Characterization of androgen receptors in a transplantable human prostatic adenocarcinoma (PC-82)

Androgen receptor is causally involved in the homeostasis of the human prostate endothelial cell

Androgen deprivation causes a reduction of blood flow in the prostate gland that precedes temporally apoptosis of the epithelium. The acute response of prostate endothelial cells to androgen deprivation suggested they represent a primary target for androgen. However, rat prostate endothelial cells were reported not to express androgen receptor (AR), and the role of the androgen axis in human prostate endothelial cell (HPEC) homeostasis was poorly characterized. In this study AR expression was detected in HPEC in vivo in clinical specimens of benign prostate and prostate cancer, and AR function as a transcription factor was demonstrated in HPEC in primary xenografts of human benign prostate tissue transplanted into severe combined immunodeficient mice by iv administration of adenoviral mouse mammary tumor virus-driven luciferase expression vector. AR expression and functionality were maintained in vitro in primary cultures of HPEC that coexpressed CD31, CD34, von Willebrand factor, intercellular adhesion molecule, vascular endothelial growth factor receptor 1, and vascular endothelial growth factor receptor 2 but did not express prostate-specific antigen. AR expression in primary cultures of HPEC isolated from surgical specimens of benign prostate was validated using RT-PCR, cDNA sequencing, immunocytochemistry, and Western blot analyses. Scatchard analyses demonstrated a single ligand-binding site for R1881 in primary cultures of HPEC, with dissociation constant of 0.25 nm, and AR-mediated transcriptional activity was demonstrated using adenoviral mouse mammary tumor virus-driven luciferase reporters. Dihydrotestosterone increased proliferation in primary cultures of HPEC in a dose-dependent manner without modulating endothelial tube formation in Matrigel (BD Biosciences, Bedford, MA). Therefore, HPECs express functional AR, and androgen plays a direct role in modulating HPEC biology.

Concentration of enzymatically active prostate-specific antigen (PSA) in the extracellular fluid of primary human prostate cancers and human prostate cancer xenograft models

BACKGROUND

Prostate-specific antigen (PSA) targeted prodrugs are under development in our laboratory. Concentrations of total PSA and enzymatically active PSA produced by various human prostate cancer xenograft models have not been well characterized.

METHODS

The concentration of PSA secreted into the extracellular fluid (ECF) in normal human prostate tissue, primary prostate cancers obtained directly from patients, and serially passageable human prostate cancer xenografts (PC-82, LNCaP, LAPC-4) were determined using Tandem assays. Percent enzymatically active PSA in the ECF and in conditioned media was also determined using a previously validated assay employing a monoclonal antibody to the PSA catalytic site. In addition, the concentration and activity of PSA within sera from men with and without prostate cancer, as well as from tumor-bearing animals, was likewise assayed.

RESULTS

Normal human prostate tissue and primary human prostate cancers have high concentrations of PSA in the ECF (i.e., 1600-2100 nM). The majority of this PSA is enzymatically active (i.e., 80-90%). Human PC-82 prostate cancer xenografts also have high concentrations of PSA in the ECF (624 +/- 360 nM), and the majority of this PSA is also enzymatically active (i.e., 66 +/- 4%). In contrast, much lower concentrations of PSA are found in the ECF from LNCaP (45 +/- 9 nM) and LAPC-4 (7.3 +/- 0.6 nM). Only a small portion of the total PSA isolated from DHT-containing, serum-free, conditioned media from these cell lines is enzymatically active (i.e., approximately 18%). While PSA was detected in all serum samples regardless of the type of host, no enzymatically active PSA was detected in any of these serum samples.

CONCLUSIONS

Prostate cancers obtained directly from patients produce and secrete large amounts of PSA, the majority of which is highly enzymatically active. In contrast, while PSA was detected in the sera, none of this PSA was enzymatically active. This is also the case for the human PC-82 prostate cancer xenografts. In contrast, LNCaP and LAPC-4 human prostate cancer xenograft models secrete approximately 70-300-fold less PSA in the ECF than prostate cancers from patients and the majority of this PSA is enzymatically inactive. Also, the serum from these animals had detectable PSA, but none of this PSA was enzymatically active. Thus, these latter two prostate cancer models define the least and the PC-82, the most, optimized xenograft model for screening PSA targeted prodrugs.

Castration-induced changes in morphology, androgen levels, and proliferative activity of human prostate cancer tissue grown in athymic nude mice

The transplantable human prostate tumor lines PC-82 and PC-EW regress after androgen depletion. The castration-induced decline in tumor volume was faster in the PC-EW tumor (half-life 6 days) than in the PC-82 tumor (half-life 18 days), despite similar castrate androgen levels of less than 3 pmol/g tissue. Androgen ablation of the PC-82 tumor induced a wave of apoptosis, whereas in the PC-EW tumor, necrotic cell death was predominantly observed. The proliferative activity (BrdU index) of PC-82 and PC-EW tumor tissue declined from 3% to less than 1% after castration. After androgen depletion, some proliferative activity remained, the major part of which was localized in the (murine) stromal compartment of the tumors. In contrast to the PC-EW tumors, regrowth of androgen-ablated PC-82 tumors was rapidly induced by androgen resubstitution. The differences in response of these tumor models to androgen depletion and repletion appear to be related to the putative involvement of different cell death pathways. The role of the stroma in these processes is unclear.

Soluble and nuclear type I and II androgen-binding sites in benign hyperplasia and cancer of the human prostate

This paper presents an approach for the assessment of the androgen receptor (AR) status in benign prostatic hyperplasia (BPH) and prostate cancer (PCa) tissues. Evaluation of AR was carried out in both soluble and nuclear fractions by a standard competition method, using tritiated mibolerone as radioligand. Based on our experience with breast and endometrial cancer, this approach focused on both type I (high affinity, low capacity) and type II (reduced affinity, higher capacity) binding sites, aiming mainly at establishing a putative "functional" receptor mechanism, i.e., the presence of type I AR in both cytosol and nucleus. Ancillary studies were carried out to exclude a potential overestimation of the AR content by interference with other steroid receptors, namely, progesterone (PgR) or glucocorticoid (GcR) receptors. Results showed that the interaction by PgR or GcR upon AR measurement was not relevant. The distribution of AR, namely the percent of positivity either in a single or in both cell compartments, was not significantly different in BPH (N = 32) or PCa (N = 24) tissues. For type I binding, the percent of positivity in both soluble and nuclear fractions (i.e., the "functional" AR status) was very close to that observed for other endocrine-related tumors, like breast cancer. Concentrations of type I AR appeared significantly higher in PCa than in BPH tissues; this was true for both soluble and nuclear fractions. In contrast, no significant difference was found in type II AR concentrations in either cell fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of Win 49,596, a novel steroidal androgen receptor antagonist, in animal models of prostate cancer

A series of experiments were conducted to evaluate the effects of Win 49,596, a novel steroidal androgen receptor antagonist, in animal models of prostate cancer. In the first experiment, oral administration of Win 49,596 at doses of 30, 100, or 300 mg/kg/day for 28 days inhibited (P less than 0.05) the growth of the androgen-sensitive PAP variant of the Dunning R-3327 prostatic carcinoma in intact male rats relative to intact controls. The degree of inhibition at 100 and 300 mg/kg/day Win 49,596 was similar (P greater than 0.10) to that observed in castrate controls as well as in intact rats administered the nonsteroidal androgen receptor antagonist flutamide orally at 15 mg/kg/day. Castration as well as treatment with either Win 49,596 or flutamide also decreased (P less than 0.05) the weight of the prostate in tumor-bearing animals. Additional studies were conducted to determine the effect of Win 49,596 on the growth of the androgen-dependent PC-82 human prostatic carcinoma xenografted into athymic nude male mice. Oral administration of Win 49,596 at 30, 100, or 300 mg/kg/day for 35 days inhibited (P less than 0.05) tumor growth relative to intact controls. The degree of tumor inhibition was similar to that observed in intact male mice administered the nonsteroidal androgen receptor antagonist flutamide orally at 30 mg/kg/day but was less than that observed following castration. Ventral prostate weights were also reduced (P less than 0.05) in castrate mice as well as in intact mice administered either Win 49,596 or flutamide. In the last experiment, at equivalent total daily dosages of either 150 or 300 mg/kg/day Win 49,596, twice a day (BID) dosing was more effective than once a day (SID) dosing in inhibiting tumor growth. The inhibitory effects of Win 49,596 at 150 mg/kg BID on tumor growth were similar to those observed following castration. Although Win 49,596 treatment reduced (P less than 0.05) ventral prostate weights relative to intact controls, there was no difference (P greater than 0.10) between SID vs. BID dosing. Based on the results of these studies and subject to further testing, Win 49,596 may have utility in the treatment of hormonally dependent metastatic prostate cancer in humans.

The androgen receptor: functional structure and expression in transplanted human prostate tumors and prostate tumor cell lines

The growth of the majority of prostate tumors is androgen-dependent, for which the presence of a functional androgen receptor is a prerequisite. Tumor growth can be inhibited by blockade of androgen receptor action. However, this inhibition is transient. To study the role of the androgen receptor in androgen-dependent and androgen-independent prostate tumor cell growth, androgen receptor mRNA expression was monitored in six different human prostate tumor cell lines and tumors, which were grown either in vitro or by transplantation on (male) nude mice. Androgen receptor mRNA was clearly detectable in three androgen-dependent (sensitive) tumors and absent or low in three androgen-independent tumors. Growth of the LNCaP prostate tumor cell line can be stimulated both by androgens and by fetal calf serum. In the former situation androgen receptor mRNA expression is downregulated, whereas in the latter no effect on androgen receptor mRNA levels can be demonstrated. Sequence analysis showed that the androgen receptor gene from LNCaP cells contains a point mutation in the region encoding the steroid-binding domain, which confers an ACT codon encoding a threonine residue to GCT, encoding alanine.

Prostate long-term epithelial cell lines. Biological and biochemical features

This review reports studies on long-term prostate cell lines using multiple experimental approaches. The main goal was to investigate the metabolism of testosterone (T) through in vitro conversion rates. Extensive studies were also carried out on growth curves, tritiated thymidine incorporation, and morphometry by either hormone-responsive or hormone-unresponsive, normal and neoplastic human (PC3 and DU-145) and canine (CAPE and CPA) cell lines. All of them were characterized for their content of both soluble and nuclear androgen receptors. Receptor studies at site I binding in both soluble and nuclear fractions were carried out to establish the hormone sensitivity status of cells. In two prostate epithelial cells, steroid metabolic conversions in vitro show predominantly an oxidative metabolism of T, forming mainly androstenedione. Conversion rates were greater than 50% in the first 24 hours and still higher after 72 hours. At the same time and under exactly the same experimental conditions, the other cells showed metabolic pathways in which reductive metabolism prevails, dihydrotestosterone (DHT) being the prevalent metabolite. Different metabolic patterns of steroids of several cell lines relate to the hormone sensitivity status of the cells; steroid receptor-endowed cells are maintaining higher levels of unconverted precursor than are receptor-empty cells. In fact, hormone-sensitive cells, such as cancer canine CPA and human DU-145, produced DHT early through slowly converting T. On the contrary, unresponsive cells such as human cancer cells PC3 and normal canine CAPE quickly metabolize T, but DHT formation was not observed. These significant differences between cells are highly reproducible provided the proportion between cell number and molar concentration of precursors is constant. Differences we observe cannot be attributed to different experimental conditions. Cell viability, extraction efficiency, and all other parameters used for monitoring cell growth kinetics do not substantiate these reported significant differences in metabolic abilities of cells. The divergent steroid metabolic pathway we observe in different prostate long-term cells appears to be an intrinsic, consistent, highly reproducible property of each cell line.

The human androgen receptor is a 110 kDa protein

The androgen receptor in human prostate carcinoma cells (LNCaP) has been studied after in situ photolabeling with [3H]R1881. Sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of whole cell extracts revealed the presence of two specifically labeled proteins of 110 kDa and 43 kDa. Both photolabeled proteins were stable in cell homogenates and generated different chymotryptic maps, suggesting that the two proteins were different. From ligand binding specificity studies could be concluded that the 110 kDa protein represents the androgen receptor. The 43 kDa protein showed binding specificity only for R1881. Both photolabeled proteins were recovered from LNCaP nuclei, but the 43 kDa protein showed a relatively higher affinity for nuclei than the 110 kDa protein. The function of this protein is unknown. It is concluded that the human androgen receptor is a protein with a molecular mass of 110 kDa.

Structure and function of the androgen receptor

The androgen receptor in several species (human, rat, calf) is a monomeric protein with a molecular mass of 100-110 kDa. The steroid binding domain is confined to a region of 30 kDa, while the DNA-binding domain has the size of approx. 10 kDa. A 40 kDa fragment containing both the DNA and steroid binding domain displayed a higher DNA binding activity than did the intact 100 kDa molecule. cDNA encoding the major part of the human androgen receptor was isolated. The cDNA contains an open reading frame of 2,277 bp but still lacks part of the 5'-coding sequence. Homology with the progesterone and glucocorticoid receptor was about 80% in the DNA binding domain and 50% in the steroid binding domain. The present data provide evidence that the androgen receptor belongs to the superfamily of ligand responsive transcriptional regulators and consists of three distinct domains each with a specialized function.

Regulation of growth and epidermal growth factor receptor levels of LNCaP prostate tumor cells by different steroids

The growth of LNCaP cells, derived from a lymph-node carcinoma of the human prostate, was stimulated by different hormones. Optimal growth (3- to 4-fold increase in DNA content per culture versus controls) was observed at 0.1 nM R1881 (a synthetic androgen), 1 nM progesterone or 10 nM estradiol. Triamcinolone acetonide had no effect. Dihydrotestosterone maximally stimulated cell growth at 10 nM. When the culture medium was changed 4 times in 6 days instead of twice, optimal growth was observed at 1 nM dihydrotestosterone. This indicates that a rapid metabolism of dihydrotestosterone influenced growth response. LNCaP cells contained considerable amounts of androgen receptors (920 fmol/mg cytosol protein) while progestagen, estrogen and glucocorticoid receptors were absent. The affinity of steroids for the androgen receptor decreased in the order of: R1881 (relative binding affinity: 100.0) greater than dihydrotestosterone (67.7) greater than progesterone (29.4) greater than testosterone (23.8) greater than estradiol (4.3) greater than triamcinolone acetonide (less than 0.1). Effects on cell growth of these steroids paralleled their affinity for the androgen receptor. The number of EGF receptors per cell increased in a dose-dependent manner upon treatment with various hormones. Again the amount of steroid needed for maximal effects reflected the affinity of the steroid for the androgen receptor. An approximately 2-fold increase in EGF receptor number was observed within 24 hr and before an increase in growth could be detected. Actinomycin-D and cycloheximide inhibited the hormonally induced increase in EGF receptor numbers.

Cloning, structure and expression of a cDNA encoding the human androgen receptor

A cDNA clone has been isolated from a library prepared of mRNA of human breast cancer T47D cells with an oligonucleotide probe homologous to part of the region encoding the DNA-binding domain of steroid receptors. The clone has a size of 1505 bp and sequence analysis revealed an open reading frame of 1356 bp. The deduced amino acid sequence displays two highly conserved regions identified as the putative DNA-binding and hormone binding domains respectively of steroid receptors. Expression of this cDNA clone in COS cells produces a nuclear protein with all the binding characteristics of the human androgen receptor (hAR). The gene encoding the cDNA is assigned to the human X-chromosome. High levels of three hybridizing mRNA species of 11, 8.5 and 4.7 kb respectively are found in the human prostate cancer cell line (LNCaP), which contains elevated levels of hAR. The present data provide evidence that we have isolated a cDNA that encodes a major part of the human androgen receptor.

Transplantable human prostatic carcinoma (PC-82) in athymic nude mice. II. Tumor growth and androgen receptors

Androgen receptor (AR) levels were measured in PC-82 tumor tissue grown in hormonally manipulated nude mice. In the nuclei of tumor tissue from intact male mice a relatively low concentration (mean 25 fmol/mg protein) of androgen receptors (ARn) was found, while no receptors for estrogens or progestins were detected. The total number of androgen receptors in the PC-82 tumor tissue (measured in the nuclei 1 h after injection of a single high dose of testosterone (T) was found to be 100 fmol/mg protein. The antiandrogen cyproterone acetate, administered in combination with the high dose of T, significantly lowered the amount of ARn in the tumor tissue. In the nuclei of tumor tissue from intact tumor-bearing male mice with T-containing Silastic implants, a 4-times higher amount of tightly associated AR was found. In addition, an increased growth rate of the tumor was observed following T implantation. This finding suggests that the increased growth rate of the PC-82 tumor is associated with a continuous occupancy of AR in the nuclei of the tumor tissue. Castration of tumor-bearing male mice, which arrests the growth of this tumor, did not affect the concentration of ARn in the tissue compared to that of tissue in the intact control situation. In addition, the total amount of AR measured after T injection was not affected by castration. Therefore, the availability of a sufficient and steady level of T in the plasma and consequently the duration of the presence of AR in the nucleus of the PC-82 tumor tissue, rather than the total concentration of AR, appear to be the limiting factors in the modulation of hormonal responses in this androgen target tissue.