NG2 proteoglycan promotes angiogenesis-dependent tumor growth in CNS by sequestering angiostatin

Differential phosphorylation of NG2 proteoglycan by ERK and PKCalpha helps balance cell proliferation and migration

Two distinct Thr phosphorylation events within the cytoplasmic domain of the NG2 proteoglycan help regulate the cellular balance between proliferation and motility. Protein kinase Calpha mediates the phosphorylation of NG2 at Thr2256, resulting in enhanced cell motility. Extracellular signal-regulated kinase phosphorylates NG2 at Thr2314, stimulating cell proliferation. The effects of NG2 phosphorylation on proliferation and motility are dependent on beta1-integrin activation. Differential cell surface localization of the two distinctly phosphorylated forms of NG2 may be the mechanism by which the NG2-beta1-integrin interaction promotes proliferation in one case and motility in the other. NG2 phosphorylated at Thr2314 colocalizes with beta1-integrin on microprotrusions from the apical cell surface. In contrast, NG2 phosphorylated at Thr2256 colocalizes with beta1-integrin on lamellipodia at the leading edges of cells. Thus, phosphorylation and the resulting site of NG2-integrin localization may determine the specific downstream effects of integrin signaling.

Approaching theProteoglycome: Molecular Interactions of Proteoglycans and Their Functional Output

[Image: see text] Through their diverse core protein modules and glycan/glycosaminoglycan moieties, proteoglycans may engage in numerous cellular and molecular interactions which are dispensable during embryogenesis, are essential for the maintenance of a healthy state and are prone to modulation in pathological conditions. Proteoglycan interactions may involve binding to other structural components of the ECM, to cell surface receptors, to membrane-associated components, and to soluble signaling molecules, which through this interaction may become entrapped in the ECM or sequestered at the cell surface. Understanding of these multiple interplays is therefore of paramount importance and requires a detailed mapping through what we define as the proteoglycome.

Mechanisms of angiogenesis in gliomas

Gliomas are the most frequent primary tumors of the central nervous system in adults. Glioblastoma multiforme, the most aggressive form of astrocytic tumors, displays a rapid progression that is accompanied by particular poor prognosis of patients. Intense angiogenesis is a distinguishing pathologic characteristic of these tumors and in fact, glioblastomas are of the most highly vascularized malignant tumors. For this reason, research and therapy strategies have focused on understanding the mechanisms leading to the origin of tumor angiogenic blood vessels in order to develop new approaches that effectively block angiogenesis and cause tumor regression. We discuss here some important features of glioma angiogenesis and we present molecules and factors and their possible functions and interactions that play a role in neovascularization. In spite of the great progress that molecular biology has achieved on investigating tumor angiogenesis, many aspects remain obscure and the complexity of the angiogenic process stands for an obstacle in identifying the exact and complete molecular pathways orchestrating new blood vessels formation, which are necessary for the survival and expansion of these tumors.

Cancer stem cells in the mammalian central nervous system

Malignant tumours intrinsic to the central nervous system (CNS) are among the most difficult of neoplasms to treat effectively. The major biological features of these tumours that preclude successful therapy include their cellular heterogeneity, which renders them highly resistant to both chemotherapy and radiotherapy, and the propensity of the component tumour cells to invade, diffusely, the contiguous nervous tissues. The tumours are classified according to perceived cell of origin, gliomas being the most common generic group. In the 1970s transplacental administration of the potent neurocarcinogen, N-ethyl-N-nitrosourea (ENU), enabled investigation of the sequential development of brain and spinal neoplasms by electron microscopy and immunohistochemistry. The significance of the primitive cells of the subependymal plate in cellular origin and evolution of a variety of glial tumours was thereby established. Since then, the development of new cell culture methods, including the in vitro growth of neurospheres and multicellular tumour spheroids, and new antigenic markers of stem cells and glial/neuronal cell precursor cells, including nestin, Mushashi-1 and CD133, have led to a reappraisal of the histological classification and origins of CNS tumours. Moreover, neural stem cells may also provide new vectors in exciting novel therapeutic strategies for these tumours. In addition to the gliomas, stem cells may have been identified in paediatric tumours including cerebellar medulloblastoma, thought to be of external granule cell neuronal derivation. Interestingly, while the stem cell marker CD133 is expressed in these primitive neuroectodermal tumours (PNETs), the chondroitin sulphate proteoglycan neuronal/glial 2 (NG2), which appears to denote increased proliferative, but reduced migratory activity in adult gliomas, is rarely expressed. This is in contrast to the situation in the histologically similar supratentorial PNETs. A possible functional 'switch' between proliferation and migration in developing neural tumour cells may exist between NG2 and ganglioside GD3. The divergent pathways of differentiation of CNS tumours and the possibility of stem cell origin, for some, if not all, such neoplasms remain a matter for debate and continued research, but the presence of self-renewing neural stem cells in the CNS of both children and adults strongly suggests a role for these cells in tumour initiation and resistance to current therapeutic strategies.

Radiation-enhanced vascular endothelial growth factor (VEGF) secretion in glioblastoma multiforme cell lines--a clue to radioresistance?

OBJECTIVE

Postoperative radiotherapy is standard treatment for patients with a glioblastoma multiforme (GBM). However, a GBM is radioresistant and almost always recurs, even after a high dose of radiation. A GBM is characterized by its extensive neo-angiogenesis, which can be attributed to the high levels of vascular endothelial growth factor (VEGF). The scope of this study is to investigate the VEGF secretion by GBM cells with different radiosensitivity after irradiation.

METHODS

Three human GBM cell lines (U251, U251-NG2 and U87) were irradiated with single doses of 0, 5, 10 and 20 Gy of gamma-rays from a (137)Cs source. VEGF levels in medium were measured by ELISA at 24, 48 and 72 h after radiation. Cell survival was measured by the XTT assay 7 days after irradiation.

RESULTS

Following single dose radiation, the VEGF levels showed a dose dependent increase in U251, U251-NG2 and U87 glioma cells. Both base-line and radiation-enhanced VEGF levels were about 10-fold higher in U87 compared to U251 and U251-NG2 cells. In addition, in the XTT assay, the U87 was more radioresistant than both U251 and U251-NG2 cell lines (dose modifying factor (DMF) = 1.6 and 1.7 resp).

CONCLUSION

Irradiation enhanced VEGF secretion in all three tested glioma cell lines (up to eight times basal levels). It is tempting to associate the radiation-enhanced VEGF secretion with an increased angiogenic potential of the tumor, which may be a factor in radioresistance.

NG2 expression regulates vascular morphology and function in human brain tumours

Tumour angiogenesis is a tightly regulated process involving cross-talk between tumour cells and the host tissue. The underlying mechanisms that regulate such interactions remain largely unknown. NG2 is a transmembrane proteoglycan whose presence on transformed cells has been demonstrated to increase proliferation in vitro and angiogenesis in vivo. To study the effects of NG2 during tumour growth and progression, we engineered an NG2 positive human glioma cell line (U251-NG2) from parental NG2 negative cells (U251-WT) and implanted both cell types stereotactically into immunodeficient nude rat brains. The tumours were longitudinally monitored in vivo using multispectral MRI employing two differently sized contrast agents (Gd-DTPA-BMA and Gadomer) to assess vascular leakiness, vasogenic oedema, tumour volumes and necrosis. Comparisons of Gd-DTPA-BMA and Gadomer revealed differences in their spatial distribution in the U251-NG2 and U251-WT tumours. The U251-NG2 tumours exhibited a higher leakiness of the larger molecular weight Gadomer and displayed a stronger vasogenic oedema (69.9 +/- 15.2, P = 0.018, compared to the controls (10.7 +/- 7.7). Moreover, immunohistochemistry and electron microscopy revealed that the U251-NG2 tumours had a higher microvascular density (11.81 +/- 0.54; P = 0.0010) compared to controls (5.76 +/- 0.87), with vessels that displayed larger gaps between the endothelial cells. Thus, tumour cells can regulate both the function and structure of the host-derived tumour vasculature through NG2 expression, suggesting a role for NG2 in the cross-talk between tumour-host compartments.

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.

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.

Adipocyte-derived collagen VI affects early mammary tumor progression in vivo, demonstrating a critical interaction in the tumor/stroma microenvironment

The interactions of transformed cells with the surrounding stromal cells are of importance for tumor progression and metastasis. The relevance of adipocyte-derived factors to breast cancer cell survival and growth is well established. However, it remains unknown which specific adipocyte-derived factors are most critical in this process. Collagen VI is abundantly expressed in adipocytes. Collagen(-/-) mice in the background of the mouse mammary tumor virus/polyoma virus middle T oncogene (MMTV-PyMT) mammary cancer model demonstrate dramatically reduced rates of early hyperplasia and primary tumor growth. Collagen VI promotes its growth-stimulatory and pro-survival effects in part by signaling through the NG2/chondroitin sulfate proteoglycan receptor expressed on the surface of malignant ductal epithelial cells to sequentially activate Akt and beta-catenin and stabilize cyclin D1. Levels of the carboxyterminal domain of collagen VIalpha3, a proteolytic product of the full-length molecule, are dramatically upregulated in murine and human breast cancer lesions. The same fragment exerts potent growth-stimulatory effects on MCF-7 cells in vitro. Therefore, adipocytes play a vital role in defining the ECM environment for normal and tumor-derived ductal epithelial cells and contribute significantly to tumor growth at early stages through secretion and processing of collagen VI.

Phosphorylation of NG2 proteoglycan by protein kinase C-alpha regulates polarized membrane distribution and cell motility

Protein kinase C (PKC)-alpha phosphorylation of recombinant NG2 cytoplasmic domain and phorbol ester-induced PKC-dependent phosphorylation of full-length NG2 expressed in U251 cells are both blocked by mutation of Thr(2256), identifying this residue as a primary phosphorylation site. In untreated U251/NG2 cells, NG2 is present along with ezrin and alpha(3)beta(1) integrin in apical cell surface protrusions. Phorbol ester treatment causes redistribution of all three components to lamellipodia, accompanied by increased cell motility. U251 cells expressing NG2 with a valine substitution at position 2256 are resistant to phorbol ester treatment: NG2 remains in membrane protrusions and cell motility is unchanged. In contrast, NG2 with a glutamic acid substitution at position 2256 redistributes to lamellipodia even without phorbol ester treatment, rendering transfected U251 cells spontaneously motile. PKC-alpha-mediated NG2 phosphorylation at Thr(2256) is therefore a key step for initiating cell polarization and motility.

NG2 proteoglycan promotes endothelial cell motility and angiogenesis via engagement of galectin-3 and alpha3beta1 integrin

The NG2 proteoglycan is expressed by microvascular pericytes in newly formed blood vessels. We have used in vitro and in vivo models to investigate the role of NG2 in cross-talk between pericytes and endothelial cells (EC). Binding of soluble NG2 to the EC surface induces cell motility and multicellular network formation in vitro and stimulates corneal angiogenesis in vivo. Biochemical data demonstrate the involvement of both galectin-3 and alpha3beta1 integrin in the EC response to NG2 and show that NG2, galectin-3, and alpha3beta1 form a complex on the cell surface. Transmembrane signaling via alpha3beta1 is responsible for EC motility and morphogenesis in this system. Galectin-3-dependent oligomerization may potentiate NG2-mediated activation of alpha3beta1. In conjunction with recent studies demonstrating the early involvement of pericytes in angiogenesis, these data suggest that pericyte-derived NG2 is an important factor in promoting EC migration and morphogenesis during the early stages of neovascularization.

Immunotoxin treatment targeted to the high-molecular-weight melanoma-associated antigen prolonging the survival of immunodeficient rats with invasive intracranial human glioblastoma multiforme

OBJECT

The aim of this study was to target immunotoxin treatment to the high-molecular-weight melanoma-associated antigen (HMW-MAA) and thereby examine any changes in the survival of immunodeficient rats with human glioblastoma multiforme (GBM).

METHODS

To target treatment specifically to human glioma cells, Pseudomonas exotoxin A (PE) was conjugated to the 9.2.27 antibody, which recognizes the HMW-MAA. Treatment of the antigen-positive glioma cell line U87MG with the resulting 9.2.27-PE caused cytotoxicity with a median inhibitory concentration of 1 ng/ml. Intratumoral 9.2.27-PE treatment of intracranial U87MG tumors in nude rats prolonged the survival of these animals by 43% compared with controls. In additional studies on the use of this targeted treatment, the authors precultured freshly dissected glioblastoma multiforme (GBM) biopsy tissue for 1 to 2 weeks. Inoculation of this tissue into the rat brain resulted in diffuse infiltrative gliomas. The markers glial fibrillary acidic protein and S100 protein were found to be expressed in the original biopsy specimens, as well as in the glioma xenografts in nude rat brains. Intratumoral immunotoxin treatment of such established tumors with 9.2.27-PE was effective and prolonged survival time from 30% to as high as 90% in animals with tumors originating from four different GBM specimens.

CONCLUSIONS

Targeted treatment of highly invasive GBMs proved effective, and these results emphasize the clinical relevance of this antigen as a target molecule for immunotoxin treatment of human GBMs.

Structural, functional, and molecular MR imaging of the microvasculature

Magnetic resonance imaging (MRI) is widely applied for functional imaging of the microcirculation and for functional and structural studies of the microvasculature. The interest in the capabilities of MRI in noninvasively monitoring changes in vascular structure and function expanded over the past years, with specific efforts directed toward the development of novel imaging methods for quantification of angiogenesis. Molecular imaging approaches hold promise for further expansion of the ability to characterize the microvasculature. Exciting applications for MRI are emerging in the study of the biology of microvessels and in the evaluation of potential pharmaceutical modulators of vascular function and development, and preclinical MRI tools can serve for the design of mechanism-of-action-based noninvasive clinical methods for monitoring response to therapy. The aim of this review is to provide a current snapshot of recent developments in this rapidly evolving field.

Angiogenesis and invasion in gliomas

Angiogenesis and tumor cell invasion are pathophysiological processes playing a pivotal role in glioma development and growth since the earliest phase. Angiogenesis and tumor invasion both can be considered as an invasive process in which cells are activated, and move away from their initial location, by modyfing the adhesiveness with the extracellular matrix, expressing new adhesion molecules, and degrading the extracellular matrix components by the active secretion of proteases. This process requires a complex cross-talking between endothelial and tumor cells, extracellular matrix components, and cellular elements of the host microenviroment. Both processes are under the tight regulation of a balance between stimulating and inhibiting factors. The existence of common mechanisms of regulation and the presence of naturally occurring factors that inihibit angiogenesis and invasion, makes the inhibition of both processes possible. Tumor cells may develop adapting mechanims that can allow the tumor to partially escape to the treatment, particularly when only one mechanism or one process is inhibited. The ideal treatment should simultaneously affect both angiogenesis and invasion, by the isolation or development of novel therapeutics capable of influencing both processes. As their efficacy seems also be dependent on the mode of delivery, additional studies are also needed to improve these modalities, in order to ultimately improve the extent and the duration of the therapeutic response. The most widely used in vitro and in vivo models to study angiogenesis and invasion are also discussed.

What the structure of angiostatin may tell us about its mechanism of action

Originally discovered in 1994 by Folkman and coworkers, angiostatin was identified through its antitumor effects in mice and later shown to be a potent inhibitor of angiogenesis. An internal fragment of plasminogen, angiostatin consists of kringle domains that are known to be lysine-binding. The crystal structure of angiostatin was the first multikringle domain-containing structure to be published. This review will focus on what is known about the structure of angiostatin and its implications in function from the current literature.

Models for Angiogenesis in Gliomas

During the last decades a lot of attention has been focussed on mechanisms of glioma vascularization, particularly in terms of investigating vascular growth factors and receptors. Recently, these efforts resulted in various approaches for antiangiogenic treatment strategies using in vitro cell culture systems as well as experimental orthotopic and non-orthotopic brain tumors. These basic science and preclinical trials need an assortment of models, which should allow investigating a variety of questions. Several objectives concerning basic endothelial cell (EC) characteristics can adequately be studied in vitro using EC monolayer assays. Three-dimensional spheroid techniques respect the more complex cell-cell and cell-environment interplay within a 3-dimensional culture. Recent advances in molecular genetic techniques offer a wide access to the genome of EC. Using these micro array or chip methods differences between micro- and macromolecular EC as well as variations within the gene pool of different organ specific EC can be assessed. To optimize the imitation of the crucial interaction of human gliomas with host endothelial cells, immunological cells and extracellular matrix, animal models are mandatory. An essential rule is to utilize an orthotopic model, since tumor-host-interaction is organ specific. To avoid alloimmunogenic responses, it is desirable to use weak or non-immunogenic glioma grafts, which is best accomplished in a syngeneic model. However, since rat gliomas poorly resemble human glioma growth patterns, human glioma xenografting into immunocompromized animals should be considered. In vivo-monitoring techniques like videoscopy via a cranial window or magnetic resonance imaging (MRI) allow for functional studies and improve the validity of the model employed. Finally, it is essentially to recognize the limitations of each model considered and to select that model which seems to be most appropriate for the objectives to be investigated.

Histological analysis of defective colonic healing as a result of angiostatin treatment

Antiangiogenic therapy is a highly promising new strategy in the treatment of cancer. One of the first angiogenesis inhibitors described was angiostatin, a 38-kDa internal proteolytically generated fragment of plasminogen. In a previous study we found that angiostatin affected physiological angiogenesis as well as tumor angiogenesis. It impaired healing when administered during repair of experimental colonic anastomoses, as reflected by a decrease in mechanical strength. On histology, we observed a decrease in factor VIII-stained vessel amount and volume in angiostatin-treated colonic anastomoses. The exact working mechanism of angiostatin has not been elucidated. Based on the available studies on proposed working mechanisms of angiostatin, we have attempted to address histological differences in physiological angiogenesis between the tissues of colonic anastomoses of mice with impaired healing and control mice. After angiostatin treatment there was more inflammatory tissue as a result of impaired healing. Furthermore, we found fewer vessels in the granulation tissue after angiostatin treatment. However, especially with respect to extracellular matrix (ECM), endothelial cell apoptosis, proliferation, or neutrophil influx, no gross differences were discerned 1 week following surgery, using histology and immunohistochemistry techniques.

Losses of NG2 and NeuN immunoreactivity but not astrocytic markers during early reperfusion following severe focal cerebral ischemia

The ability of glia to recover essential functions following a period of focal cerebral ischemia is likely to be one important factor influencing the severity of tissue damage that subsequently develops. In this study, we have compared changes in immunoreactivity of markers specific for astrocytes, NG2-positive glia and neurons in tissue subregions during early reperfusion following 3 h of middle cerebral artery occlusion to provide insights into possible differential susceptibility of these cell populations. Under the conditions used, infarction ultimately encompasses most of the perfusion territory of the occluded artery. Nonetheless, alterations in immunoreactivity during the first 3 h of recirculation were restricted to brain regions that had been subjected to severe ischemia. In the striatum, cellular immunoreactivity for NG2 and neuronal markers, NeuN and microtubule-associated protein 2, was greatly reduced by 1 h of reperfusion and declined further at 3 h. NG2 labeling of blood vessels in the striatum appeared post-ischemically, mimicking expression of this protein during development. Less severe changes were seen in the neuronal markers in overlying cerebral cortex. In contrast to the losses of other cellular proteins, immunoreactivity for the astrocytic marker, glial fibrillary acidic protein, was preserved in all tissue that had been subjected to severe ischemia and labeling of another astrocytic protein, glutamine synthetase, was increased by 3 h of reperfusion. These findings provide the first evidence of marked sensitivity of NG2-immunoreactivity to severe ischemia and suggest a greater initial resistance of astrocytes compared with neurons and NG2-positive glia to ischemia-reperfusion damage.

Loss of responsiveness to chemotactic factors by deletion of the C-terminal protein interaction site of angiomotin

We have recently identified a novel protein, named angiomotin, by its ability to bind the angiogenesis inhibitor angiostatin in the yeast two-hybrid system. Angiomotin belongs to a family with two other members, AmotL-1 and -2 characterized by coiled-coil and C-terminal PDZ binding domains. Here we show that the putative PDZ binding motif of angiomotin serves as a protein recognition site and that deletion of three amino acids in this site results in inhibition of chemotaxis. Furthermore, endothelial cells expressing mutant angiomotin failed to migrate and form tubes in an in vitro tube formation assay. To study the effect of angiomotin on embryonic angiogenesis, we generated transgenic mice expressing wild-type angiomotin and the C-terminal deletion mutant driven by the endothelial cell-specific receptor tyrosine kinase (TIE) promoter. Expression of mutant angiomotin in endothelial cells inhibited migration into the neuroectoderm and intersomitic regions resulting in death at embryonic day 9.5. In contrast, mice expressing wild-type angiomotin developed normally and were fertile. These results suggest that the putative PDZ binding motif of angiomotin plays a critical role in regulating the responsiveness of endothelial cells to chemotactic cues.

Antiangiogenic therapy against experimental glioblastoma using genetically engineered cells producing interferon-alpha, angiostatin, or endostatin

Inhibition of angiogenesis has been considered among the most promising approaches to treat highly vascularized solid tumors such as glioblastoma. In this study, we designed and validated a new in vitro assay system based on the implantation of tumor cells into organotypic brain slice cultures. We evaluated the effects of local production of three endogenous inhibitors of angiogenesis, angiostatin, endostatin, and interferon (IFN)-alpha(1), using stably transfected rat (9L) and human (GL15) glioblastoma cells on tumor vascularization and growth. Despite similar effectiveness of the three proteins in a classic in vitro endothelial cell migration assay, IFN-alpha(1) demonstrated the most potent antiangiogenic effect in organotypic brain slice cultures. In vivo, after intracerebral implantation of such genetically modified glioblastoma cells, IFN-alpha(1) caused a dramatic decrease in tumor volume revealed by magnetic resonance imaging and by postmortem histology. The mechanisms of this antitumor effect were most likely caused by the major antiangiogenic action of the cytokine, because IFN-alpha(1) expression provoked a pronounced decrease in blood vessel density, which was accompanied by extensive necrosis in the body mass of the tumors. The median survival time of rats implanted intracerebrally with IFN-alpha-expressing 9L cells tripled, and was still significantly increased when these constituted only 1% of transplanted tumor cells. A similar effect was seen when 50% of the transplanted cells were replaced by IFN-alpha-expressing bone marrow stromal cells. These data point to the local delivery of IFN-alpha(1) using cell vectors as a potent tool for the inhibition of tumor-induced angiogenesis.

Fundamental reaction mechanism for cocaine hydrolysis in human butyrylcholinesterase

Butyrylcholinesterase (BChE)-cocaine binding and the fundamental pathway for BChE-catalyzed hydrolysis of cocaine have been studied by molecular modeling, molecular dynamics (MD) simulations, and ab initio calculations. Modeling and simulations indicate that the structures of the prereactive BChE/substrate complexes for (-)-cocaine and (+)-cocaine are all similar to that of the corresponding prereactive BChE/butyrylcholine (BCh) complex. The overall binding of BChE with (-)-cocaine and (+)-cocaine is also similar to that proposed with butyrylthiocholine and succinyldithiocholine, i.e., (-)- or (+)-cocaine first slides down the substrate-binding gorge to bind to Trp-82 and stands vertically in the gorge between Asp-70 and Trp-82 (nonprereactive complex) and then rotates to a position in the catalytic site within a favorable distance for nucleophilic attack and hydrolysis by Ser-198 (prereactive complex). In the prereactive complex, cocaine lies horizontally at the bottom of the gorge. The fundamental catalytic hydrolysis pathway, consisting of acylation and deacylation stages similar to those for ester hydrolysis by other serine hydrolases, was proposed on the basis of the simulated prereactive complex and confirmed theoretically by ab initio reaction coordinate calculations. Both the acylation and deacylation follow a double-proton-transfer mechanism. The calculated energetic results show that within the chemical reaction process the highest energy barrier and Gibbs free energy barrier are all associated with the first step of deacylation. The calculated ratio of the rate constant (k(cat)) for the catalytic hydrolysis to that (k(0)) for the spontaneous hydrolysis is approximately 9.0 x 10(7). The estimated k(cat)/k(0) value of approximately 9.0 x 10(7) is in excellent agreement with the experimentally derived k(cat)/k(0) value of approximately 7.2 x 10(7) for (+)-cocaine, whereas it is approximately 2000 times larger than the experimentally derived k(cat)/k(0) value of approximately 4.4 x 10(4) for (-)-cocaine. All of the results suggest that the rate-determining step of the BChE-catalyzed hydrolysis of (+)-cocaine is the first step of deacylation, whereas for (-)-cocaine the change from the nonprereactive complex to the prereactive complex is rate-determining and has a Gibbs free energy barrier higher than that for the first step of deacylation by approximately 4 kcal/mol. A further analysis of the structural changes from the nonprereactive complex to the prereactive complex reveals specific amino acid residues hindering the structural changes, providing initial clues for the rational design of BChE mutants with improved catalytic activity for (-)-cocaine.

Angiogenesis relates to estrogen receptor negativity, c-erbB-2 overexpression and early relapse in node-negative ductal carcinoma of the breast

Tumor angiogenic activity is an important process linked to tumor growth, metastasis, and invasion. In the present study we investigated whether intratumoral microvessel density (MVD), as assessed with immunohistochemistry, is of prognostic relevance in a series of 77 breast cancer patients with node-negative disease. The mean MVD in the hot spots ranged from 9 to 106 (median 31) vessels per x200 optical field. Patients were grouped into 3 categories of low (27 pts), medium (26 pts), and high (24 pts) MVD. Angiogenesis was not related to the primary tumor dimensions (T-stage) or the histology differentiation. An inverse association of MVD with estrogen receptor (ER) expression was noted (p=0.0007), while high MVD was directly related to c-erbB-2 overexpression (p=0.04) and high MIB1 proliferation index (p=0.02). In univariate and multivariate analysis of relapse-free survival, MVD was the only variable significantly and independently linked to relapse. It is concluded that high intratumoral angiogenic activity is linked with early relapse in node-negative breast cancer.

The glial precursor proteoglycan, NG2, is expressed on tumour neovasculature by vascular pericytes in human malignant brain tumours

Glial precursor cells express NG2 and GD3 in the developing brain. These antigens are both over-expressed during neoplasia, which suggests they may have specific functions in the malignant progression of human brain tumours. This study describes the expression of NG2 and GD3 in 28 paediatric and adult brain tumours. Glioblastoma biopsy spheroids were also implanted into nude rats to assess the regional distribution of the molecules within the tumour. These xenografts showed extensive infiltration and growth that mimicked the growth patterns of human gliomas in situ. NG2 was identified in 20 out of 28 brain tumours, where the expression was confined to the main mass of the tumour, and was reduced towards the tumour periphery. NG2 was mainly associated with blood vessels on both the pericyte and basement membrane components of the tumour vasculature. Ki67 (MIB-1) labelling indicated that NG2 expression was associated with areas of high cellular proliferation. Conversely, all the tumours expressed GD3, which was present both in the tumour main mass and throughout the periphery. Thus, the expression of NG2 may be indicative of tumour progression and might be an amenable target for future therapeutic interventions.