The soluble extracellular domain of EphB4 (sEphB4) antagonizes EphB4-EphrinB2 interaction, modulates angiogenesis, and inhibits tumor growth

Improved efficacy of pembrolizumab combined with soluble EphB4-albumin in HPV-negative EphrinB2 positive head neck squamous cell carcinoma

OBJECTIVE

Patients with relapsed or metastatic head and neck squamous cell carcinoma (HNSCC) after primary local therapy have low response rates with cetuximab, systemic chemotherapy or check point inhibitor therapy. Novel combination therapies with the potential to improve outcomes for patients with HNSCC is an area of high unmet need.

METHODS

This is a phase II single-arm clinical trial of locally advanced or metastatic HNSCC patients treated with a combination of soluble EphB4-human serum albumin (sEphB4-HSA) fusion protein and pembrolizumab after platinum-based chemotherapy with up to 2 prior lines of treatment. The primary endpoints were safety and tolerability and the primary efficacy endpoint was overall response rate (ORR). Secondary endpoints included progression free survival (PFS) and overall survival (OS). HPV status and EphrinB2 expression were evaluated for outcome.

RESULTS

Twenty-five patients were enrolled. Median follow up was 40.4 months (range 9.8 - 40.4). There were 6 responders (ORR 24%). There were 5 responders in the 11 HPV-negative and EphrinB2 positive patients, (ORR 45%) with 2 of these patients achieving a complete response (CR). The median PFS in HPV-negative/EphrinB2 positive patients was 3.2 months (95% CI 1.1, 7.3). Median OS in HPV-negative/EphrinB2 positive patients was 10.9 months (95% CI 2.0, 13.7). Hypertension, transaminitis and fatigue were the most common toxicities.

DISCUSSION

The combination of sEphB4-HSA and pembrolizumab has a favorable toxicity profile and favorable activity particularly among HPV-negative EphrinB2 positive patients with HNSCC.

The Clinical Relevance of the EPH/Ephrin Signaling Pathway in Pediatric Solid and Hematologic Malignancies

Pediatric neoplasms represent a complex group of malignancies that pose unique challenges in terms of diagnosis, treatment, and understanding of the underlying molecular pathogenetic mechanisms. Erythropoietin-producing hepatocellular receptors (EPHs), the largest family of receptor tyrosine kinases and their membrane-tethered ligands, ephrins, orchestrate short-distance cell-cell signaling and are intricately involved in cell-pattern morphogenesis and various developmental processes. Unraveling the role of the EPH/ephrin signaling pathway in the pathophysiology of pediatric neoplasms and its clinical implications can contribute to deciphering the intricate landscape of these malignancies. The bidirectional nature of the EPH/ephrin axis is underscored by emerging evidence revealing its capacity to drive tumorigenesis, fostering cell-cell communication within the tumor microenvironment. In the context of carcinogenesis, the EPH/ephrin signaling pathway prompts a reevaluation of treatment strategies, particularly in pediatric oncology, where the modest progress in survival rates and enduring treatment toxicity necessitate novel approaches. Molecularly targeted agents have emerged as promising alternatives, prompting a shift in focus. Through a nuanced understanding of the pathway's intricacies, we aim to lay the groundwork for personalized diagnostic and therapeutic strategies, ultimately contributing to improved outcomes for young patients grappling with neoplastic challenges.

Inhibition of Ephrin B2 Reverse Signaling Abolishes Multiple Myeloma Pathogenesis

Bone marrow vascular endothelial cells (BM EC) regulate multiple myeloma pathogenesis. Identification of the mechanisms underlying this interaction could lead to the development of improved strategies for treating multiple myeloma. Here, we performed a transcriptomic analysis of human ECs with high capacity to promote multiple myeloma growth, revealing overexpression of the receptor tyrosine kinases, EPHB1 and EPHB4, in multiple myeloma-supportive ECs. Expression of ephrin B2 (EFNB2), the binding partner for EPHB1 and EPHB4, was significantly increased in multiple myeloma cells. Silencing EPHB1 or EPHB4 in ECs suppressed multiple myeloma growth in coculture. Similarly, loss of EFNB2 in multiple myeloma cells blocked multiple myeloma proliferation and survival in vitro, abrogated multiple myeloma engraftment in immune-deficient mice, and increased multiple myeloma sensitivity to chemotherapy. Administration of an EFNB2-targeted single-chain variable fragment also suppressed multiple myeloma growth in vivo. In contrast, overexpression of EFNB2 in multiple myeloma cells increased STAT5 activation, increased multiple myeloma cell survival and proliferation, and decreased multiple myeloma sensitivity to chemotherapy. Conversely, expression of mutant EFNB2 lacking reverse signaling capacity in multiple myeloma cells increased multiple myeloma cell death and sensitivity to chemotherapy and abolished multiple myeloma growth in vivo. Complementary analysis of multiple myeloma patient data revealed that increased EFNB2 expression is associated with adverse-risk disease and decreased survival. This study suggests that EFNB2 reverse signaling controls multiple myeloma pathogenesis and can be therapeutically targeted to improve multiple myeloma outcomes.

SIGNIFICANCE

Ephrin B2 reverse signaling mediated by endothelial cells directly regulates multiple myeloma progression and treatment resistance, which can be overcome through targeted inhibition of ephrin B2 to abolish myeloma.

Eph receptors and ephrins in cancer progression

Evidence implicating Eph receptor tyrosine kinases and their ephrin ligands (that together make up the 'Eph system') in cancer development and progression has been accumulating since the discovery of the first Eph receptor approximately 35 years ago. Advances in the past decade and a half have considerably increased the understanding of Eph receptor-ephrin signalling mechanisms in cancer and have uncovered intriguing new roles in cancer progression and drug resistance. This Review focuses mainly on these more recent developments. I provide an update on the different mechanisms of Eph receptor-ephrin-mediated cell-cell communication and cell autonomous signalling, as well as on the interplay of the Eph system with other signalling systems. I further discuss recent advances in elucidating how the Eph system controls tumour expansion, invasiveness and metastasis, supports cancer stem cells, and drives therapy resistance. In addition to functioning within cancer cells, the Eph system also mediates the reciprocal communication between cancer cells and cells of the tumour microenvironment. The involvement of the Eph system in tumour angiogenesis is well established, but recent findings also demonstrate roles in immune cells, cancer-associated fibroblasts and the extracellular matrix. Lastly, I discuss strategies under evaluation for therapeutic targeting of Eph receptors-ephrins in cancer and conclude with an outlook on promising future research directions.

Biological Significance of EphB4 Expression in Cancer

Eph receptors and their Eph receptor-interacting (ephrin) ligands comprise a vital cell communication system with several functions. In cancer cells, there was evidence of bilateral Eph receptor signaling with both tumor-suppressing and tumor-promoting actions. As a member of the Eph receptor family, EphB4 has been linked to tumor angiogenesis, growth, and metastasis, which makes it a viable and desirable target for drug development in therapeutic applications. Many investigations have been conducted over the last decade to elucidate the structure and function of EphB4 in association with its ligand ephrinB2 for its involvement in tumorigenesis. Although several EphB4-targeting drugs have been investigated, and some selective inhibitors have been evaluated in clinical trials. This article addresses the structure and function of the EphB4 receptor, analyses its possibility as an anticancer therapeutic target, and summarises knowledge of EphB4 kinase inhibitors. To summarise, EphB4 is a difficult but potential treatment option for cancers.

Progress in systemic therapy for advanced-stage urothelial carcinoma

Despite recent advances, advanced-stage urothelial carcinoma (aUC) remains incurable, with 5-year survival rates of approximately 10%. Platinum-based chemotherapy has a major role as first-line therapy for most patients with aUC. The approval of the anti-PD-L1 antibody avelumab as maintenance therapy for patients without initial disease progression on platinum-based chemotherapy is an important development that has improved the survival outcomes of patients with this disease. Otherwise, the use of first-line immune-checkpoint inhibitors (ICIs) targeting PD-1 or PD-L1 has been restricted to patients who are ineligible for platinum-containing chemotherapy regimens. Other important developments include the FDA-accelerated approval of first-line enfortumab vedotin plus pembrolizumab for patients ineligible to receive cisplatin and the availability of FGFR inhibitors, enfortumab vedotin and sacituzumab govitecan for subsequent lines of therapy. Several research questions remain unaddressed including the lack of adequate biomarkers, how to assign priority to the different treatment options for individual patients and which agents can be effective as monotherapies. The future is promising with the emergence of modalities such as antibody-drug conjugate-like drugs, next-generation ICIs, bispecific antibodies and cellular therapies. In this Review, we summarize the evolution of systemic therapy for patients with aUC and provide insights into the unmet needs.

Aberrant epithelial cell interaction promotes esophageal squamous-cell carcinoma development and progression

Epithelial-mesenchymal transition (EMT) and proliferation play important roles in epithelial cancer formation and progression, but what molecules and how they trigger EMT is largely unknown. Here we performed spatial transcriptomic and functional analyses on samples of multistage esophageal squamous-cell carcinoma (ESCC) from mice and humans to decipher these critical issues. By investigating spatiotemporal gene expression patterns and cell-cell interactions, we demonstrated that the aberrant epithelial cell interaction via EFNB1-EPHB4 triggers EMT and cell cycle mediated by downstream SRC/ERK/AKT signaling. The aberrant epithelial cell interaction occurs within the basal layer at early precancerous lesions, which expands to the whole epithelial layer and strengthens along the cancer development and progression. Functional analysis revealed that the aberrant EFNB1-EPHB4 interaction is caused by overexpressed ΔNP63 due to TP53 mutation, the culprit in human ESCC tumorigenesis. Our results shed new light on the role of TP53-TP63/ΔNP63-EFNB1-EPHB4 axis in EMT and cell proliferation in epithelial cancer formation.

Dihydroartemisinin inhibits melanoma migration and metastasis by affecting angiogenesis

Tumor angiogenesis is critical for tumor metastasis by providing oxygen, nutrients, and metastatic pathways. As a potential anti-angiogenic agent, Dihydroartemisinin (DHA) can effectively inhibit tumor metastasis. However, the mechanism how it regulates angiogenesis to affect tumor metastasis has not been fully clarified. To investigate the mechanisms of how DHA regulates melanoma progression. In this study, bioinformatics methods were used to analyze the correlation between angiogenesis and melanoma metastasis. Then, B16F10, A375, HUVECs and mouse metastasis models were adapted to clarify the inhibition of DHA in melanoma. GESA analysis revealed melanoma metastasis significantly positive correlated with angiogenesis. Meanwhile, DHA significantly decreased melanoma nodules and lung wet weight in metastatic tumor mice, and inhibited the expression of the angiogenic marker CD31 in vitro and in vivo. Similarly, DHA inhibited the expression of the angiogenic signal molecule VEGFR2 in A375 and B16F10 cells, and significantly suppressed the formation of their tubular structures. DHA-treated supernatants significantly inhibited the tubule-forming ability as well as lateral and longitudinal migration ability of HUVECs compared with untreated melanoma cell supernatants. Screening yielded the angiogenic pathways HIF-1α/VEGF, PI3K/ATK/mTOR associated with melanoma metastasis, and DHA may inhibit tumor metastasis by inhibiting these angiogenic pathways in melanoma cells to inhibit tumor metastasis. Further non-targeted metabolomics analysis revealed that DHA-treated model mice produced differential metabolites that were also associated with angiogenic pathways. DHA inhibits melanoma invasion and metastasis by mediating angiogenesis. These results have important implications for the potential use of DHA in treatment of melanoma.

Over-expression by degradation rescue of RTKs via cancer-secreted autocrine growth factors: a Phospho-degron-driven actionable layer of post-translational regulation?

Recently published work provide the first known evidence of a malignancy-associated regulatory mechanism, functionally connecting a phospho-regulated degron domain embedded in a receptor tyrosine kinase (RTK), with its ectopic expression in cancer, conditional to a specific autocrine growth factor signal. Mechanistically, the growth factor-triggered phosphorylation inhibits the degron domain present in the regulated RTK, blocking access to a specific degradation complex. This ultimately rescues the RTK from rapid ubiquitin-proteasome-system-mediated degradation and, most importantly, causes its cellular overexpression. This mechanism, which has been here assigned the new functional name "Over-Expression by Degradation Rescue" (OEDR), provides an additional layer and potentially preferential tool for the control of RTKs expression in cancer, in addition to other mechanisms acting at the transcriptional and messenger transcript stabilization levels. We propose this newly defined phosphorylation/ubiquitination switch-dependent signal to bear wider unexploited relevance in cell biology and human pathophysiology. The recently identified mechanism underlying an OEDR-regulated RTK is discussed herein in the context of physiological endocrine circuits and cancer.

EphrinB2: Expression of a novel potential target in renal cell carcinoma

Introduction

Renal cell carcinoma (RCC) is primarily managed by surgery with the use of systemic targeted therapy in a metastatic setting. Newer targeted therapeutic options are evolving; Eph-ephrin is a potential new pathway. The therapeutic potential of targeting the EphB4-EphrinB2 pathway has been demonstrated in many solid tumors; however, its expression in RCC has only been evaluated in a few studies with limited cases. We herein determine the immunohistochemical expression of EphrinB2 in RCC.

Methods

A tissue microarray comprising 110 cases of different histological subtypes of RCC and 10 normal kidney tissues were stained with monoclonal anti-EphrinB2 antibody (Abcam, AB201512). The tumor and endothelial cells expressing the EphrinB2 were examined and its expression was correlated with sex, histological subtypes, and tumor nodes metastasis (TNM) stage.

Results

Twenty cases of urothelial carcinoma and two unsatisfactory conventional clear cell RCC cases were excluded, and EphrinB2 expression was interpreted in the remaining 88 tumors. EphrinB2 was expressed in 42 out of 88 tumors (47.7%) and was negative in the normal renal parenchyma. There was a statistically significant difference in the expression of EphrinB2 in males (55%) and females (32%). However, no such difference of expression was noted for the histological subtypes and the stages. Half (51%) of Stage 1 (n = 30) and Stage 2 (n = 11) tumors showed EphrinB2 positivity.

Conclusions

EphrinB2 is expressed in approximately half of RCC cases. EphrinB2 expression in the early stage cancer might indicate its induction as an early event.

Scutellarin, a promising flavonoid in cancer treatment

Natural substances are increasingly being used as cancer treatments. Scutellarin, as a flavonoid, recently has been identified in a Chinese herbal extract called Erigeron breviscapus (Vant.). Scutellarin is being researched for its potential benefits due to the discovery that it possesses a variety of biological effects, such as neuroprotective, anti-coagulant, and anti-viral. In addition to these biological functions, scutellarin has also been found to have anti-tumor properties. Scutellarin first inhibits the activity of tumor cells by altering cancer cell signaling pathways such as Jak/STAT, ERK/AMPK, and Wnt/β-catenin. Additionally, scutellarin activates intrinsic and extrinsic apoptotic pathways, which causes the death of tumor cells, interrupts the cell cycle, and promotes its arrest. By limiting metastasis, angiogenesis, drug resistance, and other tumorigenic processes, scutellarin also reduces the aggressiveness of tumors. Utilizing scutellarin in combination with other anti-tumor therapies like 5-fluorouracil is another method to overcome tumor cell resistance. Moreover, it has been suggested that certain modifications, such as conjugation with cyclodextrin, aliphatic chains, and hybridization with nitric oxide, can enhance the pharmacogenetic capabilities of scutellarin to decrease its limited water solubility. It is believed that scutellarin may provide innovative chemotherapeutic treatments for cancer in the future.

EphrinB2 Inhibition and Pembrolizumab in Metastatic Urothelial Carcinoma

PURPOSE

Patients with metastatic urothelial carcinoma have poor prognosis after failure of standard first-line chemotherapy. Immune check point programmed death 1-programmed death ligand 1 antibodies have low response rates and thus there exists a major unmet need.

MATERIALS AND METHODS

In this phase II trial, patients with metastatic urothelial carcinoma that recurred or progressed after platinum-based chemotherapy received soluble EphB4-human serum albumin (sEphB4-HSA) in combination with pembrolizumab. The primary end points were tolerability and overall survival (OS). The secondary end points were progression-free survival (PFS), objective response rate (ORR), duration of response, and toxicity. The expression of sEphB4-HSA target EphrinB2 was correlated with outcomes.

RESULTS

Seventy patients were enrolled. The median follow up was 22.9 months (range, 1.3-54.7). The regimen had acceptable toxicity. In the intent-to-treat analysis (N = 70), the median OS was 14.6 months (95% CI, 9.2 to 21.5). Twenty-six (37%) patients had an objective response (95% CI, 26 to 48). The median PFS was 4.1 (95% CI, 1.5 to 5.7) months. Forty-six (66%) patients expressed EphrinB2, and among them, the median OS was 21.5 months (95% CI, 12.4 to not reached), the ORR was 52% (95% CI, 37 to 67), including a complete response rate of 24% (11 of 46; 95% CI, 12 to 36). The median PFS was 5.7 (95% CI, 2.7 to 27.9) months. Response was maintained at 6, 12, and 24 months in 88%, 74%, and 69% of the patients, respectively.

CONCLUSION

The combination of sEphB4-HSA and pembrolizumab appears synergistic with improved OS and ORR compared with historical data for programmed death 1/programmed death ligand 1 monotherapy.

A Phase II Study of sEphB4-HSA in Metastatic Castration-Resistant Prostate Cancer

INTRODUCTION

Ephrin receptors and their membrane-localized ligands induce bidirectional signaling and facilitate tumor-stroma interactions. Blocking the EphB4-EphrinB2 pathway, which can be accomplished by soluble EphB4 conjugated to human serum albumin (sEphB4-HSA), promotes cell death in preclinical models of aggressive prostate cancer. We hypothesized that targeting the EphB4-EphrinB2 pathway may serve as a therapeutic target in the treatment of metastatic castration resistant prostate cancer (mCRPC).

PATIENTS AND METHODS

We conducted a single arm, phase II trial in patients with progressive mCRPC who had received no more than 3 prior therapies for mCRPC. sEphB4-HSA 1000 mg IV was administered every 2 weeks, extending to 3 weeks starting from cycle 7. The primary endpoint was confirmed prostate specific antigen (PSA) response rate. We employed a Simon 2-stage Minimax design with 15 patients in the first stage and 10 additional patients in the second stage.

RESULTS

Fourteen eligible patients enrolled in the study with median age of 73.5 years (range: 52-83) and median baseline PSA of 65.11 ng/mL (range: 7.77-2850 ng/mL). Most patients received 3 prior therapies for mCRPC. The median treatment duration with sEphB4-HSA was 6.5 weeks (range: 2-35 weeks). Three patients experienced a serious adverse event potentially related to therapy, including 1 patient with a grade 5 event (cerebral vascular accident) possibly related to the study drug. No patient had a confirmed PSA response, and the study was stopped for futility. Thirteen patients had PSA progression. The median time to PSA progression was 28 days (90% CI: 28-42 days), and median time to radiologic progression was 55 days (90% CI: 54-72 days). Of 3 patients with measurable disease, 2 had stable disease and one had progressive disease.

CONCLUSION

In patients with mCRPC who progressed on prior second generation AR-targeted therapy, sEphB4-HSA monotherapy had no discernable anti-tumor activity.

EphB4 and ephrinB2 act in opposition in the head and neck tumor microenvironment

Differential outcomes of EphB4-ephrinB2 signaling offers formidable challenge for the development of cancer therapeutics. Here, we interrogate the effects of targeting EphB4 and ephrinB2 in head and neck squamous cell carcinoma (HNSCC) and within its microenvironment using genetically engineered mice, recombinant constructs, pharmacologic agonists and antagonists. We observe that manipulating the EphB4 intracellular domain on cancer cells accelerates tumor growth and angiogenesis. EphB4 cancer cell loss also triggers compensatory upregulation of EphA4 and T regulatory cells (Tregs) influx and their targeting results in reversal of accelerated tumor growth mediated by EphB4 knockdown. EphrinB2 knockout on cancer cells and vasculature, on the other hand, results in maximal tumor reduction and vascular normalization. We report that EphB4 agonism provides no additional anti-tumoral benefit in the absence of ephrinB2. These results identify ephrinB2 as a tumor promoter and its receptor, EphB4, as a tumor suppressor in HNSCC, presenting opportunities for rational drug design.

Tyrosine Phosphoproteomics of Patient-Derived Xenografts Reveals Ephrin Type-B Receptor 4 Tyrosine Kinase as a Therapeutic Target in Pancreatic Cancer

Simple Summary

Pancreatic cancer is one of the deadliest solid malignancies. Pancreatic ductal adenocarcinoma accounts for 90% of pancreatic cancer cases with minimal response to traditional chemotherapies. Protein tyrosine kinases have been shown to be hyperactivated in cancers and thus can serve as therapeutic targets. Patient-derived tumor xenografts (PDXs) in animal models such as mice are an appropriate resource to identify such activated kinases. PDXs models are excellent for the identification of therapeutic targets as compared to cell line models as they better reflect an in vivo environment. We identified ephrin type-B receptor 4 (EphB4) as hyperactivated in PDXs derived from pancreatic ductal adenocarcinoma.

Abstract

Pancreatic ductal adenocarcinoma is a recalcitrant tumor with minimal response to conventional chemotherapeutic approaches. Oncogenic signaling by activated tyrosine kinases has been implicated in cancers resulting in activation of diverse effector signaling pathways. Thus, the discovery of aberrantly activated tyrosine kinases is of great interest in developing novel therapeutic strategies in the treatment and management of pancreatic cancer. Patient-derived tumor xenografts (PDXs) in mice serve as potentially valuable preclinical models as they maintain the histological and molecular heterogeneity of the original human tumor. Here, we employed high-resolution mass spectrometry combined with immunoaffinity purification using anti-phosphotyrosine antibodies to profile tyrosine phosphoproteome across 13 pancreatic ductal adenocarcinoma PDX models. This analysis resulted in the identification of 1199 tyrosine-phosphorylated sites mapping to 704 proteins. The mass spectrometric analysis revealed widespread and heterogeneous activation of both receptor and non-receptor tyrosine kinases. Preclinical studies confirmed ephrin type-B receptor 4 (EphB4) as a potential therapeutic target based on the efficacy of human serum albumin-conjugated soluble EphB4 in mice bearing orthotopic xenografts. Immunohistochemistry-based validation using tissue microarrays from 346 patients with PDAC showed significant expression of EphB4 in >70% of patients. In summary, we present a comprehensive landscape of tyrosine phosphoproteome with EphB4 as a promising therapeutic target in pancreatic ductal adenocarcinoma.

Development of non-viral, ligand-dependent, EPHB4-specific chimeric antigen receptor T cells for treatment of rhabdomyosarcoma

Ephrin type-B receptor 4 (EPHB4), expressed in tumors including rhabdomyosarcoma, is a suitable target for chimeric antigen receptor (CAR)-T cells. Ligand-independent activation of EPHB4 causes cell proliferation and malignant transformation in rhabdomyosarcoma, whereas ligand-dependent stimulation of EPHB4 induces apoptosis in rhabdomyosarcoma. Therefore, we hypothesized that ligand-based, EPHB4-specific CAR-T cells may kill rhabdomyosarcoma cells without stimulating downstream cell proliferation mechanisms. We developed novel CAR-T cells by targeting EPHB4 via EPHRIN B2, a natural ligand of EPHB4. The generation of EPHB4-CAR-T cells via piggyBac (PB) transposon-based gene transfer resulted in sufficient T cell expansion and CAR positivity (78.5% ± 5.9%). PB-EPHB4-CAR-T cells displayed a dominant stem cell memory fraction (59.4% ± 7.2%) as well as low PD-1 expression (0.60% ± 0.21%) after 14 days of expansion. The PB-EPHB4-CAR-T cells inhibited EPHB4-positive tumor cells without activating cell proliferation downstream of EPHB4, even after multiple tumor re-challenges and suppressed tumor growth in xenograft-bearing mice. Therefore, PB-EPHB4-CAR-T cells possess a memory-rich fraction without early T cell exhaustion and show potential as promising therapeutic agents for treating rhabdomyosarcoma and other EPHB4-positive tumors.

Electric Acupuncture Treatment Promotes Angiogenesis in Rats with Middle Cerebral Artery Occlusion Through EphB4/EphrinB2 Mediated Src/PI3K Signal Pathway

BACKGROUND

Cerebral infarction is one of the most common causes of disability and death worldwide. It is reported that electric acupuncture was able to improve the prognosis of cerebral infarction by promoting angiogenesis. However, the corresponding signal pathways of angiogenesis promotes by electric acupuncture treatment needs to be further explored.

METHODS

MCAO rat was employed as the animal model, and clopidogrel hydrogen sulfate treatment was set as the positive control. Behaviors of rats, H&E staining, and TTC-staining was used to evaluate the recovery of infarcted brain tissue and nervous function. After that, immunocytochemical and immunofluorescence staining was used to quantify the angiogenesis and compensatory circulation, which including the analysis of microvessel density, field/ microvessel area ratio, and microvessel diameter. Western blot and RT-PCR for the detection of the related signal molecule, PI3K, Src, and EphB4/ephrinB2.

RESULTS

The neurologic impairment scores were decreased, and the brain tissue damage that showed with H&E and TTC-staining was relieved by the treatment of electric acupuncture in MCAO rat. The quantification of microvessel density and field/ microvessel area ratio was improved obviously, and the microvessel diameter was decreased which represent the angiogenesis of capillary in day 3 and 7 by the electric acupuncture treatment. We also found that the level of Src and PI3K was increased markedly followed by the up-regulation of EphB4 and EphrinB2 mRNA during the electric acupuncture treatment, and the pre-treatment of Src and/or PI3K inhibitor was able to disturb the angiogenesis of capillary.

CONCLUSIONS

We proved that electric acupuncture was able to accelerate the recovery of infarcted brain tissue and nervous function in MCAO rat by the promotion of angiogenesis, which was regulated by EphB4/EphrinB2 mediated Src/PI3K signal pathway. Our study provides a potential therapy and theoretical basis for the clinical treatment of cerebral infarction by the use of electric acupuncture.

Endothelial YAP/TAZ Signaling in Angiogenesis and Tumor Vasculature

Solid tumors are dependent on vascularization for their growth. The hypoxic, stiff, and pro-angiogenic tumor microenvironment induces angiogenesis, giving rise to an immature, proliferative, and permeable vasculature. The tumor vessels promote tumor metastasis and complicate delivery of anti-cancer therapies. In many types of tumors, YAP/TAZ activation is correlated with increased levels of angiogenesis. In addition, endothelial YAP/TAZ activation is important for the formation of new blood and lymphatic vessels during development. Oncogenic activation of YAP/TAZ in tumor cell growth and invasion has been studied in great detail, however the role of YAP/TAZ within the tumor endothelium remains insufficiently understood, which complicates therapeutic strategies aimed at targeting YAP/TAZ in cancer. Here, we overview the upstream signals from the tumor microenvironment that control endothelial YAP/TAZ activation and explore the role of their downstream targets in driving tumor angiogenesis. We further discuss the potential for anti-cancer treatments and vascular normalization strategies to improve tumor therapies.

Pathophysiologic Role of Molecules Determining Arteriovenous Differentiation in Adult Life

The structural differences between arteries and veins are genetically predetermined. Vascular identity markers, the molecular markers specific to veins and arteries, determine the differential development of vessels during embryogenesis and their expression persists in adult vessels. It is revealed that they can be reactivated under various pathophysiologic conditions even after vessel differentiation. Thus, once considered as quiescent in adults, vascular identity markers may actually play significant roles in vascular remodeling. Manipulation of vascular identity and the underlying molecular mechanisms might be a novel strategy to improve vascular remodeling for clinical application.

The critical role of the interplays of EphrinB2/EphB4 and VEGF in the induction of angiogenesis

The significant role of VEGF (vascular endothelial growth factor) as an angiogenesis inducer is well recognized. Besides VEGF, EphrinB2/EphB4 also plays essential roles in vascular development and postnatal angiogenesis. Compared with classical proangiogenic factors, not only does EphrinB2/EphB4 promote sprouting of new vessels, it is also involved in the vessel maturation. Given their involvement in many physiologic and pathological conditions, EphB4 and EphrinB2 are increasingly recognized as attractive therapeutic targets for angiogenesis-related diseases through modulating their expression and function. Previous works mainly focused on the individual role of VEGF and EphrinB2/EphB4 in angiogenesis, respectively, but the correlation between EphrinB2/EphB4 and VEGF in angiogenesis has not been fully disclosed. Here, we summarize the structure and bidirectional signaling of EphrinB2/EphB4, provide an overview on the relationship between EphrinB2/EphB4 signaling and VEGF pathway in angiogenesis and highlight the associated potential usefulness in anti-angiogenetic therapy.

EphrinB2 expression in prostate adenocarcinoma: Implications for targeted therapy

BACKGROUND

Prostate cancer is managed by surgery, androgen deprivation and cytotoxic chemotherapy. Targeted therapy is emerging as an important pillar in cancer therapeutics, however, efficacy in prostate cancer has been limited. Eph-ephrin is a novel pathway that is upregulated in prostate cancer and promotes the initiation and progression of cancer. The aim of this study was to determine the immunohistochemical expression of ephrinB2 in prostate adenocarcinoma.

METHODS

A tissue microarray comprising of prostate adenocarcinoma of different grade groups was stained with a monoclonal anti-ephrinB2 antibody (Abcam, AB201512). The tumor and endothelial cells expressing the ephrinB2 positivity were noted. The statistical analysis was performed to determine the difference in expression based on grade groups and the TNM stage.

RESULTS

EphrinB2 was expressed in 40 out of 72 cases (55.5 %) of prostate adenocarcinoma and was predominantly negative in the normal prostatic tissue. There was no significant difference in the expression of ephrinB2 in various grade groups (p = 0.7) or stages (p = 0.6).

CONCLUSIONS

EphrinB2 is expressed in a significant number of prostate adenocarcinoma regardless of grade and stage. Hence, there is a potential to target this molecule in the low-grade tumors with localized disease as well as high grade, high volume tumors with metastatic disease.

Targeting Forward and Reverse EphB4/EFNB2 Signaling by a Peptide with Dual Functions

The tyrosine kinase receptor EphB4 is frequently overexpressed in ovarian and other solid tumors and is involved in interactions between tumor cells and the tumor microenvironment, contributing to metastasis. Trans-interaction between EphB4 and its membrane-bound ligand ephrin B2 (EFNB2) mediates bi-directional signaling: forward EFNB2-to-EphB4 signaling suppresses tumor cell proliferation, while reverse EphB4-to-EFNB2 signaling stimulates the invasive and angiogenic properties of endothelial cells. Currently, no small molecule–based, dual-function, EphB4-binding peptides are available. Here, we report our discovery of a bi-directional ephrin agonist peptide, BIDEN-AP which, when selectively internalized via receptor-mediated endocytosis, suppressed invasion and epithelial-mesenchymal transition of ovarian cancer cells. BIDEN-AP also inhibited endothelial migration and tube formation. In vivo, BIDEN-AP and its nanoconjugate CCPM-BIDEN-AP significantly reduced growth of orthotopic ovarian tumors, with CCPM-BIDEN-AP displaying greater antitumor potency than BIDEN-AP. Both BIDEN-AP and CCPM-BIDEN-AP compromised angiogenesis by downregulating epithelial-mesenchymal transition and angiogenic pathways. Thus, we report a novel EphB4-based therapeutic approach against ovarian cancer.

Expression levels of EPHB4, EFNB2 and caspase-8 are associated with clinicopathological features and progression of esophageal squamous cell cancer

The upregulation of EPH receptor B4 (EPHB4) results in a survival advantage for tumor cells via the inhibition of the casapse-8-mediated apoptotic pathway, which begins from the cell membrane. The present study investigated the expression patterns of EPHB4, ephrin B2 (EFNB2) and caspase-8 in patients with esophageal squamous cell carcinoma (ESCC). The association between the expression patterns and certain clinicopathological characteristics of the patients was also determined. mRNA levels of EPHB4, EFNB2 and caspase-8 in paired primary ESCC samples and adjacent esophageal tissues collected from 96 patients with ESCC were quantified using quantitative PCR. Upregulation of EPHB4 and EFNB2 mRNA expression, and downregulation of caspase-8 mRNA were detected in ESCC samples compared with that in the adjacent esophageal tissues. The expression levels of EPHB4 and EFNB2 were positively correlated with each other, whereas the mRNA levels of both EPHB4 and EFNB2 exhibited a negative correlation with that of caspase-8. The mRNA levels of both EPHB4 and EFNB2 demonstrated a significant positive association with certain clinicopathological features of patients with ESCC, including family history, tumor size, metastasis and stage. Conversely, a negative association was revealed between the expression level of caspase-8 and clinicopathological features of patients with ESCC. Moreover, mRNA expression levels of EPHB4 and EFNB2 were negatively associated with survival times of patients with ESCC, whereas the level of caspase-8 was positively associated with patient outcome. The results from the present study suggested that EPHB4, EFNB2 and caspase-8 may be implicated in the tumorigenesis and progression of ESCC, and that consequently, they may serve as useful prognostic markers, as well as potential therapeutic targets.

Targeting the Eph/Ephrin System as Anti-Inflammatory Strategy in IBD

Besides their long-known critical role in embryonic growth and in cancer development and progression, erythropoietin-producing hepatocellular carcinoma type B (EphB) receptor tyrosine kinases and their ephrin-B ligands are involved in the modulation of immune responses and in remodeling and maintaining the integrity of the intestinal epithelial layer. These processes are critically involved in the pathogenesis of inflammatory-based disorders of the gut, like inflammatory bowel diseases (IBDs). Accordingly, our aim was to investigate the role of the EphB/ephrin-B system in intestinal inflammation by assessing the local and systemic effects produced by its pharmacological manipulation in 2,4,6-trinitrobenzenesulfonic acid (TNBS)- (Th1-dependent model) and dextran sulphate sodium (DSS)- (innate response model) induced colitis in mice. To this purpose, we administered chimeric Fc-conjugated proteins, allegedly able to uni-directionally activate either forward (ephrin-B1-Fc) or reverse (EphB1-Fc) signaling, and the soluble monomeric EphB4 extracellular domain protein, that, simultaneously interfering with both signaling pathways, acts as EphB/ephrin-B antagonist.The blockade of the EphB/ephrin-B forward signaling by EphB4 and EphB1-Fc was ineffective against DSS-induced colitis while it evoked remarkable beneficial effects against TNBS colitis: it counteracted all the evaluated inflammatory responses and the changes elicited on splenic T lymphocytes subpopulations, without preventing the appearance of a splice variant of ephrin-B2 gene elicited by the haptenating agent in the colon. Interestingly, EphB4, preferentially displacing EphB4/ephrin-B2 interaction over EphB1/ephrin-B1 binding, was able to promote Tumor Necrosis Factor alpha (TNFα) release by splenic mononuclear cells in vitro. On the whole, the collected results point to a potential role of the EphB/ephrin-B system as a pharmacological target in intestinal inflammatory disorders and suggest that the therapeutic efficacy of its blockade seemingly works through the modulation of immune responses, independent of the changes at the transcriptional and translational level of EphB4 and ephrin-B2 genes.

Pancreatic Tumor Microenvironment Modulation by EphB4-ephrinB2 Inhibition and Radiation Combination

PURPOSE

A driving factor in pancreatic ductal adenocarcinoma (PDAC) treatment resistance is the tumor microenvironment, which is highly immunosuppressive. One potent immunologic adjuvant is radiotherapy. Radiation, however, has also been shown to induce immunosuppressive factors, which can contribute to tumor progression and formation of fibrotic tumor stroma. To capitalize on the immunogenic effects of radiation and obtain a durable tumor response, radiation must be rationally combined with targeted therapies to mitigate the influx of immunosuppressive cells and fibrosis. One such target is ephrinB2, which is overexpressed in PDAC and correlates negatively with prognosis.Experimental Design: On the basis of previous studies of ephrinB2 ligand-EphB4 receptor signaling, we hypothesized that inhibition of ephrinB2-EphB4 combined with radiation can regulate the microenvironment response postradiation, leading to increased tumor control in PDAC. This hypothesis was explored using both cell lines and in vivo human and mouse tumor models.

RESULTS

Our data show this treatment regimen significantly reduces regulatory T-cell, macrophage, and neutrophil infiltration and stromal fibrosis, enhances effector T-cell activation, and decreases tumor growth. Furthermore, our data show that depletion of regulatory T cells in combination with radiation reduces tumor growth and fibrosis.

CONCLUSIONS

These are the first findings to suggest that in PDAC, ephrinB2-EphB4 interaction has a profibrotic, protumorigenic role, presenting a novel and promising therapeutic target.

Essential roles of EphrinB2 in mammalian heart: from development to diseases

EphrinB2, a membrane-tethered ligand preferentially binding to its receptor EphB4, is ubiquitously expressed in all mammals. Through the particular bidirectional signaling, EphrinB2 plays a critical role during the development of cardiovascular system, postnatal angiogenesis physiologically and pathologically, and cardiac remodeling after injuries as an emerging role. This review highlights the pivotal involvement of EphrinB2 in heart, from developmental cardiogenesis to pathological cardiac remodeling process. Further potential translational therapies will be discussed in targeting EphrinB2 signaling, to better understand the prevention and treatment of cardiovascular diseases.

Roles of EphA1/A2 and ephrin-A1 in cancer

The biological functions of the Eph/ephrin system have been intensively investigated and well documented so far since its discovery in 1987. Although the Eph/ephrin system has been implicated in pathological settings such as Alzheimer's disease and cancer, the molecular mechanism of the Eph/ephrin system in those diseases is not well understood. Especially in cancer, recent studies have demonstrated that most of Eph and ephrin are up‐ or down‐regulated in various types of cancer, and have been implicated in tumor progression, tumor malignancy, and prognosis. However, they lack consistency and are in controversy. The localization patterns of EphA1 and EphA2 in mouse lungs are very similar, and both knockout mice showed similar phenotypes in the lungs. Ephrin‐A1 that is a membrane‐anchored ligand for EphAs was co‐localized with EphA1 and EphA2 in lung vascular endothelial cells. We recently uncovered the molecular mechanism of ephrin‐A1‐induced lung metastasis by understanding the physiological function of ephrin‐A1 in lungs. This review focuses on the function of EphA1, EphA2, and ephrin‐A1 in tumors and an establishment of pre‐metastatic microenvironment in the lungs.

In silico fragment-based drug design with SEED

We report on two fragment-based drug design protocols, SEED2XR and ALTA, which start by high-throughput docking. SEED2XR is a two-stage protocol for fragment-based drug design. The first stage is in silico and consists of the automatic docking of 10³-10⁴ fragments using SEED, which requires about 1 s per fragment. SEED is a docking software developed specifically for fragment docking and binding energy evaluation by a force field with implicit solvent. In the second stage of SEED2XR, the 10-10² fragments with the most favorable predicted binding energies are validated by protein X-ray crystallography. The recent applications of SEED2XR to bromodomains demonstrate that the whole SEED2XR protocol can be carried out in about a week of working time, with hit rates ranging from 10% to 40%. Information on fragment-target interactions generated by the SEED2XR protocol or directly from SEED docking has been used for the discovery of hundreds of hits. ALTA is a computational protocol for screening which identifies candidate ligands that preserve the interactions between the optimal SEED fragments and the protein target. Medicinal chemistry optimization of ligands predicted by ALTA has resulted in pre-clinical candidates for protein kinases and bromodomains. The high-throughput, very low cost, sustainability, and high hit rate of the SEED-based protocols, unreachable by purely experimental techniques, make them perfectly suitable for both academic and industrial drug discovery research.

Bidirectional juxtacrine ephrinB2/Ephs signaling promotes angiogenesis of ECs and maintains self-renewal of MSCs

Co-transplantation of endothelial cells (ECs) and mesenchymal stem cells (MSCs) is an important strategy for repairing complex and large bone defects. However, the ways in which ECs and MSCs interact remain to be fully clarified. We found that forward ephrinB2/Ephs signaling from hBMSCs to hUVECs promoted the tube formation of hUVECs by activating the PI3K/AKT/mTOR pathway. Reverse ephrinB2/Ephs signaling from hUVECs to hBMSCs promoted the proliferation and maintenance of hBMSCs self-renewal via upregulation of OCT4, SOX2, and YAP1. Subcutaneous co-transplantation of ECs and MSCs in nude mice confirmed that forward ephrinB2/Ephs signaling could increase the cross-sectional area of blood vessels in the transplanted area, and reverse ephrinB2/Ephs signaling could maintain the self-renewal of transplanted hBMSCs in vivo. Based on these results, ephrinB2/Ephs bidirectional juxtacrine regulation between ECs and MSCs plays a pivotal role in improving the healing of bone defects by promoting angiogenesis and achieving a sufficient number of MSCs.

EphB4: A promising target for upper aerodigestive malignancies

The erythropoietin-producing hepatocellular carcinoma (Eph) receptors are the largest family of receptor tyrosine kinases (RTKs) that include two major subclasses, EphA and EphB. They form an important cell communication system with critical and diverse roles in a variety of biological processes during embryonic development. However, dysregulation of the Eph/ephrin interactions is implicated in cancer contributing to tumour growth, metastasis, and angiogenesis. Here, we focus on EphB4 and review recent developments in elucidating its role in upper aerodigestive malignancies to include lung cancer, head and neck cancer, and mesothelioma. In particular, we summarize information regarding EphB4 structure/function and role in disease pathobiology. We also review the data supporting EphB4 as a potential pharmacological and immunotherapy target and finally, progress in the development of new therapeutic strategies including small molecule inhibitors of its activity is discussed. The emerging picture suggests that EphB4 is a valuable and attractive therapeutic target for upper aerodigestive malignancies.

Prognostic Value of ACVRL1 Expression in Metastatic Colorectal Cancer Patients Receiving First-line Chemotherapy With Bevacizumab: Results From the Triplet Plus Bevacizumab (TRIBE) Study

BACKGROUND

No biomarkers exist to predict benefit from antiangiogenic therapy in metastatic colorectal cancer patients. ACVRL1 (activin receptor like-protein 1) encodes for ALK1, a member of the transforming growth factor-β receptor family, which directs pathologic angiogenesis. We examined the intratumoral expression of ACVRL1 and other angiogenesis pathway-related genes to identify molecular markers in the TRIBE study.

MATERIALS AND METHODS

Of 503 randomized patients, 228 had sufficient tissue for analysis. Formalin-fixed paraffin-embedded specimens were examined for expression of VEGF-A, VEGF-B, VEGF-C, VEGFR1, VEGFR2, ACVRL1, EphB4, and EGFL7 using reverse transcription polymerase chain reaction. A maximal χ² approach was used to determine the messenger RNA levels associated with progression-free survival (PFS), overall survival (OS), response rate, early tumor shrinkage, and depth of response. Recursive partitioning trees were constructed to identify composite prognostic biomarker profiles. External validation was conducted in silico using the Oncomine database.

RESULTS

High ACVRL1 expression was associated with superior OS in both treatment arms (FOLFOXIRI [5-fluorouracil, leucovorin, oxaliplatin, irinotecan]-bevacizumab, 32.7 vs. 13.5 months, hazard ratio [HR], 0.38, P = .023; FOLFIRI [5-fluorouracil, leucovorin, irinotecan]-bevacizumab, 35.1 vs. 22.0 months, HR, 0.36, P = .006) and prolonged PFS (11.7 vs. 5.9 months, multivariate HR, 0.17; P = .001) for patients receiving FOLFOXIRI-bevacizumab on univariate and multivariate analyses. In recursive partitioning analysis, ACVRL1 was the strongest discriminator of the response rate, PFS, and OS in patients receiving FOLFOXIRI-bevacizumab and of OS in patients receiving FOLFIRI-bevacizumab. In silico validation revealed significant associations between ACVRL1 expression, disease recurrence, and 1-year survival (P < .05) among all colorectal cancer stages.

CONCLUSION

ACVRL1 expression could serve as a prognostic biomarker in metastatic colorectal cancer patients receiving chemotherapy and bevacizumab and warrants further evaluation in prospective studies.

EphrinB-mediated reverse signalling controls junctional integrity and pro-inflammatory differentiation of endothelial cells

The EphB/ephrinB receptor-ligand system is pivotal for the development of the embryonic vasculature and for angiogenesis in the adult organism. We observed that (i) the expression of ephrinB2 and ephrinB1 is up-regulated in capillaries during inflammation, that (ii) these ligands are localised on the luminal endothelial surface, and that (iii) they interact with the ephrinB-receptor EphB2 on monocyte/macrophages. This study delineates the impact of ephrinB-mediated reverse signalling on the integrity and proinflammatory differentiation of the endothelium. To this end, in vitro analyses with human cultured endothelial cells reveal that knockdown of ephrinB2 or ephrinB1 impairs monocyte transmigration through the endothelium. While ephrinB2 but not ephrinB1 interacts with PECAM-1 (CD31) in this context, reverse signalling by ephrinB1 but not ephrinB2 elicits a c-Jun N-terminal kinase (JNK)-dependent up-regulation of E-selectin expression. Furthermore, treatment of endothelial cells with soluble EphB2 receptor bodies or EphB2-overexpressing mouse myeloma cells links ephrinB2 to PECAM-1 and induces its Src-dependent phosphorylation while diminishing Src homology phosphotyrosyl phosphatase-2 (SHP-2) activity and increasing endothelial cell permeability. We conclude that extravasation of EphB2 positive leukocyte populations is facilitated by lowering the integrity of endothelial cell junctions and enhancing the pro-inflammatory phenotype of the endothelium through activation of ephrinB ligands.

Scutellarin suppresses human colorectal cancer metastasis and angiogenesis by targeting ephrinb2

Tumor induced angiogenesis is an attractive target for anti-cancer drug treatment. Scutellarin, which is a native compound derived from scutellaria altissima leaves, has already been proved to possess anti-tumor activities. Nevertheless, their effects in colorectal cancer metastasis and angiogenesis have not been evaluated. In order to reveal the anti-angiogenic and anti-metastasis capacity of scutellarin, wound healing and Transwell chamber inserts invasion were done in colorectal cancer cells, and cell proliferation as wells colony formation were conducted to identify the proliferation inhibition of colorectal cancer in vitro. The growth inhibition of scutellarin was further definite by a mouse colorectal xenograft model in vivo. Herein, we demonstrated scutellarin suppressed colorectal cancer cell viability and colony formation in vitro, and remarkably reduced tumor growth in vivo mouse xenografts. Additionally, scutellarin restrained colorectal cancer cells-induced angiogenesis, inhibited human umbilical vascular endothelial cells (HUVECs) migration, tube formation of HUVECs, and micro-vessel formation in chick embnyo chorioallantoic menbreme (CAM) assay. Altogether, our results exhibited the evidence that scutellarin inhibit colorectal cancer angiogenesis and metastasis via targeting ephrinb2 signaling, with the potential of an anti-tumor agent for cancer treatment.

Targeting receptor tyrosine kinase EphB4 in cancer therapy

Eph receptors and their Eph receptor-interacting (ephrin) ligands together form an important cell communication system with diverse roles. Experimental evidence demonstrated Eph receptor bidirectional signaling with both tumor-suppressing and tumor-promoting activities in cancer cells. The tyrosine kinase EphB4, a member of the Eph receptor family, has been associated with tumor angiogenesis, growth and metastasis, thus making it a valuable and attractive target for drug design for therapeutic applications. In the past decade, many studies have focused on elucidating the structure and function of EphB4 in complex with its ligand ephrinB2 for their role in carcinogenesis. Meanwhile, an array of compounds targeting EphB4 have been studied and several selective inhibitors have been tested in clinical studies. This review discusses the structure and function of the EphB4 receptor, analyzes its potential as a target for anticancer therapy, and summarizes the information about inhibitors of EphB4 kinase activity. Conclusively, EphB4 is a challenging but promising therapeutic target in cancer.

EphB4 forward signalling mediates angiogenesis caused by CCM3/PDCD10-ablation

CCM3, also named as PDCD10, is a ubiquitous protein expressed in nearly all tissues and in various types of cells. It is essential for vascular development and post-natal vessel maturation. Loss-of-function mutation of CCM3 predisposes for the familial form of cerebral cavernous malformation (CCM). We have previously shown that knock-down of CCM3 stimulated endothelial angiogenesis via impairing DLL4-Notch signalling; moreover, loss of endothelial CCM3 stimulated tumour angiogenesis and promoted tumour growth. The present study was designed to further elucidate the inside signalling pathway involved in CCM3-ablation-mediated angiogenesis. Here we report for the first time that silencing endothelial CCM3 led to a significant up-regulation of EphB4 mRNA and protein expression and to an increased kinase activity of EphB4, concomitantly accompanied by an activation of Erk1/2, which was reversed by treatment with the specific EphB4 kinase inhibitor NVP-BHG712 (NVP), indicating that silencing CCM3 activates EphB4 kinase forward signalling. Furthermore, treatment with NVP rescued the hyper-angiogenic phenotype induced by knock-down of endothelial CCM3 in vitro and in vivo. Additional study demonstrated that the activation of EphB4 forward signalling in endothelial cells under basal condition and after CCM3-silence was modulated by DLL4/Notch signalling, relying EphB4 at downstream of DLL4/Notch signalling. We conclude that angiogenesis induced by CCM3-silence is mediated by the activation of EphB4 forward signalling. The identified endothelial signalling pathway of CCM3-DLL4/Notch-EphB4-Erk1/2 may provide an insight into mechanism of CCM3-ablation-mediated angiogenesis and could potentially contribute to novel therapeutic concepts for disrupting aberrant angiogenesis in CCM and in hyper-vascularized tumours.

EPHB4 is a therapeutic target in AML and promotes leukemia cell survival via AKT

EPHB4, an ephrin type B receptor, is implicated in the growth of several epithelial tumors and is a promising target in cancer therapy; however, little is known about its role in hematologic malignancies. In this article, we show that EPHB4 is highly expressed in ∼30% of acute myeloid leukemia (AML) samples. In an unbiased RNA interference screen of primary leukemia samples, we found that EPHB4 drives survival in a subset of AML cases. Knockdown of EPHB4 inhibits phosphatidylinositol 3-kinase/AKT signaling, and this is accompanied by a reduction in cell viability, which can be rescued by a constitutively active form of AKT. Finally, targeting EPHB4 with a highly specific monoclonal antibody (MAb131) is effective against AML in vitro and in vivo. EPHB4 is therefore a potential target in AML with high EPHB4 expression.

EphB4/EphrinB2 therapeutics in Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma affecting children and is often diagnosed with concurrent metastases. Unfortunately, few effective therapies have been discovered that improve the long-term survival rate for children with metastatic disease. Here we determined effectiveness of targeting the receptor tyrosine kinase, EphB4, in both alveolar and embryonal RMS either directly through the inhibitory antibody, VasG3, or indirectly by blocking both forward and reverse signaling of EphB4 binding to EphrinB2, cognate ligand of EphB4. Clinically, EphB4 expression in eRMS was correlated with longer survival. Experimentally, inhibition of EphB4 with VasG3 in both aRMS and eRMS orthotopic xenograft and allograft models failed to alter tumor progression. Inhibition of EphB4 forward signaling using soluble EphB4 protein fused with murine serum albumin failed to affect eRMS model tumor progression, but did moderately slow progression in murine aRMS. We conclude that inhibition of EphB4 signaling with these agents is not a viable monotherapy for rhabdomyosarcoma.

Targeting Eph/ephrin system in cancer therapy

It is well established that the Eph/ephrin system plays a central role in the embryonic development, with minor implications in the physiology of the adult. However, it is overexpressed and deregulated in a variety of tumors, with a primary involvement in tumorigenesis, tumor angiogenesis, metastasis development, and cancer stem cell regeneration. Targeting the Eph/ephrin system with biologicals, including antibodies and recombinant proteins, reduces tumor growth in animal models of hematological malignancies, breast, prostate, colon, head and neck cancers and glioblastoma. Currently, some of these biopharmaceutical agents are under investigations in phase I or phase II clinical trials. Peptides and small molecules targeting protein-protein-interaction (PPI) are in the late preclinical phase where they are showing promising activity in models of glioblastoma, ovarian and lung cancer. The present review summarizes the most critical findings proposing the Eph/ephrin signaling system as a new target in molecularly targeted oncology.

Tumor angiogenesis revisited: Regulators and clinical implications

Since Judah Folkman hypothesized in 1971 that angiogenesis is required for solid tumor growth, numerous studies have been conducted to unravel the angiogenesis process, analyze its role in primary tumor growth, metastasis and angiogenic diseases, and to develop inhibitors of proangiogenic factors. These studies have led in 2004 to the approval of the first antiangiogenic agent (bevacizumab, a humanized antibody targeting vascular endothelial growth factor) for the treatment of patients with metastatic colorectal cancer. This approval launched great expectations for the use of antiangiogenic therapy for malignant diseases. However, these expectations have not been met and, as knowledge of blood vessel formation accumulates, many of the original paradigms no longer hold. Therefore, the regulators and clinical implications of angiogenesis need to be revisited. In this review, we discuss recently identified angiogenesis mediators and pathways, new concepts that have emerged over the past 10 years, tumor resistance and toxicity associated with the use of currently available antiangiogenic treatment and potentially new targets and/or approaches for malignant and nonmalignant neovascular diseases.

Disturbed Expression of EphB4, but Not EphrinB2, Inhibited Bone Regeneration in an In Vivo Inflammatory Microenvironment

The important role of ephrinB2-EphB4 signaling pathway in bone remodeling has been well established. However, it is still unclear whether this bidirectional signaling also has effects on the regenerative processes of bone defects created in an inflammatory microenvironment. In this study, an experimental animal model of bone defects treated with lentiviruses was prepared and an inflammatory microenvironment was established. Expression levels of bone marker genes were monitored in the newly formed bone tissue using quantitative reverse transcriptase polymerase chain reaction and western blot. Immunohistochemical (IHC) staining and histomorphometric analysis were also performed to evaluate bone healing processes. Compared with the pLenti6.3-ctrl group, the pLenti6.3-ephb4siRNA group exhibited lower expression levels of bone formation marker genes and a higher level of NFATc1 in the new bone tissue. In addition, the newly formed bone was thinner and the number of giant osteoclasts was higher in the pLenti6.3-ephb4siRNA group than that in the pLenti6.3-ctrl group. In contrast, there was no significant difference between the pLenti6.3-efnb2siRNA group and the pLenti6.3-ctrl group. In conclusion, EphB4 plays an irreplaceable role in bone regeneration in an inflammatory microenvironment, whereas the functional loss of ephrinB2 can be effectively compensated, most possibly by other ephrins with similar chemical structures.

Enhancing radiosensitization in EphB4 receptor-expressing Head and Neck Squamous Cell Carcinomas

Members of the Eph family of receptor tyrosine kinases have been implicated in a wide array of human cancers. The EphB4 receptor is ubiquitously expressed in head and neck squamous cell carcinoma (HNSCC) and has been shown to impart tumorigenic and invasive characteristics to these cancers. In this study, we investigated whether EphB4 receptor targeting can enhance the radiosensitization of HNSCC. Our data show that EphB4 is expressed at high to moderate levels in HNSCC cell lines and patient-derived xenograft (PDX) tumors. We observed decreased survival fractions in HNSCC cells following EphB4 knockdown in clonogenic assays. An enhanced G2 cell cycle arrest with activation of DNA damage response pathway and increased apoptosis was evident in HNSCC cells following combined EphB4 downregulation and radiation compared to EphB4 knockdown and radiation alone. Data using HNSCC PDX models showed significant reduction in tumor volume and enhanced delay in tumor regrowth following sEphB4-HSA administration with radiation compared to single agent treatment. sEphB4-HSA is a protein known to block the interaction between the EphB4 receptor and its ephrin-B2 ligand. Overall, our findings emphasize the therapeutic relevance of EphB4 targeting as a radiosensitizer that can be exploited for the treatment of human head and neck carcinomas.

Ephrin-B2 overexpression predicts for poor prognosis and response to therapy in solid tumors

Ephrin B2 is variably expressed on tumor cells and its blockade has been shown to inhibit angiogenesis in animal models of pancreatic, colorectal, lung and head, and neck squamous cell carcinomas. However, the implications of ephrinB2 expression in cancer patients have remained elusive. In this study, we analyzed the cancer genome atlas (TCGA) for ephrinB2 expression. We report significant correlations between EFNB2 expression, overall survival and disease-free survival in head and neck squamous cell carcinoma (HNSCC, n = 519), pancreatic adenocarcinoma (n = 186), and bladder urothelial carcinoma (n = 410). In HNSCC patients, high-EFNB2 mRNA expression was associated with tumor HPV negativity, oral cavity location, alcohol intake, higher TP53 mutation, and EGFR amplification. EphrinB2 overexpression also correlated with worse response to chemotherapy and radiotherapy. The therapeutic potential of blocking ephrinB2 was validated in HNSCC patient-derived tumor xenografts and showed significant improvement in survival and tumor growth delay. Our data shows that ephrinB2 overexpression can serve as a critical biomarker for patient prognosis and response to therapy. These results should guide design of future clinical trials exploring EphrinB2 inhibition in cancer patients. © 2016 Wiley Periodicals, Inc.

Comprehensive study of angiogenic factors in women with endometriosis compared to women without endometriosis

OBJECTIVE

Endometriosis is a benign gynaecological disease, affecting women during their reproductive years. Angiogenesis represents a crucial step in the pathogenesis of endometriosis, because endometriotic lesions require neovascularization. In this study several angiogenesis-related genes have been studied in the context of endometriosis. Some of the analyzed angiogenic factors as well as their interactions were studied the first time regarding a possible association with endometriosis.

STUDY DESIGN

This case-control study consisted of 205 biopsies of 114 patients comprising 61 endometriosis patients and 53 control patients. Among them in 29 cases paired samples were obtained. VEGFA, VEGFR2, HIF1A, HGF, NRP1, PDGFB, FGF18, TNFα, TGFB2, EPHB4, EPO and ANG mRNA expression was analyzed by qRT-PCR in ectopic tissue samples, in eutopic endometrium of women with and without endometriosis, and in unaffected peritoneum of women with and without endometriosis.

RESULTS

VEGFR2, HIF1A, HGF, PDGFB, NRP1 and EPHB4 are overexpressed in ectopic lesions compared to eutopic tissues. VEGFR2, HGF, PDGFB, NRP1, and EPHB4 showed highest mRNA levels in peritoneal implants, in contrast HIF1A showed the highest expression in ovarian endometriomas. Correlation analyses of angiogenic factors in ectopic lesions revealed the strongest associations between VEGFR2, PDGFB, and EPHB4. We further showed a significant upregulation of VEGFR2, HIF1A and EPHB4 in eutopic endometrium of women with endometriosis compared to that of controls and a trend towards upregulation of HGF. Additionally, a significant downregulation for HIF1A, HGF and EPHB4 was observed in unaffected peritoneal tissues of women with endometriosis compared to controls.

CONCLUSION

We identified new genes (EPHB4 and NRP1) that may contribute to angiogenesis in endometriosis beside known factors (VEGFA, VEGFR2, HIF1A, HGF, and PDGFB). Correlation studies revealed the putative importance of EBHB4 in association with endometriosis. Our analyses support preliminary reports that angiogenic factors seem to be differently expressed in peritoneal implants, ovarian endometriomas and deep infiltrating endometriosis. Our observation that angiogenic factors are differently expressed in the unaffected peritoneum of women with endometriosis compared to women without endometriosis underlines the importance of the peritoneum in the establishment of endometriosis.

Anti-tumour effects of antibodies targeting the extracellular cysteine-rich region of the receptor tyrosine kinase EphB4

EphB4 is a membrane-bound receptor tyrosine kinase (RTK) commonly over-produced by many epithelial cancers but with low to no expression in most normal adult tissues. EphB4 over-production promotes ligand-independent signaling pathways that increase cancer cell viability and stimulate migration and invasion. Several studies have shown that normal ligand-dependent signaling is tumour suppressive and therefore novel therapeutics which block the tumour promoting ligand-independent signaling and/or stimulate tumour suppressive ligand-dependent signaling will find application in the treatment of cancer. An EphB4-specific polyclonal antibody, targeting a region of 200 amino acids in the extracellular portion of EphB4, showed potent in vitro anti-cancer effects measured by an increase in apoptosis and a decrease in anchorage independent growth. Peptide exclusion was used to identify the epitope targeted by this antibody within the cysteine-rich region of the EphB4 protein, a sequence defined as a potential ligand interacting interface. Addition of antibody to cancer cells resulted in phosphorylation and subsequent degradation of the EphB4 protein, suggesting a mechanism that is ligand mimetic and tumour suppressive. A monoclonal antibody which specifically targets this identified extracellular epitope of EphB4 significantly reduced breast cancer xenograft growth in vivo confirming that EphB4 is a useful target for ligand-mimicking antibody-based anti-cancer therapies.

Three stories on Eph kinase inhibitors: From in silico discovery to in vivo validation

Several selective and potent EphB4 inhibitors have been discovered, optimized and biophysically characterized by our groups over the past years. On the outset of these discoveries high throughput docking techniques were applied. Herein, we review the optimization campaigns started from three of these hits (Xan-A1, Pyr-A1 and Qui-A1) with emphasis on their in depth in vitro and in vivo characterization, together with previously unpublished angiogenesis and fluorescence based assays.

Role of EFNB2/EPHB4 signaling in spiral artery development during pregnancy: An appraisal

EFNB2 and EPHB4, which belong to a large tyrosine kinase receptor superfamily, are molecular markers of arterial and venous blood vessels, respectively. EFNB2/EPHB4 signaling plays an important role in physiological and pathological angiogenesis, and its role in tumor vessel development has been extensively studied. Pregnancy and tumors share similar features, including continuous cell proliferation and increased demand for a blood supply. Our previous studies showed that Efnb2 and Ephb4 were expressed dynamically in the spiral arteries, uterine natural killer cells, and trophoblasts during mouse gestation Days 6.5-12.5. Moreover, uterine natural killer cells and trophoblasts are required for the modification of spiral arteries. Oxygen tension within the pregnant uterus, which contributes to the vascular development, also affects EFNB2 and EPHB4 expression. Considering the role of EFNB2/EPHB4 signaling in embryonic and tumor vascular development, and its dynamic expression in the decidua and placenta, we hypothesize that EFNB2 and EPHB4 are involved in the regulation of spiral artery remodeling. Investigating this hypothesis will help clarify the mechanisms of pathological pregnancy that may underlie abnormal spiral artery development.