Abstract:
A method for rapidly determining the presence of functional cellular steroid receptors by assaying a tissue sample for nuclear steroid binding is disclosed which comprises treating the tissue with collagenase, incubating the isolated cells with a labelled steroid capable of complexing said receptors and measuring the bound radioactivity and the DNA of the isolated cellular nuclei.

Description:
FIELD OF THE INVENTION 
     This invention pertains to a cell culture assay for the determination of functional steroid receptor proteins in cells, and is specifically useful to determine the susceptibility of cancer cells from human tissue to steroid therapy. 
     BACKGROUND OF THE INVENTION 
     Cancer is a leading cause of death, second only to heart disease, of both men and women. In the fight against cancer numerous techniques have been developed and are the subject of current research, directed to understanding the nature and cause of the disease, and to provide techniques for control or cure thereof. 
     Since most cancers occur in tissues which are steroid target tissues, treatments using steroid therapy have been useful. Some steroids (e.g., progesterone, glucocorticoids) and antisteroids (e.g., the antiestrogen, tamoxifen) inhibit cell division in most cells. The use of pharmacologic doses of estrogens, antiestrogens or reduction of estrogen (by ablative surgery) have also proven to be effective therapies for the control of breast cancer. Progestins have been used to treat endometrial cancer and glucocorticoids have been used to treat leukemias. 
     Despite the above, it has been found clinically that within each class of cancer, certain populations do not respond to steroid therapy. Much research has been directed to determining why this is so, both to provide a clinical diagnostic tool so that time will not be lost on steroid therapy for those patients having cancers that will not respond, and also to provide insight into the nature of the disease. 
     A known difference between steroid &#34;target&#34; and &#34;nontarget&#34; tissues is the presence of specific receptor proteins for the steroids in target cells which serve as intermediaries in the action of these hormones. The generally accepted mechanism of action of steroids in target cells is (1) entrance of the steroid into cells and binding of these steroids to specific receptor proteins, (2) translocation and binding of this steroid receptor complex from somewhere in the cytoplasm or nucleus to the nuclear acceptor sites on the chromosomal material, (3) alteration of transcription of a multitude of genes, (4) processing of the messenger RNA (mRNA), and (5) translation of these mRNAs into proteins which perform or serve a variety of functions. 
     Procedures have been developed to assay these receptor proteins. In approximately 20% of cancers from steroid target tissues that have been studied, the steroid receptors are very low in concentration or are absent. As expected, these particular cancers do not respond to steroid therapy. 
     However, in studies of steroid therapy in receptor-positive cancer patients, only about half of these cancers (approximately 40% of all cancers) respond to steroid therapies. Examples of this are found in tamoxifen treatments of breast cancers and progesterone treatment of endometrial cancers. It has been speculated that the defects in the steroid action pathway are related to steps subsequent to the binding of the steroid to its receptor. 
     That defective (nonfunctional) receptors occur and may play a role in the nonresponse of many breast cancers to steroid therapy was reported by Leake and co-workers. As used herein with respect to receptors, the term &#34;nonfunctional&#34; indicates receptors incapable of nuclear translocation and binding to chromosomal material to alter gene expression. Such receptors can bind steroids but are otherwise defective with respect to the steroid action pathway. Studies by this group reported that 25 to 30% of 461 estrogen receptor (ER)-positive breast tumors showed no nuclear estrogen receptor (ERN), i.e. the receptors were nonfunctional (Laing et al., Brit. J. Cancer, 43, 59 (1977); Leake et al., The Lancet, 168 (1981)). In these studies, the cytosol estrogen receptor (ERC) was isolated from the tumors and the standard charcoal receptor quantitation assay performed according to the method of S. G. Korenman, J. Clin. Endocrinol. Metab., 28, 127 (1968). The ERN was assayed by incubating the nuclear pellet obtained from homogenized tissue with [ 3  H]-estradiol and determining the amount of ERN present. Similar results were obtained in another laboratory using an in vitro system by incubating crude [ 3  H]-ERC with isolated nuclei and assaying the salt-extracted radioactivity (Fazekas and MacFarlane, The Lancet, 565 (1982)). In both studies, a 75  to 100% correlation was found between the presence of a nuclear receptor (i.e., presence of a functional receptor) and the tumor response to steroid therapy. 
     Thus, assays effective to measure functional/nonfunctional steroid receptors allow a more accurate prediction of which patients will or will not respond to steroid treatment than do assays which simply determine the presence or absence of receptors. Reliable assays of this type will greatly assist the clinician in planning a course of treatment for these patients and would avoid the loss of treatment time due to the use of ineffective therapy. Although the Leake and MacFarlane methods have demonstrated success in discriminating between functional and nonfunctional nuclear receptors, a need exists for improved nuclear biopsy assays which (a) do not require the isolation of the nuclear receptor, (b) do not require cell-free incubations, (c) require less tissue and/or (d) can be performed rapidly with readily-available equipment. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention is directed to a cell culture assay which can rapidly and accurately identify whether or not tumor cells have functional steroid receptors. The method measures the amount of nuclear bound steroid in the cells. This assay gives the investigator a rapid indication as to how much biologically active receptor is present per mg DNA or per cell. The assay requires significantly less tissue and is believed to be more rapid than those assays requiring receptor isolation and quantitation or than those involved in measuring receptor translocations in a cell-free system. The assay may be referred to herein as the &#34;biopsy nuclear binding assay&#34; or &#34;BNB. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flow chart outlining the steps of the charcoal receptor quantitation assay. 
     FIG. 2 is a flow chart outlining the steps of an embodiment of the receptor assay of the invention. 
     FIG. 3 is a graphic depiction of the binding of [ 3  H]progesterone and [ 3  H]estradiol in normal endometrium employing the assay of the invention. 
     FIG. 4 is a graphic depiction of the effects of collagenase treatments on the nuclear binding of [ 3  H]progesterone as determine by the assay of the invention. 
     FIG. 5 is a graphic depiction of the effect of [ 3  H]estradiol and [ 3  H]progesterone concentrations in media on nuclear binding in the assay of the invention. 
     FIG. 6 is a graphic depiction of the nuclear binding of [ 3  H]progesterone in tissue culture of normal endometrium. 
     FIG. 7 is a graphic depiction summarizing the altered specificity of the nuclear binding of [ 3  H]estradiol in the assay of the invention. 
     FIG. 8 is a graphic depiction summarizing the reproducibility of the assay of the invention. 
     FIG. 9 is a graphic depiction of the effect of the tissue quantities on the nuclear binding of [ 3  H]progresterone as determined by the assay of the invention. 
     FIG. 10 is a graphic depiction comparing the results obtained with the present assay with the invivo nuclear binding of [ 3  H]progesterone in the chick oviduct. 
     FIG. 11 is a graphic depiction by the assay of the receptor concentrations determined by the assay of the invention (Panel A) and the dextran charcoal assay (Panel B) for 12 cancer patients. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to the method of the present invention, the tissue to be assayed is treated with collagenase under controlled conditions. The cells are isolated intact and incubated with the appropriate radiolabeled steroid. The cellular nuclei are isolated, and the bound steroid measured. The nuclei obtained from surgical biopsies of 10 mg (wet wt.) or more are then hydrolyzed and assayed for DNA by a standard method such as the diphenylamine assay. Alternatively, when using very small tissue samples, half of the nuclei are not filtered but are used for the measurement of the DNA by a fluorescence assay (ethidium bromide). The latter assay is about 50 times more sensitive than the diphenylamine method. Since DNA quantitation is the limiting factor when using very small biopsies, utilization of the fluorescence method allows 1 to 5 mg biopsy sections to be analyzed for both functional receptors and DNA. 
     In the practice of the present invention normal and diseased tissue is obtained, for example, from surgical biopsies from patients with normal endometrium, from patients with previously untreated endometrial carcinomas and from patients with breast carcinomas. Cells may also be obtained from cell cultures or from blood. In the examples, all normal endometrium and lung and most carcinomas were obtained from postmenopausal female patients. Following appropriate histologic assessment, representative biopsy samples are placed in sterile buffers at ambient temperature for immediate use in the present nuclear binding assay, preferably within 2 hours of surgery. Biopsies, frozen within this time and stored at -80° C. for up to two weeks can also successfully be assayed. Any excess tissue can be cryopreserved for the previously-developed, standard receptor quantitation assay. 
     Biopsy samples from human tissue are transferred to a suitable nutrient medium and fragmented, e.g. by mincing or chopping. The resultant tissue fragments are weighed, and transferred to a nutrient medium containing collagenase. A fixed ratio of about 0.5-15 units of collagenase, preferably about 1-5 units of collagenase per mg tissue is preferred for reduction of all tissue types. The fragments are gently disrupted and filtered. Any retained tissue is again incubated with fresh collagenase. Following a second gentle disruption, the suspension is again filtered. Cells in the filtrate are pelleted by centrifugation and washed. The final cell pellet is resuspended in a nutrient medium for the incubations with radiolabeled steroids. The media of replicate assays are made about 10-50 nM in labeled steroid, e.g., about 20-30 nM in [ 3  H]progesterone (or [ 3  H]estradiol). Parallel duplicate incubations are typically performed with about 20-30 nM [ 3  H]progesterone and excess unlabeled progesterone (or at least about 20-30 nM [ 3  H]estradiol and excess unlabeled estradiol) to determine the extent of nonspecific steroid binding. Incubations may be carried out at about 18°-25° C. for about 0.5-1.5 hour, preferably at about 22° C. for 1.0 hr. 
     After the incubations, the tubes are chilled to about 0°-10° C. and mixed with cold neutral medium (e.g., 5 mM HEPES buffer). The cells are sedimented by cold centrifugation. The cellular pellet is then subjected to a micronuclear isolation method which may readily be adapted to a routine clinical laboratory setting. The cells are homogenized in a cold, neutral buffer, preferably a sucrose-glycerol-KCl-Tris-Triton-X-100 (octoxynol-9, Rohm &amp; Haas) medium. The homogenate is layered over a cold, neutral medium containing sucrose, glycerol, Triton X-100, tris(hydroxymethyl) amino-methane hydrochloride and KCl. The tubes are centrifuged in the cold. The pellet of purified nuclei is resuspended in a neutral solution. An aqueous solution comprising Tris-HCL and aqueous glycerol using a weight ratio of medium to starting tissue of about 1:0.05-0.15, preferably about 1 ml per 100 mg starting tissue is useful for this purpose. 
     The nuclei are then analyzed for nuclear binding of the [ 3  H]steroid by collecting them on filters which were dried and assayed for DNA by acid hydrolysis of the filters and quantitating the solubilized nucleotides by the diphenylamine assay of Burton as set forth in Biochem. J., 62, 315 (1956). The hydrolyzed filters are then measured for radioactivity. This method allows the measurement of the total DNA and the bound radioactivity. The [ 3  H]steroid specifically bound in the nuclei is expressed as CPM/mg DNA and obtained by subtracting the nonspecific binding from the specific binding. The [ 3  H] steriod are not removed by the acid hydrolysis. 
     For the microassay of nuclear binding, which can be carried out with an initial portion of about 1-5 mg of tissue, the DNA is quantitated by the ethidium bromide fluorescence method of U. Karsten et al., Anal. Biochem., 40, 135 (1972) and K. J. Anderson et al., Anal. Biochem., 83, 703 (1977). In this method, aliquots of the nuclei containing about 0.5-5 μg DNA are isolated prior to filtration and treated with a protease (Pronase) and ribonuclease. The aliquots are cooled, mixed with ethidium bromide and the fluorescence determined. 
     The level of nuclear bound [ 3  H]steroid required for a therapeutic tumor response to steroid treatment can be estimated by: (a) measuring a biological response to various concentrations of unlabeled steroid under similar conditions of incubation as described above, and assessing the level of nuclear bound steroid using the same concentration of [ 3  H]steroid. (The particular biological response will dictate the length of exposure required for the unlabeled steroid. The incubation of cells with the [ 3  H]steroid should remain at 60 min), (b) using published reports on the normal or required concentration of steroid receptor per cell nucleus for biological responses in vivo. Typical values are approximately 2000 molecules bound per cell nucleus for minimal responses and approximately 6000 to 10,000 molecules per cell nucleus for maximal responses, or (c) the minimal levels of nuclear binding required for clinical response to steroid therapy can be more accurately determined at the end of the clinical trails. (Each responding/nonresponding tumor can be correlated with respect to its level of nuclear-bound steroid.) 
     The invention will be further described by reference to the following detailed example (Example I). The conventional method is presented in detail in the Comparative Example, presented hereinbelow. The flow charts provided in FIGS. 1 and 2 are provided to facilitate a comparison between the conventional receptor quantitation method and the present BNB, respectively. 
     EXAMPLE I 
     The Biopsy Nuclear Binding Assay for Functional Steroid Receptors 
     The following compounds are available from the sources indicated: Tritiated and unlabeled R5020 (dimethyl-19-norpregna-4,9-diene-3,20-dione), tritiated progesterone and estrogen (40-115 C/mmole) (New England Nuclear Corp., Boston, MA); all other steroids and additional other chemicals are available from Sigma Co. (St. Louis, MO) or Fischer Scientific Co. (Pittsburgh, PA). All chemicals are analytical grade reagents. The steroids are routinely analyzed for degradation using high pressure liquid chromatography in a reverse phase system (uBondapak-C18 resin). 
     A 1.0 mg/ml collagenase enzyme preparation (Sigma Chemicals, St. Louis, MO; C-0130) was used which exhibited an activity of 115-170U per ml of preparation (Cooper Biomedical, Malvern, PA). One unit of activity will liberate from collagen 1μ mole of 1-leucine equivalence in 5 hours at pH 7.4 at 37° C. in the presence of calcium ions. Ninhydrin was used to quantitate the amino acid. 
     A. Collagenase Treatment of Tissue 
     Biopsy samples from human tissue or chick oviducts are placed in MCDB-202 medium, pH 7.4, (K. C. Biologicals, Lemexa, Kansas) at ambient temperature and transported to laboratory. All tissue samples are then transferred to 202 medium containing 4% w/v bovine serum albumin and finely minced. The resultant tissue fragments are collected on a nylon screen by filtration, weighed, and transferred to 202 medium containing the collagenase enzyme. A fixed ratio of 2 units of collagenase per mg tissue was employed for all tissue types. A typical experiment for tissue digestion involves placing about 400 mg tissue and 2.0 units collagenase per mg of tissue in 6.4 ml 202 medium into 25 ml Ehrlenmeyer flasks and incubating at 37° C. on a rotary shaker water bath (Precision Instruments, Chicago, IL) at 50 rpm for 30 min. The fragments are gently disrupted by drawing them in and out of a widebore automatic pipette (25 times every 15 minutes). Following the second gentle disruption with the automatic pipette, an equal volume of 202 medium containing 4% BSA is added. The crude suspension is filtered through nylon gauze (500×500 micron apertures) into a small glass beaker. The flank and fragments on the filter are washed with an equal volume of the 202 medium with 4% BSA. Any undigested tissue on the filter is placed in fresh enzyme solution and redigested. Cells in the filtrate are pelleted by centrifugation at 50×g for 10 min and washed twice by resuspension and centrifugation in 10 ml of 202 medium with 4% BSA. The final cell pellet is resuspended in 202 medium without BSA for incubations with labeled steroids. Cell viability is determined by the Trypan blue exclusion method, which assesses the percentage of cells in the suspensions that are not permeable to the dye. In addition, the cell ultrastructure and intact membranes are examined by microscopy. The cells obtained by the above method are then assessed for nuclear binding by steroid receptors as described below. 
     B. Incubation with [ 3  H]Steroids 
     The cells isolated from the collagenase treatment are resuspended in 0.2 ml 202 medium in a 12.0 ml test tube. This method can be used with cells from 1 to 50 mg biopsy specimens. The analyses are performed on cells isolated from fresh tissue within 2 hours of surgical removal as well as from frozen tissue. A minimum of four incubations are performed. The medium of two duplicates is made 25 nM in [ 3  H]progesterone ([ 3  H]P) (or [ 3  H]estradiol). Parallel duplicate incubations are performed with mixtures of 25 nM [ 3  H]P and 2.5 μM unlabeled progesterone (or 25 nM [ 3  H]estradiol and 2.5 μM unlabeled estradiol). All incubations are performed at 22° C. for 1 hour. For endometrial carcinomas, the progesterone receptor functionality is assessed. In breast carcinomas, both the estrogen and progesterone receptor functionalities (tissue permitting) are examined. 
     C. Analysis of Nuclear Binding 
     After the incubations, the tubes are chilled to 4° C. and mixed with 5 ml of a cold Solution A [containing 5 mM HEPES and 0.2 mM EDTA, pH 7.4 at 4° C.]. The cells are sedimented by centrifugation at 6000×g for 10 min at 4° C. The cellular pellet is homogenized in 2 ml of a cold Solution B [containing 1.0M sucrose, 10% (v/v) glycerol, 0.2% Triton X-100, 0.1M KCl, 0.5M Tris, pH 7.4] in a Thomas type-A glass homogenizer using a motor drive, serrated, Teflon pestle-glass homogenizer (0.001 inch clearance). The homogenate is layered over 1 ml of cold Solution C [containing 1.4M sucrose 10% (v/v) glycerol, 0.2% Triton X-100, 0.5M Tris-HCl, 0.1M KCl, pH 7.4]. The tubes are centrifuged for 20 min at 6000×g at 4° C. The nuclear pellet is resuspended in Solution D [50 mM Tris-HCl, 10% (v/v) glycerol, pH 7.4]. Each nuclear pellet from approximately 50 mg tissue is resuspended in 0.5 ml of Solution D. The pellets of nuclei are then analyzed for nuclear binding of the [ 3  H]steroid by collecting them on nitrocellulose filters, drying the filters, quantitating the DNA on the filters and then counting them in a liquid scintillation spectrometer. This method allows the measurement of both the bound radioactivity and total DNA. Specifically, the filters are assayed for DNA by hydrolysis of the filters in 0.5 N HClO 4  (90° C. for 15 min) and quantitating the solubilized nucleotides by the diphenylamine assay of Burton. The hydrolyzed filters are dried and counted in the scintillation counter using a PCS-xylene fluor (Amersham-Searle, Arlington Heights, IL). 
     For the micro nuclear binding assay, requiring less than 20 mg tissue, the DNA is quantitated by the ethidium bromide fluorescence method. In the latter case, aliquots of the nuclei are taken before collecting them on the filters. The aliquots of nuclei (containing approximately 0.5 to 5 μg DNA) are treated with 0.2 mg Pronase (predigested 2 hours at 37° C.) and 0.2 mg ribonuclease (predigested 10 min. at 90° C.). The nuclear aliquots are then cooled and 2.5 μg ethidium bromide is added. The solution is mixed and the fluorescence is measured on a spectrofluorometer using an excitation of 3000 Å and an emission of 5900 Å. The specifically bound CPM/mg DNA is calculated as the difference between the assays with [ 3  H]steroid alone and those with [ 3  H]steroid+100-fold excess of unlabeled steroid. 
     COMPARATIVE EXAMPLE 
     Isolation and Quantitation of Cellular Progesterone Receptors (PR) and Estrogen Receptors (ER) 
     A. Quantities of Tissues Needed for the Receptor Quantitation Assay 
     The quantitation of the PR and ER by the Dextran charcoal method of Korenman using a one point determination with a nonspecific control requires a minimum of approximately 500 mg of tissue for each steroid receptor. Practically all biopsies obtained from surgery are of sufficient quantity to allow (1) the nuclear binding assay of the present invention and (2) quantitation of the receptors. Of course, the quantitation of the total receptors is not required to be performed in conjunction with the nuclear binding assay. 
     B. Preparation of Cytosol 
     All experiments are performed at 4° C. Frozen tissue is stored at -80° C. for periods not longer than two months. This storage does not cause loss in receptor quantitation. The fresh and/or frozen tissue is minced, weighed, and placed in tubes in Solution F [50 mM Tris-HCl, 1 mM EDTA, 15 mM monothioglycerol, 10 mM sodium molybdate, 2 mM PMSF, 10% (v/v) glycerol, pH 7.4]. This buffer was shown to maintain the greatest stability in the receptor preparations with the EDTA minimizing receptor aggregation, the monothioglycerol/molybdatenycerol stabilizing the receptor and the PMSF reducing proteolysis. Briefly, frozen surgical biopsy specimens are homogenized in a Teflon pestle-glass homogenizer in 4 volumes [200 μl/50 mg tissue (wet weight)] of solution F. The sample is centrifuged at 4° C. in a Beckman Microfuge for 2 min at 10,000×g to obtain the cytosol (supernatant). The pellets are saved for DNA analysis (see below). 
     C. Labeling and Exchange of [ 3  H] Steroid with the Cytosolic Receptors 
     [ 3  H]R5020 (87 Ci/mmole) or [ 3  H]estradiol (102 Ci/mmole) in benzene/ethanol (9:1, v/v) are lyophilized and redissolved in an equal volume of absolute ethanol to achieve a 5 μM [ 3  H]steroid solution. Aliquots of this stock are added to the cytosol for 4 hours at 4° C. to give 100 nM [ 3  H]steroid, an amount sufficient to saturate the receptor sites. These conditions have also been shown to exchange practically all endogenous cold steroid with the [ 3  H]steroid. For the PR assay, cortisol is also lyophilized and redissolved in the same ethanol solution to give a 50 μM cortisol solution with the [ 3  H]P. This steroid eliminates the complication caused by R5020 binding to the glucocorticoid receptor. Aliquots of the crude cytosol are then used to quantitate the steroid receptor using the Dextran charcoal method described below. 
     D. Quantitation of the PR and ER Using the Dextran Charcoal Method 
     For each assay, 100 μl aliquots of each cytosol are incubated with [ 3  H]steroid in the presence and absence of the respective unlabeled steroid at 0° C. for 4 hours as described above. The synthetic progestin (R5020) is primarily used in the cytosol studied since it does not bind to serum binding proteins which often interfere with assays. Standard progesterone may be used as a double check on the assay. For analysis of the progesterone receptor, one of the assays is made 100 nM [ 3  H]R5020 with 1 μM cortisol (to measure total binding) and half 100 nM [ 3  H]R5020+10 μM unlabeled R5020+1 μM cortisol (to measure nonspecific binding). For analysis of the estrogen receptor, one of the assays is made 100 nM [ 3  H]estradiol-17-beta+10 μM unlabeled estradiol. Each of the incubation mixtures are then treated with three volumes (about 500 μl) of 1% (w/w) Dextran-coated charcoal suspension (10 mg charcoal and 1 mg Dextran T-70 per ml of 1.5 mM MgCl 2 ). After a five-minute incubation at 4° C., the solutions are centrifuged at 2 min at 10 4 × g and 250 μl of each of the supernatants measured for radioactivity (i.e., receptor bound [ 3  H]steroid). The nonspecific bound [ 3  H]steroid (assays containing labeled and unlabeled steroid) is subtracted from the total bound [ 3  H]steroid (assays containing only labeled steroid) to obtain specifically bound [ 3  H]steroid. The latter is then plotted as fmole or pmole of bound [ 3  H]steroid per mg protein or per mg DNA. The tissue homogenate pellets are resuspended in [0.5M NaClO 4  ] (0.1 ml/mg tissue), incubated 90° C. for 30 min and then cooled and centrifuged 1000×g for 5 min. The supernatant is then analyzed for DNA as described above, using the diphenylamine assay. 
     SUMMARY OF RESULTS ACHIEVED WITH THE BIOPSY NUCLEAR BINDING (CELL CULTURE) ASSAY (BNB-ASSAY) 
     FIG. 3 shows the nuclear binding of [ 3  H] progesterone (Panel A) and [ 3  H] estrogen (Panel B) using the BNB assay. As described in the Example I, the nonspecific binding is subtracted from the total binding to obtain the specific nuclear binding of the steroids. The latter represents the specific receptor dependent nuclear binding of each of the steroids. Thus a time dependent specific nuclear binding can be measured and the 60 minute incubation period at 22° C. was found to be optimal. 
     FIG. 4 shows that the use of the collagenase to obtain isolated cells for cell culture in the assay significantly enhances the sensitivity of the assay (5-8 fold), over that of simple tissue culture. As shown, the collagenase treatment enhances the nuclear uptake of the steroids in the oviduct, breast cancer and endometrial tissues. Surprisingly, excessive collagenase treatments (higher concentrations) can inhibit the steroid receptor localization in the nuclei. About 50-1000 U of collagenase activity per ml of assay provides the best results. 
     FIG. 5 shows the effects of varying the concentrations of labelled estradiol, [ 3  H]E, and progesterone, [ 3  H]P, on the nuclear binding of these steroids in normal endometrium and lung. As expected, a nontarget organ (such as normal lung) shows little nuclear binding because it does not have the steroid receptors. In contrast, since the target tissue (normal endometrial) has the receptors which are functional, a marked nuclear binding is found with a maximum binding occurring at a steroid concentration in the media of around 25 nM for each steroid. Thus a saturable, tissue-specific nuclear binding is indicated. 
     FIGS. 6-9 illustrate four basic properties of the nuclear binding of [ 3  H]P and [ 3  H]E in normal endometrium, as determined by the assay of this invention. FIG. 6 shows that at 2° C., very little specific binding occurs compared to that achieved at the 22° C. incubation. Higher temperatures show a marked inhibition of nuclear binding (e.g., 37° C.). This supports the involvement of a receptor in the nuclear binding since receptors cannot translocate and bind to nuclear sites if not allowed to &#34;activate&#34; as achieved by increasing the temperature over about 10° C. Additional proof that a receptor is involved in the nuclear uptake of the steroid is the steroid specificity of the nuclear binding. FIG. 7 shows that only unlabelled estradiol reduces the nuclear uptake of [ 3  H]estradiol. The same effect is observed when [ 3  H]P is analyzed (data not shown). Thus, a steroid-specific, tissue-specific, time and temperature dependent, saturable nuclear binding of the [ 3  H]P has been demonstrated in the present assay. These are all properties common to receptor-dependent nuclear binding of steroids. 
     FIG. 8 shows that the nuclear binding assay is reproducible. Panel A summarizes the results of five separate assays which were performed for total binding (containing [ 3  H] steroid only). Each assay consisted of two incubations. From this value is subtracted the value obtained for the nonspecific binding (an assay containing [ 3  H] steroid+100-fold unlabeled steroid) to give a specific binding shown in Panel B. The standard error of the calculated specific binding was ±10% S.E. of the mean. 
     The effects of varying the quantities of the tissue on the amount of the nuclear radioactivity measured was also studied. FIG. 9 shows that 25 to 300 mg quantities of normal endometrium result in similar values for nuclear binding. Breast cancer biopsies using the present assay with the cell culture approach displayed the same properties of nuclear binding of [ 3  H] estradiol as did the studies described here using normal endometrium. 
     The chick oviduct was used as model system to determine whether or not the nuclear binding using the BNB assay is similar to the nuclear binding in vivo. The immature chick (7 days old) received daily injections of diethylstilbestrol (DES), 5 mg per injection, for 4 to 20 days. The oviducts in the uninjected checks are undifferentiated but gradually undergo development during the estrogen tratment. By days 16 to 20, the oviducts are fully developed. FIG. 10 shows a comparison of the nuclear binding between in vivo conditions and the BNB assay. As can be seen, the BNB assay shows similar levels of saturation of the nuclear binding as achieved in vivo. 
     FIG. 11 shows the analysis of 12 patients with endometrial carcinoma. Panel A shows the results of the present BNB assay and Panel B the results of the conventional receptor quantitation assay (the Dextran charcoal absorption method). The conventional receptor quantitation assay (Panel B) indicates that 11 of the 12 patients have sufficient progesterone receptor to predict positive effects for therapy with this steroid. However, the assay of the present invention (Panel A) (the BNB assay) predicts only five of the 12 patients (42% of the total) will respond to this therapy. The reason for this discrepancy is that six patients (indicated by asterisks on Panel A) who have adequate PR, fail to display adequate nuclear binding of the steroid receptor. Thus, nonfunctioning receptors are indicated. More studies with the present assay have shown that of the 46 patients studied, only 17 (or 37% of the total) are predicted to respond to the progesterone therapy. Similar results have been obtained with breast cancer biopsies. 
     As determined by the assay of this invention, the amount of nuclear bound steroid gives the investigator a rapid indication as to how much &#34;biologically active&#34; receptor (i.e., receptor capable of binding to nuclear acceptor sites) is contained in the tumor in question (per mg DNA or per cell). It is therefore believed that this assay can more rapidly (within one day) and more accurately predict tumor response to a steroid compared to the conventional receptor quantitation assay. Furthermore, the present assay requires about 10 times less tissue than those assays requiring receptor isolation and quantitation or than those which analyze receptor binding to isolated nuclei in a cell-free system. If desired, any excess tissue from the assay can be used to isolate the receptor for quantitative and qualitative analysis by conventional methods. 
     Nuclear steroid binding defects may be primarily, if not totally, responsible for the failure of a wide variety of cancers to respond to steroid therapy. This would apply to such cancers as lung, breast, endrometrium, testicles, prostrate, lymphocytes and myelomas, as well as pituitary and ovary. Therefore, it is expected that the present assay will substantially enhance the clinician&#39;s ability to select the appropriate therapy to be employed and save time which may be crucial to the effectiveness of the therapy selected. 
     The present assay is also expected to be useful to identify the presence or absence of functional steroid receptors in other, noncancerous pathological conditions in which steroid dependent cells are implicated. For example, the assay has positively identified functional progesterone receptors in lung tissue from a patient with pulmonary lymphangiomyomatosis. See M. L. Graham et al, Mayo Clin. Proc., 59,3 (1984), the disclosure of which is incorporated by reference herein. 
     The invention has been described with reference to various specific and preferred embodiments and techniques. However, it should be understood that many variations and modifications may be made while remaining within the spirit and scope of the invention.