Growth factor receptor expression in human gastroenteropancreatic neuroendocrine tumours

Progress in the Management of Pancreatic Neuroendocrine Tumors

Pancreatic neuroendocrine tumors (PNETs) are a heterogeneous and orphan group of neoplasms that vary in their histology, clinical features, prognosis, and management. The treatment of PNETs is highly dependent on the stage at presentation, tumor grade and differentiation, presence of symptoms from hormonal overproduction or from local growth, tumor burden, and rate of progression. The US Food and Drug Administration has recently approved many novel treatments, which have altered decision making and positively impacted the care and prognosis of these patients. In this review, we focus on the significant progress made in the management of PNETs over the past decade, as well as the active areas of research. Expected final online publication date for the Annual Review of Medicine, Volume 73 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Role of FGF System in Neuroendocrine Neoplasms: Potential Therapeutic Applications

Neuroendocrine neoplasms (NENs) are a heterogeneous group of tumors originating from neuroendocrine cells dispersed in different organs. Receptor tyrosine kinases are a subclass of tyrosine kinases with a relevant role in several cellular processes including proliferation, differentiation, motility and metabolism. Dysregulation of these receptors is involved in neoplastic development and progression for several tumors, including NENs. In this review, we provide an overview concerning the role of the fibroblast growth factor (FGF)/fibroblast growth factor receptor (FGFR) system in the development and progression of NENs, the occurrence of fibrotic complications and the onset of drug-resistance. Although no specific FGFR kinase inhibitors have been evaluated in NENs, several clinical trials on multitarget tyrosine kinase inhibitors, acting also on FGF system, showed promising anti-tumor activity with an acceptable and manageable safety profile in patients with advanced NENs. Future studies will need to confirm these issues, particularly with the development of new tyrosine kinase inhibitors highly selective for FGFR.

Targeted Therapies in the Management of Well-Differentiated Digestive and Lung Neuroendocrine Neoplasms

OPINION STATEMENT

Ongoing advances in our understanding of neuroendocrine tumor (NET) biology, genetics, and immunology, will continue to expand the availability of targeted therapies, thus improving the outcomes of patients. Well-differentiated neuroendocrine tumors (NETs) are grouped into pancreatic and non-pancreatic NETs (includes GI and thoracic NETs) for treatment considerations (Fig. 1). For panNETs, initial therapy is driven by the need of radiographic response, and targeted agents are typically reserved for second and third line based on the toxicity profile. Treatment options for non-pancreatic NETs are also expanding and while SSAs are the typical first-line option, everolimus and PRRT both remain approved therapies for future lines, and VEGF TKIs are showing promising results in research settings. Sequencing these agents and best time to incorporate peptide receptor radio therapy into the management algorithm remains an unmet need.

Multicenter phase 2 trial of nintedanib in advanced nonpancreatic neuroendocrine tumors

BACKGROUND

Antiangiogenic-targeting agents have low response rates in patients with nonpancreatic neuroendocrine tumors (NETs). Nintedanib is an oral antiangiogenic agent that has inhibitory effects on the fibroblast growth factor receptor, which is highly expressed in NETs. The authors hypothesized that nintedanib would be active in patients with nonpancreatic NETs.

METHODS

Patients with advanced, grade 1 or 2, nonpancreatic NETs who were receiving a stable dose of somatostatin analogue were enrolled. Nintedanib was administered at a dose of 200 mg twice daily in 28-day cycles. The primary endpoint was progression-free survival (PFS) at 16 weeks.

RESULTS

Thirty-two patients were enrolled, and 30 were evaluable for the primary outcome. Most had radiographic disease progression within 12 months before enrollment. The 16-week PFS rate was 83%, and the median PFS and overall survival were 11.0 months and 32.7 months, respectively. Nintedanib was well tolerated and delayed deterioration in quality of life. The baseline serotonin level had a strong, positive correlation with activated but exhausted T cells.

CONCLUSIONS

Nintedanib is active in nonpancreatic NETs. The immunosuppressive effect of serotonin should be targeted in future clinical trials.

Gastroenteropancreatic neuroendocrine neoplasms and inflammation: A complex cross-talk with relevant clinical implications

Neuroendocrine neoplasms (NENs) are a group of tumors originating from the neuroendocrine system. They mainly occur in the digestive system and the respiratory tract. It is well-know a strict interaction between neuroendocrine system and inflammation, which can play an important role in NEN carcinogenesis. Inflammatory mediators, which are produced by the tumor microenvironment, can favor cancer induction and progression, and can promote immune editing. On the other hand, a balanced immune system represents a relevant step in cancer prevention through the elimination of dysplastic and cancer cells. Therefore, an inflammatory response may be both pro- and anti-tumorigenic. In this review, we provide an overview concerning the complex interplay between inflammation and gastroenteropancreatic NENs, focusing on the tumorigenesis and clinical implications in these tumors.

Retrospective evaluation of canine heart base tumours treated with toceranib phosphate (Palladia): 2011-2018

Heart base tumours (HBT) occur commonly in older, brachycephalic dogs. A presumptive diagnosis is made based on location and appearance of the tumour via echocardiogram. Effective treatment options are limited to surgery (when feasible) or radiation therapy. Benefit of medical management is presently unknown. The goal of this retrospective study was to assess the efficacy and tolerability of toceranib phosphate for dogs with HBT. Twenty-eight dogs with histologically, cytologically confirmed or presumed HBT were evaluated retrospectively. Twenty-seven dogs were treated with single agent toceranib. One dog received combination therapy with concurrent metronomic chemotherapy. This dog was not included in response or survival analysis. Factors assessed included clinical signs, hematologic/biochemical parameters and response to treatment. For the 27 dogs receiving single agent toceranib, an overall response rate of 10% was found. Overall median survival time was 823 days (range, 68-1190 days). The overall response rate for the dogs presenting with metastasis was 28.5%, with a median survival time of 532 days (range, 77-679 days). This was not significantly different than the median survival time of 796 days for dogs who did not present with metastasis. Of the dogs displaying clinical signs at the time of diagnosis, 90% had improvement and 81% had complete resolution of signs after starting toceranib. Toxicity was seen in 54% of dogs with gastrointestinal distress as the most common toxicity but dose reductions were infrequent required. Results demonstrate that toceranib phosphate is a well-tolerated and effective treatment for inoperable canine heart base tumours including dogs with advanced or metastatic disease.

The Tumor Microenvironment in Neuroendocrine Tumors: Biology and Therapeutic Implications

Neuroendocrine tumors (NETs) include a heterogeneous group of malignancies arising in the diffuse neuroendocrine system and characterized by indolent growth. Complex interactions take place among the cellular components of the microenvironment of these tumors, and the recognition of the molecular mediators of their interplay and cross talk is crucial to discover novel therapeutic targets. NET cells overexpress a plethora of proangiogenic molecules including vascular endothelial growth factor, platelet-derived growth factor, fibroblast growth factor, semaphorins, and angiopoietins that promote both recruitment and proliferation of endothelial cell precursors, thus resulting among the most vascularized cancers with a microvessel density 10-fold higher than epithelial tumors. Also, NETs operate multifaceted interactions with stromal cells, both at local and distant sites, and whether their paracrine secretion of serotonin, connective tissue growth factor, and transforming growth factor β primarily drives the fibroblast activation to enhance the tumor proliferation, on the other side NET-derived profibrotic factors accelerate the extracellular matrix remodeling and contribute to heart valves and/or mesenteric fibrosis development, namely, major complications of functioning NETs. However, at present, little is known on the immune landscape of NETs, but accumulating evidence shows that tumor-infiltrating neutrophils, mast cells, and/or macrophages concur to promote the neoangiogenic switch of these tumors by either direct or indirect mechanisms. On the other hand, immune checkpoint molecules are heterogeneously expressed in NETs' surrounding cells, and it is unclear whether or not tumor-infiltrating lymphocytes are antitumor armed within the microenvironment, given their low mutational load. Here, we review the current knowledge on both gastroenteropancreatic and pulmonary NETs' microenvironment as well as both established and innovative treatments aimed at targeting the tumor-host interplay.

Role of the tumor microenvironment in digestive neuroendocrine tumors

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) represent a group of heterogeneous tumors whose incidence increased over the past few years. Around half of patients already present with metastatic disease at the initial diagnosis. Despite extensive efforts, cytotoxic and targeted therapies have provided only limited efficacy for patients with metastatic GEP-NETs, mainly due to the development of a certain state of resistance. One factor contributing to both the failure of systemic therapies and the emergence of an aggressive tumor phenotype may be the tumor microenvironment (TME), comprising dynamic and adaptative assortment of extracellular matrix components and non-neoplastic cells, which surround the tumor niche. Accumulating evidence shows that the TME can simultaneously support both tumor growth and metastasis and contribute to a certain state of resistance to treatment. In this review, we summarize the current knowledge of the TME of GEP-NETs and discuss the current therapeutic agents that target GEP-NETs and those that could be of interest in the (near) future.

The IGF pathway is activated in insulinomas but downregulated in metastatic disease

Clinical and molecular studies have implicated epidermal growth factor receptor (EGFR), insulin-like growth factor (IGF) and target of rapamycin (mTOR) signaling pathways in the regulation of pancreatic neuroendocrine tumor (PanNET) growth. Interpretation and comparison of these studies is complex due to clinical and molecular tumor heterogeneity. We therefore focused in this study on insulinomas, which we examined for mRNA and protein expression of EGFR, IGF and mTOR signaling pathway components by quantitative real-time PCR (n=48) and immunohistochemistry (n=86). Findings were compared with normal pancreatic islets and correlated with histopathological data and clinical outcome. Insulinomas showed low EGFR and high IGF2 expression. IGFBP2, IGFBP3 and IGFBP6 mRNA levels were 2-4 folds higher than in islets. High protein expression of IGF2, IGF1R and INSR (in 51-92% of the tumors) and low to moderate expression of mTORC1 pathway proteins p-PS6k and p-4EBP1 (7-28% of the tumors) were observed. Correlations were found between 1) ERK1 mRNA expression and that of numerous IGF pathway genes, 2) p-ERK and IGF1R protein expression and 3) decrease of IGF pathway components and both metastatic disease and shorter 10 years disease free survival. In conclusion, our observations suggest that high expression of IGF signaling pathway components is a hallmark of insulinomas, but does not necessarily lead to increased mTOR signaling. Reduced expression of IGF pathway components may be an adverse prognostic factor in insulinomas.

Can insulin-like growth factor 1 (IGF-1), IGF-1 receptor connective tissue growth factor and Ki-67 labelling index have a prognostic role in pulmonary carcinoids?

Introduction

Altered expression of Insulin-like Growth Factor-1 (IGF-1), its receptor (IGF-1R), Connective Tissue Growth Factor (CTGF) and Hypoxia Inducible Factor-1 (HIF-1), has been implicated in tumorigenesis. So far, these factors have not been studied systematically in Pulmonary Carcinoids (PCs).

Aims

To examine IGF-1, IGF-1R, CTGF and HIF-1 expression in PCs, and assess their prognostic value over established factors.

Materials & Methods

Retrospective study of 121 PCs (104 Typical and 17 Atypical). The expression of growth factors was studied immunohistochemically and tumors were considered positive if immunoreactivity appeared in >50% of cells.

Results

All studied parameters were expressed in the majority of tumors (IGF-1, IGF-1R, CTGF and HIF-1, in 78.5%, 67%, 72% and 78%, respectively). Their expression tended to be more frequent in TCs and in tumors with Ki-67≤2% (significant only for HIF-1; 82 vs. 53%; p=0.023 and 83 vs. 63%; p=0.025 respectively). CTGF was the only factor correlated with more extensive disease (larger size; presence of lymph node and distant metastases). According to logistic regression analysis, only advanced age, Ki-67≥3.4% and lymph node involvement could predict the development of distant metastases.

Conclusions

IGF-1, IGF-1R, CTGF and HIF-1 are avidly expressed in PCs; however, their presence did not appear to be of statistically significant value over established prognostic factors.

Small intestinal neuroendocrine tumours and fibrosis: an entangled conundrum

Small intestinal neuroendocrine tumours (SI-NETs) are neoplasms characterized by their ability to secrete biogenic amines and peptides. These cause distinct clinical pathology including carcinoid syndrome, marked by diarrhoea and flushing, as well as fibrosis, notably mesenteric fibrosis. Mesenteric fibrosis often results in significant morbidity by causing intestinal obstruction, oedema and ischaemia. Although advancements have been made to alleviate symptoms of carcinoid syndrome and prolong the survival of patients with SI-NETs, therapeutic options for patients with mesenteric fibrosis are still limited. As improved insight in the complex pathogenesis of mesenteric fibrosis is key to the development of new therapies, we evaluated the literature for known and putative mediators of fibrosis in SI-NETs. In this review, we discuss the tumour microenvironment, growth factors and signalling pathways involved in the complex process of fibrosis development and tumour progression in SI-NETs, in order to elucidate potential new avenues for scientific research and therapies to improve the management of patients suffering from the complications of mesenteric fibrosis.

Determination of Mammalian Target of Rapamycin Hyperactivation as Prognostic Factor in Well-Differentiated Neuroendocrine Tumors

Purpose

To evaluate the role of the activation of mTOR (phosphorylated mTOR, p-mTOR) and the expression SSTR2A and IGF-1R as prognostic factor in well-differentiated neuroendocrine tumors.

Methods

A retrospective study was conducted on data from patients with diagnosis of neuroendocrine tumor originated from pancreas (pNET) or gastrointestinal tract (stomach, appendix, and ileus; GI-NET) made between January 2003 and December 2004 and followed up at our institution. Archival material should be available for revision according to WHO 2010 neuroendocrine tumor classification and for p-mTOR, SSTR2A, and IGF-1R immunostaining, calculating a quantitative score (QS). We evaluated clinical, pathological, and immunohistochemistry features for association with the presence of advanced disease at diagnosis and disease relapse in patients who have undergone radical surgery.

Results

Archival material from 64 patients was analyzed (37 pNETs and 27 GI-NETs). In these patients, G2 grading, low SSTR2A QS, and high p-mTOR QS were associated with advanced disease at diagnosis at multivariate analysis. Risk of recurrence in 49 patients with R0-resected tumors was higher for G2 grading, stage IIIB-IV, low IGF-1R QS, and high p-mTOR QS at univariate analysis.

Conclusions

With the limits of retrospective data, activation of m-TOR is correlated with advanced disease at diagnosis and with shorter disease-free survival after R0 resection. Validation through prospective studies is needed.

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.

Optimizing Somatostatin Analog Use in Well or Moderately Differentiated Gastroenteropancreatic Neuroendocrine Tumors

BACKGROUND

Somatostatin analogues, aiming to control tumor secretion or growth, constitute the most attractive therapeutic option for patients with well-differentiated gastroenteropancreatic neuroendocrine tumors (GEP-NETs). The objective of this article is to provide a comprehensive review of the current state-of-the-art knowledge gaps and potential opportunities for future development and optimization of this therapeutic modality.

METHOD

A contextualized systematic review with a narrative component was conducted using PubMed, The Cochrane Library, EMBASE, and Google Scholar. Titles were screened, and non-English, duplicate, or irrelevant entries were excluded. Selection criteria for articles included the following: publication in English between 1995 and 2016, patients with GEP-NETs, analysis of efficacy, safety, practical management considerations, predictive factors, and/or strategies for overcoming resistance, concerning somatostatin analogs.

RESULTS

Ninety-seven studies out of 2771 screened publications met the inclusion criteria (16 randomized clinical trials, 27 phase II trials, 3 phase I trials, 3 subgroup analyses of clinical trials, 1 open-label extension of a randomized trial, 1 phase IV trial, 32 observational studies, and 14 basic research articles). The nature and scope of literature was diverse with most articles dedicated to drug efficacy or indications of use (n = 49), pharmacological issues (n = 8), assessment or predictors of response (n = 4), practical management (n = 11), combination therapy or other means to overcome resistance (n = 19), receptors and signaling pathways (n = 3), and subgroup analyses (n = 3).

CONCLUSION

In this appraisal, we have found some practical aspects that can help to the optimization of somatostatin analog (SSA) therapy in patients with well-differentiated GEP-NETs. We have also identified areas of uncertainty in an effort to guide clinical research in the coming years.

SRC family kinase FYN promotes the neuroendocrine phenotype and visceral metastasis in advanced prostate cancer

FYN is a SRC family kinase (SFK) that has been shown to be up-regulated in human prostate cancer (PCa) tissues and cell lines. In this study, we observed that FYN is strongly up-regulated in human neuroendocrine PCa (NEPC) tissues and xenografts, as well as cells derived from a NEPC transgenic mouse model. In silico analysis of FYN expression in prostate cancer cell line databases revealed an association with the expression of neuroendocrine (NE) markers such as CHGA, CD44, CD56, and SYP. The loss of FYN abrogated the invasion of PC3 and ARCaPM cells in response to MET receptor ligand HGF. FYN also contributed to the metastatic potential of NEPC cells in two mouse models of visceral metastasis with two different cell lines (PC3 and TRAMPC2-RANKL). The activation of MET appeared to regulate neuroendocrine (NE) features as evidenced by increased expression of NE markers in PC3 cells with HGF. Importantly, the overexpression of FYN protein in DU145 cells was directly correlated with the increase of CHGA. Thus, our data demonstrated that the neuroendocrine differentiation that occurs in PCa cells is, at least in part, regulated by FYN kinase. Understanding the role of FYN in the regulation of NE markers will provide further support for ongoing clinical trials of SFK and MET inhibitors in castration-resistant PCa patients.

Towards a new classification of gastroenteropancreatic neuroendocrine neoplasms

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) constitute a heterogeneous group of tumours associated with variable clinical presentations, growth rates, and prognoses. To improve the management of GEP-NENs, the WHO developed a classification system that enables tumours to be graded based on markers of cell proliferation in biopsy specimens. Indeed, histopathology has been a mainstay in the diagnosis of GEP-NENs, and the WHO grading system facilitates therapeutic decision-making; however, considerable intratumoural heterogeneity, predominantly comprising regional variations in proliferation rates, complicates the evaluation of tumour biology. The use of molecular imaging modalities to delineate the most-aggressive cell populations is becoming more widespread. In addition, molecular profiling is increasingly undertaken in the clinical setting, and genomic studies have revealed a number of chromosomal alterations in GEP-NENs, although the 'drivers' of neoplastic development have not been identified. Thus, our molecular understanding of GEP-NENs remains insufficient to inform on patient prognosis or selection for treatments, and the WHO classification continues to form the basis for management of this disease. Nevertheless, our increasing understanding of the molecular genetics and biology of GEP-NENs has begun to expose flaws in the WHO classification. We describe the current understanding of the molecular characteristics of GEP-NENs, and discuss how advances in molecular profiling measurements, including assays of circulating mRNAs, are likely to influence the management of these tumours.

Blood and tissue neuroendocrine tumor gene cluster analysis correlate, define hallmarks and predict disease status

A multianalyte algorithmic assay (MAAA) identifies circulating neuroendocrine tumor (NET) transcripts (n=51) with a sensitivity/specificity of 98%/97%. We evaluated whether blood measurements correlated with tumor tissue transcript analysis. The latter were segregated into gene clusters (GC) that defined clinical 'hallmarks' of neoplasia. A MAAA/cluster integrated algorithm (CIA) was developed as a predictive activity index to define tumor behavior and outcome. We evaluated three groups. Group 1: publically available NET transcriptome databases (n=15; GeneProfiler). Group 2: prospectively collected tumors and matched blood samples (n=22; qRT-PCR). Group 3: prospective clinical blood samples, n=159: stable disease (SD): n=111 and progressive disease (PD): n=48. Regulatory network analysis, linear modeling, principal component analysis (PCA), and receiver operating characteristic analyses were used to delineate neoplasia 'hallmarks' and assess GC predictive utility. Our results demonstrated: group 1: NET transcriptomes identified (92%) genes elevated. Group 2: 98% genes elevated by qPCR (fold change >2, P<0.05). Correlation analysis of matched blood/tumor was highly significant (R(2)=0.7, P<0.0001), and 58% of genes defined nine omic clusters (SSTRome, proliferome, signalome, metabolome, secretome, epigenome, plurome, and apoptome). Group 3: six clusters (SSTRome, proliferome, metabolome, secretome, epigenome, and plurome) differentiated SD from PD (area under the curve (AUC)=0.81). Integration with blood-algorithm amplified the AUC to 0.92±0.02 for differentiating PD and SD. The CIA defined a significantly lower SD score (34.1±2.6%) than in PD (84±2.8%, P<0.0001). In conclusion, circulating transcripts measurements reflect NET tissue values. Integration of biologically relevant GC differentiate SD from PD. Combination of GC data with the blood-algorithm predicted disease status in >92%. Blood transcript measurement predicts NET activity.

Decoding the Molecular and Mutational Ambiguities of Gastroenteropancreatic Neuroendocrine Neoplasm Pathobiology

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NEN), considered a heterogeneous neoplasia, exhibit ill-defined pathobiology and protean symptomatology and are ubiquitous in location. They are difficult to diagnose, challenging to manage, and outcome depends on cell type, secretory product, histopathologic grading, and organ of origin. A morphologic and molecular genomic review of these lesions highlights tumor characteristics that can be used clinically, such as somatostatin-receptor expression, and confirms features that set them outside the standard neoplasia paradigm. Their unique pathobiology is useful for developing diagnostics using somatostatin-receptor targeted imaging or uptake of radiolabeled amino acids specific to secretory products or metabolism. Therapy has evolved via targeting of protein kinase B signaling or somatostatin receptors with drugs or isotopes (peptide-receptor radiotherapy). With DNA sequencing, rarely identified activating mutations confirm that tumor suppressor genes are relevant. Genomic approaches focusing on cancer-associated genes and signaling pathways likely will remain uninformative. Their uniquely dissimilar molecular profiles mean individual tumors are unlikely to be easily or uniformly targeted by therapeutics currently linked to standard cancer genetic paradigms. The prevalence of menin mutations in pancreatic NEN and P27^KIP1 mutations in small intestinal NEN represents initial steps to identifying a regulatory commonality in GEP-NEN. Transcriptional profiling and network-based analyses may define the cellular toolkit. Multianalyte diagnostic tools facilitate more accurate molecular pathologic delineations of NEN for assessing prognosis and identifying strategies for individualized patient treatment. GEP-NEN remain unique, poorly understood entities, and insight into their pathobiology and molecular mechanisms of growth and metastasis will help identify the diagnostic and therapeutic weaknesses of this neoplasia.

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.

Differential expression of genes encoding proteins of the HGF/MET system in insulinomas

BACKGROUND

Insulinomas are the most common functional pancreatic neuroendocrine tumors, whereas histopathological features do not predict their biological behaviour. In an attempt to better understand the molecular processes involved in the tumorigenesis of islet beta cells, the present study evaluated the expression of genes belonging to the hepatocyte growth factor and its receptor (HGF/MET) system, namely, MET, HGF; HGFAC and ST14 (encode HGF activator and matriptase, respectively, two serine proteases that catalyze conversion of pro-HGF to active HGF); and SPINT1 and SPINT2 (encode serine peptidase inhibitors Kunitz type 1 and type 2, respectively, two inhibitors of HGF activator and of matriptase).

METHODS

Quantitative real-time reverse transcriptase polymerase chain reaction was employed to assess RNA expression of the target genes in 24 sporadic insulinomas: 15 grade 1 (G1), six grade 2 (G2) and three hepatic metastases. Somatic mutations of MET gene were searched by direct sequencing of exons 2, 10, 14, 16, 17 and 19.

RESULTS

Overexpression of MET was observed in the three hepatic metastases concomitantly with upregulation of the genes encoding HGF and matriptase and downregulation of SPINT1. A positive correlation was observed between MET RNA expression and Ki-67 proliferation index while a negative correlation was detected between SPINT1 expression and the mitotic index. No somatic mutations were found in MET gene.

CONCLUSION

The final effect of the increased expression of HGF, its activator (matriptase) and its specific receptor (MET) together with a decreased expression of one potent inhibitor of matriptase (SPINT1) is probably a contribution to tumoral progression and metastatization in insulinomas.

Genetic polymorphisms of inflammatory response gene TNF-α and its influence on sporadic pancreatic neuroendocrine tumors predisposition risk

The diagnosed incidence of pancreatic neuroendocrine tumors (pNETs) is increasing; however, their etiology remains poorly understood. PNETs are a rare, heterogeneous group of tumors arising from the endocrine cells of the pancreas, and genetic risk factors for sporadic pNETs are inadequately understood. It is known that pNETs secrete biogenic amines, hormones and growth factors, tumor necrosis factor-a (TNF-α) being one of them. Furthermore, cytokines and other proinflammatory mediators have been implicated in inflammatory pancreatic diseases including pancreatitis and cancer. The aim of our study was to analyze TNF-α promoter gene polymorphisms as risk factors for pNETs using germline DNA collected in a population-based case-control study of pancreatic cancer [42 pNET cases, 78 pancreatic ductal adenocarcinoma (PDAC) cases, 17 intraductal papillary mucinous neoplasm (IPMN) and 98 healthy controls] conducted in the Athens, Greece and Izmir, Turkey areas. For subsequent analysis, we excluded cases and controls with known genetic syndromes. The CC genotype at the -1031 position was more frequent in pNET and IPMN patients (p=0.0002 and p=0.009, respectively), suggesting its possible role in pNET development. Furthermore, the AA genotype at the -308 position was overrepresented in IPMN cases (p=0.03), and AA genotype at the -238 position was more frequent in PDAC cases (p=0.03) compared to healthy individuals. With regard to tumor characteristics, no statistically significant association was detected. Our findings suggest the putative role of TNF-α -1031 polymorphism in the development of pNET and IPMN, whereas the -308 polymorphism seems to be overrepresented among IPMN cases and -238 polymorphism among PDAC cases.

Sunitinib in the treatment of advanced solid tumors

Sunitinib is an oral multikinase inhibitor that blocks the vascular endothelial growth factor receptor (VEGFR), platelet-derived growth factor receptor (PDGFR) alpha and beta, c-kit, and other receptors. These attributes have proven to be efficacious in the treatment of metastatic renal cell carcinoma (RCC), unresectable gastrointestinal stromal tumors (GIST), and well-differentiated advanced pancreatic neuroendocrine tumors (PNET). Though activity has been reported in other tumor types, phase III trials have not yet demonstrated improved survival outcomes in these cancers. Most side effects including hypertension, hand-foot syndrome, and diarrhea are generally well manageable. This review will detail the preclinical data leading up to the results of the pivotal phase III clinical trials that have led to the widespread use of sunitinib in advanced RCC, GIST, and PNET.

Gastrointestinal hormones stimulate growth of Foregut Neuroendocrine Tumors by transactivating the EGF receptor

Foregut neuroendocrine tumors [NETs] usually pursuit a benign course, but some show aggressive behavior. The treatment of patients with advanced NETs is marginally effective and new approaches are needed. In other tumors, transactivation of the EGF receptor (EGFR) by growth factors, gastrointestinal (GI) hormones and lipids can stimulate growth, which has led to new treatments. Recent studies show a direct correlation between NET malignancy and EGFR expression, EGFR inhibition decreases basal NET growth and an autocrine growth effect exerted by GI hormones, for some NETs. To determine if GI hormones can stimulate NET growth by inducing transactivation of EGFR, we examined the ability of EGF, TGFα and various GI hormones to stimulate growth of the human foregut carcinoid,BON, the somatostatinoma QGP-1 and the rat islet tumor,Rin-14B-cell lines. The EGFR tyrosine-kinase inhibitor, AG1478 strongly inhibited EGF and the GI hormones stimulated cell growth, both in BON and QGP-1 cells. In all the three neuroendocrine cell lines studied, we found EGF, TGFα and the other growth-stimulating GI hormones increased Tyr(1068) EGFR phosphorylation. In BON cells, both the GI hormones neurotensin and a bombesin analogue caused a time- and dose-dependent increase in EGFR phosphorylation, which was strongly inhibited by AG1478. Moreover, we found this stimulated phosphorylation was dependent on Src kinases, PKCs, matrix metalloproteinase activation and the generation of reactive oxygen species. These results raise the possibility that disruption of this signaling cascade by either EGFR inhibition alone or combined with receptor antagonists may be a novel therapeutic approach for treatment of foregut NETs/PETs.

EGFR/TGFα and TGFβ/CTGF Signaling in Neuroendocrine Neoplasia: Theoretical Therapeutic Targets

Neuroendocrine neoplasms (NENs) are a heterogeneous family of malignancies whose proliferation is partially dependent on growth factors secreted by the microenvironment and the tumor itself. Growth factors which were demonstrated to be important in experimental models of NENs include EGF (epidermal growth factor), TGF (transforming growth factor) α, TGFβ and CTGF (connective tissue growth factor). EGF and TGFα bind to the EGF receptor to stimulate an intact RAS/RAF/MAPK pathway, leading to the transcription of genes associated with cell proliferation, invasion and metastasis. Theoretically, TGFα stimulation can be inhibited at several points of the MAPK pathway, but success is limited to NEN models and is not evident in the clinical setting. TGFβ1 stimulates TGFβ receptors (TGFβRI and TGFβRII) resulting in inhibition of neuroendocrine cell growth through SMAD-mediated activation of the growth inhibitor P21(WAF1/CIP1). Although some NENs are inhibited by TGFβ1, paradoxical growth is seen in experimental models of gastric and small intestinal (SI) NENs. Therapeutic targeting of TGFβ1 in NENs is therefore complicated by uncertainty of the effect of TGFβ1 secretion on the direction of proliferative regulation. CTGF expression is associated with more malignant clinical phenotypes in a variety of cancers, including NENs. CTGF promotes growth in gastric and SI-NEN models, and is implicated as a mediator of local and distant fibrosis caused by NENs of enterochromaffin cell origin. CTGF inhibitors are available, but their anti-proliferative effect has not been tested in NENs. In summary, growth factors are essential for NEN proliferation, and although interventions targeting these proteins are effective in experimental models, only limited clinical efficacy has been identified.

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.

Sorafenib inhibits tumor growth and improves survival in a transgenic mouse model of pancreatic islet cell tumors

BACKGROUND

The purpose of the study was to evaluate Sorafenib (BAY 43-9006) derived receptor tyrosine kinase inhibition on tumor progression in murine islet cell tumors. Sorafenib is considered to be a potent inhibitor of tumor angiogenesis and neovascularization in various solid tumors. Rip1Tag2 mice were treated in two different groups according to the model of tumor progression: the early treatment group received vehicle or Sorafenib from 10 to 14 weeks of age and the late treatment group from week 12 until death. Tumor surface, tumor cell proliferation, and apoptosis were measured in both treatment groups to assess the in vivo effects of Sorafenib. Survival was recorded for the late treatment group. In the early treatment group Sorafenib led to a dramatic decrease in tumor volume compared to the control group. Apoptosis was significantly augmented and cell proliferation was inhibited. As a single therapy Sorafenib significantly improved survival in the late treatment group. Conclusion. Sorafenib may provide a new paradigm for the therapy of islet cell tumors.

Neuroendocrine tumors of the digestive tract: impact of new classifications and new agents on therapeutic approaches

PURPOSE OF REVIEW

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) constitute a diverse group of neoplasms arising from the diffuse neuroendocrine cell system. During the last 2 years a new classification system, the WHO 2010, has come into clinical practice together with Tumor Nodes Metastases (TNM) staging and grading systems, developed by the European Neuroendocrine Tumor Society/American Joint Cancer Committee. At the same time new targeted agents have been developed for treatment of GEP-NETs and it is important discuss these new agents in relation to the classification and staging system.

RECENT FINDINGS

The current article is reviewing the most important clinical trials of targeting agents within the field of neuroendocrine tumors. Tyrosine kinase inhibitors as well as PI3 kinase mTOR inhibitors have been applied in the treatment of neuroendocrine tumors.

SUMMARY

Sunitinib and everolimus have recently been registered for treatment of pancreatic neuroendocrine tumors worldwide. The role of these new targeted agents in the treatment algorithm of neuroendocrine tumors will be discussed. A large number of phase I and phase II trials have been performed in GEP-NETs with rather limited results and no significant impact on the clinical management of patients with GEP-NETs. However, there are two phase III trials that have completely changed the treatment landscape for pancreatic neuroendocrine tumors, e.g., sunitinib and everolimus demonstrating an increased progression free survival of 11 vs. 5 months for the placebo group.

Connective tissue growth factor in tumor pathogenesis

Key roles for connective tissue growth factor (CTGF/CCN2) are demonstrated in the wound repair process where it promotes myofibroblast differentiation and angiogenesis. Similar mechanisms are active in tumor-reactive stroma where CTGF is expressed. Other potential roles include prevention of hypoxia-induced apoptosis and promoting epithelial-mesenchymal transistion (EMT). CTGF expression in tumors has been associated to both tumor suppression and progression. For example, CTGF expression in acute lymphoblastic leukemia, breast, pancreas and gastric cancer correlates to worse prognosis whereas the opposite is true for colorectal, lung and ovarian cancer. This discrepancy is not yet understood. High expression of CTGF is a hallmark of ileal carcinoids, which are well-differentiated endocrine carcinomas with serotonin production originating from the small intestine and proximal colon. These tumors maintain a high grade of differentiation and low proliferation. Despite this, they are malignant and most patients have metastatic disease at diagnosis. These tumors demonstrate several phenotypes potentially related to CTGF function namely: cell migration, absent tumor cell apoptosis, as well as, reactive and well vascularised myofibroblast rich stroma and fibrosis development locally and in distal organs. The presence of CTGF in other endocrine tumors indicates a role in the progression of well-differentiated tumors.

The biological hallmarks of ileal carcinoids

Endocrine tumours derived from the small intestine, ileal carcinoids, produce and secrete the hormones tachykinins and serotonin, which induces the specific symptoms related to the tumour. Because of their low proliferation rate, they are often discovered at late stages when metastases have occurred. The biology that characterizes these tumours differs in many ways from what is generally recognized for other malignancies. In this overview, the current knowledge on the development and progression of ileal carcinoids is described.

Hedgehog inhibition with cyclopamine represses tumor growth and prolongs survival in a transgenic mouse model of islet cell tumors

BACKGROUND

Blockade of aberrant hedgehog (Hh) activation has recently been proposed as a therapeutic target, but effects in models of islet cell tumors have not been examined. In this study, we address the role of the Hh pathway in tumor progression of murine islet cell tumors.

METHODS

To assess in vivo effects, Rip1Tag2 mice were treated with vehicle or cyclopamine (25 mg/kg/d) (n = 10 in each group). The effect of hedgehog pathway inhibition on survival was determined by continuous application of the small molecule smoothened antagonist cyclopamine.

RESULTS

Hh-inhibition was confirmed by downregulation of Hh-target genes. Cyclopamine response was associated with increased apoptosis, decreased tumor cell proliferation and reduced tumor volume. Furthermore, hedgehog inhibition with cyclopamine significantly prolonged median survival in the used transgenic mouse model (102 vs 124 days; P = 0.02).

CONCLUSIONS

Thus, Hh inhibitors may provide a new paradigm for therapy of islet cell tumors in various stages, particularly their use in conjunction with conventional antimetabolites should be further evaluated.

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.

Connective tissue growth factor expression in endocrine tumors is associated with high stromal expression of alpha-smooth muscle actin

OBJECTIVE

Complications due to fibrosis development are common in patients with well-differentiated endocrine carcinomas in the small intestine (ileal carcinoids). Connective tissue growth factor (CTGF) expression in ileal carcinoids may be related to this fibrosis development. This study aimed to examine CTGF expression in relation to local myofibroblast differentiation in a large series of ileal carcinoids and in different types of endocrine tumors.

METHODS

Immunoreactivity (IR) for CTGF and α-smooth muscle actin (α-SMA), a marker for myofibroblasts, was compared in serial tumor tissue sections from 42 patients with ileal carcinoids and from 80 patients with other endocrine tumors. Western blot was performed on an additional 21 patients with ileal carcinoids.

RESULTS

CTGF IR was present in >50% of tumor cells in all 42 ileal carcinoids and in 2 out of 14 endocrine pancreatic tumors, 4 out of 6 rectal carcinoids, and 1 out of 5 lung carcinoids. Tumors with abundant CTGF expression also displayed α-SMA IR in stromal fibroblast-like cells, whereas other endocrine tumors displayed less or no CTGF and α-SMA IR. Protein bands corresponding to full-length CTGF (36-42 kDa) were detected in protein lysates from ileal carcinoids.

CONCLUSION

CTGF is uniquely prevalent in ileal carcinoids when compared with most other endocrine tumor types. Immunoreactive cells are adjacent areas with increased fibrovascular stroma that express α-SMA. This supports a potential role for CTGF in myofibroblast-mediated fibrosis associated with ileal carcinoids, and indicates that CTGF should be investigated as a target for future therapy.

SSTR1 and SSTR5 subtypes are the dominant forms of somatostatin receptor in neuroendocrine tumors

The effectiveness of the long acting somatostatin analogues like octreotide and lanreotide depends on the expression of specific somatostatin receptors on the target cells. The immunohistochemical method performed on surgically removed tumors searches the expression of receptors at the level of receptor protein and gives us insight into receptor's cellular localization. The aim of study was to assess the presence of all the 5 subtypes of SSTR 1-5 (including 2A and 2B SSTR isoforms) in surgically treated human neuroendocrine tumors (NETs) to establish which receptor subtype is the dominant form of somatostatin receptor in particular tumor and thus to be able to predict which somatostatin analog will be effective in NETs treatment. 18 samples of neuroendocrine tumors (surgically excised tumors or biopsies) were immunostained with specific antibodies. Expression of SSTR was scored semiquantitatively. Only strong or moderate immunostaining was considered as positive reaction. The summarized expression pattern of SSTR in the investigated neuroendocrine tumors in our material was: SSTR 1> SSTR 5> SSTR 3> SSTR 2A> SSTR 2B. The receptors were distributed mainly in the area of cells cytoplasm with a few specimens showing only membranous or mixed: membranous--cytoplasmic localization. The observed pattern suggests that apart from octreotide and lanreotide, newly synthesized multiligand analogs such as SOM 230, KE 108 or SSTR 1 and SSTR 5 selective analogs could be effective in NETs treatment.

Standardized uptake values of (68)Ga-DOTANOC PET: a promising prognostic tool in neuroendocrine tumors

Despite the fact that several studies have been published regarding the prognostic factors of neuroendocrine tumors (NETs), there are some cases in which available data are not sufficient to predict disease progression and to define a correct therapeutic approach. To our knowledge, the role of maximum standardized uptake value (SUVmax) as a prognostic factor has never been studied in NET patients. Therefore, we prospectively investigated whether (68)Ga-[1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid]-1-NaI3-octreotide ((68)Ga-DOTANOC) PET SUVmax could be used as an accurate noninvasive marker for disease prognosis.

METHODS

Forty-seven patients with NETs were studied with (68)Ga-DOTANOC PET. All patients underwent a baseline visit and laboratory and radiologic examinations. Follow-up was performed in all cases.

RESULTS

SUVmax was significantly higher in patients with pancreatic NET and in those with well-differentiated NETs. Moreover, SUVmax was significantly higher in patients with an elevated expression of 2A-somatostatin receptor. During the follow-up, the disease was stable or presented a partial response in 25 patients, and in 19 cases the disease progressed. The patients with stable disease or a partial response had an SUVmax significantly higher than did those in the progressive disease group, with the best cutoff ranging from 17.9 to 19.3. At univariate and multivariate analysis, the significant positive prognostic factors were well-differentiated NET, an SUVmax of 19.3 or more, and a combined treatment with long-acting somatostatin analogs and radiolabeled somatostatin analogs.

CONCLUSION

We demonstrated, for the first time to our knowledge, that (68)Ga-DOTANOC PET SUVmax correlates with the clinical and pathologic features of NETs and is also an accurate prognostic index.

IL-2 -330 T/G SNP and serum values-potential new tumor markers in neuroendocrine tumors of the gastrointestinal tract and pancreas (GEP-NETs)

Cytokines participate in tumorigenesis of gastroenteropancreatic neuroendocrine tumors (GEP-NETs). Single nucleotide polymorphisms (SNPs) in cytokine genes influence expression of proteins and are evaluated in cancer susceptibility. The aim of this study was to evaluate IL-2 -330 T/G SNP and susceptibility to GEP-NETs, and analyze the correlation between G-allele and IL-2 serum values in GEP-NET patients. Moreover we assessed the value of IL-2 as a tumor serum marker. IL-2 -330 T/G SNP was examined in 101 patients and 150 healthy volunteers and IL-2 serum levels in patients and 20 controls. Patients' IL-2 serum levels were compared to IL-2 -330 T/G genotypes and tumor functional status and finally with known markers such as chromogranin A (CgA) and 5-hydroxyindolacetic acid (5-HIAA). There was a significant difference in genotype distribution of the IL-2 -330 polymorphisms between GEP-NET and control group (p = 0.0006) as well as in the frequency of G-allele (p = 0.010). G-allele correlated with higher IL-2 serum levels (p = 0.028) and elevated in all patients, being highest in patients with functional tumors (p = 0.039). Compared to CgA and 5-HIAA, IL-2 was more specific in detecting GEP-NET patients (p < 0.0001 and p < 0.0001, respectively). Our results indicate importance of IL-2 in GEP-NET development and biochemical diagnosis.

[Invasive diagnostic procedures for insulinomas of the pancreas]

Insulinomas are the most common cause for hypoglycemia with endogenous hyperinsulinism. Insulinomas are the most frequent endocrine tumor of the pancreas and 10% occur as multiple tumors (e.g. multiple endocrine neoplasia type I) or in rare cases as islet cell hyperplasia. A further 10-15% of insulinomas are malignant. Non-invasive imaging modalities, such as computed tomography (CT), magnetic resonance imaging (MRI), ultrasonography (US) and somatoreceptor scintigraphy (SRN) show a lower sensitivity for detection and localization of tumors, because in many cases insulinomas are smaller than 2 cm in size. Invasive pre-operative diagnostic procedures, such as transhepatic peripancreatic venous blood sampling (TPVB) and the intra-arterial calcium stimulation test (ASVS) are much more time-intensive compared to CT, MRI and US with an examination time of 2-3 h but achieve a more exact pre-operative detection and localization with sensitivities mostly greater than 95% and are therefore the diagnostic methods of choice.

Gastrointestinal neuroendocrine tumors: pancreatic endocrine tumors

Pancreatic endocrine tumors (PETs) have long fascinated clinicians and investigators despite their relative rarity. Their clinical presentation varies depending on whether the tumor is functional or not, and also according to the specific hormonal syndrome produced. Tumors may be sporadic or inherited, but little is known about their molecular pathology, especially the sporadic forms. Chromogranin A appears to be the most useful serum marker for diagnosis, staging, and monitoring. Initially, therapy should be directed at the hormonal syndrome because this has the major initial impact on the patient's health. Most PETs are relatively indolent but ultimately malignant, except for insulinomas, which predominantly are benign. Surgery is the only modality that offers the possibility of cure, although it generally is noncurative in patients with Zollinger-Ellison syndrome or nonfunctional PETs with multiple endocrine neoplasia-type 1. Preoperative staging of disease extent is necessary to determine the likelihood of complete resection although debulking surgery often is believed to be useful in patients with unresectable tumors. Once metastatic, biotherapy is usually the first modality used because it generally is well tolerated. Systemic or regional therapies generally are reserved until symptoms occur or tumor growth is rapid. Recently, a number of newer agents, as well as receptor-directed radiotherapy, are being evaluated for patients with advanced disease. This review addresses a number of recent advances regarding the molecular pathology, diagnosis, localization, and management of PETs including discussion of peptide-receptor radionuclide therapy and other novel antitumor approaches. We conclude with a discussion of future directions and unsettled problems in the field.

Activity of sunitinib in patients with advanced neuroendocrine tumors

PURPOSE

Standard cytotoxic chemotherapy has limited efficacy in metastatic neuroendocrine tumor patients. Neuroendocrine tumors express vascular endothelial growth factor (VEGF) and its receptor (VEGFR). Sunitinib malate, an oral tyrosine kinase inhibitor, has activity against VEGFRs as well as platelet-derived growth factor receptors, stem-cell factor receptor, glial cell line-derived neurotrophic factor, and FMS-like tyrosine kinase-3. We evaluated the efficacy of sunitinib in a two-cohort, phase II study of advanced carcinoid and pancreatic neuroendocrine tumor patients.

PATIENTS AND METHODS

Patients were treated with repeated 6-week cycles of oral sunitinib (50 mg/d for 4 weeks, followed by 2 weeks off treatment). Patients were observed for response, survival, and adverse events. Patient-reported outcomes were assessed.

RESULTS

Among 109 enrolled patients, 107 received sunitinib (carcinoid, n = 41; pancreatic endocrine tumor, n = 66). Overall objective response rate (ORR) in pancreatic endocrine tumor patients was 16.7% (11 of 66 patients), and 68% (45 of 66 patients) had stable disease (SD). Among carcinoid patients, ORR was 2.4% (one of 41 patients), and 83% (34 of 41 patients) had SD. Median time to tumor progression was 7.7 months in pancreatic neuroendocrine tumor patients and 10.2 months in carcinoid patients. One-year survival rate was 81.1% in pancreatic neuroendocrine tumor patients and 83.4% in carcinoid patients. No significant differences from baseline in patient-reported quality of life or fatigue were observed during treatment.

CONCLUSION

Sunitinib has antitumor activity in pancreatic neuroendocrine tumors; its activity against carcinoid tumors could not be definitively determined in this nonrandomized study. Randomized trials of sunitinib in patients with neuroendocrine tumors are warranted.

Treatment of gastrointestinal neuroendocrine tumors with inhibitors of growth factor receptors and their signaling pathways: recent advances and future perspectives

The limited efficacy of conventional cytotoxic treatment regimes for advanced gastrointestinal neuroendocrine cancers emphasizes the need for novel and more effective medical treatment options. Recent findings on the specific biological features of this family of neoplasms has led to the development of new targeted therapies, which take into account the high vascularization and abundant expression of specific growth factors and cognate tyrosine kinase receptors. This review will briefly summarize the status and future perspectives of antiangiogenic, mTOR- or growth factor receptor-based pharmacological approaches for the innovative treatment of gastrointestinal neuroendocrine tumors. In view of the multitude of novel targeted approaches, the rationale for innovative combination therapies, i.e. combining growth factor (receptor)-targeting agents with chemo- or biotherapeutics or with other novel anticancer drugs such as HDAC or proteasome inhibitors will be taken into account.

Phenotype reversion in fetal human liver epithelial cells identifies the role of an intermediate meso-endodermal stage before hepatic maturation

Understanding the biological potential of fetal stem/progenitor cells will help define mechanisms in liver development and homeostasis. We isolated epithelial fetal human liver cells and established phenotype-specific changes in gene expression during continuous culture conditions. Fetal human liver epithelial cells displayed stem cell properties with multilineage gene expression, extensive proliferation and generation of mesenchymal lineage cells, although the initial epithelial phenotype was rapidly supplanted by meso-endodermal phenotype in culture. This meso-endodermal phenotype was genetically regulated through cytokine signaling, including transforming growth factor beta, bone morphogenetic protein, fibroblast growth factor and other signaling pathways. Reactivation of HNF3alpha (FOXA1) transcription factor, a driver of hepatic specification in the primitive endoderm, indicated that the meso-endodermal phenotype represented an earlier developmental stage of cells. We found that fetal liver epithelial cells formed mature hepatocytes in vivo, including after genetic manipulation using lentiviral vectors, offering convenient assays for analysis of further cell differentiation and fate. Taken together, these studies demonstrate plasticity in fetal liver epithelial stem cells, offer paradigms for defining mechanisms regulating lineage switching in stem cells, and provide potential avenues for regulating cell phenotypes for applications of stem cells, such as for cell therapy.

PI(3)K-Akt-mTOR pathway as a potential therapeutic target in neuroendocrine tumors

Constitutive activation of PI(3)K-Akt-mTOR signaling is a frequently occurring event in human cancer and has also been detected in the majority of neuroendocrine tumors (NETs) of the gastroenteropancreatic system. Molecular analysis of NETs suggests, that in addition to mutations in certain tumor-suppressor genes (e.g., PTEN), multiple autocrine growth factor loops contribute to hyperactive PI(3)K-Akt-mTOR signaling, thus promoting unrestricted proliferation and resistance to apoptosis. These insights opened new perspectives for targeted therapy in NETs. In particular, several novel small-molecule inhibitors of tyrosine and serine/threonine kinases have demonstrated potent anti-tumor activity. This review will summarize current knowledge on PI(3)K-Akt-mTOR signaling, its role in proliferation and apoptosis, as well as novel therapeutic approaches targeting PI(3)K-Akt-mTOR pathway components in NET disease.

Medical management of pancreatic neuroendocrine tumors

BACKGROUND

Pancreatic neuroendocrine tumors (PNET) are rare malignancies frequently diagnosed at a late stage, with symptoms related to bulky disease. Hormonal secretion, when responsible for symptoms, permits, on the other hand, early diagnosis of the disease. Surgery remains the cornerstone of therapeutic management. However, due to advanced disease, many patients are not candidates for aggressive surgical therapy. Tumor growth control and symptom management are thus achieved through medical approaches, including somatostatin (SST) analogs, chemotherapy, interferon, and more recently, targeted therapy. The purpose of this review is to collect, examine, and analyze data available in the literature regarding contemporary therapeutic management of PNET, with emphasis on medical approaches. It also offers perspectives on the future of molecular targeted therapies in these neoplasms. However, we point out that much of the literature published to date includes noncomparative studies (mainly phase II studies), leading to thorny interpretation of the results.

METHODS

A systematic search of all the literature in English regarding PNET was performed, based on a MEDLINE search (Pubmed) carried out from January 1970 to May 2005.

RESULTS

Approximately 40 trials, including over 1,000 patients, have been retrieved from our MEDLINE search. SST analogs and interferon therapies do allow control over hormone secretion and subsequent symptoms in the majority of treated subjects, but offer a poor tumor growth control rate. Chemotherapies, although more efficient in reducing tumor burden, are often toxic. New approaches such as immunotherapy and targeted therapies are still under investigation.

CONCLUSIONS

Whether alone or in combination with surgery, conventional medical therapies represent a crucial aspect of PNET management. Hopefully, in the near future, a new era of antitumoral agents, such as targeted therapies, will strengthen our therapeutic arsenal, either alone or combined with other therapies.

Neuroendocrine tumors. Biotherapy

This review gives an introduction to the classification and staging of neuroendocrine tumors, as the prognostic implications of these classifications influence therapeutic decisions. The indications for biotherapy are given, together with a short update on the mechanism of somatostatin analogs and interferon-alpha therapy. This is followed by an in-depth description of the use of biotherapy, its results with respect to symptomatic and antiproliferative treatment, as well as its side-effects.