EphA2- and HDAC-Targeted Combination Therapy in Endometrial Cancer

Endometrial cancer is the most frequent malignant tumor of the female reproductive tract but lacks effective therapy. EphA2, a receptor tyrosine kinase, is overexpressed by various cancers including endometrial cancer and is associated with poor clinical outcomes. In preclinical models, EphA2-targeted drugs had modest efficacy. To discover potential synergistic partners for EphA2-targeted drugs, we performed a high-throughput drug screen and identified panobinostat, a histone deacetylase inhibitor, as a candidate. We hypothesized that combination therapy with an EphA2 inhibitor and panobinostat leads to synergistic cell death. Indeed, we found that the combination enhanced DNA damage, increased apoptosis, and decreased clonogenic survival in Ishikawa and Hec1A endometrial cancer cells and significantly reduced tumor burden in mouse models of endometrial carcinoma. Upon RNA sequencing, the combination was associated with downregulation of cell survival pathways, including senescence, cyclins, and cell cycle regulators. The Axl-PI3K-Akt-mTOR pathway was also decreased by combination therapy. Together, our results highlight EphA2 and histone deacetylase as promising therapeutic targets for endometrial cancer.

Molecular Determinants of EphA2 and EphB2 Antagonism Enable the Design of Ligands with Improved Selectivity

With the aim of identifying novel antagonists selective for the EphA receptor family, a combined experimental and computational approach was taken to investigate the molecular basis of the recognition between a prototypical Eph-ephrin antagonist (UniPR1447) and two representative receptors of the EphA and EphB subfamilies, namely, EphA2 and EphB2 receptors. The conformational free-energy surface (FES) of the binding state of UniPR1447 within the ligand binding domain of EphA2 and EphB2, reconstructed from molecular dynamics (MD) simulations performed on the microsecond time scale, was exploited to drive the design and synthesis of a novel antagonist selective for EphA2 over the EphB2 receptor. The availability of compounds with this pharmacological profile will help discriminate the importance of these two receptors in the insurgence and progression of cancer.

Combination of EphA2- and Wee1-Targeted Therapies in Endometrial Cancer

EphA2 tyrosine kinase is upregulated in many cancers and correlated with poor survival of patients, including those with endometrial cancer. EphA2-targeted drugs have shown modest clinical benefit. To improve the therapeutic response to such drugs, we performed a high-throughput chemical screen to discover novel synergistic partners for EphA2-targeted therapeutics. Our screen identified the Wee1 kinase inhibitor, MK1775, as a synergistic partner to EphA2, and this finding was confirmed using both in vitro and in vivo experiments. We hypothesized that Wee1 inhibition would sensitize cells to EphA2-targeted therapy. Combination treatment decreased cell viability, induced apoptosis, and reduced clonogenic potential in endometrial cancer cell lines. In vivo Hec1A and Ishikawa-Luc orthotopic mouse models of endometrial cancer showed greater anti-tumor responses to combination treatment than to either monotherapy. RNASeq analysis highlighted reduced cell proliferation and defective DNA damage response pathways as potential mediators of the combination's effects. In conclusion, our preclinical findings indicate that Wee1 inhibition can enhance the response to EphA2-targeted therapeutics in endometrial cancer; this strategy thus warrants further development.

Bicyclic Peptide Makes Targeting EphA2 Possible

A tumor-penetrating bicyclic peptide that delivers a toxic payload may have finally unlocked the therapeutic potential of targeting EphA2. According to phase I trial data, BT5528 yielded clinical responses in three patients with ovarian and urothelial cancers-without any of the toxicity issues that have plagued other EphA2-directed therapeutic candidates.

Targeting EphA2 suppresses hepatocellular carcinoma initiation and progression by dual inhibition of JAK1/STAT3 and AKT signaling

Hepatocellular carcinoma (HCC) remains one of the deadliest malignancies worldwide. One major obstacle to treatment is a lack of effective molecular-targeted therapies. In this study, we find that EphA2 expression and signaling are enriched in human HCC and associated with poor prognosis. Loss of EphA2 suppresses the initiation and growth of HCC both in vitro and in vivo. Furthermore, CRISPR/CAS9-mediated EphA2 inhibition significantly delays tumor development in a genetically engineered murine model of HCC. Mechanistically, we discover that targeting EphA2 suppresses both AKT and JAK1/STAT3 signaling, two separate oncogenic pathways in HCC. We also identify a small molecule kinase inhibitor of EphA2 that suppresses tumor progression in a murine HCC model. Together, our results suggest EphA2 as a promising therapeutic target for HCC.

Inhibition of EphA2 by Dasatinib Suppresses Radiation-Induced Intestinal Injury

Radiation-induced multiorgan dysfunction is thought to result primarily from damage to the endothelial system, leading to a systemic inflammatory response that is mediated by the recruitment of leukocytes. The Eph–ephrin signaling pathway in the vascular system participates in various disease developmental processes, including cancer and inflammation. In this study, we demonstrate that radiation exposure increased intestinal inflammation via endothelial dysfunction, caused by the radiation-induced activation of EphA2, an Eph receptor tyrosine kinase, and its ligand ephrinA1. Barrier dysfunction in endothelial and epithelial cells was aggravated by vascular endothelial–cadherin disruption and leukocyte adhesion in radiation-induced inflammation both in vitro and in vivo. Among all Eph receptors and their ligands, EphA2 and ephrinA1 were required for barrier destabilization and leukocyte adhesion. Knockdown of EphA2 in endothelial cells reduced radiation-induced endothelial dysfunction. Furthermore, pharmacological inhibition of EphA2–ephrinA1 by the tyrosine kinase inhibitor dasatinib attenuated the loss of vascular integrity and leukocyte adhesion in vitro. Mice administered dasatinib exhibited resistance to radiation injury characterized by reduced barrier leakage and decreased leukocyte infiltration into the intestine. Taken together, these data suggest that dasatinib therapy represents a potential approach for the protection of radiation-mediated intestinal damage by targeting the EphA2–ephrinA1 complex.

Design and evaluation of EphrinA1 mutants with cerebral protective effect

The activation of EphA2 receptor by its natural ligand EphrinA1 causes blood brain barrier dysfunction, and inactivation of EphA2 reduces BBB damage in ischemic stroke. Thus, EphA2 targeted antagonists may serve as neuroprotective agents. We engineered four mutants of EphrinA1, EM1, EM2, EM3 and EM4, respectively. The computational analysis showed that these four mutants were capable of interacting with EphA2. Their potential neuroprotective effects were examined in mouse focal ischemia/reperfusion (I/R) model. EM2 exhibited strong neuroprotective effects, including reduced brain infarct volume, neuronal apoptosis, cerebral edema, and improved neurological scores. The EM2-mediated protection was associated with a comparative decrease in BBB leakage, inflammatory infiltration, and higher expression levels of tight junction proteins, such as zonula occludens-1 and Occludin. I/R-induced high expression of Rho-associated protein kinase 2 (ROCK2) was down-regulated after EM2 treatment. Moreover, EM2 reduced agonist doxazosin-induced EphA2 phosphorylation and cells rounding in PC3 cells, indicating EphA2-antagonizing activity of EM2. These finding provided evidences of the neuroprotection of EphA2 antagonist and a novel approach for ischemic stroke treatment. These results also suggested that a receptor agonist can be switched to an antagonist by substituting one or more relevant residues.

Biochemical characterization of EphA2 antagonists with improved physico-chemical properties by cell-based assays and surface plasmon resonance analysis

Amino acid conjugates of lithocholic acid (LCA) have been recently described as effective disruptors of the EphA2-ephrin-A1 interaction able to inhibit EphA2 phosphorylation in intact cells and thus able to block prometastatic responses such as cellular retraction and angiogenesis. However, these LCA-based compounds were significantly more potent at disrupting the EphA2-ephrin-A1 interaction than at blocking phenotype responses in cells, which might reflect an unclear mechanism of action or a metabolic issue responsible for a reduction of the compound concentration at the cell's surface. Through the synthesis of new compounds and their examination by a combination of cell-based assays and real-time interaction analysis by surface plasmon resonance, we showed at molecular level that l-tryptophan conjugates of lithocholic acid disrupt EphA2-ephrin-A1 interaction by targeting the EphA 2 receptor and that the presence of a polar group in position 3 of steroid scaffold is a key factor to increase the effective concentration of the compounds in cancer cell lines.

Comparative Analysis of Virtual Screening Approaches in the Search for Novel EphA2 Receptor Antagonists

The EphA2 receptor and its ephrin-A1 ligand form a key cell communication system, which has been found overexpressed in many cancer types and involved in tumor growth. Recent medicinal chemistry efforts have identified bile acid derivatives as low micromolar binders of the EphA2 receptor. However, these compounds suffer from poor physicochemical properties, hampering their use in vivo. The identification of compounds able to disrupt the EphA2-ephrin-A1 complex lacking the bile acid scaffold may lead to new pharmacological tools suitable for in vivo studies. To identify the most promising virtual screening (VS) protocol aimed at finding novel EphA2 antagonists, we investigated the ability of both ligand-based and structure-based approaches to retrieve known EphA2 antagonists from libraries of decoys with similar molecular properties. While ligand-based VSs were conducted using UniPR129 and ephrin-A1 ligand as reference structures, structure-based VSs were performed with Glide, using the X-ray structure of the EphA2 receptor/ephrin-A1 complex. A comparison of enrichment factors showed that ligand-based approaches outperformed the structure-based ones, suggesting ligand-based methods using the G-H loop of ephrin-A1 ligand as template as the most promising protocols to search for novel EphA2 antagonists.

EphA2 Is a Therapy Target in EphA2-Positive Leukemias but Is Not Essential for Normal Hematopoiesis or Leukemia

Members of the Eph family of receptor tyrosine kinases and their membrane bound ephrin ligands have been shown to play critical roles in many developmental processes and more recently have been implicated in both normal and pathological processes in post-embryonic tissues. In particular, expression studies of Eph receptors and limited functional studies have demonstrated a role for the Eph/ephrin system in hematopoiesis and leukemogenesis. In particular, EphA2 was reported on hematopoietic stem cells and stromal cells. There are also reports of EphA2 expression in many different types of malignancies including leukemia, however there is a lack of knowledge in understanding the role of EphA2 in hematopoiesis and leukemogenesis. We explored the role of EphA2 in hematopoiesis by analyzing wild type and EphA2 knockout mice. Mature, differentiated cells, progenitors and hematopoietic stem cells derived from knockout and control mice were analyzed and no significant abnormality was detected. These studies showed that EphA2 does not have an obligatory role in normal hematopoiesis. Comparative studies using EphA2-negative MLL-AF9 leukemias derived from EphA2-knockout animals showed that there was no detectable functional role for EphA2 in the initiation or progression of the leukemic process. However, expression of EphA2 in leukemias initiated by MLL-AF9 suggested that this protein might be a possible therapy target in this type of leukemia. We showed that treatment with EphA2 monoclonal antibody IF7 alone had no effect on tumorigenicity and latency of the MLL-AF9 leukemias, while targeting of EphA2 using EphA2 monoclonal antibody with a radioactive payload significantly impaired the leukemic process. Altogether, these results identify EphA2 as a potential radio-therapeutic target in leukemias with MLL translocation.

Development of small RNA delivery systems for lung cancer therapy

RNA interference (RNAi) has emerged as a powerful tool for studying target identification and holds promise for the development of therapeutic gene silencing. Recent advances in RNAi delivery and target selection provide remarkable opportunities for translational medical research. The induction of RNAi relies on small silencing RNAs, which affect specific messenger RNA (mRNA) degradation. Two types of small RNA molecules, small interfering RNAs (siRNAs) and microRNAs (miRNAs), have a central function in RNAi technology. The success of RNAi-based therapeutic delivery may be dependent upon uncovering a delivery route, sophisticated delivery carriers, and nucleic acid modifications. Lung cancer is still the leading cause of cancer death worldwide, for which novel therapeutic strategies are critically needed. Recently, we have reported a novel platform (PnkRNA™ and nkRNA^®) to promote naked RNAi approaches through inhalation without delivery vehicles in lung cancer xenograft models. We suggest that a new class of RNAi therapeutic agent and local drug delivery system could also offer a promising RNAi-based strategy for clinical applications in cancer therapy. In this article, we show recent strategies for an RNAi delivery system and suggest the possible clinical usefulness of RNAi-based therapeutics for lung cancer treatment.

Small RNAs deliver a blow to ovarian cancer

Targeted therapeutic approaches have seen tremendous advances in the last decade, for good reason. Specifically intervening with a disease-causing gene can revert the deleterious phenotype while eliminating the toxicity often associated with broad-spectrum agents. Unfortunately, because these selective agents hit one target in a single location, acquired resistance is often high. An arguably better treatment approach includes coupling multiple targeted agents or using an agent that hits an individual target in several independent locations and/or alters multiple relevant targets in the disease-causing pathway(s), precisely the approach taken by Nishimura and colleagues in their recent report aimed at identifying a better treatment option for ovarian cancer.

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.

Synthesis and structure-activity relationships of amino acid conjugates of cholanic acid as antagonists of the EphA2 receptor

The Eph–ephrin system plays a critical role in tumor growth and vascular functions during carcinogenesis. We had previously identified cholanic acid as a competitive and reversible EphA2 antagonist able to disrupt EphA2-ephrinA1 interaction and to inhibit EphA2 activation in prostate cancer cells. Herein, we report the synthesis and biological evaluation of a set of cholanic acid derivatives obtained by conjugation of its carboxyl group with a panel of naturally occurring amino acids with the aim to improve EphA2 receptor inhibition. Structure-activity relationships indicate that conjugation of cholanic acid with linear amino acids of small size leads to effective EphA2 antagonists whereas the introduction of aromatic amino acids reduces the potency in displacement studies. The β-alanine derivative 4 was able to disrupt EphA2-ephrinA1 interaction in the micromolar range and to dose-dependently inhibit EphA2 activation on PC3 cells. These findings may help the design of novel EphA2 antagonists active on cancer cell lines.

Structure-activity relationships and mechanism of action of Eph-ephrin antagonists: interaction of cholanic acid with the EphA2 receptor

The Eph-ephrin system, including the EphA2 receptor and the ephrinA1 ligand, plays a critical role in tumor and vascular functions during carcinogenesis. We previously identified (3α,5β)-3-hydroxycholan-24-oic acid (lithocholic acid) as an Eph-ephrin antagonist that is able to inhibit EphA2 receptor activation; it is therefore potentially useful as a novel EphA2 receptor-targeting agent. Herein we explore the structure-activity relationships of a focused set of lithocholic acid derivatives based on molecular modeling investigations and displacement binding assays. Our exploration shows that while the 3-α-hydroxy group of lithocholic acid has a negligible role in recognition of the EphA2 receptor, its carboxylate group is critical for disrupting the binding of ephrinA1 to EphA2. As a result of our investigation, we identified (5β)-cholan-24-oic acid (cholanic acid) as a novel compound that competitively inhibits the EphA2-ephrinA1 interaction with higher potency than lithocholic acid. Surface plasmon resonance analysis indicates that cholanic acid binds specifically and reversibly to the ligand binding domain of EphA2, with a steady-state dissociation constant (K(D) ) in the low micromolar range. Furthermore, cholanic acid blocks the phosphorylation of EphA2 as well as cell retraction and rounding in PC3 prostate cancer cells, two effects that depend on EphA2 activation by the ephrinA1 ligand. These findings suggest that cholanic acid can be used as a template structure for the design of effective EphA2 antagonists, and may have potential impact in the elucidation of the role played by this receptor in pathological conditions.

EphA2 activation promotes the endothelial cell inflammatory response: a potential role in atherosclerosis

OBJECTIVE

Endothelial cell activation results in altered cell-cell interactions with adjacent endothelial cells and with infiltrating leukocytes. Eph receptors and their ephrin ligands regulate cell-cell interactions during tissue remodeling, and multiple proinflammatory mediators induce endothelial EphA receptor and ephrinA ligand expression. Therefore, we sought to elucidate the role of EphA receptors and ephrinA ligands in endothelial cell activation and atherosclerosis.

METHODS AND RESULTS

Quantitative reverse transcription-polymerase chain reaction screening for EphA/ephrinA expression in atherosclerosis-prone macrovascular endothelium identified EphA2, EphA4, and ephrinA1 as the dominant isoforms. Endothelial activation with oxidized low-density lipoprotein and proinflammatory cytokines induced EphA2 and ephrinA1 expression and sustained EphA2 activation, whereas EphA4 expression was unaffected. Atherosclerotic plaques from mice and humans showed enhanced EphA2 and ephrinA1 expression colocalizing in the endothelial cell layer. EphA2 activation with recombinant Fc-ephrinA1 induced proinflammatory gene expression (eg vascular cell adhesion molecule-1, E-selectin) and stimulated monocyte adhesion, whereas inhibiting EphA2 (small interfering RNA, pharmacological inhibitors) abrogated both ephrinA1-induced and oxidized low-density lipoprotein-induced vascular cell adhesion molecule-1 expression.

CONCLUSION

The current data suggest that enhanced EphA2 signaling during endothelial cell activation perpetuates proinflammatory gene expression. Coupled with EphA2 expression in mouse and human atherosclerotic plaques, these data implicate EphA2 as a novel proinflammatory mediator and potential regulator of atherosclerotic plaque development.

Silencing the receptor EphA2 suppresses the growth and haptotaxis of malignant mesothelioma cells

BACKGROUND

The over-expression of the ephrin-A1 ligand receptor EphA2 is associated with the growth and metastatic potential of tumors. Although EphA2 is expressed in a variety of tumors, its expression and function in malignant mesothelioma (MM) remain unknown. The authors hypothesized that expression of the receptor EphA2 in MM cells (MMCs) plays a key role in the growth and haptotactic migration of MM. They also hypothesized that silencing EphA2 expression by using small-interfering RNA (siRNA) inhibits the proliferation and haptotaxis of MMCs and induces apoptosis in MMCs.

METHODS

The expression of EphA2 in MMCs and in normal pleural mesothelial cells (PMCs) was studied by using real-time quantitative polymerase chain reaction analysis and Western blot analysis. The growth of MMCs was determined with the WST-1 cell-proliferation assay. The haptotactic migration of MMCs and PMCs was determined with a Boyden chamber assay. Expression of caspases was determined with calorimetric assays.

RESULTS

The results demonstrated that silencing the receptor EphA2 by siRNA significantly reduced the proliferation and haptotactic migration of MMCs compared with controls. Over-expression of EphA2 with plasmid pcDNA/EphA2 enhanced the proliferation and haptotaxis of MMCs significantly. Knocking down EphA2 expression initiated caspase-9-mediated apoptosis in MMCs.

CONCLUSIONS

The current results suggested that constitutive expression of EphA2 may contribute to the aggressive behavior and cellular survival of MMCs. EphA2 may be an effective therapeutic target in patients with mesothelioma. Silencing the receptor EphA2 gene is a novel approach for the containment of growth and migration of tumor in patients with malignant mesothelioma.

Efficacy and antivascular effects of EphA2 reduction with an agonistic antibody in ovarian cancer

BACKGROUND

EphA2 is an oncoprotein and tyrosine kinase receptor that is overexpressed in ovarian and many other cancers. We investigated the effects of reduced EphA2 levels on tumor growth and the tumor microenvironment in an orthotopic ovarian cancer model.

METHODS

The effect of the EphA2-agonistic monoclonal antibody EA5, alone or in combination with paclitaxel, on the growth of ovarian cancer cells (SKOV3ip1, HeyA8, and HeyA8MDR [taxane-platinum resistant]) was determined in vitro and in vivo by immunoblotting, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, and immunohistochemical analysis. Expression of EphA2 and markers of angiogenesis (CD31, vascular endothelial growth factor [VEGF], and basic fibroblast growth factor), proliferation (proliferating cell nuclear antigen), and endothelial cell apoptosis (CD31-terminal deoxynucleotidyl transferase biotin-deoxyuridine triphosphate nick-end labeling colocalization) and phosphorylation of Src were analyzed by immunoblotting, immunohistochemistry, immunofluorescence, and in situ hybridization in tumors from treated mice. Statistical tests were two-sided.

RESULTS

EA5 antibody treatment led to a more than 90% reduction in EphA2 expression in HeyA8 tumors in vivo. In mice bearing orthotopic SKOV3ip1 or HeyA8 tumors, 4 weeks of EA5 treatment resulted in tumors that weighed 31% and 45% less, respectively, than those in control (IgG-treated) mice (95% confidence interval [CI] = -0.09% to 71% and 20% to 70%, P = .27 and .01, respectively). Combination therapy with EA5 and paclitaxel reduced tumor weight by 77% and 80% (95% CI = 63% to 91% and 68% to 91%), respectively, compared with paclitaxel alone and by 92% and 88% (95% CI = 87% to 97% and 80% to 94%), respectively, compared with IgG alone. Combination therapy also reduced the weight of HeyA8MDR tumors by 47% (95% CI = 24% to 72%) compared with paclitaxel. Mice bearing SKOV3ip1 or HeyA8 tumors that were treated with combination therapy survived longer than those treated with paclitaxel alone (median survival = 144 versus 69 days and 46 versus 37 days, respectively). EA5-treated tumors had reduced microvascular density, proliferation, and VEGF protein and mRNA levels, with increased endothelial cell apoptosis. EphA2 was associated with Src, which was rapidly dephosphorylated after EA5 treatment.

CONCLUSIONS

EA5 in combination with paclitaxel decreased tumor growth in an orthotopic ovarian cancer mouse model through antiangiogenic mechanisms associated with reduced levels of VEGF and phosphorylated Src. Humanized antibody constructs against EphA2 are worthy of future study.

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.

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.

Ligation of EphA2 by Ephrin A1-Fc inhibits pancreatic adenocarcinoma cellular invasiveness

The Eph tyrosine kinases interact with ligands of the Ephrin family and have diverse cellular functions. EphA2 has been recognized to be an oncoprotein of importance in a range of cancers. Here, we examine the effect of EphA2 overexpression and ligation by chimeric Ephrin A1-Fc on the invasive phenotype of pancreatic adenocarcinoma cells. We show that EphA2 overexpression induces a FAK-dependent increase in MMP-2 expression and invasiveness. EphA2 ligation induces proteosomal degradation of EphA2, attenuates the invasive phenotype, and decreases both FAK phosphorylation and MMP-2 expression. EphA2 appears to represent a rational therapeutic target and ligation by Ephrin A1-Fc is one strategy to modulate levels of this oncoprotein.

Antiangiogenic and antitumor efficacy of EphA2 receptor antagonist

Tumor-associated angiogenesis is critical for tumor growth and metastasis and is controlled by various pro- and antiangiogenic factors. The Eph family of receptor tyrosine kinases has emerged as one of the pivotal regulators of angiogenesis. Here we report that interfering with EphA signaling resulted in a pronounced inhibition of angiogenesis in ex vivo and in vivo model systems. Administration of EphA2/Fc soluble receptors inhibited, in a dose-dependent manner, microvessel formation in rat aortic ring assay, with inhibition reaching 76% at the highest dose of 5000 ng/ml. These results were further confirmed in vivo in a porcine aortic endothelial cell-vascular endothelial growth factor (VEGF)/basic fibroblast growth factor Matrigel plug assay, in which administration of EphA2/Fc soluble receptors resulted in 81% inhibition of neovascularization. The additive effects of simultaneous inhibition of VEGF receptor 2 and EphA signaling pathways in aortic ring assay and antiangiogenic efficacy of EphA2/Fc soluble receptors against VEGF/basic fibroblast growth factor-mediated neovascularization in vivo indicated a critical and nonredundant role for EphA signaling in angiogenesis. Furthermore, in two independent experiments, we demonstrated that EphA2/Fc soluble receptors strongly (by approximately 50% versus controls) suppressed growth of ASPC-1 human pancreatic tumor s.c. xenografts. Inhibition of tumor growth was due to decreased proliferation of tumor cells. In an orthotopic pancreatic ductal adenocarcinoma model in mice, suppression of EphA signaling by i.p. administration of EphA2/Fc (30 micro g/dose, three times a week for 56 days) profoundly inhibited the growth of primary tumors and the development of peritoneal, lymphatic, and hepatic metastases. These data demonstrate a critical role of EphA signaling in tumor growth and metastasis and provide a strong rationale for targeting EphA2 receptors for anticancer therapies.

EphA2 overexpression decreases estrogen dependence and tamoxifen sensitivity

The EphA2 receptor tyrosine kinase is found at low levels on nontransformed adult breast epithelial cells but is frequently overexpressed on aggressive breast cancer cells. Recent studies have documented an inverse relationship between EphA2 and estrogen receptor expression in breast cancer cell lines. In our present study, we demonstrate that overexpression of EphA2 decreases estrogen dependence as defined using both in vitro and in vivo criteria. The EphA2-transfected cells demonstrate increased growth in vitro and form larger and more aggressive tumors in vivo. EphA2 overexpression also decreases the ability of tamoxifen to inhibit breast cancer cell growth and tumorigenesis. These effects of EphA2 overexpression can be overcome by antibody-based targeting of EphA2. In particular, certain EphA2 antibodies can resensitize EphA2-overexpressing breast tumor cells to tamoxifen. These results have important implications for understanding the molecular basis underlying estrogen dependence and provide further evidence that EphA2 may provide a much-needed therapeutic target for breast cancer.

Blockade of EphA receptor tyrosine kinase activation inhibits vascular endothelial cell growth factor-induced angiogenesis

Angiogenesis is a multistep process involving a diverse array of molecular signals. Ligands for receptor tyrosine kinases (RTKs) have emerged as critical mediators of angiogenesis. Three families of ligands, vascular endothelial cell growth factors (VEGFs), angiopoietins, and ephrins, act via RTKs expressed in endothelial cells. Recent evidence indicates that VEGF cooperates with angiopoietins to regulate vascular remodeling and angiogenesis in both embryogenesis and tumor neovascularization. However, the relationship between VEGF and ephrins remains unclear. Here we show that interaction between EphA RTKs and ephrinA ligands is necessary for induction of maximal neovascularization by VEGF. EphA2 RTK is activated by VEGF through induction of ephrinA1 ligand. A soluble EphA2-Fc receptor inhibits VEGF-, but not basic fibroblast growth factor-induced endothelial cell survival, migration, sprouting, and corneal angiogenesis. As an independent, but complementary approach, EphA2 antisense oligonucleotides inhibited endothelial expression of EphA2 receptor and suppressed ephrinA1- and VEGF-induced cell migration. Taken together, these data indicate an essential role for EphA receptor activation in VEGF-dependent angiogenesis and suggest a potential new target for therapeutic intervention in pathogenic angiogenesis.