Combined targeting of endothelin A receptor and epidermal growth factor receptor in ovarian cancer shows enhanced antitumor activity

Endothelin and the tumor microenvironment: a finger in every pie

The tumor microenvironment (TME) plays a central role in the development of cancer. Within this complex milieu, the endothelin (ET) system plays a key role by triggering epithelial-to-mesenchymal transition, causing degradation of the extracellular matrix and modulating hypoxia response, cell proliferation, composition, and activation. These multiple effects of the ET system on cancer progression have prompted numerous preclinical studies targeting the ET system with promising results, leading to considerable optimism for subsequent clinical trials. However, these clinical trials have not lived up to the high expectations; in fact, the clinical trials have failed to demonstrate any substantiated benefit of targeting the ET system in cancer patients. This review discusses the major and recent advances of the ET system with respect to TME and comments on past and ongoing clinical trials of the ET system.

Proteomic analysis of exosomes secreted during the epithelial-mesenchymal transition and potential biomarkers of mesenchymal high-grade serous ovarian carcinoma

BACKGROUND

The epithelial-mesenchymal transition (EMT) promotes cell signaling and morphology alterations, contributing to cancer progression. Exosomes, extracellular vesicles containing proteins involved in cell-cell communication, have emerged as a potential source of biomarkers for several diseases.

METHODS

Our aim was to assess the proteome content of exosomes secreted after EMT-induction to identify potential biomarkers for ovarian cancer classification. EMT was induced in the ovarian cancer cell line CAOV3 by treating it with EGF (10 ng/mL) for 96 h following 24 h of serum deprivation. Subsequently, exosomes were isolated from the supernatant using selective centrifugation after decellularization, and their characteristics were determined. The proteins present in the exosomes were extracted, identified, and quantified using Label-Free-Quantification (LFQ) via Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). To identify potential biomarkers, the obtained proteomic data was integrated with the TGGA database for mRNA expression using principal component analysis and a conditional inference tree.

RESULTS

The exosomes derived from CAOV3 cells exhibited similar diameter and morphology, measuring approximately 150 nm, regardless of whether they were subjected to EMT stimulation or not. The proteomic analysis of proteins from CAOV3-derived exosomes revealed significant differential regulation of 157 proteins, with 100 showing upregulation and 57 downregulation upon EMT induction. Further comparison of the upregulated proteins with the TCGA transcriptomic data identified PLAU, LAMB1, COL6A1, and TGFB1 as potential biomarkers of the mesenchymal HGSOC subtype.

CONCLUSIONS

The induction of EMT, the isolation of exosomes, and the subsequent proteomic analysis highlight potential biomarkers for an aggressive ovarian cancer subtype. Further investigation into the role of these proteins is warranted to enhance our understanding of ovarian cancer outcomes.

Potential roles of tumor microenvironment in gefitinib-resistant non-small cell lung cancer: A narrative review

During the course of treating non-small cell lung cancer (NSCLC) with epithelial growth factor receptor (EGFR) mutant, gefitinib resistance (GR) is unavoidable. As the environment for tumor cells to grow and survive, tumor microenvironment (TME) can significantly affect therapeutic response and clinical outcomes, offering new opportunities for addressing GR. Dynamic changes within the TME were identified during the treatment of gefitinib, suggesting the close relationship between TME and GR. Various dynamic processes like angiogenesis, hypoxia-pathway activation, and immune evasion can be blocked so as to synergistically enhance the therapeutic effects of gefitinib or reverse GR. Besides, cellular components like macrophages can be reprogrammed for the same purpose. In this review, we summarized recently proposed therapeutic targets to provide an overview of the potential roles of TME in treating gefitinib-resistant NSCLC, and discussed the difficulty of applying these targets in cancer treatment.

Systems analysis identifies endothelin 1 axis blockade for enhancing the anti-tumor effect of multikinase inhibitor

Multikinase inhibitors, such as sorafenib, are used for the treatment of advanced carcinomas but the response shows limited efficacy or varies a lot with patients. Here we adopted the systems approach combined with high-throughput data analysis to discover key mechanism embedded in the drug response. When analyzing the transcriptomic data from the Cancer Cell Line Encyclopedia (CCLE) database, endothelin 1 (EDN1) was enriched in cancer cells with low responsiveness to sorafenib. We found that the level of EDN1 is higher in the tissue and blood of hepatocellular carcinoma (HCC) patients showing poor response to sorafenib. In vitro experiment showed that EDN1 not only induces activation of angiogenic-promoting pathways in HCC cells but also stimulates proliferation and migration. Moreover, EDN1 is related with poor responsiveness to sorafenib by mitigating unfolded protein response (UPR), which was validated in both transcriptomic data analysis and in silico simulation. Finally, we found that endothelin receptor B (EDNRB) antagonists can enhance the efficacy of sorafenib in both HCC cells and xenograft mouse models. Our findings provide that EDN1 is a novel diagnostic marker for sorafenib responsiveness in HCC and a basis for testing macitentan, which is currently used for pulmonary artery hypertension, in combination with sorafenib in advanced HCC patients.

A human antibody against human endothelin receptor type A that exhibits antitumor potency

Endothelin receptor A (ET_A), a class A G-protein-coupled receptor (GPCR), is involved in the progression and metastasis of colorectal, breast, lung, ovarian, and prostate cancer. We overexpressed and purified human endothelin receptor type A in Escherichia coli and reconstituted it with lipid and membrane scaffold proteins to prepare an ET_A nanodisc as a functional antigen with a structure similar to that of native GPCR. By screening a human naive immune single-chain variable fragment phage library constructed in-house, we successfully isolated a human anti-ET_A antibody (AG8) exhibiting high specificity for ET_A in the β-arrestin Tango assay and effective inhibitory activity against the ET-1-induced signaling cascade via ET_A using either a CHO-K1 cell line stably expressing human ET_A or HT-29 colorectal cancer cells, in which AG8 exhibited IC₅₀ values of 56 and 51 nM, respectively. In addition, AG8 treatment repressed the transcription of inhibin βA and reduced the ET_A-induced phosphorylation of protein kinase B and extracellular regulated kinase. Furthermore, tumor growth was effectively inhibited by AG8 in a colorectal cancer mouse xenograft model. The human anti-ET_A antibody isolated in this study could be used as a potential therapeutic for cancers, including colorectal cancer.

A therapeutic antibody that targets a receptor involved in cancer progression shows significant anti-cancer effects in trials in mice. Endothelin receptor A (ET_A) promotes the progression and metastasis of several cancers, and patients with high ET_A expression often have poor survival rates. Several small molecule drugs that target ET_A are currently undergoing trials. Now, Sang Taek Jung at the Korea University in Seoul, together with scientists across South Korea, have identified and isolated a human antibody that specifically binds to ET_A. The team developed an antigen that mimics ET_A, and identified and isolated the antibody it bound to. The antibody exhibited potent anti-tumor effects in cell cultures and trials in mice. Such therapeutic antibodies show higher affinity for their targets than other drugs, resulting in fewer side effects and higher efficacy.

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.

G Protein-coupled Receptors in Radioiodine-refractory Thyroid Cancer in the Era of Precision Medicine

CONTEXT

Radioiodine-refractory thyroid cancers have poor outcomes and limited therapeutic options (tyrosine kinase inhibitors) due to transient efficacy and toxicity of treatments. Therefore, combinatorial treatments with new therapeutic approaches are needed. Many studies link G protein-coupled receptors (GPCRs) to cancer cell biology.

OBJECTIVE

To perform a specific atlas of GPCR expression in progressive and refractory thyroid cancer to identify potential targets among GPCRs aiming at drug repositioning.

METHODS

We analyzed samples from tumor and normal thyroid tissues from 17 patients with refractory thyroid cancer (12 papillary thyroid cancers [PTCs] and 5 follicular thyroid cancers [FTCs]). We assessed GPCR mRNA expression using NanoString technology with a custom panel of 371 GPCRs. The data were compared with public repositories and pharmacological databases to identify eligible drugs. The analysis of prognostic value of genes was also performed with TCGA datasets.

RESULTS

With our transcriptomic analysis, 4 receptors were found to be downregulated in FTC (VIPR1, ADGRL2/LPHN2, ADGRA3, and ADGRV1). In PTC, 24 receptors were deregulated, 7 of which were also identified by bioinformatics analyses of publicly available datasets on primary thyroid cancers (VIPR1, ADORA1, GPRC5B, P2RY8, GABBR2, CYSLTR2, and LPAR5). Among all the differentially expressed genes, 22 GPCRs are the target of approved drugs and some GPCRs are also associated with prognostic factors.

DISCUSSION

For the first time, we performed GPCR mRNA expression profiling in progressive and refractory thyroid cancers. These findings provide an opportunity to identify potential therapeutic targets for drug repositioning and precision medicine in radioiodine-refractory thyroid cancer.

Bombesin, endothelin, neurotensin and pituitary adenylate cyclase activating polypeptide cause tyrosine phosphorylation of receptor tyrosine kinases

Numerous peptides including bombesin (BB), endothelin (ET), neurotensin (NTS) and pituitary adenylate cyclase-activating polypeptide (PACAP) are growth factors for lung cancer cells. The peptides bind to G protein-coupled receptors (GPCRs) resulting in elevated cAMP and/or phosphatidylinositol (PI) turnover. In contrast, growth factors such as epidermal growth factor (EGF) or neuregulin (NRG)-1 bind to receptor tyrosine kinases (RTKs) such as the EGFR or HER3, increasing tyrosine kinase activity, resulting in the phosphorylation of protein substrates such as PI3K or phospholipase (PL)C. Peptide GPCRs can transactivate numerous RTKs, especially members of the EGFR/HER family resulting in increased phosphorylation of ERK, leading to cellular proliferation or increased phosphorylation of AKT, leading to cellular survival. GRCR antagonists and tyrosine kinase inhibitors are useful agents to prevent RTK transactivation and inhibit proliferation of cancer cells.

Endothelin-1-Mediated Drug Resistance in EGFR-Mutant Non-Small Cell Lung Carcinoma

Progression on therapy in non-small cell lung carcinoma (NSCLC) is often evaluated radiographically, however, image-based evaluation of said therapies may not distinguish disease progression due to intrinsic tumor drug resistance or inefficient tumor penetration of the drugs. Here we report that the inhibition of mutated EGFR promotes the secretion of a potent vasoconstrictor, endothelin-1 (EDN1), which continues to increase as the cells become resistant with a mesenchymal phenotype. As EDN1 and its receptor (EDNR) is linked to cancer progression, EDNR-antagonists have been evaluated in several clinical trials with disappointing results. These trials were based on a hypothesis that the EDN1-EDNR axis activates the MAPK-ERK signaling pathway that is vital to the cancer cell survival; the trials were not designed to evaluate the impact of tumor-derived EDN1 in modifying tumor microenvironment or contributing to drug resistance. Ectopic overexpression of EDN1 in cells with mutated EGFR resulted in poor drug delivery and retarded growth in vivo but not in vitro. Intratumoral injection of recombinant EDN significantly reduced blood flow and subsequent gefitinib accumulation in xenografted EGFR-mutant tumors. Furthermore, depletion of EDN1 or the use of endothelin receptor inhibitors bosentan and ambrisentan improved drug penetration into tumors and restored blood flow in tumor-associated vasculature. Correlatively, these results describe a simplistic endogenous yet previously unrealized resistance mechanism inherent to a subset of EGFR-mutant NSCLC to attenuate tyrosine kinase inhibitor delivery to the tumors by limiting drug-carrying blood flow and the drug concentration in tumors. SIGNIFICANCE: EDNR antagonists can be repurposed to improve drug delivery in VEGFA-secreting tumors, which normally respond to TKI treatment by secreting EDN1, promoting vasoconstriction, and limiting blood and drug delivery.

Blockade of endothelin receptor A enhances the therapeutic efficacy of gemcitabine in pancreatic cancer cells

Pancreatic adenocarcinoma is currently one of the leading causes of cancer-related death worldwide. The high rate of mortality in pancreatic cancer patients is due to the inability to detect early-stage disease and the disease being highly refractory to therapy. Gemcitabine has been the standard chemotherapy for advanced pancreatic cancer patients for the last two decades. However, gemcitabine resistance develops within a few weeks of treatment, and the associated mechanism remains poorly understood. Therefore, a novel therapeutic strategy is needed to overcome the limited clinical efficacy of gemcitabine in pancreatic adenocarcinoma. In this study, we demonstrated that ET-1/ETAR axis gene expression was upregulated in pancreatic cancer cells after treatment with gemcitabine. Additionally, ETAR expression was significantly higher in tumor tissues than in normal tissues, and patients with high ETAR expression had a notably worse overall survival rate than those with low ETAR expression. Furthermore, our results revealed that bosentan, an ETAR antagonist, enhanced the growth-inhibiting and proapoptotic effects of gemcitabine on pancreatic cancer cells. Thus, our findings indicate that blockade of the ET-1/ETAR axis signaling pathway promotes the antiproliferative effect of gemcitabine on pancreatic cancer. Therefore, combination of ETAR blockade and gemcitabine serves as an effective therapeutic approach to achieve clinical benefits in pancreatic adenocarcinoma patients.

Differences in Endothelin B Receptor Isoforms Expression and Function in Breast Cancer Cells

The endothelins and their receptors are best known for their regulation of the vascular system. Their widespread expression in epithelial cells and their overexpression in some tumors has prompted investigation into their ability to regulate cancer progression. In this study, we assessed the mRNA expression of the major endothelin B receptor gene (EDNRB) isoforms and found differences in both mRNA and protein expression in normal breast cells and breast cancer cell lines. Knocking down the EDNRB gene in breast cancer cells altered invasiveness toward endothelin 3 (ET3), and we observed EDNRB isoform-specific regulation of breast cancer cell invasion and cell signaling, as well as isoform- and subtype-specific differences in breast cancer patient survival. The results reported in this study emphasize the importance of the endothelin B receptor in breast cancer. To our knowledge, this study is the first to clarify the differential expression and roles of specific EDNRB isoforms in breast cancer.

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.

Influence of Adalimumab on the Expression Profile of Genes Associated with the Histaminergic System in the Skin Fibroblasts In Vitro

Objective

The aim of this study was to evaluate the influence of adalimumab on expression profile of genes associated with the histaminergic system in Normal Human Dermal Fibroblast (NHDF) cells stimulated with 8.00 μg/ml of adalimumab and the identification of miRNAs regulating these genes' expression.

Methods

NHDFs were cultured with or without the presence of adalimumab for 2, 8, and 24 hours. The expression profile of genes and miRNA were determined with the use of microarray technology.

Results

Among 22283 ID mRNA, 65 are associated with the histaminergic system. It can be observed that 15 mRNAs differentiate NHDFs cultures with adalimumab form control. The analysis of miRNAs showed that, among 1105 ID miRNA, 20 miRNAs are differentiating in cells treated with adalimumab for 2 hours, 9 miRNA after 8 hours, and only 3 miRNAs after 24 hours.

Conclusion

It was also determined that miRNAs play certain role in the regulation of the expression of genes associated with the histaminergic system. The results of this study confirmed the possibility of using both genes associated with this system as well as miRNAs regulating their expression, as complementary molecular markers of sensitivity to the adalimumab treatment.

RNA sequencing to determine the contribution of kinase receptor transactivation to G protein coupled receptor signalling in vascular smooth muscle cells

G protein coupled receptor (GPCR) signalling covers three major mechanisms. GPCR agonist engagement allows for the G proteins to bind to the receptor leading to a classical downstream signalling cascade. The second mechanism is via the utilization of the β-arrestin signalling molecule and thirdly via transactivation dependent signalling. GPCRs can transactivate protein tyrosine kinase receptors (PTKR) to activate respective downstream signalling intermediates. In the past decade GPCR transactivation dependent signalling was expanded to show transactivation of serine/threonine kinase receptors (S/TKR). Kinase receptor transactivation enormously broadens the GPCR signalling paradigm. This work utilizes next generation RNA-sequencing to study the contribution of transactivation dependent signalling to total protease activated receptor (PAR)-1 signalling. Transactivation, assessed as gene expression, accounted for 50 percent of the total genes regulated by thrombin acting through PAR-1 in human coronary artery smooth muscle cells. GPCR transactivation of PTKRs is approximately equally important as the transactivation of the S/TKR with 209 and 177 genes regulated respectively, via either signalling pathway. This work shows that genome wide studies can provide powerful insights into GPCR mediated signalling pathways.

Endothelin causes transactivation of the EGFR and HER2 in non-small cell lung cancer cells

Endothelin (ET)-1 is an important peptide in cancer progression stimulating cellular proliferation, tumor angiogenesis and metastasis. ET-1 binds with high affinity to the ET_A receptor (R) and ET_BR on cancer cells. High levels of tumor ET-1 and ET_AR are associated with poor survival of lung cancer patients. Here the effects of ET-1 on epidermal growth factor (EGF)R and HER2 transactivation were investigated using non-small cell lung cancer (NSCLC) cells. ET_AR mRNA was present in all 10 NSCLC cell lines examined. Addition of ET-1 to NCI-H838 or H1975 cells increased EGFR, HER2 and ERK tyrosine phosphorylation within 2min. The increase in EGFR and HER2 transactivation caused by ET-1 addition to NSCLC cells was inhibited by lapatinib (EGFR and HER2 tyrosine kinase inhibitor (TKI)), gefitinib (EGFR TKI), ZD4054 or BQ-123 (ET_AR antagonist), GM6001 (matrix metalloprotease inhibitor), PP2 (Src inhibitor) or Tiron (superoxide scavenger). ET-1 addition to NSCLC cells increased cytosolic Ca²⁺ and reactive oxygen species. ET-1 increased NSCLC clonal growth, whereas BQ123, ZD4054, lapatinib or gefitinib inhibited proliferation. The results indicate that ET-1 may regulate NSCLC cellular proliferation in an EGFR- and HER2-dependent manner.

Signaling via G proteins mediates tumorigenic effects of GPR87

G protein-coupled receptors (GPCRs) constitute a large protein family of seven transmembrane (7TM) spanning proteins that regulate multiple physiological functions. GPR87 is overexpressed in several cancers and plays a role in tumor cell survival. Here, the basal activity of GPR87 was investigated in transiently transfected HEK293 cells, revealing ligand-independent coupling to Gα_i, Gα_q and Gα_12/13. Furthermore, GPR87 showed a ligand-independent G protein-dependent activation of the downstream transcription factors CREB, NFκB, NFAT and SRE. In tetracycline-induced Flp-In T-Rex-293 cells, GPR87 induced cell clustering presumably through Gα_12/13 coupling. In a foci formation assay using retrovirally transduced NIH3T3 cells, GPR87 showed a strong in vitro transforming potential, which correlated to the in vivo tumor induction in nude mice. Importantly, we demonstrate that the transforming potential of GPR87 was correlated to the receptor signaling, as the signaling-impaired mutant R139A (Arg in the conserved "DRY"-motif at the bottom of transmembrane helix 3 of GPR87 substituted to Ala) showed a lower in vitro cell transformation potential. Furthermore, R139A lost the ability to induce cell clustering. In summary, we show that GPR87 is active through several signaling pathways and that the signaling activity is linked to the receptor-induced cell transformation and clustering. The robust surface expression of GPR87 and general high druggability of GPCRs make GPR87 an attractive future anticancer target for drugs that - through inhibition of the receptor signaling - will inhibit its transforming properties.

Salvianolic Acid A, as a Novel ETA Receptor Antagonist, Shows Inhibitory Effects on Tumor in Vitro

Endothelin-1 (ET-1) autocrine and paracrine signaling modulate cell proliferation of tumor cells by activating its receptors, endothelin A receptor (ET_AR) and endothelin B receptor (ET_BR). Dysregulation of ET_AR activation promotes tumor development and progression. The potential of ET_AR antagonists and the dual-ET_AR and ET_BR antagonists as therapeutic approaches are under preclinical and clinical studies. Salvianolic acid A (Sal A) is a hydrophilic polyphenolic derivative isolated from Salvia miltiorrhiza Bunge (Danshen), which has been reported as an anti-cancer and cardio-protective herbal medicine. In this study, we demonstrate that Sal A inhibits ET_AR activation induced by ET-1 in both recombinant and endogenous ET_AR expression cell lines. The IC₅₀ values were determined as 5.7 µM in the HEK293/ET_AR cell line and 3.14 µM in HeLa cells, respectively. Furthermore, our results showed that Sal A suppressed cell proliferation and extended the doubling times of multiple cancer cells, including HeLa, DU145, H1975, and A549 cell lines. In addition, Sal A inhibited proliferation of DU145 cell lines stimulated by exogenous ET-1 treatment. Moreover, the cytotoxicity and cardio-toxicity of Sal A were assessed in human umbilical vein endothelial cells (HUVEC) and Human-induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs), which proved that Sal A demonstrates no cytotoxicity or cardiotoxicity. Collectively, our findings indicate that Sal A is a novel anti-cancer candidate through targeting ET_AR.

Proteomic analysis of ovarian cancer cells during epithelial-mesenchymal transition (EMT) induced by epidermal growth factor (EGF) reveals mechanisms of cell cycle control

Epithelial to mesenchymal transition (EMT) is a well-orchestrated process that culminates with loss of epithelial phenotype and gain of a mesenchymal and migratory phenotype. EMT enhances cancer cell invasiveness and drug resistance, favoring metastasis. Dysregulation of transcription factors, signaling pathways, miRNAs and growth factors including EGF, TGF-beta and HGF can trigger EMT. In ovarian cancer, overexpression of the EGFR family is associated with more aggressive clinical behavior. Here, the ovarian adenocarcinoma cell line Caov-3 was induced to EMT with EGF in order to identify specific mechanisms controlled by this process. Caov-3 cells induced to EMT were thoroughly validated and a combination of subcellular proteome enrichment, GEL-LC-MS/MS and SILAC strategy allowed consistent proteome identification and quantitation. Protein network analysis of differentially expressed proteins highlighted regulation of metabolism and cell cycle. Activation of relevant signaling pathways, such as PI3K/Akt/mTOR and Ras/Erk MAPK, in response to EGF-induced EMT was validated. Also, EMT did not affected the proliferation rate of Caov-3 cells, but led to cell cycle arrest in G1 phase regulated by increased levels of p21Waf1/Cip1, independently of p53. Furthermore, a decrease in G1 and G2 checkpoint proteins was observed, supporting the involvement of EGF-induced EMT in cell cycle control.

BIOLOGICAL SIGNIFICANCE

Cancer is a complex multistep process characterized by accumulation of several hallmarks including epithelial to mesenchymal transition (EMT), which promotes cellular and microenvironmental changes resulting in invasion and migration to distant sites, favoring metastasis. EMT can be triggered by different extracellular stimuli, including growth factors such as EGF. In ovarian cancer, the most lethal gynecological cancer, overexpression of the EGFR family is associated with more aggressive clinical behavior, increasing mortality rate caused by metastasis. Our proteomic data, together with specific validation of specific cellular mechanisms demonstrated that EGF-induced EMT in Caov-3 cells leads to important alterations in metabolic process (protein synthesis) and cell cycle control, supporting the implication of EGF/EMT in cancer metastasis, cancer stem cell generation and, therefore, poor prognosis for the disease.

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.

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.

A Phase II, randomized, double-blind study of zibotentan (ZD4054) in combination with carboplatin/paclitaxel versus placebo in combination with carboplatin/paclitaxel in patients with advanced ovarian cancer sensitive to platinum-based chemotherapy (AGO-OVAR 2.14)

BACKGROUND

In platinum-sensitive relapsed ovarian cancer, paclitaxel plus carboplatin is a standard second-line treatment. Zibotentan (ZD4054) is an oral, specific ETA-receptor antagonist with demonstrated antitumour activity in xenograft models of human ovarian cancer.

METHODS

In this Phase II, randomized, placebo-controlled study, patients with relapsed ovarian cancer sensitive to platinum-based chemotherapy received zibotentan 10mg or placebo once-daily, plus paclitaxel 175 mg/m(2) iv followed by carboplatin iv (AUC 5) on day 1 of every 3-week cycle for a maximum of eight cycles. The primary endpoint was progression-free survival (PFS), evaluated by Response Evaluation Criteria In Solid Tumours (RECIST). Secondary and exploratory endpoints included objective tumour response rate, tumour size, CA-125/RECIST progression, and safety and tolerability.

RESULTS

A total of 120 patients were randomized (zibotentan: n=59; placebo: n=61). Addition of zibotentan 10mg/day to carboplatin and paclitaxel did not improve PFS compared with placebo (median PFS, 7.6 versus 10.0 months, respectively; HR=1.46, [80% CI: 1.10-1.94]; P=0.0870). No improvements in any of the secondary or exploratory efficacy endpoints were observed for patients receiving zibotentan compared with placebo. Median duration of total treatment exposure was 6.7 months. Total chemotherapy dose received was lower for zibotentan-treated versus placebo-treated patients (carboplatin: -16%; paclitaxel: -14%). The most common adverse events in the zibotentan arm were anaemia, nausea, alopecia, headache and neutropenia (43-48% of patients).

CONCLUSIONS

Zibotentan 10mg/day plus carboplatin and paclitaxel did not result in an improvement in PFS compared with chemotherapy alone in patients with advanced ovarian cancer sensitive to platinum-based chemotherapy. No unexpected safety concerns were identified.

Permissive role of endothelin receptors in tumor metastasis

Metastasis remains the major driver of mortality in patients with cancer. The multistep metastatic process requires the concerted actions of several genes and involves tumor cell invasion, epithelial mesenchymal transition (EMT), shedding from primary tumor, intravasation, arrest, extravasation and colonization at a preferential site. Understanding this complex process would provide the basis for the development of molecularly targeted therapeutics aimed at the tumor cell or its interaction with the host microenvironment. The neuropeptide hormones endothelins (specially, ET-1) have been correlated with invasiveness and metastasis of several cancers and high ET-1 levels are associated with decreased disease-specific survival. The mechanism(s) by which ET-1 promotes metastasis are being gradually unraveled. Through preferential binding to cognate receptors (ET(A)R or ET(B)R), ET-1 triggers autocrine and paracrine signaling cascades in tumor, immune and stromal cells, at both primary and distant sites, supporting cancer progression and metastasis. In this review, we will summarize the role of the ET axis in metastasis of different cancers and potential targeting of ET receptors in the therapeutic setting.

The endothelin axis in uterine leiomyomas: new insights

The endothelin axis, comprising endothelin-1 (ET-1) and its receptors (ETA and ETB), is involved in the pathophysiology of different human tumors. Here we review conventional approaches and gene expression profiling indicating the association of ET-1 and its cognate receptors with human and rat leiomyomas, the most common benign tumors of myometrium. Specifically, ET-1/ETA interactions affect human and rat leiomyoma cell proliferation through protein kinase C and mitogen-activated protein kinase-dependent signaling pathways. Recent experiments demonstrate that the ET-1 axis exerts a potent antiapoptotic effect involving sphingolipid metabolism and prostaglandin-endoperoxide synthase 2/prostaglandin system in the rat Eker leiomyoma tumor-derived ELT3 cell line. Evidence supports that steroid hormones, growth factors, and extracellular matrix are key regulators of the leiomyoma growth. Interestingly, the ET-1 axis is under steroid hormones and can cooperate with these growth factors. Therefore, ET-1 alone or in association with these factors could contribute to the complex regulation of uterine tumor growth, such as proliferation, survival, and extracellular matrix production. This review summarizes current knowledge and emerging data on ET-1 in uterine leiomyoma pathology.

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.

The endothelin A receptor and epidermal growth factor receptor signaling converge on β-catenin to promote ovarian cancer metastasis

AIMS

Endothelin A receptor (ET(A)R) and epidermal growth factor receptor (EGFR) cross-talk enhances the metastatic potential of epithelial ovarian cancer (EOC) cells activating different pathways, including β-catenin signalling. Here, we evaluated β-catenin as one of ET(A)R/EGFR downstream pathway in the invasive behaviour of EOC cells and their therapeutic potential to co-target ET(A)R and EGFR.

MAIN METHODS

The phosphorylation status and interactions of different proteins were analysed by immunoblotting and immunoprecipitation. Reporter activity and RT-PCR was used for evaluation of β-catenin transcriptional activity and gene expression. Functional effects were evaluated by gelatin zymography and cell invasion assays. An orthotopic model of metastatic human EOC in mice was used for in vivo studies.

KEY FINDINGS

In EOC cell lines, ET-1 induced Src-dependent EGFR transactivation, causing tyrosine (Y) phosphorylation of β-catenin at the residue Y654, its dissociation from E-cadherin complexes and the accumulation as an active form. This pool of Tyr-β-catenin relocalised to the nucleus promoting its transcriptional activity, and the expression of its target genes, such as MMP-2. At functional level, ET-1 and EGFR circuits enhanced protease activity and cell invasion. All these effects were significantly inhibited by the ET(A)R antagonist, zibotentan, or EGFR inhibitor, gefitinib, and are completely blocked by co-addition of both drugs. In vivo, zibotentan treatment significantly inhibited metastases, associated with reduced expression and activation of MMPs and active β-catenin, especially when combined with gefitinib.

SIGNIFICANCE

Altogether these findings provide additional support to the potential use of ET(A)R and EGFR blockade as a new therapeutic opportunity for EOC treatment.

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.

(-)-Epigallocatechin-3-gallate down-regulates EGFR, MMP-2, MMP-9 and EMMPRIN and inhibits the invasion of MCF-7 tamoxifen-resistant cells

The activation of the EGFR (epidermal growth factor receptor) signalling pathway is one of the key mechanisms underlying the development of resistance to tamoxifen in breast cancer patients. As EGCG [(-)-epigallocatechin-3-gallate], the most active catechin present in green tea, has been shown to down-regulate EGFR, we studied the effects of 10-100 μg/ml EGCG treatment on growth and invasion in a breast carcinoma cell line resistant to tamoxifen [MCF-7Tam (MCF-7 breast carcinoma cell line resistant to tamoxifen) cells] and parental MCF-7. A dose-dependent down-regulation of EGFR mRNA expression and protein level occurred after 50 μg/ml EGCG treatment of MCF-7Tam cells. EGFR molecules on the plasma membrane surface of MCF-7Tam cells significantly decreased. EGFR phosphorylation (Tyr-992, Tyr-1045 and Tyr-1068) was higher in MCF-7Tam than in MCF-7 and it was reduced by EGCG treatment. ERK (extracellular regulated kinase) and phospho-ERK p42/44 were also down-regulated by EGCG treatment and in vitro cell growth and invasion decreased. MMP-2 (matrix metalloproteinase-2) and MMP-9, which are implicated in cell invasion and metastasis, and EMMPRIN (extracellular matrix metalloproteinase inducer), a glycoprotein able to activate MMPs, were significantly reduced after 50 μg/ml EGCG treatment. In keeping with this, TIMP-1 (tissue inhibitor of metalloproteinases-1) and TIMP-2, which down-regulate MMPs, increased after EGCG treatment. Altogether, the present data demonstrated that EGCG could attenuate the tamoxifen-resistant phenotype of MCF-7Tam cells. EGCG could stop MCF-7Tam cell growth and in vitro invasion through down-regulation of EGFR and other molecules implicated in aggressive biological behaviour. The present data support the hypothesis that EGCG is an interesting molecule to be investigated in tamoxifen-resistant breast carcinoma.

Combination therapy of zibotentan with cisplatinum and paclitaxel is an effective regimen for epithelial ovarian cancer

In human ovarian carcinoma, the endothelin-1 (ET-1) / endothelin A receptor (ETAR) axis is overexpressed, correlating with tumor grade. Moreover, ETAR activation by ET-1 affects cell proliferation, survival, angiogenesis, and invasion. ETAR blockade with zibotentan (ZD4054), a specific ETAR antagonist, significantly inhibits ovarian cancer growth in vitro and in vivo, underscoring the relevance of this pathway as a target for cancer therapy. Since clinical trial results have defined the combination of platinum and taxane as the standard of care in the management of ovarian cancer, here we explored the therapeutic efficacy of the integration of zibotentan with cytotoxic drugs having different modes of action. We found that the combination of zibotentan with cisplatinum as well as zibotentan with paclitaxel was more effective at inhibiting ovarian cancer HEY cell proliferation induced by endogenous ET-1 than were the single agents alone. However, a significantly enhanced efficacy was observed when we combined zibotentan, cisplatinum, and paclitaxel. Accordingly, in HEY xenografts the coadministration of zibotentan with cisplatinum enhanced the efficacy of the cytotoxic drug alone in controlling tumor growth, associated with reduction in proliferation index and microvessel density. Remarkably, the combination of zibotentan with both cisplatinum and paclitaxel was very effective in inhibiting tumor growth, neovascularization, and cell proliferation, representing a preclinical endpoint to guide combination therapy in clinical trials.

G protein-coupled receptors: novel targets for drug discovery in cancer

G protein-coupled receptors (GPCRs) belong to a superfamily of cell surface signalling proteins that have a pivotal role in many physiological functions and in multiple diseases, including the development of cancer and cancer metastasis. Current drugs that target GPCRs - many of which have excellent therapeutic benefits - are directed towards only a few GPCR members. Therefore, huge efforts are currently underway to develop new GPCR-based drugs, particularly for cancer. We review recent findings that present unexpected opportunities to interfere with major tumorigenic signals by manipulating GPCR-mediated pathways. We also discuss current data regarding novel GPCR targets that may provide promising opportunities for drug discovery in cancer prevention and treatment.

Tumor endothelin-1 enhances metastatic colonization of the lung in mouse xenograft models of bladder cancer

Many patients with advanced bladder cancer develop lethal metastases to the lung. The vasoconstricting protein endothelin-1 (ET-1) has been implicated in this process, although the mechanism(s) by which it promotes metastasis remains unclear. Here, we have evaluated whether tumor ET-1 expression can serve as a biomarker for lung metastasis and whether it is required for metastatic disease. Evaluation of ET-1 mRNA and protein expression in four patient cohorts revealed that levels of ET-1 are higher in patients with muscle-invasive bladder cancers, which are associated with higher incidence of metastasis, and that high ET-1 levels are associated with decreased disease-specific survival. Consistent with its proinflammatory activity, we found that tumor-derived ET-1 acts through endothelin-1 receptor A (ETAR) to enhance migration and invasion of both tumor cells and macrophages and induces expression of inflammatory cytokines and proteases. Using human and mouse cancer cells depleted of ET-1 and pharmacologic blockade of ET receptors in lung metastasis models, we found that tumor ET-1 expression and ETAR activity are necessary for metastatic lung colonization and that this process is preceded by and dependent on macrophage infiltration of the lung. In contrast, tumor ET-1 expression and ETAR activity appeared less important in established primary or metastatic tumor growth. These findings strongly suggest that ETAR inhibitors might be more effective as adjuvant therapeutic agents than as initial treatment for advanced primary or metastatic disease.

The importance of endothelin axis in initiation, progression, and therapy of ovarian cancer

The endothelin-1 (ET-1)/ET A receptor (ET(A)R) axis is involved in the pathobiology of different tumors, including ovarian carcinoma. Acting selectively on ET(A)R, ET-1 regulates, through multiple signaling pathways, mitogenesis, cell survival, angiogenesis, lymphangiogenesis, invasion, and metastatic dissemination. Moreover, ET-1/ET(A)R axis appears to be critical in epithelial-to-mesenchymal transition (EMT), providing a mechanism of escape to a new, less adverse niche, in which resistance to apoptosis ensures cell survival in conditions of stress in the primary tumor, and acquisition of "stemness" ensures generation of the critical mass required for tumor progression. Emerging experimental and preclinical data demonstrate that interfering with ET(A)R pathways provides an opportunity for the development of new mechanism-based antitumor strategies by using ET(A)R antagonists alone and in combination with cytotoxic drugs or molecular inhibitors. A specific ET(A)R antagonist in combination with standard chemotherapy is currently evaluated in clinical and translational studies to provide us with new options to treat ovarian cancer and to predict response to therapy. Deeper understanding of molecular mechanism activated by ET(A)R in ovarian cancer will be of paramount importance in the study of ET(A)R-targeted therapy that, regulating EMT and other tumor-associated processes, represents an attractive but challenging approach to improve clinical management of ovarian cancer.

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.

Targeting the epidermal growth factor receptor in epithelial ovarian cancer: current knowledge and future challenges

The epidermal growth factor receptor is overexpressed in up to 60% of ovarian epithelial malignancies. EGFR regulates complex cellular events due to the large number of ligands, dimerization partners, and diverse signaling pathways engaged. In ovarian cancer, EGFR activation is associated with increased malignant tumor phenotype and poorer patient outcome. However, unlike some other EGFR-positive solid tumors, treatment of ovarian tumors with anti-EGFR agents has induced minimal response. While the amount of information regarding EGFR-mediated signaling is considerable, current data provides little insight for the lack of efficacy of anti-EGFR agents in ovarian cancer. More comprehensive, systematic, and well-defined approaches are needed to dissect the roles that EGFR plays in the complex signaling processes in ovarian cancer as well as to identify biomarkers that can accurately predict sensitivity toward EGFR-targeted therapeutic agents. This new knowledge could facilitate the development of rational combinatorial therapies to sensitize tumor cells toward EGFR-targeted therapies.

Antivascular therapy for epithelial ovarian cancer

Ovarian cancer is the fifth largest cancer killer in women. Improved understanding of the molecular pathways implicated in the pathogenesis of ovarian cancer has led to the investigation of novel targeted therapies. Ovarian cancer is characterized by an imbalance between pro- and antiangiogenic factors in favor of angiogenesis activation. Various antivascular strategies are currently under investigation in ovarian cancer. They can schematically be divided into antiangiogenic and vascular-disrupting therapies. This paper provides a comprehensive review of these new treatments targeting the tumor vasculature in this disease. Promising activities have been detected in phase II trials, and results of phase III clinical trials are awaited eagerly.

Angiogenesis inhibition in the treatment of prostate cancer

For many men, prostate cancer is an indolent disease that, even without definitive therapy, may have no impact on their quality of life or overall survival. However for those men who are either diagnosed with or eventually develop metastatic disease, prostate cancer is a painful and universally fatal disease. Testosterone-lowering hormonal therapy may control the disease for some time, but patients eventually develop resistance and progress clinically. At this point, only docetaxel has been shown to improve survival, so clearly additional therapeutic options are needed. Angiogenesis inhibition is an active area of clinical research in prostate cancer. Without angiogenesis, tumors have insufficient nutrients and oxygen to grow larger than a few millimeters and are potentially less likely to metastasize. In prostate cancer in particular, angiogenesis plays a significant role in tumor proliferation, and markers of angiogenesis appear to have prognostic significance. Several different compounds have been developed to inhibit angiogenesis, including monoclonal antibodies, multitargeted kinase inhibitors, and fusion proteins. In addition, more traditional agents may also have an impact on angiogenesis. Trials studying antiangiogenic agents have been conducted in localized and advanced prostate cancer. There are several large, ongoing phase III trials in metastatic castration-resistant prostate cancer. The findings of these and future studies will ultimately determine the role of angiogenesis inhibitors in the treatment of prostate cancer.

ETAR antagonist ZD4054 exhibits additive effects with aromatase inhibitors and fulvestrant in breast cancer therapy, and improves in vivo efficacy of anastrozole

Endothelin-1 (ET-1) and endothelin A receptor (ETAR) contribute to the development and progression of breast carcinomas by modulating cell proliferation, angiogenesis, and anti-apoptosis. We investigated antitumoral effects of the specific ETAR antagonist ZD4054 in breast cancer cells and xenografts, and assessed antitumoral efficacy of the combinations of ZD4054 with aromatase inhibitors and fulvestrant. Gene expression changes were assessed by quantitative real-time PCR. Cell proliferation was measured using alamarBlue; migration and invasion assays were performed using modified Boyden chambers. Evaluating the antitumoral efficacy of ZD4054 in vivo, different breast cancer models were employed using nude mice xenografts. ZD4054 reduced ET-1 and ETAR expression in MCF-7, MDA-MB-231, and MDA-MB-468 breast cancer cells in a concentration-dependent manner. ZD4054 inhibited invasion by up to 37.1% (P = 0.022). Combinations of ZD4054 with either anastrozole or letrozole produced significant reductions in migration of aromatase-overexpressing MCF-7aro cells (P < 0.05). Combination of ZD4054 with fulvestrant reduced MCF-7 cell migration and invasion by 36.0% (P = 0.027) and 56.7% (P < 0.001), respectively, with effects significantly exceeding those seen with either compound alone. Regarding tumor volume reduction in vivo, ZD4054 (10 mg/kg) was equipotent to fulvestrant (200 mg/kg) and exhibited additive effects with anastrozole (0.5 mg/kg). These data are the first indicating that selective ETAR antagonism by ZD4054 displays antitumoral activity on breast cancer cells in vitro and in vivo. Our data strongly support a rationale for the clinical use of ZD4054 in combination with endocrine therapies.

Epidermal growth factor-induced GnRH-II synthesis contributes to ovarian cancer cell invasion

GnRH-II modulates ovarian cancer cells invasion and is expressed in normal ovary and ovarian epithelial cancer cells; however, the upstream regulator(s) of GnRH-II expression in these cells remains unclear. We now demonstrate that epidermal growth factor (EGF) increases GnRH-II mRNA levels in several human ovarian carcinoma cell lines and up-regulates GnRH-II promoter activity in OVCAR-3 cells in a dose-dependent manner, whereas an EGF receptor inhibitor (AG148) abolishes EGF-induced increases in GnRH-II promoter activity and GnRH-II mRNA levels. EGF increases the phosphorylation of cAMP-responsive element-binding protein (p-CREB) and its association with the coregulator, CCAAT/enhancer binding protein beta, whereas blocking the EGF-induced ERK1/2 phosphorylation with MAPK inhibitors (PD98059/U0126) markedly reduced these effects. Moreover, depletion of CREB using small interfering RNA attenuated EGF-induced GnRH-II promoter activity. Chromatin immunoprecipitation assays demonstrated that EGF induces p-CREB binding to a cAMP responsive-element within the GnRH-II promoter, likely in association with CCAAT/enhancer binding protein beta, and mutagenesis of this cAMP responsive-element prevented EGF-induced GnRH-II promoter activity in OVCAR-3 cells. Importantly, GnRH-II acts additively with EGF to promote invasion of OVCAR-3 and CaOV-3 cells, but not SKOV-3 cells that express low levels of GnRH receptor (GnRHR). Treatment with GnRHR small interfering RNA also partially inhibited the EGF-induced invasion of OVCAR-3 and CaOV-3 cells. Furthermore, EGF treatment transiently increases GnRHR levels in OVCAR-3 and CaOV-3, which likely accentuates the effects of increase GnRH-II production on cell invasion. These results provide evidence that EGF is an upstream regulator of the autocrine actions of GnRH-II on the invasive properties of ovarian cancer cells.

EGF-receptor regulation of matrix metalloproteinases in epithelial ovarian carcinoma

Ovarian carcinoma is most frequently detected when disease has already disseminated intra-abdominally, resulting in a 5-year survival rate of less than 20% owing to complications of metastasis. Peritoneal ascites is often present, establishing a unique microenvironmental niche comprised of tumor and inflammatory cells, along with a wide range of bioactive soluble factors, several of which stimulate the EGF-receptor (EGFR). Elevated EGFR is associated with less favorable disease outcome in ovarian cancer, related in part to EGFR activation of signaling cascades that lead to enhanced matrix metalloproteinase expression and/or function. The available data suggest that modulating the expression or activity of the EGFR and/or matrix metalloproteinases offers opportunity for targeted intervention in patients with metastatic disease.

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.

Preclinical anticancer activity of the specific endothelin A receptor antagonist ZD4054

Endothelins are a family of small peptides (ET-1, ET-2, and ET-3) that mediate various physiological processes of mitogenesis, repair, and tissue differentiation by binding to endothelin A (ETA) and endothelin B (ETB) cell surface receptors. Activation of the ETA receptor by ET-1 has emerged as an important factor promoting tumor cell proliferation, survival, angiogenesis, migration, invasion, and metastasis in several tumor types including prostate, ovary, colon, cervix, breast, and lung. As activation of the ETB receptor has an opposing effect, inducing cell death by apoptosis, a rationale exists for specific antagonism of the ETA receptor as a treatment strategy for cancer. ZD4054 is a specific ETA receptor antagonist currently being evaluated in hormone-resistant prostate cancer in phase III clinical trials. In vitro, ZD4054 reversed ET-1-mediated inhibition of apoptosis in serum-deprived rat A10 and human VLTR-16 cells in a concentration-dependent manner. ZD4054 inhibited ET-1-mediated survival signaling pathways and decreased proliferation in ovarian OVCA 433 and HEY cells and in prostate PPC-1 and LAPC-4 cells. In A673 rhabdomyosarcoma cells, ET-1-induced phosphorylation of FAK, FAK, and paxillin was reversed with ZD4054, inhibiting the invasive phenotype mediated by these adhesion factors. In vivo, ZD4054 led to a significant reduction in tumor growth in animals bearing ovarian tumor xenografts, and significantly inhibited tumor angiogenesis. Pretreatment with ZD4054 also significantly delayed the onset of metastatic events after intracardiac injection of bladder TSU-Pr1-B1 cells in mice. These preclinical data show the potential anticancer effects of the specific blockade of the ETA receptor with ZD4054, supporting a program of clinical investigation.

Endothelin receptors and pain

The endogenous endothelin (ET) peptides participate in a remarkable variety of pain-relatedprocesses. Pain that is elevated by inflammation, by skin incision, by cancer, during a Sickle Cell Disease crisis and by treatments that mimic neuropathic and inflammatory pain and are all reduced by local administration of antagonists of endothelin receptors. Many effects of endogenously released endothelin are simulated by acute, local subcutaneous administration of endothelin, which at very high concentrations causes pain and at lower concentrations sensitizes the nocifensive reactions to mechanical, thermal and chemical stimuli.

PERSPECTIVE

In this paper we review the biochemistry, second messenger pathways and hetero-receptor coupling that are activated by ET receptors, the cellular physiological responses to ET receptor activation, and the contribution to pain of such mechanisms occurring in the periphery and the CNS. Our goal is to frame the subject of endothelin and pain for a broad readership, and to present the generally accepted as well as the disputed concepts, including important unanswered questions.

Beta-arrestin links endothelin A receptor to beta-catenin signaling to induce ovarian cancer cell invasion and metastasis

The activation of endothelin-A receptor (ET(A)R) by endothelin-1 (ET-1) has a critical role in ovarian tumorigenesis and progression. To define the molecular mechanism in ET-1-induced tumor invasion and metastasis, we focused on beta-arrestins as scaffold and signaling proteins of G protein-coupled receptors. Here, we demonstrate that, in ovarian cancer cells, beta-arrestin is recruited to ET(A)R to form two trimeric complexes: one through the interaction with Src leading to epithelial growth factor receptor (EGFR) transactivation and beta-catenin Tyr phosphorylation, and the second through the physical association with axin, contributing to release and inactivation of glycogen synthase kinase (GSK)-3beta and beta-catenin stabilization. The engagement of beta-arrestin in these two signaling complexes concurs to activate beta-catenin signaling pathways. We then demonstrate that silencing of both beta-arrestin-1 and beta-arrestin-2 inhibits ET(A)R-driven signaling, causing suppression of Src, mitogen-activated protein kinase (MAPK), AKT activation, as well as EGFR transactivation and a complete inhibition of ET-1-induced beta-catenin/TCF transcriptional activity and cell invasion. ET(A)R blockade with the specific ET(A)R antagonist ZD4054 abrogates the engagement of beta-arrestin in the interplay between ET(A)R and the beta-catenin pathway in the invasive program. Finally, ET(A)R is expressed in 85% of human ovarian cancers and is preferentially co-expressed with beta-arrestin-1 in the advanced tumors. In a xenograft model of ovarian metastasis, HEY cancer cells expressing beta-arrestin-1 mutant metastasize at a reduced rate, highlighting the importance of this molecule in promoting metastases. ZD4054 treatment significantly inhibits metastases, suggesting that specific ET(A)R antagonists, by disabling multiple signaling activated by ET(A)R/beta-arrestin, may represent new therapeutic opportunities for ovarian cancer.

Cross talk of signals between EGFR and IL-6R through JAK2/STAT3 mediate epithelial-mesenchymal transition in ovarian carcinomas

Epidermal growth factor receptor (EGFR) is overexpressed in ovarian carcinomas, with direct or indirect activation of EGFR able to trigger tumour growth. We demonstrate significant activation of both signal transducer and activator of transcription (STAT)3 and its upstream activator Janus kinase (JAK)2, in high-grade ovarian carcinomas compared with normal ovaries and benign tumours. The association between STAT3 activation and migratory phenotype of ovarian cancer cells was investigated by EGF-induced epithelial–mesenchymal transition (EMT) in OVCA 433 and SKOV3 ovarian cancer cell lines. Ligand activation of EGFR induced a fibroblast-like morphology and migratory phenotype, consistent with the upregulation of mesenchyme-associated N-cadherin, vimentin and nuclear translocation of β-catenin. This occurred concomitantly with activation of the downstream JAK2/STAT3 pathway. Both cell lines expressed interleukin-6 receptor (IL-6R), and treatment with EGF within 1 h resulted in a several-fold enhancement of mRNA expression of IL-6. Consistent with that, EGF treatment of both OVCA 433 and SKOV3 cell lines resulted in enhanced IL-6 production in the serum-free medium. Exogenous addition of IL-6 to OVCA 433 cells stimulated STAT3 activation and enhanced migration. Blocking antibodies against IL-6R inhibited IL-6 production and EGF- and IL-6-induced migration. Specific inhibition of STAT3 activation by JAK2-specific inhibitor AG490 blocked STAT3 phosphorylation, cell motility, induction of N-cadherin and vimentin expression and IL6 production. These data suggest that the activated status of STAT3 in high-grade ovarian carcinomas may occur directly through activation of EGFR or IL-6R or indirectly through induction of IL-6R signalling. Such activation of STAT3 suggests a rationale for a combination of anti-STAT3 and EGFR/IL-6R therapy to suppress the peritoneal spread of ovarian cancer.

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.