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.

Ephrin­B2 inhibits cell proliferation and motility in vitro and predicts longer metastasis­free survival in breast cancer.

The tyrosine kinase receptor EphB4 and its ligand ephrin­B2 interact through cell­to­cell contacts. Upon interaction, EphB4 transmits bidirectional signals. A forward signal inside EphB4­expressing cells is believed to suppress tumor growth, while inside the ephrin­expressing cells, an oncogenic reverse signal arises. In breast cancer cells with a high EphB4 receptor expression the forward signal is low, in part due to the low expression of the ligand ephrin­B2. Therefore, we hypothesized that by re­introducing the ligand in EphB4­positive cells, tumor suppression could be induced by the stimulation of the forward signal. This question was addressed in vitro by the stable lentiviral infection of breast cancer cells with either wild­type EFNB2 or with a mutant EFNB2­5F, unable to transmit reverse signaling. Furthermore, we investigated ephrin­B and EphB4 protein expression in 216 paraffin­embedded tumors using immunohistochemistry. The in vitro results indicated that ephrin­B2 expression was associated with a lower cell proliferation, migration and motility compared with the control cells. These effects were more pronounced when the cells lacked the ability to transmit the reverse signal (B2­5F). In clinical material, ephrin­B protein expression was associated with a positive estrogen receptor (ER) status, a low HER­2 expression and was negatively associated with Nottingham histologic grade (NHG) III. Ephrin­B expression indicated a good prognosis, whereas EphB4 expression was associated with a shorter metastasis­free survival in univariate and multivariate analysis. Furthermore, the prognostic value of EFNB2 and EPHB4 was confirmed at the gene expression level in public datasets. Thus, on the whole, the findings of this study suggest that ephrin­B2 expression is associated with less proliferation and lower motility of breast cancer cells and with a longer patient survival in breast cancer.

Retrograde perfusion in isolated perfused mouse lungs-Feasibility and effects on cytokine levels and pulmonary oedema formation.

Retrograde lung vascular perfusion can appear in high-risk surgeries. The present report is the first to study long-term retrograde perfusion of isolated perfused mouse lungs (IPLs) and to use the tyrosine kinase ephB4 and its ligand ephrinB2 as potential markers for acute lung injury. Mouse lungs were subjected to anterograde or retrograde perfusion with normal-pressure ventilation (NV) or high-pressure ventilation (=overventilation, OV) for 4 hours. Outcome parameters were cytokine, ephrinB2 and ephB4 levels in perfusate samples and bronchoalveolar lavage (BAL), and the wet-to-dry ratio. Anterograde perfusion was feasible for 4 hours, while lungs receiving retrograde perfusion presented considerable collapse rates. Retrograde perfusion resulted in an increased wet-to-dry ratio when combined with high-pressure ventilation; other physiological parameters were not affected. Cytokine levels in BAL and perfusate, as well as levels of soluble ephB4 in BAL were increased in OV, while soluble ephrinB2 BAL levels were increased in retrograde perfusion. BAL levels of ephrinB2 and ephB4 were also determined in vivo, including mice ventilated for 7 hours with normal-volume ventilation (NVV) or high-volume ventilation (HVV) with increased levels of ephB4 in HVV BAL compared to NVV. Retrograde perfusion in IPL is limited as a routine method to investigate effects due to collapse for yet unclear reasons. If successful, retrograde perfusion has an influence on pulmonary oedema formation. In BAL, ephrinB2 seems to be up-regulated by flow reversal, while ephB4 is a marker for acute lung injury.

Fetal liver hematopoietic stem cell niches associate with portal vessels.

Whereas the cellular basis of the hematopoietic stem cell (HSC) niche in the bone marrow has been characterized, the nature of the fetal liver niche is not yet elucidated. We show that Nestin(+)NG2(+) pericytes associate with portal vessels, forming a niche promoting HSC expansion. Nestin(+)NG2(+) cells and HSCs scale during development with the fractal branching patterns of portal vessels, tributaries of the umbilical vein. After closure of the umbilical inlet at birth, portal vessels undergo a transition from Neuropilin-1(+)Ephrin-B2(+) artery to EphB4(+) vein phenotype, associated with a loss of periportal Nestin(+)NG2(+) cells and emigration of HSCs away from portal vessels. These data support a model in which HSCs are titrated against a periportal vascular niche with a fractal-like organization enabled by placental circulation.

Differential protein expression and oncogenic gene network link tyrosine kinase ephrin B4 receptor to aggressive gastric and gastroesophageal junction cancers.

Transmembrane tyrosine-kinase Ephrin receptors promote tumor progression and/or metastasis of several malignancies including leukemia, follicular lymphoma, glioma, malignant pleural mesothelioma, papillary thyroid carcinoma, sarcomas and ovarian, breast, bladder and non-small cell lung cancers. They also drive intestinal stem cell proliferation and positioning, control intestinal tissue boundaries and are involved in liver, pancreatic and colorectal cancers, indicating involvement in additional digestive system malignancies. We investigated the role of Ephrin-B4 receptor (EPHB4), and its ligand EFNB2, in gastric and gastroesophageal junction cancers in patient cohorts through computational, mathematical, molecular and immunohistochemical analyses. We show that EPHB4 is upregulated in preneoplastic gastroesophageal lesions and its expression further increased in gastroesophageal cancers in several independent cohorts. The closely related EPHB6 receptor, which also binds EFNB2, was downregulated in all tested cohorts, consistent with its tumor-suppressive properties in other cancers. EFNB2 expression is induced in esophageal cells by acidity, suggesting that gastroesophageal reflux disease (GERD) may constitute an early triggering event in activating EFNB2-EPHB4 signaling. Association of EPHB4 to both Barrett's esophagus and to advanced tumor stages, and its overexpression at the tumor invasion front and vascular endothelial cells intimate the notion that EPHB4 may be associated with multiple steps of gastroesophageal tumorigenesis. Analysis of oncogenomic signatures uncovered the first EPHB4-associated gene network (false discovery rate: 7 × 10(-90) ) composed of a five-transcription factor interconnected gene network that drives proliferation, angiogenesis and invasiveness. The EPHB4 oncogenomic network provides a molecular basis for its role in tumor progression and points to EPHB4 as a potential tumor aggressiveness biomarker and drug target in gastroesophageal cancers.

EphB4 cellular kinase activity assayed using an enzymatic protein interaction system.

Receptor tyrosine kinases (RTKs) are important players in various cellular processes, including proliferation, migration, metabolism, and neuronal development. EphB4 RTK is essential for the development of a functional arterial-venous network in embryonic and adult neoangiogenesis. To develop novel inhibitors of EphB4 that might have applications in severe diseases like cancer and retinopathies, assays need to be in place that resemble, in a most physiological fashion, the activation and downstream function of the kinase. In addition, such assays need to be amenable to high-throughput screening to serve efficiently the modern drug discovery processes in the pharmaceutical industry. The authors have developed an enzyme fragment complementation assay that measures the interaction of a downstream docking protein to the activated and phosphorylated full-length EphB4 kinase in cells. The assay is specific, robust, and amenable to miniaturization and high-throughput screening. It covers most steps in the activation process of EphB4, including ligand binding, autophosphorylation, and docking of a downstream interactor. This assay format can be transferred to other RTKs and adds an important cell-based kinase assay option to researchers in the field.

Critical role for the receptor tyrosine kinase EPHB4 in esophageal cancers.

Esophageal cancer incidence is increasing and has few treatment options. In studying receptor tyrosine kinases associated with esophageal cancers, we have identified EPHB4 to be robustly overexpressed in cell lines and primary tumor tissues. In total, 94 squamous cell carcinoma, 82 adenocarcinoma, 25 dysplasia, 13 Barrett esophagus, and 25 adjacent or unrelated normal esophageal tissues were evaluated by immunohistochemistry. EPHB4 expression was significantly higher in all the different histologic categories than in adjacent normal tissues. In 13 esophageal cancer cell lines, 3 of the 9 SCC cell lines and 2 of the 4 adenocarcinomas expressed very high levels of EPHB4. An increased gene copy number ranging from 4 to 20 copies was identified in a subset of the overexpressing patient samples and cell lines. We have developed a novel 4-nitroquinoline 1-oxide (4-NQO)-induced mouse model of esophageal cancer that recapitulates the EPHB4 expression in humans. A specific small-molecule inhibitor of EPHB4 decreased cell viability in a time- and dose-dependent manner in 3 of the 4 cell lines tested. The small-molecule inhibitor and an EPHB4 siRNA also decreased cell migration (12%-40% closure in treated vs. 60%-80% in untreated), with decreased phosphorylation of various tyrosyl-containing proteins, EphB4, and its downstream target p125FAK. Finally, in a xenograft tumor model, an EPHB4 inhibitor abrogated tumor growth by approximately 60% compared with untreated control. EphB4 is robustly expressed and potentially serves as a novel biomarker for targeted therapy in esophageal cancers.

Fluorine-18 radiolabeling and radiopharmacological characterization of a benzodioxolylpyrimidine-based radiotracer targeting the receptor tyrosine kinase EphB4.

Members of the Eph receptor tyrosine kinase family play essential roles in the pathogenesis of cancer and are therefore promising candidates for molecular imaging by positron emission tomography (PET), for example. In this regard, radiochemical access to novel PET radiotracers derived from potent inhibitors that target the EphB4 kinase domain and which bear a benzodioxolylpyrimidine structural motif was developed. A synthetic route was established for a new fluorine-18-containing radiotracer and for the desired precursor based on a high-affinity benzodioxolylpyrimidine receptor tyrosine kinase inhibitor lead structure. The radiotracer [(18)F]15 was obtained in 16 % radiochemical yield with a specific activity of ∼7 GBq µmol(-1) and >95 % radiochemical purity. Due to the implication of EphB4, particularly in the progression, angiogenesis, and metastasis of melanoma, EphB4-overexpressing human melanoma cells were generated and used as a novel in vitro model for radiopharmacological evaluation of the radiotracer. We demonstrate that the corresponding non-radioactive reference compound regained its functionality as an inhibitor for both EphB4 receptor tyrosine kinase and Src kinase. EphB4 was significantly inhibited at compound concentrations >1 µM. Cellular uptake studies with [(18)F]15 revealed substantial uptake in both EphB4-overexpressing and control cells. Moreover, NMRI nu/nu mice bearing both EphB4-overexpressing tumors and control tumors were used for radiopharmacological characterization by biodistribution studies ex vivo and by dynamic small-animal PET experiments in vivo. Despite the high metabolic stability of the novel radiotracer observed in vivo, no substantial binding or accumulation in EphB4-overexpressing and control tumors was observed. Nevertheless, we point out that the approach presented herein gives convenient access to novel (18)F-labeled benzodioxolylpyrimidines and is a promising strategy for the further development of novel radiotracers for imaging Eph receptor tyrosine kinases in cancer.

Relationships among differentiation degree, contrast-enhanced ultrasound and the expression of Ephb4/Ephrinb2 in primary hepatocarcinoma.

BACKGROUND/AIMS: To explore the relationships among differentiation degree, contrast-enhanced ultrasound and the expression of EphB4/EphrinB2 in primary hepatocarcinoma. METHODOLOGY: Forty one patients that were diagnosed with hepatocarcinoma by contrast-enhanced ultrasound before operation and then confirmed to have primary hepatocarcinoma by postoperative pathology were enrolled in our study. The expression of EphB4/EphrinB2 in tumor specimens were detected by immunohistochemical assay and compared with the result of contrast-enhanced ultrasound. RESULTS: Differentiation degree was related to EphrinB2 expression and contrast-enhanced ultrasound in primary hepatocarcinoma. EphrinB2 expression was significantly higher in poorly differentiated hepatocarcinoma (88.9%, 16/18) then in moderately and well differentiated hepatocarcinoma (34.8%, 8/23) (?2=12.17, p<0.001). The 'fast-in' in arterial phase displayed by contrast-enhanced ultrasound was also significantly higher in poorly differentiated hepatocarcinoma (100%) than in moderately and well differentiated hepatocarcinoma (60.9%, 14/23) (?2=9.02, p=0.003). CONCLUSIONS: EphrinB2 is an important indicator of poorly differentiated hepatocarcinoma. There is a good correlation of EphrinB2 expression with vascular perfusion pattern and morphology in arterial phase displayed by contrast-enhanced ultrasound, so contrast-enhanced ultrasound has a certain value in evaluating differentiation degree of primary hepatocarcinoma before operation.

Peptide-conjugated polymeric micellar nanoparticles for Dual SPECT and optical imaging of EphB4 receptors in prostate cancer xenografts.

EphB4, a member of the largest family of receptor tyrosine kinases, is overexpressed in numerous tumors. In this study, we developed a new class of multimodal nanoplatform for dual single photon emission computed tomography (SPECT) and near-infrared fluorescence imaging of EphB4. EphB4-binding peptide TNYL-FSPNGPIARAW (TNYL-RAW) was conjugated to polyethylene glycol-coated, core-crosslinked polymeric micelles (CCPM) dually labeled with near-infrared fluorescence fluorophores (Cy7) and a radioisotope (indium 111). In vitro, TNYL-RAW-CCPM selectively bound to EphB4-positive PC-3M prostate cancer cells, but not to EphB4-negative A549 lung cancer cells. In vivo, PC-3M tumors were clearly visualized by both SPECT and near-infrared fluorescence tomography after intravenous administration of (111)In-labeled TNYL-RAW-CCPM. In contrast, there was little signal in A549 tumors of mice injected with (111)In-labeled TNYL-RAW-CCPM or in PC-3M tumors of mice injected with (111)In-labeled CCPM. The high accumulation of (111)In-labeled TNYL-RAW-CCPM in PC-3M tumor could be significantly reduced after co-injection with an excess amount of TNYL-RAW peptide. Immunohistochemical analysis showed that fluorescence signal from the nanoparticles correlated with their radioactivity count, and co-localized with the EphB4 expressing region. (111)In-labeled TNYL-RAW-CCPM allowed visualization of cancer cells overexpressing EphB4 by both nuclear and optical techniques. The complementary information acquired with multiple imaging techniques should be advantageous in early detection of cancer.

Overexpression of ephrinB2 and EphB4 in tumor advancement of uterine endometrial cancers.

BACKGROUND: The ligand ephrinB2 and the corresponding receptor EphB4 contribute to tumor growth in various human tumors. This prompted us to study the expression and localization of ephrinB2 and EphB4 in uterine endometrial cancers to analyze the ephrinB2/EphB4 functions against clinical backgrounds. MATERIALS AND METHODS: We carried out immunohistochemistry and real-time RT-PCR to determine the histoscores and messenger RNA (mRNA) levels of ephrinB2 and EphB4, respectively, in 68 uterine endometrial cancers and 16 normal endometrium tissue samples. Patient prognoses were analyzed with a 60-month survival rate. RESULTS: The localization of ephrinB2 and EphB4 was dominantly in the cancer cells of uterine endometrial cancer of all cases given. EphrinB2 and EphB4 histoscores were highly correlated with ephrinB2 and EphB4 mRNA levels, respectively (r = 0.864 and r = 0.615, P < 0.01). Both the histoscores and mRNA levels of ephrinB2 and EphB4 significantly increased with clinical stages (I < II < III, P < 0.01), dedifferentiation (G(1) < G(2) < G(3), P < 0.01) and myometrial invasion (A < B < C, P < 0.01 for ephrinB2 and P < 0.05 for EphB4) in uterine endometrial cancers. The 60-month survival rates of the 34 patients with high ephrinB2 and EphB4 expression were poor (59% and 62% respectively), while for the other 34 patients with low ephrinB2 and EphB4 expression, they were significantly higher (85% and 82%, respectively). CONCLUSIONS: EphrinB2 and EphB4 were overexpressed during the tumor advancement as dedifferentiation and myometrial invasion. Therefore, ephrinB2/EphB4 might work on tumor advancement and may be recognized as a novel prognostic indicator for uterine endometrial cancers.

Expression of ephrin in retinal neovascularization and iris rubeosis.

We investigated expression of ephrin-B2 and Eph-B4 in the retinal tissues of six primate eyes with neovascularization and iris rubeosis secondary to laser-induced central retinal vein occlusion and in tissue from 10 human eyes with proliferative diabetic retinopathy. Two primate eyes with rubeosis and retinal neovascularization were enucleated 1, 2 and 4 weeks after the creation of central retinal vein occlusion. Antibodies were localized using the avidin-biotin reaction. In the primate eyes, ephrin-B2 was negative at I week and positive at 2 and 4 weeks in the rubeotic tissue, but was positive only at 2 weeks in the retinal neovascular membrane. Eph-B4 was negative in all the primate eye specimens. In the human tissue, ephrin-B2 was detected in two of the five eyes with rubeosis and three of the five eyes with retinal neovascularization. These data suggest that ephrin-B2 is a key regulator of neovascularization.

The association between elevated EphB4 expression, smoking status, and advanced-stage disease in patients with head and neck squamous cell carcinoma.

OBJECTIVE: To examine the expression of EphB4 in tumor tissue, surrounding normal tissue, and metastatic lymph node in patients with head and neck squamous cell carcinoma (HNSCC) and to evaluate its association with disease stage and smoking. DESIGN: A retrospective study. SETTING: University of Southern California-University Hospital, University of Southern California and Los Angeles County Medical Center, and Department of Otolaryngology-Head and Neck Surgery, University of Southern California, Los Angeles. PATIENTS: Forty-eight patients with different stages of HNSCC (I-IV) were enrolled into this study. Staging was based on the staging system of the American Joint Committee on Cancer. MAIN OUTCOME MEASURES: EphB4 expression in tumor tissue, surrounding normal tissue, and metastatic lymph node was evaluated by immunohistochemical analysis, Western blot, and real-time polymerase chain reaction. EphB4 expression was then compared between patients based on disease stage and smoking status. RESULTS: EphB4 expression was detected in all tumor specimens and metastatic lymph nodes of patients with HNSCC, but expression levels were higher in the metastatic lymph nodes. There was a statistically significantly higher mean EphB4 protein expression and EphB4 gene amplification in patients with advanced disease (stage III or IV) vs patients with initial disease (stage I or II) and in smokers vs nonsmokers. CONCLUSIONS: Overexpression of EphB4 is associated with advanced stages of HNSCC as well as with patients who smoke. These data are the first to demonstrate the association of EphB4 with advanced stages of disease and smoking in HNSCC and hence provide a strong rationale for targeting EphB4 for HNSCC therapies.