New model for gastroenteropancreatic large-cell neuroendocrine carcinoma: establishment of two clinically relevant cell lines

Novel preclinical gastroenteropancreatic neuroendocrine neoplasia models demonstrate the feasibility of mutation-based targeted therapy

PURPOSE

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NEN) form a rare and remarkably heterogeneous group of tumors. Therefore, establishing personalized therapies is eminently challenging. To achieve progress in preclinical drug development, there is an urgent need for relevant tumor models.

METHODS

We successfully established three gastroenteropancreatic neuroendocrine tumor (GEP-NET) cell lines (NT-18P, NT-18LM, NT-36) and two gastroenteropancreatic neuroendocrine carcinoma (GEP-NEC) cell lines (NT-32 and NT-38). We performed a comprehensive characterization of morphology, NET differentiation, proliferation and intracellular signaling pathways of these five cell lines and, in addition, of the NT-3 GEP-NET cell line. Additionally, we conducted panel sequencing to identify genomic alterations suitable for mutation-based targeted therapy.

RESULTS

We found that the GEP-NEN cell lines exhibit a stable neuroendocrine phenotype. Functional kinome profiling revealed a higher activity of serine/threonine kinases (STK) as well as protein tyrosine kinases (PTK) in the GEP-NET cell lines NT-3 and NT-18LM compared to the GEP-NEC cell lines NT-32 and NT-38. Panel sequencing revealed a mutation in Death Domain Associated Protein (DAXX), sensitizing NT-18LM to the Ataxia telangiectasia and Rad3 related (ATR) inhibitor Berzosertib, and a mutation in AT-Rich Interaction Domain 1A (ARID1A), sensitizing NT-38 to the Aurora kinase A inhibitor Alisertib. Small interfering RNA-mediated knock down of DAXX in the DAXX wild type cell line NT-3 sensitized these cells to Berzosertib.

CONCLUSIONS

The newly established GEP-NET and GEP-NEC cell lines represent comprehensive preclinical in vitro models suitable to decipher GEP-NEN biology and pathogenesis. Additionally, we present the first results of a GEP-NEN-specific mutation-based targeted therapy. These findings open up new potentialities for personalized therapies in GEP-NEN.

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.

Establishment of Novel Neuroendocrine Carcinoma Patient-Derived Xenograft Models for Receptor Peptide-Targeted Therapy

Simple Summary

Gastroenteropancreatic neuroendocrine neoplasms (GEP NENs) are a family of rare cancers with rising incidence in recent years. GEP NEN tumor cells are difficult to propagate, and few cellular and patient-derived xenograft (PDX) models are available for testing new therapies and studying the heterogeneous nature of these cancers. Here, we described the establishment and characterization of two novel NEC cellular and PDX models (NEC913 and NEC1452). NEC913 PDX tumors express somatostatin receptor 2 (SSTR2), whereas NEC1452 PDX tumors are SSTR2 negative. As a proof-of-concept study, we demonstrated how these PDX models can be used for peptide imaging experiments targeting SSTR2 using fluorescently labelled octreotide. The NEC913 and NEC1452 PDX lines represent valuable new tools for accelerating the process of drug discovery for GEP NENs.

Abstract

Gastroenteropancreatic neuroendocrine neoplasms (GEP NENs) are rare cancers consisting of neuroendocrine carcinomas (NECs) and neuroendocrine tumors (NETs), which have been increasing in incidence in recent years. Few cell lines and pre-clinical models exist for studying GEP NECs and NETs, limiting the ability to discover novel imaging and treatment modalities. To address this gap, we isolated tumor cells from cryopreserved patient GEP NECs and NETs and injected them into the flanks of immunocompromised mice to establish patient-derived xenograft (PDX) models. Two of six mice developed tumors (NEC913 and NEC1452). Over 80% of NEC913 and NEC1452 tumor cells stained positive for Ki67. NEC913 PDX tumors expressed neuroendocrine markers such as chromogranin A (CgA), synaptophysin (SYP), and somatostatin receptor-2 (SSTR2), whereas NEC1452 PDX tumors did not express SSTR2. Exome sequencing revealed loss of TP53 and RB1 in both NEC tumors. To demonstrate an application of these novel NEC PDX models for SSTR2-targeted peptide imaging, the NEC913 and NEC1452 cells were bilaterally injected into mice. Near infrared-labelled octreotide was administered and the fluorescent signal was specifically observed for the NEC913 SSTR2 positive tumors. These 2 GEP NEC PDX models serve as a valuable resource for GEP NEN therapy testing.

Models of Gastroenteropancreatic Neuroendocrine Neoplasms: Current Status and Future Directions

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) are a rare, heterogeneous group of tumors that originate from the endocrine system of the gastrointestinal tract and pancreas. GEP-NENs are subdivided according to their differentiation into well-differentiated neuroendocrine tumors (NETs) and poorly differentiated neuroendocrine carcinomas (NECs). Since GEP-NENs represent rare diseases, only limited data from large prospective, randomized clinical trials are available, and recommendations for treatment of GEP-NEN are in part based on data from retrospective analyses or case series. In this context, tractable disease models that reflect the situation in humans and that allow to recapitulate the different clinical aspects and disease stages of GEP-NET or GEP-NEC are urgently needed. In this review, we highlight available data on mouse models for GEP-NEN. We discuss how these models reflect tumor biology of human disease and whether these models could serve as a tool for understanding the pathogenesis of GEP-NEN and for disease modeling and pharmacosensitivity assays, facilitating prediction of treatment response in patients. In addition, open issues applicable for future developments will be discussed.

Isolation and Characterization of Two Novel Colorectal Cancer Cell Lines, Containing a Subpopulation with Potential Stem-Like Properties: Treatment Options by MYC/NMYC Inhibition

Simple Summary

The aim of this study was to gain a better understanding of cancer stem cells, which are a small subpopulation of tumor cells with high plasticity driving tumor growth and metastasis. Here we isolated two novel colorectal cancer cell lines originating from a rectal neuroendocrine carcinoma and a colorectal adenocarcinoma, depicting stem-like properties. These in vitro models offer the possibility to evaluate pathophysiological mechanisms in order to develop tailored therapeutic strategies for distinct colorectal malignancies. Investigations revealed gene copy number gain of the N-myc proto-oncogene for both. Accordingly, inhibition of the protein–protein interaction of myc and N-myc proto-oncogenes with the myc-associated factor X utilizing small molecule KJ-Pyr-9, exhibited a significant reduction in survival of both cell lines by the induction of apoptosis. Consequently, the blockage of these interactions may serve as a possible treatment strategy for colorectal cancer cell lines with gene copy number gain of the N-myc proto-oncogene.

Abstract

Cancer stem cells (CSC) are crucial mediators of cancer relapse. Here, we isolated two primary human colorectal cancer cell lines derived from a rectal neuroendocrine carcinoma (BKZ-2) and a colorectal adenocarcinoma (BKZ-3), both containing subpopulations with potential stem-like properties. Protein expression of CSC-markers prominin-1 and CD44 antigen was significantly higher for BKZ-2 and BKZ-3 in comparison to well-established colon carcinoma cell lines. High sphere-formation capacity further confirmed the existence of a subpopulation with potential stem-like phenotype. Epithelial–mesenchymal transition markers as well as immune checkpoint ligands were expressed more pronounced in BKZ-2. Both cell populations demonstrated N-myc proto-oncogene (NMYC) copy number gain. Myc proto-oncogene (MYC)/NMYC activity inhibitor all-trans retinoic acid (ATRA) significantly reduced the number of tumor spheres for both and the volume of BKZ-2 spheres. In contrast, the sphere volume of ATRA-treated BKZ-3 was increased, and only BKZ-2 cell proliferation was reduced in monolayer culture. Treatment with KJ-Pyr-9, a specific inhibitor of MYC/NMYC-myc-associated factor X interaction, decreased survival by the induction of apoptosis of both. In summary, here, we present the novel colorectal cancer cell lines BKZ-2 and BKZ-3 as promising cellular in vitro models for colorectal carcinomas and identify the MYC/NMYC molecular pathway involved in CSC-induced carcinogenesis with relevant therapeutic potential.

Oncolytic vaccinia virus GLV-1h68 exhibits profound antitumoral activities in cell lines originating from neuroendocrine neoplasms

Background

Oncolytic virotherapy is an upcoming treatment option for many tumor entities. But so far, a first oncolytic virus only was approved for advanced stages of malignant melanomas. Neuroendocrine tumors (NETs) constitute a heterogenous group of tumors arising from the neuroendocrine system at diverse anatomic sites. Due to often slow growth rates and (in most cases) endocrine non-functionality, NETs are often detected only in a progressed metastatic situation, where therapy options are still severely limited. So far, immunotherapies and especially immunovirotherapies are not established as novel treatment modalities for NETs.

Methods

In this immunovirotherapy study, pancreatic NET (BON-1, QGP-1), lung NET (H727, UMC-11), as well as neuroendocrine carcinoma (NEC) cell lines (HROC-57, NEC-DUE1) were employed. The well characterized genetically engineered vaccinia virus GLV-1 h68, which has already been investigated in various clinical trials, was chosen as virotherapeutical treatment modality.

Results

Profound oncolytic efficiencies were found for NET/NEC tumor cells. Besides, NET/NEC tumor cell bound expression of GLV-1 h68-encoded marker genes was observed also. Furthermore, a highly efficient production of viral progenies was detected by sequential virus quantifications. Moreover, the mTOR inhibitor everolimus, licensed for treatment of metastatic NETs, was not found to interfere with GLV-1 h68 replication, making a combinatorial treatment of both feasible.

Conclusions

In summary, the oncolytic vaccinia virus GLV-1 h68 was found to exhibit promising antitumoral activities, replication capacities and a potential for future combinatorial approaches in cell lines originating from neuroendocrine neoplasms. Based on these preliminary findings, virotherapeutic effects now have to be further evaluated in animal models for treatment of Neuroendocrine neoplasms (NENs).

Relevance of neuroendocrine tumours models assessed by kinomic profiling

Although there is evidence of a significant rise of neuroendocrine tumours (NETs) incidence, current treatments are largely insufficient due to somewhat poor knowledge of these tumours. Despite many efforts achieved to expose driver oncogene mutations in NETs, the genetic landscape of NETs is characterized by relatively few mutations and chromosomal aberrations per tumour compared with other tumour types. In addition, NETs display few actionable mutations providing compelling rationale for targeted therapies. Recent works aiming at characterizing currently used NETs in vitro models at the genomic level raised concerns on their reliability as bona fide tools to study NETs biology. However, the lack of actionable mutation in NETs implies that sole use of genomic is not sufficient to describe these models and establish appropriate therapeutic strategies. Several kinases and kinase-involving signalling pathways have been demonstrated as abnormally regulated in NETs. Yet, kinases have only been investigated regardless of their involvement in large intracellular signalling networks. In order to assess the validity of in vitro NETs models to study NETs biology, "next-generation" high throughput functional technologies based on "kinome-wide activity" will demonstrate the similarities between signalling pathways in NETs models and patients' samples. These approaches will significantly assist in identifying actionable alterations in NETs signalling pathways and guide patient stratification into early-phase clinical trials based on kinase inhibition targeted therapies.

The Oncolytic Herpes Simplex Virus Talimogene Laherparepvec Shows Promising Efficacy in Neuroendocrine Cancer Cell Lines

Metastatic neuroendocrine cancer still constitutes a palliative situation, lacking promising treatment options. Oncolytic virotherapy, a novel type of virus-based immunotherapy, lyses tumor cells using genetically engineered viruses thereby activating the immune system to induce an optimized antitumor response which could bring down tumor masses to a stage of minimal residual tumor disease. The oncolytic vector talimogene laherparepvec (T-VEC, herpes simplex virus [HSV] type 1) has already shown excellent safety profiles in clinical studies and has become the first ever FDA/EMA-approved oncolytic virus (OV). This work presents a first preclinical assessment of this state-of-the-art OV, using a panel of human neuroendocrine tumor/neuroendocrine carcinoma (NET/NEC) cell lines. Cytotoxicity, transgene expression, and viral replication patterns were studied. Furthermore, the antiproliferative activity was compared to the one of mTOR inhibitor Everolimus and also interactions between the OV and Everolimus were evaluated. Moreover, virostatic effects of ganciclovir (GCV) on replication of T-VEC were assessed and electron microscopic pictures were taken to comprehend viral envelopment and details of the replication cycle of T-VEC in human neuroendocrine cancer. It could be shown that T-VEC infects, replicates in, and lyses human NET/NEC cells exhibiting high oncolytic efficiencies already at quite low virus concentrations. Interestingly, Everolimus was not found to have any relevant impact on rates of viral replication, but no additive effects could be proved using a combinatorial therapy regimen. On the other hand, GCV was shown to be able to limit replication of T-VEC, thus establishing an important safety feature for future treatments of NET/NEC patients. Taken together, T-VEC opens up a promising novel treatment option for NET/NEC patients, warranting its further preclinical and clinical development.

Mouse models in endocrine tumors

Endocrine and neuroendocrine tumors comprise a highly heterogeneous group of neoplasms that can arise from (neuro)endocrine cells, either from endocrine glands or from the widespread diffuse neuroendocrine system, and, consequently, are widely distributed throughout the body. Due to their diversity, heterogeneity and limited incidence, studying in detail the molecular and genetic alterations that underlie their development and progression is still a highly elusive task. This, in turn, hinders the discovery of novel therapeutic options for these tumors. To circumvent these limitations, numerous mouse models of endocrine and neuroendocrine tumors have been developed, characterized and used in pre-clinical, co-clinical (implemented in mouse models and patients simultaneously) and post-clinical studies, for they represent powerful and necessary tools in basic and translational tumor biology research. Indeed, different in vivo mouse models, including cell line-based xenografts (CDXs), patient-derived xenografts (PDXs) and genetically engineered mouse models (GEMs), have been used to delineate the development, progression and behavior of human tumors. Results gained with these in vivo models have facilitated the clinical application in patients of diverse breakthrough discoveries made in this field. Herein, we review the generation, characterization and translatability of the most prominent mouse models of endocrine and neuroendocrine tumors reported to date, as well as the most relevant clinical implications obtained for each endocrine and neuroendocrine tumor type.

BRAFV600E mutation: A promising target in colorectal neuroendocrine carcinoma

To determine the role of BRAF^V600E mutation and MAPK signaling as well as the effects of BRAF and MEK directed therapy in gastroenteropancreatic neuroendocrine neoplasia (GEP-NEN), with a focus on highly aggressive gastroenteropancreatic neuroendocrine carcinoma (GEP-NEC). Using Sanger sequencing of BRAF exon 15 we determined the frequency of BRAF^V600E mutations in 71 primary GEP-NENs. MEK phosphorylation was examined by immunohistochemistry in corresponding tissue samples. To evaluate the biological relevance of BRAF^V600E mutation and MAPK signaling in GEP-NECs, effects of a pharmacological BRAF and MEK inhibition were analyzed in NEC cell lines both in vitro and in vivo. BRAF^V600E mutation was detected in 9.9% of all GEP-NENs. Interestingly, only NECs of the colon harbored BRAF^V600E mutations, leading to a mutation frequency of 46.7% in this subgroup of patients. In addition, a BRAF^V600E mutation was significantly associated with high levels of MEK phosphorylation (pMEK) and advanced tumor stages. Pharmacological inhibition of BRAF and MEK abrogated NEC cell growth, inducing G1 cell cycle arrest and apoptosis only in BRAF^V600E mutated cells. BRAF inhibitor dabrafenib and MEK inhibitor trametinib prevented growth of BRAF^V600E positive NEC xenografts. High frequencies of BRAF^V600E mutation and elevated expression levels of pMEK were detected in biologically aggressive and highly proliferative colorectal NECs. We provide evidence that targeting BRAF oncogene may represent a therapeutic strategy for patients with BRAF mutant colorectal NECs.

Establishment, functional and genetic characterization of a colon derived large cell neuroendocrine carcinoma cell line

AIM

To establish cell line and patient-derived xenograft (PDX) models for neuroendocrine carcinomas (NEC) which is highly desirable for gaining insight into tumor development as well as preclinical research including biomarker testing and drug response prediction.

METHODS

Cell line establishment was conducted from direct in vitro culturing of colonic NEC tissue (HROC57). A PDX could also successfully be established from vitally frozen tumor samples. Morphological features, invasive and migratory behavior of the HROC57 cells as well as expression of neuroendocrine markers were vastly analyzed. Phenotypic analysis was done by microscopy and multicolor flow cytometry. The extensive molecular-pathological profiling included mutation analysis, assessment of chromosomal and microsatellite instability; and in addition, fingerprinting (i.e., STR analysis) was performed from the cell line in direct comparison to primary patient-derived tissues and the PDX model established. Drug responsiveness was examined for a panel of chemotherapeutics in clinical use for the treatment of solid cancers.

RESULTS

The established cell line HROC57 showed distinct morphological and molecular features of a poorly differentiated large-cell NEC with KI-67 > 50%. Molecular-pathological analysis revealed a CpG island promoter methylation positive cell line with microsatellite instability being absent. The following mutation profile was observed: KRAS (wt), BRAF (mut). A high sensitivity to etoposide, cisplatin and 5-FU could be demonstrated while it was more resistant towards rapamycin.

CONCLUSION

We successfully established and characterized a novel patient-derived NEC cell line in parallel to a PDX model as a useful tool for further analysis of the biological characteristics and for development of novel diagnostic and therapeutic options for NEC.

Establishment of preclinical chemotherapy models for gastroenteropancreatic neuroendocrine carcinoma

Gastroenteropancreatic neuroendocrine carcinoma (GEP-NEC) is a rare and devastating malignancy, and preclinical studies are needed to evaluate potential therapeutic regimens. Here, we examined the antitumor effects of cisplatin (CDDP), etoposide (ETP) and irinotecan (CPT-11) and their combinations on GEP-NEC using three small-cell GEP-NEC cell lines (pancreatic NEC, A99; esophageal NEC, TYUC-1; duodenum NEC, TCC-NECT-2). In vitro studies were conducted using cell viability assays. In vivo experiments were conducted in mice inoculated with A99 or TCC-NECT-2 and treated with no agent, CDDP, CDDP+ETP (EP) or CDDP+CPT-11 (IP). TYUC-1 was the most susceptible to all agents, whereas A99 was refractory. Classical isobolograms showed synergism in both the EP and IP combinations for the three cell lines. In the TCC-NECT-2 mouse model, the IP regimen showed a significant antitumor effect, and CDDP alone showed a marginal effect compared to the control. In contrast, no effect was detected in the A99 model, probably because A99 was established from a metastatic tumor after chemotherapy with EP. Gene expression analysis of the ATP-binding cassette transporters revealed that ATP binding cassette subfamily B member1 (ABCB1) was conspicuously expressed in A99, and ABCB1 and ATP binding cassette subfamily C member2 (ABCC2) were deficient in TYUC-1, which might explain a part of different CDDP susceptibilities between cell lines. These preclinical models indicate that CDDP is a key agent, and IP regimen might be a reasonable option, although its efficacy is moderate. Our data on the platinum-based regimen will be useful as reference information in developing new agents for GEP-NEC.

IAPs cause resistance to TRAIL-dependent apoptosis in follicular thyroid cancer

Follicular thyroid cancer's (FTC) excellent long-term prognosis is mainly dependent on postoperative radioactive iodine (RAI) treatment. However, once the tumour becomes refractory, the 10-year disease-specific survival rate drops below 10%. The aim of our study was to evaluate the prognostic and biological role of the TRAIL system in FTC and to elucidate the influence of small-molecule-mediated antagonisation of inhibitor of apoptosis proteins (IAPs) on TRAIL sensitivity in vitro Tissue microarrays were constructed from forty-four patients with histologically confirmed FTC. Expression levels of TRAIL and its receptors were correlated with clinicopathological data and overall as well as recurrence-free survival. Non-iodine-retaining FTC cell lines TT2609-bib2 and FTC133 were treated with recombinant human TRAIL alone and in combination with Smac mimetics GDC-0152 or Birinapant. TRAIL-R2/DR5 as well as TRAIL-R3/DcR1 and TRAIL-R4/DcR2 were significantly higher expressed in advanced tumour stages. Both decoy receptors were negatively associated with recurrence-free and overall survival. TRAIL-R4/DcR2 additionally proved to be an independent negative prognostic marker in FTC (HR = 1.446, 95% CI: 1.144-1.826; P < 0.001). In vitro, the co-incubation of Birinapant or GDC-0152 with rh-TRAIL-sensitised FTC cell lines for TRAIL-induced apoptosis, through degradation of cIAP1/2. The TRAIL system plays an important role in FTC tumour biology. Its decoy receptors are associated with poor prognosis as well as earlier recurrence. The specific degradation of cIAP1/2 sensitises FTC cells to TRAIL-induced apoptosis and might highlight a new point of attack in patients with RAI refractory disease.

CXCR4/CXCR7/CXCL12-Axis in Follicular Thyroid Carcinoma

Background: Follicular thyroid carcinoma's (FTC) often benign course is partially due to adjuvant radioactive iodine (RAI) treatment. However, once the tumour has spread and fails to retain RAI, the therapeutic options are limited and the outcome is poor. In this subset of patients, the identification of novel druggable biomarkers appears invaluable. Here, we investigated the stage dependent expression and functional role of the C-X-C chemokine receptors type 4 and 7 (CXCR4/7) in FTC.

Methods: CXCR4/7 expression was examined in 44 FTC and corresponding non-neoplastic thyroid specimens as well as 10 FTC distant metastases and 18 follicular adenomas using tissue microarray technology. Expression levels were correlated with clinicopathological variables as well as overall and recurrence free survival. Changes regarding cell cycle activation, tumour cell invasiveness and mRNA expression of genes related to epithelial-mesenchymal transition (EMT) were investigated after treatment with recombinant human SDF1α/CXCL12 (rh-SDF1α) and CXCR4 antagonists AMD3100 and WZ811.

Results: CXCR4/7 expression was associated with large tumour size, advanced UICC stage as well as shorter overall and recurrence free survival. CXCR4 was significantly higher expressed in distant metastases than in primary tumour cores. In addition, rh-SDF1α induced invasive growth, cell cycle activation and EMT, while CXCR4 antagonists significantly reduced FTC invasiveness in vitro.

Conclusion: Here we provide first evidence of the biological importance of the CXCR4/CXCR7/CXCL12 axis in FTC. Our findings underscore the therapeutic potential of this chemokine receptor family in advanced FTC and offer new valuable insight into the oncogenesis of metastatic FTC.

Preclinical assesement of survivin and XIAP as prognostic biomarkers and therapeutic targets in gastroenteropancreatic neuroendocrine neoplasia

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NEN) represent a rare and heterogenous tumor entity. Importantly, the highly proliferative subgroup of neuroendocrine carcinoma (GEP-NEC) is characterized by high resistance to conventional chemotherapy. Consequently, there is an urgent need to identify novel therapeutic targets, especially for GEP-NEC. Thus, we focused on Inhibitor of apoptosis protein (IAP) family members survivin and XIAP that orchestrate inhibition of apoptosis, induce resistance against chemotherapeutics and facilitate tumor metastasis. Copy number gains (CNGs) could be detected by microarray comparative genomic hybridization for survivin and XIAP in 60 % and 26.7 % of all GEP-NENs, respectively. Immunohistochemical staining of tissue specimens from 77 consecutive patients with GEP-NEN demonstrated increased survivin protein expression levels in tissue specimens of highly proliferative GEP-NEC or GEP-NEN located in the stomach and colon. In contrast, XIAP overexpression was associated with advanced tumor stages. Knockdown of survivin and XIAP markedly reduced cell proliferation and tumor growth. In vitro, YM155 induced apoptotic cell death accompanied by a reduction in cell proliferation and inhibited GEP-NEC xenograft growth. Taken together, our data provide evidence for a biological relevance of these IAPs in GEP-NEN and support a potential role of survivin as therapeutic target especially in the subgroup of aggressive GEP-NEC.

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.

Establishment of the First Well-differentiated Human Pancreatic Neuroendocrine Tumor Model

Clinical options for systemic therapy of neuroendocrine tumors (NET) are limited. Development of new drugs requires suitable representative in vitro and in vivo model systems. So far, the unavailability of a human model with a well-differentiated phenotype and typical growth characteristics has impaired preclinical research in NET. Herein, we establish and characterize a lymph node-derived cell line (NT-3) from a male patient with well-differentiated pancreatic NET. Neuroendocrine differentiation and tumor biology was compared with existing NET cell lines BON and QGP-1. In vivo growth was assessed in a xenograft mouse model. The neuroendocrine identity of NT-3 was verified by expression of multiple NET-specific markers, which were highly expressed in NT-3 compared with BON and QGP-1. In addition, NT-3 expressed and secreted insulin. Until now, this well-differentiated phenotype is stable since 58 passages. The proliferative labeling index, measured by Ki-67, of 14.6% ± 1.0% in NT-3 is akin to the original tumor (15%-20%), and was lower than in BON (80.6% ± 3.3%) and QGP-1 (82.6% ± 1.0%). NT-3 highly expressed somatostatin receptors (SSTRs: 1, 2, 3, and 5). Upon subcutaneous transplantation of NT-3 cells, recipient mice developed tumors with an efficient tumor take rate (94%) and growth rate (139% ± 13%) by 4 weeks. Importantly, morphology and neuroendocrine marker expression of xenograft tumors resembled the original human tumor.Implications: High expression of somatostatin receptors and a well-differentiated phenotype as well as a slow growth rate qualify the new cell line as a relevant model to study neuroendocrine tumor biology and to develop new tumor treatments. Mol Cancer Res; 16(3); 496-507. ©2018 AACR.

Clinicopathological and functional implications of the inhibitor of apoptosis proteins survivin and XIAP in esophageal cancer

Based on their overexpression and important roles in progression and therapy-resistance in malignant diseases, the inhibitor of apoptosis protein family (IAP) members, survivin and X-linked inhibitor of apoptosis protein (XIAP), represent attractive candidates for targeted therapy. The present study investigated the prognostic and biological relevance of survivin and XIAP in esophageal squamous-cell carcinoma (ESCC) and esophageal adenocarcinoma (EAC). Survivin and XIAP expression was analyzed by immunohistochemistry using tissue microarrays containing 120 ESCC and 90 EAC samples as well as the corresponding non-neoplastic esophageal mucosa samples. IAP expression levels were then correlated to clinicopathological parameters and overall survival to identify any associations. In addition, esophageal cancer cell lines were treated with the survivin inhibitor YM155, and the XIAP inhibitors Birinapant and GDC-0152 in vitro. Survivin and XIAP expression were significantly increased in EAC and ESCC when compared with tumor-adjacent mucosa. In patients with ESCC XIAP expression was associated with female gender and advanced tumor stages, and nuclear survivin expression was associated with poor grading. High XIAP expression was identified as an independent negative prognostic marker in ESCC. By contrast, XIAP inhibitors did not affect cancer cell viability in vitro, and the small molecule survivin inhibitor YM155 significantly reduced cell viability and proliferation in esophageal cancer cell lines. Western blot analysis revealed a dose dependent decrease of survivin accompanied by an increased poly (adenosine diphosphate-ribose) polymerase cleavage following YM155 treatment. These findings underline the potential role of survivin and XIAP in the oncogenesis of esophageal cancer and provide a rationale for future clinical studies investigating the therapeutic efficacy of IAP directed therapies in patients with esophageal cancer.

Targeted therapy of gastroenteropancreatic neuroendocrine tumours: preclinical strategies and future targets

Molecular targeted therapy of advanced neuroendocrine tumours (NETs) of the gastroenteropancreatic (GEP) system currently encompasses approved therapy with the mammalian target of rapamycin (mTOR) inhibitor everolimus and the multi-tyrosinkinase inhibitor sunitinib. However, clinical efficacy of these treatment strategies is limited by low objective response rates and limited progression-free survival due to tumour resistance. Further novel strategies for molecular targeted therapy of NETs of the GEP system are needed. This paper reviews preclinical research models and signalling pathways in NETs of the GEP system. Preclinical and early clinical data on putative novel targets for molecular targeted therapy of NETs of the GEP system are discussed, including PI3K, Akt, mTORC1/mTORC2, GSK3, c-Met, Ras-Raf-MEK-ERK, embryogenic pathways (Hedgehog, Notch, Wnt/beta-catenin, TGF-beta signalling and SMAD proteins), tumour suppressors and cell cycle regulators (p53, cyclin-dependent kinases (CDKs) CDK4/6, CDK inhibitor p27, retinoblastoma protein (Rb)), heat shock protein HSP90, Aurora kinase, Src kinase family, focal adhesion kinase and epigenetic modulation by histone deacetylase inhibitors.

Octreotide Does Not Inhibit Proliferation in Five Neuroendocrine Tumor Cell Lines

Somatostatin analogs (SSA) are well-established antisecretory drugs in functionally active neuroendocrine tumors (NET). Two placebo-controlled trials have recently demonstrated significant improvement of progression-free survival under SSA treatment. Furthermore, somatostatin receptor (SSTR) overexpression in NET has also been utilized for diagnostic imaging and peptide receptor radionuclide therapy (PRRT). However, PRRT in NET is associated mostly with partial and minor remission, while other radionuclide therapies reach complete remissions in up to 75% of cases. This study assessed a potential radiosensitizing effect of SSA treatment in five established NET cell line models: BON, QGP-1, LCC-18, H727, and UMC-11. Irradiation was found to significantly inhibit proliferation, while no additional effect by octreotide treatment was observed. Intriguingly, no impact of SSA treatment alone was found in any of these NET cell lines when systematically analyzing cell viability, proliferation, and cell cycle distribution. Investigation of the causes for this octreotide resistance led to demonstration of low octreotide binding and scarce SSTR, specifically SSTR2 expression as compared to levels found in human NETs. The resistance toward SSA treatment in viability and proliferation assays could not be overcome by re-expression of SSTR2 in two of the cell lines. These results provide systematic evidence for a lack of authentic, tumor-like SSTR expression, and function in five frequently used NET cell line models and point to the need for more physiologic tumor model systems.

CXCR4/CXCR7/CXCL12 axis promotes an invasive phenotype in medullary thyroid carcinoma

Background:

Medullary thyroid carcinoma (MTC) is a rare and challenging endocrine malignancy. Once spread, the therapeutic options are limited and the outcome poor. For these patients, the identification of new druggable biological markers is of great importance. Here, we investigated the prognostic and biological role of the C-X-C chemokine receptors type 4 and 7 (CXCR4/7) in MTC.

Methods:

Eighty-six MTC and corresponding non-neoplastic thyroid specimens were immunohistochemically stained for CXCR4/7 using tissue microarray technology and expression levels correlated with clinicopathological variables. Medullary thyroid carcinoma cell line TT was treated with recombinant human SDF1α/CXCL12 (rh-SDF1α) and CXCR4 antagonists AMD3100 and WZ811. Changes in cell cycle activation, tumour cell invasiveness as well as changes in mRNA expression levels of genes associated with epithelial–mesenchymal transition (EMT) were investigated.

Results:

High CXCR4 expression was associated with large tumour size and metastatic disease. CXCR4 antagonists significantly reduced tumour cell invasiveness, while the treatment with rh-SDF1α stimulated invasive growth, caused cell cycle activation and induced EMT.

Conclusions:

The CXCR4/CXCR7/CXCL12 axis plays an important role in MTC. We provide first evidence that the chemokine receptors might serve as potential therapeutic targets in patients with advanced MTC and offer new valuable insight into the underlying molecular machinery of metastatic MTC.

Array comparative genomic hybridization of 18 pancreatic ductal adenocarcinomas and their autologous metastases

BACKGROUND

Mortality rates of pancreatic cancer remain high, which is mainly due to advanced disease and metastasis. We hypothesized that genomic copy number alterations are enriched in metastatic cells compared to autologous primary tumors, which may inform on cancer-related pathways possibly serving as potential targets for specific therapies. We investigated 18 pancreatic ductal adenocarcinomas, including 39 lymph node and 5 distant metastases after surgical resection. Analysis was performed with array-based comparative genomic hybridization (aCGH).

RESULTS

Metastases acquire a higher frequency of copy number alterations with the highest in distant metastasis (median = 42, lymph node metastases: median = 23, primary tumors: median = 17). In lymph node metastases, gains were prevalent on chromosome bands 8q11.23-q24.3, 12q14.1, 17p12.1, 21q22.12, and losses on 3p21.31, 4p14, 8p23.3-p11.21,17p12-11.2. Genes on amplified regions are involved in cancer-related pathways such as WNT-signaling, also involved in metastasis.

CONCLUSIONS

Pancreatic cancers show a high degree of intratumor heterogeneity, which could lead to resistance of chemotherapy and worse outcome. ACGH analysis reveals regions preferentially gained or lost in synchronous metastases encoding for genes involved in cancer-related pathways, which could lead to novel therapeutic opportunities.