Somatostatin analogue treatment of neuroendocrine tumours

Pituitary apoplexy in endocrinologically silent adenoma during somatostatin analog administration for pancreatic neuroendocrine tumor: A case report

A dopamine agonist administered for prolactinoma treatment and pituitary stimulation tests are reported as risk factors for pituitary apoplexy. We report a case of an 82-year-old patient who suffered from pituitary apoplexy in an endocrinologically silent adenoma during lanreotide administration. The patient was diagnosed with a pancreatic neuroendocrine tumor with lymph node metastasis and treated with lanreotide for two years. An endoscopic endonasal transsphenoidal approach was used for tumor and hematoma removal. The specimen showed growth hormone and prolactin positivity and was diagnosed as pit1-lineage plurihormonal adenoma. The tumor also showed positivity for somatostatin receptor 2. Thus, lanreotide treatment is a risk factor for pituitary apoplexy even in silent adenoma.

Clinical, pathophysiologic, genetic and therapeutic progress in Primary Bilateral Macronodular Adrenal Hyperplasia

Patients with primary bilateral macronodular adrenal hyperplasia (PBMAH) usually present bilateral benign adrenocortical macronodules at imaging and variable levels of cortisol excess. PBMAH is a rare cause of primary overt Cushing's syndrome, but may represent up to one third of bilateral adrenal incidentalomas with evidence of cortisol excess. The increased steroidogenesis in PBMAH is often regulated by various G-protein coupled receptors aberrantly expressed in PBMAH tissues; some receptor ligands are ectopically produced in PBMAH tissues creating aberrant autocrine/paracrine regulation of steroidogenesis. The bilateral nature of PBMAH and familial aggregation, led to the identification of germline heterozygous inactivating mutations of the ARMC5 gene, in 20-25% of the apparent sporadic cases and more frequently in familial cases; ARMC5 mutations/pathogenic variants can be associated with meningiomas. More recently, combined germline mutations/pathogenic variants and somatic events inactivating the KDM1A gene were specifically identified in patients affected by GIP-dependent PBMAH. Functional studies demonstrated that inactivation of KDM1A leads to GIP-receptor (GIPR) overexpression and over or down-regulation of other GPCRs. Genetic analysis is now available for early detection of family members of index cases with PBMAH carrying identified germline pathogenic variants. Detailed biochemical, imaging, and co-morbidities assessment of the nature and severity of PBMAH is essential for its management. Treatment is reserved for patients with overt or mild cortisol/aldosterone or other steroid excesses taking in account co-morbidities. It previously relied on bilateral adrenalectomy; however recent studies tend to favor unilateral adrenalectomy, or less frequently, medical treatment with cortisol synthesis inhibitors or specific blockers of aberrant GPCR.

Metastatic medullary thyroid carcinoma presenting as ectopic Cushing's syndrome

SUMMARY

A 41-year-old male presented to the Emergency Department with a 6-month history of back and hip pain. Skeletal survey revealed bilateral pubic rami fractures and MRI of the spine demonstrated multiple thoracic and lumbar fractures. Secondary work up for osteoporosis was undertaken. There was no evidence of hyperparathyroidism and the patient was vitamin D replete. Testosterone (T) was low at 1.7 nmol/L (8.6-29.0) and gonadotrophins were undetectable. The patient failed a 1 mg dexamethasone suppression test (DST) with a morning cortisol of 570 nmol/L (<50) and subsequently a low dose DST with a cortisol post 48 h of dexamethasone of 773 nmol/L (<50) and an elevated ACTH 98 ng/L. A corticotropin-releasing factor (CRF) test suggested ectopic ACTH secretion. The patient was commenced on teriparatide for osteoporosis and metyrapone to control the hypercortisolaemia. A positron emission tomography (PET) scan to look for the source of ACTH secretion demonstrated right neck adenopathy. Biopsy and subsequent lymph node dissection were performed and histology revealed a metastatic neuroendocrine tumour. Immunostaining was positive for calcitonin and thyroid transcription factor 1 (TTF1). Serum calcitonin was also significantly elevated at 45 264 ng/L (<10). The patient proceeded to a total thyroidectomy and left neck dissection. Histology confirmed a 7 mm medullary thyroid carcinoma (MTC). Post-operatively, the patient commenced vandetanib therapy and achieved a clinical and biochemical response. After approximately 18 months of vandetanib therapy, the patient developed recurrent disease in his neck. He is currently on LOXO-292 and is doing well 36 months post-diagnosis.

LEARNING POINTS

Unexplained osteoporosis requires thorough investigation and the workup for secondary causes is not complete without excluding glucocorticoid excess. MTC should be considered when searching for sources of ectopic ACTH secretion. Resistance to tyrosine kinase inhibitors is well described with MTC and clinicians should have a low threshold for screening for recurrent disease.

Effects of Ketoconazole on ACTH-Producing and Non-ACTH-Producing Neuroendocrine Tumor Cells

Prolonged remission of hypercortisolism with steroidogenesis inhibitors has been described in patients with ectopic adrenocorticotropic hormone (ACTH) syndrome. The anti-proliferative and pro-apoptotic effect of ketoconazole in human cancer cells was previously suggested. The aim of this study was to explore the effects of ketoconazole on ACTH-producing and non-ACTH-producing neuroendocrine tumor (NET) cell lines. The effects of ketoconazole alone, and in combination with somatostatin analogs, were evaluated in two human cell lines: DMS-79 (ectopic ACTH-producing small cell lung carcinoma) and BON-1 (human pancreatic NET). Total DNA measurement, apoptosis, cell cycle, chromogranin A (CgA)/proopiomelanocortin (POMC) expression by qRT-PCR, serotonin, CgA, and ACTH secretion assays were performed. In both cell lines, ketoconazole significantly suppressed cell growth and colony formation in a dose and time-dependent manner. The effect in DMS-79 was primarily cytotoxic, while it was more apoptotic in BON-1 cells. Ketoconazole also induced increase in G0/G1 phase in both cell lines and arrest in phase G2/M of BON-1 cells. Ketoconazole did not affect the secretion of serotonin, CgA, ACTH, or the mRNA expression of CgA and POMC. Decreased serotonin secretion was observed after the combination treatment with pasireotide. These results suggest a direct effect of ketoconazole on cell proliferation, apoptosis, and cell cycle in both ACTH- and non-ACTH-producing NET cells.

New Insights in the Design of Bioactive Peptides and Chelating Agents for Imaging and Therapy in Oncology

Many synthetic peptides have been developed for diagnosis and therapy of human cancers based on their ability to target specific receptors on cancer cell surface or to penetrate the cell membrane. Chemical modifications of amino acid chains have significantly improved the biological activity, the stability and efficacy of peptide analogues currently employed as anticancer drugs or as molecular imaging tracers. The stability of somatostatin, integrins and bombesin analogues in the human body have been significantly increased by cyclization and/or insertion of non-natural amino acids in the peptide sequences. Moreover, the overall pharmacokinetic properties of such analogues and others (including cholecystokinin, vasoactive intestinal peptide and neurotensin analogues) have been improved by PEGylation and glycosylation. Furthermore, conjugation of those peptide analogues to new linkers and bifunctional chelators (such as AAZTA, TETA, TRAP, NOPO etc.), produced radiolabeled moieties with increased half life and higher binding affinity to the cognate receptors. This review describes the most important and recent chemical modifications introduced in the amino acid sequences as well as linkers and new bifunctional chelators which have significantly improved the specificity and sensitivity of peptides used in oncologic diagnosis and therapy.

Somatostatin: One of the Rare Multifunctional Inhibitors of Mammalian Species

This review article has for major main objectives to give an overlook of the major physiological effects of somatostatin on different organs. It will cover first the general aspect of the hormone, its cDNA and its protein maturation process, as well as its characterization in various organs. This aspect will be followed by the factors involved in the control of its secretion, its intracellular mode of action, and its general action on physiological processes. Secondly, the review will focus on the pancreas, looking at its in vivo and in vitro actions with special attention on its effects on normal pancreas growth and pancreatic tumors.

Epidrug-induced upregulation of functional somatostatin type 2 receptors in human pancreatic neuroendocrine tumor cells

Somatostatin receptors are a pivotal target for treatment of pancreatic neuroendocrine tumors (pNET), either with somatostatin analogues (SSA) or radiolabeled SSA. The highest affinity target for the most commonly used SSA is the somatostatin receptor type 2 (sst₂ ). An important factor that may complicate treatment efficacy, is the variable number of receptors expressed on pNETs. Gene expression is subject to complex regulation, in which epigenetics has a central role. In this study we explored the possible role of epigenetic modifications in the variations in sst₂ expression levels in two human pNET cell lines, BON-1 and QGP-1. We found upregulation of sst₂ mRNA after treatment with the epidrugs 5-aza-2'-deoxycytidine (5-aza-dC) and valproic acid (VPA), an increased uptake of radiolabeled octreotide, as well as increased sensitivity to the SSA octreotide in functional cAMP inhibition. At epigenetic level we observed low methylation levels of the sst₂ gene promoter region irrespective of expression. Activating histone mark H3K9Ac can be regulated with epidrug treatment, with an angle of effect corresponding to the effect on mRNA expression. Repressive histone mark H3K27me3 is not regulated by either 5-aza-dC or VPA. We conclude that epidrug treatment, in particular with combined 5-aza-dC and VPA treatment, might hold promise for improving and adding to current SSA treatment strategies of patients with pNETs.

New avenues in the medical treatment of Cushing's disease: corticotroph tumor targeted therapy

Cushing's disease (CD) is a condition of chronic hypercortisolism caused by an adrenocorticotropic hormone-secreting pituitary adenoma. First-line transsphenoidal surgery is not always curative and disease sometimes recurs. Radiotherapy often requires months or years to be effective, and is also not curative in many cases. Consequently, effective medical therapies for patients with CD are needed. Corticotroph adenomas frequently express both dopamine (D2) and somatostatin receptors (predominantly sstr5). Pasireotide, a somatostatin analog with high sstr5 binding affinity, has shown urinary free cortisol (UFC) reductions in most patients with CD in a large phase 3 trial, with UFC normalization and tumor shrinkage in a subset of patients. Adverse events were similar to other somatostatin analogs, with the exception of the degree and severity of hyperglycemia. Two small trials (one prospective and one retrospective) have suggested that cabergoline, a D2 receptor agonist, could be effective in normalizing UFC, but current long-term data results are conflicting. Combination treatment with pasireotide plus cabergoline and the adrenal steroidogenesis inhibitor ketoconazole has been successful, but further investigation in larger trials is necessary. Retinoic acid also showed interesting results in a recent very small prospective study. Glucocorticoid receptor blockade with mifepristone has recently demonstrated improvement in signs and symptoms of Cushing's and glycemic control; however, this modality does not address the etiology of the disease and has inherent adverse events related to its mechanism of action. Pituitary-targeted medical therapies will soon play a more prominent role in treating CD, and may potentially become first-line medical therapy when surgery fails or is contraindicated.

A review of the use of somatostatin analogs in oncology

Somatostatin is a neuropeptide produced by paracrine cells that are located throughout the gastrointestinal tract, lung, and pancreas, and is also found in various locations of the nervous system. It exerts neural control over many physiological functions including inhibition of gastrointestinal endocrine secretion through its receptors. Potent and biologically stable analogs of somatostatin have been developed. These somatostatin analogs show different efficacy on different receptors, and receptors are varyingly concentrated in specific tissues. Antitumor and antisecretory effects of somatostatin analogs in cancer have been shown in several in vivo and in vitro studies. However, these activities have not always yielded into clinically relevant patient outcome benefit. Somatostatin analogs are of clinical benefit in treating symptoms of ectopic hormone secretion (adrenocorticotropic hormone, growth hormone-releasing hormone) in lung cancer, without inducing a significant tumor response. They have also been shown to induce a statistically significant decrease in bone pain and increase in Karnofsky performance status in patients with metastatic prostate cancer. Somatostatin analogs alone or in combination with other agents have only limited antitumoral effect in breast cancer. In gastrointestinal cancers, studies have not shown an objective tumor response to somatostatin analogs except in endocrine tumors of the liver with symptomatic and biochemical improvement. In neuroendocrine tumors of the gastrointestinal system and pancreas, very high symptomatic and biochemical response rates have been achieved with somatostatin analogs. Antiproliferative activity has been clearly shown in metastatic midgut neuroendocrine tumors.

Isoproterenol induced hypertrophy and associated signaling pathways are modulated by somatostatin in H9c2 cells

BACKGROUND

Somatostatin (SST), a growth hormone inhibitory peptide plays key role in regulation of cell proliferation via modulation of mitogen activated protein kinases (MAPKs) and cell survival pathway. In cardiac physiology, β-Adrenergic receptors (β-ARs) play crucial role in regulation of downstream signaling pathways in receptor specific manner. The aim of the current study was to delineate the mechanistic insight for the role of SST on β-AR mediated signaling which promotes hypertrophy and apoptosis in rat fetal cardiomyocytes (H9c2 cells). Accordingly, SST dependent changes in signaling molecules including second messenger cAMP, PKA/CREB as well as MAPKs including ERK and p38 which are key mediators of hypertrophy and apoptosis were analyzed.

METHODS AND RESULTS

In the present study, we determined receptor specific effects on intracellular cAMP levels, signaling by western blot analysis and apoptosis by using JC-1 and Hoechst-33258 staining. Here, we present the data which indicates that SST inhibits isoproterenol induced hypertrophy and apoptosis in H9c2 cells. Importantly, SST inhibits β-ARs agonist induced cAMP activation and SST mediated inhibition of cAMP was enhanced in presence of β-ARs antagonist. SST enhances β2AR agonist formoterol mediated effects on PKA, CREB and ERK1/2 phosphorylations whereas it inhibits isoproterenol mediated ERK1/2 and p38 signaling in concentration dependent manner.

CONCLUSIONS

Taken together, these results presented here provide a novel insight for the potential role of SST in regulation of β-AR mediated effects on hypertrophy and modulation of hypertrophy promoting signaling in H9c2 cells.

Monoclonal antibodies against the human somatostatin receptor subtypes 1-5: development and immunohistochemical application in neuroendocrine tumors

BACKGROUND

Activation of somatostatin receptors (sstr1-5) by somatostatin and its analogues exerts an inhibitory effect on hormone secretion and provides the basis for the treatment of a range of endocrine diseases such as acromegaly, Cushing's disease and neuroendocrine tumors (NET). The lack of well-characterized commercially available sstr subtype-specific antibodies prevents routine identification of the sstr expression profile in patients.

METHODS

We generated and characterized new mouse monoclonal antibodies (mAbs) targeting the five human sstr subtypes using ELISA and immunohistochemistry, and tested their suitability in formalin-fixed and paraffin-embedded (FFPE) human tissues and archival samples of normal pancreatic tissue and NET.

RESULTS

All mAbs were highly specific with no cross-reactivity. The sstr1-5 immunoreactivity in gastrointestinal NET (n=67) was correlated with clinicopathologic data. With the exception of sstr3, NET were highly positive for all receptor subtypes (42, 63, 6, 32 and 65% of tumors were positive for sstr1, sstr2a, sstr3, sstr4 and sstr5, respectively). sstr1, sstr2a and sstr5 were present at the plasma membrane and in the cytoplasm of tumor cells, whereas sstr3 and sstr4 were almost exclusively cytoplasmic. Immunoreactivity of sstr1, sstr2a and sstr4 tended to decrease as tumor aggressiveness increased. sstr5 showed an opposite pattern, with higher staining in well-differentiated carcinomas compared with well-differentiated tumors. sstr5 immunoreactivity was correlated with the presence of metastases and angioinvasion, suggesting a possible association with more aggressive behavior.

CONCLUSION

Determination of the sstr1-5 by immunohistochemistry using subtype-specific mAbs is feasible in FFPE tissue and may provide a tool for routine clinical practice.

The value of 11C-5-hydroxy-tryptophan positron emission tomography in neuroendocrine tumor diagnosis and management: experience from one center

Many neuroendocrine tumors (NET) are small and may escape localization by conventional imaging techniques. In such cases, 11C-5-hydroxy-tryptophan (11C-5-HTP) positron emission tomography (PET) has been tested as an additional diagnostic tool. Nine patients with clinically, biochemically and/or histologically confirmed NET and negative computerized tomography (CT) or magnetic resonance imaging (MRI), and 111In-pentetreotide (Octreoscan) scintigraphy underwent imaging with 11C-5-HTP-PET/CT in order to: 1) detect the primary tumor lesion in three patients; 2) detect residual disease in two patients with appendiceal carcinoid, one with rectal carcinoid, one with midgut carcinoid, and one with ectopic ACTH secretion (EAS) due to residual pulmonary carcinoid; and 3) restage a patient with medullary thyroid carcinoma (MTC) and hepatic metastases. 11C-5-HTP-PET/CT detected lesions in the mediastinum in a patient with EAS due to a pulmonary carcinoid, further hepatic metastases in a patient with carcinoid syndrome (CS) from a NET of unknown primary, further hepatic metastases in the patient with MTC, and hepatic metastases in the patient with midgut carcinoid. The 11C-5-HTP-PET/CT findings contributed to radical cure of the patient with recurrent EAS, and pointed towards bilateral adrenalectomy in the patient with EAS without evident primary tumor. In addition, 11C-5- HTP-PET/CT directed towards combined surgical and medical treatment in the patient with CS and multiple rather than single hepatic metastases and in the patient with midgut carcinoid, and towards continuation of medical treatment in the patient with MTC. 11C-5-HTP-PET/CT is a useful imaging technique, providing additional information for the diagnosis, staging and decision-making regarding management of patients with NET.

Prise en charge du syndrome de Nelson: données actuelles

PURPOSE

Nelson's syndrome is a severe complication of bilateral adrenalectomy performed in the treatment of some Cushing's diseases, and its management remains difficult. Trough the observation of a patient suffering from a severe form of Nelson's syndrome for more than 10 years, the authors review the literature and discuss the main current therapeutic possibilities.

CURRENT KNOWLEDGE AND KEY POINTS

Many molecules have been used with variable results. In our observation cabergoline at 2 mg per week seems to be efficient after a 3 and a half years follow-up, in accordance with some recent publications. More than bromocriptine, this dopamine agonist provides interesting prospects for this disease's management. Moreover, if the conventional treatments as valproic acid or cyproheptadine are not very efficient, somatostatin analogs seem to be of some therapeutic interest.

FUTURE PROSPECTS AND PROJECTS

New molecules are currently evaluated, but studies are difficult to conduct because of the low disease prevalence. Tumour receptors analysis undoubtedly constitutes an attractive way to find new therapeutic targets.

A case of bronchopulmonary carcinoid tumor: the role of octreotide scanning in localization of an ectopic source of ACTH

BACKGROUND

Bronchopulmonary carcinoids are neuroendocrine tumors. They can present with Cushing's syndrome secondary to ectopic adrenocorticotropic hormone (ACTH) secretion. Curative resection is possible only after adequate localization of the ectopic source.

OBJECTIVE

To describe a case that illustrates the role of octreotide scanning in the management of a bronchopulmonary carcinoid.

RESULTS

The use of preoperative and postoperative octreotide scanning aided in performing a limited resection, thereby preserving the lung parenchyma.

CONCLUSIONS

We propose that octreotide scanning can be a very important and informative test in the management of carcinoid tumors. In situations when conventional imaging is not conclusive, octreotide scanning may be of help in determining the source of ectopic ACTH syndrome.

Carcinoid syndrome: diagnosis and medical management

Gastro-intestinal carcinoids are slow growing tumors arising from enterochromaffin or Kulchitsky cells. Their clinical presentation depends on what combination of bioactive substances is secreted. Midgut carcinoid can present with the carcinoid syndrome in the presence of liver metastases. Its most typical clinical manifestations include cutaneous flushing and diarrhea. A nonspecific biochemical tumor marker for carcinoid tumors is serum chromogranin A and a specific marker for the carcinoid syndrome is the increased urinary excretion of 5-hydroxy indole acetic acid (5-HIAA). Localizing studies in carcinoid tumors/syndrome are: transabdominal ultrasonography (US), endoscopy, endoscopic US, videocapsule endoscopy, computerized tomography, magnetic resonance imaging, selective abdominal angiography, 111In-pentetreotide scintigraphy (and intraoperative radionuclide probe), 123I (131I)-metaiodobenzylguanidine (MIBG) scintigraphy, bone scintigraphy and 11C-5-HT positron emission tomography (PET). Therapies for carcinoid tumors/syndrome are: surgery, somatostatin analogs, interferon-alpha, radiotherapy, liver dearterialization, liver (chemo, or radio)-embolization, alcohol sclerotherapy of liver metastases, radiofrequency ablation of liver metastases, cryosurgery of liver metastases, occasionally liver transplantation, radiotherapy-coupled somatostatin analogs, 131I-MIBG and occasionally chemotherapy.

Tumours of the midgut (jejunum, ileum and ascending colon, including carcinoid syndrome)

(Neuro-)endocrine tumours of the gastrointestinal tract are also called 'carcinoids'. (Neuro-)endocrine midgut tumours can be categorized according to their clinical behaviour. Most tumours are non-functioning. Functioning tumours are responsible for the carcinoid syndrome. The carcinoid syndrome is almost uniquely associated with midgut carcinoids. Symptoms of the carcinoid syndrome are caused by an excess of biogenic amines, peptides and other factors in the circulation. The typical symptoms of the carcinoid syndrome are diarrhoea, flushing, and carcinoid heart disease. Carcinoid heart disease involves the tricuspid and pulmonary valves and the endocardium. Serum chromogranin A and urinary excretion of 5-hydroxy-indoleacetic acid (5-HIAA) are biochemical markers. Carcinoid tumours express large numbers of high-affinity somatostatin receptors. These can bind the currently available octapeptide somatostatin analogues. In inoperable patients, biotherapy with somatostatin analogues and interferon-alpha is the treatment of choice. Somatostatin analogues and interferon-alpha significantly improve symptoms.

Distinct functional properties of native somatostatin receptor subtype 5 compared with subtype 2 in the regulation of ACTH release by corticotroph tumor cells

In a series of human corticotroph adenomas, we recently found predominant mRNA expression of somatostatin (SS) receptor subtype 5 (sst5). After 72 h, the multiligand SS analog SOM230, which has a very high sst5 binding affinity, but not Octreotide (OCT), significantly inhibited basal ACTH release. To further explore the role of sst5 in the regulation of ACTH release, we conducted additional studies with mouse AtT-20 cells. SOM230 showed a 7-fold higher ligand binding affinity and a 19-fold higher potency in stimulating guanosine 5'-O-(3-thiotriphosphate) binding in AtT-20 cell membranes compared with OCT. SOM230 potently suppressed CRH-induced ACTH release, which was not affected by 48-h dexamethasone (DEX) pretreatment. However, DEX attenuated the inhibitory effects of OCT on ACTH release, whereas it increased the inhibitory potency of BIM-23268, an sst5-specific analog, on ACTH release. Quantitative PCR analysis showed that DEX lowered sst(2A+2B) mRNA expression significantly after 24 and 48 h, whereas sst5 mRNA levels were not significantly affected by DEX treatment. Moreover, Scatchard analyses showed that DEX suppressed maximum binding capacity (B(max)) by 72% when 125I-Tyr3-labeled OCT was used as radioligand, whereas B(max) declined only by 17% when AtT-20 cells were treated with [125I-Tyr11]SS-14. These data suggest that the sst5 protein, compared with sst2, is more resistant to glucocorticoids. Finally, after SS analog preincubation, compared with OCT both SOM230 and BIM-23268 showed a significantly higher inhibitory effect on CRH-induced ACTH release. In conclusion, our data support the concept that the sst5 receptor might be a target for new therapeutic agents to treat Cushing's disease.

Clinical endocrinology and metabolism. Gut endocrine tumours

Endocrine tumours of the gastrointestinal tract and pancreas may present at different disease stages with either hormonal or hormone-related symptoms/syndromes, or without hormonal symptoms. They may occur either sporadically or as part of hereditary syndromes. In the therapeutic approach to a patient with these tumours, excessive hormonal secretion and/or its effects should always be controlled first. A team approach is needed to achieve a balanced opinion on the use of the different therapeutic options in patients with these tumours.

The diagnosis and medical management of advanced neuroendocrine tumors

Neuroendocrine tumors (NETs) constitute a heterogeneous group of neoplasms that originate from endocrine glands such as the pituitary, the parathyroids, and the (neuroendocrine) adrenal, as well as endocrine islets within glandular tissue (thyroid or pancreatic) and cells dispersed between exocrine cells, such as endocrine cells of the digestive (gastroenteropancreatic) and respiratory tracts. Conventionally, NETs may present with a wide variety of functional or nonfunctional endocrine syndromes and may be familial and have other associated tumors. Assessment of specific or general tumor markers offers high sensitivity in establishing the diagnosis and can also have prognostic significance. Imaging modalities include endoscopic ultrasonography, computed tomography and magnetic resonance imaging, and particularly, scintigraphy with somatostatin analogs and metaiodobenzylguanidine. Successful treatment of disseminated NETs requires a multimodal approach; radical tumor surgery may be curative but is rarely possible. Well-differentiated and slow-growing gastroenteropancreatic tumors should be treated with somatostatin analogs or alpha-interferon, with chemotherapy being reserved for poorly differentiated and progressive tumors. Therapy with radionuclides may be used for tumors exhibiting uptake to a diagnostic scan, either after surgery to eradicate microscopic residual disease or later if conventional treatment or biotherapy fails. Maintenance of the quality of life should be a priority, particularly because patients with disseminated disease may experience prolonged survival.

Insulinoma

More than 90% of insulinomas are benign tumors. Insulinomas cause hypoglycemia and thereby symptoms of neuroglycopenia and catecholamine response. During symptoms, blood glucose levels should be less than 40 mg/dl (less than 2.2 mmol/l), concomitant insulin levels should be > or =6 IU/ml (> or =43 pmol/l) and concomitant C-peptide levels > or =0.2 pmol/l. Most insulinomas can be identified intraoperatively by experienced surgeons. Initial therapy consists of administration of frequent meals and/or by glucose infusion. In patients with solitary insulinomas, complete surgical removal of the tumor should be the primary goal. In patients with metastatic insulinomas, symptoms of insulin hypersecretion will only completely disappear after complete resection of all metastases.

Is there a therapeutic role for octreotide in patients with ectopic Cushing's syndrome?

Cushing's syndrome (CS) due to ectopic ACTH secretion (EAS) has a high morbidity and mortality, because of the underlying tumor and the sequelae of severe hypercortisolemia. Therefore, rapid treatment of ectopic CS is mandatory. Scintigraphy shows that up to 80% of ectopic ACTH-producing tumors have somatostatin receptors. While this suggests that somatostatin analogs may reduce ACTH production and treat patients with EAS, the therapeutic role of these agents is still evolving. Here we demonstrate the spectrum of responses to octreotide therapy in 3 patients with EAS. Diagnostic imaging with the 111In-pentetreotide scan did not predict the therapeutic response to octreotide. Two patients with positive somatostatin receptor scintigraphy failed to respond to octreotide, while one with a negative scan reached eucortisolemia on a maintenance dose of 75 microg octreotide twice daily or octreotide LAR 30 mg per month. We conclude that octreotide is not a first line agent to control hypercortisolemia but may be a useful agent when other inhibitors of steroidogenesis fail or parenteral administration is required. Before therapy an octreotide challenge test may predict therapeutic response. Cortisol levels should be monitored regularly on somatostatin analog therapy, because of its unpredictable long-term pharmacodynamic profile.

Somatostatin analog therapy in treatment of gastrointestinal disorders and tumors

Long-acting octapeptide somatostatin analogs can effectively control symptoms resulting from excessive hormone release in patients with endocrine tumors of the gastrointestinal tract, provided that these tumors and metastases show a high expression of the somatostatin receptor subtype 2. The presence of this receptor subtype on these tumors can be demonstrated by in vitro studies, but also in vivo using 111In-pentetreotide scintigraphy. In a few studies, significant antiproliferative effects of these drugs on these tumors have also been demonstrated. The effectiveness of octapeptide somatostatin analogs in the management of chemotherapy- related and AIDS-related diarrhea and in reducing postoperative complications of pancreatic surgery have also been demonstrated. These drugs have been used to decrease the output of enterocutaneous pancreatic fistulas and are prophylactically used to prevent the development of these fistulas. Octapeptide somatostatin analog therapy is widely accepted for the initial management of acute variceal bleeding in cirrhotic patients. These drugs are currently also being evaluated for the treatment of advanced hepatocellular carcinoma and malignant intestinal obstruction. Radiotherapy with octapeptide somatostatin analogs coupled to radionuclides such as indium-111, yttrium-90, and lutetium- 177 is currently being studied in phase I-III trials.

Mutational analysis of the mouse somatostatin receptor type 5 gene promoter

We have previously characterized the structure of the murine somatostatin receptor type 5 gene (sst5). Initial transient transfection studies in pituitary somatolactotropes (GH(3)) mapped the promoter activity of this gene to a region 290 bp upstream of the transcription start site. The current study identifies the sst5 promoter region critical for basal activity. A series of deletions was generated, and promoter activity was localized to a region between -83 and -19. Similar promoter deletion patterns were evident in five pituitary cell types. Seven 10-bp transversion mutations encompassing the region between -83 and -19 were generated, and functional activity was assessed. Promoter activity was reduced by the mutations spanning -67 to -47 compared with the wild-type construct. Another mutation between -26 and -17 resulted in promoter activity reduction in GH(3) cells, but not TtT-97 thyrotropes. Deoxyribonuclease I protection analysis of the sst5 promoter region between -208/+47 was performed using GH(3) and TtT-97 nuclear extracts. The most striking protected regions, located between -61 and -41 and -25 and -3, correlated with functionally important regions identified by transfection studies. In summary, the mouse sst5 gene promoter has been characterized, and functional activity and nuclear factor interactions were mapped to two specific promoter regions. The region between -67 and -47 appears to contain a nucleotide sequence critical for basal transcriptional regulation of the mouse sst5 gene in pituitary cells.

Somatostatin and somatostatin analogues: diagnostic and therapeutic uses

Somatostatin and its octapeptide analogues exert their effects through interaction with somatostatin receptor (sst) subtypes 1 through 5 (sst 1-5 ). Somatostatin binds with high affinity to all sst subtypes, whereas the currently commercially available octapeptide analogues bind only with a high affinity to sst 2 and sst 5. Pituitary tumors, endocrine pancreatic tumors, and carcinoid tumors express multiple sst subtypes, but sst 2 predominance is found in 90% of carcinoids and 80% of endocrine pancreatic tumors. Sst 2 and sst 5 predominance is found in growth hormone-secreting pituitary tumors. In patients harboring sst 2 - or sst 5 -positive neuroendocrine tumors, clinical symptomatology can be controlled by the chronic administration of one of the currently commercially available octapeptide somatostatin analogues. Tumors and metastases that bear sst 2 or sst 5 can be visualized in vivo after injection of radiolabeled octapeptide analogues. Radiolabeled octapeptide analogues can also be used for radiotherapy of sst 2 - and sst 5 -positive advanced or metastatic neuroendocrine tumors.

Somatostatin receptor imaging, therapy and new strategies in patients with neuroendocrine tumours

BACKGROUND

Somatostatin receptors have been found on a variety of neuroendocrine tumours, such as carcinoids and paragangliomas, as well as on most pancreatic endocrine and breast tumours. Somatostatin receptor scintigraphy with a radionuclide-labelled somatostatin analogue, [111Indium- diethylenetriaminopenta-acetic acid]octreotide, is a sensitive and specific technique for visualizing in vivo the presence of somatostatin receptors on various tumours.

METHODS

Material was identified from previous review articles, references cited in original papers and a Medline search of the literature. Additional material was obtained from recently published abstracts of meetings.

RESULTS AND CONCLUSION

Somatostatin receptor imaging of neuroendocrine tumours is essential in the diagnostic evaluation of most of these tumours. The expression of somatostatin receptors in vivo not only predicts the outcome of somatostatin analogue treatment but also opens the possibility of new therapeutic strategies. Because better information about spread of the disease can be obtained, more justifiable options for therapy can be proposed.

Neuropeptides--an overview

The present article provides a brief overview of various aspects on neuropeptides, emphasizing their multitude and their wide distribution in both the peripheral and central nervous system. Interestingly, neuropeptides are also expressed in various types of glial cells under normal and experimental conditions. The recent identification of, often multiple, receptor subtypes for each peptide, as well as the development of peptide antagonists, have provided an experimental framework to explore functional roles of neuropeptides. A characteristic of neuropeptides is the plasticity in their expression, reflecting the fact that release has to be compensated by de novo synthesis at the cell body level. In several systems peptides can be expressed at very low levels normally but are upregulated in response to, for example, nerve injury. The fact that neuropeptides virtually always coexist with one or more classic transmitters suggests that they are involved in modulatory processes and probably in many other types of functions, for example exerting trophic effects. Recent studies employing transgene technology have provided some information on their functional role, although compensatory mechanisms in all probability could disguise even a well defined action. It has been recognized that both 'old' and newly discovered peptides may be involved in the regulation of food intake. Recently the first disease-related mutation in a peptidergic system has been identified, and clinical efficacy of a substance P antagonist for treatment of depression has been reported. Taken together it seems that peptides may play a role particularly when the nervous system is stressed, challenged or afflicted by disease, and that peptidergic systems may, therefore, be targets for novel therapeutic strategies.

Hepatic neuroendocrine metastases: does intervention alter outcomes?

BACKGROUND

In most instances, advanced neuroendocrine tumors follow an indolent course. Hepatic metastases are common, and although they can cause significant pain, incapacitating endocrinopathy, and even death, they are usually asymptomatic. The appropriate timing and efficacy of interventions, such as hepatic artery embolization (HAE) and operation, remain controversial.

STUDY DESIGN

The records of 85 selected patients referred for treatment of hepatic neuroendocrine tumor metastases between 1992 and 1998 were reviewed from a prospective database. A multidisciplinary group of surgeons, radiologists, and oncologists managed all patients. Overall survival among this cohort is reported and prognostic variables, which may be predictive of survival, are analyzed.

RESULTS

There were 37 men and 48 women, with a median age of 52 years. There were 41 carcinoid tumors, 26 nonfunctional islet cell tumors, and 18 functional islet cell tumors. Thirty-eight patients had extrahepatic metastases, and in 84% of patients, the liver metastases were bilobar. Eighteen patients were treated with medical therapy or best supportive care, 33 patients underwent HAE, and 34 patients underwent hepatic resection. Both the HAE-related mortality and the 30-day operative mortality rates were 6%. By univariate analysis, earlier resection of the primary tumor, curative intent of treatment, and initial surgical treatment were associated with prolonged survival (p < 0.05). On multivariate analysis, only curative intent to treat remained significant (p < 0.04). Patients with bilobar or more than 75% liver involvement by tumor were least likely to benefit from surgical resection. One-, 3-, and 5-year survival rates for the entire group were 83%, 61%, and 53%, respectively. The 1-, 3-, and 5-year survivals for patients treated with medical therapy, HAE, and operation were 76%, 39%, and not available; 94%, 83%, and 50%; and 94%, 83%, and 76%, respectively.

CONCLUSIONS

Hepatic metastases from neuroendocrine tumors are best managed with a multidisciplinary approach. Both HAE and surgical resection provide excellent palliation of hormonal and pain symptoms. In select patients, surgical resection of hepatic metastases may prolong survival, but is rarely curative.