Differential cytotoxicity of novel somatostatin and dopamine chimeric compounds on bronchopulmonary and small intestinal neuroendocrine tumor cell lines

Somatostatin and Somatostatin Receptors in Tumour Biology

Somatostatin (SST), a growth hormone inhibitory peptide, is expressed in endocrine and non-endocrine tissues, immune cells and the central nervous system (CNS). Post-release from secretory or immune cells, the first most appreciated role that SST exhibits is the antiproliferative effect in target tissue that served as a potential therapeutic intervention in various tumours of different origins. The SST-mediated in vivo and/or in vitro antiproliferative effect in the tumour is considered direct via activation of five different somatostatin receptor subtypes (SSTR1-5), which are well expressed in most tumours and often more than one receptor in a single cell. Second, the indirect effect is associated with the regulation of growth factors. SSTR subtypes are crucial in tumour diagnosis and prognosis. In this review, with the recent development of new SST analogues and receptor-specific agonists with emerging functional consequences of signaling pathways are promising therapeutic avenues in tumours of different origins that are discussed.

Carcinoid Syndrome: Preclinical Models and Future Therapeutic Strategies

Carcinoid syndrome represents a debilitating paraneoplastic disease, caused by the secretion of several substances, occurring in about 10-40% of patients with well-differentiated neuroendocrine tumors (NETs). The main signs and symptoms associated with carcinoid syndrome are flushing, diarrhea, hypotension, tachycardia, bronchoconstriction, venous telangiectasia, dyspnea and fibrotic complications (mesenteric and retroperitoneal fibrosis, and carcinoid heart disease). Although there are several drugs available for the treatment of carcinoid syndrome, the lack of therapeutic response, poor tolerance or resistance to drugs are often reported. Preclinical models are indispensable tools for investigating the pathogenesis, mechanisms for tumor progression and new therapeutic approaches for cancer. This paper provides a state-of-the-art overview of in vitro and in vivo models in NETs with carcinoid syndrome, highlighting the future developments and therapeutic approaches in this field.

Somatostatin-Dopamine Chimeric Molecules in Neuroendocrine Neoplasms

Neuroendocrine neoplasms (NENs) are a widely heterogeneous family of neoplasms arising from neuroendocrine cells, which are interspersed throughout the body. Despite NENs are relatively rare, their incidence and prevalence are constantly increasing probably due to the improvement in earlier diagnosis and patients’ management. When surgery is not curative, particularly for patients with metastatic disease, several medical options are available. Somatostatin analogues (SSA) are the first-line medical therapy for well-differentiated NENs. Interestingly, the heterodimerization of somatostatin receptors (SSTs) with dopamine receptors (DRs) has been discovered in NENs. This phenomenon results in hybrid receptors with enhanced functional activity. On these bases, chimeric molecules embracing somatostatin and dopamine features have been recently developed. The aim of this review is to provide a comprehensive overview of the available preclinical and clinical data regarding chimeric somatostatin-dopamine agonists as a new class of “magic bullet” in the therapy of NENs.

Efficacy of a Novel Second-Generation Somatostatin-Dopamine Chimera (TBR-065) in Human Medullary Thyroid Cancer: A Preclinical Study

INTRODUCTION

Somatostatin and dopamine (DA) receptors have a pivotal role in controlling hormone secretion and cell proliferation in different neuroendocrine neoplasms, including medullary thyroid cancer (MTC). In the present preclinical study, we evaluated the anti-tumor activity of TBR-065 (formerly BIM-23B065), a second-generation somatostatin-DA chimera, in 2 human MTC cell lines.

METHODS

The effects of lanreotide (LAN) and TBR-065 on cell growth and proliferation, calcitonin (CT) secretion, cell cycle, apoptosis, cell migration, and tumor-induced angiogenesis have been evaluated through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, DNA flow cytometry with propidium iodide (PI), Annexin V-FITC/PI staining, electrochemiluminescence immuno assay, wound-healing assay, and zebrafish platform, respectively.

RESULTS

TBR-065 exerted a more prominent anti-tumor activity than LAN in both MTC cell lines, as shown by inhibition of cell proliferation (maximal inhibition in TT: -50.3 and -37.6%, respectively; in MZ-CRC-1: -58.8 and -27%, respectively) and migration (in TT: -42.7 and -22.9%, respectively; in MZ-CRC-1: -75.5 and -58.2%, respectively). Only the new chimera decreased significantly the fraction of cells in S phase (TT: -33.8%; MZ-CRC-1: -18.8%) and increased cells in G2/M phase (TT: +13%; MZ-CRC-1: +30.5%). In addition, TBR-065 exerted a more prominent pro-apoptotic effect than LAN in TT cells. A concomitant decrease in CT secretion was observed after 2 days of incubation with both drugs, with a more relevant effect of TBR-065. However, neither LAN nor TBR-065 showed any effect on tumor-induced angiogenesis, as evaluated using a zebrafish/tumor xenograft model.

DISCUSSION/CONCLUSION

In MTC cell lines, a second-generation somatostatin-DA analog, TBR-065, exerts a more relevant anti-tumor activity than LAN, through modulation of cell cycle, induction of apoptosis, and reduction in migration. Further studies are required to establish whether TBR-065 has comparable potent inhibitory effects on tumor growth in vivo.

Oncological management of advanced neuroendocrine tumours (Review)

The oncological principles of managing patients with gastroenteropancreatic neuroendocrine tumours (GEP-NETs) depends on a number of factors and requires a multidisciplinary approach. Recent data have provided additional therapeutic options, including biotherapy, traditional chemotherapy and novel targeted agents. Somatostatin analogues (SSAs) inhibit multiple cellular functions, including secretion, motility and proliferation. Interferon appears to act through several mechanisms, with antisecretory effects, immunomodulatory effects and antiproliferative functions, the latter inhibiting direct growth or attenuating angiogenesis. Opinions on when to commence chemotherapy for well differentiated GEP-NETs varies among experts. In previous years, reserving chemotherapy for patients with progressive disease (well differentiated, inoperable and/or metastatic GEP-NETs) was reasonably well argued for. Most well differentiated endocrine tumours are richly vascular and many express vascular endothelial growth factor (VEGF) receptors. In a xenograft model of a human carcinoid, treatment with an anti-VEGF monoclonal antibody was revealed to inhibit tumour growth and metastasis. As the role of angiogenesis and hypoxic-associated factors appears to be associated with tumour aggressiveness, strategies using agents which target angiogenesis have been developed. Mammalian target of rapamycin (mTOR) is a conserved serine-threonine kinase that regulates the cell cycle and metabolism in response to environmental factors. In addition, mTOR inhibition suppression was demonstrated to suppress NET growth. Each patient requires an individual approach to the choice of therapy, which should be selected depending on the severity of disease.

Effects of novel somatostatin-dopamine chimeric drugs in 2D and 3D cell culture models of neuroendocrine tumors

Control of symptoms related to hormonal hypersecretion by functioning neuroendocrine tumors (NETs) is challenging. New therapeutic options are required. Since novel in vitro tumor models seem to better mimic the tumor in vivo conditions, we aimed to study the effect of somatostatin and dopamine receptor agonists (octreotide and cabergoline, respectively) and novel somatostatin-dopamine chimeric multi-receptor drugs (BIM-065, BIM-23A760) using 2D (monolayer) and 3D (spheroids) cultures. Dose-response studies in 2D and 3D human pancreatic NET cell cultures (BON-1 and QGP-1) were performed under serum-containing and serum-deprived conditions. Cell proliferation, somatostatin and dopamine receptor expression (SSTs and D2R), apoptosis, lactate dehydrogenase, as well as serotonin and chromogranin A (CgA) release were assessed. The following results were obtained. 3D cultures of BON-1/QGP-1 allowed better cell survival than 2D cultures in serum-deprived conditions. SSTs and D2R mRNA levels were higher in the 3D model vs 2D model. Octreotide/cabergoline/BIM-065/BIM-23A760 treatment did not affect cell growth or spheroid size. In BON-1 2D-cultures, only BIM-23A760 significantly inhibited CgA release -this effect being more pronounced in 3D cultures. In BON-1 2D cultures, cabergoline/BIM-065/BIM-23A760 treatment decreased serotonin release (maximal effect up to 40%), being this effect again more potent in 3D cultures (up to 67% inhibition; with BIM-23A760 having the most potent effects). In QGP-1, cabergoline/BIM-065 treatment decreased serotonin release only in the 3D model. In conclusion, cultures of NET 3D spheroids represent a promising method for evaluating cell proliferation and secretion in NET cell-line models. Compared to 2D models, 3D models grow relatively serum independent. In 3D model, SST-D2R multi-receptor targeting drugs inhibit CgA and serotonin secretion, but not NET cell growth.

Somatostatin Analogue Treatment Primarily Induce miRNA Expression Changes and Up-Regulates Growth Inhibitory miR-7 and miR-148a in Neuroendocrine Cells

Somatostatin (SST) analogues are used to control the proliferation and symptoms of neuroendocrine tumors (NETs). MicroRNAs (miRNA) are small non-coding RNAs that modulate posttranscriptional gene expression. We wanted to characterize the miRNAs operating under the control of SST to elucidate to what extent they mediate STT actions. NCI-H727 carcinoid cell line was treated with either a chimeric SST/dopamine analogue; a SST or dopamine analogue for proliferation assays and for identifying differentially expressed miRNAs using miRNA microarray. The miRNAs induced by SST analogue treatment are investigated in carcinoid cell lines NCI-H727 and CNDT2 using in situ hybridization, qPCR and proliferation assays. SST analogues inhibited the growth of carcinoid cells more potently compared to the dopamine analogue. Principal Component Analysis (PCA) of the samples based on miRNA expression clearly separated the samples based on treatment. Two miRNAs which were highly induced by SST analogues, miR-7 and miR-148a, were shown to inhibit the proliferation of NCI-H727 and CNDT2 cells. SST analogues also produced a general up-regulation of the let-7 family members. SST analogues control and induce distinct miRNA expression patterns among which miR-7 and miR-148a both have growth inhibitory properties.

Pasireotide in the treatment of neuroendocrine tumors: a review of the literature

Somatostatin analogs have an important role in the medical therapy of neuroendocrine tumors (NETs). Octreotide and lanreotide, both somatostatin analogs binding with high affinity for the somatostatin receptor (SSTR)2, can control symptoms in functional NETs. In addition, these compounds, because of their antiproliferative effects, can stabilize growth of well-differentiated NETs. Pasireotide is a novel multireceptor-targeted somatostatin analog with high affinity for SSTR1, 2, 3, and 5. This review provides an overview of the state of the art of pasireotide in the treatment of NETs, with the aim of addressing clinical relevance and future perspectives for this molecule in the management of NETs.

2. Somatostatin and dopamine receptors

The discovery of the new properties of SSRs and DRs has led to a renewed interest in agents targeting these receptors and has opened new perspectives for medical treatment of patients with pituitary and neuroendocrine tumors resistant to the “classical”, currently available analogs. Moreover, SSRs and DRs crosstalk at membrane level may trigger alternative intracellular pathways or enhance the signalling for the control of cell growth. New somatostatin analogs and hybrid molecules, which display a broader and different spectrum of activities compared to conventional analogs, seem to be a promising therapeutic alternative for the control of hormone secretion and, hopefully, to reduce tumor burden. Receptor profile characterization is crucial for the accurate selection of patients potentially responsive to a given therapy. Free full text available at www.tumorionline.it

A liquid biopsy for bronchopulmonary/lung carcinoid diagnosis

No effective blood biomarker exists to detect and clinically manage bronchopulmonary (BP) neuroendocrine tumors (NET). We developed a blood-based 51 NET-specific transcript set for diagnosis and monitoring and evaluated clinical performance metrics. It accurately diagnosed the tumor and differentiated stable from progressive disease as determined by RECIST criteria. Gene expression was evaluated in: a) publicly available BPNET transcriptomes (GSE35679); b) two BPNET cell-lines; and c) BPNET tissue with paired blood (n = 7). Blood gene expression was assessed in 194 samples including controls, benign lung diseases, malignant lung diseases and small bowel NETs. A separate validation study in 25 age- and gender-matched BPNETs/controls was performed. Gene expression measured by real-time PCR was scored (0–100%; normal: < 14%). Regression analyses, Principal Component Analysis (PCA), hierarchical clustering, Fisher's and non-parametric evaluations were undertaken. All 51 genes were identified in BPNET transcriptomes, tumor samples and cell-lines. Significant correlations were evident between paired tumor and blood (R2:0.63–0.91, p < 0.001). PCA and hierarchical clustering identified blood gene expression was significantly different between lung cancers and benign diseases, including BPNETs. Gene expression was highly correlated (R²: 0.91, p = 1.7 × 10-¹⁵) between small bowel and BPNET. For validation, all 25 BPNETs were positive compared to 20% controls (p < 0.0001). Scores were significantly elevated (p < 0.0001) in BPNETs (57 ± 28%) compared to controls (4 ± 5%). BPNETs with progressive disease (85 ± 11%) exhibited higher scores than stable disease (32 ± 7%, p < 0.0001). Blood measurements accurately diagnosed bronchopulmonary carcinoids, distinguishing stable from progressive disease. This marker panel will have clinical utility as a diagnostic liquid biopsy able to define disease activity and progression in real-time.

Somatostatin analogs in the treatment of neuroendocrine tumors: current and emerging aspects

INTRODUCTION

Neuroendocrine tumors (NETs) harbor somatostatin receptors and there is a strong rationale for using somatostatin analogs (SSAs) for treatment of NETs. Areas covered: This article discusses i) pharmacology of somatostatin and its analogs; ii) antisecretory and anti-proliferative effects of SSAs in NETs; iii) efficacy and safety of emerging therapeutic regimens with first generation SSAs administered at either high doses or in combination with antineoplastic drugs; iv) efficacy and safety of pasireotide and chimeric molecules; v) efficacy of radionuclide therapy of NETs using SSAs. Expert opinion: SSAs are the first-line medical therapy for functioning and non-functioning well-differentiated NETs. In patients not responder to first generation SSAs, the increase of drug dose over the conventional regimens, the combination of SSAs with other biotherapies or molecular targeted therapies, the switch to pasireotide or the use of SSAs in radionuclide therapy may improve the therapeutic success.

Effects of the single and combined treatment with dopamine agonist, somatostatin analog and mTOR inhibitors in a human lung carcinoid cell line: an in vitro study

Somatostatin analogues and mTOR inhibitors have been used as medical therapy in lung carcinoids with variable results. No data are available on dopamine agonists as treatment for lung carcinoids. The main aim of the current study was to evaluate the effect of the combined treatment of somatostatin analogue octreotide and the dopamine agonist cabergoline with mTOR inhibitors in an in vitro model of typical lung carcinoids: the NCI-H727 cell line. In NCI-H727 cell line, reverse transcriptase-quantitative polymerase chain reaction and immunofluorescence were assessed to characterize the expression of the somatostatin receptor 2 and 5, dopamine receptor 2 and mTOR pathway components. Fifteen typical lung carcinoids tissue samples have been used for somatostatin receptor 2, dopamine receptor 2, and the main mTOR pathway component p70S6K expression and localization by immunohistochemistry. Cell viability, fluorescence-activated cell sorting analysis and western blot have been assessed to test the pharmacological effects of octreotide, cabergoline and mTOR inhibitors, and to evaluate the activation of specific cell signaling pathways in NCI-H727 cell line. NCI-H727 cell line expressed somatostatin receptor 2, somatostatin receptor 5 and dopamine receptor 2 and all mTOR pathway components at messenger and protein levels. Somatostatin receptor 2, dopamine receptor 2, and p70S6K (non phosphorylated and phosphorylated) proteins were expressed in most typical lung carcinoids tissue samples. Octreotide and cabergoline did not reduce cell viability as single agents but, when combined with mTOR inhibitors, they potentiate mTOR inhibitors effect after long-term exposure, reducing Akt and ERK phosphorylation, mTOR escape mechanisms, and increasing the expression DNA-damage-inducible transcript 4, an mTOR suppressor. In conclusion, the single use of octreotide and cabergoline is not sufficient to block cell viability but the combined approach of these agents with mTOR inhibitors might reduce the mTOR inhibitors-induced escape mechanisms and/or activate the endogenous mTOR suppressor, potentiating the effect of the mTOR inhibitors in an in vitro model of typical lung carcinoids.

Role of Somatostatin Analogues in the Treatment of Neuroendocrine Tumors

Neuroendocrine tumors (NETs) are rare epithelial neoplasms with neuroendocrine differentiation originating most commonly in the lungs and gastroenteropancreatic. Treatment includes surgery and other local therapies; treatment of inoperable disease centers around symptom management and control of tumor growth. Somatostatin analogues (SSAs) have been a mainstay of managing hormone-related symptoms. Emerging evidence suggests that they are effective therapies for tumor control also. Peptide receptor radionuclide therapy with radiolabeled SSAs is a new, promising treatment for inoperable or metastatic NETs. This article reviews the role of SSAs in the treatment of NETs.

Effects of Somatostatin Analogs and Dopamine Agonists on Insulin-Like Growth Factor 2-Induced Insulin Receptor Isoform A Activation by Gastroenteropancreatic Neuroendocrine Tumor Cells

BACKGROUND

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) express insulin-like growth factor (IGF)-related factors [IGF1, IGF2; insulin receptor (IR)-A, IR-B; IGF-binding protein (IGFBP) 1-3] as well as somatostatin (SSTRs) and dopamine D2 receptors (D2Rs).

OBJECTIVES

To (1) compare mRNA expression of IGF-related factors in human pancreatic NET (panNET) cell lines with that in human GEP-NETs to evaluate the usefulness of these cells as a model for studying the IGF system in GEP-NETs, (2) determine whether panNET cells produce growth factors that activate IR-A, and (3) investigate whether somatostatin analogs (SSAs) and/or dopamine agonists (DAs) influence the production of these growth factors.

METHODS

In panNET cells (BON-1 and QGP-1) and GEP-NETs, mRNA expression of IGF-related factors was measured by quantitative real-time PCR. Effects of the SSAs octreotide and pasireotide (PAS), the DA cabergoline (CAB), and the dopastatin BIM-23A760 (all 100 nM) were evaluated at the IGF2 mRNA and protein level (by ELISA) and regarding IR-A bioactivity (by kinase receptor activation assay) in panNET cells.

RESULTS

panNET cells and GEP-NETs had comparable expression profiles of IGF-related factors. Especially in BON-1 cells, IGF2 and IR-A were most highly expressed. PAS + CAB inhibited IGF2 (-29.5 ± 4.9%, p < 0.01) and IGFBP3 (-20.0 ± 4.0%, p < 0.01) mRNA expression in BON-1 cells. In BON-1 cells, IGF2 protein secretion was significantly inhibited with BIM-23A760 (-23.7 ± 3.8%). BON-1- but not QGP-1- conditioned medium stimulated IR-A bioactivity. In BON-1 cells, IR-A bioactivity was inhibited by BIM-23A760 and PAS + CAB (-37.8 ± 2.1% and -30.9 ± 4.1%, respectively, p < 0.0001).

CONCLUSIONS

(1) The BON-1 cell line is a representative model for studying the IGF system in GEP-NETs, (2) BON-1 cells produce growth factors (IGF2) activating IR-A, and (3) combined SSTR and D2R targeting with PAS + CAB and BIM-23A760 suppresses IGF2-induced IR-A activation.

Exome-level comparison of primary well-differentiated neuroendocrine tumors and their cell lines

Neuroendocrine cancer cell lines are used to investigate therapeutic targets in neuroendocrine tumors (NET) and have been instrumental in the design of clinical trials targeting the PI3K/AKT/mTOR pathways, VEGF inhibitors, and somatostatin analogues. It remains unknown, however, whether the genomic makeup of NET cell lines reflect that of primary NET since comprehensive unbiased genome sequencing has not been performed on the cell lines. Four bronchopulmonary NET (BP-NET)-NCI-H720, NCI-H727, NCI-H835, and UMC11-and two pancreatic neuroendocrine tumors (panNET)-BON-1 and QGP1-were cultured. DNA was isolated, and exome sequencing was done. GATK and EXCAVATOR were used for bioinformatic analysis. We detected a total of 1,764 nonsynonymous single nucleotide variants at a rate of 8 per Mb in BP-NET and 4.3 per Mb in panNET cell lines, including 52 mutated COSMIC cancer genes in these cell lines, such as TP53, BRCA1, RB1, TSC2, NOTCH1, EP300, GNAS, KDR, STK11, and APC but not ATRX, DAXX, nor MEN1. Our data suggest that mutation rate, the pattern of copy number variations, and the mutational spectra in the BP-NET cell lines are more similar to the changes observed in small cell lung cancer than those found in primary BP-NET. Likewise, mutation rate and pattern including the absence of mutations in ATRX/DAXX, MEN1, and YY1 in the panNET cell lines BON1 and QGP1 suggest that these cell lines do not have the genetic signatures of a primary panNET. These results suggest that results from experiments with BP-NET and panNET cell lines need to be interpreted with caution.

Expression of Somatostatin Receptors 1-5 and Dopamine Receptor 2 in Lung Carcinoids: Implications for a Therapeutic Role

OBJECTIVE

The expression of somatostatin receptors (SSTRs) and dopamine receptor 2 (DR2) in neuroendocrine tumors is of clinical importance as somatostatin analogues and dopamine agonists can be used for their localization and/or treatment. The objective of this study is to examine the expression of the five SSTR subtypes and DR2 in lung carcinoids (LCs).

METHODS

We conducted a retrospective study of 119 LCs from 106 patients [typical carcinoids (TCs): n = 100, and atypical carcinoids (ACs): n = 19]. The expression of all five SSTR subtypes and DR2 was evaluated immunohistochemically and correlated to clinicopathological data. In a subgroup of cases, receptor expression was further analyzed using semiquantitative RT-PCR.

RESULTS

SSTR2A was the SSTR subtype most frequently expressed immunohistochemically (72%), followed by SSTR1 (63%), SSTR5 (40%), and SSTR3 (20%), whereas SSTR4 was negative. DR2 was expressed in 74% and co-expressed with SSTR1 in 56%, with SSTR2A in 59%, with SSTR3 in 19%, and with SSTR5 in 37% of the tumors. Receptor expression was not related to the histological subtype, tumor aggressiveness (disease extent/grading) or functionality; however, DR2 was expressed more frequently in ACs than TCs (95 vs. 70%, p = 0.017). In a subset of patients, RT-PCR findings highly suggested that the expression of SSTR2A, SSTR3, DR2, and to a lesser extent that of SSTR1 and SSTR5 is the outcome of increased gene transcription.

CONCLUSIONS

The high and variable immunohistochemical expression of the majority of SSTRs along with their co-expression with DR2 in LCs provides a rationale for their possible treatment with agents that target these receptors.

Chromogranin A and its fragments as regulators of small intestinal neuroendocrine neoplasm proliferation

INTRODUCTION

Chromogranin A is a neuroendocrine secretory product and its loss is a feature of malignant NEN de-differentiation. We hypothesized that chromogranin A fragments were differentially expressed during NEN metastasis and played a role in the regulation of NEN proliferation.

METHODS

Chromogranin A mRNA (PCR) and protein (ELISA/western blot) were studied in 10 normal human mucosa, 5 enterochromaffin cell preparations, 26 small intestinal NEN primaries and 9 liver metastases. Cell viability (WST-1 assay), proliferation (bromodeoxyuridine ELISA) and expression of AKT/AKT-P (CASE ELISA/western blot) in response to chromogranin A silencing, inhibition of prohormone convertase and mTOR inhibition (RAD001/AKT antisense) as well as different chromogranin A fragments were examined in 4 SI-NEN cell lines.

RESULTS

Chromogranin A mRNA and protein levels were increased (37-340 fold, p<0.0001) in small intestinal NENs compared to normal enterochromaffin cells. Western blot identified chromogranin A-associated processing bands including vasostatin in small intestinal NENs as well as up-regulated expression of prohormone convertase in metastases. Proliferation in small intestinal NEN cell lines was decreased by silencing chromogranin A as well as by inhibition of prohormone convertase (p<0.05). This inhibition also decreased secretion of chromogranin A (p<0.05) and 5-HT (p<0.05) as well as expression of vasostatin. Metastatic small intestinal NEN cell lines were stimulated (50-80%, p<0.05) and AKT phosphorylated (Ser473: p<0.05) by vasostatin I, which was completely reversed by RAD001 (p<0.01) and AKT antisense (p<0.05) while chromostatin inhibited proliferation (~50%, p<0.05).

CONCLUSION

Chromogranin A was differentially regulated in primary and metastatic small intestinal NENs and cell lines. Chromogranin A fragments regulated metastatic small intestinal NEN proliferation via the AKT pathway indicating that CgA plays a far more complex role in the biology of these tumors than previously considered.

Illuminating somatostatin analog action at neuroendocrine tumor receptors

Somatostatin analogs for the diagnosis and therapy of neuroendocrine tumors (NETs) have been used in clinical applications for more than two decades. Five somatostatin receptor subtypes have been identified and molecular mechanisms of somatostatin receptor signaling and regulation have been elucidated. These advances increased understanding of the biological role of each somatostatin receptor subtype, their distribution in NETs, as well as agonist-specific regulation of receptor signaling, internalization, and phosphorylation, particularly for the sst2 receptor subtype, which is the primary target of current somatostatin analog therapy for NETs. Various hypotheses exist to explain differences in patient responsiveness to somatostatin analog inhibition of tumor secretion and growth as well as differences in the development of tumor resistance to therapy. In addition, we now have a better understanding of the action of both first generation (octreotide, lanreotide, Octreoscan) and second generation (pasireotide) FDA-approved somatostatin analogs, including the biased agonistic character of some agonists. The increased understanding of somatostatin receptor pharmacology provides new opportunities to design more sophisticated assays to aid the future development of somatostatin analogs with increased efficacy.

Serotonin and the 5-HT7 receptor: the link between hepatocytes, IGF-1 and small intestinal neuroendocrine tumors

Platelet-derived serotonin (5-HT) is involved in liver regeneration. The liver is also the metastatic site for malignant enterochromaffin (EC) cell "carcinoid" (neuroendocrine) neoplasms, the principal cellular source of 5-HT. We hypothesized that 5-HT produced by metastatic EC cells played a role in the hepatic tumor-microenvironment principally via 5-HT₇ receptor-mediated activation of hepatocyte IGF-1 synthesis and secretion. Using isolated rat hepatocytes, we evaluated 5-HT₇ receptor expression (using PCR, sequencing and western blot). ELISA, cell transfection and western blots delineated 5-HT-mediated signaling pathways (pCREB, AKT and ERK). IGF-1 synthesis/secretion was evaluated using QPCR and ELISA. IGF-1 was tested on small intestinal neuroendocrine neoplasm proliferation, while IGF-1 production and 5-HT₇ expression were examined in an in vivo SCID metastasis model. Our results demonstrated evidence for a functional 5-HT₇ receptor. 5-HT activated cAMP/PKA activity, pCREB (130-205%, P < 0.05) and pERK/pAKT (1.2-1.75, P < 0.05). Signaling was reversed by the 5-HT₇ receptor antagonist SB269970. IGF-1 significantly stimulated proliferation of two small intestinal neuroendocrine neoplasm cell lines (EC₅₀: 7-70 pg/mL) and could be reversed by the small molecule inhibitor BMS-754807. IGF-1 and 5-HT were elevated (40-300×) in peri-tumoral hepatic tissue in nude mice, while 5-HT₇ was increased fourfold compared to sham-operated animals. We conclude that hepatocytes express a cAMP-coupled 5-HT₇ receptor, which, at elevated 5-HT concentrations that occur in liver metastases, signals via CREB/AKT and is linked to IGF-1 synthesis and secretion. Because IGF-1 regulates NEN proliferation, identification of a role for 5-HT₇ in the hepatic metastatic tumor microenvironment suggests the potential for novel therapeutic strategies for amine-producing mid-gut tumors.

Synergistic effect of pasireotide and teriflunomide in carcinoids in vitro

BACKGROUND/AIM

Somatostatin (SST) analogs are mainstay for controlling tumor proliferation and hormone secretion in carcinoid patients. Recent data suggest that extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation may potentiate the anti-tumor effects of SST analogs in carcinoids. Additionally, ERK1/2 phosphorylating agents have been shown to suppress biomarker expression in carcinoids. Thus, Raf-1/MEK/ERK1/2 pathway activating drugs may be synergistic with SST analogs such as pasireotide (SOM230), which may be more effective than others in its class given its elevated receptor affinity and broader binding spectrum. Here, we investigate the effects of SOM230 in combination with teriflunomide (TFN), a Raf-1 activator, in a human carcinoid cell line.

METHODS

Human pancreatic carcinoid cells (BON) were incubated in TFN, SOM230 or a combination. Cell proliferation was measured using a rapid colorimetric assay. Western analysis was performed to analyze expression levels of achaete-scute complex-like 1 (ASCL1), chromogranin A (CgA), phosphorylated and total ERK1/2, and markers for apoptosis.

RESULTS

Combination treatment with SOM230 and TFN reduced cell growth beyond the additive effect of either drug alone. Combination indices (CI) fell below 1, thus quantifiably verifying synergy between both drugs as per the Chou-Talalay CI scale. Combined treatment also reduced ASCL1 and CgA expression beyond the additive effect of either drug alone. Furthermore, it increased levels of phosphorylated ERK1/2, cleaved poly(ADP)-ribose polymerase and caspase-3, and reduced levels of anti-apoptotic biomarkers. Elevated phosphorylated ERK1/2 expression following combination therapy may underlie the synergistic interaction between the two drugs.

CONCLUSION

Since efficacy is achieved at lower doses, combination therapy may palliate symptoms at low toxicity levels. Because each drug has already been evaluated in clinical trials, combinatorial drug trials are warranted.

Translation of molecular pathways into clinical trials of neuroendocrine tumors

Current treatment options for neuroendocrine tumors (NET) include somatostatin analogs, interferon-α, peptide receptor-targeted therapy and cytotoxic chemotherapy. Most patients undergo sequential therapies since these drugs are active only in subpopulations of patients and for a limited period of time. There is a need for novel drugs that are capable of amelioration of symptomatology (syndromic control) and/or tumor growth control. A number of diverse signaling pathways are involved in the pathogenesis of NET and tumor growth, thus many potential targets are available for drug targeting. Targeted therapies therefore represent an appropriate developmental therapeutic strategy given the multiplicity of potential targets in NET. These include but are not limited to: inhibitory or activating G protein-coupled receptors, receptor tyrosine kinases, ligands, and intracellular targets such as the mammalian target of rapamycin (mTOR). Numerous drugs that utilize single or multiple targets are currently in clinical development. Recently, two target-directed agents, the multiple tyrosine kinase inhibitor sunitinib and the mTOR inhibitor everolimus, have been approved for the treatment of progressive pancreatic NET. This review provides a broad overview of established and potential molecular targets in NET, summarizes data from phase II and III clinical trials with targeted drugs and outlines future therapeutic directions.

The novel somatostatin receptor 2/dopamine type 2 receptor chimeric compound BIM-23A758 decreases the viability of human GOT1 midgut carcinoid cells

The majority of neuroendocrine tumors (NETs) of the gastroenteropancreatic system coexpress somatostatin receptors (SSTRs) and dopamine type 2 receptors (D2R), thus providing a rationale for the use of novel SSTR2/D2R chimeric compounds in NET disease. Here we investigate the antitumor potential of the SSTR2/D2R chimeric compounds BIM-23A760 and BIM-23A758 in comparison to the selective SSTR2 agonist BIM-23023 and the selective D2R agonist BIM-53097 on human NET cell lines of heterogeneous origin. While having only minor effects on human pancreatic and bronchus carcinoid cells (BON1 and NCI-H727), BIM-23A758 induced significant antitumor effects in human midgut carcinoid cells (GOT1). These effects involved apoptosis induction as well as inhibition of mitogen-activated protein kinase and Akt signaling. Consistent with their antitumor response to BIM-23A758, GOT1 cells showed relatively high expression levels of SSTR2 and D2R mRNA. In particular, GOT1 cells highly express the short transcript variant of D2R. In contrast to BIM-23A758, the SSTR2/D2R chimeric compound BIM-23A760 as well as the individual SSTR2 and D2R agonistic compounds BIM-23023 and BIM-53097 induced no or only minor antitumor responses in the examined NET cell lines. Taken together, our findings suggest that the novel SSTR2/D2R chimeric compound BIM-23A758 might be a promising substance for the treatment of NETs highly expressing SSTR2 and D2R. In particular, a sufficient expression of the short transcript variant of DR2 might play a pivotal role for effective treatment.

Long-term disease control of a non-operable neuroendocrine tumor of the lung with lanreotide: a case study

Bronchopulmonary neuroendocrine tumors (NETs) are malignant tumors that represent approximately 20% of all lung cancers. The therapeutic option for advanced or metastatic bronchopulmonary NETs is mainly palliation of symptoms; options need to be individualized and, therefore, rely on the knowledge of multidisciplinary teams. Somatostatin analogs have been widely used in NETs for control of hormonal syndromes and are currently under evaluation for their antiproliferative activity. Here, we present a case of NET of the lung, for which we achieved long-term disease control with a treatment comprising the somatostatin analog lanreotide Autogel(®) in a patient with limited therapeutic options due to considerable comorbidity, while preserving his quality of life.

Phase I study of pasireotide (SOM 230) and everolimus (RAD001) in advanced neuroendocrine tumors

Octreotide and everolimus have demonstrated efficacy in neuroendocrine tumors. Pasireotide is a somatostatin analog with binding affinity to a broader range of somatostatin receptor subtypes than octreotide. We performed a phase I study to evaluate the safety and feasibility of combining pasireotide with everolimus in patients with advanced neuroendocrine tumors. Cohorts of patients with advanced neuroendocrine tumors were treated with escalating doses of pasireotide (600-1200  μg s.c. b.i.d., followed by pasireotide LAR 40-60  mg i.m. monthly) and everolimus (5-10  mg daily). Twenty-one patients were treated. Dose-limiting toxicities consisting of grade 3 rash and grade 3 diarrhea were observed. Twelve patients were safely treated at the maximum protocol-defined dose level of pasireotide LAR 60  mg i.m. monthly and everolimus 10  mg daily. Hyperglycemia was common; other observed toxicities were consistent with the known toxicities of either agent alone. Partial tumor response was observed in one patient; 17 (81%) patients experienced at least some tumor regression as their best response to therapy. In conclusion, pasireotide LAR 60  mg i.m. monthly in combination with everolimus 10  mg daily is feasible and associated with preliminary evidence of antitumor activity in patients with advanced neuroendocrine tumors. Further studies evaluating this combination are warranted.

Microencapsulation of small intestinal neuroendocrine neoplasm cells for tumor model studies

Basic cancer research is dependent on reliable in vitro and in vivo tumor models. The serotonin (5-HT) producing small intestinal neuroendocrine tumor cell line KRJ-1 has been used in in vitro proliferation and secretion studies, but its use in in vivo models has been hampered by problems related to the xeno-barrier and tumor formation. This may be overcome by the encapsulation of tumor cells into alginate microspheres, which can function as bioreactors and protect against the host immune system. We used alginate encapsulation of KRJ-1 cells to achieve long-term functionality, growth and survival. Different conditions, including capsule size, variations in M/G content, gelling ions (Ca(2+) /Ba(2+)) and microcapsule core properties, and variations in KRJ-1 cell condition (single cells/spheroids) were tested. Viability and cell growth was evaluated with MTT, and confocal laser scanner microscopy combined with LIVE/DEAD viability stains. 5-HT secretion was measured to determine functionality. Under all conditions, single cell encapsulation proved unfavorable due to gradual cell death, while encapsulation of aggregates/spheroids resulted in surviving, functional bioreactors. The most ideal spheroids for encapsulation were 200-350 μm. Long-term survival (>30 days) was seen with solid Ca(2+) /Ba(2+) microbeads and hollow microcapsules. Basal 5-HT secretion was increased (sixfold) after hollow microcapsule encapsulation, while Ca(2+) /Ba(2+) microbeads was associated with normal basal secretion and responsiveness to cAMP/PKA activation. In conclusion, encapsulation of KRJ-1 cells into hollow microcapsules produces a bioreactor with a high constitutively activate basal 5-HT secretion, while Ca(2+) /Ba(2+) microbeads provide a more stable bioreactor similar to non-encapsulated cells. Alginate microspheres technology can thus be used to tailor different functional bioreactors for both in vitro and in vivo studies.

Balance between somatostatin and D2 receptor expression drives TSH-secreting adenoma response to somatostatin analogues and dopastatins

CONTEXT

First-line therapy for thyrotropin-secreting pituitary adenomas (TSHomas) is neurosurgery, while medical treatment rests mainly on somatostatin analogues. Clinically available sst(2) -preferring analogues, octreotide and lanreotide, induce normalization of hormone levels in approximately 90% of patients and tumour shrinkage in 45%.

OBJECTIVE

We evaluated somatostatin 1, 2, 3 and 5 and dopamine D2 receptor expression in tumour samples from three TSHomas, and the relationships between receptor expression, in vitro antiproliferative response and clinical data, including octreotide test and three months of therapy with octreotide long-acting repeatable (LAR). TSHoma cell proliferation was tested in vitro using octreotide, cabergoline and two chimeric compounds, BIM-23A760 and BIM-23A387.

RESULTS

All patients showed significant TSH lowering to acute octreotide test, but a hormonal response to long-term treatment was observed in only two patients, showing a high sst(5) /sst(2) ratio. Patient 2, characterized by high expression of sst(2) and sst(1) and a relative lower expression of sst(5) , experienced tachyphylaxis after prolonged octreotide treatment. In vitro, the somatostatin/dopamine receptor agonist BIM-23A760 caused the highest antiproliferative effect among those tested. Combined treatment with octreotide and cabergoline displayed an additive effect of magnitude comparable to that of the other chimeric compound (BIM-23A387). Octreotide resistance was confirmed in cells isolated from the nonresponder patient, although it could be overcome by treatment with the chimeric compounds.

CONCLUSIONS

  A high sst(5) /sst(2) ratio might be predictive of a positive outcome to long-term treatment with somatostatin analogues in TSHomas. Moreover, combined somatostatin and D(2) receptor targeting might be considered as a potential tool to improve the response rate in octreotide-resistant tumours.

The role of somatostatin and dopamine D2 receptors in endocrine tumors

Somatostatin (SS) and dopamine (DA) receptors have been highlighted as two critical regulators in the negative control of hormonal secretion in a wide group of human endocrine tumors. Both families of receptors belong to the superfamily of G protein-coupled receptors and share a number of structural and functional characteristics. Because of the generally reported high expression of somatostatin receptors (SSTRs) in neuroendocrine tumors (NET), somatostatin analogs (SSA) have a pronounced role in the medical therapy for this class of tumors, especially pituitary adenomas and well-differentiated gastroenteropancreatic NET (GEP NET). Moreover, NET express not only SSTR but also frequently dopamine receptors (DRs), and DA agonists targeting the D(2) receptor (D(2)) have been demonstrated to be effective in controlling hormone secretion and cell proliferation in in vivo and in vitro studies. The treatment with SSAs combined with DA agonists has already been demonstrated efficacious in a subgroup of patients with GH-secreting pituitary adenomas and few reported cases of carcinoids. The recent availability of new selective and universal SSA and DA agonists, as well as the chimeric SS/DA compounds, may shed new light on the potential role of SSTR and D(2) as combined targets for biotherapy in NET. This review provides an overview of the latest studies evaluating the expression of SSTR and DR in NET, focusing on their co-expression and the possible clinical implications of such co-expression. Moreover, the most recent insights in SSTR and D(2) pathophysiology and the future perspectives for treatment with SSA, DA agonists, and SS/DA chimeric compounds are discussed.

Therapeutic management of patients with gastroenteropancreatic neuroendocrine tumours

Patients with neuroendocrine tumours (NETs) are best managed in a specialist centre as part of a multidisciplinary team comprising gastroenterologists, oncologists, endocrinologists, gastrointestinal and hepatopancreaticobiliary surgeons, pathologists, nuclear medicine physicians and technicians, radiologists, specialist nurses, pharmacists, biochemists and dieticians. This should ideally be led by a clinician with experience and interest in NETs. Although the number of medical treatments and clinical trials has increased in the decade, there is still a lack of prospective randomised trials; thus, management is mainly based on limited often single-centre studies, although there are now formal guidelines based on consensus expert opinion. We have outlined the current optimal management of patients with NETs. We have reviewed therapeutic options including surgery, somatostatin analogues and other biotherapies and peptide receptor-targeted therapy. We have discussed the challenge in managing hepatic metastases including hepatic artery embolisation, ablation and orthotopic liver transplant. In addition, we have briefly reviewed the emerging therapies such as the mammalian target of rapamycin and angiogenic inhibitors and the newer somatostatin analogues.

Small intestinal neuroendocrine cell pathobiology: 'carcinoid' tumors

PURPOSE OF REVIEW

Neuroendocrine tumors, particularly small intestinal tumors, also grouped as 'carcinoids', are defined by an increasing incidence and prevalence, a poor response to current therapies, and confusion regarding appropriate models for drug development. Despite these issues, approximately 350 studies were published in the last year.

RECENT FINDINGS

Two sources of confusion are clearly apparent. First, pharmacotherapeutic studies using pancreatic tumor cell lines as models for small intestinal or 'carcinoid' tumor biology are considered appropriate. Second, there is continued inclusion and analysis of pancreatic endocrine tumors with small intestinal neuroendocrine tumors in clinical studies. One highlight of this year is additional data confirming the significant differences between pancreatic tumor cell lines and small intestinal cell lines, the different gene expressions, for example, PAX8, between these two tumor types, and the observations that these two tumors respond differently in clinical trials, for example, to mammalian target of rapamycin (mTOR) inhibitors. Other highlights include delineating the role of the tumor microenvironment in the development of fibrosis and developing a minimum pathology dataset and a prognostic nomogram that may have utility in stratifying patients for clinical studies.

SUMMARY

A number of interesting studies have been published during 2009-2010, but critical areas remain that require resolution. Current data, for the most part, reflect amplification of previously held concepts with modest advances in novel information.

Limitations in small intestinal neuroendocrine tumor therapy by mTor kinase inhibition reflect growth factor-mediated PI3K feedback loop activation via ERK1/2 and AKT

BACKGROUND

Treatment of small intestinal neuroendocrine tumors (SINETs) with mammalian target of rapamycin (mTOR) inhibitors alone or with somatostatin analogs has been proposed as effective therapy, because both agents have been reported to exhibit antiproliferative activity. Because adenocarcinomas escape mTOR inhibition, we examined whether the escape phenomenon occurred in SINETs and whether usage of somatostatin analogs with mTOR inhibitors surmounted loss of inhibition.

METHODS

The effects of the somatostatin analog octreotide (OCT), the mTOR inhibitor RAD001 (RAD), or the combination were evaluated in SINET cell lines (KRJ-I, H-STS) using cell viability assays, western blotting, enzyme-linked immunosorbent assay, and reverse-transcription polymerase chain reaction to assess antiproliferative signaling pathways and feedback regulation.

RESULTS

RAD (10(-9) M) incompletely decreased cell viability (-40% to +15%); growth escape (P < .001) was noted at 72 hours in both cell lines. Phosphorylated (p)mTOR/mTOR and pp70S6K/p70S6K ratios were decreased but were associated with increases in phosphorylated extracellular signal-regulated kinase (pERK)/ERK and pAKT/AKT in both cell lines, whereas phosphorylated insulin-like growth factor 1 receptor (pIGF-1R)/IGF-1R levels were elevated only in H-STS cells. Increased (P < .05) transcript levels for AKT1, MAPK, mTOR, IGF-1R, IGF-1, and TGFβ1 were evident. OCT (10(-6) M) itself had no significant effect on growth signaling in either cell line. An antiproliferative effect (66 ± 5%) using OCT+RAD was only noted in the KRJ-I cells (P < .05).

CONCLUSIONS

SINET treatment with the mTOR inhibitor RAD had no antiproliferative effect based on activation of pAKT and pERK1/2. A combinatorial approach using OCT and RAD failed to overcome this escape phenomenon. However, differences in RAD response rates in individual NET cell lines suggested that pretreatment identification of different tumor sensitivity to mTOR inhibitors could provide the basis for individualized treatment.

From targets to treatments: a review of molecular targets in pancreatic neuroendocrine tumors

Pancreatic neuroendocrine tumors (pancreatic NET) are relatively rare, slowly growing tumors, although their incidence is increasing, and patients may survive for several years with metastatic disease. Apart from symptomatic relief, there have been few treatment options for these tumors in the past. More recently, investigators have explored the potential of molecularly targeted agents in treating pancreatic NET, with some success. In this review, we consider the data supporting exploitation of different targets in pancreatic NET, including peptide receptors, receptor tyrosine kinases (involved in tumor angiogenesis and more directly supporting tumor growth), and intracellular targets, such as the mammalian target of rapamycin (mTOR), which has a central role in regulating cell growth, metabolism, and apoptosis. Probably due to the paucity of pancreatic NET, many clinical trials to date have included heterogeneous NET populations, and there are few randomized studies of this specific patient population. Very recently, promising results have been achieved in placebo-controlled, phase III trials with the multitargeted tyrosine kinase inhibitor, sunitinib, and the mTOR inhibitor, everolimus. These agents have been approved or are currently being reviewed by authorities for use in patients with pancreatic NET. Here we review potential molecular targets in pancreatic NET and summarize the available data for targeted agents from phase II and III trials open to patients with this tumor.

Octreotide LAR: safety and tolerability issues

BACKGROUND

Somatostatin analogues are the cornerstone in therapy of acromegaly and functioning neuroendocrine tumors. Long-acting retard formulations have improved patient survival and contributed considerably to quality of life. The first such compound was octreotide LAR ('long-acting release'), characterized by high affinity to somatostatin receptor subtypes 2 and 5, which has to be injected intramuscularly every 4 weeks.

OBJECTIVE

The aim was to screen all octreotide LAR-related literature and assess the compound's profile for safety and tolerability.

METHODS

An extensive literature search has been performed using the MEDLINE database to retrieve data from clinical studies evaluating the efficacy and tolerability of octreotide LAR.

RESULTS/CONCLUSION

Octreotide LAR is well tolerated; however, diarrhea and gallstone formation were identified as the main adverse events. Impairment of glucose homeostasis was a regular phenomenon, but its occurrence was unpredictable. General side effects such as headache, abdominal discomfort or fatigue were also reported. According to incidental case reports, administration during pregnancy appears to be safe for both mother and child; however, definitive evidence is missing. In addition, octreotide LAR has been evaluated for further indications including treatment of solid tumor entities, due to its antiproliferative effect. Currently, several compounds (lanreotide, SOM230) with a broader receptor spectrum are under evaluation and may improve treatment efficacy and lower incidence of side effects.

Somatostatin analogues: treatment of pituitary and neuroendocrine tumors

This chapter summarizes the most recent data on the use of the somatostatin analogues (SSAs), octreotide (OCT) and lanreotide for the treatment of patients with pituitary and neuroendocrine tumors (NETs). These two analogues have a high affinity for somatostatin receptor (SSR) sub-types 2 and 5. The major indications of these compounds are GH- and TSH-secreting pituitary adenomas, secreting NETs and non-functioning NETs in progression. Pasireotide is a new analogue, with a receptor pattern different from previous analogues since it binds with high affinity to SSR types 1, 2, 3 and 5. This analogue will be available to treat patients with ACTH-secreting adenomas in a short time. A recent study has also demonstrated a beneficial effect of OCT long-acting release in patients with non-functioning NETs independently from their progression status. These data open the treatment with SSAs in all NET patients.

Autoregulatory effects of serotonin on proliferation and signaling pathways in lung and small intestine neuroendocrine tumor cell lines

BACKGROUND

: Survival rates for gastrointestinal (GI) and bronchopulmonary (BP) neuroendocrine tumors (NETs) have not altered significantly (5-year survival rate: GI NETs, 64.1%; BP NETs, 87%-89%) in 30 years (from 1973 to 2004). No effective or specific antineoplastic agents are available to date, although somatostatin analogs inhibit NET 5-hydroxytryptophan (5-HT) secretion. Given the expression of 5-HT receptors on NETs, the authors hypothesized that 5-HT autoregulated NET proliferation.

METHODS

: Proliferation was evaluated in 3 NET cell lines using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide uptake; in addition, real-time polymerase chain reaction analyses and enzyme-linked immunosorbent assay studies were performed to delineate 5-HT-mediated signaling pathways. To determine the receptor and role of endogenous 5-HT production, the effects of ketanserin (5-HT receptor subtypes 2A and 2C [5-HT(2A/2C)]); ondansetron (5-HT(3)); and the suicide inhibitor of the rate-limiting enzyme for 5-HT synthesis, tryptophan hydroxylase (7-HTP) were investigated.

RESULTS

: Exogenously added 5-HT stimulated proliferation in atypical BP NET NCI-H720 cells (+50%; half-maximal stimulatory concentration [EC(50)] = 10 nM), in typical BP NET NCI-H727 cells (+40%; EC(50) = 0.01 nM), and in GI NET KRJ-I cells (+60%; EC(50) = 25 nM). In NCI-H720 cells, proliferation was inhibited by ketanserin (half-maximal inhibitory concentration [IC(50)] = 0.06 nM) and ondansetron (IC(50) = 0.4 nM) and also was inhibited by 7-HTP (IC(50) = 0.3 nM). In NCI-H727 cells, ketanserin and 7-HTP inhibited proliferation (IC(50) = 0.3 nM and IC(50) = 2.3 nM, respectively), whereas ondansetron had no effect. In KRJ-I cells, ketanserin (IC(50) = 0.1 nM) and 7-HTP (IC(50) = 0.6 nM), but not ondansetron, inhibited proliferation. In all cell lines, 5-HT activated proliferation through extracellular signal-regulated kinase 1 (ERK1) and ERK2 phosphorylation and c-Jun N-terminal kinase (JNK)-mediated pathways (c-JUN and Ki-67 transcription). An autoregulatory effect was indicated by the 7-HTP-mediated inhibition of extracellular 5-HT and downstream effects on NET proliferation.

CONCLUSIONS

: Lung and GI NET proliferation was autoregulated by 5-HT through alterations in ERK and JNK signaling. Targeting NET cells with 5-HT(2) receptor antagonists and 7-HTP reversed proliferation. The current results indicated that 5-HT(2) receptor subtype-specific antagonists may represent a viable antiproliferative therapeutic strategy. Cancer 2009. (c) 2009 American Cancer Society.

Accomplishments in 2008 in the management of gastrointestinal neuroendocrine tumors

Overview of the Disease ProcessIncidencePrognostic FactorsGeneral Therapy StandardsAccomplishments and Lack of Accomplishments During the YearSomatostatin AnalogsPeptide Receptor-Targeted TherapySelective Internal Radiotherapy (SIRT)CYTOTOXIC THERAPIES: TemozolomideVEGF Pathway InhibitorsmTOR InhibitorsDevelopment of BiomarkersWhat Needs to be Done (Application of the Accomplishments)Controversies and DisagreementsHistologic Classification and Staging of Neuroendocrine TumorsClinical Trial Design and End PointsFuture Directions.

Review article: future therapies for management of metastatic gastroenteropancreatic neuroendocrine tumours

BACKGROUND

Gastroenteropancreatic neuroendocrine tumours (GEP NETs) are relatively uncommon tumours that occur anywhere within the gastrointestinal tract. The prevalence of GEP NETs is estimated to be 35 per 100 000 population. Patients often present with metastatic disease and consequently, palliative treatments form the mainstay of therapy.

AIM

To review the current and novel therapeutic options for management of GEP NETs.

METHODS

Searches for all studies related to GEP NETs, NETs and carcinoid tumours in Medline and abstracts from international meetings.

RESULTS

Somatostatin analogues remain the first line therapy for management of symptoms of GEP NETs and may have anti-proliferative action. New somatostatin analogues with different somatostatin receptor affinity have been developed. Radionuclide peptide receptor therapy is established in patients with positive somatostatin scintigraphy. A number of new agents and targeted therapies are currently being evaluated in a phase I and II studies and these include angiogenic inhibitors, mammalian target of rapamycin inhibitors and immune therapies.

CONCLUSIONS

A number of nonsurgical therapies are available for management of gastroenteropancreatic neuroendocrine tumours. It is hoped, the development of some of these promising novel therapies will expand the therapeutic armamentarium.