Oncogenic H-ras stimulates tumor angiogenesis by two distinct pathways

The angiogenic regulator CD13/APN is a transcriptional target of Ras signaling pathways in endothelial morphogenesis

Angiogenesis, the formation of new blood vessels, is a critical step for tumor growth and metastasis and an integral component of the pathologic inflammatory response in arthritis and the proliferative retinopathies. The CD13/aminopeptidase N (CD13/APN) metalloprotease is an important regulator of angiogenesis where its expression on activated blood vessels is induced by angiogenic signals. Here, we show that cytokine induction of CD13/APN in endothelial cells is regulated by distinct Ras effector pathways involving Ras/mitogen-activated protein kinase (MAPK) or PI-3K. Signals transduced by activated Ras, Raf, and mitogen-induced extracellular kinase (MEK) stimulate transcription from the CD13/APN proximal promoter. Inhibition of these pathways and extracellular signal-regulated serine/threonine kinase (ERK-2) and PI-3K by expression of dominant-negative proteins or chemical inhibitors prevented induction of CD13/APN transcription in response to basic fibroblast growth factor (bFGF). We show that Ras-induced signal transduction is required for growth factor-induced angiogenesis, because inhibition of downstream mediators of Ras signaling (MEK or PI-3K) abrogated endothelial cell migration, invasion, and morphogenesis in vitro. Reintroduction of CD13/APN, a shared downstream target of these pathways, overrode the suppressive effect of these inhibitors and restored the function of endothelial cells in migration/invasion and capillary morphogenesis assays. Similarly, inhibition of MEK abrogated cell invasion and the formation of endothelial-lined capillaries in vivo, which was effectively rescued by addition of exogenous CD13/APN protein. These studies provide strong evidence that CD13/APN is an important target of Ras signaling in angiogenesis and is a limiting factor in angiogenic progression.

Promises and pitfalls of anti-angiogenic therapy in clinical trials

A significant body of research has implicated the process of angiogenesis in the growth and spread of tumors. Elucidation of the mechanisms of tumor angiogenesis has led to the development of multiple anti-angiogenic agents. However, the perceived differences between the results of preclinical studies and those of early phases of clinical trials have led to questions being asked regarding the efficacy of these agents. There are many reasons for this discrepancy, including difficulties in the appropriate interpretation of preclinical data and clinical trial design. Further insights into the complex process of angiogenesis are essential for the development of effective anti-angiogenic regimens.

Angiogenesis in endocrine glands: special reference to the expression of vascular endothelial growth factor

Recent studies have shown that several angiogenic growth factors are produced and secreted by normal endocrine cells and are increased in pathological states of endocrine glands, including inflammation, hyperplasia, and neoplasia. Expression of corresponding receptors on epithelial cells and/or endothelial cells enables these angiogenic factors to influence growth and function of the endocrine tissues by auto- or paracrine mechanisms. Some of the angiogenic factors are also considered to be involved in angiogenesis, which is a critical process in tumor formation and progression. Vascular endothelial growth factor (VEGF) is regarded as one of most important angiogenic factors with specific effects on endothelial cell growth and vascular permeability, and is isolated from a variety of normal and neoplastic endocrine cells. In this article, recent studies on angiogenic factors, especially on expression of VEGF, are reviewed in the field of endocrine systems.

Design, synthesis, and biological evaluation of angiogenesis inhibitors: aromatic enone and dienone analogues of curcumin

The quest to find new antitumor compounds is an ongoing research endeavor in many laboratories around the world. The use of small-molecule angiogenesis inhibitors promises to be a potentially effective method for cancer treatment and possible prevention. Many antiangiogenic compounds are in various stages of laboratory evaluations and clinical trials. Curcumin is a natural product that has exhibited potent antiangiogenic properties. Based on a simple pharmacophore model, using standard drug design concepts, aromatic enone and aromatic dienone analogues of curcumin were prepared and/or obtained commercially. These compounds were screened for antiangiogenic properties via an in vitro SVR assay and were found to inhibit cell proliferation.

Interleukin-2 inhibits proliferation of HPV-associated tumor cells and halts tumor growth in vivo

Previous studies have shown inhibition of cervical cancer cell growth by treatment with high concentrations of IL-2. In the present study, we evaluated the in vitro and in vivo effects of recombinant human IL-2 on HPV-associated tumor cells (3T3-16). Treatment of 3T3-16 cells with rhIL-2 for 72 h inhibited cell growth in a dose-dependent manner and this effect was evidenced at nanomolar concentrations. These tumor cells expressed mRNA for beta and gamma subunits of the IL-2 receptor, which are required for signal transduction. In experiments to explore the effect of IL-2 on the growth of the HPV-associated tumor, mice received rhIL-2 through different routes: (i) intraperitoneal; (ii) subcutaneous, at the tumor inoculation site; or (iii) subcutaneous, distant from the tumor inoculation site. An effective antitumor response was observed only in those animals that received IL-2 at the tumor site (P<0.01). These results indicate the potential adequacy of therapeutic strategies based on local administration of rhIL-2 for cervical carcinoma, not only based on the ability of this cytokine to stimulate cellular-mediated immunity but also because of its direct effects on tumor cells.

Lymphangiogenesis new mechanisms

A mouse model has been developed to study lymphangiogenesis dissociated from angiogenesis. bFGF implanted in a mouse cornea at a concentration below the threshold to induce angiogenesis potently induces lymphangiogenesis. This model has permitted a study of cellular and molecular mechanisms of lymphangiogenesis.

p38 Signaling-mediated hypoxia-inducible factor 1alpha and vascular endothelial growth factor induction by Cr(VI) in DU145 human prostate carcinoma cells

Chromium(VI) (Cr(VI)) is widely used in industry and is a potent inducer of tumors in animals. The present study demonstrates that Cr(VI) induces hypoxia-inducible factor 1 (HIF-1) activity through the specific expression of HIF-1alpha but not HIF-1beta subunit and increases the level of vascular endothelial growth factor (VEGF) expression in DU145 human prostate carcinoma cells. To dissect the signaling pathways involved in Cr(VI)-induced HIF-1 expression, we found that p38 mitogen-activated protein kinase signaling was required for HIF-1alpha expression induced by Cr(VI). Neither phosphatidylinositol 3-kinase nor extracellular signal-regulated kinase activity was required for Cr(VI)-induced HIF-1 expression. Cr(VI) induced expression of HIF-1 and VEGF through the production of reactive oxygen species in DU145 cells. The major species of reactive oxygen species responsible for the induction of HIF-1 and VEGF expression is H(2)O(2). These results suggest that the expression of HIF-1 and VEGF induced by Cr(VI) may be an important signaling pathway in the Cr(VI)-induced carcinogenesis.

BCR/ABL induces expression of vascular endothelial growth factor and its transcriptional activator, hypoxia inducible factor-1alpha, through a pathway involving phosphoinositide 3-kinase and the mammalian target of rapamycin

Recent data suggest that vascular endothelial growth factor (VEGF), a cytokine involved in autocrine growth of tumor cells and tumor angiogenesis, is up-regulated and plays a potential role in myelogenous leukemias. In chronic myelogenous leukemia (CML), VEGF is expressed at high levels in the bone marrow and peripheral blood. We show here that the CML-associated oncogene BCR/ABL induces VEGF gene expression in growth factor-dependent Ba/F3 cells. Whereas starved cells were found to contain only baseline levels of VEGF mRNA, Ba/F3 cells induced to express BCR/ABL exhibited substantial amounts of VEGF mRNA. BCR/ABL also induced VEGF promoter activity and increased VEGF protein levels in Ba/F3 cells. Moreover, BCR/ABL was found to promote the expression of functionally active hypoxia-inducible factor-1 (HIF-1), a major transcriptional regulator of VEGF gene expression. BCR/ABL-induced VEGF gene expression was counteracted by the phosphoinositide 3-kinase (PI3-kinase) inhibitor LY294002 and rapamycin, an antagonist of mammalian target of rapamycin (mTOR), but not by inhibition of the mitogen-activated protein kinase pathway. Similarly, BCR/ABL-dependent HIF-1alpha expression was inhibited by the addition of LY294002 and rapamycin. Together, our data show that BCR/ABL induces VEGF- and HIF-1alpha gene expression through a pathway involving PI3-kinase and mTOR. BCR/ABL-induced VEGF expression may contribute to the pathogenesis and increased angiogenesis in CML.

Anti-angiogenic agents for the treatment of brain tumors

It is accepted that novel therapeutic approaches are needed for the majority of patients with malignant brain tumors. The vascularity of many primary brain tumors and the encouraging preclinical studies suggest that antiangiogenic agents have the potential to become an important component of multimodality treatment of patients with brain tumors. The understanding of the biology of angiogenesis is improving rapidly, offering the hope for more specific vascular targeting of brain tumor neovasculature. Neuroimaging techniques evaluating the angiogenic process and the impact of antiangiogenic agents will be an important tool for the rapid development of these novel therapeutic agents.

Soluble Eph A receptors inhibit tumor angiogenesis and progression in vivo

The Eph family of receptor tyrosine kinases and their ligands, known as ephrins, play a crucial role in vascular development during embryogenesis. The function of these molecules in adult angiogenesis has not been well characterized. Here, we report that blocking Eph A class receptor activation inhibits angiogenesis in two independent tumor types, the RIP-Tag transgenic model of angiogenesis-dependent pancreatic islet cell carcinoma and the 4T1 model of metastatic mammary adenocarcinoma. Ephrin-A1 ligand was expressed in both tumor and endothelial cells, and EphA2 receptor was localized primarily in tumor-associated vascular endothelial cells. Soluble EphA2-Fc or EphA3-Fc receptors inhibited tumor angiogenesis in cutaneous window assays, and tumor growth in vivo. EphA2-Fc or EphA3-Fc treatment resulted in decreased tumor vascular density, tumor volume, and cell proliferation, but increased cell apoptosis. However, EphA2-Fc had no direct effect on tumor cell growth or apoptosis in culture, yet inhibited migration of endothelial cells in response to tumor cells, suggesting that the soluble receptor inhibited blood vessel recruitment by the tumor. These data provide the first functional evidence for Eph A class receptor regulation of pathogenic angiogenesis induced by tumors and support the function of A class Eph receptors in tumor progression.

Hammerhead ribozymes as therapeutic agents for bladder cancer

Hammerhead ribozymes have been investigated extensively as therapeutic agents against cancer. Aberrant or overexpression of genes related to tumorigenicity or cancer growth might be the appropriate targets for ribozyme strategies. Ribozyme-mediated gene therapy should be applied to those diseases that have no successful conventional therapy such as advanced or treatment-resistant bladder cancer. Many genetic alterations have been identified in bladder cancer related to both tumorigenesis and disease progression. Mutated H-ras, fos, and erb-B2 genes have been chosen as targets for ribozymes in previous studies, and antitumor efficacy has been demonstrated by reversion of the malignant phenotypes and by inhibition of tumor growth both in vitro and in vivo. The efficiency of various delivery systems has also been evaluated. An overview of ribozyme strategies, especially for therapeutic applications against bladder cancer, is described here.

New vessel formation and aberrant VEGF/VEGFR signaling in acute leukemia: does it matter?

Although many patients with acute leukemia achieve a hematological complete remission with aggressive intensive therapy protocols, a large proportion shows reoccurrence of disease. Novel strategies are warranted. In acute leukemia new vessel formation is observed. New vessel formation is the result of angiogenesis and vasculogenesis. The degree of neovascularization in the bone marrow is correlated with vascular endothelial growth factor (VEGF) expression in the leukemic cells. The present review discusses the impact of new vessel formation related to acute leukemia, the relation with various angiogenic factors and will focus on VEGF/VEGF receptor signaling.

Clinical translation of angiogenesis inhibitors

Angiogenesis inhibitors are a new class of drugs, for which the general rules involving conventional chemotherapy might not apply. The successful translation of angiogenesis inhibitors to clinical application depends partly on the transfer of expertise from scientists who are familiar with the biology of angiogenesis to clinicians. What are the most common questions that clinicians ask as they begin to test angiogenesis inhibitors in cancer clinical trials?

Sck is expressed in endothelial cells and participates in vascular endothelial growth factor-induced signaling

Sck, a member of the Shc family of cell signaling proteins, has only been studied in neuronal cells, though previous studies have demonstrated its expression in tissues other than brain. Using RT-PCR and RNase protection assays, we detected Sck mRNA expression in endothelial cells, and Sck protein was detected by Western blotting using polyclonal and monoclonal antibodies targeting the Sck CH1 domain. Immunohistochemistry protocols demonstrate that Sck is expressed in KDR and PECAM positive cells found in the mouse retina, mouse heart and human umbilical chord. Treatment of human umbilical vein endothelial (HUVE) cells with vascular endothelial growth factor (VEGF) leads to the recruitment of Sck to the KDR VEGF receptor and an enhanced Sck tyrosine phosphorylation. Sck is recruited to KDR tyrosine 1175, as co-immunoprecipitation of KDR and Sck is not observed in VEGF-treated porcine aortic endothelial cells expressing a receptor mutated at this autophosphorylation site. The Sck and Shc SH2 domains, and not the PTB domain, mediates its interactions with KDR, as recombinant Sck SH2 domain binds to a tyrosine phosphorylated KDR 1175-derived synthetic peptide, but not to a peptide synthesized without tyrosine phosphate. Recombinant PLCgamma SH2 domain also interacts with the phosphotyrosine 1175 containing peptide. VEGF-induced MAPK activation is dependent upon PLCgamma activity, and chimeric proteins consisting of the Shc or Sck SH2 domains fused with a cellular internalization sequence attenuated this activation. Taken together, these results demonstrate that Sck is expressed in vascular endothelial cells, and participates in VEGF-induced signal transduction.

Antiangiogenic activity of selenium in cancer chemoprevention: metabolite-specific effects

We review recent data that support a potential antiangiogenic effect of selenium (Se) in the chemoprevention of cancer and data that contrast two pools of Se metabolites, namely, methylselenol vs. hydrogen selenide, that differentially affect proteins and cellular processes crucial to tumor angiogenesis regulation. With regard to tumor angiogenesis, the chemopreventive effect of increased Se intake on chemically induced mammary carcinogenesis has been associated with reduced intratumoral microvessel density and an inhibition of the expression of vascular endothelial growth factor. The in vitro data show that monomethyl Se potently inhibits cell cycle progression of vascular endothelial cells to the S phase, endothelial expression of matrix metalloproteinase-2, and cancer epithelial expression of vascular endothelial growth factor with concentrations giving half-maximal inhibition that are within the plasma range of Se in US adults. The methyl Se-specific activities may therefore be physiologically pertinent for angiogenic switch regulation in early lesions in vivo in the context of cancer chemoprevention, which aims at retarding and blocking the growth and progression of early lesions. We argue for the antiangiogenic action of Se, especially the methyl Se pool of metabolites, as a primary mechanism for preventing avascular lesion growth. Contrary to the currently held paradigm, we speculate that there is a potential role for selenoproteins in regulating the growth and fate of transformed epithelial cells.

Regulation of endothelial barrier function and growth by VE-cadherin, plakoglobin, and beta-catenin

VE-cadherin is an endothelial-specific cadherin that plays a central role in vascular barrier function and angiogenesis. The cytoplasmic domain of VE-cadherin is linked to the cytoskeleton through interactions with the armadillo family proteins beta-catenin and plakoglobin. Growing evidence indicates that beta-catenin and plakoglobin play important roles in epithelial growth and morphogenesis. To test the role of these proteins in vascular cells, a replication-deficient retroviral system was used to express intercellular junction proteins and mutants in the human dermal microvascular endothelial cell line (HMEC-1). A mutant VE-cadherin lacking an adhesive extracellular domain disrupted endothelial barrier function and inhibited endothelial growth. In contrast, expression of exogenous plakoglobin or metabolically stable mutants of beta-catenin stimulated HMEC-1 cell growth, which suggests that the beta-catenin signaling pathway was active in HMEC-1 cells. This possibility was supported by the finding that a dominant-negative mutant of the transcription factor TCF-4, designed to inhibit beta-catenin signaling, also inhibited HMEC-1 cell growth. These observations suggest that intercellular junction proteins function as components of an adhesion and signaling system that regulates vascular barrier function and growth.

Persistence of microscopic human cancers in mice: alterations in the angiogenic balance accompanies loss of tumor dormancy

Some human tumor lines do not form visible tumors when inoculated into immunosuppressed mice. The fate of these human tumor lines was followed by transfecting them with green fluorescence protein before inoculating them into mice. Although the tumor lines failed to grow progressively, they formed small dormant microscopic foci maintained at constant mass by balanced proliferation and apoptosis. Transfecting the cells with either VEGF165 or activated c-Ha-ras induced loss of dormancy, which correlated with a shift in the angiogenic balance toward increased vascularity with reduced tumor cell apoptosis. These results support a model in which loss of dormancy is controlled in part by a switch to an angiogenic phenotype. These tumor lines may serve as models for investigating the cellular mechanisms controlling dormancy and identifying those factors that promote the loss of balanced proliferation and apoptosis. Finally, these models may prove useful in the design and testing of therapies directed toward eradicating dormant tumors and preventing tumor recurrence.

Adenovirus-mediated transfer of BAX driven by the vascular endothelial growth factor promoter induces apoptosis in lung cancer cells

Apoptosis induction is a promising approach for cancer gene therapy. Bax is a death-promoting member of the Bcl2 family of genes that are intimately involved in apoptosis. Overexpression of BAX protein can accelerate cell death by homodimers that promote apoptosis in a variety of cancer cell lines. The cytotoxic effect of BAX was evaluated in vitro by a recombinant adenovirus system expressing the human BAX gene under control of human vascular endothelial growth factor (VEGF) promoter element (AdVEGFBAX). Overexpression of BAX in human lung carcinoma cells resulted in apoptosis induction, caspase activation, and cell growth suppression, none of which were observed in BEAS-2B normal human bronchial epithelial cells that do not overexpress VEGF under normoxic conditions. To examine the hypoxia responsiveness of the VEGF promoter, lung cancer cells were transiently exposed to hypoxia; this treatment increased enhanced green fluorescent protein (EGFP) expression after AdVEGFEGFP infection in both normal and cancer cell lines, and enhanced apoptosis and decreased the number of surviving cancer cells compared with the Ad/BAX plus Ad/Cre binary adenoviral system. These results suggest a possible therapeutic application of cancer-specific expression of the pro-apoptotic Bax gene driven by the VEGF promoter.

Phosphorylation by mitogen-activated protein kinase mediates the hypoxia-induced turnover of the TAL1/SCL transcription factor in endothelial cells

The basic helix-loop-helix transcription factor TAL1 (or SCL), originally identified from its involvement by a chromosomal rearrangement in T-cell acute lymphoblastic leukemia, is required for hematopoietic development. TAL1 also has a critical role in embryonic vascular remodeling and is expressed in endothelial cells postnatally, although little is known about its function or regulation in this cell type. We report here that the important proangiogenic stimulus hypoxia stimulates phosphorylation, ubiquitination, and proteasomal breakdown of TAL1 in endothelial cells. Tryptic phosphopeptide mapping and chemical inhibitor studies showed that hypoxia induced the mitogen-activated protein kinase-mediated phosphorylation of a single serine residue, Ser(122), in the protein, and site-directed mutagenesis demonstrated that Ser(122) phosphorylation was necessary for hypoxic acceleration of TAL1 turnover in an immortalized murine endothelial cell line. Finally, whereas TAL1 expression was detected in endothelial cells from both large and small vessels, hypoxia-induced TAL1 turnover was observed only in microvascular endothelial cells. Besides their implications for TAL1 function in angiogenic processes, these results demonstrate that a protein kinase(s) important for mitogenic signaling is also utilized in hypoxic endothelial cells to target a transcription factor for destruction.

Antitumor activity of cytotoxic T lymphocytes engineered to target vascular endothelial growth factor receptors

The demonstration that angiogenesis is required for the growth of solid tumors has fueled an intense interest in the development of new therapeutic strategies that target the tumor vasculature. Here we report the development of an immune-based antiangiogenic strategy that is based on the generation of T lymphocytes that possess a killing specificity for cells expressing vascular endothelial growth factor receptors (VEGFRs). To target VEGFR-expressing cells, recombinant retroviral vectors were generated that encoded a chimeric T cell receptor comprised of VEGF sequences linked to intracellular signaling sequences derived from the zeta chain of the T cell receptor. After transduction of primary murine CD8 lymphocytes by such vectors, the transduced cells were shown to possess an efficient killing specificity for cells expressing the VEGF receptor, Flk-1, as measured by in vitro cytotoxicity assays. After adoptive transfer into tumor-bearing mice, the genetically modified cytotoxic T lymphocytes strongly inhibited the growth of a variety of syngeneic murine tumors and human tumor xenografts. An increased effect on in vivo tumor growth inhibition was seen when this therapy was combined with the systemic administration of TNP-470, a conventional angiogenesis inhibitor. The utilization of the immune system to target angiogenic markers expressed on tumor vasculature may prove to be a powerful means for controlling tumor growth.

Expression and regulation of the PD-L1 immunoinhibitory molecule on microvascular endothelial cells

OBJECTIVE

To evaluate the expression and regulation of a novel B7-like protein, PD-L1, the ligand for the immunoinhibitory receptor PD-1 expressed on activated T-cells, on microvascular endothelial cells (ECs)

METHODS

PD-L1 expression on ECs in vitro and in vivo was quantified by using a dual radiolabeled antibody technique after treatment with interferons (IFN) and IL-12, respectively. Changes in the level of PD-L1 mRNA were determined by using RT-PCR.

RESULTS

PD-L1 was observed to be present on ECs under basal conditions. Treatment of ECs with IFN-alpha, -beta and -gamma, but not LPS, was observed to induce elevations in the mRNA and surface expression of PD-L1 on ECs. By using a dual radiolabeled monoclonal antibody (mAb) technique, PD-L1 expression in various tissues of control and IL-12 challenged wild-type and IFN-gamma-deficient mice was measured. A significant increase in PD-L1 expression was observed in tissues at 24 hours after IL-12-challenge, with peak levels of PD-L1 occurring 72 hours after IL-12 challenge. IL-12 was not effective at inducing PD-L1 expression in tissues of IFN-gamma-deficient mice.

CONCLUSIONS

These data show the expression of a novel B7-like molecule on murine ECs that is mediated by IFN-alpha, -beta, and -gamma, and suggest a potential pathway by which ECs may modulate T-cell function.

The significance of immunohistochemistry in the diagnosis and therapy of neoplasms

This review article details the diagnostical significance of immunohistochemistry, which has developed during the last quarter of the century. Certainly, the advancement of monoclonal antibody technology has been of great significance in assuring the place of immunohistochemistry in the modern accurate microscopic diagnosis of human neoplasms, as a method of choice in histopathology. The fact still remains that in order to properly assess any immunohistochemical reactivity used for differential diagnostic purposes, the target cells have to be identified as neoplastically transformed cells by routine histopathological techniques. Selected groups of target molecules of great significance in cancer biology are discussed. The discovery of neoplasm-associated antigens has not only made the more accurate diagnosis of human cancer feasible but has also shed light on the extensive immunophenotypical heterogeneity of even the most closely linked human malignancies. The identification of disseminated neoplastically transformed cells by immunohistochemistry has allowed for a clearer picture of cancer invasion and metastasis, as well as the evolution of the tumour cell associated immunophenotype towards increased malignancy. Some possibilities of neoplasm-associated antigen targeted, receptor-directed immunotherapy are discussed and reviewed in this manuscript. Future antineoplastic therapeutical approaches should see the inclusion of a variety of immunotherapies, in the form of an individualised 'cocktail' specific for the particular immunophenotypical pattern associated with each individual patient's neoplastic disease.

TEL Induces Aggregation in Transformed Cells and Induces Tube Formation in NIH3T3-UCLA Cells

TEL/ETV6 is the frequent target of translocations associated with lymphoid and myeloid leukemias and solid tumors. We show that TEL induces aggregation of immortalized and transformed fibroblasts, endothelial cells and astrocytes. These aggregates form cellular cords in NIH3T3-UCLA by a cell autonomous process, which occurs when the monolayer is made up of over 75% of cells expressing exogenous TEL. Cords with a diameter of 15-25 microm contain a lumen and occur as tube structures. The possible relevance for vasculogenic mimicry is discussed. By contrast TEL did not induce aggregation of regular NIH3T3 cells, an effect that could only be induced by co-expression of oncogenic RAS/Lys12. Also transduction of TEL and RAS retroviral vectors into the endothelial MS1 cell line and TEL alone in the highly transformed glioblastoma cell lines EH-A and EH-B resulted in extensive aggregation. Thus, the induction of cellular aggregation by TEL correlates with transformation.

Tuberous sclerosis-associated lesions of the kidney, brain, and skin are angiogenic neoplasms

BACKGROUND

Tuberous sclerosis is an autosomal dominant condition characterized by the development of benign neoplasms of the brain, kidney, and skin. Progressive growth and malignant transformation of brain and kidney lesions constitute the major cause of morbidity and mortality in adults with tuberous sclerosis. In addition, growth of skin lesions may be disfiguring to patients.

OBJECTIVE

The purpose of this study was to determine whether benign tumors in patients with tuberous sclerosis are angiogenic.

METHODS

Brain, kidney, and skin tumors from patients with tuberous sclerosis were stained with CD31, a specific marker of vascular endothelium. In addition, we used Northern blot analysis to demonstrate that renal angiomyolipoma cells express the potent angiogenesis stimulator vascular endothelial growth factor (VEGF).

RESULTS

Brain, kidney, and skin neoplasms from patients with tuberous sclerosis are highly angiogenic. Renal angiomyolipoma cells produce the potent angiogenic factor VEGF.

CONCLUSION

Benign neoplasms of patients with tuberous sclerosis are highly vascular. Our results provide a rationale for antiangiogenic therapy in the treatment and prevention of tuberous sclerosis-associated neoplasms.

Prerequisites for effective adenovirus mediated gene therapy of colorectal liver metastases in the rat using an intracellular neutralizing antibody fragment to p21-Ras

Ras mutations are present in 40-50% of colorectal cancers. Inactivating this oncogene may therefore reduce proliferation capacity. In order to target ras we studied the transduction efficacy and anti tumour activity of an adenoviral vector expressing an intracellular, neutralizing single chain antibody to p21-ras (Y28). In in vitro studies transfection levels of the K-ras mutated rat colon carcinoma cell line CC531 were studied using the LacZ marker gene. In our in vivo liver metastases model different routes of administration were evaluated to determine which regimen resulted in the best transfection levels and tumour responses: intravenous injection, intratumoural injection, isolated liver perfusion, or hepatic artery infusion. CC531 cells are readily transfected in vitro, resulting in significant inhibition of tumour cell proliferation by the Y28 construct. Intravenous injection did not result in any measurable transfection. Intratumoural injection resulted only in the transfection of tumour cells along the needle track. IHP as well as single HAI achieved low transfection levels of tumour tissue. Expression of Y28 was demonstrated in tumours after IT injection, HAI and IHP. Whereas, repeated HAI's clearly achieved expression in and around tumour associated vessels. Only five times repeated HAI's with Y28 resulted in a tumour response: in all animals tumour growth was inhibited, and in three rats out of eight a complete regression of the liver tumours was observed.

Reactive oxygen generated by Nox1 triggers the angiogenic switch

The reactive oxygen-generating enzyme Nox1 transforms NIH 3T3 cells, rendering them highly tumorigenic and, as shown herein, also increases tumorigenicity of DU-145 prostate epithelial cells. Although Nox1 modestly stimulates cell division in both fibroblasts and epithelial cells, an increased mitogenic rate alone did not account fully for the marked tumorigenicity. Herein, we show that Nox1 is a potent trigger of the angiogenic switch, increasing the vascularity of tumors and inducing molecular markers of angiogenesis. Vascular endothelial growth factor (VEGF) mRNA becomes markedly up-regulated by Nox1 both in cultured cells and in tumors, and VEGF receptors (VEGFR1 and VEGFR2) are highly induced in vascular cells in Nox1-expressing tumors. Matrix metalloproteinase activity, another marker of the angiogenic switch, also is induced by Nox1. Nox1 induction of VEGF is eliminated by coexpression of catalase, indicating that hydrogen peroxide signals part of the switch to the angiogenic phenotype.

Vascular endothelial growth factor induction of the angiogenic phenotype requires Ras activation

We investigated the role of Ras in vascular endothelial growth factor (VEGF)-mediated signal transduction and the promotion of angiogenic changes primary endothelial cells. We find that VEGF potently induces Ras activation and that this step is essential for the stimulation by VEGF of several cellular changes associated with angiogenesis, including proliferation, migration, and branching morphogenesis in three-dimensional culture. Inhibition of Ras signaling induced subtle changes in the actin architecture but had no effect on the phosphatidylinositol 3-kinase (PI3K) or p38 signaling pathways. In contrast, activation of ERK was largely dependent on Ras. Although inhibiting ERK activity completely suppressed cell proliferation and partially blocked in vitro differentiation, neither ERK nor PI3K activity was required for VEGF-induced migration. These data provide the first direct demonstration that inhibition of Ras signal transduction is anti-angiogenic. Interestingly, VEGF signal transduction bifurcates both upstream and downstream of Ras, with different Ras-dependent signals controlling endothelial cell proliferation and migration, essential components of the angiogenic response.

Neuroendocrine lung tumors: grade correlates with proliferation but not angiogenesis

Angiogenesis has been implicated in the progression of human neoplasia from benign precursor to invasive and metastatic phenotypes. The acquisition of dominant oncogenes in preneoplastic cells in vitro and in vivo has been associated with the increased ability of tumor cells to secrete angiogenic mediators and recruit blood vessels. However, in a subset of benign lesions, high levels of angiogenesis have been found before the conversion to invasive and metastatic phenotypes. In many of these benign lesions, dominant oncogenic pathways are activated first; then as malignant potential is acquired, there is a loss of nuclear tumor suppressor genes, such as p53 and p16. We studied neuroendocrine lung tumors (NLT) ranging from typical and atypical carcinoid tumors to large cell neuroendocrine and small cell carcinomas in order to determine whether angiogenesis (as assessed by mean vessel density) and proliferation rates (as assessed by MIB-1 nuclear immunohistochemical staining) correlate with tumor type. We found that increased rates of proliferation, but not angiogenesis, correlate with tumor type. The association of increased proliferation and tumor type may prove to be clinically useful and shed light on the role of sequential oncogenic alterations in NLT.

Transforming growth factor beta1 (TGF-beta1) promotes endothelial cell survival during in vitro angiogenesis via an autocrine mechanism implicating TGF-alpha signaling

Mouse capillary endothelial cells (1G11 cell line) embedded in type I collagen gels undergo in vitro angiogenesis. Cells rapidly reorganize and form capillary-like structures when stimulated with serum. Transforming growth factor beta1 (TGF-beta1) alone can substitute for serum and induce cell survival and tubular network formation. This TGF-beta1-mediated angiogenic activity depends on phosphatidylinositol 3-kinase (PI3K) and p42/p44 mitogen-activated protein kinase (MAPK) signaling. We showed that specific inhibitors of either pathway (wortmannin, LY-294002, and PD-98059) all suppressed TGF-beta1-induced angiogenesis mainly by compromising cell survival. We established that TGF-beta1 stimulated the expression of TGF-alpha mRNA and protein, the tyrosine phosphorylation of a 170-kDa membrane protein representing the epidermal growth factor (EGF) receptor, and the delayed activation of PI3K/Akt and p42/p44 MAPK. Moreover, we showed that all these TGF-beta1-mediated signaling events, including tubular network formation, were suppressed by incubating TGF-beta1-stimulated endothelial cells with a soluble form of an EGF receptor (ErbB-1) or tyrphostin AG1478, a specific blocker of EGF receptor tyrosine kinase. Finally, addition of TGF-alpha alone poorly stimulated angiogenesis; however, by reducing cell death, it strongly potentiated the action of TGF-beta1. We therefore propose that TGF-beta1 promotes angiogenesis at least in part via the autocrine secretion of TGF-alpha, a cell survival growth factor, activating PI3K/Akt and p42/p44 MAPK.

Regulation of tumor angiogenesis by dietary fatty acids and eicosanoids

Angiogenesis is a prerequisite for tumor growth and metastasis. Vascular endothelial cell proliferation, migration, and capillary formation are stimulated by angiogenic growth factors, which include the proteins vascular endothelial growth factor, basic fibroblast growth factor, and transforming growth factor-beta, and eicosanoids synthesized from n-6 fatty acids. Clinical studies have shown that angiogenesis in solid tumors relates to a poor prognosis and, in premalignant lesions, indicates potential for cancerous transformation. High-fat, n-6 fatty acid-rich diets were associated with a relatively poor prognosis in breast cancer patients; in a nude mouse model the same diet enhanced breast cancer progression, whereas n-3 fatty acids exerted suppressive effects that were associated with impaired angiogenesis. Lipoxygenase and cyclooxygenase products of n-6 fatty acid metabolism are angiogenic in in vitro assays. This activity is blocked by pharmacological inhibitors of eicosanoid biosynthesis, and one, indomethacin, suppressed n-6 fatty acid-stimulated murine mammary carcinoma growth and metastasis and tumor vascularization. Review of the experimental data suggests that selective inhibitors of eicosanoid-synthesizing enzymes and dietary intervention with n-3 fatty acids merit clinical evaluation as adjuvant therapy and chemopreventive agents.

Akt/PKB promotes cancer cell invasion via increased motility and metalloproteinase production

The Akt/protein kinase B (PKB) serine/threonine kinase is well known as an important mediator of many cell survival signaling pathways. Here, we demonstrate for the first time a major role of Akt/PKB in the cell invasion properties of the highly metastatic cell line HT1080. Using confocal microscopic analyses of live samples, we found Akt/PKB to be localized in the leading edge membrane area of migrating HT1080 cells. This localization was dependent on phosphoinositide 3-kinase and required the lipid binding ability of the phosphoinositide binding pleckstrin homology domain of Akt/PKB. We examined the possible function of Akt/PKB in HT1080 invasion. Surprisingly, Akt/PKB potently promoted HT1080 invasion, by increasing cell motility and matrix metalloproteinase-9 (MMP-9) production, in a manner highly dependent on its kinase activity and membrane-translocating ability. The increase in MMP-9 production was mediated by activation of nuclear factor-kappaB transcriptional activity by Akt/PKB. However, Akt/PKB did not affect the cell-cell or cell-matrix adhesion properties of HT1080. Our findings thus establish Akt/PKB as a major factor in the invasive abilities of cancer cells.

The hemostatic system and angiogenesis in malignancy

Coagulopathy and angiogenesis are among the most consistent host responses associated with cancer. These two respective processes, hitherto viewed as distinct, may in fact be functionally inseparable as blood coagulation and fibrinolysis, in their own right, influence tumor angiogenesis and thereby contribute to malignant growth. In addition, tumor angiogenesis appears to be controlled through both standard and non-standard functions of such elements of the hemostatic system as tissue factor, thrombin, fibrin, plasminogen activators, plasminogen, and platelets. "Cryptic" domains can be released from hemostatic proteins through proteolytic cleavage, and act systemically as angiogenesis inhibitors (e.g., angiostatin, antiangiogenic antithrombin III aaATIII). Various components of the hemostatic system either promote or inhibit angiogenesis and likely act by changing the net angiogenic balance. However, their complex influences are far from being fully understood. Targeted pharmacological and/or genetic inhibition of pro-angiogenic activities of the hemostatic system and exploitation of endogenous angiogenesis inhibitors of the angiostatin and aaATIII variety are under study as prospective anti-cancer treatments.

Identification of an angiogenic mitogen selective for endocrine gland endothelium

The known endothelial mitogens stimulate growth of vascular endothelial cells without regard to their tissue of origin. Here we report a growth factor that is expressed largely in one type of tissue and acts selectively on one type of endothelium. This molecule, called endocrine-gland-derived vascular endothelial growth factor (EG-VEGF), induced proliferation, migration and fenestration (the formation of membrane discontinuities) in capillary endothelial cells derived from endocrine glands. However, EG-VEGF had little or no effect on a variety of other endothelial and non-endothelial cell types tested. Similar to VEGF, EG-VEGF possesses a HIF-1 binding site, and its expression is induced by hypoxia. Both EG-VEGF and VEGF resulted in extensive angiogenesis and cyst formation when delivered in the ovary. However, unlike VEGF, EG-VEGF failed to promote angiogenesis in the cornea or skeletal muscle. Expression of human EG-VEGF messenger RNA is restricted to the steroidogenic glands, ovary, testis, adrenal and placenta and is often complementary to the expression of VEGF, suggesting that these molecules function in a coordinated manner. EG-VEGF is an example of a class of highly specific mitogens that act to regulate proliferation and differentiation of the vascular endothelium in a tissue-specific manner.

The generation and characterization of a cell line derived from a sporadic renal angiomyolipoma: use of telomerase to obtain stable populations of cells from benign neoplasms

Angiomyolipomas are benign tumors of the kidney derived from putative perivascular epithelioid cells, that may undergo differentiation into cells with features of melanocytes, smooth muscle, and fat. To gain further insight into angiomyolipomas, we have generated the first human angiomyolipoma cell line by sequential introduction of SV40 large T antigen and human telomerase into human angiomyolipoma cells. These cells show phenotypic characteristics of angiomyolipomas, namely differentiation markers of smooth muscle (smooth muscle actin), adipose tissue (peroxisome proliferator-activator receptor gamma, PPARgamma), and melanocytes (microophthalmia, MITF), thus demonstrating that a single cell type can exhibit all of these phenotypes. These cells should serve as a valuable tool to elucidate signal transduction pathways underlying renal angiomyolipomas.

Angiogenesis and antiangiogenic approaches to sarcomas

Established chemotherapy regimens for advanced or metastatic sarcoma generally have low response rates and substantial toxicity, and resistance often arises quickly, making sarcoma an ideal target for alternative treatment approaches. Antiangiogenic therapies have a number of potential advantages including decreased resistance, fewer side effects, and a broad spectrum of activity. This paper reviews the evidence supporting the use of antiangiogenic therapies for adult soft tissue sarcomas. Human sarcomas express a number of proangiogenic factors that may represent therapeutic targets, with vascular endothelial growth factor being the best characterized, and inhibitors of angiogenesis have antitumor activity in animal models of human sarcomas. Clinical trials are in early stages, although promising results have already been seen. In the future, improved drugs, refined molecular profiling of tumors, and new ways of combining antiangiogenic agents with cytotoxic agents may lead to more effective and tolerable therapies for sarcomas.

Magnetic resonance imaging of ethyl-nitrosourea-induced rat gliomas: a model for experimental therapeutics of low-grade gliomas

Human low-grade gliomas represent a population of brain tumors that remain a therapeutic challenge. Preclinical evaluation of agents, to test their preventive or therapeutic efficacy in these tumors, requires the use of animal models. Spontaneous gliomas develop in models of chemically induced carcinogenesis, such as in the transplacental N-ethyl-N-nitrosourea (ENU) rat model. However, without the ability to detect initial tumor formation, multiplicity or to measure growth rates, it is difficult to test compounds for their interventional or preventional capabilities. In this study Fisher-334 rats, treated transplacentally with ENU, underwent magnetic resonance imaging (MRI) examination in order to evaluate this approach for detection of tumor formation and growth. ENU-induced intracranial cerebral tumors were first observable in T2-weighted images beginning at 4 months of age and grew with a mean doubling time of 0.487 +/- 0.112 months. These tumors were found histologically to be predominately mixed gliomas. Two therapeutic interventions were evaluated using MRI, vitamin A (all-trans retinol palmitate, RP), as a chemopreventative agent and the anti-angiogenic drug SU-5416. RP was found to significantly delay the time to first tumor observation by one month (P = 0.05). No differences in rates of tumor formation or growth rates were observed between control and RP-treated groups. MRI studies of rats treated with SU-5416 resulted in reduction in tumor growth rates compared to matched controls. These results show that MRI can be used to provide novel information relating to the therapeutic efficacy of agents against the ENU-induced tumor model.

3D microvascular architecture of pre-cancerous lesions and invasive carcinomas of the colon

Despite the significance of tumour neoangiogenesis and the extensive knowledge on the molecular basis of blood vessel formation currently no quantitative data exist on the 3D microvascular architecture in human primary tumours and their precursor lesions. This prompted us to examine the 3D vascular network of normal colon mucosa, adenomas and invasive carcinomas by means of quantitative microvascular corrosion casting. Fresh hemicolectomy specimens from 20 patients undergoing cancer or polyposis coli surgery were used for corrosion casting, factor VIII and VEGF immunostaining. In addition, immunostaining was done on colorectal tissue from 33 patients with metastatic and non-metastatic carcinomas, polyposis coli and adenomas. This first quantitative analysis of intervessel and interbranching distances, branching angles and vessel diameters in human cancer specimens revealed distinct patterns of the microvascular unit in the tumour centre and periphery. Irrespective of the tumour localization and grading all individual tumours displayed qualitatively and quantitatively the same vascular architecture. This gives further evidence for the existence of a tumour type-specific vascular architecture as recently demonstrated for experimental tumours. Metastatic tumours displayed different vascular architectures only within hot spots, in terms of smaller intervascular distances than in non-metastatic tumours. Pre-cancerous lesions have in part virtually the same vascular architecture like invasive carcinomas. Comparison of VEGF immunostaining also suggests that angiogenesis sets in long before the progress towards invasive phenotypes and that the so-called angiogenic switch is more likely a sequence of events. © 2001 Cancer Research Campaign www.bjcancer.com

Mutant epidermal growth factor receptor enhances induction of vascular endothelial growth factor by hypoxia and insulin-like growth factor-1 via a PI3 kinase dependent pathway

Over-expression of truncated epidermal growth factor receptor (EGFR) occurs in a variety of malignancies including glioblastoma multiforme, breast and lung cancer. The truncation deletes an extracellular domain and results in constitutive activation of the receptor. NIH3T3 cells were transfected with full length or truncated human EGFR and differences in growth rates in vivo and in vitro analysed. A growth advantage was seen for cells expressing mutant receptor compared to full length EGFR in vivo only. Administration of an anti-mutant EGFR antibody to mice transiently reduced the growth rates of mutant tumours, confirming that the mutant receptor itself was important in this enhanced tumorigenicity. This showed that stimuli present in vivo and not in vitro may be contributing to growth. We therefore analysed the regulation of the angiogenic factor vascular endothelial growth factor (VEGF). Although levels of secreted VEGF did not differ significantly between wild-type and mutant EGFR cell lines when grown in vitro under normoxic conditions, following exposure to 0.1% hypoxia levels of VEGF produced by mutant cells increased 3.5–6.6 fold compared to 2 or less for full length EGFR cells. The fold induction was influenced by experimental conditions, including cell confluence and percentage of fetal bovine serum, but was consistently higher for mutant cell lines. The increase in VEGF under hypoxic conditions was blocked by the addition of PI3 kinase inhibitors, indicating that the latter pathway is important in the hypoxic stress response. Basal levels were not affected. Addition of insulin-like growth factor-1 also increased levels of VEGF under normoxic conditions in the mutant cells and no further increase was seen when added to cells exposed to 0.1% oxygen, indicating that levels of VEGF were already maximally stimulated. These results show that the mutant EGFR interacts with other growth factors and hypoxia to regulate VEGF via a PI3 kinase pathway, and suggests a specific role for anti-mutant EGFR antibodies and PI3 kinase inhibitors as therapy of this specific tumour target. © 2001 Cancer Research Campaign www.bjcancer.com

Excessive tumor-elaborated VEGF and its neutralization define a lethal paraneoplastic syndrome

Vascular endothelial growth factor (VEGF) is a potent endothelial cell mitogen and key regulator of both physiologic and pathologic (e.g., tumor) angiogenesis. In the course of studies designed to assess the ability of constitutive VEGF to block tumor regression in an inducible RAS melanoma model, mice implanted with VEGF-expressing tumors sustained high morbidity and mortality that were out of proportion to the tumor burden. Documented elevated serum levels of VEGF were associated with a lethal hepatic syndrome characterized by massive sinusoidal dilation and endothelial cell proliferation and apoptosis. Systemic levels of VEGF correlated with the severity of liver pathology and overall clinical compromise. A striking reversal of VEGF-induced liver pathology and prolonged survival were achieved by surgical excision of VEGF-secreting tumor or by systemic administration of a potent VEGF antagonist (VEGF-TRAP(R1R2)), thus defining a paraneoplastic syndrome caused by excessive VEGF activity. Moreover, this VEGF-induced syndrome resembles peliosis hepatis, a rare human condition that is encountered in the setting of advanced malignancies, high-dose androgen therapy, and Bartonella henselae infection. Thus, our findings in the mouse have suggested an etiologic role for VEGF in this disease and may lead to diagnostic and therapeutic options for this debilitating condition in humans.

Phase I study of the matrix metalloproteinase inhibitor, BAY 12-9566

BACKGROUND

Matrix metalloproteinases (MMPs) are involved in tumor invasion and metastasis and have been implicated in breast, ovarian, colorectal, and lung cancer growth. We undertook a phase I study of BAY 12-9566, an inhibitor of MMP-2, MMP-9, and MMP-3, in patients with solid tumors to determine its safety, pharmacokinetics, and effects on potential surrogate markers of biologic activity.

PATIENTS AND METHODS

BAY 12-9566 was orally administered daily at four dose levels; 400 mg daily, 400 mg b.i.d., 400 mg t.i.d., and 800 mg b.i.d. Drug disposition was determined on days 1 and 29 with weekly trough levels measured during the first four weeks. Plasma vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and urinary pyridinoline and deoxypyridinoline crosslinks were determined at baseline, once weekly for four weeks, and then every four weeks.

RESULTS

Thirteen patients were entered on trial. BAY 12-9566 was well tolerated, with only one grade 3 headache, one grade 3 anemia, one grade 3 thrombocytopenia, and no musculoskeletal effects. The median treatment duration was 57 days (range 7-560). Mean trough levels of BAY 12-9566 on day 28 ranged from 80.5 to 108.6 mg/l. Plasma trough levels were 1500-42,000-fold above the Ki's for MMP-2, MMP-3, and MMP-9 at the 800 mg p.o. b.i.d. dose level. There was no significant change in VEGF, bFGF, pyridinoline, and deoxypyridinoline crosslinks with BAY 12-9566 administration.

CONCLUSIONS

The recommended dose for further testing is 800 mg p.o. b.i.d.

Angiogenesis: regulators and clinical applications

Angiogenesis is a fundamental process in reproduction and wound healing. Under these conditions, neovascularization is tightly regulated. Unregulated angiogenesis may lead to several angiogenic diseases and is thought to be indispensable for solid tumor growth and metastasis. The construction of a vascular network requires different sequential steps including the release of proteases from "activated" endothelial cells with subsequent degradation of the basement membrane surrounding the existing vessel, migration of endothelial cells into the interstitial space, endothelial cell proliferation, and differentiation into mature blood vessels. These processes are mediated by a wide range of angiogenic inducers, including growth factors, chemokines, angiogenic enzymes, endothelial specific receptors, and adhesion molecules. Finally, when sufficient neovascularization has occurred, angiogenic factors are down-regulated or the local concentration of inhibitors increases. As a result, the endothelial cells become quiescent, and the vessels remain or regress if no longer needed. Thus, angiogenesis requires many interactions that must be tightly regulated in a spatial and temporal manner. Each of these processes presents possible targets for therapeutic intervention. Synthetic inhibitors of cell invasion (marimastat, Neovastat, AG-3340), adhesion (Vitaxin), or proliferation (TNP-470, thalidomide, Combretastatin A-4), or compounds that interfere with angiogenic growth factors (interferon-alpha, suramin, and analogues) or their receptors (SU6668, SU5416), as well as endogenous inhibitors of angiogenesis (endostatin, interleukin-12) are being evaluated in clinical trials against a variety of solid tumors. As basic knowledge about the control of angiogenesis and its role in tumor growth and metastasis increases, it may be possible in the future to develop specific anti-angiogenic agents that offer a potential therapy for cancer and angiogenic diseases.

Differential expression of active mitogen-activated protein kinase in cutaneous endothelial neoplasms: implications for biologic behavior and response to therapy

BACKGROUND

Tumors of endothelium range from benign hemangiomas of infancy to highly malignant angiosarcomas of the elderly. Hemangiomas are the most common tumors in infants and may affect up to 10% of all children. The biologic behavior of these lesions ranges from self-resolving, in the case of hemangiomas and pyogenic granulomas, to lethal metastatic neoplasms in the case of angiosarcoma. Although the clinical outcomes of these diseases are easily distinguished, the biologic basis for these differences is not well understood. Activation of mitogen-activated protein kinase (MAPK) is an important signal transduction mechanism that may predict response of a tumor to chemotherapy.

OBJECTIVE

Our purpose was to examine expression of phosphorylated (activated) MAPK in hemangiomas of infancy, pyogenic granulomas, hemangioendotheliomas, and angiosarcomas to determine whether phosphorylated MAPK was expressed in endothelial tumors. In addition, we examined endothelial tumors of infectious origin, Kaposi's sarcoma, and verruga peruana.

METHODS

Skin sections from benign and malignant endothelial tumors, including hemangioma of infancy, angiosarcoma, and infectious endothelial lesions (Kaposi's sarcoma, verruga peruana) were stained with an antibody specific for phosphorylated MAPK.

RESULTS

We demonstrated strong expression of phosphorylated MAPK in benign endothelial tumors, including capillary hemangioma of infancy and pyogenic granuloma, and greatly decreased expression in angiosarcoma. In addition, infectious endothelial tumors stained strongly with this antibody, similar to benign tumors. The presence of immunoreactive phosphorylated MAPK appears to be inversely correlated with degree of malignancy.

CONCLUSION

We demonstrate that the use of antibodies specific for signal transduction pathways is feasible in paraffin-fixed tissue. Thus the activity of a given signal transduction pathway can be ascertained in a biopsy specimen. Immunohistochemistry for phosphorylated MAPK may help the pathologist distinguish benign from malignant endothelial processes and thus guide therapy.

Rational approaches to design of therapeutics targeting molecular markers

This paper introduces novel therapeutic strategies focusing on a molecular marker relevant to a particular hematologic malignancy. Four different approaches targeting specific molecules in unique pathways will be presented. The common theme will be rational target selection in a strategy that has reached the early phase of human clinical trial in one malignancy, but with a much broader potential applicability to the technology. In Section I Dr. Richard Klasa presents preclinical data on the use of antisense oligonucleotides directed at the bcl-2 gene message to specifically downregulate Bcl-2 protein expression in non-Hodgkin's lymphomas and render the cells more susceptible to the induction of apoptosis. In Section II Dr. Alan List reviews the targeting of vascular endothelial growth factor (VEGF) and its receptor in anti-angiogenesis strategies for acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS). In Section III Dr. Bruce Cheson describes recent progress in inhibiting cell cycle progression by selectively disrupting cyclin D1 with structurally unique compounds such as flavopiridol in mantle cell lymphoma as well as describing a new class of agents that affect proteasome degradation pathways.

Regulation of angiogenesis and tumorigenesis by signal transduction cascades: lessons from benign and malignant endothelial tumors

Oncogenes and tumor suppressor genes are implicated in the regulation of the angiogenic switch. Much of the data accumulated to date uses NIH 3T3 cells, which are deficient in the tumor suppressor gene p16, as models for these studies. We have used a novel system, derived by sequential introduction of a temperature-sensitive SV40 large T antigen and oncogenic H-ras, to study the angiogenic switch. The results from our studies differ from those using NIH3T3 cells, but have been confirmed by multiple other groups. The data from all of these studies suggest that there is synergy between inactivation of the p53 tumor suppressor gene and activation of the phosphoinositol-3-kinase pathway (PI-3-K), as well as synergy between inactivation of the p16 tumor suppressor gene and activation of the MAP kinase pathway. These findings suggest that there are predictable behaviors of tumors that may be assessed by the status of p53 or p16 in a biopsy, and that these predictable changes in signal transduction may be useful both prognostically and in the design of rationally based drug therapy of benign and malignant tumors.

Oncogenes and angiogenesis: signaling three-dimensional tumor growth

Three-dimensional tumor growth is dependent on the perpetual recruitment of host blood vessels to the tumor site. This recruitment process (mainly via angiogenesis) is thought to be triggered, at least in part, by the very same set of genetic alterations (activated oncogenes, inactivated/lost tumor suppressor genes) as those responsible for other aspects of malignant transformation (e.g., aberrant mitogenesis, resistance to apoptosis). Potent oncogenes are able to deregulate expression of both angiogenesis stimulators and inhibitors in cancer cells. For example, mutant ras expression is associated with increased production of vascular endothelial growth factor (VEGF) and downregulation of thrombospondin-1 (TSP-1). Upregulation of VEGF and angiogenesis can also be induced by constitutive activation of other oncogenic proteins (e.g., EGFR, Raf, MEK, PI3K) acting at various levels on the Ras signaling pathway. The mode and the magnitude of such proangiogenic influences can be significantly modified by cell type (fibroblastic or epithelial origin), epigenetic factors (hypoxia, changes in cell density), and/or presence of additional genetic lesions (e.g., preceding loss of p16 or p53 tumor suppressor genes). Activated oncogenes (e.g., ras, src, HER-2) induce co-expression of angiogenic properties concomitantly with several highly selectable traits (increased mitogenesis, resistance to apoptosis), a circumstance that may accelerate selection of the angiogenic phenotype at the cell population level. On the other hand oncogene-induced reduction in growth requirements may also endow tumor cells with a diminished (albeit not abrogated) dependence on (close) proximity to blood vessels, i.e., with reduced vascular dependence. Thus, oncogenes can impact several interconnected aspects of cellular growth, survival, and angiogenesis. Experimental evidence suggests that, in principle, many of these properties (including angiogenesis) can be simultaneously suppressed (and tumor stasis or regression induced) by effective use of the specific oncogene antagonists and signal transduction inhibitors.

Overexpression of c-H-ras p21 is correlated with vascular endothelial growth factor expression and neovascularization in advanced gastric carcinoma

BACKGROUND AND AIMS

ras Gene and its product (p21) have been reported to be associated with vascular endothelial growth factor (VEGF), which is one of the most important angiogenic factors, and tumor-associated angiogenesis. We tried to evaluate the correlation between the expression of c-H-ras gene product p21 and angiogenesis in advanced gastric carcinoma.

METHODS

Immunohistochemical expression of c-H-ras p21 and VEGF was examined in 49 advanced gastric adenocarcinomas. In addition, double immunohistochemical staining was performed using anti-CD34 and anti-Ki-67 antibodies, and the intratumoral microvessel densities and their endothelial proliferative labeling indices were then counted to evaluate the degree of angiogenesis.

RESULTS

The expression of c-H-ras p21 was demonstrated in 43 out of 49 gastric adenocarcinomas (87.8%). It did not correlate with histologic type, depth of invasion or metastasis. However, the degree of c-H-ras p21 expression was correlated with VEGF. In addition, the degree of c-H-ras p21 expression was correlated with increased intratumoral microvascular density and endothelial proliferative activity.

CONCLUSIONS

We suggest that c-H-ras oncogene product p21 contributes to the upregulation of tumor-associated angiogenesis by the increased production of VEGF in advanced gastric carcinomas. Therefore, treatment involving the targeting of ras oncogene could inhibit solid tumor growth by suppressing tumor-associated angiogenesis.

Inhibition of MAP kinase kinase causes morphological reversion and dissociation between soft agar growth and in vivo tumorigenesis in angiosarcoma cells

Activated ras causes increased activity of several signal transduction systems, including the mitogen-activated protein kinase kinase (MAPKK) pathway and the phosphoinositol-3-kinase (PI-3-K) pathway. We have previously shown that the PI-3-K pathway plays a major role in regulation of ras-mediated tumor angiogenesis in angiosarcoma cells. However, the contribution of the MAPKK pathway to tumorigenesis and angiogenesis is not fully understood. Overexpression of constitutively active forms of MAPKK has previously been shown to transform nonmalignant NIH3T3 fibroblasts, but the effect of down-regulation of MAPKK on tumorigenesis and angiogenesis in a well established tumor has not been fully explored. We introduced a dominant negative MAPKK gene into SVR murine angiosarcoma cells. Introduction of a dominant negative MAPKK causes a significant decrease in proliferation rate in vitro and morphological reversion. Cells expressing the dominant negative MAPKK have a greatly decreased ability to form colonies in soft agar compared with wild-type cells. Despite the decreased cell growth in vitro and inability to grow in soft agar, the cells were equally tumorigenic in nude mice. Our results suggest that the MAPKK pathway is required for soft agar growth of angiosarcoma cells, and separates the phenotypes of soft agar growth versus in vivo tumorigenicity. These findings have implications in the development of signal transduction modulators as potential antineoplastic agents.

Expression and regulation of neuropilin-1 in human astrocytomas

Vascular endothelial growth factor (VEGF), through activation of its endothelial receptors VEGFR-1 and VEGFR-2, is an important positive modulator of tumor angiogenesis and edema in solid tumors such as malignant astrocytomas. Neuropilin-1 (Npn-1) is a transmembrane receptor expressed by both endothelial and non-endothelial cells, including tumor cells. Npn-1 has been postulated to function as a co-factor in activation of the biologically relevant VEGFR-2, by the most abundant VEGF165 isoform. However, the function of Npn-1 in normal and pathological angiogenesis, its expression pattern in relation to VEGF in tumors such as astrocytomas and whether it is similarly or differentially regulated compared to VEGF remain unknown. In our study, the expression pattern of Npn-1 and VEGF by human astrocytoma cell lines and specimens was closely correlated and associated with malignant astrocytomas. Mitogens, such as epidermal growth factor and activation of p21-Ras, previously demonstrated to be relevant in astrocytoma proliferation and induction of VEGF, also induce Npn-1 expression. Hypoxia, the main physiological inducer of VEGF expression, decreased Npn-1 expression. Increased Npn-1 expression was also demonstrated in a transgenic mouse astrocytoma model. Astrocytomas are an ideal system for furthering our understanding of the functional relevance, if any, of Npn-1 in tumor angiogenesis.