The endothelin system in human glioblastoma

ImmunoPET imaging-based pharmacokinetic profiles of an antibody and its Fab targeting endothelin A receptors on glioblastoma stem cells in a preclinical orthotopic model

BACKGROUND

The resistance of glioblastoma stem cells (GSCs) to treatment is one of the causes of glioblastoma (GBM) recurrence. Endothelin A receptor (ETA) overexpression in GSCs constitutes an attractive biomarker for targeting this cell subpopulation, as illustrated by several clinical trials evaluating the therapeutic efficacy of endothelin receptor antagonists against GBM. In this context, we have designed an immunoPET radioligand combining the chimeric antibody targeting ETA, chimeric-Rendomab A63 (xiRA63), with 89Zr isotope and evaluated the abilities of xiRA63 and its Fab (ThioFab-xiRA63) to detect ETA+ tumors in a mouse model xenografted orthotopically with patient-derived Gli7 GSCs.

RESULTS

Radioligands were intravenously injected and imaged over time by µPET-CT imaging. Tissue biodistribution and pharmacokinetic parameters were analyzed, highlighting the ability of [89Zr]Zr-xiRA63 to pass across the brain tumor barrier and achieve better tumor uptake than [89Zr]Zr-ThioFab-xiRA63.

CONCLUSIONS

This study shows the high potential of [89Zr]Zr-xiRA63 in specifically targeting ETA+ tumors, thus raising the possibility of detecting and treating ETA+ GSCs, which could improve the management of GBM patients.

Results of a phase I trial to assess the safety of macitentan in combination with temozolomide for the treatment of recurrent glioblastoma

Background

There is an urgent need for additional therapies to treat recurrent glioblastoma (GBM). Preclinical studies suggest that high dose macitentan, an oral dual endothelin receptor antagonist, enhances the cytotoxic effects of temozolomide (TMZ) in GBM, improving survival. This phase I trial investigated the maximum tolerated dose of macitentan combined with TMZ in patients with recurrent GBM and assessed the safety and tolerability of high dose macitentan in these patients (NCT01499251).

Methods

Adults with recurrent GBM received ascending doses of macitentan from 30 mg once daily concomitantly with TMZ. Safety and tolerability were assessed in addition to exploratory efficacy and pharmacokinetic endpoints. An ancillary study examined biomarker expression following macitentan treatment prior to surgical resection of recurrent GBM.

Results

Thirty-eight patients with recurrent GBM were administered macitentan doses up to 300 mg once daily; no dose-limiting toxicities were observed, and a maximum tolerated dose was not determined. All patients experienced at least one treatment-emergent adverse event (TEAE), the majority associated with GBM or TMZ treatment. TEAEs related to macitentan and TMZ were reported for 16 (42.1%) and 26 (68.4%) patients, respectively, with no serious macitentan-related TEAEs. Macitentan concentrations increased with dose, with no plateau in exposure. Substantial heterogeneity was observed in the expression of efficacy biomarkers within tumors. The Kaplan-Meier estimate of median overall survival across all dose groups was 9.4 (95% CI 8.5, 13.4) months.

Conclusion

High-dose macitentan was well tolerated in recurrent GBM patients concomitantly receiving TMZ. TEAEs were consistent with those seen in patients receiving either drug individually.

Endothelin Receptor Antagonists: Status Quo and Future Perspectives for Targeted Therapy

The endothelin axis, recognized for its vasoconstrictive action, plays a central role in the pathology of pulmonary arterial hypertension (PAH). Treatment with approved endothelin receptor antagonists (ERAs), such as bosentan, ambrisentan, or macitentan, slow down PAH progression and relieves symptoms. Several findings have indicated that endothelin is further involved in the pathogenesis of certain other diseases, making ERAs potentially beneficial in the treatment of various conditions. In addition to PAH, this review summarizes the use and perspectives of ERAs in cancer, renal disease, fibrotic disorders, systemic scleroderma, vasospasm, and pain management. Bosentan has proven to be effective in systemic sclerosis PAH and in decreasing the development of vasospasm-related digital ulcers. The selective ERA clazosentan has been shown to be effective in preventing cerebral vasospasm and delaying ischemic neurological deficits and new infarcts. Furthermore, in the SONAR (Study Of Diabetic Nephropathy With Atrasentan) trial, the selective ERA atrasentan reduced the risk of renal events in patients with diabetes and chronic kidney disease. These data suggest atrasentan as a new therapy in the treatment of diabetic nephropathy and possibly other renal diseases. Preclinical studies regarding heart failure, cancer, and fibrotic diseases have demonstrated promising effects, but clinical trials have not yet produced measurable results. Nevertheless, the potential benefits of ERAs may not be fully realized.

Mechanisms regulating T-cell infiltration and activity in solid tumors

T-lymphocytes play a critical role in cancer immunity as evidenced by their presence in resected tumor samples derived from long-surviving patients, and impressive clinical responses to various immunotherapies that reinvigorate them. Indeed, tumors can upregulate a wide array of defense mechanisms, both direct and indirect, to suppress the ability of Tcells to reach the tumor bed and mount curative responses upon infiltration. In addition, patient and tumor genetics, previous antigenic experience, and the microbiome, are all important factors in shaping the T-cell repertoire and sensitivity to immunotherapy. Here, we review the mechanisms that regulate T-cell homing, infiltration, and activity within the solid tumor bed. Finally, we summarize different immunotherapies and combinatorial treatment strategies that enable the immune system to overcome barriers for enhanced tumor control and improved patient outcome.

Differential somatostatin, CXCR4 chemokine and endothelin A receptor expression in WHO grade I-IV astrocytic brain tumors

PURPOSE

Glioblastomas represent the most common primary malignant tumor of the nervous system and the most frequent type of astrocytic tumors. Despite improved therapeutic options, prognosis has remained exceptionally poor over the last two decades. Therefore, new treatment approaches are urgently needed. An overexpression of somatostatin (SST) as well as chemokine CXCR4 and endothelin A (ETA) receptors has been shown for many types of cancer. Respective expression data for astrocytic brain tumors, however, are scarce and contradictory.

METHODS

SST subtype, CXCR4 and ETA expression was comparatively evaluated in a total of 57 grade I-IV astrocytic tumor samples by immunohistochemistry using well-characterized monoclonal antibodies.

RESULTS

Overall, receptor expression on the tumor cells was only very low. SST5 was the most prominently expressed receptor, followed by SST3, ETA, SST2 and CXCR4. In contrast, tumor capillaries displayed strong SST2, SST3, SST5, CXCR4 and ETA expression. Presence of SST5, CXCR4 and ETA on tumor cells and of SST3, CXCR4 and ETA on microvessels gradually increased from grade II to grade IV tumors. Ki-67 values correlated significantly with CXCR4 expression on tumor cells and with vascular SST3, CXCR4 or ETA positivity. SST5 or CXCR4 positivity of tumor cells and vascular SST3 or CXCR4 expression negatively correlated with patient outcome.

CONCLUSIONS

Though having some prognostic value, SST, CXCR4 or ETA expression on astrocytic tumor cells is clearly of no therapeutic relevance. Indirect targeting of these highly vascularized tumors via SST3, SST5, CXCR4 or ETA on the microvessels, in contrast, may represent a promising additional therapeutic strategy.

Renin angiotensin system and its role in biomarkers and treatment in gliomas

Gliomas are the most common primary intrinsic tumor in the brain and are classified as low- or high-grade according to the World Health Organization (WHO). Patients with high-grade gliomas (HGG) who undergo surgical resection with adjuvant therapy have a mean overall survival of 15 months and 100% recurrence. The renin-angiotensin system (RAS), the primary regulator of cardiovascular circulation, exhibits local action and works as a paracrine system. In the context of this local regulation, the expression of RAS peptides and receptors has been detected in different kinds of tumors, including gliomas. The dysregulation of RAS components plays a significant role in the proliferation, angiogenesis, and invasion of these tumors, and therefore in their outcomes. The study and potential application of RAS peptides and receptors as biomarkers in gliomas could bring advantages against the limitations of current tumoral markers and should be considered in the future. The targeting of RAS components by RAS blockers has shown potential of being protective against cancer and improving immunotherapy. In gliomas, RAS blockers have shown a broad spectrum for beneficial effects and are being considered for use in treatment protocols. This review aims to summarize the background behind how RAS plays a role in gliomagenesis and explore the evidence that could lead to their use as biomarkers and treatment adjuvants.

Overexpression of endothelin B receptor in glioblastoma: a prognostic marker and therapeutic target?

Background

Glioblastoma (GBM) is the most common malignant brain tumor with median survival of 12-15 months. Owing to uncertainty in clinical outcome, additional prognostic marker(s) apart from existing markers are needed. Since overexpression of endothelin B receptor (ETBR) has been demonstrated in gliomas, we aimed to test whether ETBR is a useful prognostic marker in GBM and examine if the clinically available endothelin receptor antagonists (ERA) could be useful in the disease treatment.

Methods

Data from The Cancer Genome Atlas and the Gene Expression Omnibus database were analyzed to assess ETBR expression. For survival analysis, glioblastoma samples from 25 Swedish patients were immunostained for ETBR, and the findings were correlated with clinical history. The druggability of ETBR was assessed by protein-protein interaction network analysis. ERAs were analyzed for toxicity in in vitro assays with GBM and breast cancer cells.

Results

By bioinformatics analysis, ETBR was found to be upregulated in glioblastoma patients, and its expression levels were correlated with reduced survival. ETBR interacts with key proteins involved in cancer pathogenesis, suggesting it as a druggable target. In vitro viability assays showed that ERAs may hold promise to treat glioblastoma and breast cancer.

Conclusions

ETBR is overexpressed in glioblastoma and other cancers and may be a prognostic marker in glioblastoma. ERAs may be useful for treating cancer patients.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4012-7) contains supplementary material, which is available to authorized users.

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.

Cellular Microbiology of Mycoplasma canis

Mycoplasma canis can infect many mammalian hosts but is best known as a commensal or opportunistic pathogen of dogs. The unexpected presence of M. canis in brains of dogs with idiopathic meningoencephalitis prompted new in vitro studies to help fill the void of basic knowledge about the organism's candidate virulence factors, the host responses that it elicits, and its potential roles in pathogenesis. Secretion of reactive oxygen species and sialidase varied quantitatively (P < 0.01) among strains of M. canis isolated from canine brain tissue or mucosal surfaces. All strains colonized the surface of canine MDCK epithelial and DH82 histiocyte cells and murine C8-D1A astrocytes. Transit through MDCK and DH82 cells was demonstrated by gentamicin protection assays and three-dimensional immunofluorescence imaging. Strains further varied (P < 0.01) in the extents to which they influenced the secretion of tumor necrosis factor alpha (TNF-α) and the neuroendocrine regulatory peptide endothelin-1 by DH82 cells. Inoculation with M. canis also decreased major histocompatibility complex class II (MHC-II) antigen expression by DH82 cells (P < 0.01), while secretion of gamma interferon (IFN-γ), interleukin-6 (IL-6), interleukin-10 (IL-10), and complement factor H was unaffected. The basis for differences in the responses elicited by these strains was not obvious in their genome sequences. No acute cytopathic effects on any homogeneous cell line, or consistent patterns of M. canis polyvalent antigen distribution in canine meningoencephalitis case brain tissues, were apparent. Thus, while it is not likely a primary neuropathogen, M. canis has the capacity to influence meningoencephalitis through complex interactions within the multicellular and neurochemical in vivo milieu.

The brain tissue response to surgical injury and its possible contribution to glioma recurrence

Surgery is the first line therapy for glioma. However, glioma recurs in 90 % of the patients in the resection margin. The impact of surgical brain injury (SBI) on glioma recurrence is largely overlooked. Herein, we review some of the mechanisms involved in tissue repair that may impact glioma recurrence at the resection margin. Many processes or molecules involved in tissue repair after brain injury are also critical for glioma growth. They include a wide array of secreted growth factors, cytokines and transcription factors including NFКB and STAT3 which in turn activate proliferative and anti-apoptotic genes and processes such as angiogenesis and inflammation. Because some residual glioma cells always remain in the tumor resection margin, there are now compelling arguments to suggest that some aspects of the brain tissue response to SBI can also participate to glioma recurrence at the resection margin. Brain tissue response to SBI recruits angiogenesis and inflammation that precede and then follow tumor recurrence at the resection margin. The healing response to SBI is double edged, as inflammation is involved in regeneration and healing, and has both pro- and anti-tumorigenic functions. A promising therapeutic approach is to normalize and re-educate the molecular and cellular responses at the resection margin to promote anti-tumorigenic processes involved in healing while inhibiting pro-tumorigenic activities. Manipulation of the inflammatory response to SBI to prevent local recurrence could also enhance the efficacy of other therapies such as immunotherapy. However, our current knowledge is far from sufficient to achieve this goal. Acknowledging, understanding and manipulating the double-edged role played by SBI in glioma recurrence is surely challenging, but it cannot be longer delayed.

Macitentan, a Dual Endothelin Receptor Antagonist, in Combination with Temozolomide Leads to Glioblastoma Regression and Long-term Survival in Mice

PURPOSE

The objective of the study was to determine whether astrocytes and brain endothelial cells protect glioma cells from temozolomide through an endothelin-dependent signaling mechanism and to examine the therapeutic efficacy of the dual endothelin receptor antagonist, macitentan, in orthotopic models of human glioblastoma.

EXPERIMENTAL DESIGN

We evaluated several endothelin receptor antagonists for their ability to inhibit astrocyte- and brain endothelial cell-induced protection of glioma cells from temozolomide in chemoprotection assays. We compared survival in nude mice bearing orthotopically implanted LN-229 glioblastomas or temozolomide-resistant (LN-229(Res) and D54(Res)) glioblastomas that were treated with macitentan, temozolomide, or both. Tumor burden was monitored weekly with bioluminescence imaging. The effect of therapy on cell division, apoptosis, tumor-associated vasculature, and pathways associated with cell survival was assessed by immunofluorescent microscopy.

RESULTS

Only dual endothelin receptor antagonism abolished astrocyte- and brain endothelial cell-mediated protection of glioma cells from temozolomide. In five independent survival studies, including temozolomide-resistant glioblastomas, 46 of 48 (96%) mice treated with macitentan plus temozolomide had no evidence of disease (P < 0.0001), whereas all mice in other groups died. In another analysis, macitentan plus temozolomide therapy was stopped in 16 mice after other groups had died. Only 3 of 16 mice eventually developed recurrent disease, 2 of which responded to additional cycles of macitentan plus temozolomide. Macitentan downregulated proteins associated with cell division and survival in glioma cells and associated endothelial cells, which enhanced their sensitivity to temozolomide.

CONCLUSIONS

Macitentan plus temozolomide are well tolerated, produce durable responses, and warrant clinical evaluation in glioblastoma patients.

Endothelin B receptors targeted by iron oxide nanoparticles functionalized with a specific antibody: toward immunoimaging of brain tumors

Vasculature enhancement is observed in mouse brain after intravenous injection of iron oxide nanoparticles functionalized with antibody targeting endothelin B receptors over-expressed in glioma.

Role of the endothelin axis in astrocyte- and endothelial cell-mediated chemoprotection of cancer cells

BACKGROUND

Recent evidence suggests that astrocytes protect cancer cells from chemotherapy by stimulating upregulation of anti-apoptotic genes in those cells. We investigated the possibility that activation of the endothelin axis orchestrates survival gene expression and chemoprotection in MDA-MB-231 breast cancer cells and H226 lung cancer cells.

METHODS

Cancer cells, murine astrocytes, and murine fibroblasts were grown in isolation, and expression of endothelin (ET) peptides and ET receptors (ETAR and ETBR) compared with expression on cancer cells and astrocytes (or cancer cells and fibroblasts) that were co-incubated for 48 hours. Type-specific endothelin receptor antagonists were used to evaluate the contribution of ETAR and ETBR to astrocyte-induced activation of the protein kinase B (AKT)/mitogen-activated protein kinase (MAPK) signal transduction pathways, anti-apoptotic gene expression, and chemoprotection of cancer cells. We also investigated the chemoprotective potential of brain endothelial cells and microglial cells.

RESULTS

Gap junction signaling between MDA-MB-231 cancer cells and astrocytes stimulates upregulation of interleukin 6 (IL-6) and IL-8 expression in cancer cells, which increases ET-1 production from astrocytes and ET receptor expression on cancer cells. ET-1 signals for activation of AKT/MAPK and upregulation of survival proteins that protect cancer cells from taxol. Brain endothelial cell-mediated chemoprotection of cancer cells also involves endothelin signaling. Dual antagonism of ETAR and ETBR is required to abolish astrocyte- and endothelial cell-mediated chemoprotection.

CONCLUSIONS

Bidirectional signaling between astrocytes and cancer cells involves upregulation and activation of the endothelin axis, which protects cancer cells from cytotoxicity induced by chemotherapeutic drugs.

Role of endothelin B receptor in oligodendroglioma proliferation and survival: In vitro and in vivo evidence

In this study, the role of the endothelin B receptor (ETBR) in oligodendroglioma cell proliferation and survival was investigated in vitro and in vivo. The overexpression and knockdown of ETBR was conducted in Hs683 human oligodendroglioma cells, and cell proliferation and activation (phosphorylation) of extracellular signal-regulated kinase (ERK) were measured in vitro. An orthotopic xenograft oligodendroglioma mouse model was established. Mouse survival times and immunohistochemical Ki67 staining in the xenografts were examined. In vitro experiments demonstrated that the overexpression of ETBR significantly enhanced the proliferation of oligodendroglioma cells and the activation of ERK compared with the controls, which was eliminated by the selective ETBR inhibitor BQ788 and ERK-specific inhibitor U0126, but not selective endothelin A receptor inhibitor BQ123. By contrast, the knockdown of endogenous ETBR markedly decreased oligodendroglioma cell proliferation and the activation of ERK compared with the controls. Overexpression of ETBR significantly increased immunohistochemical Ki67 staining in the Hs683 cell orthotopic xenograft and decreased animal survival. By contrast, knockdown of ETBR significantly decreased Ki67 staining and increased mouse survival times. Intratumoral injection of BQ788, but not BQ123, significantly decreased Ki67 staining and prolonged mouse survival times. In conclusion, ETBR was demonstrated to mediate the proliferation of oligodendroglioma cells according to an ERK-dependent mechanism. Using an orthotopic xenograft oligodendroglioma mouse model, it was demonstrated in vivo that ETBR promotes oligodendroglioma proliferation and that the selective ETBR antagonist effectively inhibits the proliferation of oligodendroglioma cells and prolongs survival times. This study provides a novel insight into the role of ETBR in oligodendroglioma proliferation and survival, and provides the first in vivo evidence that ETBR-specific antagonists are a potential therapeutic alternative for oligodendrogliomas.

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.

Antivascular therapy for multidrug-resistant ovarian tumors by macitentan, a dual endothelin receptor antagonist

Endothelin receptors (ETRs) are often overexpressed in ovarian tumors, which can be resistant to conventional therapies. Thus, we investigated whether blockage of the ETR pathways using the dual ETR antagonist macitentan combined with taxol or cisplatinum can produce therapy for orthotopically growing multidrug-resistant (MDR) human ovarian carcinoma. In several studies, nude mice were injected in the peritoneal cavity with HeyA8-MDR human ovarian cancer cells. Ten days later, mice were randomized to receive vehicle (saline), macitentan (oral, daily), taxol (intraperitoneal, weekly), cisplatinum (intraperitoneal, weekly), macitentan plus taxol, or macitentan plus cisplatinum. Moribund mice were killed, and tumors were collected, weighed, and prepared for immunohistochemical analysis. The HeyA8-MDR tumors did not respond to taxol, cisplatinum, or macitentan administered as single agents. In contrast, combination therapy with macitentan and taxol or macitentan and cisplatinum significantly decreased the tumor incidence and weight and significantly increased the survival of mice and their general condition. Multiple immunohistochemical analyses revealed that treatment with macitentan and macitentan plus taxol or cisplatinum inhibited the phosphorylation of ETRs, decreased the levels of pVEGFR2, pAkt, and pMAPK in tumor cells after 2 weeks of treatment and induced a first wave of apoptosis in tumor-associated endothelial cells followed by apoptosis in surrounding tumor cells. Our study shows that ovarian cancer cells, which express the endothelin axis and are multidrug resistant, are exquisitely sensitive to treatment with a dual ET antagonist and can be resensitized to both taxol and cisplatinum. This combined therapy led to a significant reduction in tumor weight.

Autocrine endothelin-3/endothelin receptor B signaling maintains cellular and molecular properties of glioblastoma stem cells

Glioblastoma stem cells (GSC) express both radial glial cell and neural crest cell (NCC)-associated genes. We report that endothelin 3 (EDN3), an essential mitogen for NCC development and migration, is highly produced by GSCs. Serum-induced proliferative differentiation rapidly decreased EDN3 production and downregulated the expression of stemness-associated genes, and reciprocally, two glioblastoma markers, EDN1 and YKL-40 transcripts, were induced. Correspondingly, patient glioblastoma tissues express low levels of EDN3 mRNA and high levels of EDN1 and YKL-40 mRNA. Blocking EDN3/EDN receptor B (EDNRB) signaling by an EDNRB antagonist (BQ788), or EDN3 RNA interference (siRNA), leads to cell apoptosis and functional impairment of tumor sphere formation and cell spreading/migration in culture and loss of tumorigenic capacity in animals. Using exogenous EDN3 as the sole mitogen in culture does not support GSC propagation, but it can rescue GSCs from undergoing cell apoptosis. Molecular analysis by gene expression profiling revealed that most genes downregulated by EDN3/EDNRB blockade were those involved in cytoskeleton organization, pause of growth and differentiation, and DNA damage response, implicating the involvement of EDN3/EDNRB signaling in maintaining GSC migration, undifferentiation, and survival. These data suggest that autocrine EDN3/EDNRB signaling is essential for maintaining GSCs. Incorporating END3/EDNRB-targeted therapies into conventional cancer treatments may have clinical implication for the prevention of tumor recurrence.

Endothelin B receptor expression in human astrocytoma: association with clinicopathological variables and survival outcomes

The endothelin (ET) axis has been implicated in astrocytoma growth and progression. Selective ETB receptor antagonists blocked proliferation and induced apoptosis in astrocytoma cell lines, suggesting that the ETB receptor could be a therapeutic target for astrocytomas. In the present study, we explored the association of the ETB receptor expression with clinicopathological variables and the prognosis of human astrocytomas, by examining the ETB receptor expression and Ki-67 staining in 71 surgically resected astrocytomas with immunohistochemistry. High expression of the ETB receptor was significantly associated with high grade of astrocytomas (p < .0001) and high Ki-67 labeling index (LI; p < .0001). Kaplan-Meier survival analysis showed that the ETB receptor high expression group had significantly shorter disease-free survival (DFS) and overall survival (OS) rates than the low expression group (p < .001). Multivariate analysis with the Cox's proportional hazards model revealed that high expression of the ETB receptor, high WHO grade, and high Ki-67 LI were independent factors for shorter DFS and OS (p < .05 for each comparison). In conclusion, high expression of the ETB receptor is closely associated with high malignancy and poor prognosis of human astrocytomas, which suggests that the ETB receptor could be a promising therapeutic target for astrocytomas, particularly high-grade astrocytomas.

Angiogenesis and the tumor vasculature as antitumor immune modulators: the role of vascular endothelial growth factor and endothelin

Cancer immunotherapies have yielded promising results in recent years, but new approaches must be utilized if more patients are to experience the benefits of these therapies. Angiogenesis and the tumor endothelium confer unique immune privilege to a growing tumor, with significant effects on diverse immunological processes such as hematopoietic cell maturation, antigen presentation, effector T cell differentiation, cytokine production, adhesion, and T cell homing and extravasation. Here, we review the role of angiogenesis and the tumor endothelium on regulation of the antitumor immune response. We place particular emphasis on the role of vascular endothelial growth factor (VEGF) in the suppression of numerous immunological processes that control tumor progression. Further, we describe the unique crosstalk between the VEGF and endothelin systems, and how their interactions may shape the antitumor immune response. These insights establish new targets for combinatorial approaches to modify existing cancer immunotherapies.

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.

Electroporation-aided DNA immunization generates polyclonal antibodies against the native conformation of human endothelin B receptor

Endothelin B receptor (ET(B)R) is a G protein-coupled receptor (GPCR) specific for endothelin peptides (including endothelin-1, ET1), which mediates a variety of key physiological functions in normal tissues, such as modulation of vasomotor tone, tissue differentiation, or cell proliferation. Moreover, ET(B)R, overexpressed in various cancer cells including melanoma, has been implicated in the growth and progression of tumors, as well as in controlling T cell homing to tumors. To gather information on receptor structure and function, antibodies are generally considered choice molecular probes, but generation of such reagents against the native conformation of GPCRs is a real technical challenge. Here, we show that electroporation-aided genetic immunization, coupled to cardiotoxin pretreatment, is a simple and very efficient method to raise large amounts of polyclonal antibodies highly specific for native human ET(B)R (hET(B)R), as assessed by both flow cytometry analysis of different stably transfected cell lines and a new and rapid cell-based enzyme-linked immunosorbent assay that we also describe. The antibodies recognized two major epitopes on hET(B)R, mapped within the N-terminal extracellular domain. They were used to reveal hET(B)R on membranes of three different human melanoma cell lines, by flow cytometry and confocal microscopy, a method that we show is more relevant than mRNA polymerase chain reaction in assessing receptor expression. In addition, ET-1 partially competed with antibodies for receptor binding. The strategy described here, thus, efficiently generated new immunological tools to further analyze the role of ET(B)R under both normal and pathological conditions, including cancers. Above all, it can now be used to raise monoclonal antibodies against hET(B)R and, more generally, against GPCRs that constitute, by far, the largest reservoir of potential pharmacological targets.

Endothelin-1: a predictor of extracapsular extension in clinically localized prostate cancer?

OBJECTIVE

To assess the value of endothelin-1 (ET-1) expression in predicting extracapsular extension (ECE) in clinically localized prostate cancer (PCa).

PATIENTS AND METHODS

ET-1 expression was determined by immunohistochemistry on archival needle biopsies (NBs) from 94 patients (49 pT2 and 45 pT3a) who underwent radical prostatectomy (RP) for clinical T1-T2 PCa. Each sample was analysed independently by two pathologists blinded to the clinical data.

RESULTS

In univariate analysis, high ET-1 expression in NBs, pre-operative prostate-specific antigen (PSA) level >10 ng/ml, percentage of positive biopsy cores and NB Gleason score ≥7 were significantly associated with ECE as determined on subsequent RP. No significant association was found between clinical stage and ECE. In multivariate analysis, there was a significant association with high ET-1 expression in NBs (p = 0.006), pre-operative PSA level >10 ng/ml (p = 0.049), and NB Gleason score ≥7 (p = 0.002). These three pre-operative factors combined provided the best model for predicting ECE with 93.3% sensitivity, 49% specificity, 62.5% positive predictive value, 88.9% negative predictive value. The combination yielded a higher concordance index (0.760 vs 0.720) and offered a higher log partial likelihood than the same model without ET1 (112.8 vs 105.7, p = 0.01).

CONCLUSIONS

ET-1 expression was strongly associated with ECE and, when combined with pre-operative PSA level and Gleason score, improved the predictive accuracy of pre-operative NBs. Its assessment in patients with localized PCa might be useful when making treatment decisions. Further studies with standardisation of immunohistochemical staining and multi-institutional validation are now needed to establish the appropriate use of ET-1 staining in PCa staging and to evaluate inter-observer reproducibility.

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 B receptor antagonists block proliferation and induce apoptosis in glioma cells

The proliferative and antiapoptotic actions of endothelin (ET)-1 in cancer cells have been documented and ET receptor antagonists have been exploited as potential anticancer drugs. Glioblastoma cell lines express both ETA and ETB receptors and previous works have shown that ETB receptors are involved in the proliferation of different cancer cell types. In this study we have investigated the effects of two structurally unrelated ETB receptor antagonists, BQ788 and A192621, on cell survival, proliferation and apoptosis in 1321-N1, U87 and IPDDCA2 glioma cell lines. BQ788 and A192621 reduced glioma cells viability and proliferation assessed by BrdU incorporation and cell cycle analysis by flow cytometry, while in contrast the ETA receptor antagonist BQ123 had no effect on cell survival. TUNEL assay and immunocytochemical experiments showed that BQ788 and A192621 trigger apoptotic processes mainly via activation of the intrinsic mitochondrial pathway involving caspase-9 activation, AIF release and cytochrome c translocation. Furthermore, treatment with ETB antagonists downregulates ERK- and p38MAPK-dependent pathways but does not affect VEGF mRNA levels. Our findings support the hypothesis that ETB antagonists represent a new promising therapeutic strategy for the treatment of high grade gliomas.

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

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

Endothelin B receptor, a new target in cancer immune therapy

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

Endothelin receptor B antagonists decrease glioma cell viability independently of their cognate receptor

BACKGROUND

Endothelin receptor antagonists inhibit the progression of many cancers, but research into their influence on glioma has been limited.

METHODS

We treated glioma cell lines, LN-229 and SW1088, and melanoma cell lines, A375 and WM35, with two endothelin receptor type B (ETRB)-specific antagonists, A-192621 and BQ788, and quantified viable cells by the capacity of their intracellular esterases to convert non-fluorescent calcein AM into green-fluorescent calcein. We assessed cell proliferation by labeling cells with carboxyfluorescein diacetate succinimidyl ester and quantifying the fluorescence by FACS analysis. We also examined the cell cycle status using BrdU/propidium iodide double staining and FACS analysis. We evaluated changes in gene expression by microarray analysis following treatment with A-192621 in glioma cells. We examined the role of ETRB by reducing its expression level using small interfering RNA (siRNA).

RESULTS

We report that two ETRB-specific antagonists, A-192621 and BQ788, reduce the number of viable cells in two glioma cell lines in a dose- and time-dependent manner. We describe similar results for two melanoma cell lines. The more potent of the two antagonists, A-192621, decreases the mean number of cell divisions at least in part by inducing a G2/M arrest and apoptosis. Microarray analysis of the effects of A-192621 treatment reveals up-regulation of several DNA damage-inducible genes. These results were confirmed by real-time RT-PCR. Importantly, reducing expression of ETRB with siRNAs does not abrogate the effects of either A-192621 or BQ788 in glioma or melanoma cells. Furthermore, BQ123, an endothelin receptor type A (ETRA)-specific antagonist, has no effect on cell viability in any of these cell lines, indicating that the ETRB-independent effects on cell viability exhibited by A-192621 and BQ788 are not a result of ETRA inhibition.

CONCLUSION

While ETRB antagonists reduce the viability of glioma cells in vitro, it appears unlikely that this effect is mediated by ETRB inhibition or cross-reaction with ETRA. Instead, we present evidence that A-192621 affects glioma and melanoma viability by activating stress/DNA damage response pathways, which leads to cell cycle arrest and apoptosis. This is the first evidence linking ETRB antagonist treatment to enhanced expression of DNA damage-inducible genes.

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

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

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

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

Targeted therapy for malignant gliomas

The identification of markers that are associated with tumour but not normal tissue has allowed the development of highly-specific targeted therapies. Monoclonal antibodies, either alone or linked to radioisotopes or toxins, have provided a powerful tool for research, as well as the basis for promising therapeutic agents with less side effects than standard radiotherapy or chemotherapy. A new class of drugs, the tyrosine kinase inhibitors, which interfere with the function of key molecules in cancer-promoting pathways, have had a dramatic effect in haematological malignancy and are being trialled in solid tumours, including glioma. Although the problem of achieving specific, high-level delivery of these various agents to tumours in the brain remains a major issue, encouraging early results with some targeted agents support the attractive theoretical principles of this new paradigm. Further work to identify new molecular targets and to develop agents exploiting them, is needed, as well as confirmation of their safety and efficacy by clinical trials.

A phase II study of bosentan, a dual endothelin receptor antagonist, as monotherapy in patients with stage IV metastatic melanoma

There is no effective systemic therapy for disseminated metastatic melanoma. Data suggest that endothelin may play a role in pathophysiology of melanoma and that the dual endothelin receptor antagonist bosentan may have anti-tumor activity. This multicenter, open-label, single-arm, prospective, proof-of-concept study assessed the effects of bosentan monotherapy (500 mg oral tablets, bid) on tumor response in patients with stage IV metastatic melanoma. Patients were treated until disease progression, death or serious adverse event leading to premature study drug discontinuation. Tumor response was assessed at 6-weekly intervals using the Response Evaluation Criteria in Solid Tumors (RECIST). Among the 35 patients included in this study with stage IV metastatic melanoma, 21 (60%) were stage M1C, 10 (29%) stage M1B and 4 (11%) stage M1A (American Joint Committee on Cancer [AJCC] classification). Nine patients (26%) had received prior therapy for stage IV melanoma. Disease stabilization was observed in 6 of the 32 patients analyzed per protocol at week 6 with confirmatory evaluation at week 12, 5 of whom were still stable at > or =24 weeks. Of the 6 patients with disease stabilization, 2 were stage M1A, 1 was stage M1B and the remaining 3 were stage M1C. Partial or complete response was not observed. Progressive disease was observed in 17 (49%) patients at week 12 and in 25 (71%) patients at the end of the study (data base closure). The most frequent adverse events were typical for the underlying disease or known to be associated with bosentan: headache (43%), fatigue (34%), nausea (31%), back pain (23%) and abnormal hepatic function (23%). Bosentan might have benefit in disease stabilization in certain patients with metastatic melanoma and deserves further investigation in combination with other anticancer drugs.

Nonclassic Endogenous Novel Regulators of Angiogenesis

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

Endothelin-1 promotes cell survival in renal cell carcinoma through the ET(A) receptor

Endothelin-1 (ET-1) is a potent vasoconstrictor that has been shown to significantly impact many benign and malignant tissues by signaling through its two cognate receptors: ET(A) and ET(B). As ET-1 has a role in both normal and diseased kidney, we initiated studies to investigate endothelin axis expression and function in renal cell carcinoma (RCC). In this study, relatively high levels of ET-1 were detected in all six human RCC cell lines investigated. RT-PCR and Southern analyses revealed that all six RCC cell lines expressed ET(A) receptor mRNA, while 3/6 cell lines also expressed ET(B) mRNA. High affinity ET-1 binding occurred in all but one RCC cell line and quantitative RT-PCR demonstrated ET(A) mRNA expression in all six cell lines. Methylation of the ET(B) promoter (EDNRB) in 4/6 RCC cell lines was observed, suggesting a mechanism for repressed ET(B) expression. Moreover, methylation occurred in 32/48 of renal tumors and in 27/55 of histologically normal adjacent tissue samples studied, while no methylation was evident in any normal tissue isolated from nephrectomy or at autopsy. Functionally, ET-1 significantly inhibited paclitaxel-induced apoptosis in RCC cells through binding ET(A) with the ET-1 signaling mediated via the PI3-kinase/Akt pathway. Collectively, these data support the therapeutic targeting of the ET(A) receptor as a novel treatment strategy for RCC.

Expression of endothelins and their receptors in glioblastoma cell lines

The endothelins (ETs) are a family of three peptides named ET-1, ET-2 and ET-3 that have been initially isolated as potent vasoactive peptides; ETs are synthesized as precursor proteins (preproETs) and are activated by proteolytic cleavage. ETs exert their biological effects through the activation of two receptors subtypes, ETA and ETB. Recent studies have shown that, besides its vascular effects, ET-1 appears to play a major role also in the growth and progression of various types of cancers and ETA or ETB are alternatively indicated as mediators of the ET-1 biological effects. In this study we have investigated the expression and the amounts of preproET-1, preproET-2, ETA and ETB receptors mRNA by classical RT-PCR and quantitative real-time PCR in one human low grade astrocytoma cell line and eight human glioblastoma cell lines. PCR products corresponding to ETB receptor and preproET-1 were detectable in all the cell lines whilst ETA receptor and preproET-2 were only detected in five cell lines. Quantitative real-time PCR experiments showed wide differences in the amounts of mRNAs among the cell lines examined. Range values were 0.23-4860.51 fg/mug total cDNA for preproET-1; 0.13-3330.18 fg/mug total cDNA for preproET-2; 0.63-286.12 fg/mug total cDNA for ETA and 14.40-6720.67 fg/mug total cDNA for ETB. We measured the ET-1 released in the extracellular medium by an ELISA assay and we found an excellent correlation (correlation coefficient r = 0.9526, P = 0.0003) between the amounts of preproET-1 mRNA and released ET-1 peptide. Finally, in the 1321N1 cell line ETB receptors are functionally coupled to intracellular signaling pathways because the stimulation of ETB receptors by ET-1 induces the phosphorylation of the extracellular regulated kinases (ERKs). Although the majority of glioblastoma cell lines in culture express ET isoforms and ET receptors, we conclude that ET-1 and the ETB receptors are likely to mediate the effects of the ET system in glioblastoma cell lines.

A cDNA-microarray analysis of camptothecin resistance in glioblastoma cell lines

Chemotherapy, as generally available, is of a limited value in curing malignant brain tumors (gliomas), which often develop resistance to drugs, becoming completely unresponsive to any standard therapeutic approach. Camptothecins, a family of topoisomerase I inhibitor drugs, represent a new promising treatment strategy and are currently under evaluation for testing the clinical efficacy. We selected a CPT-resistant sub-line (U87CPT-R) from U87-MG grade III-IV astrocytoma cells, and compared the expression profile of the two cell lines by cDNA-microarray, as a preliminary screening of the molecular mechanisms involved in the acquisition of CPT resistance in glioma cells. The relevant role of IL-1 beta overproduction as well as a generalised up-regulation of genes implicated in angiogenesis and inflammatory response are discussed in details.

Angiogenesis in gliomas: biology and molecular pathophysiology

Glioblastoma multiforme (GBM) is characterized by exuberant angiogenesis, a key event in tumor growth and progression. The pathologic mechanisms driving this change and the biological behavior of gliomas remain unclear. One mechanism may involve cooption of native blood vessels by glioma cells inducing expression of angiopoietin-2 by endothelial cells. Subsequently, vascular apoptosis and involution leads to necrosis and hypoxia. This in turn induces angiogenesis that is associated with expression of hypoxia-inducible factor (HIF)-1alpha and vascular endothelial growth factor (VEGF) in perinecrotic pseudopalisading glioma cells. Here we review the molecular and cellular mechanisms implicated in HIF-1-dependent and HIF-1-independent glioma-associated angiogenesis. In GBMs, both tumor hypoxia and genetic alterations commonly occur and act together to induce the expression of HIF-1. The angiogenic response of the tumor to HIF-1 is mediated by HIF-1-regulated target genes leading to the upregulation of several proangiogenic factors such as VEGF and other adaptive response molecules. Understanding the roles of these regulatory processes in tumor neovascularization, tumor growth and progression, and resistance to therapy will ultimately lead to the development of improved antiangiogenic therapies for GBMs.

The endothelin B (ETB) receptor agonist IRL 1620 is highly vasoconstrictive in two syngeneic rat tumour lines: potential for selective tumour blood flow modification

The vascular effects of the endothelin B (ET_B) receptor agonist IRL 1620 were investigated in the rat P22 carcinosarcoma and a range of normal tissues in BDIX rats. Tissue blood flow rate was calculated from measurements of tissue uptake of radiolabelled iodoantipyrine. A comparison of vascular effects in the P22 tumour and the HSN sarcoma growing in CBH/CBi rats was made using laser Doppler flowmetry, showing similar effects of IRL 1620, with red cell flux rapidly decreasing by 50–60% and then returning to control levels within approximately 30 min. This corresponded to similar levels but different spatial organisation of ET_B binding sites in the two tumours, as measured by autoradiography. The decrease in tumour blood flow and an increase in vascular resistance suggest that the vascular component of ET_B receptors in the P22 tumour is localised on contractile elements rather than on endothelial cells. ET_A receptors were also identified. Vasoconstriction occurred uniformly throughout the P22 tumour mass, consistent with a measured homogeneous distribution of ET_B receptors. IRL 1620 caused vasoconstriction in normal skeletal muscle, kidney and small intestine of the BDIX rat as well as in tumour, but did not affect blood flow in other tissues. These effects could be useful for limiting toxicity of certain chemotherapeutic agents. Fully functional ET_B receptors are clearly expressed on tumour vasculature and IRL 1620 shows promise for short-term modification of tumour blood flow. Expression levels of ET_B receptors on the tumour vasculature could be useful for predicting which tumours are likely to respond to IRL 1620.

Functionalized Pyrrolidines Inhibit α-Mannosidase Activity and Growth of Human Glioblastoma and Melanoma Cells

New substituted pyrrolidine-3,4-diol derivatives were prepared from d-(-)- and l-(+)-phenyl glycinol. The influence of the configuration and the substitution of the lateral side chain of these derivatives on the inhibition of 25 commercial glycosidases were determined. (2R,3R,4S)-2-({[(1R)-2-Hydroxy-1-phenylethyl]amino}methyl)pyrrolidine-3,4-diol ((+)-7a) was a potent and selective inhibitor of jack bean alpha-mannosidase (K(i) = 135 nM). However, when evaluated on human tumor cells, 7a, and the reference compound swainsonine, did not efficiently inhibit the growth of glioblastoma cells. Further derivatization of the hydroxyl group with lipophilic groups to increase bioavailability improved their growth inhibitory properties for human glioblastoma and melanoma cells. In particular, the 4-bromobenzoyl derivative 26 demonstrated high efficacy for human tumor cells whereas primary human fibroblasts were less sensitive to 26. Therefore, functionalized pyrrolidines have the potential to inhibit the growth of tumor cells and display selectivity for tumor cells when compared to normal cells.

Hypoxia and the hypoxia-inducible-factor pathway in glioma growth and angiogenesis

Glioblastomas, like other solid tumors, have extensive areas of hypoxia and necrosis. The importance of hypoxia in driving tumor growth is receiving increased attention. Hypoxia-inducible factor 1 (HIF-1) is one of the master regulators that orchestrate the cellular responses to hypoxia. It is a heterodimeric transcription factor composed of alpha and beta subunits. The alpha subunit is stable in hypoxic conditions but is rapidly degraded in normoxia. The function of HIF-1 is also modulated by several molecular mechanisms that regulate its synthesis, degradation, and transcriptional activity. Upon stabilization or activation, HIF-1 translocates to the nucleus and induces transcription of its downstream target genes. Most important to gliomagenesis, HIF-1 is a potent activator of angiogenesis and invasion through its upregulation of target genes critical for these functions. Activation of the HIF-1 pathway is a common feature of gliomas and may explain the intense vascular hyperplasia often seen in glioblastoma multiforme. Activation of HIF results in the activation of vascular endothelial growth factors, vascular endothelial growth factor receptors, matrix metalloproteinases, plasminogen activator inhibitor, transforming growth factors alpha and beta, angiopoietin and Tie receptors, endothelin-1, inducible nitric oxide synthase, adrenomedullin, and erythropoietin, which all affect glioma angiogenesis. In conclusion, HIF is a critical regulatory factor in the tumor microenvironment because of its central role in promoting proangiogenic and invasive properties. While HIF activation strongly promotes angiogenesis, the emerging vasculature is often abnormal, leading to a vicious cycle that causes further hypoxia and HIF upregulation.

Functional endothelin ET B receptors are selectively expressed in human oligodendrogliomas

Endothelin-1 (ET-1), a vasoactive and mitogenic peptide mainly produced by vascular endothelial cells, may be involved in the progression of several human tumors. Here, we present an immunohistochemical analysis of the expression pattern of ET-1 receptor subtypes (ET(A)-R and ET(B)-R) and a functional study of their potential role in human oligodendrogliomas and oligoastrocytomas. By comparison, we assessed the corresponding expression patterns of glioblastomas. Interestingly, a nuclear localization of ET-1 receptor subtypes (associated or not with a cytoplasmic labeling) was constantly observed in tumor cells from all three glioma types. Moreover, we noted a distinct receptor distribution in the different gliomas: a nuclear expression of ET(B)-R by tumor cells was found to be restricted to oligodendrogliomas and oligoastrocytomas, while a nuclear expression of ET(A)-R was only detected in tumor cells from some glioblastomas. Using primary cultures of oligodendroglial tumor cells, we confirmed the selective expression of nuclear ET(B)-R, together with a plasma membrane expression, and further demonstrated that this receptor was functionally coupled to intracellular signaling pathways known to be involved in cell survival and/or proliferation: extracellular signal-regulated kinase and focal adhesion kinase activation, actin cytoskeleton reorganization. In addition, impairment of ET(B)-R activation in these cells by in vitro treatment with an ET(B)-R-specific antagonist induced cell death. These data point to ET-1 as a possible survival factor for oligodendrogliomas via ET(B)-R activation and suggest that ET(B)-R-specific antagonists might constitute a potential therapeutic alternative for oligodendrogliomas.

Pertussis toxin-sensitive modulation of glutamate transport by endothelin-1 type A receptors in glioma cells

Endothelin-1 (ET-1) is a 21 amino acids peptide that exerts several biological activities through interaction with specific G-protein coupled receptors. Increased ET-1 expression is frequently associated with pathological situations involving alterations in glutamate levels. In the present study, a brief exposure to ET-1 was found to increase aspartate uptake in C6 glioma cells, which endogenously express the neuronal glutamate transporter EAAC1 (pEC50 of 9.89). The stimulatory effect of ET-1 mediated by ETA receptors corresponds to a 62% increase in the Vmax with no modification of the affinity for the substrate. While protein kinase C activity is known to participate in the regulation of EAAC1, the effect of ET-1 on the glutamate uptake was found to be independent of this kinase activation. In contrast, the inactivation of Go/i type G-protein dependent signaling with pertussis toxin was found to impair ET-1-mediated regulation of EAAC1. An examination of the cell surface expression of EAAC1 by protein biotinylation studies or by confocal analysis of immuno-fluorescence staining demonstrated that ET-1 stimulates EAAC1 translocation to the cell surface. Hence, the disruption of the cytoskeleton with cytochalasin D prevented ET-1-stimulated aspartate uptake. Together, the data presented in the current study suggest that ET-1 participates in the acute regulation of glutamate transport in glioma cells. Considering the documented role of glutamate excitotoxicity in the development of brain tumors, endothelinergic system constitutes a putative target for the pharmacological control of glutamate transmission at the vicinity of glioma cells.

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

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

CONCLUSION

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

Localization of the endothelin system in human diffuse astrocytomas

BACKGROUND

Endothelin-1 (ET-1), a vasoconstrictor and mitogen, has recently been implicated in the pathogenesis of human glioblastoma, neuroblastoma, and meningioma. ET-1, formed by proteolysis of the propeptide big ET-1 by endothelin-converting enzyme-1 (ECE-1), mediates its cellular actions through ETA and ETB receptors. Because only immunoreactive ET-1 has been observed within human astrocytic tumor cells, the authors investigated the localization of the entire ET-1 system (ET-1 mRNA, ET-1, ECE-1, ETA and ETB receptors) in surgical samples of human diffuse astrocytomas WHO Grade II (n = 6).

METHODS

ET-1 mRNA expression was elucidated by in situ reverse transcriptase polymerase chain reaction (RT-PCR) using synthetic primers. Polyclonal antibodies were used to localize ET-1, ECE-1, ETA and ETB receptors by immunocytochemistry.

RESULTS

All ET components were detected in the six tumor samples. Intense (3+) cytoplasmic ET-1 mRNA labeling was observed in more than 75% of cells in all 6 astrocytomas. Up to 75% of tumor cells displayed intense ET-1 and ECE-1 immunolabeling distributed throughout their cytoplasm. Immunoreactive ETA and ETB receptors, observed in 25% to 75% of astrocytic tumor cells, were of moderate intensity. In addition, all components of the ET system were seen within endothelial cells of tumor blood vessels.

CONCLUSIONS

The presence of ET-1 mRNA, ECE-1, and ET-1 within tumor astrocytes suggests local ET synthesis and processing. The mitogenic and antiapoptotic properties of ET-1, as well as the vasodilatory signaling of ETB receptors, may promote tumorigenesis.

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

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

Endothelin axis expression is markedly different in the two main subtypes of renal cell carcinoma

BACKGROUND

The endothelin axis has been implicated in cancer growth, angiogenesis, and metastasis, but to the authors' knowledge the expression of endothelin genes has not been defined in renal cell carcinoma (RCC).

METHODS

Tissue specimens were harvested from both normal and tumor-affected regions at the time of radical nephrectomy from 35 patients with RCC (22 with clear cell RCC [ccRCC] and 13 with papillary RCC [PRCC]). Real-time reverse transcriptase-polymerase chain reaction analysis determined the expression profile of the preproendothelins (PPET-1, PPET-2, and PPET-3), the endothelin receptors (ET(A) and ET(B)), and the endothelin-converting enzymes (ECE-1 and ECE-2).

RESULTS

PPET-1 was found to be up-regulated in ccRCC tumor specimens and down-regulated in PRCC tumor specimens. ET(A) was significantly down-regulated in PRCC tumor specimens. ECE-1 was expressed in all tissue specimens at comparable levels, with moderate but significant elevation in normal tissue specimens associated with PRCC. Of the other genes, PPET-2 and ET(B) were expressed in all tissue specimens and no differences were observed between tumor subtypes or tumor-affected and normal tissue specimens, whereas PPET-3 and ECE-2 were present in all tissue specimens but were barely detectable.

CONCLUSIONS

The endothelin axis was expressed differently in the two main subtypes of RCC and appeared to match macroscopic features commonly observed in these tumors (i.e., high expression of PPET-1 in hypervascular ccRCC contrasted against low PPET-1 and ET(A) expression in hypovascular PRCC). The presence of ECE-1 mRNA in these tissue specimens suggested that active endothelin ligands were present, indicating endothelin axis activity was elevated in ccRCC compared with normal kidney, but impaired in PRCC. The current study provided further evidence that it is not appropriate to consider ccRCC and PRCC indiscriminately in regard to treatment.

Immunolocalisation of endothelin-1 in human brain

The potent vasoconstrictor endothelin-1 (ET-1) may function as a neuropeptide and be a contributing factor in some neurological disorders, e.g. Alzheimer's dementia. The presence of ET-1 has been studied more extensively in the rat and porcine nervous systems than in the human brain. Also, the recent description of the extensive ET-1 mRNA localisation in human neural tissue supports expression in regions of human brain not previously investigated. Using specific anti-ET-1 polyclonal antiserum, we immunolocalised ET-1 in 24 regions of human brain autopsy tissues, and correlated this with ET-1 mRNA distribution. ET-1 immunoreactivity was observed within some cells of all the 24 areas examined. Neuronal staining for ET-1 was demonstrated within the diencephalon, brainstem, basal nuclei, cerebral cortex, cerebellar hemisphere, amygdala and hippocampus. In addition, ET-1 immunolabelling was visualised in the pituitary gland as well as in the choroid plexus. The primary sensory cortex and pineal gland also contained immunoreactive ET-1, although ET-1 mRNA had never been detected in these regions previously. The localisation of ET-1 and its subsequent correlation with ET-1 mRNA in most of the regions investigated suggest a more extensive distribution of the ET system in the human brain than was previously identified.

Renin and angiotensinogen expression and functions in growth and apoptosis of human glioblastoma

The expression and function in growth and apoptosis of the renin-angiotensin system (RAS) was evaluated in human glioblastoma. Renin and angiotensinogen (AGT) mRNAs and proteins were found by in situ hybridisation and immunohistochemistry in glioblastoma cells. Angiotensinogen was present in glioblastoma cystic fluids. Thus, human glioblastoma cells produce renin and AGT and secrete AGT. Human glioblastoma and glioblastoma cells expressed renin, AGT, renin receptor, AT(2) and/or AT(1) mRNAs and proteins determined by RT-PCR and/or Western blotting, respectively. The function of the RAS in glioblastoma was studied using human glioblastoma cells in culture. Angiotensinogen, des(Ang I)AGT, tetradecapaptide renin substrate (AGT1-14), Ang I, Ang II or Ang III, added to glioblastoma cells in culture, did not modulate their proliferation, survival or death. Angiotensin-converting enzyme inhibitors did not diminish glioblastoma cell proliferation. However, the addition of selective synthetic renin inhibitors to glioblastoma cells decreased DNA synthesis and viable tumour cell number, and induced apoptosis. This effect was not counterbalanced by concomitant addition of Ang II. In conclusion, the complete RAS is expressed by human glioblastomas and glioblastoma cells in culture. Inhibition of renin in glioblastoma cells may be a potential approach to control glioblastoma cell proliferation and survival, and glioblastoma progression in combination therapy.