Design, synthesis, and validation of Axl-targeted monoclonal antibody probe for microPET imaging in human lung cancer xenograft.

Accumulating experimental evidence indicates that overexpression of the oncogenic receptor tyrosine kinase, Axl, plays a key role in the tumorigenesis and metastasis of various types of cancer. The objective of this study is to design a novel imaging probe based on the monoclonal antibody, h173, for microPET imaging of Axl expression in human lung cancer. A bifunctional chelator, DOTA, was conjugated to h173, followed by radiolabeling with (64)Cu. The binding of DOTA-h173 to the Axl receptor was first evaluated by a cell uptake assay and flow cytometry analysis using human lung cancer cell lines. The probe (64)Cu-DOTA-h173 was further evaluated by microPET imaging, and ex vivo histology studies in the Axl-positive A549 tumors. In vitro cellular study showed that Axl probe, (64)Cu-DOTA-h173, was highly immuno-reactive with A549 cells. Western blot analysis confirmed that Axl is highly expressed in the A549 cell line. For microPET imaging, the A549 xenografts demonstrated a significantly higher (64)Cu-DOTA-h173 uptake compared to the NCI-H249 xenograft (a negative control model). Furthermore, (64)Cu-DOTA-h173 uptake in A549 is significantly higher than that of (64)Cu-DOTA-hIgG. Immuno-fluorescence staining was consistent with the in vivo micro-PET imaging results. In conclusion, (64)Cu-DOTA-h173 could be potentially used as a probe for noninvasive imaging of Axl expression, which could collect important information regarding tumor response to Axl-targeted therapeutic interventions.

EphB4 as a therapeutic target in mesothelioma.

BACKGROUND: Malignant pleural mesothelioma (MPM) often develops decades following exposure to asbestos. Current best therapy produces a response in only half of patients, and the median survival with this therapy remains under a year. A search for novel targets and therapeutics is underway, and recently identified targets include VEGF, Notch, and EphB4-Ephrin-B2. Each of these targets has dual activity, promoting tumor cell growth as well as tumor angiogenesis. METHODS: We investigated EphB4 expression in 39 human mesothelioma tissues by immunohistochemistry. Xenograft tumors established with human mesothelioma cells were treated with an EphB4 inhibitor (monomeric soluble EphB4 fused to human serum albumin, or sEphB4-HSA). The combinatorial effect of sEphB4-HSA and biologic agent was also studied. RESULTS: EphB4 was overexpressed in 72% of mesothelioma tissues evaluated, with 85% of epithelioid and 38% of sarcomatoid subtypes demonstrating overexpression. The EphB4 inhibitor sEphB4-HSA was highly active as a single agent to inhibit tumor growth, accompanied by tumor cell apoptosis and inhibition of PI3K and Src signaling. Combination of sEphB4-HSA and the anti-VEGF antibody (Bevacizumab) was superior to each agent alone and led to complete tumor regression. CONCLUSION: EphB4 is a potential therapeutic target in mesothelioma. Clinical investigation of sEphB4-HSA as a single agent and in combination with VEGF inhibitors is warranted.

Targeting the EphB4 receptor for cancer diagnosis and therapy monitoring.

Accumulating evidence suggests that EphB4 plays key roles in cancer progression in numerous cancer types. In fact, therapies focusing on EphB4 have become potentially important components of various cancer treatment strategies. However, tumor sensitivity to EphB4 suppression may not be uniform for different cancers. In this study, we developed near-infrared fluorescence (NIRF) probes for EphB4 targeted imaging, based on EphB4-specific humanized monoclonal antibody hAb47. NIRF dye Cy5.5 was introduced to hAb47 either through the reaction with amino groups (named hAb47-Cy5.5) or sulfhydryl groups (named hAb47-Cy5.5-Mal). The resulting probes were evaluated in both HT-29 xenograft and the mAb131 (anti-EphB4) treated models. Although these methods lead to modifications of both the heavy chain and light chain of the antibody, the majority of the EphB4 binding affinity was maintained (81.62 ± 2.08% for hAb47-Cy5.5 and 77.14 ± 2.46% for hAb47-Cy5.5-Mal, respectively). hAb47-Cy5.5 was then chosen for in vivo NIRF imaging of EphB4 expression. In HT29 colorectal tumor xenografts, hAb47-Cy5.5 demonstrated significantly higher tumor uptake compared with that of the hIgG-Cy5.5 control, which was further confirmed by immunofluorescent staining. Moreover, hAb47-Cy5.5 successfully imaged the decreased EphB4 expression (confirmed by Western blot) in EphB4-targeted immunotherapy using another EphB4-specific antibody, mAb131. Collectively, hAb47-Cy5.5 could be used as a specific NIRF contrast agent for noninvasive imaging of EphB4 expression, which may predict whether an individual tumor would likely respond to EphB4 targeted interventions, as well as monitor the therapeutic response.

EphB4-targeted imaging with antibody h131, h131-F(ab')2 and h131-Fab.

Accumulating evidence suggests that overexpression of the tyrosine kinase receptor EphB4, a mediator of vascular development, is a novel target for tumor diagnosis, prognosis and therapy. Noninvasive imaging of EphB4 expression could therefore be valuable for evaluating disease course and therapeutic efficacy at the earliest stages of anti-EphB4 treatment. In this study, we systematically investigated the use of anti-EphB4 antibody h131 (150 kDa) and its fragments (h131-F(ab')2, 110 kDa; h131-Fab, 50 kDa) for near-infrared fluorescence (NIRF) imaging of EphB4 expression in vivo. h131-F(ab')2 and h131-Fab were produced through pepsin and papain digestion of h131 respectively, whose purity was confirmed by FPLC and SDS-PAGE. After conjugation with Cy5.5, in vivo characteristics of h131, h131-F(ab')2 and h131-Fab were evaluated in EphB4-positive HT29 tumor model. Although h131-Cy5.5 demonstrated highest tumor uptake among these probes, its optimal tumor uptake level was obtained at 2 days post injection (p.i.). For h131-Fab-Cy5.5, maximum tumor uptake was achieved at 4 h p.i. However, no significant difference was observed between h131-Fab-Cy5.5 and hIgG-Fab-Cy5.5, indicating the tumor accumulation was mainly caused by passive targeting. In contrast, h131-F(ab')2-Cy5.5 demonstrated prominent tumor uptake at 6 h p.i. The target specificity was confirmed by hIgG-F(ab')2-Cy5.5 control and immunofluorescent staining. Collectively, h131-F(ab')2 exhibited prominent and specific tumor uptake at early time points, which suggests it is a promising agent for EphB4-targeted imaging.

Inhibition of Notch signaling by Dll4-Fc promotes reperfusion of acutely ischemic tissues.

Notch pathway regulates vessel development and maturation. Dll4, a high-affinity ligand for Notch, is expressed predominantly in the arterial endothelium and is induced by hypoxia among other factors. Inhibition of Dll4 has paradoxical effects of reducing the maturation and perfusion in newly forming vessels while increasing the density of vessels. We hypothesized that partial and/or intermittent inhibition of Dll4 may lead to increased vascular response and still allow vascular maturation to occur. Thus tissue perfusion can be restored rapidly, allowing quicker recovery from ischemia or tissue injury. Our studies in two different models (hindlimb ischemia and skin flap) show that inhibition of Dll4 at low dose allows faster recovery from vascular and tissue injury. This opens a new possibility for Dll4 blockade's therapeutic application in promoting recovery from vascular injury and restoring blood supply to ischemic tissues.

Novel EphB4 monoclonal antibodies modulate angiogenesis and inhibit tumor growth.

EphB4 receptor tyrosine kinase and its cognate ligand EphrinB2 regulate induction and maturation of newly forming vessels. Inhibition of their interaction arrests angiogenesis, vessel maturation, and pericyte recruitment. In addition, EphB4 is expressed in the vast majority of epithelial cancers and provides a survival advantage to most. Here, we describe two anti-EphB4 monoclonal antibodies that inhibit tumor angiogenesis and tumor growth by two distinct pathways. MAb131 binds to fibronectin-like domain 1 and induces degradation of human EphB4, but not murine EphB4. MAb131 inhibits human endothelial tube formation in vitro and growth of human tumors expressing EphB4 in vivo. In contrast, MAb47 targets fibronectin-like domain 2 of both human and murine EphB4 and does not alter EphB4 receptor levels, but inhibits angiogenesis and growth of both EphB4-positive and EphB4-negative tumors in a mouse s.c. xenograft model. Combination of MAb47 and bevacizumab enhances the antitumor activity and induces tumor regression. Indeed, humanized antibodies hAb47 and hAb131 showed similar affinity for EphB4 and retained efficacy in the inhibition of primary tumor development and experimental metastasis.

The role of Ephs, Ephrins, and growth factors in Kaposi sarcoma and implications of EphrinB2 blockade.

Kaposi sarcoma (KS) is associated with human herpesvirus (HHV)-8 and is dependent on the induction of vascular endothelial growth factors (VEGFs). VEGF regulates genes that provide arterial or venous identity to endothelial cells, such as the induction of EphrinB2, which phenotypically defines arterial endothelial cells and pericytes, and represses EphB4, which defines venous endothelial cells. We conducted a comprehensive analysis of the Eph receptor tyrosine kinases to determine which members are expressed and therefore contribute to KS pathogenesis. We demonstrated limited Eph/Ephrin expression; notably, the only ligand highly expressed is EphrinB2. We next studied the biologic effects of blocking EphrinB2 using the extracellular domain of EphB4 fused with human serum albumin (sEphB4-HSA). sEphB4-HSA inhibited migration and invasion of the KS cells in vitro in response to various growth factors. Finally, we determined the biologic effects of combining sEphB4-HSA and an antibody to VEGF. sEphB4-HSA was more active than the VEGF antibody, and combination of the 2 had at least additive activity. sEphB4-HSA reduced blood vessel density, pericyte recruitment, vessel perfusion, and increased hypoxia, with an associated increase in VEGF and DLL4 expression. The combination of sEphB4-HSA and VEGF antibody is a rational treatment combination for further investigation.

Tyrosine Phosphoproteomics of Patient-Derived Xenografts Reveals Ephrin Type-B Receptor 4 Tyrosine Kinase as a Therapeutic Target in Pancreatic Cancer.

Pancreatic ductal adenocarcinoma is a recalcitrant tumor with minimal response to conventional chemotherapeutic approaches. Oncogenic signaling by activated tyrosine kinases has been implicated in cancers resulting in activation of diverse effector signaling pathways. Thus, the discovery of aberrantly activated tyrosine kinases is of great interest in developing novel therapeutic strategies in the treatment and management of pancreatic cancer. Patient-derived tumor xenografts (PDXs) in mice serve as potentially valuable preclinical models as they maintain the histological and molecular heterogeneity of the original human tumor. Here, we employed high-resolution mass spectrometry combined with immunoaffinity purification using anti-phosphotyrosine antibodies to profile tyrosine phosphoproteome across 13 pancreatic ductal adenocarcinoma PDX models. This analysis resulted in the identification of 1199 tyrosine-phosphorylated sites mapping to 704 proteins. The mass spectrometric analysis revealed widespread and heterogeneous activation of both receptor and non-receptor tyrosine kinases. Preclinical studies confirmed ephrin type-B receptor 4 (EphB4) as a potential therapeutic target based on the efficacy of human serum albumin-conjugated soluble EphB4 in mice bearing orthotopic xenografts. Immunohistochemistry-based validation using tissue microarrays from 346 patients with PDAC showed significant expression of EphB4 in >70% of patients. In summary, we present a comprehensive landscape of tyrosine phosphoproteome with EphB4 as a promising therapeutic target in pancreatic ductal adenocarcinoma.

Combination of Dll4/Notch and Ephrin-B2/EphB4 targeted therapy is highly effective in disrupting tumor angiogenesis.

BACKGROUND: Dll4/Notch and Ephrin-B2/EphB4 pathways play critical roles in tumor vessel development and maturation. This study evaluates the efficacy of the inhibition of both signaling pathways, alone and in combination, in reducing the growth of an autochthonous mouse tumor and assesses potential adverse effects. METHODS: We used the transgenic RIP1-Tag2 tumor model to study the effects of 1) inhibition of Dll4/Notch by either Dll4 allelic deletion or use of a soluble extracellular Dll4 (sDll4), 2) inhibition of Ephrin-B2/EphB4 signaling by a soluble extracellular EphB4 fused to albumin (sEphB4-Alb), and 3) inhibition of both pathways by sEphB4-Alb combined with either Dll4 allelic deletion or sDll4. To investigate adverse effects, we used inducible endothelial-specific Dll4 knock-out mice, treated with sEphB4-Alb, and carried out histopathological analysis. RESULTS: Dll4 allele deletion or soluble Dll4 treatment resulted in increased tumor vessel density, reduced mural cell recruitment and vessel perfusion which resulted in reduced tumor size. The soluble EphB4 instead reduced vessel density and vessel perfusion, leading to reduction of tumor size. Greater efficacy was observed when sEphB4-Alb was combined with either Dll4 allele deletion or sDll4 in regards to tumor size, vessel perfusion and mural cell recruitment. Induced endothelial specific Dll4 loss-of-function caused hepatic vascular alterations, which were prevented by concomitant sEphB4-Alb treatment. CONCLUSION: Combination targeting of Dll4/Notch and Ephrin-B2/EphB4 has potential for clinical investigation, providing cumulative efficacy and increased safety over Dll4/Notch inhibition alone.

Dissociation of the subunits of the calcium-independent receptor of alpha-latrotoxin as a result of two-step proteolysis.

CIRL (the calcium-independent receptor of alpha-latrotoxin), a neuronal cell surface receptor implicated in the regulation of exocytosis, is a member of the GPS family of chimeric cell adhesion/G protein-coupled receptors. The predominant form of CIRL is a membrane-bound complex of two subunits, p120 and p85. Extracellularly oriented p120 contains hydrophilic cell adhesion domains, whereas p85 is a heptahelical membrane protein. Both subunits are encoded by the same gene and represent products of intracellular proteolytic processing of the CIRL precursor. In this study, we demonstrate that a soluble form of CIRL also exists in vitro and in vivo. It results from the further cleavage of CIRL by a second protease. The site of the second cleavage is located in the short N-terminal extracellular tail of p85, between the GPS domain and the first transmembrane segment of CIRL. Thus, the soluble form of CIRL represents a complex of p120 noncovalently bound to a 15 amino acid residue N-terminal peptide fragment of p85. We have previously shown that mutations of CIRL in the GPS domain inhibit intracellular proteolytic processing and also result in the absence of the receptors from the cell surface. Our current data suggest that although CIRL trafficking to the cell membrane is impaired by mutations in the GPS region, it is not blocked completely. However, at the cell surface, the noncleaved mutants are preferentially targeted by the second protease that sheds the extracellular subunit. Therefore, the two-step proteolytic processing may represent a regulatory mechanism that controls cell surface expression of membrane-bound and soluble forms of CIRL.

Framework shuffling of antibodies to reduce immunogenicity and manipulate functional and biophysical properties.

We report here the humanization of two mouse monoclonal antibodies (mAb) using framework shuffling of human germline genes. mAbs EA2 and 47 were raised against the human receptor tyrosine kinase EphA2 and EphB4, respectively, which exhibit increased expression levels in many cancer cell lines. One- and two-step strategies were carried out, in which the light and heavy chains of each parental mAb were simultaneously or sequentially humanized. We characterized in detail these newly humanized antibodies in terms of binding affinity to their respective antigen, functional activity, thermostability, electric charge and expression yields. Three previously described framework shuffled, humanized versions of another mouse anti-human EphA2 antibody (mAb B233) were similarly characterized. We show that several of these parameters were either maintained or improved in all humanized molecules when compared with their respective chimaeric counterpart. Therefore, this humanization approach is generally applicable to non-human IgGs and allows for the specific selection of antibodies and antibody fragments exhibiting favorable functional, biochemical and biophysical properties.

EphB4 expression and biological significance in prostate cancer.

Prostate cancer is the most common cancer in men. Advanced prostate cancer spreading beyond the gland is incurable. Identifying factors that regulate the spread of tumor into the regional nodes and distant sites would guide the development of novel diagnostic, prognostic, and therapeutic targets. The aim of our study was to examine the expression and biological role of EphB4 in prostate cancer. EphB4 mRNA is expressed in 64 of 72 (89%) prostate tumor tissues assessed. EphB4 protein expression is found in the majority (41 of 62, 66%) of tumors, and 3 of 20 (15%) normal prostate tissues. Little or no expression was observed in benign prostate epithelial cell line, but EphB4 was expressed in all prostate cancer cell lines to varying degrees. EphB4 protein levels are high in the PC3 prostate cancer cell line and several folds higher in a metastatic clone of PC3 (PC3M) where overexpression was accompanied by EphB4 gene amplification. EphB4 expression is induced by loss of PTEN, p53, and induced by epidermal growth factor/epidermal growth factor receptor and insulin-like growth factor-I/insulin-like growth factor-IR. Knockdown of the EphB4 protein using EphB4 short interfering RNA or antisense oligodeoxynucleotide significantly inhibits cell growth/viability, migration, and invasion, and induces apoptosis in prostate cancer cell lines. Antisense oligodeoxynucleotide targeting EphB4 in vivo showed antitumor activity in murine human tumor xenograft model. These data show a role for EphB4 in prostate cancer and provide a rationale to study EphB4 for diagnostic, prognostic, and therapeutic applications.

EPHB4 is a therapeutic target in AML and promotes leukemia cell survival via AKT.

EPHB4, an ephrin type B receptor, is implicated in the growth of several epithelial tumors and is a promising target in cancer therapy; however, little is known about its role in hematologic malignancies. In this article, we show that EPHB4 is highly expressed in ∼30% of acute myeloid leukemia (AML) samples. In an unbiased RNA interference screen of primary leukemia samples, we found that EPHB4 drives survival in a subset of AML cases. Knockdown of EPHB4 inhibits phosphatidylinositol 3-kinase/AKT signaling, and this is accompanied by a reduction in cell viability, which can be rescued by a constitutively active form of AKT. Finally, targeting EPHB4 with a highly specific monoclonal antibody (MAb131) is effective against AML in vitro and in vivo. EPHB4 is therefore a potential target in AML with high EPHB4 expression.

EphB4/EphrinB2 therapeutics in Rhabdomyosarcoma.

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma affecting children and is often diagnosed with concurrent metastases. Unfortunately, few effective therapies have been discovered that improve the long-term survival rate for children with metastatic disease. Here we determined effectiveness of targeting the receptor tyrosine kinase, EphB4, in both alveolar and embryonal RMS either directly through the inhibitory antibody, VasG3, or indirectly by blocking both forward and reverse signaling of EphB4 binding to EphrinB2, cognate ligand of EphB4. Clinically, EphB4 expression in eRMS was correlated with longer survival. Experimentally, inhibition of EphB4 with VasG3 in both aRMS and eRMS orthotopic xenograft and allograft models failed to alter tumor progression. Inhibition of EphB4 forward signaling using soluble EphB4 protein fused with murine serum albumin failed to affect eRMS model tumor progression, but did moderately slow progression in murine aRMS. We conclude that inhibition of EphB4 signaling with these agents is not a viable monotherapy for rhabdomyosarcoma.

Up-regulation of EphB4 in mesothelioma and its biological significance.

PURPOSE: Mesothelioma is a rare malignancy that is incurable and carries a short survival despite surgery, radiation, or chemotherapy. This study was designed to identify novel targets for diagnostic, prognostic, and therapeutic approaches. EXPERIMENTAL DESIGN: The expression and functional significance of the receptor tyrosine kinase EphB4 was studied in vitro and in a murine model of mesothelioma. RESULTS: EphB4 was highly expressed in mesothelioma cell lines and primary tumor tissues but not in normal mesothelium. Knockdown of EphB4 using small interfering RNA and antisense oligodeoxynucleotide showed reduction in cell survival, migration, and invasion. EphB4 knockdown initiated a caspase-8-mediated apoptosis and down-regulation of the anti-apoptotic protein bcl-xl. EphB4 knockdown also resulted in reduced phosphorylation of Akt and down-regulation of matrix metalloproteinase-2 transcription. In addition, murine tumor xenograft studies using EphB4 oligodeoxynucleotides showed a marked reduction in tumor growth accompanied by a specific decline in EphB4 protein levels, reduced cell division, apoptosis in tumor tissue, and decreased microvascular density. CONCLUSIONS: EphB4 is expressed in mesothelioma, provides a survival advantage to tumor cells, and is therefore a potential novel therapeutic target.

Enhancing radiosensitization in EphB4 receptor-expressing Head and Neck Squamous Cell Carcinomas.

Members of the Eph family of receptor tyrosine kinases have been implicated in a wide array of human cancers. The EphB4 receptor is ubiquitously expressed in head and neck squamous cell carcinoma (HNSCC) and has been shown to impart tumorigenic and invasive characteristics to these cancers. In this study, we investigated whether EphB4 receptor targeting can enhance the radiosensitization of HNSCC. Our data show that EphB4 is expressed at high to moderate levels in HNSCC cell lines and patient-derived xenograft (PDX) tumors. We observed decreased survival fractions in HNSCC cells following EphB4 knockdown in clonogenic assays. An enhanced G2 cell cycle arrest with activation of DNA damage response pathway and increased apoptosis was evident in HNSCC cells following combined EphB4 downregulation and radiation compared to EphB4 knockdown and radiation alone. Data using HNSCC PDX models showed significant reduction in tumor volume and enhanced delay in tumor regrowth following sEphB4-HSA administration with radiation compared to single agent treatment. sEphB4-HSA is a protein known to block the interaction between the EphB4 receptor and its ephrin-B2 ligand. Overall, our findings emphasize the therapeutic relevance of EphB4 targeting as a radiosensitizer that can be exploited for the treatment of human head and neck carcinomas.

Soluble EphB4 regulates choroidal endothelial cell function and inhibits laser-induced choroidal neovascularization.

PURPOSE: The purpose of this study was to evaluate the effect of a soluble monomeric form of the EphB4 extracellular domain (sEphB4) on choroidal endothelial cell (CEC) migration and tube formation and on experimental laser-induced choroidal neovascularization (CNV). METHODS: EphrinB2 and EphB4 expression in CECs was investigated by Western blot analysis and immunohistochemistry. Effects of sEphB4 (0.5-3 microg/mL) on CEC migration were evaluated with a modified Boyden chamber assay. Tube formation was assayed in CEC cultures in collagen gel. CNV was induced in rats by laser photocoagulation. The effects of intravitreal injection of sEphB4 on CNV development were evaluated at day 14 by fluorescein angiography (FA), confocal volumetric analysis of isolectin-B4 labeled flatmounts, and histologic examination of CNV membranes. RESULTS: CEC cells express both EphB4 and EphrinB2, according to Western blot analysis. Immunohistochemical sections of rat eye showed immunoreactivity for both EphB4 and EphrinB2 in the choroidal endothelium. sEphB4 reduced CEC migration in response to vascular endothelial growth factor (P < 0.01). Similarly, sEphB4 inhibited CEC tube formation in a dose-dependent manner. EphB4, and to a lesser extent EphrinB2, were detected on vascular channels within laser-induced CNV membranes. Intravitreal injection of sEphB4 inhibited laser-induced CNV formation. CNV membranes showed a reduction in leakage score (P < 0.05), and membrane volumes were reduced in size (P < 0.05). Histologic analysis revealed that vascularity was reduced in sEphB4-treated membranes. CONCLUSIONS: Recombinant soluble monomeric EphB4 exerts an inhibitory effect on choroidal angiogenesis in vitro and in vivo. It should be further evaluated for its potential as a novel therapy for CNV.

Small-Animal PET Imaging of Pancreatic Cancer Xenografts Using a 64Cu-Labeled Monoclonal Antibody, MAb159.

UNLABELLED: Overexpression of the GRP78 receptor on cell surfaces has been linked with tumor growth, metastasis, and resistance to therapy. We developed a (64)Cu-labeled probe for PET imaging of tumor GRP78 expression based on a novel anti-GRP78 monoclonal antibody, MAb159. METHODS: MAb159 was conjugated with the (64)Cu-chelator DOTA through lysines on the antibody. DOTA-human IgG was also prepared as a control that did not bind to GRP78. The resulting PET probes were evaluated in BXPC3 pancreatic cancer xenografts in athymic nude mice. RESULTS: The radiotracer was synthesized with a specific activity of 0.8 MBq/µg of antibody. In BXPC3 xenografts, (64)Cu-DOTA-MAb159 demonstrated prominent tumor accumulation (4.3 ± 1.2, 15.4 ± 2.6, and 18.3 ± 1.0 percentage injected dose per gram at 1, 17, and 48 after injection, respectively). In contrast, (64)Cu-DOTA-human IgG had low BXPC3 tumor accumulation (4.8 ± 0.5, 7.5 ± 0.7, and 4.6 ± 0.8 percentage injected dose per gram at 1, 17, and 48 h after injection, respectively). CONCLUSION: We demonstrated that GRP78 can serve as a valid target for pancreatic cancer imaging. The success of this approach will be valuable for evaluating disease course and therapeutic efficacy at the earliest stages of anti-GRP78 treatment. Moreover, these newly developed probes may have important applications in other types of cancer overexpressing GRP78.

Axl-targeted cancer imaging with humanized antibody h173.

PURPOSE: The tyrosine kinase receptor Axl is overexpressed in various types of cancer and correlated with cancer malignancy. Selective Axl blockade reduces tumor growth and metastasis. The purpose of this study was to examine whether the humanized anti-Axl antibody humanized 173 (h173) labeled with near-infrared fluorescence (NIRF) dye Cy5.5 could be applied as a molecular imaging probe for NIRF imaging of Axl expression in tumor models. PROCEDURES: NIRF dye Cy5.5 was conjugated to h173 or human normal immunoglobulin G (hIgG) control through amino groups. The resulting probes were evaluated in both A549 (Axl positive) and NCI-H249 (Axl negative) lung cancer xenografts through in vivo NIRF imaging. Ex vivo imaging and probe distribution assay were also carried out to confirm the in vivo imaging results. RESULTS: After conjugation, binding activity of h173-Cy5.5 was determined to be 97.75 % ± 2.09 % of the unmodified h173. In vitro fluorescence-activated cell sorting (FACS) and fluorescence microscopy analysis validated the specific binding of h173 toward Axl-positive A549 cells. h173-Cy5.5 was then applied to image Axl expression in vivo. In A549 (Axl positive) cancer xenografts, the tumor uptake of h173-Cy5.5 was significantly higher than that of the hIgG-Cy5.5 control (P < 0.05) at late time points (1, 2, 3, 4, and 7 days). On the contrary, in NCI-H249 (Axl negative) cancer xenografts, the tumor uptake of both hIgG-Cy5.5 and h173-Cy5.5 was low and showed no significant difference (P > 0.05) at all time points examined. Ex vivo imaging and immunofluorescence staining analysis further validated the in vivo imaging results. CONCLUSIONS: Collectively, all in vitro, in vivo, and ex vivo data suggested that h173-Cy5.5 could serve as a valid probe for Axl-targeted cancer imaging, which could therefore aid in tumor diagnosis, prognosis, and treatment monitoring.

The differential expression of EphB2 and EphB4 receptor kinases in normal bladder and in transitional cell carcinoma of the bladder.

Effective treatment of transitional cell carcinoma (TCC) of the bladder requires early diagnosis. Identifying novel molecular markers in TCC would guide the development of diagnostic and therapeutic targets. Ephrins mediate signals via tyrosine kinase activity that modulates diverse physiologic and developmental processes, and ephrins are increasingly implicated in carcinogenesis. The aim of our study was to examine the differential regulation of EphB4 and EphB2 in normal bladder and in TCC of the bladder in 40 patients undergoing radical cystectomy for curative intent. Immunostaining and Western blotting revealed that normal urothelium expresses EphB2 (20 of 24 cases, 83% of the time) not EphB4 (0 of 24 cases, 0%). In sharp contrast, TCC specimens show loss of EphB2 expression (0 of 34 cases, 0%) and gain of EphB4 expression (32 of 34, 94%). Furthermore, EphB4 signal strength statistically correlated with higher tumor stage, and trended toward the presence of carcinoma in situ (CIS). These results are confirmed by analysis of normal urothelial and tumor cell lines. EphB2 is not a survival factor in normal urothelium, while EphB4 is a survival factor in TCC. Treatment of bladder tumor xenograft with an EphB4 inhibitor sEphB4-HSA leads to 62% tumor regression and complete remission when combined with Bevacizumab. Furthermore, tissue analysis revealed that sEphB4-HSA led to increased apoptosis, decreased proliferation, and reduced vessel density, implicating direct tumor cell targeting as well as anti-angiogenesis effect. In summary loss of EphB2 and gain of EphB4 expression represents an inflection point in the development, growth and possibly progression of TCC. Therapeutic compounds targeting EphB4 have potential for diagnosing and treating TCC.