Immunolocalization of the keratinocyte growth factor in benign and neoplastic human prostate and its relation to androgen receptor

Nuclear action of FGF members in endocrine-related tissues and cancer: Interplay with steroid receptor pathways

Dysregulation of the fibroblast growth factors/fibroblast growth factor receptor (FGF/FGFR) pathway has been implicated in a wide range of human disorders and several members have been localized in the nuclear compartment. Hormone-activated steroid receptors or ligand independent activated receptors form nuclear complexes that activate gene transcription. This review aims to highlight the interplay between the steroid receptor and the FGF/FGFR pathways and focuses on the current knowledge on nuclear action of FGF members in endocrine-related tissues and cancer. The nuclear trafficking and targets of FGF/FGFR members and the available evidence on the interplay with steroid hormones and receptors is described. Finally, the data on aberrant FGF/FGFR signaling is summarized and the nuclear action of FGF members on endocrine resistant breast cancer is highlighted. Identifying the mechanisms underlying FGF-induced endocrine resistance will be important to understand how to efficiently target endocrine-related diseases and even enhance or restore endocrine sensitivity in hormone receptor positive tumors.

New Insights in Prostate Cancer Development and Tumor Therapy: Modulation of Nuclear Receptors and the Specific Role of Liver X Receptors

Prostate cancer (PCa) incidence has been dramatically increasing these last years in westernized countries. Though localized PCa is usually treated by radical prostatectomy, androgen deprivation therapy is preferred in locally advanced disease in combination with chemotherapy. Unfortunately, PCa goes into a castration-resistant state in the vast majority of the cases, leading to questions about the molecular mechanisms involving the steroids and their respective nuclear receptors in this relapse. Interestingly, liver X receptors (LXRα/NR1H3 and LXRβ/NR1H2) have emerged as new actors in prostate physiology, beyond their historical roles of cholesterol sensors. More importantly LXRs have been proposed to be good pharmacological targets in PCa. This rational has been based on numerous experiments performed in PCa cell lines and genetic animal models pointing out that using selective liver X receptor modulators (SLiMs) could actually be a good complementary therapy in patients with a castration resistant PCa. Hence, this review is focused on the interaction among the androgen receptors (AR/NR3C4), estrogen receptors (ERα/NR3A1 and ERβ/NR3A2), and LXRs in prostate homeostasis and their putative pharmacological modulations in parallel to the patients' support.

AR Signaling and the PI3K Pathway in Prostate Cancer

Prostate cancer is a leading cause of cancer-related death in men worldwide. Aberrant signaling in the androgen pathway is critical in the development and progression of prostate cancer. Despite ongoing reliance on androgen receptor (AR) signaling in castrate resistant disease, in addition to the development of potent androgen targeting drugs, patients invariably develop treatment resistance. Interactions between the AR and PI3K pathways may be a mechanism of treatment resistance and inhibitors of this pathway have been developed with variable success. Herein we outline the role of the PI3K pathway in prostate cancer and, in particular, its association with androgen receptor signaling in the pathogenesis and evolution of prostate cancer, as well as a review of the clinical utility of PI3K targeting.

The importance of non-nuclear AR signaling in prostate cancer progression and therapeutic resistance

The androgen receptor (AR) remains the major oncogenic driver of prostate cancer, as evidenced by the efficacy of androgen deprivation therapy (ADT) in naïve patients, and the continued effectiveness of second generation ADTs in castration resistant disease. However, current ADTs are limited to interfering with AR ligand binding, either through suppression of androgen production or the use of competitive antagonists. Recent studies demonstrate 1) the expression of constitutively active AR splice variants that no longer depend on androgen, and 2) the ability of AR to signal in the cytoplasm independently of its transcriptional activity (non-genomic); thus highlighting the need to consider other ways to target AR. Herein, we review canonical AR signaling, but focus on AR non-genomic signaling, some of its downstream targets and how these effectors contribute to prostate cancer cell behavior. The goals of this review are to 1) re-highlight the continued importance of AR in prostate cancer as the primary driver, 2) discuss the limitations in continuing to use ligand binding as the sole targeting mechanism, 3) discuss the implications of AR non-genomic signaling in cancer progression and therapeutic resistance, and 4) address the need to consider non-genomic AR signaling mechanisms and pathways as a viable targeting strategy in combination with current therapies.

Androgen Receptor-Mediated Growth Suppression of HPr-1AR and PC3-Lenti-AR Prostate Epithelial Cells

The androgen receptor (AR) mediates the developmental, physiologic, and pathologic effects of androgens including 5α-dihydrotestosterone (DHT). However, the mechanisms whereby AR regulates growth suppression and differentiation of luminal epithelial cells in the prostate gland and proliferation of malignant versions of these cells are not well understood, though they are central to prostate development, homeostasis, and neoplasia. Here, we identify androgen-responsive genes that restrain cell cycle progression and proliferation of human prostate epithelial cell lines (HPr-1AR and PC3-Lenti-AR), and we investigate the mechanisms through which AR regulates their expression. DHT inhibited proliferation of HPr-1AR and PC3-Lenti-AR, and cell cycle analysis revealed a prolonged G₁ interval. In the cell cycle, the G₁/S-phase transition is initiated by the activity of cyclin D and cyclin-dependent kinase (CDK) complexes, which relieve growth suppression. In HPr-1AR, cyclin D1/2 and CDK4/6 mRNAs were androgen-repressed, whereas CDK inhibitor, CDKN1A, mRNA was androgen-induced. The regulation of these transcripts was AR-dependent, and involved multiple mechanisms. Similar AR-mediated down-regulation of CDK4/6 mRNAs and up-regulation of CDKN1A mRNA occurred in PC3-Lenti-AR. Further, CDK4/6 overexpression suppressed DHT-inhibited cell cycle progression and proliferation of HPr-1AR and PC3-Lenti-AR, whereas CDKN1A overexpression induced cell cycle arrest. We therefore propose that AR-mediated growth suppression of HPr-1AR involves cyclin D1 mRNA decay, transcriptional repression of cyclin D2 and CDK4/6, and transcriptional activation of CDKN1A, which serve to decrease CDK4/6 activity. AR-mediated inhibition of PC3-Lenti-AR proliferation occurs through a similar mechanism, albeit without down-regulation of cyclin D. Our findings provide insight into AR-mediated regulation of prostate epithelial cell proliferation.

Androgens and androgen receptor signaling in prostate tumorigenesis

Androgens and androgen receptor (AR) signaling are necessary for prostate development and homeostasis. AR signaling also drives the growth of nearly all prostate cancer cells. The role of androgens and AR signaling has been well characterized in metastatic prostate cancer, where it has been shown that prostate cancer cells are exquisitely adept at maintaining functional AR signaling to drive cancer growth. As androgens and AR signaling are so intimately involved in prostate development and the proliferation of advanced prostate cancer, it stands to reason that androgens and AR are also involved in prostate cancer initiation and the early stages of cancer growth, yet little is known of this process. In this review, we summarize the current state of knowledge concerning the role of androgens and AR signaling in prostate tissue, from development to metastatic, castration-resistant prostate cancer, and use that information to suggest potential roles for androgens and AR in prostate cancer initiation.

Potential dual role of KGF/KGFR as a target option in novel therapeutic strategies for the treatment of cancers and mucosal damages

INTRODUCTION

Keratinocyte growth factor (KGF) and its receptor KGFR play a pivotal role in regulating cell proliferation, migration, differentiation and survival, in response to injury and tissue repair. Altered expression of this pathway in cancer opened the way to the development of targeted therapy to achieve KGFR inhibition. Nevertheless, KGF administration has been demonstrated to ameliorate oral mucositis resulting from chemoradiotherapy, besides protecting epithelial cells against radiation-induced damage.

AREAS COVERED

This review focuses on the potential therapeutic interest of KGF/KGFR in two different areas: selective inhibition of KGFR signaling for the treatment of cancers characterized by upregulation of this pathway and administration of KGF to protect epithelial cells from induced damage. The review presents an overview of therapeutic strategies in both directions.

EXPERT OPINION

KGF/KGFR signaling can contribute to enhancing the malignant potential of epithelial cells and to promoting tumorigenesis. On the other hand, the therapeutic use of KGF in cancer patients provides epithelial protection, reducing chemotherapy side effects. FGFRs have become attractive antitumor targets and various inhibitors have been used to contrast tumor cell growth. The identification of KGFR-specific molecules might represent a promising therapeutic strategy that could increase the window of available agents and treatment methods.

The differential effects of prostate stromal cells derived from different zones on prostate cancer epithelial cells under the action of sex hormones

It is well known that prostate cancer (PCa) occurs predominantly in the peripheral zone (PZ), whereas benign prostatic hyperplasia (BPH) typically develops in the transition zone. To identify possible mechanisms underlying zonal differences, we compared the effects of prostate stromal cells derived from the peripheral zone (PZsc) and the transition zone (TZsc) on a PCa epithelial cell line (PC3) in the presence of sex hormones. First, we observed that androgen receptor (AR) mRNA was more highly expressed in PZsc than TZsc when the cells were treated with dihydrotestosterone (DHT) and β-oestradiol (E2) (P<0.05). By ELISA, we looked for differences in the secretion of peptide growth factors from PZsc and TZsc. We found that keratinocyte growth factor (KGF) secretion increased with increasing concentrations of DHT (P<0.01) and was higher in PZsc than TZsc. Under treatment with DHT plus E2, PZsc secreted more transforming growth factor-β1 (TGF-β1) than TZsc, but this pattern was reversed when the cells were treated with E2 only. With increasing concentrations of DHT, insulin-like growth factor-1 (IGF-1) secretion increased in PZsc but decreased in TZsc. To further characterize the effects of PZsc and TZsc on PC3 cells, we developed a coculture model and performed MTT assays, Western blot analysis and real-time RT-PCR. We found that PZsc promoted PC3 cell proliferation and progression better than TZsc, particularly when treated with 10 nmol l(-1) DHT plus 10 nmol l(-1) E2. In conclusion, our data suggest that PZsc may have a greater capacity to induce PCa development and progression than TZsc via growth factors regulated by sex hormones. These findings provide possible mechanisms underlying zonal differences in prostate diseases, which may aid the search for novel therapeutic targets for PCa.

Effect of tumour-cell-derived or recombinant keratinocyte growth factor (KGF) on proliferation and radioresponse of human epithelial tumour cells (HNSCC) and normal keratinocytes in vitro

Purpose of this work was to test the effect of tumour-cell-derived keratinocyte growth factor (KGF) or recombinant KGF (palifermin) on cell proliferation and radiation response of human HNSCC cells and normal keratinocytes in vitro. Four tumour cell cultures derived from head and neck squamous cell carcinomas, primary keratinocytes, and immortalized keratinocytes were analysed. Fibroblasts, the natural source of KGF protein, served as controls. KGF expression was observed in primary and immortalized keratinocytes, fibroblasts, and in tumour cells, while significant KGF receptor expression was only found in keratinocytes. Recombinant KGF as well as tumour-cell-derived KGF caused a significant growth stimulation and radioprotection in keratinocytes, which was abolished by a neutralizing anti-KGF antibody. This indicates that tumour-cell-derived KGF is biologically active. In the tumour cell lines, no significant growth stimulation was induced by recombinant KGF, and the neutralizing antibody did not influence tumour cell growth or radiation response. Our results indicate that the normal, paracrine KGF regulatory mechanisms, which are based on KGF receptor expression, are lost in malignant cells, with the consequence of irresponsiveness of the tumour cells to exogenous KGF. In face of the amelioration of the radiation response of normal epithelia, demonstrated in various clinical and various preclinical animal studies, recombinant KGF represents a candidate for the selective protection of normal epithelia during radio(chemo) therapy of squamous cell carcinoma.

Matched pairs of human prostate stromal cells display differential tropic effects on LNCaP prostate cancer cells

Prostate stromal cells may play binary roles in the process of prostate cancer development. As the first to be encountered by infiltrating prostate cancer cells, prostate stromal cells form the first defense line against prostate cancer progression and metastasis. However, interaction between prostate cancer and stromal cells may facilitate the formation of a tumor microenvironment favoring cancer cell growth and survival. To establish an experimental system for studying the interaction between cancer and stromal cells, we isolated three matched pairs of normal and cancer-associated human prostate stromal clones. In this report, we describe the morphologic and behavioral characteristics of these cells and their effect on LNCaP prostate cancer cells in co-culture. Unlike LNCaP prostate cancer cells, the isolated prostate stromal clones are large fibroblast-like cells with a slow proliferation rate. Growth and survival of these clones are not affected by androgens. The stromal cells display high resistance to serum starvation, while cancer-associated stromal clones have differentiated survival ability. In co-culture experiments, the stromal cells protected some LNCaP prostate cancer cells from death by serum starvation, and cancer-associated stromal clones showed more protection. This work thus established a panel of valuable human prostate stromal cell lines, which could be used in co-culture to study the interaction between prostate cancer and prostate stromal cells.

Chronic inflammation in the pathogenesis of benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) is a common disorder affecting 50-80% of the aged male population. Androgens and age have been traditionally considered the main determinants of prostate enlargement, but in the last years a potentially important role of chronic inflammation in BPH pathogenesis has emerged. Bacterial and non-infectious chronic prostatitis could represent inciting factors leading to tissue hyperproliferation, possibly via the recently demonstrated antigen-presenting capacity of prostatic stromal cells, enabling them to induce and sustain intraglandular immune responses. The prostate growth-promoting chemokine IL-8 could represent a direct link between chronic prostate inflammation and autocrine/paracrine stromal cell proliferation, in agreement with its marked secretion induced in BPH stromal cells by a combination of Th1 and Th17 cell-derived inflammatory cytokines. BPH stromal cells express the vitamin D receptor (VDR), which is up-regulated by exposure to inflammatory stimuli. The non-hypercalcaemic VDR agonist elocalcitol, shown to arrest BPH development by decreasing the intra-prostatic androgen signalling without directly interfering with systemic androgen action, exerts immunoregulatory and anti-inflammatory properties in different prostatic pathology characterized by growth and inflammation. The mechanism of action of VDR agonists supports an important role of chronic inflammation in BPH pathogenesis and strengthens the concept of these agents as a therapeutic option for pharmacological treatment of BPH.

Growth factors in benign prostatic hyperplasia: basic science implications

Benign prostatic hyperplasia (BPH) is the most common proliferative disease of the prostate of men in the United States. The histopathology of BPH strongly implicates local paracrine and autocrine growth factors and inflammatory cytokines in its pathogenesis. A complex milieu of growth-regulatory proteins includes members of the fibroblast, insulin-like, and transforming growth factor families. It appears that these proteins and downstream effector molecules, in addition to a variety of interleukins, are overexpressed in BPH and, working together, create a landscape of increased stromal and epithelial growth and mesenchymal transdifferentiation that leads to disease progression. Inflammation, commonly present in BPH, may contribute to tissue injury, and cytokines produced by inflammatory cells may serve to drive local growth factor production and angiogenesis in the tissues as a "wound healing" response. As we begin to unravel the precise mechanisms involved, new treatments for BPH aimed at these interacting pathways may emerge.

Protease-activated receptor-1 upregulates fibroblast growth factor 7 in stroma of benign prostatic hyperplasia

BACKGROUND

Benign prostatic hyperplasia (BPH) is characterized by abnormal epithelial and stromal proliferation causing urinary obstruction. Prostate growth is regulated by a variety of growth factors secreted from the stroma, including fibroblast growth factor 7 (FGF-7), a potent epithelial-specific growth factor which is increased in hyperplastic prostate. However, the mediator(s) of FGF-7 over-expression is unclear. Protease-activated receptor-1 (PAR-1) is a G-protein coupled receptor known to induce multiple biological processes, but its effect on BPH pathogenesis is mostly unknown. The aim of this study was to investigate the role of PAR-1 as a mediator of BPH development.

METHODS

PAR-1 expression was investigated in BPH and normal prostate tissues by immunohistochemistry. Prostate stromal cells were isolated from BPH specimens, cultured and immunohistochemically characterized. Cultured stromal cells were stimulated with PAR-1 agonists, and extracellular-signal regulated kinase (ERK1/2) activation and cell proliferation were examined. PAR-1 mediated FGF-7 production by cultured stromal cells was assessed by RT-PCR and immunoassays, and verified by small interfering RNA (siRNA).

RESULTS

PAR-1 expression was increased in BPH stroma. In stromal cells isolated from BPH tissues, PAR-1 agonists activated ERK1/2 in a time- and concentration-dependent manner and with resultant enhanced cell proliferation. Pertussis toxin-sensitive G protein/(betagamma-subunits)-phosphatidylinositol 3-kinase and protein kinase C pathways were involved in ERK1/2 phosphorylation. PAR-1 activation strikingly induced FGF-7 production from cultured stromal cells mediated predominantly via ERK1/2 signaling pathway, and PAR-1 siRNA decreased the elicited FGF-7 upregulation.

CONCLUSIONS

The expression and function of PAR-1 in BPH stroma indicate PAR-1 may play important roles in BPH pathogenesis.

ETV1 is a novel androgen receptor-regulated gene that mediates prostate cancer cell invasion

Androgens and the androgen receptor (AR) act in cells by modulating gene expression. Through gene microarray studies, we have identified Ets Variant Gene 1 (ETV1) as a novel androgen-regulated gene. Our data demonstrate that ETV1 mRNA and protein are up-regulated in response to ligand-activated AR in androgen-dependent LNCaP cells, but there is no detectable ETV1 expression in normal prostate cells. The ETV1 promoter is induced by androgens and recruits the AR in the context of chromatin. ETV1-regulated endogenous matrix metalloproteinase genes can be induced by ligand-activated AR. In contrast to the hormone-induced expression in androgen-dependent LNCaP cells, ETV1 expression in androgen-independent LNCaP cells is high and unresponsive to androgen. This androgen-independent ETV1 expression contrasts with the hormone-dependent expression observed for TMPRSS2 in these androgen-independent prostate cancer cells. ETV1 is overexpressed in prostate cancer independent of the TMPRSS2:ETV1 translocation. Disruption of ETV1 expression in both androgen-dependent and androgen-independent prostate cancer cells significantly compromises the invasion capacity of these cells, suggesting an important role for ETV1 in prostate cancer metastasis. Collectively, these results demonstrate that ETV1 expression transitions from androgen-induced to androgen-independent as prostate cancer cells switch from hormone-dependent to hormone-refractory and suggest that this transition may be in part responsible for the elevated levels of ETV1 observed in prostate tumors. Additionally, our data provide an indirect mechanism of AR regulation of gene expression, via the transactivation of the transcription factor ETV1.

Pre-clinical evidence and clinical translation of benign prostatic hyperplasia treatment by the vitamin D receptor agonist BXL-628 (Elocalcitol)

The active form of vitamin D, 1,25-dihydroxyvitamin D3, is a secosteroid hormone that binds to the vitamin D receptor (VDR), a member of the superfamily of nuclear receptors, and exerts a number of diverse biological functions. The natural hormone and synthetic VDR agonists are well known for their capacity to control calcium and bone metabolism, but they also regulate proliferation and differentiation of many cell types, and possess exquisite immunoregulatory properties, mostly by targeting dendritic cells (DC) and T cells. These properties have been clinically exploited in the treatment of different diseases, from secondary hyperparathyroidism to osteoporosis to psoriasis. The VDR is expressed by most cell types, including cells of the urogenital system such as prostate and bladder cells. In particular, the prostate has been recognized as a target organ of VDR agonists and represents an extra-renal synthesis site of 1,25-dihydroxyvitamin D3, but its capacity to respond to VDR agonists has, so far, been probed only for the treatment of prostate cancer. We have taken a different approach, and have analysed the capacity of VDR agonists to treat benign prostatic hyperplasia (BPH), a complex syndrome characterized by a static component related to prostate overgrowth, a dynamic component responsible for urinary irritative symptoms, and a possible inflammatory component. Pre-clinical data reviewed here demonstrate that VDR agonists, and notably BXL-628 (Elocalcitol), reduce the static component of BPH by inhibiting the activity of intra-prostatic growth factors downstream of the androgen receptor, and the dynamic component by targeting bladder cells. These data have led to a proof-of-concept clinical study that has successfully shown arrest of prostate growth in BPH patients treated with BXL-628. Ongoing clinical studies will assess the capacity of this VDR agonist to reduce symptoms and ameliorate flow parameters in BPH-affected individuals. The pronounced effects of BXL-628 on bladder smooth muscle cells and its anti-inflammatory properties indeed anticipate beneficial effects also on BPH-related lower urinary tract symptoms.

Effect of keratinocyte growth factor on cell viability in primary cultured human prostate cancer stromal cells

In normal prostate, keratinocyte growth factor (KGF), also known as fibroblast growth factor-7 (FGF-7) serves as a paracrine growth factor synthesized in stromal cells that acts on epithelial cells through its receptor, KGFR. KGF and KGFR were found in human cancer epithelial cells as well as stromal cells. Since KGF expressed in epithelial cells of benign prostatic hyperplasia (BPH) and in prostate cancer, it has been suggested that KGF might act as an autocrine factor in BPH and prostate cancer. To investigate the roles of KGF in cancerous stroma, primary cultured human prostate cancer stromal cells (PCSCs) were isolated and evaluated. These PCSCs possessed estrogen receptors and KGFR, but not androgen receptor as determined by RT-PCR and Western blot, respectively. KGF exhibited mitogenic and anti-apoptotic effects that correlated with induction of cyclin-D1, Bcl-2, Bcl-xL and phospho-Akt expression in PCSCs, where treatment with KGF antiserum abolished cell proliferation and anti-apoptotic protein expression. PCSCs exposed to KGF for various time periods resulted in phosphorylation of Akt and subsequent up-regulation of Bcl-2. KGF modulated dynamic protein expression indicated that KGF triggered cell cycle machinery and then activated anti-apoptotic actions in PCSCs. Cell proliferation analysis indicated that tamoxifen or ICI 182,780 reduced cell viability in a dose-dependent manner; however, KGF prevented this inhibition, which further demonstrated KGF triggered anti-apoptotic machinery through activating Bcl-2 and phospho-Akt expression. In summary, KGF has an autocrine effect and serves as a survival factor in primary cultured human prostate cancer stromal cells.

Keratinocyte growth factor expression and activity in cancer: implications for use in patients with solid tumors

Keratinocyte growth factor (KGF) is a locally acting epithelial mitogen that is produced by cells of mesenchymal origin and has an important role in protecting and repairing epithelial tissues. Use of recombinant human KGF (palifermin) in patients with hematologic malignancies reduces the incidence and duration of severe oral mucositis experienced after intensive chemoradiotherapy. These results suggest that KGF may be useful in the treatment of patients with other kinds of tumors, including those of epithelial origin. However, its application in this context raises issues that were not pertinent to its use in hematologic cancer because epithelial tumor cells, unlike blood cells, often express the KGF receptor (FGFR2b). Thus, it is important to examine whether KGF could promote the growth of epithelial tumors or protect such tumor cells from the effects of chemotherapy agents. Analyses of KGF and FGFR2b expression in tumor specimens and of KGF activity on transformed cells in vitro and in vivo do not indicate a definitive role for KGF in tumorigenesis. On the contrary, restoring FGFR2b expression to certain malignant cells can induce cell differentiation or apoptosis. However, other observations suggest that, in specific situations, KGF may contribute to epithelial tumorigenesis. Thus, further studies are warranted to examine the nature and extent of KGF involvement in these settings. In addition, clinical trials in patients with solid tumors are underway to assess the potential benefits of using KGF to protect normal tissue from the adverse effects of chemoradiotherapy and its possible impact on clinical outcome.

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

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

The vitamin D analogue BXL-628 inhibits growth factor-stimulated proliferation and invasion of DU145 prostate cancer cells

PURPOSE

Suppression of the invasive phenotype is essential in developing new therapeutic tools to treat advanced prostate cancer (PC) indicating that androgen-independent prostate cancer (AI-PC) is characterized by increased metastatic potential. In the present study, we have investigated the effect of the nonhypercalcemic vitamin D analogue BXL-628 on proliferation and invasive properties of the human PC cell line DU145. In particular, the effect of the analogue was tested following stimulation with a potent growth factor, keratinocyte growth factor (KGF), which stimulates both proliferation and invasion of these cells. We have also evaluated the effect of the analogue on KGF stimulation of PI3K/AKT signaling pathway.

METHODS

Cell proliferation was determined by cell counting. Invasion through Matrigel was evaluated using Boyden chambers. PI3K activity was measured by immunokinase assay and AKT phosphorylation was evaluated by western blot analysis. Keratinocyte growth factor receptor (KGFR) autotransphosphorylation was evaluated by western blot after immunoprecipitation of the receptor.

RESULTS

BXL-628 is able to inhibit both proliferation and invasion of DU145 cells in basal conditions and in response to KGF. Following stimulation with KGF, the inhibition is due to suppression of KGFR autotransphosphorylation and downstream PI3K/AKT activation, both achieved following a brief (5 min) incubation with the analogue. This effect on KGFR autophosphorylation was still present when cells were treated with the alpha-amanitin, an inhibitor of RNA transcription, indicating a rapid, nongenomic effect.

CONCLUSIONS

Our results demonstrate that the vitamin D analogue BXL-628 is able to suppress KGF-induced proliferation and invasion of AI-PC cells in vitro, prospecting a possible use of the drug, which is currently in phase II clinical studies for benign prostatic hyperplasia, in the treatment of advanced prostate cancer.

Studies on the differentiation pathway and growth characteristics of epithelial culture cells of the human prostate

We established explant primary cultures in order to study the growth and hormone responsiveness, and the differentiation process of prostatic epithelial cells. Cell outgrowth was achieved from explant tissue by using a new DU145-cell-conditioned medium and special plastic coverslips. To define the present model, proliferation assays were tested by [3H]thymidine assay and planimetric analysis. Cells were analyzed using immunocytochemistry, light, phase contrast and electron microscopy, polymerase chain reaction, telomerase ELISA and immunoassay (PSA). Morphology and electron microscopy revealed typical epithelial differentiation. Immunocytochemistry showed the content of basal and secretory epithelial cells, endocrine paracrine cells and a high level of proliferation. With increasing culture time, mature epithelial differentiation (PSA) increases and the initial increase of alpha-smooth muscle actin (alpha-SMA) decreases again. After further passaging, alpha-SMA expression is no longer detected and PSA expression decreases. Furthermore, epithelial cells showed both androgen responsiveness and androgen receptor expression. These findings show the presence of epithelial cells in a process of differentiation with endocrine paracrine cells and a high level of proliferation. This model may maintain the cellular and functional properties more closely related to the human prostate and may provide a valuable tool for studying stem cells and differentiation characteristics.

In vitro culturing and characteristics of transit amplifying epithelial cells from human prostate tissue

The prostatic epithelium is functionally organized in stem cell units. This unit consists of a slow turn over stem cell within the basal epithelial layer which can replenish itself and provide progeny which differentiate down either a neuroendocrine or exocrine pathway. The maturation along the exocrine pathway initially involves transit amplifying cells within the basal layer proliferating and subsequently the progeny maturing into intermediate cells. These intermediate cells migrate into the luminal layer where they terminally differentiate into non-proliferative secretory luminal cells which express prostate specific differentiation markers, like PSA. A growing body of experimental evidence has identified the proliferating transit amplifying/intermediate cells as the cells of origin for the common prostatic adenocarcinomas. Using a series of growth characteristics, and mRNA and protein markers, we have validated that primary cultures can be established in serum free defined media from surgically resected human prostates which are composed of essentially pure population of transit amplifying cells. At each serial passage, the subsequent cultures undergo enhanced maturation into intermediate cells and by the 7-10th passage these cells eventually lose their proliferative ability. This study validates that these cells are a useful and relevant system for the determination of molecular events involved in prostatic carcinogenesis.

Relationship between upregulated oestrogen receptors and expression of growth factors in cultured, human, prostatic stromal cells exposed to estradiol or dihydrotestosterone

This study investigated the hypothesis that, in benign prostatic hyperplasia (BPH), upregulated oestrogen receptors (ER) and the action of androgens differentially regulate expression of stromal growth factors. Eight human prostatic stromal cell strains were subjected to a procedure to upregulate their ER by exposing them to 1 micromol 17beta-estradiol for 10 days followed by passage and growth in the absence of steroids. Four of the cell strains instead received 100 nmol dihydrotestosterone for 48 h. Immunoexpression of ERalpha, AR and six growth factors was quantified by flow cytometry in each case. Expression of ERalpha was significantly increased in six of eight cell strains. Expressions of six growth factors (FGF-2, FGF-7, IGF-1, TGF-beta1 NGF and e NOS) were elevated but only for FGF-7 was it significant. There was a significant positive correlation between the change in ERalpha and the change in FGF-2 and FGF-7, but not the other growth factors. Exposure to dihydrotestosterone reduced expression of ERalpha and all six growth factors, compared with oestrogen-treated cells but not significantly. It is concluded that upregulated ERalpha in prostatic stroma may have a greater modulating influence on synthesis of certain growth factors than the direct action of androgens and, by enhancing synthesis of FGF-2 and FGF-7, could play a significant role in the development of BPH.

Inhibition of spontaneous and androgen-induced prostate growth by a nonhypercalcemic calcitriol analog

We have recently found that analog V (BXL-353, a calcitriol analog) inhibits growth factor (GF)-stimulated human benign prostate hyperplasia (BPH) cell proliferation by disrupting signal transduction, reducing Bcl-2 expression, and inducing apoptosis. We now report that BXL-353 blocks in vitro and in vivo testosterone (T) activity. BPH cells responded to T and dihydrotestosterone (DHT) with dose-dependent growth and reduced apoptosis. Exposure of BPH cells to BXL-353 significantly antagonized both T- and DHT-induced proliferation and induced apoptosis, even in the presence of T. To verify whether BXL-353 reduced prostate growth in vivo, we administered it orally to either intact or castrated rats, supplemented with T enanthate. Nonhypercalcemic doses of BXL-353 time- and dose-dependently reduced the androgen effect on ventral prostate weight, similarly to finasteride. Comparable results were obtained after chronic administration of BXL-353 to intact rats. Clusterin (an atrophy marker) gene and protein were up-regulated by BXL-353 in rat prostate, and nuclear fragmentation was widely present. The antiandrogenic properties of BXL-353 did not interfere with pituitary and testis function, as assessed by serum determination of rat LH and T. BXL-353 did not compete for androgen binding to BPH homogenates and failed to inhibit 5alpha-reductase type 1 and type 2 activities. In conclusion, BXL-353 blocks in vitro and in vivo androgen-stimulated prostate cell growth, probably acting downstream from the androgen receptor, without affecting calcemia or sex hormone secretion. BXL-353 and other vitamin D(3) analogs might thus represent an interesting class of compounds for treating patients with BPH.

Upregulation of estrogen and androgen receptors modulate expression of FGF-2 and FGF-7 in human, cultured, prostatic stromal cells exposed to high concentrations of estradiol

This study was performed to develop an experimental model in which expression of estrogen receptors (ER) by human prostatic stromal cells could be reproducibly enhanced relative to similar cells with low ER expression. The second aim was to characterise changes in expression of ER, androgen receptor (AR), FGF-2 and FGF-7 in stromal cells exposed to high and low concentrations of estradiol and testosterone mimicking the different sex hormone levels between young and elderly men. Five strains of human prostatic stromal cells, isolated from BPH resections, were grown in steroid-free medium plus 1 micromol 17beta-estradiol. After 10 days, cells were passaged and grown in the same medium without estradiol until confluent. In a second study four cell strains were exposed to high and low concentrations of 17beta-estradiol and testosterone for 10 days. Cells were labelled with fluorescent antibodies to ERalpha, AR, FGF-2 and FGF-7 and the fluorescence intensity measured by flow cytometry. Following exposure to 1 micromol estradiol, stromal cells showed reduced expression of AR and ERalpha but after passage without estradiol they showed a 25% increase in both receptors over controls. Different combinations of sex hormones induced inconsistent changes with respect to expression of ER, AR and FGFs in the various cell-strains. However, there was a highly significant correlation between AR, ER and FGF-2 and FGF-7, which was cell strain-specific. Thus, changes in sex hormone balance per se may not be solely responsible for the observed increases in prostatic ER levels in BPH. Since expression of ER is correlated with synthesis of FGF-2 and FGF-7, it is likely that increases in stromal ER may mediate the synthesis of stromally-derived growth factors which contribute to the aetiopathogenesis of benign prostatic hyperplasia.

Possible involvement of keratinocyte growth factor and its receptor in enhanced epithelial-cell proliferation and acquired recurrence of middle-ear cholesteatoma

Middle-ear cholesteatoma is characterized by enhanced proliferation of epithelial cells and granular tissue formation. However, the molecular mechanism underlying these pathological changes is largely unknown. Keratinocyte growth factor (KGF) is a mesenchymal cell-derived paracrine growth factor that specifically stimulates epithelial cell proliferation. In the present study, we investigated the possible involvement of KGF and its receptor, KGFR, in the pathogenesis of cholesteatoma using in situ hybridization and immunohistochemistry, respectively. We examined 56 cholesteatoma specimens, and 8 normal skin areas as control. KGF and KGFR expression was examined by immunohistochemistry using rabbit anti-human KGF and anti-human KGFR polyclonal antisera raised in our laboratories against synthetic peptides corresponding to parts of human KGF and KGFR, respectively. KGF protein and mRNA were detected exclusively in stromal fibroblasts and infiltrating T lymphocytes in 80% of cholesteatoma cases, whereas KGFR protein and mRNA were localized in the epithelium in 72% of cases. Assessment of the proliferative activity of cholesteatoma using the labeling index for Ki-67 showed a significantly higher Ki-67 labeling index (66%) in KGF+/KGFR+ cases than other cases. There was a significant correlation between KGF+/KGFR+ expression and recurrence. Our results indicate the possible involvement of both KGF and KGFR in enhanced epithelial cell proliferative activity and recurrence of cholesteatoma.

Vitamin D3 analogue inhibits keratinocyte growth factor signaling and induces apoptosis in human prostate cancer cells

BACKGROUND

Prostate cancer is a worldwide significant health care problem, due to its high incidence and mortality. In particular, androgen-independent tumors have the worst prognosis, because they are refractory to almost all kinds of available therapy. Hence, there is the need of new treatment opportunities targeting androgen-independent, growth factor-mediated, tumor signaling. One of these new promising opportunities is vitamin D3 and its related analogues.

METHODS

We investigated the effect of a vitamin D3 analogue, analogue (V), on proliferation of several human prostate cancer cells in basal condition and after treatment with KGF, one of the intraprostatic growth factors that might participate in the progression of prostate cancer. In addition, in the androgen-independent cell line DU 145, we also studied the effect of analogue (V), KGF, and their mutual interaction on protein tyrosine phosphorylation, bcl-2 expression and apoptosis.

RESULTS

Overall, we found that analogue (V) dose-dependently decreased basal and KGF-induced prostate cancer cell growth, although to a different extent. Maximal effect was obtained in DU 145 cells. In these cells, KGF stimulated tyrosine phosphorylation of a protein corresponding to its receptor, induced bcl-2 expression, and prolonged cell survival. Analogue (V) not only counteracted all these KGF-mediated events, but also decreased basal bcl-2 expression, therefore, allowing DU 145 cells to undergo an apoptotic program.

CONCLUSIONS

Our results indicated that in prostate cancer cells analogue (V) decreased basal and KGF-induced cell proliferation. This effect, at least in DU 145 cells, is in part mediated by negative interactions with cell survival and KGF signaling.

Thrombospondin-1, vascular endothelial growth factor and fibroblast growth factor-2 are key functional regulators of angiogenesis in the prostate

BACKGROUND

Prostate cells secrete many molecules capable of regulating angiogenesis; however, which of these actually function as essential regulators of neovascularization is not yet clear.

METHODS

Functional angiogenic mediators secreted by normal and diseased prostate cells were identified using an in vitro angiogenesis assay. These factors were quantified by immunoblot or ELISA and localized in tissue by immunohistochemistry.

RESULTS

Normal prostate epithelial cell secretions were anti-angiogenic due to inhibitory thrombospondin-1 (TSP-1) whereas this inhibitor was decreased in the pro-angiogenic secretions derived from benign prostatic hyperplasia (BPH) and cancer cells. This pro-angiogenic activity depended primarily on fibroblast growth factor-2 (FGF-2) and/or vascular endothelial growth factor (VEGF) whose secretion was increased. Immunolocalization studies confirmed that the changes detected in vitro also occurred in vivo.

CONCLUSIONS

During disease progression in the prostate, production of TSP-1, the major inhibitor, is down-regulated while that of stimulatory FGF-2 and/or VEGF rise, leading to the induction of the new vessels necessary to support tumor growth.

Complexities of androgen action

Androgens mediate a wide range of processes during embryogenesis and in the adult. In mammals, the principal androgens are testosterone and its 5alpha-reduced metabolite, 5alpha-dihydrotestosterone (DHT). Although these androgenic hormones are diverse in character, it is believed that their effects are mediated via the protein products of a single androgen receptor gene encoded on the X-chromosome. A great deal of information has now accumulated pertaining to the mechanisms by which nuclear receptors, such as the androgen receptor, modulate the activity of responsive genes. The studies have demonstrated the participation of a number of ancillary proteins in modulating activation or repression by nuclear receptors. In addition to studies focused on the mechanisms of nuclear receptor function, additional work has illuminated the mechanism by which androgens are metabolized in selected tissues. This information provides a perspective on the number of levels of complexity by which differential gene regulation by androgens may occur in different tissues and in different cell types.

New concepts in the pathology of prostatic epithelial carcinogenesis

The development of drugs to prevent prostate cancer is underway, yet monitoring the potential efficacy of these agents during clinical trials relies on measuring intermediate endpoints. In this review, various candidate markers are presented that are under different stages of evaluation as intermediate endpoint biomarkers. In addition, the near future will bring an unprecedented wave of new potential biomarkers. For instance, through genomics-based methods many new genes are being discovered whose altered expression may be involved in different phases of prostate cancer development and progression. In the development of rational approaches for selecting which of these untested biomarkers may be useful to measure systematically, there must be an improved understanding of the mechanisms of prostatic carcinogenesis. We submit that this improved understanding will come through new knowledge of the biology of normal prostate epithelial cells, the determination of the precise target cells of transformation, and how their growth regulation is genetically and epigenetically perturbed during the phases of initiation and progression. In this review, therefore, we also present our recent immune-mediated oxidant injury and regeneration hypothesis of why and how the prostate is targeted for carcinogenesis.

Cultured stromal cells: an in vitro model of prostatic mesenchymal biology

BACKGROUND

Initial efforts to develop in vitro models to study prostatic biology focused on the culture and characterization of epithelial cells. Recently, attention has turned towards inclusion of stromal cells in experimental systems.

METHODS

Improved methods to isolate and culture stromal cells have been developed. An array of markers are employed to characterize subtypes of stromal cells, with particular interest in smooth muscle differentiation.

RESULTS

Defined, serum-free media are available for certain experimental applications. Conditions that promote smooth muscle differentiation have been identified. Investigators have characterized hormonal and peptide factors that regulate the growth of prostatic stromal cells, and have also described paracrine factors produced by stromal cells that influence epithelial biology.

CONCLUSIONS

Prostatic stromal-cell cultures are now widely employed by a large number of investigators for a diverse array of experimental purposes. While further refinement is required to obtain model systems that fully mimic in vivo processes, the availability of stromal- and epithelial-cell cultures provides a valuable resource for studying normal prostatic biology as well as benign prostatic hyperplasia (BPH) and cancer.