Molecular and cellular biology of neuroendocrine lung tumors: Evidence for separate biological entities

Pulmonary neuroendocrine tumors (NETs) are traditionally described as comprising a spectrum of neoplasms, ranging from low grade typical carcinoids (TCs) via the intermediate grade atypical carcinoids (ACs) to the highly malignant small cell lung cancers (SCLCs) and large cell neuroendocrine carcinomas (LCNECs). Recent data, however, suggests that two categories can be distinguished on basis of molecular and clinical data, i.e. the high grade neuroendocrine (NE) carcinomas and the carcinoid tumors. Bronchial carcinoids and SCLCs may originate from the same pulmonary NE precursor cells, but a precursor lesion has only been observed in association with carcinoids, termed diffuse idiopathic pulmonary neuroendocrine cell hyperplasia. The occurrence of mixed tumors exclusively comprising high grade NE carcinomas also supports a different carcinogenesis for these two groups. Histopathologically, high grade NE lung tumors are characterized by high mitotic and proliferative indices, while carcinoids are defined by maximally 10 mitoses per 2mm(2) (10 high-power fields) and rarely have Ki67-proliferative indices over 10%. High grade NE carcinomas are chemosensitive tumors, although they usually relapse. Surgery is often not an option due to extensive disease at presentation and early metastasis, especially in SCLC. Conversely, carcinoids are often insensitive to chemo- and radiation therapy, but cure can usually be achieved by surgery. A meta-analysis of comparative genomic hybridization studies performed for this review, as well as gene expression profiling data indicates separate clustering of carcinoids and carcinomas. Chromosomal aberrations are much more frequent in carcinomas, except for deletion of 11q, which is involved in the whole spectrum of NE lung tumors. Deletions of chromosome 3p are rare in carcinoids but are a hallmark of the high grade pulmonary NE carcinomas. On the contrary, mutations of the multiple endocrine neoplasia type 1 (MEN1) gene are restricted to carcinoid tumors. Many of the differences between carcinoids and high grade lung NETs can be ascribed to tobacco consumption, which is strongly linked to the occurrence of high grade NE carcinomas. Smoking causes p53 mutations, very frequently present in SCLCs and LCNECs, but rarely in carcinoids. It further results in other early genetic events in SCLCs and LCNECs, such as 3p and 17p deletions. Smoking induces downregulation of E-cadherin and associated epithelial to mesenchymal transition. Also, high grade lung NETs display higher frequencies of aberrations of the Rb pathway, and of the intrinsic and extrinsic apoptotic routes. Carcinoid biology on the other hand is not depending on cigarette smoke intake but rather characterized by aberrations of other specific genetic events, probably including Menin or its targets and interaction partners. This results in a gradual evolution, most likely from proliferating pulmonary NE cells via hyperplasia and tumorlets towards classical carcinoid tumors. We conclude that carcinoids and high grade NE lung carcinomas are separate biological entities and do not comprise one spectrum of pulmonary NETs. This implies the need to reconsider both diagnostic as well as therapeutic approaches for these different groups of malignancies.     

Genetic and molecular coordinates of neuroendocrine lung tumors,with emphasis on small-cell lung carcinomas

The aim of this review is to present the advances in our understanding of the progression of tumorigenesis in neuroendocrine lung tumors. Current information on established and putative diagnostic and prognostic markers of neuroendocrine tumors are evaluated, with a special reference to small-cell lung carcinoma, due to its higher incidence and aggressive behavior. The genetic and molecular changes that accompany these neoplasms are highlighted, and factors that influence cell-cycle progression, apoptosis, drug resistance, and escape from immune surveillance are critically assessed.     

Oncolytic viruses for the treatment of neuroendocrine tumors

Oncolytic viruses are emerging as anticancer agents, and they have also shown great promise for use against neuroendocrine tumors. Many viruses have a natural tropism for replication in tumor cells. Others can be genetically engineered to selectively kill tumor cells. Viruses have some advantages as therapeutic agents over current cytotoxic drugs and small molecules. They replicate in tumor cells and thereby increase in number over time leading to increased dosage. They are immunogenic and can alter the immunosuppressive tumor microenvironment and activate immune effector cells. They have also been shown to be able to kill drug-resistant cancer stem cells. This article reviews the recent literature on oncolytic viruses used so far for neuroendocrine tumors and indicates important issues to focus on in the future.     

Somatostatin-dopamine chimeras: a novel approach to treatment of neuroendocrine tumors

A combination of basic research observations concerning the interaction of somatostatin (SST) and dopamine (DA) receptors, and clinical reports of enhanced efficacy of combined SST and DA analogue treatment in suppressing GH hypersecretion, lead to the concept of creating chimeric molecules combining structural features of both compound classes. The resulting SST/DA chimeras retain the ability to interact with receptors of both families and display greatly enhanced potency and efficacy, as compared with that of individual SST or DA receptor agonists. In vitro studies with pituitary adenoma cells from acromegalic patients have demonstrated that the chimeric molecules have exceptional activity with regard to suppression of GH and prolactin secretion. Similarly, potent suppression of ACTH secretion from Cushing's-causing corticotroph tumors, and suppression of nonfunctioning pituitary adenoma proliferation has been observed. The chimeric SST/DA compounds are also quite potent and efficacious in suppressing both GH and IGF1 in vivo when tested in nonhuman primates, with no effect on either insulin secretion or glycemic control. Initial clinical studies examining acute, subcutaneous administration of the chimeric SST/DA compound, BIM-23A760, revealed both prolonged circulating half-life and extended duration of biological effect. With chronic administration, however, BIM-23A760 was found to produce a metabolite with dopaminergic activity that gradually accumulates and interferes with the activity of the parent compound. Consequently, efforts are currently underway to produce a second-generation chimera for treatment of neuroendocrine disease.     

Biology of advanced uveal melanoma and next steps for clinical therapeutics

Uveal melanoma is the most common intraocular malignancy although it is a rare subset of all melanomas. Uveal melanoma has distinct biology relative to cutaneous melanoma, with widely divergent patient outcomes. Patients diagnosed with a primary uveal melanoma can be stratified for risk of metastasis by cytogenetics or gene expression profiling, with approximately half of patients developing metastatic disease, predominately hepatic in location, over a 15‐yr period. Historically, no systemic therapy has been associated with a clear clinical benefit for patients with advanced disease, and median survival remains poor. Here, as a joint effort between the Melanoma Research Foundation's ocular melanoma initiative, CURE OM and the National Cancer Institute, the current understanding of the molecular and immunobiology of uveal melanoma is reviewed, and on‐going laboratory research into the disease is highlighted. Finally, recent investigations relevant to clinical management via targeted and immunotherpies are reviewed, and next steps in the development of clinical therapeutics are discussed.     

Novel therapeutic agents for the treatment of gastroenteropancreatic neuroendocrine tumors

Neuroendocrine tumors (NET) are frequently diagnosed late and not amenable to curative surgery due to metastatic disease to the liver and lymph nodes. The disease is complex and heterogeneous given the various functionalities, distinct tumor growth patterns, and tumor spread upon diagnosis. Established therapies include somatostatin analogues, alpha-interferon, systemic chemotherapy, and loco-regional therapies of the liver. The availability of novel agents and expression of targets, such as growth factor receptors, different subtypes of somatostatin receptors, and the mammalian target of rapamycin (mTOR) have led to the exploration of different classes of drugs and offer new treatment opportunities in neuroendocrine tumors. This review provides an overview on novel drugs, focus on the impact of recently approved drugs on the management of NET disease, and outline future perspectives.     

Targeting the LPS export pathway for the development of novel therapeutics

The rapid rise of multi-resistant bacteria is a global health threat. This is especially serious for Gram-negative bacteria in which the impermeable outer membrane (OM) acts as a shield against antibiotics. The development of new drugs with novel modes of actions to combat multi-drug resistant pathogens requires the selection of suitable processes to be targeted. The LPS export pathway is an excellent under exploited target for drug development. Indeed, LPS is the major determinant of the OM permeability barrier, and its biogenetic pathway is conserved in most Gram-negatives. Here we describe efforts to identify inhibitors of the multiprotein Lpt system that transports LPS to the cell surface. Despite none of these molecules has been approved for clinical use, they may represent valuable compounds for optimization. Finally, the recent discovery of a link between inhibition of LPS biogenesis and changes in peptidoglycan structure uncovers additional targets to develop novel therapeutic strategies.     

Modulation of angiogenesis with siRNA inhibitors for novel therapeutics

Cancer and many other serious diseases are characterized by the uncontrolled growth of new blood vessels. Recently, RNA interference (RNAi) has reinvigorated the therapeutic prospects for inhibiting gene expression and promises many advantages over binding inhibitors, including high specificity, which is essential for targeted therapeutics. This article describes the latest developments using small-interfering RNA (siRNA) inhibitors to downregulate various angiogenic and tumor-associated factors, both in cell-culture assays and in animal disease models. The majority of research efforts are currently focused on understanding gene function, as well as proof-of-concept for siRNA-mediated anti-angiogenesis. The prospects for siRNA therapeutics, both advantages and looming hurdles, are evaluated.     

Salivary glands: novel target sites for gene therapeutics

Directing the local or systemic expression of therapeutic proteins is a potentially important clinical application of gene transfer technology. Gene-based therapeutics theoretically offer many advantages over protein therapeutics. Numerous tissues have been evaluated for this purpose in animal models, most commonly the liver and skeletal muscle. Based on pre-clinical studies, we suggest that salivary glands are a valuable, yet under-appreciated, target tissue for both systemic and upper gastrointestinal tract gene therapeutic applications.     

Biomarkers and molecular imaging in gastroenteropancreatic neuroendocrine tumors

Neuroendocrine gastrointestinal and pancreatic tumors (GEP-NETs) are a heterogenous group of cancers with various clinical expressions. All tumors produce and secret various amines and peptides, which can be used as tissue and circulating markers. Chromogranin A (CgA) is a general tumor marker stored in secretory granules within the tumor cell and released upon stimulation. CgA is the best general tumor marker at the moment, expressed in 80-90% in all patients with GEP-NETs. CgA and NSE are used as tissue markers for the delineation of the neuroendocrine features of the tumors, but recently also the proliferation marker Ki-67 has been included in the standard procedure for evaluation of the proliferation. GEP-NETs are classified into well differentiated neuroendocrine tumors (Ki-67<2%), well-differentiated neuroendocrine carcinoma (Ki-67 2-20%), poorly differentiated neuroendocrine carcinoma (Ki-67>20%). The molecular imaging of NETs is based on the ability of these tumor cells to express somatostatin receptors as well as the APUD features. Octreoscan has been applied for imaging and staging of the disease for more than 2 decades and will nowadays be replaced by 68Ga-DOTA-Octreotate, with higher specificity and sensitivity. 18Fluoro-DOPA and 11C-5HTP are specific tracers for NETs with high specificity and selectivity. A new potential biomarker is auto-antibodies to paraneoplastic antigen MA2, which might indicate early recurrence of carcinoids after surgery with a curative intent. Circulating tumor cells (CTC) have been applied in GEP-NETs quite recently. There is still an unmet need for new markers.     

Transport characteristics of a novel peptide platform for CNS therapeutics

New and effective therapeutics that cross the blood‐brain barrier (BBB) are critically needed for treatment of many brain diseases. We characterize here a novel drug development platform that is broadly applicable for the development of new therapeutics with increased brain penetration. The platform is based on the Angiopep‐2 peptide, a sequence derived from ligands that bind to low‐density lipoprotein receptor‐related protein‐1 (LRP‐1), a receptor expressed on the BBB. Fluorescent imaging studies of a Cy5.5Angiopep‐2 conjugate and immunohistochemical studies of injected Angiopep‐2 in mice demonstrated efficient transport across the BBB into brain parenchyma and subsequent co‐localization with the neuronal nuclei‐selective marker NeuN and the glial marker glial fibrillary acidic protein (GFAP). Uptake of [¹²⁵I]‐Angiopep‐2 into brain endothelial cells occurred by a saturable mechanism involving LRP‐1. The primary sequence and charge of Angiopep‐2 were crucial for its passage across the BBB. Overall, the results demonstrate the significant potential of this platform for the development of novel neurotherapeutics.     

Spatiotemporal heterogeneity and clinical challenge of pancreatic neuroendocrine tumors

During the course of pancreatic neuroendocrine tumors (NETs), they generally become more heterogeneous with individual cells exhibiting distinct molecular fingerprints. This heterogeneity manifests itself through an unequal distribution of genetically-variant, tumor cell subpopulations within disease locations (i.e., spatial heterogeneity) or changes in the genomic landscape over time (i.e., temporal heterogeneity); these characteristics complicate clinical diagnosis and treatment. Effective, feasible tumor heterogeneity detection and eradication methods are essential to overcome the clinical challenges of pancreatic NETs. This review explores the molecular fingerprints of pancreatic NETs and the spectrum of tumoral heterogeneity. We then describe the challenges of assessing heterogeneity by liquid biopsies and imaging modalities and the therapeutic challenges for pancreatic NETs. In general, navigating these challenges, refining approaches for translational research, and ultimately improving patient care are available once we have a better understanding of intratumoral spatiotemporal heterogeneity.     

促泌素在胃肠道神经内分泌肿瘤中的表达及其临床意义

目的 比较促泌素(secretagogin,SCGN)与传统的神经内分泌标记物在胃肠道神经内分泌肿瘤中的表达差异.方法 收集胃肠道手术标本共88例,其中实验组为8例类癌和20例非典型类癌,对照组为40例腺癌伴神经内分泌分化和20例腺癌.所有标本均使用SCGN、PGP9.5、CD56、NSE、Syn及CgA进行免疫组织化学SP两步法染色.结果 SCGN可在胃肠道粘膜同有层腺体的弥散性神经内分泌细胞中表达,多显示“开放型”的神经内分泌细胞.除CD56和NSE各在1例胃肠道腺癌中阳性表达外,SCGN及其它标记物在20例腺癌中均无表达,所有标记物之间均无统计学差异(P＞0.05).SCGN在40例胃肠道腺癌伴神经内分泌分化、20例非典型类癌和8例类癌巾的阳性表达率均最高,分别为62.5％ (25/40)、90％(18/20)和100％(8/8),PGP9.5阳性表达率均最低分别为32.5％(13/40)、45％ (9/20)和37.5％(3/8),两标记物在这三组肿瘤中的表达均有显著统计学差异(P＜0.01),而CD56、NSE、Syn和CgA在以上三组肿瘤中的表达率均较高,与SCGN比较均无统计学差异(P＞0.05).所有标记物在腺癌伴神经内分泌分化、非典型类癌和类癌中的阳性表达率均明显高于腺癌(P＜0.01);SCGN、Syn和CgA在非典型类癌和类癌巾的阳性表达均高于腺癌伴神经内分泌分化(P＜0.05);所有标记物在非典型类癌和类癌之间的阳性表达率均无统计学差异(P＞0.05).结论 SCGN作为一种新型的神经内分泌标记物与传统标记物Syn和CgA联合,可应用于胃肠道神经内分泌肿瘤的临床病理诊断.     

PLGA nanoparticles for peptide receptor radionuclide therapy of neuroendocrine tumors: a novel approach towards reduction of renal radiation dose

Background

Peptide receptor radionuclide therapy (PRRT), employed for treatment of neuroendocrine tumors (NETs) is based on over-expression of Somatostatin Receptors (SSTRs) on NETs. It is, however, limited by high uptake and retention of radiolabeled peptide in kidneys resulting in unnecessary radiation exposure thus causing nephrotoxicity. Employing a nanocarrier to deliver PRRT drugs specifically to the tumor can reduce the associated nephrotoxicity. Based on this, ¹⁷⁷Lu-DOTATATE loaded PLGA nanoparticles (NPs) were formulated in the present study, as a potential therapeutic model for NETs.

Methodology and Findings

DOTATATE was labeled with Lutetium-177 (¹⁷⁷Lu) (labeling efficiency 98%; R_f∼0.8). Polyethylene Glycol (PEG) coated ¹⁷⁷Lu-DOTATATE-PLGA NPs (50∶50 and 75∶25) formulated, were spherical with mean size of 304.5±80.8 and 733.4±101.3 nm (uncoated) and 303.8±67.2 and 494.3±71.8 nm (coated) for PLGA(50∶50) and PLGA(75∶25) respectively. Encapsulation efficiency (EE) and In-vitro release kinetics for uncoated and coated NPs of PLGA (50∶50 & 75∶25) were assessed and compared. Mean EE was 77.375±4.98% & 67.885±5.12% (uncoated) and 65.385±5.67% & 58.495±5.35% (coated). NPs showed initial burst release between 16.64–21.65% with total 42.83–44.79% over 21days. The release increased with coating to 20.4–23.95% initially and 60.97–69.12% over 21days. In-vivo studies were done in rats injected with ¹⁷⁷Lu-DOTATATE and ¹⁷⁷Lu-DOTATATE-NP (uncoated and PEG-coated) by imaging and organ counting after sacrificing rats at different time points over 24 hr post-injection. With ¹⁷⁷Lu-DOTATATE, renal uptake of 37.89±10.2%ID/g was observed, which reduced to 4.6±1.97% and 5.27±1.66%ID/g with uncoated and coated ¹⁷⁷Lu-DOTATATE-NP. The high liver uptake with uncoated ¹⁷⁷Lu-DOTATATE-NP (13.68±3.08% ID/g), reduced to 7.20±2.04%ID/g (p = 0.02) with PEG coating.

Conclusion

PLGA NPs were easily formulated and modified for desired release properties. PLGA 50∶50 NPs were a more suitable delivery vehicle for ¹⁷⁷Lu-DOTATATE than PLGA 75∶25 because of higher EE and slower release rate. Reduced renal retention of ¹⁷⁷Lu-DOTATATE and reduced opsonisation strongly advocate the potential of ¹⁷⁷Lu-DOTATATE-PLGA-PEG NPs to reduce radiation dose in PRRT.     

Comparative proteomics of pulmonary tumors with neuroendocrine differentiation

We aimed to evaluate neuroendocrine pulmonary tumors (NEPT) by a novel method involving map tree construction by comparing all of the protein spots. We performed a proteomics analysis to assess the similarities in protein expression between neuroendocrine pulmonary tumors (NEPT), including typical carcinoids (TC), atypical carcinoids (AC), large cell neuroendocrine carcinomas (LCNEC) and small cell carcinomas (SCLC). Total protein lysates were obtained from seven histologically confirmed frozen NEPT tissues, including 1TC, 2 SCLC, and 4 cases ranging from AC to LCNEC. 2-DE demonstrated that TC was similar to normal lung. AC, LCNEC, and SCLC were similar to each other, forming a group separate from TC, however, SCLC at an early stage showed a similarity to TC. MALDI analysis detected 9 surrogate endpoint biomarkers, including eIF5A1, GST M3, cytokeratin 18 (CK 18), FK506-binding protein p59, p63, MAGE-D2, mitochondrial short-chain enoyl-coenzyme A hydratase 1, tranferrin and poly (rC) binding protein 1. Immunohistochemical staining revealed a gradual decrease in expression rate of p63 and CK 18 with poor differentiation of NEPT. Our results demonstrate that (1) the comparative proteomics of NEPT match the WHO classification except for AC and LCNEC; (2) SCLC show differences in their proteomics according to tumor stage; and (3) CK 18 and p63 may be useful as diagnostically and prognostically available markers.     

The biological relevance of gastric neuroendocrine tumors.

Gastric neuroendocrine tumors were originally thought to have a low incidence (three percent). Since endoscopic diagnostic procedures have become clinical routine, they are now found more frequently (relative incidence up to 41 percent). In recent years, classifications have been developed that attempt to consider the biological relevance of these tumors. Four types of gastric neuroendocrine tumor may be distinguished: Type 1 gastric neuroendocrine tumor is most common. It is associated with chronic atrophic fundus gastritis, hypergastrinemia and often with pernicious anemia. Usually it is multicentric and smaller than one cm, does not produce any symptoms and has an excellent prognosis. Type 2 gastric neuroendocrine tumor is second in frequency. It has no association with other diseases, is solitary and has no predilection for a particular localization. It may be larger than 1 cm, produce a carcinoid syndrome or Zollinger-Ellison syndrome and have a metastasis rate of up to 30 percent. Type 3 gastric neuroendocrine tumor is rare and always associated with Zollinger-Ellison syndrome and multiple endocrine neoplasia type I. It occurs as multiple lesions in the gastric body fundus and has a lower metastatic rate than type 2 gastric neuroendocrine tumor. Type 4 gastric neuroendocrine tumor corresponds to a small-cell carcinoma.