EphA2: a determinant of malignant cellular behavior and a potential therapeutic target in pancreatic adenocarcinoma

EphA4 receptor, overexpressed in pancreatic ductal adenocarcinoma, promotes cancer cell growth

To isolate novel diagnostic markers and drug targets for pancreatic ductal adenocarcinoma (PDAC), we previously performed expression profile analysis of PDAC cells using a genome-wide cDNA microarray combined with laser microdissection. Among dozens of up-regulated genes identified in PDAC cells, we herein focused on one tyrosine kinase receptor, Eph receptor A4 (EphA4), as a molecular target for PDAC therapy. Immunohistochemical analysis validated EphA4 overexpression in approximately half of the PDAC tissues. To investigate its biological function in PDAC cells, we knocked down EphA4 expression by siRNA, which drastically attenuated PDAC cell viability. In concordance with the siRNA experiment, PDAC-derivative cells that were designed to constitutively express exogenous EphA4 showed a more rapid growth rate than cells transfected with mock vector, suggesting a growth-promoting effect of EphA4 on PDAC cells. Furthermore, the expression analysis for ephrin ligand family members indicated the coexistence of ephrinA3 ligand in PDAC cells with EphA4 receptor, and knockdown of ephrinA3 by siRNA also attenuated PDAC cell viability. These results suggest that the EphA4-ephrinA3 pathway is likely to be a promising molecular target for pancreatic cancer therapy.

Filopodia formation via a specific Eph family member and PI3K in immortalized cholangiocytes

Biliary ducts are lined with epithelial cells, which consist of at least two types of cholangiocytes, small and large. In contrast to large cholangiocytes, which are involved in secretion, the role of small cholangiocytes has not been elucidated. To address this question, we analyzed the migration-based characteristics of these cells that may help to understand their functions in vivo. Interestingly, dibutyryl cAMP induced marked filopodia formation and cdc42 activation in the normal mouse cholangiocyte (NMC)-small cell line compared with the NMC-large cell line. Analysis of members of the ephrin (Eph)A family of guidance molecules revealed a distinct subcellular distribution of EphA5 and EphA8 members: EphA8 was equally expressed by both cell types and localized subcellularly in peripheral cell membranes, whereas EphA5 was expressed predominantly in NMC-S and localized to filopodia. Moreover, cAMP-inducible filopodia formation in these cells was abrogated using EphA5 short interfering RNA. Finally, we found that the Rho family GTPase cdc42 was activated in a manner dependent on EphA5. Wortmannin, a specific inhibitor of phosphotidylinositol 3-kinase (PI3K), abolished the activation of cdc42 dependent on EphA5, suggesting the involvement of PI3K in the EphA5-cdc42 pathway. Together, our findings suggest a cAMP-EphA5-cdc42-dependent regulation of small cholangiocyte migration, which are anticipated to facilitate the understanding of the nature of cholangiocytes and to explain certain general aspects of cAMP-cdc42 activation signaling with regard to cell morphogenesis.

Therapeutic potential of RNA interference against cancer

One of the most dramatic events of the past 5 years in the field of molecular biology has been the discovery of RNA interference (RNAi). Although RNAi is an evolutionarily conserved phenomenon for sequence-specific gene silencing in mammalian cells, exogenous small interfering RNA (siRNA) and vector-based short hairpin RNA (shRNA) can also invoke RNAi responses. Both are now not only experimental tools for analyzing gene function but are expected to be excellent avenues for drug target discovery and the emerging class of gene medicine for targeting incurable diseases such as cancer. The success of cancer therapeutic use of RNAi relies on the development of safe and efficacious delivery systems that introduce siRNA and shRNA expression vectors into target tumor cells. For their delivery, a variety of strategies have been used, most of them based on traditional gene therapy delivery systems. In this review, we present siRNA delivery method strategies and discuss the potential of RNAi-based gene therapy in cancer treatment.

Prospects of RNA interference therapy for cancer

RNA interference (RNAi) is a powerful gene-silencing process that holds great promise in the field of cancer therapy. The discovery of RNAi has generated enthusiasm within the scientific community, not only because it has been used to rapidly identify key molecules involved in many disease processes including cancer, but also because RNAi has the potential to be translated into a technology with major therapeutic applications. Our evolving understanding of the molecular pathways important for carcinogenesis has created opportunities for cancer therapy employing RNAi technology to target the key molecules within these pathways. Many gene products involved in carcinogenesis have already been explored as targets for RNAi intervention, and RNAi targeting of molecules crucial for tumor-host interactions and tumor resistance to chemo- or radiotherapy has also been investigated. In most of these studies, the silencing of critical gene products by RNAi technology has generated significant antiproliferative and/or proapoptotic effects in cell-culture systems or in preclinical animal models. Nevertheless, significant obstacles, such as in vivo delivery, incomplete suppression of target genes, nonspecific immune responses and the so-called off-target effects, need to be overcome before this technology can be successfully translated into the clinical arena. Significant progress has already been made in addressing some of these issues, and it is foreseen that early phase clinical trials will be initiated in the very near future.

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.

Detachment-induced upregulation of XIAP and cIAP2 delays anoikis of intestinal epithelial cells

Detachment of normal epithelial cells from the extracellular matrix triggers apoptosis, a phenomenon called anoikis. Conversely, carcinoma cells tend to be relatively more anoikis-resistant than their normal counterparts, and this increased resistance represents a critical feature of the malignant phenotype. Mechanisms that control susceptibility and resistance to anoikis are not fully understood. It is now known that detachment of non-malignant epithelial cells triggers both pro- and antiapoptotic signals, and it is the balance between these signals and the duration of detachment that determine further fate of the cells. Detachment-induced antiapoptotic events delay anoikis and if cells reattach relatively soon after detachment they survive. Direct regulators of apoptosis responsible for this delay of anoikis are unknown. We found that detachment of non-malignant intestinal epithelial cells triggers upregulation of inhibitors of apoptosis protein (IAP) family, such as X-chromosome-linked inhibitor of apoptosis protein and cellular inhibitor of apoptosis-2 (cIAP2). We demonstrated that this upregulation requires detachment-dependent activation of the transcription factor nuclear factor-kappaB. We further observed that various IAP antagonists accelerate anoikis, indicating that upregulation of the IAPs delays detachment-triggered apoptosis. We conclude that the IAPs are important regulators of the balance between detachment-triggered life and death signals. Perhaps, not by coincidence, these proteins are often upregulated in carcinomas, tumors composed of cells that tend to be anoikis-resistant.

RNA interference in the mouse vascular endothelium by systemic administration of siRNA-lipoplexes for cancer therapy

RNA interference (RNAi) entails the potential for novel therapeutic strategies through the silencing of disease-causing genes in vivo. However, recent studies have raised an issue regarding applicable routes of administration for small interfering RNA (siRNA) molecules as therapeutics. In this study, we demonstrate that liposomally formulated siRNA molecules, the so-called siRNA-lipoplexes, but not naked siRNAs, are delivered to the tumor endothelial cells in vivo by microscopy. In addition, functional intracellular delivery of formulated siRNA targeting the tumor suppressor PTEN is shown in endothelial cells of the liver and tumor. Finally, the therapeutic potential of systemically administered siRNA(CD31)-lipoplexes is established by inhibition of tumor growth in two different xenograft mouse models. Our findings corroborate the applicability of this liposomal siRNA delivery technology for inducing RNAi to modulate gene expression levels in angiogenesis-dependent processes. In addition, our results advocate CD31 as a promising therapeutic target for antiangiogenic intervention. Therefore, our study provides a basis for the development of antiangiogenic cancer therapies based on RNAi.

The prognostic impact of EphB2/B4 expression on patients with advanced ovarian carcinoma

OBJECTIVES

To analyze expressions of the EphB2 and EphB4 receptors in ovarian carcinomas and explore their clinicopathological correlations and prognostic value.

METHODS

115 patients with advanced ovarian carcinoma FIGO IIB to IV were involved. RT-PCR and immunohistochemistry were used to examine the expressions of EphB2/B4 receptor mRNA and protein. Correlations between protein expression and clinicopathological factors were also analyzed.

RESULTS

Ovarian carcinoma patients with age elder than 60 years had higher EphB2 expression than younger patients. Expression of EphB2 and EphB4 protein did not significantly correlate with any other clinical variables, including FIGO stage, residual tumor, histological type and differentiation grade. No significant correlation between mRNA and protein expression level for both of these receptors was seen. It was found that patients with strong immunostaining for EphB2 (P = 0.03) or EphB4 (P = 0.003) receptors had poorer survival, and patients with strong immunostaining for EphB4 receptor showed poorer response to chemotherapy (P = 0.036).

CONCLUSIONS

These studies suggest that EphB2 and B4 receptors are of prognostic value and EphB4 receptor may be an independent predictor of chemotherapy response in ovarian cancer patients.

Differential gene expression analysis reveals generation of an autocrine loop by a mutant epidermal growth factor receptor in glioma cells

The epidermal growth factor receptor (EGFR) gene is commonly amplified and rearranged in glioblastoma multiforme leading to overexpression of wild-type and mutant EGFRs. Expression of wild-type EGFR ligands, such as transforming growth factor-alpha (TGF-alpha) or heparin-binding EGF (HB-EGF), is also often increased in gliomas resulting in an autocrine loop that contributes to the growth autonomy of glioma cells. Glioblastoma multiformes express a characteristic EGFR mutant (EGFRvIII, de 2-7) that does not bind ligand, signals constitutively, and is more tumorigenic than the wild-type receptor. However, the downstream signals that mediate this increased tumorigenicity are not well understood. We hypothesized that signals induced specifically by EGFRvIII and not the wild-type receptor are more likely to mediate its increased tumorigenic activity and examined the gene expression profiles resulting from inducible expression of comparable levels of either wild-type EGFR or EGFRvIII in a U251-MG glioma cell line. Expression of EGFRvIII resulted in specific up-regulation of a small group of genes. Remarkably, all these genes, which include TGFA, HB-EGF, EPHA2, IL8, MAP4K4, FOSL1, EMP1, and DUSP6, influence signaling pathways known to play a key role in oncogenesis and function in interconnected networks. Increased expression of EGFRvIII-induced genes was validated by real-time PCR. The mutant receptor does not bind ligand, and EGFRvIII-induced expression of TGF-alpha and HB-EGF suggests that EGFRvIII plays a role in generating an autocrine loop using the wild-type EGFR in glioma. It also raises the possibility that EGFRvIII may signal, at least in part, through the wild-type receptor. Indeed, we show that inhibiting the activity of HB-EGF, a potent mitogen, with neutralizing antibodies reduces cell proliferation induced by expression of EGFRvIII. This suggests that the EGFRvIII-HB-EGF-wild-type EGFR autocrine loop plays an important role in signal transduction by EGFRvIII in glioma cells. We also show by immunohistochemistry that HB-EGF expression correlates with the presence of EGFRvIII in glioblastoma multiforme. Thus, our study provides a new insight into oncogenic signaling by EGFRvIII and improves our understanding of how autocrine loops are generated in glioma.

EphA2 as a novel molecular marker and target in glioblastoma multiforme

We investigated the presence of EphA2, and its ligand, ephrinA1, in glioblastoma multiforme (GBM), a malignant neoplasm of glial cells, and normal brain. We also initially examined the functional importance of the interaction between EphA2 and ephrinA1 in glioma cells. Expression and localization of EphA2 and ephrinA1 in human GBM and normal brain were examined using Western blotting, immunofluorescence, and immunohistochemistry. A functional role for EphA2 was investigated by assessing the activation status of the receptor and the effect of ephrinA1 on the anchorage-independent growth and invasiveness of GBM cells. We found EphA2 to be elevated in approximately 90% of GBM specimens and cell lines but not in normal brain, whereas ephrinA1 was present at consistently low levels in both GBM and normal brain. EphA2 was activated and phosphorylated by ephrinA1 in GBM cells. Furthermore, ephrinA1 induced a prominent, dose-dependent inhibitory effect on the anchorage-independent growth and invasiveness of GBM cells highly overexpressing EphA2, which was not seen in cells expressing low levels of the receptor. Thus, EphA2 is both specifically overexpressed in GBM and expressed differentially with respect to its ligand, ephrinA1, which may reflect on the oncogenic processes of malignant glioma cells. EphA2 seems to be functionally important in GBM cells and thus may play an important role in GBM pathogenesis. Hence, EphA2 represents a new marker and novel target for the development of molecular therapeutics against GBM.

Anti-EphA2 antibodies decrease EphA2 protein levels in murine CT26 colorectal and human MDA-231 breast tumors but do not inhibit tumor growth

The EphA2 receptor tyrosine kinase has been shown to be over-expressed in cancer and a monoclonal antibody (mAb) that activates and down-modulates EphA2 was reported to inhibit the growth of human breast and lung tumor xenografts in nude mice. Reduction of EphA2 levels by treatment with anti-EphA2 siRNA also inhibited tumor growth, suggesting that the anti-tumor effects of these agents are mediated by decreasing the levels of EphA2. As these studies employed human tumor xenograft models in nude mice with reagents whose cross reactivity with murine EphA2 is unknown, we generated a mAb (Ab20) that preferentially binds, activates, and induces the degradation of murine EphA2. Treatment of established murine CT26 colorectal tumors with Ab20 reduced EphA2 protein levels to approximately 12% of control tumor levels, yet had no effect on tumor growth. CT26 tumor cell colonization of the lung was also not affected by Ab20 administration despite having barely detectable levels of EphA2. We also generated and tested a potent agonistic mAb against human EphA2 (1G9-H7). No inhibition of humanMDA-231 breast tumor xenograft growth was observed despite evidence for >85% reduction of EphA2 protein levels in the tumors. These results suggest that molecular characteristics of the tumors in addition to EphA2 over-expression may be important for predicting responsiveness to EphA2-directed therapies.

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

Receptor tyrosine kinases of the Eph family are upregulated in several different types of cancer. One family member in particular, the EphA2 receptor, has been linked to breast, prostate, lung and colon cancer, as well as melanoma. However, mechanisms by which EphA2 contributes to tumor progression are far from clear. In certain tumor cell lines, EphA2 receptor is underphosphorylated, raising the question of whether ligand-induced receptor phosphorylation and its kinase activity play a role in oncogenesis. To test directly the role of EphA2 receptor phosphorylation/kinase activity in tumor progression, we generated EphA2 receptor variants that were either lacking the cytoplasmic domain or carrying a point mutation that inhibits its kinase activity. Expression of these EphA2 mutants in breast cancer cells resulted in decreased tumor volume and increased tumor apoptosis in primary tumors. In addition, the numbers of lung metastases were significantly reduced in both experimental and spontaneous metastasis models. Reduced tumor volume and metastasis are not due to defects in tumor angiogenesis, as there is no significant difference in tumor vessel density between wild-type tumors and tumors expressing EphA2-signaling-defective mutants. In contrast, tumor cells expressing the EphA2 mutants are defective in RhoA GTPase activation and cell migration. Taken together, these results suggest that receptor phosphorylation and kinase activity of the EphA2 receptor, at least in part, contribute to tumor malignancy.

Gene silencing in primary and metastatic tumors by small interfering RNA delivery in mice: quantitative analysis using melanoma cells expressing firefly and sea pansy luciferases

Silencing of oncogenes or other genes contributing to tumor malignancy or progression by RNA interference (RNAi) offers a promising approach to treating tumor patients. To achieve RNAi-based tumor therapy, a small interfering RNA (siRNA) or siRNA-expressing vector needs to be delivered to tumor cells, but little information about its in vivo delivery has been reported. In this study, we examined whether the expression of the target gene in tumor cells can be suppressed by the delivery of RNAi effectors to primary and metastatic tumor cells. To quantitatively evaluate the RNAi effects in tumor cells, mouse melanoma B16-BL6 cells were stably transfected with both firefly (a model target gene) and sea pansy (an internal standard gene) luciferase genes to obtain B16-BL6/dual Luc cells. The target gene expression in subcutaneous primary tumors of B16-BL6/dual Luc cells was significantly suppressed by direct injection of the RNAi effectors followed by electroporation. The expression in metastatic hepatic tumors was also significantly reduced by an intravenous injection of either RNAi effector by the hydrodynamics-based procedure. These results indicate that the both RNAi effectors have a potential to silence target gene in tumor cells in vivo when successfully delivered to tumor cells.

Impaired tumor microenvironment in EphA2-deficient mice inhibits tumor angiogenesis and metastatic progression

EphA2 belongs to a unique family of receptor tyrosine kinases that play critical roles in development and disease. Since EphA2 is required for ephrin-A1 ligand-induced vascular remodeling and is overexpressed in a variety of vascularized human adenocarcinomas, we assessed tumor angiogenesis and metastatic progression in EphA2-deficient host animals. 4T1 metastatic mammary adenocarcinoma cells transplanted subcutaneously and orthotopically into EphA2-deficient female mice displayed decreased tumor volume, tumor cell survival, microvascular density, and lung metastasis relative to tumor-bearing littermate controls. To determine if the phenotype in EphA2-deficient mice was endothelial cell intrinsic, we also analyzed endothelial cells isolated from EphA2-deficient animals for their ability to incorporate into tumor vessels in vivo, as well as to migrate in response to tumor-derived signals in vitro. EphA2-deficient endothelial cells displayed impaired survival and failed to incorporate into tumor microvessels in vivo, and displayed impaired tumor-mediated migration in vitro relative to controls. These data suggest that host EphA2 receptor tyrosine kinase function is required in the tumor microenvironment for tumor angiogenesis and metastatic progression.

The therapeutic potential of RNA interference

In recent years, we have witnessed the discovery of a new mechanism of gene regulation called RNA interference (RNAi), which has revitalized interest in the development of nucleic acid‐based technologies for therapeutic gene suppression. This review focuses on the potential therapeutic use of RNAi, discussing the theoretical advantages of RNAi‐based therapeutics over previous technologies as well as the challenges involved in developing RNAi for clinical use. Also reviewed, are the in vivo proof‐of principle experiments that provide the preclinical justification for the continued development of RNAi‐based therapeutics.

Efficient delivery of small interfering RNA to bone-metastatic tumors by using atelocollagen in vivo

Silencing of gene expression by small interfering RNAs (siRNAs) is rapidly becoming a powerful tool for genetic analysis and represents a potential strategy for therapeutic product development. However, there are no reports of systemic delivery for siRNAs toward treatment of bone-metastatic cancer. Accordingly, we report here that i.v. injection of GL3 luciferase siRNA complexed with atelocollagen showed effective reduction of luciferase expression from bone-metastatic prostate tumor cells developed in mouse thorax, jaws, and/or legs. We also show that the siRNA/atelocollagen complex can be efficiently delivered to tumors 24 h after injection and can exist intact at least for 3 days. Furthermore, atelocollagen-mediated systemic administration of siRNAs such as enhancer of zeste homolog 2 and phosphoinositide 3'-hydroxykinase p110-alpha-subunit, which were selected as candidate targets for inhibition of bone metastasis, resulted in an efficient inhibition of metastatic tumor growth in bone tissues. In addition, upregulation of serum IL-12 and IFN-alpha levels was not associated with the in vivo administration of the siRNA/atelocollagen complex. Thus, for treatment of bone metastasis of prostate cancer, an atelocollagen-mediated systemic delivery method could be a reliable and safe approach to the achievement of maximal function of siRNA.

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.

Rnai as an experimental and therapeutic tool to study and regulate physiological and disease processes

Over the past four years RNA interference (RNAi) has exploded onto the research scene as a new approach to manipulate gene expression in mammalian systems. More recently, RNAi has garnered much interest as a potential therapeutic strategy. In this review, we briefly summarize the current understanding of RNAi biology and examine how RNAi has been used to study the genetic basis of physiological and disease processes in mammalian systems. We also explore some of the new developments in the use of RNAi for disease therapy and highlight the key challenges that currently limit its application in the laboratory, as well as in the clinical setting.

RNA interference in biology and disease

RNA interference (RNAi) is a conserved biologic response to double-stranded RNA that results in the sequence-specific silencing of target gene expression. Over the past 5 years, an intensive research effort has facilitated the rapid movement of RNAi from a relatively obscure biologic phenomenon to a valuable tool used to silence target gene expression and perform large-scale functional genomic screens. In fact, recent studies reported in this journal and others have demonstrated success using RNAi to address the role of oncogene expression in leukemia cell lines and to validate the therapeutic potential of RNAi for treating these blood disorders. In order to advance these applications and gain an appreciation for the future of RNAi both in basic research and in the treatment of diseases caused by aberrant gene expression, it is important to have an understanding of the process of RNAi and its limitations.

EPHA2/EFNA1 expression in human gastric cancer

The erythropoietin-producing hepatocellular (EPH)A2 receptor, tyrosine kinase, is overexpressed and phosphorylated in several types of human tumors and has been associated with malignant transformation. A recent report, however, indicated that stimulation of the EPHA2 receptor ligand, ephrinA1 (EFNA1), inhibits the growth of EPHA2-expressing breast cancer. The authors examined the expression of EPHA2 and EFNA1 using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) in four gastric cancer cell lines and 49 primary gastric cancer samples, as well as in normal gastric tissue. EPHA2 was more highly expressed in tumor tissue than in normal tissue in 27 cases (55%). EFNA1 was overexpressed in tumor tissue in 28 cases (57%). No significant correlation was detected between the expression levels and histologic features such as tumor size, age, vessel invasion, or lymph node involvement. However, EPHA2 overexpression was more prominent in macroscopic type 3 and 4 tumors than in type 1 or 2 advanced gastric cancer. The authors observed EPHA2 expression in three of the four gastric cancer cell lines (AGS, KATO3, and MKN74) that were examined. In one cell line, TMK1, EPHA2 expression was barely detectable using northern blotting, RT-PCR, and western blotting. In contrast, EFNA1 was detected in all cell lines. In the gastric cancer cell lines that endogenously expressed EPHA2, stimulation with ephrinA1-Fc led to decreased EPHA2 protein expression and increased EPHA2 phosphorylation. Finally, the growth of EPHA2-expressing cells was inhibited by repetitive stimulation with soluble ephrinA1-Fc. Taken together, these findings suggest that EPHA2 and EFNA1 expression may influence the behavior of human gastric cancer.

Expression of EphA2 is Prognostic of Disease-Free Interval and Overall Survival in Surgically Treated Patients with Renal Cell Carcinoma

Whereas normally expressed at sites of cell-to-cell contact in adult epithelial tissues, recent studies have shown that the receptor tyrosine kinase EphA2 is overexpressed in numerous epithelial-type carcinomas, with the greatest level of EphA2 expression observed in metastatic lesions. In the current study, we have assessed EphA2 expression in archived renal cell carcinoma (RCC) tissues as it relates to patient disease course.

Using specific anti-EphA2 monoclonal antibody 208 and immunohistochemistry, we evaluated EphA2 protein expression levels in RCC specimens surgically resected from 34 patients (including 30 conventional clear-cell RCC, 3 papillary, and 1 chromophobic RCC cases) resulting in clinical cures.

Regardless of histopathologic subtype, RCC lesions expressing higher levels of EphA2 tended to be of a higher grade (P &lt; 0.05) and larger (P = 0.093), more-highly-vascularized tumors (P = 0.005). Perhaps most notable, the degree of EphA2 overexpression (versus normal matched autologous kidney tissue) seemed predictive of short-term (&lt;1 year) versus longer-term (≥1 year) disease-free interval (P &lt; 0.001) and of overall survival (P &lt; 0.001) among the RCC patients evaluated.

These data suggest that EphA2 expression level may serve as a useful prognostic tool in the clinical management of patients who have been successfully treated with surgery, but who are at greater risk for accelerated disease recurrence and who have a poorer prognosis.

Systemic siRNA-mediated gene silencing: a new approach to targeted therapy of cancer

OBJECTIVE

RNA interference (RNAi), mediated by small interfering RNA (siRNA), silences genes with a high degree of specificity and potentially represents a general approach for molecularly targeted anticancer therapy. The aim of this study was to evaluate the ability of systemically administered siRNA to silence gene expression in vivo and to assess the effect of this approach on tumor growth using a murine pancreatic adenocarcinoma xenograft model.

SUMMARY BACKGROUND DATA

Carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6) is widely overexpressed in human gastrointestinal cancer. Overexpression of CEACAM6 promotes cell survival under anchorage independent conditions, a characteristic associated with tumorigenesis and metastasis.

METHODS

CEACAM6 expression was quantified by real-time polymerase chain reaction (PCR) and Western blot. Mice (n = 10/group) were subcutaneously xenografted with 2 x 10 BxPC3 cells (which inherently overexpress CEACAM6). Tumor growth, CEACAM6 expression, cellular proliferation (Ki-67 immunohistochemistry), apoptosis, angiogenesis (CD34 immunohistochemistry), and survival were compared for mice administered either systemic CEACAM6-specific or control single-base mismatch siRNA over 6 weeks, following orthotopic tumor implantation.

RESULTS

Treatment with CEACAM6-specific siRNA suppressed primary tumor growth by 68% versus control siRNA (P < 0.05) and was associated with a decreased proliferating cell index, impaired angiogenesis and increased apoptosis in the xenografted tumors. CEACAM6-specific siRNA completely inhibited metastasis (0% of mice versus 60%, P < 0.05) and significantly improved survival, without apparent toxicity.

CONCLUSIONS

Our data demonstrate the efficacy of systemically administered siRNA as a therapeutic modality in experimental pancreatic cancer. This novel therapeutic strategy may be applicable to a broad range of cancers and warrants investigation in patients with refractory disease.

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.

Reference Systems for Kinase Drug Discovery: Chemical Genetic Approaches to Cell-Based Assays

Protein kinases play key roles in a number of diseases, including cancer, inflammation, and diabetes. Disregulation of kinase-based signal transduction networks results in aberrant cell differentiation, activation, proliferation, and invasion. The growing importance of kinases as a major class of drug targets across multiple large clinical indications, together with the large number of kinases in the genome (~518), has generated a critical need for technologies that enable the identification of potent and selective kinase inhibitors with good drug-like properties. In this review, we describe methods used for developing cell-based assays for kinase inhibitors, discuss advantages and disadvantages of each approach, and describe new chemical genetic methods as reference systems for establishing cell-based assays and their use for functional selectivity profiling of kinase inhibitors.

CEACAM6 cross-linking induces caveolin-1-dependent, Src-mediated focal adhesion kinase phosphorylation in BxPC3 pancreatic adenocarcinoma cells

Despite lacking transmembrane or intracellular domains, glycosylphosphatidylinositol-anchored proteins can modulate intracellular signaling events, in many cases through aggregation within membrane "lipid raft" microdomains. CEACAM6 is a glycosylphosphatidylinositol-linked cell surface protein of importance in the anchorage-independent survival and metastasis of pancreatic adenocarcinoma cells. We examined the effects of antibody-mediated cross-linking of CEACAM6 on intracellular signaling events and anchorage-independent survival of the CEACAM6-overexpressing pancreatic ductal adenocarcinoma cell line, BxPC3. CEACAM6 cross-linking increased c-Src activation and induced tyrosine phosphorylation of p125(FAK) focal adhesion kinase. Focal adhesion kinase phosphorylation was dependent on c-Src kinase activation, for which caveolin-1 was required. CEACAM6 cross-linking induced a significant increase in cellular resistance to anoikis. These observations represent the first characterization of the mechanism through which this important cell surface oncoprotein influences intracellular signaling events and hence malignant cellular behavior.