Decreased tumorigenic potential of EphA2-overexpressing breast cancer cells following treatment with adenoviral vectors that express EphrinA1

The multifaceted roles of Eph/ephrin signaling in breast cancer

Eph receptors and their membrane-bound ligands are intimately involved in the control of morphogenic processes during embryonic development and adult tissue homeostasis. By their ability to orchestrate cell migration, pattern formation and tissue integrity they are also prone to be involved in carcinogenic growth. In this review we concentrate on their involvement in the normal and carcinogenic development of the breast. In this context we summarize their multi-faceted functions as tumor suppressors, tumor promoters, angiogenic inducers and regulators of stem cell homeostasis.

EphB3 suppresses non-small-cell lung cancer metastasis via a PP2A/RACK1/Akt signalling complex

Eph receptors are implicated in regulating the malignant progression of cancer. Here we find that despite overexpression of EphB3 in human non-small-cell lung cancer, as reported previously, the expression of its cognate ligands, either ephrin-B1 or ephrin-B2, is significantly downregulated, leading to reduced tyrosine phosphorylation of EphB3. Forced activation of EphB3 kinase in EphB3-overexpressing non-small-cell lung cancer cells inhibits cell migratory capability in vitro as well as metastatic seeding in vivo. Furthermore, we identify a novel EphB3-binding protein, the receptor for activated C-kinase 1, which mediates the assembly of a ternary signal complex comprising protein phosphatase 2A, Akt and itself in response to EphB3 activation, leading to reduced Akt phosphorylation and subsequent inhibition of cell migration. Our study reveals a novel tumour-suppressive signalling pathway associated with kinase-activated EphB3 in non-small-cell lung cancer, and provides a potential therapeutic strategy by activating EphB3 signalling, thus inhibiting tumour metastasis.

EphB2 receptor controls proliferation/migration dichotomy of glioblastoma by interacting with focal adhesion kinase

Glioblastoma multiforme (GBM) are the most frequent and aggressive primary brain tumors in adults. Uncontrolled proliferation and abnormal cell migration are two prominent spatially and temporally disassociated characteristics of GBMs. In this study, we investigated the role of the receptor tyrosine kinase EphB2 in controlling the proliferation/migration dichotomy of GBM. We studied EphB2 gain-of-function and loss-of function in glioblastoma-derived stem-like neurospheres (GBM-SCs), whose in vivo growth pattern closely replicates human GBM. EphB2 expression stimulated GBM neurosphere cell migration and invasion, and inhibited neurosphere cell proliferation in vitro. In parallel, EphB2 silencing increased tumor cell proliferation and decreased tumor cell migration. EphB2 was found to increase tumor cell invasion in vivo using an internally controlled dual-fluorescent xenograft model. Xenografts derived from EphB2 overexpressing GBM neurospheres also showed decreased cellular proliferation. The non-receptor tyrosine kinase focal adhesion kinase (FAK) was found to be co-associated with and highly activated by EphB2 expression and FAK activation facilitated focal adhesion formation, cytoskeleton structure change and cell migration in EphB2-expression GBM neurosphere cells. Taken together, our findings indicate that EphB2 has pro-invasive and anti-proliferative actions in GBM stem-like neurospheres mediated, in part, by interactions between EphB2 receptors and FAK. These novel findings suggest that tumor cell invasion can be therapeutically targeted by inhibiting EphB2 signaling and that optimal anti-tumor responses to EphB2 targeting may require the concurrent use of anti-proliferative agents.

Evidence for a dual function of EphB4 as tumor promoter and suppressor regulated by the absence or presence of the ephrin-B2 ligand

Overexpression of the receptor tyrosine kinase EphB4 is common in epithelial cancers and linked to tumor progression by promoting angiogenesis, increasing survival and facilitating invasion and migration. However, other studies have reported loss of EphB4 suggesting a tumor suppressor function in some cancers. These opposing roles may be regulated by (i) the presence of the primary ligand ephrin-B2 that regulates pathways involved in tumor suppression or (ii) the absence of ephrin-B2 that allows EphB4 signaling via ligand-independent pathways that contribute to tumor promotion. To explore this theory, EphB4 was overexpressed in the prostate cancer cell line 22Rv1 and the mammary epithelial cell line MCF-10A. Overexpressed EphB4 localized to lipid-rich regions of the plasma membrane and confirmed to be ligand-responsive as demonstrated by increased phosphorylation of ERK1/2 and internalization. EphB4 overexpressing cells demonstrated enhanced anchorage-independent growth, migration and invasion, all characteristics associated with an aggressive phenotype, and therefore supporting the hypothesis that overexpressed EphB4 facilitates tumor promotion. Importantly, these effects were reversed in the presence of ephrin-B2 which led to a reduction in EphB4 protein levels, demonstrating that ligand-dependent signaling is tumor suppressive. Furthermore, extended ligand stimulation caused a significant decrease in proliferation that correlated with a rise in caspase-3/7 and -8 activities. Together, these results demonstrate that overexpression of EphB4 confers a transformed phenotype in the case of MCF-10A cells and an increased metastatic phenotype in the case of 22Rv1 cancer cells and that both phenotypes can be restrained by stimulation with ephrin-B2, in part by reducing EphB4 levels.

Navigating breast cancer: axon guidance molecules as breast cancer tumor suppressors and oncogenes

Slit, Netrin, Ephrin, and Semaphorin's roles in development have expanded greatly in the past decade from their original characterization as axon guidance molecules (AGMs) to include roles as regulators of tissue morphogenesis and development in diverse organs. In the mammary gland, AGMs are important for maintaining normal cell proliferation and adhesion during development. The frequent dysregulation of AGM expression during tumorigenesis and tumor progression suggests that AGMs also play a crucial role as tumor suppressors and oncogenes in breast cancer. Moreover, these findings suggest that AGMs may be excellent targets for new breast cancer prognostic tests and more effective therapeutic strategies.

EphrinA1 inhibits malignant mesothelioma tumor growth via let-7 microRNA-mediated repression of the RAS oncogene

EphrinA1 binding with receptor EphA2 suppresses malignant mesothelioma (MM) growth. The mechanisms whereby EphrinA1 attenuates the MM cell (MMC) growth are not clear. In this study, we report that the activation of MMCs with EphrinA1 leads to an induction of let-7 microRNA (miRNA) expression, repression of RAS proto-oncogene and the attenuation of MM tumor growth. The expression of miRNAs was determined by reverse transcription-quantitative polymerase chain reaction and in situ hybridization. RAS expression was determined by q-PCR, western blotting and immunofluorescence. MMC proliferation and tumor growth were determined by WST-1 and Matrigel assay, respectively. EphrinA1 activation induced several fold increases in let-7a1, let-7a3, let-7f1 and let-7f2 miRNA expression in MMCs. In contrast, EphrinA1 activation significantly downregulated H-RAS, K-RAS and N-RAS expression and inhibited MMC proliferation and tumor growth. In MMCs transfected with 2'-O-methyl antisense oligonucleotides to let-7 miRNA, EphrinA1 activation failed to inhibit the proliferative response and tumor growth. In mismatch antisense oligonucleotide-treated MMCs, the proliferation and tumor growth were comparable to untreated proliferating cells. Furthermore, the transfection of MMCs with let-7a miRNA precursor inhibited RAS expression and attenuated MMC tumor growth. Our data revealed that EphrinA1 signaling induces let-7 miRNA expression and attenuates MM tumor growth by targeting RAS proto-oncogene in MMCs.

Emerging strategies for EphA2 receptor targeting for cancer therapeutics

IMPORTANCE OF THE FIELD

High mortality rates with cancers warrant further development of earlier diagnostics and better treatment strategies. Membrane-bound erythropoietin-producing hepatocellular receptor tyrosine kinase class A2 (EphA2) is overexpressed in breast, prostate, urinary bladder, skin, lung, ovary and brain cancers.

AREAS COVERED IN THIS REVIEW

EphA2 overexpression in cancers, its signaling mechanisms and strategies to target its deregulation.

WHAT THE READER WILL GAIN

High EphA2 expression in cancer cells is correlated with a poor prognosis associated with recurrence due to enhanced metastasis. Interaction of the EphA2 receptor with its ligand (e.g., ephrinA1) triggers events that are deregulated and implicated in carcinogenesis. EphrinA1-independent oncogenic activity and ephrinA1-dependent tumor suppressor roles for EphA2 are described. Molecular interactions of EphA2 with signaling proteins are associated with the modulation of cytoskeleton dynamics, cell adhesion, proliferation, differentiation and metastasis. The deregulated signaling by EphA2 and its involvement in oncogenesis provide multiple avenues for the rational design of intervention approaches.

TAKE HOME MESSAGE

EphA2 has been tested as a drug target using multiple approaches such as agonist antibodies, RNA interference, immunotherapy, virus vector-mediated gene transfer, small-molecule inhibitors and nanoparticles. With over a decade of research, encouraging results with targeting of EphA2 expression in various pre-clinical cancer models necessitate further studies.

Soluble ephrin a1 is necessary for the growth of HeLa and SK-BR3 cells

Background

Ephrin A1 (EFNA1) is a member of the A-type ephrin family of cell surface proteins that function as ligands for the A-type Eph receptor tyrosine kinase family. In malignancy, the precise role of EFNA1 and its preferred receptor, EPHA2, is controversial. Several studies have found that EFNA1 may suppress EPHA2-mediated oncogenesis, or enhance it, depending on cell type and context. However, little is known about the conditions that influence whether EFNA1 promotes or suppresses tumorigenicity. EFNA1 exists in a soluble form as well as a glycophosphatidylinositol (GPI) membrane attached form. We investigated whether the contradictory roles of EFNA1 in malignancy might in part be related to the existence of both soluble and membrane attached forms of EFNA1 and potential differences in the manner in which they interact with EPHA2.

Results

Using a RNAi strategy to reduce the expression of endogenous EFNA1 and EPHA2, we found that both EFNA1 and EPHA2 are required for growth of HeLa and SK-BR3 cells. The growth defects could be rescued by conditioned media from cells overexpressing soluble EFNA1. Interestingly, we found that overexpression of the membrane attached form of EFNA1 suppresses growth of HeLa cells in 3D but not 2D. Knockdown of endogenous EFNA1, or overexpression of full-length EFNA1, resulted in relocalization of EPHA2 from the cell surface to sites of cell-cell contact. Overexpression of soluble EFNA1 however resulted in more EPHA2 distributed on the cell surface, away from cell-cell contacts, and promoted the growth of HeLa cells.

Conclusions

We conclude that soluble EFNA1 is necessary for the transformation of HeLa and SK-BR3 cells and participates in the relocalization of EPHA2 away from sites of cell-cell contact during transformation.

Structure-activity relationship analysis of peptides targeting the EphA2 receptor

The EphA2 receptor tyrosine kinase has emerged as a promising new therapeutic target in cancer because of its high level of expression in tumors. EphA2-specific antibodies have been used to deliver drugs and toxins to tumor cells, leading to inhibition of tumor growth and metastatic dissemination. We previously identified two related peptides, YSA and SWL, that selectively bind to the ligand-binding domain of EphA2 but not other Eph receptors and could therefore be useful as selective targeting agents. Here we characterize the two peptides and a series of derivatives. On the basis of systematic amino acid replacements, only five YSA residues appear to be critical for high-affinity receptor binding. Furthermore, a peptide comprising only the first five residues of YSA retains selectivity for EphA2. Similar to ephrin-A1, the physiological ligand for EphA2, both YSA and SWL activate EphA2 and inhibit downstream oncogenic signaling pathways in PC3 cancer cells. The two peptides and derivatives are quite stable in conditioned cell culture medium and show promise for delivering drugs and imaging agents to EphA2-expressing tumors.

Up-regulation of EphA2 and down-regulation of EphrinA1 are associated with the aggressive phenotype and poor prognosis of malignant glioma

Malignant gliomas display over-expression of the receptor tyrosine kinase EphA2. However, expression levels of the EphA2 ligand, EphrinA1, have not been fully elucidated. Seventy-eight patients with primary gliomas were included in this study who underwent surgical resection, radiation, and chemotherapy. The expression of EphA2 and EphrinA1 in tumors was assessed by immunohistochemistry and was statistically analyzed in combination with the follow-up data of patients. EphA2 was highly expressed in most malignant gliomas, but EphrinA1 was expressed at low levels in these tumors. The increased EphA2 expression is associated with higher-grade histology and poor patient prognosis. Contrary to this, the increased EphrinA1 expression is associated with lower-grade histology, but not associated with poor patient prognosis. Moreover, patients with tumors positive for EphA2 and negative for EphrinA1 had significantly shorter overall and progression-free survival than patients with tumors positive for both EphA2 and EphrinA1, negative for both EphA2 and EphrinA1, or negative for EphA2 and positive for EphrinA1. RNAi-mediated suppression of endogenous EphA2 in human glioblastoma multiforme cells resulted in increased EphrinA1 levels, as well as decreased cell viability, anchorage independence and in vitro invasion, and increased apoptosis. Furthermore, suppression of EphA2 resulted in delayed tumor growth in mice xenografts. Together, these data indicate that up-regulation of EphA2 and down-regulation of Ephrina1 may correlate with poor prognosis for patients with high-grade glioma. EphA2 suppression partially reversed the aggressive phenotypes of malignant gliomas, possibly through up-regulating EphrinA1 expression, which may help explain how EphA2 modulates the malignant progression of gliomas.

Evaluation of cross-reactive cell-mediated immune responses among human, bovine and porcine adenoviruses

The absence of preexisting immunity against porcine adenovirus (Ad) serotype 3 (PAd3) and bovine Ad serotype 3 (BAd3) in humans makes them attractive alternatives to human Ad serotype 5 (HAd5) vectors. To determine whether there is significant cross-reactivity among HAd5, BAd3 and PAd3 at the level of cell-mediated immune responses, BALB/c mice were inoculated intraperitoneally with wild-type (WT) or replication-defective (RD) HAd5, BAd3 or PAd3. After 35 days of the first inoculation, cross-reactive CD8+ cytotoxic T cells, as well as CD4+ Th1- and Th2-helper T cells, in the spleen were analyzed by enzyme-linked-immunospot, flow cytometry and cytotoxic T lymphocyte assays. Virus-neutralization assays were used to evaluate humoral cross-reactivity. CD8+ or CD4+ T cells primed with WT or RD HAd5, PAd3 or BAd3 showed significant (P<0.005) reactivity with homologous Ad antigens, whereas only minimal cross-reactivity was observed on stimulation with heterologous Ad antigens. Ad-neutralizing antibodies were found to be homologous Ad specific. Overall, these results suggest that there is no significant immunological cross-reactivity among HAd5, BAd3 and PAd3, thereby supporting the rationale for the use of BAd3 and PAd3 as alternative HAd vectors to circumvent anti-HAd immunity in humans.

Eph receptors and ephrins in cancer: bidirectional signalling and beyond

The Eph receptor tyrosine kinases and their ephrin ligands have intriguing expression patterns in cancer cells and tumour blood vessels, which suggest important roles for their bidirectional signals in many aspects of cancer development and progression. Eph gene mutations probably also contribute to cancer pathogenesis. Eph receptors and ephrins have been shown to affect the growth, migration and invasion of cancer cells in culture as well as tumour growth, invasiveness, angiogenesis and metastasis in vivo. However, Eph signalling activities in cancer seem to be complex, and are characterized by puzzling dichotomies. Nevertheless, the Eph receptors are promising new therapeutic targets in cancer.

EphA2 in the early pathogenesis and progression of non-small cell lung cancer

Overexpression of the receptor tyrosine kinase EphA2 occurs in non-small cell lung cancer (NSCLC) and a number of other human cancers. This overexpression correlates with a poor prognosis, smoking, and the presence of Kirsten rat sarcoma (K-Ras) mutations in NSCLC. In other cancers, EphA2 has been implicated in migration and metastasis. To determine if EphA2 can promote NSCLC progression, we examined the relationship of EphA2 with proliferation and migration in cell lines and with metastases in patient tumors. We also examined potential mechanisms involving AKT, Src, focal adhesion kinase, Rho guanosine triphosphatases (GTPase), and extracellular signal-regulated kinase (ERK)-1/2. Knockdown of EphA2 in NSCLC cell lines decreased proliferation (colony size) by 20% to 70% in four of five cell lines (P < 0. 04) and cell migration by 7% to 75% in five of six cell lines (P < 0. 03). ERK1/2 activation correlated with effects on proliferation, and inhibition of ERK1/2 activation also suppressed proliferation. In accordance with the in vitro data, high tumor expression of EphA2 was an independent prognostic factor in time to recurrence (P = 0.057) and time to metastases (P = 0.046) of NSCLC patients. We also examined EphA2 expression in the putative premalignant lung lesion, atypical adenomatous hyperplasia, and the noninvasive bronchioloalveolar component of adenocarcinoma because K-Ras mutations occur in atypical adenomatous hyperplasia and are common in lung adenocarcinomas. Both preinvasive lesion types expressed EphA2, showing its expression in the early pathogenesis of lung adenocarcinoma. Our data suggest that EphA2 may be a promising target for treating and preventing NSCLC.

Antibody-dependent cell-mediated cytotoxicity effector-enhanced EphA2 agonist monoclonal antibody demonstrates potent activity against human tumors

EphA2 is a receptor tyrosine kinase that has been shown to be overexpressed in a variety of human tumor types. Previous studies demonstrated that agonist monoclonal antibodies targeting EphA2 induced the internalization and degradation of the receptor, thereby abolishing its oncogenic effects. In this study, the in vitro and in vivo antibody-dependent cell-mediated cytotoxicity (ADCC) activity of EphA2 effector-enhanced agonist monoclonal antibodies was evaluated. With tumor cell lines and healthy human peripheral blood monocytes, the EphA2 antibodies demonstrated approximately 80% tumor cell killing. In a dose-dependent manner, natural killer (NK) cells were required for the in vitro ADCC activity and became activated as demonstrated by the induction of cell surface expression of CD107a. To assess the role of NK cells on antitumor efficacy in vivo, the EphA2 antibodies were evaluated in xenograft models in severe compromised immunodeficient (SCID) mice (which have functional NK cells and monocytes) and SCID nonobese diabetic (NOD) mice (which largely lack functional NK cells and monocytes). Dosing of EphA2 antibody in the SCID murine tumor model resulted in a 6.2-fold reduction in tumor volume, whereas the SCID/nonobese diabetic model showed a 1.6-fold reduction over the isotype controls. Together, these results demonstrate that the anti-EphA2 monoclonal antibodies may function through at least two mechanisms of action: EphA2 receptor activation and ADCC-mediated activity. These novel EphA2 monoclonal antibodies provide additional means by which host effector mechanisms can be activated for selective destruction of EphA2-expressing tumor cells.

Heat shock protein 90 inhibitor 17-dimethylaminoethylamino-17-demethoxygeldanamycin enhances EphA2+ tumor cell recognition by specific CD8+ T cells

EphA2, a member of the receptor tyrosine kinase family, is commonly expressed by a broad range of cancer types, where its level of (over)expression correlates with poor clinical outcome. Because tumor cell expressed EphA2 is a nonmutated "self" protein, specific CD8(+) T cells are subject to self-tolerance mechanisms and typically exhibit only moderate-to-low functional avidity, rendering them marginally competent to recognize EphA2(+) tumor cells in vitro or in vivo. We have recently reported that the ability of specific CD8(+) T cells to recognize EphA2(+) tumor cells can be augmented after the cancer cells are pretreated with EphA2 agonists that promote proteasomal degradation and up-regulated expression of EphA2/class I complexes on the tumor cell membrane. In the current study, we show that treatment of EphA2(+) tumor cells with the irreversible heat shock protein 90 inhibitor, 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG), similarly enhances their recognition by EphA2-specific CD8(+) T-cell lines and clones in vitro via a mechanism that is dependent on proteasome and transporter-associated protein function as well as the retrotranslocation of EphA2 into the tumor cytoplasm. When 17-DMAG and agonist anti-EphA2 monoclonal antibodies are coapplied, T-cell recognition of tumor cells is further increased over that observed for either agent alone. These studies suggest that EphA2 represents a novel heat shock protein 90 client protein and that the treatment of cancer patients with 17-DMAG-based "pulse" therapy may improve the antitumor efficacy of CD8(+) T effector cells reactive against EphA2-derived epitopes.

Adenoviral vector-based strategies for cancer therapy

Definitive treatment of cancer has eluded scientists for decades. Current therapeutic modalities like surgery, chemotherapy, radiotherapy and receptor-targeted antibodies have varied degree of success and generally have moderate to severe side effects. Gene therapy is one of the novel and promising approaches for therapeutic intervention of cancer. Viral vectors in general and adenoviral (Ad) vectors in particular are efficient natural gene delivery systems and are one of the obvious choices for cancer gene therapy. Clinical and preclinical findings with a wide variety of approaches like tumor suppressor and suicide gene therapy, oncolysis, immunotherapy, anti-angiogenesis and RNA interference using Ad vectors have been quite promising, but there are still many hurdles to overcome. Shortcomings like increased immunogenicity, prevalence of preexisting anti-Ad immunity in human population and lack of specific targeting limit the clinical usefulness of Ad vectors. In recent years, extensive research efforts have been made to overcome these limitations through a variety of approaches including the use of conditionally-replicating Ad and specific targeting of tumor cells. In this review, we discuss the potential strengths and limitations of Ad vectors for cancer therapy.

Loss of EphA2 receptor tyrosine kinase reduces ApcMin/+ tumorigenesis

The Eph receptor A2 (EphA2) is overexpressed in a range of human epithelial cancers, a phenotype that is associated with cancer cell proliferation, progression and angiogenesis. Mouse models of mammary neoplasia have confirmed the role of EphA2 as mice carrying a knockout allele of EphA2 were resistant to breast cancer, a phenotype that was associated with interactions between EphA2 and ErbB2. We investigated in vivo the role of EphA2 in GI cancer. To determine whether EphA2 influences intestinal tumorigenesis, we used qRT-PCR to examine the mRNA expression levels of EphA2 in tumors from the small intestine and colon of Apc(Min/+) mice. We found that EphA2 was significantly up-regulated in tumors from both regions when compared with normal control tissues. We then evaluated the spatial expression patterns of EphA2 protein using immunohistochemistry in both the small intestine and colon and found that in normal tissues EphA2 was robustly expressed in highly differentiated cells, such as cells of the villi, but that EphA2 expression was largely absent from the stem cell niche and proliferative zones of intestinal crypts. In contrast, in tumors EphA2 was broadly expressed. Finally, we created a strain of Apc(Min/+) mice carrying a genetic knockout of the EphA2 gene. These mice developed significantly fewer and smaller tumors in both the small and large intestine. Overall, our results indicate that EphA2 plays an oncogenic role in the mammalian intestine suggesting that strategies to target EphA2 activity may offer new therapeutic modalities for colorectal cancer.

EphA2 engages Git1 to suppress Arf6 activity modulating epithelial cell-cell contacts

ADP-ribosylation factor (Arf) 6 activity is crucially involved in the regulation of E-cadherin-based cell-cell adhesions. Erythropoietin-producing hepatocellular carcinoma (Eph)-family receptors recognize ligands, namely, ephrins, anchored to the membrane of apposing cells, and they mediate cell-cell contact-dependent events. Here, we found that Arf6 activity is down-regulated in Madin-Darby canine kidney cells, which is dependent on cell density and calcium ion concentration, and we provide evidence of a novel signaling pathway by which ligand-activated EphA2 suppresses Arf6 activity. This EphA2-mediated suppression of Arf6 activity was linked to the induction of cell compaction and polarization, but it was independent of the down-regulation of extracellular signal-regulated kinase 1/2 kinase activity. We show that G protein-coupled receptor kinase-interacting protein (Git) 1 and noncatalytic region of tyrosine kinase (Nck) 1 are involved in this pathway, in which ligand-activated EphA2, via its phosphorylated Tyr594, binds to the Src homology 2 domain of Nck1, and then via its Src homology 3 domain binds to the synaptic localizing domain of Git1 to suppress Arf6 activity. We propose a positive feedback loop in which E-cadherin-based cell-cell contacts enhance EphA-ephrinA signaling, which in turn down-regulates Arf6 activity to enhance E-cadherin-based cell-cell contacts as well as the apical-basal polarization of epithelial cells.

The EphA2 receptor and ephrinA1 ligand in solid tumors: function and therapeutic targeting

The Eph receptor tyrosine kinases and ephrin ligands have been studied extensively for their roles in developmental processes. In recent years, Eph receptors and ephrins have been found to be integral players in cancer formation and progression. Among these are EphA2 and ephrinA1, which are involved in the development and maintenance of many different types of solid tumors. The function of EphA2 and ephrinA1 in tumorigenesis and tumor progression is complex and seems to be dependent on cell type and microenvironment. These variables affect the expression of the EphA2 and ephrinA1 proteins, the pathways through which they induce signaling, and the functional consequences of that signaling on the behavior of tumor cells and tumor-associated cells. This review will specifically focus on the roles that EphA2 and ephrinA1 play in the different cell types that contribute to the malignancy of solid tumors, with emphasis on the opportunities for therapeutic targeting.

Soluble monomeric EphrinA1 is released from tumor cells and is a functional ligand for the EphA2 receptor

The ephrinA1 ligand exerts antioncogenic effects in tumor cells through activation and downregulation of the EphA2 receptor and has been described as a membrane-anchored protein requiring clustering for function. However, while investigating the ephrinA1/EphA2 system in the pathobiology of glioblastoma multiforme (GBM), we uncovered that ephrinA1 is released from GBM and breast adenocarcinoma cells as a soluble, monomeric protein and is a functional form of the ligand in this state. Conditioned media containing a soluble monomer of ephrinA1 caused EphA2 internalization and downregulation, dramatic alteration of cell morphology and suppression of the Ras-MAPK pathway. Moreover, soluble monomeric ephrinA1 was functional in a physiological context, eliciting collapse of embryonic neuronal growth cones. We also found that ephrinA1 is cleaved from the plasma membrane of GBM cells, an event which involves the action of a metalloprotease. Thus, the ephrinA1 ligand can, indeed, function as a soluble monomer and may act in a paracrine manner on the EphA2 receptor without the need for juxtacrine interactions. These findings have important implications for further deciphering the function of these proteins in pathology and physiology, as well as for the design of ephrinA1-based EphA2-targeted antitumor therapeutics.

Bovine adenoviral vector-based H5N1 influenza vaccine overcomes exceptionally high levels of pre-existing immunity against human adenovirus

Because of the high prevalence of adenovirus (Ad) infections in humans, it is believed that pre-existing Ad-neutralizing antibodies (vector immunity) may negatively impact the immune response to vaccine antigens when delivered by human Ad (HAd) vectors. In order to evaluate whether bovine Ad subtype 3 (BAd3), a non-HAd vector, can effectively elude high levels of pre-existing vector immunity, naïve and HAd serotype 5 (HAd)-primed mice were immunized with BAd-H5HA [BAd3 vector expressing the hemagglutinin (HA) gene from H5N1 influenza virus]. Even in the presence of very high levels of HAd-specific neutralizing antibody, no significant reductions in HA-specific humoral and cell-mediated immune (CMI) responses were observed in HAd-primed mice immunized with BAd-H5HA. In naïve mice immunized with HAd-H5HA (HAd5 vector expressing H5N1 HA) and boosted with BAd-H5HA, the humoral responses elicited were significantly higher (P < 0.01) than with either HAd-H5HA or BAd-H5HA alone, while the CMI responses were comparable in the groups. This finding underlines the importance of a heterologous prime-boost approach for achieving an enhanced immune response. The immunization of naïve or HAd-primed mice with BAd-H5HA bestowed full protection from morbidity and mortality following a potentially lethal challenge with A/Hong Kong/483/97. These results demonstrate the importance of BAd vectors as an alternate or supplement to HAd vectors for influenza pandemic preparedness.

The receptor tyrosine kinase EphA2 promotes mammary adenocarcinoma tumorigenesis and metastatic progression in mice by amplifying ErbB2 signaling

Overexpression of the receptor tyrosine kinase EPH receptor A2 (EphA2) is commonly observed in aggressive breast cancer and correlates with a poor prognosis. However, while EphA2 has been reported to enhance tumorigenesis, proliferation, and MAPK activation in several model systems, other studies suggest that EphA2 activation diminishes these processes and inhibits the activity of MAPK upon ligand stimulation. In this study, we eliminated EphA2 expression in 2 transgenic mouse models of mammary carcinoma. EphA2 deficiency impaired tumor initiation and metastatic progression in mice overexpressing ErbB2 (also known as Neu) in the mammary epithelium (MMTV-Neu mice), but not in mice overexpressing the polyomavirus middle T antigen in mammary epithelium (MMTV-PyV-mT mice). Histologic and ex vivo analyses of MMTV-Neu mouse mammary epithelium indicated that EphA2 enhanced tumor proliferation and motility. Biochemical analyses revealed that EphA2 formed a complex with ErbB2 in human and murine breast carcinoma cells, resulting in enhanced activation of Ras-MAPK signaling and RhoA GTPase. Additionally, MMTV-Neu, but not MMTV-PyV-mT, tumors were sensitive to therapeutic inhibition of EphA2. These data suggest that EphA2 cooperates with ErbB2 to promote tumor progression in mice and may provide a novel therapeutic target for ErbB2-dependent tumors in humans. Moreover, EphA2 function in tumor progression appeared to depend on oncogene context, an important consideration for the application of therapies targeting EphA2.

A novel, potent, and specific ephrinA1-based cytotoxin against EphA2 receptor expressing tumor cells

We have previously shown that the EphA2 receptor tyrosine kinase is overexpressed in glioblastoma multiforme (GBM) and represents a novel, attractive therapeutic target for the treatment of brain tumors. Here, we have developed an EphA2-targeted agent, ephrinA1-PE38QQR, a novel cytotoxin composed of ephrinA1, a ligand for EphA2, and PE38QQR, a mutated form of Pseudomonas aeruginosa exotoxin A. EphrinA1-PE38QQR showed potent and dose-dependent killing of GBM cells overexpressing the EphA2 receptor in cell viability and clonogenic survival assays, with an average IC(50) of approximately 10(-11) mol/L. The conjugate was also highly effective in killing breast and prostate cancer cells overexpressing EphA2. The cytotoxic effect of ephrinA1-PE38QQR was specific, as it was neutralized by an excess of EphA2 ligands. Moreover, normal human endothelial cells and breast cancer cells that do not overexpress EphA2, as well as GBM cells that have down-regulated EphA2, were not susceptible to the cytotoxin. EphrinA1-PE38QQR-mediated cytotoxicity induced caspase-dependent apoptosis, which was, however, not responsible for cell death in response to the conjugate. In addition, the conjugate elicited no changes in the activity of survival pathways such as phosphoinositide 3-kinase, measured by AKT phosphorylation. This is the first attempt to create a cytotoxic therapy using any of the ephrin ligands of either class (A or B) conjugated to a bacterial toxin. EphrinA1-PE38QQR is very potent and specific, produces cell death that is caspase independent, and forms the basis for the further development of clinically applicable EphA2-targeted cytotoxins.

Interleukin-13 receptor alpha 2, EphA2, and Fos-related antigen 1 as molecular denominators of high-grade astrocytomas and specific targets for combinatorial therapy

PURPOSE

We investigated the expression of interleukin-13 receptor alpha2 (IL-13R alpha 2), EphA2, and Fos-related antigen 1 (Fra-1) in astrocytomas and normal brain. We sought to document whether the expression of the three factors changed with progression to higher grade malignancy and whether two or three targets in combination might be sufficient to target all patients with high-grade astrocytomas.

EXPERIMENTAL DESIGN

Immunohistochemistry was done for IL-13R alpha 2, EphA2, and Fra-1 using human brain tumor tissue microarrays containing 30 specimens of WHO grades II and III astrocytomas, 46 glioblastoma multiformes (GBM), and 9 normal brain samples. Sections were scored based on frequency and intensity of expression. Western blotting was done for all three markers using GBM tumor specimens and xenograft cell lines. Two cytotoxins, IL-13.E13K.PE38QQR and ephrinA1-PE38QQR, which target IL-13R alpha 2 or EphA2, respectively, were tested for cytotoxicity against human GBM primary explant cells and established cells.

RESULTS

Expression of all three proteins was significantly higher in GBM compared with normal brain, low-grade, and anaplastic astrocytomas. Greater than 95% of GBM overexpressed at least two of the three markers. Importantly, every GBM overexpressed at least one marker. Human GBM primary explant cells and cell lines were potently killed by IL-13.E13K.PE38QQR and ephrinA1-PE38QQR, in accordance with their level of expression of IL-13R alpha 2 and EphA2, respectively.

CONCLUSIONS

IL-13R alpha 2, EphA2, and Fra-1 are attractive therapeutic targets representing molecular denominators of high-grade astrocytomas. One hundred percent of GBM tumors overexpress at least one of these proteins, providing the basis for rational combinatorial targeted therapies/diagnostics suitable for all patients with this disease.

Receptor EphA2 activation with ephrinA1 suppresses growth of malignant mesothelioma (MM)

The objective of this study was to understand the possible mechanisms of activation of receptor EphA2 by its ligand ephrinA1 in malignant mesothelioma cell (MMC) growth. Activation of receptor EphA2 by its ligand ephrinA1 triggered the phosphorylation of EphA2. Ligand activation of EphA2 also induced phosphorylation of ERK1/2 and significantly decreased MMC proliferation. Ligand activated and ephrinA1 vector (pcDNA/EFNA1) transfected MMC demonstrated decreased clonal growth in 3-D matrigels when compared to resting MMC. These studies suggest that EphA2 activation by its ligand ephrinA1 transmits intracellular signals from cell membrane to nucleus via ERK1/2 signaling cascade and inhibits MM growth.

Quantitative radioimmunoPET imaging of EphA2 in tumor-bearing mice

PURPOSE

EphA2 receptor tyrosine kinase is significantly overexpressed in a wide variety of cancer types. High EphA2 expression has been correlated with increased metastatic potential and poor patient survival. Although many recent reports have focused on blocking the EphA2 signaling pathway in cancer, the in vivo imaging of EphA2 has not yet been investigated.

METHODS

We labeled 1C1, a humanized monoclonal antibody against both human and murine EphA2, with (64)Cu through the chelating agent 1,4,7,10-tetraazacyclododecane N,N',N'',N'''-tetraacetic acid (DOTA) and carried out positron emission tomography (PET) imaging of eight tumor models with different EphA2 expression levels. Western blotting of tumor tissue lysate was performed to correlate the EphA2 expression level with (64)Cu-DOTA-1C1 uptake in the tumors. Immunofluorescence staining and biodistribution studies were also carried out to validate the in vivo results.

RESULTS

The radiolabeling yield was 88.9 +/- 9.5% (n = 7) and the specific activity of (64)Cu-DOTA-1C1 was 1.32 +/- 0.14 GBq/mg of 1C1 mAb. The antibody retained antigen-binding affinity/specificity after DOTA conjugation as measured by FACS analysis. The uptake of (64)Cu-DOTA-1C1 in CT-26 tumors was as high as 25.1 +/- 2.5 %ID/g (n = 3) at 18 h post injection. (64)Cu-DOTA-IgG, an isotype-matched control, exhibited minimal non-specific uptake in all eight tumor models. In vivo EphA2 specificity of (64)Cu-DOTA-1C1 was confirmed by successful blocking of CT-26 tumor uptake by unlabeled 1C1. Most importantly, the tumor uptake value obtained from PET imaging had excellent linear correlation with the relative tumor tissue EphA2 expression level measured by Western blot, where r (2) equals 0.90 and 0.92 at 18 h and 42 h post injection, respectively.

CONCLUSION

The tumor uptake of (64)Cu-DOTA-1C1 measured by microPET imaging reflects tumor EphA2 expression level in vivo. This is, to our knowledge, the first report of quantitative radioimmunoPET imaging of EphA2 in living subjects. Future clinical investigation of (64)Cu-DOTA-1C1 is warranted.

Expression and prognostic significance of EFNB2 and EphB4 genes in patients with oesophageal squamous cell carcinoma

OBJECTIVE

Tyrosine kinases and its receptors play important roles in growth, migration, and invasion of malignant cells. Among those, there are only few reports examining the expression pattern of Eph/ephrin signalling system in oesophageal carcinoma. The prognostic importance of ephrin-B2 ligand (EFNB2) and its receptor EphB4, and its correlation with clinicopathologic characteristics are yet to be delineated in patients with oesophageal carcinoma.

MATERIALS AND METHODS

EFNB2 gene and EphB4 receptor gene were examined of mRNA specimens in 61 patients with oesophageal squamous cell carcinoma using reverse-transcriptase polymerase chain reaction. EFNB2 protein was selectively examined using an immunohistochemical analysis.

RESULTS

EFNB2 mRNA expression was detected in 38 (62.3%) and EphB4 expression was found in 44 (72.1%) out of 61 cancer tissues analysed. There was a statistically significant correlation between EFNB2 expression and number of lymph node metastasis (P<0.05), and a trend toward statistical significance for correlation between EFNB2 expression and American Joint Committee on Cancer Classification Stage (P<0.1), indicating that EFNB2 expression was up-regulated by advancement of the disease process. EFNB2 protein was strongly expressed in tumour with high mRNA EFNB2 expression and was weakly expressed in tumour with low mRNA expression in some representative tumours. The 5-year overall survival rate (23%) of patients with positive EFNB2 gene expression was significantly worse than 55% of negative expression (P<0.05). The results of multivariate analysis of prognosticators for survival showed that positive EFNB2 gene expression (P<0.01) and number of lymph node metastasis (P<0.05) were identified as significant factors indicative of a poorer survival.

CONCLUSIONS

EFNB2 gene expression may be a biological marker and a useful prognostic indicator in patients with oesophageal squamous cell carcinoma.

Inhibition of tumor angiogenesis by p53: a new role for the guardian of the genome

The p53 tumor suppressor protein has long been recognized as the central factor protecting humans from cancer. It has been famously dubbed "the guardian of the genome" due to its ability to respond to genotoxic stress, such as DNA damage and other stress signals, and to protect the genome by inducing a variety of biological responses including DNA repair, cell cycle arrest, and apoptosis. However, the tumor suppressive effects of p53 go far beyond its roles in mediating these three processes. There is growing evidence that p53 also exerts its effects on multiple aspects of tumor formation, including suppression of metastasis and, as summarized in this review, inhibition of new blood vessel development (angiogenesis). The p53 protein has been shown to limit angiogenesis by at least three mechanisms: (1) interfering with central regulators of hypoxia that mediate angiogenesis, (2) inhibiting production of proangiogenic factors, and (3) directly increasing the production of endogenous angiogenesis inhibitors. The combination of these effects allows p53 to efficiently shut down the angiogenic potential of cancer cells. Inactivation of p53, which occurs in approximately half of all tumors, reverses these effects; as a consequence, tumors carrying p53 mutations appear more vascularized and are often more aggressive and correlate with poor prognosis for treatment. Thus, the loss of functional p53 during tumorigenesis likely represents an essential step in the switch to an angiogenic phenotype that is displayed by aggressive tumors.

Expression of EphA2 in human astrocytic tumors: correlation with pathologic grade, proliferation and apoptosis

A high expression of EphA2 has been detected in many non-central nervous system tumors; however, the EphA2 expression in brain astrocytic tumors remains unclear. In this study, we investigated the expression of EphA2 mRNA and protein in 90 cases of human astrocytic tumors by reverse transcription polymerase chain reaction and immunohistochemistry, respectively. The proliferative index (PI) of tumor cells was evaluated by Ki-67 immunohistochemistry, and the apoptotic index (AI) was determined by TdT-mediated dUTP nick end labeling assay. The correlation between EphA2 expression, pathologic grade, proliferation and apoptosis of astrocytic tumors was further analyzed. The results showed that 47.8% of cases expressed EphA2 mRNA and 43.3% of cases expressed EphA2 protein. With increasing pathologic grade, the positive rate of EphA2 mRNA and protein, as well as the EphA2 immunoreactivity score (IRS), increased markedly. The PI in the EphA2-positive group was significantly higher than in the EphA2-negative group. In addition, the PI was positively correlated with EphA2 IRS. Although there was no significant difference between the AI in the EphA2-positive group and that in the EphA2-negative group, the AI was inversely correlated with EphA2 IRS. Therefore, EphA2 may be a new biomarker for astrocytic tumors. It may also affect the proliferation and apoptosis of tumor cells and be an attractive therapy target for astrocytic tumors.

EphA2 overexpression is associated with angiogenesis in ovarian cancer

BACKGROUND

EphA2 is overexpressed in the majority of ovarian cancers and predicts poor clinical outcome. Based on EphA2's emerging role in angiogenesis, we hypothesized that tumors overexpressing EphA2 demonstrate greater microvessel density (MVD) and matrix metalloproteinase (MMP) expression.

METHODS

After Institutional Review Board (IRB) approval, 77 invasive epithelial ovarian tumors were analyzed for CD31, EphA2, MMP-2, MMP-9, and MT1-MMP expression.

RESULTS

The median age of the patients was 59 years (range, 34-83). EphA2 was overexpressed in 76% of tumors and was associated with advanced-stage disease (P < .001) and high-grade histology (P = .04). MVD was stratified into high (>12.7 vessels/high-power field [HPF]) versus low (<or=12.7 vessels/HPF) counts. High MVD was significantly associated with advanced stage (P < .001), presence of ascites (P < .001), and suboptimal surgical cytoreduction (P = .01). MMP expression was scored separately in the stromal (percentage of tumors with high expression: MMP-2 = 43%; MMP-9 = 74%; MT1-MMP = 40%) and epithelial (percentage of tumors with high expression: MMP-2 = 52%; MMP-9 = 61%; MT1-MMP = 44%) compartments. Endothelial cell EphA2 overexpression correlated with epithelial MMP-9 (P = .02), whereas EphA2 overexpression in tumor cells was significantly associated with high MVD (P = .002), as well as strong stromal and epithelial MMP-9 (P = .01 and P = .04, respectively), epithelial MMP-2 (P = .006), and epithelial MT1-MMP (P = .01) expression.

CONCLUSIONS

EphA2 overexpression in endothelial and ovarian cancer cells was strongly associated with critical factors involved in angiogenesis and invasion. These findings may explain the poor clinical outcome of patients with EphA2 overexpression.

Patterns of EphA2 protein expression in primary and metastatic pancreatic carcinoma and correlation with genetic status

EphA2 is a transmembrane receptor tyrosine kinase that functions in the regulation of cell growth, survival, angiogenesis, and migration and EphA2 targeting has been proposed as a novel therapeutic strategy for neoplasms that overexpress this protein. EphA2 overexpression has been correlated with increased invasive and metastatic ability in pancreatic cancer cell lines. However, the patterns of EphA2 expression in human pancreatic cancers and associated metastases is unknown, as are the genetics of EphA2 in this tumor type. We collected clinicopathologic data and paraffin-embedded materials from 98 patients with primary and/or metastatic pancreatic cancer and performed immunohistochemical labeling for EphA2 protein. EphA2 protein immunolabeling was found in 207 of 219 samples (95%). The expression was predominantly cytoplasmic, although predominant membranous staining was observed in a minority of cases. When evaluated specifically for labeling intensity, primary and metastatic carcinomas were more strongly positive compared to benign ducts and PanIN lesions (P < 0.00001 and P < 0.01, respectively) and poorly differentiated carcinomas were more strongly positive for EphA2 than well and moderately differentiated tumors (P < 0.005). When primary carcinomas without metastatic disease were specifically compared to carcinomas with associated metastatic disease, the advanced carcinomas showed relatively less strong positive labeling for EphA2 (P < 0.008). Moreover, decreased EphA2 labeling was more commonly found in liver (P < 0.002), lung (P < 0.004) or peritoneal metastases (P < 0.01) as compared to distant lymph node metastases (P < 0.01). Genetic sequencing of the tyrosine kinase domain of EPHA2 in 22 samples of xenograft enriched pancreatic cancer did not reveal any inactivating mutations. However, EPHA2 amplification was found in 1 of 33 pancreatic cancers corresponding to a lymph node metastasis, indicating EPHA2 genomic amplification may underlie EphA2 overexpression in a minority of patients. Our data confirms that EphA2 is overexpressed in pancreatic cancer, but suggests a relative loss of EphA2 in co-existent pancreatic cancer metastases as well as a role for EPHA2 in organ specific metastasis.

Ephrin-A1 facilitates mammary tumor metastasis through an angiogenesis-dependent mechanism mediated by EphA receptor and vascular endothelial growth factor in mice

Ephrin-A1, the prototypic ligand for EphA receptor tyrosine kinases, is overexpressed in vascularized tumors relative to normal tissue. Moreover, ephrin-A1-Fc fusion proteins induce endothelial cell sprouting, migration, and assembly in vitro, and s.c. vascular remodeling in vivo. Based on these data, we hypothesized that native, membrane-bound ephrin-A1 regulates tumor angiogenesis and progression. We tested this hypothesis using a transplantable mouse mammary tumor model. Small interfering RNA-mediated ephrin-A1 knockdown in metastatic mammary tumor cells significantly diminishes lung metastasis without affecting tumor volume, invasion, intravasation, or lung colonization upon i.v. injection in vivo. Ephrin-A1 knockdown reduced tumor-induced endothelial cell migration in vitro and microvascular density in vivo. Conversely, overexpression of ephrin-A1 in nonmetastatic mammary tumor cells elevated microvascular density and vascular recruitment. Overexpression of ephrin-A1 elevated wild-type but not EphA2-deficient endothelial cell migration toward tumor cells, suggesting that activation of EphA2 on endothelial cells is one mechanism by which ephrin-A1 regulates angiogenesis. Furthermore, ephrin-A1 knockdown diminished, whereas overexpression of ephrin-A1 elevated, vascular endothelial growth factor (VEGF) levels in tumor cell-conditioned medium, suggesting that ephrin-A1-mediated modulation of the VEGF pathway is another mechanism by which membrane-tethered ephrin-A1 regulates angiogenic responses from initially distant host endothelium. These data suggest that ephrin-A1 is a proangiogenic signal, regulating VEGF expression and facilitating angiogenesis-dependent metastatic spread.

A genome-wide screen reveals functional gene clusters in the cancer genome and identifies EphA2 as a mitogen in glioblastoma

A novel genome-wide screen that combines patient outcome analysis with array comparative genomic hybridization and mRNA expression profiling was developed to identify genes with copy number alterations, aberrant mRNA expression, and relevance to survival in glioblastoma. The method led to the discovery of physical gene clusters within the cancer genome with boundaries defined by physical proximity, correlated mRNA expression patterns, and survival relatedness. These boundaries delineate a novel genomic interval called the functional common region (FCR). Many FCRs contained genes of high biological relevance to cancer and were used to pinpoint functionally significant DNA alterations that were too small or infrequent to be reliably identified using standard algorithms. One such FCR contained the EphA2 receptor tyrosine kinase. Validation experiments showed that EphA2 mRNA overexpression correlated inversely with patient survival in a panel of 21 glioblastomas, and ligand-mediated EphA2 receptor activation increased glioblastoma proliferation and tumor growth via a mitogen-activated protein kinase-dependent pathway. This novel genome-wide approach greatly expanded the list of target genes in glioblastoma and represents a powerful new strategy to identify the upstream determinants of tumor phenotype in a range of human cancers.

The EphB4 receptor suppresses breast cancer cell tumorigenicity through an Abl–Crk pathway

Recent evidence supports a role for EphB receptor tyrosine kinases as tumour suppressors in colorectal and prostate cancer. However, it is unclear how these receptors inhibit cancer cell tumorigenicity - an activity that is highly unusual for a family of receptor tyrosine kinases. Here, we report that the EphB4 receptor can behave as a tumour suppressor in a mouse xenograft model of breast cancer when stimulated by its ligand, ephrin-B2. In breast cancer cells, EphB4 activates an antioncogenic pathway involving Abl family tyrosine kinases and the Crk adaptor protein. This Abl-Crk pathway inhibits breast cancer cell viability and proliferation in addition to motility and invasion, and also downregulates the pro-invasive matrix metalloprotease, MMP-2. Consistent with these effects, EphB4 and the Abl-Crk pathway are constitutively active in non-transformed mammary epithelial cells. These findings identify a novel Eph receptor signalling pathway with tumour-suppressor activity and predict that therapeutic intervention to activate EphB4 signalling will inhibit tumour progression.

EphA2 as a target for ovarian cancer therapy

EphA2 is a receptor tyrosine kinase that is overexpressed by many human cancers, and is often associated with poor prognostic features. It is involved in many processes crucial to malignant progression, such as migration, invasion, metastasis, proliferation, survival and angiogenesis. Inducing EphA2 downregulation by any one of several mechanisms (antibody-mediated inhibition of signalling, antibody-mediated downregulation of total EphA2 expression and siRNA-mediated inhibition of expression) has been shown to decrease tumour growth, prolong survival and inhibit angiogenesis in multiple preclinical models of ovarian, breast and pancreatic cancer. Targeting EphA2 is especially attractive in ovarian cancer, in which overexpression is present in > 75% of cases. This disease is highly responsive to chemotherapy, and EphA2 inhibition is especially effective in combination with taxanes. This demonstrated efficacy, along with the low expression of EphA2 by normal adult tissues and lack of demonstrable toxicities in preclinical models, suggest that long-term treatment with EphA2-targeting agents is an attractive approach for ovarian cancer therapy.

Expression and purification of the intact cytoplasmic domain of the human ephrin receptor A2 tyrosine kinase in Escherichia coli

The ephrin receptor A2 (EphA2) is an integral membrane protein tyrosine kinase and a member of the Eph family, the largest known family of receptor tyrosine kinases. EphA2 overexpression is sufficient to transform normal epithelial cells into an aggressive, metastatic phenotype. In normal cells, EphA2 negatively regulates cell growth and invasiveness. Here we report expression of the intact cytoplasmic domain (juxtamembrane linker, tyrosine kinase, and sterile alpha motif domains) of the human EphA2 receptor in an Escherichia coli system. The expressed protein was purified to near homogeneity by use of metal chelation chromatography combined with removal of vector-encoded tags by specific proteolysis. The cytoplasmic domains of EphA2 are expressed as an active kinase, with the expressed protein found to contain phosphorylated tyrosine residues. In addition, protein tyrosine phosphorylation appears only after EphA2 expression is induced and is removable with alkaline phosphatase treatment. The enzyme was purified 5-fold in yields that average 10-30 mg/L of active EphA2 cytoplasmic domains, which will now be used for further biophysical and structural characterization.

Expression of EphA2 and Ephrin A-1 in carcinoma of the urinary bladder

PURPOSE

The EphA2 receptor tyrosine kinase is believed to play a role in tumor growth and metastasis. The clinical significance of the expression of EphA2 was observed in breast, prostate, colon, skin, cervical, ovarian, and lung cancers. The purpose of this work was to determine the expression of EphA2 and its ligand, Ephrin A-1, and E-cadherin in carcinoma of the urinary bladder, and determine EphA2 as a new target for therapy in bladder cancer.

EXPERIMENTAL DESIGN

EphA2 mRNA and protein expression was investigated by reverse transcription-PCR and Western blot, respectively, in bladder cancer cell lines. In addition, the expression of EphA2, Ephrin A-1, and E-cadherin in tissues from patients with different stages of urinary bladder cancer was determined by immunohistochemistry. Furthermore, the ability of Ephrin A-1 to inhibit growth of bladder cancer cells was also investigated using an adenoviral delivery system.

RESULTS

Western blot analysis showed high EphA2 expression in TCCSUP, T24, and UMUC-3 cell lines. In tissues, the staining intensity of EphA2 was less in normal urothelium but increased greatly in advancing stages of urothelial carcinoma (P < 0.05). Similarly, the staining intensity of Ephrin A-1 was low in normal tissues and high in cancerous tissues, but it was similar across the various stages of urothelial carcinoma (T(a)-T(4)). E-cadherin immunoreactivity decreased in urothelial cancer. Association of EphA2 and Ephrin A-1 expression was found to be significant between T(a) stage and T(1)-T(2) (P < 0.04) and T(a) and T(3)-T(4) stages (P < 0.0001). Adenovirus delivery of Ephrin A-1 inhibited proliferation of TCCSUP cells.

CONCLUSION

EphA2 may serve as a novel target for bladder cancer therapy.

Development of adenoviral-vector-based pandemic influenza vaccine against antigenically distinct human H5N1 strains in mice

INTRODUCTION

Avian H5N1 influenza viruses currently circulating in southeast Asia could potentially cause the next pandemic. However, currently licensed human vaccines are subtype-specific and do not protect against these H5N1 viruses. We aimed to develop an influenza vaccine and assessed its immunogenicity and efficacy to confer protection in BALB/c mice.

METHODS

We developed an egg-independent strategy to combat the avian influenza virus, because the virus is highly lethal to chickens and the maintenance of a constant supply of embryonated eggs would be difficult in a pandemic. We used a replication-incompetent, human adenoviral-vector-based, haemagglutinin subtype 5 influenza vaccine (HAd-H5HA), which induces both humoral and cell-mediated immune responses against avian H5N1 influenza viruses isolated from people.

FINDINGS

Immunisation of mice with HAd-H5HA provided effective protection from H5N1 disease, death, and primary viral replication (p<0.0001) against antigenically distinct strains of H5N1 influenza viruses. Unlike the recombinant H5HA vaccine, which is based on a traditional subunit vaccine approach, HAd-H5HA vaccine induced a three-fold to eight-fold increase in HA-518-epitope-specific interferon-gamma-secreting CD8 T cells (p=0.01).

INTERPRETATION

Our findings highlight the potential of an Ad-vector-based delivery system, which is both egg-independent and adjuvant-independent and offers stockpiling options for the development of a pandemic influenza vaccine.

TherapeuticEphA2Gene TargetingIn vivoUsing Neutral Liposomal Small Interfering RNA Delivery

Inducing destruction of specific mRNA using small interfering RNA (siRNA) is a powerful tool in analysis of protein function, but its use as a therapeutic modality has been limited by inefficient or impractical delivery systems. We have used siRNA incorporated into the neutral liposome 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) for efficient in vivo siRNA delivery. In nude mice bearing i.p. ovarian tumors, nonsilencing siRNA tagged with the fluorochrome Alexa 555 was encapsulated into DOPC liposomes and shown to be taken up by the tumor as well as many major organs. Furthermore, DOPC-encapsulated siRNA targeting the oncoprotein EphA2 was highly effective in reducing in vivo EphA2 expression 48 hours after a single dose as measured by both Western blot and immunohistochemistry. Therapy experiments in an orthotopic mouse model of ovarian cancer were initiated 1 week after injection of either HeyA8 or SKOV3ip1 cell lines. Three weeks of treatment with EphA2-targeting siRNA-DOPC (150 microg/kg twice weekly) reduced tumor growth when compared with a nonsilencing siRNA (SKOV3ip1: 0.35 versus 0.70 g; P = 0.020; HeyA8: 0.98 versus 1.51 g; P = 0.16). When EphA2-targeting siRNA-DOPC was combined with paclitaxel, tumor growth was dramatically reduced compared with treatment with paclitaxel and a nonsilencing siRNA (SKOV3ip1: 0.04 versus 0.22 g; P < 0.001; HeyA8: 0.21 versus 0.84 g; P = 0.0027). These studies show the feasibility of siRNA as a clinically applicable therapeutic modality.

Eph receptor signalling casts a wide net on cell behaviour

Eph receptor tyrosine kinases mould the behaviour of many cell types by binding membrane-anchored ligands, ephrins, at sites of cell-cell contact. Eph signals affect both of the contacting cells and can produce diverse biological responses. New models explain how quantitative variations in the densities and signalling abilities of Eph receptors and ephrins could account for the different effects that are elicited on axon guidance, cell adhesion and cell migration during development, homeostasis and disease.

Immunocompetent mouse model of breast cancer for preclinical testing of EphA2-targeted therapy

EphA2, a receptor tyrosine kinase, is elevated in many invasive human breast cancers, and the majority of EphA2 remains unphosphorylated. The successful attachment of ligand EphrinA1 present on the surface of adjacent cells to EphA2 initiates EphA2 phosphorylation leading to its turnover. In vivo efficacy of various approaches targeting EphA2 for breast cancer therapy is usually evaluated in nude mice bearing human breast cancer xenografts. In order to establish an immunocompetent mouse model of breast cancer for EphA2-targeted therapies, we evaluated a mouse breast cancer cell line (MT1A2) for EphA2 expression and phosphorylation. Overexpression of EphA2 was observed in MT1A2 cells and the majority of it remained unphosphorylated signifying that EphA2 in MT1A2 cells behaved similar to that of human breast cancer cells. Human adenovirus subtype 5 (HAd5) vectors expressing secretory forms of EphrinA1 were used for in vitro and in vivo targeting of MT1A2-derived EphA2. MT1A2 cells infected with HAd-EphrinA1-Fc (HAd expressing extracellular domain of human EphrinA1 attached to Fc portion of human IgG1 heavy chain) induced EphA2 activation and its turnover. This led to inhibition in MT1A2 cell colony formation in soft agar and cell viability in monolayer culture. In addition, MT1A2 cells-infected with HAd-EphrinA1-Fc failed to form tumors in syngeneic FVB/n mice at least 32 days postinoculation. Moreover, intratumoral inoculation of FVB/n mice-bearing MT1A2-induced tumors with HAd-EphrinA1-Fc slowed the tumor growth and also resulted in the development of vector-specific immune response. These results indicate that FVB/n mice-bearing MT1A2-induced tumors could serve as an immunocompetent model of breast cancer for EphA2-targeted therapeutic strategies.

Porcine adenoviral vectors evade preexisting humoral immunity to adenoviruses and efficiently infect both human and murine cells in culture

Preexisting immunity against human adenoviruses (HAd) limits the efficiency of transduction of HAd vectors in humans. In addition, development of a vector-specific immune response after the first inoculation with a HAd vector further lowers vector uptake following readministration. We investigated the usefulness of porcine adenovirus serotype 3 (PAd3)-based vectors as a supplement to HAd vectors. Here we demonstrate that preexisting HAd-specific neutralizing antibodies in humans do not cross-neutralize PAd3. In order to generate E1A-deleted PAd3 vectors, an E1-complementing cell line of porcine origin was produced. E1A-deleted PAd3 vector expressing green fluorescent protein; GFP (PAd-GFP) and E1-deleted HAd5 vector expressing GFP (HAd-GFP) transduced human cell lines with comparable efficiencies. Both of these vectors efficiently transduced murine MT1A2 breast cancer cell line, while PAd-GFP transduced murine NIH 3T3 fibroblast cell line significantly better (P < 0.05) than HAd-GFP. These results suggest that PAd3 vectors would be promising supplement to HAd vectors as a delivery vehicle for recombinant vaccines and gene therapy applications.