Androgen receptor: a key molecule in the progression of prostate cancer to hormone independence

ACTR/AIB1/SRC-3 and androgen receptor control prostate cancer cell proliferation and tumor growth through direct control of cell cycle genes

BACKGROUND

Co-factor ACTR is frequently overexpressed and/or amplified in multiple types of tumors. The mechanism of its function in prostate cancer (CaP) is still unclear.

METHODS

The effects of ACTR and androgen receptor (AR) depletion on cell proliferation and gene expression and their functions were analyzed in a panel of androgen-dependent and -independent CaP cells and CWR22 xenograft.

RESULTS

ACTR and AR, but not TIF2, are required for proliferation of androgen-dependent and -independent cells, and for tumor growth. While AR depletion inhibited the expression of cyclin D1, cyclin B, and cdc2, ACTR depletion reduced the expression of cyclin E and cdk2. In response to serum stimulation, AR and ACTR are recruited to the corresponding target gene promoters to activate their expression in androgen-independent manner.

CONCLUSION

These findings suggest that AR and ACTR may play important roles in androgen ablation resistance by controlling key cell cycle gene expression.

Molecular markers in the diagnosis of prostate cancer

The genetic alterations leading to prostate cancer are gradually being discovered. A wide variety of genes have been associated with prostate cancer development as well as tumor progression. Knowledge of gene polymorphisms associated with disease aid in the understanding of important pathways involved in this process and may result in the near future in clinical applications. Urinary molecular markers will soon be available to aid in the decision of repeat prostate biopsies. Recent findings suggest the importance of androgen signaling in disease development and progression. The further understanding of interaction of inflammation, diet, and genetic predisposition will improve risk stratification in the near future.

Involvement of arginine methyltransferase CARM1 in androgen receptor function and prostate cancer cell viability

BACKGROUND

Androgen receptor (AR) may play a role in prostate cancer progression. Coactivator-associated arginine methyltransferase (CARM1) catalyzes methylation of histone H3 at Arg-17.

METHODS

Immunohistochemistry of CARM1 was performed on primary prostate cancer specimens. CARM1 recruitment and histone methylation was analyzed by chromatin immunoprecipitation. The effect of CARM1 overexpression or CARM1 knockdown was assessed on reporter assays, cell proliferation, apoptosis, and endogenous androgen target gene expression.

RESULTS

CARM1 expression was increased in the nucleus of castration-resistant, but not androgen-stimulated prostate cancer. Androgen stimulation led to CARM1 recruitment and methylation of histone H3 at androgen responsive enhancers. Overexpression of CARM1 stimulated and CARM1 knockdown inhibited AR reporter activity. CARM1 knockdown inhibited cell proliferation and induced apoptosis. CARM1 knockdown inhibited androgen-dependent prostate specific antigen (PSA) and hK2 mRNA expression.

CONCLUSIONS

CARM1 is essential for AR function and may play a role in prostate cancer progression. CARM1 may represent a novel therapeutic target in prostate cancer.

Targeting and killing of prostate cancer cells using lentiviral constructs containing a sequence recognized by translation factor eIF4E and a prostate-specific promoter

To develop a gene therapy that would selectively kill prostate cancer cells while sparing normal cells, we have constructed lentiviral vectors that contain a therapeutic gene with a short DNA sequence in the 5'-untranslated region (UTR) that is recognized by the translation initiation factor, eIF4E, which is often overexpressed in malignant cells. Infection of cancer (LNCaP, PC-3M, DU145, and MCF-7 cells) and noncancer cell lines (BPH-1, 267-B1, Plat-E, and Huvec-c cells) with lentivirus having a CMV-promoter and EGFP reporter resulted in high levels of EGFP expression in all cells, whereas, inclusion of the eIF4E UTR recognition sequence restricted high expression to cancer cells and Plat-E cells, which also express substantial levels of eIF4E. Infection of the cells with lentiviral vectors having this UTR in front of the HSV thymidine kinase suicide gene resulted in differential sensitivity to the killing effects of ganciclovir, with at least 100-fold more drug required to kill noncancer cells than cancer cells. Furthermore, in experiments where the CMV promoter was replaced by the prostate-specific ARR(2)PB promoter, the killing effects of ganciclovir were restricted to prostate cancer cells and not seen in nonprostate cancer cells. Our results indicate that combined translational regulation, by incorporation of an eIF4E-UTR recognition sequence into a therapeutic gene, together with transcriptional regulation with a prostate-specific promoter, may provide a means to selectively destroy prostate cancer cells while sparing normal prostate cells.

New Insights into Prostate Cancer Biology

Prostate cancer is common, biologically heterogeneous, and protean in its clinical manifestations. Through the use and analysis of isogenic cell lines, xeno-grafts, transgenic mice, and human tumors, one begins to deconvolute the precise biologic mechanisms that combine to create the native complexity and heterogeneity of this disease. In this article, the authors have underscored compelling recent discoveries in prostate cancer so as to provide the reader with molecular paradigms with which to interpret future insights into its biology. Although it was inevitably necessary to omit a significant amount of important research in prostate cancer, the work discussed here is exemplary of current prostate cancer research. Looking forward, it is hoped that the collective work of mapping genetic and biologic interactions among key regulators of prostate epithelial cells, epithelial-stromal interactions, host immune system, and host genetics will eventually result in a comprehensive understanding of prostate cancer. Although it is likely that the molecular characteristics of an individual's prostate cancer will be analyzed using limited molecular tools in the near future, eventual application of genomic technologies and nanotechnology offers the promise of robust future characterization. Such a characterization is likely to be required to maximize our ability to optimize and individualize preventive and treatment strategies.

Positive selection in the evolution of cancer

We hypothesize that forms of antagonistic coevolution have forged strong links between positive selection at the molecular level and increased cancer risk. By this hypothesis, evolutionary conflict between males and females, mothers and foetuses, hosts and parasites, and other parties with divergent fitness interests has led to rapid evolution of genetic systems involved in control over fertilization and cellular resources. The genes involved in such systems promote cancer risk as a secondary effect of their roles in antagonistic coevolution, which generates evolutionary disequilibrium and maladaptation. Evidence from two sources: (1) studies on specific genes, including SPANX cancer/testis antigen genes, several Y-linked genes, the pem homebox gene, centromeric histone genes, the breast cancer gene BRCA1, the angiogenesis gene ANG, cadherin genes, cytochrome P450 genes, and viral oncogenes; and (2) large-scale database studies of selection on different functional categories of genes, supports our hypothesis. These results have important implications for understanding the evolutionary underpinnings of cancer and the dynamics of antagonistically-coevolving molecular systems.

Phase II study evaluating oral triamcinolone in patients with androgen-independent prostate cancer

OBJECTIVES

To assess the effect of triamcinolone administration on the serum prostate-specific antigen (PSA) response and the time to progression in patients with androgen-independent prostate cancer (AIPC).

METHODS

Patients with AIPC were prospectively treated with oral triamcinolone 4 mg twice daily, and their serum PSA and cortisol levels were measured monthly. Patients with greater than 25% increases in serum PSA from baseline were considered to have progressive disease and were removed from the study. Those patients who had a decrease in serum PSA levels or stable disease continued in the study until disease progression. Bone scans were obtained every 12 weeks and at progression.

RESULTS

Twenty-four patients with AIPC were treated from November 2002 to June 2004. A partial response with a more than 50% decrease in serum PSA level was seen in 29%. Another 21% achieved stable disease. No statistically significant difference was found in the time to progression in the partial responders and patients with stable disease. The median time to progression in both groups was 7.5 months. Treatment was well tolerated without any grade 3 or 4 toxicity.

CONCLUSIONS

Oral triamcinolone was well tolerated by patients with AIPC, with 50% of the patients exhibiting a good response to therapy in terms of serum PSA level and time to progression.

[Pharmacological potential of phytoestrogens in the treatment of prostate cancer]

INTRODUCTION

Phytoestrogenes are plant-derived compounds that have been shown to exert an antiproliferative potential on prostate cancer cells, although the exact mechanisms are still unclear. In prostate cancer cells proliferation is regulated by modulation of the IGF-1 receptor (IGF-R-1) by the androgen receptor (AR) and its co-activator prostate derived Ets factor (PDEF). Phytooestrogenes interact with these mechanisms as demonstrated exemplarily in the presented study with the isoflavone tectorigenin derived from Belamcanda chinensis.

MATERIAL AND METHODS

Cultured androgen-sensitive LNCaP prostate cancer cells were treated with tectorigenin of 100 microM for 24 hours. The mRNA-expression of AR, PSA, PDEF, hTERT, TIMP-3 and IGF-R-1 were quantified by real-time RT-PCR. Furthermore, the expression or activity of PSA, telomerase and IGF-R-1 was measured on the protein level. In addition, we investigated in nude mice the influence of a diet of extracts of Belamcanda chinensis on the growth of subcutaneously injected LNCaP cells versus a control group of animals fed with a soy-free diet.

RESULTS

In cultured LNCaP cells treatment with tectorigenin resulted in a significant down-regulation of the gene expression of AR, PDEF, PSA, IGF-R-1 and hTERT. On the protein level PSA secretion and the activity of telomerase and IGF-R-1 expression was also decreased. The gene expression of TIMP-3 was distinctly up-regulated by tectorigenin. Nude mice fed with Belamcanda chinensis extract showed a significantly decreased incidence and tumor growth compared to controls.

CONCLUSIONS

Tectorigenin shows an inhibition of the IGF-1-R modulated cell proliferation of PCa-Cells, due to modulation of the activity the co-activator PDEF independently from the AR. Furthermore, tectorigenin has pro-apoptotic effects and decreases tissue invasion by up-regulation of TIMP-3. Therefore, phytooestrogenes are an interesting option in the therapy of prostate especially advanced prostate cancer.

The expression of transcription factor activating transcription factor 3 in the human prostate and its regulation by androgen in prostate cancer

PURPOSE

ATF3 is a member of the basic leucine zipper/cyclic adenosine monophosphate responsive element binding protein family of transcription factors. There is overwhelming evidence that it is a stress inducible factor acting in a signal-type and cell-type dependent manner, and it is involved in cell proliferation and survival. We found that ATF3 was differently expressed in an in vitro prostate cancer tumor progression model and we investigated the possible role of ATF3 in prostate cancer.

MATERIALS AND METHODS

ATF3 up-regulation in vivo/in vitro and androgen regulation were assessed by immunohistochemistry and immunoblot analysis. Results after forced ATF3 transfection were evaluated by proliferation assay and cell cycle analysis.

RESULTS

Immunohistochemistry and immunoblot analysis revealed ATF3 up-regulation in prostate cancer in vitro and in vivo, and stimulation of expression by androgens. Antiandrogen treatment decreased ATF3 expression in androgen sensitive cells but acted as a stimulator in long-term androgen ablated cells representing a model for therapy refractory disease. Expression in tumors increased with higher Gleason scores and highest expression was observed in samples of therapy refractory tumor tissue. Forced ATF3 over expression in a prostate cancer cell line induced cell proliferation and accelerated cell cycle progression from G1 to S-phase.

CONCLUSIONS

These data provide new insight into the role of ATF3 in prostate cancer development and/or progression. They indicate that ATF3 is an androgen regulated gene that is highly expressed in prostate tumors and stimulating cell proliferation. It represents a possible target for prostate cancer therapy.

Androgen receptor mutation (T877A) promotes prostate cancer cell growth and cell survival

Alteration of the AR functions due to amplification, overexpression and somatic mutation of the AR itself or altered interaction of AR with other cell growth regulatory proteins, may contribute to a significant subset of advanced prostate cancer (CaP). Very little is known about the pathways impacted by AR dysfunctions, although CaP associated AR alterations suggest the biological role of the AR dysfunction in disease progression. Comparative evaluations of wild type (wt) AR and mutant (mt) ARs in appropriate experimental models should provide a better understanding of the functional impact of AR alterations in CaP. Here, we provide direct evidence showing cell growth/cell survival promoting effects of the widely studied CaP associated AR mutation (T877A). In contrast to Ad-wtAR or Ad-control infected LNCaP or LAPC4 cells, Ad-mtAR (T877A) infected LNCaP or LAPC4 cells continued to grow in the androgen-deprived medium and exhibited an androgen independent AR-transcription factor activity. Further, Ad-mtAR (T877A) infected LNCaP or LAPC4 cells exhibited enhanced cell growth in the presence of lower concentrations of the synthetic androgen, R1881. Of note, Ad-mtAR (T877A) infected LNCaP cells showed striking resistance to cell growth inhibition/apoptosis mediated by the wt p53. Taken together, these findings provide novel insights into the AR dysfunctions resulting from the T877A mutation and functionally similar AR alterations may provide selective cell growth/survival advantage for CaP progression. These observations have important implications for developing biology-based prognostic biomarkers and therapeutic strategies for CaP showing such AR dysfunctions.

The methyl-CpG-binding protein MECP2 is required for prostate cancer cell growth

The incidence of prostate cancer is increasing in western countries because of population aging. Prostate cancer begins as an androgen-dependent disease, but it can become androgen independent at a later stage or in tumors recurring after an antihormonal treatment. Although many genetic events have been described to be involved in androgen-dependent and/or -independent prostate cancer growth, little is known about the contribution of epigenetic events. Here we have examined the possibility that the methyl-CpG-binding protein MECP2 might play a role in controlling the growth of prostate cancer cells. Inhibition of MECP2 expression by stable short hairpin RNA stopped the growth of both normal and cancer human prostate cells. In addition, ectopic expression of the MECP2 conferred a growth advantage to human prostate cancer cells. More importantly, this expression allowed androgen-dependent cells to grow independently of androgen stimulation and to retain tumorigenic properties in androgen-depleted conditions. Analysis of signaling pathways showed that this effect is independent of androgen receptor signaling. Instead, MECP2 appears to act by maintaining a constant c-myc level during antihormonal treatment. We further show that MECP2-expressing cells possess a functional p53 pathway and are still responsive to chemotherapeutic drugs.

Molecular chaperones throughout the life cycle of the androgen receptor

Aberrant signaling by the androgen receptor contributes to the initiation and progression of prostate cancer. The involvement of molecular chaperones in the processes of folding, activation, trafficking, and transcriptional activity of the androgen receptor provide different points along the signaling axis where regulation of androgen receptor activity can be hijacked to provide growth signals for clonal selection in cancer progression. Evidence exists of abnormal chaperone expression that could contribute to the upregulation of AR activity in prostate tumors. Regardless of whether chaperones are involved in the causation of prostate carcinogenesis, molecular chaperones provide therapeutic targets for the treatment of prostate cancer.

Molecular modelling of the androgen receptor axis: rational basis for androgen receptor intervention in androgen-independent prostate cancer

Androgen depletion in combination with antiandrogenic agents is initially highly effective for treating prostate cancer, and is the recommended treatment for more advanced or higher-grade tumours. However, many tumours eventually become insensitive to androgens, even though the androgen receptor (AR) continues to be expressed. Computational chemistry combined with structural analysis of nuclear receptors and determination of binding affinities of natural and designed coregulators (coactivators and corepressors) provides the theoretical framework for the rational design of novel therapeutic agents directed at the AR. Adding alternative groups to various sites throughout the receptor can alter the conformation of the molecule and its functional binding with coactivators or corepressors. Possible molecules can be identified thoroughly and systematically using intelligent high-throughput screening and FASTrack chemistry (three-dimensional crystallography). Applying these techniques should eventually result in therapeutic agents for androgen-independent prostate cancer that can block binding of AR coactivators while simultaneously increasing binding of AR corepressors.

Regulator of G-protein signaling 2 (RGS2) inhibits androgen-independent activation of androgen receptor in prostate cancer cells

Hormones acting through G protein-coupled receptors (GPCRs) can cause androgen-independent activation of androgen receptor (AR) in prostate cancer cells. Regulators of G-protein signaling (RGS) proteins, through their GTPase activating protein (GAP) activities, inhibit GPCR-mediated signaling by inactivating G proteins. Here, we identified RGS2 as a gene specifically downregulated in androgen-independent prostate cancer cells. Expression of RGS2, but not other RGS proteins, abolished androgen-independent AR activity in androgen-independent LNCaP cells and CWR22Rv1 cells. In LNCaP cells, RGS2 inhibited G(q)-coupled GPCR signaling. Expression of exogenous wild-type RGS2, but not its GAP-deficient mutant, significantly reduced AR activation by constitutively activated G(q)Q209L mutant whereas silencing endogenous RGS2 by siRNA enhanced G(q)Q209L-stimulated AR activity. RGS2 had no effect on RGS-insensitive G(q)Q209L/G188S-induced AR activation. Furthermore, extracellular signal-regulated kinase 1/2 (ERK1/2) was found to be involved in RGS2-mediated regulation of androgen-independent AR activity. In addition, RGS2 functioned as a growth suppressor for androgen-independent LNCaP cells whereas androgen-sensitive LNCaP cells with RGS2 silencing had a growth advantage under steroid-reduced conditions. Finally, RGS2 expression level was significantly decreased in human prostate tumor specimens. Taken together, our results suggest RGS2 as a novel regulator of AR signaling and its repression may be an important step during prostate tumorigenesis and progression.

Vav3, a Rho GTPase guanine nucleotide exchange factor, increases during progression to androgen independence in prostate cancer cells and potentiates androgen receptor transcriptional activity

The progression of prostate cancer from androgen dependence to androgen independence is often accompanied by enhanced androgen receptor (AR) transcriptional activity. We observed a marked increase in the expression of Vav3, a Rho GTPase guanine nucleotide exchange factor (GEF), during the progression of human prostate cancer LNCaP cells to the androgen-independent derivative, LNCaP-R1. GEFs activate Rho family GTPases by promoting the exchange of GDP for GTP. Reporter gene assays showed that Vav3 potentiated AR transcriptional activity, and knock down of Vav3 resulted in decreased AR transactivation. Vav3 also increased androgen-induced levels of prostate-specific antigen mRNA. Furthermore, Vav3 enhanced AR activity at subnanomolar concentrations of androgen. This finding is particularly relevant because low androgen levels may be present in prostate tissue of patients undergoing androgen deprivation therapy. Enhancement of AR activity by Vav3 required amino terminal activation function 1 (AF1) of AR; however, Vav3 did not interact with AR or increase AR levels. Neither GEF function nor the C-terminal domains of Vav3 were required for Vav3-mediated enhancement of AR activity; however, the pleckstrin homology domain was obligatory. These data show that Vav3 levels rise during progression to androgen independence and support continued AR signaling (even under conditions of low androgen) by a novel GEF-independent cross-talk mechanism.

Testosterone and dihydrotestosterone tissue levels in recurrent prostate cancer

PURPOSE

Prostate cancer eventually recurs during androgen deprivation therapy despite castrate levels of serum androgens. Expression of androgen receptor and androgen receptor-regulated proteins suggests androgen receptor activation in recurrent prostate cancer. Many groups have pursued mechanisms of ligand-independent androgen receptor activation but we found high levels of testicular androgens in recurrent prostate cancer tissue using RIA.

EXPERIMENTAL DESIGNS

Prostate specimens from 36 men were procured preserving blood flow to prevent ischemia and cyropreserved immediately. Recurrent prostate cancer specimens from 18 men whose cancer recurred locally during androgen deprivation therapy and androgen-stimulated benign prostate specimens from 18 men receiving no hormonal treatments were studied. Tissue levels of testosterone and dihydrotestosterone were measured in each specimen using liquid chromatography/electrospray tandem mass spectrometry. Testosterone and dihydrotestosterone levels were compared with clinical variables and treatment received.

RESULTS

Testosterone levels were similar in recurrent prostate cancer (3.75 pmol/g tissue) and androgen-stimulated benign prostate (2.75 pmol/g tissue, Wilcoxon two-sided, P=0.30). Dihydrotestosterone levels decreased 91% in recurrent prostate cancer (1.25 pmol/g tissue) compared with androgen-stimulated benign prostate (13.7 pmol/g tissue; Wilcoxon two-sided, P < 0.0001) although dihydrotestosterone levels in most specimens of recurrent prostate cancer were sufficient for androgen receptor activation. Testosterone or dihydrotestosterone levels were not related to metastatic status, antiandrogen treatment, or survival (Wilcoxon rank sum, all P > 0.2).

CONCLUSIONS

Recurrent prostate cancer may develop the capacity to biosynthesize testicular androgens from adrenal androgens or cholesterol. This surprising finding suggests intracrine production of dihydrotestosterone and should be exploited for novel treatment of recurrent prostate cancer.

Validation of molecular targets in prostate cancer

As prostate cancer is not a single disease, it is important to identify the pivotal pathway in the patient being treated. The molecular environment is the site of current oncological research to define new therapeutic targets for hormone-refractory disease, offering the potential to eventually individualize treatment through stratification of pathways. Targets may be validated either phenotypically (e.g. androgen receptor, cadherin) or functionally (e.g. prostate cancer-specific genes). In addition, several other candidates are potentially suitable, while others await discovery. Important initial steps have been made in the search for prostate cancer stem cells; identifying stem cells and the stromal, hormonal, and other signalling molecules that influence their behaviour would have important implications for managing prostate cancer. Although individual therapeutic pathways might be ineffective in a particular molecular environment, combinations of approaches might be capable of producing synergistic effects. A multimodal approach thus might be the best solution. Determining where best to search for a molecular target, and validating whether the target is associated with a sufficiently aggressive malignant process to justify further study is difficult, but the potential benefits are enormous.

Hormone treatment for prostate cancer: current issues and future directions

Most prostate cancers are androgen-dependent and essentially respond to androgen ablation therapy. However, these tumors eventually become androgen-independent and progress despite androgen ablation. Since the androgen receptor (AR) sequence was determined, numerous studies have shown that AR plays a critical role in the development of androgen-refractory prostate cancer. Amplification of AR, mutations of AR, and deregulation of growth factors, cytokines and AR co-activators, which could be classified as AR-dependent pathways, are frequently observed in this condition. There are other pathways, AR-independent pathways that bypass AR, which involve neuroendocrine differentiation of prostate cancer cells, deregulation of apoptotic genes and unknown mechanisms related to down-regulation of AR. Androgen-refractory prostate cancers with the AR-dependent pathway could be treated by suppressing AR activity, whereas AR-independent tumors would require alternative management strategies. When more cell survival pathways are defined, improvement of patients' survival could be achieved by developing specific gene-targeting therapies that interfere with those pathways.

Efficacy of nilutamide as secondary hormonal therapy in androgen-independent prostate cancer

OBJECTIVE

To evaluate the activity of nilutamide as secondary hormonal therapy in patients with androgen-independent prostate cancer (AIPC), as treatment options are limited for these patients and secondary hormonal therapy with antiandrogens has advantages, including low toxicity, oral administration and high patient acceptance.

PATIENTS AND METHODS

We retrospectively identified 45 patients with AIPC who were treated with nilutamide as secondary hormonal therapy in two institutions. The decrease in prostate-specific antigen (PSA) levels, side-effects of treatment, and the relationship between baseline characteristics, type and duration of previous therapy and response to nilutamide were assessed. Most patients received oral nilutamide at 150 mg/day.

RESULTS

Eighteen of 45 evaluable patients (40%) had a PSA level decrease of > or = 50%. Responders (PSA decline > or = 50%) had a median (range) time to progression of 4.4 (0.31-44.7) months. There were responses to nilutamide whether used as the second to fifth line of hormonal therapy. There were no differences in response to nilutamide based on clinical stage, type of local therapy, PSA level at diagnosis or initiation of nilutamide, or type of previous antiandrogen therapy. Responders were more likely to have received monotherapy with luteinizing hormone-releasing hormone analogues or orchidectomy as first-line hormonal treatment (P = 0.02). The most common reversible adverse effects were mild to moderate visual adaptation effects, reported in 20% of patients.

CONCLUSIONS

Nilutamide appears to be an effective secondary hormonal therapy in patients with AIPC and is associated with a mild toxicity profile.

Modulation of Androgen Receptor Transactivation by FoxH1

Androgen signaling plays key roles in the development and progression of prostate cancer, and numerous ongoing studies focus on the regulation of androgen receptor (AR) transactivity to develop novel therapies for the treatment of androgen-independent prostate cancer. FoxH1, a member of the Forkhead-box (FOX) gene family of transcription factors, takes part in mediating transforming growth factor-beta/activin signaling through its interaction with the Smad2.Smad4 complex. Using a series of experiments, we found that FoxH1 repressed both ligand-dependent and -independent transactivation of the AR on androgen-induced promoters. This action of FoxH1 was independent of its transactivation capacity and activin A but relieved by Smad2.Smad4. In addition, the repression of the AR by FoxH1 did not require deacetylase activity. A protein-protein interaction was identified between the AR and FoxH1 independently of dihydrotestosterone. Furthermore, a confocal microscopic analysis of LNCaP cells revealed that the interaction between the AR and FoxH1 occurred in the nucleus and that FoxH1 specifically blocked the foci formation of dihydrotestosterone-activated AR, which has been shown to be correlated with the AR transactivation potential. Taken together, our results indicate that FoxH1 functions as a new corepressor of the AR. Our observations not only strengthen the role of FoxH1 in AR-mediated transactivation but also suggest that therapeutic interventions based on AR-coregulator interactions could be designed to block both androgen-dependent and -independent growth of prostate cancer.

Recent advances on multiple tumorigenic cascades involved in prostatic cancer progression and targeting therapies

Recent advances on differently-expressed gene products and their functions during the progression from localized androgen-dependent states into androgen-independent and metastatic forms of prostate cancer are reported. The expression levels of numerous oncogenes and tumor suppressor genes in distinct prostatic cancer epithelial cell lines and tissues relative to normal prostate cells are described. This is carried out to identify the signaling elements that are altered during the initiation, progression and metastatic process of prostate cancer. Additional information on the interactions between certain deregulated signaling pathways such as androgen receptor (AR), estrogen receptors, epidermal growth factor receptor (EGFR), hedgehog and Wnt/beta-catenin cascades in controlling the proliferation, survival and invasion of tumor prostate epithelial cells during the disease progression is described. The emphasis is on the critical functions of the AR and EGF-EGFR systems at all stages during prostate carcinogenesis. Of therapeutic interest, new strategies for the diagnosis and treatment of localized and metastatic forms of prostate cancer by targeting multiple tumorigenic signaling elements are also reported.

Overexpression of PKCε sensitizes LNCaP human prostate cancer cells to induction of apoptosis by bryostatin 1

Phorbol 12-myristate 13-acetate (PMA)-induced apoptosis of androgen sensitive LNCaP human prostate cancer cells is a well known phenomenon that involves prolonged translocation of multiple protein kinase C (PKC) isozymes to nonnuclear membranes. We have shown recently that PMA-induced death of C4-2 cells, androgen hypersensitive derivatives of LNCaP cells, requires both PKCdelta and a redundant pathway that includes PKCs alpha and epsilon. In contrast, it has been reported that overexpression of murine PKCepsilon in LNCaP cells renders those cells resistant to PMA-induced death, as well as androgen insensitive. Here we report that inducible or constitutive overexpression of human PKCepsilon does not alter the sensitivity of LNCaP cells to either PMA or androgen, nor does it alter expression of caveolin-1 or phosphorylated Rb, reported effects of overexpression of murine PKCepsilon. Moreover, overexpression of very high amounts of PKCepsilon sensitized LNCaP cells to induction of apoptosis by bryostatin 1, a non tumor-promoting activator and down-regulator of PKC isozymes that blocks PMA-induced apoptosis of parental LNCaP cells, mimicked our previous results with overexpression of PKCalpha in LNCaP cells. Given reports that overexpression of PKCepsilon is frequent in human prostate tumors, our results may have important implications for a potential prostate cancer therapy.

Regulation of androgen receptor levels: implications for prostate cancer progression and therapy

Androgen deprivation has been the standard therapy for advanced and metastatic prostate cancer for over half a century, as prostate tumors are initially dependent on androgens for growth and survival. Unfortunately, in most patients undergoing androgen ablation, relapse (recurrent tumor growth) eventually occurs. The actions of the principal androgens, testosterone and dihydrotestosterone (DHT), are mediated via androgen receptors (ARs), ligand-activated transcription factors that belong to the nuclear receptor superfamily. Because of the presence of transcriptionally active ARs in tumors from recurrent or androgen-independent disease, there is a heightened interest in new therapeutic paradigms that target the AR and its regulatory pathways. The regulation of AR levels is highly complex with control exerted by several pathways and in a cell-, tissue-, and developmental-stage specific manner. Androgens are important regulators of AR mRNA and protein through transcriptional and post-transcriptional mechanisms. This article reviews the evidence implicating the AR in recurrent prostate cancer and discusses the multiple mechanisms that regulate AR levels in normal and neoplastic cells. The complexity of AR regulation suggests that there will be an ample array of potential new drug targets for modulating levels of this receptor, a key signaling molecule in prostate cancer.

Acquisition of androgen independence by human prostate epithelial cells during arsenic-induced malignant transformation

Lethal phenotypes of human prostate cancer are characterized by progression to androgen independence, although the mechanisms behind this progression remain unclear. Arsenic is a potential human prostate carcinogen that may affect tumor progression. In this study, we used a prostate cancer cell model in which an immortalized, nontumorigenic human prostate epithelial cell line (RWPE-1) had been malignantly transformed by chronic low-level arsenic to help determine whether arsenic affects prostate tumor progression. Control and CAsE-PE (chronic-arsenic-exposed human prostate epithelial) cells were continuously maintained in a complete medium [keratinocyte serum-free medium (K-SFM) with bovine pituitary extract and epidermal growth factor] or in a steroid-depleted medium (K-SFM alone). The arsenic-transformed cells showed a more rapid proliferation rate in complete medium than did control cells and also showed sustained proliferation in steroid-reduced medium. Although both control and CAsE-PE cells showed similar levels of androgen receptor (AR), androgens were less effective in stimulating cell proliferation and AR-related gene expression in CAsE-PE cells. For instance, dihydrotestosterone caused a 4.5-fold increase in prostate-specific antigen transcript in control cells but only a 1.5-fold increase in CAsE-PE cells. CAsE-PE cells also showed relatively low levels of growth stimulation by nonandrogen steroids, such as estradiol. Thus, arsenic-induced malignant transformation is associated with acquired androgen independence in human prostate cells. This acquired androgen independence was apparently not due to AR up-regulation, increased activity, or altered ligand specificity. The precise manner in which arsenic altered CAsE-PE growth and progression is undefined but may involve a bypass of AR involving direct stimulation of downstream signaling pathways.

A 5'-distal enhanceosome in the PDGF-A gene is activated in choriocarcinoma cells via ligand-independent binding of vitamin D receptor and constitutive jun kinase signaling

Overexpression of platelet-derived growth factor A-chain (PDGF-A) is clearly linked to autocrine and paracrine stimulation of malignant growth in many human cancers. We have shown previously that PDGF-A overexpression in choriocarcinoma, hepatoma and lung carcinoma cell lines is driven by the activity of a 66 bp enhancer element (ACE66) located approximately 7 kb upstream of the PDGF-A transcription start site. In this study, the ACE66 element is shown to be activated in JEG-3 choriocarcinoma cells through synergistic interactions between consensus DNA motifs for binding of vitamin D receptor, AP1 and ELK1. Binding of the vitamin D/retinoid-X receptor (VDR/RXRalpha) heterodimer to the ACE66 element was reconstituted in vitro with recombinant VDR/RXRalpha and with JEG-3 nuclear extract, and was verified in living JEG-3 cells by chromatin immunoprecipitation analysis. Transcriptional activity of the ACE66 element, as well as occupancy of the element by VDR/RXRalpha, was shown to be independent of stimulation with the hormonal VDR ligand, 1,25-dihydroxyvitamin D3. The jun kinase pathway of mitogen-activated protein kinase (MAPK) signaling was shown to activate the ACE66 enhancer, most likely through activation of factors binding to the AP1 element. These results identify a novel mechanism of transcriptional enhancement involving ligand-independent activity of the VDR/RXR heterodimer and MAPK signaling pathways that appears to play an important role in the overexpression of PDGF in many different settings of human malignancy.

AGR2, an androgen-inducible secretory protein overexpressed in prostate cancer

AGR2, the human homologue of Xenopus anterior gradient 2 (XAG2), was identified by a suppression subtractive hybridization-based technique as an androgen-inducible gene. There are two AGR2 transcripts, which encode the same secretory protein of 175 amino acids. The androgen induction was time- and dose-dependent, with more than a 10-fold increase in the level of AGR2 mRNA after 48 hr of treatment with 10(-9) M R1881. Expression of AGR2 mRNA was specifically detected in limited human tissue rich in epithelial cells, including the prostate gland. Analysis of 46 microdissected primary prostate adenocarcinoma samples showed that AGR2 mRNA expression was markedly elevated in the majority of tumors as compared to matched adjacent benign tissues. Androgen-induced AGR2 protein expression was demonstrated in LNCaP cells by Western blot analysis with an anti-AGR2 antibody. Immunohistochemistry analysis indicated that AGR2 protein expression was highly restricted to the secretory epithelial cells in the prostate gland. In tissue sections from radical prostatectomy specimens, immunohistochemical staining of AGR2 showed markedly increased expression in high-grade prostatic intraepithelial neoplasia and Gleason pattern 3-4 prostatic adenocarcinoma. Therefore, the androgen-induced secretory protein AGR2 may serve as a potential therapeutic target and/or molecular marker for prostate cancer.

Relative importance of PSA in prostate cancer treatment

METHODS AND MATERIALS

A retrospective study was conducted to (1) determine the relationship between baseline prostate-specific antigen (PSA) levels and initial treatment decisions for prostate cancer (surgery, hormone therapy, radiation, or watchful waiting) and (2) estimate the impact of PSA progression (doubling or three consecutive rises) on subsequent treatment decisions. Patient records (n=1116) from three community urology practices and a large academic health system were reviewed. Multivariate models were fitted to assess the relationship between initial treatment and baseline PSA, Gleason score, race, number of comorbid conditions and age and between PSA progression and time to subsequent therapy (adjusted for other factors).

RESULTS

Baseline PSA was a significant predictor of initial treatment among men with localized disease with the likelihood of hormone therapy increasing with higher PSA levels and the likelihood of surgery decreasing steadily with higher PSA levels. PSA was the strongest predictor of hormone therapy as first choice followed by age. Age followed by PSA was the strongest predictor of surgery as first treatment as well as radiation therapy. Initial PSA levels did not predict the choice of watchful waiting. Patients with PSA progression were eight times (95% CI: 5.3-12.1) more likely to initiate a subsequent therapy than patients who did not have PSA progression when controlling for other predictors.

CONCLUSIONS

In clinical practice, PSA significantly impacts the urologist's primary therapy choice and determines when they introduce subsequent treatments.

The structural basis of androgen receptor activation: intramolecular and intermolecular amino-carboxy interactions

Nuclear receptors (NRs) are ligand-regulated transcription factors important in human physiology and disease. In certain NRs, including the androgen receptor (AR), ligand binding to the carboxy-terminal domain (LBD) regulates transcriptional activation functions in the LBD and amino-terminal domain (NTD). The basis for NTD-LBD communication is unknown but may involve NTD-LBD interactions either within a single receptor or between different members of an AR dimer. Here, measurement of FRET between fluorophores attached to the NTD and LBD of the AR established that agonist binding initiated an intramolecular NTD-LBD interaction in the nucleus and cytoplasm. This intramolecular folding was followed by AR self-association, which occurred preferentially in the nucleus. Rapid, ligand-induced intramolecular folding and delayed association also were observed for estrogen receptor-alpha but not for peroxisome proliferator activated receptor-gamma2. An antagonist ligand, hydroxyflutamide, blocked the NTD-LBD association within AR. NTD-LBD association also closely correlated with the transcriptional activation by heterologous ligands of AR mutants isolated from hormone-refractory prostate tumors. Intramolecular folding, but not AR-AR affinity, was disrupted by mutation of an alpha-helical ((23)FQNLF(27)) motif in the AR NTD previously described to interact with the AR LBD in vitro. This work establishes an intramolecular NTD-LBD conformational change as an initial component of ligand-regulated NR function.

The ErbB3-binding protein Ebp1 suppresses androgen receptor-mediated gene transcription and tumorigenesis of prostate cancer cells

Down-regulation of the androgen receptor (AR) is being evaluated as an effective therapy for the advanced stages of prostate cancer. We report that Ebp1, a protein identified by its interactions with the ErbB3 receptor, down-regulates expression of AR and AR-regulated genes in the LNCaP prostate cancer cell line. Using microarray analysis, we identified six endogenous AR target genes, including the AR itself, that are down-regulated by ebp1 overexpression. Chromatin immunoprecipitation assays revealed that Ebp1 was recruited to the prostate-specific antigen gene promoter in response to the androgen antagonist bicalutamide, suggesting that Ebp1 directly affected the expression of AR-regulated genes in response to androgen antagonists. Ebp1 expression was reduced in cells that had become androgen-independent. Androgens failed to stimulate either the growth of ebp1 transfectants or transcription of AR-regulated reporter genes in these cells. The agonist activity of the antiandrogen cyproterone acetate was abolished in ebp1 transfectants. In severe combined immunodeficient mice, Ebp1 overexpression resulted in a reduced incidence of LNCaP tumors and slower tumor growth. These findings suggest that Ebp1 is a previously unrecognized therapeutic target for treatment of hormone refractory prostate cancer.

A human- and male-specific protocadherin that acts through the wnt signaling pathway to induce neuroendocrine transdifferentiation of prostate cancer cells

Protocadherin-PC (PCDH-PC) is a gene on the human Y chromosome that is selectively expressed in apoptosis- and hormone-resistant human prostate cancer cells. The protein encoded by PCDH-PC is cytoplasmically localized and has a small serine-rich domain in its COOH terminus that is homologous to the beta-catenin binding site of classical cadherins. Variants of prostate cancer cells that express PCDH-PC have high levels of nuclear beta-catenin protein and increased wnt-signaling. In this study, we show that transfection of human prostate cancer cells (LNCaP) with PCDH-PC or culture of these cells in androgen-free medium (a condition that up-regulates PCDH-PC expression) activates wnt signaling as assessed by nuclear accumulation of beta-catenin, increased expression of luciferase from a reporter vector promoted by Tcf binding elements and increased expression of wnt target genes. Moreover, LNCaP cells transfected with PCDH-PC or grown in androgen-free medium transdifferentiate to neuroendocrine-like cells marked by elevated expression of neuron-specific enolase and chromogranin-A. Neuroendocrine transdifferentiation was also observed when LNCaP cells were transfected by stabilized beta-catenin. Increased wnt signaling and neuroendocrine transdifferentiation of LNCaP cells induced by culture in androgen-free medium was suppressed by short interfering RNAs that target PCDH-PC as well as by dominant-negative Tcf or short interfering RNA against beta-catenin, supporting the hypothesis that increased expression of PCDH-PC is driving neuroendocrine transdifferentiation by activating wnt signaling. These findings have significant implications for the process through which prostate cancers progress to hormone resistance in humans.

The serine/threonine protein kinase, p90 ribosomal S6 kinase, is an important regulator of prostate cancer cell proliferation

An increase in the activity of mitogen-activated protein kinase (MAPK) has been correlated with the progression of prostate cancer to advanced disease in humans. The serine/threonine protein kinase p90-kDa ribosomal S6 kinase (RSK) is an important downstream effector of MAPK but its role in prostate cancer has not previously been examined. Increasing RSK isoform 2 (RSK2) levels in the human prostate cancer line, LNCaP, enhanced prostate-specific antigen (PSA) expression, an important diagnostic marker for prostate cancer, whereas inhibiting RSK activity using a RSK-specific inhibitor, 3Ac-SL0101, decreased PSA expression. The RSK2 regulation of PSA expression occurred via a mechanism involving both RSK2 kinase activity and its ability to associate with the coactivator, p300. RNA interference of the androgen receptor (AR) showed that the AR was important in the RSK2-mediated increase in PSA expression. RSK levels are higher in approximately 50% of human prostate cancers compared with normal prostate tissue, which suggests that increased RSK levels may participate in the rise in PSA expression that occurs in prostate cancer. Furthermore, 3Ac-SL0101 inhibited proliferation of the LNCaP line and the androgen-independent human prostate cancer line, PC-3. These results suggest that proliferation of some prostate cancer cells is dependent on RSK activity and support the hypothesis that RSK may be an important chemotherapeutic target for prostate cancer.

Androgen receptor mutants detected in recurrent prostate cancer exhibit diverse functional characteristics

BACKGROUND

Alterations in the function of androgen receptor (AR) and its signaling pathway may be responsible for the progression of prostate cancer. The goal of the present study was to investigate the potential roles of AR structural and functional alterations in the progression of prostate cancer, and the relationship between the structure and function of the AR.

METHODS

AR gene in 58 prostate cancer samples was examined for mutations using PCR-single strand conformation polymorphism (SSCP) analysis and DNA sequencing. Effects of mutations on the structure and function of AR were investigated by androgen-binding assays and transactivation assays, respectively.

RESULTS

Four novel somatic mutations (G142V, D221H, E872Q, and M886I) were identified from recurrent prostate cancer samples. None of the AR mutants differed from wild-type AR (wtAR) in their abilities to bind the synthetic androgen methyltrienolone. However, these mutated AR exhibited diverse functional characteristics as compared with wtAR. G142V and D221H showed increased responses to DHT. E872Q could be abnormally activated by 17beta-estradiol, progesterone, and cyproterone acetate (CPA). Furthermore, E872Q and M886I presented increased responses to DHT in the presence of coactivators TIF-2 and CBP, but not p300. On the other hand, although overexpression of corepressors N-CoR and SMRT could result in evident inhibition on DHT- or CPA-induced transactivity of wtAR and the AR mutants, N-CoR displayed stronger inhibitory effects on DHT-induced transactivity of the AR mutants (especially for E872Q and M886I) than that of wtAR. To our knowledge, this is the first characterization of enhanced inhibitory effects of corepressors on the transactivity of the AR mutants found in prostate cancer.

CONCLUSIONS

The data presented here demonstrate that AR mutants found in prostate cancer had different functional alterations, which might play an important role in the progression of prostate cancer.

Androgen receptor is targeted to distinct subcellular compartments in response to different therapeutic antiandrogens

PURPOSE

Antiandrogens are routinely used in the treatment of prostate cancer. Although they are known to prevent activation of the androgen receptor (AR), little is known about the mechanisms involved. This report represents the first study of the localization of wild-type AR following expression at physiologic relevant levels in prostate cells and treatment with androgen and antiandrogens.

EXPERIMENTAL DESIGN

We have characterized a cellular model for prostate cancer using in situ cellular fractionation, proteomics, and confocal microscopy and investigated the effect of antiandrogens in clinical use on the subcellular localization of the AR.

RESULTS

Different antiandrogens have diverse effects on the subcellular localization of the AR. Treatment with androgen results in translocation from the cytoplasm to the nucleoplasm, whereas the antiandrogens hydroxyflutamide and bicalutamide lead to reversible association with the nuclear matrix. In contrast, treatment with the antiandrogen cyproterone acetate results in AR association with cytoplasmic membranes and irreversible retention within the cytoplasm. In addition, we demonstrate that AR translocation requires ATP and the cytoskeleton, regardless of ligand.

CONCLUSIONS

These results reveal that not all antiandrogens work via the same mechanism and suggest that an informed sequential treatment regime may benefit prostate cancer patients. The observed subnuclear and subcytoplasmic associations of the AR suggest new areas of study to investigate the role of the AR in the response and resistance of prostate cancer to antiandrogen therapy.

Tectorigenin and other phytochemicals extracted from leopard lily Belamcanda chinensis affect new and established targets for therapies in prostate cancer

Isoflavones have been shown to exert antiproliferative effects on cancer cells by steroid receptor signaling. In this study, we demonstrate the potential of plant constituents extracted from Belamcanda chinensis as anticancer drugs, which regulate the aberrant expression of genes relevant in proliferation, invasion, immortalization and apoptosis. LNCaP cells were treated with B.chinensis extract, tectorigenin or other isoflavones and mRNA expression was quantified by using real time RT-PCR. In addition, ELISA, TRAP assays and western blots were used to measure protein expression or activity. Male nude mice (n=18) were injected subcutaneously with LNCaP cells and were fed with extracts from B.chinensis, and tumor development was monitored versus a control animal group (n=18). Tectorigenin and several other phytochemicals downregulated PDEF, PSA and IGF-1 receptor mRNA expression in vitro. Furthermore, PSA secretion and IGF-1 receptor protein expression were diminished, and hTERT mRNA expression and telomerase activity decreased after tectorigenin treatments. However, TIMP-3 mRNA was upregulated on tectorigenin treatment. Growth of subcutaneous tumors in nude mice was delayed and diminished in animals fed with extracts from B.chinensis. The downregulation of PDEF, PSA, hTERT and IGF-1 receptor gene expression by tectorigenin demonstrates the antiproliferative potential of these agents. The upregulation of TIMP-3 gene expression indicates a pro-apoptotic function of the drug and a reduction of the invasiveness of tumors. The animal experiments demonstrate that B.chinensis markedly inhibited the development of tumors in vivo. Thus, these compounds may be useful for the prevention or treatment of human prostate cancer.

Retracted: Additive antitumor effects of the epidermal growth factor receptor tyrosine kinase inhibitor, gefitinib (Iressa), and the nonsteroidal antiandrogen, bicalutamide (Casodex), in prostate cancer cellsin vitro

Progression from an androgen-dependent to an androgen-independent state often occurs in patients with prostate cancer (PCa) who undergo hormonal therapy. We have investigated whether inhibition of the epidermal growth factor receptor (EGFR) signaling pathway affects the antitumor effect of a nonsteroidal antiandrogen. Gefitinib (Iressa), an EGFR tyrosine kinase inhibitor, and bicalutamide (Casodex), a nonsteroidal antiandrogen [androgen receptor (AR) antagonist], were administered alone and in combination to AR-positive human PCa cell lines. FACS analysis showed lower EGFR expression levels on AR-positive cells (LNCaP, CWR22, CWR22R 2152 and AR-transfected DU145 cell lines) compared with AR-negative cells (DU145, PC3 and TSU-Pr1). Moreover, in AR-transfected DU145 cells, chronic treatment with bicalutamide increased EGFR expression to levels similar to androgen-independent DU145 cells. All AR-positive PCa cell lines were sensitive to gefitinib (IC50 = 0.1-0.6 microM), whereas higher concentrations of bicalutamide were needed to reduce AR-positive PCa cell line proliferation (IC50 = 0.8-2.0 microM). Low doses of gefitinib increased the antitumor effects of bicalutamide by strongly reducing the IC50 of bicalutamide (approximately 10-fold). Similarly, bicalutamide increased the antiproliferative effects of gefitinib by reducing the IC50 of gefitinib (approximately 5-fold). Taken together, our data suggest that in androgen-dependent cell lines, addition of gefitinib in combination with bicalutamide results in concurrent dual inhibition of AR and EGFR/HER2 pathways. This causes a significant delay in the onset of EGFR-driven androgen independence.

Small-interfering RNA–induced androgen receptor silencing leads to apoptotic cell death in prostate cancer

Prostate cancer is the second leading cause of cancer death in the United States and, thus far, there has been no effective therapy for the treatment of hormone-refractory disease. Recently, the androgen receptor (AR) has been shown to play a critical role in the development and progression of the disease. In this report, we showed that knocking down the AR protein level by a small interfering RNA (siRNA) approach resulted in a significant apoptotic cell death as evidenced by an increased annexin V binding, reduced mitochondrial potential, caspase-3/6 activation, and DFF45 and poly(ADP-ribose) polymerase cleavage. The apoptotic response was specifically observed in those siRNA-transfected cells that harbor a native AR gene. No cell death was found in the AR-null prostate cancer cell PC-3 or its subline that has been reconstituted with an exogenous AR gene, as well as two breast cancer cell lines that are AR positive. Moreover, in parallel with the siRNA-induced AR silencing, the antiapoptotic protein Bcl-xL was significantly reduced, which might account for the apoptotic cell death because ectopic enforced expression of Bcl-xL protein partially inhibited apoptosis after AR silencing. Taken together, our data showed that knocking down the AR protein level in prostate cancer cells leads to apoptosis by disrupting the Bcl-xL-mediated survival signal downstream of AR-dependent survival pathway.

Androgen ablation mitigates tolerance to a prostate/prostate cancer-restricted antigen

To understand the T cell response to prostate cancer, we created transgenic mice that express a model antigen in a prostate-restricted pattern and crossed these animals to TRAMP mice that develop spontaneous prostate cancer. Adoptive transfer of prostate-specific CD4 T cells shows that, in the absence of prostate cancer, the prostate gland is mostly ignored. Tumorigenesis allows T cell recognition of the prostate gland--but this recognition is tolerogenic, resulting in abortive proliferation and ultimately in hyporesponsiveness at the systemic level. Androgen ablation (the most common treatment for metastatic prostate cancer) was able to mitigate this tolerance--allowing prostate-specific T cells to expand and develop effector function after vaccination. These results suggest that immunotherapy for prostate cancer may be most efficacious when administered after androgen ablation.

Targeting multiple signaling pathways as a strategy for managing prostate cancer: multifocal signal modulation therapy

The aberrant behavior of cancer reflects upregulation of certain oncogenic signaling pathways that promote proliferation, inhibit apoptosis, and enable the cancer to spread and evoke angiogenesis. Theoretically, it should be feasible to decrease the activity of these pathways-or increase the activity of pathways that oppose them-with noncytotoxic agents. Since multiple pathways are dysfunctional in most cancers, and cancers accumulate new oncogenic mutations as they progress, the greatest and most durable therapeutic benefit will likely be achieved with combination regimens that address several targets. Thus, a multifocal signal modulation therapy (MSMT) of cancer is proposed. This concept has already been documented by researchers who have shown that certain combinations of signal modulators-of limited utility when administered individually-can achieve dramatic suppression of tumor growth in rodent xenograft models. The present essay attempts to guide development of MSMTs for prostate cancer. Androgen ablation is a signal-modulating measure already in standard use in the management of delocalized prostate cancer. The additional molecular targets considered here include the type 1 insulin-like growth factor receptor, the epidermal growth factor receptor, mammalian target of rapamycin, NF-kappaB, hypoxia-inducible factor-1alpha, hsp90, cyclooxygenase-2, protein kinase A type I, vascular endothelial growth factor, 5-lipoxygenase, 12-lipoxygenase, angiotensin II receptor type 1, bradykinin receptor type 1, c-Src, interleukin-6, ras, MDM2, bcl-2/bclxL, vitamin D receptor, estrogen receptor-beta, and PPAR-. Various nutrients and phytochemicals suspected to have potential utility in prostate cancer prevention and therapy, but whose key molecular targets are still unknown, might reasonably be incorporated into MSMTs for prostate cancer; these include lycopene, selenium, green tea polyphenols, genistein, and silibinin. MSMTs can be developed systematically by testing various combinations of signal-modulating agents, in concentrations that can feasibly be achieved and maintained clinically, on human prostate cancer cell lines; combinations that appear promising can then be tested in xenograft models and, ultimately, in the clinic. Some signal modulators can increase response to cytotoxic drugs by upregulating effectors of apoptosis. When MSMTs fail to raise the spontaneous apoptosis rate sufficiently to achieve tumor stasis or regression, incorporation of appropriate cytotoxic agents into the regimen may improve the clinical outcome.

Characterization of the autochthonous transgenic adenocarcinoma of the mouse prostate (TRAMP) as a model to study effects of castration therapy

BACKGROUND

In order to learn more about short- and long-term effects of castration therapy, relevant model systems for prostate cancer are required. In this study, we examined whether the transgenic adenocarcinoma of the mouse prostate (TRAMP) tumor response to castration in C57BL/6 mice mimics that seen in patients.

METHODS

Transgenic animals were examined before and 3 days after castration, at the ages of 17, 24, and 36 weeks. Moreover, 24-weeks old animals were castrated and followed for 6 months. Immunohistochemistry (IHC) and stereology were used to evaluate epithelial cell proliferation and death, blood vessel volume, androgen receptor (AR) expression, and transgenic expression of SV40 large T.

RESULTS

Cancer developed preferentially in the dorso-lateral prostate lobe. Tumor burden and incidence of metastases increased with age. The majority of tumors were well differentiated, while poorly differentiated, large tumors and macroscopic metastases developed in 8% of the animals. Well and moderately differentiated tumors responded to castration with cessation of proliferation and induction of apoptosis. Poorly differentiated tumors and metastases did not respond. Castration prevented local tumor growth for at least 6 months in 82% of the cases. Although, 45% of the treated animals developed wide-spread metastatic disease suggesting that castration may enhance growth of distant metastases.

CONCLUSIONS

The C57Bl/6 TRAMP tumor in several ways mimics how prostate cancer in patients responds to castration both in the short and long term, but some differences may also exist. This model can preferably be used to elucidate how this treatment works, and to test how it can be improved by additional therapies.

Synthesis and secretion of angiotensin II by the prostate gland in vitro

The renin angiotensin system has been shown to have tissue-related functions that are distinct from its systemic roles. We showed that angiotensin II type 1 (AT1) receptors are present in mammalian sperm, and angiotensin II stimulates sperm motility and capacitation. In addition, angiotensin II is present in human seminal plasma at concentrations higher than found in blood. In testing the possibility that the prostate may be the source of seminal plasma angiotensin II, mRNA coding for angiotensinogen, (pro)renin, and angiotensin-converting enzyme were identified by RT-PCR in rat and human prostate and in prostate LNCaP cells, as well as the angiotensin receptors types 1 and 2 (AT1 and AT2) in human tissues and AT1 in rat. In human tissue, immunocytochemistry showed cellular colocalization of renin with the AT1 receptor in secretory epithelial cells. Confirmation of the capacity of the prostate to secrete angiotensin II was shown by the detection of immunoreactive angiotensin in media removed from rat prostate organ cultures and LNCaP cells. Rat prostate angiotensin secretion was enhanced by dihydrotestosterone, but LNCaP angiotensin was stimulated by estradiol. This stimulation was blocked by tamoxifen. Rat prostate AT1 receptor expression was much greater in prepuberal than in postpuberal rats but was not affected by a low-sodium diet. It was, however, significantly enhanced by captopril pretreatment. These findings all suggest the independence of prostate and systemic renin angiotensin system regulation. The data presented here suggest that the prostate may be a source of the secreted angiotensin II found in seminal plasma.

Xenoestrogen Action in Prostate Cancer: Pleiotropic Effects Dependent on Androgen Receptor Status

Androgen is critical for prostate development, growth, and survival. Therapies for advanced prostate cancer aim to block androgen receptor (AR) action. However, recurrent tumors ultimately arise, which harbor restored AR activity. One mechanism of such reactivation occurs through AR mutations, rendering the receptor responsive to noncanonical ligands. We have shown previously that a known xenoestrogen, bisphenol A (BPA), activates a tumor-derived AR mutant (T877A), leading to androgen-independent prostate cancer cell proliferation. Here, we show that BPA cooperates with androgen to activate AR-T877A as shown by both reporter assays and increased levels of prostate-specific antigen expression. Further investigations using both yeast and mammalian model systems revealed that multiple AR alleles are responsive to BPA, thus expanding the potential influence of xenoestrogens on prostate cancer. Moreover, in vitro radioligand binding assay revealed that BPA alters 5α-dihydrotestosterone binding to AR-T877A likely through noncompetitive inhibition. We also show that higher concentrations of BPA block proliferation of AR-positive, androgen-dependent prostate adenocarcinoma cells (LNCaP and LAPC-4), with a more modest inhibitory effect on androgen-independent cells (22Rv-1). By contrast, AR-negative prostate cancer cells failed to show growth inhibition after exposure to high BPA dose. Together, these data show that BPA can serve as a potential “hormone sensitizer” of the mutant ARs present in advanced prostate adenocarcinomas, thereby possibly contributing toward therapeutic relapse in advanced prostate cancer patients and supporting the notion that nonsteroidal environmental compounds can alter the function of nuclear receptor complexes.

Redundancy of biological regulation as the basis of emergence of multidrug resistance

Active efflux of xenobiotics is a major mechanism of cell adaptation to environmental stress. The ATP-dependent transmembrane transporter P-glycoprotein (Pgp) confers long-term cell survival in the presence of different toxins, including anticancer drugs (this concept is referred to as multidrug resistance, or MDR). The vital importance of this mechanism for cell survival dictates the reliability and promptness of its acquisition. To fulfill this requirement, the MDR1 gene that encodes Pgp in humans must be readily upregulated in cells that express low to null levels of MDR1 mRNA prior to stress. The MDR1 gene and a stable MDR phenotype can be induced after short-term exposure of cells to a variety of cues. This effect is implemented by activation of MDR1 transcription and mRNA stabilization. The MDR1 message abundance is regulated by mechanisms generally involved in stress response, namely activation of phospholipase C, protein kinase C and mitogen-activated protein kinase cascades, mobilization of intracellular Ca2+, and nuclear factor kappa B activation. Furthermore, the proximal MDR1 promoter sites critical for induction are not unique for the MDR1 gene; they are common regulatory elements in eukaryotic promoters. Moreover, MDR1 induction can result from activation of (an) intermediate gene(s) whose product(s), in turn, directly activate(s) the MDR1 promoter and/or cause(s) mRNA stabilization. Redundancy of signal transduction and transcriptional mechanisms is the basis for the virtually ubiquitous inducibility of the MDR1 gene. Thus, the complex network of MDR1 regulation ensures rapid emergence of pleiotropic resistance in cells.

Cyclin D1 binding to the androgen receptor (AR) NH2-terminal domain inhibits activation function 2 association and reveals dual roles for AR corepression

The androgen receptor (AR) is a member of the nuclear receptor superfamily, the activity of which is critical for the development and progression of prostate cancer. We and others have previously demonstrated that cyclin D1 is a potent corepressor of the AR. Although cyclin D1 is suspected to recruit histone deacetylases to the AR complex, previous studies have demonstrated that this activity alone is insufficient for cyclin D1 function. Here, we uncover a novel, secondary means of cyclin D1-mediated repression, through modulation of AR amino-carboxy terminal interactions. We show that cyclin D1 predominantly binds the N-terminal domain of the AR, dependent on the AR 23FxxLF27 motif. Through this motif, cyclin D1 abrogates the ability of the AR N-terminal domain to interact with the C terminus. Secondary amino-terminal domain sites capable of fostering interaction with the C terminus were refractory to cyclin D1 action, indicating that the ability of cyclin D1 to modulate AR amino-carboxy terminal interactions is specific to 23FxxLF27. Deletion of the N-terminal cyclin D1 binding site severely compromised AR activity (due to loss of FxxLF) but unmasked a repressor action through interaction with the AR C terminus. In summary, these data reveal novel, unexpected mechanisms of cyclin D1 activity and demonstrate that this function of cyclin D1 is critical for AR modulation.