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

Endothelin and the tumor microenvironment: a finger in every pie

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

Adult IDH Wild-Type Glioblastoma Ultrastructural Investigation Suggests a Possible Correlation between Morphological Biomarkers and Ki-67 Index

Glioblastoma is an aggressive brain tumor with an average life expectancy between 14 and 16 months after diagnosis. The Ki-67 labeling index (LI), a measure of cellular proliferation, is emerging as a prognostic marker in GBM. In this study, we investigated the ultrastructure of glioblastoma tissue from 9 patients with the same molecular profile (adult IDH wild-type glioblastoma, wild-type ATRX, and positive for TP53 expression, GFAP expression, and EGFR overexpression) to find possible ultrastructural features to be used as biomarkers and correlated with the only parameter that differs among our samples, the Ki-67 LI. Our main results were the visualization of the anatomical basis of astrocyte-endothelial cells crosstalk; the ultrastructural in situ imaging of clusters of hyperactivated microglia cells (MsEVs); the ultrastructural in situ imaging of microglia cells storing lipid vesicles (MsLVs); the ultrastructural in situ imaging of neoplastic cells mitophagy (NCsM). The statistical analysis of our data indicated that MsEVs and MsLVs correlate with the Ki-67 LI value. We can thus assume they are good candidates to be considered morphological biomarkers correlating to Ki-67 LI. The role of NCsM instead must be further evaluated. Our study findings demonstrate that by combining ultrastructural characteristics with molecular information, we can discover biomarkers that have the potential to enhance diagnostic precision, aid in treatment decision-making, identify targets for therapy, and enable personalized treatment plans tailored to each patient. However, further research with larger sample sizes is needed to validate these findings and fully utilize the potential of ultrastructural analysis in managing glioblastoma.

Cancer Stem Cell and Aggressiveness Traits Are Promoted by Stable Endothelin-Converting Enzyme-1c in Glioblastoma Cells

Glioblastoma (GBM) is the most common and aggressive type of brain tumor due to its elevated recurrence following treatments. This is mainly mediated by a subpopulation of cells with stemness traits termed glioblastoma stem-like cells (GSCs), which are extremely resistant to anti-neoplastic drugs. Thus, an advancement in the understanding of the molecular processes underlying GSC occurrence should contribute significantly towards progress in reducing aggressiveness. High levels of endothelin-converting enzyme-1 (ECE1), key for endothelin-1 (ET-1) peptide activation, have been linked to the malignant progression of GBM. There are four known isoforms of ECE1 that activate ET-1, which only differ in their cytoplasmic N-terminal sequences. Isoform ECE1c is phosphorylated at Ser-18 and Ser-20 by protein kinase CK2, which increases its stability and hence promotes aggressiveness traits in colon cancer cells. In order to study whether ECE1c exerts a malignant effect in GBM, we designed an ECE1c mutant by switching a putative ubiquitination lysine proximal to the phospho-serines Lys-6-to-Arg (i.e., K6R). This ECE1c^K6R mutant was stably expressed in U87MG, T98G, and U251 GBM cells, and their behavior was compared to either mock or wild-type ECE1c-expressing clone cells. ECE1c^K6R behaved as a highly stable protein in all cell lines, and its expression promoted self-renewal and the enrichment of a stem-like population characterized by enhanced neurospheroid formation, as well as increased expression of stem-like surface markers. These ECE1c^K6R-derived GSC-like cells also displayed enhanced resistance to the GBM-related chemotherapy drugs temozolomide and gemcitabine and increased expression of the ABCG2 efflux pump. In addition, ECE1c^K6R cells displayed enhanced metastasis-associated traits, such as the modulation of adhesion and the enhancement of cell migration and invasion. In conclusion, the acquisition of a GSC-like phenotype, together with heightened chemoresistance and invasiveness traits, allows us to suggest phospho-ECE1c as a novel marker for poor prognosis as well as a potential therapeutic target for GBM.

Tumor microenvironment and exosomes in brain metastasis: Molecular mechanisms and clinical application

Metastasis is one of the important biological features of malignant tumors and one of the main factors responsible for poor prognosis. Although the widespread application of newer clinical technologies and their continuous development have significantly improved survival in patients with brain metastases, there is no uniform standard of care. More effective therapeutic measures are therefore needed to improve prognosis. Understanding the mechanisms of tumor cell colonization, growth, and invasion in the central nervous system is of particular importance for the prevention and treatment of brain metastases. This process can be plausibly explained by the “seed and soil” hypothesis, which essentially states that tumor cells can interact with various components of the central nervous system microenvironment to produce adaptive changes; it is this interaction that determines the development of brain metastases. As a novel form of intercellular communication, exosomes play a key role in the brain metastasis microenvironment and carry various bioactive molecules that regulate receptor cell activity. In this paper, we review the roles and prospects of brain metastatic tumor cells, the brain metastatic tumor microenvironment, and exosomes in the development and clinical management of brain metastases.

The Interplay of Tumor Vessels and Immune Cells Affects Immunotherapy of Glioblastoma

Immunotherapies with immune checkpoint inhibitors or adoptive cell transfer have become powerful tools to treat cancer. These treatments act via overcoming or alleviating tumor-induced immunosuppression, thereby enabling effective tumor clearance. Glioblastoma (GBM) represents the most aggressive, primary brain tumor that remains refractory to the benefits of immunotherapy. The immunosuppressive immune tumor microenvironment (TME), genetic and cellular heterogeneity, and disorganized vasculature hinder drug delivery and block effector immune cell trafficking and activation, consequently rendering immunotherapy ineffective. Within the TME, the mutual interactions between tumor, immune and endothelial cells result in the generation of positive feedback loops, which intensify immunosuppression and support tumor progression. We focus here on the role of aberrant tumor vasculature and how it can mediate hypoxia and immunosuppression. We discuss how immune cells use immunosuppressive signaling for tumor progression and contribute to the development of resistance to immunotherapy. Finally, we assess how a positive feedback loop between vascular normalization and immune cells, including myeloid cells, could be targeted by combinatorial therapies with immune checkpoint blockers and sensitize the tumor to immunotherapy.

Oral administration of a dual ETA/ETB receptor antagonist promotes neuroprotection in a rodent model of glaucoma

PURPOSE

Glaucoma is a neurodegenerative disease associated with elevated intraocular pressure and characterized by optic nerve axonal degeneration, cupping of the optic disc, and loss of retinal ganglion cells (RGCs). The endothelin (ET) system of vasoactive peptides (ET-1, ET-2, ET-3) and their G-protein coupled receptors (ET_A and ET_B receptors) have been shown to contribute to the pathophysiology of glaucoma. The purpose of this study was to determine whether administration of the endothelin receptor antagonist macitentan was neuroprotective to RGCs and optic nerve axons when administered after the onset of intraocular pressure (IOP) elevation in ocular hypertensive rats.

METHODS

Male and female Brown Norway rats were subjected to the Morrison model of ocular hypertension by injection of hypertonic saline through the episcleral veins. Following IOP elevation, macitentan (5 mg/kg body wt) was administered orally 3 days per week, and rats with IOP elevation were maintained for 4 weeks. RGC function was determined by pattern electroretinography (PERG) at 2 and 4 weeks post-IOP elevation. Rats were euthanized by approved humane methods, and retinal flat mounts were generated and immunostained for the RGC-selective marker Brn3a. PPD-stained optic nerve sections were imaged by confocal microscopy. RGC and axon counts were conducted in a masked manner and compared between the treatment groups.

RESULTS

Significant protection against loss of RGCs and optic nerve axons was found following oral administration of macitentan in rats with elevated IOP. In addition, a protective trend for RGC function, as measured by pattern ERG analysis, was evident following macitentan treatment.

CONCLUSIONS

Macitentan treatment had a neuroprotective effect on RGCs and their axons, independent of its IOP-lowering effect, suggesting that macitentan may complement existing treatments to prevent neurodegeneration during ocular hypertension. The findings presented have implications for the use of macitentan as an oral formulation to promote neuroprotection in glaucoma patients.

Glioblastoma Microenvironment and Cellular Interactions

Simple Summary

This paper summarizes the crosstalk between tumor/non-tumor cells and other elements of the glioblastoma (GB) microenvironment. In tumor pathology, glial cells result in the highest number of cancers, and GB is considered the most lethal tumor of the central nervous system (CNS). The tumor microenvironment (TME) is a complex peritumoral hallo composed of tumor cells and several non-tumor cells (e.g., nervous cells, stem cells, fibroblasts, vascular and immune cells), which might be a key factor for the ineffective treatment since the microenvironment modulates the biologic status of the tumor with the increase in its evasion capacity. A deeper understanding of cell–cell interactions in the TME and with the tumor cells could be the basis for a more efficient therapy.

Abstract

The central nervous system (CNS) represents a complex network of different cells, such as neurons, glial cells, and blood vessels. In tumor pathology, glial cells result in the highest number of cancers, and glioblastoma (GB) is considered the most lethal tumor in this region. The development of GB leads to the infiltration of healthy tissue through the interaction between all the elements of the brain network. This results in a GB microenvironment, a complex peritumoral hallo composed of tumor cells and several non-tumor cells (e.g., nervous cells, stem cells, fibroblasts, vascular and immune cells), which might be the principal factor for the ineffective treatment due to the fact that the microenvironment modulates the biologic status of the tumor with the increase in its evasion capacity. Crosstalk between glioma cells and the brain microenvironment finally inhibits the beneficial action of molecular pathways, favoring the development and invasion of the tumor and its increasing resistance to treatment. A deeper understanding of cell–cell interactions in the tumor microenvironment (TME) and with the tumor cells could be the basis for a more efficient therapy.

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.

The Glioblastoma Microenvironment: Morphology, Metabolism, and Molecular Signature of Glial Dynamics to Discover Metabolic Rewiring Sequence

Different functional states determine glioblastoma (GBM) heterogeneity. Brain cancer cells coexist with the glial cells in a functional syncytium based on a continuous metabolic rewiring. However, standard glioma therapies do not account for the effects of the glial cells within the tumor microenvironment. This may be a possible reason for the lack of improvements in patients with high-grade gliomas therapies. Cell metabolism and bioenergetic fitness depend on the availability of nutrients and interactions in the microenvironment. It is strictly related to the cell location in the tumor mass, proximity to blood vessels, biochemical gradients, and tumor evolution, underlying the influence of the context and the timeline in anti-tumor therapeutic approaches. Besides the cancer metabolic strategies, here we review the modifications found in the GBM-associated glia, focusing on morphological, molecular, and metabolic features. We propose to analyze the GBM metabolic rewiring processes from a systems biology perspective. We aim at defining the crosstalk between GBM and the glial cells as modules. The complex networking may be expressed by metabolic modules corresponding to the GBM growth and spreading phases. Variation in the oxidative phosphorylation (OXPHOS) rate and regulation appears to be the most important part of the metabolic and functional heterogeneity, correlating with glycolysis and response to hypoxia. Integrated metabolic modules along with molecular and morphological features could allow the identification of key factors for controlling the GBM-stroma metabolism in multi-targeted, time-dependent therapies.

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

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

YAP and endothelin-1 signaling: an emerging alliance in cancer

The rational making the G protein-coupled receptors (GPCR) the centerpiece of targeted therapies is fueled by the awareness that GPCR-initiated signaling acts as pivotal driver of the early stages of progression in a broad landscape of human malignancies. The endothelin-1 (ET-1) receptors (ET-1R), known as ET_A receptor (ET_AR) and ET_B receptor (ET_BR) that belong to the GPCR superfamily, affect both cancer initiation and progression in a variety of cancer types. By the cross-talking with multiple signaling pathways mainly through the scaffold protein β-arrestin1 (β-arr1), ET-1R axis cooperates with an array of molecular determinants, including transcription factors and co-factors, strongly affecting tumor cell fate and behavior. In this scenario, recent findings shed light on the interplay between ET-1 and the Hippo pathway. In ET_AR highly expressing tumors ET-1 axis induces the de-phosphorylation and nuclear accumulation of the Hippo pathway downstream effectors, the paralogous transcriptional cofactors Yes-associated protein (YAP) and Transcriptional coactivator with PDZ-binding motif (TAZ). Recent evidence have discovered that ET-1R/β-arr1 axis instigates a transcriptional interplay involving YAP and mutant p53 proteins, which share a common gene signature and cooperate in a oncogenic signaling network. Mechanistically, YAP and mutp53 are enrolled in nuclear complexes that turn on a highly selective YAP/mutp53-dependent transcriptional response. Notably, ET-1R blockade by the FDA approved dual ET-1 receptor antagonist macitentan interferes with ET-1R/YAP/mutp53 signaling interplay, through the simultaneous suppression of YAP and mutp53 functions, hampering metastasis and therapy resistance. Based on these evidences, we aim to review the recent findings linking the GPCR signaling, as for ET-1R, to YAP/TAZ signaling, underlining the clinical relevance of the blockade of such signaling network in the tumor and microenvironmental contexts. In particular, we debate the clinical implications regarding the use of dual ET-1R antagonists to blunt gain of function activity of mutant p53 proteins and thereby considering them as a potential therapeutic option for mutant p53 cancers. The identification of ET-1R/β-arr1-intertwined and bi-directional signaling pathways as targetable vulnerabilities, may open new therapeutic approaches able to disable the ET-1R-orchestrated YAP/mutp53 signaling network in both tumor and stromal cells and concurrently sensitizes to high-efficacy combined therapeutics.

Targeting the endothelin axis as a therapeutic strategy for oral cancer metastasis and pain

Metastasis reduces survival in oral cancer patients and pain is their greatest complaint. We have shown previously that oral cancer metastasis and pain are controlled by the endothelin axis, which is a pathway comprised of the endothelin A and B receptors (ET_AR and ET_BR). In this study we focus on individual genes of the pathway, demonstrating that the endothelin axis genes are methylated and dysregulated in cancer tissue. Based on these findings in patients, we hypothesize that ET_AR and ET_BR play dichotomous roles in oral carcinogenesis and pain, such that ET_AR activation and silenced ET_BR expression result in increased carcinogenesis and pain. We test a treatment strategy that targets the dichotomous functions of the two receptors by inhibiting ET_AR with macitentan, an ET_AR antagonist approved for treatment of pulmonary hypertension, and re-expressing the ET_BR gene with adenovirus transduction, and determine the treatment effect on cancer invasion (i.e., metastasis), proliferation and pain in vitro and in vivo. We demonstrate that combination treatment of macitentan and ET_BR gene therapy inhibits invasion, but not proliferation, in cell culture and in a mouse model of tongue cancer. Furthermore, the treatment combination produces an antinociceptive effect through inhibition of endothelin-1 mediated neuronal activation, revealing the analgesic potential of macitentan. Our treatment approach targets a pathway shown to be dysregulated in oral cancer patients, using gene therapy and repurposing an available drug to effectively treat both oral cancer metastasis and pain in a preclinical model.

Endothelin-1 axis fosters YAP-induced chemotherapy escape in ovarian cancer

The majority of ovarian cancer (OC) patients recur with a platinum-resistant disease. OC cells activate adaptive resistance mechanisms that are only partially described. Here we show that OC cells can adapt to chemotherapy through a positive-feedback loop that favors chemoresistance. In platinum-resistant OC cells we document that the endothelin-1 (ET-1)/endothelin A receptor axis intercepts the YAP pathway. This cross-talk occurs through the LATS/RhoA/actin-dependent pathway and contributes to prevent the chemotherapy-induced apoptosis. Mechanistically, β-arrestin1 (β-arr1) and YAP form a complex shaping TEAD-dependent transcriptional activity on the promoters of YAP target genes, including EDN1, which fuels a feed-forward signaling circuit that sustains a platinum-tolerant state. The FDA approved dual ET-1 receptor antagonist macitentan in co-therapy with cisplatin sensitizes resistant cells to the platinum-based therapy, reducing their metastatic potential. Furthermore, high ET_AR/YAP gene expression signature is associated with a poor platinum-response in OC patients. Collectively, our findings identify in the networking between ET-1 and YAP pathways an escape strategy from chemotherapy. ET-1 receptor blockade interferes with such adaptive network and enhances platinum-induced apoptosis, representing a promising therapeutic opportunity to restore drug sensitivity in OC patients.

Endothelin: 30 Years From Discovery to Therapy

Discovered in 1987 as a potent endothelial cell-derived vasoconstrictor peptide, endothelin-1 (ET-1), the predominant member of the endothelin peptide family, is now recognized as a multifunctional peptide with cytokine-like activity contributing to almost all aspects of physiology and cell function. More than 30 000 scientific articles on endothelin were published over the past 3 decades, leading to the development and subsequent regulatory approval of a new class of therapeutics-the endothelin receptor antagonists (ERAs). This article reviews the history of the discovery of endothelin and its role in genetics, physiology, and disease. Here, we summarize the main clinical trials using ERAs and discuss the role of endothelin in cardiovascular diseases such as arterial hypertension, preecclampsia, coronary atherosclerosis, myocardial infarction in the absence of obstructive coronary artery disease (MINOCA) caused by spontaneous coronary artery dissection (SCAD), Takotsubo syndrome, and heart failure. We also discuss how endothelins contributes to diabetic kidney disease and focal segmental glomerulosclerosis, pulmonary arterial hypertension, as well as cancer, immune disorders, and allograft rejection (which all involve ET_A autoantibodies), and neurological diseases. The application of ERAs, dual endothelin receptor/angiotensin receptor antagonists (DARAs), selective ET_B agonists, novel biologics such as receptor-targeting antibodies, or immunization against ET_A receptors holds the potential to slow the progression or even reverse chronic noncommunicable diseases. Future clinical studies will show whether targeting endothelin receptors can prevent or reduce disability from disease and improve clinical outcome, quality of life, and survival in patients.

Identification of Transcriptional Markers and microRNA-mRNA Regulatory Networks in Colon Cancer by Integrative Analysis of mRNA and microRNA Expression Profiles in Colon Tumor Stroma

The aberrant expression of microRNAs (miRNAs) and genes in tumor microenvironment (TME) has been associated with the pathogenesis of colon cancer. An integrative exploration of transcriptional markers (gene signatures) and miRNA–mRNA regulatory networks in colon tumor stroma (CTS) remains lacking. Using two datasets of mRNA and miRNA expression profiling in CTS, we identified differentially expressed miRNAs (DEmiRs) and differentially expressed genes (DEGs) between CTS and normal stroma. Furthermore, we identified the transcriptional markers which were both gene targets of DEmiRs and hub genes in the protein–protein interaction (PPI) network of DEGs. Moreover, we investigated the associations between the transcriptional markers and tumor immunity in colon cancer. We identified 17 upregulated and seven downregulated DEmiRs in CTS relative to normal stroma based on a miRNA expression profiling dataset. Pathway analysis revealed that the downregulated DEmiRs were significantly involved in 25 KEGG pathways (such as TGF-β, Wnt, cell adhesion molecules, and cytokine–cytokine receptor interaction), and the upregulated DEmiRs were involved in 10 pathways (such as extracellular matrix (ECM)-receptor interaction and proteoglycans in cancer). Moreover, we identified 460 DEGs in CTS versus normal stroma by a meta-analysis of two gene expression profiling datasets. Among them, eight upregulated DEGs were both hub genes in the PPI network of DEGs and target genes of the downregulated DEmiRs. We found that three of the eight DEGs were negative prognostic factors consistently in two colon cancer cohorts, including COL5A2, EDNRA, and OLR1. The identification of transcriptional markers and miRNA–mRNA regulatory networks in CTS may provide insights into the mechanism of tumor immune microenvironment regulation in colon cancer.

β-arrestin1/YAP/mutant p53 complexes orchestrate the endothelin A receptor signaling in high-grade serous ovarian cancer

The limited clinical response observed in high-grade serous ovarian cancer (HG-SOC) with high frequency of TP53 mutations (mutp53) might be related to mutp53-driven oncogenic pathway network. Here we show that β-arrestin1 (β-arr1), interacts with YAP, triggering its cytoplasmic-nuclear shuttling. This interaction allows β-arr1 to recruit mutp53 to the YAP-TEAD transcriptional complex upon activation of endothelin-1 receptors (ET-1R) in patient-derived HG-SOC cells and in cell lines bearing mutp53. In parallel, β-arr1 mediates the ET-1R-induced Trio/RhoA-dependent YAP nuclear accumulation. In the nucleus, ET-1 through β-arr1 orchestrates the tethering of YAP and mutp53 to YAP/mutp53 target gene promoters, including EDN1 that ensures persistent signals. Treatment of patient-derived xenografts reveals synergistic antitumoral and antimetastatic effects of the dual ET-1R antagonist macitentan in combination with cisplatinum, shutting-down the β-arr1-mediated YAP/mutp53 transcriptional programme. Furthermore, ETAR/β-arr1/YAP gene signature correlates with a worst prognosis in HG-SOC. These findings support effective combinatorial treatment for repurposing the ET-1R antagonists in HG-SOC.

Long noncoding RNA HOXD-AS2 regulates cell cycle to promote glioma progression

Now, numerous exciting findings have been found that long noncoding RNAs (lncRNAs) play a vital role in cancer malignant progression. However, their potential involvement in glioma is not well understood. Here, we performed a high-throughput microarray to detect the lncRNA expression profiles between glioma cell lines and normal astrocyte cell lines. HOXD-AS2 was increased in glioma cells and it was associated with glioma grade and poor prognosis. Loss of HOXD-AS2 can inhibit glioma cell growth by inducing cell-cycle G1 arrest in vitro. The proliferation of glioma was inhibited followed by knocking down the expression of HOXD-AS2 not only in subcutaneous injection model but also in orthotopic implantation model. These findings indicate that HOXD-AS2 promotes the glioma progression and may serve as a potential target for glioma diagnosis and therapy.

A Blazing Landscape: Neuroinflammation Shapes Brain Metastasis

Brain metastases are more common than primary CNS tumors and confer grave prognosis on patients, as existing treatments have very limited efficacy. The tumor microenvironment has a central role in facilitating tumorigenesis and metastasis. In recent years, there has been much progress in our understanding of the functional role of the brain metastatic microenvironment. In this review, we discuss the latest advances in brain metastasis research, with special emphasis on the role of the brain microenvironment and neuroinflammation, integrating insights from comparable findings in neuropathologies and primary CNS tumors. In addition, we overview findings on the formation of a hospitable metastatic niche and point out the major gaps in knowledge toward developing new therapeutics that will cotarget the stromal compartment in an effort to improve the treatment and prevention of brain metastases.

Targeting Endothelin-1 Receptor/β-Arrestin-1 Axis in Ovarian Cancer: From Basic Research to a Therapeutic Approach

Recent studies imply a key role of endothelin-1 receptor (ET-1R), belonging to the largest family of G protein-coupled receptors (GPCR), in the regulation of a plethora of processes involved in tumorigenesis and metastatic progression. β-arrestin-1 (β-arr1) system has been recognized as a critical hub controlling GPCR signaling network, directing the GPCR's biological outcomes. In ovarian cancer, ET-1R/β-arr1 axis enables cancer cells to engage several integrated signaling, and represents an actionable target for developing novel therapeutic approaches. Preclinical research studies demonstrate that ET-1R blockade by the approved dual ET_AR/ET_BR antagonist macitentan counteracts β-arr1-mediated signaling network, and hampers the dialogue among cancer cells and the tumor microenvironment, interfering with metastatic progression and drug response. In light of major developments in the ET-1R signaling paradigm, this review article discusses the emerging evidence of the dual ET-1R antagonist treatment in cancer, and outlines our challenge in preclinical studies warranting the repurposing of ET-1R antagonists for the design of more effective clinical trials based on combinatorial therapies to overcome, or prevent, the onset of drug resistance.

Cannabidiol Affects Extracellular Vesicle Release, miR21 and miR126, and Reduces Prohibitin Protein in Glioblastoma Multiforme Cells

Glioblastoma multiforme (GBM) is the most common and aggressive form of primary malignant brain tumor in adults, with poor prognosis. Extracellular vesicles (EVs) are key-mediators for cellular communication through transfer of proteins and genetic material. Cancers, such as GBM, use EV release for drug-efflux, pro-oncogenic signaling, invasion and immunosuppression; thus the modulation of EV release and cargo is of considerable clinical relevance. As EV-inhibitors have been shown to increase sensitivity of cancer cells to chemotherapy, and we recently showed that cannabidiol (CBD) is such an EV-modulator, we investigated whether CBD affects EV profile in GBM cells in the presence and absence of temozolomide (TMZ). Compared to controls, CBD-treated cells released EVs containing lower levels of pro-oncogenic miR21 and increased levels of anti-oncogenic miR126; these effects were greater than with TMZ alone. In addition, prohibitin (PHB), a multifunctional protein with mitochondrial protective properties and chemoresistant functions, was reduced in GBM cells following 1 h CBD treatment. This data suggests that CBD may, via modulation of EVs and PHB, act as an adjunct to enhance treatment efficacy in GBM, supporting evidence for efficacy of cannabinoids in GBM.

Dysregulation of the endothelin pathway in lymphangioleiomyomatosis with no direct effect on cell proliferation and migration

LAM is a rare low-grade metastasizing lung neoplasm. Inhibitors of mTOR improve clinical outcome of LAM patients by preventing loss of lung function. Nevertheless, other cell targets may be of interest for drug development. Therefore, we explored the potential role of EDN1 (endothelin) in LAM. We report an increased endothelin blood level in LAM patients as well as EDN1 overexpression and EDN1 receptor downregulation in LAM-derived primary cells and in TSC2^NEG cells mutated in TSC2. We evidenced EDN pathway dysregulation based on EDN1, EDNRA, EDNRB and ARRB1 mRNA expression in LAM-derived primary cells. We showed overexpression of EDN1 and ARRB1 mRNAs in TSC2^NEG cells; these cells lost their ability to respond to stimulation by endothelin. We analyzed the effects of endothelin receptor antagonists alone or in combination with rapamycin, an mTOR inhibitor, on proliferation and migration of LAM cells. Rapamycin treatment of TSC2^NEG cells significantly reduced cell proliferation or migration, while none of the tested inhibitors of EDN receptors impaired these functions. We showed that TSC2^NEG cells have acquired a transformed phenotype as showed by their ability to grow as spheroids in semi-solid medium and that unlike endothelin receptors antagonists, rapamycin reduced anchorage-independent cell growth and prevented expansion of TSC2^NEG spheroids.

Apatinib suppresses cell growth and metastasis and promotes antitumor activity of temozolomide in glioma

Apatinib, a small-molecule multi-targeted tyrosine kinase inhibitor, is widely used to treat various types of solid tumors. In the present study, it was investigated whether apatinib has therapeutic potential for glioma. Cell Counting Kit-8 and colony formation assays were utilized to determine the cell viability of p53- and EGFR-mutated U251MG glioma cells, and wild-type U-87MG ATCC glioma cells. Furthermore, apoptosis, and the invasion and migration abilities of glioma cells were investigated by flow cytometry, invasion assays and wound-healing assays. The potential of the combination of apatinib with temozolomide (TMZ) for glioma therapy was also investigated. The results demonstrate that apatinib significantly inhibited cell proliferation and colony formation through promoting cell apoptosis in p53- and EGFR-mutated and wild-type glioma cells. Cell invasion and migration abilities were notably decreased following treatment with apatinib. Overall, the present study indicates a synergistic antitumor effect of apatinib and TMZ in glioma, and presents a basis for the use of apatinib in glioma treatment.

STAT3 labels a subpopulation of reactive astrocytes required for brain metastasis

The brain microenvironment imposes a particularly intense selective pressure on metastasis-initiating cells, but successful metastases bypass this control through mechanisms that are poorly understood. Reactive astrocytes are key components of this microenvironment that confine brain metastasis without infiltrating the lesion. Here, we describe that brain metastatic cells induce and maintain the co-option of a pro-metastatic program driven by signal transducer and activator of transcription 3 (STAT3) in a subpopulation of reactive astrocytes surrounding metastatic lesions. These reactive astrocytes benefit metastatic cells by their modulatory effect on the innate and acquired immune system. In patients, active STAT3 in reactive astrocytes correlates with reduced survival from diagnosis of intracranial metastases. Blocking STAT3 signaling in reactive astrocytes reduces experimental brain metastasis from different primary tumor sources, even at advanced stages of colonization. We also show that a safe and orally bioavailable treatment that inhibits STAT3 exhibits significant antitumor effects in patients with advanced systemic disease that included brain metastasis. Responses to this therapy were notable in the central nervous system, where several complete responses were achieved. Given that brain metastasis causes substantial morbidity and mortality, our results identify a novel treatment for increasing survival in patients with secondary brain tumors.

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.

Promoting oligodendroglial-oriented differentiation of glioma stem cell: a repurposing of quetiapine for the treatment of malignant glioma

As a major contributor of chemotherapy resistance and malignant recurrence, glioma stem cells (GSCs) have been proposed as a target for the treatment of gliomas. To evaluate the therapeutic potential of quetiapine (QUE), an atypical antipsychotic, for the treatment of malignant glioma, we established mouse models with GSCs-initiated orthotopic xenograft gliomas and subcutaneous xenograft tumors, using GSCs purified from glioblastoma cell line GL261. We investigated antitumor effects of QUE on xenograft gliomas and its underlying mechanisms on GSCs. Our data demonstrated that (i) QUE monotherapy can effectively suppress GSCs-initiated tumor growth; (ii) QUE has synergistic effects with temozolomide (TMZ) on glioma suppression, and importantly, QUE can effectively suppress TMZ-resistant (or -escaped) tumors generated from GSCs; (iii) mechanistically, the anti-glioma effect of QUE was due to its actions of promoting the differentiation of GSCs into oligodendrocyte (OL)-like cells and its inhibitory effect on the Wnt/β-catenin signaling pathway. Together, our findings suggest an effective approach for anti-gliomagenic treatment via targeting OL-oriented differentiation of GSCs. This also opens a door for repurposing QUE, an FDA approved drug, for the treatment of malignant glioma.

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.

PDGFRα depletion attenuates glioblastoma stem cells features by modulation of STAT3, RB1 and multiple oncogenic signals

Platelet derived growth factor receptors (PDGFRs) play an important role in tumor pathogenesis, and they are frequently overexpressed in glioblastoma (GBM). Earlier we have shown a higher protein expression of PDGFR isoforms (α and β) in peritumoral-tissue derived cancer stem cells (p-CSC) than in tumor core (c-CSC) of several GBM affected patients. In the current study, in order to assess the activity of PDGFRα/PDGF-AA signaling axis, we performed time course experiments to monitor the effects of exogenous PDGF-AA on the expression of downstream target genes in c-CSC vs p-CSC. Interestingly, in p-CSC we detected the upregulation of Y705-phosphorylated Stat3, concurrent with a decrement of Rb1 protein in its active state, within minutes of PDGF-AA addition. This finding prompted us to elucidate the role of PDGFRα in self-renewal, invasion and differentiation in p-CSC by using short hairpin RNA depletion of PDGFRα expression. Notably, in PDGFRα-depleted cells, protein analysis revealed attenuation of stemness-related and glial markers expression, alongside early activation of the neuronal marker MAP2a/b that correlated with the induction of tumor suppressor Rb1. The in vitro reduction of the invasive capacity of PDGFRα-depleted CSC as compared to parental cells correlated with the downmodulation of markers of epithelial-mesenchymal transition phenotype and angiogenesis. Surprisingly, we observed the induction of anti-apoptotic proteins and compensatory oncogenic signals such as EDN1, EDNRB, PRKCB1, PDGF-C and PDGF-D. To conclude, we hypothesize that the newly discovered PDGFRα/Stat3/Rb1 regulatory axis might represent a potential therapeutic target for GBM treatment.

Targeting the perivascular niche in brain tumors

PURPOSE OF REVIEW

Brain tumors are composed of primary tumors of the central nervous system, such us glioblastoma (GBM), and secondary metastatic tumors, such as melanoma, non-Hodgkin lymphoma as well as lung and breast cancers. Brain tumors are highly deadly, and unfortunately not many improvements have been achieved to improve the survival of patients with brain tumors. Chemoradiation resistance is one of the most clinically relevant challenges faced in patients with brain tumors. The perivascular niche is one of the most relevant microenvironment hubs in brain tumors. The understanding of the cellular crosstalk established within the brain tumor perivascular niche might provide us with key discoveries of new brain tumor vulnerabilities.

RECENT FINDINGS

Radio and chemoresistance in GBM and brain metastases is attributed to cancer stem cells (CSCs), which intrinsically modulate several pathways that make them resistant to therapy. Growing evidence, however, highlights the perivascular space as a niche for CSC survival, resistance to therapy, progression and dissemination. Here, I review the latest discoveries on the components and features of brain tumor vascular niches and the possible therapeutic strategies aimed at targeting its vulnerabilities, thus preventing GBM and metastasis chemoradiation resistance and recurrence.

SUMMARY

Recent discoveries suggest that targeting the brain perivascular niche has the potential of sensitizing brain tumors to therapies and reducing the occurrence of metastases.

Reactive Astrocytes in Brain Metastasis

Brain metastasis, the secondary growth of malignant cells within the central nervous system (CNS), exceeds the incidence of primary brain tumors (i.e., gliomas) by tenfold and are seemingly on the rise owing to the emergence of novel targeted therapies that are more effective in controlling extracranial disease relatively to intracranial lesions. Despite the fact that metastasis to the brain poses a unmet clinical problem, with afflicted patients carrying significant morbidity and a fatal prognosis, our knowledge as to how metastatic cells manage to adapt to the tissue environment of the CNS remains limited. Answering this question could pave the way for novel and more specific therapeutic modalities in brain metastasis by targeting the specific makeup of the brain metastatic niche. In regard to this, astrocytes have emerged as the major host cell type that cancer cells encounter and interact with during brain metastasis formation. Similarly to other CNS disorders, astrocytes become reactive and respond to the presence of cancer cells by changing their phenotype and significantly influencing the outcome of disseminated cancer cells within the CNS. Here, we summarize the current knowledge on the contribution of reactive astrocytes in brain metastasis by focusing on the signaling pathways and types of interactions that play a crucial part in the communication with cancer cells and how these could be translated into innovative therapies.

Macitentan, a double antagonist of endothelin receptors, efficiently impairs migration and microenvironmental survival signals in chronic lymphocytic leukemia

The crosstalk between chronic lymphocytic leukemia (CLL) cells and tumor microenvironment is essential for leukemic clone maintenance, supporting CLL cells survival, proliferation and protection from drug-induced apoptosis. Over the past years, the role of several soluble factors involved in these processes has been studied. CLL cells express higher levels of endothelin 1 (ET-1) and ET_A receptor as compared to normal B cells. Upon ET-1 stimulation, CLL cells improve their survival and proliferation and reduce their sensitivity to the phosphoinositide-3-kinase δ inhibitor idelalisib and to fludarabine. Here, we demonstrate that CLL cells express not only ET_A receptor but also ET_B receptor. ET-1 acts as a homing factor supporting CLL cells migration and adhesion to microenvironmental cells. In addition, ET-1 stimulates a pro-angiogenic profile of CLL cells increasing VEGF expression through hypoxia-inducible factor-1 (HIF-1α) accumulation in CLL cells. Macitentan, a specific dual inhibitor of ET_A and ET_B receptors, targets CLL cells affecting leukemic cells migration and adhesion and overcoming the pro-survival and proliferation signals mediated by microenvironment. Furthermore, macitentan cooperates with ibrutinib inhibiting the BCR pathway and with ABT-199 disrupting BCL2 pathway. Our data describe the biological effects of a new drug, macitentan, able to counteract essential processes in CLL pathobiology as survival, migration, trafficking and drug resistance. These findings envision the possibility to interfere with ET receptors activity using macitentan as a possible novel therapeutic strategy for CLL patients.

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.

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

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

Chains of magnetosomes with controlled endotoxin release and partial tumor occupation induce full destruction of intracranial U87-Luc glioma in mice under the application of an alternating magnetic field

Previous studies showed that magnetic hyperthermia could efficiently destroy tumors both preclinically and clinically, especially glioma. However, antitumor efficacy remained suboptimal and therefore required further improvements. Here, we introduce a new type of nanoparticles synthesized by magnetotactic bacteria, called magnetosomes, with improved properties compared with commonly used chemically synthesized nanoparticles. Indeed, mice bearing intracranial U87-Luc glioma tumors injected with 13μg of nanoparticles per mm³ of tumor followed by 12 to 15 of 30min alternating magnetic field applications displayed either full tumor disappearance in 40% of mice or no tumor regression using magnetosomes or chemically synthesized nanoparticles, respectively. Magnetosome superior antitumor activity could be explained both by a larger production of heat and by endotoxins release under alternating magnetic field application. Most interestingly, this behavior was observed when magnetosomes occupied only 10% of the whole tumor volume, which suggests that an indirect mechanism, such as an immune reaction, takes part in tumor regression. This is desired for the treatment of infiltrating tumors, such as glioma, for which whole tumor coverage by nanoparticles can hardly be achieved.

Pharmacotherapeutic Targeting of G Protein-Coupled Receptors in Oncology: Examples of Approved Therapies and Emerging Concepts

G protein-coupled receptors (GPCRs) are involved in numerous physio-pathological processes, including the stimulation of cancer progression. In this regard, it should be mentioned that although GPCRs may represent major pharmaceutical targets, only a few drugs acting as GPCR inhibitors are currently used in anti-tumor therapies. For instance, certain pro-malignancy effects mediated by GPCRs are actually counteracted by the use of small molecules and peptides that function as receptor antagonists or inverse agonists. Recently, humanized monoclonal antibodies targeting GPCRs have also been developed. Here, we review the current GPCR-targeted therapies for cancer treatment, summarizing the clinical studies that led to their official approval. We provide a broad overview of the mechanisms of action of the available anti-cancer drugs targeting gonadotropin-releasing hormone, somatostatin, chemokine, and Smoothened receptors. In addition, we discuss the anti-tumor potential of novel non-approved molecules and antibodies able to target some of the aforementioned GPCRs in different experimental models and clinical trials. Likewise, we focus on the repurposing in cancer patients of non-oncological GPCR-based drugs, elucidating the rationale behind this approach and providing clinical evidence on their safety and efficacy.

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

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

[Tumor Cells and Micro-environment in Brain Metastases]

近年来，随着早期诊断的方法的出现及精准治疗的应用，肺癌患者的生存及生活质量都得到很大改善。然而，对于肺癌的脑转移病灶，目前仍缺乏一个理想的治疗方案，严重影响了该部分患者生存状态。了解肿瘤细胞如何在中枢神经系统定植、生长和侵袭等相关生物学行为及其产生机制对预防及治疗肿瘤细胞脑转移病灶具有重大的意义。“种子-土壤”这一假说可以很好的解释这一过程，这一假说的关键即肿瘤细胞可与中枢神经系统微环境各组成之间产生相互适应性变化，正是这种相互作用决定了脑转移病灶的发生发展。本文就脑转移肿瘤细胞、脑转移肿瘤微环境及他们之间的相互作用进行综述，旨在为脑转移病灶的治疗提供新的思路。

The Microenvironmental Landscape of Brain Tumors

The brain tumor microenvironment (TME) is emerging as a critical regulator of cancer progression in primary and metastatic brain malignancies. The unique properties of this organ require a specific framework for designing TME-targeted interventions. Here, we discuss a number of these distinct features, including brain-resident cell types, the blood-brain barrier, and various aspects of the immune-suppressive environment. We also highlight recent advances in therapeutically targeting the brain TME in cancer. By developing a comprehensive understanding of the complex and interconnected microenvironmental landscape of brain malignancies we will greatly expand the range of therapeutic strategies available to target these deadly diseases.

Treatment of experimental human breast cancer and lung cancer brain metastases in mice by macitentan, a dual antagonist of endothelin receptors, combined with paclitaxel

BACKGROUND

We recently demonstrated that brain endothelial cells and astrocytes protect cancer cells from chemotherapy through an endothelin-dependent signaling mechanism. Here, we evaluated the efficacy of macitentan, a dual endothelin receptor (ETAR and ETBR) antagonist, in the treatment of experimental breast and lung cancer brain metastases.

METHODS

The effect of macitentan on astrocyte- and brain endothelial cell-mediated chemoprotective properties was measured in cytotoxic assays. We compared survival of mice bearing established MDA-MB-231 breast cancer or PC-14 non-small cell lung cancer (NSCLC) brain metastases that were treated with vehicle, macitentan, paclitaxel, or macitentan plus paclitaxel. Cell division, apoptosis, tumor vasculature, and expression of survival-related proteins were assessed by immunofluorescent microscopy.

RESULTS

Cancer cells and tumor-associated endothelial cells expressed activated forms of AKT and MAPK in vehicle- and paclitaxel-treated groups in both metastasis models, but these proteins were downregulated in metastases of mice that received macitentan. The survival-related proteins Bcl2L1, Gsta5, and Twist1 that localized to cancer cells and tumor-associated endothelial cells in vehicle- and paclitaxel-treated tumors were suppressed by macitentan. Macitentan or paclitaxel alone had no effect on survival. However, when macitentan was combined with paclitaxel, we noted a significant reduction in cancer cell division and marked apoptosis of both cancer cells and tumor-associated endothelial cells. Moreover, macitentan plus paclitaxel therapy significantly increased overall survival by producing complete responses in 35 of 35 mice harboring brain metastases.

CONCLUSIONS

Dual antagonism of ETAR and ETBR signaling sensitizes experimental brain metastases to paclitaxel and may represent a new therapeutic option for patients with brain metastases.

β-arrestin1 at the cross-road of endothelin-1 signaling in cancer

The advent of targeted therapeutics in human cancer has begun to find novel druggable targets and, in this context, the endothelin-1 receptor (ET-1R), namely ET_A receptor (ET_AR) and ET_B receptor, among the GPCR family represents a class of highly druggable molecules in cancer. ET-1R are aberrantly expressed in human malignancies, potentially representing prognostic factors. Their activation by ligand stimulation initiate signaling cascades activating different downstream effectors, allowing precise control over multiple signaling pathways. ET-1R regulates cell proliferation, survival, motility, cytoskeletal changes, angiogenesis, metastasis as well as drug resistance. The molecular events underlying these responses are the activation of transcriptional factors and coactivators, and downstream genes, acting as key players in tumor growth and progression. ET-1R represent crucial cancer targets that have been exploited for ET-1R therapeutics. Importantly, efforts to explore new information of ET_AR in cancer have uncovered that their functions are crucially regulated by multifunctional scaffold protein β-arrestins (β-arrs) which orchestrate the multidimensionality of ET_AR signaling into highly regulated and distinct signaling complexes, a property that is highly advantageous for tumor signaling. Moreover, the role of β-arr1 in ET-1 signaling in cancer highlights why the pleiotropic effects of ET-1 and its dynamic signaling are more complex than previously recognized. In order to improve therapeutic strategies that interfere with the widespread effects of ET-1R, it is important to consider antagonists able to turn the receptors “off” selectively controlling β-arr1-dependent signaling, highlighting the possibility that targeting ET_AR/β-arr1 may display a large therapeutic window in cancer.

Nuclear β-arrestin1 is a critical cofactor of hypoxia-inducible factor-1α signaling in endothelin-1-induced ovarian tumor progression

Hypoxia-inducible factor-1α (HIF-1α) mediates the response to hypoxia or other stimuli, such as growth factors, including endothelin-1 (ET-1), to promote malignant progression in numerous tumors. The importance of cofactors that regulate HIF-1α signalling within tumor is not well understood. Here we elucidate that ET-1/ET(A) receptor (ET(A)R)-induced pathway physically and functionally couples the scaffold protein β-arrestin1 (β-arr1) to HIF-1α signalling. In epithelial ovarian cancer (EOC) cells, ET-1/ET(A)R axis induced vascular-endothelial growth factor (VEGF) expression through HIF-1α nuclear accumulation. In these cells, activation of ET(A)R by ET-1, by mimicking hypoxia, promoted the nuclear interaction between β-arr1 and HIF-1α and the recruitment of p300 acetyltransferase to hypoxia response elements on the target gene promoters, resulting in enhanced histone acetylation, and HIF-1α target gene transcription. Indeed, β-arr1-HIF-1α interaction regulated the enhanced expression and release of downstream targets, such as ET-1 and VEGF, required for tumor cell invasion and pro-angiogenic effects in endothelial cells. These effects were abrogated by β-arr1 or HIF-1α silencing or by pharmacological treatment with the dual ET-1 receptor antagonist macitentan. Interestingly, ET(A)R/β-arr1 promoted the self-amplifying HIF-1α-mediated transcription of ET-1 that sustained a regulatory circuit involved in invasive and angiogenic behaviors. In a murine orthotopic model of metastatic human EOC, treatment with macitentan, or silencing of β-arr1, inhibits intravasation and metastasis formation. Collectively, these findings reveal the interplay of β-arr1 with HIF-1α in the complexity of ET-1/ET(A)R signalling, mediating epigenetic modifications directly involved in the metastatic process, and suggest that targeting ET-1-dependent β-arr1/HIF-1α pathway by using macitentan may impair EOC progression.

Endothelin therapeutics in cancer: Where are we?

In human cancers, the autocrine and paracrine loop mediated by the aberrantly activation of endothelin-1 (ET-1) receptor (ET-1R) elicits pleiotropic effects, preferentially mediated by the scaffold protein β-arrestin 1 (β-arr1), on tumor cells and on the host microenvironment, providing a strong rationale for targeting ET-1 receptors. This review describes the most up-to-date preclinical and clinical results obtained by using ET-1 therapeutics. The previous negative clinical results of ET-1 therapeutics should not prevent us from setting the standard of this class of drugs for future well-designed clinical trials. The preclinical data obtained with the dual ETAR and ETBR antagonist macitentan indicate that this molecule, which targets cancer cells and tumor-associated microenvironmental elements, could be a cancer therapeutic option. The field of ET-1 therapeutics will be improved in the next decade, facilitated by the new knowledge on the genomic landscape of the human stroma and tumor, and by the low invasive approaches based on liquid biopsies for the discovery of predictive biomarkers. The information obtained from preclinical studies in patient-derived models and from the Cancer Genome Atlas will set the scene of precision medicine for cancer. Results from these studies are expected to open the possibility that ET-1R antagonists might be more efficacious as molecular cancer therapeutics, able to hamper the functional β-arr1-dependent signaling complexes, either alone or coupled with new targeted approaches.

miR-30a inhibits endothelin A receptor and chemoresistance in ovarian carcinoma

Drug resistance remains the major clinical barrier to successful treatment in epithelial ovarian carcinoma (EOC) patients, and the evidence of microRNA involvement in drug resistance has been recently emerging. Endothelin-1 (ET-1)/ETA receptor (ETAR) axis is aberrantly activated in chemoresistant EOC cells and elicits pleiotropic effects promoting epithelial-to-mesenchymal transition (EMT) and the acquisition of chemoresistance. However, the relationship between ETAR and miRNA is still unknown. Hence, in this study we evaluated whether dysregulation of miRNA might enhance ETAR expression in sensitive and resistant EOC cells. Based on bioinformatic tools, we selected putative miRNA able to recognize the 3'UTR of ETAR. An inverse correlation was observed between the expression levels of miR-30a and ETAR in both EOC cell lines and tumor samples. miR-30a was found to specifically bind to the 3'UTR of ETAR mRNA, indicating that ETAR is a direct target of miR-30a. Overexpression of miR-30a decreased Akt and mitogen activated protein kinase signaling pathway activation, cell proliferation, invasion, plasticity, EMT marker levels, and vascular endothelial growth factor release. Interestingly, ectopic expression of miR-30a re-sensitized platinum-resistant EOC cells to cisplatinum-induced apoptosis. Consistently, resistant EOC xenografts overexpressing miR-30a resulted in significantly less tumor growth than controls. Together our study provides a new perspective on the regulatory mechanism of ETAR gene. Interestingly, our findings highlight that blockade of ETAR regulatory axis is the mechanism underlying the tumor suppressor function of miR-30a in chemoresistant EOC cells.

Macitentan blocks endothelin-1 receptor activation required for chemoresistant ovarian cancer cell plasticity and metastasis

AIMS

In epithelial ovarian cancer (EOC), activation of endothelin-1 (ET-1)/endothelin A receptor (ETAR) and ET-1/ETBR signaling is linked to many tumor promoting effects, such as proliferation, angiogenesis, invasion, metastasis and chemoresistance. Understanding how to hamper the distinct mechanisms that facilitate epithelial plasticity and propagation is therefore central for improving the clinical outcome for EOC patients.

MAIN METHODS

The phosphorylation status of Akt and MAPK was evaluated by immunoblotting in A2780 and 2008 EOC cell lines and their cisplatinum-resistant variants. Vasculogenic mimicry was analyzed by vascular tubules formation assay. Tumor growth and metastases inhibition was performed in chemoresistant EOC xenografts.

KEY FINDINGS

We found that the dual ETAR/ETBR antagonist macitentan was able to inhibit the ET-1-induced activation of Akt and MAPK signaling pathways in chemoresistant EOC cells. Moreover, chemoresistant EOC cells displayed higher capability to engage vasculogenic mimicry compared to sensitive cells that was inhibited after treatment with macitentan. Finally, the specific ETAR antagonist zibotentan was less efficacious compared to macitentan to suppress tumor growth in chemoresistant EOC xenografts and the co-treatment of macitentan and cisplatinum reduced the metastatic progression.

SIGNIFICANCE

Our findings better clarify the ET-1-induced molecular mechanisms underlying the aggressive behavior of chemoresistant EOC cells. These results also support the use of macitentan in combination with chemotherapy as a rational therapeutic strategy for circumventing drug resistance in EOC.

Glioblastoma: Defining Tumor Niches

Glioblastomas (GBM) are one of the most recalcitrant brain tumors because of their aggressive invasive growth and resistance to therapy. They are highly heterogeneous malignancies at both the molecular and histological levels. Specific histological hallmarks including pseudopalisading necrosis and microvascular proliferation distinguish GBM from lower-grade gliomas, and make GBM one of the most hypoxic as well as angiogenic tumors. These microanatomical compartments present specific niches within the tumor microenvironment that regulate metabolic needs, immune surveillance, survival, invasion as well as cancer stem cell maintenance. Here we review features and functions of the distinct GBM niches, detail the different cell constituents and the functional status of the vasculature, and discuss prospects of therapeutically targeting GBM niche constituents.

Endothelin A receptor drives invadopodia function and cell motility through the β-arrestin/PDZ-RhoGEF pathway in ovarian carcinoma

The endothelin-1 (ET-1)/ET A receptor (ETAR) signalling pathway is a well-established driver of epithelial ovarian cancer (EOC) progression. One key process promoted by ET-1 is tumor cell invasion, which requires the scaffolding functions of β-arrestin-1 (β-arr1) downstream of the receptor; however, the potential role of ET-1 in inducing invadopodia, which are crucial for cellular invasion and tumor metastasis, is completely unknown. We describe here that ET-1/ETAR, through β-arr1, activates RhoA and RhoC GTPase and downstream ROCK (Rho-associated coiled coil-forming kinase) kinase activity, promoting actin-based dynamic remodelling and enhanced cell invasion. This is accomplished by the direct interaction of β-arr1 with PDZ-RhoGEF (postsynaptic density protein 95/disc-large/zonula occludens-RhoGEF). Interestingly, ETAR-mediated invasive properties are related to the regulation of invadopodia, as evaluated by colocalization of actin with cortactin, as well as with TKS5 and MT1-MMP (membrane type 1-matrix metalloproteinase) with areas of matrix degradation, and activation of cofilin pathway, which is crucial for regulating invadopodia activity. Depletion of PDZ-RhoGEF, or β-arr1, or RhoC, as well as the treatment with the dual ET-1 receptor antagonist macitentan, significantly impairs invadopodia function, MMP activity and invasion, demonstrating that β-arr1/PDZ-RhoGEF interaction mediates ETAR-driven ROCK-LIMK-cofilin pathway through the control of RhoC activity. In vivo, macitentan is able to inhibit metastatic dissemination and cofilin phosphorylation. Collectively, our data unveil a noncanonical activation of the RhoC/ROCK pathway through the β-arr1/PDZ-RhoGEF complex as a regulator of ETAR-induced motility and metastasis, establishing ET-1 axis as a novel regulator of invadopodia protrusions through the RhoC/ROCK/LIMK/cofilin pathway during the initial steps of EOC invasion.