Discovery of 4-(3-aminopyrrolidinyl)-3-aryl-5-(benzimidazol-2-yl)-pyridines as potent and selective SST5 agonists for the treatment of congenital hyperinsulinism.

SST5 receptor activation potently inhibits insulin secretion from pancreatic ß-cells, and an orally available nonpeptide selective SST5 agonist may be used to effectively manage the blood glucose levels of congenital HI patients to avoid severe hypoglycemia. Our medicinal chemistry efforts have led to the discovery of 4-(3-aminopyrrolidinyl)-3-aryl-5-(benzimidazol-2-yl)-pyridine analogs as potent SST5 agonists. This class of molecules exhibits excellent human SST5 potency and selectivity against SST1, SST2, SST3 and SST4 receptors. Leading compound 3-{4-[(3S)-3-aminopyrrolidin-1-yl]-5-(4-methyl-1H-1,3-benzodiazol-2-yl)pyridin-3-yl-5-fluorobenzonitrile (28, CRN02481) showed limited off-target activity and good pharmacokinetic profiles in both male Sprague Dawley rats and Beagle dogs to advance into further preclinical evaluations.

Somatostatin contributes to long-term potentiation at excitatory synapses onto hippocampal somatostatinergic interneurons.

Somatostatin-expressing interneurons (SOM-INs) are a major subpopulation of GABAergic cells in CA1 hippocampus that receive excitation from pyramidal cells (PCs), and, in turn, provide feedback inhibition onto PC dendrites. Excitatory synapses onto SOM-INs show a Hebbian long-term potentiation (LTP) mediated by type 1a metabotropic glutamate receptors (mGluR1a) that is implicated in hippocampus-dependent learning. The neuropeptide somatostatin (SST) is also critical for hippocampal long-term synaptic plasticity, as well as learning and memory. SST effects on hippocampal PCs are well documented, but its actions on inhibitory interneurons remain largely undetermined. In the present work, we investigate the involvement of SST in long-term potentiation of CA1 SOM-IN excitatory synapses using pharmacological approaches targeting the somatostatinergic system and whole cell recordings in slices from transgenic mice expressing eYFP in SOM-INs. We report that application of exogenous SST14 induces long-term potentiation of excitatory postsynaptic potentials in SOM-INs via somatostatin type 1-5 receptors (SST1-5Rs) but does not affect synapses of PC or parvalbumin-expressing interneurons. Hebbian LTP in SOM-INs was prevented by inhibition of SSTRs and by depletion of SST by cysteamine treatment, suggesting a critical role of endogenous SST in LTP. LTP of SOM-IN excitatory synapses induced by SST14 was independent of NMDAR and mGluR1a, activity-dependent, and prevented by blocking GABAA receptor function. Our results indicate that endogenous SST may contribute to Hebbian LTP at excitatory synapses of SOM-INs by controlling GABAA inhibition, uncovering a novel role for SST in regulating long-term synaptic plasticity in somatostatinergic cells that may be important for hippocampus-dependent memory processes.

MECHANISMS IN ENDOCRINOLOGY: The physiology of neuronostatin.

In 2008, the first evidence of a new hormone called neuronostatin was published. The hormone was discovered using a bioinformatic method and found to originate from the same preprohormone as somatostatin. This small peptide hormone of 13 amino acids and a C-terminal amidation was soon found to exert pleiotropic physiological effects. In animal studies, neuronostatin has been shown to reduce food intake and delay gastric emptying and gastrointestinal transit. Furthermore, neuronostatin has been shown to affect glucose metabolism by increasing glucagon secretion during situations when glucose concentrations are low. Additionally, neuronostatin has been shown to affect neural tissue and cardiomyocytes by suppressing cardiac contractility. The effects of neuronostatin have not yet been delineated in humans, but if the effects found in animal studies translate to humans it could position neuronostatin as a promising target in the treatment of obesity, hypertension and diabetes. In this review, we describe the discovery of neuronostatin and the current understanding of its physiological role and potential therapeutic applicability.

Versatile Functions of Somatostatin and Somatostatin Receptors in the Gastrointestinal System.

Somatostatin (SST) and somatostatin receptors (SSTRs) play an important role in the brain and gastrointestinal (GI) system. SST is produced in various organs and cells, and the inhibitory function of somatostatin-containing cells is involved in a range of physiological functions and pathological modifications. The GI system is the largest endocrine organ for digestion and absorption, SST-endocrine cells and neurons in the GI system are a critical effecter to maintain homeostasis via SSTRs 1-5 and co-receptors, while SST-SSTRs are involved in chemo-sensory, mucus, and hormone secretion, motility, inflammation response, itch, and pain via the autocrine, paracrine, endocrine, and exoendocrine pathways. It is also a power inhibitor for tumor cell proliferation, severe inflammation, and post-operation complications, and is a first-line anti-cancer drug in clinical practice. This mini review focuses on the current function of producing SST endocrine cells and local neurons SST-SSTRs in the GI system, discusses new development prognostic markers, phosphate-specific antibodies, and molecular imaging emerging in diagnostics and therapy, and summarizes the mechanism of the SST family in basic research and clinical practice. Understanding of endocrines and neuroendocrines in SST-SSTRs in GI will provide an insight into advanced medicine in basic and clinical research.

Input-Specific Synaptic Location and Function of the α5 GABAA Receptor Subunit in the Mouse CA1 Hippocampal Neurons.

Hippocampus-dependent learning processes are coordinated via a large diversity of GABAergic inhibitory mechanisms. The α5 subunit-containing GABAA receptor (α5-GABAAR) is abundantly expressed in the hippocampus populating primarily the extrasynaptic domain of CA1 pyramidal cells, where it mediates tonic inhibitory conductance and may cause functional deficits in synaptic plasticity and hippocampus-dependent memory. However, little is known about synaptic expression of the α5-GABAAR and, accordingly, its location site-specific function. We examined the cell- and synapse-specific distribution of the α5-GABAAR in the CA1 stratum oriens/alveus (O/A) using a combination of immunohistochemistry, whole-cell patch-clamp recordings and optogenetic stimulation in hippocampal slices obtained from mice of either sex. In addition, the input-specific role of the α5-GABAAR in spatial learning and anxiety-related behavior was studied using behavioral testing and chemogenetic manipulations. We demonstrate that α5-GABAAR is preferentially targeted to the inhibitory synapses made by the vasoactive intestinal peptide (VIP)- and calretinin-positive terminals onto dendrites of somatostatin-expressing interneurons. In contrast, synapses made by the parvalbumin-positive inhibitory inputs to O/A interneurons showed no or little α5-GABAAR. Inhibiting the α5-GABAAR in control mice in vivo improved spatial learning but also induced anxiety-like behavior. Inhibiting the α5-GABAAR in mice with inactivated CA1 VIP input could still improve spatial learning and was not associated with anxiety. Together, these data indicate that the α5-GABAAR-mediated phasic inhibition via VIP input to interneurons plays a predominant role in the regulation of anxiety while the α5-GABAAR tonic inhibition via this subunit may control spatial learning.SIGNIFICANCE STATEMENT The α5-GABAAR subunit exhibits high expression in the hippocampus, and regulates the induction of synaptic plasticity and the hippocampus-dependent mnemonic processes. In CA1 principal cells, this subunit occupies mostly extrasynaptic sites and mediates tonic inhibition. Here, we provide evidence that, in CA1 somatostatin-expressing interneurons, the α5-GABAAR subunit is targeted to synapses formed by the VIP- and calretinin-expressing inputs, and plays a specific role in the regulation of anxiety-like behavior.

Distinct learning-induced changes in stimulus selectivity and interactions of GABAergic interneuron classes in visual cortex.

How learning enhances neural representations for behaviorally relevant stimuli via activity changes of cortical cell types remains unclear. We simultaneously imaged responses of pyramidal cells (PYR) along with parvalbumin (PV), somatostatin (SOM), and vasoactive intestinal peptide (VIP) inhibitory interneurons in primary visual cortex while mice learned to discriminate visual patterns. Learning increased selectivity for task-relevant stimuli of PYR, PV and SOM subsets but not VIP cells. Strikingly, PV neurons became as selective as PYR cells, and their functional interactions reorganized, leading to the emergence of stimulus-selective PYR-PV ensembles. Conversely, SOM activity became strongly decorrelated from the network, and PYR-SOM coupling before learning predicted selectivity increases in individual PYR cells. Thus, learning differentially shapes the activity and interactions of multiple cell classes: while SOM inhibition may gate selectivity changes, PV interneurons become recruited into stimulus-specific ensembles and provide more selective inhibition as the network becomes better at discriminating behaviorally relevant stimuli.

Optogenetic dissection of roles of specific cortical interneuron subtypes in GABAergic network synchronization.

KEY POINTS: An increase in the excitability of GABAergic cells has typically been assumed to decrease network activity, potentially producing overall anti-epileptic effects. Recent data suggest that inhibitory networks may actually play a role in initiating epileptiform activity. We show that activation of GABAergic interneurons can elicit synchronous long-lasting network activity. Specific interneuron subpopulations differentially contributed to GABA network synchrony, indicating cell type-specific contributions of interneurons to cortical network activity. Interneurons may critically contribute to the generation of aberrant network activity characteristic of epilepsy, warranting further investigation into the contribution of distinct cortical interneuron subpopulations to the propagation and rhythmicity of epileptiform activity. ABSTRACT: In the presence of the A-type K+ channel blocker 4-aminopyrdine, spontaneous synchronous network activity develops in the neocortex of mice of either sex. This aberrant synchrony persists in the presence of excitatory amino acid receptor antagonists (EAA blockers) and is considered to arise from synchronous firing of cortical interneurons (INs). Although much attention has been given to the mechanisms underlying this GABAergic synchrony, the contribution of specific IN subtypes to the generation of these long-lasting discharges (LLDs) is incompletely understood. We employed genetically-encoded channelrhodopsin and archaerhodopsin opsins to investigate the sufficiency and necessity, respectively, of activation of parvalbumin (PV), somatostatin (SST) and vasointestinal peptide (VIP)-expressing INs for the generation of synchronous neocortical GABAergic discharges. We found light-induced activation of PV or SST INs to be equally sufficient for the generation of LLDs, whereas activation of VIP INs was not. By contrast, light-induced inhibition of PV INs strongly reduced LLD initiation, whereas suppression of SST or VIP IN activity only partially attenuated LLD magnitude. These results suggest neocortical INs perform cell type-specific roles in the generation of aberrant GABAergic cortical network activity.

Delay activity of specific prefrontal interneuron subtypes modulates memory-guided behavior.

Memory-guided behavior requires maintenance of task-relevant information without sensory input, but the underlying circuit mechanism remains unclear. Calcium imaging in mice performing a delayed Go or No-Go task revealed robust delay activity in dorsomedial prefrontal cortex, with different pyramidal neurons signaling Go and No-Go action plans. Inhibiting pyramidal neurons by optogenetically activating somatostatin- or parvalbumin-positive interneurons, even transiently during the delay, impaired task performance, primarily by increasing inappropriate Go responses. In contrast, activating vasoactive intestinal peptide (VIP)-positive interneurons enhanced behavioral performance and neuronal action plan representation. Furthermore, while endogenous activity of somatostatin and parvalbumin neurons was strongly biased toward Go trials, VIP neurons were similarly active in Go and No-Go trials. Somatostatin or VIP neuron activation also impaired or enhanced performance, respectively, in a delayed two-alternative forced-choice task. Thus, dorsomedial prefrontal cortex is a crucial component of the short-term memory network, and activation of its VIP neurons improves memory retention.

Research Resource: Real-Time Analysis of Somatostatin and Dopamine Receptor Signaling in Pituitary Cells Using a Fluorescence-Based Membrane Potential Assay.

Stable somatostatin analogues and dopamine receptor agonists are the mainstay for the pharmacological treatment of functional pituitary adenomas; however, only a few cellular assays have been developed to detect receptor activation of novel compounds without disrupting cells to obtain the second messenger content. Here, we adapted a novel fluorescence-based membrane potential assay to characterize receptor signaling in a time-dependent manner. This minimally invasive technique provides a robust and reliable read-out for ligand-induced receptor activation in permanent and primary pituitary cells. The mouse corticotropic cell line AtT-20 endogenously expresses both the somatostatin receptors 2 (sst2) and 5 (sst5). Exposure of wild-type AtT-20 cells to the sst2- and sst5-selective agonists BIM-23120 and BIM-23268, respectively, promoted a pertussis toxin- and tertiapin-Q-sensitive reduction in fluorescent signal intensity, which is indicative of activation of G protein-coupled inwardly rectifying potassium (GIRK) channels. After heterologous expression, sst1, sst3, and sst4 receptors also coupled to GIRK channels in AtT-20 cells. Similar activation of GIRK channels by dopamine required overexpression of dopamine D2 receptors (D2Rs). Interestingly, the presence of D2Rs in AtT-20 cells strongly facilitated GIRK channel activation elicited by the sst2-D2 chimeric ligand BIM-23A760, suggesting a synergistic action of sst2 and D2Rs. Furthermore, stable somatostatin analogues produced strong responses in primary pituitary cultures from wild-type mice; however, in cultures from sst2 receptor-deficient mice, only pasireotide and somatoprim, but not octreotide, induced a reduction in fluorescent signal intensity, suggesting that octreotide mediates its pharmacological action primarily via the sst2 receptor.

BMP-6 modulates somatostatin effects on luteinizing hormone production by gonadrotrope cells.

The effects of somatostatin analogs and roles of BMP-6 in the regulation of luteinizing hormone (LH) secretion were investigated using mouse gonadotrope LßT2 cells. LH mRNA expression and LH secretion induced by GnRH were suppressed by treatments with somatostatin analogs, including octreotide and pasireotide, in LßT2 cells. Of note, the inhibitory effects of somatostatin analogs on LH secretion were enhanced by the action of BMP-6. BMP-6 increased the expression levels of somatostatin receptor (SSTR)5, suggesting that BMP-6 upregulates SSTR activity that leads to reduction of GnRH-induced LH secretion. In addition, GnRH-induced phosphorylation of MAPKs including ERK, but not P38 or SAPK, was suppressed by pasireotide in the presence of BMP-6. Given that each inhibitor of ERK, JNK or P38 signaling suppressed GnRH-induced LH transcription, MAPKs are individually involved in the induction of LH production by LßT2 cells. Somatostatin analogs also impaired BMP-6-induced Smad1/5/8 phosphorylation by suppressing BMPRs and augmenting Smad6/7 expression. Collectively, the results indicate that somatostatin analogs have dual effects on the modulation of GnRH-induced MAPK signaling and BMP activity. The pituitary BMP system may play a regulatory role in GnRH-induced LH secretion by tuning the responsiveness to somatostatin analogs in gonadotrope cells.

An acetylcholine-activated microcircuit drives temporal dynamics of cortical activity.

Cholinergic modulation of cortex powerfully influences information processing and brain states, causing robust desynchronization of local field potentials and strong decorrelation of responses between neurons. We found that intracortical cholinergic inputs to mouse visual cortex specifically and differentially drive a defined cortical microcircuit: they facilitate somatostatin-expressing (SOM) inhibitory neurons that in turn inhibit parvalbumin-expressing inhibitory neurons and pyramidal neurons. Selective optogenetic inhibition of SOM responses blocked desynchronization and decorrelation, demonstrating that direct cholinergic activation of SOM neurons is necessary for this phenomenon. Optogenetic inhibition of vasoactive intestinal peptide-expressing neurons did not block desynchronization, despite these neurons being activated at high levels of cholinergic drive. Direct optogenetic SOM activation, independent of cholinergic modulation, was sufficient to induce desynchronization. Together, these findings demonstrate a mechanistic basis for temporal structure in cortical populations and the crucial role of neuromodulatory drive in specific inhibitory-excitatory circuits in actively shaping the dynamics of neuronal activity.

The clinical significance of somatostatin in pancreatic diseases.

The aim of the study was to provide knowledge on somatostatin and its action on the body, particularly the pancreas - in physiological and pathological conditions. In order to get to know the properties of somatostatin, a hormone discovered over forty years ago, many studies that define its structure and the mechanisms by which it operates have been conducted. The properties of somatostatin receptors and the effect of somatostatin on the body - both a healthy one and in various disease stages - were determined. It was proven that the somatostatin had an inhibitive effect on the endo- and exocrine secretion of this organ, which allowed a hypothesis that it might play an important role in the pathophysiology of diabetes. In patients with severe acute pancreatitis, both somatostatin and octreotide appear to reduce the mortality rate significantly, without any effect on the incidence of complications. Nevertheless, somatostatin analogues may be the cause of acute pancreatitis. With regard to severe chronic pancreatitis, refractory to other forms of therapy, it was demonstrated that octreotide significantly alleviated pain in many patients. A similar risk of death, and generally a lower risk of complications were found in the group of somatostatin-treated patients with chronic pancreatitis when compared to those receiving placebo or untreated. The occurrence of hyperglycemia after the application of somatostatin analogues, and in particular after pasireotide, is disturbing. Somatostatin analogues have found application in the treatment of cancers. They may improve symptoms in patients with gastroenteropancreatic neuroendocrine tumors (NETs) and stabilize the tumor growth (PROMID study). However, the optimal hormone dose sizes and frequencies necessary to ensure a full therapeutic effect in selected diseases of the pancreas have not been completely determined.

Somatostatin system: molecular mechanisms regulating anterior pituitary hormones.

The somatostatin (SRIF) system, which includes the SRIF ligand and receptors, regulates anterior pituitary gland function, mainly inhibiting hormone secretion and to some extent pituitary tumor cell growth. SRIF-14 via its cognate G-protein-coupled receptors (subtypes 1-5) activates multiple cellular signaling pathways including adenylate cyclase/cAMP, MAPK, ion channel-dependent pathways, and others. In addition, recent data have suggested SRIF-independent constitutive SRIF receptor activity responsible for GH and ACTH inhibition in vitro. This review summarizes current knowledge on ligand-dependent and independent SRIF receptor molecular and functional effects on hormone-secreting cells in the anterior pituitary gland.

Neuropeptides in learning and memory.

Dementia conditions and memory deficits of different origins (vascular, metabolic and primary neurodegenerative such as Alzheimer's and Parkinson's diseases) are getting more common and greater clinical problems recently in the aging population. Since the presently available cognitive enhancers have very limited therapeutical applications, there is an emerging need to elucidate the complex pathophysiological mechanisms, identify key mediators and novel targets for future drug development. Neuropeptides are widely distributed in brain regions responsible for learning and memory processes with special emphasis on the hippocampus, amygdala and the basal forebrain. They form networks with each other, and also have complex interactions with the cholinergic, glutamatergic, dopaminergic and GABA-ergic pathways. This review summarizes the extensive experimental data in the well-established rat and mouse models, as well as the few clinical results regarding the expression and the roles of the tachykinin system, somatostatin and the closely related cortistatin, vasoactive intestinal polypeptide (VIP) and pituitary adenylate-cyclase activating polypeptide (PACAP), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), opioid peptides and galanin. Furthermore, the main receptorial targets, mechanisms and interactions are described in order to highlight the possible therapeutical potentials. Agents not only symptomatically improving the functional impairments, but also inhibiting the progression of the neurodegenerative processes would be breakthroughs in this area. The most promising mechanisms determined at the level of exploratory investigations in animal models of cognitive disfunctions are somatostatin sst4, NPY Y2, PACAP-VIP VPAC1, tachykinin NK3 and galanin GALR2 receptor agonisms, as well as delta opioid receptor antagonism. Potent and selective non-peptide ligands with good CNS penetration are needed for further characterization of these molecular pathways to complete the preclinical studies and decide if any of the above described targets could be appropriate for clinical investigations.

[Radionuclide imaging of neurendocrine tumors: biological basis and diagnostic results]. / Imaging con radionuclidi dei tumori neuroendocrini: basi biologiche e risultati diagnostici.

Many radiopharmaceuticals have been successfully used in nuclear medicine to detect neuroendocrine tumors, and many of them are based on a specific mechanism of uptake, while others are non-specific probes. This "review" focuses on the clinical applications of metaiodobenzylguanidine, (111)In-pentreotide and positron emission tomography (PET) tracers. New avances in diagnostic imaging will be discussed. Molecular imaging serves these diagnostic functions and provides powerful means for non-invasively detecting disease.

Tlx3 controls cholinergic transmitter and Peptide phenotypes in a subset of prenatal sympathetic neurons.

The embryonic sympathetic nervous system consists of predominantly noradrenergic neurons and a very small population of cholinergic neurons. Postnatal development further allows target-dependent switch of a subset of noradrenergic neurons into cholinergic phenotype. How embryonic cholinergic neurons are specified at the prenatal stages remains largely unknown. In this study, we found that the expression of transcription factor Tlx3 was progressively restricted to a small population of embryonic sympathetic neurons in mice. Immunostaining for vesicular acetylcholine transporter (VAChT) showed that Tlx3 was highly expressed in cholinergic neurons at the late embryonic stage E18.5. Deletion of Tlx3 resulted in the loss of Vacht expression at E18.5 but not E12.5. By contrast, Tlx3 was required for expression of the cholinergic peptide vasoactive intestinal polypeptide (VIP), and somatostatin (SOM) at both E12.5 and E18.5. Furthermore, we found that, at E18.5 these putative cholinergic neurons expressed glial cell line-derived neurotrophic factor family coreceptor Ret but not tyrosine hydroxylase (Ret(+)/TH(-)). Deletion of Tlx3 also resulted in disappearance of high-level Ret expression. Last, unlike Tlx3, Ret was required for the expression of VIP and SOM at E18.5 but not E12.5. Together, these results indicate that transcription factor Tlx3 is required for the acquisition of cholinergic phenotype at the late embryonic stage as well as the expression and maintenance of cholinergic peptides VIP and SOM throughout prenatal development of mouse sympathetic neurons.

Comparison of the activation of somatostatin- and neuropeptide Y-containing neuronal populations of the rat amygdala following two different anxiogenic stressors.

Rats exposed to the odor of a predator or to the elevated plus maze express fear behaviors without a prior exposure to either stimulus. The expression of innate fear provides for an ideal model of anxiety which can aid in the elucidation of brain circuits involved in anxiety-related behaviors. The current experiments compared activation of neuropeptide-containing neuronal populations in the amygdala of rats exposed to either the elevated plus maze (EPM; 5 min) versus home cage controls, or predator ferret odor versus butyric acid, or no odor (30 min). Sections of the brains were prepared for dual-labeled immunohistochemistry and counts of c-Fos co-localized with somatostatin (SOM) or neuropeptide Y (NPY) were made in the basolateral (BLA), central (CEA), medial (MEA) nuclei of the amygdala. Ferret odor and butyric acid exposure significantly decreased the percentage of SOM-positive neurons also immunoreactive for c-Fos in the anterior BLA compared to controls, whereas EPM exposure yielded a significant increase in the activation of SOM-positive neurons versus home cage controls. In the CEA, ferret odor and butyric exposure significantly decreased the percentage of SOM-positive neurons also immunoreactive for c-Fos compared to no-odor controls whereas EPM exposure yielded no change versus controls. In the MEA, both ferret odor exposure and EPM exposure resulted in increased SOM co-localized with c-Fos compared to control groups whereas NPY co-localized with c-Fos occurred following ferret odor exposure, but not EPM exposure. These results indicate that phenotypically distinct neuronal populations of the amygdala are differentially activated following exposure to different anxiogenic stimuli. These studies further elucidate the fundamental neurocircuitry of anxiety and could possibly explain the differential behavioral effects of predator versus novelty-induced stress.

Somatostatin and somatostatin analogues reduce PDGF-induced endometrial cell proliferation and motility.

BACKGROUND: Endometriosis is characterized by ectopic implantation of endometrial cells, which show increased proliferation and migration. Somatostatin (SST) and its analogues inhibit normal and cancer cell growth and motility through the SST receptors, sst1-5. Cortistatin (CST), which displays high structural and functional homology with SST, binds all ssts, as well as MrgX2. Our objective was to investigate the gene expression of the SST/CST system and to determine the effect of SST and its analogues on platelet-derived growth factor (PDGF)-induced proliferation and motility in telomerase-immortalized human endometrial stromal cell (T HESC) line and in primary endometrial stromal cell (ESCs) isolated from human endometriotic tissues. METHODS: Ectopic endometrial tissues were collected from women (n= 23) undergoing laparoscopic surgery for endometriosis (Stage III/IV). Gene expression was evaluated by real-time PCR, cell motility by wound healing assay, protein expression and ß-actin rearrangement by immunofluorescence, cell proliferation by the Alamar blue assay and ERK1/2 and Akt phosphorylation by western blot. RESULTS: Human endometriotic tissues, primary ESCs and T HESCs expressed SST, CST and ssts. SST, its analogues SOM230 and octreotide, as well as CST, counteracted PDGF-induced proliferation and migration in both ESCs and T HESCs. SST also inhibited vascular endothelial growth factor and metalloprotease-2 mRNA expression, and reduced basal and PDGF-induced ERK1/2 phosphorylation. CONCLUSION: These results indicate that the SST/CST system is expressed in endometriotic tissues and cells. The inhibitory effects of SST and its analogues on PDGF-induced proliferation and motility suggest that these peptides may represent promising tools in the treatment of endometriosis.

Notch1-mediated tumor suppression in cervical cancer with the involvement of SST signaling and its application in enhanced SSTR-targeted therapeutics.

The role of Notch signaling in cervical cancer is seemingly controversial. To confirm the function of Notch signaling in this type of cancer, we established a stable Notch1-activated cervical cancer HeLa cell line. We found that Notch1 activation resulted in apoptosis, cell cycle arrest, and tumor suppression. At the molecular level, we found that a variety of genes associated with cyclic AMP, G protein-coupled receptor, and cancer signaling pathways contributed to Notch1-mediated tumor suppression. We observed that the expression of somatostatin (SST) was dramatically induced by Notch1 signaling activation, which was accompanied by enhanced expression of the cognate SST receptor subtype 1 (SSTR1) and SSTR2. Certain genes, such as tumor protein 63 (TP63, p63), were upregulated, whereas others, such as B-cell lymphoma 2 (BCL-2), Myc, Akt, and STAT3, were downregulated. Subsequently, knockdown of Notch1-induced SST reversed Notch1-induced decrease of BCL-2 and increase of p63, indicating that Notch1-induced tumor suppression may be partly through upregulating SST signaling. Our findings support a possible crosstalk between Notch signaling and SST signaling. Moreover, Notch-induced SSTR activation could enhance SSTR-targeted cancer chemotherapy. Valproic acid (VPA), a histone deacetylase inhibitor, suppressed cell growth and upregulated the expression of Notch1 and SSTR2. A combination therapy with VPA and the SSTR2-targeting cytotoxic conjugate CPT-SST strongly led to greater suppression, as compared to each alone. Our findings thus provide us with a promising clinical opportunity for enhanced cancer therapy using combinations of Notch1-activating agents and SSTR2-targeting agents.