Endothelin receptors as novel targets in tumor therapy

Molecular landscape of prostate cancer bone metastasis

Prostate cancer (PC) has a high propensity to develop bone metastases, causing severe pain and pathological fractures that profoundly impact a patients' normal functions. Current clinical intervention is mainly palliative focused on pain management, and tumor progression is refractory to standard therapeutic regimens. This limited treatment efficacy is at least partially due to a lack of comprehensive understanding of the molecular landscape of the disease pathology, along with the intensive overlapping of physiological and pathological molecular signaling. The niche is overwhelmed with diverse cell types with inter- and intra-heterogeneity, along with growth factor-enriched cells that are supportive of invading cell proliferation, providing an additional layer of complexity. This review seeks to provide molecular insights into mechanisms underlying PC bone metastasis development and progression.

Identification of EDNRA as the Key Biomarker for Hypercholesterolemia and Colorectal Cancer

Some studies have investigated the role of cholesterol in the progression of colorectal cancer (CRC). However, the underlying mechanism of action is not clear. In this study, we used bioinformatics tools to elucidate the molecular mechanisms involved. We initially obtained CRC datasets from the Gene Expression Omnibus (GEO) database and hypercholesterolemia data from GeneCards and DisGeNE. Common differentially expressed genes (DEGs) were determined by using Venn diagram web tools. Next, we performed Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses using the Database for Annotation, Visualization, and Integrated Discovery (DAVID). The hub gene was identified through common expression pattern analysis and survival analysis. Finally, we conducted an immune regulatory point analysis and predicted target drugs based on the hub gene. The results of our analysis revealed 13 common DEGs, with endothelin receptor type A (EDNRA) identified as the hub gene linking hypercholesterolemia and CRC. The results of the GO analysis showed that the common DEGs were primarily associated with the G-protein coupled receptor signaling pathway, extracellular space, and receptor binding. The results of the KEGG pathway enrichment analysis indicated enrichment in pathways related to cancer and the phospholipase D signaling pathway. Additionally, we identified potential target drugs, including Podocarpus montanus, Diospyros kaki, Herba Salviae japoniae, sitaxentan, and ambrisentan. We found that EDNRA might be an underlying biomarker for both hypercholesterolemia and CRC. The predicted target drugs provide new strategies for treating CRC.

Conversion of raltegravir carrying a 1,3,4-oxadiazole ring to a hydrolysis product upon pH changes decreases its antiviral activity

Raltegravir (RAL), a human immunodeficiency virus (HIV)-1 integrase inhibitor, has been administered as part of antiretroviral therapy. Studies in patients with HIV-1 have shown high variability in the pharmacokinetics of RAL, and in healthy volunteers, coadministration of proton-pump inhibitors has been shown to increase the plasma RAL concentrations. Here, we found that RAL containing a 1,3,4-oxadiazole ring is converted to a hydrolysis product (H-RAL) with a cleaved 1,3,4-oxadiazole ring at pH 1.0 and 13.0 conditions in vitro, thereby reducing the anti-HIV activity of the drug. The inclusion of cyclodextrins (beta-cyclodextrin [βCD], random methyl-βCD [RAM-βCD], and hydroxypropyl-βCD [HP-βCD]) can protect RAL from pH-induced changes. The conversion of RAL to H-RAL was detected by using various mass spectrometry analyses. The chromatogram of H-RAL increased in a time-dependent manner similar to another 1,3,4-oxadiazole-containing drug, zibotentan, using high-performance liquid chromatography. Oral bioavailability and target protein interactions of H-RAL were predicted to be lower than those of RAL. Moreover, H-RAL exhibited significantly reduced anti-HIV-1 activity, whereas combinations with βCD, RAM-βCD, and HP-βCD attenuated this effect in cell-based assays. These findings suggest that βCDs can potentially protect against the conversion of RAL to H-RAL under acidic conditions in the stomach, thereby preserving the anti-HIV-1 effect of RAL. Although clinical trials are needed for evaluation, we anticipate that protective devices such as βCDs may improve the pharmacokinetics of RAL, leading to better treatment outcomes, including reduced dosing, long-term anti-HIV-1 activity, and deeper HIV-1 suppression.

The (pro)renin receptor as a pharmacological target in cardiorenal diseaes

The (pro)renin receptor ((P)RR) is not only a member of the renin-angiotensin system (RAS) but also exerts several RAS-independent functions due to its multiple signal transductions pathways. In this mini-review, we shortly discuss the molecular functions of this receptor and its pathophysiological significance with a focus on cardiorenal diseases. Finally, we provide a short summary regarding a drug discovery and drug development program on small molecule-based renin/ prorenin receptor blockers (RERBs).

Targeting signaling pathways in prostate cancer: mechanisms and clinical trials

Prostate cancer (PCa) affects millions of men globally. Due to advances in understanding genomic landscapes and biological functions, the treatment of PCa continues to improve. Recently, various new classes of agents, which include next-generation androgen receptor (AR) signaling inhibitors (abiraterone, enzalutamide, apalutamide, and darolutamide), bone-targeting agents (radium-223 chloride, zoledronic acid), and poly(ADP-ribose) polymerase (PARP) inhibitors (olaparib, rucaparib, and talazoparib) have been developed to treat PCa. Agents targeting other signaling pathways, including cyclin-dependent kinase (CDK)4/6, Ak strain transforming (AKT), wingless-type protein (WNT), and epigenetic marks, have successively entered clinical trials. Furthermore, prostate-specific membrane antigen (PSMA) targeting agents such as ¹⁷⁷Lu-PSMA-617 are promising theranostics that could improve both diagnostic accuracy and therapeutic efficacy. Advanced clinical studies with immune checkpoint inhibitors (ICIs) have shown limited benefits in PCa, whereas subgroups of PCa with mismatch repair (MMR) or CDK12 inactivation may benefit from ICIs treatment. In this review, we summarized the targeted agents of PCa in clinical trials and their underlying mechanisms, and further discussed their limitations and future directions.

Targeting GPCRs and Their Signaling as a Therapeutic Option in Melanoma

Simple Summary

Sixteen G-protein-coupled receptors (GPCRs) have been involved in melanogenesis or melanomagenesis. Here, we review these GPCRs, their associated signaling, and therapies.

Abstract

G-protein-coupled receptors (GPCRs) serve prominent roles in melanocyte lineage physiology, with an impact at all stages of development, as well as on mature melanocyte functions. GPCR ligands are present in the skin and regulate melanocyte homeostasis, including pigmentation. The role of GPCRs in the regulation of pigmentation and, consequently, protection against external aggression, such as ultraviolet radiation, has long been established. However, evidence of new functions of GPCRs directly in melanomagenesis has been highlighted in recent years. GPCRs are coupled, through their intracellular domains, to heterotrimeric G-proteins, which induce cellular signaling through various pathways. Such signaling modulates numerous essential cellular processes that occur during melanomagenesis, including proliferation and migration. GPCR-associated signaling in melanoma can be activated by the binding of paracrine factors to their receptors or directly by activating mutations. In this review, we present melanoma-associated alterations of GPCRs and their downstream signaling and discuss the various preclinical models used to evaluate new therapeutic approaches against GPCR activity in melanoma. Recent striking advances in our understanding of the structure, function, and regulation of GPCRs will undoubtedly broaden melanoma treatment options in the future.

Role of Endothelin 1 on Proliferation and Migration of Human MCF-7 Cells

Objective

The aim of this study was to explore the role of endothelin 1 (ET-1) in human breast cancer proliferation and migration and antagonism of endothelin receptor A (ETAR) and endothelin receptor B (ETBR) by using the non-selective dual ETA/ETB receptor antagonist bosentan and determine its anti-proliferative, anti-metastatic, and apoptotic effects demonstrated by nuclear factor kappa B (NF-kB), vascular endothelial growth factor (VEGF), Caspase 3 and Caspase 9 expression on endothelin-induced proliferation of MCF-7 cell line in vitro.

Materials and Methods

A total of 8,000 cells were seeded into e-plates 24 hours after the cells were incubated with or without 10-4 M BOS (1 hour before ET-1 treatment); 10-7, 10-8, and 10-9 M ET-1 for 1-4 days.

Results

Whether ET-1 is present or not in the tumor area, bosentan exerts anti-proliferative effect on breast cancer. However, ET-1 and bosentan group showed important inhibitory effect on tumor migration compared to bosentan alone, which can be attributed to increased activity of ET-1 axis in the presence of ET-1. The imbalance among the NF-kB, caspases, and VEGF, which are predictive factors of carcinogenesis significantly improved after bosentan administration.

Conclusion

Our study definitely demonstrated ET-1 and its critical role in cancer progression with apoptotic and anti-apoptotic pathways (NF-κB) and VEGF expression, and migration analyses were also performed. The second major finding was that bosentan inhibited ET-1-mediated effects on tumor proliferation and migration.

Prognostic values of EDNRB in triple-negative breast cancer

Triple-negative breast cancer (TNBC) has a high degree of malignancy. The endothelin B receptor (EDNRB) serves an important role in the occurrence and development of cancer. The present study aimed to investigate the prognostic value of EDNRB in TNBC. A total of 99 cases of TNBC were collected from the Henan Cancer Hospital database and 159 cases of TNBC were collected from The Cancer Genome Atlas database. A χ² test was used to analyze the association between EDNRB and clinicopathological data. Kaplan-Meier analysis and multivariate Cox regression analysis were used to analyze the association between EDNRB and prognosis, and to establish two models. The discrimination degree of the models was evaluated using time-dependent receiver operating characteristic curves and concordance index (C-index), whereas the accuracy and net benefit of the models were evaluated using integrated discriminant improvement (IDI) and decision curves. EDNRB expression was low in TNBC samples (P<0.01). Age (P=0.01), tumor size (P=0.04) and N stage (P=0.01) were associated with EDNRB expression. EDNRB expression was positively associated with stromal score (P<0.01), but not immune score. High expression levels of EDNRB indicated favorable disease-free survival time (hazard ratio, 0.38; 95% CI, 0.15–0.98; P=0.04). The integrated area under the curve and C-index of the new model were increased compared with the old model following the addition of EDNRB expression as a parameter. The IDI values for prediction of the 3- and 5-year survival rates were 0.04 (P=0.02) and 0.05 (P=0.01), respectively. The results of decision curve analysis showed that the new model had higher clinical net benefit than the old model in the range of 3-year survival rate <0.52. In conclusion, EDNRB was associated with a favorable prognosis in patients with TNBC, and may be used as a novel prognostic biomarker.

The role of endothelin B receptor in bone modelling during orthodontic tooth movement: a study on ETB knockout rats

The endothelin system has an important role in bone modelling during orthodontic tooth movement (OTM); however, little is known about the involvement of endothelin B receptors (ET_B) in this process. The aim of this study was to evaluate the role of ET_B in bone modelling during OTM using ET_B knockout rats (ET_B-KO). Thirty-two male rats were divided into 4 groups (n = 8 per group): the ET_B-KO appliance group, ET_B-KO control group, wild type (ET_B-WT) appliance group, and ET_B-WT control group. The appliance consisted of a super-elastic closed-coil spring placed between the first and second left maxillary molar and the incisors. Tooth movement was measured on days 0 and 35, and maxillary alveolar bone volume, osteoblast, and osteoclast volume were determined histomorphometrically on day 35 of OTM. Next, we determined the serum endothelin 1 (ET-1) level and gene expression levels of the osteoclast activity marker cathepsin K and osteoblast activity markers osteocalcin and dentin matrix acidic phosphoprotein 1 (DMP1) on day 35. The ET_B-KO appliance group showed significantly lower osteoblast activity, diminished alveolar bone volume and less OTM than the ET_B-WT appliance group. Our results showed that ET_B is involved in bone modelling in the late stage of OTM.

Sleeve gastrectomy ameliorates endothelial function and prevents lung cancer by normalizing endothelin-1 axis in obese and diabetic rats

BACKGROUND

Previous evidence has implied that obesity is an independent risk factor for developing cancer. Being closely related to obesity, type 2 diabetes mellitus provides a suitable environment for the formation and metastasis of tumors through multiple pathways. Although bariatric surgeries are effective in preventing and lowering the risk of various types of cancer, the underlying mechanisms of this effect are not clearly elucidated.

AIM

To uncover the role and effect of sleeve gastrectomy (SG) in preventing lung cancer in obese and diabetic rats.

METHODS

SG was performed on obese and diabetic Wistar rats, and the postoperative transcriptional and translational alterations of the endothelin-1 (ET-1) axis in the lungs were compared to sham-operated obese and diabetic rats and age-matched healthy controls to assess the improvements in endothelial function and risk of developing lung cancer at the postoperative 4^th, 8^th, and 12^th weeks. The risk was also evaluated using nuclear phosphorylation of H2A histone family member X as a marker of DNA damage (double-strand break).

RESULTS

Compared to obese and diabetic sham-operated rats, SG brought a significant reduction to body weight, food intake, and fasting blood glucose while improving oral glucose tolerance and insulin sensitivity. In addition, ameliorated levels of gene and protein expression in the ET-1 axis as well as reduced DNA damage indicated improved endothelial function and a lower risk of developing lung cancer after the surgery.

CONCLUSION

Apart from eliminating metabolic disorders, SG improves endothelial function and plays a protective role in preventing lung cancer via normalized ET-1 axis and reduced DNA damage.

Sulfisoxazole inhibits the secretion of small extracellular vesicles by targeting the endothelin receptor A

Inhibitors of the secretion of cancer exosomes, which promote cancer progression and metastasis, may not only accelerate exosome biology research but also offer therapeutic benefits for cancer patients. Here we identify sulfisoxazole (SFX) as an inhibitor of small extracellular vesicles (sEV) secretion from breast cancer cells through interference with endothelin receptor A (ETA). SFX, an FDA-approved oral antibiotic, showed significant anti-tumor and anti-metastatic effects in mouse models of breast cancer xenografts, the reduced expression of proteins involved in biogenesis and secretion of sEV, and triggered co-localization of multivesicular endosomes with lysosomes for degradation. We demonstrate the important role of ETA, as target of SFX, by gain- and loss-of-function studies of the ETA protein, through a direct binding assay, and pharmacological and genetic approaches. These findings may provide a foundation for sEV-targeted cancer therapies and the mechanistic studies on sEV biology.

Extracellular vesicles are released from cells and permit communication between different cell types. Here, the authors identify that the FDA approved antibiotic sulfisoxazole, can block the release of these vesicles in breast cancer cells resulting in reduced cell growth in vitro and in vivo.

Endothelin-1 in the tumor microenvironment correlates with melanoma invasion

Endothelin-1 (ET-1) is a vasoactive peptide that also plays a role in the tanning response of the skin. Animal and cell culture studies have also implicated ET-1 in melanoma progression, but no association studies have been performed to link ET-1 expression and melanoma in humans. Here, we present the first in-vivo study of ET-1 expression in pigmented lesions in humans: an ET-1 immunohistochemical screen of melanocytic nevi, melanoma in situ lesions, invasive melanomas, metastatic melanomas, and blue nevi was performed. Twenty-six percent of melanocytic nevi and 44% of melanoma in situ lesions demonstrate ET-1 expression in the perilesional microenvironment, whereas expression in nevus or melanoma cells was rare to absent. In striking contrast, 100% of moderately to highly pigmented invasive melanomas contained numerous ET-1-positive cells in the tumor microenvironment, with 79% containing ET-1-positive melanoma cells, confirmed by co-staining with melanoma tumor marker HMB45. Hypopigmented invasive melanomas had reduced ET-1 expression, suggesting a correlation between ET-1 expression and pigmented melanomas. ET-1-positive perilesional cells were CD68-positive, indicating macrophage origin. Sixty-two percent of highly pigmented metastatic melanomas demonstrated ET-1 expression in melanoma cells, in contrast to 28.2% of hypopigmented specimens. Eighty-nine percent of benign nevi, known as blue nevi, which have a dermal localization, were associated with numerous ET-1-positive macrophages in the perilesional microenvironment, but no ET-1 expression was detected in the melanocytes. We conclude that ET-1 expression in the microenvironment increases with advancing stages of melanocyte transformation, implicating a critical role for ET-1 in melanoma progression, and the importance of the tumor microenvironment in the melanoma phenotype.

Determination of the endothelin-1 recognition sites of endothelin receptor type A by the directed-degeneration method

G-protein coupled receptors (GPCRs) play indispensable physiological roles in cell proliferation, differentiation, and migration; therefore, identifying the mechanisms by which ligands bind to GPCRs is crucial for developing GPCR-targeting pharmaceutics and for understanding critical biological functions. Although some structural information is available regarding the interactions between GPCRs and their small molecule ligands, knowledge of how GPCRs interact with their corresponding macromolecule ligands, such as peptides and proteins, remains elusive. In this study, we have developed a novel strategy to investigate the precise ligand recognition mechanisms involved in the interaction of endothelin receptor type A (ET_A) with its ligand, endothelin-1 (ET-1); we call this method “directed degeneration” method. Through flow cytometric screening of a randomized ET_A library, statistical analysis of the identified sequences, and biochemical studies, the ligand interaction map was successfully obtained.

Effect of radiation on brain tissue endothelin-1 level and tumor development

BACKGROUND

Radiotherapy causes injury in the endothelial cells of blood vessels and the production of vasoactive amines such as endothelin-1 (ET-1). ET-1 is an important peptide in cancer development. In this study, the effects of radiation on brain tissue ET-1 level were evaluated. Is it possible to suggest a mechanism using ET-1 level in the production of this adverse effect? In this paper, the relationship between the development of brain tumors and the ET-1 level has been discussed.

MATERIALS AND METHODS

Twenty-eight adult Sprague Dawley rats were used in the experiments. The rats were divided into four groups (n = 7) as follows: control group: radiation was not applied during the experiment; Group 1: Decapitated on the 1^st day following radiation; Group 2: Decapitated on the 7^th day following radiation; and Group 3: Decapitated on the 30^th day following radiation. ET-1 levels were measured with enzyme-linked immunosorbent assay (ELISA) method. The t-test, variance analysis, and Tukey honestly significant difference (HSD) tests were used in the statistical analysis. A value of P < 0.05 was accepted as significant.

RESULTS

No statistical differences were observed in the tissue ET-1 levels between the control group and other groups. According to the variance analysis and Tukey test, the differences between the groups were not significant.

CONCLUSION

We observed in this study that the effects of radiation on brain tumor development or malignant transformation are not mediated by ET-1 levels. In addition, these results support the hypothesis of the fact that medical treatment with ET-1 antagonists in clinical cases receiving radiotheraphy is unnecessary.

Endothelin Promotes Colorectal Tumorigenesis by Activating YAP/TAZ

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

Endothelin Receptors, Mitochondria and Neurogenesis in Cerebral Ischemia

Background: Neurogenesis is most active during pre-natal development, however, it persists throughout the human lifespan. The putative role of mitochondria in neurogenesis and angiogenesis is gaining importance. Since, ET_B receptor mediated neurogenesis and angiogenesis has been identified, the role of these receptors with relevance to mitochondrial functions is of interest.

Methods: In addition to work from our laboratory, we undertook an extensive search of bibliographic databases for peer-reviewed research literature. Specific technical terms such as endothelin, mitochondria and neurogenesis were used to seek out and critically evaluate literature that was relevant.

Results: The ET family consists of three isopeptides (ET-1, ET-2 and ET-3) that produce biological actions by acting on two types of receptors (ET_A and ET_B). In the central nervous system (CNS) ET_A receptors are potent constrictors of the cerebral vasculature and appear to contribute in the causation of cerebral ischemia. ET_A receptor antagonists have been found to be effective in animal model of cerebral ischemia; however, clinical studies have shown no efficacy. Mitochondrial functions are critically important for several neural development processes such as neurogenesis, axonal and dendritic growth, and synaptic formation. ET appears to impair mitochondrial functions through activation of ET_A receptors. On the other hand, blocking ET_B receptors has been shown to trigger apoptotic processes by activating intrinsic mitochondrial pathway. Mitochondria are important for their role in molecular regulation of neurogenesis and angiogenesis. Stimulation of ET_B receptors in the adult ischemic brain has been found to promote angiogenesis and neurogenesis mediated through vascular endothelial growth factor and nerve growth factor. It will be interesting to investigate the effect of ET_B receptor stimulation on mitochondrial functions in the CNS following cerebral ischemia.

Conclusion: The findings of this review implicate brain ET_B receptors in angiogenesis and neurogenesis following cerebral ischemia, it is possible that the positive effect of stimulating ET_B receptors in cerebral ischemia may be mediated through mitochondrial functions.

Endothelin-1 Expression in Prostate Needle Biopsy Specimens Correlated With Aggressiveness of Prostatic Cancer

BACKGROUND & OBJECTIVE

As the prostate adenocarcinoma is one of the most common malignant tumors in males, looking for a marker to effectively predict aggressiveness and metastatic potential in an apparently localized cancer in initial needle biopsy specimens can help the clinicians to make more appropriate decision for treatment, planning, and choosing appropriate targeted therapy. The present study assessed the value of Endothelin-1 expression to predict prognosis of prostatic cancer.

METHODS

In a cross sectional study, 83 patients who underwent radical prostatectomy in Hasheminejad Kidney Center in 2008 through 2012 were assigned to two groups including 43 with and 40 without extra-prostatic extension (EPE). Endothelin-1 staining was performed on Paraffin Embedded blocks of preoperative needle biopsies.

RESULTS

The expression of Endothelin-1 increased in 72% of patients in the group with EPE (P<0.001). The group with Endothelin-1 positivity showed higher serum level of prostate specific antigen (PSA) (p = 0.039). Endothelin-1 expression was positive in 67% of patients with perineurial invasion (P<0.001). Adjusting the baseline variables of PSA and PN in a multivariable logistic regression model, the Endothelin-1 positivity could effectively predict EPE in patients with prostatic cancer (OR: 5.46, p = 0.010).

CONCLUSION

Correlation of Endothelin-1 expression in needle biopsy specimens in expected with extra-prostatic extension of tumor in radical prostatectomy specimens, perineurial invasion and serum PSA level at the time of diagnosis.

Endothelin-1 (ET-1) induces resistance to bortezomib in human multiple myeloma cells via a pathway involving the ETB receptor and upregulation of proteasomal activity

PURPOSE

Bortezomib (BTZ) is used for the treatment of multiple myeloma (MM). However, a significant proportion of patients may be refractory to the drug. This study aimed to investigate whether the endothelin (ET-1) axis may act as an escape mechanism to treatment with bortezomib in MM cells.

METHODS

NCI-H929 and RPMI-8226 (human MM cell lines) were cultured with or without ET-1, BTZ, and inhibitors of the endothelin receptors. ET-1 levels were determined by ELISA, while the protein levels of its receptors and of the PI3K and MAPK pathways' components by western blot. Effects of ET-1 on cell proliferation were studied by MTT and on the ubiquitin proteasome pathway by assessing the chymotryptic activity of the 20S proteasome in cell lysates.

RESULTS

Endothelin receptors A and B (ETAR and ETBR, respectively) were found to be expressed in both cell lines, with the RPMI-8226 cells that are considered resistant to BTZ, expressing higher levels of ETBR and in addition secreting ET-1. Treatment of the NCI-H929 cells with ET-1 increased proliferation, while co-incubation of these cells with ET-1 and BTZ decreased BTZ efficacy with concomitant upregulation of 20S proteasomal activity. Si-RNA silencing or chemical blockade of ETBR abrogated the protective effects of ET-1. Finally, data suggest that the predominant signaling pathway involved in ET-1/ETBR-induced BTZ resistance in MM cells may be the MAPK pathway.

CONCLUSION

Our data suggest a possible role of the ET-1/ETBR axis in regulating the sensitivity of MM cells to BTZ. Thus, combining bortezomib with strategies to target the ET-1 axis could prove to be a novel promising therapeutic approach in MM.

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

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

Epigenetic silencing of endothelin-3 in colorectal cancer

Endothelins are expressed in a variety of human tissue and are involved in the processes as proliferation, migration and differentiation. The signal transduction pathway is a result of the endothelin-1-3 (ET1-3) binding to their receptors (ETAR, ETBR). ET-3 is a new candidate tumour suppressor gene, which is often downregulated or silenced in human cancer.The aim of the study was to examine DNA methylation of ET-3 genes in colorectal cancer (CRC) tissue samples in relation to the clinical stage (CS) of cancer. The paper is a continuation of our previously published results, which showed a four-fold transcriptional silencing of the ET-3 gene in the samples of colorectal cancer in comparison to normal tissues.A total of 66 paired CRC and normal (surgical margin) tissue samples were used in the study. The tumour tissues were collected from CRC patients in CS I-IV according the 7th edition of UICC TNM Classification of Malignant Tumours (CS I, n = 8; CS II, n = 20; CS III, n = 27; CS IV, n = 11). Assessment of epigenetic silencing of the ET-3 encoding gene was performed in three steps. The silencing of the ET-3 encoding gene was a result from methylation of the promoter sequence using methylation-specific PCR (MS-PCR). Analyses were performed using primers complementary for a CpG island in the first exon of the gene encoding ET-3. An epigenetic silence through methylation of 7.5% (5/66) in comparison to control was observed, including 10% of CS II (2/20), 7% of CS III (2/27) and 9% of CS IV (1/11). The controls and the samples of tumour in CS I showed no epigenetic silencing via methylation. In conclusion, epigenetic silencing of ET-3 in CRC could play a role in the progression than in the induction process. EDN3 would be a future target for epigenetic therapy in colorectal cancer, but further clinical studies are needed.

Expression of endothelin-1 and endothelin-1 receptor A in canine mammary tumours

Endothelins and their receptors have been implicated in numerous diseases and have recently emerged as relevant players in a variety of malignancies. Tumours overexpress the Endothelin-1 (ET-1) and the Endothelin-A receptors (ETAR) and their interaction enhances tumour growth and metastasis by promoting tumour cell survival, proliferation and angiogenesis. In this study we have evaluated the expression of ET-1 and ETAR in 50 canine mammary tumours, compared to normal controls. Results demonstrated a progressive increase in ET-1 and ETAR expression from benign tumour to grade 1 and to grade 2 malignant mammary tumours with a decrease of expression in grade 3 carcinomas. Co-localization of ET-1 and ETAR was observed in benign mammary tumours and in G1 and G2 carcinomas, while absent in G3 carcinomas. Concluding, ET-1/ETAR can be considered reliable markers for evaluating malignancy of canine mammary tumours and could have importance for the development of specific anticancer therapies.

The endothelin-integrin axis is involved in macrophage-induced breast cancer cell chemotactic interactions with endothelial cells

Elevated macrophage infiltration in tumor tissues is associated with breast cancer metastasis. Cancer cell migration/invasion toward angiogenic microvasculature is a key step in metastatic spread. We therefore studied how macrophages stimulated breast cancer cell interactions with endothelial cells. Macrophages produced cytokines, such as interleukin-8 and tumor necrosis factor-α, to stimulate endothelin (ET) and ET receptor (ETR) expression in breast cancer cells and human umbilical vascular endothelial cells (HUVECs). ET-1 was induced to a greater extent from HUVECs than from breast cancer cells, resulting in a density difference that facilitated cancer cell chemotaxis toward HUVECs. Macrophages also stimulated breast cancer cell adhesion to HUVECs and transendothelial migration, which were repressed by ET-1 antibody or ETR inhibitors. The ET axis induced integrins, such as αV and β1, and their counterligands, such as intercellular adhesion molecule-2 and P-selectin, in breast cancer cells and HUVECs, and antibodies against these integrins efficiently suppressed macrophage-stimulated breast cancer cell interactions with HUVECs. ET-1 induced Ets-like kinase-1 (Elk-1), signal transducer and activator of transcription-3 (STAT-3), and nuclear factor-κB (NF-κB) phosphorylation in breast cancer cells. The use of inhibitors to prevent their phosphorylation or ectopic overexpression of dominant-negative IκBα perturbed ET-1-induced integrin αV and integrin β1 expression. The physical associations of these three transcriptional factors with the gene promoters of the two integrins were furthermore evidenced by a chromatin immunoprecipitation assay. Finally, our mouse orthotopic tumor model revealed an ET axis-mediated lung metastasis of macrophage-stimulated breast cancer cells, suggesting that the ET axis was involved in macrophage-enhanced breast cancer cell endothelial interactions.

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.

Bone targeted therapies in metastatic castration-resistant prostate cancer

Prostate cancer is the most common male cancer. About 90% of metastatic patients will develop bone metastases. Bone disease is responsible of pain, deterioration of quality of life and serious bone complications. Proliferation of prostate cancer cells in the bone marrow induces osteoclast activation and osteolysis. Targeting the bone microenvironment reduces morbidity. Relevant preclinical and clinical studies of bone-targeted therapies in castration-resistant prostate cancer were identified in PubMed and clinical trial databases. Different drugs are available or in development that target bone resorption (bisphosphonates, RANK ligand inhibitors), bone formation (endothelin 1 inhibitors), cancer cell migration (SRC-family kinase inhibitors, vascular endothelial growth factor-MET inhibitors), and survival (radiopharmaceuticals). In phase III trials, zoledronic acid, denosumab, and radium-223 were shown to significantly delay skeletal-related events. Radium-223 was also shown to improve overall survival. Biomarkers of bone resorption (urinary N-telopeptide) and bone making (alkaline phosphatase) have an independent prognostic impact. Targeting the bone microenvironment is an important component of castration-resistant prostate cancer management to reduce bone complications and improve overall survival. Biomarkers of bone turnover have an independent prognostic impact.

Advances in prevention and treatment of bone metastases in prostate cancer. Role of RANK/RANKL inhibition

BACKGROUND

Bone metastases are a common complication of prostate cancer, so treatment and prevention are essential to slow the progression of the disease and the occurrence of skeletal related events (SREs), which have devastating consequences for the quality of life of patients.

SUMMARY OF EVIDENCE

Bone metastases are characterized by increased bone turnover and altered balance between osteogenesis and osteolysis, with activation of the RANK and its ligand (RANKL). In patients with metastatic prostate cancer, bisphosphonates have been the bone-targeted agents most commonly used to date. Zoledronic acid has demonstrated efficacy in the reduction and delay of SREs in patients with bone metastases. Denosumab, a RANKL inhibitor, has been demonstrated to be superior to zoledronic acid in the prevention of SREs in castration-resistant prostate cancer (CRPC). Both agents are being considered, along with other new bone-targeted agents, for the prevention of bone metastases in patients with nonmetastatic CRPC, where denosumab has already demonstrated superiority over placebo.

CONCLUSIONS

Denosumab and zoledronic acid prevent SREs in patients with prostate cancer and bone metastases. Denosumab also has a potential role in delaying bone metastases in nonmetastatic patients. Advances in the treatment of CRPC include an increasing focus on prevention of the progression of bone disease.

Generation and characterization of rendomab-B1, a monoclonal antibody displaying potent and specific antagonism of the human endothelin B receptor

Endothelin B receptor (ETBR) is a G protein-coupled receptor able to bind equally to the three identified human endothelin peptides. It is expressed primarily on vascular endothelial cells and involved in various physiological processes including vascular tone homeostasis, enteric nervous system development, melanogenesis and angiogenesis. Furthermore, overactivation or overexpression of ETBR have been associated with the development of various diseases such as cardiovascular disorders and cancers. Therefore, ETBR appears to be relevant target for the therapy or diagnosis of highly prevalent human diseases. In this study, we report the in vitro characterization of rendomab-B1, a monoclonal antibody (mAb) obtained by genetic immunization, which selectively recognizes the native form of human ETBR (hETBR). Rendomab-B1 is the first-reported mAb that behaves as a potent antagonist of hETBR. It recognizes an original extracellular conformational epitope on the receptor, distinct from the endothelin-1 (ET-1) binding site. Rendomab-B1 not only blocks ET-1-induced calcium signaling pathway and triggers rapid receptor internalization on recombinant hETBR-expressing cells, but also exerts pharmacological activities on human vascular endothelial cells, reducing both cell viability and ET-1-induced hETBR synthesis. In addition, binding experiments using rendomab-B1 on different melanoma cell lines reveal the structural and functional heterogeneity of hETBR expressed at the surface of these cancer cells, strongly suggesting the existence of tumor-specific receptors. Collectively, our results underscore the value of rendomab-B1 for research, therapeutic and diagnostic applications dealing with hETBR.

Endothelin receptor-A is required for the recruitment of antitumor T cells and modulates chemotherapy induction of cancer stem cells

BACKGROUND

The endothelin receptor-A (ETRA) plays an important role in tumor cell migration, metastasis, and proliferation. The endothelin receptor B (ETRB) plays a critical role in angiogenesis and the inhibition of anti-tumor immune cell recruitment. Thus dual blockade of ETRA and ETRB could have significant anti-tumor effects.

RESULTS

Dual ETRA/ETRB blockade with macitentan (or the combination of the ETRA and ETRB antagonists BQ123 and BQ788) did not enhance antitumor immune cell recruitment. In vitro studies demonstrate that ETRA inhibition prevents the induction of ICAM1 necessary for immune cell recruitment. When used as a single agent against human tumor xenografts, macitentan demonstrated non-significant anti-tumor activity. However, when used in combination with chemotherapy, macitentan specifically reduced tumor growth in cell lines with CD133+ cancer stem cells. We found that ETRA is primarily expressed on CD133+ CSC in both cell lines and primary human tumor cells. ETRA inhibition of CSC prevented chemotherapy induced increases in tumor stem cells. Furthermore, ETRA inhibition in combination with chemotherapy reduced the formation of tumor spheres.

METHODS

We tested the dual ETRA/ETRB antagonist macitentan in conjunction with (1) an anti-tumor vaccine and (2) chemotherapy, in order to assess the impact of dual ETRA/ETRB blockade on anti-tumor immune cell infiltration and ovarian tumor growth. In vitro murine and human cell line, tumor sphere assays and tumor xenograft models were utilized to evaluate the effect of ETRA/ETRB blockade on cell proliferation, immune cell infiltration and cancer stem cell populations.

CONCLUSIONS

These studies indicate a critical role for ETRA in the regulation of immune cell recruitment and in the CSC resistance to chemotherapy.

Endothelin-1 promotes MMP-13 production and migration in human chondrosarcoma cells through FAK/PI3K/Akt/mTOR pathways

Tumor malignancy is associated with several cellular properties including proliferation and ability to metastasize. Endothelin-1 (ET-1) the most potent vasoconstrictor plays a crucial role in migration and metastasis of human cancer cells. We found that treatment of human chondrosarcoma (JJ012 cells) with ET-1 increased migration and expression of matrix metalloproteinase (MMP)-13. ET-1-mediated cell migration and MMP-13 expression were reduced by pretreatment with inhibitors of focal adhesion kinase (FAK), phosphatidylinositol 3-kinase (PI3K), Akt, and mammalian target of rapamycin (mTOR), as well as the NF-κB inhibitor and the IκB protease inhibitor. In addition, ET-1 treatment induced phosphorylation of FAK, PI3K, AKT, and mTOR, and resulted in increased NF-κB-luciferase activity that was inhibited by a specific inhibitor of PI3K, Akt, mTOR, and NF-κB cascades. Taken together, these results suggest that ET-1 activated FAK/PI3K/AKT/mTOR, which in turn activated IKKα/β and NF-κB, resulting in increased MMP-13 expression and migration in human chondrosarcoma cells.

Assessment of endothelin-A receptor expression in subcutaneous and orthotopic thyroid carcinoma xenografts in vivo employing optical imaging methods

Endothelin (ET) receptor dysregulation has been described in a number of pathophysiological processes, including cardiovascular disorders, renal failure, and cancer. The aim of this study was to evaluate the expression of the ET-A receptor (ET(A)R) in murine models of thyroid carcinoma using optical imaging methods. A recently developed near-infrared fluorescent tracer was first assessed in isolated artery preparations for its functional performance in comparison with known ET(A)R antagonists BQ123 and PD156707. Before evaluation of the tracer in vivo, different thyroid carcinoma cell lines were characterized with respect to their ET receptor expression by RT-PCR and autoradiography. In vivo, sc and orthotopic papillary thyroid tumor xenografts were clearly visualized by fluorescence reflectance imaging and fluorescence-mediated tomography up to 48 h after injection of the tracer. Binding specificity of the probe was demonstrated by predosing with PD156707 as a competing inhibitor. In conclusion, optical imaging with a fluorescent ET(A)R tracer allows the noninvasive imaging of tumor-associated ET(A)R expression in vivo. In the future, this technique may help surgeons to evaluate lesion dimensions in intraoperative settings (e.g. thyroidectomy).

Recent developments in treatments targeting castration-resistant prostate cancer bone metastases

BACKGROUND

Prostate cancer is the most common male cancer and one of the top causes of male cancer-related death. Most patients with prostate cancer respond to initial androgen deprivation therapy before progressing to castration-resistant prostate cancer (CRPC) and eventually developing bone metastases. Growth of prostate cancer metastases in the bone microenvironment produces numerous factors that disrupt the dynamic equilibrium of osteogenesis and osteolysis existing in healthy bone, leading to progressive morbidity, poor quality of life, and increased treatment costs.

MATERIALS AND METHODS

Relevant studies of CRPC and targeted therapies were identified from literature and clinical trial databases, websites, and conference abstracts.

RESULTS

Available data on agents potentially targeting bone metastatic CRPC or the bone microenvironment in patients with CRPC are discussed, including inhibitors of tumor growth/survival and bone turnover (SRC family kinase inhibitors, endothelin-1 inhibitors, MET inhibitors, and thalidomide and its derivatives), inhibitors of bone turnover (bisphosphonates and receptor activator of nuclear factor-kB ligand inhibitors), antiangiogenic agents (vascular endothelial growth factor receptor and platelet-derived growth factor blockers), prostate cancer vaccines, and bone-directed radiopharmaceuticals.

CONCLUSIONS

With increasing data availability demonstrating tumor-bone microenvironment interactions and routine incorporation of bone-related end points into CRPC trials, bone microenvironment-targeted agents are likely to become an increasingly important component of CRPC treatment.

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.

Synthesis, toxicology and potential of ordered mesoporous materials in nanomedicine

Although ordered mesoporous silica materials have been studied for almost 20 years, their utilization within life science applications is relatively new and unexplored. An increasing number of researchers are transcending their respective fields in order to bridge the knowledge gap between materials chemistry and biotechnology, and to exploit the potential of mesoporous materials. Their intricate porosity with order in the nanoscale translates into high surface areas above 1000 m(2)/g, high selectivity for the encapsulation of biorelevant molecules as well as controlled surface chemistry. Their uses in pharmaceutics to improve drug formulation, drug bioavailability, mitigate drug toxicity and in cellular targeting, through controlled drug delivery strategies, have been shown. The incorporation of a high concentration of fluorescent and nuclear markers within their pores, whilst retaining good diffusion through their porous matrix, has shown them to be ideal candidates for sensing devices, in immunoassays such as flow cytometry and for their use in novel theranostic applications. This article aims to bring to the forefront some of the most important properties of mesoporous materials, which prove advantageous for their use in nanomedical applications and to highlight some of the potential areas into which the field may now emerge.

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.

Disposition and metabolism of the specific endothelin A receptor antagonist zibotentan (ZD4054) in healthy volunteers

Zibotentan (ZD4054) is a specific endothelin A (ET(A)) receptor antagonist that is in clinical development for the treatment of castration-resistant prostate cancer (CRPC) and has shown a promising signal for improvement in overall survival compared with placebo in a Phase II study of patients with metastatic CRPC. In this study, the pharmacokinetics, disposition and metabolism of zibotentan were evaluated following administration of a single oral dose of [(14)C]-zibotentan 15 mg to six healthy subjects. Zibotentan was rapidly absorbed, with the maximum zibotentan plasma concentration being observed 1 hour after administration. Excretion was rapid with the majority of the dose being excreted in the urine (71-94%). Total recovery of radioactivity over the 5 days of the study was high (mean 93%), with 78% of the dose being recovered within 24 hours. Concentrations of radioactivity in the plasma were similar up to 12 hours post dose, and diverged thereafter, indicating the presence of circulating metabolites. The main circulating component was zibotentan with a number of metabolites being identified in excreta. Zibotentan was well absorbed and was cleared via metabolism and urinary excretion with zibotentan-related material predominantly excreted via the urine.

Preliminary study of the specific endothelin a receptor antagonist zibotentan in combination with docetaxel in patients with metastatic castration-resistant prostate cancer

BACKGROUND

This two-part study assessed the safety and tolerability of combined treatment with zibotentan (ZD4054), a specific endothelin A receptor antagonist, plus docetaxel in patients with metastatic castration-resistant prostate cancer.

METHODS

Part A was an open-label, dose-finding phase to determine the safety and toxicity profile of zibotentan in combination with docetaxel. Patients received once-daily oral zibotentan 10 mg (initial cohort) or 15 mg in combination with docetaxel 75 mg/m(2) (administered on day 1 of each 21-day cycle) for up to 10 cycles. Part B was a double-blind phase which evaluated the safety and preliminary activity of zibotentan plus docetaxel. Patients were randomized 2:1 to receive zibotentan (at the highest tolerated dose identified in part A) plus docetaxel or placebo plus docetaxel.

RESULTS

Six patients were enrolled in part A (n  = 3, zibotentan 10 mg; n = 3, zibotentan 15 mg). No dose-limiting toxicity was observed, thus zibotentan 15 mg in combination with docetaxel was evaluated in part B (n = 20, zibotentan plus docetaxel; n = 11, placebo plus docetaxel). CTCAE grade ≥3, most commonly neutropenia or leucopenia, were reported in 10 (50%) and nine (82%) patients in the zibotentan and placebo groups, respectively. One (17%) patient receiving placebo achieved complete response, two (22%) patients receiving zibotentan achieved partial response and stable disease occurred in six (67%) and three (50%) patients receiving zibotentan and placebo, respectively.

CONCLUSIONS

The tolerability of zibotentan plus docetaxel was consistent with the known profiles of each drug. Sufficient preliminary activity was seen with this combination to merit continued development.

Pharmacokinetics and tolerability of zibotentan (ZD4054) in subjects with hepatic or renal impairment: two open-label comparative studies

BACKGROUND

Zibotentan (ZD4054) is a specific endothelin A (ETA) receptor antagonist being investigated for the treatment of prostate cancer. As zibotentan is eliminated by renal and metabolic routes, clearance may be reduced in patients with hepatic or renal impairment, leading to greater drug exposure.

METHODS

Open-label studies investigated the PK and tolerability of zibotentan in subjects with hepatic or renal impairment, compared with those with normal organ function. In the hepatic and renal studies, respectively, subjects were divided into categories using Child-Pugh classification or 24-hour urine creatinine clearance (mild, moderate, or severe impairment and normal function). Each subject received a single oral dose of zibotentan 10 mg and PK sampling was undertaken. Within the hepatic study, AUC and Cmax were expressed as the ratio of geometric means and 90% CI for each impairment group compared with the normal function group. The possibility that hepatic impairment had a clinically relevant effect on exposure was considered if the upper 90% CI for the ratio exceeded 2. In the renal study, AUC, Cmax and t1/2 were analyzed using linear regression fitting effects for creatinine clearance and age.

RESULTS

In the hepatic and renal studies respectively, 32 subjects (eight per group) and 48 subjects received treatment (n = 18 normal, n = 12 mild, n = 9 moderate, n = 9 severe). Zibotentan Cmax was not significantly affected by hepatic or renal impairment. Compared with the normal function group, zibotentan AUC was 40% (1.40; 90% CI 0.91-2.17), 45% (1.45; 90% CI 0.94-2.24) and 190% (2.90; 90% CI 1.88-4.49) higher in subjects with mild, moderate and severe hepatic impairment, respectively, and 66% (1.66; 90% CI 1.38-1.99), 89% (1.89; 90% CI 1.50-2.39) and 117% (2.17; 90% CI 1.64-2.86) higher in subjects with mild, moderate and severe renal impairment, respectively. In both studies mean t1/2 increased and zibotentan clearance decreased with the degree of impairment. Headache was the most common AE in all groups.

CONCLUSIONS

Zibotentan absorption was unchanged, however, exposure was higher in subjects with hepatic or renal impairment due to slower clearance. This increased exposure did not result in differences in the range or severity of AEs observed.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00672581 and AstraZeneca study number D4320C00016 (renal trial; conducted in Germany).

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-1 regulates rat bone sialoprotein gene transcription

Endothelin-1 (ET-1) was originally discovered as a vasoconstrictor protein excreted by vascular endothelial cells. Recently, tumor-produced ET-1 has been considered to stimulate osteoblasts to form new bone, and to be an important mediator of osteoblastic bone metastasis. ET-1 has high affinity for two different membrane receptors, ET(A)R and ET(B)R, which are expressed by many types of cells including osteoblasts. Bone sialoprotein (BSP) is a phosphorylated and sulfated glycoprotein associated with mineralized connective tissues. To investigate the effects of ET-1 on BSP transcription, we used rat osteoblast-like ROS17/2.8 cells. Levels of BSP and osteopontin mRNA were increased at 12 h after treatment with ET-1 (10 ng/ml), and ET-1 at the same concentration induced luciferase activity of a -116 to +60 BSP promoter construct at 6 h. Transcriptional activity of -84BSPLUC, which contains the cAMP response element (CRE), was increased by ET-1. Furthermore, at 6 h, ET-1 (10 ng/ml) increased the binding of nuclear protein to CRE, the FGF2 response element (FRE) and the homeodomain protein-binding site (HOX). Antibodies against CREB1, JunD and Fra2 disrupted the formation of CRE-protein complexes, while antibodies against Runx2 and Dlx5 reduced the formation of FRE- and HOX-protein complexes. These findings indicate that ET-1 increases BSP transcription via the CRE, FRE and HOX sites in the rat BSP gene promoter.

Modulation of G-protein coupled receptor sample quality by modified cell-free expression protocols: a case study of the human endothelin A receptor

G-protein coupled receptors still represent one of the most challenging targets in membrane protein research. Here we present a strategic approach for the cell-free synthesis of these complex membrane proteins exemplified by the preparative scale production of the human endothelin A receptor. The versatility of the cell-free expression system was used to modulate sample quality by alteration of detergents hence presenting different solubilization environments to the synthesized protein at different stages of the production process. Sample properties after co-translational and post-translational solubilization have been analysed by evaluation of homogeneity, protein stability and receptor ligand binding competence. This is a first quality evaluation of a membrane protein obtained in two different cell-free expression modes and we demonstrate that both can be used for the production of ligand-binding competent endothelin A receptor in quantities sufficient for structural approaches. The presented strategy of cell-free expression protocol development could serve as basic guideline for the production of related receptors in similar systems.

Tumor angiogenesis and novel antiangiogenic strategies

Angiogenesis is essential for the development and growth of tumors. It is a highly regulated process that requires cross-talk between signaling pathways at all stages of blood vessel development and tumor growth, from the recruitment of endothelial cells to vessel maturation. This review summarizes tumor angiogenesis and describes the key signaling pathways governing blood vessel development. The role of angiogenesis in various tumor types is discussed, but the focus is on invasive breast cancer, a disease that will affect approximately 182,000 women in the USA in 2008. Research efforts over the past decade have identified numerous potential, as well as proven therapies with activity in breast cancer. These include chemotherapeutics as well as therapies that inhibit specific angiogenic pathways known as targeted agents. Some of the data from single- and multitargeted antiangiogenic agents are described in this review. "Published 2008 Wiley-Liss, Inc. This article is a US Government work, and, as such, is in the public domain in the United States of America."