Endothelin-1 in the human prostate: tissue levels, source of production and isometric tension studies

Re-evaluation of the immunohistochemical distribution of isoforms of nitric oxide synthase in the human prostate: A light and electron microscopical study

Up until today, there are still uncertainties regarding the occurrence of isoforms of the nitric oxide synthase (eNOS, nNOS) in the human prostate. While nNOS was exclusively seen in slender nerve fibres branching within the transition zone, eNOS was reported in glandular structures and also in small vessels interspersing the tissue. This study aimed to re-evaluate by means of light and electron microscopy (LM, EM), the distribution of eNOS and nNOS in the transition zone of the human prostate. Tissue specimens were obtained from 16 patients who underwent surgery for pelvic malignancies. Using specific antibodies in conjunction with advanced fixation and staining procedures, the occurrence of eNOS and nNOS was investigated. nNOS was detected in nerve fibres interspersing the tissue and was also seen in glandular structures. EM revealed that in glandular epithelial cells immunoreaction for nNOS was limited to the cytoplasmic compartment. Vascular endothelial cells of small vessels transversing glandular structures significantly stained for eNOS, while epithelial layers of prostatic glandules appeared free of eNOS. The results implicate that, in the prostate, nNOS is a mediator of stromal and glandular tissue function, and counteract the assumption of eNOS activity in glandular epithelial cells as a source of NO synthesis.

Generation and Regulation of Spontaneous Contractions in the Prostate

Spontaneous myogenic contractions have been shown to be significantly upregulated in prostate tissue collected from men with Benign Prostatic Hyperplasia (BPH), an extremely common disorder of the ageing male. Although originally thought likely to be involved in 'housekeeping' functions, mixing prostatic secretions to prevent stagnation, these spontaneous myogenic contractions provide a novel opportunity to understand and treat BPH. This treatment potential differs from previous models, which focused exclusively on attenuating nerve-mediated neurogenic contractions. Previous studies in the rodent prostate have provided an insight into the mechanisms underlying the regulation of myogenic contractions. 'Prostatic Interstitial Cells' (PICs) within the prostate appear to generate pacemaker potentials, which arise from the summation of number of spontaneous transient depolarisations triggered by the spontaneous release of Ca²⁺ from internal stores and the opening of Ca²⁺-activated Cl^- channels. Pacemaker potentials then conduct into neighbouring smooth muscle cells to generate spontaneous slow waves. These slow waves trigger the firing of 'spike-like' action potentials, Ca²⁺ entry and contraction, which are not attenuated by blockers of neurotransmission. However, these spontaneous prostatic contractions can be modulated by the autonomic nervous system. Here, we discuss the mechanisms underlying rodent and human prostate myogenic contractions and the actions of existing and novel pharmacotherapies for the treatment of BPH. Understanding the generation of human prostatic smooth muscle tone will confirm the mechanism of action of existing drugs, inform the identification and effectiveness of new pharmacotherapies, as well as predict patient outcomes.

Non-Adrenergic, Tamsulosin-Insensitive Smooth Muscle Contraction is Sufficient to Replace α1 -Adrenergic Tension in the Human Prostate

BACKGROUND

Lower urinary tract symptoms (LUTS) suggestive of benign prostatic hyperplasia may be caused by prostate smooth muscle contraction. Although α₁ -blockers may improve symptoms by prostate smooth muscle relaxation, their efficacy is limited. This may be explained by non-adrenergic mediators causing contraction in parallel to α₁ -adrenoceptors. However, little is known about the relevance and cooperative actions of non-adrenergic mediators in the prostate.

METHODS

Prostate tissues were obtained from radical prostatectomy (n = 127 patients). Contractile responses were studied in an organ bath.

RESULTS

Endothelin-1 and noradrenaline induced contractions of similar magnitude (116 ± 23 and 117 ± 18% of KCl-induced contractions). Endothelin-2- and -3-induced maximum contractions of 63 ± 8.6 and 71 ± 19% of KCl, while contractions by the thromboxane analog U46619 amounted up to 63 ± 9.4%. Dopamine-induced contractions averaged to 22 ± 4.5% of KCl, while maximum contractions by serotonin, histamine, and carbachol stayed below 10% of KCl-induced. While noradrenaline-induced contractions were inhibited by tamsulosin (300 nM), endothelin-1-, -2-, or -3-induced contraction were not. No additive effects were observed if endothelins and noradrenaline were applied consecutively to the same samples. If endothelin-1 was applied after U46619, resulting tension (172 ± 43% of KCl) significantly exceeded noradrenaline-induced contraction. Tensions following combined application of endothelin-2 or -3 with U46619 stayed below noradrenaline-induced contractions. Tension following combined application of all three endothelins with U46619 resembled maximum noradrenaline-induced tone.

CONCLUSIONS

Contractions following concomitant confrontation of human prostate tissue with noradrenaline and endothelin-1 are not additive. Endothelin-1 is sufficient to induce a smooth muscle tone resembling that of noradrenaline. This may replace lacking α₁ -adrenergic tone under therapy with α₁ -blockers, explaining the limited efficacy of α₁ -blockers in LUTS treatment. Contractions by thromboxane and endothelin-1 may be additive, and may exceed α₁ -adrenergic tone. Prostate 77:697-707, 2017. © 2017 Wiley Periodicals, Inc.

Novel drug targets for the pharmacotherapy of benign prostatic hyperplasia (BPH)

Benign prostatic hyperplasia (BPH) is the major cause of lower urinary tract symptoms in men aged 50 or older. Symptoms are not normally life threatening, but often drastically affect the quality of life. The number of men seeking treatment for BPH is expected to grow in the next few years as a result of the ageing male population. Estimates of annual pharmaceutical sales of BPH therapies range from $US 3 to 10 billion, yet this market is dominated by two drug classes. Current drugs are only effective in treating mild to moderate symptoms, yet despite this, no emerging contenders appear to be on the horizon. This is remarkable given the increasing number of patients with severe symptoms who are required to undergo invasive and unpleasant surgery. This review provides a brief background on prostate function and the pathophysiology of BPH, followed by a brief description of BPH epidemiology, the burden it places on society, and the current surgical and pharmaceutical therapies. The recent literature on emerging contenders to current therapies and novel drug targets is then reviewed, focusing on drug targets which are able to relax prostatic smooth muscle in a similar way to the α(1) -adrenoceptor antagonists, as this appears to be the most effective mechanism of action. Other mechanisms which may be of benefit are also discussed. It is concluded that recent basic research has revealed a number of novel drug targets such as muscarinic receptor or P2X-purinoceptor antagonists, which have the potential to produce more effective and safer drug treatments.

Zibotentan for the treatment of castrate-resistant prostate cancer

IMPORTANCE OF THE FIELD

Patients with prostate cancer who have progression of their disease while on androgen deprivation therapy have limited therapeutic options. Docetaxel is currently the only agent that increases overall survival in patients with metastatic, castration-resistant prostate cancer; additional agents are needed.

AREAS COVERED IN THIS REVIEW

This review will describe the importance of endothelin-1 (ET-1) for growth of prostate cancer cells, development of bone metastases, and pain responses; the preclinical data for zibotentan, a specific inhibitor of the ET(A) receptor; and the clinical development of atrasentan, a first-generation ET receptor inhibitor, and zibotentan, a more selective inhibitor of the ET(A) receptor.

WHAT THE READER WILL GAIN

Readers will understand the importance of ET-1 as a novel pathway to target for patients with castration-resistant prostate cancer due to its association with prostate cancer growth, metastases to bone, and pain. Readers will learn about the preclinical and clinical development of zibotentan, including the promising Phase II results that have resulted in an extensive Phase III clinical trials program.

TAKE HOME MESSAGE

Modulating the activity of ET-1 through the ET(A) receptor is a novel target for treating patients with metastatic, castration-resistant prostate cancer. There are currently three ongoing Phase III trials with zibotentan, a selective ET(A) inhibitor, to determine the effect of this agent on overall survival in these patients.

Endothelin modulates the cardiovascular effects of clonidine in the rat

Clonidine decreases mean arterial pressure (MAP) by acting as an α(2)-adrenergic receptor (AR) agonist in the central nervous system; it also acts on peripheral α-ARs to produce vasoconstriction. Endothelin (ET) has been shown to modulate the action of ARs. The present study was conducted to determine the involvement of ET in cardiovascular effects of clonidine. Intravenous administration of clonidine (10, 30 and 90μgkg(-1)) produced a dose-dependent decrease in MAP and heart rate (HR). Treatment with ET-1 (100, 300 and 900ngkg(-1)) significantly attenuated clonidine (10μgkg(-1)) induced fall in MAP and HR. Rats treated with ET-1 (900ngkg(-1)) showed an increase in MAP and HR after clonidine administration compared to untreated rats, while ET(A/B) antagonist, TAK-044 (1mgkg(-1)) and ET(A) antagonist, BMS-182874 (9mgkg(-1)) potentiated the hypotensive effect of clonidine. ET(B) receptor agonist, IRL-1620 (5μgkg(-1)) produced significant attenuation of clonidine induced fall in MAP and HR, while ET(B) receptor antagonist, BQ-788 (0.3mgkg(-1)), potentiated the hypotensive effect of clonidine. Prazosin (0.1mgkg(-1)) completely blocked ET-1 induced changes in cardiovascular effects of clonidine. Clonidine-induced contraction of rat abdominal aortic ring was potentiated by ET-1, which was completely blocked by prazosin. Clonidine produced an increase in ET(A) receptor expression in the brain and abdominal aorta while ET(B) receptors were not affected. It is concluded that ET enhances the responsiveness of vascular ARs to the constrictor effect of clonidine and ET antagonists potentiate the hypotensive effect of clonidine suggesting that a combination of ET antagonist with clonidine may be a useful option to treat hypertension.

Mechanisms involved in the effects of endothelin-1 in pig prostatic small arteries

Since endothelin-1 (ET-1) is involved in prostatic disorders, the current study investigated the mechanisms underlying the ET-1-induced effects in pig prostatic small arteries. The experiments were performed in rings mounted in microvascular myographs containing physiological saline solution at 37oC for isometric force recordings. On basal tension, ET-1 (0.1-30 nM) evoked concentration-dependent contractions, which were enhanced by endothelium removal. ET-1 contractions were inhibited by blockade of endothelin ETA and ETB receptors, extracellular Ca2+ removal and blockade of voltage-dependent (L-type)- and non-voltage-dependent-Ca2+ channels. On endothelium intact rings precontracted with noradrenaline, the ETB endothelin receptor agonist BQ3020 promoted a concentration-dependent relaxation which was reduced by blockade of ETB receptors, nitric oxide synthase, guanylyl cyclase and prostanoids synthesis. Endothelium removal abolished its relaxant response and unmasked a BQ3020-induced contraction. Tetraethylammonium and 4-aminopyridine, blockers of non-selective K+ channels and voltage-dependent K+ (Kv) channels, respectively, inhibited the relaxations to BQ3020. Iberiotoxin, apamin and glibenclamide, blockers of large and small Ca2+-activated- and ATP-dependent- K+ channels, respectively, failed to modify these responses. These data suggest that ET-1 promotes contraction of pig prostatic small arteries by activating vascular smooth muscle contractile endothelin ETA and ETB receptors coupled to extracellular Ca2+ entry, via voltage-dependent (L-type)- and non-voltage-dependent Ca2+ channels, also being due to intracellular Ca2+ mobilization. In addition, a population of endothelial ETB receptors mediates vasorelaxation via NO-cGMP pathway, vasodilator cyclooxygenase product(s) and Kv channels.

Endothelin-1 inhibits prostate cancer growth in vivo through vasoconstriction of tumor-feeding arterioles

The vasoactive peptide endothelin-1 (ET-1) has been implicated in promoting the progression of prostate and other cancers though its precise mechanism(s)-of-action remain unclear. To better define the role of ET-1 in prostate cancer progression, we generated prostate cancer cell lines (PC-3 and 22Rv1) that express elevated levels of ET-1. As anticipated, increased ET-1 lead to modest autocrine growth stimulation of PC-3 cells in monolayer culture and increased colony formation in soft agar by both cell lines. Unexpectedly, however, metastatic colonization of 22Rv1 cells expressing elevated levels of ET-1 was reduced, as was the size of subcutaneous tumors produced by both 22Rv1- and PC-3 cells. Based on these data, we hypothesized that high levels of ET-1 may negatively impact the tumor microenvironment. We found that increased ET-1 expression did not consistently inhibit angiogenesis, indicating that this was not the cause of poor tumor growth. As an alternative explanation, we examined whether elevated ET-1 results in local vasoconstriction and thus reduces the blood supply available to the tumor. Consistent with this hypothesis, treatment of mice bearing PC-3 xenografts with a vasodilator increased tumor perfusion and partially restored tumor growth. Moreover, analysis of tumor vascular casts indicated vasoconstriction of tumor-feeding arterioles. Taken together, our data suggest that the local concentration of the ET-1 peptide is critical for determining a balance between its previously unrecognized tumor growth-suppressing activity (vasoconstriction) and known growth-promoting (mitogenesis, survival and angiogenesis) activities. These findings may have implications for the modification of current prostate cancer therapies involving ET-1.

Distinct patterns of endothelin axis expression in primary prostate cancer

OBJECTIVES

Emerging evidence supports a role for endothelin-1 (ET-1), endothelin A and B receptors (ET(A) and ET(B), respectively), and neutral endopeptidase (NEP) in the progression of prostate carcinoma. In clinical trials for advanced prostate cancer, ET axis blockade significantly delayed the time to disease progression in a subset of patients. We examined ET axis expression in prostate cancer, prostatic intraepithelial neoplasia, and normal adjacent tissue and then analyzed the relationship of the protein levels with disease progression.

METHODS

The expression levels of ET(A), ET(B), and NEP were determined in 120 prostate cancer specimens obtained at surgery or biopsy by immunohistochemistry. In situ hybridization on a subset of the specimens was used to confirm the immunohistochemistry findings.

RESULTS

In regions of adenocarcinoma, immunohistochemistry analysis demonstrated high ET(A) expression in 72% of the specimens. ET(A) expression was significantly elevated with increased pathologic stage and grade. ET(B) and NEP levels were significantly decreased in adenocarcinoma compared with normal adjacent tissue and prostatic intraepithelial neoplasia; however, reduced expression did not correlate with tumor grade or stage. Patients with prostate-specific antigen recurrence had significantly greater ET(A) levels in their primary tumors than did patients who were disease free 5 years after prostatectomy. Patients with high ET(A) expression in the adenocarcinoma regions with low ET(B) and NEP had a significantly decreased interval to prostate-specific antigen progression compared with patients with low ET(A) or high ET(B)/NEP expression.

CONCLUSIONS

These data suggest two patterns of ET(A) expression in primary prostate cancer, with increased expression correlating with more advanced disease. The use of these expression patterns to identify patients more likely to respond to ET axis blockade might enhance treatment outcomes.

RhoA/Rho kinase-mediated Ca2+ sensitization in the contraction of human prostate

AIMS

The contractile mechanisms of prostatic smooth muscle have been extensively investigated at the receptor level. However, the intracellular mechanisms have not yet been fully elucidated, especially in human tissue. In the present study, we examined the functional role of RhoA/Rho kinase (ROCK), one of the major intracellular molecules involved in smooth muscle contraction, in the contraction of the human prostate.

METHODS

Ring preparations made of cultured human prostatic stromal cells (CHPSCs) or fresh human prostatic tissue was used for an isometric tension study. Gene transfer using baculovirus vector and alpha-toxin permeabilized preparations were also used.

RESULTS

RhoA, ROCK I and ROCK II proteins were all expressed in CHPSCs and fresh human prostatic tissue. In CHPSCs ring preparations, the contraction induced by endothelin (ET)-1 was enhanced by over-expression of RhoA and inhibited by ROCK inhibitor. In alpha-toxin permeabilized preparations, ET-1 or GTP-gammaS induced an additional contraction at a constant [Ca2+]i, that was inhibited by ROCK inhibitor. In fresh human prostatic tissue, norepinephrine (NE)-induced contraction was inhibited by ROCK inhibitor at a constant [Ca2+]i in alpha-toxin permeabilized preparations.

CONCLUSIONS

These results suggested that RhoA/ROCK-mediated Ca2+ sensitization is likely involved in the contraction of the human prostate. The antagonisms of this pathway may thus be useful as an alternative target in the treatment of benign prostatic hyperplasia (BPH).

Regional differences in the functional and biochemical properties of endothelin receptor subtypes in the rabbit prostatic urethra

OBJECTIVE

To examine the regional differences in the functional (pharmacological) and biochemical properties of endothelin (ET) receptors in the rabbit prostatic urethra.

MATERIALS AND METHODS

The properties of ET receptors in 6-month-old male rabbit prostatic urethras were examined using isolated muscle-bath and radioligand receptor-binding techniques. Using plasma membrane suspensions, saturation and inhibition experiments with [(125)I]ET-1 and unlabelled agonists and antagonists (ET(A)-selective antagonist BQ123, and ET(B)-selective agonist sarafotoxin 6c, STX6c) were done to determine the ET receptor densities and their subtype specificities in the different regions of the urethra.

RESULTS

The ETs (ET-1 and ET-3) produced significant concentration-dependent contractile responses in the smooth muscle strips from the different regions of the urethra. Although the maximum contractile responses induced by ET-1 were similar in the different regions, the maximum contractile responses induced by ET-3 were greater in the distal region than in the proximal or middle regions, suggesting that the contractile response to ET-1 is more potent than that to ET-3 in all regions, and that there are region-specific differences in the responses to ET-3 but not ET-1. Moreover, the ET-3-induced contractile response was suppressed by BQ788 (a selective antagonist of the ET(B) receptor) suggesting that the ET(B) receptor subtype contributes to the contractile responses mediated by ET-3. The ET receptors were expressed in higher concentrations in the distal than in the proximal or middle regions. BQ123 and STX6c inhibited [(125)I]ET-1 binding in all regions with high and low affinity constants, indicating the presence of both ET(A) and ET(B) receptor subtypes. The proportions of high-affinity binding sites for BQ123, representing ET(A) receptors, were approximately 68%, 63% and 42% in the proximal, middle and distal regions, respectively. By contrast, the proportions of high-affinity binding sites for STX6c, representing ET(B) receptors, were approximately 27%, 35% and 52% in the proximal, middle, and distal regions, respectively. These data indicate the presence of regional differences in the densities and subtype specificities of ET receptor subtypes, and the existence of regional differences in the rabbit prostatic urethra.

CONCLUSION

The results suggest regional differences in ET(B) receptor subtypes that mediate contractile responses to ET-3, reflecting differences in the densities and specificities of the ET receptor subtypes in the rabbit prostatic urethra.

LUTS treatment: Future treatment options

Lower urinary tract symptoms (LUTS) are commonly divided into storage, voiding, and postmicturition symptoms, and may occur in both men and women. Male LUTS have historically been linked to benign prostatic hyperplasia (BPH), but are not necessarily prostate related. The focus of treatment for LUTS has thus shifted from the prostate to the bladder and other extraprostatic sites. LUTS include symptoms of the overactive bladder (OAB), which are often associated with detrusor overactivity. Treatment for LUTS suggestive of BPH has traditionally involved the use of alpha(1)-adrenoceptor (AR) antagonists; 5alpha-reductase inhibitors; and phytotherapy-however, several new therapeutic principles have shown promise. Selective beta(3)-adrenoceptor agonists and antimuscarinics are potentially useful agents for treating LUTS, particularly for storage symptoms secondary to outflow obstruction. Other agents of potential or actual importance are antagonists of P2X(3) receptors, botulinum toxin type A, endothelin (ET)-converting enzyme inhibitors, and drugs acting at vanilloid, angiotensin, and vitamin D(3) receptor sites. Drugs interfering with the nitric oxide/cGMP-cAMP pathway, Rho-kinase and COX inhibitors, as well as drugs targeting receptors and mechanisms within the CNS, are also of interest and deserving of further study for the treatment of LUTS.

Endothelin receptor A blockade enhances taxane effects in prostate cancer

Endothelin (ET) 1 is important in the growth of prostate cancer cells through the activation of the endothelin A (ET(A)) receptor. ET receptor blockade is a new therapeutic target in treating advanced prostate cancer. This study investigates the impact of the combination of the ET(A) antagonist atrasentan (ABT-627) and taxane chemotherapy on prostate cancer cell survival in vitro and on the delay of prostate cancer in a xenograft mouse model. In vitro, PPC-1 cells transfected with an ET(A)-overexpressing vector were treated with ABT-627, paclitaxel/docetaxel, or both. Clonogenic viability and cell death assays were used to determine cell survival and apoptosis, respectively. ABT-627 and docetaxel combination treatment was used in vivo to treat mice with established ET(A)-overexpressing PPC-1 xenograft tumors, and tumor growth rates were assessed. Cell proliferation and vascularity were determined with Ki-67 and CD31 staining, respectively. Cells treated with combination therapy had significantly fewer viable cells and more programmed cell death than cells given monotherapy. Xenograft tumor growth rates were significantly lower in mice treated with combination therapy than in animals given a single agent. Ki-67 immunostaining demonstrated significantly fewer proliferative cells following combination therapy than following monotherapy. This study demonstrates ABT-627 to have additive antitumor effects when used in combination with taxane drugs both in vitro and in vivo.

Targeted therapies for prostate cancer

The development of targeted therapies for prostate cancer has exploited various elements of prostate biology. The androgen-dependence of prostate cancer continues to be the focus for the development of new drugs and the analysis of details of the intermolecular interactions of the androgen receptor. Importantly, new applications of androgen ablation therapy have proven to have the greatest effect on cause-specific and overall survival during the last decade. Prostate epithelial cells express a number of tissue-specific proteins that have been the target either for antibody-directed therapies, in the case of prostate-specific membrane antigen, or target-activated therapies in the case of prostate-specific antigen, a serine protease. Prostate-specific proteins have also been targeted by the development of vaccines that have entered clinical trials. Humanized monoclonal antibodies and small molecules designed to inhibit oncogenic signalling pathways have been subjected to clinical trials in prostate cancer with limited success. The application of pathway inhibitors to prostate cancer therapy has been limited because no common dominant oncogenic mutation affecting signal kinase activation in prostate cancer has yet been identified. The interaction of signal kinase inhibitors with androgen ablation and with cytotoxic chemotherapy remains to be explored.

Pathogenesis of bone metastasis: a review

BACKGROUND

Metastasic deposits from malignancies frequently lodge in the skeleton, including the jaw bones.

METHOD

A review of the literature was performed in order to provide a coherent overview on the pathogenesis of bone metastasis.

RESULTS

Bone metastasis follows complex molecular interactions that enable tumor cells to detach from the primary site, invade the extracellular matrix, intra-vasate, extra-vasate, and proliferate within bone. They induce local bone changes that could manifest radiologically as either osteolytic or radiodense. In addition to the direct bone changes, malignancies can elaborate mediators that are released in circulation, leading to generalized osteopenia.

CONCLUSIONS

The spread of malignant neoplasms to bone is not a random process but rather a cascade of specific molecular events orchestrated through complex interactions between neoplastic cells and their environment.

Current models of human prostate contractility

1. The human prostate is a compact gland contributing to seminal fluid. With increasing age, most humans will develop benign prostatic hyperplasia, a condition of prostatic enlargement and contractility that leads to occlusion of the urethra. Over many years, investigators have used a variety of animal and cell culture models to elucidate some of the contractile and proliferative mechanisms that may be associated with the development of this condition. 2. This review briefly assesses the current state of knowledge of the mechanisms underlying human prostatic contractility and compares it with that of animal and cell culture models. It is not intended as a comprehensive methodological review, nor is it intended to indicate our preferences for either model. Our aim is to correlate findings from animal and cell culture models with the current understanding of human prostate contractility. 3. We hope that the present review will increase awareness of the suitability of the current models in developing our understanding of benign prostatic hyperplasia.

Transgenic mice over-expressing endothelin-1 in testis transactivated by a Cre/loxP system showed decreased testicular capillary blood flow

It is generally believed that too high or low levels of endothelin-1 (ET-1), a strong vasoconstrictor, may be detrimental to animals. Therefore, in order to understand the in vivo function of ET-1, we used a conditional transgenic approach, Cre/loxP recombination system, to generate transgenic mice that over-express ET-1 in a tissue-specific manner. In such a strategy a single transgenic mouse line, ELSE, was initially generated where a general promoter, human elongation factor 1alpha (hEF1alpha) promoter, was used to drive the expression of a loxP-flanked sequence containing the lacZ reporter gene and a STOP cassette before the ET-1 cDNA, the recombinational competency of which was confirmed in an Escherichia coli test system. In ELSE mice, expression of the reporter lacZ was limited to spermatozoa and spermatogonia as well as Sertoli, Leydig and endothelial cells in the testis, thus confirming the suitability of these mice for the generation of testes-limited ET-1 expression. To generate transgenic progeny with ET-1 over-expression in the testis (successful recombination, ELSE/ELT), ELSE mice were mated with EIIa-cre mice expressing Cre recombinase in pre-implantation mouse embryos. These ELSE/ELT mice exhibiting testis-specific ET-1 over-expression had normal reproductive function and showed no obvious alterations in gross testicular morphology. Although over-expression of ET-1 leads to reduction of testicular blood flow, young adult ELSE/ELT mice showed no obvious signs of inflammation, fibrosis or abnormal proliferation of cells in the testes of young ELSE/ELT mice by histochemical analyses.

Endothelin receptor antagonists

Hormone refractory prostate cancer remains true to its middle name: it is largely refractory to attempts to delay its progression. New targets and new therapies are demanded. Through a review of the available literature on endothelin and several preclinical observations, the endothelin axis has emerged as one such target. In phase II and III clinical trials of atrasentan, a potent and selective endothelin receptor A subtype (ET(A)) antagonist, disease progression was delayed in some men. This well tolerated, oral agent may help convert advanced prostate cancer to a more chronic disease. This review will discuss the endothelin axis, preclinical rationale and some of the available clinical trial data on this promising new approach.

Evaluation of the mouse prostate as a suitable model for the study of human prostate function

INTRODUCTION

Research into prostate development and function is mainly carried out in rats and guinea pigs. While these animals have proven to be good models of human prostate function, their use is limited when compared with what could be achieved using the various currently available gene knockout mice. This study aimed to ascertain whether the mouse prostate was a viable model for studying human prostate function.

METHODS

Sections from mouse prostate glands were histochemically processed to visualise the neurotransmitters and receptors present. Isolated organ bath studies were conducted in Krebs-Henseleit solution at 37 degrees C to delineate the physiological mechanisms involved in contractility.

RESULTS

Positive histochemical staining for noradrenaline and acetylcholinesterase (AChE) was observed in the fibromuscular stroma. AChE-positive staining was also observed in epithelial cells lining prostatic acini. Immunoreactivity to P2X(1) and P2X(7) purinoceptors was observed in the fibromuscular stroma and immunoreactivity to P2X(4) purinoceptors in the glandular epithelium. Positive immunostaining for neuropeptide Y, big endothelin, calcitonin gene-related peptide (CGRP), substance P, and neurokinin A was observed in the fibromuscular stroma. Frequency-response curves (1.0 ms pulse duration, 60 V, 0.1-20 Hz) to electrical field stimulation yielded frequency-dependent contractions that were attenuated by tetrodotoxin (P < .001), guanethidine (P < .001), and prazosin (P = .01). Suramin (P = .21), alpha,beta-methylene ATP (P = .84), and atropine (P = .76) caused no significant effects. Concentration-response curves to endogenously administered phenylephrine yielded concentration-dependent contractions (pEC(50) = 6.1 +/- 0.3, maximum response 0.20 +/- 0.03 g), which were attenuated by prazosin (P < .001).

DISCUSSION

Histochemistry suggests that mouse prostates have a similar innervation to that of humans and other laboratory animals. Furthermore, responses to nerve stimulation are noradrenergic and mediated by alpha(1)-adrenoceptors. Therefore, the mouse prostate is a suitable model for human prostate function and a viable isolated preparation for contractility studies.

Functional role of PKC in contraction of cultured human prostatic stromal cells

The contractile activity of prostatic stromal cells contributes to symptoms of benign prostatic hyperplasia (BPH). However, the mechanisms for this contraction have not yet been fully elucidated. In this study, we investigated the role of protein kinase C (PKC) in prostatic contraction by measuring the isometric tension development of cultured human prostatic stromal cells (CHPSCs) derived from BPH patients. Fresh human BPH tissue was used only in a Western blot analysis. A ring preparation made of CHPSCs and collagen gel could develop an isometric tension during activation with various agonists. Phorbol 12,13 dibutyrate (PDBu), a PKC activator, induced a relaxation. A Western blot analysis revealed the expression of PKC-potentiated protein phosphatase-1 inhibitory protein (CPI-17) in both CHPSCs and fresh human BPH tissue to be much lower than that in the rabbit aorta. When CPI-17 was over-expressed, PDBu induced a large contraction, but the agonist-induced contraction did not become larger than expected. In alpha-toxin permeabilized preparations, PDBu induced a relaxation in control CHPSCs, while it induced a contraction at a constant [Ca2+]i in CPI-17 over-expressing CHPSCs. These results indicated that the activation of PKC in CHPSCs induces a relaxation probably due to low expression level of CPI-17 and also that the PKC-CPI-17 pathway does not appear to play a major role in the agonist-induced contraction even when CPI-17 was over-expressed.

Function and survival of dendritic cells depend on endothelin-1 and endothelin receptor autocrine loops

The biologic effects of endothelin-1 (ET-1) are not limited to its potent vasoconstricting activity. The endothelin receptors, ETA and ETB, have differential tissue and functional distributions. Here we showed that dendritic cells (DCs), the major antigen-presenting cells in the adaptive limb of the immune system, produce large amounts of ET-1 and significantly increase the expression of endothelin receptors upon maturation. Selective blockade of the ETA receptor significantly reduced expression of the mature DC marker CD83, decreased the production of the immunostimulatory cytokine interleukin-12, down-regulated DC ability to stimulate T cells, and promoted DC apoptosis. Selective ETB receptor blockade, on the other hand, resulted in increased expression of CD83 and improved DC survival. Therefore, ET-1/ETA/ETB autocrine/paracrine loops on DCs appear to be essential for the normal maturation and function of human DCs, presenting a unique target for immunomodulatory therapies.

Changing aspects in the evaluation and treatment of patients with benign prostatic hyperplasia

Lower urinary tract symptoms are a common clinical symptom among men and a frequent reason for referring to a urologist. The most important information comes from the patient history because evaluation of symptoms is fundamental in the diagnosis and treatment planning for LUTS. Other aspects of the initial evaluation, such as the physical examination and initial laboratory values, can provide valuable additional information about the severity of the disease and the need for treatment. If treatment is warranted based on this information, additional diagnostic tests may be appropriate to set a pretreatment baseline, rule out other conditions, and plan treatment approach. Fortunately, a variety of effective medical and surgical treatments are available to treat this common disease.

Regulatory effect of castration on endothelins, their receptors and endothelin-converting enzyme in rat seminal vesicle

OBJECTIVE

To investigate the effects of castration on the expression of endothelins (ETs), ET receptors and ET converting enzyme-1 (ECE-1) in the rat seminal vesicle (RSV).

MATERIALS AND METHODS

Sprague-Dawley rats (3 months old) were surgically castrated or sham-operated, and then killed 7 days after surgery. Biochemical and pharmacological properties and the location of ET receptors in the RSV were determined by a series of binding experiments with [125I]ET-1, using membrane particulates and slide-mounted frozen sections of RSV. Expression levels of ETA and ETB receptor subtypes, ET-1, ET-3 and ECE-1 mRNAs were assessed by relative multiplex reverse-transcription polymerase chain reaction (RT-PCR).

RESULTS

The density of total ET receptors increased significantly in the seminal vesicle of the castrated rat. The predominance of the ETA receptor subtype in the RSV did not change with castration. Autoradiographic studies showed the presence of ET receptors on the smooth muscle and epithelium of the RSV. In addition, RT-PCR showed an up-regulation in the expression of ETA and ETB receptor subtypes, ET-1 and ECE-1 mRNAs in the seminal vesicle of the castrated rat. However, castration caused no significant change in the expression levels of ET-3 mRNA.

CONCLUSION

These findings suggest a regulatory role for testosterone in the expression of the ET receptor system in the RSV.

Pharmacological characterization of TA-0201, an endothelin receptor antagonist, with recombinant and human prostate endothelin receptors

The pharmacological profile of N-(6-(2-(5-bromopyrimidine-2-yloxy)ethoxy)-5-(4-methylphenyl)pyrimidin-4-yl)-4-(2-hydroxy-1,1-dimethylethyl) benzensulfonamide sodium salt sesquihydrate (TA-0201), a new antagonist of endothelin receptors, was examined, using human recombinant and prostate endothelin receptors. In binding experiments with [125I]endothelin-1, TA-0201 showed extremely high affinity for recombinant endothelin ET(A) receptors (pK(i)=10.7), as compared with that for recombinant endothelin ET(B) receptors (pK(i)=7.8). Endothelin ET(A) and ET(B) receptors coexisted in human prostate with different proportions (endothelin ET(A) receptor: approximately 70%), which were distinguished by TA-0201 in the same manner as with recombinant receptors. Human prostate strips contracted in response to endothelin-1 and sorafotoxin S6c, but the maximum contraction induced by endothelin-1 was approximately three times greater than that induced by sarafotoxin S6c. The response to endothelin-1, but not to sarafotoxin S6c, was inhibited by TA-0201 and cyclo(D-Asp-Pro-D-Val-Leu-D-Trp) (BQ123) (endothelin ET(A) receptor antagonist) but not by BQ788 (endothelin ET(B) receptor antagonist). These results suggest that TA-0201 is a highly selective endothelin ET(A) receptor antagonist and will be useful for understanding the physiological and pathological roles of the endothelin ET(A) receptor in human prostate and other tissues.

Effect of endothelin-A receptor blockade with atrasentan on tumor progression in men with hormone-refractory prostate cancer: a randomized, phase II, placebo-controlled trial

PURPOSE

To evaluate the efficacy and safety of atrasentan (ABT-627), an endothelin-A receptor antagonist, in the treatment of asymptomatic, hormone-refractory prostatic adenocarcinoma.

PATIENTS AND METHODS

A double-blind, randomized, placebo-controlled clinical trial of hormone-refractory prostate cancer (HRPCa) patients was conducted in the United States and Europe. Two hundred eighty-eight asymptomatic patients with HRPCa and evidence of metastatic disease were randomly assigned to one of three study groups receiving a once-daily oral dose of placebo, 2.5 mg atrasentan, or 10 mg atrasentan, respectively. Primary end point was time to progression; secondary end points included time to prostate-specific antigen (PSA) progression, bone scan changes, and changes in bone and tumor markers.

RESULTS

The three treatment groups were similar in all baseline characteristics. Median time to progression in intent-to-treat (ITT) patients (n = 288) was longer in the 10-mg atrasentan group compared with the placebo group: 183 v 137 days, respectively; (P =.13). Median time to progression in evaluable patients (n = 244) was significantly prolonged, from 129 days (placebo group) to 196 days (10-mg atrasentan group; P =.021). For both ITT and evaluable populations in the 10-mg atrasentan group, median time to PSA progression was twice that of the placebo group (155 v 71 days; P =.002). Patients who received placebo continued to have significant increases from baseline in serum (lactate dehydrogenase [LDH]), a marker of disease burden; elevations in LDH were uniformly attenuated by atrasentan in the ITT population. Headache, peripheral edema, and rhinitis were primary side effects, typically of mild to moderate severity. Quality of life was not adversely affected by atrasentan.

CONCLUSION

Atrasentan is an oral, targeted therapy with favorable tolerability and the potential to delay progression of HRPCa.

Effects of cyclic stretch on prostatic cells in culture

PURPOSE

The fundamental process in the development of benign prostatic hyperplasia (BPH) is a loss of homeostasis between cell proliferation and apoptosis. Prostatic smooth muscle cells contract under adrenergic control. The response of a cell to stretch may have a role in the pathogenesis of BPH.

MATERIALS AND METHODS

Monolayer cultures of human prostatic stromal and epithelial cell lines were exposed to cyclic stretch for 48 hours.

RESULTS

Cyclic stretch conferred resistance to etoposide induced apoptosis. Underlying this apoptotic resistance was increased expression of the anti-apoptotic Bcl-2 family of proteins. As measured by thymidine incorporation, the rate of proliferation also increased in benign epithelial cells under cyclic stretch conditions. Furthermore, an increase in the production of platelet-derived growth factor by stromal cells and transforming growth factor-beta by epithelial cells occurred under such conditions.

CONCLUSIONS

The observed changes in proliferation and apoptosis may contribute to the understanding of BPH, ultimately leading to therapeutic and preventive applications.

Endothelin-1 as a target for therapeutic intervention in prostate cancer

The endothelins, a family of potent vasoconstricting peptides, have been implicated in the pathophysiology of advanced prostate cancer. Two endothelin receptors, ET-A and ET-B are found in normal prostate tissue. Malignant prostate cells are notable for the loss of ET-B receptors and increased levels of endothelin-1 [ET-1]; this distortion of the endothelin system may be a significant factor in the progression of prostate cancer. Proposed roles for endothelin in prostate cancer include growth promotion, apoptosis inhibition, bone formation, and stimulation of nociceptive receptors. ET-1 can act alone as a mitogen, but its effects are greatest as a comitogen with a variety of growth factors, including basic fibroblast growth factor, insulin-like growth factors, and platelet derived growth factor. Although their exact functions are unclear, ET-1, in conjunction with vascular endothelial growth factor, appears to play a major role in tumor angiogenesis. By a variety of methods, ET-1 alters the balance of osteoblast and osteoclasts to the favor new bone formation that is characteristic of metastatic disease. Several studies indicate that the refractory pain of metastatic cancer is related to the direct nociceptive effects ET-1. These findings suggest that ET receptors are promising therapeutic targets for pharmacologic intervention. Early clinical trials indicate that the ET-A receptor antagonist used in prostate cancer is reasonably well tolerated with mild but pervasive symptoms related to ET-1's vasoconstrictive effects. Results of ongoing clinical trials are eagerly awaited in order to see if the hypothetical promise of ET antagonism will result in clinical success.

Neuroendocrine pathogenesis in adenocarcinoma of the prostate

BACKGROUND

In the prostate, the importance of sex hormones for its normal development and function is well known. However, it has been proposed that various neuroendocrine (NE) hormones and growth factors may be involved in the pathogenesis of prostatic carcinoma (CaP). Neuroendocrine differentiation appears to be associated with tumour progression and the androgen-independent state, for which there is currently no successful therapy. Therefore, we need to improve our understanding of NE cells, their regulatory products and influence on the prostate gland. Finally, new therapeutic protocols need to be developed.

METHODS

Information is presented on prostatic NE cells and neuroendocrine differentiation (NED) in prostatic carcinoma. Neuroendocrine secretory products and interactions with epithelial prostate cells are investigated in order to understand their significance for the pathogenesis of the prostate gland, prognosis and therapy.

RESULTS

Recent research suggests that NE-secreted products. such as serotonin, somatostatin and bombesin, may influence growth, invasiveness, metastatic processes and angiogenesis in CaP. During recent years. new experimental models for NED have been developed to provide evidence that NE products may promote proliferation and confer antiapoptotic capabilities on non-neuroendocrine cells in close proximity to NE cells. Cancerous epithelial cells may become more responsive to NE factors by upregulation of receptors for neuropeptides, or may induce NE cells to upregulate the secretion and synthesis of NE factors. In the androgen independent state, neuropeptides and their intracellular signals may activate the androgen receptor. Furthermore, androgen ablation may lead to downregulation of neural endopeptidase 24.11 (a zinc-dependent metalloproteinase) and PSA, which would lead to increased levels of NE products becoming available. These studies confirm that NE cells and NED may have a significant impact on prostate cancer, especially in the androgen independent state.

CONCLUSIONS

Recent developments in molecular biology and pathophysiology of prostate cancer have increased our understanding of the NE regulatory mechanisms. Hopefully, this will lead to the development of entirely new therapeutic modalities. For example, somatostatin agonists may suppress angiogenesis and proliferation, and simultaneously promote apoptosis in prostate cancer cells. Somatostatin may thus have an important role in tumour biology, and in the future there may be a potential role for somatostatin analogues in the treatment of prostate cancer, but also for serotonin and bombesin receptor antagonists. However, a review of the accumulated knowledge in this field suggests that we still need to improve our understanding of NE cells and their regulatory products and influence on the prostate gland. and that clinical trials are needed, to test drugs based on neuroendocrine hormones and their agonists/antagonists.

Big endothelin-1 but not endothelin-1 is present in the smooth muscle stroma of the prostate gland of the rat

Immunohistochemical techniques were employed to localize the presence of endothelins in the mature rat prostate gland. Immunoreactivity for big endothelin-1 but not endothelin-1 was observed in the fibromuscular stroma of the rat prostate gland. No immunoreactivity was seen in the glandular epithelium. Double staining procedures showed big endothelin-1 immunoreactivity to be co-localized with alpha-actin immunoreactivity. The stroma of the prostate gland also contained nerve fibres coursing through it which are immunopositive for tyrosine hydroxylase. These results suggest that big endothelin-1 but not endothelin-1 is co-localized with alpha-actin in the smooth muscle cells of the rat prostate gland. This implies that endothelin-1 is synthesized on demand from big endothelin-1 in the fibromuscular stroma of the rat prostate.

Endothelin-1 production by prostate cancer cell lines is up-regulated by factors involved in cancer progression and down-regulated by androgens

BACKGROUND

Recent data demonstrate that endothelin-1 (ET-1) concentration increases in plasma of men with advanced, hormone-refractory prostate adenocarcinoma. In addition, ET-1 is involved in osteblastic remodelling and new bone formation, suggesting a role for this vasoactive peptide in the metastatic progression of prostate cancer to the bone.

METHODS

We investigated the regulation of ET-1 expression in androgen-sensitive and insensitive prostate cancer cell lines by androgens and several factors involved in progression of prostate cancer (EGF) and bone remodelling (TGFbeta-1, IL1-alpha and IGF-1).

RESULTS

Northern analysis and radio immunoassay demonstrated that all the ET-1 pathways are tuned off in the androgen-sensitive LNCaP cell line when compared to the androgen-insensitive PC-3 and DU145. In PC-3 cells transfected with a full-length androgen receptor expression vector (PC-3-AR), treatment with androgens reduced gene expression and secretion of ET-1 without affecting the gene expression of ET-3. Collectively, these data support a role for androgens in the regulation of ET-1 production by prostate adenocarcinoma cells. In PC-3 and DU145 cells, ET-1 gene expression and secretion were up-regulated by TGFbeta-1, EGF and IL1-alpha, whereas IGF-1 was ineffective. Conversely, none of the treatments affected ECE-1 or ET-3 gene expression.

CONCLUSIONS

In conclusion, ET-1 production by prostate adenocarcinoma cells is down-regulated by androgens and up-regulated by factors involved in tumour progression indicating a role for this peptide in the biology of prostate cancer. In view of the role exerted by ET-1 in the process of bone metastasis, our data suggest the use of ET-1 receptor antagonists in the treatment of advanced prostate cancer.

Nonandrogenic mediators of prostatic growth

Prostate growth and development are primarily under the control of androgens; however, other factors can also influence prostatic growth through alternative pathways. This article discusses some of the major nonandrogenic mediators of prostate growth. Information on the pathways by which these factors exert their effects is also reviewed.

Endothelin-1 in human prostatic carcinoma treated with androgen withdrawal: an immunohistochemical study

BACKGROUND

Various reports suggest a role for endothelin-1 in prostatic carcinoma. The objective of the current study was to evaluate the changes of the immunodetectable endothelin-1 in prostatic carcinomas characterized by different grades of regression due to total androgen withdrawal.

METHODS

An immunohistochemical study was made on eleven prostatic carcinomas treated with neoadjuvant hormonal therapy for 3 months, followed by radical prostatectomy. Another ten specimens of untreated carcinomas were studied for comparison. An appraisal of androgen receptors was associated. A highly specific polyclonal antibody against endothelin-1 and a commercial monoclonal mouse antibody for androgenic receptors were used.

RESULTS

In all cases, a prevalent quantity of androgenic receptor-positive tumor cells were present. Neoplastic cells of untreated carcinomas showed a strong and heterogeneous staining for endothelin -1. In unregressed areas of treated cases, the features of endothelin-1 and androgen-receptor staining were the same as those of untreated cases. In areas characterized by moderate histologic regression, the endothelin-1 staining became more heterogeneous. In areas of strong histologic regression, a diffuse membrane staining was often noted. Only in completely regressed cancer cells was a definite loss of immunodetectable endothelin-1 and androgenic receptors observed.

CONCLUSIONS

Endothelin-1 is one of the proteins intrinsic to prostatic epithelial cells, both benign and malignant. In cases treated with androgen withdrawal, histologic regression is not uniform. In unmodified areas, immunodetectable endothelin-1 and androgenic receptors also are unmodified, thus suggesting some mechanism that substitutes for the action of androgen. Only neoplastic cells with complete histologic regression also lose androgenic receptors and endothelin-1, whereas the preserved immunostaining in deeply modified prostatic neoplastic cells seems to indicate that these cells still are potentially active.

The contractile effects of endothelins on the smooth muscle of the rat prostate gland

Endothelin-1 elicited tonic contractions of rat prostatic smooth muscle that were unaffected by prazosin (0.5 microM), tetrodotoxin (1 microM) or guanethidine (10 microM). The rank order of potency of the endothelin isopeptides was endothelin-1>endothelin-2> or =endothelin-3. Sarafotoxin S6B was approximately equipotent with endothelin-1 in eliciting tonic contractions, but neither of the selective endothelin ET(B) receptor-agonists, sarafotoxin S6C (0.1 nM-0.3 microM) and BQ3020 (Ac-[Ala (11,15)]endothelin-1(6-21); 0.1 nM-0.3 microM), affected prostatic smooth muscle tone. The selective endothelin ET(A) receptor antagonist, BQ123 (cyclo(D-Asp-L-Pro-D-Val-L-Leu-D-Trp; 1 microM), attenuated responses to endothelin-1, -2 and -3, while the non-selective endothelin receptor antagonist bosentan (1 microM) and the selective endothelin ET(B) receptor antagonist BQ788, (Dmpc-gamma-MeLeu(9)-D-Trp(l-CO(2)CH(3))-D-Nle-OH; 1 microM) attenuated responses to endothelin-3 only. Contractions induced by exogenous administration of noradrenaline were unaffected by preincubation of tissues in BQ123 (1 microM) indicating the selectivity of this antagonist. These data suggest that endothelins mediate contractions of the rat prostate by action at endothelin ET(A) receptors.

Expression of endothelin receptor subtypes and their messenger RNAs in diabetic rat prostate: effect of insulin treatment

Streptozotocin (STZ)-induced diabetes causes an upregulation in the expression of endothelin (ET) receptors in the rat prostate (Eur J Pharmacol 310:197, 1996). We examined the effects of insulin treatment, started 8 weeks after the induction of diabetes, on the expression and distribution of ET receptors and their respective mRNAs in the rat prostate. The densities, pharmacological properties and distribution of ET receptors in the rat prostate were examined using radioligand receptor binding and autoradiographic studies, and gene expression of ET receptors was evaluated utilizing the reverse transcription-polymerase chain reaction (RT-PCR). STZ-injected rats had smaller prostates and reduced serum testosterone levels than control and insulin treated diabetic animals. ET receptor density was shown to be significantly higher in the prostate from diabetic rats than those from either control or insulin treated diabetic animals. The pharmacological profile of prostatic ET receptors was similar in all groups (approximately 80% ET(A); 20% ET(B) subtype). ET receptors were predominantly localized to the prostatic stroma. Induction of diabetes increased the expression of mRNA levels of ET(A) and ET receptors, and insulin treatment reversed this upregulation to control levels. These results indicate that (1) ET receptor subtypes are expressed in the rat prostate as transcription and translation products; (2) insulin can normalize the diabetes-induced upregulation in the expression of ET receptors and their respective mRNAs; and (3) diabetes-induced regression of the prostate may involve an alteration in ET receptors.

Endothelium-derived factors as paracrine mediators of prostate cancer progression

BACKGROUND

Vascular endothelium represents a complex network of cells producing a large number of active substrates affecting physiologic, metabolic, and immunologic properties of the whole organism, as well as particular organs or tissues. The potential influence of endothelium-derived paracrine factors on prostate cancer progression has only begun to be examined.

METHODS

This review summarizes recent literature on endothelium-derived factors, including vasoactive agents, peptide growth factors, cytokines, and colony-stimulating factors, involved in the development and progression of prostate cancer.

RESULTS

Endothelial cells produce an array of active substrates, many of which have been shown to influence prostate cancer growth. Available data demonstrate the positive impact of such molecules as endothelin-1, basic FGF, TGF-beta, IL-6, and IL-8 on prostate cancer progression. Many other endothelium-derived factors NO, IGF, PDGF, IL-1, G-CSF, and GM-CSF (Nitric Oxide, Insulin-Like Growth Factor, Platelet-Derived Growth Factor, Interleukin-1, Granulocyte Colony Stimulating Factor, and Granulocyte-Macrophage Colony Stimulating Factor) are, at best, implicated in prostate cancer growth, and in most cases support cancer progression.

CONCLUSIONS

A better understanding of endothelium-derived factors, as paracrine mediators of prostate carcinogenesis and progression, should aid in the development of novel therapeutic strategies.