Multimodality imaging of the ischemic right ventricle: an overview and proposal of a diagnostic algorithm.

Right ventricular (RV) involvement is frequently detected in patients presenting with acute left ventricular myocardial infarction. The ischemic right ventricle carries a dismal outcome by predisposing the heart to arrhythmic events and mechanical or hemodynamic complications. A comprehensive RV evaluation by multimodality imaging could guide clinical practice but has always been a conundrum for the imagers. Two-dimensional echocardiography is the best first-line tool due to its availability of bedside capabilities. More advanced imaging techniques provide a more comprehensive evaluation of the complex RV geometry but are mostly reserved for the post-acute setting. Three-dimensional echocardiography has improved the evaluation of RV volumes and function. The recent application of speckle-tracking echocardiography to the right ventricle appears promising, allowing the earlier detection of subtle RV dysfunction. Cardiac magnetic resonance imaging is considered the gold standard for the RV assessment. Cardiac multidetector computed tomography could be a reliable alternative. The aim of this review is to focus on the growing importance of multimodality imaging of the ischemic right ventricle and to propose a diagnostic algorithm, in order to reach a comprehensive assessment of this too frequently neglected chamber.

Exogenous hormonal regulation in breast cancer cells by phytoestrogens and endocrine disruptors.

Observations on the role of ovarian hormones in breast cancer growth, as well as interest in contraception, stimulated research into the biology of estrogens. The identification of the classical receptors ERα and ERß and the transmembrane receptor GPER and the resolution of the structure of the ligand bound to its receptor established the principal molecular mechanisms of estrogen action. The presence of estrogen-like compounds in many plants used in traditional medicine or ingested as food ingredients, phytoestrogens, as well as the estrogenic activities of many industrial pollutants and pesticides, xenoestrogens, have prompted investigations into their role in human health. Phyto- and xenoestrogens bind to the estrogen receptors with a lower affinity than the endogenous estrogens and can compete or substitute the hormone. Xenoestrogens, which accumulate in the body throughout life, are believed to increase breast cancer risk, especially in cases of prenatal and prepuberal exposure whereas the role of phytoestrogens is still a matter of debate. At present, the application of phytoestrogens appears to be limited to the treatment of post-menopausal symptoms in women where the production of endogenous estrogens has ceased. In this review we discuss chemistry, structure and classification, estrogen signaling and the consequences of the interactions of estrogens, phytoestrogens and xenoestrogens with their receptors, the complex interactions of endogenous and exogenous ligands, the evaluation of the health risks related to xenoestrogens, and the perspectives toward the synthesis of potent third generation selective estrogen receptor modulators (SERMs).

Endocrine disruptor agent nonyl phenol exerts an estrogen-like transcriptional activity on estrogen receptor positive breast cancer cells.

Several substances widely dispersed in the environment including hormones, industrial by-products and pollutants exert hormone like activity affecting steroid-responsive physiological systems. These compounds, named endocrine disruptors, are suspected to affect the mammalian reproductive system. However it is still unclear whether these substances are able to elicit estrogen like activity at the low concentrations encountered in the environment. Here we compare the effects of the endocrine disruptor nonylphenol with the effects elicited by 17-ß-estradiol on gene transcription in the human breast cancer cell line MCF7. The correlation of the nonylphenol induced gene expression alterations with a reference profile of estradiol treated cells shows that nonylphenol at a concentration of 100 nM exerts a significant effect on estrogen responsive gene transcription in MCF7 cells. Most of the genes regulated by 17-ß-estradiol respond to the nonylphenol in the same direction though to a much lesser extent. Molecular modeling of the potential interaction of nonylphenol with the estrogen receptor α shows that nonylphenol is likely to bind to the estrogen receptor α.

Vibrational spectrum of solid picene (C22H14).

Recently, Mitsuhashi et al observed superconductivity with a transition temperature up to 18 K in potassium doped picene (C(22)H(14)), a polycyclic aromatic hydrocarbon compound (Mitsuhashi et al 2010 Nature 464 76). Theoretical analysis indicates the importance of electron-phonon coupling in the superconducting mechanisms of these systems, with different emphasis on inter- and intra-molecular vibrations, depending on the approximations used. Here we present a combined experimental and ab initio study of the Raman and infrared spectrum of undoped solid picene, which allows us to unambiguously assign the vibrational modes. This combined study enables the identification of the modes which couple strongly to electrons and hence can play an important role in the superconducting properties of the doped samples.

Cannabidiol inhibits angiogenesis by multiple mechanisms.

BACKGROUND AND PURPOSE: Several studies have demonstrated anti-proliferative and pro-apoptotic actions of cannabinoids on various tumours, together with their anti-angiogenic properties. The non-psychoactive cannabinoid cannabidiol (CBD) effectively inhibits the growth of different types of tumours in vitro and in vivo and down-regulates some pro-angiogenic signals produced by glioma cells. As its anti-angiogenic properties have not been thoroughly investigated to date, and given its very favourable pharmacological and toxicological profile, here, we evaluated the ability of CBD to modulate tumour angiogenesis. EXPERIMENTAL APPROACH: Firstly, we evaluated the effect of CBD on human umbilical vein endothelial cell (HUVEC) proliferation and viability - through [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay and FACS analysis - and in vitro motility - both in a classical Boyden chamber test and in a wound-healing assay. We next investigated CBD effects on different angiogenesis-related proteins released by HUVECs, using an angiogenesis array kit and an ELISA directed at MMP2. Then we evaluated its effects on in vitro angiogenesis in treated HUVECs invading a Matrigel layer and in HUVEC spheroids embedded into collagen gels, and further characterized its effects in vivo using a Matrigel sponge model of angiogenesis in C57/BL6 mice. KEY RESULTS: CBD induced HUVEC cytostasis without inducing apoptosis, inhibited HUVEC migration, invasion and sprouting in vitro, and angiogenesis in vivo in Matrigel sponges. These effects were associated with the down-modulation of several angiogenesis-related molecules. CONCLUSIONS AND IMPLICATIONS: This study reveals that CBD inhibits angiogenesis by multiple mechanisms. Its dual effect on both tumour and endothelial cells supports the hypothesis that CBD has potential as an effective agent in cancer therapy.

Diet-derived phytochemicals: from cancer chemoprevention to cardio-oncological prevention.

Cardiovascular diseases and cancer are the leading causes of death in most countries. These diseases share many common risk factors as well as pathogenetic determinants, and their incidence is related to age in an exponential manner. Furthermore, it has become apparent that several treatments used in therapy or even in prevention of cancer can impair the structural and functional integrity of the cardiovascular system, giving rise to an interdisciplinary field: cardio-oncology. However, tumors and cardiovascular diseases also share common protective factors: they can be prevented either by avoiding exposure to recognized risk factors, and/or by favoring the intake of protective compounds and by modulating the host defense machinery. These latter approaches are generally known as chemoprevention. A great variety of dietary and pharmacological agents have been shown to be potentially capable of preventing cancer in preclinical models, most of which are of plant origin. Phytochemicals, in particular diet-derived compounds, have therefore been proposed and applied in clinical trials as cancer chemopreventive agents. There is now increasing evidence that some phytochemicals can be also protective for the heart, having the potential to reduce cancer, cardiovascular disease and even anticancer drug-induced cardiotoxicity. We introduce the concept that these compounds induce pre-conditioning, a low level cellular stress that induces strong protective mechanisms conferring resistance to toxins such as cancer chemotherapeutics. Cancer cells and cardiomyocytes have fundamental differences in their metabolism and sensitivity to preconditioning, autophagy and apoptosis, so that dosage of the prevention compounds is important. Here we discuss the mechanisms responsible for the cardiotoxicity of anticancer drugs, the possibility to prevent them and provide examples of diet-derived phytochemicals and other biological substances that could be exploited for protecting the cardiovascular system according to a joint cardio-oncological preventative approach.

Cancer stem cells and the tumor microenvironment: soloists or choral singers.

The idea of cancer stem cell (CSC) has recently moved to the forefront of cancer research. There is still a lack of a widespread consensus on their description and definition. ,The increasing literature on CSCs has compelled researchers worldwide to rewrite the natural history of cancer including those cells as principal players as well as to revise their views on tumor formation and progression. CSCs are tumor cell components that can initiate a new tumor after an apparent therapeutic eradication. A functional definition of cancer stem cell or cancer initiating cell is that of a cell which, when transplanted in a mouse model, can give rise to a tumor recapitulating the original one or even a phenotypically diverse tumor related to the tumor of origin. Since the characteristic asymmetric division of stem cells is somewhat anomalous in cancer, it might be advisable to refer to them as "stemloids". Stemness in cancer is not as much as an identity but rather a status. There is increasing evidence of the importance of the tumor and the host micro-environment in conditioning the stem cell status itself. The cancer stem cell micro-environment may be the key in the development of therapeutic strategies. We must think in terms of targeting "standard" tumor cells, cancer stem cells, and also their niche and tumor micro-environment. Here we discuss some features of cancer stem cells, and the role of the micro-environment, envisaging a choral view of cancer stem cell development and-or latency, towards development of specific therapeutic approaches. Here we propose models of replication and quiescence and the modulation by cells, genes and miRNAs. We also summarize in a table surface makers useful for the identification and isolation of CSCs.

The tumor microenvironment: biology of a complex cellular and tissue society.

The tumor microenvironment is a "complex society" of many cell types and their extracellular matrix. All these cell types and the matrix take part to the generation of a tumor "tissue". It is well established that preneoplastic proliferating cells cannot give origin to a tumor without an appropriate blood supply. In fact, angiogenesis could be considered the rate limiting step of tumor growth. In this context microenvironment components play a pivotal role in the regulation of the angiogenic switch and in cancer progression. For these reasons the comprehension of biological and molecular mechanisms involved in the relationship between tumor cells and the microenvironment could unveil new therapeutic and preventive approaches to cancer. In this complex scenario molecular imaging of the microenvironment is crucial to dissect cellular and stromal dynamic contributions.

Cell delivery of Met docking site peptides inhibit angiogenesis and vascular tumor growth.

Hepatocyte growth factor (HGF) and its receptor Met are responsible for a wide variety of cellular responses, both physiologically during embryo development and tissue homeostasis, and pathologically, particularly during tumor growth and dissemination. In cancer, Met can act as an oncogene on tumor cells, as well as a pro-angiogenic factor activating endothelial cells and inducing new vessel formation. Molecules interfering with Met activity could be valuable therapeutic agents. Here we have investigated the antiangiogenic properties of a synthetic peptide mimicking the docking site of the Met carboxyl-terminal tail, which was delivered into the cells by fusion with the internalization sequences from Antennapedia or HIV-Tat. We showed that these peptides inhibit ligand-dependent endothelial cell proliferation, motility, invasiveness and morphogenesis in vitro to an even greater extent and with much less toxicity than the Met inhibitor PHA-665752, which correlated with interference of HGF-dependent downstream signaling. In vivo, the peptides inhibited HGF-induced angiogenesis in the matrigel sponge assay and impaired xenograft tumor growth and vascularization in Kaposi's sarcoma. These data show that interference with the Met receptor intracellular sequence impairs HGF-induced angiogenesis, suggesting the use of antidocking site compounds as a therapeutic strategy to counteract angiogenesis in cancer as well as in other diseases.

Growth factors and chemokines: a comparative functional approach between invertebrates and vertebrates.

Growth factors and cytokines control and coordinate a broad spectrum of fundamental cellular functions, and are evolutionarily conserved both in vertebrates and invertebrates. In this review, we focus our attention on the functional phylogenetic aspects of growth factors/cytokines like the Transforming Growth Factor-beta (TGF-beta), the Connective Tissue Growth Factor (CTGF), and the Vascular Endothelial Growth Factor (VEGF). We will also delve into the activites of two chemokine families, interleukin (IL)-8 (or CXCL8) and CC chemokine ligand 2/monocyte chemoattractant protein-1 (CCL2). These molecules have been selected for their involvement in immune responses and wound healing processes, where they mediate and finely regulate various regeneration processes like angiogenesis or fibroplasia, not only in vertebrates, but also in invertebrates.

Cytokines and chemokines as regulators of angiogenesis in health and disease.

The intricate interplay between the endothelium and immune cells has been well recognized in the context of immune responses. However, the fact that this inter-relation extends well beyond immune regulation is becoming increasingly recognized, with particular regards to the influence of the immune system on the essential endothelial process of angiogenesis, where the contribution of cytokines drives the angiogenic process. As angiogenesis is an important component of numerous pathological states, among these chronic inflammatory conditions and cancer, understanding the role of cytokines and chemokines in guiding new vessel formation provides key insight into novel therapeutic modalities. Here we review the actions of principal cytokines and chemokines on the angiogenic process and discuss how both can be considered potential pharmaceutical targets or pharmaceuticals themselves for modulation of angiogenesis in chronic inflammation associated with cancer, rheumatoid arthritis and other inflammatory diseases.

TRAIL inhibits angiogenesis stimulated by VEGF expression in human glioblastoma cells.

Tumour growth is tightly related to new blood vessel formation, tissue remodelling and invasiveness capacity. A number of tissular factors fuel the growth of glioblastoma multiforme, the most aggressive brain neoplasm. In fact, gene array analyses demonstrated that the proapoptotic cytokine tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) inhibited mRNA expression of VEGF, along with those of matrix metalloproteinase-2 (MMP-2), its inhibitor tissue inhibitor of matrix metalloproteinases-2 (TIMP-2), as well as the tumour invasiveness-related gene secreted protein acid rich in cysteine (SPARC) in different human glioblastoma cell lines. Particularly, VEGF mRNA and protein expression and release from glioblastoma cells were also inhibited by TRAIL. The latter also exerted antimitogenic effects on human umbilical vein endothelial cells (HUVECs). With the same cells, TRAIL inhibited new vessel formation in the in vitro matrigel model, as well as it exerted powerful inhibition of blood vessel formation induced by an angiogenic cocktail administered in subcutaneous pellets in vivo in the C57 mouse. Moreover, the expression of MMP-2, its inhibitor TIMP-2 and the tumour invasiveness-related protein SPARC were effectively inhibited by TRAIL in glioblastoma cell lines. In conclusion, our data indicate that TRAIL inhibits the orchestra of factors contributing to glioblastoma biological aggressiveness. Thus, the TRAIL system could be regarded as a molecular target to exploit for innovative therapy of this type of tumour.

The expression of CD154 by Kaposi's sarcoma cells mediates the anti-apoptotic and migratory effects of HIV-1-TAT protein.

Kaposi's sarcoma (KS) is a malignancy associated to conditions of immune system impairment such as HIV-1 infection and post-transplantation therapy. Here we report that HIV-1-Tat protein, at concentrations well below those detected in AIDS patients, up-regulates the expression of both CD40 and CD154 on KS cells. This occurred also in the presence of vincristine, that at doses shown to induce apoptosis decreased the expression of both CD40 and CD154 on KS cells. The treatment with a soluble CD40-muIg fusion protein (CD40 fp) that prevents the binding of CD154 with cell surface CD40, as well as the transfection with a vector for soluble CD40 (KS sCD40), decreased the anti-apoptotic effect of Tat. Moreover, Tat-induced motility of KS cells was inhibited by soluble CD40 fp. Tat also enhanced the expression of intracellular proteins known to transduce signals triggered by CD40 engagement, in particular TRAF-3. Tat as well as soluble CD154 (sCD154) prevented vincristine-induced reduction of TRAF-3 in KS cells transfected with a vector for neomycin resistance (KS psv-neo), but not in KS sCD40. Immunoprecipitation studies showed that Tat induced CD40 / TRAF-3 association and that this binding was abrogated upon the incubation with the soluble CD40 fp. These data suggest that Tat activates the CD40-CD154 pathway by enhancing the membrane expression of CD40 and in particular of CD154, and by activating the TRAF-3-dependent signaling pathway of CD40. These findings indicate that the CD40-CD154 pathway mediates the anti-apoptotic and migratory effects of HIV-1- Tat, suggesting the potential therapeutic benefits of blocking CD40 activation in HIV-1-associated KS.

Microarray expression profiles of angiogenesis-related genes predict tumor cell response to artemisinins.

Artemisinin (ARS) and its derivatives are used for the second-line therapy of malaria infections with Plasmodium falciparum and P. vivax. ARSs also reveal profound antitumor activity in vitro and in vivo. In the present investigation, we correlated the mRNA expression data of 89 angiogenesis-related genes obtained by microarray hybridization from the database of the US National Cancer Institute with the 50% growth inhibition concentration values for eight ARSs (ARS, arteether (ARE), artesunate (ART), artemisetene, arteanuine B, dihydroartemisinylester stereoisomers 1 and 2). The constitutive expression of 30 genes correlated significantly with the cellular response to ARSs. By means of hierarchical cluster analysis and cluster image mapping expression, profiles were identified that determined significantly the cellular response to ART, ARE, artemether and dihydroartemisinylester stereoisomer 1. We have exemplarily validated the microarray data of six out of these 30 genes by real-time RT-PCR in seven cell lines. The fact that sensitivity and resistance of tumor cells could be predicted by the mRNA expression of angiogenesis-related genes indicate that ARSs reveal their antitumor effects at least in part by inhibition of tumor angiogenesis. As many chemopreventive drugs exert antiangiogenic features, ARSs might also be chemopreventive in addition to their cytotoxic effects.

WT1 expression in angiogenic tumours of the skin.

AIMS: To determine the expression of WT1 in endothelial proliferations and tumours. Endothelial cells are derived from angioblasts which differentiate into bone marrow stem cells (BMSC). BMSC are characterized by the constitutive expression of the WT1 gene and we have postulated that its expression may be maintained during the differentiation of angioblasts to endothelial cells. METHODS AND RESULTS: The expression of WT1 was studied in human umbilical vein-derived (HUVEC) and brain microvascular endothelial cells (HBME) as well as in a Kaposi sarcoma (KS) cell line in vitro. Forty-two human skin biopsy samples of endothelial proliferations and tumours were analysed for the protein expression of WT1 using the monoclonal antibodies for wt-WT1 (6F-H2) and its 17AA+ variant (2C12). WT1 expression was detectable in HUVEC and KS cells and all WT1 splice variants examined (17AA+/- KTS+/-) were detectable in KS cells, while the 17AA+/- and KTS- variants were present in HUVEC. Immunohistochemical analysis of the 42 human skin biopsy samples revealed cytoplasmic WT1 expression using wild-type specific antibody (6FH2) in microvessels, which is maintained during neoangiogenesis (inflammation, haemorrhage, peritumoral angiogenesis). Around one-third of haemangiomas (3/10) and non-HIV-Kaposi sarcomas (7/18) expressed the WT1 protein in the cytoplasm of tumour cells compared with its frequent expression in angiosarcomas (7/8) using the same antibody (6FH2). The nuclear 17AA+ isoform of WT1 was detectable at protein level in a small proportion of KS cases exclusively (3/7). CONCLUSION: Our data suggest that WT1 protein expression is maintained during angiogenesis and malignant transformation of endothelial cells and can be considered as a new endothelial marker.

Expression of CD44v3 protein in human endothelial cells in vitro and in tumoral microvessels in vivo.

The most universal angiogenic cytokines (VEGF, bFGF, HGF) are all heparin-binding proteins, the function of which is dependent on cell surface heparan sulfate proteoglycans (HSPG). Several proteoglycans have been demonstrated in endothelial cells, but only glypican-1 from the cell surface HSPG subfamily was documented at protein level. Here, we show that CD44v3 is expressed in human immortalized endothelial cells [anchorage-dependent human umbilical vein endothelial cells (HUVEC) and anchorage-independent Kaposi sarcoma (KS-Imm)] at mRNA and protein level, but is absent from the primary culture of human brain microvascular endothelial cells. We have shown that CD44v3 has a large cytoplasmic pool in endothelial cells, but a limited surface expression, mainly at filopodia, colocalized with MMP-2. Angiogenic factors like VEGF or bFGF did not affect surface detection of CD44v3 suggesting a constitutive expression. The putative functional role for endothelial cell surface CD44v3 was identified in chemotaxis assay when anti-CD44v3 antibody pretreatment proved to be inhibitory for HUVEC. Furthermore, we provided evidence for the CD44v3 protein expression in human endothelial cells in vivo in peritumoral microvessels of both human melanoma and glottic cancers, suggesting a role for this part-time heparan sulfate proteoglycan in tumor induced angiogenesis.

Prevention of angiogenesis by naked DNA IL-12 gene transfer: angioprevention by immunogene therapy.

IL-12 is thought to induce a cytokine cascade with antiangiogenic effects mediated by IFN-gamma and angiostatic CXCR3 chemokine ligands. Naked DNA intramuscular injection of an expression vector plasmid producing IL-12 resulted in significant, well-tolerated elevation of serum IL-12 levels. Injection of the IL-12 plasmid at least 2 days, and up to 20 days, before subcutaneous injection of matrigel with angiogenic factors resulted in strong prevention of angiogenesis in both C57/bl and nude mice. A single injection of the IL-12 plasmid contemporarily with the matrigel or 2 days after resulted in partial, statistically not significant, inhibition. Control plasmid injection did not affect either angiogenesis or angiogenesis inhibition by IL-12 protein in vivo. Angiogenesis inhibition was observed in NK cell-depleted C57/bl and nude mice as well as in IFN-gamma(-/-) and CXCR3(-/-) knockout mice, indicating that NK- and/or T-cell-initiated IFN-gamma-chemokine cascades were not involved in the angiogenesis inhibition observed in vivo. Finally, IL-12 plasmid DNA gene transfer significantly prevented the growth and vascularization of highly angiogenic KS-Imm Kaposi's sarcoma and TS/A murine mammary carcinoma tumors in nude and/or syngeneic mice. These data suggest that a preventive gene therapy approach using antiangiogenic cytokines can effectively inhibit tumor angiogenesis and KS, representing an example of angioimmunoprevention.

Anti-angiogenesis and angioprevention: mechanisms, problems and perspectives.

The recognition that angiogenesis is a key early event in tumor progression and metastasis has led to the development of new strategies for cancer therapy. The generation of a new blood vessel network under physiological conditions is regulated by the concerted action of activators and inhibitors. Perturbation of this balance, as it occurs in solid tumor growth and metastasis, appears to be a critical point in tumorigenesis. This has led to the "angiogenic switch" hypothesis: the point at which a tumor acquires the potential to induce angiogenesis is a critical step towards malignancy. Based on experimental evidence, prevention of blood vessel development appears to be the mechanism of action of many successful chemopreventive drugs of natural or synthetic origin: a novel concept that we termed "angioprevention". The hypothesis that anti-angiogenesis is at the basis of tumor prevention also suggests that many anti-angiogenic drugs could be used for chemoprevention in higher risk populations or in early intervention. There is a growing body of experimental evidence that anti-angiogenic strategies will contribute to the future therapy of cancer, several compounds with anti-angiogenic properties are now under clinical investigation including anti-inflammatory compounds, as inflammation may play a key role in angiogenesis. We must persevere in the development of novel, powerful and safer angiogenesis inhibitors and in the use of anti-angiogenic drugs in combination with other natural or synthetic anti-cancer agents in a biological therapy strategy.

Antiangiogenic activity of chemopreventive drugs.

Tumors growing within the host form dynamic aberrant tissue that consists of host components, including the stroma, an expanding vasculature and often chronic inflammation, in addition to the tumor cells themselves. These host components can contribute to, rather than limit, tumor expansion, whereas deprivation of vessel formation has the potential to confine tumors in small, clinically silent foci. Therapeutic inhibition of vessel formation could be best suited to preventive strategies aimed at the suppression of angiogenesis in primary tumors in subjects at risk, or of micrometastases after surgical removal of a primary tumor. Our analysis of potential cancer chemopreventive molecules including N-acetylcysteine, green tea flavonoids and 4-hydroxyphenyl-retinamide has identified antiangiogenic activities that could account--at least in part--for the tumor prevention effects observed with these compounds. These drugs appear to target common mechanisms of tumor angiogenesis that may permit identification of critical targets for antiangiogenic therapy and antiangiogenic chemoprevention.

Somatostatin inhibits tumor angiogenesis and growth via somatostatin receptor-3-mediated regulation of endothelial nitric oxide synthase and mitogen-activated protein kinase activities.

Somatostatin was reported to inhibit Kaposi's sarcoma (KS) cell (KS-Imm) xenografts through an antiangiogenic activity. Here, we show that somatostatin blocks growth of established KS-Imm tumors with the same efficacy as adriamycin, a clinically effective cytotoxic drug. Whereas KS-Imm cells do not express somatostatin receptors (SSTRs), endothelial cells express several SSTRs, in particular SSTR3. We investigated the molecular mechanisms and receptor specificity of somatostatin inhibition of angiogenesis. Somatostatin significantly inhibited angiogenesis in vivo in the matrigel sponge assay; this inhibition was mimicked by the SSTR3 agonist L-796778 and reversed by the SSTR3 antagonist BN81658, demonstrating involvement of SSTR3. In vitro experiments showed that somatostatin directly affected different endothelial cell line proliferation through a block of growth-factor-stimulated MAPK and endothelial nitric oxide (NO) synthase (eNOS) activities. BN81658 reversed somatostatin inhibition of cell proliferation, NO production, and MAPK activity, indicating that SSTR3 activation is required for the effects of somatostatin in vitro. Finally in vivo angiogenesis assays demonstrated that eNOS inhibition was a prerequisite for the antiangiogenic effects of somatostatin, because high concentrations of sodium nitroprusside, an NO donor, abolished the somatostatin effects. In conclusion, we demonstrate that somatostatin is a powerful antitumor agent in vivo that inhibits tumor angiogenesis through SSTR3-mediated inhibition of both eNOS and MAPK activities.