Somatostatin, acting at receptor subtype 1, inhibits Rho activity, the assembly of actin stress fibers, and cell migration

Therapy Resistant Gastroenteropancreatic Neuroendocrine Tumors

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) are a heterogenous group of malignancies originating from neuroendocrine cells of the gastrointestinal tract, the incidence of which has been increasing for several decades. While there has been significant progress in the development of therapeutic options for patients with advanced or metastatic disease, these remain limited both in quantity and durability of benefit. This review examines the latest research elucidating the mechanisms of both up-front resistance and the eventual development of resistance to the primary systemic therapeutic options including somatostatin analogues, peptide receptor radionuclide therapy with lutetium Lu 177 dotatate, everolimus, sunitinib, and temozolomide-based chemotherapy. Further, potential strategies for overcoming these mechanisms of resistance are reviewed in addition to a comprehensive review of ongoing and planned clinical trials addressing this important challenge.

Inhibiting DNA methylation as a strategy to enhance adipose-derived stem cells differentiation: Focus on the role of Akt/mTOR and Wnt/β-catenin pathways on adipogenesis

Adipose-derived mesenchymal stem cells (ASCs) represent a valid therapeutic option for clinical application in several diseases, due to their ability to repair damaged tissues and to mitigate the inflammatory/immune response. A better understanding of the underlying mechanisms regulating ASC biology might represent the chance to modulate their in vitro characteristics and differentiation potential for regenerative medicine purposes. Herein, we investigated the effects of the demethylating agent 5-azacytidine (5-aza) on proliferation, clonogenicity, migration, adipogenic differentiation and senescence of ASCs, to identify the molecular pathways involved. Through functional assays, we observed a detrimental effect of 5-aza on ASC self-renewal capacity and migration, accompanied by actin cytoskeleton reorganization, with decreased stress fibers. Conversely, 5-aza treatment enhanced ASC adipogenic differentiation, as assessed by lipid accumulation and expression of lineage-specific markers. We analyzed the involvement of the Akt/mTOR, MAPK and Wnt/β-catenin pathways in these processes. Our results indicated impairment of Akt and ERK phosphorylation, potentially explaining the reduced cell proliferation and migration. We observed a 5-aza-mediated inhibition of the Wnt signaling pathway, this potentially explaining the pro-adipogenic effect of the drug. Finally, 5-aza treatment significantly induced ASC senescence, through upregulation of the p53/p21 axis. Our data may have important translational implications, by helping in clarifying the potential risks and advantages of using epigenetic treatment to improve ASC characteristics for cell-based clinical approaches.

Somatostatin Primes Endothelial Cells for Agonist-Induced Hyperpermeability and Angiogenesis In Vitro

Somatostatin is an inhibitory peptide, which regulates the release of several hormones, and affects neurotransmission and cell proliferation via its five G_i protein-coupled receptors (SST_1-5). Although its endocrine regulatory and anti-tumour effects have been thoroughly studied, little is known about its effect on the vascular system. The aim of the present study was to analyse the effects and potential mechanisms of somatostatin on endothelial barrier function. Cultured human umbilical vein endothelial cells (HUVECs) express mainly SST₁ and SST₅ receptors. Somatostatin did not affect the basal HUVEC permeability, but primed HUVEC monolayers for thrombin-induced hyperpermeability. Western blot data demonstrated that somatostatin activated the phosphoinositide 3-kinases (PI3K)/protein kinase B (Akt) and p42/44 mitogen-activated protein kinase (MAPK) pathways by phosphorylation. The HUVEC barrier destabilizing effects were abrogated by pre-treating HUVECs with mitogen-activated protein kinase kinase/extracellular signal regulated kinase (MEK/ERK), but not the Akt inhibitor. Moreover, somatostatin pre-treatment amplified vascular endothelial growth factor (VEGF)-induced angiogenesis (3D spheroid formation) in HUVECs. In conclusion, the data demonstrate that HUVECs under quiescence conditions express SST₁ and SST₅ receptors. Moreover, somatostatin primes HUVECs for thrombin-induced hyperpermeability mainly via the activation of MEK/ERK signalling and promotes HUVEC proliferation and angiogenesis in vitro.

Two neuroendocrine G protein-coupled receptor molecules, somatostatin and melatonin: Physiology of signal transduction and therapeutic perspectives

Recent studies have shown that G protein-coupled receptors (GPCRs), the largest signal-conveying receptor family, are targets for mutations occurring frequently in different cancer types. GPCR alterations associated with cancer development represent significant challenges for the discovery and the advancement of targeted therapeutics. Among the different molecules that can activate GPCRs, we focused on two molecules that exert their biological actions regulating many typical features of tumorigenesis such as cellular proliferation, survival, and invasion: somatostatin and melatonin. The modulation of signaling pathways, that involves these two molecules, opens an interesting scenario for cancer therapy, with the opportunity to act at different molecular levels. Therefore, the aim of this review is the analysis of the biological activity and the therapeutic potential of somatostatin and melatonin, displaying a high affinity for GPCRs, that interfere with cancer development and maintenance.

Large-scale gene analysis of rabbit atherosclerosis to discover new biomarkers for coronary artery disease

Atherosclerosis is the pathological basis of coronary artery disease (CAD) and causes high mortality. Thus, early detection is thought to be crucial in reducing the risk of CAD. Uncovering the mechanisms of the progression and regression of atherosclerosis will provide insights into discovering novel biomarkers to identify subjects at risk for CAD and improve prevention. We established atherosclerosis progression and regression in a rabbit model. Then, we extracted mRNA of the abdominal aorta from control, model and recovery groups to perform gene chip analysis. Candidate biomarkers were screened by large-scale gene analysis and validated in patients with CAD or with CAD recovery by ELISA. The differentially expressed genes in the progression and regression of atherosclerosis were mainly enriched in four clusters. Genes associated with inflammation and extracellular matrix were returned to normal or close-to-normal levels much earlier than genes associated with metabolism and sarcoplasmic proliferation, and they were maintained downregulated or upregulated after feeding a normal diet. We then selected four candidate biomarkers and found that lipoprotein lipase (LPL), bone morphogenetic protein 7 and somatostatin concentrations could indicate CAD diagnosis. In addition, LPL and macrophage cationic peptide 2 can be indicators of the prognosis of CAD. Molecular changes during the progression and regression of atherosclerosis in rabbits were revealed, and candidate regulators were identified. The identified factors could be used as novel biomarkers and targets for improving the diagnosis and prognosis of human CAD in the future.

Biological and Biochemical Basis of the Differential Efficacy of First and Second Generation Somatostatin Receptor Ligands in Neuroendocrine Neoplasms

Endogenous somatostatin shows anti-secretory effects in both physiological and pathological settings, as well as inhibitory activity on cell growth. Since somatostatin is not suitable for clinical practice, researchers developed synthetic somatostatin receptor ligands (SRLs) to overcome this limitation. Currently, SRLs represent pivotal tools in the treatment algorithm of neuroendocrine tumors (NETs). Octreotide and lanreotide are the first-generation SRLs developed and show a preferential binding affinity to somatostatin receptor (SST) subtype 2, while pasireotide, which is a second-generation SRL, has high affinity for multiple SSTs (SST₅ > SST₂ > SST₃ > SST₁). A number of studies demonstrated that first-generation and second-generation SRLs show distinct functional properties, besides the mere receptor affinity. Therefore, the aim of the present review is to critically review the current evidence on the biological effects of SRLs in pituitary adenomas and neuroendocrine tumors, by mainly focusing on the differences between first-generation and second-generation ligands.

International Union of Basic and Clinical Pharmacology. CV. Somatostatin Receptors: Structure, Function, Ligands, and New Nomenclature

Somatostatin, also known as somatotropin-release inhibitory factor, is a cyclopeptide that exerts potent inhibitory actions on hormone secretion and neuronal excitability. Its physiologic functions are mediated by five G protein-coupled receptors (GPCRs) called somatostatin receptor (SST)1-5. These five receptors share common structural features and signaling mechanisms but differ in their cellular and subcellular localization and mode of regulation. SST₂ and SST₅ receptors have evolved as primary targets for pharmacological treatment of pituitary adenomas and neuroendocrine tumors. In addition, SST₂ is a prototypical GPCR for the development of peptide-based radiopharmaceuticals for diagnostic and therapeutic interventions. This review article summarizes findings published in the last 25 years on the physiology, pharmacology, and clinical applications related to SSTs. We also discuss potential future developments and propose a new nomenclature.

Somatostatin receptor subtype 1 might be a predictor of better response to therapy in medullary thyroid carcinoma

PURPOSE

Medullary thyroid carcinoma (MTC) is a malignant neoplasm of parafollicular cells. Because it is a neuroendocrine tumor, it has known somatostatin receptors (SSTRs). The actual frequencies of the SSTR subtypes and their potential influences (by binding with endogenous somatostatin) on MTC cell proliferation have not been fully elucidated to date. The present study evaluated the occurrence of SSTR subtypes 1, 2, 3 and 5 as well as the possible role that each subtype plays in the clinical evolution of patients with MTC.

METHODS

This retrospective, longitudinal study analyzed thyroid surgical material from 42 patients with MTC. Immunohistochemical staining was performed with monoclonal antibodies against subtypes 1, 2, 3 and 5 of SSTR. The histological material was classified as negative, focal positive or diffuse positive, in relation to each of the SSTR subtypes. The initial response to treatment, clinical course and patient mortality rate were assessed and related to the presence of SSTR subtypes.

RESULTS

The most prevalent SSTR subtype was SSTR 3, which was found in 81% of the patients, when considering any pattern of positivity. However, subtype 2 had the lowest number of positive patients, with 28.6% demonstrating any positive pattern. Subtypes 1 and 5 had an intermediate prevalence of positivity, with subtype 1 present in 45.2% of the patients and subtype 5 positive in 54.8% of the patients, when considering any pattern of positivity. The presence of STR 1, in the form of diffuse positivity, independently predicted a better response to the initial therapy, with a hazard ratio (HR) of 4.80 (p = 0.03).

CONCLUSION

This is the first study to show the correlation of the presence of SSTR1, detected by monoclonal immunohistochemical techniques, and better response to initial treatment and possibly better long-term clinical response in patients with MTC. In addition, these patients had low positivity rates for SSTR2, which might explain the low sensitivity of diagnostic and limited therapeutic response to octrotide based radioisotopes.

Current and future medical treatments for patients with acromegaly

INTRODUCTION

Acromegaly is a relatively rare condition of growth hormone (GH) excess associated with significant morbidity and, when left untreated, high mortality. Therapy for acromegaly is targeted at decreasing GH and insulin-like growth hormone 1 levels, ameliorating patients' symptoms and decreasing any local compressive effects of the pituitary adenoma. The therapeutic options for acromegaly include surgery, medical therapies (such as dopamine agonists, somatostatin receptor ligands and the GH receptor antagonist pegvisomant) and radiotherapy. However, despite all these treatments option, approximately 50% of patients are not adequately controlled.

AREAS COVERED

In this paper, the authors discuss: 1) efficacy and safety of current medical therapy 2) the efficacy and safety of the new multireceptor-targeted somatostatin ligand pasireotide 3) medical treatments currently under clinical investigation (oral octreotide, ITF2984, ATL1103), and 4) preliminary data on the use of new injectable and transdermal/transmucosal formulations of octreotide.

EXPERT OPINION

This expert opinion supports the need for new therapeutic agents and modalities for patients with acromegaly.

Therapeutic uses of somatostatin and its analogues: Current view and potential applications

Somatostatin is an endogeneous cyclic tetradecapeptide hormone that exerts multiple biological activities via five ubiquitously distributed receptor subtypes. Classified as a broad inhibitory neuropeptide, somatostatin has anti-secretory, anti-proliferative and anti-angiogenic effects. The clinical use of native somatostatin is limited by a very short half-life (1 to 3min) and the broad spectrum of biological responses. Thus stable, receptor-selective agonists have been developed. The majority of these somatostatin therapeutic agonists bind strongly to two of the five receptor subtypes, although recently an agonist of wider affinity has been introduced. Somatostatin agonists are established in the treatment of acromegaly with recently approved indications in the therapy of neuroendocrine tumours. Potential therapeutic uses for somatostatin analogues include diabetic complications like retinopathy, nephropathy and obesity, due to inhibition of IGF-1, VEGF together with insulin secretion and effects upon the renin-angiotensin-aldosterone system. Wider uses in anti-neoplastic therapy may also be considered and recent studies have further revealed anti-inflammatory and anti-nociceptive effects. This review provides a comprehensive, current view of the biological functions of somatostatin and potential therapeutic uses, informed by the wide range of pharmacological advances reported since the last published review in 2004 by P. Dasgupta. The pharmacology of somatostatin receptors is explained, the current uses of somatostatin agonists are discussed, and the potential future of therapeutic applications is explored.

RhoA Kinase (Rock) and p90 Ribosomal S6 Kinase (p90Rsk) phosphorylation of the sodium hydrogen exchanger (NHE1) is required for lysophosphatidic acid-induced transport, cytoskeletal organization and migration

The sodium hydrogen exchanger isoform one (NHE1) plays a critical role coordinating asymmetric events at the leading edge of migrating cells and is regulated by a number of phosphorylation events influencing both the ion transport and cytoskeletal anchoring required for directed migration. Lysophosphatidic acid (LPA) activation of RhoA kinase (Rock) and the Ras-ERK growth factor pathway induces cytoskeletal reorganization, activates NHE1 and induces an increase in cell motility. We report that both Rock I and II stoichiometrically phosphorylate NHE1 at threonine 653 in vitro using mass spectrometry and reconstituted kinase assays. In fibroblasts expressing NHE1 alanine mutants for either Rock (T653A) or ribosomal S6 kinase (Rsk; S703A) we show that each site is partially responsible for the LPA-induced increase in transport activity while NHE1 phosphorylation by either Rock or Rsk at their respective site is sufficient for LPA stimulated stress fiber formation and migration. Furthermore, mutation of either T653 or S703 leads to a higher basal pH level and a significantly higher proliferation rate. Our results identify the direct phosphorylation of NHE1 by Rock and suggest that both RhoA and Ras pathways mediate NHE1-dependent ion transport and migration in fibroblasts.

Regulation of somatostatin receptor 4-mediated cytostatic effects by CD26 in malignant pleural mesothelioma

Background:

Malignant pleural mesothelioma (MPM) is an aggressive neoplasm arising from mesothelial lining of pleura. CD26 molecules preferentially expressed on epithelioid type of MPM. This study investigates the molecular mechanisms of CD26 regulating MPM cells in vitro and in vivo.

Methods:

Biochemical and cell biological approaches were used for identifying a novel molecular target of MPM. Its contribution to tumour expansion has been also assessed using animal models. The clinical samples of MPM were also assessed for its expression.

Results:

We identify that cytostatic effects in MPM are mediated by somatostatin (SST) receptor 4 (SSTR4), being inhibited by the interaction of CD26 molecules. We also indicates that SSTR4-mediated cytostatic effects are regulated by SHP-2 PTP, and that this inhibitory effect by SST agonist is enhanced via lipid raft clustering of associated molecules following crosslinking of anti-CD26 antibody. Finally, using an in vivo xenograft model, we demonstrate that the anti-tumour effect of anti-CD26 mAb is enhanced when combined with SSTR4 agonist treatment, and that SSTR4 is highly coexpressed with CD26 on epithelioid or biphasic types of MPM tissues obtained from patients' surgical specimens.

Conclusions:

Combination therapy with humanised anti-CD26 mAb and SSTR4 agonist may therefore potentiate anti-tumour effect on MPM.

Somatostatin analogs: does pharmacology impact antitumor efficacy?

Somatostatin is an endogenous inhibitor of secretion and cell proliferation. These features render somatostatin a logical candidate for the management of neuroendocrine tumors that express somatostatin receptors. Synthetic somatostatin analogs (SSAs) have longer half-lives than somatostatin, but have similar activities, and are used for the treatment of these types of disorders. Interest has focused on novel multireceptor analogs with broader affinity to several of the five somatostatin receptors, thereby presenting putatively higher antitumor activities. Recent evidence indicates that SSAs cannot be considered mimics of native somatostatin in regulating signaling pathways downstream of receptors. Here we review this knowledge, discuss the concept of biased agonism, and highlight what considerations need to be taken into account for the optimal clinical use of SSAs.

Somatostatin receptors: from signaling to clinical practice

Somatostatin is a peptide with a potent and broad antisecretory action, which makes it an invaluable drug target for the pharmacological management of pituitary adenomas and neuroendocrine tumors. Somatostatin receptors (SSTR1, 2A and B, 3, 4 and 5) belong to the G protein coupled receptor family and have a wide expression pattern in both normal tissues and solid tumors. Investigating the function of each SSTR in several tumor types has provided a wealth of information about the common but also distinct signaling cascades that suppress tumor cell proliferation, survival and angiogenesis. This provided the rationale for developing multireceptor-targeted somatostatin analogs and combination therapies with signaling-targeted agents such as inhibitors of the mammalian (or mechanistic) target of rapamycin (mTOR). The ability of SSTR to internalize and the development of rabiolabeled somatostatin analogs have improved the diagnosis and treatment of neuroendocrine tumors.

LIM kinase 1 (LIMK1) interacts with tropomyosin-related kinase B (TrkB) and Mediates brain-derived neurotrophic factor (BDNF)-induced axonal elongation

BDNF/TrkB signaling plays critical roles in axonal outgrowth of neurons, the process of which requires the remodeling of the cytoskeleton structure, including microtubules and filamentous actin. However, the mechanism by which BDNF/TrkB signaling regulates cytoskeleton reorganization is still unclear. Here, we identified a novel interaction between LIMK1 and TrkB, which is required for the BDNF-induced axonal elongation. We demonstrated that BDNF-induced TrkB dimerization led to LIMK1 dimerization and transphosphorylation independent of TrkB kinase activity, which could further enhance the activation and stabilization of LIMK1. Moreover, activated LIMK1 translocated to the membrane fraction and phosphorylated its substrate cofilin, thus promoting actin polymerization and axonal elongation. Our findings provided evidence of a novel mechanism for the BDNF-mediated signal transduction leading to axonal elongation.

Somatostatin receptors in non-neuroendocrine malignancies: the potential role of somatostatin analogs in solid tumors

Somatostatin receptors (sstrs) are G-protein-coupled receptors that mediate various physiological effects when activated by the neuropeptide somatostatin or its synthetic analogs. In addition to the well-documented antisecretory effects of sstr2-preferential somatostatin analogs octreotide and lanreotide, ligand binding to sstr initiates an inhibitory action on tumor growth. This effect may result from both indirect actions (suppression of growth factors and growth-promoting hormones [e.g., GH/IGF-1 axis] and inhibition of angiogenesis) and direct actions (activation of antigrowth activities [e.g., apoptosis]). As solid tumor cells express multiple sstrs, there is a rationale to evaluate the potential antitumor effects of pasireotide (SOM230), a multireceptor-targeted somatostatin analog with high binding affinity for sstr1–3 and sstr5. Pasireotide reduces systemic IGF-1 levels more potently than currently available somatostatin analogs and has been well tolerated in clinical trials.

Effects of somatostatin and octreotide on the interactions between neoplastic gastroenteropancreatic endocrine cells and endothelial cells: a comparison between in vitro and in vivo properties

BACKGROUND/AIMS

Experimental studies in vitro suggest that somatostatin and some of its analogues used in clinical practice, such as octreotide, may have potent antiangiogenic properties. However, the clinical transposition of these data is difficult.

METHODS

To address this issue, we designed a comparative study of the effects of somatostatin and octreotide on the interactions between neoplastic endocrine cells and endothelial cells in several in vitro and in vivo experimental models, including primary cultures of human umbilical vein endothelial cells (HUVEC), indirect cocultures between HUVEC and the somatostatin-producing endocrine cell line STC-1, and an animal model of intrahepatic dissemination of STC-1 cells.

RESULTS

10(-8)M octreotide markedly inhibited both basal and VEGF-stimulated HUVEC proliferation, had no effect on endothelial cell migration, but inhibited endothelial tubule formation. HUVEC cocultured with the somatostatin- and VEGF-producing STC-1 cells presented a markedly decreased proliferation, a slightly increased motility and an increased capacity of tubule formation; in this system, the inhibition of endothelial cell proliferation was abolished by neutralizing anti-somatostatin but was restored in the presence of anti-VEGF antibodies. This suggests that somatostatin is able to antagonize the effects of VEGF on endothelial cell proliferation but not on endothelial cell sprouting. Finally, no significant effect of octreotide on tumor growth and intratumoral microvascular density was detected in an experimental model of intrahepatic dissemination of STC-1 cells.

CONCLUSION

The in vitro antiangiogenic effects of somatostatin and its analogues are likely to be efficiently counterbalanced in the tumor microenvironment by the concomitant release of proangiogenic factors like VEGF.

Somatostatin and somatostatin receptors: implications for neoplastic growth and cancer biology

Somatostatin agonists (SM-As) are capable of achieving durable symptomatic relief and significant clinical responses in certain tumours. Herein, we review the diverse direct and indirect mechanisms of antineoplastic activity elicited by SM-As as well as the hurdles that complicate their use as monotherapies in a broader range of malignancies. Emphasis is placed on recent clinical attempts to neutralise the IGF-mediated survival factor effects in the bone metastasis microenvironment in advanced prostate cancer. The first clinical trials of this 'anti-survival factor manipulation' strategy utilised the ability of SM-As to suppress the growth hormone-dependent liver-derived IGF-I bioavailability in combination with other drugs, such as dexamethasone, zolendronate and oestrogens, acting systemically and at the bone metastasis microenvironment. These regimens restored androgen ablation responsiveness in stage D3 prostate cancer patients and successfully produced objective clinical responses while only mild toxicities were observed. Furthermore, we focus on the preclinical experimental data of a targeted SM-A coupled to the super-potent doxorubicin derivative AN-201. The resulting conjugate (AN-238) has shown increased antitumour potency with a favourable toxicity profile. The potential use of novel SM-As as anticancer drugs is discussed in relation to data suggesting other direct and indirect treatment approaches pertaining to the somatostatin system.

Somatostatin receptor subtype 1 is a PDZ ligand for synapse-associated protein 97 and a potential regulator of growth cone dynamics

We report that somatostatin receptor subtype 1 (sst1) associates in vivo and in vitro with synapse-associated protein SAP) 97, a membrane-associated guanylate kinase homolog implicated as a scaffolding protein in the structural organization of specialized membrane complexes in various tissues, including the CNS. SAP97 and sst1 were coimmuno-precipitated from rodent brain and from transfected human embryonic kidney (HEK) 293 cells, and pull-down experiments demonstrated that the interaction is dependent on the class I PDZ binding motif in sst1 carboxyterminus. Calorimetric titration indicated that the postsynaptic density-95/discs large/zona occludens-1 (PDZ) 2 domain of SAP97 provides the main contribution to the interaction. We noticed substantial sst1 immunoreactivity in differentiating cortical neurons in culture which declined as the cultures matured. The sst1 immunoreactivity extended, together with SAP97 to neuronal growth cones. Somatostatin (1 microM) triggered retraction of the filopodia and lamellipodia in the growth cones. This growth cone collapse was enhanced by overexpression of green fluorescent protein-tagged sst1, whereas sst1 mutant lacking the PDZ binding motif had no effect. These findings suggest a role for somatostatin signaling in the regulation of growth cone stability, which may involve PDZ domain proteins interacting with sst1 and/or other somatostatin receptors. Consistent with a developmental role, sst1 immunoreactivity was present transiently in the developing mouse cortex, peaking at postnatal day 5 and declining thereafter to low levels in the adult cortex.

In vitro antiangiogenic activity of selective somatostatin subtype-1 receptor agonists

BACKGROUND

Endothelial cells of human blood vessels (arteries and veins) show high levels of somatostatin subtype-1 receptor (sst(1)). The aim of the present study is to investigate the inhibitory effects of novel somatostatin analogs, highly selective for human sst(1), on in vitro angiogenesis and their modulation of vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptor-2 (VEGFR-2) expression.

MATERIALS AND METHODS

Somatostatin analogs BIM-23745 and BIM-23926 were tested for their ability to prevent proliferation and migration of human endothelial HMEC-1 cells, to modulate VEGF and VEGFR-2 expression and to inhibit sprouting of microvessels from cultured human placental vessel explants in fibrin matrix for 28 days.

RESULTS

The somatostatin sst(1 )receptor-selective agonists, BIM-23745 and BIM-23926 showed a suppression of endothelial proliferation (e.g. 10(-6) M BIM-23475, 40.0 +/- 2.1% vs. 100% of controls; 10(-7) M BIM-23926, 55.3 +/- 3.3% vs. 100% of controls), migration (e.g. 10(-7) M BIM-23475, 35.0 +/- 1.56% vs. 100% of controls; 10(-7) M BIM-23926, 53.7 +/- 1.77% vs. 100% of controls) and microvessel sprouting (e.g. 10(-8) M BIM-23475, 42.8 +/- 5.6% vs. 100% of controls; 10(-7) M BIM-23926, 17.2 +/- 11.8% vs. 100% of controls). A small but significant percentage of cells exposed to BIM-23745 and BIM-23926 for 24 h and for 72 h presented typical apoptotic morphology. Moreover, both the analogs significantly inhibit VEGF and VEGFR-2 gene expression in endothelial cells grown for 144 h in a fibrin matrix and the VEGF secretion in conditioned media.

CONCLUSIONS

The inhibition of endothelial activities suggests potential therapeutic utility for administration of somatostatin sst(1 )receptor-selective agonists in the proliferative diseases involving angiogenesis.

alpha(1)-Adrenergic receptor stimulation of cell motility requires phospholipase D-mediated extracellular signal-regulated kinase activation

Phospholipase D is suspected to play a role in tumorigenesis, and the inhibition of phospholipase D has been associated with changes in several cellular events including invasion and migration. We report here that the specific alpha(1)-adrenergic receptor agonist, phenylepherine, signals to a growth factor pathway in a manner that requires phospholipase D activity in CCL39 fibroblasts. Phenylepherine increased extracellular signal-regulated kinase phosphorylation eightfold and promoted stress fiber formation threefold. Stress fiber formation was blocked when extracellular signal-regulated kinase activation was inhibited. Stimulation of CCL39 fibroblasts by phenylepherine increased the rate of wound healing fourfold in a wounding assay, while treatment with the MEK inhibitor, PD98059 reduced the closure of phenylepherine-induced wound healing to control levels. Addition of 1-butanol but not 2-butanol inhibited extracellular signal-regulated kinase activation by phenylepherine, presumably by blocking the formation of phosphatidic acid. Exogenously added cell permeable phosphatidic acid increased extracellular signal-regulated kinase activation in a time- and dose-dependent manner as well as stimulated the formation of stress fibers. 1-butanol also significantly inhibited the ability of phenylepherine to stimulate stress fiber formation and wound healing. Taken together, these results indicate a novel role for phospholipase D in the activation of the extracellular signal-regulated kinase growth factor pathway to stimulate early cellular events induced by phenylepherine.

Differentiation-inducing activity of lupane triterpenes on a mouse melanoma cell line

Lupane triterpenes were found to promote melanogenesis, a hallmark of B16 2F2 mouse melanoma cell differentiation. Studies of the structure-activity relationships demonstrated that the keto function at C-3 of the lupane skeleton played important roles in the melanogenic activities of lupane triterpenes on melanoma cells. The carbonyl group at C-17 of lupane triterpenes was essential against their apoptosis-inducing activity against human cancer cells via the inhibition of topoisomerase I. We investigated whether signaling mechanisms were involved in the stimulative effects of lupane triterpenes on the melanogenesis of B16 2F2 cells. In experiments using selective inhibitors against various signal transduction molecules and Western blotting analysis, it was suggested that p38 MAPK was involved in melanoma cell differentiation as a downstream effector of PKA. Lupeol (compound 1), a lupane triterpene, induced dendrite formations, a morphological hallmark of B16 2F2 cell differentiation by rearrangement of the actin cytoskeleton. The activation of cofilin, an actin depolymerizing factor, by compound 1 caused actin fiber disassembly in B16 2F2 cells. Furthermore, compound 1 was shown to inhibit the cell motilities of human melanoma and neuroblastoma in vitro.

Is caveolin-1 a viable therapeutic target to reduce cancer metastasis?

Caveolin-1 is the major structural protein in caveolae; small Omega-shaped invaginations within the plasma membrane. Caveolae are involved in signal transduction, wherein caveolin-1 acts as a scaffold to organise multiple molecular complexes regulating a variety of cellular events. Caveolin-1 has both tumour suppressor and oncogenic activities. However, recent evidence suggests a role for caveolin-1 in promoting cancer cell migration and metastasis with both loss and overexpression of caveolin-1 being described as a marker for progression in a variety of tumour types. Further studies are beginning to determine the molecular mechanisms by which caveolin-1 acts in promoting a metastatic phenotype. Targeting caveolin-1 expression may present a novel means of preventing metastasis. The purpose of this review is twofold: firstly, to survey the current knowledge of the contribution of caveolin-1 in promoting a metastasis, and secondly, to explore the viability of targeting caveolin-1 with novel therapeutics.

Remodeling of Actin Cytoskeleton in Lupeol-Induced B16 2F2 Cell Differentiation

Lupeol induces the formation of dendrites in B16 2F2 melanoma cells. The remodeling of cytoskeletal components contributes to the dendricity of melanoma cells. We studied the effects of lupeol on the remodeling of cytoplasmic filaments in B16 2F2 cells. Western blotting revealed no change in the levels of actin and tubulin. Lupeol attenuated stress fiber assembly, but did not promote the remodeling of microtubular networks. We examined the activation of cofilin, an actin-depolymerizing factor, in lupeol-treated B16 2F2 cells by western blotting. The level of phospho-cofilin was found to decrease in a time-dependent manner. Inhibition of p38 MAPK by SB203580 blocked tyrosinase induction by lupeol, but did not influence the disruption of stress fiber assembly or the dephosphorylation of cofilin. Furthermore, we studied the effects of lupeol on cell migration. At 10 microM, lupeol markedly inhibited the haptotaxis of B16 2F2 cells to fibronectin. Additionally, lupeol strongly inhibited the migration of human melanoma and neuroblastoma cells, and weakly suppressed the migration of lung adenocarcinoma cells. However, lupeol did not affect the motility of other cancer cells. The results suggest that lupeol suppresses the migration of malignant melanoma cells by disassembling the actin cytoskeleton.

Systemic distribution of somatostatin receptor subtypes in human: an immunohistochemical study

Somatostatin is well known to inhibit the hormone secretion of various peptides. This action has been considered to be generally mediated via six different specific somatostatin receptors (sstr), sstr1, sstr2A, sstr2B, sstr3, sstr4, and sstr5. It then becomes very important to demonstrate the localization of these sstr subtypes in order to elucidate the possible biological and/or clinical significance of somatostatin actions. These sstr subtypes have been demonstrated to be expressed throughout the human body, including the central nervous system, gastrointestinal tract, pancreas, kidney, and other organs, but its details, especially its systemic distribution and localization in tissue compartments, have yet to be examined thoroughly in human. Therefore, in this study, we examined the systemic localization of all six somatostatin receptors in normal human organs using immunohistochemistry with recently developed specific antibodies against these receptor subtypes. In all of the human tissues examined, various sstr subtypes were detected not only in parenchymal cells but also in various stromal cells such as lymphocytes, fibroblasts, and endothelial cells. Among human tissues in which the presence of sstr has not been previously reported, the parotid gland demonstrated immunoreactivity for sstr2B and sstr5, bronchial gland for sstr1, 2B, 3, 4, 5, parathyroid gland for sstr1, 3, 4, and duodenum for all subtypes immunoreactivity. The great majority of other organs examined demonstrated results consistent with those of previously reported biochemical studies. In pancreatic islet cells, only sstr2A was positive in all the cases but other sstr subtypes were associated with marked intraislet heterogeneity in their distribution. In stomach, all subtypes of receptor were detected in various cell types of the mucosa, but none in ECL cells of fundic gland. These findings demonstrated the broad systemic actions of somatostatin in non-endocrine cells.

Gene deregulation in gastric cancer

Despite its decreasing frequency in the Western world during recent decades, gastric cancer is still one of the leading causes of cancer-related deaths worldwide. Due to the oligosymptomatic course of early gastric cancer, most cases are diagnosed in the advanced stages of the disease. The curative potential of current standard treatment continues to be unsatisfactory, despite multimodal approaches involving surgery, chemotherapy and radiotherapy. Novel therapeutics including small molecules and monoclonal antibodies are being developed and have been partially introduced into clinical use in connection with neoplastic diseases such as chronic myeloid leukemia, non-Hodgkin's lymphoma and colorectal cancer. Thorough understanding of the changes in gene expression occurring during gastric carcinogenesis may help to develop targeted therapies and improve the treatment of this disease. Novel molecular biology techniques have generated a wealth of data on up- and down-regulation, activation and inhibition of specific pathways in gastric cancer. Here, we provide an overview of the different aspects of aberrant gene expression patterns in gastric cancer.

Differential regulation of somatostatin receptors 1 and 2 mRNA and protein expression by tamoxifen and estradiol in breast cancer cells

Somatostatin (SST) inhibition of hormone hypersecretion from tumors is mediated by somatostatin receptors (SSTRs). SSTRs also play an important role in controlling tumor growth through specific antiproliferative actions. These receptors are well expressed in numerous normal and tumor tissues and are susceptible to regulation by a variety of factors. Estradiol, a potent trophic and mitogenic hormone in its target tissues, is known to modulate the expression of SST and its receptors. Accordingly, in the present study, we determined the effects of tamoxifen, a selective estrogen receptor (ER) modulator (SERM), and estradiol on SSTR1 and SSTR2 expression at the mRNA and protein levels in ER-positive and -negative breast cancer cells. We found that SSTR1 was upregulated by tamoxifen in a dose-dependent manner but no effect was seen with estradiol. In contrast, SSTR2 was upregulated by both tamoxifen and estradiol. Combined treatment caused suppression of SSTR1 below control levels but had no significant effect on SSTR2. Treatment with SSTR1-specific agonist was significantly more effective in suppressing cell proliferation of cells pre-treated with tamoxifen. Taking these data into consideration, we suggest that tamoxifen and estradiol exert variable effects on SSTR1 and SSTR2 mRNA and protein expression and distributional pattern of the receptors. These changes are cell subtype-specific and affect the ability of SSTR agonists to inhibit cell proliferation.

Somatostatin receptors 2 and 5 are preferentially expressed in proliferating endothelium

Angiogenesis is characterised by activation, migration and proliferation of endothelial cells and is central to the pathology of cancer, cardiovascular disease and chronic inflammation. Somatostatin is an inhibitory polypeptide that acts through five receptors (sst 1, 2, 3, 4, 5). Sst has previously been reported in endothelium, but their role remains obscure. Here, we report the expression of sst in human umbilical vein endothelial cells (HUVECs) in vitro, during proliferation and quiescence. A protocol for culturing proliferating and quiescent HUVECs was established, and verified by analysing cell cycle distribution in propidium-iodide-stained samples using flow cytometry. Sst mRNA was then quantified in nine proliferating and quiescent HUVEC lines using quantitative reverse transcriptase–polymerase chain reaction. Sst 2 and 5 were preferentially expressed in proliferating HUVECs. All samples were negative for sst 4. Sst 1 and 3 expression and cell cycle progression were unrelated. Immunostaining for sst 2 and 5 showed positivity in proliferating but not quiescent cells, confirming sst 2 and 5 protein expression. Inhibition of proliferating cells with somatostatin analogues Octreotide and SOM230, which have sst 5 activity, was found (Octreotide 10⁻¹⁰–10⁻⁶ M: 48.5–70.2% inhibition; SOM230 10⁻⁹–10⁻⁶ M: 44.9–65.4% inhibition) in a dose-dependent manner, suggesting that sst 5 may have functional activity in proliferation. Dynamic changes in sst 2 and 5 expression during the cell cycle and the inhibition of proliferation with specific analogues suggest that these receptors may have a role in angiogenesis.

Inhibition of endothelial proliferation by the somatostatin analogue SOM230

OBJECTIVE

Somatostatin (SST) modulates exocrine and endocrine secretion, proliferation and apoptosis via five G protein-linked receptors (SSTRs 1-5). Long-acting SST analogues such as Octreotide, and the new analogue SOM230, have been developed for the treatment of neuroendocrine tumours. Octreotide has previously been reported to inhibit endothelial proliferation. We wished to determine if SOM230 is a more potent inhibitor of endothelial cell proliferation than Octreotide.

DESIGN

We have determined the expression of SSTRs in proliferating human umbilical vein endothelial cells (HUVECs) in vitro, and determined their response to the somatostatin analogues SOM230 and Octreotide, following vascular endothelial growth factor (VEGF) stimulation.

MEASUREMENTS

Quantitative RT-PCR and western blotting were used to determine the expression of SSTRs 1-5 in proliferating HUVECs. These cells were grown in media containing 200 pg/ml VEGF and treated with 10(-11) to 10(-6) M Octreotide or SOM230. The WST-1 assay was then used to determine the effects of these analogues on HUVEC proliferation.

RESULTS

Using quantitative RT-PCR and western blotting, HUVECs were found to express SSTRs 1, 2 and 5. SSTRs 3 and 4 were not detected. Using the WST-1 assay, SOM230 was found to significantly inhibit proliferation by up to 46.0% +/- 9.4% (10(-6)-10(-7) M; P < 0.05), whereas in parallel studies Octreotide failed to inhibit HUVEC proliferation.

CONCLUSIONS

The pan SST analogue SOM230 inhibits proliferation of HUVECs, which are unaffected by Octreotide. SOM230 may thus represent a suitable candidate drug for antiangiogenic therapy.

Helicobacter pylori infection targets adherens junction regulatory proteins and results in increased rates of migration in human gastric epithelial cells

The human gastric pathogen Helicobacter pylori attaches to antral epithelial cells in vivo. Cultured human antral epithelial cells, AGS and NCI-N87 cell lines, were grown in the absence or presence of H. pylori and compared with respect to gene transcript levels, protein expression, organization of the actin cytoskeleton, and the regulation of cell migration. The Clontech Neurobiology array detected differentially expressed transcripts, while Western blots were used to investigate related changes in protein levels. Infection with H. pylori consistently upregulated annexin II, S100 A7, Rho-GTP, and IQGAP-1, whereas SSTR-1 was downregulated upon H. pylori infection. In the adherens junction, E-cadherin and IQGAP-1 were translocated from the plasma membrane to intracellular vesicles. The primary and NCI-N87 cells were similar with respect to cell-cell and cell-matrix adhesion and cell migratory behavior; in contrast the AGS cells were significantly different from the primary gastric epithelial cell preparations, and thus caution must be used when using this cell line for studies of gastric disease. These studies demonstrate a correlation between H. pylori infection and alterations to epithelial cell adhesion molecules, including increased levels of Rho-GTP and cell migration. These data indicate that destabilizing epithelial cell adherence is one of the factors increasing the risk of H. pylori-infected individuals developing gastric cancer.

Somatostatin analogues: multiple roles in cellular proliferation, neoplasia, and angiogenesis

Angiogenesis, the development of new blood vessels is a crucial process both for tumor growth and metastatic dissemination. Additionally, dysregulation in angiogenesis has been implicated in the pathogenesis of cardiovascular disease, proliferative retinopathy, diabetic nephropathy, and rheumatoid arthritis (RA). The neuropeptide somatostatin has been shown to be a powerful inhibitor of neovascularization in several experimental models. Furthermore, somatostatin receptors (sst) are expressed on endothelial cells; particularly, sst2 has been found to be uniquely up-regulated during the angiogenic switch, from quiescent to proliferative endothelium. The present manuscript reviews the anti-angiogenic activity of somatostatin and its analogues in neoplastic and nonneoplastic disease. The role of sst subtypes particularly sst2 in mediating its angioinhibitory activity is described. Somatostatin agonists may also exert their anti-angiogenic activity indirectly by inhibition of growth factors like vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis or through its immunomodulatory effects. However, the therapeutic utility of somatostatin agonists as anti-angiogenic drugs in these diseases remains confusing because of conflicting results from different studies. More basic research, as well as patient-oriented studies, is required to firmly establish the clinical potential of somatostatin agonists in therapeutic angiogenesis. The currently available somatostatin agonists have high affinity of sst2 with lower affinities for sst3 and sst5. The emergence of novel somatostatin agonists especially bispecific analogues (agonists targeting multiple cellular receptors) and conjugates (synthesized by chemically linking somatostatin analogues with other antineoplastic agents) with improved receptor specificity signify a new generation of anti-angiogenics, which may represent novel strategies in the treatment of neovascularization-related diseases.

Galphaz inhibits serum response factor-dependent transcription by inhibiting Rho signaling

Galpha12/13 or Galphaq signals induce activation of Rho GTPase, leading to serum response factor (SRF)-mediated gene transcription and actin cytoskeletal organization; however, less is known regarding how Rho pathway signals are down-regulated. Here we report that Galphaz signals inhibit serum response factor (SRF)-dependent transcription. Galphaz expression inhibits Galpha12/13-, Galphaq-, and Rho guanine nucleotide exchange factor (GEF)-induced serum response element (SRE) reporter activation in human embryonic kidney 293T and PC-12 cells. Expression of Galphaz mutants with defective fatty acylation has no inhibitory effect. Expression of Galphaz, but not Galphai, attenuates serum-induced SRE reporter activation, suggesting that Galphaz can down-regulate endogenous signals leading to SRF. Whereas Galphaz also blocks SRE reporter induction by the activated mutant RhoAL63, it does not affect Galpha12- or Rho GEF-induced RhoA activation or RhoAL63-GTP binding in vivo. Moreover, Galphaz does not inhibit SRE reporter induction by an activated form of Rho kinase. Because Galphaz inhibits RhoAL63/A188-induced reporter activation, phosphorylation of RhoA on serine 188 does not seem to be involved; furthermore, RhoA subcellular localization was not affected. Use of pharmacologic inhibitors implies that Galphaz-induced reduction of SRE reporter activation occurs via a mechanism other than adenylate cyclase modulation. These findings suggest that Galphaz signals may attenuate Rho-induced stimulation of SRF-mediated transcription.

Molecular signaling of somatostatin receptors

Somatostatin is a neuropeptide family that is produced by neuroendocrine, inflammatory, and immune cells in response to different stimuli. Somatostatin acts as an endogenous inhibitory regulator of various cellular functions including secretions, motility, and proliferation. Its action is mediated by a family of G-protein-coupled receptors (called sst1-sst5) that are widely distributed in the brain and periphery. The five receptors bind the natural peptides with high affinity, but only sst2, sst5, and sst3 bind the short synthetic analogs used to treat acromegaly and neuroendocrine tumors. This review covers the current knowledge in somatostatin receptor biology and signaling.

Somatostatin receptors and regulation of cell proliferation

Somatostatin is an inhibitory neuropeptide, which acts on various targets throughout the body to regulate a variety of physiological functions including inhibition of endocrine and exocrine secretions, modulation of neurotransmission, motor and cognitive functions, inhibition of intestinal motility, absorption of nutrients and ions, vascular contractility and inhibition of normal and tumour cell proliferation. It exerts its effects through interaction with five somatostatin receptors (sst1-sst5), which belong to the family of G-protein-coupled receptors with seven transmembrane spanning domains and are variably expressed in a variety of tumours such as gastroenteropancreatic tumours, pituitary tumours, and carcinoid tumours. This review covers the present knowledge regarding the molecular mechanisms involved in somatostatin antineoplastic activity. Evidence that sst2 receptor acts as a tumour suppressor is also discussed.

Role of Rho in rabbit parietal cell

Rho is known as an important regulator of actin microfilament formation. We were led to study it because a dynamic rearrangement of actin filaments occurs during activation of gastric acid secretion. In order to use specific probes, the rabbit gastric gland culture system was employed and the various genes were expressed using adenovirus vector. When the constitutive active mutant of Rho (RhoAV14) was expressed, histamine- or carbachol-stimulated acid secretion monitored by (14)C-aminopyrine accumulation was inhibited. Conversely, expression of C3 toxin, the specific inhibitor of Rho, and expression of G(12/13)-specific regulator of G-protein signaling domain, the specific inhibitor of G(12/13) which is considered to be an upstream mediator of Rho, both potentiated acid secretion stimulated by the agonists. F-actin staining of parietal cell expressing RhoAV14 revealed that the microfilament supporting the intracellular canaliculi (not on the basolateral membrane) almost disappeared. No clear changes in the intracellular localization of Rho were observed during stimulation of parietal cell. In resting glands, the endogenous active form of Rho was relatively high, and it decreased during histamine stimulation. The finding that any treatment which inhibit Rho augment acid secretion whereas those that activate Rho inhibit secretion strongly suggests that the Rho-pathway conducts a negatively regulating signal in parietal cell activation, possibly via site-specific regulation of actin microfilaments.

Pharmacological rationale for the use of somatostatin and analogues in portal hypertension

Somatostatin and its analogue octreotide have been used for two decades to treat oesophageal variceal haemorrhage. The drug was introduced because of its capacity to decrease portal venous pressure without major side effects. In clinical trials assessing the efficacy of somatostatin and long-acting analogues in arresting variceal haemorrhage, conflicting results have been obtained. Furthermore, in haemodynamic studies evaluating the effects of somatostatin and analogues in patients with cirrhosis, divergent effects were observed. The main reason for these differences is probably related to different affinities of the drugs for different somatostatin receptor subtypes. The effects of somatostatin and analogues are mediated via five different G-protein coupled receptors (somatostatin receptor subtypes 1-5), which regulate the activity of ion channels (Ca2+, K+, Na+ and Cl-) and enzymes (adenyl cyclase, phospholipase C, phospholipase A2, phosphoinositide 3-kinase and guanylate cyclase) responsible for the synthesis or degradation of intracellular second messengers including cyclic AMP, inositol 1,4,5-trisphosphate, diacylglycerol and cyclic GMP. Despite universal use of somatostatin, the cellular and biochemical mechanisms of its effects in portal hypertension are relatively poorly studied and remain incompletely understood. In this review, we summarize relevant signal transduction of somatostatin and analogues, the haemodynamic effects of the drugs and the possible mechanisms by which these effects are mediated.