Relationship between concentrations of extractable and matrix-bound nuclear androgen receptor and clinical response to endocrine therapy for prostatic adenocarcinoma

Androgen receptor activity is affected by both nuclear matrix localization and the phosphorylation status of the heterogeneous nuclear ribonucleoprotein K in anti-androgen-treated LNCaP cells

The androgen receptor (AR) plays a central role in the development and progression of prostate cancer (PCa) and anti-androgen therapy is a standard treatment. Unfortunately, after a few years, the majority of patients progress, developing androgen-independent PCa. AR-driven gene transcription recruits a large number of co-activator/co-repressor complexes; among these, the heterogeneous nuclear ribonucleoprotein K (hnRNP K) directly interacts with and regulates the AR translational apparatus. Here we examined AR and hnRNP K expression in response to the treatment of LNCaP cells with anti-androgen cyproterone acetate (CPA) or bicalutamide (BIC). AR and hnRNP K modulation and compartmentalization were studied by Western blot and confocal microscopy. Phosphate-affinity gel electrophoresis was employed to examine how anti-androgens modified hnRNP K phosphorylation. 10(-6) M CPA significantly stimulated LNCaP proliferation, whereas for 10(-4) M CPA or 10(-5) M BIC an antagonistic effect was observed. After anti-androgen treatment, AR expression was remarkably down-regulated within both the cytoplasm and the nucleus; however, when CPA had an agonist activity, the AR associated with the nuclear matrix (NM) increased approximately 2.5 times. This increase was synchronous with a higher PSA expression, indicating that the NM-associated AR represents the active complex. After BIC treatment, hnRNP K expression was significantly lower in the NM, the protein was hypophosphorylated and the co-localization of AR and hnRNP K decreased. In contrast, CPA as an agonist caused hnRNP K hyperphosphorylation and an increase in the co-localization of two proteins. These findings demonstrate that, in vitro, there is a strong relationship between NM-associated AR and both cell viability and PSA levels, indicating that AR transcriptional activity is critically dependent on its subnuclear localization. Moreover, the agonistic/antagonistic activity of anti-androgens is associated with modifications in hnRNP K phosphorylation, indicating an involvement of this protein in the AR transcriptional activity and likely in the onset of the androgen-independent phenotype.

Molecular biology of the androgen receptor

Androgen receptor (AR) is a member of the steroid hormone receptor family of molecules. AR primarily is responsible for mediating the physiologic effects of androgens by binding to specific DNA sequences that influence transcription of androgen-responsive genes. The three-dimensional structure of the AR ligand-binding domain has shown it is similar to other steroid hormone receptors and that ligand binding alters the protein conformation to allow binding of coactivator molecules that amplify the hormone signal and mediate transcriptional initiation. However, AR also undergoes intramolecular interactions that regulate its interactions with coactivators and influence its activity. A large number of naturally occurring mutations of the human AR gene have provided important information about AR molecular structure and intermolecular interactions. AR is also a critical mediator of prostate cancer promotion, conferring growth signals to prostate cancer cells throughout the natural history of the disease. Late-stage prostate cancer, unresponsive to hormonal deprivation, sustains AR signaling through a diverse array of molecular strategies. Variations in the AR gene may also confer genetic predisposition to prostate cancer development and severity. Further understanding of AR action and new strategies to interfere with AR signaling hold promise for improving prostate cancer therapy.

Androgen receptors and hormone sensitivity of a human prostatic cancer cell line (PC-3) are modulated by natural beta-interferon

Androgen receptors are expressed at a low level in the cell line PC-3, which does not respond to either androgens or antiandrogens. If these cells are exposed to natural beta-interferon (beta-IFN) a reduction in cell growth and an increase in androgen receptors, evaluated by both biochemical and immunocytochemical techniques, occur. This increase seems not to be related to a selective block of PC-3 in any phase of the cell cycle. Pretreatment with beta-IFN determines in PC-3 cells a partial responsiveness to the androgen dihydrotestosterone as reflected by the increase in cell number. Moreover, the antiandrogen hydroxyflutamide shows agonistic properties by increasing the cell number of PC-3 cells pre-exposed to beta-IFN. When the antiandrogen is tested in combination with interferon, it produces a reduction in the beta-IFN-induced inhibition of cell growth. It is not known whether these unexpected effects are due to the increase in androgen receptors or to other mechanisms.

Immunohistochemistry of the androgen receptor in human benign and malignant prostate tissue

The role of the androgen receptor in the development and progression of prostatic carcinoma has not been defined. The development of androgen receptor antibodies has provided new opportunities for direct immunohistochemical analysis. We compared the androgen receptor staining characteristics of fresh human prostatic carcinoma with benign prostatic hyperplasia (BPH) using an avidin-biotin complex method. Cancer and BPH obtained from the same radical retropubic prostatectomy specimen in 10 prostate cancer patients (68.5 +/- 7.3 years old standard deviation) and BPH from 10 noncancer patients (71.5 +/- 7.7 years old) were incubated with AR52, a rabbit polyclonal antibody against a synthetic androgen receptor peptide. Nuclei within each section were graded for intensity of androgen receptor staining (0-absent, 1-weak, 2-moderate or 3-strong) and the percentage (0 to 100%) of nuclei sampled staining at each of these intensity levels was determined. A total intensity score (0 to 300) was the summation of the products of each intensity score (0 to 3) and their corresponding percentages. Cancer sections (166 +/- 69) stained less intensely and more heterogeneously than BPH in cancer patients (246 +/- 41, Student's t test p < 0.05) and noncancer patients (225 +/- 39, p < 0.05). The decreased intensity and greater heterogeneity of androgen receptor staining in cancer tissue may implicate a quantitative or functional difference in androgen receptor between prostatic carcinoma and BPH.

Nuclear localization of androgen receptor in heterogeneous samples of normal, hyperplastic and neoplastic human prostate

To facilitate an understanding of how androgens participate in the genesis of human benign hyperplasia and carcinoma we assayed androgen receptor in the epithelium and stroma of human prostatic tissue from 57 patients. Immunohistochemical staining of human androgen receptor was performed on 106 sections of normal prostate, benign prostatic hyperplasia (BPH) and prostate cancer. To determine variability of androgen receptor staining sections taken from different portions of the gland were studied. Frozen tissue sections were incubated with monoclonal antiandrogen receptor antibodies and staining was completed by the indirect avidin-biotin peroxidase method. Antibody staining was found mainly in the nucleus of prostatic epithelial cells, although some stromal cells also showed positive staining. Unlike normal prostate, there was a heterogeneous distribution of androgen receptor in BPH and prostate cancer. The androgen receptor content in well differentiated adenocarcinoma epithelium was significantly higher compared to moderately (p less than 0.05) and poorly (p less than 0.05) differentiated adenocarcinoma. Regardless of the origin of stromal tissue, some staining was observed. In each specimen studied the androgen receptor staining was consistent qualitatively and quantitatively for each pathological component throughout the specimen. These data confirm that androgen receptor is a nuclear receptor protein. Furthermore, they show the ability of monoclonal antibodies to reveal cellular/subcellular distribution of androgen receptor, and demonstrate a correlation between the degree of tumor differentiation and androgen receptor content in epithelial but not in stromal cells. These observations may have important implications for understanding the variable tumor response to hormone therapy.

Androgen receptor assays in specimens of prostatic tissue obtained by transurethral resection and transvesical adenomectomy

The main goal of this study was to ascertain whether routine transurethral resection (TUR) of prostate may provide useful material for the evaluation of androgen receptor (AR) status. At the same time, either intracellular distribution of binding affinity and capacity of receptor molecules were particularly taken into account. Based on our previous findings in breast and endometrial cancer, we suggest that a "functional" receptor status may correspond to the presence of type I (high affinity, low capacity) AR in both soluble and nuclear fractions. However, the precise significance of type II (lower affinity, higher capacity) binding sites remains to be clarified. Ten samples of large prostatic adenomas, obtained by transvesical adenomectomy (TVA), were compared with ten parallel specimens obtained by an in vitro TUR, whereby a pure cutting current was used. The AR assay was carried out with a standard competition method using tritiated mibolerone as the radioligand and Scatchard analysis for data processing. No significant difference between the TUR and TVA groups emerged concerning type I AR content of soluble, nuclear or soluble together with nuclear fractions; this was also true when the results were expressed either as fmol/ml homogenate or as fmol/mg DNA. Similarly, concentrations of type II AR in TVA and TUR samples did not differ significantly in either cell compartment, although they were widely scattered, especially in the soluble fraction. In the light of our findings, it is suggested that TUR specimens represent suitable material for receptor studies, provided that only cutting current is employed and that the use of coagulation current, to control bleeding from the prostatic bed, is confined to the final step of the TUR procedure.

Benign prostatic hyperplasia--video image analysis and its relationship to androgen and epidermal growth factor receptor expression

Androgens are essential for the development and maintenance of the prostate. However, prostatic growth may be mediated by epidermal growth factor (EGF) and the expression of the EGF receptor (EGFR) may be influenced by the androgenic milieu. We have characterized the expression of cytosolic androgen receptor (ARc), nuclear salt extractable androgen receptor (ARn) and EGFR in 89 consecutive cases of benign prostatic hyperplasia, 84 of which were treated by transurethral prostatic resections. Image analysis morphometry was performed on the histological sections to determine the epithelial content of the gland. Our results indicate that there is a vast heterogeneity of receptor expression in benign prostatic hyperplasia. Expression of ARc ranged from zero to 1312 fmol/gm. tissue (mean +/- SD 265 +/- 290), ARn ranged from zero to 531 fmol/gm. tissue (mean +/- SD 145 +/- 98) and EGFR ranged from zero to 316 fmol/gm. tissue (mean +/- SD 121 +/- 76). A statistically significant association was found between expression of ARn and EGFR, and these were both significantly correlated with the epithelial content of the gland.

Hormonal therapy for prostate cancer

Since the demonstration in 1941 by Huggins and Hodges that prostatic cancers are androgen dependent, hormonal treatment by androgen ablation has been the principal treatment for patients with advanced adenocarcinoma of the prostate. Although not able to permanently and totally eradicate every cancer cell since prostate cancer cells are quite heterogeneous in their sensitivity to androgens, hormonal therapy can produce dramatic subjective improvement as well as objective remissions. This results in an improved quality of survival and for patients with metastatic adenocarcinoma, endocrine therapy does reduce the death rate from cancer, and if death from other concurrent illness is controlled, there is an absolute increase in survival. At present, a variety of strategies are available for ablation of testicular and adrenal androgens, but results are not clinically significantly better than orchiectomy.

Establishment and characterization of monoclonal antibody against androgen receptor

Hybrid cell lines were prepared by the fusion of BALB/c myeloma NS-1 cells with the lymphocytes of BALB/c mice that were immunized with partially purified androgen receptor (AR) from human prostates. Nine clones of the hybrid progeny were determined for the production of antibodies against AR by immunoprecipitation assay. One of the clones, referred to as "5F4", was chosen for analysis of the detailed specificity. The clone "5F4" secreted IgM class antibodies against AR. Competition study demonstrated that "5F4" antibody inhibited androgen binding of AR, suggesting that the antibody identifies androgen binding site of AR. Immunoblotting analysis showed that the antibody identified the ARs as two proteins, 95 kD and 41 kD proteins, on a sodium dodecyl sulfate polyacrylamide gel. It is suspected that a 95 kD protein should be a monomeric AR and a 41 kD protein is a proteolytic fragment of AR. Immunohistochemical analysis demonstrated that androgen-dependent tissues--human prostatic hypertrophy tissues, an AR abundant prostatic cancer tissue and fibroblast cells from human genital skin--were stained intensely with "5F4" monoclonal antibody, while androgen-independent tissues--fibroblast cells from lymph nodes, an AR deficient prostatic cancer tissue and human prostatic cancer cell line, PC-3--showed no staining. These results also support the specificity of the antibody for AR.

Measurement of nuclear oestrogen receptors in human breast tumours

Recent reports suggest that oestrogen receptors detected in the cytosolic fraction of homogenized human breast tumours might be mainly nuclear receptor released into the cytoplasm during tissue processing. This study thus compares the tumour content of steroid hormone receptors in conventional cytosolic receptor assays with direct measurements of receptor in the cell nucleus. Unoccupied cytoplasmic oestrogen receptors (cER), cytoplasmic progesterone receptors (cPR) and total (occupied plus unoccupied) nuclear oestrogen receptors (nER) have been measured in parallel in human breast tumour tissue using biochemical radioreceptor assay. Of 125 tumours, 62% and 61% were positive for cER and cPR, respectively, 50% contained nER with high affinity for oestradiol (nER I) and 13% expressed nER with low affinity for oestradiol (nER II). The concentration of cER correlated significantly with age, cPR and log nER I. A significant proportion of tumours which were positive for both cytosol receptors also possessed nuclear receptors with high and low affinity for oestrogen. It is possible that this group of tumours which are positive for cER, cPR, nER I and nER II will respond well to hormone therapy.

Androgen and oestrogen receptor status in benign and neoplastic prostate disease. Study of prevalence and influence on time to progression and survival in prostate cancer treated by hormone manipulation

TUR chips from 89 men were analysed prospectively for androgen and oestrogen nuclear and cytoplasmic receptors (ANR, ACR, ONR, OCR). Patients were selected on the basis of suspicion of neoplastic change on clinical feel of the prostate. A control group of benign cases was also collected prospectively. Histological examination showed that 46 patients had prostatic carcinoma and 43 had benign prostatic hyperplasia. No difference was found between the 2 groups in terms of prevalence of any of the receptors or in levels of receptor in those who were positive. The patients with neoplastic changes were followed up for a median of 53 months (range 47-64). No significant effect on duration of survival was noted with any of the receptor variables but there was a beneficial association between cytoplasmic oestrogen receptor positivity and progression-free interval. Patients with T category 3 or 4 had a significantly higher chance of being ANR positive than those of lower T category and this may reflect sampling error. There appears to be some evidence to suggest that cytosol oestrogen receptor positivity has a prognostic role in prostate cancer, in terms of time to progression on hormone therapy. Receptor status did not influence survival.

A nuclear binding assay for measurement of biologically active androgen receptors in animal tissues and human prostate cancer

A nuclear binding (NB) assay has been developed for the measurement in intact viable cells of biologically active (functional) estrogen and progesterone receptors, i.e. those capable of binding to nuclear acceptor sites [Spelsberg et al., Endocrinology 121: 631 (1987)]. This paper describes the application of this assay to analyses of androgen receptors in the guinea pig seminal vesicle and in human prostatic carcinoma. Cells from fresh animal seminal vesicles or human prostate carcinoma are isolated using collagenase and are incubated with [3H]R1881 for 1 h at 22 degrees C, after which nuclei are isolated at 4 degrees C and assayed for DNA and radioactivity. This NB assay demonstrates a saturable, temperature dependent, steroid and tissue specific nuclear binding of [3H]R1881 for the guinea pig-seminal vesicle system. The nuclear binding is of high affinity and low capacity. The NB assay reveals several important aspects of the androgen and estrogen receptors in target tissues: (1) the nuclear acceptor sites for androgen receptor (AR) are steroid receptor specific; (2) there are different concentrations of the androgen and estrogen receptors between the epithelium and the fibromuscular components of the guinea pig seminal vesicle; and finally (3) some biopsies of human prostate cancer appear to contain biologically inactive AR. This assay may be useful in the analyses of functional receptors in biopsies of human cancer cells.

Binding of the androgen receptor to the nuclear matrix of human foreskin

The nuclear matrix (NM) is a salt and nuclease-resistant nuclear substructure. It is associated with active DNA transcription and has been shown to contain acceptor sites for steroid receptors in a number of specific target tissues. We have investigated the presence of acceptor sites for the androgen receptor (AR) in the NM of human newborn foreskin. The NM was prepared from the 800 g pellet by successive treatments with detergent, DNase and high salt extraction. It contained 13 +/- 7% of total proteins and 10 +/- 6% of total DNA. After extensive washing, the NM spheres were incubated in the presence of cytosol and [3H]methyltrienolone +/- 200-fold excess of unlabeled steroid. Maximal binding of the AR to NM was reached in 30 min and decreased slightly thereafter to reach an equilibrium which was maintained for 18 h. Binding was saturable. In the absence of AR, the steroid did not bind to NM. When Scatchard analysis was performed on cytosol previously incubated with NM, cytosolic binding capacity significantly decreased relative to preincubation values (3.6 +/- 1.9 to 1.3 +/- 1.2 fmol/mg protein, P less than 0.05, n = 6). In contrast, apparent binding affinity was not changed. 0.8 mg of NM protein could bind AR from 2.4 mg of cytosol protein. In conclusion, NM from human foreskin binds the AR with high affinity. This binding is rapid and is maintained for at least 18 h. This is consistent with a potential role of NM in the mechanism of action of androgens in their target tissues.

Androphilic protein studied histochemically in stage D2 prostatic cancer

Androphilic protein in prostatic cancer was histochemically observed with dihydrotestosterone (DHT), R 1881, and mibolerone as ligands. Cancer cells were equally stained with fluorescent R 1881 and mibolerone, and this fluorescence seems to be made up of both the androgen receptor and progestin-binding protein. The staining with fluorescent DHT was weak. Sixty-two Stage D2 prostatic cancer patients were examined with histochemical androphilic protein, and they then received endocrine therapy. The presence of fluorescence of R 1881 was not correlated with grade, but a relationship between the presence of fluorescence and the response to endocrine therapy was noticed 6 months after the start of treatment. Moreover, fluorescence-positive patients showed better survival than fluorescence-negative patients. An examination with fluorescent DHT revealed a similar tendency to that of R 1881, but the frequency of positive fluorescence was lower, indicating that R 1881 is a suitable ligand in this type of study.

Androgen binding as evidenced by a whole cell assay system using cultured canine prostatic epithelial cells

The androgen receptor content in the prostate has been usually evaluated using subcellular fractions without taking into account cellular and functional heterogeneity of the gland. Using enriched populations of immature canine prostatic epithelial cells cultured in primary monolayers, a whole cell assay system was developed to measure androgen receptors. Tritiated dihydrotestosterone (DHT) and/or methyltrienolone (R1881) in serum-free medium were used as ligands and Triamcinolone acetonide (0.5 microM) was added to prevent the binding of R1881 to other types of receptors. The amount of radiolabelled ligand specifically bound to the cells was determined at equilibrium. Specific binding was proportional to the number of cells seeded. Scatchard analysis revealed the presence of at least two types of binding sites. The Kd for the high affinity binding site was 2 x 10(-9) M. Competition studies indicated that this component was specific for androgens; Methyltrienolone, Mibolerone and the antiandrogen RU 23908 were the most efficient competitors. They were followed by DHT, 5 alpha-androstane-3 alpha, 17 beta-diol, testosterone, estradiol and estrone. Progesterone, 5 alpha-androstane-3 beta, 17 beta-diol and epitestosterone were not inhibitors. The level of specific binding was 11.0 +/- 7.6 fmol of bound R1881 per 10(6) cells (n = 34) or 2075 +/- 1434 fmol per mg of DNA; these values correspond to an average of 6624 +/- 4577 sites per cell. Thus, using this whole cell assay system, specific and androgen receptors were detected in immature prostatic epithelial cells in culture. This assay will therefore be useful to study the interrelationship between androgen binding activity and specific cell functions.

Prediction of time to progression after orchiectomy by the nuclear androgen receptor content from multiple biopsy specimens in patients with advanced prostate cancer

The nuclear androgen receptor (ARn) content of cancerous prostatic tissue has been investigated as a prognosticator for time to progression under endocrine therapy. In 1981 a prospective study was started to investigate whether the ARn content in biopsy specimens of patients with prostatic carcinoma predicts the duration of response following hormonal treatment. ARn was estimated by a microassay which involves extraction of nuclear pellets with a heparin-containing buffer, exchange labeling of the nuclear extract with 3H-R1881, and quantitation of the receptor with protamine sulphate precipitation. One hundred and fifteen patients with prostatic cancer entered this study; 47 patients had evidence of metastatic disease as proven by bone scan. Forty-two patients were treated by orchiectomy; 37 of these patients are evaluable with a minimal follow-up of 30 months. A relationship between the nuclear androgen receptor content and the time to progression following orchiectomy in these patients with metastatic disease of the prostate was not found. This could possibly be attributed to the heterogeneous nature of the prostatic tumor tissue with respect to the distribution of the ARn. We conclude that androgen receptor assay in needle biopsies, at least in this study, had no value for the prediction of the time to progression after orchiectomy.

Establishment of a new prostatic carcinoma cell line (TSU-Pr1)

A new epithelial cell line, TSU-Pr1, from a human prostatic adenocarcinoma metastatic to lymph node has been established in long term tissue culture. The cultured cells show loss of contact inhibition, rapid growth in vitro and growth in athymic nude mice. Karyotypic analysis demonstrated an aneuploid karyotype with a modal chromosome number of 80 including a Y-chromosome and at least 10 marker chromosomes. The cells produced only a small amount of prostatic acid phosphatase, and heterotransplanted tumors did not have nuclear androgen receptors.

Relationship between androgen receptor binding activity in human prostate cancer and clinical response to endocrine therapy

The authors investigated the ability of androgen receptor binding in prostate cancer tissue to predict the response of prostate cancer patients to endocrine therapy. The clinical response of 37 previously untreated patients with various grades and stages of prostate cancer was correlated with androgen receptor binding and detailed histologic data obtained before treatment. All patients underwent cold-punch transurethral resection of the prostate and received endocrine therapy. The association between time to progression and cytosolic androgen binding was not significant. However, the associations of time to progression to nuclear binding and to total androgen binding were significant (P = 0.029 and 0.038, respectively). The authors found no association between clinical stage and time to progression, but did find an association between time to progression and pathologic grade (P = 0.003); grade 4 lesions were the least responsive to hormone therapy. When grade 4 lesions were excluded (N = 3), binding levels were still predictive of progression independently of grade and stage. The authors conclude that nuclear receptor binding activity in localized and metastatic prostate cancer tissue is predictive of response to hormonal manipulation.

Applicability of nuclear androgen receptor quantification to human prostatic adenocarcinoma

It has been proposed that concentrations of nuclear androgen receptor may be predictive of tumor hormone dependence in cases of advanced human prostatic cancer. We have investigated the ability of this receptor population to reflect patient prognosis during endocrine therapy in 12 cases of stage D disease. KCl-extractable, nuclear matrix-bound and total nuclear androgen receptor concentrations showed a significant positive correlation with duration of patient survival (p less than 0.05) while cytosolic and total cellular androgen receptor concentrations were not significantly correlated with survival. However, use of selected threshold concentrations of receptors revealed that only cytosolic, nuclear KCl-extractable and total cellular receptors could significantly differentiate long-term and short-term survivors. Even given the small number of patients studied, the potential use of this androgen receptor assay as an index of both tumor hormone-dependence and patient prognosis was evident. Therefore, in order to make these androgen receptor assays more applicable, we attempted to simplify the methods for use on readily available tissues. Similar amounts of nuclear androgen binding were observed in crude and purified nuclear pellets, in nuclei treated with DNase and KCl in differing orders or in nuclei from tissue homogenized using glass or Polytron homogenization procedures. More importantly, nuclear androgen receptor concentrations in specimens of prostatic cancer or benign hyperplasia taken by needle biopsy or transurethral resection involving electrocautery did not differ from those of parallel specimens taken by Thompson cold punch. Simplified nuclear androgen receptor assays of needle biopsy or electrocautery specimens are accurate and should prove clinically applicable.