Zebrafish as an innovative model for neuroendocrine tumors

Antitumor Activity of Axitinib in Lung Carcinoids: A Preclinical Study

Lung carcinoids (LCs) comprise well-differentiated neuroendocrine tumors classified as typical (TCs) and atypical (ACs) carcinoids. Unfortunately, curative therapies remain elusive for metastatic LCs, which account for 25-30% of cases. This study evaluated the antitumor activity of axitinib (AXI), a second-generation tyrosine kinase inhibitor selectively targeting vascular endothelial growth factor receptors (VEGFR-1, VEGFR-2, VEGFR-3) in human lung TC (NCI-H727, UMC-11, NCI-H835) and AC (NCI-H720) cell lines. In vitro and in vivo (zebrafish) assays were performed following AXI treatment to gather several read-outs about cell viability, cell cycle, the secretion of proangiogenic factors, apoptosis, tumor-induced angiogenesis and migration. AXI demonstrated relevant antitumor activity in human LC cells, with pronounced effects observed in UMC-11 and NCI-H720, characterized by cell cycle perturbation and apoptosis induction. AXI significantly hindered tumor induced-angiogenesis in Tg(fli1a:EGFP)y1 zebrafish embryos implanted with all LC cell lines and also reduced the invasiveness of NCI-H720 cells, as well as the secretion of several proangiogenic factors. In conclusion, our study provides initial evidence supporting the potential anti-tumor activity of AXI in LC, offering a promising basis for future investigations in mammalian animal models and, eventually, progressing to clinical trials.

Models in Pancreatic Neuroendocrine Neoplasms: Current Perspectives and Future Directions

Pancreatic neuroendocrine neoplasms (pNENs) are a heterogeneous group of tumors derived from multiple neuroendocrine origin cell subtypes. Incidence rates for pNENs have steadily risen over the last decade, and outcomes continue to vary widely due to inability to properly screen. These tumors encompass a wide range of functional and non-functional subtypes, with their rarity and slow growth making therapeutic development difficult as most clinically used therapeutics are derived from retrospective analyses. Improved molecular understanding of these cancers has increased our knowledge of the tumor biology for pNENs. Despite these advances in our understanding of pNENs, there remains a dearth of models for further investigation. In this review, we will cover the current field of pNEN models, which include established cell lines, animal models such as mice and zebrafish, and three-dimensional (3D) cell models, and compare their uses in modeling various disease aspects. While no study model is a complete representation of pNEN biology, each has advantages which allow for new scientific understanding of these rare tumors. Future efforts and advancements in technology will continue to create new options in modeling these cancers.

Carcinoid Syndrome: Preclinical Models and Future Therapeutic Strategies

Carcinoid syndrome represents a debilitating paraneoplastic disease, caused by the secretion of several substances, occurring in about 10-40% of patients with well-differentiated neuroendocrine tumors (NETs). The main signs and symptoms associated with carcinoid syndrome are flushing, diarrhea, hypotension, tachycardia, bronchoconstriction, venous telangiectasia, dyspnea and fibrotic complications (mesenteric and retroperitoneal fibrosis, and carcinoid heart disease). Although there are several drugs available for the treatment of carcinoid syndrome, the lack of therapeutic response, poor tolerance or resistance to drugs are often reported. Preclinical models are indispensable tools for investigating the pathogenesis, mechanisms for tumor progression and new therapeutic approaches for cancer. This paper provides a state-of-the-art overview of in vitro and in vivo models in NETs with carcinoid syndrome, highlighting the future developments and therapeutic approaches in this field.

The inhibition of protein translation promotes tumor angiogenic switch

The ‘angiogenic switch’ is critical for tumor progression. However, the pathological details and molecular mechanisms remain incompletely characterized. In this study, we established mammal xenografts in zebrafish to visually investigate the first vessel growth (angiogenic switch) in real-time, by inoculating tumor cells into the perivitelline space of live optically transparent Transgenic (flk1:EGFP) zebrafish larvae. Using this model, we found that hypoxia and hypoxia-inducible factor (HIF) signaling were unnecessary for the angiogenic switch, whereas vascular endothelial growth factor A gene (Vegfa) played a crucial role. Mechanistically, transcriptome analysis showed that the angiogenic switch was characterized by inhibition of translation, but not hypoxia. Phosphorylation of eukaryotic translation initiation factor 2 alpha (Eif2α) and the expression of Vegfa were increased in the angiogenic switch microtumors, and 3D tumor spheroids, and puromycin-treated tumor cells. Vegfa overexpression promoted early onset of the angiogenic switch, whereas Vegfa knockout prevented the first tumor vessel from sprouting. Pretreatment of tumor cells with puromycin promoted the angiogenic switch in vivo similarly to Vegfa overexpression, whereas Vegfa knockdown suppressed the increase. This study provides direc and dynamic in vivo evidences that inhibition of translation, but not hypoxia or HIF signaling promotes the angiogenic switch in tumor by increasing Vegfa transcription.

Preclinical Models of Neuroendocrine Neoplasia

Neuroendocrine neoplasia (NENs) are a complex and heterogeneous group of cancers that can arise from neuroendocrine tissues throughout the body and differentiate them from other tumors. Their low incidence and high diversity make many of them orphan conditions characterized by a low incidence and few dedicated clinical trials. Study of the molecular and genetic nature of these diseases is limited in comparison to more common cancers and more dependent on preclinical models, including both in vitro models (such as cell lines and 3D models) and in vivo models (such as patient derived xenografts (PDXs) and genetically-engineered mouse models (GEMMs)). While preclinical models do not fully recapitulate the nature of these cancers in patients, they are useful tools in investigation of the basic biology and early-stage investigation for evaluation of treatments for these cancers. We review available preclinical models for each type of NEN and discuss their history as well as their current use and translation.

Preclinical Evaluation of Novel Tyrosine-Kinase Inhibitors in Medullary Thyroid Cancer

Simple Summary

Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor arising from parafollicular calcitonin-secreting C cells of the thyroid. Most of the patients affected by MTC, especially the familial form, harbor a mutation of the RET proto-oncogene. In patients with advanced disease, medical therapy is represented by two tyrosine-kinase inhibitors: cabozantinib and vandetanib. However, their usage is limited by several adverse events and drug-resistance onset. The aim of this preclinical study was to evaluate the antitumor activity of novel molecules for the therapy of MTC: SU5402, an inhibitor of the fibroblast growth factor receptor type 1 (FGFR-1) and vascular endothelial growth factor receptor (VEGFR)-2; sulfatinib, a multi-target kinase inhibitor selective for FGFR-1 and the VEGFR-1, -2, and -3; SPP86, a RET-specific inhibitor. Our results suggest a potential role in targeting the FGFR and VEGFR signaling pathways as an alternative strategy for resistant tumors and a significative antitumor activity of this new RET-specific inhibitor.

Abstract

Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor arising from parafollicular C cells of the thyroid gland. In this preclinical study, we tested three tyrosine-kinase inhibitors (TKIs): SU5402, a selective inhibitor of fibroblast growth factor receptor (FGFR)-1 and vascular endothelial growth factor receptor (VEGFR)-2; sulfatinib, an inhibitor of FGFR-1 and VEGFR-1, -2, -3; and SPP86, a RET-specific inhibitor. The effects of these compounds were evaluated in vitro in two human MTC cell lines (TT and MZ-CRC-1), and in vivo using xenografts of MTC cells in zebrafish embryos. SU5402, sulfatinib and SPP86 decreased cell viability. Sulfatinib and SPP86 significantly induced apoptosis in both cell lines. Sulfatinib and SPP86 inhibited the migration of TT and MZCRC-1 cells, while SU5402 was able to inhibit migration only in TT cells. In vivo we observed a significant reduction in TT cell-induced angiogenesis in zebrafish embryos after incubation with sulfatinib and SPP86. In conclusion, sulfatinib and SPP86 displayed a relevant antitumor activity both in vitro and in vivo. Moreover, this work suggests the potential utility of targeting FGFR and VEGFR signaling pathways as an alternative therapy for MTC.

Modeling Lung Carcinoids with Zebrafish Tumor Xenograft

Lung carcinoids are neuroendocrine tumors that comprise well-differentiated typical (TCs) and atypical carcinoids (ACs). Preclinical models are indispensable for cancer drug screening since current therapies for advanced carcinoids are not curative. We aimed to develop a novel in vivo model of lung carcinoids based on the xenograft of lung TC (NCI-H835, UMC-11, and NCI-H727) and AC (NCI-H720) cell lines and patient-derived cell cultures in Tg(fli1a:EGFP)^y1 zebrafish embryos. We exploited this platform to test the anti-tumor activity of sulfatinib. The tumorigenic potential of TC and AC implanted cells was evaluated by the quantification of tumor-induced angiogenesis and tumor cell migration as early as 24 h post-injection (hpi). The characterization of tumor-induced angiogenesis was performed in vivo and in real time, coupling the tumor xenograft with selective plane illumination microscopy on implanted zebrafish embryos. TC-implanted cells displayed a higher pro-angiogenic potential compared to AC cells, which inversely showed a relevant migratory behavior within 48 hpi. Sulfatinib inhibited tumor-induced angiogenesis, without affecting tumor cell spread in both TC and AC implanted embryos. In conclusion, zebrafish embryos implanted with TC and AC cells faithfully recapitulate the tumor behavior of human lung carcinoids and appear to be a promising platform for drug screening.

Angpt2/Tie2 autostimulatory loop controls tumorigenesis

Invasive nonfunctioning (NF) pituitary neuroendocrine tumors (PitNETs) are non‐resectable neoplasms associated with frequent relapses and significant comorbidities. As the current therapies of NF‐PitNETs often fail, new therapeutic targets are needed. The observation that circulating angiopoietin‐2 (ANGPT2) is elevated in patients with NF‐PitNET and correlates with tumor aggressiveness prompted us to investigate the ANGPT2/TIE2 axis in NF‐PitNETs in the GH3 PitNET cell line, primary human NF‐PitNET cells, xenografts in zebrafish and mice, and in MENX rats, the only autochthonous NF‐PitNET model. We show that PitNET cells express a functional TIE2 receptor and secrete bioactive ANGPT2, which promotes, besides angiogenesis, tumor cell growth in an autocrine and paracrine fashion. ANGPT2 stimulation of TIE2 in tumor cells activates downstream cell proliferation signals, as previously demonstrated in endothelial cells (ECs). Tie2 gene deletion blunts PitNETs growth in xenograft models, and pharmacological inhibition of Angpt2/Tie2 signaling antagonizes PitNETs in primary cell cultures, tumor xenografts in mice, and in MENX rats. Thus, the ANGPT2/TIE2 axis provides an exploitable therapeutic target in NF‐PitNETs and possibly in other tumors expressing ANGPT2/TIE2. The ability of tumor cells to coopt angiogenic signals classically viewed as EC‐specific expands our view on the microenvironmental cues that are essential for tumor progression.

The crucial role of model systems in understanding the complexity of cell signaling in human neurocristopathies

Animal models are useful to study the molecular, cellular, and morphogenetic mechanisms underlying normal and pathological development. Cell-based study models have emerged as an alternative approach to study many aspects of human embryonic development and disease. The neural crest (NC) is a transient, multipotent, and migratory embryonic cell population that generates a diverse group of cell types that arises during vertebrate development. The abnormal formation or development of the NC results in neurocristopathies (NCPs), which are characterized by a broad spectrum of functional and morphological alterations. The impaired molecular mechanisms that give rise to these multiphenotypic diseases are not entirely clear yet. This fact, added to the high incidence of these disorders in the newborn population, has led to the development of systematic approaches for their understanding. In this article, we have systematically reviewed the ways in which experimentation with different animal and cell model systems has improved our knowledge of NCPs, and how these advances might contribute to the development of better diagnostic and therapeutic tools for the treatment of these pathologies. This article is categorized under: Congenital Diseases > Genetics/Genomics/Epigenetics Congenital Diseases > Stem Cells and Development Congenital Diseases > Molecular and Cellular Physiology Neurological Diseases > Genetics/Genomics/Epigenetics.

Tools in Pharmacogenomics Biomarker Identification for Cancer Patients

The understanding of the biological differences which underlie the inter-individual variability in drug response improved the efficacy of cancer therapy in the era of precision medicine. In fact molecularly targeted drugs and immunotherapy represent a revolution in cancer treatment. The identification of genetic predictive and/or prognostic biomarkers linked to drug pharmacokinetics (PK) and pharmacodynamics (PD) is allowed by the development of high-throughput omics tools for detecting and understanding biological differences among individuals, in order to improve drug efficacy and minimize risk of toxicity. Personalized medicine in cancer treatment reduces costs of the healthcare system. Unfortunately, pharmacogenomics biomarkers discovery is influenced by complexity, need of high-quality evidence, and a validation process for regulatory purposes. This chapter is focused on the critic analysis of presently available pharmacogenomics tools for discovering or testing genetic polymorphic variants in drug metabolizing enzyme to be introduced in clinical practice for the prospective stratification of cancer patients.

Long-term effects of somatostatin analogues in rat GH-secreting pituitary tumor cell lines

PURPOSE

First-generation somatostatin analogs, octreotide (OCT) and lanreotide, are the cornerstone for the medical treatment of growth hormone (GH)-secreting pituitary tumors. A new multireceptor analog, such as pasireotide (PAS), showed better activity than OCT in long-term treatment of patients with acromegaly, but modulation of intracellular key processes is still unclear in vitro. In this study, we evaluated the antitumor activity of OCT and PAS in two GH-secreting pituitary tumor cell lines, GH3 and GH4C1, after a long-term incubation.

METHODS

The effects of PAS and OCT on the cell viability, cell cycle, apoptosis, GH secretion, and tumor-induced angiogenesis have been evaluated through a colorimetric method (MTS Assay), DNA flow cytometry with propidium iodide, and Annexin V-FITC/propidium iodide staining, ELISA assay and zebrafish platform, respectively.

RESULTS

PAS showed a more potent antitumor activity compared to OCT in GH3 cell line exerted through inhibition of cell viability, perturbation of cell cycle progression, and induction of apoptosis after 6 days of incubation. A concomitant decrease in GH secretion has been observed after 2 days of incubation only with PAS. No effect on tumor-induced angiogenesis has been reported after treatment with OCT or PAS in zebrafish/tumor xenograft model.

CONCLUSION

Long-term incubation with PAS showed a more potent antitumor activity than that reported after OCT in GH3 cells, mainly modulated by a cell cycle perturbation and a relevant induction in apoptosis.

Zebrafish Avatar to Develop Precision Breast Cancer Therapies

BACKGROUND

Zebrafish (Danio rerio) is a vertebrate that has become a popular alternative model for the cellular and molecular study of human tumors and for drug testing and validating approaches. Notably, zebrafish embryos, thanks to their accessibility, allow rapid collection of in vivo results prodromal to validation in the murine models in respect to the 3R principles. The generation of tumor xenograft in zebrafish embryos and larvae, or zebrafish avatar, represents a unique opportunity to study tumor growth, angiogenesis, cell invasion and metastatic dissemination, interaction between tumor and host in vivo avoiding immunogenic rejection, representing a promising platform for the translational research and personalized therapies.

OBJECTIVE

In this mini-review we report recent advances in breast cancer research and drug testing that took advantage of the zebrafish xenograft model using both breast cancer cell lines and patient's biopsy.

CONCLUSION

Patient derived xenograft, together with the gene editing, the omics biotechnology, the in vivo time lapse imaging and the high-throughput screening that are already set up and largely used in zebrafish, could represent a step forward towards precision and personalized medicine in the breast cancer research field.

Vandetanib versus Cabozantinib in Medullary Thyroid Carcinoma: A Focus on Anti-Angiogenic Effects in Zebrafish Model

Medullary thyroid carcinoma (MTC) is a tumor deriving from the thyroid C cells. Vandetanib (VAN) and cabozantinib (CAB) are two tyrosine kinase inhibitors targeting REarranged during Transfection (RET) and other kinase receptors and are approved for the treatment of advanced MTC. We aim to compare the in vitro and in vivo anti-tumor activity of VAN and CAB in MTC. The effects of VAN and CAB on viability, cell cycle, and apoptosis of TT and MZ-CRC-1 cells are evaluated in vitro using an MTT assay, DNA flow cytometry with propidium iodide, and Annexin V-FITC/propidium iodide staining, respectively. In vivo, the anti-angiogenic potential of VAN and CAB is evaluated in Tg(fli1a:EGFP)^y1 transgenic fluorescent zebrafish embryos by analyzing the effects on the physiological development of the sub-intestinal vein plexus and the tumor-induced angiogenesis after TT and MZ-CRC-1 xenotransplantation. VAN and CAB exert comparable effects on TT and MZ-CRC-1 viability inhibition and cell cycle perturbation, and stimulated apoptosis with a prominent effect by VAN in MZ-CRC-1 and CAB in TT cells. Regarding zebrafish, both drugs inhibit angiogenesis in a dose-dependent manner, in particular CAB shows a more potent anti-angiogenic activity than VAN. To conclude, although VAN and CAB show comparable antiproliferative effects in MTC, the anti-angiogenic activity of CAB appears to be more relevant.

Efficacy of a Novel Second-Generation Somatostatin-Dopamine Chimera (TBR-065) in Human Medullary Thyroid Cancer: A Preclinical Study

INTRODUCTION

Somatostatin and dopamine (DA) receptors have a pivotal role in controlling hormone secretion and cell proliferation in different neuroendocrine neoplasms, including medullary thyroid cancer (MTC). In the present preclinical study, we evaluated the anti-tumor activity of TBR-065 (formerly BIM-23B065), a second-generation somatostatin-DA chimera, in 2 human MTC cell lines.

METHODS

The effects of lanreotide (LAN) and TBR-065 on cell growth and proliferation, calcitonin (CT) secretion, cell cycle, apoptosis, cell migration, and tumor-induced angiogenesis have been evaluated through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, DNA flow cytometry with propidium iodide (PI), Annexin V-FITC/PI staining, electrochemiluminescence immuno assay, wound-healing assay, and zebrafish platform, respectively.

RESULTS

TBR-065 exerted a more prominent anti-tumor activity than LAN in both MTC cell lines, as shown by inhibition of cell proliferation (maximal inhibition in TT: -50.3 and -37.6%, respectively; in MZ-CRC-1: -58.8 and -27%, respectively) and migration (in TT: -42.7 and -22.9%, respectively; in MZ-CRC-1: -75.5 and -58.2%, respectively). Only the new chimera decreased significantly the fraction of cells in S phase (TT: -33.8%; MZ-CRC-1: -18.8%) and increased cells in G2/M phase (TT: +13%; MZ-CRC-1: +30.5%). In addition, TBR-065 exerted a more prominent pro-apoptotic effect than LAN in TT cells. A concomitant decrease in CT secretion was observed after 2 days of incubation with both drugs, with a more relevant effect of TBR-065. However, neither LAN nor TBR-065 showed any effect on tumor-induced angiogenesis, as evaluated using a zebrafish/tumor xenograft model.

DISCUSSION/CONCLUSION

In MTC cell lines, a second-generation somatostatin-DA analog, TBR-065, exerts a more relevant anti-tumor activity than LAN, through modulation of cell cycle, induction of apoptosis, and reduction in migration. Further studies are required to establish whether TBR-065 has comparable potent inhibitory effects on tumor growth in vivo.

Jagged Ligands Enhance the Pro-Angiogenic Activity of Multiple Myeloma Cells

Simple Summary

The Jagged family of ligands are aberrantly expressed during multiple myeloma progression and contributes to activate Notch signaling both in myeloma cells and in the nearby bone marrow cell populations activating several pro-tumor effects. This work elucidates, in vitro, in vivo as well as in patients’ bone marrow biopsies, different mechanisms by which tumor cell-derived Jagged1 and 2 contribute to myeloma-associated angiogenesis. These include the ability to induce myeloma and bone marrow stromal cell secretion of VEGF along with a direct activation of the pro-angiogenic Notch signaling pathway in endothelial cells. This research provides a rational for a Jagged-directed therapy in multiple myeloma.

Abstract

Multiple myeloma (MM) is an incurable plasma cell malignancy arising primarily within the bone marrow (BM). During MM progression, different modifications occur in the tumor cells and BM microenvironment, including the angiogenic shift characterized by the increased capability of endothelial cells to organize a network, migrate and express angiogenic factors, including vascular endothelial growth factor (VEGF). Here, we studied the functional outcome of the dysregulation of Notch ligands, Jagged1 and Jagged2, occurring during disease progression, on the angiogenic potential of MM cells and BM stromal cells (BMSCs). Jagged1–2 expression was modulated by RNA interference or soluble peptide administration, and the effects on the MM cell lines’ ability to induce human pulmonary artery cells (HPAECs) angiogenesis or to indirectly increase the BMSC angiogenic potential was analyzed in vitro; in vivo validation was performed on a zebrafish model and MM patients’ BM biopsies. Overall, our results indicate that the MM-derived Jagged ligands (1) increase the tumor cell angiogenic potential by directly triggering Notch activation in the HPAECs or stimulating the release of angiogenic factors, i.e., VEGF; and (2) stimulate the BMSCs to promote angiogenesis through VEGF secretion. The observed pro-angiogenic effect of Notch activation in the BM during MM progression provides further evidence of the potential of a therapy targeting the Jagged ligands.

Modeling oncolytic virus dynamics in the tumor microenvironment using zebrafish

We have adapted a zebrafish (Danio rerio) tumor xenograft model for use in the study of oncolytic virotherapy. Following implantation of mammalian cancer cells into the perivitelline space of developing zebrafish embryos, both local and intravenous oncolytic virus treatments produce a tumor-specific infection with measurable antitumor effects. Tumor cells are injected at 48 h post fertilization, with oncolytic virus treatment then being administered 24 h later to allow for an initial period of tumor development and angiogenesis. Confocal fluorescent imaging is used to quantify dynamics within the tumor environment. The natural translucency of zebrafish at the embryo stage, coupled with the availability of strains with fluorescent immune and endothelial cell reporter lines, gives the model broad potential to allow for real time, in vivo investigation of important events within tumors throughout the course of virotherapy. Zebrafish xenografts offer a system with biologic fidelity to processes in human cancer development that influence oncolytic virus efficacy, and to our knowledge this is the first demonstration of the model's use in the context of virotherapy. Compared with other models, our protocol offers a powerful, inexpensive approach to evaluating novel oncolytic viruses and oncolytic virus-based combination therapies, with potential application to investigating the impacts of virotherapy on immune response, tumor vasculature, and metastatic disease.

Experimental Evidence and Clinical Implications of Pituitary Adenoma Stem Cells

Pituitary adenomas, accounting for 15% of diagnosed intracranial neoplasms, are usually benign and pharmacologically and surgically treatable; however, the critical location, mass effects and hormone hypersecretion sustain their significant morbidity. Approximately 35% of pituitary tumors show a less benign course since they are highly proliferative and invasive, poorly resectable, and likely recurring. The latest WHO classification of pituitary tumors includes pituitary transcription factor assessment to determine adenohypophysis cell lineages and accurate designation of adenomas, nevertheless little is known about molecular and cellular pathways which contribute to pituitary tumorigenesis. In malignant tumors the identification of cancer stem cells radically changed the concepts of both tumorigenesis and pharmacological approaches. Cancer stem cells are defined as a subset of undifferentiated transformed cells from which the bulk of cancer cells populating a tumor mass is generated. These cells are able to self-renew, promoting tumor progression and recurrence of malignant tumors, also conferring cytotoxic drug resistance. On the other hand, the existence of stem cells within benign tumors is still debated. The presence of adult stem cells in human and murine pituitaries where they sustain the high plasticity of hormone-producing cells, allowed the hypothesis that putative tumor stem cells might exist in pituitary adenomas, reinforcing the concept that the cancer stem cell model could also be applied to pituitary tumorigenesis. In the last few years, the isolation and phenotypic characterization of putative pituitary adenoma stem-like cells was performed using a wide and heterogeneous variety of experimental models and techniques, although the role of these cells in adenoma initiation and progression is still not completely definite. The assessment of possible pituitary adenoma-initiating cell population would be of extreme relevance to better understand pituitary tumor biology and to identify novel potential diagnostic markers and pharmacological targets. In this review, we summarize the most updated studies focused on the definition of pituitary adenoma stem cell phenotype and functional features, highlighting the biological processes and intracellular pathways potentially involved in driving tumor growth, relapse, and therapy resistance.

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

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

Urotensin-II-Targeted Liposomes as a New Drug Delivery System towards Prostate and Colon Cancer Cells

Urotensin-II (UT-II) and its receptor (UTR) are involved in the occurrence of different epithelial cancers. In particular, UTR was found overexpressed on colon, bladder, and prostate cancer cells. The conjugation of ligands, able to specifically bind receptors that are overexpressed on cancer cells, to liposome surface represents an efficient active targeting strategy to enhance selectivity and efficiency of drug delivery systems. The aim of this study was to develop liposomes conjugated with UT-II (LipoUT) for efficient targeting of cancer cells that overexpress UTR. The liposomes had a mean diameter between 150 nm and 160 nm with a narrow size distribution (PI ≤ 0.1) and a doxo encapsulation efficiency of 96%. Moreover, the conjugation of UT-II to liposomes weakly reduced the zeta potential. We evaluated UTR expression on prostate (DU145, PC3, and LNCaP) and colon (WIDR and LoVo) cancer cells by FACS and western blotting analysis. UTR protein was expressed in all the tested cell lines; the level of expression was higher in WIDR, PC3, and LNCaP cells compared with LoVo and DU145. MTT cell viability assay showed that LipoUT-doxo was more active than Lipo-doxo on the growth inhibition of cells that overexpressed UTR (PC3, LNCaP, and WIDR) while in LoVo and DU145 cell lines, the activity was similar to or lower than that one of Lipo-doxo, respectively. Moreover, we found that cell uptake of Bodipy-labeled liposomes in PC3 and DU145 was higher for LipoUT than the not-armed counterparts but at higher extent in UTR overexpressing PC3 cells (about 2-fold higher), as evaluated by both confocal and FACS. In conclusion, the encapsulation of doxo in UT-II-targeted liposomes potentiated its delivery in UTR-overexpressing cells and could represent a new tool for the targeting of prostate and colon cancer.

Resistance to targeted treatment of gastroenteropancreatic neuroendocrine tumors

The mammalian target of rapamycin (mTOR) is part of the phosphoinositide-3-kinase (PI3K)/protein kinase B (Akt)/mTOR signaling. The PI3K/Akt/mTOR pathway has a pivotal role in the oncogenesis of neuroendocrine tumors (NETs). In addition, vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) drive angiogenesis in NETs and therefore contributes to neuroendocrine tumor development. Hence, mTOR and angiogenesis inhibitors have been developed. Everolimus, a first-generation mTOR inhibitor, has shown significant survival benefit in advanced gastroenteropancreatic NETs. Sunitinib, a pan-tyrosine kinase inhibitor that targets the VEGF receptor, has proven to increase progression-free survival in advanced pancreatic NETs. Nevertheless, primary and acquired resistance to rapalogs and sunitinib has limited the clinical benefit for NET patients. Despite the identification of multiple molecular mechanisms of resistance, no predictive biomarker has made it to the clinic. This review is focused on the mTOR signaling and angiogenesis in NET, the molecular mechanisms of primary and acquired resistance to everolimus and sunitinib and how to overcome this resistance by alternative drug compounds.

Evaluation of anaesthetic protocols for laboratory adult zebrafish (Danio rerio)

In the last decades, the use of zebrafish (Danio rerio) in biomedical research has increased. Anaesthesia is daily used in fish during experimental procedures to avoid discomfort, stress or pain. Also, fish welfare and the reliability of results can be compromised if an unsuitable anaesthetic protocol is used. Therefore, we aimed to refine anaesthetic protocols to be used in adult zebrafish by evaluating the efficacy of different anaesthetics, used alone or in combination. For that, zebrafish were randomly assigned to 8 different groups: 100 μg/mLMS-222 (MS); 0.2 μg/mL etomidate (E); 0.2 μg/mL etomidate + 100 μg/mL lidocaine (E+L); 1.25 μg/mL propofol (P); 1.25 μg/mL propofol + 100 μg/mL lidocaine (P+L); 100 μg/mL ketamine (K); 100 μg/mL ketamine + 1.25 μg/mL medetomidine (K+M); and 100 μg/mL ketamine + 1.25 μg/mL medetomidine/3.125 μg/mL atipamezole (K+M/A). The animals were placed in an anaesthetic water bath, then, the following parameters were registered: time for equilibrium loss and anaesthesia induction, loss of sensitivity to soft and painful stimuli, respiratory rate, recovery time, and activity after recovery. The combined forms of E+L, P+L and K+M were the fastest to induce a surgical anaesthetic stage. Nevertheless, E+L induced respiratory depression, while K+M was shown to have the longer recovery time compared to MS-222, even when atipamezole was added. In conclusion, the P+L combination was shown to provide good anaesthesia with analgesia, without causing a major respiratory depression, providing as well a quick recovery, similar to MS-222.

Gastroenteropancreatic neuroendocrine neoplasms: genes, therapies and models

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) refer to a group of heterogeneous cancers of neuroendocrine cell phenotype that mainly fall into one of two subtypes: gastroenteropancreatic neuroendocrine tumors (GEP-NETs; well differentiated) or gastroenteropancreatic neuroendocrine carcinomas (GEP-NECs; poorly differentiated). Although originally defined as orphan cancers, their steadily increasing incidence highlights the need to better understand their etiology. Accumulating epidemiological and clinical data have shed light on the pathological characteristics of these diseases. However, the relatively low number of patients has hampered conducting large-scale clinical trials and hence the development of novel treatment strategies. To overcome this limitation, tractable disease models that faithfully reflect clinical features of these diseases are needed. In this Review, we summarize the current understanding of the genetics and biology of these diseases based on conventional disease models, such as genetically engineered mouse models (GEMMs) and cell lines, and discuss the phenotypic differences between the models and affected humans. We also highlight the emerging disease models derived from human clinical samples, including patient-derived xenograft models and organoids, which may provide biological and therapeutic insights into GEP-NENs.

Non-mammalian models of multiple endocrine neoplasia type 2

Twenty-five years ago, RET was identified as the primary driver of multiple endocrine neoplasia type 2 (MEN2) syndrome. MEN2 is characterized by several transformation events including pheochromocytoma, parathyroid adenoma and, especially penetrant, medullary thyroid carcinoma (MTC). Overall, MTC is a rare but aggressive type of thyroid cancer for which no effective treatment currently exists. Surgery, radiation, radioisotope treatment and chemotherapeutics have all shown limited success, and none of these approaches have proven durable in advanced disease. Non-mammalian models that incorporate the oncogenic RET isoforms associated with MEN2 and other RET-associated diseases have been useful in delineating mechanisms underlying disease progression. These models have also identified novel targeted therapies as single agents and as combinations. These studies highlight the importance of modeling disease in the context of the whole animal, accounting for the complex interplay between tumor and normal cells in controlling disease progression as well as response to therapy. With convenient access to whole genome sequencing data from expanded thyroid cancer patient cohorts, non-mammalian models will become more complex, sophisticated and continue to complement future mammalian studies. In this review, we explore the contributions of non-mammalian models to our understanding of thyroid cancer including MTC, with a focus on Danio rerio and Drosophila melanogaster (fish and fly) models.

Utilizing Zebrafish to Identify Anti-(Lymph)Angiogenic Compounds for Cancer Treatment: Promise and Future Challenges

Cancer metastasis which predominantly occurs through blood and lymphatic vessels, is the leading cause of death in cancer patients. Consequently, several anti-angiogenic agents have been approved as therapeutic agents for human cancers such as metastatic renal cell carcinoma. Also, anti-lymphangiogenic drugs such as monoclonal antibodies VGX-100 and IMC-3C5 have undergone phase I clinical trials for advanced and metastatic solid tumors. Although anti-tumor-associated angiogenesis has proven to be a promising therapeutic strategy for human cancers, this approach is fraught with toxicities and development of drug resistance. This emphasizes the need for alternative anti-(lymph)angiogenic drugs. The use of zebrafish has become accepted as an established model for high-throughput screening, vascular biology, and cancer research. Importantly, various zebrafish transgenic lines have now been generated that can readily discriminate different vascular compartments. This now enables detailed in vivo studies that are relevant to both human physiological and tumor (lymph)angiogenesis to be conducted in zebrafish. This review highlights recent advancements in the zebrafish anti-vascular screening platform and showcases promising new anti-(lymph)angiogenic compounds that have been derived from this model. In addition, this review discusses the promises and challenges of the zebrafish model in the context of anti-(lymph)angiogenic compound discovery for cancer treatment.

Animal models of MEN1

Animal models of cancer have been instrumental in advancing our understanding of the biology of tumor initiation and progression, in studying gene function and in performing preclinical studies aimed at testing novel therapies. Several animal models of the MEN1 syndrome have been generated in different organisms by introducing loss-of-function mutations in the orthologues of the human MEN1 gene. In this review, we will discuss MEN1 and MEN1-like models in Drosophila, mice and rats. These model systems with their specific advantages and limitations have contributed to elucidate the function of Menin in tumorigenesis, which turned out to be remarkably conserved from flies to mammals, as well as the biology of the disease. Mouse models of MEN1 closely resemble the human disease in terms of tumor spectrum and associated hormonal changes, although individual tumor frequencies are variable. Rats affected by the MENX (MEN1-like) syndrome share some features with MEN1 patients albeit they bear a germline mutation in Cdkn1b (p27) and not in Men1 Both Men1-knockout mice and MENX rats have been exploited for therapy-response studies testing novel drugs for efficacy against neuroendocrine tumors (NETs) and have provided promising leads for novel therapies. In addition to presenting well-established models of MEN1, we also discuss potential models which, if implemented, might broaden even further our knowledge of neuroendocrine tumorigenesis. In the future, patient-derived xenografts in zebrafish or mice might allow us to expand the tool-box currently available for preclinical studies of MEN1-associated tumors.

Patient-derived xenograft in zebrafish embryos: a new platform for translational research in neuroendocrine tumors

Preclinical research on neuroendocrine tumors usually involves immortalized cell lines and few animal models. In the present study we described an in vivo model based on patient-derived xenografts of neuroendocrine tumor cells in zebrafish (Danio rerio) embryos, allowing a rapid analysis of the angiogenic and invasive potential. Patient-derived neuroendocrine tumor cells were transplanted in 48 hours post-fertilization Tg(fli1a:EGFP) ^y1 zebrafish embryos that express enhanced green fluorescent protein in the entire vasculature. Neuroendocrine tumor cells, stained with CM-Dil, were injected into the subperidermal (perivitelline) space, close to the developing subintestinal venous plexus. A proper control group, represented by zebrafish injected with only D-PBS, was included in this study. Angiogenic and invasive potentials of each patient-derived xenograft were evaluated by both epifluorescence and confocal microscopes. Six out of eight neuroendocrine tumor samples were successfully transplanted in zebrafish embryos. Although the implanted tumor mass had a limited size (about 100 cells for embryos), patient-derived xenografts showed pro-angiogenic (5 cases) and invasive (6 cases) behaviors within 48 hours post injection. Patient-derived xenograft in zebrafish embryos appears to be a reliable in vivo preclinical model for neuroendocrine tumors, tumors with often limited cell availability. The rapidity of this procedure makes our model a promising platform to perform preclinical drug screening and opens a new scenario for personalized treatment in patients with neuroendocrine tumors.

Dopamine receptor type 2 (DRD2) and somatostatin receptor type 2 (SSTR2) agonists are effective in inhibiting proliferation of progenitor/stem-like cells isolated from nonfunctioning pituitary tumors

The role of progenitor/stem cells in pituitary tumorigenesis, resistance to pharmacological treatments and tumor recurrence is still unclear. This study investigated the presence of progenitor/stem cells in non-functioning pituitary tumors (NFPTs) and tested the efficacy of dopamine receptor type 2 (DRD2) and somatostatin receptor type 2 (SSTR2) agonists to inhibit in vitro proliferation. They found that 70% of 46 NFPTs formed spheres co-expressing stem cell markers, transcription factors (DAX1, SF1, ERG1) and gonadotropins. Analysis of tumor behavior showed that spheres formation was associated with tumor invasiveness (OR = 3,96; IC: 1.05-14.88, p = 0.036). The in vitro reduction of cell proliferation by DRD2 and SSTR2 agonists (31 ± 17% and 35 ± 13% inhibition, respectively, p < 0.01 vs. basal) occurring in about a half of NFPTs cells was conserved in the corresponding spheres. Accordingly, these drugs increased cyclin-dependent kinase inhibitor p27 and decreased cyclin D3 expression in spheres. In conclusion, they provided further evidence for the existence of cells with a progenitor/stem cells-like phenotype in the majority of NFPTs, particularly in those with invasive behavior, and demonstrated that the antiproliferative effects of dopaminergic and somatostatinergic drugs were maintained in progenitor/stem-like cells.

Animal models of medullary thyroid cancer: state of the art and view to the future

Medullary thyroid carcinoma is a neuroendocrine tumour originating from parafollicular C cells accounting for 5-10% of thyroid cancers. Increased understanding of disease-specific molecular targets of therapy has led to the regulatory approval of two drugs (vandetanib and cabozantinib) for the treatment of medullary thyroid carcinoma. These drugs increase progression-free survival; however, they are often poorly tolerated and most treatment responses are transient. Animal models are indispensable tools for investigating the pathogenesis, mechanisms for tumour invasion and metastasis and new therapeutic approaches for cancer. Unfortunately, only few models are available for medullary thyroid carcinoma. This review provides an overview of the state of the art of animal models in medullary thyroid carcinoma and highlights future developments in this field, with the aim of addressing salient features and clinical relevance.

Imaging Cancer Angiogenesis and Metastasis in a Zebrafish Embryo Model

Tumor angiogenesis and metastasis are key steps of cancer progression. In vitro and animal model studies have contributed to partially elucidating the mechanisms involved in these processes and in developing therapies. Besides the improvements in fundamental research and the optimization of therapeutic regimes, cancer still remains a major health threatening condition and therefore the development of new models is needed. The zebrafish is a powerful tool to study tumor angiogenesis and metastasis, because it allows the visualization of fluorescently labelled tumor cells inducing vessel remodeling, disseminating and invading surrounding tissues in a whole transparent embryo. The embryo model has also been used to address the contribution of the tumor stroma in sustaining tumor angiogenesis and spreading. Simultaneously, new anti-angiogenic drugs and compounds affecting malignant cell survival and migration can be tested by simply adding the compound into the water of living embryos. Therefore the zebrafish model offers the opportunity to gain more knowledge on cancer angiogenesis and metastasis in vivo with the final aim of providing new translational insights into therapeutic approaches to help patients.

Phenotypical and Pharmacological Characterization of Stem-Like Cells in Human Pituitary Adenomas

The presence and functional role of tumor stem cells in benign tumors, and in human pituitary adenomas in particular, is a debated issue that still lacks a definitive formal demonstration. Fifty-six surgical specimens of human pituitary adenomas were processed to establish tumor stem-like cultures by selection and expansion in stem cell-permissive medium or isolating CD133-expressing cells. Phenotypic and functional characterization of these cells was performed (1) ex vivo, by immunohistochemistry analysis on paraffin-embedded tissues; (2) in vitro, attesting marker expression, proliferation, self-renewal, differentiation, and drug sensitivity; and (3) in vivo, using a zebrafish model. Within pituitary adenomas, we identified rare cell populations expressing stem cell markers but not pituitary hormones; we isolated and expanded in vitro these cells, obtaining fibroblast-free, stem-like cultures from 38 pituitary adenoma samples. These cells grow as spheroids, express stem cell markers (Oct4, Sox2, CD133, and nestin), show sustained in vitro proliferation as compared to primary cultures of differentiated pituitary adenoma cells, and are able to differentiate in hormone-expressing pituitary cells. Besides, pituisphere cells, apparently not tumorigenic in mice, engrafted in zebrafish embryos, inducing pro-angiogenic and invasive responses. Finally, pituitary adenoma stem-like cells express regulatory pituitary receptors (D2R, SSTR2, and SSTR5), whose activation by a dopamine/somatostatin chimeric agonist exerts antiproliferative effects. In conclusion, we provide evidence that human pituitary adenomas contain a subpopulation fulfilling biological and phenotypical signatures of tumor stem cells that may represent novel therapeutic targets for therapy-resistant tumors.

Advances in clinical and basic research of gastroentero-pancreatic neuroendocrine neoplasms

Gastroentero-pancreatic neuroendocrine neoplasms (GEP-NENs) are a group of relatively rare tumors, which mainly originate from the peptidergic neuron and neuroendocrine cells of the gastroentero-pancreatic system. They are characterized by secretion of peptide hormones and neuroendocrine markers (such as synaptic vesicle proteins and chromaffin granule A). Surgery is the most effective therapy for GEP-NENs at early stages. For GEP-NENs at progressive stages, biological target therapies have aroused great interest. Current studies about the molecular basis of biological target therapies have focused on the GEP-NEN gene mutations and related signaling pathways. These studies have led to the clinical application with significant progress in GEP-NEN treatment. In this paper, we review the recent advances in the clinical and basic research of GEP-NENs.

The study of glioma by xenotransplantation in zebrafish early life stages

Zebrafish (Danio rerio) and their transparent embryos are becoming an increasingly popular tool for studying processes involved in tumor progression and in the search for novel tumor treatment approaches. The xenotransplantation of fluorescently labeled mammalian cancer cells into zebrafish embryos is an approach enabling relatively high-throughput in vivo analyses. The small size of the embryos as well as the relative simplicity of their manipulation and maintenance allow for large numbers of embryos to be processed efficiently in a short time and at low cost. Furthermore, the possibility of fluorescence microscopic imaging of tumor progression within zebrafish embryos and larvae holds unprecedented potential for the real-time visualization of these processes in vivo. This review presents the methodologies of xenotransplantation studies on zebrafish involving research on tumor invasion, proliferation, tumor-induced angiogenesis and screening for antitumor therapeutics. We further focus on the application of these zebrafish to the study of glioma; in particular, its most common and malignant form, glioblastoma.

Zebrafish: a new companion for translational research in oncology

In an era of high-throughput "omic" technologies, the unprecedented amount of data that can be generated presents a significant opportunity but simultaneously an even greater challenge for oncologists trying to provide personalized treatment. Classically, preclinical testing of new targets and identification of active compounds against those targets have entailed the extensive use of established human cell lines, as well as genetically modified mouse tumor models. Patient-derived xenografts in zebrafish may in the near future provide a platform for selecting an appropriate personalized therapy and together with zebrafish transgenic tumor models represent an alternative vehicle for drug development. The zebrafish is readily genetically modified. The transparency of zebrafish embryos and the recent development of pigment-deficient zebrafish afford researchers the valuable capacity to observe directly cancer formation and progression in a live vertebrate host. The zebrafish is amenable to transplantation assays that test the serial passage of fluorescently labeled tumor cells as well as their capacity to disseminate and/or metastasize. Progress achieved to date in genetic engineering and xenotransplantation will establish the zebrafish as one of the most versatile animal models for cancer research. A model organism that can be used in transgenesis, transplantation assays, single-cell functional assays, and in vivo imaging studies make zebrafish a natural companion for mice in translational oncology research.