Synthesis, radiolabelling and initial biological characterisation of 18F-labelled xanthine derivatives for PET imaging of Eph receptors.

Eph receptor tyrosine kinases, particularly EphA2 and EphB4, represent promising candidates for molecular imaging due to their essential role in cancer progression and therapy resistance. Xanthine derivatives were identified to be potent Eph receptor inhibitors with IC50 values in the low nanomolar range (1-40 nm). These compounds occupy the hydrophobic pocket of the ATP-binding site in the kinase domain. Based on lead compound 1, we designed two fluorine-18-labelled receptor tyrosine kinase inhibitors ([18F]2/3) as potential tracers for positron emission tomography (PET). Docking into the ATP-binding site allowed us to find the best position for radiolabelling. The replacement of the methyl group at the uracil residue ([18F]3) rather than the methyl group of the phenoxy moiety ([18F]2) by a fluoropropyl group was predicted to preserve the affinity of the lead compound 1. Herein, we point out a synthesis route to [18F]2 and [18F]3 and the respective tosylate precursors as well as a labelling procedure to insert fluorine-18. After radiolabelling, both radiotracers were obtained in approximately 5% radiochemical yield with high radiochemical purity (>98%) and a molar activity of >10 GBq µmol-1. In line with the docking studies, first cell experiments revealed specific, time-dependent binding and uptake of [18F]3 to EphA2 and EphB4-overexpressing A375 human melanoma cells, whereas [18F]2 did not accumulate at these cells. Since both tracers [18F]3 and [18F]2 are stable in rat blood, the novel radiotracers might be suitable for in vivo molecular imaging of Eph receptors with PET.

EphA2-positive human umbilical cord-derived mesenchymal stem cells exert anti-fibrosis and immunomodulatory activities via secretion of prostaglandin E2.

OBJECTIVE: Previous study has demonstrated that EphA2 is a biomarker of mesenchymal stem cells (MSCs) from human placenta or umbilical cord and is able to distinguish MSCs from fibroblasts. In this study, we further examine the potential efficacy of EphA2+ human umbilical cord-derived MSCs (hUC-MSCs). MATERIALS AND METHODS: MSCs specific markers, EphA2 and CD146 expression on the surface of hUC-MSCs were determined by flow cytometry analysis. Quantitative real time polymerase chain reaction was used to examine pro-fibrotic gene expression of TGF-ß1-stimulated lung fibroblast (MRC-5 cells). On the other hand, ELISA was used to analyze the content of pro-inflammatory cytokines (TNF-ɑ; and IP-10) in the LPS-activated macrophages culture supernatant. RESULTS: The pro-fibrotic gene (TGF-ß1, CTGF, fibronectin, collagen I and TIMP-1) expression in TGF-ß1-activated MRC-5 cells and the pro-inflammatory cytokines (TNF-ɑ and IP-10) in the LPS-activated macrophages culture supernatant were both attenuated when in present of EphA2+ hUC-MSCs. Moreover, once EphA2+ hUC-MSCs treated with prostaglandin E2 specific inhibitor NS-398, both anti-fibrotic and anti-inflammatory effects of EphA2+ hUC-MSCs were abolished. CONCLUSION: EphA2+ hUC-MSCs possess immunomodulatory and anti-fibrotic properties, and PGE2 plays an important role in these activities. This implies that EphA2+ hUC-MSCs have potentially effectiveness for treatment of acute inflammatory and chronic fibrotic lung diseases.

Clinical implications of the plasma EphA2 receptor level in critically ill patients with septic shock.

The Eph/ephrin receptor ligand system is known to play a role in inflammation induced by infection, injury, and inflammatory diseases. The present study aimed to evaluate plasma EphA2 receptor levels in critically ill patients with sepsis. This study was a prospective cohort study evaluating samples and clinical data from the medical intensive care unit (MICU) of a 2000-bed university tertiary referral hospital in South Korea. Positive correlations of the plasma EphA2 receptor level with the acute physiology and chronic health evaluation (APACHE) II score and the sequential organ failure assessment (SOFA) score were observed. The area under the curve (AUC) for the plasma EphA2 receptor level on a receiver operating characteristic curve was 0.690 (95% confidence interval [CI], 0.608-0.764); the AUCs for the APACHE II score and SOFA scores were 0.659 (95% CI, 0.576-0.736) and 0.745 (95% CI, 0.666-0.814), respectively. A Cox proportional hazard model identified an association between an increased plasma EphA2 receptor level (>51.5 pg mL-1) and increased risk of 28-day mortality in the MICU (hazard ratio = 3.22, 95% CI, 1.709-6.049). An increased plasma EphA2 receptor level was associated with sepsis severity and 28-day mortality among sepsis patients.

Ephrin-A1 is a negative regulator in glioma through down-regulation of EphA2 and FAK.

Eph receptors, the largest receptor tyrosine kinases, and their ephrin ligands play important roles in axon guidance and cell migration during development of the nervous system. Recently, these molecules are also found involved in tumorigenesis of different kinds of cancers. In this study, we demonstrated that expression of ephrin-A1 was dramatically down-regulated in glioma cell lines and in primary gliomas compared to the matched normal tissues. Forced expression of ephrin-A1 attenuated cell migration, cell proliferation, and adhesion-independent growth in human glioma U251 cells. EphA2, a receptor for ephrin-A1 and an oncoprotein, was greatly decreased in ephrin-A1-transfected glioma cells. Overexpression of ephrin-A1 stimulated activation of EphA2 by phosphorylation and led to its degradation. Furthermore, focal adhesion kinase (FAK), a known downstream molecule of EphA2, was also down-regulated in the ephrin-A1 transfected cells. These results suggested that ephrin-A1 serves as a critical negative regulator in the tumorigenesis of gliomas by down-regulating EphA2 and FAK, which may provide potential valuable targets for therapeutic intervention.

Ephrin A/EphA controls the rostral turning polarity of a lateral commissural tract in chick hindbrain.

Most post-crossing commissural axons turn into longitudinal paths to make synaptic connections with their targets. Mechanisms that control their rostrocaudal turning polarity are still poorly understood. We used the hindbrain as a model system to investigate the rostral turning of a laterally located commissural tract, identified as the caudal group of contralateral cerebellar-projecting second-order vestibular neurons (cC-VC). We found that the caudal hindbrain possessed a graded non-permissive/repulsive activity for growing cC-VC axons. This non-permissiveness/repulsion was in part mediated by glycosyl-phosphatidylinositol (GPI)-anchored ephrin A. We further demonstrated that ephrin A2 was distributed in a caudal-high/rostral-low gradient in the caudolateral hindbrain and cC-VC axons expressed EphA receptors. Finally, perturbing ephrin A/EphA signalling both in vitro and in vivo led to rostrocaudal pathfinding errors of post-crossing cC-VC axons. These results suggest that ephrin A/EphA interactions play a key role in regulating the polarity of post-crossing cC-VC axons as they turn into the longitudinal axis.

Ephrin A2 may play a role in axon guidance during hair cell regeneration.

OBJECTIVE: Hair cell regeneration in the avian cochlea is accompanied by frequency specific reinnervation and recovery of physiologic function. The molecular cues that guide ganglion cells to tonotopically appropriate new hair cells have not been identified. We investigated the potential of ephrin A2 in this process. STUDY DESIGN: Ephrin A2 expression was characterized in acoustic ganglion cells of normal and gentamicin-treated early post hatch chicks. METHODS: Ephrin A2 expression was determined by Western analysis of total protein isolated from acoustic ganglia in normal animals. Protein localization was characterized by fluorescence immunohistochemistry in sections of acoustic ganglia of normal and gentamicin treated animals. Patterns of ephrin A2 expression in acoustic ganglia were determined and quantified during hair cell regeneration. RESULTS: Ephrin A2 expression was found in acoustic ganglia by Western analysis. Localization of this protein by immunofluorescence revealed its presence in acoustic ganglion cells in normal chicks. After gentamicin treatment, ephrin A2 expression was lost in a subset of acoustic ganglion cells. The spatial and temporal pattern of ephrin A2 loss coincides with the pattern of hair cell loss and regeneration. CONCLUSIONS: The changes in ephrin A2 immunoreactivity in acoustic ganglion cells during cochlear damage and regeneration suggests that ephrin A2 may be involved in the guidance of ganglion cells to tonotopically appropriate hair cell targets during regeneration. Ephrin A2 in hair cell regeneration.

Ephrin-A2 regulates position-specific cell affinity and is involved in cartilage morphogenesis in the chick limb bud.

In the developing limb bud, mesenchymal cells show position-specific affinity, suggesting that the positional identity of the cells is represented as their surface properties. Since the affinity is regulated by glycosylphosphatidylinositol (GPI)-anchored cell surface proteins, and by EphA4 receptor tyrosine kinase, we hypothesized that the GPI-anchored ligand, the ephrin-A family, also contributes to the affinity. Here, we describe the role of ephrin-A2 in the chick limb bud. Ephrin-A2 protein is uniformly distributed in the limb bud during early limb development. As the limb bud grows, expression of ephrin-A2 is strong in its proximal-to-intermediate regions, but weak distally. The position-dependent expression is maintained in vitro, and is regulated by FGF protein, which is produced in the apical ectodermal ridge. To investigate the role of ephrin-A2 in affinity and in cartilage morphogenesis of limb mesenchyme, we ectopically expressed ephrin-A2 in the limb bud using the retrovirus vector, RCAS. Overexpressed ephrin-A2 modulated the affinity of the mesenchymal cells that differentiate into autopod elements. It also caused malformation of the autopod skeleton and interfered with cartilage nodule formation in vitro without inhibiting chondrogenesis. These results suggest that ephrin-A2 regulates the position-specific affinity of limb mesenchyme and is involved in cartilage pattern formation in the limb.

EphA receptors and ephrin-A ligands exhibit highly regulated spatial and temporal expression patterns in the developing olfactory system.

The spatiotemporal expression patterns of the chemorepulsive EphA receptors, EphA4 and EphA7, and three ephrins-A2, A4 and A5, were examined in the developing rat primary olfactory system. Unlike the visual system that has simple and stable gradients of Ephs and ephrins, the olfactory system demonstrates complex spatiotemporal expression patterns of these molecules. Using immunohistochemistry, we demonstrate that expression of these molecules is dynamic and tightly regulated both within and between different cell types. We reveal restricted targeting of these proteins within subcellular compartments of some neurons. EphA4, ephrin-A2 and ephrin-A5 were expressed by primary olfactory axons during the embryonic formation of the olfactory nerve. There were no gradients in expression along the rostrocaudal or ventrodorsal axes in the nasal cavity and olfactory bulb. However, during the early neonatal period, axons expressing different levels of ephrin-A5 sorted out and terminated in a subpopulation of glomeruli that were mosaically dispersed throughout the bulb. The expression of EphA4 and ephrin-A2 was dramatically down-regulated on all axons during the early neonatal period of glomerular formation. The uniform co-expression of receptors and ligands before glomerular formation suggests they play a generic role in axon-axon interactions in the olfactory nerve and nerve fibre layer. In contrast, loss of EphA4 from axons during glomerular formation may facilitate the interaction of ephrin-A5 with Eph receptors on target cells in the bulb. While EphA4, EphA5 and EphA7 are not mosaically expressed by bulbar neurons, other Eph receptors may have expression patterns complementary to the ephrin-A5-positive subpopulation of glomeruli.