Role of somatostatins in gastroenteropancreatic neuroendocrine tumor development and therapy.

The incidence and prevalence of gastroenteropancreatic neuroendocrine tumors (GEP-NETs) have increased in the past 20 years. GEP-NETs are heterogeneous tumors, in terms of clinical and biological features, that originate from the pancreas or the intestinal tract. Some GEP-NETs grow very slowly, some grow rapidly and do not cause symptoms, and others cause hormone hypersecretion and associated symptoms. Most GEP-NETs overexpress receptors for somatostatins. Somatostatins inhibit the release of many hormones and other secretory proteins; their effects are mediated by G protein-coupled receptors that are expressed in a tissue-specific manner. Most GEP-NETs overexpress the somatostatin receptor SSTR2; somatostatin analogues are the best therapeutic option for functional neuroendocrine tumors because they reduce hormone-related symptoms and also have antitumor effects. Long-acting formulations of somatostatin analogues stabilize tumor growth over long periods. The development of radioactive analogues for imaging and peptide receptor radiotherapy has improved the management of GEP-NETs. Peptide receptor radiotherapy has significant antitumor effects, increasing overall survival times of patients with tumors that express a high density of SSTRs, particularly SSTR2 and SSTR5. The multi-receptor somatostatin analogue SOM230 (pasireotide) and chimeric molecules that bind SSTR2 and the dopamine receptor D2 are also being developed to treat patients with GEP-NETs. Combinations of radioactive labeled and unlabeled somatostatin analogues and therapeutics that inhibit other signaling pathways, such as mammalian target of rapamycin (mTOR) and vascular endothelial growth factor, might be the most effective therapeutics for GEP-NETs.

NETest liquid biopsy is diagnostic of small intestine and pancreatic neuroendocrine tumors and correlates with imaging.

INTRODUCTION: Current monoanalyte biomarkers are ineffective in gastroenteropancreatic neuroendocrine tumors (GEP-NETs). NETest, a novel multianalyte signature, provides molecular information relevant to disease biology. AIM(S): Independently validate NETest to diagnose GEP-NETs and identify progression in a tertiary referral center. MATERIALS AND METHODS: Cohorts: 67 pancreatic NET (PNETs), 44 small intestine NETs (SINETs), 63 controls. Well-differentiated (WD): PNETs, n=62, SINETs, all (n=44). Disease extent assessment at blood draw: anatomical (n=110)- CT(n=106), MRI(n=7) and/or functional- 68Ga-SSA-PET/CT(n=69) or 18F-FDG-PET/CT (n=8). Image positive disease (IPD) was defined as either CT/MRI or 68Ga-SSA-PET/CT/18F-FDG-PET/CT-positive. Both CT/MRI and 68Ga-SSA-PET/CT-negative in WD-NETs was considered image negative disease (IND). NETest (normal: 20): PCR (spotted plates). DATA: mean±SD. RESULTS: Diagnosis: NETest was significantly increased in NETs (n=111; 26±21) vs. controls (8±4, p<0.0001). 75 (42 PNET, 33 SINET) were image-positive. Eleven (8 PNET, 3 SINET; all WD) were IND. In IPD, NETest was significantly higher (36±22) vs. IND (8±7, p<0.0001). NETest accuracy, sensitivity, specificity: 97%, 99%, 95%. Concordance with imaging: NETest was 92% (101/110) concordant with anatomical imaging, 94% (65/69) with 68Ga-SSA-PET/CT, 96% (65/68) dual modality (CT/MRI and 68Ga-SSA-PET/CT). In 70 CT/MRI-positive, NETest was elevated in all (37±22). In 40 CT/MRI-negative, NETest was normal (11±10) in 31. In 56 68Ga-SSA-PET/CT-positive, NETest was elevated (36±22) in 55. In 13 68Ga-SSA-PET/CT-negative, NETest was normal (9±8) in 10. Disease status: NETest was significantly higher in progressive (61±26; n=11) vs. stable disease (29±14; n=64; p<0.0001) (RECIST 1.1). CONCLUSION: NETest is an effective diagnostic for PNETs and SINETs. Elevated NETest is as effective as imaging in diagnosis and accurately identifies progression.

Treatment with combined streptozotocin and liposomal doxorubicin in metastatic endocrine pancreatic tumors.

UNLABELLED: Treatment with combined streptozotocin and liposomal doxorubicin is safe and efficient in patients with endocrine pancreatic tumors (EPTs). No cardiac toxicity was reported. BACKGROUND: The combination of streptozotocin and doxorubicin has been shown to be superior to streptozotocin and fluorouracil in the treatment of metastatic EPTs. However, the risk of cardiac toxicity from anthracyclins hampers the usefulness of the drug combination. Liposomal doxorubicin has a lower frequency of cardiac adverse events compared to doxorubicin. We wanted to assess the efficacy and safety of combined streptozotocin and liposomal doxorubicin in patients with metastatic EPTs. METHODS: Thirty patients with metastatic EPTs were recruited from three medical centers in Norway and Sweden during a time period of 3 years. All patients had histopathologically confirmed diagnoses and bidimensionally measurable lesions. 30 mg/m(2) of liposomal doxorubicin was administered on day 1 of each cycle. During the first course, 1 g of streptozotocin was given on 5 consecutive days. Thereafter, 2 g of streptozotocin was given on day 1 only. Treatment was repeated every 3 weeks. RESULTS: Twelve of 30 patients (40%) achieved an objective radiological response with a median duration of 9 months. Stabilization of disease was achieved in 17 of 30 patients (57%) for a median duration of 11 months. Only one patient had progressive disease as best response. The 2-year progression-free survival was 18% and the 2-year overall survival was 72%. The treatment was well tolerated. None of the patients experienced cardiac toxicity. CONCLUSION: We conclude that combined streptozotocin and liposomal doxorubicin is a safe and efficient treatment for EPTs. The efficacy seems to be comparable to that of combined streptozotocin and doxorubicin, whereas the cardiac toxicity clearly favors using the liposomal drug combination.

Somatostatin induces rapid contraction of neuroendocrine cells.

The peptide hormone somatostatin, as well as the somatostatin analog octreotide, induces rapid morphological changes in neuroendocrine cells. The effect can be detected in less than 2 min: retraction fibers are formed, cells round up and cell-cell contacts are broken. Somatostatin-dependent cell contraction is inhibited by Y-27632, indicating that this effect is dependent on Rho kinase. In BON1 cells, the somatostatin-induced inhibition of forskolin-induced secretion of chromogranin A is not blocked by Y-27632. It is therefore concluded that the inhibitory effect of somatostatin in forskolin-stimulated cells is not dependent on cell contraction.

Expression of molecular targets for tyrosine kinase receptor antagonists in malignant endocrine pancreatic tumors.

PURPOSE: Molecular targeting with monoclonal antibodies and tyrosine kinase inhibitors is a novel approach to cancer treatment. We have examined the expression of molecular targets in patients with malignant endocrine pancreatic tumors, which is necessary to justify additional studies investigating the potential benefit from such treatment. EXPERIMENTAL DESIGN: Thirty-eight tumor tissues from malignant endocrine pancreatic tumors were examined with immunohistochemistry using specific polyclonal antibodies with regard to the expression pattern of platelet-derived growth factor receptors (PDGFRs) alpha and beta, c-kit, and epidermal growth factor receptor (EGFR). RESULTS: All 38 tissue specimens expressed PDGFRalpha on tumor cells, and 21 of 37 specimens (57%) expressed PDGFRalpha in tumor stroma (1 specimen was nonevaluable). Twenty-eight samples (74%) stained positive for PDGFRbeta on tumor cells, and 36 of 37 samples (97%) stained positive for PDGFRbeta in the stroma (1 specimen was nonevaluable). Thirty-five tumor tissues (92%) stained positive for c-kit, and 21 (55%) stained positive for EGFR on tumor cells. No differences were seen between syndromes or between poorly differentiated or well-differentiated tumors. Previous treatment did not influence expression pattern. Receptor expression pattern varied considerably between individuals. CONCLUSIONS: We have found that tyrosine kinase receptors PDGFRs alpha and beta, EGFR, and c-kit are expressed in more than half of the patients with endocrine pancreatic tumors. Because these receptors represent molecular targets for STI571 and ZD1839 (tyrosine kinase inhibitors) and IMC-C225 (a monoclonal antibody), we propose that patients suffering from EPTs might benefit from this new treatment strategy. However, because of great variability in receptor expression pattern, all patients' individual receptor expression should be examined.

Malignant gastric ghrelinoma with hyperghrelinemia.

A characteristic feature of neuroendocrine tumors is production and release of peptide hormone. Ghrelin is a 28-amino acid hormone that stimulates GH release. In this paper, we describe a patient with a metastasizing gastric neuroendocrine tumor displaying intense immunoreactivity for ghrelin and extremely high circulating levels of ghrelin. Tumor tissue biopsies from the primary tumor and one liver metastasis were examined by immunohistochemistry. Ghrelin and several other hormones and tumor markers were measured in blood. The clinical course of the patient was followed. Tumor tissue biopsies showed immunoreactivity for cytokeratin, chromogranin A, human synaptic vesicle protein 2, synaptophysin, and ghrelin. Grossly elevated circulating levels of total ghrelin, 2100 microg/liter (reference interval < 5 microg/liter) and active ghrelin, 28 microg/liter (reference interval < 0.1 microg/liter) were found at presentation. Chromogranin A, chromogranin B, and calcitonin levels were also increased. Both total and active ghrelin increased, despite treatment, during follow-up of the patient. We have identified and characterized a patient with a malignant gastric neuroendocrine tumor secreting ghrelin as the main hormone. This might be a new tumor entity of the stomach, and it is suggested that patients with malignant gastric neuroendocrine tumors should be investigated for ghrelin production.

High-dose treatment with a long-acting somatostatin analogue in patients with advanced midgut carcinoid tumours.

OBJECTIVE: High-dose somatostatin analogue treatment has shown an antiproliferative effect in one study including patients with neuroendocrine tumours. To explore this therapeutic strategy further, we have studied the effect of a high-dose formula of octreotide, octreotide pamoate, in midgut carcinoid patients. DESIGN AND METHODS: Twelve patients with advanced midgut carcinoid tumours with a median duration of disease of more than 5 years were included. All were in a progressive state despite several previous treatment modalities. Octreotide pamoate (160 mg) was given as an intramuscular injection every 2 weeks for 2 months and then monthly. Radiological and biochemical responses were monitored. RESULTS: Tumour size and biochemical markers were stabilised for a median of 12 months in 75% of the patients. Ten patients had symptomatic improvement of flush and diarrhoea. CONCLUSION: In this group of patients with advanced midgut carcinoid tumours and progressive disease, octreotide pamoate managed to improve symptoms, and stabilise hormone production and tumour growth in 75% of the patients. We believe that high-dose treatment with somatostatin analogues can be an important addition to the therapeutic arsenal for patients with advanced progressive midgut carcinoid tumours.

Pasireotide (SOM230) shows efficacy and tolerability in the treatment of patients with advanced neuroendocrine tumors refractory or resistant to octreotide LAR: results from a phase II study.

Pasireotide (SOM230) is a novel multireceptor-targeted somatostatin (sst) analog with high binding affinity for sst receptor subtype 1, 2, 3 (sst(1,2,3)) and sst(5). Because of this binding profile, pasireotide may offer symptom control in patients with neuroendocrine tumors (NETs) and carcinoid syndrome no longer responsive to octreotide LAR. This was a phase II, open-label, multicenter study of pasireotide in patients with advanced NET whose symptoms of carcinoid syndrome (diarrhea/flushing) were inadequately controlled by octreotide LAR. Patients received s.c. pasireotide 150 µg twice daily (bid), escalated to a maximum dose of 1200 µg bid until a clinical response was achieved. Forty-four patients were evaluated for efficacy and 45 for tolerability. Pasireotide 600-900 µg s.c. bid effectively controlled the symptoms of diarrhea and flushing in 27% of patients. Evaluation of tumor response in 23 patients showed 13 with stable disease and ten with progressive disease at study end. The most common drug-related adverse events were nausea (27%), abdominal pain (20%), weight loss (20%), and hyperglycemia (16%) and most were of mild or moderate severity. Pasireotide 600-900 µg s.c. bid was effective and generally well tolerated in controlling the symptoms of carcinoid syndrome in 27% of patients with advanced NET refractory or resistant to octreotide LAR therapy.

Management of neuroendocrine tumors: current and future therapies.

Neuroendocrine tumors (NETs) are a genetically diverse group of malignancies that sometimes produce peptides that cause characteristic hormonal syndromes. NETs can be clinically symptomatic (functioning) or silent (nonfunctioning); both types frequently synthesize more than one peptide, although often these are not associated with specific syndromes. Based on data from various sources, the incidence and prevalence of NETs is increasing. The primary treatment goal for patients with NETs is curative, with symptom control and the limitation of tumor progression as secondary goals. Surgery is the only possible curative approach and so represents the traditional first-line therapy. However, as most patients with NETs are diagnosed once metastases have occurred, curative surgery is generally not possible. Patients therefore require chronic postoperative medical management with the aim of relieving symptoms and, in recent years, suppressing tumor growth and spread. Somatostatin analogues, such as octreotide long-acting repeatable (LAR), can improve the symptoms of carcinoid syndrome and stabilize tumor growth in many patients. Results from the placebo-controlled, double-blind, prospective randomized study on the effect of octreotide LAR in the control of tumor growth in patients with metastatic neuroendocrine midgut tumors (PROMID study) demonstrate that octreotide LAR 30 mg is an effective antiproliferative treatment in patients with newly diagnosed, functionally active or inactive, well-differentiated metastatic midgut NETs. An antiproliferative effect can also be achieved with everolimus, and combination therapy with octreotide LAR has shown synergistic antiproliferative activity. Sunitinib, a tyrosine kinase inhibitor, is active in pancreatic NETs. In the future, pasireotide, the multireceptor targeted somatostatin analogue, has the potential to be an effective therapy for de novo or octreotide-refractory carcinoid syndrome and for inhibiting tumor cell proliferation. Peptide receptor radiotherapy with 90Yttrium-DOTATOC or 177Lutetium-DOTATE is also a new interesting treatment option for NETs.

Chromogranin A and neuron-specific enolase as prognostic markers in patients with advanced pNET treated with everolimus.

CONTEXT: Everolimus, an oral inhibitor of mammalian target of rapamycin, significantly prolongs progression-free survival (PFS) in patients with advanced pancreatic neuroendocrine tumors (pNET). Chromogranin A (CgA) and neuron-specific enolase (NSE) are considered general biomarkers of these tumors. OBJECTIVE: The objective of the study was to evaluate the prognostic value of CgA and NSE in patients with pNET treated with everolimus. PATIENTS AND METHODS: Patients with low- to intermediate-grade advanced pNET enrolled in two phase 2 studies [RAD001 in Advanced Neuroendocrine Tumors (RADIANT-1) and single institution phase II study at The University of Texas M. D. Anderson Cancer Center] received everolimus. Blood samples were collected and analyzed by a central laboratory at baseline and monthly thereafter. PFS and overall survival (OS) were evaluated in patients with elevated and nonelevated baseline CgA/NSE levels. RESULTS: In RADIANT-1, elevated vs. nonelevated baseline CgA was associated with shorter median PFS (8.34 vs. 15.64 months; P = 0.03) and OS (16.95 months vs. not reached; P < 0.001). Elevated vs. nonelevated baseline NSE resulted in shorter median PFS (7.75 vs. 12.29 months; P = 0.01) and OS (13.96 vs. 24.90 months; P = 0.005). Median PFS was prolonged in patients with early CgA or NSE response (11.0 vs. 5.0 months) compared with those without early biomarker response. More patients with CgA (87 vs. 50%) or NSE (81 vs. 14%) response experienced tumor shrinkage compared with those without response. CgA response data from the single-institution phase II study at The University of Texas M. D. Anderson Cancer Center study are consistent with data from the RADIANT-1 study. CONCLUSIONS: Elevated baseline CgA/NSE provided prognostic information on PFS and survival; early CgA/NSE responses are potential prognostic markers for treatment outcomes in patients with advanced pNET.