A kinase-dependent role for EphA2 receptor in promoting tumor growth and metastasis

TAK-901, a novel EPHA2 inhibitor as a therapeutic strategy against prostate cancer

Prostate cancer is the most common cancer and remains a leading cause of cancer-related deaths among men worldwide. Androgen deprivation therapy continues to be the cornerstone of treatment for prostate cancer. However, the efficacy of this treatments is often limited, leading to the emergence of drug resistance and tumor recurrence. TAK-901, an inhibitor of Aurora kinase B, has been shown to inhibit tumor growth both in vitro and in vivo models. To date, the effect of TAK-901 on prostate cancer and the underlying mechanism remain unknown. In this study, we found that TAK-901 could inhibit proliferation, colony formation and migration, while also inducing apoptosis in prostate cancer cells. We further demonstrated that TAK-901 activates the CHK1 signaling pathway, leading to G2/M-phase arrest in these cells. Additionally, we identified EPHA2 as a novel therapeutic target of TAK-901. By mutating the binding sites between EPHA2 and TAK-901, we discovered that these mutations could reverse the anti-proliferative effects of TAK-901 in prostate cancer models. Our study is the first to reveal that TAK-901 induces apoptosis in prostate cancer cells and inhibits cell growth by targeting EPHA2. These findings provide valuable insights into the underlying mechanisms of TAK-901 and may develop its therapeutic applications in prostate cancer.

Multiple anti-tumor programs are activated by blocking BAD phosphorylation

The Bcl-2 family member BAD is a candidate disease modulator because it stimulates apoptosis in a cell context basis and inhibits cell migration during normal mammary gland morphogenesis. This activity depends on 3 key regulatory serines (S75, 99, 118) in the unphosphorylated state. Given that developmental programs are often hijacked in cancer, we hypothesized that BAD would impede breast cancer progression. We generated breast cancer mouse models representing loss-of-function or phosphorylation deficient mutations (PyMT-Bad-/- and PyMT-Bad3SA/3SA, respectively). Preventing BAD phosphorylation significantly decreased breast cancer progression and metastasis. The knock-out phenocopied the control PyMT-Bad+/+ suggesting that phosphorylated BAD protein was inert. Thus, the BAD3SA mutation unmasked latent anti-tumor activity. Indeed, transcriptomics showed PyMT-Bad3SA/3SA activated multiple anti-tumor programs including apoptosis, inflammation, cellular differentiation, and diminished cell migration. This anti-tumor effect associated with clinical survival of breast cancer patients whose tumors had high levels of unphosphorylated BAD. Kinase screens identified ERK as the major BAD kinase in breast cells, and ERK inhibition impeded tumoroid invasion. Our data suggest that unphosphorylated BAD modulates anti-tumor pathways that contribute to excellent patient prognosis. Thus, targeting ERK to dephosphorylate BAD may be an exciting therapeutic opportunity in the future.

Canonical ligand-dependent and non-canonical ligand-independent EphA2 signaling in the eye lens of wild-type, knockout, and aging mice

Disruption of Eph-ephrin bidirectional signaling leads to human congenital and age-related cataracts, but the mechanisms for these opacities in the eye lens remain unclear. Eph receptors bind to ephrin ligands on neighboring cells to induce canonical ligand-mediated signaling. The EphA2 receptor also signals non-canonically without ligand binding in cancerous cells, leading to epithelial-to-mesenchymal transition (EMT). We have previously shown that the receptor EphA2 and the ligand ephrin-A5 have diverse functions in maintaining lens transparency in mice. Loss of ephrin-A5 leads to anterior cataracts due to EMT. Surprisingly, both canonical and non-canonical EphA2 activation are present in normal wild-type lenses and in the ephrin-A5 knockout lenses. Canonical EphA2 signaling is localized exclusively to lens epithelial cells and does not change with age. Non-canonical EphA2 signaling is in both epithelial and fiber cells and increases significantly with age. We hypothesize that canonical ligand-dependent EphA2 signaling is required for the morphogenesis and organization of hexagonal equatorial epithelial cells while non-canonical ligand-independent EphA2 signaling is needed for complex membrane interdigitations that change during fiber cell differentiation and maturation. This is the first demonstration of non-canonical EphA2 activation in a non-cancerous tissue or cell and suggests a possible physiological function for ligand-independent EphA2 signaling.

Targeting the EphA2 pathway: could it be the way for bone sarcomas?

Bone sarcomas are malignant tumors of mesenchymal origin. Complete surgical resection is the cornerstone of multidisciplinary treatment. However, advanced, unresectable forms remain incurable. A crucial step towards addressing this challenge involves comprehending the molecular mechanisms underpinning tumor progression and metastasis, laying the groundwork for innovative precision medicine-based interventions. We previously showed that tyrosine kinase receptor Ephrin Type-A Receptor 2 (EphA2) is overexpressed in bone sarcomas. EphA2 is a key oncofetal protein implicated in metastasis, self-renewal, and chemoresistance. Molecular, genetic, biochemical, and pharmacological approaches have been developed to target EphA2 and its signaling pathway aiming to interfere with its tumor-promoting effects or as a carrier for drug delivery. This review synthesizes the main functions of EphA2 and their relevance in bone sarcomas, providing strategies devised to leverage this receptor for diagnostic and therapeutic purposes, with a focus on its applicability in the three most common bone sarcoma histotypes: osteosarcoma, chondrosarcoma, and Ewing sarcoma.

EPHA2 is a novel cell surface marker of OCT4-positive undifferentiated cells during the differentiation of mouse and human pluripotent stem cells

Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) possess the intrinsic ability to differentiate into diverse cellular lineages, marking them as potent instruments in regenerative medicine. Nonetheless, the proclivity of these stem cells to generate teratomas post-transplantation presents a formidable obstacle to their therapeutic utility. In previous studies, we identified an array of cell surface proteins specifically expressed in the pluripotent state, as revealed through proteomic analysis. Here we focused on EPHA2, a protein found to be abundantly present on the surface of undifferentiated mouse ESCs and is diminished upon differentiation. Knock-down of Epha2 led to the spontaneous differentiation of mouse ESCs, underscoring a pivotal role of EPHA2 in maintaining an undifferentiated cell state. Further investigations revealed a strong correlation between EPHA2 and OCT4 expression during the differentiation of both mouse and human PSCs. Notably, removing EPHA2+ cells from mouse ESC-derived hepatic lineage reduced tumor formation after transplanting them into immune-deficient mice. Similarly, in human iPSCs, a larger proportion of EPHA2+ cells correlated with higher OCT4 expression, reflecting the pattern observed in mouse ESCs. Conclusively, EPHA2 emerges as a potential marker for selecting undifferentiated stem cells, providing a valuable method to decrease tumorigenesis risks after stem-cell transplantation in regenerative treatments.

Targeting EPHA2 with Kinase Inhibitors in Colorectal Cancer

The ephrin type-A 2 receptor tyrosine kinase (EPHA2) is involved in the development and progression of various cancer types, including colorectal cancer (CRC). There is also evidence that EPHA2 plays a key role in the development of resistance to the endothelial growth factor receptor (EGFR) monoclonal antibody Cetuximab used clinically in CRC. Despite the promising pharmacological potential of EPHA2, only a handful of specific inhibitors are currently available. In this concept paper, general strategies for EPHA2 inhibition with molecules of low molecular weight (small molecules) are described. Furthermore, available examples of inhibiting EPHA2 in CRC using small molecules are summarized, highlighting the potential of this approach.

EPHA2, EPHA4, and EPHA7 Expression in Triple-Negative Breast Cancer

Ongoing research continues to elucidate the complex role of ephrin receptors (EPHs) and their ligands (ephrins) in breast cancer pathogenesis, with their varying expression patterns implied to have an important impact on patients’ outcome. The current study aims to investigate the clinical significance of EPHA2, EPHA4, and EPHA7 expression in triple-negative breast cancer (TNBC) cases. EPHA2, EPHA4, and EPHA7 protein expression was assessed immunohistochemically on formalin-fixed and paraffin-embedded (FFPE) TNBC tissue sections from 52 TNBC patients and correlated with key clinicopathologic parameters and patients’ survival data (overall survival (OS); disease-free survival (DFS)). EPHA2, EPHA4, and EPHA7 expression was further examined in TNBC cell lines. EPHA2 overexpression was observed in 26 (50%) of the TNBC cases, who exhibited a shorter OS and DFS than their low-expression counterparts, with EPHA2 representing an independent prognostic factor for OS and DFS (p = 0.0041 and p = 0.0232, respectively). EPHA4 overexpression was associated with lymph node metastasis in TNBC patients (p = 0.0546). Alterations in EPHA2, EPHA4, and EPHA7 expression levels were also noted in the examined TNBC cell lines. Our study stresses that EPHA2 expression constitutes a potential prognostic factor for TNBC patients. Given the limited treatment options and poorer outcome that accompany the TNBC subtype, EPHA2 could also pose as a target for novel, more personalized, and effective therapeutic approaches for those patients.

Low Expression of EphB2, EphB3, and EphB4 in Bladder Cancer: Novel Potential Indicators of Muscular Invasion

PURPOSE

Eph receptors are differentially expressed in numerous malignant tumors. This study intended to analyze the roles of EphB receptors (EphB2, B3, and B4) in urinary bladder cancer.

MATERIALS AND METHODS

Tissue microarray-based immunohistochemical analysis was used to investigate the expression patterns of EphB2, EphB3, and EphB4 in 154 bladder cancer specimens. Immunohistochemical staining was conducted examining the extent of stained cells and staining intensity. EphB was considered to be highly expressed when the intensity of staining was more than moderate in >25% of cells in the tissue section. Small interfering RNA (siRNA) was used to knock down EphB expression in bladder cancer cell lines (T24, 5637) to determine the effects of EphB on tumor cell invasion, proliferation, and migration.

RESULTS

EphB receptors (B2, B3, and B4) were detected in 40.9% (EphB2, 63/154), 71.4% (EphB3, 110/154), and 53.2% (EphB4, 82/154) of bladder cancer specimens. Low expression of EphB2, B3, and B4 receptors were significantly associated with higher tumor grade (EphB2, p<0.001; EphB3, p=0.032; EphB4, p<0.001) and muscular invasion (EphB2, p=0.002; EphB3, p=0.009; EphB4, p<0.001). No obvious correlation was observed with other clinicopathological variables, such as age, sex, recurrence, lymph node involvement, metastasis, and overall survival. Inactivation of EphB receptors by siRNA transfection increased cell viability, tumor cell invasion, proliferation, and migration in comparison with untransfected cancer cells.

CONCLUSION

Low expression of EphB receptors (B2, B3, and B4) can be a predictive marker for muscular invasion of bladder cancer.

The Value of EphB2 Receptor and Cognate Ephrin Ligands in Prognostic and Predictive Assessments of Human Breast Cancer

Cell–cell communication proteins Eph and ephrin constitute the largest family of receptor tyrosine kinases (RTKs). They are distinguished by the fact that both receptors and ligands are membrane-bound, and both can drive intracellular signaling in their respective cells. Ever since these RTKs have been found to be involved in cancer development, strategies to target them therapeutically have been actively pursued. However, before this goal can be rationally achieved, the contributions of either Eph receptors or their ephrin ligands to cancer development and progression should be scrutinized in depth. To assess the clinical pertinence of this concern, we performed a systematic review and meta-analysis of the prognostic/predictive value of EphB2 and its multiple cognate ephrin ligands in breast cancer. We found that EphB2 has prognostic value, as indicated by the association of higher EphB2 expression levels with lower distant metastasis-free survival (DMFS), and the association of lower EphB2 expression levels with poorer relapse-free survival (RFS). We also found that higher EphB2 expression could be a prognostic factor for distant metastasis, specifically in the luminal subtypes of breast cancer. EFNB2 showed a marked correlation between higher expression levels and shorter DMFS. EFNA5 or EFNB1 overexpression is correlated with longer RFS. Increased EFNB1 expression is correlated with longer OS in lymph node (LN)-negative patients and the luminal B subtype. Higher levels of EFNB2 or EFNA5 are significantly correlated with shorter RFS, regardless of LN status. However, while this correlation with shorter RFS is true for EFNB2 in all subtypes except basal, it is also true for EFNA5 in all subtypes except HER2+. The analysis also points to possible predictive value for EphB2. In systemically treated patients who have undergone either endocrine therapy or chemotherapy, we found that higher expression of EphB2 is correlated with better rates of RFS. Bearing in mind the limitations inherent to any mRNA-based profiling method, we complemented our analysis with an immunohistochemical assessment of expression levels of both the EphB2 receptor and cognate ephrin ligands. We found that the latter are significantly more expressed in cancers than in normal tissues, and even more so in invasive and metastatic samples than in ductal carcinoma in situ (DCIS). Finally, in an in vitro cellular model of breast cancer progression, based on H-Ras-transformation of the MCF10A benign mammary cell line, we observed dramatic increases in the mRNA expression of EphB2 receptor and EFNB1 and EFNB2 ligands in transformed and invasive cells in comparison with their benign counterparts. Taken together, these data show the clinical validity of a model whereby EphB2, along with its cognate ephrin ligands, have dual anti- and pro-tumor progression effects. In so doing, they reinforce the necessity of further biological investigations into Ephs and ephrins, prior to using them in targeted therapies.

SOD3 Is a Non-Mutagenic Growth Regulator Affecting Cell Migration and Proliferation Signal Transduction

Superoxide dismutase (SOD) family isoenzymes, SOD1, SOD2, and SOD3, synthesize hydrogen peroxide (H₂O₂), which regulates the signal transduction. H₂O₂ is a second messenger able to enter into the cells through aquaporin 3 cell membrane channels and to modify protein tyrosine phosphatase activity. SOD3 has been shown to activate signaling pathways in tissue injuries, inflammation, and cancer models. Similar to the H₂O₂ response in the cells, the cellular response of SOD3 is dose-dependent; even a short supraphysiological concentration reduces the cell survival and activates the growth arrest and apoptotic signaling, whereas the physiological SOD3 levels support its growth and survival. In the current work, we studied the signaling networks stimulated by SOD3 overexpression demonstrating a high diversity in the activation of signaling cascades. The results obtained suggest that SOD3, although inducing cell growth and affecting various biological processes, does not cause detectable long-term DNA aberrations. Therefore, according to the present data, SOD3 is not a mutagen. Additionally, we compared SOD3-driven immortalized mouse embryonic fibroblasts to SV40 immortalized NIH3T3 cells, demonstrating a marked difference in the activation of cellular kinases. The data presented may contain important druggable targets to abrogate unwanted cell growth.

Oncogenic functions and therapeutic targeting of EphA2 in cancer

More than 25 years of research and preclinical validation have defined EphA2 receptor tyrosine kinase as a promising molecular target for clinical translation in cancer treatment. Molecular, genetic, biochemical, and pharmacological targeting strategies have been extensively tested in vitro and in vivo, and drugs like dasatinib, initially designed to target SRC family kinases, have been found to also target EphA2 activity. Other small molecules, therapeutic targeting antibodies, and peptide-drug conjugates are being tested, and more recently, approaches harnessing antitumor immunity against EphA2-expressing cancer cells have emerged as a promising strategy. This review will summarize preclinical studies supporting the oncogenic role of EphA2 in breast cancer, lung cancer, glioblastoma, and melanoma, while delineating the differing roles of canonical and noncanonical EphA2 signaling in each setting. This review also summarizes completed and ongoing clinical trials, highlighting the promise and challenges of targeting EphA2 in cancer.

EphA2 Is a Clinically Relevant Target for Breast Cancer Bone Metastatic Disease

EphA2 receptor tyrosine kinase (RTK) is highly expressed in breast tumor cells across multiple molecular subtypes and correlates with poor patient prognosis. In this study, the potential role of EphA2 in this clinically relevant phenomenon is investigated as metastasis of breast cancer to bone is a major cause of morbidity and mortality in patients. It was found that the EphA2 function in breast cancer cells promotes osteoclast activation and the development of osteolytic bone disease. Blocking EphA2 function molecularly and pharmacologically in breast tumors reduced the number and size of bone lesions and the degree of osteolytic disease in intratibial and intracardiac mouse models, which correlated with a significant decrease in the number of osteoclasts at the tumor-bone interface. EphA2 loss of function in tumor cells impaired osteoclast progenitor differentiation in coculture, which is mediated, at least in part, by reduced expression of IL-6. EPHA2 transcript levels are enriched in human breast cancer bone metastatic lesions relative to visceral metastatic sites; EphA2 protein expression was detected in breast tumor cells in bone metastases in patient samples, supporting the clinical relevance of the study's findings. These data provide a strong rationale for the development and application of molecularly targeted therapies against EphA2 for the treatment of breast cancer bone metastatic disease. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

EphA2 and EGFR: Friends in Life, Partners in Crime. Can EphA2 Be a Predictive Biomarker of Response to Anti-EGFR Agents?

The Eph receptors represent the largest group among Receptor Tyrosine kinase (RTK) families. The Eph/ephrin signaling axis plays center stage during development, and the deep perturbation of signaling consequent to its dysregulation in cancer reveals the multiplicity and complexity underlying its function. In the last decades, they have emerged as key players in solid tumors, including colorectal cancer (CRC); however, what causes EphA2 to switch between tumor-suppressive and tumor-promoting function is still an active theater of investigation. This review summarizes the recent advances in understanding EphA2 function in cancer, with detail on the molecular determinants of the oncogene-tumor suppressor switch function of EphA2. We describe tumor context-specific examples of EphA2 signaling and the emerging role EphA2 plays in supporting cancer-stem-cell-like populations and overcoming therapy-induced stress. In such a frame, we detail the interaction of the EphA2 and EGFR pathway in solid tumors, including colorectal cancer. We discuss the contribution of the EphA2 oncogenic signaling to the resistance to EGFR blocking agents, including cetuximab and TKIs.

Activation of EPHA2-ROBO1 Heterodimer by SLIT2 Attenuates Non-canonical Signaling and Proliferation in Squamous Cell Carcinomas

The tyrosine kinase receptor ephrin receptor A2 (EPHA2) is overexpressed in lung (LSCC) and head and neck (HNSCC) squamous cell carcinomas. Although EPHA2 can inhibit tumorigenesis in a ligand-dependent fashion via phosphorylation of Y588 and Y772, it can promote tumorigenesis in a ligand-independent manner via phosphorylation of S897. Here, we show that EPHA2 and Roundabout Guidance Receptor 1 (ROBO1) interact to form a functional heterodimer. Furthermore, we show that the ROBO1 ligand Slit Guidance Ligand 2 (SLIT2) and ensartinib, an inhibitor of EPHA2, can attenuate growth of HNSCC cells and act synergistically in LSCC cells. Our results suggest that patients with LSCC and HNSCC may be stratified and treated based on their EPHA2 and ROBO1 expression patterns. Although ~73% of patients with LSCC could benefit from SLIT2+ensartinib treatment, ~41% of patients with HNSCC could be treated with either SLIT2 or ensartinib. Thus, EPHA2 and ROBO1 represent potential LSCC and HNSCC theranostics.

Effect of EphA2 knockdown on melanoma metastasis depends on intrinsic ephrinA1 level

PURPOSE

Upregulation of receptor tyrosine kinase EphA2 has been found to be associated with a poor prognosis in many types of cancer and is considered an attractive therapeutic target. As yet, few efforts have been focused on its tumor suppressive activity triggered by its ligand, ephrinA1. Here, we aimed to determine the potential of ephrinA1 as an important player in melanoma metastasis.

METHODS

Data from the Cancer Genome Atlas (TCGA) and the Cancer Cell Line Encyclopedia (CCLE) were analyzed to explore the expression and prognostic implications of EphA2 and ephrinA1 in melanoma. Western blotting, shRNA, colony formation and immunofluorescence assays, as well as two in vivo xenograft models (subcutaneous and metastatic) were used to evaluate the role of EphA2 in melanoma progression. Akt inhibition and ephrinA1-Fc were used to confirm the influence of Akt activation and ephrinA1 levels on the EphA2 effects. Immunohistochemistry (IHC) was performed on xenograft and patient melanoma tissues.

RESULTS

We found that high levels of ephrinA1, but not EphA2, were negatively correlated with melanoma metastasis. The expression levels of EphA2 and ephrinA1 were not correlated. After EphA2 downregulation, colony forming abilities and lung metastatic growth were reduced in melanoma cell lines with a low ephrinA1 expression, but were increased in melanoma cell lines with a high ephrinA1 expression. EphA2-mediated colony formation in EphA2-high/ephrinA1-low cells was found to be Akt-dependent and to be inhibited by the addition of ephrinA1-Fc. IHC staining of primary melanoma specimens revealed that EphA2-high/ephrinA1-low patients exhibited poorer outcomes than EphA2-high/ephrinA1-high patients.

CONCLUSIONS

From our data we conclude that evaluation of ephrinA1 levels may be helpful for the application of EphA2-targeted therapies and for prognostic predictions in melanoma patients.

A new scfv-based recombinant immunotoxin against EPHA2-overexpressing breast cancer cells; High in vitro anti-cancer potency

Immunotoxin therapy is one of the immunotherapy strategies providing a new, effective and high potency treatment against various cancers. Breast cancer is the most common cancer among women in many countries. The EPH receptors are a large part of tyrosine kinase receptors family and play an effective role in tumor development and angiogenesis. Among EPH receptors, EPHA2 is more commonly well-known and widely expressed in many cancers like breast cancer. In this study, we evaluated the specification of a designed immunotoxin formed by EPHA2-specific scfv linked with PE38KDEL on EPHA2-overexpressing breast cancer cell line. This new scfv-based recombinant immunotoxin was studied in terms of features such as binding potency, cytotoxicity effects, apoptosis induction ability, and internalization. The flow cytometry results showed that the immunotoxin can significantly (approximately 99%) bind to EPHA2-overexpressing breast cancer cell line (MDA-MB-231) in a low concentration (2.5 ng/ul) while cannot significantly bind to the normal cell line (HEK-293) or even EPHA2-very low expressing cell line (MCF-7). Using the MTT assay and Annexin V/Propidium iodide (PI) double staining method by flow cytometry, we observed significant killing and apoptosis induction of the MDA-MB-231 cells at different concentrations. Immunotoxin tracking by confocal microscopy at 2 h and 6 h revealed a massive presence of immunotoxin in the cytoplasm. Finally, given the in vitro results, it seems that this immunotoxin is competent enough to serve as a good candidate for in vivo studies to further explore the possibility of breast cancer treatment.

Eph receptor signalling: from catalytic to non-catalytic functions

Eph receptors, the largest subfamily of receptor tyrosine kinases, are linked with proliferative disease, such as cancer, as a result of their deregulated expression or mutation. Unlike other tyrosine kinases that have been clinically targeted, the development of therapeutics against Eph receptors remains at a relatively early stage. The major reason is the limited understanding on the Eph receptor regulatory mechanisms at a molecular level. The complexity in understanding Eph signalling in cells arises due to following reasons: (1) Eph receptors comprise 14 members, two of which are pseudokinases, EphA10 and EphB6, with relatively uncharacterised function; (2) activation of Eph receptors results in dimerisation, oligomerisation and formation of clustered signalling centres at the plasma membrane, which can comprise different combinations of Eph receptors, leading to diverse downstream signalling outputs; (3) the non-catalytic functions of Eph receptors have been overlooked. This review provides a structural perspective of the intricate molecular mechanisms that drive Eph receptor signalling, and investigates the contribution of intra- and inter-molecular interactions between Eph receptors intracellular domains and their major binding partners. We focus on the non-catalytic functions of Eph receptors with relevance to cancer, which are further substantiated by exploring the role of the two pseudokinase Eph receptors, EphA10 and EphB6. Throughout this review, we carefully analyse and reconcile the existing/conflicting data in the field, to allow researchers to further the current understanding of Eph receptor signalling.

Tumor cell-intrinsic EPHA2 suppresses anti-tumor immunity by regulating PTGS2 (COX-2)

Resistance to immunotherapy is one of the biggest problems of current oncotherapeutics. WhileT cell abundance is essential for tumor responsiveness to immunotherapy, factors that define the T cell inflamed tumor microenvironment are not fully understood. We conducted an unbiased approach to identify tumor-intrinsic mechanisms shaping the immune tumor microenvironment(TME), focusing on pancreatic adenocarcinoma because it is refractory to immunotherapy and excludes T cells from the TME. From human tumors, we identified EPHA2 as a candidate tumor intrinsic driver of immunosuppression. Epha2 deletion reversed T cell exclusion and sensitized tumors to immunotherapy. We found that PTGS2, the gene encoding cyclooxygenase-2, lies downstream of EPHA2 signaling through TGFβ and is associated with poor patient survival. Ptgs2 deletion reversed T cell exclusion and sensitized tumors to immunotherapy; pharmacological inhibition of PTGS2 was similarly effective. Thus, EPHA2-PTGS2 signaling in tumor cells regulates tumor immune phenotypes; blockade may represent a novel therapeutic avenue for immunotherapy-refractory cancers. Our findings warrant clinical trials testing the effectiveness of therapies combining EPHA2-TGFβ-PTGS2 pathway inhibitors with anti-tumor immunotherapy, and may change the treatment of notoriously therapy-resistant pancreatic adenocarcinoma.

Roles of EphA2 Receptor in Angiogenesis Signaling Pathway of Glioblastoma Multiforme

Glioblastoma multiforme (GBM) is one of the most common primary brain tumours in adults, accounting for almost 65% of all cases. Among solid tumours, GBM is characterised by strong angiogenesis, including the highest degree of vascular proliferation and endothelial cell hyperplasia. Despite numerous improvements in existing treatment approaches, the prognosis of GBM patients remains poor, with a mean survival of only 14.6 months. Growing evidence has shown significant overexpression of the ephrin type-A receptor 2 (EphA2) receptor in various malignancies, including GBM, as well as a correlation to poor prognoses. It is believed that EphA2 receptors play important roles in mediating GBM tumourigenesis, including invasion, metastasis, and angiogenesis. Despite the clinical and pathological importance of tumour-associated vasculature, the underlying mechanism involving EphA2 is poorly known. Here, we have summarised the current knowledge in the field regarding EphA2 receptors’ roles in the angiogenesis of GBM.

Inhibition of HDACs-EphA2 Signaling Axis with WW437 Demonstrates Promising Preclinical Antitumor Activity in Breast Cancer

Histone deacetylase inhibitors (HDACi) are small molecules targeting epigenetic enzymes approved for hematologic neoplasms, which have also demonstrated clinical activities in solid tumors. In our present study, we screened our internal compound library and discovered a novel HDACi, WW437, with potent anti-breast cancer ability in vitro and in vivo. WW437 significantly inhibited phosphorylated EphA2 and EphA2 expression. Further study demonstrated WW437 blocked HDACs-EphA2 signaling axis in breast cancer. In parallel, we found that EphA2 expression positively correlates with breast cancer progression; and combined use of WW437 and an EphA2 inhibitor (ALW-II-41-27) exerted more remarkable effect on breast cancer growth than either drug alone. Our findings suggested inhibition of HDACs-EphA2 signaling axis with WW437 alone or in combination with other agents may be a promising therapeutic strategy for advanced breast cancer.

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WW437 is a novel HDACi, which displays potent anticancer activity in breast cancer.

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HDACs-EphA2 signaling axis represents a novel target in breast cancer.

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WW437 is a promising therapeutic agent for advanced breast cancer, alone or in combination with EphA2 inhibitor.

Histone deacetylase inhibitors (HDACi) are small molecules targeting epigenetic enzymes approved for cutaneous T-cell lymphoma (CTCL), peripheral T-cell lymphoma (PTCL) and multiple myeloma (MM) treatment, which have also demonstrated clinical activities in solid tumors, including lung cancer and breast cancer. Herein we report a novel HDACi WW437, which displays potent anticancer activity in both cultured cancer cells and xenograft models. Importantly, our work reveals WW437 significantly blocked the HDACs-EphA2 signaling axis in breast cancer. WW437 exhibited significant inhibitory effects on tumor growth and metastases with little toxicity, and tumors from treated mice showed decreased EphA2 expression, suggesting that EphA2 may be a useful biomarker of response to WW437. We also found that EphA2 expression positively correlates with tumor progression in aggressive breast cancer.

Spatially modulated ephrinA1:EphA2 signaling increases local contractility and global focal adhesion dynamics to promote cell motility

Recent studies have revealed pronounced effects of the spatial distribution of EphA2 receptors on cellular response to receptor activation. However, little is known about molecular mechanisms underlying this spatial sensitivity, in part due to lack of experimental systems. Here, we introduce a hybrid live-cell patterned supported lipid bilayer experimental platform in which the sites of EphA2 activation and integrin adhesion are spatially controlled. Using a series of live-cell imaging and single-molecule tracking experiments, we map the transmission of signals from ephrinA1:EphA2 complexes. Results show that ligand-dependent EphA2 activation induces localized myosin-dependent contractions while simultaneously increasing focal adhesion dynamics throughout the cell. Mechanistically, Src kinase is activated at sites of ephrinA1:EphA2 clustering and subsequently diffuses on the membrane to focal adhesions, where it up-regulates FAK and paxillin tyrosine phosphorylation. EphrinA1:EphA2 signaling triggers multiple cellular responses with differing spatial dependencies to enable a directed migratory response to spatially resolved contact with ephrinA1 ligands.

Differential Expression Patterns of Eph Receptors and Ephrin Ligands in Human Cancers

Eph receptors constitute the largest family of receptor tyrosine kinases, which are activated by ephrin ligands that either are anchored to the membrane or contain a transmembrane domain. These molecules play important roles in the development of multicellular organisms, and the physiological functions of these receptor-ligand pairs have been extensively documented in axon guidance, neuronal development, vascular patterning, and inflammation during tissue injury. The recognition that aberrant regulation and expression of these molecules lead to alterations in proliferative, migratory, and invasive potential of a variety of human cancers has made them potential targets for cancer therapeutics. We present here the involvement of Eph receptors and ephrin ligands in lung carcinoma, breast carcinoma, prostate carcinoma, colorectal carcinoma, glioblastoma, and medulloblastoma. The aberrations in their abundances are described in the context of multiple signaling pathways, and differential expression is suggested as the mechanism underlying tumorigenesis.

Reduction of Circulating Cancer Cells and Metastases in Breast-Cancer Models by a Potent EphA2-Agonistic Peptide-Drug Conjugate

EphA2 overexpression has been associated with metastasis in multiple cancer types, including melanomas and ovarian, prostate, lung, and breast cancers. We have recently proposed the development of peptide–drug conjugates (PDCs) using agonistic EphA2-targeting agents, such as the YSA peptide or its optimized version, 123B9. Although our studies indicated that YSA– and 123B9–drug conjugates can selectively deliver cytotoxic drugs to cancer cells in vivo, the relatively low cellular agonistic activities (i.e., the high micromolar concentrations required) of the agents toward the EphA2 receptor remained a limiting factor to the further development of these PDCs in the clinic. Here, we report that a dimeric version of 123B9 can induce receptor activation at nanomolar concentrations. Furthermore, we demonstrated that the conjugation of dimeric 123B9 with paclitaxel is very effective at targeting circulating tumor cells and inhibiting lung metastasis in breast-cancer models. These studies represent an important step toward the development of effective EphA2-targeting PDCs.

Optogenetic activation of EphB2 receptor in dendrites induced actin polymerization by activating Arg kinase

Erythropoietin-producing hepatocellular (Eph) receptors regulate a wide array of developmental processes by responding to cell-cell contacts. EphB2 is well-expressed in the brain and known to be important for dendritic spine development, as well as for the maintenance of the synapses, although the mechanisms of these functions have not been fully understood. Here we studied EphB2's functions in hippocampal neurons with an optogenetic approach, which allowed us to specify spatial regions of signal activation and monitor in real-time the consequences of signal activation. We designed and constructed OptoEphB2, a genetically encoded photoactivatable EphB2. Photoactivation of OptoEphB2 in fibroblast cells induced receptor phosphorylation and resulted in cell rounding ------- a well-known cellular response to EphB2 activation. In contrast, local activation of OptoEphb2 in dendrites of hippocampal neurons induces rapid actin polymerization, resulting dynamic dendritic filopodial growth. Inhibition of Rac1 and CDC42 did not abolish OptoEphB2-induced actin polymerization. Instead, we identified Abelson tyrosine-protein kinase 2 (Abl2/Arg) as a necessary effector in OptoEphB2-induced filopodia growth in dendrites. These findings provided new mechanistic insight into EphB2's role in neural development and demonstrated the advantage of OptoEphB as a new tool for studying EphB signaling.

One-Bead-Two-Compound Thioether Bridged Macrocyclic γ-AApeptide Screening Library against EphA2

Identification of molecular ligands that recognize peptides or proteins is significant but poses a fundamental challenge in chemical biology and biomedical sciences. Development of cyclic peptidomimetic library is scarce, and thus discovery of cyclic peptidomimetic ligands for protein targets is rare. Herein we report the unprecedented one-bead-two-compound (OBTC) combinatorial library based on a novel class of the macrocyclic peptidomimetics γ-AApeptides. In the library, we utilized the coding peptide tags synthesized with Dde-protected α-amino acids, which were orthogonal to solid phase synthesis of γ-AApeptides. Employing the thioether linkage, the desired macrocyclic γ-AApeptides were found to be effective for ligand identification. Screening the library against the receptor tyrosine kinase EphA2 led to the discovery of one lead compound that tightly bound to EphA2 (K_d = 81 nM) and potently antagonized EphA2-mediated signaling. This new approach of macrocyclic peptidomimetic library may lead to a novel platform for biomacromolecular surface recognition and function modulation.

Overexpression and correlation of HIF-2α, VEGFA and EphA2 in residual hepatocellular carcinoma following high-intensity focused ultrasound treatment: Implications for tumor recurrence and progression

Rapid growth of residual tumors can occur as a result of their recurrence and progression. The present study aimed to investigate the expression of hypoxia inducible factor-2 subunit α (HIF-2α), vascular endothelial growth factor A (VEGFA), erythropoietin-producing hepatocellular A2 (EphA2) and angiogenesis in residual hepatocellular carcinoma (HCC), following treatment with high-intensity focused ultrasound (HIFU) ablation, in order to investigate the association between protein expression and tumor recurrence and growth. Athymic BALB/c (nu/nu) mice were subcutaneously inoculated with the HCC cell line HepG2, in order to create xenograft tumors. Approximately 30 days post-inoculation, eight mice were treated with HIFU, whereas eight mice received no treatment and acted as the control group. Residual tumor tissues were obtained from the experimental groups after one month. Levels of HIF-2α, VEGFA, EphA2 and cluster of differentiation 31 (CD31) expression was measured by immunohistochemical staining. CD31-positive vascular endothelial cells were counted to calculate microvascular density (MVD), and western blot analysis was performed to determine levels of HIF-2α, VEGFA, and EphA2 protein. It was found that the expression levels of HIF-2α, VEGFA, EphA2, and MVD proteins in residual HCC tissues were significantly higher than in the control group tissues (P<0.05). Tumor MVD was strongly correlated with VEGFA (R=0.957, P<0.01) and EphA2 (R=0.993, P<0.01) protein expression levels. Furthermore, there was a significant positive correlation between HIF-2α and EphA2 expression (R=0.991, P<0.01). The correlation between VEGFA and EphA2 expression was also positive (R=0.985, P<0.01). These data suggest that overexpression of HIF-2α, VEGFA and EphA2 is related to angiogenesis in residual HCC following HIFU ablation, potentially via their association with key mediators of recurrence.

Tyrosine Kinase Receptor Landscape in Lung Cancer: Therapeutical Implications

Lung cancer is a heterogeneous disease responsible for the most cases of cancer-related deaths. The majority of patients are clinically diagnosed at advanced stages, with a poor survival rate. For this reason, the identification of oncodrivers and novel biomarkers is decisive for the future clinical management of this pathology. The rise of high throughput technologies popularly referred to as “omics” has accelerated the discovery of new biomarkers and drivers for this pathology. Within them, tyrosine kinase receptors (TKRs) have proven to be of importance as diagnostic, prognostic, and predictive tools and, due to their molecular nature, as therapeutic targets. Along this review, the role of TKRs in the different lung cancer histologies, research on improvement of anti-TKR therapy, and the current approaches to manage anti-TKR resistance will be discussed.

Dysregulation of EGFR Pathway in EphA2 Cell Subpopulation Significantly Associates with Poor Prognosis in Colorectal Cancer

PURPOSE

EphA2 receptor is involved in multiple cross-talks with other cellular networks, including EGFR, FAK, and VEGF pathways, with which it collaborates to stimulate cell migration, invasion, and metastasis. Colorectal cancer (CRC) EphA2 overexpression has also been correlated to stem-like properties of cells and tumor malignancy. We investigated the molecular cross-talk and miRNAs modulation of the EphA2 and EGFR pathways. We also explored the role of EphA2/EGFR pathway mediators as prognostic factors or predictors of cetuximab benefit in patients with CRC.

EXPERIMENTAL DESIGN

Gene expression analysis was performed in EphA2_high cells isolated from CRC of the AOM/DSS murine model by FACS-assisted procedures. Six independent cohorts of patients were stratified by EphA2 expression to determine the potential prognostic role of a EphA2/EGFR signature and its effect on cetuximab treatment response.

RESULTS

We identified a gene expression pattern (EphA2, Efna1, Egfr, Ptpn12, and Atf2) reflecting the activation of EphA2 and EGFR pathways and a coherent dysregulation of mir-26b and mir-200a. Such a pattern showed prognostic significance in patients with stage I-III CRC, in both univariate and multivariate analysis. In patients with stage IV and WT KRAS, EphA2/Efna1/Egfr gene expression status was significantly associated with poor response to cetuximab treatment. Furthermore, EphA2 and EGFR overexpression showed a combined effect relative to cetuximab resistance, independently from KRAS mutation status.

CONCLUSIONS

These results suggest that EphA2/Efna1/Egfr genes, linked to a possible control by miR-200a and miR-26b, could be proposed as novel CRC prognostic biomarkers. Moreover, EphA2 could be linked to a mechanism of resistance to cetuximab alternative to KRAS mutations. Clin Cancer Res; 23(1); 159-70. ©2016 AACR.

Phosphoproteomic analysis of interacting tumor and endothelial cells identifies regulatory mechanisms of transendothelial migration

The exit of metastasizing tumor cells from the vasculature, extravasation, is regulated by their dynamic interactions with the endothelial cells that line the internal surface of vessels. To elucidate signals controlling tumor cell adhesion to the endothelium and subsequent transendothelial migration, we performed phosphoproteomic analysis to map cell-specific changes in protein phosphorylation that were triggered by contact between metastatic MDA-MB-231 breast cancer cells and endothelial cells. From the 2669 unique phosphorylation sites identified, 77 and 43 were differentially phosphorylated in the tumor cells and endothelial cells, respectively. The receptor tyrosine kinase ephrin type A receptor 2 (EPHA2) exhibited decreased Tyr(772) phosphorylation in the cancer cells upon endothelial contact. Knockdown of EPHA2 increased adhesion of the breast cancer cells to human umbilical vein endothelial cells (HUVECs) and their transendothelial migration in coculture cell assays, as well as early-stage lung colonization in vivo. EPHA2-mediated inhibition of transendothelial migration of breast cancer cells depended on interaction with the ligand ephrinA1 on HUVECs and phosphorylation of EPHA2-Tyr(772). When EPHA2 phosphorylation dynamics were compared between cell lines of different metastatic ability, EPHA2-Tyr(772) was rapidly dephosphorylated after ephrinA1 stimulation specifically in cells targeting the lung. Knockdown of the phosphatase LMW-PTP reduced adhesion and transendothelial migration of the breast cancer cells. Overall, cell-specific phosphoproteomic analysis provides a bidirectional map of contact-initiated signaling between tumor and endothelial cells that can be further investigated to identify mechanisms controlling the transendothelial cell migration of cancer cells.

Identification of an Interfering Ligand Aptamer for EphB2/3 Receptors

The Eph receptors are transmembrane proteins that belong to the receptor tyrosine kinases superfamily. Elevated Eph/ephrin expression levels have been associated with angiogenesis and tumor vasculature in many types of human cancers, including breast, lung, and prostate cancers, melanoma, and leukemia. In glioblastoma (GBM), the dysregulated expression of Eph receptors and of corresponding ephrin ligands has been associated with higher tumor grade and poor prognosis making them effective targets for therapeutic drugs. In this study, we describe the GL43.T, an anti-Eph aptamer, able to bind at high-affinity EphB3 and EphB2. Moreover, the GL43.T aptamer inhibits the glioma cell vitality and interferes with ephrine-B1 inhibition of chemotactic serum-stimulated cell migration. GL43.T aptamer represents a promising therapeutic molecule for EphB3-dependent cancers.

Overexpression of Ephrin A2 receptors in cancer stromal cells is a prognostic factor for the relapse of gastric cancer

BACKGROUND

Microenvironments control cancer growth and progression. We explored the prognostic impact of stromal reaction and cancer stromal cells on relapse risk and survival after curative gastrectomy in gastric cancer patients.

METHODS

Tissue samples were obtained from 107 patients with gastric adenocarcinoma who underwent curative (R0) gastrectomy. Primary stromal cells isolated from gastric cancer tissue (GCSC) and normal gastric tissue (Gastric stromal cell: GSC) in each patient were cultured and subjected to comprehensive proteome (LC-MS/MS) and real-time RT-PCR analysis. Expression of Ephrin A2 receptors (EphA2) in cancers and GCSC was evaluated immunohistochemically. Intermingling of EphA2-positive cancer cells and GCSC (IC/A2+) and overexpression of EphA2 in cancer cells (Ca/A2+) in invasive parts of tumors were assessed, as were relationships of IC/A2+, Ca/A2+, and clinicopathological factors with relapse-free survival and overall survival.

RESULTS

Proteome analysis showed that EphA2 expression was significantly higher in GCSC than GSC. Real-time RT-PCR analysis showed that levels of EphA1/A2/A3/A5 and EphB2/B4 were ≥2.0-fold higher in GCSC than GSC. Ca/A2 and IC/A2 were positive in 65 (60.7 %) and 26 (24.3 %) patients, respectively. Relapse was significantly more frequent in IC/A2-positive than in IC/A2-negative (HR, 2.12; 95 % CI, 1.16-5.41; p = 0.0207) patients. Among the 54 patients who received S-1 adjuvant chemotherapy, relapse-free survival (RFS) was significantly shorter in those who were IC/A2-positive than in those who were IC/A2-negative and Ca/A2-negative (HR, 2.83; 95 % CI, 1.12-12.12; p = 0.0339). Multivariable analysis indicated that pathological stage (p = 0.010) and IC/A2+ (p = 0.008) were independent risk factors for recurrence.

CONCLUSION

IC/A2+ was predictive of relapse after curative (R0) gastrectomy.

miR-200a inhibits migration of triple-negative breast cancer cells through direct repression of the EPHA2 oncogene

Triple-negative breast cancer (TNBC) is characterized by aggressiveness and affects 10-20% of breast cancer patients. Since TNBC lacks expression of ERα, PR and HER2, existing targeted treatments are not effective and the survival is poor. In this study, we demonstrate that the tumor suppressor microRNA miR-200a directly regulates the oncogene EPH receptor A2 (EPHA2) and modulates TNBC migration. We show that EPHA2 expression is correlated with poor survival specifically in basal-like breast cancer and that its expression is repressed by miR-200a through direct interaction with the 3'UTR of EPHA2. This regulation subsequently affects the downstream activation of AMP-activated protein kinase (AMPK) and results in decreased cell migration of TNBC. We establish that miR-200a directs cell migration in a dual manner; in addition to regulating the well-characterized E-cadherin pathway it also regulates a EPHA2 pathway. The miR-200a-EPHA2 axis is a novel mechanism highlighting the possibility of utilizing miR-200a delivery to target TNBC metastases.

HGF-induced serine 897 phosphorylation of EphA2 regulates epithelial morphogenesis of MDCK cells in 3D culture

Expression of EphA2 is upregulated in various cancers that are derived from epithelial cells and correlates with the ability of a cancer cell to undergo migration and invasion. Here we have investigated the role of EphA2 in the epithelial morphogenesis of Madin-Darby canine kidney (MDCK) cells in three-dimensional culture. We show that EphA2 is phosphorylated on serine residue 897 through hepatocyte growth factor (HGF) stimulation using a phosphatidylinositol 3-kinase (PI3K)-Akt-dependent mechanism and that this phosphorylation is required for the formation of extensions, the first step of tubulogenesis, in MDCK cysts. By contrast, stimulation using the ligand ephrinA1 dephosphorylates EphA2 on serine residue 897 and suppresses the HGF-induced morphological change. Furthermore, activation of the small GTPase RhoG is involved in the HGF-induced formation of extensions downstream of EphA2. These observations suggest that a ligand-independent activity of EphA2 contributes to epithelial morphogenesis.

EPHA2 is a mediator of vemurafenib resistance and a novel therapeutic target in melanoma

BRAF(V600E) is the most common oncogenic lesion in melanoma and results in constitutive activation of the MAPK pathway and uncontrolled cell growth. Selective BRAF inhibitors such as vemurafenib have been shown to neutralize oncogenic signaling, restrain cellular growth, and improve patient outcome. Although several mechanisms of vemurafenib resistance have been described, directed solutions to overcome these resistance lesions are still lacking. Herein, we found that vemurafenib resistance can be (i) mediated by EPHA2, a member of the largest receptor tyrosine kinases (RTK) subfamily erythropoietin-producing hepatocellular (EPH) receptors, and (ii) associated with a greater phenotypic dependence on EPHA2. Furthermore, we developed a series of first-in-class EPHA2 inhibitors and show that these new compounds potently induce apoptosis, suppress viability, and abrogate tumorigenic growth of melanoma cells, including those that are resistant to vemurafenib. These results provide proof of concept that RTK-guided growth, and therapeutic resistance, can be prospectively defined and selectively targeted.

SIGNIFICANCE

In this study, we show that resistance to selective BRAF inhibitors can be mediated by the RTK EPHA2. Furthermore, direct targeting of EPHA2 can successfully suppress melanoma growth and mitigate therapeutic resistance.

Elevated Slit2 Activity Impairs VEGF-Induced Angiogenesis and Tumor Neovascularization in EphA2-Deficient Endothelium

Angiogenic remodeling during embryonic development and in adult tissue homeostasis is orchestrated by cooperative signaling between several distinct molecular pathways, which are often exploited by tumors. Indeed, tumors upregulate proangiogenic molecules while simultaneously suppressing angiostatic pathways to recruit blood vessels for growth, survival, and metastatic spread. Understanding how cancers exploit proangiogenic and antiangiogenic signals is a key step in developing new, molecularly targeted antiangiogenic therapies. While EphA2, a receptor tyrosine kinase (RTK), is required for VEGF-induced angiogenesis, the mechanism through which these pathways intersect remains unclear. Slit2 expression is elevated in EphA2-deficient endothelium, and here it is reported that inhibiting Slit activity rescues VEGF-induced angiogenesis in cell culture and in vivo, as well as VEGF-dependent tumor angiogenesis, in EphA2-deficient endothelial cells and animals. Moreover, blocking Slit activity or Slit2 expression in EphA2-deficient endothelial cells restores VEGF-induced activation of Src and Rac, both of which are required for VEGF-mediated angiogenesis. These data suggest that EphA2 suppression of Slit2 expression and Slit angiostatic activity enables VEGF-induced angiogenesis in vitro and in vivo, providing a plausible mechanism for impaired endothelial responses to VEGF in the absence of EphA2 function.

IMPLICATIONS

Modulation of angiostatic factor Slit2 by EphA2 receptor regulates endothelial responses to VEGF-mediated angiogenesis and tumor neovascularization.

Geldanamycin mediates the apoptosis of gastric carcinoma cells through inhibition of EphA2 protein expression

The aim of the present study was to investigate the role of EphA2 in the carcinogenesis and progression of gastric carcinoma. Moreover, we aimed to determine the effect of geldanamycin (GA), an inhibitor of Hsp90, on the proliferation and apoptosis of human gastric carcinoma cells. Gastric carcinoma tissues, paired adjacent mucosa and paired normal mucosa were obtained from resected surgical specimens of gastric carcinoma, and EphA2 mRNA and protein levels were assessed by RT-PCR, immunohistochemistry and western blot analysis. FCM was used to detect cell cycle distribution and apoptosis. MGC803 cell proliferation and apoptosis were assessed by MTT and FCM, respectively. We found that EphA2 protein was increased in the carcinogenesis of gastric epithelial cells. Proliferation index (PI) was significantly upregulated following an increase in EphA2 expression in gastric carcinoma compared with dysplasia and normal samples, and was notably correlated with grade and lymph node metastasis. Knockdown of EphA2 increased the apoptosis rate and decreased the PI of MGC803 cells, which overexpressed the EphA2 protein. GA inhibited the cell proliferation of MGC803 cells in a dose- and time-dependent manner and induced cell apoptosis. In addition, GA decreased the EphA2 protein expression in MGC803 cells. Overexpression of EphA2 inhibited cell growth, blocked cells in the G0/G1 stage and increased cell apoptosis induced by GA in MGC803 cells. However, knockdown of EphA2 in MGC803 cells increased the apoptosis ratio induced by GA. In conclusion, EphA2 overexpression is an important characteristic in the carcinogenesis of gastric epithelial cells, followed by an increase in apoptosis and cell cycle arrest. Knockdown of EphA2 blocked MGC803 cell proliferation and induced cell apoptosis. In conclusion GA inhibits MGC803 cell proliferation and induces cell apoptosis by upregulating expression of EphA2.

Eph- and ephrin-dependent mechanisms in tumor and stem cell dynamics

The erythropoietin-producing hepatocellular (Eph) receptors comprise the largest family of receptor tyrosine kinases (RTKs). Initially regarded as axon-guidance and tissue-patterning molecules, Eph receptors have now been attributed with various functions during development, tissue homeostasis, and disease pathogenesis. Their ligands, ephrins, are synthesized as membrane-associated molecules. At least two properties make this signaling system unique: (1) the signal can be simultaneously transduced in the receptor- and the ligand-expressing cell, (2) the signaling outcome through the same molecules can be opposite depending on cellular context. Moreover, shedding of Eph and ephrin ectodomains as well as ligand-dependent and -independent receptor crosstalk with other RTKs, proteases, and adhesion molecules broadens the repertoire of Eph/ephrin functions. These integrated pathways provide plasticity to cell-microenvironment communication in varying tissue contexts. The complex molecular networks and dynamic cellular outcomes connected to the Eph/ephrin signaling in tumor-host communication and stem cell niche are the main focus of this review.

Eph receptor tyrosine kinases in cancer stem cells

Eph receptor tyrosine kinases (RTKs) and their ligands, ephrins, play critical roles in development, tissue homeostasis, and cancer. Because Eph receptors are expressed in most adult stem cell niches and in many types of cancers, it has been long suspected that this family of RTKs may also regulate the function of cancer stem-like cells (CSCs). This review will focus on recent studies to elucidate the contribution of Eph/ephrin molecules in CSC self-renewal and tumorigenicity, as well as describe efforts to target these molecules in cancer. Because CSCs are often resistant to therapeutic intervention and have been shown to depend on Eph RTKs for self-renewal, targeting Eph receptors may hold promise for the treatment of drug-resistant cancers.

EphA receptors regulate prostate cancer cell dissemination through Vav2-RhoA mediated cell-cell repulsion

Metastatic prostate cancer cells display EphB receptor-mediated attraction when they contact stromal fibroblasts but EphA-driven repulsion when they contact one another. The impact of these ‘social’ interactions between cells during cancer cell invasion and the signalling mechanisms downstream of Eph receptors are unclear. Here we show that EphA receptors regulate prostate cancer cell dissemination in a 2D dispersal assay and in a 3D cancer cell spheroid assay. We show that EphA receptors signal via the exchange factor Vav2 to activate RhoA and that both Vav2 and RhoA are required for prostate cancer cell–cell repulsion. Furthermore, we find that in EphA2/EphA4, Vav2 or RhoA siRNA-treated cells, contact repulsion can be restored by partial microtubule destabilisation. We propose that EphA–Vav2–RhoA-mediated repulsion between contacting cancer cells at the tumour edge could enhance their local invasion away from the primary tumour.

Receptor tyrosine kinase alterations and therapeutic opportunities in squamous cell carcinoma of the lung

PURPOSE

Targeted therapy has greatly improved the treatment for adenocarcinoma of the lung, but not squamous cell carcinoma (SCC) of the lung. The current paper describes the abnormalities of receptor tyrosine kinases (RTK) in lung SCC in a hope to stimulate the development of therapeutics that can have clinical impact.

METHODS

We reviewed both clinical and preclinical studies published in English regarding RTK abnormalities and/ or RTK-targeting treatment for SCC of the lung.

RESULTS

RTK alterations have been demonstrated as biological signature for SCC of the lung. A number of clinical trials of RTK-targeting therapy have been carried out or are ongoing, with encouraging results.

CONCLUSIONS

SCC of the lung should be treated as an independent disease with unique treatment options based on molecular changes, particularly RTK.

Genetic and pharmacologic inhibition of EPHA2 promotes apoptosis in NSCLC

Genome-wide analyses determined previously that the receptor tyrosine kinase (RTK) EPHA2 is commonly overexpressed in non-small cell lung cancers (NSCLCs). EPHA2 overexpression is associated with poor clinical outcomes; therefore, EPHA2 may represent a promising therapeutic target for patients with NSCLC. In support of this hypothesis, here we have shown that targeted disruption of EphA2 in a murine model of aggressive Kras-mutant NSCLC impairs tumor growth. Knockdown of EPHA2 in human NSCLC cell lines reduced cell growth and viability, confirming the epithelial cell autonomous requirements for EPHA2 in NSCLCs. Targeting EPHA2 in NSCLCs decreased S6K1-mediated phosphorylation of cell death agonist BAD and induced apoptosis. Induction of EPHA2 knockdown within established NSCLC tumors in a subcutaneous murine model reduced tumor volume and induced tumor cell death. Furthermore, an ATP-competitive EPHA2 RTK inhibitor, ALW-II-41-27, reduced the number of viable NSCLC cells in a time-dependent and dose-dependent manner in vitro and induced tumor regression in human NSCLC xenografts in vivo. Collectively, these data demonstrate a role for EPHA2 in the maintenance and progression of NSCLCs and provide evidence that ALW-II-41-27 effectively inhibits EPHA2-mediated tumor growth in preclinical models of NSCLC.

Eph receptors and ephrins as targets for cancer therapy

Eph receptor tyrosine kinases and their ephrin ligands are involved in various signalling pathways and mediate critical steps of a wide variety of physiological and pathological processes. Increasing experimental evidence demonstrates that both Eph receptor and ephrin ligands are overexpressed in a number of human tumours, and are associated with tumour growth, invasiveness and metastasis. In this regard, the Eph/ephrin system provides the foundation for potentially exciting new targets for anticancer therapies for Eph-expressing tumours. The purpose of this review is to outline current advances in the role of Eph receptors and ephrin ligands in cancer, and to discuss novel therapeutic approaches of anticancer therapies.

Role of the EphB2 receptor in autophagy, apoptosis and invasion in human breast cancer cells

The Eph and Ephrin proteins, which constitute the largest family of receptor tyrosine kinases, are involved in normal tissue development and cancer progression. Here, we examined the expression and role of the B-type Eph receptor EphB2 in breast cancers. By immunohistochemistry using a progression tissue microarray of human clinical samples, we found EphB2 to be expressed in benign tissues, but strongly increased in cancers particularly in invasive and metastatic carcinomas. Subsequently, we found evidence that EphB2, whose expression varies in established cell breast lines, possesses multiple functions. First, the use of a DOX-inducible system to restore EphB2 function to low expressers resulted in decreased tumor growth in vitro and in vivo, while its siRNA-mediated silencing in high expressers increased growth. This function involves the onset of apoptotic death paralleled by caspases 3 and 9 activation. Second, EphB2 was also found to induce autophagy, as assessed by immunofluorescence and/or immunoblotting examination of the LC3, ATG5 and ATG12 markers. Third, EphB2 also has a pro-invasive function in breast cancer cells that involves the regulation of MMP2 and MMP9 metalloproteases and can be blocked by treatment with respective neutralizing antibodies. Furthermore, EphB2-induced invasion is kinase-dependent and is impeded in cells expressing a kinase-dead mutant EphB2. In summary, we identified a mechanism involving a triple role for EphB2 in breast cancer progression, whereby it regulates apoptosis, autophagy, and invasion.

Variable metastatic potentials correlate with differential plectin and vimentin expression in syngeneic androgen independent prostate cancer cells

Prostate cancer is a clinically heterogeneous disease, ranging from indolent asymptomatic disease to very aggressive metastatic and life threatening forms of the disease. Distant metastasis represents the major lethal cause of prostate cancer. The most critical clinical challenge in the management of the patients is identifying those individuals at risk of developing metastatic disease. To understand the molecular mechanisms of prostate cancer metastasis and identify markers with metastatic potential, we have analyzed protein expression in two syngeneic prostate cancer cells lines PC3-N2 and PC3-ML2 using isobaric tags for relative and absolute quantitation labeling and multi-dimensional protein identification technology liquid chromatography matrix assisted laser desorption ionization tandem mass spectrometry. PC3-N2 is lowly metastatic while PC3-ML2 highly metastatic. A total of 1,756 proteins were identified in the analyses with 130 proteins showing different expression levels (p<0.01) in the two cell lines. Out of these, 68 proteins were found to be significantly up-regulated while 62 are significantly down-regulated in PC3-ML2 cells compared with PC3-N2 cells. The upregulation of plectin and vimentin which were the most significantly differentially expressed were validated by Western blot and their functional relevance with respect to invasion and migration was determined by siRNA gene silencing. To our knowledge, this study is the first to demonstrate that up-regulation of vimentin and plectin expression positively correlates with the invasion and metastasis of androgen-independent PCA.

Genetic changes in squamous cell lung cancer: a review

Identifying specific somatic mutations that drive tumor growth has transformed the treatment of lung cancer. For example, cancers with sensitizing epidermal growth factor receptor mutations and echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase translocations can have remarkable responses to epidermal growth factor receptor and ALK inhibitors respectively, leading to significant clinical benefit. However, effective molecularly targeted therapies have disproportionately impacted adenocarcinomas compared to squamous cell carcinomas, and never or light smokers compared to heavy smokers. Further progress in non-small-cell lung cancer will require the identification and effective targeting of molecular alterations in all subtypes of lung cancer. Here, we review the current knowledge about the molecular alterations found in squamous cell carcinoma of the lung. First, we will discuss the ongoing efforts to comprehensively assess the squamous cell carcinoma genome. We will then discuss the evidence supporting the role of specific genes in driving squamous cell carcinomas. By describing the landscape of somatic targets in squamous cell lung cancer, we hope to crystallize the current understanding of potential targets, spur development of therapies that can have clinical impact, and underscore the importance of new discoveries in this field.

The ephrin receptor tyrosine kinase A2 is a cellular receptor for Kaposi's sarcoma–associated herpesvirus

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi's sarcoma(1), a highly vascularized tumor originating from lymphatic endothelial cells, and of at least two different B cell malignancies(2,3). A dimeric complex formed by the envelope glycoproteins H and L (gH-gL) is required for entry of herpesviruses into host cells(4). We show that the ephrin receptor tyrosine kinase A2 (EphA2) is a cellular receptor for KSHV gH-gL. EphA2 co-precipitated with both gH-gL and KSHV virions. Infection of human epithelial cells with a GFP-expressing recombinant KSHV strain, as measured by FACS analysis, was increased upon overexpression of EphA2. Antibodies against EphA(2) and siRNAs directed against EphA2 inhibited infection of endothelial cells. Pretreatment of KSHV with soluble EphA2 resulted in inhibition of KSHV infection by up to 90%. This marked reduction of KSHV infection was seen with all the different epithelial and endothelial cells used in this study. Similarly, pretreating epithelial or endothelial cells with the soluble EphA2 ligand ephrinA4 impaired KSHV infection. Deletion of the gene encoding EphA2 essentially abolished KSHV infection of mouse endothelial cells. Binding of gH-gL to EphA2 triggered EphA2 phosphorylation and endocytosis, a major pathway of KSHV entry(5,6). Quantitative RT-PCR and in situ histochemistry revealed a close correlation between KSHV infection and EphA2 expression both in cultured cells derived from human Kaposi's sarcoma lesions or unaffected human lymphatic endothelium, and in situ in Kaposi's sarcoma specimens, respectively. Taken together, our results identify EphA2, a tyrosine kinase with known functions in neovascularization and oncogenesis, as an entry receptor for KSHV.