Illuminating somatostatin analog action at neuroendocrine tumor receptors

Neuroendocrine Tumors: Diagnostics

Neuroendocrine neoplasms (NEN) are rare tumors arising from neuroendocrine cells. NEN are ideally suited for a theragnostic approach due to their specific expression of somatostatin receptors (SSTR). SSTR imaging of NEN dates back to the 1980s, but has evolved recently due to the introduction of more sensitive SSTR PET radiotracers. SSTR PET is a primary imaging modality for identifying NEN and characterizing SSTR expression. SSTR PET is complementary to anatomic imaging for assessing tumor response to treatment. SSTR PET is mandated to determine eligibility for peptide receptor radionuclide therapy. Here, the role of imaging to aid management of NEN is reviewed.

[177Lu]Lu-DOTA-TATE plus long-acting octreotide versus high‑dose long-acting octreotide for the treatment of newly diagnosed, advanced grade 2-3, well-differentiated, gastroenteropancreatic neuroendocrine tumours (NETTER-2): an open-label, randomised, phase 3 study

BACKGROUND

There are currently no standard first-line treatment options for patients with higher grade 2-3, well-differentiated, advanced, gastroenteropancreatic neuroendocrine tumours. We aimed to investigate the efficacy and safety of first-line [177Lu]Lu-DOTA-TATE (177Lu-Dotatate) treatment.

METHODS

NETTER-2 was an open-label, randomised, parallel-group, superiority, phase 3 trial. We enrolled patients (aged ≥15 years) with newly diagnosed higher grade 2 (Ki67 ≥10% and ≤20%) and grade 3 (Ki67 >20% and ≤55%), somatostatin receptor-positive (in all target lesions), advanced gastroenteropancreatic neuroendocrine tumours from 45 centres across nine countries in North America, Europe, and Asia. We used interactive response technologies to randomly assign (2:1) patients to receive four cycles (cycle interval was 8 weeks ± 1 week) of intravenous 177Lu-Dotatate plus intramuscular octreotide 30 mg long-acting repeatable (LAR) then octreotide 30 mg LAR every 4 weeks (177Lu-Dotatate group) or high-dose octreotide 60 mg LAR every 4 weeks (control group), stratified by neuroendocrine tumour grade (2 vs 3) and origin (pancreas vs other). Tumour assessments were done at baseline, week 16, and week 24, and then every 12 weeks until disease progression or death. The primary endpoint was progression-free survival by blinded, independent, central radiology assessment. We did the primary analysis at 101 progression-free survival events as the final progression-free survival analysis. NETTER-2 is registered with ClinicalTrials.gov, NCT03972488, and is active and not recruiting.

FINDINGS

Between Jan 22, 2020, and Oct 13, 2022, we screened 261 patients, 35 (13%) of whom were excluded. We randomly assigned 226 (87%) patients (121 [54%] male and 105 [46%] female) to the 177Lu-Dotatate group (n=151 [67%]) and control group (n=75 [33%]). Median progression-free survival was 8·5 months (95% CI 7·7-13·8) in the control group and 22·8 months (19·4-not estimated) in the 177Lu-Dotatate group (stratified hazard ratio 0·276 [0·182-0·418]; p<0·0001). During the treatment period, adverse events (of any grade) occurred in 136 (93%) of 147 treated patients in the 177Lu-Dotatate group and 69 (95%) of 73 treated patients in the control group. There were no study drug-related deaths during the treatment period.

INTERPRETATION

First-line 177Lu-Dotatate plus octreotide LAR significantly extended median progression-free survival (by 14 months) in patients with grade 2 or 3 advanced gastroenteropancreatic neuroendocrine tumours. 177Lu-Dotatate should be considered a new standard of care in first-line therapy in this population.

FUNDING

Advanced Accelerator Applications, a Novartis Company.

Connexin 36 Mediated Intercellular Endoplasmic Reticulum Stress Transmission Induces SSTA Resistance in Growth Hormone Pituitary Adenoma

Somatostatin analogues (SSTA) are first-line pharmacological treatment choice for acromegaly, which received satisfying tumor shrinkage and normalization of growth hormone. However, there are still patients unresponsive to SSTA, and the underline mechanism remains unknown. Besides, there is no evidence regarding the role of endoplasmic reticulum stress (ERS) and its transmission in SSTA resistance, which also require investigation. Primary growth hormone adenoma cells and cell lines were treated with SSTA; autophagy double-labeled LC3 (mRFP-GFP) adenovirus transfection, flow cytometry sorting, western blotting, calcium imaging as well as immunofluorescence staining were used to determine ERS and autophagy signal transmission; xenograft and syngeneic tumor in vivo model were exploited to confirm the ERS signal transmission mediated effect. Our results revealed that SSTA induces ERS in pituitary growth hormone (GH) adenoma cells. The ERS signals can be intercellularly transmitted, leading to less responsible to SSTA treatment. Moreover, SSTA stimulates inositol triphosphate (IP3) elevation, mediating ERS intercellular transfer. In addition, connexin 36 tunnels ERS transmission, and its blocker, Quinine, exhibits a synergistic effect with SSTA treating GH adenoma. Our study provided insight into ERS intercellular transmission mediated SSTA resistance, which could be translated into clinical usage to improve SSTA efficiency in GH adenoma treatment.

Definitive Treatment of Brain Metastases From a Neuroendocrine Tumor With Peptide Receptor Radionuclide Therapy With 177Lutetium DOTATATE: A Case Report

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) are rare malignancies that arise from secretory endocrine cells of the gastroenteropancreatic system. Clinical outcomes have improved for patients with GEP-NETs due to the development and recent FDA approval of 177Lutetium DOTATATE. However, the response of brain metastases from GEP-NETs from 177Lutetium DOTATATE is unreported. We present the case of an 81-year-old man with low-grade small bowel GEP-NET with liver and brain metastases treated with a total of six cycles of 177Lutetium DOTATATE. With over three years of follow-up from his initial treatment, his brain metastases have had complete or partial responses, with no need for brain radiotherapy or radiosurgery.

Late Pseudoprogression: A Potential Pitfall in 68Ga-DOTATATE PET/CT for Glioma

ABSTRACT

Recognition of pseudoprogression in malignant glioma is one of the major challenges in the Response Assessment in Neuro-Oncology criteria. Somatostatin receptors were overexpressed on the surface of the most high-grade glioma. The corresponding PET imaging is used for planning radiation and radionuclide therapy. However, the heterogeneity of somatostatin receptors distribution is mainly responsible for the lack of specificity. Here we reported a case of a 35-year-old man with mesenchymal oligodendroglioma operation and radiotherapy 19 months ago. 68 Ga-DOTATATE PET showed intense uptake near the operation region, which has been misinterpreted as tumor recurrence.

Addressing the need for more therapeutic options in neuroendocrine prostate cancer

INTRODUCTION

Neuroendocrine prostate cancer (NEPC) is an aggressive form of prostate cancer frequently seen after prolonged treatment of castration resistant prostate cancer (CRPC). NEPC has become increasingly prevalent over the last 20 years, with a poor prognosis caused by a late diagnosis and limited treatment options. Recent advances in PET/CT imaging and targeted radioimmunotherapy are promising, but more research into additional treatment options is needed.

AREAS COVERED

The aim of this review is to analyze the current imaging and treatment options for NEPC, and to highlight future potential treatment strategies. A Pubmed search for 'Neuroendocrine Prostate Cancer' was performed and relevant articles were reviewed.

EXPERT OPINION

The recent FDA approval and success of 177 PSMA Lutetium in CRPC is promising, as 177 Lutetium could potentially be paired with a NEPC specific biomarker for targeted therapy. Recent laboratory studies pairing DLL3, which is overexpressed in NEPC, with 177 Lutetium and new PET agents have showed good efficacy in identifying and treating NEPC. The success of future development of NEPC therapies may depend on the availability of 177 Lutetium, as current supplies are limited. Further research into additional imaging and treatment options for NEPC is warranted.

Immunohistochemical assessment and clinical, histopathologic, and molecular correlates of membranous somatostatin type-2A receptor expression in high-risk pediatric central nervous system tumors

INTRODUCTION

177Lu-DOTATATE, a radionuclide therapy that binds somatostatin type-2A receptors (SST2A), has demonstrated efficacy in neuroendocrine tumors and evidence of central nervous system (CNS) penetration, supporting potential expansion within pediatric neuro-oncology. Understanding the prevalence of SST2A expression across pediatric CNS tumors is essential to identify patients who may benefit from somatostatin receptor-targeted therapy and to further elucidate the oncogenic role of SST2A.

METHODS

SST2A immunohistochemistry (IHC) was performed on tumor specimens and interpreted by an experienced pathologist (blinded), utilizing semi-quantitative scoring of membranous expression within viable tumor. Immunoreactive cell percentage was visually scored as 0 (none), 1 (<10%), 2 (10-50%), 3 (51-80%), or 4 (>80%). Staining intensity was scored as 0 (none), 1 (weak), 2 (moderate), or 3 (strong). Combined scores for each specimen were calculated by multiplying percent immunoreactivity and staining intensity values (Range: 0-12).

RESULTS

A total of 120 tumor samples from 114 patients were analyzed. Significant differences in SST2A IHC scores were observed across histopathologic diagnoses, with consistently high scores in medulloblastoma (mean ± SD: 7.5 ± 3.6 [n=38]) and meningioma (5.7 ± 3.4 [n=15]), compared to minimal or absent expression in ATRT (0.3 ± 0.6 [n=3]), ETMR (1.0 ± 0 [n=3]), ependymoma (grades I-III; 0.2 ± 0.7 [n=27]), and high-grade glioma (grades III-IV; 0.4 ± 0.7 [n=23]). Pineoblastoma (3.8 ± 1.5 [n=4]) and other embryonal tumors (2.0 ± 4.0 [n=7]) exhibited intermediate, variable expression. Among medulloblastomas, SST2A IHC scores were higher in non-SHH (8.5 ± 3.1) than SHH (5.0 ± 3.3) molecular subgroups (p=0.033). In a subset of paired primary and recurrent specimens from four patients, SST2A IHC scores remained largely unchanged.

DISCUSSION

High membranous SST2A expression was demonstrated in medulloblastoma, meningioma, and some rarer embryonal tumors with potential diagnostic, biologic, and therapeutic implications. Somatostatin receptor-targeted therapy such as 177Lu-DOTATATE deserves further investigation in these highly SST2A-expressing pediatric CNS tumors.

Recent advances in diagnosis and treatment of gastroenteropancreatic neuroendocrine neoplasms

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) are a rare group of tumors originating from neuroendocrine cells of the digestive system. Their incidence has increased over the last decades. The specific pathogenetic mechanisms underlying GEP-NEN development have not been completely revealed. Unfunctional GEP-NENs are usually asymptomatic; some grow slowly and thus impede early diagnosis, which ultimately results in a high rate of misdiagnosis. Therefore, many GEP-NEN patients present with later staged tumors. Motivated hereby, research attention for diagnosis and treatment for GEP-NENs increased in recent years. The result of which is great progress in clinical diagnosis and treatment. According to the most recent clinical guidelines, improved grading standards can accurately define poorly differentiated grade 3 neuroendocrine tumors and neuroendocrine carcinomas (NECs), which are subclassified into large and small cell NECs. Combining different functional imaging methods facilitates precise diagnosis. The expression of somatostatin receptors helps to predict prognosis. Genetic analyses of mutations affecting death domain associated protein (DAXX), multiple endocrine neoplasia type 1 (MEN 1), alpha thalassemia/intellectual disability syndrome X-linked (ATRX), retinoblastoma transcriptional corepressor 1 (RB 1), and mothers against decapentaplegic homolog 4 (SMAD 4) help distinguishing grade 3 NENs from poorly differentiated NECs. The aim of this review is to summarize the latest research progress on diagnosis and treatment of GEP-NENs.

Role of filamin A in the pathogenesis of neuroendocrine tumors and adrenal cancer

Cell cytoskeleton proteins are involved in tumor pathogenesis, progression and pharmacological resistance. Filamin A (FLNA) is a large actin-binding protein with both structural and scaffold functions implicated in a variety of cellular processes, including migration, cell adhesion, differentiation, proliferation and transcription. The role of FLNA in cancers has been studied in multiple types of tumors. FLNA plays a dual role in tumors, depending on its subcellular localization, post-translational modification (as phosphorylation at Ser2125) and interaction with binding partners. This review summarizes the experimental evidence showing the critical involvement of FLNA in the complex biology of endocrine tumors. Particularly, the role of FLNA in regulating expression and signaling of the main pharmacological targets in pituitary neuroendocrine tumors, pancreatic neuroendocrine tumors, pulmonary neuroendocrine tumors and adrenocortical carcinomas, with implications on responsiveness to currently used drugs in the treatment of these tumors, will be discussed.

Epigenetic and post-transcriptional regulation of somatostatin receptor subtype 5 (SST5 ) in pituitary and pancreatic neuroendocrine tumors

Somatostatin receptor subtype 5 (SST₅) is an emerging biomarker and actionable target in pituitary (PitNETs) and pancreatic (PanNETs) neuroendocrine tumors. Transcriptional and epigenetic regulation of SSTR5 gene expression and mRNA biogenesis is poorly understood. Recently, an overlapping natural antisense transcript, SSTR5‐AS1, potentially regulating SSTR5 expression, was identified. We aimed to elucidate whether epigenetic processes contribute to the regulation of SSTR5 expression in PitNETs (somatotropinomas) and PanNETs. We analyzed the SSTR5/SSTR5‐AS1 human locus in silico to identify CpG islands. SSTR5 and SSTR5‐AS1 expression was assessed by quantitative real‐time PCR (qPCR) in 27 somatotropinomas, 11 normal pituitaries (NPs), and 15 PanNETs/paired adjacent (control) samples. We evaluated methylation grade in four CpG islands in the SSTR5/SSTR5‐AS1 genes. Results revealed that SSTR5 and SSTR5‐AS1 were directly correlated in NP, somatotropinoma, and PanNET samples. Interestingly, selected CpG islands were differentially methylated in somatotropinomas compared with NPs. In PanNETs cell lines, SSTR5‐AS1 silencing downregulated SSTR5 expression, altered aggressiveness features, and influenced pasireotide response. These results provide evidence that SSTR5 expression in PitNETs and PanNETs can be epigenetically regulated by the SSTR5‐AS1 antisense transcript and, indirectly, by DNA methylation, which may thereby impact tumor behavior and treatment response.

Current treatments and future potential of surufatinib in neuroendocrine tumors (NETs)

Neuroendocrine tumors (NETs) are rare, heterogeneous, often indolent tumors that predominantly originate in the lungs and gastrointestinal tract. An understanding of the biology and tumor microenvironment of NETs has led to the development of molecularly targeted treatment options including somatostatin analogs, tyrosine kinase inhibitors, mammalian target of rapamycin inhibitors and peptide receptor radionuclide therapy. Although increases in progression-free survival have been demonstrated, most currently approved NET therapies are limited by the development of tumor resistance. Surufatinib (HMPL-012, previously known as sulfatinib) is a new, oral, small-molecule tyrosine kinase inhibitor that potently inhibits vascular endothelial growth-factor receptor 1-3, fibroblast growth-factor receptor 1, and colony-stimulating-factor-1 receptor. This unique combination of molecular activities inhibits tumor angiogenesis, regulates tumor-immune evasion, and may decrease tumor resistance. Surufatinib demonstrated statistically significant, clinically meaningful antitumor activity, including tumor shrinkage, in two phase III studies recently completed in China in advanced pancreatic NETs and advanced extrapancreatic NETs. The safety profile of surufatinib in neuroendocrine tumors studies was consistent with previous surufatinib clinical studies. In an ongoing study in United States (US) patients with NETs of pancreatic origin and NETs of extrapancreatic origin previously treated with everolimus or sunitinib, surufatinib has also demonstrated promising efficacy. Furthermore, the pharmacokinetic and safety profile of surufatinib in US patients is similar to data collected in studies done in China. These positive phase III results support the efficacy of surufatinib in patients with advanced, progressive, well-differentiated NETs regardless of tumor origin.

Advancements in folate receptor targeting for anti-cancer therapy: A small molecule-drug conjugate approach

Targeted delivery combined with controlled release of drugs has a crucial role in future of personalized medicine. The majority of cancer drugs are intended to interfere with one or more cellular events. Anticancer agents can also be toxic to healthy cells, as healthy cells may also need to proliferate and avoid apoptosis. The focus of this review covers the principles, advantages, drawbacks and summarize criteria that must be met for design of small molecule-drug conjugates (SMDCs) to achieve the desired therapeutic potency with minimal toxicity. SMDCs are composed of a targeting ligand, a releasable bridge, a spacer, and a therapeutic payload. We summarize the criteria for the effective design that influences the selection of tumor specific receptor and optimum elements in the design of SMDCs. We also discuss the criteria for selecting the optimal therapeutic drug payload, spacer and linker. The linker chemistries and cleavage strategies are also discussed. Finally, we review the folate receptor targeting SMDCs that are in preclinical development and in clinical trials.

A Cyanine-Bridged Somatostatin Hybrid Probe for Multimodal SSTR2 Imaging in Vitro and in Vivo: Synthesis and Evaluation

Multimodal imaging probes have attracted the interest of ongoing research, for example, for the surgical removal of tumors. Modular synthesis approaches allow the construction of hybrid probes consisting of a radiotracer, a fluorophore and a targeting unit. We present the synthesis of a new asymmetric bifunctional cyanine dye that can be used as a structural and functional linker for the construction of such hybrid probes. 68 Ga-DOTATATE, a well-characterized radiopeptide targeting the overexpressed somatostatin receptor subtype 2 (SSTR2) in neuroendocrine tumors, was labeled with our cyanine dye, thus providing additional information along with the data obtained from the radiotracer. We tested the SSTR2-targeting and imaging properties of the resulting probe 68 Ga-DOTA-ICC-TATE in vitro and in a tumor xenograft mouse model. Despite the close proximity between dye and pharmacophore, we observed a high binding affinity towards SSTR2 as well as elevated uptake in SSTR2-overexpressing tumors in the positron emission tomography (PET) scan and histological examination.

The PDZ Domain Protein SYNJ2BP Regulates GRK-Dependent Sst2A Phosphorylation and Downstream MAPK Signaling

The somatostatin receptor 2A (SST2) is a G-protein-coupled receptor (GPCR) that is expressed in neuroendocrine tissues within the gastrointestinal tract and brain, and is commonly overexpressed in many neuroendocrine tumors. Moreover, SST2 agonists are used clinically as the primary pharmacological treatment to suppress excess hormone secretion in a variety of neuroendocrine tumors. Despite its wide clinical use, mechanisms controlling the trafficking and signaling of SST2 are not fully understood. SST2 contains a C-terminal post-synaptic density 95, Drosophila discs large, zona-occludens 1 (PDZ) domain-binding motif that has been shown to interact with 3 different PDZ domain-containing proteins. However, the consequences of these interactions are not well understood, nor is it known whether additional PDZ domain proteins interact with SST2. Through unbiased screening we have identified 10 additional PDZ domain proteins that interact with SST2. We chose one of these, SYNJ2BP, for further study. We observed that SYNJ2BP interacted with SST2 in an agonist-dependent manner, and that this required the PDZ binding site of SST2. Importantly, overexpression of SYNJ2BP enhanced ligand-stimulated receptor internalization. Mechanistically, SYNJ2BP interacted with G-protein-coupled receptor kinase 2 (GRK2) and promoted GRK-dependent phosphorylation of the receptor after somatostatin stimulation. Interaction with GRK2 required the C-terminus of SYNJ2BP. Binding to SYNJ2BP did not affect the ability of SST2 to suppress 3',5'-cyclic adenosine 5'-monophosphate production, but was required for optimal agonist-stimulated extracellularly regulated kinase 1/2 activation. These data indicated that SYNJ2BP is an SST2-interacting protein that modulates agonist-stimulated receptor regulation and downstream signaling.

AGTR1 Is Overexpressed in Neuroendocrine Neoplasms, Regulates Secretion and May Potentially Serve as a Target for Molecular Imaging and Therapy

Simple Summary

Clinical management of neuroendocrine neoplasms (NEN), especially of those low in target molecules such as somatostatin receptors, may benefit from the discovery of novel targets. This study identified and confirmed angiotensin II (ATII) as a strong activator of signaling in NEN cells and its cognate receptor AGTR1 as overexpressed in human small intestinal NEN. NEN cells with high AGTR1 expression exhibited cellular activation and secretion upon stimulation with ATII. AGTR1 ligand saralasin coupled to a fluorescent dye demonstrated tumor accumulation in an animal model of NEN. This proof of concept establishes AGTR1 as a novel target in NEN, paving the way for its potential use in diagnostic PET imaging and radioligand therapy.

Abstract

This study identified and confirmed angiotensin II (ATII) as a strong activator of signaling in neuroendocrine neoplasm (NEN) cells. Expression analyses of the ATII receptor type 1 (AGTR1) revealed an upregulation of mRNA levels (RT-qPCR) and radioligand binding (autoradiography) in small-intestinal (n = 71) NEN tissues compared to controls (n = 25). NEN cells with high AGTR1 expression exhibited concentration-dependent calcium mobilization and chromogranin A secretion upon stimulation with ATII, blocked by AGTR1 antagonism and Gαq inhibition. ATII also stimulated serotonin secretion from BON cells. AGTR1 ligand saralasin was coupled to a near-infrared fluorescent (NIRF) dye and tested for its biodistribution in a nude mouse model bearing AGTR1-positive BON and negative QGP-1 xenograft tumors. NIRF imaging showed significantly higher uptake in BON tumors. This proof of concept establishes AGTR1 as a novel target in NEN, paving the way for translational chelator-based probes for diagnostic PET imaging and radioligand therapy.

Characterization of agonist-dependent somatostatin receptor subtype 2 trafficking in neuroendocrine cells

BACKGROUND

Somatostatin (SOM) receptor subtype 2 (SSTR2) is the major receptor subtype mediating SOM effects throughout the neuraxis. We previously demonstrated that the non-selective agonist [D-Trp⁸]-SOM induces intracellular sequestration of SSTR2, whereas this receptor is maintained at the cell surface after treatment with the SSTR2-selective agonist L-779,976 in cells co-expressing SSTR2 and SSTR5.

METHODS AND RESULTS

In this study, we knocked-out SSTR5 in AtT20 cells endogenously expressing both SSTR2 and SSTR5 and used immuno-labeling and confocal microscopy to investigate the effect of SSTR5 on regulation of SSTR2 trafficking. Our results indicate that unlike [D-Trp⁸]-SOM-induced intracellular sequestration, L-779,976 stimulation results in the maintenance of SSTR2 at the cell surface regardless of whether SSTR5 is present or not. We then examined the trafficking pathways of SSTR2 upon stimulation by either agonist. We found that both [D-Trp⁸]-SOM and L-779,976 induce SSTR2 internalization via transferrin-positive vesicles. However, SSTR2 internalized upon L-779,976 treatment undergoes rapid recycling to the plasma membrane, whereas receptors internalized by [D-Trp⁸]-SOM recycle slowly after washout of the agonist. Furthermore, [D-Trp⁸]-SOM stimulation induces degradation of a fraction of internalized SSTR2 whereas L-779,976-dependent, rapid SSTR2 recycling appears to protect internalized SSTR2 from degradation. In addition, Octreotide which has preferential SSTR2 affinity, induced differential effects on both SSTR2 trafficking and degradation.

CONCLUSION

Our results indicate that the biased agonistic property of L-779,976 protects against SSTR2 surface depletion by rapidly initiating SSTR2 recycling while SSTR5 does not regulate L-779-976-dependent SSTR2 trafficking.

Treatment Outcomes in Patients with Metastatic Neuroendocrine Tumors: a Retrospective Analysis of a Community Oncology Database

Purpose

Metastatic neuroendocrine tumors (mNETs) are rare, heterogeneous tumors that present diagnostic and treatment challenges, with limited data on the management of mNETs in clinical practice. The present study was designed to identify current diagnostic and treatment patterns in mNET patients treated in the US community oncology setting.

Methods

Patient-level data was collected from medical records of adults with mNETs from the Vector Oncology Data Warehouse, a comprehensive US community oncology network database.

Results

Of the 263 patients included (median follow-up, 22 months; range, 0.1–193.9), 30.4% (80/263) had intestinal tumors, 11.0% (29/263) had pancreatic, and 58.6% (154/263) had tumors of other or unknown location. Progression-free survival (PFS) from the start of first-line therapy differed significantly by tumor grade (log rank P = 0.0016) and location (P = 0.0044), as did overall survival (OS) (grade, P < 0.0001; location, P = 0.0068). Median PFS and OS for patients with undocumented tumor grade were shorter than for patients with G1/G2 tumors and longer than patients with G3 tumors. Median PFS and OS for patients with other or unknown tumors were shorter than for patients with intestinal tumors.

Conclusions

While potentially confounded by the high number of patients with other or unknown tumor locations, this retrospective study of patients in a US community oncology setting identified the importance of awareness of tumor grade and tumor location at diagnosis, as these were direct correlates of PFS and OS.

Paracrine signaling in islet function and survival

The pancreatic islet is a dense cellular network comprised of several cell types with endocrine function vital in the control of glucose homeostasis, metabolism, and feeding behavior. Within the islet, endocrine hormones also form an intricate paracrine network with supportive cells (endothelial, neuronal, immune) and secondary signaling molecules regulating cellular function and survival. Modulation of these signals has potential consequences for diabetes development, progression, and therapeutic intervention. Beta cell loss, reduced endogenous insulin secretion, and dysregulated glucagon secretion are hallmark features of both type 1 and 2 diabetes that not only impact systemic regulation of glucose, but also contribute to the function and survival of cells within the islet. Advancing research and technology have revealed new islet biology (cellular identity and transcriptomes) and identified previously unrecognized paracrine signals and mechanisms (somatostatin and ghrelin paracrine actions), while shifting prior views of intraislet communication. This review will summarize the paracrine signals regulating islet endocrine function and survival, the disruption and dysfunction that occur in diabetes, and potential therapeutic targets to preserve beta cell mass and function.

Management of Diarrhea in Patients With Carcinoid Syndrome

Neuroendocrine tumors (NETs) arise from enterochromaffin cells found in neuroendocrine tissues, with most occurring in the gastrointestinal tract. The global incidence of NETs has increased in the past 15 years, likely due to better diagnostic methods. Small-bowel NETs are frequently associated with carcinoid syndrome (CS). Carcinoid syndrome diarrhea occurs in 80% of CS patients and poses a substantial symptomatic and economic burden. Patients with CS diarrhea frequently suffer from diarrhea and flushing and report corresponding impairment in quality of life, requiring substantial changes in daily activities and lifestyle. Treatment paradigms range from surgical debulking to liver-directed therapies to treatment with somatostatin analogs, nonspecific anti-diarrheal agents, and a tryptophan hydroxylase inhibitor. Other causes of diarrhea, including steatorrhea, short bowel syndrome, and bile acid malabsorption, should be considered in NET patients with refractory diarrhea. More therapeutic options are needed for symptomatic management of patients with NETs, and better understanding of the pathophysiology can empower clinicians with improved patient care.

Biological and Biochemical Basis of the Differential Efficacy of First and Second Generation Somatostatin Receptor Ligands in Neuroendocrine Neoplasms

Endogenous somatostatin shows anti-secretory effects in both physiological and pathological settings, as well as inhibitory activity on cell growth. Since somatostatin is not suitable for clinical practice, researchers developed synthetic somatostatin receptor ligands (SRLs) to overcome this limitation. Currently, SRLs represent pivotal tools in the treatment algorithm of neuroendocrine tumors (NETs). Octreotide and lanreotide are the first-generation SRLs developed and show a preferential binding affinity to somatostatin receptor (SST) subtype 2, while pasireotide, which is a second-generation SRL, has high affinity for multiple SSTs (SST₅ > SST₂ > SST₃ > SST₁). A number of studies demonstrated that first-generation and second-generation SRLs show distinct functional properties, besides the mere receptor affinity. Therefore, the aim of the present review is to critically review the current evidence on the biological effects of SRLs in pituitary adenomas and neuroendocrine tumors, by mainly focusing on the differences between first-generation and second-generation ligands.

Systemic treatment for lung carcinoids: from bench to bedside

In the huge spectrum of lung neuroendocrine neoplasms, typical and atypical carcinoids should be considered as a separate biological entity from poorly differentiated forms, harboring peculiar molecular alterations. Despite their indolent behavior, lung carcinoids correlate with a worse survival. To date, only limited therapeutic options are available and novel drugs are strongly needed. In this work, we extensively reviewed scientific literature exploring available therapeutic options, new molecular targets and future perspectives in the management of well differentiated neoplasms of bronchopulmonary tree. Systemic therapy represents the main option in advanced and unresectable disease; accepted choices are somatostatin analogs, peptide receptor radionuclide therapy, everolimus and chemotherapy. To date, an univocal treatment strategy has not been identified yet, thus tailored therapeutic algorithms should consider treatment efficacy as well as safety profiles. Several molecular alterations found in carcinoid tumors might act as molecular targets leading to development of new therapeutic options. Further studies are necessary to identify new potential “druggable” molecular targets in the selected subset of low-grade lung carcinoids. Furthermore, evaluating the available therapies in more homogeneous population might improve their efficacy through a perfect tailoring of treatment options.

Interaction between somatostatin analogues and targeted therapies in neuroendocrine tumor cells

Somatostatin analogues (SSA) represent the standard of care for symptom control in patients with functional gastro-entero-pancreatic neuroendocrine tumors (GEP-NET). In addition, SSA exert significant anti-proliferative effects in mid-gut and pancreatic NET (PanNET). In parallel, molecularly targeted therapies (MTT) have been shown to improve progression free survival (PFS) in patients with PanNET. However, due to either primary or acquired resistance to MTT, their impact on overall survival (OS) remains unclear. To date, various hypotheses exist to explain differences in patient responsiveness to SSA and MTT. However, data addressing one of the most pivotal questions, whether combining SSA with novel MTT will result in synergistic or additive efficacy compared to monotherapy, are lacking. The aim of this study is to characterize the interaction, optimal sequence and dosing of SSA-based and molecularly targeted therapies in PanNET. Somatostatin receptor subtypes 1–5 (SSTR) were evaluated in the neuroendocrine cell lines Bon1, QGP1 and Ins-1 via immunoblot and qRT-PCR. The impact of the SSA-analogue lanreotide alone or in combination with the MTT sunitinib, everolimus and regorafenib on intracellular signalling, hormone secretion and cell proliferation was determined in cell lysates and supernatants. In addition, synergistic effects of SSA and MTT in various sequential therapeutic approaches were investigated. SSTR were differently expressed in the examined neuroendocrine tumor cell lines. SSTR modulation via lanreotide moderately influenced proliferation, mainly via modulating AKT and ERK signalling, which was paralleled by decreased chromogranin A (CgA) expression and secretion. Interestingly, MTT treatment with regorafenib upregulated the expression of SSTR-2 and -5, while sunitinib and everolimus did not significantly alter SSTR expression. Cell viability was significantly reduced by all MTT, with regorafenib exerting the most significant effects. However, compared to the marked effects of MTT alone, synergistic effects of combined MTT and lanreotide treatment were only modest and time- and dose-dependent. SSTR are differentially expressed in various NEN cell lines. Their expression is influenced by MTT treatment. Various sequential or simultaneous combinations of lanreotide and MTT did not lead to significant synergistic effects.

Somatostatin Receptor Expression Is Associated With Metastasis and Patient Outcome in Pulmonary Carcinoid Tumors

CONTEXT

Pulmonary carcinoids (PCs) belong to neuroendocrine tumors that often overexpress somatostatin receptors (SSTRs). This overexpression provides a molecular basis for tumor imaging and treatment with somatostatin analogs.

OBJECTIVE

To evaluate SSTR1 to SSTR5 distribution in a large set of PC tumors and to investigate whether the expression is associated with clinicopathological and outcome data.

DESIGN, SETTING, AND PATIENTS

This retrospective study was conducted at Helsinki University Hospital and University of Helsinki. It included 178 PC tumors coupled with patients' clinical data retrieved through Finnish biobanks. After histological reclassification, tissue specimens were processed into next-generation tissue microarray format and stained immunohistochemically with monoclonal SSTR1 to SSTR5 antibodies.

MAIN OUTCOME MEASURE

SSTR1 to SSTR5 expression in PC tumors.

RESULTS

Expression of SSTR1 to SSTR5 was detected in 52%, 75%, 56%, 16%, and 32% of the tumors, respectively. Membrane-bound staining was observed for all receptors. SSTR2 negativity and SSTR4 positivity was associated with lymph node involvement at the time of surgery (P = 0.014 and P = 0.017, respectively) and with distant metastasis (P = 0.027 and P = 0.015, respectively). SSTR3 and SSTR4 expression was associated with increased risk of shorter survival [P = 0.046, hazard ratio (HR) 4.703, 95% CI 1.027 to 21.533; and P = 0.013, HR 6.64, 95% CI 1.48 to 29.64, respectively], whereas expression of SSTR1 and SSTR2 was associated with improved outcome (P = 0.021, HR 0.167, 95% CI 0.037 to 0.765; and P = 0.022, HR 0.08, 95% CI 0.01 to 0.70, respectively).

CONCLUSION

SSTR1 to SSTR5 expression is observed in PCs. As SSTR expression is associated with the tumor's metastatic potential and patient outcome, these receptors may offer the possibility for individualized prognosis estimation.

Molecular determinants of the response to medical treatment of growth hormone secreting pituitary neuroendocrine tumors

Acromegaly is a chronic systemic disease mainly caused by a growth hormone (GH)-secreting pituitary neuroendocrine tumor (PitNETs), which is associated with many health complications and increased mortality when not adequately treated. Transsphenoidal surgery is considered the treatment of choice in GH-secreting PitNETs, but patients in whom surgery cannot be considered or with persistent disease after surgery require medical therapy. Treatment with available synthetic somatostatin analogues (SSAs) is considered the mainstay in the medical management of acromegaly which exert their beneficial effects through the binding to a family of G-protein coupled receptors encoded by 5 genes (SSTR1-5). However, although it has been demonstrated that the SST1-5 receptors are physically present in tumor cells, SSAs are in many cases ineffective (i.e. approximately 10-30% of patients with GH-secreting PitNET are unresponsive to SSAs), suggesting that other cellular/molecular determinants could be essential for the response to the pharmacological treatment in patients with GH-secreting PitNETs. Therefore, the scrutiny of these determinants might be used for the identification of subgroups of patients in whom an appropriate pharmacological treatment can be successfully employed (responders vs. non-responders). In this review, we will describe some of the existing, classical and novel, genetic and molecular determinants involved in the response of patients with GH-secreting PitNETs to the available therapeutic treatments, as well as new molecular/therapeutic approaches that could be potentially useful for the treatment of GH-secreting PitNETs.

Regulation of Somatostatin Receptor 2 Trafficking by C-Tail Motifs and the Retromer

The Gi-coupled somatostatin receptor 2 (SST2) is a G protein-coupled receptor (GPCR) that mediates many of somatostatin's neuroendocrine actions. Upon stimulation, SST2 is rapidly internalized and transported to early endosomes before being recycled to the plasma membrane. However, little is known about the intracellular itinerary of SST2 after it moves to the early endosomal compartment or the cytoplasmic proteins that regulate its trafficking. As postsynaptic density protein/discs large 1/zonula occludens-1 (PDZ) domain interactions often regulate the trafficking and signaling potential of GPCRs, we examined the role of the SST2 PDZ ligand and additional C-terminal residues in controlling its intracellular trafficking. We determined that SST2 can recycle to the plasma membrane via multiple pathways, including a LAMP1/Rab7-positive late endosome to the trans-Golgi network (TGN) pathway. Trafficking from the late endosome to the TGN is often regulated by the retromer complex of endosomal coat proteins, and disrupting the retromer components sorting nexins 1/2 inhibits the budding of SST2 from late endosomes. Moreover, trafficking through the late endosomal/TGN pathway is dependent on an intact PDZ ligand and C-terminal tail, as truncating either the 3 or 10 C-terminal amino acids of SST2 alters the pathway through which it recycles to the plasma membrane. Moreover, addition of these amino acids to a heterologous receptor is sufficient to redirect it from a degradation pathway to a recycling itinerary. Our results demonstrate that endosomal trafficking of SST2 is dependent on numerous regulatory mechanisms controlled by its C terminus and the retromer machinery.

Effects of somatostatin analog treatment on cardiovascular parameters in patients with acromegaly: A systematic review

Background:

There is a belief that in patients with acromegaly, first-generation somatostatin analogs (SSAs) might improve cardiovascular (CV) structure and function. However, most published clinical trials involved only a few patients and their results are rather variable. We aimed to conduct a systematic review on available studies on the impact of these drugs on CV parameters.

Materials and Methods:

A literature search was conducted in MEDLINE (OVID), EMBase, Cochrane, and ISI Web of Science for citations published until April 30 2018 to identify studies on our objective that considered changes in CV parameters. For this search, we established a Boolean search strategy using keywords related to “acromegaly,” “Somatostatin analog,” and “cardiovascular diseases and parameters.” All study types except for case reports or conference abstracts were included. Twenty-four studies (n = 558) fulfilled the inclusion criteria and were selected for final analysis.

Results:

In 12 studies (n = 350), decrease in heart rate (HR) and in 4 studies (n = 128), decrease in blood pressure (BP) was significant. In 15 studies (n = 320), left ventricular mass index (LVMi) changes were significant. In 9 studies (n = 202), the early diastole to peak velocity flow in late diastole (E/A ratio) was evaluated, and in 5 of them (n = 141), the improvement was significant. Eighteen studies (n = 366) examined changes in left ventricular ejection fraction (LVEF), 5 of which (n = 171) reported that these changes were significant. Decrease of left ventricular end-diastolic diameter was reported in only 2 studies (n = 27).

Conclusion:

We found that first-generation SSAs have a beneficial effect on cardiac parameters such as HR and LVMi. For other parameters such as LVEF, BP, LV diameter, and E/A ratio, we were not able to draw a firm conclusion.

Specific Targeting of Somatostatin Receptor Subtype-2 for Fluorescence-Guided Surgery

PURPOSE

Clinically available intraoperative imaging tools to assist surgeons in identifying occult lesions are limited and partially responsible for the high rate of disease recurrence in patients with neuroendocrine tumors (NET). Using the established clinical efficacy of radiolabeled somatostatin analogs as a model, we demonstrate the ability of a fluorescent somatostatin analog to selectively target tumors that overexpress somatostatin receptor subtype-2 (SSTR2) and demonstrate utility for fluorescence-guided surgery (FGS).

EXPERIMENTAL DESIGN

A multimodality chelator (MMC) was used as a "radioactive linker" to synthesize the fluorescently labeled somatostatin analog, ^67/68Ga-MMC(IR800)-TOC. In vivo studies were performed to determine the pharmacokinetic profile, optimal imaging time point, and specificity for SSTR2-expressing tissues. Meso- and microscopic imaging of resected tissues and frozen sections were also performed to further assess specific binding, and binding to human NETs was examined using surgical biospecimens from patients with pancreatic NETs.

RESULTS

Direct labeling with ⁶⁷Ga/⁶⁸Ga provided quantitative biodistribution analysis that was in agreement with fluorescence data. Receptor-mediated uptake was observed in vivo and ex vivo at the macro-, meso-, and microscopic scales. Surgical biospecimens from patients with pancreatic NETs also displayed receptor-specific agent binding, allowing clear delineation of tumor boundaries that matched pathology findings.

CONCLUSIONS

The radioactive utility of the MMC allowed us to validate the binding properties of a novel FGS agent that could have a broad impact on cancer outcomes by equipping surgeons with real-time intraoperative imaging capabilities.

Evaluation of preclinical efficacy of everolimus and pasireotide in thyroid cancer cell lines and xenograft models

BACKGROUND

Signaling through mTOR and somatostatin pathway is implicated in thyroid cancer development.

METHOD

We evaluated everolimus, an mTOR inhibitor and pasireotide, a multi receptor somatostatin analogue as potential therapy of thyroid cancer focusing on the in vitro and in vivo efficacy, as well as possible mechanism to explain any observed interaction.

RESULTS

Both everolimus and pasireotide inhibit the growth of thyroid cancer cell lines in vitro with varied efficacy that correlates with tumor origin and somatostatin receptor (SSTR) expression profile of the cell lines. In vitro activity of everolimus show positive correlation with the expression of SSTR types 1, 4 and 5 (CC: 0.9; 0.85, 0.87) while pasireotide activity show negative correlation with SSTR2 (CC: -0.87). Although there is greater modulation of pS6 when pasireotide is combined with everolimus, there is no significant abrogation of the expected feedback upregulation of AKT induced by everolimus. Also, the combination is not significantly better than each agent alone in short and long term in vitro assays. Continuous administration of everolimus at a low dose as opposed to high intermittent dosing schedule has greater antitumor efficacy against thyroid cancer xenografts in vivo. Pasireotide LAR has modest in vivo efficacy and the combination of everolimus and pasireotide LAR achieve greater tumor growth inhibition than each agent alone in TPC-1 xenograft model of thyroid cancer (p = 0.048).

CONCLUSION

Our findings provide support for the clinical evaluation of everolimus and pasireotide in thyroid cancer and other neuroendocrine tumors.

Subclinical Lipopolysaccharide from Salmonella Enteritidis Induces Dysregulation of Bioactive Substances from Selected Brain Sections and Glands of Neuroendocrine Axes

Bacterial lipopolysaccharide (LPS) can contribute to the pathogenesis and the clinical symptoms of many diseases such as cancer, mental disorders, neurodegenerative as well as metabolic diseases. The asymptomatic carrier state of Salmonella spp. is a very important public health problem. A subclinical single dose of LPS obtained from S. Enteritidis (5 μg/kg, i.v.) was administered to discern the consequences of changes of various brain peptides such as corticotropin-releasing hormone (CRH), gonadotropin-releasing hormone (GnRH), thyrotropin-releasing hormone (TRH), galanin (GAL), neuropeptide Y (NPY), somatostatin (SOM), substance P (SP), and vasoactive intestinal polypeptide (VIP) in selected clinically important brain sections and endocrine glands of the hypothalamic-pituitary-adrenal (HPA), -thyroid (HPT), -ovarian (HPO) axes. The study was conducted on ten immature crossbred female pigs. The brain peptides were extracted from the hypothalamus (medial basal hypothalamus, preoptic area, lateral hypothalamic area, mammillary bodies, and the stalk median eminence), and pituitary gland (adenohypophysis and neurohypophysis) sections and from the ovaries and adrenal and thyroid glands. There was no difference in health status between LPS and the control groups during the period of the experiment. Nevertheless, even a low single dose of LPS from S. Enteritidis that did not result in any clinical symptoms of disease induced dysregulation of various brain peptides, such as CRH, GnRH, TRH, GAL, NPY, SOM, SP, and VIP in selected brain sections of hypothalamus, pituitary gland and in the endocrine glands of the HPA, HPO, and HPT axes. In conclusion, the obtained results clearly show that subclinical LPS from S. Enteritidis can affect the brain chemistry structure and dysregulate bioactive substance from selected brain sections and glands of the neuroendocrine axes. The exact mechanisms by which LPS can influence major neuroendocrine axes are not fully understood and require further studies.

The Evolving Landscape of Cancer Therapeutics

The last 100 years have seen a dramatic alteration in the treatment of cancer. Aside from small molecule inhibitors of protein tyrosine kinases, monoclonal antibodies have also been found to provide valuable therapeutic approaches for modulating tumour pathophysiology. As our knowledge of cancer biology improves, the specificity of this new generation of drugs is generally delivering an improved therapeutic ratio compared to traditional cytotoxic agents. However, patient selection through the use of biomarkers is key in optimising efficacy and improving cost-effectiveness. The most recent wave of revolutionary new systemic therapy approaches to cancer has arrived in recent years in the form of immune checkpoint inhibitors, now clinically validated as modulators of immune-regulatory pathways. The future of oncology therapeutics includes a combination of cytotoxic agents, targeted therapies and immunotherapy.

Treatment with Lanreotide Depot Following Octreotide Long-Acting Release Among Patients with Gastroenteropancreatic Neuroendocrine Tumors

Objective: To examine patients with metastatic gastroenteropancreatic neuroendocrine tumors (GEP-NETs) who receive sequential treatment with somatostatin analogs. Materials and Methods: This retrospective chart review examined lanreotide depot/autogel tolerability and efficacy among GEP-NET patients who received lanreotide after octreotide long-acting release (LAR) at Tufts University Medical Center. Information obtained included background patient characteristics, dosing, adverse events (AEs), radiologic response, and biochemical markers. Results: Patients (n = 16; 43-81 years; mean age, 64.25 years; 11 female) with nonfunctional, low-grade GEP-NETs receiving octreotide LAR 30-60 mg were transitioned to lanreotide because of patient decision (n = 6), disease progression (n = 6), AEs (n = 2), poor tolerance (n = 1), and injection discomfort/pain (n = 1). Lanreotide doses started at 120 mg (n = 13), 90 mg (n = 1), or 60 mg (n = 2); 8 patients received concomitant therapies, mostly liver-directed (radiofrequency ablation/radioembolization). AEs associated with lanreotide experienced by ≥2 patients were fatigue, diarrhea, nausea, hypertension, pancreatic enzyme deficiency, and hyperglycemia. Radiologic treatment responses of the combination of lanreotide with other therapeutic modalities included complete response (n = 1), partial response (n = 5), and stable disease (n = 9). One patient had radiologic progression. Serum serotonin and chromogranin levels decreased, but urinary 5-hydroxyindoleacetic acid levels appeared relatively unchanged. Conclusion: Among post-octreotide GEP-NET patients, including those with disease progression or poor octreotide tolerance, lanreotide alone or with concomitant therapies was well tolerated and associated with radiologic responses.

Somatostatin receptor 2A protein expression characterizes anaplastic oligodendrogliomas with favorable outcome

Diffuse gliomas are classified according to the 2016 WHO Classification of Tumors of the Central Nervous System, which now defines entities by both histology and molecular features. Somatostatin receptor subtype 2A (SSTR2A) expression has been reported in various solid tumors as associated with favorable outcomes. Its expression has been reported in gliomas with uncertain results regarding its prognostic value. The objective of this study was to assess the prognostic impact of SSTR2A protein expression in a large cohort of grade III and IV gliomas classified according to the updated 2016 WHO classification. We further validated our result with an independent cohort of low grade glioma using dataset generated by The Cancer Genome Atlas (TCGA) Research Network.We analyzed clinical and molecular data from 575 patients. SSTR2A protein expression was evaluated using immunohistochemistry on tissue microarrays. High expression of SSTR2A protein associated with the anaplastic oligodendroglioma IDH-mutant and 1p/19q-codeleted subgroup (p < 0.001). Among these tumors, SSTR2A protein expression was significantly associated with a lower proliferative index, the absence of microvascular proliferation and the absence of necrosis (p < 0.001). Furthermore SSTR2A protein expression associated with better overall survival (p = 0.007) and progression-free survival (p = 0.01) in both univariate and multivariate analysis when adjusted by the age, the presence of necrosis and the mitotic index. Similar results were obtained regarding SSTR2 mRNA expression in the TCGA low grade glioma, subtype IDH-mutant and 1p/19q-codeleted, dataset.SSTR2A might represent an attractive biomarker and therapeutic target in anaplastic oligodendroglioma IDH-mutant and 1p/19q-codeleted specific subgroup. Understanding the implicated molecular pathways may represent a step forward to improve therapeutic approaches.

Large cell neuroendocrine carcinoma of the lung with atypical evolution and a remarkable response to lutetium Lu 177 dotatate

Large cell neuroendocrine carcinoma of the lung (LCNEC) is a high-grade, poorly differentiated tumor that typically does not express somatostatin receptors. Thus, it does not benefit from treatment with somatostatin analogs and peptide receptor radionuclide therapy (PRRT). The current study objective was to demonstrate that treatment with PRRT may be a valid option in neuroendocrine carcinomas with high expression of somatostatin receptors. This is a case report of a 58-year-old man who was diagnosed with LCNEC and received chemotherapy treatment with little benefit. Extensive hepatic and bone metastasis was detected on ¹¹¹In-pentetreotide scintigraphy following high uptake of the radionuclide by the tumors. The patient benefitted from neuroendocrine treatment initially and from lutetium Lu 177 dotatate subsequently. A significant clinical and radiological response was observed, along with an improvement in quality of life. The use of PRRT is a valid alternative to chemotherapy in patients with LCNEC involving the expression of somatostin receptors.

The somatostatin-secreting pancreatic δ-cell in health and disease

The somatostatin-secreting δ-cells comprise ~5% of the cells of the pancreatic islets. The δ-cells have complex morphology and might interact with many more islet cells than suggested by their low numbers. δ-Cells contain ATP-sensitive potassium channels, which open at low levels of glucose but close when glucose is elevated. This closure initiates membrane depolarization and electrical activity and increased somatostatin secretion. Factors released by neighbouring α-cells or β-cells amplify the glucose-induced effects on somatostatin secretion from δ-cells, which act locally within the islets as paracrine or autocrine inhibitors of insulin, glucagon and somatostatin secretion. The effects of somatostatin are mediated by activation of somatostatin receptors coupled to the inhibitory G protein, which culminates in suppression of the electrical activity and exocytosis in α-cells and β-cells. Somatostatin secretion is perturbed in animal models of diabetes mellitus, which might explain the loss of appropriate hypoglycaemia-induced glucagon secretion, a defect that could be mitigated by somatostatin receptor 2 antagonists. Somatostatin antagonists or agents that suppress somatostatin secretion have been proposed as an adjunct to insulin therapy. In this Review, we summarize the cell physiology of somatostatin secretion, what might go wrong in diabetes mellitus and the therapeutic potential of agents targeting somatostatin secretion or action.

Multilayered heterogeneity as an intrinsic hallmark of neuroendocrine tumors

Neuroendocrine tumors (NETs) comprise a complex and highly heterogeneous group of neoplasms that can arise all over the body, originating from neuroendocrine cells. NETs are characterized by a general lack of symptoms until they are in advanced phase, and early biomarkers are not as available and useful as required. Heterogeneity is an intrinsic, pivotal feature of NETs that derives from diverse causes and ultimately shapes tumor fate. The different layers that conform NET heterogeneity include a wide range of distinct characteristics, from the mere location of the tumor to its clinical and functional features, and from its cellular properties, to the core signaling and (epi)genetic components defining the molecular signature of the tumor. The importance of this heterogeneity resides in that it translates into a high variability among tumors and, hence, patients, which hinders a more precise diagnosis and prognosis and more efficacious treatment of these diseases. In this review, we highlight the significance of this heterogeneity as an intrinsic hallmark of NETs, its repercussion on clinical approaches and tumor management, and some of the possible factors associated to such heterogeneity, including epigenetic and genetic elements, post-transcriptional regulation, or splicing alterations. Notwithstanding, heterogeneity can also represent a valuable and actionable feature, towards improving medical approaches based on personalized medicine. We conclude that NETs can no longer be viewed as a single disease entity and that their diagnosis, prognosis and treatment must reflect and incorporate this heterogeneity.

The somatostatin-secreting pancreatic δ-cell in health and disease

The somatostatin-secreting δ-cells comprise ~5% of the cells of the pancreatic islets. The δ-cells have complex morphology and might interact with many more islet cells than suggested by their low numbers. δ-Cells contain ATP-sensitive potassium channels, which open at low levels of glucose but close when glucose is elevated. This closure initiates membrane depolarization and electrical activity and increased somatostatin secretion. Factors released by neighbouring α-cells or β-cells amplify the glucose-induced effects on somatostatin secretion from δ-cells, which act locally within the islets as paracrine or autocrine inhibitors of insulin, glucagon and somatostatin secretion. The effects of somatostatin are mediated by activation of somatostatin receptors coupled to the inhibitory G protein, which culminates in suppression of the electrical activity and exocytosis in α-cells and β-cells. Somatostatin secretion is perturbed in animal models of diabetes mellitus, which might explain the loss of appropriate hypoglycaemia-induced glucagon secretion, a defect that could be mitigated by somatostatin receptor 2 antagonists. Somatostatin antagonists or agents that suppress somatostatin secretion have been proposed as an adjunct to insulin therapy. In this Review, we summarize the cell physiology of somatostatin secretion, what might go wrong in diabetes mellitus and the therapeutic potential of agents targeting somatostatin secretion or action.

In Vitro Evaluation of Molecular Tumor Targets in Nuclear Medicine: Immunohistochemistry Is One Option, but Under Which Conditions?

The identification of new molecular targets for diagnostic and therapeutic applications using in vitro methods is an important challenge in nuclear medicine. One such method is immunohistochemistry, increasingly popular because it is easy to perform. This review presents the case for conducting receptor immunohistochemistry to evaluate potential molecular targets in human tumor tissue sections. The focus is on the immunohistochemistry of G-protein-coupled receptors, one of the largest families of cell surface proteins, representing a major class of drug targets and thus playing an important role in nuclear medicine. This review identifies common pitfalls and challenges and provides guidelines on performing such immunohistochemical studies. An appropriate validation of the target is a prerequisite for developing robust and informative new molecular probes.

Imaging of Neuroendocrine Tumors: Indications, Interpretations, Limits, and Pitfalls

Imaging is critical in the diagnosis, prognosis, and management of neuroendocrine tumors (NETs). NETs share common imaging features, but each type exhibits unique features. Computed tomography scans or MRI of the abdomen is used to assess tumor burden routinely. Functional imaging with octreotide scan or gallium-68 somatostatin analog PET is used selectively to confirm diagnosis and guide therapy. Clinicians and radiologists should be familiar with the indications and interpretations of imaging modalities. Novel functional imaging modalities likely will be developed to detect small NETs, predict prognosis, guide therapeutic choices, and design novel therapies.

Structure and Function of Peptide-Binding G Protein-Coupled Receptors

G protein-coupled receptors (GPCRs) are the largest family of cell surface receptors and are important human drug targets. Of the 826 human GPCRs, 118 of them recognize endogenous peptide or protein ligands, and 30 of the 118 are targeted by approved drug molecules, including the very high-profile class B glucagon-like peptide 1 receptor. In this review, we analyze the 21 experimentally determined three-dimensional structures of the known peptide-binding GPCRs in relation to the endogenous peptides and drug molecules that modulate their cell signaling processes. Our integrated analyses reveal that half of the marketed drugs and most of the drugs in clinical trials that interact with peptide GPCRs are small molecules with a wide range of binding modes distinct from those of large peptide ligands. As we continue to collect additional data on these receptors from orthogonal approaches, including nuclear magnetic resonance and electron microscopy, we are beginning to understand how these receptors interact with their ligands at the molecular level and how improving the pharmacology of GPCR signal transduction requires us to study these receptors using multiple biophysical techniques.

A Modular Dual-Labeling Scaffold That Retains Agonistic Properties for Somatostatin Receptor Targeting

Fluorescence-guided surgery is an emerging imaging technique that can enhance the ability of surgeons to detect tumors when compared with visual observation. To facilitate characterization, fluorescently labeled probes have been dual-labeled with a radionuclide to enable cross-validation with nuclear imaging. In this study, we selected the somatostatin receptor imaging agent DOTATOC as the foundation for developing a dual-labeled analog. We hypothesized that a customized dual-labeling approach with a multimodality chelation (MMC) scaffold would minimize steric effects of dye conjugation and retain agonist properties. Methods: An MMC conjugate (MMC-TOC) was synthesized on solid-phase and compared with an analog prepared using conventional methods (DA-TOC). Both analogs were conjugated to IRDye 800 using copper-free click chemistry. The resulting compounds, MMC(IR800)-TOC and DA(IR800)-TOC, were labeled with Cu and ⁶⁴Cu and tested in vitro in somatostatin receptor subtype 2-overexpressing HEK-293 cells to assess agonist properties, and in AR42J rat pancreatic cancer cells to determine receptor binding characteristics. Multimodality imaging was performed in AR42J xenografts. Results: Cu-MMC(IR800)-TOC demonstrated higher potency for cyclic adenosine monophosphate inhibition (half maximal effective concentration [EC₅₀]: 0.21 ± 0.18 vs. 1.38 ± 0.54 nM) and receptor internalization (EC₅₀: 41.9 ± 29.8 vs. 455 ± 299 nM) than Cu-DA(IR800)-TOC. Radioactive uptake studies showed that blocking with octreotide caused a dose-dependent reduction in ⁶⁴Cu-MMC(IR800)-TOC uptake whereas ⁶⁴Cu-DA(IR800)-TOC was not affected. In vivo studies revealed higher tumor uptake for ⁶⁴Cu-MMC(IR800)-TOC than ⁶⁴Cu-DA(IR800)-TOC (5.2 ± 0.2 vs. 3.6 ± 0.4 percentage injected dose per gram). In vivo blocking studies with octreotide reduced tumor uptake of ⁶⁴Cu-MMC(IR800)-TOC by 66%. Excretion of ⁶⁴Cu-MMC(IR800)-TOC was primarily through the liver and spleen whereas ⁶⁴Cu-DA(IR800)-TOC was cleared through the kidneys. Ex vivo analysis at 24 h confirmed PET/CT data by showing near-infrared fluorescence signal in tumors and a tumor-to-muscle ratio of 5.3 ± 0.8 as determined by γ-counting. Conclusion: The findings demonstrate that drug design affected receptor pharmacology and suggest that the MMC scaffold is a useful tool for the development of dual-labeled imaging agents.

The LARO-MEN1 study: a longitudinal clinical experience with octreotide Long-Acting Release in patients with Multiple Endocrine Neoplasia type 1 Syndrome

Multiple endocrine neoplasia type 1 (MEN1) is a rare hereditary tumoral syndrome, featured by a combination of neoplasms of various endocrine and nonendocrine tissues. Approximately 33% of MEN1-related deaths are due to the malignant behaviour of well-differentiated neuroendocrine tumors (NETs), for which a preventive surgical treatment is not feasible. Somatostatin analogues (SSA) have been employed in the treatment of NETs in the stage of advanced or metastatic disease, in order to control the growth and secretion of tumor lesions. A longitudinal, open label study named "LARO-MEN1" was undertaken in order to assess whether early medical treatment with long-acting SSA could act as a preventive approach in small MEN1-related gastroenteropancreatic (GEP) NETs. Thirty consecutive patients affected by MEN1 were screened and 8 patients with small (<2 cm) NETs and abnormal laboratory values of at least one of the GEP hormones were administered octreotide acetate slow-release formulation (LAR) (10 mg i.m. every 28 days). Octreotide LAR was effective in decreasing GEP hormones and overall safe in the majority of patients up to six years of treatment, maintaining the disease stable also in terms of tumor size. The positive outcomes of this study in MEN1 patients reinforce the results obtained in advanced NETs on the use of SSA, opening to the opportunity for preventive use of octreotide LAR, aimed to delay or even avoid surgery in these patients.

Somatostatin receptor ligands in the treatment of acromegaly

First-generation somatostatin receptors ligands (SRL) are the mainstay in the medical treatment of acromegaly, however the percentage of patients controlled with these drugs significantly varies in the different studies. Many factors are involved in the resistance to SRL. In this review, we update the physiology of somatostatin and its receptors (sst), the use of SRL in the treatment of acromegaly and the factors involved in the response to these drugs. The SRL act through interaction with the sst, which up to now have been characterized as five subtypes. The first-generation SRL, octreotide and lanreotide, are considered sst2 specific and have biochemical response rates varying from 20 to 70%. Tumor volume reduction can be found in 36-75% of patients. Several factors may determine the response to these drugs, such as sst, AIP, E-cadherin, ZAC1, filamin A and β-arrestin expression in the somatotropinomas. In patients resistant to first-generation SRL, alternative medical treatment options include: SRL high dose regimens, SRL in combination with cabergoline or pegvisomant, or the use of pasireotide. Pasireotide is a next-generation SRL with a broader pattern of interaction with sst. In the light of the recent increase of treatment options in acromegaly and the deeper knowledge of the determinants of response to the current first-line therapy, a shift from a trial-and-error treatment to a personalized one could be possible.

Clinical and Preclinical Advances in Gastroenteropancreatic Neuroendocrine Tumor Therapy

The molecular events leading to gastroenteropancreatic neuroendocrine tumor (GEP-NET) formation are largely unknown. Over the past decades, systemic chemotherapies have been replaced by therapies directed at particular molecular targets such as the somatostatin receptors, mTOR complexes or proangiogenic molecules. These approaches have demonstrated some success in subtypes of this heterogeneous tumor group, but responses are still widely varied. This review highlights the clinical trials ongoing for neuroendocrine tumors (NETs) and includes emerging immunotherapy, which holds great promise for NETs based on successes in other tumor types. Current avenues of preclinical research, including Notch and PI3K/AKT, will lead to additional targeted therapies based on genome-wide studies that have cast a wide net in the search for driver mutations. Future preclinical and clinical investigations are required to identify those mutations predictive of therapeutic response or disease progression. Results of current clinical trials outlined here will better inform patient management with respect to agent selection, timing, duration and combination therapy in the treatment of NETs.

Association Between Somatostatin Receptor Expression and Clinical Outcomes in Neuroendocrine Tumors

OBJECTIVE

Somatostatin receptors (SSTRs), products of gene superfamily SSTR1-5, are commonly expressed in neuroendocrine tumors (NETs). Somatostatin analogs (SSAs) bind to SSTRs and are used as therapeutic agents in patients with advanced NETs. We hypothesized that tumor SSTR expression status would be associated with clinical outcomes in NET.

METHODS

Expression of the 5 SSTRs was evaluated by immunohistochemistry, using tissue microarrays comprising 173 primary NETs, 24 matched metastases, and 22 metastatic NETs from 195 patients. Cox proportional hazards regression analysis was used to assess the association of SSTR expression status (high vs low) with clinical outcomes, adjusting for potential confounders.

RESULTS

High expression of SSTR2 was associated with longer overall survival (OS) in the cohort overall (multivariate hazard ratio, 0.42; 95% confidence interval, 0.21-0.84; P = 0.013). In a subgroup of patients with metastatic small intestine NET treated with SSAs and evaluable for progression, SSTR2 expression was associated with both longer progression-free survival (PFS) and OS. No associations with PFS or OS were observed with expression of other SSTRs.

CONCLUSIONS

Our study demonstrated that expression of SSTR2, but not other SSTRs, is associated with longer OS. In patients treated with SSAs, expression of SSTR2 is associated with longer PFS survival.

Liposomal drug delivery systems for targeted cancer therapy: is active targeting the best choice?

Liposomes are biodegradable and biocompatible self-forming spherical lipid bilayer vesicles. They can encapsulate and deliver one or more hydrophobic and hydrophilic therapeutic agents with poor therapeutic indices to tumor sites. Properties such as lipid bilayer fluidity, charge, size and surface hydration can be modified to extend liposome circulation time in the bloodstream and enhance efficacy. The focus of this review is on ligand-conjugated liposomes and their potential application in tumor-targeted delivery. Ligand-conjugated liposomes are designed to target receptors which are overexpressed on tumor cells to decrease drugs side effects by enhancing their selective delivery to tumor site. Despite the extensive research in this area, no small molecule ligand-conjugated liposome has been approved up to date for cancer therapy.

Proteomics Suggests a Role for APC-Survivin in Response to Somatostatin Analog Treatment of Neuroendocrine Tumors

CONTEXT

Somatostatin analogs are established in the treatment of neuroendocrine tumors (NETs) including small intestinal NET; however, the molecular mechanisms are not well known. Here, we examined the direct effects of lanreotide in NET cell line models.

SETTING AND DESIGN

The cell lines HC45 and H727 were treated with 10nM lanreotide for different time periods and alterations of the proteome were analyzed by in-depth high-resolution isoelectric focusing tandem liquid chromatography-mass spectrometry. We next investigated whether the observed suppression of survivin was mediated by adenomatous polyposis coli (APC) and possible effects on tumor proliferation in vitro. Expression of survivin was assessed by immunohistochemistry in 112 NET cases and compared with patient outcome.

RESULTS

We quantified 6451 and 7801 proteins in HC45 and H727, respectively. After short time lanreotide treatment APC was increased and survivin reduced. Overexpression of APC in H727 cells decreased, and APC knock-down elevated the survivin level. The lanreotide regulation of APC-survivin could be suppressed by small interfering RNA against somatostatin receptor 2. Although lanreotide only gave slight inhibition of proliferation, targeting of survivin with the small molecule YM155 dramatically reduced proliferation. Moderate or high as compared with low or absent total survivin expression was associated with shorter progression-free survival, independent of tumor stage, grade, and localization.

CONCLUSIONS

We report a proteome-wide analysis of changes in response to lanreotide in NET cell lines. This analysis suggests a connection between somatostatin analog, APC, and survivin levels. Survivin is a possible prognostic factor and a new potential therapeutic target in NETs.

Therapeutic innovations in endocrine diseases - Part 4 : Pasireotide: Long-acting release somatostatin analogue

Pasireotide, the latest long-acting release somatostatin analogue, is distributed more widely to the various somatostatin receptors, which theoretically increases its strength and broadens its scope. Does this reflect genuine therapeutic progress? Or rather does its reduced specificity cause too many adverse reactions to make it a significant therapeutic achievement?