Eph/ephrin signaling as a potential therapeutic target after central nervous system injury

Recent work indicates that the expression of Eph and ephrin proteins is upregulated after injury in the central nervous system (CNS). Although to date, much of the interest in these protein families in the nervous system has been on their roles during development, their presence in the adult CNS at multiple time points after injury suggest that they play significant roles in key aspects of the nervous system's response to damage. Several fundamental features of Eph and ephrin biology, such as bidirectional signaling, promiscuity of ligand-receptor binding, and potential cis regulation of function, present challenges for the formulation of rational and effective Eph/ephrin based strategies for CNS axon regeneration. However, recent work that have identified specific functions for individual Ephs and ephrins in injury-induced phenomena such as axon sprouting, cellular remodeling, and scar formation has begun to tease apart their contributions and may provide a number of potential entry points for beneficial therapeutic intervention.     

A disalicylic acid-furanyl derivative inhibits ephrin binding to a subset of Eph receptors

Eph receptor tyrosine kinases and ephrin ligands control many physiological and pathological processes, and molecules interfering with their interaction are useful probes to elucidate their complex biological functions. Moreover, targeting Eph receptors might enable new strategies to inhibit cancer progression and pathological angiogenesis as well as promote nerve regeneration. Because our previous work suggested the importance of the salicylic acid group in antagonistic small molecules targeting Eph receptors, we screened a series of salicylic acid derivatives to identify novel Eph receptor antagonists. This identified a disalicylic acid-furanyl derivative that inhibits ephrin-A5 binding to EphA4 with an IC(50) of 3 μm in ELISAs. This compound, which appears to bind to the ephrin-binding pocket of EphA4, also targets several other Eph receptors. Furthermore, it inhibits EphA2 and EphA4 tyrosine phosphorylation in cells stimulated with ephrin while not affecting phosphorylation of EphB2, which is not a target receptor. In endothelial cells, the disalicylic acid-furanyl derivative inhibits EphA2 phosphorylation in response to TNFα and capillary-like tube formation on Matrigel, two effects that depend on EphA2 interaction with endogenous ephrin-A1. These findings suggest that salicylic acid derivatives could be used as starting points to design new small molecule antagonists of Eph receptors.     

Polyphenol rich botanicals used as food supplements interfere with EphA2–ephrinA1 system

The Eph tyrosine kinase receptors and their ephrin ligands play a central role in several human cancers and their deregulated expression or function promotes tumorigenesis, inducing aggressive tumor phenotypes. Green tea extracts (GTE) have been recently found to inhibit Eph-kinase phosphorylation. In order to evaluate the potential contribution of edible and medicinal plants on EphA2–ephrinA1 modulation, 133 commercially available plant extracts used as food supplements, essential and fixed oils were screened with an ELISA-based binding assay. Nine plant extracts, rich of polyphenols, reversibly inhibited binding in a dose-dependent manner (IC₅₀ 0.83–24 μg/ml). Functional studies on PC3 prostate adenocarcinoma cells revealed that active extracts antagonized ephrinA1-Fc-induced EphA2-phosphorylation at non-cytotoxic concentrations (IC₅₀ 0.31–11.3 μg/ml) without interfering with EGF-induced EGFR activation, suggesting a specific effect. These findings could furnish an interesting starting point regarding the potential relationship between diet, edible plant secondary metabolites and Eph–ephrin system, suggesting their possible involvement in cancer development modulation.     

Ephrins and pain

Introduction: The ephrin receptor family is the largest family of receptor tyrosine kinases, which comprises 14 members that are divided into A and B subclasses. The ephrin receptor (Eph-receptor) ligands are named ephrins. Ephrins/Eph receptors interact with a variety of membrane receptors that respond to chemokines, neurotransmitters or growth factors. A growing body of evidence indicates that ephrins/Eph receptors are involved in the modulation of different types of pain.

Areas covered: A literature review summarizing the most recent data in terms of ephrins and their ligands and their association with different types of pain. Moreover, the latest knowledge regarding the involvement of ephrins/Eph receptors in pain modulation as well as its possible therapeutic perspectives are presented.

Expert opinion: The ephrins/Eph receptors system seems to be an emerging target for pain drug discovery, because it is involved in the pathophysiology of many types of pain. The modulation of different types of pain by selective agonists or antagonists may hold tremendous therapeutic potential in various pain conditions mentioned in this review. However, the current limited but promising data, merit consideration and further investigation.     

Growth factor receptors in hematopoietic stem cells: EPH family expression in CD34+ and CD133+ cell populations from mobilized peripheral blood

Cell-surface antigen expression of hematopoietic stem cells has a crucial role in characterizing cell subpopulation with distinct functional properties. The Eph receptors are the largest receptor tyrosine kinase family being involved in processes like vascular remodelling during development and physiological and pathological angiogenesis. Some Eph/Ephrin members are expressed in hematopoietic cells. The ability to isolate purified cell populations co-expressing CD34 and CD133 antigens as most commonly used markers for identification of hematopoietic progenitors has provided the opportunity to identify their surface-receptor profile. As positively expressed CD34 and CD133 cells take place not only in hematopoietic but also in endothelial differentiation, we aimed to define the Eph/Ephrin characteristic of these cells and relate these findings to new therapy strategies. Positive selections of CD34 and CD133 cells from PBPC in lymphoma patients were performed using magnetic beads and AutoMACS (Miltenyi Biotec) device. The purity of isolated cells was tested by flow cytometry. Immunocytochemistry was used to assess the Eph/Ephrin expression profile of positively selected samples. Our study revealed that all samples (10 from CD34+ and 8 from CD133+ cells) expressed one or more of Eph/Ephrin antigens in different proportions. All CD34+ cell samples, and 6 of 8 in the CD133+ cell fraction were strongly immunoreactive for EphA2. EphB2 was strongly expressed in all CD133+ cases, but 50% of the CD34 positive group lacked or weakly expressed this receptor. EphB4 was negative in 9 of 10 CD34+ cases and in all CD133+ cells. Thus, we have shown the surface marker profile of positively selected CD34 and CD133 cells in leukapheresis samples from lymphoma patients with regard to Eph/Ephrin receptors and discussed their biological clinical potential.     

Eph receptor tyrosine kinases in tumor and tumor microenvironment

Eph receptors are a unique family of receptor tyrosine kinases (RTK) that play critical roles in embryonic patterning, neuronal targeting, and vascular development during embryogenesis. In adults, Eph RTKs and their ligands, the ephrins, are frequently overexpressed in a variety of cancers and tumor cell lines, including breast, prostate, non-small cell lung and colon cancers, melanomas, and neuroblastomas. Unlike traditional oncogenes that often function only in tumor cells, recent data show that Eph receptors mediate cell-cell interaction both in tumor cells and in tumor microenvironment, namely the tumor stroma and tumor vasculature. As such, Eph RTKs represent attractive potential targets for drug design, as targeting these molecules could attack several aspects of tumor progression simultaneously. This review will focus on recent advances in dissecting the role of Eph RTKs in tumor cells, tumor angiogenesis, and possible contribution to trafficking of inflammatory cells in cancer.     

EphA2 receptor tyrosine kinase as a promising target for cancer therapeutics

Eph receptors are a unique family of receptor tyrosine kinases (RTK) that play critical roles in embryonic patterning, neuronal targeting, and vascular development during normal embryogenesis. Eph RTKs and their ligands, the ephrins, are also frequently overexpressed in a variety of cancers and tumor cell lines. In particular, one family member, EphA2, is overexpressed in breast, prostate, lung, and colon cancers. Unlike traditional oncogenes that often function only in tumor cells, recent data show that Eph receptors mediate cell-cell interactions both in tumor cells and in the tumor microenvironment, namely the tumor stroma and tumor vasculature. Thus, EphA2 receptors are attractive targets for drug design, as targeting these molecules could simultaneously inhibit several aspects of tumor progression. This review focuses on the multiple roles of EphA2 in cancer progression, the mechanisms by which EphA2 inhibition may halt this progression, and the pre-clinical results of EphA2 inhibition in various cancer model systems.     

Eph家族蛋白研究进展

Eph家族蛋白包括Eph受体和Ephrin配体,是蛋白酪氨酸激酶家族中的最大成员。由于其具有独特的受体-配体复合物的结构特点及其受体与配体间特有的相互作用模式,所以它们极有可能成为疾病治疗的药物靶标,故该蛋白家族的相关领域研究日益受到重视。该文首先从Eph家族蛋白的分类、表达特点、结构和受体-配体相互作用特点以及其在神经系统中的功能等几个方面简要综述了其相关领域的最新研究进展,进而从结构、作用模式、功能几方面对Eph家族蛋白在神经系统疾患防治中的潜在价值和未来的研究方向进行了探讨和展望。     

The relationship between oncogene expression and clinical outcome in endometrial carcinoma

The mechanism of oncogenesis is extremely complicated and controlled by various factors, most of which are based on cell proliferation, tumor invasion, neovascularization, and inhibition of apoptosis. We have investigated the relationship between thirty three oncogenes expression and histopathological prognostic factors of endometrial carcinomas, including clinical stage, histological grade, presence of invasion to greater than one-half the myometrium, clinical outcome, and survival rate. Scoring on the basis of the percentage of positive cells indicated that Plks, EphB4, ephrin-B2, Id1, CaMKIV, c-Ets1, Elf-1, and survivin expression were significantly associated with PCNA-labeling index, clinical stage, histological grade, the presence of invasion to greater than one-half the myometrium, and clinical outcome. Survival data were available for all patients, and univariate Cox regression analysis showed that Plks, CaMKIV, Elf-1, and survivin expression were significantly associated with poor prognosis. Our results demonstrate that some oncogenes expression in endometrial carcinoma correlate with the malignant potential of these tumors. Thus, in addition to being of diagnostic value, modulation of these oncogenes activity in the tumors by chemotherapeutic agents or gene therapy may prove to be of therapeutic value. In this review, we demonstrate the biologic behavior of seven novel molecules (Plks, Eph/ephrin, Id family, CaMK, c-Ets1, Elf-1, and survivin) in the endometrial carcinoma.     

UniPR129 is a competitive small molecule Eph-ephrin antagonist blocking in vitro angiogenesis at low micromolar concentrations

Background and Purpose

The Eph receptor tyrosine kinases and their ephrin ligands are key players in tumorigenesis and many reports have correlated changes in their expression with a poor clinical prognosis in many solid tumours. Agents targeting the Eph-ephrin system might emerge as new tools useful for the inhibition of different components of cancer progression. Even if different classes of small molecules targeting Eph-ephrin interactions have been reported, their use is hampered by poor chemical stability and low potency. Stable and potent ligands are crucial to achieve robust pharmacological performance.

Experimental Approach

UniPR129 (the L-homo-Trp conjugate of lithocholic acid) was designed by means of computational methods, synthetized and tested for its ability to inhibit the interaction between the EphA2 receptor and the ephrin-A1 ligand in an elisa binding study. The ability of UniPR129 to disrupt EphA2-ephrin-A1 interaction was functionally evaluated in a prostate adenocarcinoma cell line and its anti-angiogenic effect was tested in vitro using cultures of HUVECs.

Key Results

UniPR129 disrupted EphA2-ephrin-A1 interaction with K_i = 370 nM in an elisa binding assay and with low micromolar potency in cellular functional assays, including inhibition of EphA2 activation, inhibition of PC3 cell rounding and disruption of in vitro angiogenesis, without cytotoxic effects.

Conclusions and Implications

The discovery of UniPR129 represents not only a major advance in potency compared with the existing Eph-ephrin antagonists but also an improvement in terms of cytotoxicity, making this molecule a useful pharmacological tool and a promising lead compound.     

Heterologous expression of xenobiotic mammalian-metabolizing enzymes in mutagenicity tester bacteria: an update and practical considerations

There is an increasing need for metabolic competent cell systems for the mechanistic studies of biotransformation of xenobiotics in toxicology in general and in genotoxicology in particular. These cell systems combine the heterologous expression of a particular mammalian biotransformation enzyme with a specific target/ end point by which a functional analysis of the expressed gene product in the (geno)toxicity of chemicals can be performed. cDNAs of an increasing number of mammalian biotransformation enzymes is being cloned. The construction of specific expression vectors permits their heterologous expression in laboratory bacteria, such as Escherichia coli strains. This development does not only allow biochemical and enzymatic studies of (pure) enzyme preparations but also facilitates the engineering of metabolically competent mutagenicity tester bacteria, thereby providing new tools for genotoxicity testing and for studying of the roles of biotransformation in chemical carcinogenesis. In this review, we describe an update as well as an evaluation of enzymes expressed in mutagenicity tester bacteria. Four types of biotransformation enzymes are now expressed in these bacteria, namely, GSTs, CYPs, NATs, and STs. The expression of these enzymes in the tester bacteria and their subsequent application in mutagenicity assays demonstrates that heterologous expression in this type of bacteria has a number implications for the functionality of the biotransformation enzymes as well as for the functioning of the tester bacteria in mutagenicity detection. We also describe here a number of practical considerations in this regard.     

Heterologous Expression of Xenobiotic Mammalian-Metabolizing Enzymes in Mutagenicity Tester Bacteria: An Update and Practical Considerations

There is an increasing need for metabolic competent cell systems for the mechanistic studies of biotransformation of xenobiotics in toxicology in general and in genotoxicology in particular. These cell systems combine the heterologous expression of a particular mammalian biotransformation enzyme with a specific target/ end point by which a functional analysis of the expressed gene product in the (geno)toxicity of chemicals can be performed. cDNAs of an increasing number of mammalian biotransformation enzymes is being cloned. The construction of specific expression vectors permits their heterologous expression in laboratory bacteria, such as Escherichia coli strains. This development does not only allow biochemical and enzymatic studies of (pure) enzyme preparations but also facilitates the engineering of metabolically competent mutagenicity tester bacteria, thereby providing new tools for genotoxicity testing and for studying of the roles of biotransformation in chemical carcinogenesis. In this review, we describe an update as well as an evaluation of enzymes expressed in mutagenicity tester bacteria. Four types of biotransformation enzymes are now expressed in these bacteria, namely, GSTs, CYPs, NATs, and STs. The expression of these enzymes in the tester bacteria and their subsequent application in mutagenicity assays demonstrates that heterologous expression in this type of bacteria has a number implications for the functionality of the biotransformation enzymes as well as for the functioning of the tester bacteria in mutagenicity detection. We also describe here a number of practical considerations in this regard.     

VEGF-receptor inhibitors for anti-angiogenesis

Angiogenesis is deeply involved in the progression of major diseases such as cancer, diabetes, and rheumatoid arthritis. Molecular mechanism on angiogenesis was extensively studied, and several signaling systems including VEGF (VEGF-A), angiopoietin, PDGF, and ephrin were shown to be crucial for physiological angiogenesis. Interestingly, among these factors, VEGF appears to play key roles in most of the pathological angiogenesis, and other factors are considered to have additional effects on its development depending on the situation. VEGF binds and activates two tyrosine kinase receptors, VEGFR-1 (Flt-1) and VEGFR-2 (KDR/Flk-1), and stimulates endothelial cell growth, survival, and vascular permeability. VEGF induces not only tumor angiogenesis but also blood-vessel-dependent metastasis. Based on the importance of VEGF in diseases, many companies and institutes are now trying to generate appropriate small molecules as well as proteins that strongly antagonize the VEGF-VEGFR system. Several molecules quite effective for suppression of tumorigenesis and pathological angiogenesis in animal models are under clinical trials.     

Coordination of chemokine and adhesion systems in intratumoral T cell migration responsible for the induction of tumor regression

T cell migration into tumor masses is critical to the process of immunologically induced tumor regression. Like other lymphoid populations, T cells are recruited to inflammatory sites depending on the interaction of T cell integrin receptors with their ligands expressed on vasculature. It is increasingly becoming evident that the adhesive capacity of integrins is upregulated by signals from chemokine receptors. A model of intratumoral T cell migration has been established using IL-12 to induce tumor regression. Focusing on this particular model, we review how IL-12 works to upregulate the expression and/or function of chemokines/chemokine receptors as well as adhesion molecules and to induce collaboration between chemokine and adhesion systems. This article will also describe why such an IL-12-induced activation of chemokine and adhesion systems leads to T cell-mediated tumor regression in some tumor models, but not in others.