Modulation of human colon tumor-stromal interactions by the endothelin system

The Tetraspanin Tspan8 Associates with Endothelin Converting Enzyme ECE1 and Regulates Its Activity

Tspan8 is a member of the tetraspanins family of cell surface molecules. The ability of tetraspanins to organize membrane microdomains with other membrane molecules and interfere with their function suggests that they could act as surface integrators of external or internal signals. Among the first identified tetraspanins, Tspan8 promotes tumor progression and metastasis, presumably by stimulating angiogenesis and cell motility. In patients, its expression on digestive tract tumors seems to be associated with a bad prognosis. We showed previously that Tspan8 associates with E-cadherin and EGFR and modulates their effects on cell motility. Using Mass spectrometry and western blot, we found a new partner, the endothelin converting enzyme ECE1, and showed that Tspan8 amplifies its activity of conversion of the endothelin-1 precursor bigET1 to endothelin. This was observed by transduction of the colon carcinoma cell line Isreco1, which does not express Tspan8, and on ileum tissue fragments of tspan8ko mice versus wild type mice. Given these results, Tspan8 appears to be a modulator of the endothelin axis, which could possibly be targeted in case of over-activity of endothelins in biological processes of tissues expressing Tspan8.

Endothelin-1 axes in the framework of predictive, preventive and personalised (3P) medicine

Endothelin-1 (ET-1) is involved in the regulation of a myriad of processes highly relevant for physical and mental well-being; female and male health; in the modulation of senses, pain, stress reactions and drug sensitivity as well as healing processes, amongst others. Shifted ET-1 homeostasis may influence and predict the development and progression of suboptimal health conditions, metabolic impairments with cascading complications, ageing and related pathologies, cardiovascular diseases, neurodegenerative pathologies, aggressive malignancies, modulating, therefore, individual outcomes of both non-communicable and infectious diseases such as COVID-19. This article provides an in-depth analysis of the involvement of ET-1 and related regulatory pathways in physiological and pathophysiological processes and estimates its capacity as a predictor of ageing and related pathologies,a sensor of lifestyle quality and progression of suboptimal health conditions to diseases for their targeted preventionand as a potent target for cost-effective treatments tailored to the person.

Effect of an Endothelin B Receptor Agonist on the Tumor Accumulation of Nanocarriers

Enhancing blood flow to tumors is a prominent strategy for improving the tumor accumulation of macromolecular drugs through the enhanced permeability and retention (EPR) effect. IRL-1620 is an agonist of the endothelin B receptor, and is a promising molecule to enhance tumor blood flow by activating endothelial nitric oxide synthase. However, contradictory effects on tumor blood flow modulation have been reported because the effects of IRL-1620 may differ in different animal models. Here, we examined for the first time the effect of IRL-1620 on the EPR effect for PEGylated liposomes in a CT-26 murine colon cancer model. Co-injection of IRL-1620 at an optimum dose (3 nmol/kg) nearly doubled the tumor accumulation of liposomes compared with controls, indicating that IRL-1620 enhanced the EPR effect in the present colon cancer model. Co-injection of IRL-1620 is a promising strategy to improve the therapeutic effects of macromolecular drugs while reducing their side effects.

Modulation of the Endothelin System in Colorectal Cancer Liver Metastasis: Influence of Epigenetic Mechanisms?

Targeting of endothelin system genes is a promising strategy in cancer therapy. The modulation of these genes was explored in a model of colorectal cancer (CRC) liver metastasis and in a panel of CRC tumor cell lines that were exposed to the demethylating agent decitabine. The CC531 rat model mimicking CRC liver metastasis was used for tumor cell re-isolation and analysis of the endothelin system genes and DNA methyltransferases (DNMTs) by microarray. To mimic the effects caused by methylation changes, a panel of seven CRC cell lines was treated with the demethylating agent decitabine. Three genes of the endothelin system were potently modulated at messenger RNA (mRNA) level in rat CC531 cells during liver colonization. The concomitant decrease of two DNMTs suggested an influence from altered methylation. Changes in gene expression were also accomplished by exposure of CRC cells to the demethylating agent decitabine, when using daily low concentrations for 3 days, with minimal cytotoxic effects. Sensitive human SW480 cells showed an almost 100fold upregulation of endothelin-1 mRNA compared to untreated cells. This, however, was different in LS174T cells, which showed no significant increase in gene expression although the methylation levels were significantly decreased at a variety of corresponding loci. We suggest that the mechanism induced by methylation on gene expression in metastatic CRC cells can be compromised. The results question the overall success of treating metastatic CRC by methylation inhibitors.

Endothelin Promotes Colorectal Tumorigenesis by Activating YAP/TAZ

Endothelin receptor A (ETAR) promotes tumorigenesis by stimulating cell proliferation, migration, and survival. However, the mechanism of ETAR in promoting tumor growth is largely unknown. In this study, we demonstrate that ETAR stimulates colon cell proliferation, migration, and tumorigenesis through the activation of YAP/TAZ, two transcription coactivators of the Hippo tumor suppressor pathway. Endothelin-1 treatment induced YAP/TAZ dephosphorylation, nuclear accumulation, and transcriptional activation in multiple colon cancer cells. ETAR stimulation acted via downstream G-protein Gαq/11 and Rho GTPase to suppress the Hippo pathway, thus leading to YAP/TAZ activation, which was required for ETAR-induced tumorigenesis. Overall, these results indicate a critical role of the YAP/TAZ axis in ETAR signaling. Cancer Res; 77(9); 2413-23. ©2017 AACR.

Endothelin-Receptor Antagonists beyond Pulmonary Arterial Hypertension: Cancer and Fibrosis

The endothelin axis and in particular the two endothelin receptors, ETA and ETB, are targets for therapeutic intervention in human diseases. Endothelin-receptor antagonists are in clinical use to treat pulmonary arterial hypertension and have been under clinical investigation for the treatment of several other diseases, such as systemic hypertension, cancer, vasospasm, and fibrogenic diseases. In this Perspective, we review the molecules that have been evaluated in human clinical trials for the treatment of pulmonary arterial hypertension, as well as other cardiovascular diseases, cancer, and fibrosis. We will also discuss the therapeutic consequences of receptor selectivity with regard to ETA-selective, ETB-selective, or dual ETA/ETB antagonists. We will also consider which chemical characteristics are relevant to clinical use and the properties of molecules necessary for efficacy in treating diseases against which known molecules displayed suboptimal efficacy.

Melatonin reduces endothelin-1 expression and secretion in colon cancer cells through the inactivation of FoxO-1 and NF-κβ

Melatonin is an indoleamine that is synthesised from tryptophan under the control of the enzymes arylalkylamine N-acetyltransferase (AA-NAT) and acetylserotonin methyltransferase (ASMT). Melatonin inhibits colon cancer growth in both in vivo and in vitro models; however, a precise mechanism responsible for inhibiting tumour growth has not been clearly described. Endothelin-1 (ET-1) is a peptide that acts as a survival factor in colon cancer, inducing cell proliferation, protecting carcinoma cells from apoptosis and promoting angiogenesis. The data presented show that melatonin inhibits edn-1 mRNA expression (the first step in ET-1 synthesis), ECE-1 protein expression and the release of ET-1 from colorectal cancer cells in vitro. ET-1 levels in cultured media present a similar inhibition pattern to that of edn-1 mRNA expression despite the inhibition of ECE-1 protein after melatonin treatment, which suggests that an endopeptidase other than ECE-1 could be mainly responsible for ET-1 synthesis. The inhibition of edn-1 expression is due to an inactivation of FoxO1 and NF-κβ transcription factors. FoxO1 inactivation is associated with an increased Src phosphorylation, due to elevated cAMP content and PKA activity, whereas NF-κβ inactivation is associated with the blockade of Akt and ERK phosphorylation due to the inhibition of PKC activity after melatonin treatment. Melatonin also inhibits edn-1 promoter activity regulated by FoxO1 and NF-κβ. Finally, a significant correlation was observed between AA-NAT and edn-1 expression downregulation in human colorectal cancer tissues. In conclusion, melatonin may be useful in treating colon carcinoma in which the activation of ET-1 plays a role in tumour growth and progression.

A review of the profile of endothelin axis in cancer and its management

The endothelins and their associated receptors are important controllers of vascular growth, inflammation and vascular tone. In cancer, they have roles in the control of numerous factors in cancer development and progression, including angiogenesis, stromal reaction, epithelial mesenchymal transitions, apoptosis, invasion, metastases and drug resistance. Also, we consider current information on the role of this signalling system in cancer and examine the state of the current cell, animal and clinical trials utilizing endothelin targeted drugs for cancer management. Although targeting the endothelin axis in cell lines and xenografts show some promise in retarding cellular growth, results from limited clinical trials in prostatic cancer are less encouraging and did not offer significant survival benefit. The ability to target both cancer cells and vasculature via endothelin is an important consideration that necessitates the further refining of therapeutic strategies as we continue to explore the possibilities of the endothelin axis in cancer treatment.

Endothelin 1 in cancer: biological implications and therapeutic opportunities

Activation of autocrine and paracrine signalling by endothelin 1 (ET1) binding to its receptors elicits pleiotropic effects on tumour cells and on the host microenvironment. This activation modulates cell proliferation, apoptosis, migration, epithelial-to-mesenchymal transition, chemoresistance and neovascularization, thus providing a strong rationale for targeting ET1 receptors in cancer. In this Review, we discuss the advances in our understanding of the diverse biological roles of ET1 in cancer and describe the latest preclinical and clinical progress that has been made using small-molecule antagonists of ET1 receptors that inhibit ET1-driven signalling.

Endothelin-1 enriched tumor phenotype predicts breast cancer recurrence

Introduction. Breast cancer recurrence can develop years after primary treatment. Crosstalk between breast cancer cells and their stromal microenvironment may influence tumor progression. Our primary study aim was to determine whether endothelin-1 (ET-1) expression in tumor and stroma predicts breast cancer relapse. The secondary aim was to determine ET-1/endothelin receptor A (ETAR) role on signaling pathways and apoptosis in breast cancer. Experimental Design. Patients with histologically documented stages I-III invasive breast cancer were included in the study. ET-1 expression by immunohistochemistry (IHC) in tumor cells and stroma was analyzed. Association between ET-1 expression and clinical outcome was assessed using multivariate Cox proportional hazard model. Kaplan-Meier curves were used to estimate disease-free survival (DFS). In addition, the effect of ET-1/ETAR on signaling pathways and apoptosis was evaluated in MCF-7 and MDA-MB-231 breast cancer cells. Results. With a median followup of 7 years, ET-1 non-enriched tumor phenotype had a significant association with favorable disease-free survival (HR = 0.16; 95% CI 0.03-0.77; P value <0.02). ER negativity, advanced stage of disease and ET-1-enriched tumor phenotype were all associated with a higher risk for recurrence. Experimental study demonstrated that ET-1 stimulation promoted Akt activation in MCF-7 and MDA-MB-231 cells. Furthermore, silencing of ETAR induced apoptosis in both hormone receptor negative and hormone receptor positive breast cancer cells. Conclusions. We found ET-1 expression in tumor and stroma to be an independent prognostic marker for breast cancer recurrence. Prospective studies are warranted to examine whether ET-1 expression in tumor/stroma could assist in stratifying patients with hormone receptor positive breast cancer for adjuvant therapy.

Roles of substance P and ATP in the subepithelial fibroblasts of rat intestinal villi

The ingestion of food and water induces chemical and mechanical signals that trigger peristaltic reflexes and also villous movement in the gut. In the intestinal villi, subepithelial fibroblasts under the epithelium form contractile cellular networks and closely contact to the varicosities of substance P and nonsubstance P afferent neurons. Subepithelial fibroblasts of the duodenal villi possess purinergic receptor P2Y1 and tachykinin receptor NK1. ATP and substance P induce increase in intracellular Ca(2+) and cell contraction in subepithelial fibroblasts. They are highly mechanosensitive and release ATP by mechanical stimuli. Released ATP spreads to form an ATP "cloud" with nearly 1μM concentration and activates the surroundings via P2Y1 and afferent neurons via P2X receptors. These findings suggest that villous subepithelial fibroblasts and afferent neurons interact via ATP and substance P. This mutual interaction may play important roles in the signal transduction of mechano reflex pathways including a coordinate villous movement and also in the maturation of the structure and function of the intestinal villi.

Biologics against cancer-specific receptors - challenges to personalised medicine from early trial results

Understanding molecular mechanisms of tumourigenesis underlies new therapeutic strategies that specifically target tumours. This has led to the evolution of personalised therapy that was first used in breast cancer when hormone receptor status was determined. More recently in colorectal cancer treatment the Epidermal Growth Factor receptor and its tumourigenic role has led to its targeting by using Cetuximab and Panitumumab. Addition of these drugs to existing drug regimes (FOLFOX and FOLFIRI) showed improved respectability rates in patients with liver metastasis. Most recently the Endothelin receptor has been implicated in multiple tumourigenic processes. Interest has grown in using Endothelin A receptor antagonists as adjuvant or combination therapy as suggested by the FOLFERA and FOLFIRI trials currently on-going.

Determination of cell-specific receptor binding using a combination of immunohistochemistry and in vitro autoradiography: relevance to therapeutic receptor targeting in cancer

Mapping of receptor binding to specific structures, or cells within tissue samples, provides valuable information regarding biological and pathological mechanisms. Such information may potentially be translated into targeted therapies, especially in the field of cancer treatment. In this chapter, a receptor localization technique is described which utilises frozen sections of human tissue and combines immunohistochemistry (IHC) and micro-autoradiography. IHC utilises antibodies tagged to an enzymatic complex to identify specific cell types (such as epithelial cells or fibroblasts) within the tissue under investigation; this step is immediately followed by the second technique which is based on the use of radiolabelled compounds (radioligands) that selectively bind to preselected membrane receptors. This approach allows visualisation of cells of interest by immunohistochemical staining of tissue sections (colour product) in combination with the use of radiolabelled compounds that are detected following exposure to radiation-sensitive film or emulsion to produce a map of receptor distribution or localisation of cell-specific receptor binding. The system described has been used to compare receptor binding to cells in normal human colorectal tissue with that in colorectal cancer specimens.

Expression patterns of endothelin-1 and its receptors in colorectal cancer

BACKGROUND AND OBJECTIVES

Endothelin-1 (ET-1), a potent vasoconstricting peptide, plays an important role in carcinogenesis. Previous in vitro studies have shown that colorectal cancer cells produce ET-1.

METHODS

ET-1 and its receptors ET-A (ET(A) R) and ET-B (ET(B) R) were analyzed in colorectal cancer cell lines and tumors by Western blot and immunohistochemistry. Also, ET-1 levels were measured by ELISA in blood samples collected before and after tumor resection.

RESULTS

ET-1 was immunohistochemically expressed by tumor cells at a variable level in 39 cases tested. The adjacent normal mucosa was negative for ET-1 expression. Strong ET(A) R expression observed in the deeper infiltrating areas at the periphery of neoplastic tissue correlated significantly with tumor stage. ET(B) R levels were very low or undetectable. Western blot analysis in paired (normal, tumor) fresh-frozen samples of colorectal cancers and in four colon carcinoma cell lines confirmed these findings. In addition, lower levels of ET-1 in the peripheral circulation after the tumor resection were found by ELISA as compared to those observed before surgery.

CONCLUSIONS

ET-1 and ET(A) R, but not ET(B) R, are expressed at a higher level in primary and cultured colon carcinoma cells as compared to normal colon mucosa cells. Further functional studies are needed to explore the role of ET-1/ET(A) R axis in colon carcinogenesis.

Role of the endothelin axis and its antagonists in the treatment of cancer

The endothelins (ET) are a group of proteins that act through G-protein coupled receptors. Endothelin-1 (ET-1) was initially identified as a potent vasoconstrictor and dysregulation of the ET axis contributes to pathological processes responsible for cardiovascular disease states. More recently, the ET axis, in particular ET-1 acting through the endothelin A receptor (ET(A) ), has been implicated in the development of several cancers through activation of pathways involved in cell proliferation, migration, invasion, epithelial-mesenchymal transition, osteogenesis and angiogenesis. The endothelin B receptor (ET(B) ) may counter tumour progression by promoting apoptosis and clearing ET-1; however, it has recently been implicated in the development of some tumour types including melanomas and oligodendrogliomas. Here, we review emerging preclinical and clinical data outlining the role of the ET axis in cancer, and its antagonism as an attractive and challenging approach to improve clinical cancer management. Clinical data of ET(A) antagonists in patients with prostate cancer are encouraging and provide promise for new ET(A) antagonist-based treatment strategies. Given the unexpected opportunities to affect pleiotrophic tumorigenic signals by targeting ET(A)-mediated pathways in a number of cancers, the evaluation of ET-targeted therapy in cancer warrants further investigation.

Macitentan (ACT-064992), a tissue-targeting endothelin receptor antagonist, enhances therapeutic efficacy of paclitaxel by modulating survival pathways in orthotopic models of metastatic human ovarian cancer

Potential treatments for ovarian cancers that have become resistant to standard chemotherapies include modulators of tumor cell survival, such as endothelin receptor (ETR) antagonist. We investigated the therapeutic efficacy of the dual ETR antagonist, macitentan, on human ovarian cancer cells, SKOV3ip1 and IGROV1, growing orthotopically in nude mice. Mice with established disease were treated with vehicle (control), paclitaxel (weekly, intraperitoneal injections), macitentan (daily oral administrations), or a combination of paclitaxel and macitentan. Treatment with paclitaxel decreased tumor weight and volume of ascites. Combination therapy with macitentan and paclitaxel reduced tumor incidence and further reduced tumor weight and volume of ascites when compared with paclitaxel alone. Macitentan alone occasionally reduced tumor weight but alone had no effect on tumor incidence or ascites. Immunohistochemical analyses revealed that treatment with macitentan and macitentan plus paclitaxel inhibited the phosphorylation of ETRs and suppressed the survival pathways of tumor cells by decreasing the levels of pVEGFR2, pAkt, and pMAPK. The dose of macitentan necessary for inhibition of phosphorylation correlated with the dose required to increase antitumor efficacy of paclitaxel. Treatment with macitentan enhanced the cytotoxicity mediated by paclitaxel as measured by the degree of apoptosis in tumor cells and tumor-associated endothelial cells. Collectively, these results show that administration of macitentan in combination with paclitaxel prevents the progression of ovarian cancer in the peritoneal cavity of nude mice in part by inhibiting survival pathways of both tumor cells and tumor-associated endothelial cells.

The prognostic value of circulating big endothelin-1 in patients undergoing potentially curative resection for colorectal cancer

AIM

Elevated circulating endothelin-1 (ET-1) has been demonstrated in patients with colorectal cancer (CRC). The aim of this study was to examine the prognostic value of plasma big ET-1, the stable precursor of ET-1, in cancer-specific survival in patients having curative surgery for CRC.

METHOD

Seventy-seven patients undergoing potentially curative surgery for CRC between January 2000 and January 2001 were studied. Clinicopathological data were obtained from a prospectively maintained database including long-term follow-up information (median follow up 84 months). The influence of plasma big ET-1 and clinicopathological variables upon over cancer-specific survival was determined by univariate and multivariable analysis.

RESULTS

On univariate analysis, advanced Dukes' stage, tumour size and patient age were associated with shortened overall survival. Advanced Dukes' stage was the only factor associated with shortened survival on multivariable analysis. Plasma big ET-1 showed no association with either overall or cancer-specific survival following CRC resection.

CONCLUSION

Plasma big ET-1 appears to have no prognostic value in primary CRC.

Endothelin--biology and disease

Endothelins are important mediators of physiological and pathophysiologic processes including cardiovascular disorders, pulmonary disease, renal diseases and many others. Additionally, endothelins are involved in many other important processes such as development, cancer biology, wound healing, and even neurotransmission. Here, we review the cell and molecular biology as well as the prominent pathophysiological aspects of the endothelin system.

Therapeutic potential of endothelin receptor modulators: lessons from human clinical trials

The endothelin system, and in particular endothelin receptors, are targets for therapeutic intervention in human diseases. Endothelin receptor antagonists have reached clinical use for treating pulmonary arterial hypertension, and are under clinical investigation for several other diseases, such as cancer, vasospasm or fibrogenic diseases. We review the molecules that have been evaluated in the main clinical trials, from the point of view of receptor selectivity and of their chemical characteristics which were important for efficacy in pulmonary hypertension. We will also discuss future use of antagonists to endothelin receptor(s) in several human diseases and what should be the necessary properties of the future molecules for efficacy in diseases where the presently tested molecules displayed suboptimal efficacy.

Stromal endothelin B receptor-deficiency inhibits breast cancer growth and metastasis

The endothelin (ET) axis, often deregulated in cancers, is a promising target for anticancer strategies. Whereas previous investigations have focused mostly on ET action in malignant cells, we chose a model allowing separate assessment of the effects of ETs and their receptors ET(A)R and ET(B)R in the tumor cells and the stromal compartment, which is increasingly recognized as a key player in cancer progression. In homozygous spotting lethal rats (sl/sl), a model of constitutive ET(B)R deficiency, we showed significant reduction of growth and metastasis of MAT B III rat mammary adenocarcinoma cells overexpressing ET(A)R and ET-1 but negative for ET(B)R. Lack of stromal ET(B)R expression did not influence angiogenesis. However, it was correlated with diminished infiltration by tumor-associated macrophages and with reduced production of tumor necrosis factor-alpha, both known as powerful promoters of tumor progression. These effects were almost completely abolished in transgenic sl/sl rats, wherein ET(B)R function is restored by expression of an intact ET(B)R transgene. This shows that tumor growth and metastasis are critically dependent on ET(B)R function in cells of the microenvironment and suggests that successful ETR antagonist therapy should also target the stromal component of ET signaling

Endothelin receptor antagonism and cancer

The endothelin peptides have an important role in the cancer-stromal interactions that promote tumour growth. Endothelin-1 (ET-1), clinically the most investigated endothelin, is a vital agent in the growth and progression of several tumours including prostate, ovarian, colorectal, bladder, breast and lung carcinomas. ET-1 exerts its effects through the activation of two distinct receptors, ET(A) and ET(B). Once activated, these receptors transmit signals via numerous intracellular signalling pathways. The effects of ET receptor stimulation in cancer cells or cancer-associated cells include proliferation, resistance to apoptosis, angiogenesis, migration and subsequent invasion. At present, the manipulation of the endothelin axis within the pre-clinical setting is the subject of intense investigation. Recent studies into ET receptor antagonism have produced interesting results highlighting the fact that these receptors may provide novel targets for a new generation of chemotherapeutic agents in a variety of cancers.

Endothelin-3 stimulates survival of goblet cells in organotypic cultures of fetal human colonic epithelium

Cells within the normal human colonic epithelium undergo a dynamic cycle of growth, differentiation, and death. The organotypic culture system of human fetal colonic epithelial cells seeded on top of collagen gels with embedded colonic fibroblasts allowed prolonged culture of the colonic epithelial cells (Kalabis J, Patterson MJ, Enders GM, Marian B, Iozzo RV, Rogler G, Gimotty PA, Herlyn M. FASEB J 17: 1115-1117, 2003). Herein, we have evaluated the role of endothelin-3 (ET3) and both cognate endothelin receptors (ETRA, ETRB) for human colonic epithelial cell growth and survival. ET3 was produced continuously by the fibroblasts as a result of adenovirus-mediated gene transfer. The presence and function of the endothelin receptors (ETRs) in epithelial cells was evaluated by [(3)H]thymidine incorporation using primary epithelial cells in monoculture and by immunohistochemistry on human fetal and adult paraffin-embedded tissues. In organotypic culture, ET3 increased the number of goblet cells but not of enteroendocrine cells. The increase in goblet cells was caused by prolonged cell survival and differentiation. The inhibition of both ETRA and ETRB significantly decreased the number of goblet cells and proliferation in epithelial cells, whereas the number of enteroendocrine cells remained unchanged. ET3 induced activation of IkappaB and MAPK in the epithelial cells, suggesting that these signaling pathways mediate its proproliferation and prosurvival activities. Our results demonstrate that ET3 is involved in regulating human colonic epithelial cell proliferation and survival, particularly for goblet cells, and may be an important component of colonic homeostasis.

The endothelin axis in cancer: the promise and the challenges of molecularly targeted therapy

The endothelin (ET) axis, which includes ET-1, ET-2, ET-3, and 2 G protein-coupled receptor subtypes, ET AR and ET BR, promotes growth and progression of a variety of tumors, such as prostatic, ovarian, renal, pulmonary, colorectal, cervical, breast, lung, bladder, endometrial carcinoma, Kaposi's sarcoma, brain tumors, and melanoma. Acting on selective receptors, ET-1 regulates mitogenesis, cell survival, angiogenesis, bone remodeling, stimulation of nociceptors, tumor-infiltrating immune cells, epithelial-to-mesenchymal transition, invasion, and metastatic dissemination. At the molecular level, endothelin receptor antagonists, besides providing ideal tools for dissecting the ET axis, have demonstrated their potential in developing novel therapeutic strategies. Emerging experimental and clinical data demonstrate that interfering with endothelin receptors provides an opportunity for the development of rational combinatorial approaches using endothelin receptor antagonists in combination with chemotherapy or molecularly targeted therapy.

Isoforms of endothelin-converting enzyme-1 (ECE-1) have opposing effects on prostate cancer cell invasion

Cross-talk between tumour and stromal cells can profoundly influence cancer cell invasion by increasing the availability of mitogenic peptides such as endothelin-1 (ET-1). Endothelin-1 is elevated in men with metastatic prostate cancer (PC), and can exert both an autocrine (epithelial) and a paracrine (stromal) influence on growth. Endothelin-1 is generated from its inactive precursor big-ET-1 by endothelin-converting enzyme 1 (ECE-1). We and others have demonstrated that ECE-1 expression is significantly elevated in tumours and surrounding stromal tissue. Our current data show siRNA-mediated knockdown of stromal ECE-1 reduces epithelial (PC-3) cell invasion in coculture. Interestingly, readdition of ET-1 only partially recovers this effect suggesting a novel role for ECE-1 independent of ET-1 activation. Parallel knockdown of ECE-1 in both stromal and epithelial compartments results in an additive decrease in cell invasion. We extrapolated this observation to the four recognised isoforms ECE-1a, ECE-1b, ECE-1c and ECE-1d. Only ECE-1a and ECE-1c were significant but with reciprocal effects on cell invasion. Transient ECE-1c overexpression increased PC-3 invasiveness through matrigel, whereas transient ECE-1a expression suppressed invasion. Furthermore, transient ECE-1a expression in stromal cells strongly counteracts the effect of transient ECE-1c expression in PC-3 cells. The ECE-1 isoforms may, therefore, be relevant targets for antiinvasive therapy in prostate and other cancers.

Transcription analysis in the MeLiM swine model identifies RACK1 as a potential marker of malignancy for human melanocytic proliferation

BACKGROUND

Metastatic melanoma is a severe disease. Few experimental animal models of metastatic melanoma exist. MeLiM minipigs exhibit spontaneous melanoma. Cutaneous and metastatic lesions are histologically similar to human's. However, most of them eventually spontaneously regress. Our purpose was to investigate whether the MeLiM model could reveal markers of malignancy in human melanocytic proliferations.

RESULTS

We compared the serial analysis of gene expression (SAGE) between normal pig skin melanocytes and melanoma cells from an early pulmonary metastasis of MeLiM minipigs. Tag identification revealed 55 regulated genes, including GNB2L1 which was found upregulated in the melanoma library. In situ hybridisation confirmed GNB2L1 overexpression in MeLiM melanocytic lesions. GNB2L1 encodes the adaptor protein RACK1, recently shown to influence melanoma cell lines tumorigenicity. We studied the expression of RACK1 by immunofluorescence and confocal microscopy in tissues specimens of normal skin, in cutaneous and metastatic melanoma developped in MeLiM minipigs and in human patients. In pig and human samples, the results were similar. RACK1 protein was not detected in normal epidermal melanocytes. By contrast, RACK1 signal was highly increased in the cytoplasm of all melanocytic cells of superficial spreading melanoma, recurrent dermal lesions and metastatic melanoma. RACK1 partially colocalised with activated PKCalphabeta. In pig metastases, additional nuclear RACK1 did not associate to BDNF expression. In human nevi, the RACK1 signal was low.

CONCLUSION

RACK1 overexpression detected in situ in human melanoma specimens characterized cutaneous and metastatic melanoma raising the possibility that RACK1 can be a potential marker of malignancy in human melanoma. The MeLiM strain provides a relevant model for exploring mechanisms of melanocytic malignant transformation in humans. This study may contribute to a better understanding of melanoma pathophysiology and to progress in diagnosis.

Altered endothelin receptor subtypes in colorectal cancer

BACKGROUND

The vasoactive peptide endothelin-1 (ET-1) acts via two endothelin receptor subtypes, ETA (ETAR) and ETB (ETBR). ET-1 and ETAR are overexpressed in colorectal cancer tissues. In vitro, ET-1 acting via ETAR, is a mitogen for colorectal cancer cells. To identify other potential stimulatory loops, we investigated the distribution and cell-specific localization of both ETAR and ETBR in tissue sections from patients with colorectal cancer.

METHODS

Frozen sections from specimens of colorectal cancer (n=9) and normal colon (n=9) were cut and subjected to either (i) autoradiography or (ii) a combination of cell type-specific immunohistochemistry, using antibodies against fibroblasts (AS02), endothelial cells (CD31) or nerve fibres (NF200) and in-vitro receptor microautoradiography, using ETAR-specific and ETBR-specific radioligands.

RESULTS

ETARs were upregulated in all cell types, apart from nerve, in cancer compared with normal colon (1:1.59 normal to cancer). Specifically, ETAR binding was highest in cancer-associated blood vessels and fibroblasts and to a lesser extent in epithelial cancer cells. In contrast, ETBRs were the predominant receptors in normal colon (1:0.59 normal to cancer) and were markedly down-regulated in cancer-associated blood vessels, fibroblasts and to a lesser extent in epithelial cells. Nerve colocalization was demonstrated, but remained unchanged for all tissues.

CONCLUSION

The shift in ET receptor binding observed in epithelial cancer cells and cancer-associated fibroblasts and endothelial cells may favour ET-1 signals contributing to colorectal cancer growth and neovascularization via ETAR. This may provide the basis for therapeutic use of specific ETAR antagonists as adjuvant treatment of colorectal cancer.

ZD4054, a specific antagonist of the endothelin A receptor, inhibits tumor growth and enhances paclitaxel activity in human ovarian carcinoma in vitro and in vivo

The autocrine endothelin (ET)-1/endothelin A receptor (ET(A)R) pathway is an important regulator of several processes involved in ovarian cancer progression, and its overexpression is associated with aggressive disease. These features have led to the proposal of the ET(A)R receptor as a potential target for improving ovarian cancer treatment. In this study, we evaluated in vitro and in vivo the effects of ZD4054, an orally active antagonist that specifically binds ET(A)R, as monotherapy, and in combination with paclitaxel. In the human ovarian cancer ET(A)R-positive cell lines HEY, OVCA 433, SKOV-3, and A-2780, ZD4054 effectively inhibited the basal and ET-1-induced cell proliferation, associated with the inhibition of AKT and p42/44MAPK phosphorylation, and with increased apoptosis, through the inhibition of bcl-2 and activation of caspase-3 and poly(ADP-ribose) polymerase proteins. ZD4054 treatment also resulted in a reduction of ET(A)R-driven angiogenesis and invasive mediators, such as vascular endothelial growth factor, cyclooxygenase-1/2, and matrix metalloproteinase (MMP). The combination of ZD4054 and paclitaxel led to the potentiation of all these effects, indicating that ZD4054, by blocking the ET(A)R-dependent proliferative, invasive, and antiapoptotic signals, can enhance sensitivity to paclitaxel. In HEY ovarian cancer xenografts, ZD4054 significantly inhibited tumor growth to the same degree as paclitaxel. Furthermore, ZD4054-dependent tumor growth inhibition was associated with a reduction in proliferation index, microvessel density, and MMP-2 expression. Interestingly, the combination of ZD4054 and paclitaxel produced additive antitumor effects, with 40% of mice remaining tumor-free, supporting a rationale for the clinical use of ZD4054 as monotherapy or in combination with cytotoxic drugs.

Nonclassic Endogenous Novel Regulators of Angiogenesis

Angiogenesis, the process through which new blood vessels arise from preexisting ones, is regulated by several "classic" factors, among which the most studied are vascular endothelial growth factor (VEGF) and fibroblast growth factor-2 (FGF-2). In recent years, investigations showed that, in addition to the classic factors, numerous endogenous peptides play a relevant regulatory role in angiogenesis. Such regulatory peptides, each of which exerts well-known specific biological activities, are present, along with their receptors, in the blood vessels and may take part in the control of the "angiogenic switch." An in vivo and in vitro proangiogenic effect has been demonstrated for erythropoietin, angiotensin II (ANG-II), endothelins (ETs), adrenomedullin (AM), proadrenomedullin N-terminal 20 peptide (PAMP), urotensin-II, leptin, adiponectin, resistin, neuropeptide-Y, vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP), and substance P. There is evidence that the angiogenic action of some of these peptides is at least partly mediated by their stimulating effect on VEGF (ANG-II, ETs, PAMP, resistin, VIP and PACAP) and/or FGF-2 systems (PAMP and leptin). AM raises the expression of VEGF in endothelial cells, but VEGF blockade does not affect the proangiogenic action of AM. Other endogenous peptides have been reported to exert an in vivo and in vitro antiangiogenic action. These include somatostatin and natriuretic peptides, which suppress the VEGF system, and ghrelin, that antagonizes FGF-2 effects. Investigations on "nonclassic" regulators of angiogenesis could open new perspectives in the therapy of diseases coupled to dysregulation of angiogenesis.

Endothelin-3 growth factor levels decreased in cervical cancer compared with normal cervical epithelial cells

We used cDNA microarray analysis of RNA extracted from normal, dysplastic, and cancerous cervical tissues to identify the changes in gene expression during the procession from normal to cancerous cervical epithelial cells. We found the expression of 5 genes in cancerous cervical epithelial cells that were not found in normal cervical epithelial cells, among which were lymphoid-restricted membrane protein, protease serine 2, WD repeat domain 59, thyrotropin-releasing hormone degrading enzyme, and the endothelin-3 growth factor. We then analyzed the expression levels of endothelin growth factors 1, 2, and 3 (ET-1, ET-2, and ET-3) and their receptors A and B (ETR-A and ETR-B) by reverse transcriptase-polymerase chain reaction in 3 cervical cancer cell lines and by immunohistochemical staining in cervical normal, dysplastic, and cancer tissues. ET-1, ET-2, and ET-3 growth factor levels were detectable in the maturing layer of cervical epithelium but not in the germinal layer. All 3 growth factors (ET-1, ET-2, and ET-3) were detected in the cytoplasm of the maturing normal cervical epithelial cells. In addition, there were decreased levels of ET-3 and increased levels of ET-1, ET-2, ETR-A, and ETR-B in cancerous cervical epithelial cells compared with normal cervical epithelial cells. These results suggest that the reduction of ET-3 growth factor levels may be important in the transition from normal to cancerous cervical epithelium.

Intestinal microcirculatory dysfunction during the development of experimental necrotizing enterocolitis

The aim of this study was to evaluate changes in intestinal microcirculation during necrotizing enterocolitis (NEC) and to examine the effect of endothelin (ET)-1 on the intestinal microcirculation. Prematurely born rats were either hand-fed formula (NEC) or dam fed (DF) and were exposed to asphyxia and cold stress twice daily to induce disease. At 0, 2, 3, and 4 d after the birth, the microcirculation in the ileum was examined using in vivo microscopic methods. The nutritive microvascular perfusion in the NEC group was progressively compromised from d 3 to d 4 (35% and 50% decrease, respectively) when compared with DF rats. Concomitantly, intestinal blood flow assessed by laser Doppler flowmetry was significantly reduced at d 2, 3, and 4 (by 31%, 36%, and 73%, respectively). Levels of ET-1 mRNA in the ileum were increased 3.7-fold. Microvascular responses to topically applied ET-1 were significantly increased in the NEC group, which was associated with decreased expression of ETB receptor. These results suggest that microcirculatory dysfunction in the distal ileum of neonatal rats with NEC contributes to disease progression and that enhanced microvascular responsiveness to ET-1 may participate in these microcirculatory disturbances.

Subepithelial fibroblasts in intestinal villi: roles in intercellular communication

Ingestion of food and water induces chemical and mechanical signals that trigger peristaltic reflexes in the gut. Intestinal villi are motile, equipped with chemosensors and mechanosensors, and transduce signaling to sensory neurons, but the exact mechanisms have not yet been elucidated. Subepithelial fibroblasts located under the villous epithelium form contractile cellular networks via gap junctions. The networks ensheathe lamina propria and are in close contact with epithelium, neural and capillary networks, smooth muscles, and immune cells. Unique characteristics of subepithelial fibroblasts have been revealed by primary cultures isolated from rat duodenal villi. They include rapid reversal changes in cell shape by cAMP reagents and endothelins, cell shape-dependent mechanosensitivity that induces ATP release as a paracrine mediator, contractile ability, and expression of various receptors for vasoactive and neuroactive substances. Herein, we review these characteristics that play a key role in the villi. They serve as a barrier/sieve, flexible mechanical frame, mechanosensor, and signal transduction machinery in the intestinal villi, which are regulated locally and dynamically by rapid cell shape conversion.

Mechanisms of endothelin 1-stimulated proliferation in colorectal cancer cell lines

Background

The peptide endothelin (ET) 1 promotes proliferation in a number of epithelial cancers. The aim of this study was to identify the mechanism of ET-1-stimulated proliferation in colorectal cancer cells in vitro.

Methods

The effects of ET-1 on colorectal cancer cell lines HT29, LIM1215 and SW620 were studied. Cells were cultured with ET-1 plus antagonists/inhibitors to ETA or ETB receptors, G protein subtypes, phosphoinositide 3-kinase (PI3K) or protein kinase C (PKC). DNA replication and apoptosis were investigated by 5-bromo-2′-deoxyuridine incorporation and Annexin V staining. Transactivation of the epidermal growth factor (EGF) receptor was investigated by blockade of the receptor in the presence of ET-1, measurement of levels of phosphorylated EGF receptor in the presence of ET-1, and comparing the effects of ET-1 and EGF on cell proliferation.

Results

ET-1 significantly stimulated growth of all cell lines via ETA receptors. ET-1 stimulated DNA replication, not apoptosis. ET-1-stimulated growth was inhibited by antagonism of pertussis toxin-sensitive G proteins, PI3K and PKC. Inhibition of the EGF receptor reduced the effect of ET-1. ET-1 increased levels of phosphorylated EGF receptor via the ETA receptor.

Conclusion

ET-1 increased DNA replication in colorectal cancer cells via the ETA receptor. This mitogenic action was mediated via pertussis toxin-sensitive G proteins, PI3K, PKC and transactivation of the EGF receptor.

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.

Endothelin receptor antagonists: rationale, clinical development, and role in prostate cancer therapeutics

The endothelins (ETs), which include ET-1, ET-2, ET-3, and their receptors ET-A and ET-B, play a major role in tumor growth, proliferation, apoptosis, angiogenesis, and bone metastasis. Atrasentan is a novel and selective inhibitor of ET-1 and ET-A. In vitro and in vivo data show that this oral agent is capable of inhibiting tumor cells in vitro. More recently, this agent was studied in several phase I trials with refractory carcinoma patients. Subsequently, phase II and III clinical trials evaluating atrasentan in patients with hormone-refractory prostate carcinoma have suggested that targeting this pathway may be a new therapeutic strategy in the treatment of solid malignancies, specifically, prostate cancer.

Endothelin-3 controls growth of colonic epithelial cells by mediating epithelial-mesenchymal interaction

It has been repeatedly reported that endothelin-3 (ET-3) is expressed by gastrointestinal mesenchymes, and that paracrine signaling between ET-3 and its receptor plays an essential role in controlling differentiation of the enteric nervous system in the gut, especially in the colon. However it remains to be solved whether ET-3 plays a role in regulating the growth of gastrointestinal epithelial cells. We have previously reported culture systems for forestomach, glandular stomach and duodenal epithelial cells, but a system for colonic epithelial cells has not been established. In the present study, we examined optimal culture conditions for colonic epithelial cells, and examined whether ET-3 affects the growth of gastrointestinal epithelial cells, with special reference to colonic cells. We found that ET-3 dose-dependently and region-specifically stimulated their growth in primary culture: colonic epithelial cells were most responsive, followed by duodenal and glandular stomach epithelial cells. Reverse transcription-polymerase chain reaction analysis showed that ET-3 and a receptor for ET-3 were expressed by both colonic mesenchymes and epithelia, but the levels were much higher in mesenchymes than in epithelia. These results suggest that ET-3 plays an important role in the growth control of colonic epithelial cells, possibly by mediating epithelial-mesenchymal interactions.

Anti-Progressive Effect of Neutral Endopeptidase 24.11 (NEP/CD10) on Cervical Carcinoma in vitro and in vivo

OBJECTIVES

Neutral endopeptidase 24.11 (NEP) is known to play important roles in the maintenance of homeostasis or in neoplastic transformation and tumor progression in certain human malignancies through the enzymatic inactivation of bioactive peptides such as endothelin-1 (ET-1), angiotensin-II, and bombesin.

METHODS

In this study, we first investigated NEP expression in cervical carcinoma by immunohistochemical staining and Western blot analysis. Next, we examined NEP functions in vitro and in vivo by generating NEP-overexpressing cervical carcinoma cells.

RESULTS

We found a significant decrease in cellular proliferative and invasive abilities with a reduced ET-1 concentration in the conditioned medium by NEP overexpression in cervical carcinoma CaSki cells, which have an ET-1 autocrine loop. In addition, these potentials were cancelled by blockade of NEP activity with a specific inhibitor. Although vector-transfected CaSki cells could grow even in serum-free media, NEP-overexpressing cells failed to proliferate in these media. Furthermore, we demonstrated that NEP suppressed tumor formation of subcutaneous xenografts using nude mice.

CONCLUSIONS

Our results indicated that NEP functions as a tumor-suppressor gene in cervical carcinoma cells, and its expression may have prognostic significance. Further elucidation of the mechanism underlying the observed effect of NEP will contribute to a better understanding of its role in the pathophysiology of cervical carcinoma.

beta-Catenin activates the growth factor endothelin-1 in colon cancer cells

Endothelin-1 (EDN1) is a growth factor that is frequently produced by cancer cells and plays a critical role in tumorigenesis. However, the molecular mechanism controlling the expression of EDN1 in cancers is unknown. Constitutive activation of beta-catenin pathway is responsible for the initiation of the vast majority of colon cancers. Here we show that the EDN1 gene is directly regulated by beta-catenin in colon cancer cells. A specific DNA element within the EDN1 promoter is required for activation, and is associated with beta-catenin's cognate DNA binding partner, TCF4, in vivo. Inhibition of beta-catenin signaling results in lowered expression of EDN1, while enhancement of beta-catenin signaling leads to further activation of the gene. Significantly elevated EDN1 expression occurs in 80% of primary human colon cancers, consistent with it being a direct target of beta-catenin. Furthermore, EDN1 is able to rescue colon cancer cells from growth arrest and apoptosis resulting from inhibition of beta-catenin signaling, implicating a key role of EDN1 in promoting the oncogenic function of beta-catenin. These results indicate EDN1 overexpression as a major cause in colon cancers and reveal further details of the genetic programs responsible for tumorigenesis of colon cancers.

The expression and function of the endothelin system in contractile properties of vaginal myofibroblasts of women with uterovaginal prolapse

OBJECTIVE

The endothelin-1 system regulates (myo)fibroblast contraction in wound healing. Our aim was to determine endothelin-1 system expression and function in contractile properties of vaginal myofibroblasts of women with uterovaginal prolapse.

STUDY DESIGN

Cultures of alpha-smooth muscle actin-positive myofibroblasts that were established at the time of repair surgery for prolapse (n = 30; mean age, 56 +/- 14 years) were analyzed and compared for their expression of the endothelin-1 system and contractile properties to myofibroblasts from primiparous women.

RESULTS

Myofibroblasts expressed the complete endothelin system but did not secrete endothelin-1. Endothelin-1 binding was mediated exclusively by the endothelin B-receptor. In 3-dimensional collagen gels, spontaneous contraction of myofibroblasts from estrogen-treated women with prolapse was statistically significantly lower than from young primiparous women. Exogenous addition of endothelin-1 decreased the spontaneous contraction of myofibroblasts.

CONCLUSION

Genital myofibroblasts of women with uterovaginal prolapse are poorly contractile, and endothelin-1 further decreases vaginal myofibroblast contraction, which is opposite to observations in skin myofibroblasts.

Inhibition of cyclooxygenase-1 and -2 expression by targeting the endothelin a receptor in human ovarian carcinoma cells

PURPOSE AND EXPERIMENTAL DESIGN

New therapies against cancer are based on targeting cyclooxygenase (COX)-2. Activation of the endothelin A receptor (ET(A)R) by endothelin (ET)-1 is biologically relevant in several malignancies, including ovarian carcinoma. In this tumor, the ET-1/ET(A)R autocrine pathway promotes mitogenesis, apoptosis protection, invasion, and neoangiogenesis. Because COX-1 and COX-2 are involved in ovarian carcinoma progression, we investigated whether ET-1 induced COX-1 and COX-2 expression through the ET(A)R at the mRNA and protein level in HEY and OVCA 433 ovarian carcinoma cell lines by Northern blot, reverse transcription-PCR, Western blot, and immunohistochemistry; we also investigated the activity of the COX-2 promoter by luciferase assay and the release of prostaglandin (PG) E(2) by ELISA.

RESULTS

ET-1 significantly increases the expression of COX-1 and COX-2, COX-2 promoter activity, and PGE(2) production. These effects depend on ET(A)R activation and involve multiple mitogen-activated protein kinase (MAPK) signaling pathways, including p42/44 MAPK, p38 MAPK, and transactivation of the epidermal growth factor receptor. COX-2 inhibitors and, in part, COX-1 inhibitor blocked ET-1-induced PGE(2) and vascular endothelial growth factor release, indicating that both enzymes participate in PGE(2) production to a different extent. Moreover, inhibition of human ovarian tumor growth in nude mice after treatment with the potent ET(A)R-selective antagonist ABT-627 is associated with reduced COX-2 and vascular endothelial growth factor expression.

CONCLUSIONS

These results indicate that impairing COX-1 and COX-2 and their downstream effect by targeting ET(A)R can be therapeutically advantageous in ovarian carcinoma treatment. Pharmacological blockade of the ET(A)R is an attractive strategy to control COX-2 induction, which has been associated with ovarian carcinoma progression and chemoresistance.

Endothelin-Converting Enzyme-1 Inhibition and Growth of Human Glioblastoma Cells

Endothelin-1 (ET-1) is mitogenic and/or antiapoptotic in human cancers, and antagonists to ET-1 receptors are under evaluation for cancer treatment. Inhibition of ET-1 activation by the endothelin-converting enzymes 1(a)(-)(d) (ECE-1(a)(-)(d); EC 3.4.24.71) represents another approach to block the ET-1 effect in cancer. To evaluate this potential, we synthesized and characterized a series of low nanomolar nonpeptidic thiol-containing ECE-1 inhibitors, and evaluated their effect, as well as the effect of inhibitors for the related metalloproteases neprilysin (NEP; EC 3.4.24.11) and angiotensin-converting enzyme (ACE; EC 3.4.15.1), on human glioblastoma cell growth. Only ECE-1 inhibitors inhibited DNA synthesis by human glioblastoma cells. Exogenous addition of ET-1 or bigET-1 to glioblastoma cells did not counterbalance the growth inhibition elicited by ECE-1 inhibitors, suggesting that ECE-1 inhibitors block the proliferation of human glioblastoma cells most likely via a mechanism not involving extracellular production of ET-1. This class of molecules may thus represent novel therapeutic agents for the potential treatment of human cancer.

Endothelin receptors as novel targets in tumor therapy

The endotelin (ET) axis, that includes ET-1, ET-2, ET-3, and the ET receptors, ET_A and ET_B, plays an important physiological role, as modulator of vasomotor tone, tissue differentiation and development, cell proliferation, and hormone production. Recently, investigations into the role of the ET axis in mitogenesis, apoptosis inhibition, invasiveness, angiogenesis and bone remodeling have provided evidence of the importance of the ET-1 axis in cancer. Data suggest that ET-1 participates in the growth and progression of a variety of tumors such as prostatic, ovarian, renal, pulmonary, colorectal, cervical, breast carcinoma, Kaposi's sarcoma, brain tumors, melanoma, and bone metastases. ET-1 receptor antagonists beside providing ideal tools for dissecting the ET axis at molecular level have demonstrated their potential in developing novel therapeutic opportunity. The major relevance of ET_A receptor in tumor development has led to an extensive search of highly selective antagonists. Atrasentan, one of such antagonists, is orally bioavailable, has suitable pharmacokinetic and toxicity profiles for clinical use. Preliminary data from clinical trials investigating atrasentan in patients with prostate cancer are encouraging. This large body of evidence demonstrates the antitumor activity of endothelin receptor antagonists and provides a rationale for the clinical evaluation of these molecules alone and in combination with cytotoxic drugs or molecular inhibitors leading to a new generation of anticancer therapies targeting endothelin receptors.

À quoi sert le système endothéline ?

Endothelins are a family of three peptides of 21 amino acids with strong vasoconstrictor effects. The three peptides are encoded by three different genes and derived from precursors (" big endothelins") which are cleaved by metalloproteases, named endothelin-converting enzyme. Two receptors have been cloned, ET-A and ET-B which bind the three endothelins with various affinities. The diverse expression pattern of the endothelin system (ET) components is associated with a complex pharmacology and its counteracting physiological actions. New modulators of the ET system have been described : retinoic acid, leptin, prostaglandins, hypoxia. Endothelins can be considered as regulators working in paracrine and autocrine fashion in a variety of organs in different cellular types. The ET system has beneficial and detrimental roles in mammals. The different components have been shown to be essential for a normal embryonic and neonatal development, for renal homeostasis and maintenance of basal vascular tone. They are involved in physiological and tumoral angiogenesis. They affect the physiology and pathophysiology of the liver, muscle, skin, adipose tissue and reproductive tract. The endothelin system participates in the development of atherosclerosis as well as pulmonary hypertension, and mediates cardiac remodeling in heart failure. Elaboration of new animal models (knock-out, pathophysiological models em leader ) will allow the clear genetic dissection of physiological and pathophysiological roles of the endothelin system.

Structure, evolutionary conservation, and functions of angiotensin- and endothelin-converting enzymes

Angiotensin-converting enzyme, a member of the M2 metalloprotease family, and endothelin-converting enzyme, a member of the M13 family, are key components in the regulation of blood pressure and electrolyte balance in mammals. From this point of view, they serve as important drug targets. Recently, the involvement of these enzymes in the development of Alzheimer's disease was discovered. The existence of homologs of these enzymes in invertebrates indicates that these enzyme systems are highly conserved during evolution. Most invertebrates lack a closed circulatory system, which excludes the need for blood pressure regulators. Therefore, these organisms represent excellent targets for gaining new insights and revealing additional physiological roles of these important enzymes. This chapter reviews the structural and functional aspects of ACE and ECE and will particularly focus on these enzyme homologues in invertebrates.

Immunohistochemical Localization of Endothelin-Converting Enzyme-1 in Neuroendocrine Tumors and Normal Human Tissue

Endothelin-converting enzyme-1 (ECE-1) is the key enzyme of endothelin biosynthesis, catalyzing the final step in the process. In this study, we investigated the cellular distribution of ECE-1 in 19 normal human tissues and 16 neuroendocrine tumors using immunohistochemical staining with antigen retrieval. ECE-1 was expressed in vessel endothelial cells as well as nearly all epithelial cells, glands and duct cells in normal human tissues including the esophagus, stomach, small intestine, appendix, colon, liver, gallbladder, pancreas, endometrium, cervix, breast, skin, prostate, urinary bladder, lung, kidney, sympathetic ganglion, thyroid gland, and adrenal gland. The most interesting finding was that ECE-1 was expressed in normal neuroendocrine cells. ECE-1 was also expressed in all 16 neuroendocrine tumors, including three paragangliomas, five pheochromocytomas, three carcinoid tumors, four medullary carcinomas of the thyroid, and one islet cell tumor of the pancreas. In conclusion, ECE-1 is enriched in neuroendocrine cells and neuroendocrine tumors, suggesting an important biologic role for the enzyme in the neuroendocrine system.

Endothelin-1 decreases gap junctional intercellular communication by inducing phosphorylation of connexin 43 in human ovarian carcinoma cells

Endothelin-1 (ET-1) is overexpressed in ovarian carcinoma and acts as an autocrine factor selectively through the ETA receptor (ETAR) to promote tumor cell proliferation, survival, neovascularization, and invasiveness. Loss of gap junctional intercellular communication (GJIC) is critical for tumor progression by allowing the cells to escape growth control. Exposure of HEY and OVCA 433 ovarian carcinoma cell lines to ET-1 led to a 50-75% inhibition in intercellular communication and to a decrease in the connexin 43 (Cx43)-based gap junction plaques. To investigate the phosphorylation state of Cx43, ovarian carcinoma cell lysates were immunoprecipitated and transient tyrosine phosphorylation of Cx43 was detected in ET-1-treated cells. BQ 123, a selective ETAR antagonist, blocked the ET-1-induced Cx43 phosphorylation and cellular uncoupling. Gap junction closure was prevented by tyrphostin 25 and by the selective c-Src inhibitor, PP2. Furthermore, the increased Cx43 tyrosine phosphorylation was correlated with ET-1-induced increase of c-Src activity, and PP2 suppressed the ET-1-induced Cx43 tyrosine phosphorylation, indicating that inhibition of Cx43-based GJIC is mainly mediated by the Src tyrosine kinase pathway. In vivo, the inhibition of human ovarian tumor growth in nude mice induced by the potent ETAR antagonist, ABT-627, was associated with a reduction of Cx43 phosphorylation. These findings indicate that the signaling mechanisms involved in GJIC disruption on ovarian carcinoma cells depend on ETAR activation, which leads to the Cx43 tyrosine phosphorylation mediated by c-Src, suggesting that ETAR blockade may contribute to the control of ovarian carcinoma growth and progression also by preventing the loss of GJIC.

Expression of Tie-2 in human peripheral and autonomic nervous system

Tie-2, a tyrosine kinase receptor, is essential for vascular integrity by regulating cellular adhesion between pericytes and endothelial cells. The aim of this study was to identify sites of expression of Tie-2 other than the vasculature. Tie-2 expression was first detected in human colon by Western blotting and reverse-transcription-polymerase chain reaction (RT-PCR) in tissue extracts. The presence of the Tie-2 mRNA and protein was detected by immunohistochemistry and in situ hybridization in cells of the colon myenteric and submucosal plexus, in both neuronal and Schwann cells. Tie-2 protein was also found in the nervous system of the female urogenital tract. In the human sciatic nerve and schwannoma, RT-PCR, Western blotting and immunohistochemistry analysis further confirmed the presence of Tie-2 mRNA and protein in non-autonomic peripheral nervous tissue. In conclusion, using several approaches and tissues we have demonstrated the presence of Tie-2 in human peripheral and autonomic nervous tissue, suggesting a role for Tie-2 in neural tissue. Thus, attempts to disrupt the tumour vessels by manipulation of the Tie-2 system in tumours may result in side-effects in peripheral nerves.