Isolation and characterization of a novel receptor-type protein tyrosine kinase (hek) from a human pre-B cell line

EphA3-targeted chimeric antigen receptor T cells are effective in glioma and generate curative memory T cell responses

BACKGROUND

High-grade gliomas including glioblastoma (GBM) and diffuse midline gliomas (DMG) represent the most lethal and aggressive brain cancers where current treatment modalities offer limited efficacy. Chimeric antigen receptor (CAR) T cell therapies have emerged as a promising strategy, boasting tumor-specific targeting and the unique ability to penetrate the blood-brain barrier. However, the effective clinical application hinges on the optimal choice of antigen, with a limited number, currently under investigation.

METHODS

We employed cell surface proteomic analysis of primary human high-grade glioma samples from both adult and pediatric patients. This led to the identification of Ephrin type-A receptor 3 (EphA3) as a prevalently expressed target. We engineered a second-generation EphA3-targeted CAR T cell and assessed function using in vitro and in vivo models of GBM and DMG.

RESULTS

EphA3-targeted CAR T cells demonstrated robust antigen-specific killing of human GBM and DMG cell lines in vitro. In an orthotopic xenograft NSG mouse model, EphA3-targeted CAR T cells not only effectively eradicated tumors but also established a functional T cell population protective on rechallenge. Remarkably, mice rechallenged with a second contralateral orthotopic tumor implantation achieved complete tumor clearance and maintained a sustained complete response 6 months following initial treatment.

CONCLUSION

Building on the proven safety profile of EphA3 antibodies in clinical settings, our study provides compelling preclinical evidence supporting the efficacy of EphA3-targeted CAR T cells against high-grade gliomas. These findings underscore the potential for transitioning this innovative therapy into clinical trials, aiming to revolutionize the treatment landscape for patients afflicted with these formidable brain cancers.

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.

Development of an Anti-EphB4 Monoclonal Antibody for Multiple Applications Against Breast Cancers

The erythropoietin-producing hepatocellular carcinoma (Eph) receptors are the largest receptor tyrosine kinase family. EphB4 is essential for cell adhesion and motility during embryogenesis. Pathologically, EphB4 is overexpressed and contributes to poor prognosis in various tumors. Therefore, specific monoclonal antibodies (mAbs) should be developed to predict the prognosis for multiple tumors with high EphB4 expression, including breast and gastric cancers. This study aimed to develop specific anti-EphB4 mAbs for multiple applications using the Cell-Based Immunization and Screening method. EphB4-overexpressed Chinese hamster ovary (CHO)-K1 (CHO/EphB4) cells were immunized into mice, and we established an anti-EphB4 mAb (clone B4Mab-7), which is applicable for flow cytometry, Western blot, and immunohistochemistry (IHC). B4Mab-7 reacted with endogenous EphB4-positive breast cancer cell line, MCF-7, but did not react with EphB4-knockout MCF-7 (BINDS-52) in flow cytometry. Dissociation constant (KD) values were determined to be 2.9 × 10-9 M and 1.3 × 10-9 M by flow cytometric analysis for CHO/EphB4 and MCF-7 cells, respectively. B4Mab-7 detected the EphB4 protein bands from breast cancer cells in Western blot, and stained breast cancer tissues in IHC. Altogether, B4Mab-7 is very useful for detecting EphB4 in various applications.

EPH/Ephrin Signaling in Normal Hematopoiesis and Hematologic Malignancies: Deciphering Their Intricate Role and Unraveling Possible New Therapeutic Targets

Erythropoietin-producing hepatocellular carcinoma receptors (EPHs) represent the largest family of receptor tyrosine kinases (RTKs). EPH interaction with ephrins, their membrane-bound ligands, holds a pivotal role in embryonic development, while, though less active, it is also implicated in various physiological functions during adult life. In normal hematopoiesis, different patterns of EPH/ephrin expression have been correlated with hematopoietic stem cell (HSC) maintenance and lineage-committed hematopoietic progenitor cell (HPC) differentiation, as well as with the functional properties of their mature offspring. Research in the field of hematologic malignancies has unveiled a rather complex involvement of the EPH/ephrinsignaling pathway in the pathophysiology of these neoplasms. Aberrations in genetic, epigenetic, and protein levels have been identified as possible players implicated both in tumor progression and suppression, while correlations have also been highlighted regarding prognosis and response to treatment. Initial efforts to therapeutically target the EPH/ephrin axis have been undertaken in the setting of hematologic neoplasia but are mainly confined to the preclinical level. To this end, deciphering the complexity of this signaling pathway both in normal and malignant hematopoiesis is necessary.

Eph Receptors in Cancer

Eph receptor tyrosine kinases play critical functions during development, in the formation of tissue and organ borders, and the vascular and neural systems. Uniquely among tyrosine kinases, their activities are controlled by binding to membrane-bound ligands, called ephrins. Ephs and ephrins generally have a low expression in adults, functioning mainly in tissue homeostasis and plasticity, but are often overexpressed in cancers, where they are especially associated with undifferentiated or progenitor cells, and with tumour development, vasculature, and invasion. Mutations in Eph receptors also occur in various tumour types and are suspected to promote tumourigenesis. Ephs and ephrins have the capacity to operate as both tumour promoters and tumour suppressors, depending on the circumstances. They have been demonstrated to impact tumour cell proliferation, migration, and invasion in vitro, as well as tumour development, angiogenesis, and metastases in vivo, making them potential therapeutic targets. However, successful development of therapies will require detailed understanding of the opposing roles of Ephs in various cancers. In this review, we discuss the variations in Eph expression and functions in a variety of malignancies. We also describe the multiple strategies that are currently available to target them in tumours, including preclinical and clinical development.

EPHA3 Could Be a Novel Prognosis Biomarker and Correlates with Immune Infiltrates in Bladder Cancer

PURPOSE

To assess the mechanism of EPH receptor A3 (EPHA3) and its potential value for immunotherapy in BLCA.

MATERIALS AND METHODS

The Cancer Genome Atlas (TCGA) bladder cancer (BLCA) database and the Gene Expression Omnibus (GEO) database were used for assessing whether EHPA3 could be used to predict BLCA prognosis. This work carried out in vitro and in vivo assays for exploring how EPHA3 affected the biological behaviors. The downstream pathway was explored using a Western blotting technique. The CIBERSORT, ESTIMATE, TIMER, and TIDE tools were used to predict the immunotherapy value of EPHA3 in BLCA.

RESULTS

EPHA3 was poorly expressed in BLCA (p < 0.05), its high expression is related to a good survival prognosis (p = 0.027 and p = 0.0275), and it has a good predictive ability for the histologic grade and status of BLCA (area under curve = 0.787 and 0.904). Overexpressed EPHA3 could inhibit BLCA cell biological behaviors, and it be associated with the downregulation of the Ras/pERK1/2 pathway. EPHA3 was correlated with several immune-infiltrating cells and the corresponding marker genes.

CONCLUSIONS

EPHA3 could be regarded as an acceptable anti-cancer biomarker in BLCA. EPHA3 plays an inhibiting role in BLCA, and it could be the candidate immunotherapeutic target for BLCA.

Temozolomide hexadecyl ester targeted plga nanoparticles for drug-resistant glioblastoma therapy via intranasal administration

Introduction: Temozolomide (TMZ) is the first-line drug for glioblastoma (GBM), but it is limited in clinical use due to the drug resistance, poor brain targeting, and side effects. Temozolomide hexadecyl ester (TMZ16e), a TMZ derivative with high lipophilicity, membrane permeability, and high anti-glioma properties, has the potential to reverse drug resistance. In this study, anti-ephrin type-A receptor 3 (EphA3) modified TMZ16e loaded nanoparticles (NPs) were prepared for targeted GBM therapy via intranasal administration to deliver TMZ16e to the brain, treat drug-resistant glioma effectively, and reduce peripheral toxicity.

Methods: TMZ16e loaded NPs were prepared by emulsion solvent evaporation method followed by modified with anti-EphA3 (anti-EphA3-TMZ16e-NPs). In vitro evaluations were performed by an MTT assay and flow cytometry analysis. The orthotopic nude mice models were used to evaluate the anti-glioma effect in vivo. Additionally, we investigated the anti-drug resistant mechanism by western blot analysis.

Results: The particle size of the prepared NPs was less than 200 nm, and the zeta potential of TMZ16e-NPs and anti-EphA3-TMZ16e-NPs were -23.05 ± 1.48 mV and -28.65 ± 1.20mV, respectively, which is suitable for nasal delivery. In vitro studies have shown that anti-EphA3 modification increased the cellular uptake of nanoparticles in T98G cells. The cytotoxicity in the anti-EphA3-TMZ16e-NPs treated group was significantly higher than that of the TMZ16e-NPs, TMZ16e, and TMZ groups (p < 0.01), and the cell cycle was blocked. Western blotting analysis showed that the TMZ16e-loaded NPs were able to effectively downregulate the expression level of O6-methylguanine-deoxyribonucleic acid-methyltransferase (MGMT) protein in T98G cells and reverse drug resistance. In vivo studies showed that the median survival time of tumor-bearing nude mice in the anti-EphA3-TMZ16e-NPs group was extended to 41 days, which was 1.71-fold higher than that of the saline group and the TUNEL staining results of the brain tissue section indicated that the TMZ16e-loaded NPs could elevate apoptosis in T98G cells.

Conclusion: In conclusion, the TMZ16e-loaded NPs can be effectively delivered to the brain and targeted to gliomas, exhibiting better anti-glioma activity, indicating they possess great potential in the treatment of drug-resistant glioma.

The Hippo effector YAP1/TEAD1 regulates EPHA3 expression to control cell contact and motility

The EPHA3 protein tyrosine kinase, a member of the ephrin receptor family, regulates cell fate, cell motility, and cell-cell interaction. These cellular events are critical for tissue development, immunological responses, and the processes of tumorigenesis. Earlier studies revealed that signaling via the STK4-encoded MST1 serine-threonine protein kinase, a core component of the Hippo pathway, attenuated EPHA3 expression. Here, we investigated the mechanism by which MST1 regulates EPHA3. Our findings have revealed that the transcriptional regulators YAP1 and TEAD1 are crucial activators of EPHA3 transcription. Silencing YAP1 and TEAD1 suppressed the EPHA3 protein and mRNA levels. In addition, we identified putative TEAD enhancers in the distal EPHA3 promoter, where YAP1 and TEAD1 bind and promote EPHA3 expression. Furthermore, EPHA3 knockout by CRISPR/Cas9 technology reduced cell-cell interaction and cell motility. These findings demonstrate that EPHA3 is transcriptionally regulated by YAP1/TEAD1 of the Hippo pathway, suggesting that it is sensitive to cell contact-dependent interactions.

The Ephb2 Receptor Uses Homotypic, Head-to-Tail Interactions within Its Ectodomain as an Autoinhibitory Control Mechanism

The Eph receptor tyrosine kinases and their ephrin ligands direct axon pathfinding and neuronal cell migration, as well as mediate many other cell-cell communication events. Their dysfunctional signaling has been shown to lead to various diseases, including cancer. The Ephs and ephrins both localize to the plasma membrane and, upon cell-cell contact, form extensive signaling assemblies at the contact sites. The Ephs and the ephrins are divided into A and B subclasses based on their sequence conservation and affinities for each other. The molecular details of Eph-ephrin recognition have been previously revealed and it has been documented that ephrin binding induces higher-order Eph assemblies, which are essential for full biological activity, via multiple, distinct Eph-Eph interfaces. One Eph-Eph interface type is characterized by a homotypic, head-to-tail interaction between the ligand-binding and the fibronectin domains of two adjacent Eph molecules. While the previous Eph ectodomain structural studies were focused on A class receptors, we now report the crystal structure of the full ectodomain of EphB2, revealing distinct and unique head-to-tail receptor-receptor interactions. The EphB2 structure and structure-based mutagenesis document that EphB2 uses the head-to-tail interactions as a novel autoinhibitory control mechanism for regulating downstream signaling and that these interactions can be modulated by posttranslational modifications.

Cell-Extrinsic Differentiation Block Mediated by EphA3 in Pre-Leukaemic Thymus Contributes to Disease Progression

Simple Summary

The NUP98-HOXD13 (NHD13) mouse is a model of T-cell leukaemia (T-ALL) featuring a pre-leukemic phase, in which T-cell progenitors from the thymus of an NHD13 mouse can engraft into the thymus of a recipient mouse—an ability that normal T-cell progenitors do not possess. However, loss of this engraftment ability (by deletion of the Lyl1 gene) did not result in any loss of leukemogenesis activity, indicating the activity of redundant oncogenic pathways in this model. Having observed an overexpression of the EphA3 protein in the NHD13 thymocytes, we hypothesized that this gene might be involved in a redundant leukaemogenic pathway. Deletion of EphA3 did not affect the engraftment ability of the thymocytes, but did reduce the incidence of T-ALL. We thus uncovered a distinct mechanism of leukaemogenesis, which we believe operates in parallel to that mediated by Lyl1.

Abstract

We recently characterised the NUP98-HOXD13 (NHD13) mouse as a model of T-cell pre-leukaemia, featuring thymocytes that can engraft in recipient animals and progress to T-cell acute lymphoblastic leukaemia (T-ALL). However, loss of this engraftment ability by deletion of Lyl1 did not result in any loss of leukemogenesis activity. In the present study, we observe that NHD13 thymocytes overexpress EPHA3, and we characterise thymocyte behaviour in NHD13 mice with deletion of EphA3, which show a markedly reduced incidence of T-ALL. Deletion of EphA3 from the NHD13 mice does not prevent the abnormal accumulation or transplantation ability of these thymocytes. However, upon transplantation, these cells are unable to block the normal progression of recipient wild type (WT) progenitor cells through the normal developmental pathway. This is in contrast to the EphA3^+/+ NHD13 thymocytes, which block the progression of incoming WT progenitors past the DN1 stage. Therefore, EphA3 is not critical for classical self-renewal, but is essential for mediating an interaction between the abnormally self-renewing cells and healthy progenitors—an interaction that results in a failure of the healthy cells to differentiate normally. We speculate that this may orchestrate a loss of healthy cell competition, which in itself has been demonstrated to be oncogenic, and that this may explain the decrease in T-ALL incidence in the absence of EphA3. We suggest that pre-leukaemic self-renewal in this model is a complex interplay of cell-intrinsic and -extrinsic factors, and that multiple redundant pathways to leukaemogenesis are active.

IL-26 mediates epidermal growth factor receptor-tyrosine kinase inhibitor resistance through endoplasmic reticulum stress signaling pathway in triple-negative breast cancer cells

Triple-negative breast cancer (TNBC) has a poor prognosis compared to other breast cancer subtypes. Although epidermal growth factor receptor (EGFR) is overexpressed in TNBC, clinical trials with EGFR inhibitors including tyrosine kinase inhibitors (EGFR-TKI) in TNBC have heretofore been unsuccessful. To develop effective EGFR-targeted therapy for TNBC, the precise mechanisms of EGFR-TKI resistance in TNBC need to be elucidated. In this study, to understand the molecular mechanisms involved in the differences in EGFR-TKI efficacy on TNBC between human and mouse, we focused on the effect of IL-26, which is absent in mice. In vitro analysis showed that IL-26 activated AKT and JNK signaling of bypass pathway of EGFR-TKI in both murine and human TNBC cells. We next investigated the mechanisms involved in IL-26-mediated EGFR-TKI resistance in TNBC. We identified EphA3 as a novel functional receptor for IL-26 in TNBC. IL-26 induced dephosphorylation and downmodulation of EphA3 in TNBC, which resulted in increased phosphorylation of AKT and JNK against EGFR-TKI-induced endoplasmic reticulum (ER) stress, leading to tumor growth. Meanwhile, the blockade of IL-26 overcame EGFR-TKI resistance in TNBC. Since the gene encoding IL-26 is absent in mice, we utilized human IL-26 transgenic (hIL-26Tg) mice as a tumor-bearing murine model to characterize the role of IL-26 in the differential effect of EGFR-TKI in human and mice and to confirm our in vitro findings. Our findings indicate that IL-26 activates the bypass pathway of EGFR-TKI, while blockade of IL-26 overcomes EGFR-TKI resistance in TNBC via enhancement of ER stress signaling. Our work provides novel insights into the mechanisms of EGFR-TKI resistance in TNBC via interaction of IL-26 with its newly identified receptor EphA3, while also suggesting IL-26 as a possible therapeutic target in TNBC.

Protein Tyrosine Kinases: Their Roles and Their Targeting in Leukemia

Simple Summary

Protein phosphorylation is a key regulatory mechanism that controls a wide variety of cellular responses. This process is catalysed by the members of the protein kinase superfamily that are classified into two main families based on their ability to phosphorylate either tyrosine or serine and threonine residues in their substrates. Massive research efforts have been invested in dissecting the functions of tyrosine kinases, revealing their importance in the initiation and progression of human malignancies. Based on these investigations, numerous tyrosine kinase inhibitors have been included in clinical protocols and proved to be effective in targeted therapies for various haematological malignancies. In this review, we provide insights into the role of tyrosine kinases in leukaemia and discuss their targeting for therapeutic purposes with the currently available inhibitory compounds.

Abstract

Protein kinases constitute a large group of enzymes catalysing protein phosphorylation and controlling multiple signalling events. The human protein kinase superfamily consists of 518 members and represents a complicated system with intricate internal and external interactions. Protein kinases are classified into two main families based on the ability to phosphorylate either tyrosine or serine and threonine residues. Among the 90 tyrosine kinase genes, 58 are receptor types classified into 20 groups and 32 are of the nonreceptor types distributed into 10 groups. Tyrosine kinases execute their biological functions by controlling a variety of cellular responses, such as cell division, metabolism, migration, cell–cell and cell matrix adhesion, cell survival and apoptosis. Over the last 30 years, a major focus of research has been directed towards cancer-associated tyrosine kinases owing to their critical contributions to the development and aggressiveness of human malignancies through the pathological effects on cell behaviour. Leukaemia represents a heterogeneous group of haematological malignancies, characterised by an uncontrolled proliferation of undifferentiated hematopoietic cells or leukaemia blasts, mostly derived from bone marrow. They are usually classified as chronic or acute, depending on the rates of their progression, as well as myeloid or lymphoblastic, according to the type of blood cells involved. Overall, these malignancies are relatively common amongst both children and adults. In malignant haematopoiesis, multiple tyrosine kinases of both receptor and nonreceptor types, including AXL receptor tyrosine kinase (AXL), Discoidin domain receptor 1 (DDR1), Vascular endothelial growth factor receptor (VEGFR), Fibroblast growth factor receptor (FGFR), Mesenchymal–epithelial transition factor (MET), proto-oncogene c-Src (SRC), Spleen tyrosine kinase (SYK) and pro-oncogenic Abelson tyrosine-protein kinase 1 (ABL1) mutants, are implicated in the pathogenesis and drug resistance of practically all types of leukaemia. The role of ABL1 kinase mutants and their therapeutic inhibitors have been extensively analysed in scientific literature, and therefore, in this review, we provide insights into the impact and mechanism of action of other tyrosine kinases involved in the development and progression of human leukaemia and discuss the currently available and emerging treatment options based on targeting these molecules.

Critical role of EphA3 in cancer and current state of EphA3 drug therapeutics

The erythropoietin-producing human hepatocellular (Eph) receptors are transmembrane glycoprotein members of the tyrosine kinase receptors family. The Ephs may bind to various ephrin ligands resulting in the phosphorylation of their tyrosine kinase domain and the activation of the Eph receptor. In this review we focus on EphA3, one receptor of the 14 different Ephs, as it carries out both redundant and restricted functions in the germline development of mammals and in the maintenance of various adult tissues. The loss of EphA3 regulation is correlated with various human malignancies, the most notable being cancer. This receptor is overexpressed and/or mutated in multiple tumors, and is also associated with poor prognosis and decreased survival in patients. Here we highlight the role of EphA3 in normal and malignant tissues that are specific to cancer; these include hematologic disorders, gastric cancer, glioblastoma multiforme, colorectal cancer, lung cancer, renal cell carcinoma, and prostate cancer. Moreover, various anticancer agents against EphA3 have been developed to either inhibit its kinase domain activity or to function as agonists. Thus, we examine the most potent small molecule drugs and mAb-based therapeutics against EphA3 that are currently in pre-clinical or clinical stages.

Antibody Targeting of Eph Receptors in Cancer

The Eph subfamily of receptor tyrosine kinases mediate cell-cell communication controlling cell and tissue patterning during development. While generally less active in adult tissues, they often re-emerge in cancers, particularly on undifferentiated or progenitor cells in tumors and the tumor microenvironment, associated with tumor initiation, angiogenesis and metastasis. Eph receptors are thus attractive therapeutic targets, and monoclonal antibodies have been commonly developed and tested for anti-cancer activity in preclinical models, and in some cases in the clinic. This review summarizes 20 years of research on various antibody-based approaches to target Eph receptors in tumors and the tumor microenvironment, including their mode of action, tumor specificity, and efficacy in pre-clinical and clinical testing.

Emerging Roles for Eph Receptors and Ephrin Ligands in Immunity

Eph receptors are the largest family of receptor tyrosine kinases and mediate a myriad of essential processes in humans from embryonic development to adult tissue homeostasis through interactions with membrane-bound ephrin ligands. The ubiquitous expression of Eph receptors and ephrin ligands among the cellular players of the immune system underscores the importance of these molecules in orchestrating an optimal immune response. This review provides an overview of the various roles of Eph receptors and ephrin ligands in immune cell development, activation, and migration. We also discuss the role of Eph receptors in disease pathogenesis as well as the implications of Eph receptors as future immunotherapy targets. Given the diverse and critical roles of Eph receptors and ephrin ligands throughout the immune system during both resting and activated states, this review aims to highlight the critical yet underappreciated roles of this family of signaling molecules in the immune system.

EphA3 Downregulation by Hypermethylation Associated with Lymph Node Metastasis and TNM Stage in Colorectal Cancer

BACKGROUND

EphA3 is a member of Eph receptors, which is involved in tumorigenesis. The expression and clinical significance of EphA3 in colorectal cancer (CRC) have not been fully investigated.

METHODS

Four colon cancer cell lines and a set of CRC tissues were examined for EphA3 expression. The methylation status of a CpG island within the EphA3 promoter, the presence of four somatic EPHA3 mutations, and EPHA3 gene copy number variations were also analyzed in colon cancer cell lines.

RESULTS

EphA3 expression was lost in all colon cancer cell lines examined. EphA3 expression was lower in tumor tissues when compared with normal intestinal tissues (P < 0.001). A comparison of EphA3 immunohistochemical scores for tumor and matched normal intestinal tissues revealed that the protein was downregulated in 82/164 (50.0%), unchanged in 52/164 (31.7%), and upregulated in 30/164 (18.3%) cases of CRC. EphA3 expression was negatively associated with lymph node metastasis (P =0.014, r_s=- 0.192) and TNM stage (P =0.001, r_s=- 0.260). Downregulation of expression was more common in older patients (P =0.013, r_s=0.193). Methylated promoter DNA was detected in all four colon cancer cell lines. Somatic mutations or EphA3 gene deletion was not detected.

CONCLUSIONS

EphA3 was downregulated in the majority of CRC. Hypermethylation of a CpG island within the EPHA3 promoter provides a possible mechanism. Loss of EphA3 expression was associated with lymph node metastasis and TNM stage and may therefore prove useful as a predictor for tumor spread in CRC.

EphA3 Pay-Loaded Antibody Therapeutics for the Treatment of Glioblastoma

The EphA3 receptor has recently emerged as a functional tumour-specific therapeutic target in glioblastoma (GBM). EphA3 is significantly elevated in recurrent disease, is most highly expressed on glioma stem cells (GSCs), and has a functional role in maintaining self-renewal and tumourigenesis. An unlabelled EphA3-targeting therapeutic antibody is currently under clinical assessment in recurrent GBM patients. In this study, we assessed the efficacy of EphA3 antibody drug conjugate (ADC) and radioimmunotherapy (RIT) approaches using orthotopic animal xenograft models. Brain uptake studies, using positron emission tomography/computed tomography (PET/CT) imaging, show EphA3 antibodies are effectively delivered across the blood-tumour barrier and accumulate at the tumour site with no observed normal brain reactivity. A robust anti-tumour response, with no toxicity, was observed using EphA3, ADC, and RIT approaches, leading to a significant increase in overall survival. Our current research provides evidence that GBM patients may benefit from pay-loaded EphA3 antibody therapies.

EphA3 inhibits migration and invasion of esophageal cancer cells by activating the mesenchymal‑epithelial transition process

Eph receptor tyrosine kinases are critical for cell‑cell communication during normal and oncogenic development. Eph receptor A3 (EphA3) expression is associated with tumor promotion in certain types of cancer; however, it acts as a tumor suppressor in others. The expression levels of EphA3 and its effects on tumor progression in esophageal squamous cell carcinoma (ESCC) cell lines were determined using reverse transcription‑quantitative polymerase chain reaction analysis and a Transwell invasion assay. The present study demonstrated that EphA3 expression was decreased in ESCC tissues and cell lines. Treatment with the DNA methylation inhibitor 5‑aza‑2'‑deoxycytidine increased the mRNA expression levels of EphA3 in the ESCC cell lines KYSE510 and KYSE30. In addition, overexpression of EphA3 in KYSE450 and KYSE510 cells inhibited cell migration and invasion. EphA3 overexpression also decreased RhoA GTPase. Furthermore, EphA3 overexpression induced mesenchymal‑epithelial transition, as demonstrated by epithelial‑like morphological alterations, increased expression of epithelial proteins (E‑cadherin and the tight junction protein 1 zonula occludens‑1) and decreased expression of mesenchymal proteins (Vimentin, N‑cadherin and Snail). Conversely, silencing EphA3 in KYSE410 cells triggered epithelial‑mesenchymal transition, and promoted cell migration and invasion. These results suggested that EphA3 may serve a tumor‑suppressor role in ESCC.

MiR-340 suppresses the metastasis by targeting EphA3 in cervical cancer

MicroRNAs (miRNAs) play key roles in cervical cancer metastasis progression. Accumulated evidences have revealed that miRNAs are related to the pathophysiological process. However, the role of miR-340 in cervical cancer and how it works is still not fully interpreted. Using qRT-PCR to examine the expression of miR-340 in cervical cancer tissues. Transwell migration and invasion experiments were used to detect the role of miR-340 in migration and invasion. Luciferase reporter assay, qRT-PCR, and Western blot were used to detect the relationship between miR-340 and EphA3. Using Transwell migration and invasion experiments to investigate the role of EphA3 on migration and invasion. Restoration expriments were also performed. Western blot was used to assay the influence of miR-340 and EphA3 on EMT. We found that miR-340 was downregulated in cervical cancer tissues compared with the normal tissues. Transwell migration and invasion experiments indicated that overexpression of miR-340 frequently inhibited the migration and invasion of cervical cancer cells. EphA3 is a target of miR-340, and ectopic expression of EphA3 can promote the migration and invasion of cervical cancer cells, whereas restoration of EphA3 in miR-340-overexpressing cervical cancer cells reversed the suppressive effects of miR-340. What's more, the process of migration and invasion which regulated by miR-340/EphA3 was depended on adjusting the EMT way. These findings indicate that miR-340 may act as an anti-tumor factor during the process of tumor metastasis through targeting EphA3, suggesting that miR-340 might be a potential new diagnostic and therapeutic molecule for the treatment of cervical cancer.

Epha3 acts as proangiogenic factor in multiple myeloma

This study investigates the role of ephrin receptor A3 (EphA3) in the angiogenesis of Multiple Myeloma (MM) and the effects of a selective target of EphA3 by a specific monoclonal antibody on primary bone marrow endothelial cells (ECs) of MM patients.

EphA3 mRNA and protein were evaluated in ECs of MM patients (MMECs), in ECs of patients with monoclonal gammopathies of undetermined significance (MGECs) and in ECs of healthy subjects (control ECs). The effects of EphA3 targeting by mRNA silencing (siRNA) or by the anti EphA3 antibody on the angiogenesis were evaluated. We found that EphA3 is highly expressed in MMECs compared to the other EC types. Loss of function of EphA3 by siRNA significantly inhibited the ability of MMECs to adhere to fibronectin, to migrate and to form tube like structures in vitro, without affecting cell proliferation or viability. In addition, gene expression profiling showed that knockdown of EphA3 down modulated some molecules that regulate adhesion, migration and invasion processes. Interestingly, EphA3 targeting by an anti EphA3 antibody reduced all the MMEC angiogenesis-related functions in vitro. In conclusion, our findings suggest that EphA3 plays an important role in MM angiogenesis.

Targeted therapies in hematological malignancies using therapeutic monoclonal antibodies against Eph family receptors

The use of monoclonal antibodies (mAbs) and molecules derived from them has achieved considerable attention and success in recent years, establishing this mode of therapy as an important therapeutic strategy in many cancers, in particular hematological tumors. mAbs recognize cell surface antigens expressed on target cells and mediate their function through various mechanisms such as antibody-dependent cellular cytotoxicity, complement-dependent cytotoxicity, or immune system modulation. The efficacy of mAb therapy can be improved when they are conjugated to a highly potent payloads, including cytotoxic drugs and radiolabeled isotopes. The Eph family of proteins has received considerable attention in recent years as therapeutic targets for treatment of both solid and hematological cancers. High expression of Eph receptors on cancer cells compared with low expression levels in normal adult tissues makes them an attractive candidate for cancer immunotherapy. In this review, we detail the modes of action of antibody-based therapies with a focus on the Eph family of proteins as potential targets for therapy in hematological malignancies.

EphA3 targeting reduces in vitro adhesion and invasion and in vivo growth and angiogenesis of multiple myeloma cells

PURPOSE

Multiple myeloma (MM) is a hematologic malignancy characterized by a clonal expansion of plasma cells (PCs) in the bone marrow (BM). Since MM has so far remained incurable, further insights into its pathogenesis and the concomitant identification of new therapeutic targets are urgently needed. The tyrosine kinase receptor EphA3 is known to be involved in various cellular processes including cell viability, cell movement and cell-cell interactions. Recently, EphA3 has emerged as a potential therapeutic target in several hematologic and solid tumors. Here, we aimed to uncover the role of EphA3 in MM.

METHODS

EphA3 mRNA and protein expression in primary MM bone marrow plasma cells (BMPCs), in MM-derived cell lines and in healthy controls (HCs) was assessed using qRT-PCR, Western blotting and flow cytometry. The effects of siRNA-mediated EphA3 silencing and anti EphA3 antibody (EphA3mAb) treatment on MM PC trafficking and viability were evaluated using in vitro assays. The effects of EphA3mAb treatment were also assessed in two MM-derived mouse xenograft models.

RESULTS

We found that EphA3 was overexpressed in primary MM BMPCs and MM-derived cell lines compared to HCs. We also found that siRNA-mediated EphA3 silencing and EphA3mAb treatment significantly inhibited the ability of MM PCs to adhere to fibronectin and stromal cells and to invade in vitro, without affecting cell proliferation and viability. Gene expression profiling showed that EphA3 silencing resulted in expression modulation of several molecules that regulate adhesion, migration and invasion processes. Importantly, we found that EphA3mAb treatment significantly inhibited in vivo tumor growth and angiogenesis in two MM-derived mouse xenograft models.

CONCLUSIONS

Our findings suggest that EphA3 plays an important role in the pathogenesis of MM and provide support for the notion that its targeting may represent a novel therapeutic opportunity for MM.

EphA3 as a target for antibody immunotherapy in acute lymphoblastic leukemia

The human EphA3 gene was discovered in a pre-B acute lymphoblastic leukemia (pre-B-ALL) using the EphA3-specific monoclonal antibody (mAb), IIIA4, which binds and activates both human and mouse EphA3. We use two models of human pre-B-ALL to examine EphA3 function, demonstrating effects on pre-B-cell receptor signaling. In therapeutic targeting studies, we demonstrated antitumor effects of the IIIA4 mAb in EphA3-expressing leukemic xenografts and no antitumor effect in the xenografts with no EphA3 expression providing evidence that EphA3 is a functional therapeutic target in pre-B-ALL. Here we show that the therapeutic effect of the anti-EphA3 antibody was greatly enhanced by adding an α-particle-emitting ²¹³Bismuth payload.

KB004, a first in class monoclonal antibody targeting the receptor tyrosine kinase EphA3, in patients with advanced hematologic malignancies: Results from a phase 1 study

EphA3 is an Ephrin receptor tyrosine kinase that is overexpressed in most hematologic malignancies. We performed a first-in-human multicenter phase I study of the anti-EphA3 monoclonal antibody KB004 in refractory hematologic malignancies in order to determine safety and tolerability, along with the secondary objectives of pharmacokinetics (PK) and pharmacodynamics (PD) assessments, as well as preliminary assessment of efficacy. Patients were enrolled on a dose escalation phase (DEP) initially, followed by a cohort expansion phase (CEP). KB004 was administered by intravenous infusion on days 1, 8, and 15 of each 21-day cycle in escalating doses. A total of 50 patients (AML 39, MDS/MPN 3, MDS 4, DLBCL 1, MF 3) received KB004 in the DEP; an additional 14 patients were treated on the CEP (AML 8, MDS 6). The most common toxicities were transient grade 1 and grade 2 infusion reactions (IRs) in 79% of patients. IRs were dose limiting above 250mg. Sustained exposure exceeding the predicted effective concentration (1ug/mL) and covering the 7-day interval between doses was achieved above 190mg. Responses were observed in patients with AML, MF, MDS/MPN and MDS. In this study, KB004 was well tolerated and clinically active when given as a weekly infusion.

Loss of EphA3 Protein Expression Is Associated With Advanced TNM Stage in Clear-Cell Renal Cell Carcinoma

BACKGROUND

Erythropoietin-producing hepatocellular carcinoma (Eph) receptors constitute the largest family of receptor tyrosine kinases. Ephs and their ligands ephrins play an important role in development and carcinogenesis. The expression of EphA3, an Eph family member, has been investigated in a variety of human cancers, with mixed results. High levels of EphA3 protein expression have been reported in colorectal, prostate, and gastric cancers, whereas loss of protein expression has been reported in lung and hematopoietic cancers. EphA3 expression in clear-cell renal cell carcinoma (ccRCC) and its association with clinicopathological parameters has not previously been examined. The aim of this study was to determine the cancerous value of EphA3 protein expression in patients with ccRCC.

MATERIALS AND METHODS

This study included 68 patients with ccRCC. EphA3 protein expression was examined in ccRCC tissue samples using immunohistochemistry and a specific polyclonal antibody, and the correlation between EphA3 expression and clinicopathological parameters was subsequently evaluated.

RESULTS

High EphA3 protein expression was observed in all normal renal tubules. In the 68 ccRCC patient samples examined, EphA3 protein expression was detected in 19 cases (27.9%) and undetectable in 49 cases (72.1%). EphA3 protein expression was significantly associated with tumor diameter (P = .016) and tumor, node metastases stage (P = .029). No significant association between protein expression and sex (P = .387), age (P = .727), or nuclear grade (P = .243) was found.

CONCLUSION

Ourdata indicate that EphA3 protein expression is reduced in ccRCC, suggesting the possibility that this receptor functions as a tumor suppressor in this disease.

EphA2 Is a Therapy Target in EphA2-Positive Leukemias but Is Not Essential for Normal Hematopoiesis or Leukemia

Members of the Eph family of receptor tyrosine kinases and their membrane bound ephrin ligands have been shown to play critical roles in many developmental processes and more recently have been implicated in both normal and pathological processes in post-embryonic tissues. In particular, expression studies of Eph receptors and limited functional studies have demonstrated a role for the Eph/ephrin system in hematopoiesis and leukemogenesis. In particular, EphA2 was reported on hematopoietic stem cells and stromal cells. There are also reports of EphA2 expression in many different types of malignancies including leukemia, however there is a lack of knowledge in understanding the role of EphA2 in hematopoiesis and leukemogenesis. We explored the role of EphA2 in hematopoiesis by analyzing wild type and EphA2 knockout mice. Mature, differentiated cells, progenitors and hematopoietic stem cells derived from knockout and control mice were analyzed and no significant abnormality was detected. These studies showed that EphA2 does not have an obligatory role in normal hematopoiesis. Comparative studies using EphA2-negative MLL-AF9 leukemias derived from EphA2-knockout animals showed that there was no detectable functional role for EphA2 in the initiation or progression of the leukemic process. However, expression of EphA2 in leukemias initiated by MLL-AF9 suggested that this protein might be a possible therapy target in this type of leukemia. We showed that treatment with EphA2 monoclonal antibody IF7 alone had no effect on tumorigenicity and latency of the MLL-AF9 leukemias, while targeting of EphA2 using EphA2 monoclonal antibody with a radioactive payload significantly impaired the leukemic process. Altogether, these results identify EphA2 as a potential radio-therapeutic target in leukemias with MLL translocation.

Targeting EphA3 inhibits cancer growth by disrupting the tumor stromal microenvironment

Eph receptor tyrosine kinases are critical for cell-cell communication during normal and oncogenic tissue patterning and tumor growth. Somatic mutation profiles of several cancer genomes suggest EphA3 as a tumor suppressor, but its oncogenic expression pattern and role in tumorigenesis remain largely undefined. Here, we report unexpected EphA3 overexpression within the microenvironment of a range of human cancers and mouse tumor xenografts where its activation inhibits tumor growth. EphA3 is found on mouse bone marrow-derived cells with mesenchymal and myeloid phenotypes, and activation of EphA3(+)/CD90(+)/Sca1(+) mesenchymal/stromal cells with an EphA3 agonist leads to cell contraction, cell-cell segregation, and apoptosis. Treatment of mice with an agonistic α-EphA3 antibody inhibits tumor growth by severely disrupting the integrity and function of newly formed tumor stroma and microvasculature. Our data define EphA3 as a novel target for selective ablation of the tumor microenvironment and demonstrate the potential of EphA3 agonists for anticancer therapy.

A high affinity recombinant antibody to the human EphA3 receptor with enhanced ADCC activity

EphA3 is expressed in solid tumors and leukemias and is an attractive target for the therapy. We have generated a panel of Humaneered® antibodies to the ligand-binding domain using a Fab epitope-focused library that has the same specificity as monoclonal antibody mIIIA4. A high-affinity antibody was selected that competes with the mIIIA4 antibody for binding to EphA3 and has an improved affinity of ∼1 nM. In order to generate an antibody with potent cell-killing activity the variable regions were assembled with human IgG1k constant regions and expressed in a Chinese hamster ovary (CHO) cell line deficient in fucosyl transferase. Non-fucosylated antibodies have been reported to have enhanced binding affinity for the IgG receptor CD16a (FcγRIIIa). The affinity of the antibody for recombinant CD16a was enhanced approximately 10-fold. This resulted in enhanced antibody-dependent cell-mediated cytotoxicity (ADCC) activity against EphA3-expressing leukemic cells, providing a potent antibody for the evaluation as a therapeutic agent.

EphA3 biology and cancer

Eph receptor tyrosine kinases control cell-cell interactions during normal and oncogenic development, and are implicated in a range of processes including angiogenesis, stem cell maintenance and metastasis. They are thus of great interest as targets for cancer therapy. EphA3, originally isolated from leukemic and melanoma cells, is presently one of the most promising therapeutic targets, with multiple tumor-promoting roles in a variety of cancer types. This review focuses on EphA3, its functions in controlling cellular behavior, both in normal and pathological development, and most particularly in cancer.

Effects of ephrinB2 gene siRNA on the biological behavior of human colorectal cancer cells

Colorectal cancer (CRC) is a common gastrointestinal malignancy worldwide and is a lethal and aggressive malignancy with a dismal prognosis. EphrinB2 is a membrane-bound ligand and has an intracellular domain that also possesses an intrinsic signaling capacity called 'reverse signaling'. In the present study, CRC cell lines were screened for high expression of ephrinB2. Small interfering RNA (siRNA) knockdown of ephrinB2 was performed in human SW480 CRC cells. The levels of expression of ephrinB2, VEGF, CD105 and matrix metalloproteinase 9 (MMP9) protein were measured by western blotting, and messenger RNA (mRNA) levels were measured using real-time PCR. Apoptosis and cell cycle distribution were determined using flow cytometry. Cell proliferation was measured by a methyl thiazole tetrazolium (MTT) test and a scratch healing experiment was used to measure the extent of cell migration. A Transwell assay was used to detect the extent of cell invasion. The results showed that RNA interference (RNAi) of ephrinB2 effectively silenced the ephrinB2 gene at both the mRNA and protein levels in SW480 cells and inhibited the proliferation, invasion, migration and angiogenesis and induced apoptosis in SW480 cells. These effects may be attributed to VEGF and MMP9 regulation.

Hypoxia-controlled EphA3 marks a human endometrium-derived multipotent mesenchymal stromal cell that supports vascular growth

Eph and ephrin proteins are essential cell guidance cues that orchestrate cell navigation and control cell-cell interactions during developmental tissue patterning, organogenesis and vasculogenesis. They have been extensively studied in animal models of embryogenesis and adult tissue regeneration, but less is known about their expression and function during human tissue and organ regeneration. We discovered the hypoxia inducible factor (HIF)-1α-controlled expression of EphA3, an Eph family member with critical functions during human tumour progression, in the vascularised tissue of regenerating human endometrium and on isolated human endometrial multipotent mesenchymal stromal cells (eMSCs), but not in other highly vascularised human organs. EphA3 affinity-isolation from human biopsy tissue yielded multipotent CD29⁺/CD73⁺/CD90⁺/CD146⁺ eMSCs that can be clonally propagated and respond to EphA3 agonists with EphA3 phosphorylation, cell contraction, cell-cell segregation and directed cell migration. EphA3 silencing significantly inhibited the ability of transplanted eMSCs to support neovascularisation in immunocompromised mice. In accord with established roles of Eph receptors in mediating interactions between endothelial and perivascular stromal cells during mouse development, our findings suggest that HIF-1α-controlled expression of EphA3 on human MSCs functions during the hypoxia-initiated early stages of adult blood vessel formation.

Silencer of death domains controls cell death through tumour necrosis factor-receptor 1 and caspase-10 in acute lymphoblastic leukemia

Resistance to apoptosis remains a significant problem in drug resistance and treatment failure in malignant disease. NO-aspirin is a novel drug that has efficacy against a number of solid tumours, and can inhibit Wnt signaling, and although we have shown Wnt signaling to be important for acute lymphoblastic leukemia (ALL) cell proliferation and survival inhibition of Wnt signaling does not appear to be involved in the induction of ALL cell death. Treatment of B lineage ALL cell lines and patient ALL cells with NO-aspirin induced rapid apoptotic cell death mediated via the extrinsic death pathway. Apoptosis was dependent on caspase-10 in association with the formation of the death-inducing signaling complex (DISC) incorporating pro-caspase-10 and tumor necrosis factor receptor 1 (TNF-R1). There was no measurable increase in TNF-R1 or TNF-α in response to NO-aspirin, suggesting that the process was ligand-independent. Consistent with this, expression of silencer of death domain (SODD) was reduced following NO-aspirin exposure and lentiviral mediated shRNA knockdown of SODD suppressed expansion of transduced cells confirming the importance of SODD for ALL cell survival. Considering that SODD and caspase-10 are frequently over-expressed in ALL, interfering with these proteins may provide a new strategy for the treatment of this and potentially other cancers.

High-level expression of a full-length Eph receptor

Eph receptors are the largest family of Receptor Tyrosine Kinases containing a single membrane-spanning segment. They are involved in a various developmental and cell-cell communication events. Although there is extensive structural information available on both the extra- and intracellular regions of Eph's in isolation, no structures are available for the entire receptor. To facilitate structural studies on functionally relevant Eph/ephrin complexes, we have developed an expression system for producing the full-length human EphA2 receptor. We successfully expressed milligram amounts of the receptor using baculovirus-based vector and insect cells. We were also able to extract the protein from the cell membranes and purify it to near homogeneity in two simple steps. The purified receptor was shown to retain its biological activity in terms of both binding to its functional ligands and being able to auto-phosphorylate the key tyrosine residues of the cytoplasmic kinase domain.

High levels of EphA3 expression are associated with high invasive capacity and poor overall survival in hepatocellular carcinoma

Although EphA3 expression has been associated with progression or prognosis in several types of tumors, the role of EphA3 in hepatocellular carcinoma (HCC) remains unknown. This study sought to investigate the clinicopathological and prognostic relevance of EphA3 expression in HCC as well as the underlying mechanisms responsible. EphA3 protein was mainly localized within the cytoplasm and at the cell membrane. High EphA3 expression was correlated with tumor size, tumor grade, metastasis, venous invasion and AJCC TNM stage (P<0.05), and patients with high levels of EphA3 expression were at a significantly increased risk for shortened survival time (P<0.05). In vitro, the downregulation of EphA3 expression decreased the invasive capacity of HCC cells via the regulation of VEGF. EphA3 may represent a novel candidate marker for patient prognosis as well a molecular target for HCC therapy.

EphA3 maintains tumorigenicity and is a therapeutic target in glioblastoma multiforme

Significant endeavor has been applied to identify functional therapeutic targets in glioblastoma (GBM) to halt the growth of this aggressive cancer. We show that the receptor tyrosine kinase EphA3 is frequently overexpressed in GBM and, in particular, in the most aggressive mesenchymal subtype. Importantly, EphA3 is highly expressed on the tumor-initiating cell population in glioma and appears critically involved in maintaining tumor cells in a less differentiated state by modulating mitogen-activated protein kinase signaling. EphA3 knockdown or depletion of EphA3-positive tumor cells reduced tumorigenic potential to a degree comparable to treatment with a therapeutic radiolabelled EphA3-specific monoclonal antibody. These results identify EphA3 as a functional, targetable receptor in GBM.

Effects of cancer-associated EPHA3 mutations on lung cancer

BACKGROUND

Cancer genome sequencing efforts recently identified EPHA3, which encodes the EPHA3 receptor tyrosine kinase, as one of the most frequently mutated genes in lung cancer. Although receptor tyrosine kinase mutations often drive oncogenic conversion and tumorigenesis, the oncogenic potential of the EPHA3 mutations in lung cancer remains unknown.

METHODS

We used immunoprecipitation, western blotting, and kinase assays to determine the activity and signaling of mutant EPHA3 receptors. A mutation-associated gene signature was generated from one large dataset, mapped to another training dataset with survival information, and tested in a third independent dataset. EPHA3 expression levels were determined by quantitative reverse transcription-polymerase chain reaction in paired normal-tumor clinical specimens and by immunohistochemistry in human lung cancer tissue microarrays. We assessed tumor growth in vivo using A549 and H1299 human lung carcinoma cell xenografts in mice (n = 7-8 mice per group). Tumor cell proliferation was measured by bromodeoxyuridine incorporation and apoptosis by multiple assays. All P values are from two-sided tests.

RESULTS

At least two cancer-associated EPHA3 somatic mutations functioned as dominant inhibitors of the normal (wild type) EPHA3 protein. An EPHA3 mutation-associated gene signature that was associated with poor patient survival was identified. Moreover, EPHA3 gene copy numbers and/or expression levels were decreased in tumors from large cohorts of patients with lung cancer (eg, the gene was deleted in 157 of 371 [42%] primary lung adenocarcinomas). Reexpression of wild-type EPHA3 in human lung cancer lines increased apoptosis by suppression of AKT activation in vitro and inhibited the growth of tumor xenografts (eg, for H1299 cells, mean tumor volume with wild-type EPHA3 = 437.4 mm(3) vs control = 774.7 mm(3), P < .001). Tumor-suppressive effects of wild-type EPHA3 could be overridden in trans by dominant negative EPHA3 somatic mutations discovered in patients with lung cancer.

CONCLUSION

Cancer-associated EPHA3 mutations attenuate the tumor-suppressive effects of normal EPHA3 in lung cancer.

Aberrant expression of EphA3 in gastric carcinoma: correlation with tumor angiogenesis and survival

BACKGROUND

EphA3, a member of the Eph receptor tyrosine kinases, plays important roles in tumor angiogenesis and progression. However, the function of EphA3 in solid tumors has not been widely studied. We aimed to explore EphA3 expression in gastric carcinoma and analyze its role as a potential prognostic factor.

METHODS

Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to assess EphA3 mRNA in a normal gastric mucosa cell line and carcinoma cell lines. Immunohistochemistry for EphA3 and vascular endothelial growth factor (VEGF) was performed in 318 cases of gastric carcinoma. CD34 immunohistochemical staining was used for microvessel density (MVD) counting. Western blotting was used to analyze EphA3 expression in the cell lines and to determine the expression of EphA3 and VEGF in 75 cases of gastric carcinoma and matched normal mucosa.

RESULTS

EphA3 mRNA and protein expression was significantly higher in gastric cancer than that in normal mucosa (all P < 0.001). EphA3 was significantly correlated with TNM stage and poor prognosis (all P < 0.001). Multivariate analysis showed that EphA3 had an independent effect on survival (P = 0.037). EphA3 was positively correlated with VEGF (P < 0.001), and MVD (P < 0.001). According to Western blot analysis, both EphA3 and VEGF expression were significantly higher in carcinoma than that in normal mucosa (all P < 0.001). A positive correlation was observed between EphA3 and VEGF expression in cancer (P < 0.001, r = 0.513).

CONCLUSIONS

EphA3 may play important roles in the angiogenesis and prognosis of gastric carcinoma, and thus may become a useful target for therapeutic intervention and a potential indicator for clinical assessment of tumor prognosis.

Cancer somatic mutations disrupt functions of the EphA3 receptor tyrosine kinase through multiple mechanisms

The Eph receptor tyrosine kinases make up an important family of signal transduction molecules that control many cellular processes, including cell adhesion and movement, cell shape, and cell growth. All of these are important aspects of cancer progression, but the relationship between Eph receptors and cancer is complex and not fully understood. Genetic screens of tumor specimens from cancer patients have revealed somatic mutations in many Eph receptors. The most highly mutated Eph receptor is EphA3, but its functional role in cancer is currently not well established. Here we show that many EphA3 mutations identified in lung, colorectal, and hepatocellular cancers, melanoma, and glioblastoma impair kinase activity or ephrin ligand binding and/or decrease the level of receptor cell surface localization. These results suggest that EphA3 has ephrin- and kinase-dependent tumor suppressing activities, which are disrupted by somatic cancer mutations.

Complex expression patterns of Eph receptor tyrosine kinases and their ephrin ligands in colorectal carcinogenesis

Aberrant expression of Eph and ephrin proteins in human cancers is extensively documented. However, data are frequently limited to one gene and therefore incomplete and in some instances conflicting. We analysed expression of all Eph and ephrin genes in colorectal cancer (CRC) cell lines and 153 clinical specimens, providing for the first time a comprehensive analysis of this system in CRC. Eph/ephrin mRNA expression was assessed by quantitative real-time PCR and correlated with protein expression (flow cytometry, Western blotting and immunocytochemistry). These data show that EphA1, EphA2, EphB2 and EphB4 were significantly over expressed in CRC. In all cases, at least one Eph gene was found in normal colon (EphA1, EphA2, EphB2, EphB4), where expression was observed at high levels in most CRCs. However, other Eph gene expression was lost in individual CRCs compared to the corresponding normal, EphA7 being a striking example. Loss of expression was more common in advanced disease and thus correlated with poor survival. This is consistent with the redundant functionality of Eph receptors, such that expression of a single Eph gene is sufficient for effector function. Overall, the data suggest a progressive loss of expression of individual Eph genes suggesting that individual CRCs need to be phenotyped to determine which Eph genes are highly expressed. Targeted therapies could then be selected from a group of specific antibodies, such as those developed for EphA1.

A semisynthetic Eph receptor tyrosine kinase provides insight into ligand-induced kinase activation

We have developed a methodology for generating milligram amounts of functional Eph tyrosine kinase receptor using the protein engineering approach of expressed protein ligation. Stimulation with ligand induces efficient autophosphorylation of the semisynthetic Eph construct. The in vitro phosphorylation of key Eph tyrosine residues upon ligand-induced activation was monitored via time-resolved, quantitative phosphoproteomics, suggesting a precise and unique order of phosphorylation of the Eph tyrosines in the kinase activation process. To our knowledge, this work represents the first reported semisynthesis of a receptor tyrosine kinase and provides a potentially general method for producing single-pass membrane proteins for structural and biochemical characterization.

Global gene expression profiling of somatic motor neuron populations with different vulnerability identify molecules and pathways of degeneration and protection

Different somatic motor neuron subpopulations show a differential vulnerability to degeneration in diseases such as amyotrophic lateral sclerosis, spinal muscular atrophy and spinobulbar muscular atrophy. Studies in mutant superoxide dismutase 1 over-expressing amyotrophic lateral sclerosis model mice indicate that initiation of disease is intrinsic to motor neurons, while progression is promoted by astrocytes and microglia. Therefore, analysis of the normal transcriptional profile of motor neurons displaying differential vulnerability to degeneration in motor neuron disease could give important clues to the mechanisms of relative vulnerability. Global gene expression profiling of motor neurons isolated by laser capture microdissection from three anatomical nuclei of the normal rat, oculomotor/trochlear (cranial nerve 3/4), hypoglossal (cranial nerve 12) and lateral motor column of the cervical spinal cord, displaying differential vulnerability to degeneration in motor neuron disorders, identified enriched transcripts for each neuronal subpopulation. There were striking differences in the regulation of genes involved in endoplasmatic reticulum and mitochondrial function, ubiquitination, apoptosis regulation, nitrogen metabolism, calcium regulation, transport, growth and RNA processing; cellular pathways that have been implicated in motor neuron diseases. Confirmation of genes of immediate biological interest identified differential localization of insulin-like growth factor II, guanine deaminase, peripherin, early growth response 1, soluble guanylate cyclase 1A3 and placental growth factor protein. Furthermore, the cranial nerve 3/4-restricted genes insulin-like growth factor II and guanine deaminase protected spinal motor neurons from glutamate-induced toxicity (P < 0.001, ANOVA), indicating that our approach can identify factors that protect or make neurons more susceptible to degeneration.

Activation of ephrin A proteins influences hematopoietic stem cell adhesion and trafficking patterns

OBJECTIVE

To determine if Eph receptors and ephrins can modulate the homing of hematopoietic cells in a murine bone marrow transplantation model.

MATERIALS AND METHODS

EphA and ephrin A gene expression by mouse hematopoietic stem cells and the progenitor cell line FDCP-1 was determined by real-time reverse transcription polymerase chain reaction and flow cytometry. The effect of ephrin A activation on adhesion of hematopoietic progenitors was determined by in vitro adhesion assays in which cells were exposed to fibronectin or vascular cell adhesion molecule-1 (VCAM-1) and an increasing gradient of immobilized EphA3-Fc. Adhesion to fibronectin and VCAM-1 was further investigated using soluble preclustered EphA3-Fc. We used soluble unclustered EphA3-Fc as an antagonist to block endogenous EphA-ephrin A interactions in vivo. The effect of injecting soluble EphA3-Fc on the mobilization of hematopoietic progenitor cells was examined. We determined the effect on short-term homing by pretreating bone marrow cells with EphA3-Fc or the control IgG before infusion into lethally irradiated mice.

RESULTS

Preclustered and immobilized EphA3-Fc increased adhesion of progenitor cells and FDCP-1 to fibronectin and VCAM-1 (1.6- to 2-fold higher adhesion; p < 0.05) relative to control (0 μ/cm(2) EphA3-Fc extracellular molecule alone). Injection of the antagonist soluble EphA3-Fc increased progenitor cell and colony-forming unit-spleen cells in the peripheral blood (42% greater colony-forming unit in culture; p < 0.05, 3.8-fold higher colony-forming unit-spleen) relative to control.

CONCLUSION

Treating bone marrow cells with EphA3-Fc resulted in a reduction by 31% in donor stem cells homing to the bone marrow and accumulation of donor cells in recipient spleens (50% greater than control) and greater recovery of donor stem cells from the peripheral blood.

Expression profile of Eph receptors and ephrin ligands in healthy human B lymphocytes and chronic lymphocytic leukemia B-cells

Increasing information relates some Eph receptors and their ligands, ephrins (EFN), with the immune system. Herein, we found that normal B-cells from peripheral blood (PB) and lymph nodes (LN) showed a differential expression of certain Eph/EFN members, some of them being modulated upon in vitro stimulation including EFNA1, EFNA4, EphB6 and EphA10. In contrast, PB CLL B-cells showed a more heterogeneous Eph/EFN profile than their normal PB B-cell counterparts, expressing Eph/EFN members frequently found within the LN and activated B-cells, specially EFNA4, EphB6 and EphA10. Two of them, EphB6 and EFNA4 were further related with the clinical course of CLL patients. EphB6 expression correlated with a high content of ZAP-70 mRNA and a poor prognosis. High serum levels of a soluble EFNA4 isoform positively correlated with increasing peripheral blood lymphocyte counts and lymphadenopathy. These findings suggest that Eph/EFN might be relevant in normal B-cell biology and could represent new potential prognostic markers and therapeutic targets for CLL.

Elevated protein tyrosine phosphatase activity provokes Eph/ephrin-facilitated adhesion of pre-B leukemia cells

Signaling by Eph receptors and cell-surface ephrin ligands modulates adhesive cell properties and thereby coordinates cell movement and positioning in normal and oncogenic development. While cell contact–dependent Eph activation frequently leads to cell-cell repulsion, also the diametrically opposite response, cell-cell adhesion, is a probable outcome. However, the molecular principles regulating such disparate functions have remained controversial. We have examined cell-biologic mechanisms underlying this switch by analyzing ephrin-A5–induced cell-morphologic changes of EphA3-positive LK63 pre-B acute lymphoblastic leukemia cells. Their exposure to ephrin-A5 surfaces leads to a rapid conversion from a suspended/nonpolarized to an adherent/polarized cell type, a transition that relies on EphA3 functions operating in the absence of Eph-kinase signaling. Cell morphology change and adhesion of LK63 cells are effectively attenuated by endogenous protein tyrosine phosphatase (PTP) activity, whereby PTP inhibition and productive EphA3-phosphotyrosine signaling reverse the phenotype to nonadherent cells with a condensed cytoskeleton. Our findings suggest that Eph-associated PTP activities not only control receptor phosphorylation levels, but as a result switch the response to ephrin contact from repulsion to adhesion, which may play a role in the pathology of hematopoietic tumors.

Effects of Emdogain on osteoblast gene expression

OBJECTIVE

Emdogain (EMD) is a protein extract purified from porcine enamel and has been introduced in clinical practice to obtain periodontal regeneration. EMD is composed mainly of amelogenins (90%), while the remaining 10% is composed of non-amelogenin enamel matrix proteins such as enamelins, tuftelin, amelin and ameloblastin. Enamel matrix proteins seem to be involved in root formation. EMD has been reported to promote proliferation, migration, adhesion and differentiation of cells associated with healing periodontal tissues in vivo.

DESIGN

How this protein acts on osteoblasts is poorly understood. We therefore attempted to address this question by using a microarray technique to identify genes that are differently regulated in osteoblasts exposed to enamel matrix proteins.

RESULTS

By using DNA microarrays containing 20,000 genes, we identified several upregulated and downregulated genes in the osteoblast-like cell line (MG-63) cultured with enamel matrix proteins (Emd). The differentially expressed genes cover a broad range of functional activities: (i) signaling transduction, (ii) transcription, (iii) translation, (iv) cell cycle regulation, proliferation and apoptosis, (v) immune system, (vi) vesicular transport and lysosome activity, and (vii) cytoskeleton, cell adhesion and extracellular matrix production.

CONCLUSIONS

The data reported are the first genome-wide scan of the effect of enamel matrix proteins on osteoblast-like cells. These results can contribute to our understanding of the molecular mechanisms of bone regeneration and as a model for comparing other materials with similar clinical effects.

Concurrent binding of anti-EphA3 antibody and ephrin-A5 amplifies EphA3 signaling and downstream responses: potential as EphA3-specific tumor-targeting reagents

The Eph receptor tyrosine kinases and their membrane-bound ephrin ligands form a unique cell-cell contact-mediated system for controlling cell localization and organization. Their high expression in a wide variety of human tumors indicates a role in tumor progression, and relatively low Eph and ephrin levels in normal tissues make these proteins potential targets for anticancer therapies. The monoclonal antibody IIIA4, previously used to isolate EphA3, binds with subnanomolar affinity to a conformation-specific epitope within the ephrin-binding domain that is closely adjacent to the "low-affinity" ephrin-A5 heterotetramerization site. We show that similar to ephrin-A5, preclustered IIIA4 effectively triggers EphA3 activation, contraction of the cytoskeleton, and cell rounding. BIAcore analysis, immunoblot, and confocal microscopy of wild-type and mutant EphA3 with compromised ephrin-A5 or IIIA4-binding capacities indicate that IIIA4 binding triggers an EphA3 conformation which is permissive for the assembly of EphA3/ephrin-A5-type signaling clusters. Furthermore, unclustered IIIA4 and ephrin-A5 Fc applied in combination initiate greatly enhanced EphA3 signaling. Radiometal conjugates of ephrin-A5 and IIIA4 retain their affinity, and in mouse xenografts localize to, and are internalized rapidly into EphA3-positive, human tumors. These findings show the biological importance of EphA3/ephrin-A5 interactions and that ephrin-A5 and IIIA4 have great potential as tumor targeting reagents.

Three Distinct Molecular Surfaces in Ephrin-A5 Are Essential for a Functional Interaction with EphA3

Eph receptor tyrosine kinases (Ephs) function as molecular relays that interact with cell surface-bound ephrin ligands to direct the position of migrating cells. Structural studies revealed that, through two distinct contact surfaces on opposite sites of each protein, Eph and ephrin binding domains assemble into symmetric, circular heterotetramers. However, Eph signal initiation requires the assembly of higher order oligomers, suggesting additional points of contact. By screening a random library of EphA3 binding-compromised ephrin-A5 mutants, we have now determined ephrin-A5 residues that are essential for the assembly of high affinity EphA3 signaling complexes. In addition to the two interfaces predicted from the crystal structure of the homologous EphB2.ephrin-B2 complex, we identified a cluster of 10 residues on the ephrin-A5 E alpha-helix, the E-F loop, the underlying H beta-strand, as well as the nearby B-C loop, which define a distinct third surface required for oligomerization and activation of EphA3 signaling. Together with a corresponding third surface region identified recently outside of the minimal ephrin binding domain of EphA3, our findings provide experimental evidence for the essential contribution of three distinct protein-interaction interfaces to assemble functional EphA3 signaling complexes.

Recruitment of Eph receptors into signaling clusters does not require ephrin contact

Eph receptors and their cell membrane-bound ephrin ligands regulate cell positioning and thereby establish or stabilize patterns of cellular organization. Although it is recognized that ephrin clustering is essential for Eph function, mechanisms that relay information of ephrin density into cell biological responses are poorly understood. We demonstrate by confocal time-lapse and fluorescence resonance energy transfer microscopy that within minutes of binding ephrin-A5-coated beads, EphA3 receptors assemble into large clusters. While remaining positioned around the site of ephrin contact, Eph clusters exceed the size of the interacting ephrin surface severalfold. EphA3 mutants with compromised ephrin-binding capacity, which alone are incapable of cluster formation or phosphorylation, are recruited effectively and become phosphorylated when coexpressed with a functional receptor. Our findings reveal consecutive initiation of ephrin-facilitated Eph clustering and cluster propagation, the latter of which is independent of ephrin contacts and cytosolic Eph signaling functions but involves direct Eph-Eph interactions.