Stem cell differentiation within the human prostate epithelium: implications for prostate carcinogenesis

Cancer Stem Cell Markers for Urinary Carcinoma

Cancer stem cell (CSC) refers to cancer cells with stem cell properties, that is, they have the ability of “self-renewal” and “differentiation.” Cancer stem cells exist in cancer cells and are the “culprit” of cancer recurrence and metastasis. It is difficult to be found because of its small amount, and it is difficult for anticancer drugs to produce effects on it. At present, the isolation and identification of cancer stem cells from many solid tumors are still quite difficult, mainly due to the lack of specific molecular markers of cancer stem cells. In this review, cancer stem cell surface markers and functional markers in urinary system were summarized. These markers can provide molecular targets for cancer therapy.

TGF-BETA IN THE NATURAL HISTORY OF PROSTATE CANCER

All transforming growth factors beta (TGFß) are cytokines that regulate several cellular functions such as cell growth, differentiation and motility. They may also have a role in immunosuppression. Their role is important for normal prostate development. TGFß is active in the regulation of balance between epithelial cell proliferation and apoptosis through stromal epithelia via the androgen receptor action. TGFß protects and maintains prostate stem cells, an important population necessary for prostate tissue regeneration. However, TGFß is shown to have a contrasting role in prostate tumor genesis. In the early stages of tumor development, TGFß acts as a tumor suppressor, whereas in the later stages, TGFß becomes a tumor promoter by inducing proliferation, invasion and metastasis. In this review, we outline complex interactions that TGFß-mediated signaling has on prostate tumor genesis, focusing on the role of these interactions during the course of prostate cancer and, in particular, during disease progression.

Reversibility of castration resistance status after Radium-223 dichloride treatment: clinical evidence and review of the literature

In the history of prostate cancer, some of the patients progressed to castration-resistant prostate cancer (CRPC) stage and, although new drugs and treatment protocols have been introduced, CRPC presents poor prognosis. This review is focused on biological mechanisms, underlying CRPC described in scientific literature in order to explain the reversion of resistance to castration. We present the case of a 73-year-old man, affected by bone metastatic CRPC, early treated with Radium-223 with a complete response. After 15 months from Radium-223 treatment, prostate-specific antigen increased with radiological progression. Androgen deprivation therapy was again performed and was effective, despite previous CRPC condition and no known mechanisms that may explain the reversion of this condition. Therefore, to our knowledge, he is the unique described case of the reversion of resistance to castration. Nevertheless, promising aspects may be lack of intrametastatic production of androgen or the suppression of bypass androgen receptor signaling pathways. Furthermore, the cytotoxic action of Radium-223 on cancer stem cell (CSC), due to surrounding clones with high-bone turnover, or the immune response that underlying the abscopal effect, may also modulate the reversion of CRPC after Radium-223. If confirmed by multicenter trials, the reversion of CRPC may impact on the management of prostate cancer.

Neuroendocrine Differentiation in Prostatic Malignancy

Neuroendocrine differentiation in prostatic malignancy is receiving considerable attention; this occurs commonly as a “focal” histological variant and, most rarely, in the form of small cell carcinoma (“oat cell carcinoma”) and carcinoid tumor. In prostate cancer, neuroendocrine differentiation may be the response to androgen deprivation and neuroendocrine products, either biogenic amines or peptides, have been shown to stimulate proliferation of androgen-ablation refractory cancer cells. Serum chromogranins, neuron-specific enolase and other neuroendocrine products as well as 111-In-chromogranin A “three step” immunoscintigraphy and somatostatin-receptor scintigraphy may be useful for predicting tumor behaviour and patient prognosis.

Several of the neuroendocrine products, particularly somatostatin analogues, are candidates for new therapeutic approaches. The paper aims to outline the advances in this field on the basis of the review of the literature.

Ecotropic viral integration site 1, a novel oncogene in prostate cancer

Prostate cancer (PCa) is the most commonly diagnosed non-cutaneous cancer in men in the western world. Mutations in tumor suppressor genes and in oncogenes are important for PCa progression, whereas the role of stem cell proteins in prostate carcinogenesis is insufficiently examined. This study investigates the role of the transcriptional regulator Ecotropic Viral Integration site 1 (EVI1), known as an essential modulator of hematopoietic and leukemic stem cell biology, in prostate carcinogenesis. We show that in healthy prostatic tissue, EVI1 expression is confined to the prostate stem cell compartment located at the basal layer, as identified by the stem cell marker CD44. Instead, in a PCa progression cohort comprising 219 samples from patients with primary PCa, lymph node and distant metastases, EVI1 protein was heterogeneously distributed within samples and high expression is associated with tumor progression (P<0.001), suggesting EVI1 induction as a driver event. Functionally, short hairpin RNA-mediated knockdown of EVI1 inhibited proliferation, cell cycle progression, migratory capacity and anchorage-independent growth of human PCa cells, while enhancing their apoptosis sensitivity. Interestingly, modulation of EVI1 expression also strongly regulated stem cell properties (including expression of the stem cell marker SOX2) and in vivo tumor initiation capacity. Further emphasizing a functional correlation between EVI1 induction and tumor progression, upregulation of EVI1 expression was noted in experimentally derived docetaxel-resistant PCa cells. Importantly, knockdown of EVI1 in these cells restored sensitivity to docetaxel, in part by downregulating anti-apoptotic BCL2. Together, these data indicate EVI1 as a novel molecular regulator of PCa progression and therapy resistance that may control prostate carcinogenesis at the stem cell level.

Current Stem Cell Biomarkers and Their Functional Mechanisms in Prostate Cancer

Currently there is little effective treatment available for castration resistant prostate cancer, which is responsible for the majority of prostate cancer related deaths. Emerging evidence suggested that cancer stem cells might play an important role in resistance to traditional cancer therapies, and the studies of cancer stem cells (including specific isolation and targeting on those cells) might benefit the discovery of novel treatment of prostate cancer, especially castration resistant disease. In this review, we summarized major biomarkers for prostate cancer stem cells, as well as their functional mechanisms and potential application in clinical diagnosis and treatment of patients.

Therapy escape mechanisms in the malignant prostate

Androgen receptor (AR) is the main target for prostate cancer therapy. Clinical approaches for AR inactivation include chemical castration, inhibition of androgen synthesis and AR antagonists (anti-androgens). However, treatment resistance occurs for which an important number of therapy escape mechanisms have been identified. Herein, we summarise the current knowledge of molecular mechanisms underlying therapy resistance in prostate cancer. Moreover, the tumour escape mechanisms are arranged into the concepts of target modification, bypass signalling, histologic transformation, cancer stem cells and miscellaneous mechanisms. This may help researchers to compare and understand same or similar concepts of therapy resistance in prostate cancer and other cancer types.

Different Growth Patterns of Canine Prostatic Carcinoma Suggests Different Models of Tumor-Initiating Cells

Controversies remain regarding the cell type from which human prostate cancer originates, and many attempts have been made to identify the cellular origin of canine prostate cancer but without definitive proof. This study aims to evaluate the expression of luminal (androgen receptor [AR], cytokeratin [CK]8/18) and basal (CK14, CK5) cell markers in different histologic subtypes of canine prostatic carcinoma (PC) and to suggest the most likely tumor-initiating cells. Normal prostates (n = 8) were characterized by AR+CK8/18+ luminal cells and few CK5+ basal cells, while CK14 was absent. Similar pattern was observed in all 35 prostates with benign prostatic hyperplasia, except few scattered CK14+ basal cells in 13 samples (37.14%). AR was localized in the nucleus of both normal and hyperplastic cells. In 34 samples of PC, the following growth patterns were identified: cribriform (44.12%), solid (32.35%), small acinar/ductal (20.59%), and micropapillary (2.94%). Most PCs expressed AR and CK8/18, while CK5 and CK14 expression was observed in 25% and 20% of cases, respectively. AR revealed a variable intracellular distribution, both nuclear and cytoplasmic. Solid PC was characterized by an undifferentiated or aberrant phenotype with a reduced expression of AR and CK8/18, increased number of CK14+ cells, and 7 antigen expression patterns. This study demonstrated a predominance of differentiated luminal cell types in canine prostatic tumors, although the role of basal cells in prostate carcinogenesis should also be considered. Moreover, few scattered CK5+ cells in AR+CK8/18+ tumors identified the existence of intermediate cells, from which neoplastic transformation may alternatively commence.

Prostate stem cells in the development of benign prostate hyperplasia and prostate cancer: emerging role and concepts

Benign Prostate hyperplasia (BPH) and prostate cancer (PCa) are the most common prostatic disorders affecting elderly men. Multiple factors including hormonal imbalance, disruption of cell proliferation, apoptosis, chronic inflammation, and aging are thought to be responsible for the pathophysiology of these diseases. Both BPH and PCa are considered to be arisen from aberrant proliferation of prostate stem cells. Recent studies on BPH and PCa have provided significant evidence for the origin of these diseases from stem cells that share characteristics with normal prostate stem cells. Aberrant changes in prostate stem cell regulatory factors may contribute to the development of BPH or PCa. Understanding these regulatory factors may provide insight into the mechanisms that convert quiescent adult prostate cells into proliferating compartments and lead to BPH or carcinoma. Ultimately, the knowledge of the unique prostate stem or stem-like cells in the pathogenesis and development of hyperplasia will facilitate the development of new therapeutic targets for BPH and PCa. In this review, we address recent progress towards understanding the putative role and complexities of stem cells in the development of BPH and PCa.

Targeting the unique methylation pattern of androgen receptor (AR) promoter in prostate stem/progenitor cells with 5-aza-2'-deoxycytidine (5-AZA) leads to suppressed prostate tumorigenesis

Androgen receptor (AR) expression surveys found that normal prostate/prostate cancer (PCa) stem/progenitor cells, but not embryonic or mesenchymal stem cells, expressed little AR with high methylation in the AR promoter. Mechanism dissection revealed that the differential methylation pattern in the AR promoter could be due to differential expression of methyltransferases and binding of methylation binding protein to the AR promoter region. The low expression of AR in normal prostate/PCa stem/progenitor cells was reversed after adding 5-aza-2'-deoxycytidine, a demethylating agent, which could then lead to decreased stemness and drive cells into a more differentiated status, suggesting that the methylation in the AR promoter of prostate stem/progenitor cells is critical not only in maintaining the stemness but also critical in protection of cells from differentiation. Furthermore, induced AR expression, via alteration of its methylation pattern, led to suppression of the self-renewal/proliferation of prostate stem/progenitor cells and PCa tumorigenesis in both in vitro assays and in vivo orthotopic xenografted mouse studies. Taken together, these data prove the unique methylation pattern of AR promoter in normal prostate/PCa stem/progenitor cells and the influence of AR on their renewal/proliferation and differentiation. Targeting PCa stem/progenitor cells with alteration of methylated AR promoter status might provide a new potential therapeutic approach to battle PCa because the PCa stem/progenitor cells have high tumorigenicity.

Prostate cancer stem cells: are they androgen-responsive?

The prostate gland is highly dependent on androgens for its development, growth and function. Consequently, the prostatic epithelium predominantly consists of androgen-dependent luminal cells, which express the androgen receptor at high levels. In contrast, androgens are not required for the survival of the androgen-responsive, but androgen-independent, basal compartment in which stem cells reside. Basal and luminal cells are linked in a hierarchical pathway, which most probably exists as a continuum with different stages of phenotypic change. Prostate cancer is also characterised by heterogeneity, which is reflected in its response to treatment. The putative androgen receptor negative cancer stem cell (CSC) is likely to form a resistant core after most androgen-based therapies, contributing to the evolution of castration-resistant disease. The development of CSC-targeted therapies is now of crucial importance and identifying the phenotypic differences between CSCs and both their progeny will be key in this process.

New therapy targeting differential androgen receptor signaling in prostate cancer stem/progenitor vs. non-stem/progenitor cells

The androgen deprivation therapy (ADT) to systematically suppress/reduce androgens binding to the androgen receptor (AR) has been the standard therapy for prostate cancer (PCa); yet, most of ADT eventually fails leading to the recurrence of castration resistant PCa. Here, we found that the PCa patients who received ADT had increased PCa stem/progenitor cell population. The addition of the anti-androgen, Casodex, or AR-siRNA in various PCa cells led to increased stem/progenitor cells, whereas, in contrast, the addition of functional AR led to decreased stem/progenitor cell population but increased non-stem/progenitor cell population, suggesting that AR functions differentially in PCa stem/progenitor vs. non-stem/progenitor cells. Therefore, the current ADT might result in an undesired expansion of PCa stem/progenitor cell population, which explains why this therapy fails. Using various human PCa cell lines and three different mouse models, we concluded that targeting PCa non-stem/progenitor cells with AR degradation enhancer ASC-J9 and targeting PCa stem/progenitor cells with 5-azathioprine and γ-tocotrienol resulted in a significant suppression of the tumors at the castration resistant stage. This suggests that a combinational therapy that simultaneously targets both stem/progenitor and non-stem/progenitor cells will lead to better therapeutic efficacy and may become a new therapy to battle the PCa before and after castration resistant stages.

Increased expression of putative cancer stem cell markers in primary prostate cancer is associated with progression of bone metastases

BACKGROUND

A number of putative stem cell markers have been associated with aggressiveness of prostate cancer, including alpha 2 and alpha 6 integrin and c-met. The study aimed to test the hypothesis that the development of bone metastasis correlates with the proportion of prostate cancer stem cell-like cells present in the primary tumor.

METHODS

Prostate tissue samples were obtained from patients with high-risk prostatic adenocarcinoma. Prostate cancer tumor tissue samples underwent immunohistochemical staining for alpha 2 and alpha 6 integrin and c-met; positive and negative controls were included. Samples were scored as positive if >5% of cells within the sample stained positively. Survival and bone metastasis-free survival curves on the patient cohort were estimated by the actuarial method of Kaplan-Meier.

RESULTS

A total of 62 patients were included in the study. Bone metastases progression rate was 46% at 105 months with a median time of 46 months (95% CI: 1-62.5 months); prostate cancer-specific survival was 33% at 122 months with a median survival time of 69.4 months (95% CI: 63.5-109.4 months). Survival curves show that c-met-, alpha 2, and alpha 6 integrin-positive tumors were positively associated with the occurrence of bone metastasis-free survival. There was a higher level of significance when at least c-met and either alpha 2 or alpha 6 integrin was positive.

CONCLUSION

It can be concluded that percentage of stem cell-like prostate cancer cells has a prognostic impact especially on the risk of metastatic bone progression.

Prostate cancer as a model system for genetic diversity in tumors

This chapter will summarize novel understandings of the early molecular events in prostatic carcinogenesis that may underlie both the genetic and clinical heterogeneity. Areas covered include preneoplasia, stem cell concepts, telomere abnormalities, and the nature of tumor-stromal interactions. The oncogenomics of prostate cancer is reviewed with emphasis on androgen signaling, ETS gene family aberrations, and PTEN deletion. The notion that "field cancerization," coupled with genomic instability may explain both the occurrence of multifocal disease, and the recent observations of genetic diversity of ERG alteration in individual tumors are discussed. Collectively, genomic studies are rapidly moving human prostate cancer closer to the promise of personalized medicine, so that specific genetic profiles of individual tumors will determine the best therapeutic approaches.

Prostate epithelial stem cell culture

The prostate gland is the site of the second most common cancer in men in the UK, with 9,280 deaths recorded in 2000. Another common disease of the prostate is benign prostatic hyperplasia and both conditions are believed to arise as a result of changes in the balance between cell proliferation and differentiation. There are three types of prostatic epithelial cell, proliferative basal, secretory luminal, and neuroendocrine. All three are believed to be derived from a common stem cell through differentiation along different pathways but the mechanisms behind these processes is poorly understood. In particular, there has until recently been very little information about prostate stem cell growth and differentiation. This review will discuss ways of distinguishing these prostate cell types using markers, such as keratins. Methods available for the culture of prostate epithelial cells and for the characterisation of stem cells both in monolayer and three-dimensional models are examined.

Molecular marks for epigenetic identification of developmental and cancer stem cells

Epigenetic regulations of genes by reversible methylation of DNA (at the carbon-5 of cytosine) and numerous reversible modifications of histones play important roles in normal physiology and development, and epigenetic deregulations are associated with developmental disorders and various disease states, including cancer. Stem cells have the capacity to self-renew indefinitely. Similar to stem cells, some malignant cells have the capacity to divide indefinitely and are referred to as cancer stem cells. In recent times, direct correlation between epigenetic modifications and reprogramming of stem cell and cancer stem cell is emerging. Major discoveries were made with investigations on reprogramming gene products, also known as master regulators of totipotency and inducer of pluoripotency, namely, OCT4, NANOG, cMYC, SOX2, Klf4, and LIN28. The challenge to induce pluripotency is the insertion of four reprogramming genes (Oct4, Sox2, Klf4, and c-Myc) into the genome. There are always risks of silencing of these genes by epigenetic modifications in the host cells, particularly, when introduced through retroviral techniques. In this contribution, we will discuss some of the major discoveries on epigenetic modifications within the chromatin of various genes associated with cancer progression and cancer stem cells in comparison to normal development of stem cell. These modifications may be considered as molecular signatures for predicting disorders of development and for identifying disease states.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s13148-010-0016-0) contains supplementary material, which is available to authorized users.

An overview of concepts for cancer stem cells

For many years, cancer research has focused on the adult stem cells present in malignant tumors. It is believed that current cancer treatments sometimes fail because they do not target these cells. According to classic models of carcinogenesis, these events can occur in any cell. In contrast, the cancer stem cell (CSC) hypothesis states that the preferential targets of oncogenic transformation are tissue stem cells or early progenitor cells that have acquired the potential for self-renewal. These tumor-initiating cells, or CSCs, in turn, are characterized by their ability to undergo self-renewal, a process that drives tumorigenesis and differentiation, which contributes to the cellular heterogeneity of tumors. Herein, we discuss the definitions and properties of CSCs in the major human cancers.

TGF-beta signalling and immunity in prostate tumourigenesis

IMPORTANCE OF THE FIELD

The TGF-beta's are pleiotropic cytokines that regulate multiple cellular functions. Their role in the prostate is important for normal prostate development and also in prostate tumourigenesis.

AREAS COVERED IN THIS REVIEW

The interactions TGF-beta-mediated signalling has with maintaining prostate health, as well as its role in prostate tumourigenesis and prostate tumour immune evasion, with emphasis on how a breakdown in these interactions may influence disease progression.

WHAT THE READER WILL GAIN

That TGF-beta influences normal prostate growth and differentiation by regulating the balance between epithelial cell proliferation and apoptosis, and involving the androgen receptor pathway. That TGF-beta protects and maintains prostate stem cells and a review of the contrasting role TGF-beta has in prostate tumourigenesis and tumour development, where TGF-beta acts as a tumour suppressor and then switches roles to become a tumour promoter, and creates a local immunosuppressive niche leading to systemic tumour tolerance.

TAKE HOME MESSAGE

TGF-beta signalling in prostate cancer is a valid target for the treatment of this disease; however any therapeutic regimen will require an understanding of all aspects of the TGF-beta-signalling nexus, otherwise by the very pleiotrophic nature of TGF-beta, limited clinical benefits may result.

Arsenic exposure transforms human epithelial stem/progenitor cells into a cancer stem-like phenotype

BACKGROUND

Inorganic arsenic is a ubiquitous environmental carcinogen affecting millions of people worldwide. Evolving theory predicts that normal stem cells (NSCs) are transformed into cancer stem cells (CSCs) that then drive oncogenesis. In humans, arsenic is carcinogenic in the urogenital system (UGS), including the bladder and potentially the prostate, whereas in mice arsenic induces multi-organ UGS cancers, indicating that UGS NSCs may represent targets for carcino-genic initiation. However, proof of emergence of CSCs induced by arsenic in a stem cell population is not available.

METHODS

We continuously exposed the human prostate epithelial stem/progenitor cell line WPE-stem to an environmentally relevant level of arsenic (5 microM) in vitro and determined the acquired cancer phenotype.

RESULTS

WPE-stem cells rapidly acquired a malignant CSC-like phenotype by 18 weeks of exposure, becoming highly invasive, losing contact inhibition, and hyper-secreting matrix metalloproteinase-9. When hetero-transplanted, these cells (designated As-CSC) formed highly pleomorphic, aggressive tumors with immature epithelial- and mesenchymal-like cells, suggesting a highly pluripotent cell of origin. Consistent with tumor-derived CSCs, As-CSCs formed abundant free-floating spheres enriched in CSC-like cells, as confirmed by molecular analysis and the fact that only these floating cells formed xeno-graft tumors. An early loss of NSC self-renewal gene expression (p63, ABCG2, BMI-1, SHH, OCT-4, NOTCH-1) during arsenite exposure was sub-sequently reversed as the tumor suppressor gene PTEN was progressively suppressed and the CSC-like phenotype acquired.

CONCLUSIONS

Arsenite transforms prostate epithelial stem/progenitor cells into CSC-like cells, indicating that it can produce CSCs from a model NSC population.

The path toward identifying prostatic stem cells

The concept that stem cells reside in prostate epithelia is well accepted and has led to significant efforts aimed at isolating and characterizing adult prostate stem/progenitor cells from both human and rodent prostate tissues. Understanding how prostatic stem and/or progenitor cells give rise to prostate epithelia during development and maintain homeostasis of the prostate gland in adulthood is a major research focus. Furthermore, the ability to identify and manipulate prostatic stem cells (PSCs) holds enormous promise for the development of new approaches to manage and treat prostate cancer. This review maps the pathways to identifying, isolating, characterizing, and understanding the differentiation capacity of PSCs.

Prostate cancer stem cells

Despite the discovery over 60 years ago by Huggins and Hodges that prostate cancers respond to androgen deprivation therapy, hormone-refractory prostate cancer remains a major clinical challenge. There is now mounting evidence that solid tumours originate from undifferentiated stem cell-like cells coexisting within a heterogeneous tumour mass that drive tumour formation, maintain tumour homeostasis and initiate metastases. This review focuses upon current evidence for prostate cancer stem cells, addressing the identification and properties of both normal and transformed prostate stem cells.

Delta-like 1 (Dlk-1), a novel marker of prostate basal and candidate epithelial stem cells, is downregulated by notch signalling in intermediate/transit amplifying cells of the human prostate

BACKGROUND

There is a lack of understanding of the processes that regulate differentiation in the prostate.

OBJECTIVE

To determine localisation, activity, and regulation of cytodifferentiation-modulatory proteins in the human adult prostate.

DESIGN, SETTINGS, AND PARTICIPANTS

Eighteen volunteering patients with organ-confined prostate cancer were prospectively enrolled at a single university hospital.

INTERVENTION

All patients underwent radical prostatectomy, and normal/benign tissue was excised and obtained from the transition zone.

MEASUREMENTS

Expression and activity of Notch-protein family members, including the Notch-homologous protein Delta-like 1 (Dlk-1/Pref1), were investigated immunohistochemically in normal/benign tissue and explant cultures. The effect of the Notch inhibitor L-685,458 on Dlk-1 expression and cell number was investigated in primary cell cultures, and data were analysed with Student t test.

RESULTS AND LIMITATIONS

Mature luminal cells were found to co-express Notch-1 and its ligand Jagged1, but epithelia in normal/benign tissue showed no active Notch signalling. The basal cell layer, rare candidate epithelial stem cells, and a subpopulation of neuroendocrine cells expressed the differentiation protein Dlk-1. In explant cultures, luminal cells and Jagged1 expression were lost, whereas intermediate cells downregulated Dlk-1 concomitant with Notch-1 upregulation and activation. Notch inhibition in primary cell cultures led to lower cell densities (p<0.001) and suppressed downregulation of Dlk-1. This is a small study; current results need to be confirmed in larger investigations.

CONCLUSIONS

We demonstrate that Notch-1 is upregulated in differentiation of prostate epithelia, and that the novel prostate progenitor marker Dlk-1 is downregulated by Notch signalling in intermediate cells. The identification of Dlk-1-expressing candidate stem and neuroendocrine cells suggests a hierarchical relationship.

Cancer statistics, 2007

Each year, the American Cancer Society (ACS) estimates the number of new cancer cases and deaths expected in the United States in the current year and compiles the most recent data on cancer incidence, mortality, and survival based on incidence data from the National Cancer Institute, Centers for Disease Control and Prevention, and the North American Association of Central Cancer Registries and mortality data from the National Center for Health Statistics. This report considers incidence data through 2003 and mortality data through 2004. Incidence and death rates are age-standardized to the 2000 US standard million population. A total of 1,444,920 new cancer cases and 559,650 deaths for cancers are projected to occur in the United States in 2007. Notable trends in cancer incidence and mortality rates include stabilization of the age-standardized, delay-adjusted incidence rates for all cancers combined in men from 1995 through 2003; a continuing increase in the incidence rate by 0.3% per year in women; and a 13.6% total decrease in age-standardized cancer death rates among men and women combined between 1991 and 2004. This report also examines cancer incidence, mortality, and survival by site, sex, race/ethnicity, geographic area, and calendar year, as well as the proportionate contribution of selected sites to the overall trends. While the absolute number of cancer deaths decreased for the second consecutive year in the United States (by more than 3,000 from 2003 to 2004) and much progress has been made in reducing mortality rates and improving survival, cancer still accounts for more deaths than heart disease in persons under age 85 years. Further progress can be accelerated by supporting new discoveries and by applying existing cancer control knowledge across all segments of the population.

SOX9 Is Expressed in Normal Prostate Basal Cells and Regulates Androgen Receptor Expression in Prostate Cancer Cells

SOX9 is a member of the SOX [Sry-related high-mobility group (HMG) box] family of HMG DNA-binding domain transcription factors and is required for the development and differentiation of multiple cell lineages. This report shows that basal epithelial cells express SOX9 in normal prostate, with no detectable expression in luminal epithelial cells. In contrast, SOX9 is expressed in primary prostate cancers in vivo, at a higher frequency in recurrent prostate cancer and in prostate cancer cell lines (LNCaP, CWR22, PC3, and DU145). SOX9 message and protein levels in prostate cancer cells were increased by treatment with glycogen synthase kinase 3beta inhibitor (SB415286), and SOX9 was reduced when beta-catenin was down-regulated by small interfering RNA (siRNA), indicating that SOX9 expression in prostate cancer is regulated by Wnt/beta-catenin signaling. SOX9 bound specifically to androgen receptor (AR) DNA-binding domain glutathione S-transferase fusion proteins, and this interaction was dependent on a short peptide immediately COOH-terminal to the DNA-binding domain (the C-terminal extension), which is required for interactions between steroid hormone receptors and the architectural HMG proteins. Exogenous SOX9 expressed at high nonphysiologic levels decreased AR expression and activity; however, at lower levels, SOX9 increased AR protein expression. Significantly, down-regulation of SOX9 by siRNA in prostate cancer cells reduced endogenous AR protein levels, and cell growth indicating that SOX9 contributes to AR regulation and decreased cellular proliferation. These results indicate that SOX9 in prostate basal cells supports the development and maintenance of the luminal epithelium and that a subset of prostate cancer cells may escape basal cell requirements through SOX9 expression.

The ageing male reproductive tract

Ageing of the male reproductive system is characterized by changes in the endocrine system, hypogonadism, erectile dysfunction and proliferative disorders of the prostate gland. Stochastic damage accumulating within ageing leads to progressive dysregulation at each level of the hypothalamic-pituitary-gonadal (HPG) axis and in local auto/paracrine interactions, thereby inducing morphological changes in reproductive target organs, such as the prostate, testis and penis. Despite age-related changes in the HPG axis, endocrine functions are generally sufficient to maintain fertility in elderly men. Ageing of the male reproductive system can give rise to clinically relevant manifestations, such as benign prostatic hyperplasia (BPH), prostate cancer (PCa) and erectile dysfunction (ED). In this review, we discuss morphological/histological changes occurring in these organs and current views and concepts of the underlying pathology. Moreover, we emphasize the molecular/cellular pathways leading to reduced testicular/penile function and proliferative disorders of the prostate gland.

Prostate cancer stem cells

Prostate cancer is the most frequently diagnosed cancer in men. Despite recent advances in the detection of early prostate cancer there is little effective therapy for patients with locally advanced and/or metastatic disease. The majority of patients with advanced disease respond initially to androgen ablation therapy. However, most go on to develop androgen-independent tumours that inevitably are fatal. A similar response is seen to chemotherapeutic and radiotherapy treatments. As a result, metastatic prostate cancer remains an incurable disease by current treatment strategies. Recent reports of cancer stem cells have prompted questions regarding the involvement of normal stem/progenitor cells in prostate tumour biology, their potential contribution to the tumour itself and whether they are the cause of tumour initiation and progression. Although still controversial, the cancer stem cell is likely to be the most crucial target in the treatment of prostate cancer, and a thorough understanding of its biology, particularly of how the cancer stem cell differs from the normal stem cell, might allow it to be targeted selectively and eliminated, thus improving therapeutic outcome.

Effect of a new leuprorelin formulation on testosterone levels in patients with advanced prostate cancer

BACKGROUND AND SCOPE

Leuprorelin is a well known luteinising hormone releasing hormone (LHRH) agonist. The drug is effective in the treatment of advanced prostate cancer and is well tolerated. This article reviews published literature (based on a search of PubMed, EMBASE and Biosis databases to the end of 2005) and other sources of data on a new formulation of leuprorelin acetate (Eligard) for use in the treatment of hormone-dependent advanced prostate cancer. This product takes advantage of a novel delivery system (Atrigel) which forms an implant in situ that is capable of delivering double doses of leuprorelin consistently to provide better, more sustained testosterone suppression compared with a microsphere leuprolide acetate formulation. Two formulations, 7.5 mg and 22.5 mg, are currently available with duration of action of 1 and 3 months, respectively. The 2-week stability at room temperature prior to mixing facilitates its use and reduces the potential for waste.

FINDINGS

In clinical studies of the new leuprorelin acetate formulation reviewed here, all patients achieved testosterone levels < or = 50 ng/dL and up to 98% of patients showed levels comparable to those resulting from surgical bilateral orchidectomy (< or = 20 ng/dL). Both formulations showed minimal breakthroughs, defined as a rise in testosterone levels after reaching levels of 50 ng/dL. The safety profile is typical of LHRH agonists, with mild to moderately severe 'hot flushes' being the most common adverse event. The higher dose of 22.5 mg, with a volume of 0.375 mL is administered subcutaneously via a small 20G needle, causing little local discomfort.

CONCLUSION

Prostate cancer remains a major cause of morbidity and mortality in older men. In the majority of cases, suppression of serum testosterone levels is very effective. The level of testosterone suppression is currently under debate, with ideal suppression levels ranging from 20 to 50 ng/dL. Not all LHRH agonist therapy achieves the same degree of testosterone suppression as bilateral orchidectomy. The new leuprorelin acetate (Eligard) appears to achieve a testosterone suppression of 20 ng/dL in 98% of patients, while maintaining a side effect profile comparable to other products in its class.

Stem/progenitor and intermediate cell types and the origin of human prostate cancer

Theories of cell lineage in human prostatic epithelium, based on protein expression, propose that basal and luminal cells: 1) are either independently capable of self-renewal or 2) arise from stem cells expressing a full spectrum of proteins (p63, cytokeratins CK5/14, CK8/18, and glutathione-S-transferase-pi [GST-pi]) similar to cells of the embryonic urogenital sinus (UGS). Such embryonic-like stem cells are thought to give rise to mature basal cells and secretory luminal cells. By single cell cloning of an immortalized, normal human prostate-derived, non-tumorigenic RWPE-1 cell line, we isolated and characterized two epithelial cell types, WPE-stem and WPE-int. WPE-stem cells show: i) strong, sixfold greater nuclear expression of p63; ii) nearly twofold greater expression of CK14; iii) threefold less CK18, and iv) low androgen receptor (AR) expression as compared with WPE-int cells. WPE-stem cells are androgen-independent for growth and survival. WPE-int cells express very low p63 and CK5/14, and high CK18. WPE-int cells are androgen-independent for growth and survival but are highly responsive as shown by androgen induction of AR and prostate specific antigen (PSA). Compared with WPE-int cells, WPE-stem cells are smaller and show more rapid growth. WPE-stem cells can grow in an anchorage-independent manner in agar with 4.5-fold greater cloning efficiency and as free floating "prostaspheres" in liquid medium; and express over 40-fold higher matrix metalloproteinase-2 activity. These results indicate that WPE-stem cells express several features characteristic of stem/progenitor cells present in the UGS and in adult prostatic epithelium. In contrast, WPE-int cells have an intermediate, committed phenotype on the pathway to luminal cell differentiation. We propose that in normal prostatic epithelium, cells exist at many stages in a continuum of differentiation progressing from stem cells to definitive basal and luminal cells. Establishment and characterization of clones of human prostatic epithelial cells provide novel models for determining cell lineages, the origin of prostate cancer, and for developing new strategies for tumor prevention and treatment.

Prospective identification of tumorigenic prostate cancer stem cells

Existing therapies for prostate cancer eradicates the bulk of cells within a tumor. However, most patients go on to develop androgen-independent disease that remains incurable by current treatment strategies. There is now increasing evidence in some malignancies that the tumor cells are organized as a hierarchy originating from rare stem cells that are responsible for maintaining the tumor. We report here the identification and characterization of a cancer stem cell population from human prostate tumors, which possess a significant capacity for self-renewal. These cells are also able to regenerate the phenotypically mixed populations of nonclonogenic cells, which express differentiated cell products, such as androgen receptor and prostatic acid phosphatase. The cancer stem cells have a CD44+/alpha2beta1hi/CD133+ phenotype, and we have exploited these markers to isolate cells from a series of prostate tumors with differing Gleason grade and metastatic states. Approximately 0.1% of cells in any tumor expressed this phenotype, and there was no correlation between the number of CD44+/alpha2beta1hi/CD133+ cells and tumor grade. The identification of a prostate cancer stem cell provides a powerful tool to investigate the tumorigenic process and to develop therapies targeted to the stem cell.

Fas Ligand Expression and Its Correlation with Apoptosis and Proliferation in Lobund-Wistar Prostate Carcinomas

OBJECTIVE

The Fas (CD95) interaction with its receptor Fas ligand (FasL) is one of the main mechanisms of cell apoptosis. High expression of FasL has been consistently observed in a variety of human cancers. In this study, we evaluated FasL and its relationship with apoptosis and proliferation in Lobund-Wistar (L-W) cancers. The L-W rat strain develops spontaneous and induced adenocarcinomas in the anterior prostate and seminal vesicles. Although FasL expression has been observed in a subset of human prostate carcinomas, this multistage model allowed in vivo evaluation of subclones of malignant cells with a single genetic susceptibility.

METHODS

Apoptosis was evaluated in spontaneous, induced and transplanted tumors as well as metastasis using the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) technique and transmission electron microscopy. Proliferating cell nuclear antigen (PCNA) and FasL expression were detected using immunohistochemistry and analyzed according to the number of positive cells and intensity of staining using a semiquantitive method.

RESULTS

Apoptotic indexes were significantly higher in spontaneous tumors compared to induced (p < 0.008), transplanted tumors (p < 0.0112) and metastases (p < 0.009). TUNEL-positive cells were frequently observed in the leukocytic infiltrate of the stroma in transplanted carcinomas and metastases. These findings were confirmed by electron microscopy. FasL expression was not uniformly localized in L-W carcinomas and its highest expression was observed in transplanted tumors and metastasis (p < 0.005). Moreover, PCNA indices were directly correlated with cancers showing high FasL total scores (Hscores).

CONCLUSIONS

In this model, high FasL expression was associated with cells displaying low apoptotic indexes and high PCNA index. Therefore, analysis of FasL may have clinical relevance in detecting the malignant potential of prostate cancers.

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.

Novel method of generating prostate-specific Cre-LoxP gene switching via intraductal delivery of adenovirus

BACKGROUND

In order to facilitate elucidation of oncogene or tumor suppressor gene function on initiation and progression of prostate cancer, it would be advantageous to develop an effective method to generate spatially and temporally controlled gene modification in murine prostates.

METHODS

Adenovirus expressing Cre-recombinase (Adeno-Cre) was intraductally injected into the prostate of ROSA26 reporter mice. Immmunohistochemical and X-gal staining were performed on prostate tissue sections harvested from mice at various time points following viral injection to confirm expression and activity of Cre-recombinase, respectively.

RESULTS

Adenovirus was intraductally delivered to the anterior lobe of the mouse prostate. Using this method of intraductal injection, we were able to precisely obtain Adeno-Cre infection to a majority of epithelial cells but not in the stromal cells or other organs. We further demonstrated that Adeno-Cre infected epithelial cells not only expressed Cre-recombinase enzyme but more importantly, Cre-recombinase activity was revealed through positive X-gal staining in Rosa26 reporter mice, thus, confirming epithelial-specific Cre-loxP recombination in Adeno-Cre infected prostate tissue sections.

CONCLUSIONS

This novel method of direct genetic delivery into adult murine prostates could provide an alternative to the more expensive and time-consuming transgenic/knockout approaches. The latter also have other limitations such as the availability of cell-type specific or temporally-regulated promoters, and the complication of genetic background differences, which can potentially be complemented by the technology we describe here.

Role of p63 and basal cells in the prostate

The prostate contains two major epithelial cell types - luminal and basal cells - both of which develop from urogenital sinus epithelium. The cell linage relationship between these two epithelial types is not clear. Here we demonstrate that luminal cells can develop independently of basal cells, but that basal cells are essential for maintaining ductal integrity and the proper differentiation of luminal cells. Urogenital sinus (UGS) isolated from p63(+/+) and p63(-/-) embryos developed into prostate when grafted into adult male nude mice. Prostatic tissue that developed in p63(-/-) UGS grafts contained neuroendocrine and luminal cells, but basal cells were absent. Therefore, p63 is essential for differentiation of basal cells, but p63 and thus basal cells are not required for differentiation of prostatic neuroendocrine and luminal epithelial cells. p63(-/-) prostatic grafts also contained atypical mucinous cells, which appeared to differentiate from luminal cells via activation of Src. In the response to castration, regression of p63(-/-) prostate was inordinately severe with almost complete loss of ducts, resulting in the formation of residual cystic structures devoid of epithelium. Therefore, basal cells play critical roles in maintaining ductal integrity and survival of luminal cells. However, regressed p63(-/-) prostate did regenerate in response to androgen administration, indicating that basal cells were not essential for prostatic regeneration.

Evidence of pluripotent human prostate stem cells in a human prostate primary xenograft model

INTRODUCTION

The phenotypic plasticity of the human prostate stem cell within human prostate tissue was examined to determine the response of the stem cell to changes in the androgenic environment.

METHODS

Prostate xenografts were transplanted into athymic nu/nu mice implanted with testosterone pellets, allowed to establish for 1 month time point, the hosts were castrated and pellets removed, and following 1 month of androgen deprivation, the hosts were stimulated with androgen for 2 days to induce proliferation of the residual population of stem cells (2-month time point).

RESULTS

Glands in benign xenografts harvested at the 1- and 2-month time points contained basal cell layers that expressed p63 and high molecular weight cytokeratin, and in which essentially all of the cellular proliferation was localized, consistent with the proposed localization of the prostate stem cell. Benign glandular structures in the xenografts were populated by basal, secretory epithelial, neuroendocrine (NE), or squamous cells overlaying the basal cell layer, whereas, adenocarcinoma glands in the xenografts resembled the original prostate cancer (CaP) tissue.

CONCLUSIONS

In this human prostate primary xenograft model, the residual stem cell population that survives transplantation, or androgen deprivation, maintains significant pluripotentiality as demonstrated by the capacity to generate progeny that differentiate along multiple lineages in response to microenvironmental signals, particularly along the secretory epithelial lineage in response to androgen, and along the NE cell lineage in response to androgen deprivation.

Upregulation and nuclear recruitment of HDAC1 in hormone refractory prostate cancer

BACKGROUND

Histone deacetylase 1 (HDAC1) is a co-repressor involved in differentiation and proliferation control. It is upregulated in malignant compared to benign tissue, and targets a number of transcription factors including p53.

METHODS

By immunohistochemistry, HDAC1 protein expression was investigated in human prostate specimens and the CWR22 mouse xenograft model. Flow cytometry and deconvolution immunofluorescence were also performed.

RESULTS

HDAC1 was upregulated in pre-malignant and malignant lesions, with the highest increase in expression in hormone refractory (HR) cancer. Using the CWR22 xenograft model we showed androgen dependent regulation of HDAC1. HDAC1 overexpression led to a significant increase in proliferation and a shift towards the undifferentiated cytokeratin (CK) profile in a PC3M derivative clone constitutively expressing HDAC1.

CONCLUSION

This study underlines the importance of HDAC1 in cell proliferation and the development of prostate cancer (CaP) and proposes a mechanism for HDAC1 nuclear recruitment. HDAC1 may constitute a crucial therapeutic target particularly in the most lethal phase of androgen independence.

Epithelial cell differentiation in the human prostate epithelium: implications for the pathogenesis and therapy of prostate cancer

Within the human prostate epithelium four cell populations are discriminated by their expression of keratins (K). While basal cells co-localize K5 and K14 combined with low levels of K18 (K5(++)/14(++)/18(+)), luminal cells highly express K18 (K18(++)). In addition, two intermediate subpopulations are characterized either by basal K5(++)/18(+)- or luminal K5(+)/18(++)- expression. The entire prostate epithelium is putatively derived from a basal stem cell population. They give rise to intermediate cells that transiently proliferate and mature towards differentiated luminal epithelium. Within prostate carcinoma luminal exocrine, neuro-endocrine and intermediate cells are distinguished. Intermediate cells have been postulated as progenitors for prostate carcinogenesis and targets for androgen-independent tumor progression. Androgen-independency is associated with an enrichment of intermediate cells and over-expression of peptide growth factor receptors. Targeting intermediate cells by inhibition of their peptide growth factor receptors, therefore, offers novel treatment modalities for prostate cancer.

Intermediate cells in human prostate epithelium are enriched in proliferative inflammatory atrophy

Within the human prostate epithelium four cell populations can be discriminated based on their expression of keratins (K). Basal cells express high levels of K5 and K14, as well as p63, whereas they have very low levels of androgen receptor, prostate-specific antigen (PSA), K8, and K18. Luminal secretory cells lack p63, K5, and K14 but express high levels of K8, K18, androgen receptor, and PSA. Additionally, cells have been identified with a keratin phenotype intermediate between basal and luminal cells that co-express high levels of K5 and K18 (K5/18) as well as hepatocyte growth factor receptor c-MET. Although intermediate cells have been proposed as precursor cells of prostate cancer, their biology is ill defined. Epithelial cells in proliferative inflammatory atrophy (PIA) appear to be cycling rapidly as indicated by expression of Ki-67, and morphological transitions have been identified between PIA and high-grade prostate intraepithelial neoplasia. Many of the atrophic epithelial luminal cells in PIA are candidates for intermediate cells based in part on weak expression of PSA and androgen receptor, high levels of K8/18, and lack of p63. The objective of this study was to further clarify the phenotype of the proposed intermediate cells in PIA and to quantitatively determine the level in which these intermediate cells preferentially occur in PIA lesions. Intermediate cells were immunohistochemically demonstrated using antibodies to K5, K14, K18, and c-MET. Using radical prostatectomy specimens (n = 15) the area fraction of intermediate cells in normally differentiated prostate epithelium and PIA were quantified by a grid point counting method. Atrophic luminal cells of PIA lesions expressed K5 in 39.2 +/- 7.4% of cells compared to 2.4 +/- 2.3% in normal epithelium (P < 0.00001). By contrast, K14 was only expressed in 3.0 +/- 3.2% of the luminal cells. Previous studies have shown that virtually 100% of these atrophic luminal cells are strongly positive for K8/18. c-MET was present in 44.1 +/- 14.1% of luminal cells in PIA but only in 2.1 +/- 2.8% of luminal cells in normal epithelium (P < 0.00001). To unambiguously determine whether intermediate luminal cells in PIA show increased proliferative activity and decreased p27(kip1) expression, double-staining immunofluorescence of Ki-67 and K5, as well as p27(Kip1) and K5 was performed. Luminal cells in PIA often co-expressed K5 and Ki-67. Although p27(Kip1) was strongly expressed in K5-negative differentiated cells in normal epithelium, p27(Kip1) staining was absent in many of the K5-positive cells in the luminal compartment of PIA. We conclude that cells phenotypically intermediate between basal and secretory cells are enriched in PIA lesions. The finding of a large number of highly proliferating intermediate cells in PIA provides further support that these cells may serve as preferred target cells in prostate carcinogenesis.

Prostatic stem cells

Multipotent cells within the epithelial compartment, together with phenotypically 'plastic' mesenchyma cells (stromal stem cells), provide a repository of protected genetic information from which the structure, stability and functionality of the prostate gland can be maintained. However, mere preservation of cells in a non-dividing state is insufficient to provide the necessary reservoir of information from which the structure and function of the prostate gland can be retained or recreated. Rather, there is a constant dynamic interaction, at the level of information exchange, between stem cells (whether epithelial or mesenchymal) and their surrounding environment (both humoral and physical). Thus, with respect to epithelial stem cells, these reside within environmental 'niches' which allow their controlled and limited proliferation while preserving genomic integrity. Similar 'mesenchymal niches' are also predicted to occur, although not yet identified, thus providing the multipotent source from which the full spectrum of stromal phenotypes might be regenerated. Recent data from studies of the haematopoietic and hepato-biliary systems indicate that the potential scope of stem cells far exceeds the immediate phenotypic complement of those tissues within which they originate, being dependent upon their precise environment as well as their genomic integrity.