Glioblastoma expression of vitronectin and the alpha v beta 3 integrin. Adhesion mechanism for transformed glial cells

Liposomes Modified with Cyclic RGD Peptide for Tumor Targeting

Cyclic RGD peptide anchored sterically stabilized liposomes (RGD-SL) were investigated for selective and preferential presentation of carrier contents at angiogenic endothelial cells overexpressing alphavbeta3 integrins on and around tumor tissue and thus for assessing their targetabilty. Liposomes were prepared using distearoylphosphatidylcholine (DSPC), cholesterol and distearoylphosphatidylethanolamine-polyethyleneglycol-RGD peptide conjugate (DSPE-PEG-RGD) in a molar ratio 56:39:5. The control RAD peptide anchored sterically stabilized liposomes (RAD-SL) and liposome with 5 mol% PEG (SL) without peptide conjugate which had similar lipid composition were used for comparison. The average size of all liposome preparations prepared was approximately 105 nm and maximum drug entrapment was 10.5+/- 1.1%. In vitro endothelial cell binding of liposomes exhibited 7-fold higher binding of RGD-SL to HUVEC in comparison to the SL and RAD-SL. Spontaneous lung metastasis and angiogenesis assays show that RGD peptide anchored liposomes are significantly (p<0.01) effective in the prevention of lung metastasis and angiogenesis compared to free 5-FU, SL and RAD-SL. In therapeutic experiments, 5-FU, SL, RGD-SL and RAD-SL were administered intravenously on day 4 at the dose of 10 mg 5-FU/kg body weight to B16F10 tumor bearing BALB/c mice resulting in effective regression of tumors compared with free 5-FU, SL and RAD-SL. Results indicate that cyclic RGD peptide anchored sterically stabilized liposomes bearing 5-FU are significantly (p<0.01) active against primary tumor and metastasis than the non-targeted sterically stabilized liposomes and free drug. Thus cyclic RGD peptide anchored sterically stabilized liposomes hold potential of targeted cancer chemotherapeutics.

Metastatic cancer cell

Metastasis is the result of cancer cell adaptation to a tissue microenvironment at a distance from the primary tumor. Metastatic cancer cells require properties that allow them not only to adapt to a foreign microenvironment but to subvert it in a way that is conducive to their continued proliferation and survival. Recent conceptual and technological advances have contributed to our understanding of the role of the host tissue stroma in promoting tumor cell growth and dissemination and have provided new insight into the genetic makeup of cancers with high metastatic proclivity.

Fusion of tumour cells with bone marrow-derived cells: a unifying explanation for metastasis

The causes of metastasis remain elusive despite vast information on cancer cells. We posit that cancer cell fusion with macrophages or other migratory bone marrow-derived cells (BMDCs) provides an explanation. BMDC-tumour hybrids have been detected in numerous animal models and recently in human cancer. Molecular studies indicate that gene expression in such hybrids reflects a metastatic phenotype. Should BMDC-tumour fusion be found to underlie invasion and metastasis in human cancer, new approaches for therapy would surely follow.

Expression of integrin alphavbeta3 in gliomas correlates with tumor grade and is not restricted to tumor vasculature

In malignant gliomas, the integrin adhesion receptors seem to play a key role for invasive growth and angiogenesis. However, there is still a controversy about the expression and the distribution of α_vβ₃ integrin caused by malignancy. The aim of our study was to assess the extent and pattern of α_vβ₃ integrin expression within primary glioblastomas (GBMs) compared with low‐grade gliomas (LGGs). Tumor samples were immunostained for the detection of α_vβ₃ integrin and quantified by an imaging software. The expression of α_vβ₃ was found to be significantly higher in GBMs than in LGGs, whereby focal strong reactivity was restricted to GBMs only. Subsequent analysis revealed that not only endothelial cells but also, to a large extent, glial tumor cells contribute to the overall amount of α_vβ₃ integrin in the tumors. To further analyze the integrin subunits, Western blots from histologic sections were performed, which demonstrated a significant difference in the expression of the β₃ integrin subunit between GBMs and LGGs. The presented data lead to new insights in the pattern of α_vβ₃ integrin in gliomas and are of relevance for the inhibition of α_vβ₃ integrin with specific RGD peptides and interfering drugs to reduce angiogenesis and tumor growth.

Substrate-bound insulin-like growth factor (IGF)-I-IGF binding protein-vitronectin-stimulated breast cell migration is enhanced by coactivation of the phosphatidylinositide 3-Kinase/AKT pathway by alphav-integrins and the IGF-I receptor

IGF-I can bind to the extracellular matrix protein vitronectin (VN) through the involvement of IGF-binding proteins-2, -3, -4, and -5. Because IGF-I and VN have established roles in tumor cell dissemination, we were keen to investigate the functional consequences of the interaction of IGF-I, IGF binding proteins (IGFBPs), and VN in tumor cell biology. Hence, functional responses of MCF-7 breast carcinoma cells and normal nontumorgenic MCF-10A mammary epithelial cells were investigated to allow side-by-side comparisons of these complexes in both cancerous and normal breast cells. We demonstrate that substrate-bound IGF-I-IGFBP-VN complexes stimulate synergistic increases in cellular migration in both cell types. Studies using IGF-I analogs determined this stimulation to be dependent on both heterotrimeric IGF-I-IGFBP-VN complex formation and the involvement of the IGF-I receptor (IGF-IR). Furthermore, the enhanced cellular migration was abolished on incubation of MCF-7 and MCF-10A cells with function blocking antibodies directed at VN-binding integrins and the IGF-IR. Analysis of the signal transduction pathways underlying the enhanced cell migration revealed that the complexes stimulate a transient activation of the ERK/MAPK signaling pathway while simultaneously producing a sustained activation of the phosphatidylinositide 3-kinase/AKT pathway. Experiments using pharmacological inhibitors of these pathways determined a requirement for phosphatidylinositide 3-kinase/AKT activation in the observed response. Overexpression of wild type and activated AKT further increases substrate-bound IGF-I-IGFBP-VN-stimulated migration. This study provides the first mechanistic insights into the action of IGF-I-IGFBP-VN complexes and adds further evidence to support the involvement of VN-binding integrins and their cooperativity with the IGF-IR in the promotion of tumor cell migration.

Induction of glioma cell migration by vitronectin in human serum and cerebrospinal fluid

OBJECT

Malignant gliomas are often highly invasive and can migrate along blood vessels. The purpose of the current study was to identify the substance in human serum and/or cerebrospinal fluid (CSF) that promotes glioma cell migration.

METHODS

The authors used a Boyden chamber cell migration assay to study the effect of serum from patients with glioma and healthy volunteers on chemotaxis of A172 human glioma cells. Heat inactivation, trypsinization, and ultrafiltration of serum were used to establish the nature of the active factor. Vitronectin and fibronectin were chosen for further investigations; chemotactic effects were studied in both serum and CSF.

RESULTS

Serum from both patients with glioma and healthy volunteers was found to promote chemotaxis of human glioma cells. This activity was greatly reduced by heat inactivation or trypsinization. Fractionation of the serum by ultrafiltration through membranes with various pore sizes showed that the active molecule was larger than 50 kD. Antibodies against integrin alphav or alphavbeta5 or arginine-glycine-aspartic acid-containing peptides, both of which block the vitronectin-glioma cell interactions, significantly reduced serum-induced cell migration, whereas blocking the interaction of glioma cells with fibronectin had no effect. Furthermore, the ability of serum to promote the migration of A 172 or T98G glioma cells was suppressed by immunodepletion of vitronectin and restored by the addition of exogenous vitronectin. The migration of glioma cells induced by CSF collected from the postoperative cavity of a malignant glioma patient was also reduced by blocking the interaction of glioma cells with vitronectin.

CONCLUSIONS

These results suggest that vitronectin is one of the major factors in serum- and CSF-induced glioma cell migration.

Differences in binding of (99m)Tc-disintegrins to integrin alphavbeta3 on tumor and vascular cells

Disintegrins, which contain an Arg-Gly-Asp sequence in their binding domains are antagonists of integrins such as alphavbeta3. The purpose of this study was to compare a range of disintegrins with different integrin selectivities for their binding behavior in vitro to vascular endothelial cells bearing alphavbeta3 and to cultured tumor cells which express alphavbeta3.

METHODS

Five disintegrins (bitistatin, kistrin, flavoridin, VLO4 and echistatin) and a cyclic pentapeptide, c[RGDyK], were radiolabeled with (99m)Tc and tested for binding to cells in vitro.

RESULTS

(99m)Tc-Kistrin, flavoridin and VLO4 had the highest binding, (99m)Tc-echistatin had moderate binding, and (99m)Tc-bitistatin and (99m)Tc-c[RGDyK] had low binding to cells. The observed binding was attributed to alphavbeta3 to various extents: echistatin, bitistatin>kistrin>flavoridin>VLO4. Cancer cells internalized bound disintegrins after binding, but endothelial cells did not. After binding to endothelial cells, (99m)Tc-kistrin was not displaced by competing peptide or plasma proteins.

CONCLUSIONS

These data suggest that radiolabeled kistrin, flavoridin and VLO4 may have advantages over labeled bitistatin and small cyclic peptides for targeting alphavbeta3 in vivo. Since receptor-bound radioligand is not internalized by endothelial cells, disintegrins may provide an advantage for targeting alphavbeta3 on vasculature because they bind strongly to surface receptors and are not readily displaced.

In vivo optical imaging of integrin alphaV-beta3 in mice using multivalent or monovalent cRGD targeting vectors

Background

The cRGD peptide is a promising probe for early non-invasive detection of tumors. This study aimed to demonstrate how RAFT-c(-RGDfK-)₄, a molecule allowing a tetrameric presentation of cRGD, improved cRGD-targeting potential using in vivo models of α_Vβ₃-positive or negative tumors.

Results

We chose the human embryonic kidney cells HEK293(β₃) (high levels of α_Vβ₃) or HEK293(β₁) (α_Vβ₃-negative but expressing α_V and β1) engrafted subcutaneously (s.c.) in mice. Non-invasive in vivo optical imaging demonstrated that as compared to its monomeric cRGD analogue, Cy5-RAFT-c(-RGDfK-)₄ injected intravenously had higher uptake, prolonged retention and markedly enhanced contrast in HEK293(β₃) than in the HEK293(β₁) tumors. Blocking studies further demonstrated the targeting specificity and competitive binding ability of the tetramer.

Conclusion

In conclusion, we demonstrated that Cy5-RAFT-c(-RGDfK-)₄ was indeed binding to the α_Vβ₃ receptor and with an improved activity as compared to its monomeric analog, confirming the interest of using multivalent ligands. Intravenous injection of Cy5-RAFT-c(-RGDfK-)₄ in this novel pair of HEK293(β₃) and HEK293(β₁) tumors, provided tumor/skin ratio above 15. Such an important contrast plus the opportunity to use the HEK293(β₁) negative control cell line are major assets for the community of researchers working on the design and amelioration of RGD-targeted vectors or on RGD-antagonists.

Phase I and correlative biology study of cilengitide in patients with recurrent malignant glioma

PURPOSE

This multi-institutional phase I trial was designed to determine the maximum-tolerated dose (MTD) of cilengitide (EMD 121974) and to evaluate the use of perfusion magnetic resonance imaging (MRI) in patients with recurrent malignant glioma.

PATIENTS AND METHODS

Patients received cilengitide twice weekly on a continuous basis. A treatment cycle was defined as 4 weeks. Treatment-related dose-limiting toxicity (DLT) was defined as any grade 3 or 4 nonhematologic toxicity or grade 4 hematologic toxicity of any duration.

RESULTS

A total of 51 patients were enrolled in cohorts of six patients to doses of 120, 240, 360, 480, 600, 1,200, 1,800, and 2,400 mg/m2 administered as a twice weekly intravenous infusion. Three patients progressed early and were inevaluable for toxicity assessment. The DLTs observed were one thrombosis (120 mg/m2), one grade 4 joint and bone pain (480 mg/m2), one thrombocytopenia (600 mg/m2) and one anorexia, hypoglycemia, and hyponatremia (800 mg/m2). The MTD was not reached. Two patients demonstrated complete response, three patients had partial response, and four patients had stable disease. Perfusion MRI revealed a significant relationship between the change in tumor relative cerebral blood flow (rCBF) from baseline and area under the plasma concentration versus time curve after 16 weeks of therapy.

CONCLUSION

Cilengitide is well tolerated to doses of 2,400 mg/m2, durable complete and partial responses were seen in this phase I study, and clinical response appears related to rCBF changes.

Construction, expression, and characterization of a new targeted bifunctional fusion protein: tumstatin45-132-TNF

The anti-angiogenic activity of tumstatin45-132 is mediated by binding to alphaVbeta3 on endothelial cells and tumor vascular endothelium showing increased expression of alphaVbeta3. Tumor necrosis factor alpha (TNF-alpha) is known to not only possess direct cytotoxicity against tumor cells, but also induces tumor vessel disruption, however, clinical use of TNF-alpha as an anticancer drug is hampered by severe systemic toxicity. In this study, we explore the possibility of fusing tumstatin45-132 with human TNF-alpha in the hope of generating a targeting, bi-functional protein in tumor treatment. Tumstatin45-132-TNF was constructed and expressed in E. coli. The recombinant fusion protein was shown to be insoluble and in an inclusion body form. An effective strategy for refolding and purification of tumstatin45-132-TNF resulted in final purified yields of 3 mg purified fusion protein recovered from 1 liter of E. coli culture. The refolded tumstatin45-132-TNF with a purity of 98% assessed by denaturing SDS - PAGE showed a single band on gels. Endothelial cell proliferation assay and standard cytolytic assays against L929 indicated that the fusion protein maintains tumstatin45-132 and TNF-alpha activity. More importantly, tumstatin45-132-TNF inhibits endothelial cell proliferation more than tumstatin45-132 alone. Cell adhesion assays and competitive binding experiments with anti-integrin antibodies showed that the tumstatin45-132 moiety specifically interacts with alphaVbeta3 integrin. These results lay the solid foundation for further investigation of antitumor activity of tumstatin45-132-TNF in vivo.

Targeted and shielded adenovectors for cancer therapy

Conditionally replicative adenovirus (CRAd) vectors are novel vectors with utility as virotherapy agents for alternative cancer therapies. These vectors have already established a broad safety record in humans and overcome some of the limitations of non-replicative adenovirus (Ad) vectors. In addition, one potential problem with these vectors, attainment of tumor or tissue selectivity has widely been addressed. However, two confounding problems limiting efficacy of these drug candidates remains. The paucity of the native Ad receptor on tumor tissues, and host humoral response due to pre-existing titers of neutralizing antibodies against the vector itself in humans have been highlighted in the clinical context. The well-characterized CRAd, AdDelta24-RGD, is infectivity enhanced, thus overcoming the lack of coxsackievirus and adenovirus receptor (CAR), and this agent is already rapidly progressing towards clinical translation. However, the perceived host humoral response potentially will limit gains seen from the infectivity enhancement and therefore a strategy to blunt immunity against the vector is required. On the basis of this caveat a novel strategy, termed shielding, has been developed in which the genetic modification of a virion capsid protein would provide uniformly shielded Ad vectors. The identification of the pIX capsid protein as an ideal locale for genetic incorporation of shielding ligands to conceal the Ad vector from pre-existing neutralizing antibodies is a major progression in the development of shielded CRAds. Preliminary data utilizing an Ad vector with HSV-TK fused to the pIX protein indicates that a shield against neutralizing antibodies can be achieved. The utility of various proteins as shielding molecules is currently being addressed. The creation of AdDelta24S-RGD, an infectivity enhanced and shielded Ad vector will provide the next step in the development of clinically and commercially feasible CRAds that can be dosed multiple times for maximum effectiveness in the fight against cancers in humans.

RGD-dependent binding of procathepsin X to integrin alphavbeta3 mediates cell-adhesive properties

Secreted lysosomal cysteine proteases (cathepsins) are involved in degradation and remodeling of the extracellular matrix, thus contributing to cell adhesion and migration. Among the eleven human lysosomal cysteine proteases, only procathepsin X contains an RGD motif located in a highly exposed region of the propeptide, which may allow binding of the proenzyme to RGD-recognizing integrins. Here, we have tested procathepsin X for cell-adhesive properties and found that it supports integrin alpha(v)beta(3)-dependent attachment and spreading of human umbilical vein endothelial cells. Using site-directed mutants of procathepsin X, we proved that this effect is mediated by the RGD sequence within the proregion of the protease. Endogenous procathepsin X is transported to the plasma membrane, accumulates in vesicles at lamellipodia of the human umbilical vein endothelial cell, and is partly associated with the cell surface, as shown by immunofluorescence. In addition, procathepsin X is partly co-localized with integrin beta(3), as detected by immunogold electron microscopy. A direct interaction between endogenous procathepsin X and alpha(v)beta(3) was demonstrated by co-immunoprecipitation. Moreover, surface plasmon resonance analysis revealed significant and RGD-dependent binding of procathepsin X to integrin alpha(v)beta(3). Our results provide for the first time evidence that the extracellular function of cathepsin X may include binding to integrins thereby modulating the attachment of migrating cells to ECM components.

In Vivo Near-Infrared Fluorescence Imaging of Integrin αvβ3 in an Orthotopic Glioblastoma Model

PURPOSE

Expression of cell adhesion molecule integrin alpha(v)beta(3) is significantly up-regulated during tumor growth, and sprouting of tumor vessels and correlates well with tumor aggressiveness. The purpose of this study was to visualize tumor integrin alpha(v)beta(3) expression in vivo by using near-infrared fluorescence (NIRF) imaging of Cy5.5-linked cyclic arginine-glycine-aspartic acid (RGD) peptide in an orthotopic brain tumor model.

PROCEDURES

U87MG glioma cells transfected with the firefly luciferase gene were stereotactically injected into nude mice in the right frontal lobe. Bioluminescence imaging (BLI) using D: -luciferin substrate and small animal magnetic resonance imaging (MRI) using gadolinium contrast enhancement were conducted weekly after tumor cell inoculation to monitor intracranial tumor growth. Integrin alpha(v)beta(3) expression was assessed by using a three-dimensional optical imaging system (IVIS 200) 0-24 hours after administration of 1.5 nmol monomeric Cy5.5-RGD via the tail vein. Animals were injected intravenously with both Texas Red-tomato lectin and Cy5.5-RGD prior to sacrifice to visualize peptide localization to tumor vasculature using histology.

RESULTS

Fluorescence microscopy demonstrated specific Cy5.5-RGD binding to both U87MG tumor vessels and tumor cells with no normal tissue binding. NIRF imaging showed highest tumor uptake and tumor to normal brain tissue ratio two hours postinjection (2.64 +/- 0.20). Tumor uptake of Cy5.5-RGD was effectively blocked by using unlabeled c(RGDyK), and injection of Cy5.5 dye alone showed nonspecific binding.

CONCLUSIONS

Optical imaging via BLI and NIRF offer a simple, effective, and rapid technique for noninvasive in vivo monitoring and semiquantitative analysis of intracranial tumor growth and integrin alpha(v)beta(3) expression. This study suggests that NIRF via fluorescently labeled RGD peptides may provide enhanced surveillance of tumor angiogenesis and anti-integrin treatment efficacy in orthotopic brain tumor models.

Small molecule drug activity in melanoma models may be dramatically enhanced with an antibody effector

Monoclonal antibody (mAb) 38C2 belongs to a group of catalytic antibodies that were generated by reactive immunization and contains a reactive lysine. 38C2 catalyzes aldol and retro-aldol reactions, using an enamine mechanism, and mechanistically mimics natural aldolase enzymes. In addition, mAb 38C2 can be redirected to target integrins alpha(v)beta(3) and alpha(v)beta(5) through the formation of a covalent bond between a beta-diketone derivative of an arginine-glycine-aspartic acid (RGD) peptidomimetic and the reactive lysine residue in the antibody combining site to provide the chemically programmed mAb cp38C2. In this study, we investigated the potential of enhancing the activity of receptor-binding small molecule drug (SCS-873) through antibody conjugation. Using a M21 human melanoma xenograft model in nude mice, cp38C2 inhibited the growth of the tumor by 81%. The chemically programmed antibody was shown to be highly active at a low concentration while SCS-873 alone was ineffective even at dosages 1,000-fold higher than those used for the chemically programmed antibody. In vitro programming of the catalytic antibody was shown to be as effective as in vivo programming. In an experimental metastasis assay, treatment with mAb cp38C2 significantly prolonged overall survival of tumor-bearing severe combined immuno-deficient (SCID) mice when compared to treatment with unprogrammed mAb 38C2, SCS-873 alone or the integrin-specific monoclonal antibody LM609. In vitro, cp38C2 inhibited human and mouse endothelial and human melanoma cell adhesion, migration and invasion. Additionally, cp38C2 inhibited human and mouse endothelial cell proliferation and was active in complement-dependent cytotoxicity assays. These studies establish the potential of chemically programmed monoclonal antibodies as a novel and effective class of immunotherapeutics that combine the merits of traditional small molecule drug design with immunotherapy.

Molecular mediators of alphavbeta3-induced endothelial cell survival

The alphavbeta3 integrin interaction with the extracellular matrix (ECM) plays an essential role in inhibiting apoptosis in endothelial cells. We have recently shown that alphavbeta3 ligation on rat aortic endothelial cells (RAECs) specifically activates the transcription factor nuclear factor kappaB (NF-kappaB) and promotes cell survival. Inhibiting NF-kappaB nuclear translocation abolished the protective effect of alphavbeta3 ligands. Here, we report that ligation of alphavbeta3 by its ligand, osteopontin (OPN), induces the phosphorylation and activation of inhibitory kappa B kinase beta IKKbeta and promotes the specific degradation of inhibitory kappa Balpha (IkappaBalpha) in RAECs. Overexpression of a dominant negative (DN) IKKbeta protein prevents IkappaBalpha phosphorylation, NF-kappaB activation, and inhibits the protective effects of OPN. The NF-kappaB-inducing kinase (NIK) has been shown to be one of the upstream kinases involved in IKK activation. OPN-mediated NF-kappaB activity is increased upon NIK wild-type (WT) overexpression and blocked following NIK DN overexpression. In addition, NIK-/-mouse embryonic fibroblasts (MEFs) plated on OPN display reduced NF-kappaB activity and decreased IkappaBalpha phosphorylation compared to NIK+/+MEFs. Finally, functional inhibition of integrin beta3-dependent NF-kappaB signaling decreases OPN-induced IkappaBalpha, IKKbeta and NIK phosphorylation. These studies for the first time show that the alphavbeta3-NF-kappaB-dependent endothelial survival pathway is dependent on IkappaBalpha, IKKbeta, and NIK.

Modulation of response to tumor therapies by the extracellular matrix

The composition of the extracellular matrix in tumors is vastly different from that found in the normal tissue counterparts. As the extracellular matrix can signal to cells via integrin binding and activation, which is known to modulate cell proliferation, survival and migration, it may influence the response of both tumor and endothelial cells to anticancer therapies. Certain tumor-associated extracellular matrix proteins have been shown to confer resistance to chemotherapeutic drugs, radiation and anti-angiogenic factors. The current literature regarding this phenomenon and the potential therapeutic modalities to overcome extracellular matrix-induced resistance will be discussed.

Potent mimicry of fibronectin-induced intracellular signaling in glioma cells by the homodimeric snake venom disintegrin contortrostatin

OBJECTIVE

The snake venom disintegrin contortrostatin (CN) is able to inhibit tumor progression and angiogenesis in vivo and therefore is of considerable interest as a potential antitumor drug. CN specifically binds to certain integrins on the tumor cell and angiogenic endothelial cell surface and inhibits their interaction with the extracellular matrix, resulting in blockage of cell motility and invasiveness. To understand the molecular consequences of CN binding to integrins, we set out to investigate and compare the effects of CN and fibronectin (FN) on integrin-induced signaling and the resulting alteration in cellular cytoskeletal morphology.

METHODS

Two different malignant glioma cell lines were exposed to soluble or immobilized CN, FN, or both, and the consequences for intracellular signaling and cellular adhesion to matrix were investigated.

RESULTS

CN binding to integrins can mimic the intracellular signaling cascade evoked by FN, because the phosphorylation of the key signaling proteins focal adhesion kinase, paxillin, and p130 Crk-associated substrate and the association of Src with focal adhesion kinase are similar. However, CN is at least one order of magnitude more potent than FN. When soluble CN is added to cells that are already attached to an FN-coated matrix, it effectively disrupts the binding of integrin to FN, leading to a decrease in integrin signaling, which, in turn, results in the disruption of the cytoskeleton and cellular detachment.

CONCLUSION

Our results provide a mechanistic explanation of how soluble CN might block cellular migration and invasion, namely, by disrupting and preventing the binding of integrins to the extracellular matrix. We envision that this property of CN could be used in the treatment of gliomas, namely, by intratumoral infusion of CN to prevent glioma and endothelial cell interactions with the extracellular matrix, leading to inhibition of cell invasion.

Proteases and glioma angiogenesis

Angiogenesis, the process by which new branches sprout from existing vessels, requires the degradation of the vascular basement membrane and remodeling of the ECM in order to allow endothelial cells to migrate and invade into the surrounding tissues. Serine, metallo, and cysteine proteinases are 3 types of a family of enzymes that proteolytically degrade various components of extracellular matrix. These proteases release various growth factors and also increase adhesive molecules and signaling pathway molecules upon their activation, which plays a significant role in angiogenesis. Downregulation of these molecules by antisense/siRNA or synthetic inhibitors decreases the levels of these molecules, inhibits the release of growth factors, and decreases the levels of various signaling pathway molecules, thereby leading to the inhibition of angiogenesis. Furthermore, MMPs degrade specific substrates and release angiogenic inhibitors which inhibit angiogenesis. Downregulation of 2 molecules, such as uPA and uPAR, uPAR and MMP-9, or Cathepsin B and MMP-9, are more effective to inhibit angiogenesis rather than downregulation of single molecules. However, careful testing of these combinations are most important because multiple effects of these combinations play a significant role in angiogenesis.

Use of RNA interference to inhibit integrin subunit alphaV-mediated angiogenesis

One of the central molecules in capillary formation during angiogenesis is the integrin alphaVbeta3. The aim of this study was to inhibit alphaV-mediated angiogenesis in vitro using RNAs (siRNA) as well as antisense oligodeoxyribonucleotides (asON). Five siRNAs, against the alphaV chain of alphaVbeta3, and three asON, which had the respective sequence of the antisense sequence of three of the siRNAs molecules, were examined. Two of the siRNAs and their respective asON were designed on the basis of computer-predicted secondary structure analysis of alphaV mRNA. The different molecules were transfected into human umbilical vein endothelials cells (HUVEC) using lipofection. Following stimulation by PMA, two siRNAs showed a dose-dependent inhibition of PMA-induced alphaV mRNA and protein upregulation, as assessed by real-time RT-PCR and flow cytometry. At a concentration of 25 nM a complete inhibition of protein upregulation was found using siRNAs while transfection of the respective asON sequences reduced the protein upregulation only by 44%. To evaluate the anti-angiogenic potential a cell culture model of human angiogenesis based on the co-cultivation of endothelial cells and dermal fibroblasts was used. Transfection of the siRNA sequence (50 nM) resulted in an inhibition of the total length of capillary-like tubules by 40.6% in comparison to 21.1% using the respective asON sequence. In conclusion, siRNA-based downregulation of alphaV expression showed a stronger inhibition of capillary tube formation in an angiogenesis in vitro assay, than asON having the same sequence as the antisense strand of the siRNAs. Therefore, siRNAs are useful tools for functional alphaV knock-down experiments and might be a therapeutic alternative for antagonists which bind directly to the integrins alphaVbeta3 or alphaVbeta5.

Retargeting of adenoviral vector using basic fibroblast growth factor ligand for malignant glioma gene therapy

Object. Adenovirus vector (AdV)—mediated gene delivery has been recently demonstrated in clinical trials as a novel potential treatment for malignant gliomas. Combined coxsackievirus B and adenovirus receptor (CAR) has been shown to function as an attachment receptor for multiple adenovirus serotypes, whereas the vitronectin integrins (αvβ3 and αvβ5) are involved in AdV internalization. In resected glioma specimens, the authors demonstrated that malignant gliomas have varying levels of CAR, αvβ3, and αvβ5 expression.

Methods. A correlation between CAR expression and the transduction efficiency of AdV carrying the green fluorescent protein in various human glioblastoma multiforme (GBM) cell lines and GBM primary cell lines was observed. To increase transgene activity in in vitro glioma cells with low or deficient levels of CAR, the authors used basic fibroblast growth factor (FGF2) as a targeting ligand to redirect adenoviral infection through its cognate receptor, FGF receptor 1 (FGFR1), which was expressed at high levels by all glioma cells. These findings were confirmed by in vivo study data demonstrating enhanced transduction efficiency of FGF2-retargeted AdV in CAR-negative intracranial gliomas compared with AdV alone, without evidence of increased angiogenesis.

Conclusions. Altogether, the results demonstrated that AdV-mediated gene transfer using the FGF2/FGFR system is effective in gliomas with low or deficient levels of CAR and suggested that FGF2-retargeting of AdV may be a promising approach in glioma gene therapy.

Activation of nuclear factor kappa B (NF-kappaB) by connective tissue growth factor (CCN2) is involved in sustaining the survival of primary rat hepatic stellate cells

Background/Aims

Connective tissue growth factor (CCN2) is a matricellular protein that plays a role in hepatic stellate cell (HSC)-mediated fibrogenesis. The aim of this study was to investigate the regulation by CCN2 of cell survival pathways in primary HSC.

Methods

Primary HSC were obtained by in situ enzymatic perfusion of rat liver. NF-κB activation was assessed by immunoblotting for IκBα phosphorylation and degradation and by NF-κB p50 or p65 nuclear accumulation. NF-κB DNA-binding activity was determined by gel mobility shift assay while NF-κB response gene expression was evaluated using a luciferase reporter. Cell viability was assessed by Trypan blue staining or ATP luminescent assay while apoptosis was evaluated by caspase-3 activity.

Results

CCN2 induced IκBα phosphorylation and degradation as well as nuclear accumulation of NF-κB. Activated NF-κB comprised three dimers, p65/p65, p65/p50 and p50/p50, that individually bound to DNA-binding sites and subsequently triggered transcriptional activity. This was confirmed by showing that CCN2 promoted activity of a NF-κB luciferase reporter. CCN2 promoted survival of serum-starved HSC and protected the cells from death induced by blocking the NF-κB signaling pathway using Bay-11-7082, a specific inhibitor of IκBα phosphorylation.

Conclusion

CCN2 contributes to the survival of primary HSC through the NF-κB pathway.

Integrins as a distinct subtype of dependence receptors

In the absence of their cognate ligand, dependence receptors trigger programmed cell death. This function is the defining feature of dependence receptors, which include members of several different protein families. The integrins are a family of heterodimeric receptors for extracellular matrix (ECM) proteins, mediating cell anchorage and migration. Integrins share characteristics with dependence receptors, and integrin binding to substrate ECM ligands is essential for cell survival. Although integrins do not conform in all characteristics to the established definitions of dependence receptors, alterations in the expression of integrins and their ligands during physiological and pathological events, such as wound healing, angiogenesis and tumorigenesis, do regulate cell fate in a ligand-dependent manner. This biosensory function of integrins fits well with our current concept of dependence receptor action, and thus integrins may rightly be considered to comprise a distinct subclass of dependence receptor.

The role of contortrostatin, a snake venom disintegrin, in the inhibition of tumor progression and prolongation of survival in a rodent glioma model

OBJECT

Malignant gliomas are not curable because of diffuse brain invasion. The tumor cells invade the surrounding brain tissue without a clear tumor-brain demarcation line, making complete resection impossible. Therapy aimed at inhibition of invasion is crucial not only for prevention of tumor spread, but also for selectively blocking migrating cells that may be more resistant to chemotherapy and radiation. Recently, investigations have shown that the snake venom disintegrin contortrostatin specifically binds to certain integrins on the surface of glioma cells and thereby inhibits their interaction with the extracellular matrix (ECM), resulting in a blockage of cell motility and invasiveness. To translate these in vitro findings into clinical settings, the authors examined the effect of contortrostatin on glioma progression in a rodent model.

METHODS

Athymic mice were intracranially or subcutaneously injected with U87 glioma cells, and the effect of intratumorally administered contortrostatin on tumor progression and animal survival was then studied. In addition, the authors evaluated the pharmacological safety of contortrostatin use in the brains of tumor-free animals.

CONCLUSIONS

The results demonstrate that contortrostatin is able to inhibit tumor growth and angiogenesis and to prolong survival in a rodent glioma model. Moreover, contortrostatin appears to be well tolerated by the animal and lacks obvious neurotoxic side effects. Thus, contortrostatin may have potential as a novel therapeutic agent for the treatment of malignant gliomas.

The extracellular space and matrix of gliomas

Changes in the properties of extracellular space (ECS)--its volume, shape, and composition--play an important role in influencing the biological behavior of brain tumors. Experimental methods allowing assessment of the volume and geometry of ECS by means of analyzing the diffusion of molecules within ECS have revealed a dramatic increase in the ECS volume of gliomas when compared with that of unaffected brain cortex, also correlating with increases in malignancy. However, the newly enlarged ECS of high-grade gliomas does not remain empty; ECS shape becomes more complicated than in normal brain tissue. In contrast to the low-grade tumors, where the diffusion of molecules is reduced mainly by the presence of a dense network of tumor cell processes, the increase of ECS barriers in high-grade gliomas is caused by the overproduction of certain components of the extracellular matrix (ECM), mainly of tenascin. These aberrantly or "overproduced" ECM glycoproteins not only stabilize the ECS volume, but also serve as a substrate for adhesion and subsequent migration of the tumor cells through the enlarged ECS. Interestingly, these same alterations in ECS structure may hinder the diffusion of neuroactive substances or even molecules of drugs into the neoplastic tissue. The presence of tenascin in the ECS of the neoplasm correlates significantly with increased malignancy and poor clinical outcome of the disease, which makes its immunohistochemical detection useful as a marker of an aggressive biological behavior of the tumors.

The role of the extracellular matrix in angiogenesis in malignant glioma tumors

Angiogenesis is a promising target for the development of effective strategies for the treatment of malignant brain tumors in that it has the potential to starve large tumors and prevent the regrowth of residual margins. Two critical steps in angiogenesis, the proliferation of activated endothelial cells and their migration into the perivascular space (sprouting), require adherence of the endothelial cells to the extracellular matrix (ECM). Thus, the availability of the appropriate ligands within the ECM contributes to the regulation of angiogenesis. In addition, several components of the ECM can act through other mechanisms to further promote angiogenesis or inhibit it. Current evidence suggests that the regulation of angiogenesis is a dynamic process in which the endothelial cells can promote angiogenesis by secreting proteases that remodel the ECM, tumor cells can further promote angiogenesis by secreting ECM components and actively remodeling their environment, and stromal cells may respond to angiogenesis associated with tumors and inflammatory reactions by secreting inhibitory molecules. Here, we provide a critical review of the protein and proteoglycan components of the ECM that have been implicated in angiogenesis with an emphasis on their role in promoting or inhibiting angiogenesis in brain tumors.

Lyn kinase activity is the predominant cellular SRC kinase activity in glioblastoma tumor cells

Cellular Src activity modulates cell migration, proliferation, and differentiation, and recent reports suggest that individual members of the Src family may play specific roles in these processes. As we have found that Lyn, but not Fyn, activity promotes migration of glioblastoma cells in response to the cooperative signal generated by platelet-derived growth factor receptor beta and integrin alpha(v)beta3, we compared the activity and expression of Lyn and Fyn in glioblastoma (grade IV) tumor biopsy samples with that in anaplastic astrocytoma (grade III) tumors, nonneoplastic brain, and normal autopsy brain samples. Lyn kinase activity was significantly elevated in glioblastoma tumor samples. Notably, the Lyn kinase activity accounted for >90% of pan-Src kinase activity in glioblastoma samples but only approximately 30% of pan-Src kinase activity in the other groups. The levels of phosphorylation of the autophosphorylation site were consistent with significantly higher Lyn activity in glioblastoma tumor tissue than nonneoplastic brain. Although the normalized levels of Lyn protein and the relative levels of Lyn message were significantly higher in glioblastoma samples than nonneoplastic brain, the normalized levels of Lyn protein did not correlate with Lyn activity in the glioblastoma samples. There was no significant difference in the normalized levels of c-Src and Fyn protein and message in the glioblastoma and nonneoplastic brain. Immunostaining revealed that Lyn is located primarily in the glioblastoma cells in the tumor biopsies. These data indicate that Lyn kinase activity is significantly elevated in glioblastoma tumors and suggest that it is the Lyn activity that promotes the malignant phenotype in these tumors.

alpha(v)beta(3) Integrin in central nervous system tumors

alpha(v)beta(3) Is an integrin specifically expressed in endothelial cells of newly forming blood vessels. Integrin-mediated angiogenesis is hypothesized to play a central role in the development and the progression of central nervous system neoplasms. Accordingly, it is considered a potential target for antiangiogenic therapy. In the current study, we compare the expression of alpha(v)beta(3) in ependymomas, oligodendrogliomas, pilocytic astrocytomas, medulloblastomas, and vestibular schwannomas (acoustic neuromas). Samples of 5 tumors of each of the 5 tumor types were harvested surgically and frozen. After the pathological diagnosis was confirmed, immunohistochemistry was performed using an anti- alpha(v)beta(3) monoclonal antibody (LM609). The expression of alpha(v)beta(3) was assessed using a 4-tiered (0-3) grading scheme reflecting the percentage of positively staining vessels. All vestibular schwannomas demonstrated strong (grade 3) alpha(v)beta(3) expression. The expression was uniformly prominent in Antoni B regions of the tumors. Of 5 ependymomas, 4 demonstrated uniformly strong alpha(v)beta(3). Oligodendrogliomas, medulloblastomas, and pilocytic astrocytomas demonstrated more variable alpha(v)beta(3). alpha(v)beta(3) may contribute significantly to angiogenesis in vestibular schwannomas and ependymomas. Despite the high vascular density of oligodendrogliomas, pilocytic astrocytomas, and medulloblastomas, these tumors had variable moderate alpha(v)beta(3) expression. This discrepancy suggests temporal and/or regional variability in the angiogenesis in these types of tumor. This study provides the first demonstration of alpha(v)beta(3) expression in vestibular schwannomas, medulloblastomas, and pilocytic astrocytomas.

Characterization of the Integrin αvβ3 in Arteriovenous Malformations and Cavernous Malformations

BACKGROUND

Alpha V beta 3 (alphavbeta3) is an integrin specifically expressed on the endothelial cells of central nervous system (CNS) neoplasms. However, no data exist on the expression of alphavbeta3 in vascular malformations of the CNS. In this study, we investigate the expression of alphavbeta3 in arteriovenous malformations (AVMs) and cavernous malformations (CMs).

METHOD

Frozen samples of AVMs from 12 patients and CMs from 5 patients were obtained intraoperatively. Once the final pathology had been confirmed, immunohistochemistry was performed using an antibody to the integrin alphavbeta3. The alphavbeta3 expression pattern was graded according to the percentage of positively staining vessels.

RESULTS

Ten of 12 AVMs demonstrated alphavbeta3 immunopositivity. Six of these 10 AVMs had moderate or strong staining. Most notably, 5 of the 6 moderate or strongly staining AVMs came from patients 22 years of age or younger. Four of these 6 AVMs had previously been embolized. None of the cavernous malformations demonstrated alphavbeta3 immunopositivity.

DISCUSSION

alphavbeta3 may contribute to the formation of AVMs in younger patients. alphavbeta3 may also provide a potential therapeutic target. The lack of alphavbeta3 expression in cavernous malformations, despite their high vascular densities, suggests that the pathophysiology of their formation differs from that of AVMs.

Expression, purification, and characterization of a neovasculature targeted rmhTNF-alpha in Escherichia coli

The tumor vasculature is a suitable target for cancer treatment. RGD-4C (CDCRGDCFC) peptide can bind to human alphav integrins, which are known to be selectively expressed in human tumor blood vessels. Some studies showed that coupling anticancer drugs or peptides to the RGD peptides yielded compounds with increased efficacy against tumors and lowered toxicity to normal tissues in mice. TNF-alpha mutant (rmhTNF-alpha) that we previously constructed has been proved to have stronger antitumor effect compared with TNF-alpha. To increase antitumor effect and lower toxicity of rmhTNF-alpha, we coupled RGD4C to the N-terminal of rmhTNF-alpha (termed RGD4C-rmhTNF) and expressed RGD4C-rmhTNF in Escherichia coli. Here, we describe the expression, purification, and characterization of RGD4C-rmhTNF.

Endogenous inhibitors of angiogenesis in malignant gliomas: nature's antiangiogenic therapy

Angiogenesis is necessary for tumor growth beyond a volume of approximately 2 mm(3). This observation, along with the accessibility of tumor vessels to therapeutic targeting, has resulted in a research focus on inhibitors of angiogenesis. A number of endogenous inhibitors of angiogenesis are found in the body. Some of these are synthesized by specific cells in different organs, and others are created by extracellular proteolytic cleavage of plasma-derived or extracellular matrix-localized proteins. In this review, we focus on angiostatin, endostatin, PEX, pigment epithelial-derived factor, and thrombospondin (TSP)-1 and -2, either because these molecules are expressed in malignant glioma biopsies or because animal studies in malignant glioma models have suggested that their therapeutic administration could be efficacious. We review the known mechanisms of action, potential receptors, expression in glioma biopsy samples, and studies testing their potential therapeutic efficacy in animal models of malignant glioma. Two conclusions can be made regarding the mechanisms of action of these inhibitors: (1) Several of these inhibitors appear to mediate their antiangiogenic effect through multiple protein-protein interactions that inhibit the function of proangiogenic molecules rather than through a specific receptor-mediated signaling event, and (2) TSP-1 and TSP-2 appear to mediate their antiangiogenic effect, at least in part, through a specific receptor, CD36, which initiates the antiangiogenic signal. Although not proven in gliomas, evidence suggests that expression of specific endogenous inhibitors of angiogenesis in certain organs may be part of a host antitumor response. The studies reviewed here suggest that new antiangiogenic therapies for malignant gliomas offer exciting promise as nontoxic, growth-inhibitory agents.

Quantification of thrombospondin-1 secretion and expression of alphavbeta3 and alpha3beta1 integrins and syndecan-1 as cell-surface receptors for thrombospondin-1 in malignant glioma cells

Malignant glioma cells secrete thrombospondin-1 (TSP-1) which participates in the motility of glioma cells, and binds to cell surface alphavbeta3 and alpha3beta1 integrins, and syndecan-1. This study evaluated the amount of TSP-1 secretion from malignant glioma cells, and the expression of alphavbeta3 and alpha3beta1 integrins, and syndecan-1. The amounts of TSP-1 in the supernatants from 10 malignant glioma cell lines and eight non-glioma malignant tumor cell lines were measured by enzyme-linked immunosorbent assay. Expression of alphavbeta3 and alpha3beta1 integrins, and syndecan-1 were examined by flow cytometry. The amounts of TSP-1 secreted by malignant glioma cells were 43 to 2431 ng/l x 10(6) cells/24 h (mean +/- SD = 626 +/- 792). Seven of 10 glioma cell lines secreted more than 100 ng of TSP-1 and three of these cell lines secreted more than 1 microg. Seven of eight non-glioma cell lines secreted less than 100 ng of TSP-1. All glioma cell lines expressed alpha3beta1 integrin and syndecan-1, and seven of 10 glioma cell lines expressed alphavbeta3 integrin. Treatment of the glioma cell lines with TGF-beta2 did not change the expression of alphavbeta3 integrin. These results suggest that malignant glioma cells secrete high levels of TSP-1, which may be important in the migration of glioma cells via interactions with alphavbeta3 and alpha3beta1 integrins, and syndecan-1.

Glioma cell integrin expression and their interactions with integrin antagonists: Research Article

A panel of human glioma cell explants was screened for integrin expression by flow cytometry using α(ν)β-specific antibodies. A lower percentage of the glioma cells were positive for the α(ν)β3 (mean % positive = 20.8%) integrin, whereas higher percentages were positive for the ανβ5 (mean % positive = 72.7%), VLA5α (mean % positive = 87%) and VLAβ1 (mean % positive = 41.7%) integrins. A series of RGD peptides was designed, synthesized and tested for binding to integrin receptors. Based on the results of the binding to the isolated integrin receptors and the expression of integrins on glioma cell lines, a peptide that binds potently to the α(ν)β3, α(ν)β5 and α(5)β(1) was selected for further investigations with regards to its effect on glioma cells. The peptide, Ac-c[(Pen)-Tyr(Me)-Ala-Arg-Gly-Asp-Asn-Tic-Cys]NH(2) (RGD peptide), exhibited high potential for use in clinical intracranial administration since it had good stability in rat brain cell homogenates placed into artificial cerebrospinal fluid. Using an HPLC method for quantification of peptides in rat brain cell homogenates, we could demonstrate the half-life of the RGD peptide approximated 20 hr. Relative to a scrambled peptide control (non-RGD sequence, same amino acids), the experimental RGD peptide significantly decreased glioma cell proliferation of the entire panel of rat and human glioma cells tested. Adhesion of recently passaged glioma cells to glioma-derived extracellular matrix protein-coated plates was inhibited significantly by the RGD peptide. The peptide also reversed attachment of plated glioma cells. The RGD peptide caused some, but not substantial, glioma cell injury, as evidenced by a quantitative in vitro nuclear DNA morphologic assay and by a flow cytometric assay employing 7-amino actinomycin D (7AAD). We histologically monitored for toxicity caused by various doses of the RGD peptide infused repeatedly into normal cannulated rat brain. At safe doses, the experimental RGD peptide-treated brains did not show significant differences from those infused with scrambled peptide or buffer-treated controls. In tumor-bearing brains, slightly smaller tumor areas were measured with a higher necrotic-to-tumor index in the RGD peptide treated relative to the scrambled peptide-treated controls. This was obtained with intracranial peptide administrations or combined intracranial and intraperitoneal injections. From this in vitro work, we conclude that the anti-glioma effects of the RGD peptide tested resulted from lowered glioma proliferation and adhesion/mobility, rather than from significant glioma cell injury in the timeframe analyzed. Although other mechanisms not discerned from our limited histopathological observations may be operational, from our in vivo work, we conclude that repeated administration of RGD peptide into brain is safe but that better delivery of the peptides to infiltrating tumor cells is necessary.

Spontaneous regression of experimental gliomas--an immunohistochemical and MRI study of the C6 glioma spheroid implantation model

OBJECTIVE

The orthotopic C6 glioma spheroid implantation model has been used to examine factors of neoangiogenesis, growth factor release, and protease expression as well the effect of antitumor agents. The present study systematically investigates the long-term course of orthotopically implanted C6 spheroid gliomas.

METHODS

Reaggregated C6 spheroid tumors were implanted into the forebrain of 48 male Sprague-Dawley rats (32 immunocompetent, 16 thymectomized). The animals were examined by MRI at postoperative day (POD) 7, 14, 21, 28, 32, 45, 60, and 70. The MRI protocol included a T2-w and T1-w SE sequence before and after application of contrast medium and a CISS 3D sequence for volumetry. A total of six animals were selected after each MR exam from both groups and sacrificed for HE light microscopy and CD8+ T-lymphocyte, ED1+ macrophage, CD31+ endothelial cell immunohistochemistry.

RESULTS

The tumors progressed to reach a maximum volume on day 28: 0.23 +/- 0.05 ml in the thymectomized and 0.16 +/- 0.021 ml in the immunocompetent group. Tumors then consistently regressed to vanish completely by POD 70. The influx of cytotoxic CD8+ T-lymphocytes correlated with tumor progression and the tumors reached a larger size in the thymectomized group. However, the time course of tumor regression was the same for both groups.

CONCLUSION

The present data suggest that the orthotopic C6 glioma implanted into Sprague-Dawley rats will progress within a time span of approximately 4 weeks and can then retrogress again spontaneously. This finding has to be taken into account when deciding on a study protocol and the appropriate animal model. The C6 glioma model may be suitable to study the cell biological steps involved in the phenomenon of spontaneous tumor regression.

Ultrasonic analysis of peptide- and antibody-targeted microbubble contrast agents for molecular imaging of alphavbeta3-expressing cells

The goal of targeted ultrasound contrast agents is to significantly and selectively enhance the detection of a targeted vascular site. In this manuscript, three distinct contrast agents targeted to the alphavbeta3 integrin are examined. The alphavbeta3 integrin has been shown to be highly expressed on metastatic tumors and endothelial cells during neovascularization, and its expression has been shown to correlate with tumor grade. Specific adhesion of these contrast agents to alphavbeta3-expressing cell monolayers is demonstrated in vitro, and compared with that of nontargeted agents. Acoustic studies illustrate a backscatter amplitude increase from monolayers exposed to the targeted contrast agents of up to 13-fold (22 dB) relative to enhancement due to control bubbles. A linear dependence between the echo amplitude and bubble concentration was observed for bound agents. The decorrelation of the echo from adherent targeted agents is observed over successive pulses as a function of acoustic pressure and bubble density. Frequency-domain analysis demonstrates that adherent targeted bubbles exhibit high-amplitude narrowband echo components, in contrast to the primarily wideband response from free microbubbles. Results suggest that adherent targeted contrast agents are differentiable from free-floating microbubbles, that targeted contrast agents provide higher sensitivity in the detection of angiogenesis, and that conventional ultrasound imaging techniques such as signal subtraction or decorrelation detection can be used to detect integrin-expressing vasculature with sufficient signal-to-noise.

Integrin signalling during tumour progression

During progression from tumour growth to metastasis, specific integrin signals enable cancer cells to detach from neighbouring cells, re-orientate their polarity during migration, and survive and proliferate in foreign microenvironments. There is increasing evidence that certain integrins associate with receptor tyrosine kinases (RTKs) to activate signalling pathways that are necessary for tumour invasion and metastasis. The effect of these integrins might be especially important in cancer cells that have activating mutations, or amplifications, of the genes that encode these RTKs.

Vitronectin's basic domain is a syndecan ligand which functions in trans to regulate vitronectin turnover

During the process of tissue remodeling, vitronectin (Vn) is deposited in the extracellular matrix where it plays a key role in the regulation of pericellular proteolysis and cell motility. In previous studies we have shown that extracellular levels of vitronectin are controlled by receptor-mediated endocytosis and that this process is dependent upon vitronectin binding to sulfated proteoglycans. We have now identified vitronectin's 12 amino acid "basic domain" which is contained within the larger 40 amino acid heparin binding domain, as a syndecan binding site. Recombinant vitronectins representing wild type vitronectin (rVn) and vitronectin with the basic domain deleted (rVnDelta347-358) were prepared in a baculoviral expression system. The rVn as well as a glutathione S-transferase (GST) fusion protein, consisting of vitronectin's 40 amino acid heparin binding domain (GST-VnHBD), exhibited dose dependent binding to HT-1080 cell surfaces, which was attenuated following deletion of the basic domain. In addition, GST-VnHBD supported both HT-1080 and dermal fibroblast cell adhesion, which was also dependent upon the basic domain. Similarly, ARH-77 cells transfected with syndecans -1, -2, or -4, but not Glypican-1, adhered to GST-VnHBD coated wells, while adhesion of these same cells was lost following deletion of the basic domain. HT-1080 cells were unable to degrade rVnDelta347-358. Degradation of rVnDelta347-358 was completely recovered in the presence of GST-VnHBD but not in the presence of GST-VnHBDDelta347-358. These results indicate that turnover of soluble vitronectin requires ligation of vitronectin's basic domain and that this binding event can work in trans to regulate vitronectin degradation.

Activated vitronectin as a target for anticancer therapy with human antibodies

The formation of a provisional extracellular matrix represents an important step during tumor growth and angiogenesis. Proteins that participate in this process become activated and undergo conformational changes that expose biologically active cryptic sites. Activated matrix proteins express epitopes not found on their native counterparts. We hypothesized that these epitopes may have a restricted tissue distribution, rendering them suitable targets for therapeutic human monoclonal antibodies (huMabs). In this study, we exploited phage antibody display technology and subtractive phage selection to generate human monoclonal antibody fragments that discriminate between the activated and native conformation of the extracellular matrix protein vitronectin. One of the selected antibody fragments, scFv VN18, was used to construct a fully human IgG/kappa monoclonal antibody with an affinity of 9.3 nM. In immunohistochemical analysis, scFv and huMab VN18 recognized activated vitronectin in tumor tissues, whereas hardly any activated vitronectin was detectable in normal tissues. Iodine 123-radiolabeled huMabVN18 was shown to target to Rous sarcoma virus-induced tumors in chickens, an animal model in which the epitope for huMab VN18 is exposed during tumor development. Our results establish activated vitronectin as a potential target for tumor therapy in humans.

The Solution Structure of the N-terminal Domain of Human Vitronectin

The three-dimensional structure of an N-terminal fragment comprising the first 51 amino acids from human plasma vitronectin, the somatomedin B (SMB) domain, has been determined by two-dimensional NMR approaches. An average structure was calculated, representing the overall fold from a set of 20 minimized structures. The core residues (18-41) overlay with a root mean square deviation of 2.29 +/- 0.62 A. The N- and C-terminal segments exhibit higher root mean square deviations, reflecting more flexibility in solution and/or fewer long-range NOEs for these regions. Residues 26-30 form a unique single-turn alpha-helix, the locus where plasminogen activator inhibitor type-1 (PAI-1) is bound. This structure of this helix is highly homologous with that of a recombinant SMB domain solved in a co-crystal with PAI-1 (Zhou, A., Huntington, J. A., Pannu, N. S., Carrell, R. W., and Read, R. J. (2003) Nat. Struct. Biol. 10, 541-544), although the remainder of the structure differs. Significantly, the pattern of disulfide cross-links observed in this material isolated from human plasma is altogether different from the disulfides proposed for recombinant forms. The NMR structure reveals the relative orientation of binding sites for cell surface receptors, including an integrin-binding site at residues 45-47, which was disordered and did not diffract in the co-crystal, and a site for the urokinase receptor, which overlaps with the PAI-1-binding site.

Targeted ultrasonic contrast agents for molecular imaging and therapy

Targeted contrast agents are expanding the detectability and diagnosis of pathology from a strict anatomic to biochemical basis. Moreover, these new agents, in their various forms, offer the potential for site-specific drug and gene delivery, i.e., the "magic bullet" first postulated by Paul Erhlich 100 years ago. The ability to direct drugs to the molecular signatures of disease, to confirm noninvasively their presence at the site-of-interest, and to quantify the adequacy of local drug concentration at the time of treatment, ie, rational targeted drug delivery, offers exciting new clinical paradigms in the near future.

Micro-PET Imaging of α v β 3 -Integrin Expression with 18 F-Labeled Dimeric RGD Peptide

The alphav integrins, which act as cell adhesion molecules, are closely involved with tumor invasion and angiogenesis. In particular, alphavbeta3 integrin, which is specifically expressed on proliferating endothelial cells and tumor cells, is a logical target for development of a radiotracer method to assess angiogenesis and anti-angiogenic therapy. In this study, a dimeric cyclic RGD peptide E[c(RGDyK)]2 was labeled with 18F (t(1/2) = 109.7 min) by using a prosthetic 4-[18F]fluorobenzoyl moiety to the amino group of the glutamate. The resulting [18F]FB-E[c(RGDyK)]2, with high specific activity (200-250 GBq/micromol at the end of synthesis), was administered to subcutaneous U87MG glioblastoma xenograft models for micro-PET and autoradiographic imaging as well as direct tissue sampling to assess tumor targeting efficacy and in vivo kinetics of this PET tracer. The dimeric RGD peptide demonstrated significantly higher tumor uptake and prolonged tumor retention in comparison with a monomeric RGD peptide analog [18F]FB-c(RGDyK). The dimeric RGD peptide had predominant renal excretion, whereas the monomeric analog was excreted primarily through the biliary route. Micro-PET imaging 1 hr after injection of the dimeric RGD peptide exhibited tumor to contralateral background ratio of 9.5 +/- 0.8. The synergistic effect of polyvalency and improved pharmacokinetics may be responsible for the superior imaging characteristics of [18F]FB-E[c(RGDyK)]2.

Ultrasonic Analysis of Peptide- and Antibody-Targeted Microbubble Contrast Agents for Molecular Imaging of α v β 3 -Expressing Cells

The goal of targeted ultrasound contrast agents is to significantly and selectively enhance the detection of a targeted vascular site. In this manuscript, three distinct contrast agents targeted to the alphavbeta3 integrin are examined. The alphavbeta3 integrin has been shown to be highly expressed on metastatic tumors and endothelial cells during neovascularization, and its expression has been shown to correlate with tumor grade. Specific adhesion of these contrast agents to alphavbeta3-expressing cell monolayers is demonstrated in vitro, and compared with that of nontargeted agents. Acoustic studies illustrate a backscatter amplitude increase from monolayers exposed to the targeted contrast agents of up to 13-fold (22 dB) relative to enhancement due to control bubbles. A linear dependence between the echo amplitude and bubble concentration was observed for bound agents. The decorrelation of the echo from adherent targeted agents is observed over successive pulses as a function of acoustic pressure and bubble density. Frequency-domain analysis demonstrates that adherent targeted bubbles exhibit high-amplitude narrowband echo components, in contrast to the primarily wideband response from free microbubbles. Results suggest that adherent targeted contrast agents are differentiable from free-floating microbubbles, that targeted contrast agents provide higher sensitivity in the detection of angiogenesis, and that conventional ultrasound imaging techniques such as signal subtraction or decorrelation detection can be used to detect integrin-expressing vasculature with sufficient signal-to-noise.

Mechanisms of glioma cell invasion

Invasive growth is one of the characteristics of gliomas--local infiltration into the surrounding nerve tissue decisively restricts all treatment strategies. Particularly the merit of all local treatment modalities is queried. The question whether a glioma represents a diffuse disease of the CNS or a local disturbance with unrestrained expansion tendency is still at issue. Understanding of the invasion mechanisms is of importance inasmuch as biologically reasonable and effective strategies of limiting and suppressing glioma invasion can only hence be derived. The affinity of glioma cells towards certain structures of the extracellular matrix as well as taking advantage of tumour vascularisation with regard to extension play a decisive role. Still not fully understood are tumour host interactions. Future thinking will have to take into account these interactions as well as evidence to be derived from development neurobiology and regeneration capacity of the CNS. The present review is meant to give a short overview and disclose many questions.

Expression of alphav integrin family in gastric carcinomas: increased alphavbeta6 is associated with lymph node metastasis

To investigate the alterations as to integrin expression in human gastric carcinomas, we analyzed the alphav subunit and 5 types of beta subunits using reverse transcription-polymerase chain reaction (RT-PCR) and competitive RT-PCR. The incidence of alphav, beta6 and beta8 expression was significantly higher in carcinoma tissues than in non-neoplastic gastric mucosal tissues (NGMTs). Out of 18 carcinoma cases with coexpression of alphav and beta6 subunits, which was demonstrated by RT-PCR, 17 cases (94%) showed lymph node metastasis (p = 0.0033). This tendency was confirmed by immunohistochemistry; most cases (23/28, 82%) in which alphavbeta6 integrin was immunohistochemically detected showed lymph node metastasis (p = 0.0193). RT-PCR and immunohistochemical studies showed that gastric carcinoma tissues expressed beta5 subunit in all cases. Furthermore, in a quantitative analysis using competitive RT-PCR, the mean level of beta5 expression was approximately 140 times higher in gastric carcinomas than in NGMTs. Most gastric carcinoma cases (27/38, 71%) were immunohistochemically positive for beta8 subunit. These findings suggest that some members of the alphav integrin family (alphavbeta5, alphavbeta6, alphavbeta8) are up-regulated, and that alphavbeta6 integrin may be involved in the lymphatic metastasis of gastric carcinomas.

Extracellular matrix glycoproteins and diffusion barriers in human astrocytic tumours

The extracellular matrix (ECM) and changes in the size and geometry of the extracellular space (ECS) in tumour tissue are thought to be of critical importance in influencing the migratory abilities of tumour cells as well as the delivery of therapeutic agents into the tumour. In 21 astrocytic neoplasms, the ECM composition was investigated in situ by the immunohistochemical detection of ECM glycoproteins (tenascin, laminin, vitronectin, fibronectin, collagen types I-VI). To explain the changes in ECS size and to detect barriers to diffusion in the tumour tissue, the ECM composition, the cellularity, the density of glial fibrillary acidic protein (GFAP)-positive tumour cell processes and the proliferative activity of the tumours were compared with the size and geometry of the ECS. The ECS volume fraction and the complex of hindrances to diffusion in the ECS (i.e. the tortuosity) were revealed by the real-time iontophoretic tetramethylammonium method. Increased proliferative activity of the tumours correlated with increased ECS volume fraction and tortuosity. The tortuosity of the tumour tissue was not significantly influenced by tumour cell density. Higher tortuosity was found in low-grade astrocytomas associated with the presence of a dense net of GFAP-positive fibrillary processes of the tumour cells. The increase in tortuosity in high-grade tumours correlated with an increased accumulation of ECM molecules, particularly of tenascin. We conclude that the increased malignancy of astrocytic tumours correlates with increases in both ECS volume and ECM deposition.