differentiation, the edification of acini with dense microvillus coating was best in suspension culture. When sections were made perpendicular to the plane of cultures on collagen gel rafts two other phenomena were noted: decrease in intercellular junctions, resulting in reduced cell to cell cohesion, and accumulation biodegradation products in the collagen lattice. This suggested a hormone-mediated interaction between the metastatic cells and the fibrillar substrate, collagen I, one of the major constituents of tissue stroma. This estrogen response might be related to the metastatic phenotype and must be distinct from their hormone sensitivity in terms of growth and differentiation since hormone receptivity is generally considered to be a favorable prognosis for breast cancer.