Biology of progressive, castration-resistant prostate cancer: directed therapies targeting the androgen-receptor signaling axis

Overexpression of the potential kinase serine/ threonine/tyrosine kinase 1 (STYK 1) in castration-resistant prostate cancer

Despite high response rates and clinical benefits, androgen ablation often fails to cure advanced or relapsed prostate cancer because castration-resistant prostate cancer (CRPC) cells inevitably emerge. CRPC cells not only grow under castration, but also behave more aggressively, indicating that a number of malignant signaling pathways are activated in CRPC cells as well as androgen receptor signaling. Based on information from the gene expression profiles of clinical CRPC cells, we here identified one overexpressed gene, serine/threonine/tyrosine kinase 1 (STYK1), encoding a potential kinase, as a molecular target for CRPC. RNA and immunohistochemical analyses validated the overexpression of STYK1 in prostate cancer cells, and its expression was distinct in CRPC cells. Knockdown of STYK1 by siRNA resulted in drastic suppression of prostate cancer cell growth and, concordantly, enforced expression of STYK1 promoted cell proliferation, whereas ectopic expression of a kinase-dead mutant STYK1 did not. An in vitro kinase assay using recombinant STYK1 demonstrated that STYK1 could have some potential as a kinase, although its specific substrates are unknown. These findings suggest that STYK1 could be a possible molecular target for CRPC, and small molecules specifically inhibiting STYK1 kinase could be a possible approach for the development of novel CRPC therapies.

HDAC6 regulates androgen receptor hypersensitivity and nuclear localization via modulating Hsp90 acetylation in castration-resistant prostate cancer

The development of castration-resistant prostate cancer (PCa) requires that under castration conditions, the androgen receptor (AR) remains active and thus nuclear. Heat shock protein 90 (Hsp90) plays a key role in androgen-induced and -independent nuclear localization and activation of AR. Histone deacetylase 6 (HDAC6) is implicated, but has not been proven, in regulating AR activity via modulating Hsp90 acetylation. Here, we report that knockdown of HDAC6 in C4-2 cells using short hairpin RNA impaired ligand-independent nuclear localization of endogenous AR and inhibited PSA expression and cell growth in the absence or presence of dihydrotestosterone (DHT). The dose-response curve of DHT-stimulated C4-2 colony formation was shifted by shHDAC6 such that approximately 10-fold higher concentration of DHT is required, indicating a requirement for HDAC6 in AR hypersensitivity. HDAC6 knockdown also inhibited C4-2 xenograft tumor establishment in castrated, but not in testes-intact, nude mice. Studies using HDAC6-deficient mouse embryonic fibroblasts cells showed that inhibition of AR nuclear localization by HDAC6 knockdown can be largely alleviated by expressing a deacetylation mimic Hsp90 mutant. Taken together, our studies suggest that HDAC6 regulates AR hypersensitivity and nuclear localization, mainly via modulating HSP90 acetylation. Targeting HDAC6 alone or in combination with other therapeutic approaches is a promising new strategy for prevention and/or treatment of castration-resistant PCa.

Novel flufenamic acid analogues as inhibitors of androgen receptor mediated transcription

The androgen receptor (AR), which mediates the signals of androgens, plays a crucial role in prostate-related diseases. Although widely used, currently marketed anti-androgenic drugs have significant side effects. Several studies have revealed that non-steroidal anti-inflammatory drugs, such as flufenamic acid, block AR transcriptional activity. Herein we describe the development of small molecule analogues of flufenamic acid that antagonize AR. This novel class of AR inhibitors binds to the hormone binding site, blocks AR transcription activity, and acts on AR target genes.

Clinical utility of antioxidant gene expression levels in circulating cancer cell clusters for the detection of prostate cancer in patients with prostate-specific antigen levels of 4-10 ng/mL and disease prognostication after radical prostatectomy

OBJECTIVES

To test antioxidant genes (AOX) expression in circulating cancer cell clusters (CCC). A novel method using molecular, polymerase chain reaction (PCR)-based detection of CCC was applied for predicting prostate cancer and to assess the effect of radical prostatectomy (RP) on reducing CCC and for prognostication of relapse-free survival (RFS), as serum total prostate-specific antigen (tPSA) has limited specificity at 4-10 ng/mL.

PATIENTS AND METHODS

In all, 240 patients were enrolled in the study, 129 for tumour diagnosis and 111 after RP for disease prognostication. Filtration assay in previously fractionated mononuclear cells (MNC) was used to enrich the CCC and large cells, which were retained in a mesh of 20 microm width. To establish the malignant nature of these cells they were analysed for genomic imbalances detected via PCR-assays of loss of heterozygosity in tumour suppressor loci and of DNA amplification in protooncogen loci. As a screening test in daily practice, real-time reverse transcription (RT)-PCR of AOX was introduced to overcome the laborious and expensive DNA tests. The AOX chosen were glutathione peroxidase (GPX1), Mn-dependent superoxide dismutase 2 (SOD2) and thioredoxine reductase (TXNRD1); selected from 67 marker candidate genes according to sensitivity and specificity data. AOX overexpression in CCC serves as a general marker for solid tumours needing, however, organ markers to relate to the organ of origin. Androgen receptor (AR), PSA and prostate-specific membrane antigen mRNAs served as organ markers for the prostate. Signals were detected in patients' MNC and to a minor level in CCC, rendering to CCC a substantial loss in epithelial features equivalent to a lower grade of epithelial differentiation. Organ markers in the MNC fraction were positive in <85% of AOX testing.

RESULTS

The AOX test was tumour predicting (P < 0.001) with a sensitivity of 86%, specificity 82%, positive predictive value 69%, negative predictive value 92%, accuracy 83% and odds ratio (OR) of 28. SOD2 and TXNRD1 expression correlated to tumour size and Gleason score. Objective assessment for the evaluation of the molecular cell markers was achieved by receiver operating characteristic (ROC) curves. The areas under the ROC curve values of the AOXs were 0.7-0.9. RP was followed by a complete clearance of AOX-expressing cells. After RP, a subgroup of patients had residual CCC over-expressing only SOD2 and GPX1 indicating incomplete clearance by RP. Sustained overexpression of SOD2 and GPX1 accounted as risk factors for distant tumour recurrence (P = 0.003) mainly for bone metastases (97% M1b) as evaluated by Kaplan-Meier curves. In univariate analysis the tumour size had a limited effect on the probability of RFS (P = 0.05). In multivariate analysis tumour size, nodal status and Gleason score had no effect. This can partially be attributed to the higher risk level of pathological variables in the AOX over-expressing group but also to ineffective endocrine therapy resulting in marked overexpression of ARs and GPX1, the lead prognosticator gene. The AOX expression level allowed the identification of patients with high progression risk, who have more favourable pathological variables.

CONCLUSION

The AOX testing of CCC is a novel method with excellent prognostic and predictive properties enabling the monitoring of therapies, e.g. effects of RP and endocrine therapy. We speculate that the continuing elevated expression of AOX with special emphasis on GPX1 acts as survival and defence mechanism in CCC required in an atypical environment prone to escape from immune surveillance.

Castration resistance of prostate cancer cells caused by castration-induced oxidative stress through Twist1 and androgen receptor overexpression

There are few successful therapies for castration-resistant prostate cancer (CRPC). Recently, CRPC has been thought to result from augmented androgen/androgen receptor (AR) signaling pathway, for most of which AR overexpression has been observed. In this study, Twist1, a member of basic helix-loop-helix transcription factors as well as AR was upregulated in response to hydrogen peroxide, and the response to which was abolished by an addition of N-acetyl-L-cysteine and Twist1 knockdown. In addition, castration-resistant LNCaP derivatives and hydrogen peroxide-resistant LNCaP derivatives exhibited a similar phenotype to each other. Then, both castration and AR knockdown increased intracellular reactive oxygen species level. Moreover, Twist1 was shown to regulate AR expression through binding to E-boxes in AR promoter region. Silencing of Twist1 suppressed cell growth of AR-expressing LNCaP cells as well as castration-resistant LNCaP derivatives by inducing cell-cycle arrest at G1 phase and cellular apoptosis. These findings indicated that castration-induced oxidative stress may promote AR overexpression through Twist1 overexpression, which could result in a gain of castration resistance. Modulation of castration-induced oxidative stress or Twist1/AR signaling might be a useful strategy for developing a novel therapeutics in prostate cancer, even in CRPC, which remains dependent on AR signaling by overexpressing AR.

Sulforaphane destabilizes the androgen receptor in prostate cancer cells by inactivating histone deacetylase 6

High consumption of cruciferous vegetables is associated with a reduced risk of prostate cancer in epidemiological studies. There is preliminary evidence that sulforaphane, derived from glucoraphanin found in a number of crucifers, may prevent and induce regression of prostate cancer and other malignancies in preclinical models, but the mechanisms that may explain these effects are not fully defined. Recent reports show that sulforaphane may impair prostate cancer growth through inhibition of histone deacetylases, which are up-regulated in cancer. Indeed, one of these enzymes, histone deacetylase 6 (HDAC6), influences the acetylation state of a key androgen receptor (AR) chaperone, HSP90. AR is the central signaling pathway in prostate cancer, and its inhibition is used for both prevention and treatment of this disease. However, it is not known whether the effects of sulforaphane involve suppression of AR. We hypothesized that sulforaphane treatment would lead to hyperacetylation of HSP90 and that this would destabilize AR and attenuate AR signaling. We confirmed this by demonstrating that sulforaphane enhances HSP90 acetylation, thereby inhibiting its association with AR. Moreover, AR is subsequently degraded in the proteasome, which leads to reduced AR target gene expression and reduced AR occupancy at its target genes. Finally, sulforaphane inhibits HDAC6 deacetylase activity, and the effects of sulforaphane on AR protein are abrogated by overexpression of HDAC6 and mimicked by HDAC6 siRNA. The inactivation by sulforaphane of HDAC6-mediated HSP90 deacetylation and consequent attenuation of AR signaling represents a newly defined mechanism that may help explain this agent's effects in prostate cancer.

The neuroendocrine-derived peptide parathyroid hormone-related protein promotes prostate cancer cell growth by stabilizing the androgen receptor

During progression to an androgen-independent state following androgen ablation therapy, prostate cancer cells continue to express the androgen receptor (AR) and androgen-regulated genes, indicating that AR is critical for the proliferation of hormone-refractory prostate cancer cells. Multiple mechanisms have been proposed for the development of AR-dependent hormone-refractory disease, including changes in expression of AR coregulatory proteins, AR mutation, growth factor-mediated activation of AR, and AR protein up-regulation. The most prominent of these progressive changes is the up-regulation of AR that occurs in >90% of prostate cancers. A common feature of the most aggressive hormone-refractory prostate cancers is the accumulation of cells with neuroendocrine characteristics that produce paracrine factors and may provide a novel mechanism for the regulation of AR during advanced stages of the disease. In this study, we show that neuroendocrine-derived parathyroid hormone-related protein (PTHrP)-mediated signaling through the epidermal growth factor receptor (EGFR) and Src pathways contributes to the phenotype of advanced prostate cancer by reducing AR protein turnover. PTHrP-induced accumulation of AR depended on the activity of Src and EGFR and consequent phosphorylation of the AR on Tyr(534). PTHrP-induced tyrosine phosphorylation of AR resulted in reduced AR ubiquitination and interaction with the ubiquitin ligase COOH terminus of Hsp70-interacting protein. These events result in increased accumulation of AR and thus enhanced growth of prostate cancer cells at low levels of androgen.

Androgen receptor abnormalities in castration-recurrent prostate cancer

The androgen receptor (AR) plays a critical role in prostate cancer (PCa) development and progression. Despite the success of androgen-deprivation therapy, remission occurs in almost all cases. This stage of the disease is called castration-recurrent PCa (CRPC). CRPC cells adapt to low circulating levels of androgens, and active AR is maintained by numerous cellular mechanisms. Some mutations in the AR make it more responsive to lower androgen levels or other steroids. Furthermore, in this advance stage of the disease, PCa cells express the enzymes necessary for de novo synthesis of androgens. AR is also activated in a ligand-independent manner. Therefore, it is important to understand the mechanisms of AR activation and its deregulation during CRPC. The purpose of this article is to discuss mechanisms that are involved in modulation of AR activity and specificity.

Androgen receptor regulates a distinct transcription program in androgen-independent prostate cancer

The evolution of prostate cancer from an androgen-dependent state to one that is androgen-independent marks its lethal progression. The androgen receptor (AR) is essential in both, though its function in androgen-independent cancers is poorly understood. We have defined the direct AR-dependent target genes in both androgen-dependent and -independent cancer cells by generating AR-dependent gene expression profiles and AR cistromes. In contrast to what is found in androgen-dependent cells, AR selectively upregulates M-phase cell-cycle genes in androgen-independent cells, including UBE2C, a gene that inactivates the M-phase checkpoint. We find that epigenetic marks at the UBE2C enhancer, notably histone H3K4 methylation and FoxA1 transcription factor binding, are present in androgen-independent cells and direct AR-enhancer binding and UBE2C activation. Thus, the role of AR in androgen-independent cancer cells is not to direct the androgen-dependent gene expression program without androgen, but rather to execute a distinct program resulting in androgen-independent growth.

Signalling pathways in prostate carcinogenesis: potentials for molecular-targeted therapy

Prostate cancer represents a major health issue and its incidence is rising globally. In developed countries, prostate cancer is the most frequently diagnosed cancer and the second most common cause of death from cancer in men. Androgen deprivation reduces tumour activity in approx. 80% of patients with advanced disease, but most tumours relapse within 2 years to an incurable hormone-resistant state. Even for patients with early disease at the time of diagnosis, a proportion of patients will unfortunately develop relapsed disease following radical therapy. Treatment options for patients with hormone-resistant prostate cancer are very limited and, even with toxic therapy, such as docetaxel, the life expectancy is only improved by a median of 2 months. Advances in molecular oncology have identified key signalling pathways that are considered to be driving events in prostate carcinogenesis. The activation of multiple signalling pathways increases further the possibility of cross-talk among 'linear' signalling cascades. Hence signalling networks that may incorporate distinct pathways in prostate cancer, particularly in hormone-resistant disease, are increasingly appreciated in drug development programmes. With the development of potent small-molecule inhibitors capable of specifically suppressing the activities of individual 'linear' cascades, it may be that, by combining these agents as guided by the molecular signature of prostate cancer, a more efficient therapeutic regime may be developed. Therefore the present review focuses on evidence of abnormal signalling in prostate cancer and the potential of these targets in drug development, and incorporates key findings of relevant clinical trials to date.

Using surrogate biomarkers to predict clinical benefit in men with castration-resistant prostate cancer: an update and review of the literature

Recurrent prostate cancer has a complex molecular etiology and a prolonged disease course. Although initially responsive to androgen ablation, many men eventually become castration resistant, develop skeletal metastases, and are palliatively treated with docetaxel-based chemotherapy, radiation therapy, bisphosphonates, and best supportive care. Given the modest success rates of the current standard of care, clinical trial enrollment is encouraged. Castration-resistant prostate cancer (CRPC) is a heterogeneous disease, both in clinical manifestations and outcomes, requiring an individualized approach to both patient care and trial design. Herein, we review surrogate markers of disease progression and treatment efficacy in advanced prostate cancer in light of recently published guidelines that have redefined eligibility, response criteria, and suitable endpoints in prostate cancer drug development. The guidelines have refined outcome measures to potentially better capture clinical benefit and the ability of novel targeted molecular and biologic agents to impact favorably on this disease. We consider prostate-specific antigen changes, circulating tumor cells, bone scan alterations, markers of bone metabolism (urinary N-telopeptide and bone-specific alkaline phosphatase), pain improvements, and progression-free survival. To illustrate the role and challenges of these potential biomarkers and endpoints in drug development, we discuss a class of novel molecularly targeted agents, the src kinase inhibitors. Given that there are currently no validated surrogate markers of overall survival for assessing early clinical benefit from systemic therapy in metastatic CRPC, incorporation of relevant biomarkers into all phases of clinical development is essential to accelerate drug development in this field.

Genomic approaches to outcome prediction in prostate cancer

Prostate cancer remains a common cause of cancer death in men. Applications of emerging genomic technologies to high-quality prostate cancer models and patient samples in multiple contexts have made significant contributions to our molecular understanding of the development and progression of prostate cancer. Genomic analysis of DNA, RNA, and protein alterations allows for the global assessment of this disease and provides the molecular framework to improve risk classification, outcome prediction, and development of targeted therapies. In this review, the author focused on highlighting recent work in genomics and its role in evaluating molecular modifiers of prostate cancer risk and behavior and the development of predictive models that anticipate the risk of developing prostate cancer, prostate cancer progression, and the response of prostate cancer to therapy. This framework has the exciting potential to be predictive and to provide personalized and individual treatment to the large number of men diagnosed with prostate cancer each year. Cancer 2009;115(13 suppl):3046-57. (c) 2009 American Cancer Society.

Systems pathology: a paradigm shift in the practice of diagnostic and predictive pathology

Diagnostic tumor pathology in the context of personalized medicine has progressed from an interpretive, subjective science to a more objective, evidence-based practice. This has resulted in the development of several tissue-based, molecular-driven tests that provide information regarding prognosis and response to therapy. The challenge, however, for both the pathologist and the treating physician is how best to effectively integrate this data into a comprehensive treatment plan that includes a patient-specific risk assessment. To address this need, the authors developed a systems pathology approach to the practice of clinical molecular medicine through technical advances in object-oriented image analysis, and phenotyping at the microanatomical level using deparaffinized tissue section and quantitative biomarker multiplexing. With support vector regression for censored data, they have been able to integrate complex information and provide a patient-specific risk profile based on the clinical endpoint under investigation. Cancer 2009;115(13 suppl):3078-84. (c) 2009 American Cancer Society.

Integrated expression profiling and ChIP-seq analyses of the growth inhibition response program of the androgen receptor

Background

The androgen receptor (AR) plays important roles in the development of male phenotype and in different human diseases including prostate cancers. The AR can act either as a promoter or a tumor suppressor depending on cell types. The AR proliferative response program has been well studied, but its prohibitive response program has not yet been thoroughly studied.

Methodology/Principal Findings

Previous studies found that PC3 cells expressing the wild-type AR inhibit growth and suppress invasion. We applied expression profiling to identify the response program of PC3 cells expressing the AR (PC3-AR) under different growth conditions (i.e. with or without androgens and at different concentration of androgens) and then applied the newly developed ChIP-seq technology to identify the AR binding regions in the PC3 cancer genome. A surprising finding was that the comparison of MOCK-transfected PC3 cells with AR-transfected cells identified 3,452 differentially expressed genes (two fold cutoff) even without the addition of androgens (i.e. in ethanol control), suggesting that a ligand independent activation or extremely low-level androgen activation of the AR. ChIP-Seq analysis revealed 6,629 AR binding regions in the cancer genome of PC3 cells with an FDR (false discovery rate) cut off of 0.05. About 22.4% (638 of 2,849) can be mapped to within 2 kb of the transcription start site (TSS). Three novel AR binding motifs were identified in the AR binding regions of PC3-AR cells, and two of them share a core consensus sequence CGAGCTCTTC, which together mapped to 27.3% of AR binding regions (1,808/6,629). In contrast, only about 2.9% (190/6,629) of AR binding sites contains the canonical AR matrix M00481, M00447 and M00962 (from the Transfac database), which is derived mostly from AR proliferative responsive genes in androgen dependent cells. In addition, we identified four top ranking co-occupancy transcription factors in the AR binding regions, which include TEF1 (Transcriptional enhancer factor), GATA (GATA transcription factors), OCT (octamer transcription factors) and PU1 (PU.1 transcription factor).

Conclusions/Significance

Our data provide a valuable data set in understanding the molecular basis for growth inhibition response program of the AR in prostate cancer cells, which can be exploited for developing novel prostate cancer therapeutic strategies.

Erlotinib has moderate single-agent activity in chemotherapy-naïve castration-resistant prostate cancer: final results of a phase II trial

OBJECTIVES

To investigate the efficacy and toxicity of single-agent erlotinib in chemotherapy-naive castration-resistant prostate cancer.

METHODS

Eligible patients received erlotinib at 150 mg daily until disease progression. Toxicity was assessed every 2 weeks and responses every 8 weeks. Primary end point was assessing the overall clinical benefit measured as the sum of stable disease, partial response, and complete response. Secondary end points included time to disease progression, overall survival, and toxicity using the National Cancer Institute Common Toxicity Criteria version 3.0.

RESULTS

A total of 29 patients were enrolled in this study. Median age was 77 and median prostate-specific antigen was 66.3 ng/mL. Of 22 evaluable patients, 2 met the criteria for partial response and 5 demonstrated stable disease for an overall clinical benefit of 31%. PSA-doubling time improved in all responding patients to a median of 6 months from 3 months before entry into the study. One patient remained in study at 28 months, and 2 had > 50% decrease in their serum PSA level. Median time to disease progression was 2 months, but at 12 months, 9% of patients were progression-free. Median overall survival was 16.3 months, with 1- and 2-year survival rates of 58% and 27%, respectively. Erlotinib was well tolerated, with only 2 patients requiring dose reductions. Adverse events were as expected with grade 3 or 4 diarrhea, fatigue, and rash occurring in 10%, 6%, and 6% of patients, respectively.

CONCLUSIONS

Erlotinib has moderate activity in chemotherapy-naive castration-resistant prostate cancer, with some patients showing biochemical response. Future studies investigating this agent in combination are warranted. (This trial was registered at http://NCI.gov, NCT00272038).

Transcriptionally regulated, prostate-targeted gene therapy for prostate cancer

Prostate cancer is the most frequently diagnosed cancer and the second leading cause of cancer deaths in American males today. Novel and effective treatment such as gene therapy is greatly desired. The early viral based gene therapy uses tissue-nonspecific promoters, which causes unintended toxicity to other normal tissues. In this chapter, we will review the transcriptionally regulated gene therapy strategy for prostate cancer treatment. We will describe the development of transcriptionally regulated prostate cancer gene therapy in the following areas: (1) Comparison of different routes for best viral delivery to the prostate; (2) Study of transcriptionally regulated, prostate-targeted viral vectors: specificity and activity of the transgene under several different prostate-specific promoters were compared in vitro and in vivo; (3) Selection of therapeutic transgenes and strategies for prostate cancer gene therapy (4) Oncolytic virotherapy for prostate cancer. In addition, the current challenges and future directions in this field are also discussed.

Steroidogenesis inhibitors alter but do not eliminate androgen synthesis mechanisms during progression to castration-resistance in LNCaP prostate xenografts

In castration-resistant prostate cancer (CRPC) many androgen-regulated genes become re-expressed and tissue androgen levels increase despite low serum levels. We and others have recently reported that CRPC tumor cells can de novo synthesize androgens from adrenal steroid precursors or cholesterol and that high levels of progesterone exist in LNCaP tumors after castration serving perhaps as an intermediate in androgen synthesis. Herein, we compare androgen synthesis from [(3)H-progesterone] in the presence of specific steroidogenesis inhibitors and anti-androgens in steroid starved LNCaP cells and CRPC tumors. Similarly, we compare steroid profiles in LNCaP tumors at different stages of CRPC progression. Steroidogenesis inhibitors targeting CYP17A1 and SRD5A2 significantly altered but did not eliminate androgen synthesis from progesterone in steroid starved LNCaP cells and CRPC tumors. Upon exposure to inhibitors of steroidogenesis prostate cancer cells adapt gradually during CRPC progression to synthesize DHT in a compensatory manner through alternative feed-forward mechanisms. Furthermore, tumors obtained immediately after castration are significantly less efficient at metabolizing progesterone ( approximately 36%) and produce a different steroid profile to CRPC tumors. Optimal targeting of the androgen axis may be most effective when tumors are least efficient at synthesizing androgens. Confirmatory studies in humans are required to validate these findings.

A novel androgen receptor amino terminal region reveals two classes of amino/carboxyl interaction-deficient variants with divergent capacity to activate responsive sites in chromatin

The androgen receptor (AR) is an important signaling molecule in multiple tissues, yet its mode of action and cell-specific activities remain enigmatic. AR function has been best studied in the prostate, in which it is essential for growth and homeostasis of the normal organ as well as each stage of cancer development. Investigation of mechanisms responsible for continued AR action that evolve during prostate cancer progression or after hormonal management of the disease have been instructive in defining AR signaling pathways. In the current paper, we use sequence similarity and the collocation of somatic mutations in prostate cancer to define residues 501-535 of the AR amino-terminal domain as an important mediator of receptor function. Specifically, the 501-535 region is required for optimal interaction of the amino-terminal domain with both the p160 coactivator, nuclear receptor coactivator-2, and the AR-ligand binding domain in the amino/carboxyl (N/C) interaction. The N/C interaction is decreased by deletion of the 501-535 region but is distinct from deletion of the (23)FQNLF(27) peptide in that it does not affect the capacity of the AR to activate transcription from a chromatin integrated reporter or recruitment of the receptor to androgen-responsive loci in vivo. Collectively, we have been able to outline two classes of N/C-deficient AR variant that are divergent in their capacity to act in a chromatin context, thereby further defining the interplay between N/C interaction and coregulator recruitment via multiple receptor domains. These mechanisms are likely to be key determinants of the cell and promoter specific activities of the AR.

Selective expression of CD44, a putative prostate cancer stem cell marker, in neuroendocrine tumor cells of human prostate cancer

BACKGROUND

Hormonal therapy is effective for advanced prostate cancer (PC) but the disease often recurs and becomes hormone-refractory. It is hypothesized that a subpopulation of cancer cells, that is, cancer stem cells (CSCs), survives hormonal therapy and leads to tumor recurrence. CD44 expression was shown to identify tumor cells with CSC features. PC contains secretory type epithelial cells and a minor population of neuroendocrine cells. Neuroendocrine cells do not express androgen receptor and are quiescent, features associated with CSCs. The purpose of the study was to determine the expression of CD44 in human PC and its relationship to neuroendocrine tumor cells.

METHODS

Immunohistochemistry and immunofluorescence were performed to study CD44 expression in PC cell lines, single cells from fresh PC tissue and archival tissue sections of PC. We then determined if CD44+ cells represent neuroendocrine tumor cells.

RESULTS

In human PC cell lines, expression of CD44 is associated with cells of NE phenotype. In human PC tissues, NE tumor cells are virtually all positive for CD44 and CD44+ cells, excluding lymphocytes, are all NE tumor cells.

CONCLUSIONS

Selective expression of the stem cell-associated marker CD44 in NE tumor cells of PC, in combination with their other known features, further supports the significance of such cells in therapy resistance and tumor recurrence.

Stanniocalcin 2 overexpression in castration-resistant prostate cancer and aggressive prostate cancer

Prostate cancer is usually androgen-dependent and responds well to androgen ablation therapy based on castration. However, at a certain stage some prostate cancers eventually acquire a castration-resistant phenotype where they progress aggressively and show very poor response to any anticancer therapies. To characterize the molecular features of these clinical castration-resistant prostate cancers, we previously analyzed gene expression profiles by genome-wide cDNA microarrays combined with microdissection and found dozens of trans-activated genes in clinical castration-resistant prostate cancers. Among them, we report the identification of a new biomarker, stanniocalcin 2, as an overexpressed gene in castration-resistant prostate cancer cells. Real-time polymerase chain reaction and immunohistochemical analysis confirmed overexpression of stanniocalcin 2, a 302-amino-acid glycoprotein hormone, specifically in castration-resistant prostate cancer cells and aggressive castration-naïve prostate cancers with high Gleason scores (8-10). The gene was not expressed in normal prostate, nor in most indolent castration-naïve prostate cancers. Knockdown of stanniocalcin 2 expression by short interfering RNA in a prostate cancer cell line resulted in drastic attenuation of prostate cancer cell growth. Concordantly, stanniocalcin 2 overexpression in a prostate cancer cell line promoted prostate cancer cell growth, indicating its oncogenic property. These findings suggest that stanniocalcin 2 could be involved in aggressive phenotyping of prostate cancers, including castration-resistant prostate cancers, and that it should be a potential molecular target for development of new therapeutics and a diagnostic biomarker for aggressive prostate cancers.

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.

Molecular biology of androgen-independent prostate cancer: the role of the androgen receptor pathway

Prostate cancer (PC) cells express the androgen receptor (AR) and need the presence of androgens to survive. Androgen suppression is the gold standard first-line therapy for metastatic disease. Almost all PC patients initially respond to hormonal therapy, but most of them gradually develop resistance to castration. There is evidence that these tumours that are considered castration-resistant continue to depend on AR signalling. Several mechanisms that enhance AR signalling in an androgen-depleted environment have been elucidated: (1) AR mutations that allow activation by low androgen levels or by other endogenous steroids, (2) AR amplification and/or overexpression, (3) increased local intracrine synthesis of androgens, (4) changes in AR cofactors and (5) cross-talk with cytokines and growth factors. Today, there are a number of novel agents targeting the AR signalling pathway under development, including more effective antiandrogens; inhibitors of CYP17, inhibitors of HSP90, inhibitors of histone deacetylases and inhibitors of tyrosine kinase inhibitors.

Genomic Strategy for Targeting Therapy in Castration-Resistant Prostate Cancer

Purpose

Despite treatments which lower circulating androgens, advanced prostate cancers often maintain androgen receptor (AR) signaling. The variable response to secondary hormonal manipulations in men with castrate-resistant prostate cancer (CRPC) creates a compelling need for strategies to individualize therapy based on the molecular features of each patient's tumor.

Methods

A transcription-based AR activity signature was developed from an androgen-sensitive prostate cancer cell (LNCaP) and tested on independent data sets of prostate cancer cell lines and human tumors to assess its precision and accuracy in detecting AR activity. The AR signature was applied to multiple sets of prostate specimens to determine how AR activity changes with hormone therapy and progression and oncogenic pathway analysis was used to identify biologic pathways correlating with AR activity.

Results

A robust AR signature accurately predicts AR activity in multiple prostate cancer cell lines, has minimal variation between replicate samples, and accurately reflects an individual's hormone status and intraprostatic dihydrotestosterone levels. The AR signature finds AR activity to be high in local, untreated prostate tumors and decreased in prostate tissue after neoadjuvant hormone therapy and in CRPC. Heterogeneity of AR activity exists along the spectrum of prostate cancer progression and decreasing predicted AR activity correlates with increasing predicted Src activity and sensitivity to dasatinib (Src-targeting kinase inhibitor).

Conclusion

A transcription-based AR signature can detect AR activity within individual prostate cancer specimens and has the potential to help individualize and improve care for patients with CRPC.

Non-competitive androgen receptor inhibition in vitro and in vivo

Androgen receptor (AR) inhibitors are used to treat multiple human diseases, including hirsutism, benign prostatic hypertrophy, and prostate cancer, but all available anti-androgens target only ligand binding, either by reduction of available hormone or by competitive antagonism. New strategies are needed, and could have an important impact on therapy. One approach could be to target other cellular mechanisms required for receptor activation. In prior work, we used a cell-based assay of AR conformation change to identify non-ligand inhibitors of AR activity. Here, we characterize 2 compounds identified in this screen: pyrvinium pamoate, a Food and Drug Administration-approved drug, and harmol hydrochloride, a natural product. Each compound functions by a unique, non-competitive mechanism and synergizes with competitive antagonists to disrupt AR activity. Harmol blocks DNA occupancy by AR, whereas pyrvinium does not. Pyrvinium inhibits AR-dependent gene expression in the prostate gland in vivo, and induces prostate atrophy. These results highlight new therapeutic strategies to inhibit AR activity.

Development of a second-generation antiandrogen for treatment of advanced prostate cancer

Metastatic prostate cancer is treated with drugs that antagonize androgen action, but most patients progress to a more aggressive form of the disease called castration-resistant prostate cancer, driven by elevated expression of the androgen receptor. Here we characterize the diarylthiohydantoins RD162 and MDV3100, two compounds optimized from a screen for nonsteroidal antiandrogens that retain activity in the setting of increased androgen receptor expression. Both compounds bind to the androgen receptor with greater relative affinity than the clinically used antiandrogen bicalutamide, reduce the efficiency of its nuclear translocation, and impair both DNA binding to androgen response elements and recruitment of coactivators. RD162 and MDV3100 are orally available and induce tumor regression in mouse models of castration-resistant human prostate cancer. Of the first 30 patients treated with MDV3100 in a Phase I/II clinical trial, 13 of 30 (43%) showed sustained declines (by >50%) in serum concentrations of prostate-specific antigen, a biomarker of prostate cancer. These compounds thus appear to be promising candidates for treatment of advanced prostate cancer.

Androgen receptor controls EGFR and ERBB2 gene expression at different levels in prostate cancer cell lines

EGFR or ERBB2 contributes to prostate cancer (PCa) progression by activating the androgen receptor (AR) in hormone-poor conditions. Here, we investigated the mechanisms by which androgens regulate EGFR and ERBB2 expression in PCa cells. In steroid-depleted medium (SDM), EGFR protein was less abundant in androgen-sensitive LNCaP than in androgen ablation-resistant 22Rv1 cells, whereas transcript levels were similar. Dihydrotestosterone (DHT) treatment increased both EGFR mRNA and protein levels and stimulated RNA polymerase II recruitment to the EGFR gene promoter, whereas it decreased ERBB2 transcript and protein levels in LNCaP cells. DHT altered neither EGFR or ERBB2 levels nor the abundance of prostate-specific antigen (PSA), TMEPA1, or TMPRSS2 mRNAs in 22Rv1 cells, which express the full-length and a shorter AR isoform deleted from the COOH-terminal domain (ARDeltaCTD). The contribution of both AR isoforms to the expression of these genes was assessed by small interfering RNAs targeting only the full-length or both AR isoforms. Silencing of both isoforms strongly reduced PSA, TMEPA1, and TMPRSS2 transcript levels. Inhibition of both AR isoforms did not affect EGFR and ERBB2 transcript levels but decreased EGFR and increased ERBB2 protein levels. Proliferation of 22Rv1 cells in SDM was inhibited in the absence of AR and ARDeltaCTD. A further decrease was obtained with PKI166, an EGFR/ERBB2 kinase inhibitor. Overall, we showed that ARDeltaCTD is responsible for constitutive EGFR expression and ERBB2 repression in 22Rv1 cells and that ARDeltaCTD and tyrosine kinase receptors are necessary for sustained 22Rv1 cell growth.

Genome-wide impact of androgen receptor trapped clone-27 loss on androgen-regulated transcription in prostate cancer cells

The androgen receptor (AR) directs diverse biological processes through interaction with coregulators such as AR trapped clone-27 (ART-27). Our results show that ART-27 is recruited to AR-binding sites by chromatin immunoprecipitation analysis. In addition, the effect of ART-27 on genome-wide transcription was examined. The studies indicate that loss of ART-27 enhances expression of many androgen-regulated genes, suggesting that ART-27 inhibits gene expression. Surprisingly, classes of genes that are up-regulated upon ART-27 depletion include regulators of DNA damage checkpoint and cell cycle progression, suggesting that ART-27 functions to keep expression levels of these genes low. Consistent with this idea, stable reduction of ART-27 by short-hairpin RNA enhances LNCaP cell proliferation compared with control cells. The effect of ART-27 loss was also examined in response to the antiandrogen bicalutamide. Unexpectedly, cells treated with ART-27 siRNA no longer exhibited gene repression in response to bicalutamide. To examine ART-27 loss in prostate cancer progression, immunohistochemistry was conducted on a tissue array containing samples from primary tumors of individuals who were clinically followed and later shown to have either recurrent or nonrecurrent disease. Comparison of ART-27 and AR staining indicated that nuclear ART-27 expression was lost in the majority of AR-positive recurrent prostate cancers. Our studies show that reduction of ART-27 protein levels in prostate cancer may facilitate antiandrogen-resistant disease.

Osteoblast-induced EGFR/ERBB2 signaling in androgen-sensitive prostate carcinoma cells characterized by multiplex kinase activity profiling

Bone metastases in prostate cancer are predominantly osteoblastic. To study regulatory mechanisms underlying the establishment of prostate cancer within an osteoblastic microenvironment, human androgen-sensitive prostate carcinoma cells (LNCaP) were treated with culture medium conditioned by human osteoblast-derived sarcoma cells (OHS), and activated signalling pathways in the carcinoma cells were analyzed using microarrays with tyrosine kinase substrates. Network interaction analysis of substrates with significantly increased phosphorylation levels revealed that signalling pathways mediated by EGFR and ERBB2 were activated in LNCaP cells under OHS influence but also by androgen treatment. Activation of EGFR/ERBB2 signalling was also found in LNCaP cells in cocultures with OHS cells or osteoblastic cells that had been differentiated from human mesenchymal stem cells. Our experimental data suggests osteoblast-directed induction of signalling activity via EGFR and ERBB2 in prostate carcinoma cells and may provide a rationale for the use of EGFR or ERBB2 inhibition in systemic prevention or treatment of metastatic prostate cancer in the androgen-sensitive stage of the disease.

Heterogeneous nuclear ribonucleoprotein K is a novel regulator of androgen receptor translation

The regulation of androgen receptor (AR) expression in prostate cancer is still poorly understood. The activation of the epidermal growth factor receptor (EGFR) in prostate cancer cells was previously shown to lower AR expression by a rapamycin-sensitive, posttranscriptional mechanism involving the AR mRNA 5'-untranslated region (5'-UTR). In a search for an intermediate within the EGFR/phosphoinositide 3-kinase/Akt/mammalian target of rapamycin pathway that regulates AR at this site, we identified the nucleic acid-binding protein, heterogeneous nuclear ribonucleoprotein K (hnRNP-K), by mass spectrometric analysis of Akt immune complexes from lipid raft-enriched subcellular fractions. We show here that hnRNP-K is a novel inhibitor of AR mRNA translation that regulates androgen-responsive gene expression and prostate cancer cell proliferation. A functional hnRNP-K binding site involved in down-regulating AR protein levels was identified in the AR mRNA 5'-UTR. Further analysis revealed that hnRNP-K is also able to inhibit AR translation in the absence of the 5'-UTR, consistent with the presence of additional predicted hnRNP-K binding sites within the AR open reading frame and in the 3'-UTR. Immunohistochemical analysis of a human prostate cancer tissue microarray revealed an inverse correlation between hnRNP-K expression and AR protein levels in organ-confined prostate tumors and a substantial decline in cytoplasmic hnRNP-K in metastases, despite an overall increase in hnRNP-K levels in metastatic tumors. These data suggest that translational inhibition of AR by hnRNP-K may occur in organ-confined tumors but possibly at a reduced level in metastases. HnRNP-K is the first protein identified that directly interacts with and regulates the AR translational apparatus.

Testosterone deficiency syndrome: treatment and cancer risk

Testosterone deficiency syndrome (TDS) can be linked to premature mortality and to a number of co-morbidities (such as sexual disorders, diabetes, metabolic syndrome, ...). Testosterone deficiency occurs mainly in ageing men, at a time when prostate disease (benign or malign) start to emerge. New testosterone preparations via different route of administration appeared during the last decade allowing optimized treatment to these patients. One potential complication of this treatment is the increased risk of prostate and breast cancer. Consequently, the guidelines from the agencies and the institutions, the recommendations of the scientific expert committees and the attitude of the clinicians to who, when and how to treat hypogonadal patients, is very conservative, not to say, highly restrictive. To date, as documented in many reviews on the subject, nothing has been found to support the evidence that restoring testosterone levels within normal range increases the incidence of prostate cancer. In our experience, during a long-term clinical study including 200 hypogonadal patients receiving a patch of testosterone, 50 patients ended 5 years of treatment and no prostate cancer have been reported. In fact, the incidence of prostate cancer in primary or secondary testosterone treated hypogonadal men is lower than the incidence observed in the untreated eugonadal population. However, even if the number of patients treated in well-conducted clinical trials for whom cancer of the prostate has been reported is insignificant (a very few), the observed population is still too small to raise definite conclusions. Low testosterone levels have been reported in patients undergoing radical prostatectomy and the outcomes are of worse diagnostic in this population; at a later stage, testosterone deficiency can be induced by anti hormonal manipulation of patient with a prostate cancer, leading to the symptoms of hypogonadism. The question is to know whether it is justified, in case of profound symptoms, to supplement those patients with testosterone. Some attempts have been made and the results are encouraging: so it is time to re-examine our position and to question about the definite recommendation that patients with prostate cancer should never receive testosterone supplementation therapy; this is already the situation when intermittent androgen blockade is initiated if the biological response is satisfactory. Furthermore, it has been advocated that, under a rigorous surveillance, patients cured of prostate cancer can be treated with testosterone supplementation with beneficial results.

Inhibition of AR-mediated transcription by binding of Oct1 to a motif enriched in AR-occupied regions

BACKGROUND

The androgen receptor (AR) plays roles in prostate development and cancer (PCa). In response to androgens, the AR binds to androgen-response elements (AREs) to modulate gene transcription. The responses of such genes are dependent on the cellular milieu and on sequences around the AREs, which attract other transcription factors. Previously, bioinformatic analysis of 62 AR-occupied regions (ARORs) in PCa cells revealed enrichment for both AREs and a TTGGCAAATA-like motif. We undertook the present study to investigate the significance of the TTGGCAAATA-like motif.

METHODS

Prostate cancer cell lines, LNCaP and C4-2B, were analyzed by transient transfections of wild-type and mutant reporter constructs, electro-mobility shift assays (EMSAs), and RT-qPCR analysis of endogenous genes.

RESULTS

In two of six tested ARORs, point mutations in the TTGGCAAATA-like motif resulted in inhibition of DHT-mediated enhancer activity. EMSA revealed that Oct1 bound the motif, and that the mutations that abolished DHT responsiveness in the transfection assays augmented Oct1 binding. These results suggest a role for Oct1 as a context-dependent negative coregulator of AR. Consistent with this, siRNA knockdown of Oct1 increased the DHT-mediated enhancer activity of transfected reporters as well as an endogenous AR target gene, transglutaminase 2.

CONCLUSIONS

Oct1 negatively regulates DHT-mediated enhancer activity in a subset of ARORs. The enrichment of ARORs for the Oct-binding, TTGGCAAATA-like motif may reflect a mechanism that utilizes Oct1 to keep AR activity in check at some ARORs, while augmenting AR activity in other ARORs. Therefore, Oct1 may have regulatory functions in prostate development and cancer progression.

A century of deciphering the control mechanisms of sex steroid action in breast and prostate cancer: the origins of targeted therapy and chemoprevention

The origins of the story to decipher the mechanisms that control the growth of sex hormone-dependent cancers started more than 100 years ago. Clinical observations of the apparently random responsiveness of breast cancer to endocrine ablation (hormonal withdrawal) provoked scientific inquiries in the laboratory that resulted in the development of effective strategies for targeting therapy to the estrogen receptor (ER; or androgen receptor in the case of prostate cancer), the development of antihormonal treatments that dramatically enhanced patient survival, and the first successful testing of agents to reduce the risk of developing any cancer. Most importantly, elucidating the receptor-mediated mechanisms of sex steroid-dependent growth and the clinical success of antihormones has had broad implication in medicinal chemistry with the synthesis of new selective hormone receptor modulators for numerous clinical applications. Indeed, the successful translational research on the ER was the catalyst for the current strategy for developing targeted therapies to the tumor and the start of "individualized medicine." During the past 50 years, ideas about the value of antihormones translated effectively from the laboratory to improve clinical care, improve national survival rates, and significantly reduced the burden of cancer.

Id-1 expression in androgen-dependent prostate cancer is negatively regulated by androgen through androgen receptor

This study discovered that Id-1 expression in androgen-dependent prostate cancer decreased immediately after androgen deprivation but increased after longer androgen deprivation both in vivo and in vitro. Id-1 expression in androgen-independent LNCaP cells was about 6 fold as that in their parental cells. As was the case with LNCaP cells, when androgen receptor (AR) was introduced into AR-negative PC-3 cells, dihydrotestosterone inhibited while flutamide increased Id-1 expression. Thus, Id-1 expression in androgen-dependent prostate cancer was negatively regulated by androgen in a receptor-dependent way. The re-increased Id-1 might partially contribute to the emergence of androgen-independent prostate cancer after longer androgen deprivation therapy.

Ligand-independent androgen receptor variants derived from splicing of cryptic exons signify hormone-refractory prostate cancer

Suppression of androgen production and function provides palliation but not cure in men with prostate cancer (PCa). Therapeutic failure and progression to hormone-refractory PCa (HRPC) are often accompanied by molecular alterations involving the androgen receptor (AR). In this study, we report novel forms of AR alteration that are prevalent in HRPC. Through in silico sequence analysis and subsequent experimental validation studies, we uncovered seven AR variant transcripts lacking the reading frames for the ligand-binding domain due to splicing of "intronic" cryptic exons to the upstream exons encoding the AR DNA-binding domain. We focused on the two most abundantly expressed variants, AR-V1 and AR-V7, for more detailed analysis. AR-V1 and AR-V7 mRNA showed an average 20-fold higher expression in HRPC (n = 25) when compared with hormone-naive PCa (n = 82; P < 0.0001). Among the hormone-naive PCa, higher expression of AR-V7 predicted biochemical recurrence following surgical treatment (P = 0.012). Polyclonal antibodies specific to AR-V7 detected the AR-V7 protein frequently in HRPC specimens but rarely in hormone-naive PCa specimens. AR-V7 was localized in the nuclei of cultured PCa cells under androgen-depleted conditions, and constitutively active in driving the expression of canonical androgen-responsive genes, as revealed by both AR reporter assays and expression microarray analysis. These results suggest a novel mechanism for the development of HRPC that warrants further investigation. In addition, as expression markers for lethal PCa, these novel AR variants may be explored as potential biomarkers and therapeutic targets for advanced PCa.

Short alleles of both GGN and CAG repeats at the exon-1 of the androgen receptor gene are associated to increased PSA staining and a higher Gleason score in human prostatic cancer

The exon 1 of the human androgen receptor (AR) gene contains two length polymorphisms of CAG (polyglutamine) and GGN (polyglycine). "In vitro" experiments suggest that the larger GGN repeats provide a lower AR-protein yield, whereas the larger CAG repeats decrease the AR transcriptional activity, both decreasing the AR signalling intensity. Here we have tested such possibilities in human prostatic cancer (CaP) specimens. We used 72 archival samples of radical prostatectomy. Parallel slides were used for AR protein or PSA immunohistochemistry, and for genotyping studies. Polymorphisms were genotyped by PCR, fragment length analysis and sequencing selected samples. The AR staining was positively correlated with the Gleason score (r=0.320; P=0.005), but it was not correlated to CAG or GGN repeat length or PSA staining. The number of GGN repeats was negatively correlated to the intensity of PSA staining (r=-0.243; P=0.04). Combination of short alleles of both tracts was significantly higher in: the heavier stained tertiles for PSA (P=0.03) and AR (P=0.06); and in the subgroup of samples having a Gleason score of 7 or higher (P=0.021). The results support the hypothesis that the shorter alleles of CAG and GGN repeats in the AR gene are associated to an increased AR signalling intensity in human prostate cancer, and with more aggressive forms of the disease.

[Management of metastatic androgeno-independent prostate cancer]

After first line hormonal therapy (agonist LHRH), metastasic prostate cancer becomes androgen independent in a period of 18 months on average. After this period and after having verified the castration by blood testosterone level, a few options are possible: either inhibit adrenal androgens by maximum androgen blockage (+anti androgens) or by specific adrenal androgen inhibitors. It is also possible to use estrogen or, in a few cases, to propose chemotherapy.

Circulating tumor cells predict survival benefit from treatment in metastatic castration-resistant prostate cancer

PURPOSE

A method for enumerating circulating tumor cells (CTC) has received regulatory clearance. The primary objective of this prospective study was to establish the relationship between posttreatment CTC count and overall survival (OS) in castration-resistant prostate cancer (CRPC). Secondary objectives included determining the prognostic utility of CTC measurement before initiating therapy, and the relationship of CTC to prostate-specific antigen (PSA) changes and OS at these and other time points.

EXPERIMENTAL DESIGN

Blood was drawn from CRPC patients with progressive disease starting a new line of chemotherapy before treatment and monthly thereafter. Patients were stratified into predetermined Favorable or Unfavorable groups (<5 and > or =5 CTC/7.5mL).

RESULTS

Two hundred thirty-one of 276 enrolled patients (84%) were evaluable. Patients with Unfavorable pretreatment CTC (57%) had shorter OS (median OS, 11.5 versus 21.7 months; Cox hazard ratio, 3.3; P < 0.0001). Unfavorable posttreatment CTC counts also predicted shorter OS at 2 to 5, 6 to 8, 9 to 12, and 13 to 20 weeks (median OS, 6.7-9.5 versus 19.6-20.7 months; Cox hazard ratio, 3.6-6.5; P < 0.0001). CTC counts predicted OS better than PSA decrement algorithms at all time points; area under the receiver operator curve for CTC was 81% to 87% and 58% to 68% for 30% PSA reduction (P = 0.0218). Prognosis for patients with (a) Unfavorable baseline CTC who converted to Favorable CTC improved (6.8 to 21.3 months); (b) Favorable baseline CTC who converted to Unfavorable worsened (>26 to 9.3 months).

CONCLUSIONS

CTC are the most accurate and independent predictor of OS in CRPC. These data led to Food and Drug Administration clearance of this assay for the evaluation of CRPC.

EBP1, an ErbB3-binding protein, is decreased in prostate cancer and implicated in hormone resistance

Aberrant activation of the androgen receptor (AR) by the ErbB2/ErbB3 heterodimer contributes to the development of hormone resistance in prostate cancer. EBP1, an ErbB3-binding protein, acts as an AR corepressor. As EBP1 is decreased in preclinical models of hormone-refractory prostate cancer, we studied the expression of EBP1 in human prostate cancer. We found that the expression of the EBP1 gene was significantly decreased in prostate cancer tissues compared with benign prostate at both mRNA and protein levels. Restoration of EBP1 expression in the hormone-refractory LNCaP C81 cell line led to an amelioration of the androgen-independent phenotype based on established biological criteria and a reduction in the expression of a cohort of AR target genes. The ability of the ErbB3 ligand heregulin (HRG) to stimulate growth and AKT phosphorylation of hormone-refractory prostate cancer cells was abolished. Abrogation of EBP1 expression by short hairpin RNA in hormone-dependent LNCaP cells, which undergo apoptosis in response to HRG, resulted in HRG-stimulated cell growth. Restoration of EBP1 expression decreased the tumorigenicity of C81 xenografts in female mice, whereas elimination of EBP1 expression enhanced the ability of LNCaP cells to grow in female mice. Our data support a role for EBP1 in the development of hormone-refractory prostate cancer via inhibition of both AR- and HRG-stimulated growth and present a novel strategy for treating androgen-refractory prostate cancer.

Genomic androgen receptor-occupied regions with different functions, defined by histone acetylation, coregulators and transcriptional capacity

BACKGROUND

The androgen receptor (AR) is a steroid-activated transcription factor that binds at specific DNA locations and plays a key role in the etiology of prostate cancer. While numerous studies have identified a clear connection between AR binding and expression of target genes for a limited number of loci, high-throughput elucidation of these sites allows for a deeper understanding of the complexities of this process.

METHODOLOGY/PRINCIPAL FINDINGS

We have mapped 189 AR occupied regions (ARORs) and 1,388 histone H3 acetylation (AcH3) loci to a 3% continuous stretch of human genomic DNA using chromatin immunoprecipitation (ChIP) microarray analysis. Of 62 highly reproducible ARORs, 32 (52%) were also marked by AcH3. While the number of ARORs detected in prostate cancer cells exceeded the number of nearby DHT-responsive genes, the AcH3 mark defined a subclass of ARORs much more highly associated with such genes -- 12% of the genes flanking AcH3+ARORs were DHT-responsive, compared to only 1% of genes flanking AcH3-ARORs. Most ARORs contained enhancer activities as detected in luciferase reporter assays. Analysis of the AROR sequences, followed by site-directed ChIP, identified binding sites for AR transcriptional coregulators FoxA1, CEBPbeta, NFI and GATA2, which had diverse effects on endogenous AR target gene expression levels in siRNA knockout experiments.

CONCLUSIONS/SIGNIFICANCE

We suggest that only some ARORs function under the given physiological conditions, utilizing diverse mechanisms. This diversity points to differential regulation of gene expression by the same transcription factor related to the chromatin structure.

Novel tracers and their development for the imaging of metastatic prostate cancer

There are presently no accurate methods of imaging prostate cancer metastases to bone. An unprecedented number of novel imaging agents, based on the biology of the disease, are now available for testing. We reviewed contemporary molecular imaging modalities that have been tested in humans with metastatic prostate cancer, with consideration of the studies' adherence to current prostate cancer clinical trial designs. Articles from the years 2002 to 2008 on PET using (18)F-FDG, (11)C-choline, (18)F-choline, (18)F-flouride, (11)C-acetate, (11)C-methionine, and (18)F-fluoro-5alpha-dihydrotestosterone in patients with metastatic prostate cancer were reviewed. Although these studies are encouraging, most focus on the rising population with prostate-specific antigen, and many involve small numbers of patients and do not adhere to consensus criteria for clinical trial designs in prostate cancer. Hence, although many promising agents are available for testing, such studies would benefit from closer collaboration between those in the fields of medical oncology and nuclear medicine.