Adrenal steroids in human prostatic cancer cell lines

Prostate Cancer Mortality Associated with Aggregate Polymorphisms in Androgen-Regulating Genes: The Atherosclerosis Risk in the Communities (ARIC) Study

Genetic variations in androgen metabolism may influence prostate cancer (PC) prognosis. Clinical studies consistently linked PC prognosis with four single nucleotide polymorphisms (SNPs) in the critical androgen-regulating genes: 3-beta-hydroxysteroid dehydrogenase (HSD3B1) rs1047303, 5-alpha-reductase 2 (SRD5A2) rs523349, and solute carrier organic ion (SLCO2B1) rs1789693 and rs12422149. We tested the association of four androgen-regulating SNPs, individually and combined, with PC-specific mortality in the ARIC population-based prospective cohort. Men diagnosed with PC (N = 622; 79% White, 21% Black) were followed for death (N = 350) including PC death (N = 74). Cox proportional hazards regression was used to estimate hazard ratios (HR) and 95%CI adjusting for center, age, stage, and grade at diagnosis using separate hazards for races. A priori genetic risk score (GRS) was created as the unweighted sum of risk alleles in the four pre-selected SNPs. The gain-of-function rs1047303C allele was associated PC-specific mortality among men with metastatic PC at diagnosis (HR = 4.89 per risk allele, p = 0.01). Higher GRS was associated with PC-specific mortality (per risk allele: HR = 1.26, p = 0.03). We confirmed that the gain-of-function allele in HSD3B1 rs1047303 is associated with greater PC mortality in men with metastatic disease. Additionally, our findings suggest a cumulative effect of androgen-regulating genes on PC-specific mortality; however, further validation is required.

Testosterone accumulation in prostate cancer cells is enhanced by facilitated diffusion

BACKGROUND

Testosterone is a driver of prostate cancer (PC) growth via ligand-mediated activation of the androgen receptor (AR). Tumors that have escaped systemic androgen deprivation, castration-resistant prostate cancers (CRPC), have measurable intratumoral levels of testosterone, suggesting that a resistance mechanism still depends on androgen-simulated growth. However, AR activation requires an optimal intracellular concentration of androgens, a situation challenged by low circulating testosterone concentrations. Notably, PC cells may optimize their androgen levels by regulating the expression of steroid metabolism enzymes that convert androgen precursors into androgens. Here we propose that testosterone entry into the cell could be another control point.

METHODS

To determine whether testosterone enters cells via a transporter, we performed in vitro 3 H-testosterone uptake assays in androgen-dependent LNCaP and androgen and AR-independent PC3 cells. To determine if the uptake mechanism depended on a concentration gradient, we modified UGT2B17 levels in LNCaP cells and measured androgen levels by liquid-liquid extraction-mass spectrometry. We also analyzed CRPC metastases for expression of AKR1C3 to determine whether this enzyme that converts adrenal androgens to testosterone was present in the tumor stroma (microenvironment) in addition to its expression in the tumor epithelium.

RESULTS

Testosterone uptake followed a concentration gradient but unlike in passive diffusion, was saturable and temperature-dependent, thus suggesting facilitated transport. Suppression of UGT2B17 to abrogate a testosterone gradient reduced testosterone transport while overexpression of the enzyme enhanced it. The facilitated transport suggests a paracrine route of testosterone uptake for maintaining optimal intracellular levels. We found that AKR1C3 was expressed in the tumor microenvironment of CRPC metastases in addition to epithelial cells and the pattern of relative abundance of the enzyme in epithelium vs stroma varied substantially between the metastatic sites.

CONCLUSIONS

Our findings suggest that in addition to testosterone transport and metabolism by tumor epithelium, testosterone could also be produced by components of the tumor microenvironment. Facilitated testosterone uptake by tumor cells supports a cell nonautonomous mechanism for testosterone signaling in CRPC.

Canonical and Noncanonical Androgen Metabolism and Activity

Androgens are critical drivers of prostate cancer. In this chapter we first discuss the canonical pathways of androgen metabolism and their alterations in prostate cancer progression, including the classical, backdoor and 5α-dione pathways, the role of pre-receptor DHT metabolism, and recent findings on oncogenic splicing of steroidogenic enzymes. Next, we discuss the activity and metabolism of non-canonical 11-oxygenated androgens that can activate wild-type AR and are less susceptible to glucuronidation and inactivation than the canonical androgens, thereby serving as an under-recognized reservoir of active ligands. We then discuss an emerging literature on the potential non-canonical role of androgen metabolizing enzymes in driving prostate cancer. We conclude by discussing the potential implications of these findings for prostate cancer progression, particularly in context of new agents such as abiraterone and enzalutamide, which target the AR-axis for prostate cancer therapy, including mechanisms of response and resistance and implications of these findings for future therapy.

A single-center experience with abiraterone as treatment for metastatic castration-resistant prostate cancer

BACKGROUND

Continuous stimulation of the androgen receptor (AR) axis is a prerequisite for growth in castration-resistant prostate cancer (CRPC). Abiraterone acetate (AA) is a potent inhibitor of extracellular and intracellular androgen synthesis by inhibition of the CYP-17 enzyme system, which has been shown to be up-regulated in CRPC. AA was recently introduced in the management of patients with metastatic CRPC (mCRPC) both before and after taxane-based chemotherapy. The purpose of this study is to report the initial clinical experience obtained from mCRPC patients managed on AA at Rigshospitalet, Denmark, and compare the results with phase III trial outcomes.

MATERIAL AND METHODS

Single-centre, retrospective study including consecutive patients managed on AA for more than 2-year period. Treatment consisted of 1,000mg AA and 5mg prednisone twice daily. Outcomes of interest were prostate-specific antigen (PSA) response, clinical and radiological progression, and overall survival.

RESULTS

A total of 73 consecutive patients with mCRPC undergoing treatment with AA between November 2012 and October 2014 were included. Median follow-up was 9.9 (0.9-23.4) months. PSA decline>50% was found in 39% of the patients. Time to biochemical and radiological progression was 3.5 and 4.9 months, respectively. Overall survival was 13.2 months (95% CI: 9.0-17.4).

CONCLUSION

Our initial experience with AA in the routine management of patients with mCRPC demonstrates an efficacy-effectiveness gap compared with clinical trial. Except for PSA response (>50% decline) in patients managed with AA, postchemotherapy results were inferior to phase III studies. This is most likely because of patient selection, which is a typical weakness when transferring results from phase III trials into clinical practice.

Targeting the adrenal gland in castration-resistant prostate cancer: a case for orteronel, a selective CYP-17 17,20-lyase inhibitor

Androgen and the androgen receptor (AR) pathway remain the key targets for emerging new therapies against castration-resistant prostate cancer (CRPC). Adrenal androgens and intratumoral testosterone production appear to be sufficient to activate AR in the castration-resistant setting. This process re-engages AR and allows it to continue to be the primary target responsible for prostate cancer progression. Adrenal androgen production can be blocked by inhibiting cytochrome P450 17α-hydroxylase/17,20-lyase (CYP17), a key enzyme for androgen synthesis in adrenal glands and peripheral tissues. Therapeutic CYP17 inhibition by ketoconazole or by the recently approved adrenal inhibitor abiraterone acetate is the only available choice to target this pathway in CRPC. A new CYP17 inhibitor, with more selective inhibition of 17,20-lyase over 17α-hydroxylase, orteronel (TAK-700), is currently undergoing phase III clinical trials in pre- and postchemotherapy CRPC. In a completed phase II trial in CRPC patients, orteronel demonstrated its efficacy by lowering the levels of circulating androgens, reducing prostate-specific antigen (PSA) levels, and decreasing the levels of circulating tumor cells. Ongoing studies evaluating orteronel in CRPC will further define its safety and role in the management of this disease.

Abiraterone acetate in castration-resistant prostate cancer

The palliative goal of the treatment of metastatic prostate cancer is to prolong survival and decrease cancer-related complications. Androgen ablation therapy is widely accepted as the initial treatment of choice; when the disease becomes resistant to castration-resistant prostate cancer (CRPC), docetaxel-based chemotherapy aids in prolonging overall survival and controlling disease-related symptoms. Until a few years ago, no drug had showed efficacy in docetaxel-resistant patients. Recently, cabazitaxel, a taxane family compound, has been shown to help prolong survival in patients previously treated with docetaxel, even if a high grade of myelotoxicity has been reported. Moreover, a better understanding of the biology of CRPC has demonstrated that prostate cancer proliferation is largely mediated through the androgen receptor, which could be reactivated by androgens produced by the adrenal glands. Abiraterone acetate is an orally active acetate salt of the steroidal compound abiraterone with antiandrogen activity. Abiraterone inhibits the enzymatic activity of steroid 17α-monooxygenase, a member of the cytochrome P450 family that catalyzes the 17α-hydroxylation of steroid intermediates involved in testosterone synthesis from the adrenal glands. This review focuses on abiraterone acetate, the first compound that, through the inhibition of adrenal gland production of testosterone, increases the overall survival in CRPC patients. The role of possible predictive biomarkers and future perspectives are also discussed.

Novel agents for the management of castration-resistant prostate cancer

PURPOSE OF REVIEW

Over the past 2 years, four new treatments have entered the treatment armamentarium for patients with castration-resistant prostate cancer (CRPC). Although these novel agents differ in their mechanism of action, they all face the same challenges: patient selection, timing of therapy and the cost/benefit of their use. In this review, we will discuss their development and implications when selecting treatment options for CRPC patients.

RECENT FINDINGS

Over the past few years, a better understanding of the biology of CRPC has allowed us to develop rational therapies that have resulted in an improvement in the outcome of prostate cancer patients. Immunotherapy has entered the field and despite its limitations and challenges is here to stay. A better understanding of the long-term complications of androgen deprivation has changed the initial approach to most patients with advanced disease, and bone health has become a major focus in their management. Understanding the importance of the androgen receptor and other ligands has led to a dramatic paradigm shift in the treatment of patients with metastatic disease in which the androgen receptor becomes a central therapeutic target in the disease. Specific adrenal inhibitors and engineered super androgen receptor inhibitors have become the most promising agents in the disease. Similarly, chemotherapy has demonstrated clinical benefit and is now a standard of care in docetaxel-refractory patients.

SUMMARY

The management of CRPC patients continues to evolve. Novel treatments recently approved by the US Food and Drug Administration have significantly impacted the outcome of CRPC. With the economic impact of their use, selecting the right patient, defining the appropriate timing and sequence of therapy have become critical facts that need to be followed when defining the contemporary treatment options for men with CRPC.

Testosterone in prostate cancer: the Bethesda consensus

OBJECTIVE

• Androgen stimulation of prostate cancer (PCa) cells has been extensively studied. The increasing trend of using serum testosterone as an absolute surrogate for castration state means that the diagnostic measurement of testosterone and the values potentially influencing prognosis must be better understood. This is especially important when PCa progresses from an endocrine to an intracrine status.

PATIENTS AND METHODS

• We performed a literature review using the MEDLINE database for publications on: (i) hormonal changes with androgen deprivation therapy (ADT); (ii) monitoring hormonal therapy with testosterone measurement; (iii) the efficacy of intermittent androgen deprivation (IAD) compared with continuous androgen deprivation; (iv) the underlying mechanisms of castration-resistance; and (v) novel treatments for castration-resistant PCa (CRPCa).

RESULTS

• The optimum serum castration levels to be achieved with ADT are still debated. Recently, the 50 ng/dL threshold has been questioned because of reports indicating worse outcomes when levels between 20 and 50 ng/dL were studied. Instead, a 20 ng/dL threshold for serum testosterone after ADT in patients with advanced prostate cancer was recommended.

CONCLUSION

• Understanding the mechanisms of androgen biosynthesis relating to PCa as well as prognostic implications might achieve a consensus regarding the role of ADT for both the androgen-sensitive and -insensitive disease state.

Castration-resistant prostate cancer: many treatments, many options, many challenges ahead

Although the long natural history of prostate cancer presents challenges in the development of novel therapeutics, major contributions have been observed recently. A better understanding of the long-term complications of androgen deprivation has changed the initial approach to most patients with advanced disease. Specifically, recognition of the limitations of prostate-specific antigen has driven the pursuit of new tools capable of becoming true surrogates for disease outcome. Understanding the molecular biology of castration-resistant prostate cancer (CRPC) has led to a dramatic paradigm shift in the treatment of patients with metastatic disease where the androgen receptor becomes a central therapeutic target. Specific adrenal inhibitors and engineered super androgen receptor inhibitors have become the most promising agents in the disease. Novel immune therapies have been shown to improve survival in selected patients with castration-resistant disease despite the inability to impact traditional markers of response. Similarly, agents such as cabazitaxel and abiraterone acetate have demonstrated clinical benefit are now a standard of care in docetaxel-refractory metastatic CRPC patients. All these changes have occurred in a relatively short period and are likely to change the prostate cancer treatment paradigm. This review summarizes the current management of CRPC and discusses potential future directions.

New hormonal therapies for castration-resistant prostate cancer

Continued activation of the androgen receptor (AR) axis despite castration remains a critical force in the development of castration-resistant prostate cancer (CRPC). Therapeutic strategies designed to more effectively ablate tumoral androgen activity are required to improve clinical efficacy and prevent disease progression. Tumor-based alterations in expression and activity of the AR and in steroidogenic pathways mediating ligand generation facilitate the development of CRPC. This article reviews AR and ligand-dependent mechanisms underlying CRPC progression and the status of novel hormonal therapies targeting the AR axis that are currently in clinical and preclinical development.

Abiraterone acetate, a novel adrenal inhibitor in metastatic castration-resistant prostate cancer

The androgen receptor remains the key player in patients with castration-resistant prostate cancer (CRPC). Available agents capable of blocking early adrenal androgen production have limited activity and can lead to significant toxicities. Abiraterone acetate, a pregnenolone analog, is a small molecule that irreversibly inhibits CYP17, a rate-limiting enzyme in androgen biosynthesis. Several clinical trials have demonstrated the safety and efficacy of this compound in men with metastatic CRPC. Recently, a randomized phase 3 trial evaluating abiraterone acetate in docetaxel-refractory CRPC patients demonstrated a survival improvement over placebo-treated patients (14.8 vs 10.9 months; HR 0.646; P < 0.0001). A similar trial in the pre-chemotherapy setting has completed accrual and is undergoing analysis. Here we review the rationale and clinical development of abiraterone acetate in men with CRPC.

Castration-resistant prostate cancer: targeting androgen metabolic pathways in recurrent disease

Emerging evidence suggests that despite testicular androgen ablation, residual androgens, likely of adrenal--though potentially of prostatic--origin, play a critical role in the progression of prostate cancer to recurrent "castration-resistant" disease. Thus, a reassessment of the concept of total androgen deprivation is warranted. Current treatment strategies may not only lack optimal efficacy, but may actually contribute to the selection of neoplastic clones adapted to exist and proliferate in a low (but not zero) androgen environment. Moreover, the adequacy of androgen receptor (AR) pathway inhibition cannot be surmised from serum or plasma androgen levels, but must be ascertained at the tissue and molecular level prior to drawing conclusions regarding clinical efficacy or failure. Recent studies by our group and others indicate that prostate cancers undergo an adaptive response to castration that is associated with the up-regulation of transcripts encoding enzymes involved in the biosynthesis of androgens. Targeting these metabolic enzymes either individually or using combinations of agents to inhibit testicular, adrenal, and intracrine sources may provide enhanced clinical responses in the setting of both localized and metastatic disease.

Activators of the farnesoid X receptor negatively regulate androgen glucuronidation in human prostate cancer LNCAP cells

Androgens are major regulators of prostate cell growth and physiology. In the human prostate, androgens are inactivated in the form of hydrophilic glucuronide conjugates. These metabolites are formed by the two human UGT2B15 [UGT (UDP-glucuronosyltransferase) 2B15] and UGT2B17 enzymes. The FXR (farnesoid X receptor) is a bile acid sensor controlling hepatic and/or intestinal cholesterol, lipid and glucose metabolism. In the present study, we report the expression of FXR in normal and cancer prostate epithelial cells, and we demonstrate that its activation by chenodeoxycholic acid or GW4064 negatively interferes with the levels of UGT2B15 and UGT2B17 mRNA and protein in prostate cancer LNCaP cells. FXR activation also causes a drastic reduction of androgen glucuronidation in these cells. These results point out activators of FXR as negative regulators of androgen-conjugating UGT expression in the prostate. Finally, the androgen metabolite androsterone, which is also an activator of FXR, dose-dependently reduces the glucuronidation of androgens catalysed by UGT2B15 and UGT2B17 in an FXR-dependent manner in LNCaP cells. In conclusion, the present study identifies for the first time the activators of FXR as important regulators of androgen metabolism in human prostate cancer cells.

DHT and testosterone, but not DHEA or E2, differentially modulate IGF-I, IGFBP-2, and IGFBP-3 in human prostatic stromal cells

Prostate cancer is one of the four most common cancers in the United States, affecting one of six men. Increased serum levels of androgens and IGF-I are associated with an augmented risk of prostate cancer. Dihydrotestosterone (DHT) and testosterone (T) stimulate prostate cancer cell growth, development, and function, whereas the effects of DHT and T in prostate stromal cells, and of dehydroepiandrosterone (DHEA) in prostate cancer or stromal cells, are uncertain. We investigated the actions of DHT, T, DHEA, and estradiol (E2) on insulin-like growth factor (IGF)-I, IGF-II, IGF-I receptor (R), IGF-binding protein (IGFBP)-2, IGFBP-3, and IGFBP-5 in primary cultures of human prostatic stromal cells by assessing cell proliferation, mRNA expression, and protein secretion by MTT growth assay, quantitative real-time PCR, and ELISA, respectively. DHT and T each increased IGF-I (7-fold) and decreased IGFBP-3 (2-fold) mRNA expression and protein secretion in a dose- and time-dependent manner and increased IGFBP-2 (2-fold) mRNA in a dose- and time-dependent manner. DHEA and E2 did not significantly alter these measures. Flutamide abolished the DHT-modulated increases in IGF-I and IGFBP-2, suggesting that the influences of DHT and T on these measures were androgen receptor mediated. None of the four steroids significantly affected IGF-IR, IGF-II, or IGFBP-5 mRNA levels or stromal cell proliferation. The effects of DHT on IGF-I, IGFBP-2, and IGFBP-3 were more pronounced in stromal cultures that did not express desmin. These data suggest that DHT and T promote prostate growth partly via modulation of the stromal cell IGF axis, with potential paracrine effects on prostate epithelial cells.

Stepping-stones to the further advancement of androgen-deprivation therapy for prostate cancer

Androgen-deprivation therapy has remained the critical therapeutic option for patients with advanced prostate cancer for over 60 years. Patients with poorly differentiated prostate cancer have low dihydrotestosterone levels in the prostate. After androgen-deprivation therapy, dihydrotestosterone levels in the prostate remain at approximately 25% of the level measured before therapy. The addition of a nonsteroidal anti-androgen to luteinizing hormone-releasing hormone analog or surgical castration significantly reduces the risk of all causes of death by 8%, which translates into a small, but significant, improvement in the 5-year survival of 2.9% over castration alone. The biologically aggressive prostate cancer cells may have an androgen receptor with heightened sensitivity to low dihydrotestosterone levels from the early stage of androgen-dependent disease. It is necessary to consider the androgen environment and the status of the androgen receptor in the prostate in order to improve the clinical efficacy of androgen-deprivation therapy and the quality of life of patients.

The influence of androgen deprivation therapy on dihydrotestosterone levels in the prostatic tissue of patients with prostate cancer

PURPOSE

The influence of androgen deprivation therapy on dihydrotestosterone levels in the prostatic tissue is not clearly known. Changes in dihydrotestosterone levels in the prostatic tissue during androgen deprivation therapy in the same patients have not been reported. We analyzed dihydrotestosterone levels in prostatic tissue before and after androgen deprivation therapy.

EXPERIMENTAL DESIGN

A total of 103 patients who were suspected of having prostate cancer underwent prostatic biopsy. Sixty-nine patients were diagnosed as having prostate cancer whereas the remaining 34 were negative. Serum samples were collected before biopsy or prostatectomy. Dihydrotestosterone levels in prostatic tissue and serum were analyzed using liquid chromatography/electrospray ionization-mass spectrometry after polar derivatization. In 30 of the patients with prostate cancer, dihydrotestosterone levels in prostatic tissue were determined by performing rebiopsy or with prostate tissues excised after 6 months on androgen deprivation therapy with castration and flutamide.

RESULTS

Dihydrotestosterone levels in prostate tissue after androgen deprivation therapy remained at approximately 25% of the amount measured before androgen deprivation therapy. Dihydrotestosterone levels in serum decreased to approximately 7.5% after androgen deprivation therapy. The level of dihydrotestosterone in prostatic tissue before androgen deprivation therapy was not correlated with the serum level of testosterone. Serum levels of adrenal androgens were reduced to approximately 60% after androgen deprivation therapy.

CONCLUSIONS

The source of dihydrotestosterone in prostatic tissue after androgen deprivation therapy involves intracrine production within the prostate, converting adrenal androgens to dihydrotestosterone. Dihydrotestosterone still remaining in prostate tissue after androgen deprivation therapy may require new therapies such as treatment with a combination of 5alpha-reductase inhibitors and antiandrogens, as well as castration.

Comparative effects of DHEA vs. testosterone, dihydrotestosterone, and estradiol on proliferation and gene expression in human LNCaP prostate cancer cells

Serum levels of the adrenal androgen dehydroepiandrosterone (DHEA) peak in men and women in the third decade of life and decrease progressively with age. Increasing numbers of middle-aged and older individuals consume over-the-counter preparations of DHEA, hoping it will retard aging by increasing muscle and bone mass and strength, decreasing fat, and improving immunologic and neurobehavioral functions. Because DHEA can serve as a precursor to more potent androgens and estrogens, like testosterone (T), dihydrotestosterone (DHT), and 17beta-estradiol (E2), supplemental DHEA use may pose a cancer risk in patients with nascent or occult prostate cancer. The steroid-responsive human LNCaP prostate cancer cells, containing a functional but mutated androgen receptor (AR), were used to compare effects of DHEA with those of T, DHT, and E2 on cell proliferation and protein and/or gene expression of AR, prostate-specific antigen (PSA), IGF-I, IGF-I receptor (IGF-IR), IGF-II, IGF-binding proteins-2, -3, and -5, (IGFBPs-2, -3, and -5), and estrogen receptor-beta (ERbeta). Cell proliferation assays revealed significant stimulation by all four steroids. DHEA- and E2-induced responses were similar but delayed and reduced compared with that of T and DHT. All four hormones increased gene and/or protein expression of PSA, IGF-IR, IGF-I, and IGFBP-2 and decreased that of AR, ERbeta, IGF-II, and IGFBP-3. There were no significant effects of hormone treatment on IGFBP-5 mRNA. DHEA and E2 responses were similar, and distinct from those of DHT and T, in time- and dose-dependent studies. Further studies of the mechanisms of DHEA effects on prostate cancer epithelial cells of varying AR status, as well as on prostate stromal cells, will be required to discern the implications of DHEA supplementation on prostatic health.

Mechanisms of the development of androgen independence in prostate cancer

The effectiveness of androgen ablation in the management of advanced prostate cancer is of limited duration, with the median length of response being only 18-24 months. The transition of the prostate cancer cell to an androgen independent phenotype is a complex process that involves selection and outgrowth of pre-existing clones of androgen-independent cells (clonal selection) as well as adaptive up-regulation of genes that help the cancer cells survive and grow after androgen ablation (adaptation). These two mechanisms share an important pre-requisite characteristic: prostate cancers are heterogeneous tumours comprised of various subpopulations of cells that respond differently to androgen withdrawal therapy. This tumour heterogeneity may reflect either a multifocal origin, adaptation to environmental stimuli, and/or genetic instability of the initial cancer. This review will reexamine the different mechanisms that enable prostate cancer cells to proliferate in an androgen depleted environment.

Mechanisms of the development of androgen independence in prostate cancer

The effectiveness of androgen ablation in the management of advanced prostate cancer is of limited duration, with the median length of response being only 18-24 months. The transition of the prostate cancer cell to an androgen independent phenotype is a complex process that involves selection and outgrowth of pre-existing clones of androgen-independent cells (clonal selection) as well as adaptive up-regulation of genes that help the cancer cells survive and grow after androgen ablation (adaptation). These two mechanisms share an important pre-requisite characteristic: prostate cancers are heterogeneous tumours comprised of various subpopulations of cells that respond differently to androgen withdrawal therapy. This tumour heterogeneity may reflect either a multifocal origin, adaptation to environmental stimuli, and/or genetic instability of the initial cancer. This review will reexamine the different mechanisms that enable prostate cancer cells to proliferate in an androgen depleted environment.

NE-10 neuroendocrine cancer promotes the LNCaP xenograft growth in castrated mice

Increases in neuroendocrine (NE) cells and their secretory products are closely correlated with tumor progression and androgen-independent prostate cancer. However, the mechanisms by which NE cells influence prostate cancer growth and progression, especially after androgen ablation therapy, are poorly understood. To investigate the role of NE cells on prostate cancer growth, LNCaP xenograft tumors were implanted into nude mice. After the LNCaP tumors were established, the NE mouse prostate allograft (NE-10) was implanted on the opposite flank of these nude mice to test whether NE tumor-derived systemic factors can influence LNCaP growth. Mice bearing LNCaP tumors with or without NE allografts were castrated 2 weeks after NE tumor inoculation, and changes in LNCaP tumor growth rate and gene expression were investigated. After castration, LNCaP tumor growth decreased in mice bearing LNCaP tumors alone, and this was accompanied by a loss of nuclear androgen receptor (AR) localization. In contrast, in castrated mice bearing both LNCaP and NE-10 tumors, LNCaP tumors continued to grow, had increased levels of nuclear AR, and secreted prostate-specific antigen. Therefore, in the absence of testicular androgens, NE secretions were sufficient to maintain LNCaP cell growth and androgen-regulated gene expression in vivo. Furthermore, in vitro experiments showed that NE secretions combined with low levels of androgens activated the AR, an effect that was blocked by the antiandrogen bicalutamide. Because an increase in AR level has been reported to be sufficient to account for hormone refractory prostate cancers, the NE cell population ability to increase AR level/activity can be another mechanism that allows prostate cancer to escape androgen ablation therapy.

Interlaboratory comparison of four in vitro assays for assessing androgenic and antiandrogenic activity of environmental chemicals

We evaluated and compared four in vitro assays to detect androgen agonists and antagonists in an international interlaboratory study. Laboratory 1 used a cell proliferation assay (assay 1) with human mammary carcinoma cells stably transfected with human androgen receptor. The other laboratories used reporter gene assays, two based on stably transfected human prostate carcinoma cells (assay 2) or human mammary carcinoma cells (assay 4), and the third based on transient transfection of Chinese hamster ovary cells (assay 3). Four laboratories received four coded compounds and two controls: two steroidal androgens, two antiandrogens, an androgenic control, 5alpha-dihydrotestosterone (DHT), and an antiandrogenic control, bicalutamide (ICI 176,334). All laboratories correctly detected the androgenic activity of 4-androsten-3,17-dione and 17alpha-methyltestosterone. For both compounds, the calculated androgenic potencies relative to the positive control (RAPs) remained within one order of magnitude. However, laboratory 3 calculated a 50-fold higher RAP for 4-androsten-3,17-dione. All assays detected and quantified the antiandrogenic effect of vinclozolin [median inhibitory concentration (IC50) values ranging from 1.1 times symbol 10(-7) M to 4.7 times symbol 10(-7) M]. In assays 2 and 3, vinclozolin showed partial androgenic activity at the highest concentrations tested. For vinclozolin, calculated antiandrogenic potencies relative to bicalutamide (RAAPs) differed no more than a factor of 10, and IC50 values matched those of bicalutamide. Similarly, we found antiandrogenic activity for tris-(4-chlorophenyl)methanol. RAAP values were between 0.086 and 0.37. Three assays showed cytotoxicity for this compound at or above 1 times symbol 10(-5) M. In summary, all assays proved sensitive screening tools to detect and quantify androgen receptor-mediated androgenic and antiandrogenic effects of these chemicals accurately, with coefficients of variation between 8 and 90%.

Evidence that dehydroepiandrosterone, DHEA, directly inhibits GnRH gene expression in GT1-7 hypothalamic neurons

Dehydroepiandrosterone (DHEA) has been reported to have diverse effects on overall physiology, although its mechanism of action and specific receptor are not yet known. We have used the immortalized, clonal GT1-7 hypothalamic neurons to study DHEA effects on gonadotropin-releasing hormone (GnRH) gene expression. DHEA (10(-4) M) downregulates GnRH transcription by 39, 70 and 83% at 24, 36, and 48 h, respectively, while DHEA-sulphate had no effect. Hydroxyflutamide a specific androgen receptor (AR) antagonist, and cyproterone acetate or trilostane, both inhibitors of 3 beta-hydroxysteroid dehydrogenase/delta 4,5 isomerase, the rate-limiting enzyme for the conversion of DHEA to sex steroids, did not affect the ability of DHEA to downregulate GnRH gene expression. We found that GT1-7 cells did not express aromatase, thereby precluding conversion to estrogen. Analysis of [(14)C] DHEA metabolism by thin layer chromatography indicates that the main metabolites produced are 7 alpha- and 7 beta-hydroxy DHEA, and 7-oxo DHEA, although these steroids were not able to repress GnRH gene expression alone. Cell viability studies indicated that the transcriptional repression observed is not due to GT1-7 cell death. Interestingly, SV40 T-antigen mRNA levels, under the control of 2.3 kb of the rat GnRH gene 5' regulatory region, are also repressed by DHEA. Our studies indicate that DHEA has direct effects on GnRH transcription that appear to be unique from those observed after conversion to other steroidogenic compounds.

Evaluation of androgenic bioactivity in human serum by recombinant cell line: preliminary results

Besides the measurement of circulating conjugated metabolites of dihydrotestosterone (DHT), which reflects androgenic activity, only one assay to measure androgenic bioactivity in human serum has been proposed thus far. This recombinant bioassay is based on the androgen-dependent interaction between the LBD and NT domains of AR fused to the Gal 4 DNA-binding domain, but its construction is highly complex. We have developed a mammalian cell (CHO 515) bioassay that measures total androgen bioactivity in human serum. The AR-deficient Chinese hamster ovary (CHO) cells were stably transfected with pSG5-puro-hAR and pMMTV-neo-Luc. After selection with puromycin and neomycin, five highly inducible clones were isolated and one was selected. The expression of human androgen receptor (hAR) was confirmed by Western blot and steroid-binding assays on the whole cells. The transcriptional activity of the clone was measured after 24 h of incubation with increasing concentrations of various androgenic and non-androgenic steroid compounds in a 96-well plate. The EC50s for each tested androgenic steroid compound were 4 x 10(-11) M, 1.5 x 10(-11) M, 1 x 10(-9) M, 2 x 10(-10) M, 3 x 10(-10) M for testosterone, DHT, dehydroepiandrosterone (DHEA), delta5-androstenediol, and delta4-androstenedione, respectively. In the physiological concentrations of the non-androgenic steroids, estradiol, cortisol, aldosterone, and progesterone, no interference was noted with the AR transactivation level. Evaluation of androgenic bioactivity in human serum was performed by incubation of CHO 515 cells with 100 microl of patient serum, diluted at 1/100 = 1% in DMEM-F12 without phenol red. The sensitivity of the assay was < 0.3 ng/ml. The mean androgenic bioactivity expressed in testosterone equivalents was 0.6 +/- 0.2 ng/ml in normal prepubertal boys, and 12.4 +/- 2 and 1.7 +/- 0.1 ng/ml in normal pubertal boys and girls, respectively. In conclusion, this new recombinant cell bioassay is today the only assay that takes into account testosterone, DHT, DHEA, delta5-androstenediol, and delta4-androstenedione. It should be of particular use in male children with cryptorchidism, delayed puberty or hypogonadotrophic hypogonadism, i.e., in pediatric patients with low androgen levels.