Endothelin receptor expression in colorectal cancer

Repurposing of the Drug Tezosentan for Cancer Therapy

Tezosentan is a vasodilator drug that was originally developed to treat pulmonary arterial hypertension. It acts by inhibiting endothelin (ET) receptors, which are overexpressed in many types of cancer cells. Endothelin-1 (ET1) is a substance produced by the body that causes blood vessels to narrow. Tezosentan has affinity for both ET_A and ET_B receptors. By blocking the effects of ET1, tezosentan can help to dilate blood vessels, improve the blood flow, and reduce the workload on the heart. Tezosentan has been found to have anticancer properties due to its ability to target the ET receptors, which are involved in promoting cellular processes such as proliferation, survival, neovascularization, immune cell response, and drug resistance. This review intends to demonstrate the potential of this drug in the field of oncology. Drug repurposing can be an excellent way to improve the known profiles of first-line drugs and to solve several resistance problems of these same antineoplastic drugs.

Endothelin-A receptor in gastric cancer and enhanced antitumor activity of trastuzumab in combination with the endothelin-A receptor antagonist ZD4054

Endothelin-A receptor (ETAR) is overexpressed in cancers and can function through transactivation of the epidermal growth factor receptor. We explored ETAR in gastric cancer and investigated the antitumor effect of trastuzumab in combination with the ETAR antagonist ZD4054. The expression of ETAR was significantly correlated with the expression of vascular endothelial growth factor. Univariate and multivariate analyses further showed that ETAR expression correlated with reduced survival in gastric cancer patients. In vitro, ZD4054 increased the antiproliferative effect of trastuzumab in gastric cancer cell lines. Moreover, the addition of ZD4054 to trastuzumab significantly increased apoptosis in gastric cancer cell lines. In vivo, tumor growth was considerably inhibited by treatment with ZD4054 and trastuzumab, and the tumor volume in the trastuzumab and ZD4054 combination group was smaller than in the other groups. The detection of ETAR could help predict the prognosis of gastric cancer patients. Additionally, this study provides support for the therapeutic use of the combination of ZD4054 and trastuzumab as an anticancer treatment, especially for gastric cancer.

Targeting Mucosal Endothelin-A-Receptor Expression by Fluorescence Endoscopy is Feasible to Detect and Characterize Colitis-Associated Cancer in Mice

BACKGROUND

To facilitate onsite decision-making during endoscopy, both accurate detection and in vivo characterization of preneoplasia are prerequisites. However, no endoscopy technique is available that meets both demands satisfactorily. We evaluated endothelin-receptor A (ETAR)-guided fluorescence endoscopy (FE) in vivo and fluorescence reflectance imaging (FRI) ex vivo for detection and characterization of early dysplastic colitis-associated colonic lesions.

METHODS

Colorectal cancerogenesis was investigated in the inflammatory driven AOM-DSS model and spontaneous adenoma development in ApcMin mice. A Cy5.5-labeled nonpeptidic ETAR-specific imaging probe was injected intravenously to assess tumor development in vivo by white light endoscopy (WLE) and FE. Ex vivo tumors were evaluated by FRI, histological examination, and western blot analysis. In addition, tissue samples from patients with colitis-associated malignant and nonmalignant mucosal alterations were analyzed. Specificity experiments were performed using an unspecific Cy3.5-glycine tracer.

RESULTS

Overall, 62 adenomas were observed. FE was able to detect and quantify ETAR expression targeting the ETAR-specific photoprobe. A significantly higher fluorescent contrast was detected in colonic adenomas compared to adjacent nonmalignant mucosa by FE (64.3 ± 7.9 vs. 56.6. ± 7.0; P < 0.001). These results were confirmed by FRI examination, immunochemistry, and western blot analysis. Additionally, ETAR expression in samples from human patients with colitis-associated cancer was highly elevated compared to nonmalignant alterations. Specificity experiments indicated a high binding-specificity of the applied ETAR photoprobe (1.4 ± 0.3 vs. 2.5 ± 0.7; P < 0.001).

CONCLUSIONS

We introduced ETAR guided FE in mice for successful in vivo detection and characterization of colorectal neoplasia on a molecular level.

Blocking endothelin-1-receptor/β-catenin circuit sensitizes to chemotherapy in colorectal cancer

The limited clinical response to conventional chemotherapeutics observed in colorectal cancer (CRC) may be related to the connections between the hyperactivated β-catenin signaling and other pathways in CRC stem-like cells (CRC-SC). Here, we show the mechanistic link between the endothelin-1 (ET-1)/ET-1 receptor (ET-1R) signaling and β-catenin pathway through the specific interaction with the signal transducer β-arrestin1 (β-arr1), which initiates signaling cascades as part of the signaling complex. Using a panel of patient-derived CRC-SC, we show that these cells secrete ET-1 and express ET_AR and β-arr1, and that the activation of ET_AR/β-arr1 axis promotes the cross-talk with β-catenin signaling to sustain stemness, epithelial-to-mesenchymal transition (EMT) phenotype and response to chemotherapy. Upon ET_AR activation, β-arr1 acts as a transcription co-activator that binds β-catenin, thereby promoting nuclear complex with β-catenin/TFC4 and p300 and histone acetylation, inducing chromatin reorganization on target genes, such as ET-1. The enhanced transcription of ET-1 increases the self-sustained ET-1/β-catenin network. All these findings provide a strong rationale for targeting ET-1R to hamper downstream β-catenin/ET-1 autocrine circuit. Interestingly, treatment with macitentan, a dual ET_AR and ET_BR antagonist, able to interfere with tumor and microenvironment, disrupts the ET-1R/β-arr1-β-catenin interaction impairing pathways involved in cell survival, EMT, invasion, and enhancing sensitivity to oxaliplatin (OX) and 5-fluorouracil (5-FU). In CRC-SC xenografts, the combination of macitentan and OX or 5-FU enhances the therapeutic effects of cytotoxic drugs. Together, these results provide mechanistic insight into how ET-1R coopts β-catenin signaling and offer a novel therapeutic strategy to manage CRC based on the combination of macitentan and chemotherapy that might benefit patients whose tumors show high ET_AR and β-catenin expression.

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.

Role of endothelin A receptor in colon cancer metastasis: in vitro and in vivo evidence

The endothelin (ET)-1/endothelin A receptor (ETAR) axis is reportedly involved in tumor cell invasion, survival, and metastasis. However, the role of ETAR in colon cancer metastasis and the underlying mechanisms have not been defined. In the present study, we assessed the role of ETAR in colon cancer metastasis in vitro and in vivo. Overexpression and knockdown of ETAR were respectively performed in SW480 and SW620 human colon cancer cells. Overexpression of ETAR in SW480 cells significantly increased cell survival against cisplatin, cell invasion, and matrix metalloproteinase (MMP)-2 expression, which was strengthened by exogenous ET-1 and abolished by selective ETAR antagonist BQ123 and phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002. Knockdown of ETAR in SW620 cells markedly decreased cell survival against cisplatin, cell invasion, and MMP-2 expression, which was strengthened by BQ123 and LY294002, and partially rescued by exogenous ET-1. In a colon cancer liver metastasis mouse model, while ETAR overexpression promoted colon cancer liver metastases, ETAR knockdown markedly decreased liver metastases. In conclusion, our in vitro data demonstrate that ETAR mediates the promoting effects of ET-1 on colon cancer cell survival, invasion and MMP-2 expression by a PI3K-mediated mechanism. Our in vivo data indicate that ETAR markedly promotes colon cancer liver metastasis. This study provides direct evidence for a critical role of ETAR in colon cancer metastasis, which suggests that ETAR antagonism could benefit patients with metastatic colon cancer.

Efficacy of the specific endothelin a receptor antagonist zibotentan (ZD4054) in colorectal cancer: a preclinical study

Endothelin 1 (ET-1) is overexpressed in cancer, contributing to disease progression. We previously showed that ET-1 stimulated proliferative, migratory, and contractile tumorigenic effects via the ET(A) receptor. Here, for the first time, we evaluate zibotentan, a specific ET(A) receptor antagonist, in the setting of colorectal cancer, in cellular models. Pharmacologic characteristics were further determined in patient tissues. Colorectal cancer lines (n = 4) and fibroblast strains (n = 6), isolated from uninvolved areas of colorectal cancer specimens, were exposed to ET-1 and/or ET(A)/(B) receptor antagonists. Proliferation (methylene blue), migration (scratch wounds), and contraction (gel lattices) were assessed. Receptor distribution and binding characteristics (K(d), B(max)) were determined using autoradiography on tissue sections and homogenates and cytospun cells, supported by immunohistochemistry. Proliferation was inhibited by ET(A) (zibotentan > BQ123; P < 0.05), migration by ET(B) > ET(A), and contraction by combined ET(A) and ET(B) antagonism. Intense ET-1 stromal binding correlated with fibroblasts and endothelial cells. Colorectal cancer lines and fibroblasts revealed high density and affinity ET-1 binding (B(max) = 2.435 fmol/1 × 10(6) cells, K(d) = 367.7 pmol/L; B(max) = 3.03 fmol/1 × 10(6) cells, K(d) = 213.6 pmol/L). In cancer tissues, ET(A) receptor antagonists (zibotentan; BQ123) reduced ET-1 binding more effectively (IC(50): 0.1-10 μmol/L) than ET(B) receptor antagonist BQ788 (∼IC(50), 1 mmol/L). ET-1 stimulated cancer-contributory processes. Its localization to tumor stroma, with greatest binding/affinity to fibroblasts, implicates these cells in tumor progression. ET(A) receptor upregulation in cancer tissues and its role in tumorigenic processes show the receptor's importance in therapeutic targeting. Zibotentan, the most specific ET(A) receptor antagonist available, showed the greatest inhibition of ET-1 binding. With its known safety profile, we provide evidence for zibotentan's potential role as adjuvant therapy in colorectal cancer.

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.

Enhanced expressions of endothelin-converting enzyme and endothelin receptors in human colonic tissues of Crohn's disease

Endothelin-1, a powerful vasoconstrictor, forms the endothelin system together with endothelin-converting enzyme and endothelin type A and type B receptors. These endothelin system components are considered to participate in inflammatory and wound healing responses. Previous reports have suggested a role for the endothelin-1 in the pathology of Crohn’s disease. In the present study, we immunohistochemically investigated the expressions of the endothelin system components in affected human intestinal tissues of Crohn’s disease. Eighteen surgical specimens of colonic tissue obtained from patients with Crohn’s disease and 12 normal colonic tissues as controls were examined. Frozen tissue sections cut from the samples were subjected to the immunohistochemical single and double staining. The endothelin system components were expressed mainly in the muscular layers and blood vessels. In diseased colonic tissues, inflammatory infiltration and fibrotic tissue reactions with marked smooth muscle cell proliferation were frequently seen, and were closely associated with increased expressions of the endothelin system components. These results strongly suggest that endothelin-converting enzyme and endothelin type A and type B receptors collectively play a role in the inflammatory and fibrogenic processes of Crohn’s disease. Especially, submucosal smooth muscle proliferation, a histological hallmark of strictures, may be attributable to the upregulated endothelin system.

Endothelin and hepatic wound healing

Liver wound healing is a coordinated response to injury caused by infections (hepatitis) or toxins (alcohol) or other processes where activation of hepatic stellate cells are a central component. During stellate cell activation, a major phenotypic transformation occurs which leads to increased production of increased extracellular matrix proteins and smooth muscle α-actin the results is organ dysfunction due to gross architectural disruption and impaired blood flow. Endothelin-1 (ET-1) is produced in increased amounts and the cellular source of ET-1 shifts from endothelial cells to stellate cells during liver injury thus setting a feedback loop which accentuates further activation, stellate cell proliferation, and production of extracellular matrix proteins. Therapy directed at intervening the ET-1 signaling pathway has significant therapeutic potential in patients with liver disease.

Anti-endothelin drugs in solid tumors

IMPORTANCE OF THE FIELD

The endothelin (ET) axis, which includes the biological functions of ETs and their receptors, has played a physiological role in normal tissue, acting as a modulator of vasomotor tone, tissue differentiation and development, cell proliferation and hormone production. Interestingly, it also functions in the growth and progression of various tumors. Several researchers have identified the blockade of the ET-1 receptor as a promising therapeutic approach.

AREAS COVERED IN THIS REVIEW

The clinical investigation of an orally bioavailable ET antagonist, atrasentan, in prostate cancer, is encouraging. In this neoplasia, it has shown antitumor activity, bone metastasis control and amelioration of cancer-related pain but improvement in time to progression and overall survival has still not been demonstrated. The clinical trials of other ET antagonists are reported. Literature research was performed by Pubmed and Pharmaprojects.

WHAT THE READER WILL GAIN

A comprehensive view about the use of atrasentan in the treatment of castration-resistant prostate cancer (CRPC) is provided together with the scientific rationale based on the function of ET and its receptor in various cancer development mechanisms.

TAKE HOME MESSAGE

Atrasentan seems to be active in CRPC, although strong scientific evidence is still to be found. Interesting clinical findings regard zibotentan.

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.

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 B receptor, a new target in cancer immune therapy

The endothelins and their G protein-coupled receptors A and B have been implicated in numerous diseases and have recently emerged as pivotal players in a variety of malignancies. Tumors overexpress the endothelin 1 (ET-1) ligand and the endothelin-A-receptor (ET(A)R). Their interaction induces tumor growth and metastasis by promoting tumor cell survival and proliferation, angiogenesis, and tissue remodeling. On the basis of results from xenograft models, drug development efforts have focused on antagonizing the autocrine-paracrine effects mediated by ET-1/ET(A)R. In this review, we discuss a novel role of the endothelin-B-receptor (ET(B)R) in tumorigenesis and the effect of its blockade during cancer immune therapy. We highlight key characteristics of the B receptor such as its specific overexpression in the tumor compartment; and specifically, in the tumor endothelium, where its activation by ET-1 suppresses T-cell adhesion and homing to tumors. We also review our recent findings on the effects of ET(B)R-specific blockade in increasing T-cell homing to tumors and enhancing the efficacy of otherwise ineffective immunotherapy.

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.

Expression of the endothelin axis in noninvasive and superficially invasive bladder cancer: relation to clinicopathologic and molecular prognostic parameters

BACKGROUND

The endothelin (ET) axis plays a role in cancer biology and plays a potential role as a target for molecular therapy in urogenital tumours. Alterations of several proteins of the ET axis were detected in invasive bladder cancer.

OBJECTIVES

To examine the potential role of the expression of ET axis proteins compared to other prognostic parameters (kinase inhibitor 67 [Ki-67], tumour protein 53 [TP53], and fibroblast growth factor receptor 3 gene [FGFR3] mutations) in noninvasive and invasive bladder cancer.

DESIGN, SETTING, AND PARTICIPANTS

Tissue microarrays from 154 consecutive patients with pTa-pT2 urothelial bladder cancer were immunohistochemically stained for endothelin 1 (ET-1), endothelin A and B receptors (ET(A)R, ET(B)R), TP53, and Ki-67. FGFR3 mutations were detected by SNaPshot analysis.

MEASUREMENTS

The results were correlated with clinicopathologic parameters and disease-specific survival, overall survival, and recurrence-free survival.

RESULTS AND LIMITATIONS

Proteins of the ET axis were frequently expressed in bladder cancer (ET-1 in 62% of tumours, ET(A)R in 93% of tumours, and ET(B)R in 84% of tumours). ET-1 expression was strongly correlated with tumour stage (p=0.015), histologic grade (p=0.008), and low proliferation status (p=0.003). ET(A)R immunostaining was only associated with low proliferation status (p=0.015). Kaplan-Meier survival analysis showed a significantly longer overall survival for patients with ET-1-expressing tumours (p=0.007). A significantly longer disease-free survival was found in patients with ET(A)R-expressing tumours (p=0.040), whereas ET(B)R expression was significantly correlated to a longer disease-free survival only in subgroups of patients with multifocal tumours (p=0.031), low proliferation index (Ki-67 ≤10; p=0.050), low TP53 expression (≤10; p=0.018), and tumours with an FGFR3 mutation (p=0.026). In the global model for recurrence-free survival, only high-grade (p=0.048) and negative ET(A)R immunoreactivity (p=0.048) were correlated with poor prognosis.

CONCLUSIONS

In addition to other factors, particularly age at diagnosis and growth pattern, lack of ET-1 expression may be an independent negative prognostic factor for the overall-survival probability of bladder cancer patients. Lack of ET(A)R expression may be an independent negative marker for recurrence-free survival.

Response to endothelin-1 in arteries from human colorectal tumours: role of endothelin receptors

To examine the reaction of tumour arteries to endothelin-1, we obtained arteries supplying blood flow to colorectal tumours from patients, as well as mesenteric arteries supplying the normal colon tissue from the same patients and mesenteric arteries from patients without a colorectal tumour pathology. The contraction in response to endothelin-1 and the relaxation produced by bradykinin was recorded in each of these arteries. Accordingly, the sensitivity to endothelin-1 but not the maximal response, was higher in the arteries supplying colorectal tumours than in mesenteric arteries supplying normal colon or in mesenteric arteries from patients with no tumour pathology. The contraction produced by endothelin-1 was not modified by exposure to L-NAME or meclofenamate in arteries supplying both the tumour and the normal colon. The endothelin ET(A) andET(B) receptors were expressed similarly in arteries supplying the tumour or normal colon. However, the antagonist of the endothelin ET(B) receptors BQ788 (10(-6) M) decreased the contractions in the arteries supplying the tumour but not in those supplying the normal colon. By contrast, the antagonist of endothelin ET(A) receptors BQ123 (10(-6) M) reduced the contraction equally in both these types of arteries. Likewise, in arteries precontracted with U46619, the relaxation in response to bradykinin was similar in all three types of arteries. Together, these results suggest that the arteries supplying human colorectal tumours are more sensitive to endothelin-1, which could be due to the enhanced activity of endothelin ET(B) receptors in the absence of any change in the modulatory effect of nitric oxide or prostanoids in the arterial response to this peptide.

Endothelin-3 is produced by metastatic melanoma cells and promotes melanoma cell survival

BACKGROUND

Endothelin-3 (ET-3) is an essential paracrine factor for the proliferation, migration, and survival of embryonic melanocytes during fetal development. Its expression is tightly regulated, being completely turned off in adult skin.

OBJECTIVE

In this study, results are presented that demonstrate abnormal expression of ET-3 by metastatic melanoma cells in both tissue biopsies and cell culture. Further, in vitro experiments showed that metastatic melanoma cells have the capacity to respond to ET-3 stimulation by increasing survival.

CONCLUSION

Therefore, an abnormal autocrine stimulation pathway involving ET-3 is present in metastatic melanoma cells. Blocking this signal transduction pathway may prove useful for the treatment of metastatic melanoma.

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.

Therapeutic targeting of the endothelin a receptor in human nasopharyngeal carcinoma

The endothelin A receptor (ET(A)R) autocrine pathway is overexpressed in many malignancies, including nasopharyngeal carcinoma (NPC). In this tumor, ET(A)R expression is an independent determinant of survival and a robust independent predictor of distant metastasis. To evaluate whether ET(A)R represents a new target in NPC treatment, we tested the therapeutic role of ET(A)R in NPC. Cell proliferation was inhibited by the ET(A)R-selective antagonist ABT-627 in two ET(A)R-positive NPC cells in a dose-dependent manner. Proliferation of ET(A)R-negative NPC cells was not decreased. ET(A)R blockade also resulted in sensitization to cisplatin and 5-fluorouracil-induced apoptosis. In nude mice, ABT-627 inhibited the growth of NPC cell xenografts. Combined treatment of ABT-627 with the cytotoxic drug cisplatin or 5-fluorouracil produced additive antitumor effects. The antitumor activity of ABT-627 was demonstrated finally on an experimental lung metastasis by a reduction in the number of tumors. These results support the rationale of combining ABT-627 with current standard chemotherapy to further improve the therapeutic ratio in the treatment of NPC.

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-1 (ET-1) promotes MMP-2 and MMP-9 induction involving the transcription factor NF-kappaB in human osteosarcoma

In the present study, we have investigated the effect of (i) ET-1 (endothelin-1) and its precursor, big ET-1, on MMP (matrix metalloproteinase)-2 and MMP-9 synthesis and activity in osteosarcoma tissue, and (ii) ET-1 receptor antagonists on cell invasion. Using Western blotting, zymography, RT-PCR (reverse transcription-PCR), immunohistochemistry, immunofluorescence and Northern blotting, we have shown that ET-1 and ET-1 receptors (ET(A) and ET(B)) were expressed in these cells. Additionally, we have demonstrated that ET-1 markedly induced the synthesis and activity of MMP-2, which was significantly increased when compared with MMP-9. Furthermore, inhibition of NF-kappaB (nuclear factor kappaB) activation blocked MMP-2 production and activity, indicating the involvement of NF-kappaB, a ubiquitous transcription factor playing a central role in the differentiation, proliferation and malignant transformation. Since ET-1 acts as an autocrine mediator through gelatinase induction and because inhibition of ET(A) receptor is beneficial for reducing both basal and ET-1-induced osteosarcoma cell invasion, targeting this receptor could be an attractive therapeutic alternative for the successful treatment of osteosarcoma.

Endothelin system in oral squamous carcinoma cells: Specific siRNA targeting of ECE-1 blocks cell proliferation

The present study focused on the endothelin axis in human oral squamous cell carcinoma (SCC) cells. We investigated the expression and distribution of endothelin-1 (ET-1), its receptors (endothelin-A receptor (ET(A)R) and endothelin-B receptor (ET(B)R)) and isoforms of its specific converting enzyme (ECE-1a, 1b, 1c) and the report on their relative influences on cell proliferation. We also investigated the effect of an ECE-specific inhibitor (ECE-i) and siRNA targeting of the ECE-1 gene on SCC cell proliferation. We observed the expression of ET-1, ET(A)R, ET(B)R and all endothelin-converting enzyme-1 (ECE-1) isoforms in oral SCC cells, but only the expression of ET-1, ET(B)R and ECE-1 was increased when compared to normal human epidermal keratinocytes. ET-1 alone stimulated proliferation of oral SCC cells. Antagonists of either ET(A)R or ET(B)R inhibited ET-1-mediated proliferation. Decreased ECE-1 expression after ECE siRNA treatment reduced SCC cell proliferation. Antiproliferative effects were also observed by inhibiting ECE activity with ECE-i. In conclusion, the present study demonstrates that modulation of the endothelin system in oral SCC cells might provide a novel therapeutic protocol for oral cancer.

Expression of the Endothelin Axis in Bladder Cancer: Relationship to Clinicopathologic Parameters and Long-term Survival

OBJECTIVES

Endothelin-1 (ET-1) and its receptors ET(A)R and ET(B)R, referred to as the Endothelin-axis, play an emerging role in cancer. We examined the ET-axis immunohistochemically in invasive bladder cancer.

METHODS

Tumor specimens from 157 patients after cystectomy were stained immunohistochemically for ET-1, ET(A)R and ET(B)R. After semiquantitative analysis the staining results were correlated with clinicopathological parameters and survival rates.

RESULTS

Overexpression of ET-1, ET(A)R and ET(B)R was identified in 26.8%, 58.8% and 76.9% of cases, respectively. No association with TNM staging and histologic grading was found. However, patients with ET(B)R expression tended to have organ-confined tumors (p=0.16) and no vascular invasion (p=0.09), the latter being statistically significant in the subgroup of G3 tumors (p=0.02). ET(B)R overexpression was associated with favorable disease-free survival (p=0.04).

CONCLUSIONS

The ET-axis is overexpressed in bladder cancer, ET(B)R predominating in this entity and being associated with a more favorable prognosis. Further studies are warranted to elucidate the role of the ET-axis as a molecular target in bladder cancer.

Expression of endothelin-A-receptor predicts unfavourable response to neoadjuvant chemotherapy in locally advanced breast cancer

Endothelin-1 (ET-1) and its receptors (ET_AR and ET_BR), referred to as the endothelin (ET) axis, are overexpressed in breast carcinomas and appear to influence tumour growth and progression. The objective of this study was to determine the effect of expression of the ET axis in breast carcinomas on response to cytotoxic chemotherapy. The study included 44 patients with locally advanced breast cancer participating in a prospective phase III study evaluating high-dose neoadjuvant chemotherapy of epirubicin and cyclophosphamide. Expression of ET-1, ET_AR and ET_BR was determined by semiquantitative immunohistochemical analysis of breast cancer tissue from prechemotherapy tru-cut biopsies. Immunohistochemical staining was positive for ET-1 in 61.5%, for ET_AR in 35% and for ET_BR in 35.9% of breast carcinomas. Pathological response to chemotherapy was significantly decreased in ET_AR-positive patients (P=0.002). In total, 50% of ET_AR-positive patients as compared to 7.7% of ET_AR-negative patients attained pathologically ‘no change’. Logistic regression confirmed ET_AR as an independent predictive marker for pathological response (P=0.009). These data indicate that increased expression of ET_AR in breast carcinomas is associated with resistance to chemotherapy. Determination of ET_AR status may serve as a predictive marker for identifying patients less likely to be responsive to conventional chemotherapy.

Tumour-cell migration, invasion, and metastasis: navigation by neurotransmitters

Cancer starts as a localised disease, which, if detected early, can often be treated successfully by removal of the primary tumour. A pernicious progression is the invasion of tumour cells into surrounding tissues, resulting in development of distant metastases. Because active migration of tumour cells is a prerequisite for tumour-cell invasion and metastasis, a pressing goal in tumour biology has been the elucidation of factors regulating the migratory activity of these cells. The most prominent regulatory factors are ligands to serpentine receptors-eg, chemokines and neurotransmitters. Many types of neurotransmitter receptors are expressed on tumour cells, supporting the theory that psychosocial factors are involved in the progression of cancer. Understanding how such receptors regulate migration and the availability of specific receptor antagonists could open up new avenues for chemoprevention of tumour-cell migration and metastatic development.

The endothelin system in Morris hepatoma-7777: an endothelin receptor antagonist inhibits growth in vitro and in vivo

1. Plasma concentrations of endothelin are increased in patients with hepatocellular cancer as well as in patients with liver metastasis. However, the impact of these findings remains uncertain. 2. We thus analyzed the endothelin system in a rat hepatoma model (Morris hepatoma 7777) in vitro and in vivo. 3. Our study revealed that tissue concentrations of endothelin-1 (ET-1) and big-ET-1, the precursor of ET-1, were significantly elevated in Morris hepatoma 7777 as compared to normal liver. The ETA receptor density was significantly elevated, whereas the density of the ETB receptor was decreased in Morris hepatoma 7777. 4. We could also demonstrate that hepatoma cells secrete ET-1. 5. Exogenously added ET-1 enhances hepatoma cell growth in a dose-dependent manner. Endothelin receptor antagonists (ETA and combined ETA/ETB receptor antagonists) inhibit tumor cell growth in vitro. Since the combined ETA/ETB receptor antagonist was more effective in vitro, we used this compound also for in vivo studies and could demonstrate that a combined ETA/ETB receptor antagonist is able to reduce hepatoma growth in vivo. 6. In conclusion, the endothelin system is activated in Morris hepatoma 7777 and contributes to hepatoma growth. Since endothelin receptor antagonists are well-tolerated upcoming clinically used drugs without major side effects, our data might provide a new pharmacological approach to reduce hepatoma growth in vivo.

Endothelin-1: a multifunctional molecule in cancer

Endothelin-1 is a small vasoconstrictor peptide that was first identified in 1988. Here we review the evidence implicating ET-1 in tumorigenesis. In particular, we concentrate on the role of ET-1 in mitogenesis, apoptosis, angiogenesis, tumour invasion and metastasis, and discuss the potential for endothelin-system modulation as an adjuvant therapeutic strategy.

Increased endothelin-1 in colorectal cancer and reduction of tumour growth by ET(A) receptor antagonism

Endothelin-1 (ET-1) is a vasoconstrictor peptide which stimulates proliferation in vitro in different cell types, including colorectal cancer cells. Raised ET-1 levels have been detected both on tissue specimens and in the plasma of patients with cancers. To investigate the role of ET-1 in colorectal cancer: (i) ET-1 plasma levels in patients with colorectal cancer were measured by radioimmunoassay: group 1 = controls (n = 22), group 2 = primary colorectal cancer only (n = 39), group 3 = liver metastases only (n = 26); (ii) ET-1 expression in primary colorectal cancer specimens (n =10) was determined immunohistochemically and (iii) the effect of intraportally infused antagonists to the two ET-1 receptors, ET(A) and ET(B), on the growth of liver metastases in a rat model was assessed. ET-1 plasma levels were significantly increased in both patients with primary tumour and patients with metastases, compared to controls (P < 0.01, 3.9 +/- 1.4, 4.5 +/- 1.5, vs. 2.75 +/- 1.37 pg/ml, respectively). Immunohistochemically, strong expression of ET-1 was found in the cytoplasm, stroma and blood vessels of cancers, unlike the normal colon where only the apical layer of the epithelium, vascular endothelial cells and surrounding stroma were positively stained. In the rat model, there was significant reduction in liver tumour weights compared to controls, following treatment with the ET(A) antagonist (BQ123) 30 min after the intraportal inoculation of tumour cells (P < 0.05). These results suggest ET-1 is produced by colorectal cancers and may play a role in the growth of colorectal cancer acting through ET(A) receptors. ET(A) antagonists are indicated as potential anti-cancer agents.