Recent advances in histogenesis research of lung neuroendocrine cancers: Evidence obtained from functional analyses of primitive neural/neuroendocrine cell-specific transcription factors

Involvement of Epithelial-Mesenchymal Transition Genes in Small Cell Lung Cancer Phenotypic Plasticity

Small cell lung cancer (SCLC) is an aggressive cancer recalcitrant to treatment, arising predominantly from epithelial pulmonary neuroendocrine (NE) cells. Intratumor heterogeneity plays critical roles in SCLC disease progression, metastasis, and treatment resistance. At least five transcriptional SCLC NE and non-NE cell subtypes were recently defined by gene expression signatures. Transition from NE to non-NE cell states and cooperation between subtypes within a tumor likely contribute to SCLC progression by mechanisms of adaptation to perturbations. Therefore, gene regulatory programs distinguishing SCLC subtypes or promoting transitions are of great interest. Here, we systematically analyze the relationship between SCLC NE/non-NE transition and epithelial to mesenchymal transition (EMT)-a well-studied cellular process contributing to cancer invasiveness and resistance-using multiple transcriptome datasets from SCLC mouse tumor models, human cancer cell lines, and tumor samples. The NE SCLC-A2 subtype maps to the epithelial state. In contrast, SCLC-A and SCLC-N (NE) map to a partial mesenchymal state (M1) that is distinct from the non-NE, partial mesenchymal state (M2). The correspondence between SCLC subtypes and the EMT program paves the way for further work to understand gene regulatory mechanisms of SCLC tumor plasticity with applicability to other cancer types.

Endocrine secretory granule production is caused by a lack of REST and intragranular secretory content and accelerated by PROX1

Endocrine secretory granules (ESGs) are morphological characteristics of endocrine/neuroendocrine cells and store peptide hormones/neurotransmitters. ESGs contain prohormones and ESG-related molecules, mainly chromogranin/secretogranin family proteins. However, the precise mechanism of ESG formation has not been elucidated. In this study, we experimentally induced ESGs in the non-neuroendocrine lung cancer cell line H1299. Since repressive element 1 silencing transcription factor (REST) and prospero homeobox 1 (PROX1) are closely associated with the expression of ESG-related molecules, we edited the REST gene and/or transfected PROX1 and then performed molecular biology, immunocytochemistry, and electron and immunoelectron microscopy assays to determine whether ESG-related molecules and ESGs were induced in H1299 cells. Although chromogranin/secretogranin family proteins were induced in H1299 cells by knockout of REST and the induction was accelerated by the PROX1 transgene, the ESGs could not be defined by electron microscopy. However, a small number of ESGs were detected in the H1299 cells lacking REST and expressing pro-opiomelanocortin (POMC) by electron microscopy. Furthermore, many ESGs were produced in the REST-lacking and PROX1- and POMC-expressing H1299 cells. These findings suggest that a lack of REST and the expression of genes related to ESG content are indispensable for ESG production and that PROX1 accelerates ESG production.

Trial registration: Not applicable.

Merkel Cell Carcinoma: An Immunotherapy Fairy-Tale?

Merkel cell carcinoma (MCC) is a rare, highly aggressive, neuroendocrine cutaneous tumor. The incidence of MCC is growing worldwide, and the disease-related mortality is about three-fold higher than melanoma. Since a few years ago, very little has been known about this disease, and chemotherapy has been the standard of care. Nowadays, new discoveries about the pathophysiology of this neoplasm and the introduction of immunotherapy allowed to completely rewrite the history of these patients. In this review, we provide a summary of the most important changes in the management of Merkel cell carcinoma, with a focus on immunotherapy and a landscape of future treatment strategies.

LRIG1 is a positive prognostic marker in Merkel cell carcinoma and Merkel cell carcinoma expresses epithelial stem cell markers

Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine malignancy of the skin. The cell of origin of MCC is thus far unknown and proposed cells of origin include Merkel cells, pro-/pre- or pre-B cells, epithelial stem cells, and dermal stem cells. In this study, we aimed to shed further light on the possibility that a subset of MCC tumors arise from epithelial stem cells of the skin by examining the expression of hair follicle and epidermal stem cell markers in MCC and normal human skin. We also aimed to elucidate any correlation between the expression of these markers and tumor Merkel cell polyomavirus (MCPyV) status or other clinicopathological characteristics or patient survival. Expression of CK19, SOX9, LGR5, and LRIG1 in MCC and normal human skin was studied by immunohistochemistry, and the staining patterns or intensities were statistically correlated with patient, tumor, MCPyV, and survival parameters. In a cohort of 137 cases of MCC, we observed dot-like immunoexpression of CK19 in 30 cases (22.1%) and homogeneous expression in 103 cases (75.7%). We also observed positive immunoexpression of SOX9 in 21 cases (15.3%), LGR5 in 118 cases (86.1%), and LRIG1 in 117 cases (86.0%). Immunoexpression of LRIG1 was found to correlate with better overall and MCC-specific survival. We observed frequent immunoexpression of several hair follicle and epidermal stem cell markers in MCC and found LRIG1 to be a positive prognostic marker in MCC.

Diagnosis and Molecular Profiles of Large Cell Neuroendocrine Carcinoma With Potential Targets for Therapy

Large cell neuroendocrine carcinoma (LCNEC) together with small cell carcinoma (SCLC) and typical and atypical carcinoids form the group of pulmonary neuroendocrine tumors. LCNEC and SCLC are high-grade carcinomas. Although both can be found outside the thoracic cavity, they are most common in the lung. LCNEC differs from SCLC by morphologic pattern, and by cytological features such as nuclear size, nucleoli, chromatin pattern, but also by genetic differences. Originally thought to represent a single entity, it became evident, that three subgroups of LCNEC can be identified at the molecular level: a SCLC-like type with loss of retinoblastoma 1 gene (RB1) and TP53 mutations; a non-small cell lung carcinoma (NSCLC)-like type with wildtype RB1, TP53 mutation, and activating mutations of the phosphoinositol-3 kinase (PI3K-CA), or loss of PTEN; and a carcinoid-like type with MEN1 gene mutation. These subtypes can be identified by immunohistochemical staining for RB1, p53, and molecular analysis for PI3K and MEN1 mutations. These subtypes might also respond differently to chemotherapy. Immuno-oncologic treatment has also been applied to LCNEC, however, in addition to the evaluation of tumor cells the stroma evaluation seems to be important. Based on personal experiences with these tumors and available references this review will try to encompass our present knowledge in this rare entity and provoke new studies for better treatment of this carcinoma.

Histogenesis of Merkel Cell Carcinoma: A Comprehensive Review

Merkel cell carcinoma (MCC) is a primary neuroendocrine carcinoma of the skin. This neoplasia features aggressive behavior, resulting in a 5-year overall survival rate of 40%. In 2008, Feng et al. identified Merkel cell polyomavirus (MCPyV) integration into the host genome as the main event leading to MCC oncogenesis. However, despite identification of this crucial viral oncogenic trigger, the nature of the cell in which MCC oncogenesis occurs is actually unknown. In fact, several hypotheses have been proposed. Despite the large similarity in phenotype features between MCC tumor cells and physiological Merkel cells (MCs), a specialized subpopulation of the epidermis acting as mechanoreceptor of the skin, several points argue against the hypothesis that MCC derives directly from MCs. Alternatively, MCPyV integration could occur in another cell type and induce acquisition of an MC-like phenotype. Accordingly, an epithelial as well as a fibroblastic or B-cell origin of MCC has been proposed mainly based on phenotype similarities shared by MCC and these potential ancestries. The aim of this present review is to provide a comprehensive review of the current knowledge of the histogenesis of MCC.

Molecular imaging and therapy of somatostatin receptor positive tumors

Somatostatin receptors (SSTR) are upregulated in the cells of origin that define numerous neuroendocrine neoplasms. PET imaging with ⁶⁸Ga-DOTATATE allows specific targeting of SSTR2A, a single species of SSTR receptor, which is commonly overexpressed in a variety of gastroenteropancreatic neuroendocrine tumors, as well as pulmonary carcinoid and head and neck tumors. Due to more specific targeting of SSTR2 as well as lower radiation dose, shorter study length, ability to quantify uptake, and lower cost, ⁶⁸Ga-DOTATATE has demonstrated superior imaging attributes when compared to ¹¹¹In-pentetreotide. As with any novel imaging modality, dedicated training, increasing experience and staying up-to-date with scientific publications are required to provide optimal patient care. The purpose of this review is to summarize the current state of the art in SSTR-targeted molecular imaging and discuss ongoing and future potential diagnostic and therapeutic applications.

Neuroendocrine Key Regulator Gene Expression in Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is a highly aggressive non-melanoma skin cancer of the elderly which is associated with the Merkel cell polyomavirus (MCPyV). MCC reveals a trilinear differentiation characterized by neuroendocrine, epithelial and pre/pro B-cell lymphocytic gene expression disguising the cellular origin of MCC. Here we investigated the expression of the neuroendocrine key regulators RE1 silencing transcription factor (REST), neurogenic differentiation 1 (NeuroD1) and the Achaete-scute homolog 1 (ASCL1) in MCC. All MCCs were devoid of REST and were positive for NeuroD1 expression. Only one MCC tissue revealed focal ASCL1 expression. This was confirmed in MCPyV-positive MCC cell lines. Of interest, MCPyV-negative cell lines did express REST. The introduction of REST expression in REST-negative, MCPyV-positive MCC cells downregulated the neuroendocrine gene expression. The lack of the neuroendocrine master regulator ASCL1 in almost all tested MCCs points to an important role of the absence of the negative regulator REST towards the MCC neuroendocrine phenotype. This is underlined by the expression of the REST-regulated microRNAs miR-9/9* in REST-negative MCC cell lines. These data might provide the basis for the understanding of neuroendocrine gene expression profile which is expected to help to elucidate the cellular origin of MCC.

Clinicopathological characteristics of thyroid transcription factor 1-negative small cell lung cancers

Limitations in obtaining surgically resected or biopsy samples of small cell lung cancer (SCLC) tumors make comprehensive biological analyses difficult. The loss of thyroid transcription factor 1 (TTF-1) has been associated with the aggressive behavior of non-small cell lung cancer; however, clinicopathological features of TTF-1-negative SCLC remain unclear. This study aimed to elucidate the characteristics of TTF-1-negative SCLC. We studied the associations between the expression of TTF-1 and the clinicopathological factors associated with SCLC, including survival and expression of neuroendocrine markers (synaptophysin, chromogranin A, and CD56), neuroendocrine cell-specific transcription factors (ASCL1, BRN2), a proliferation marker (Ki-67 labeling index), and an oncogene (NF1B). Formalin-fixed and paraffin-embedded sections of SCLC tumors were subjected to immunohistochemistry and quantitative reverse-transcription polymerase chain reaction analyses. In a case-control cohort matched for basic clinical factors, expression of ProGRP, synaptophysin, chromogranin A, and ASCL1 was significantly decreased in TTF-1-negative SCLC samples. In contrast, there was no significant correlation between Ki-67 labeling index and TTF-1. In a larger serial case cohort, TTF-1-negative SCLC cases were older at diagnosis, but there was no significant difference in the overall survival of patients with TTF-1-negative and TTF-1-positive SCLC. In conclusion, TTF-1-negative SCLC showed decreased neuroendocrine differentiation, and significantly worse clinical outcomes were not observed.

Effect of A549 neuroendocrine differentiation on cytotoxic immune response

The present study was designed to determine the effects of factors secreted by the lung adenocarcinoma cell line with the neuroendocrine phenotype, A549_NED, on cytotoxic T lymphocytes (CTLs) activity in vitro A perspective that integrates the nervous, endocrine and immune system in cancer research is essential to understand the complexity of dynamic interactions in tumours. Extensive clinical research suggests that neuroendocrine differentiation (NED) is correlated with worse patient outcomes; however, little is known regarding the effects of neuroendocrine factors on the communication between the immune system and neoplastic cells. The human lung cancer cell line A549 was induced to NED (A549_NED) using cAMP-elevating agents. The A549_NED cells showed changes in cell morphology, an inhibition of proliferation, an overexpression of chromogranin and a differential pattern of biogenic amine production (decreased dopamine and increased serotonin [5-HT] levels). Using co-cultures to determine the cytolytic CTLs activity on target cells, we showed that the acquisition of NED inhibits the decrease in the viability of the target cells and release of fluorescence. Additionally, the conditioned medium of A549_NED and 5-HT considerably decreased the viability and proliferation of the Jurkat cells after 24 h. Thus, our study successfully generated a neuroendocrine phenotype from the A549 cell line. In co-cultures with CTLs, the pattern of secretion by A549_NED impaired the proliferation and cytotoxic activity of CTLs, which might be partly explained by the increased release of 5-HT.

Expression of developing neural transcription factors in diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH)

DIPNECH is characterized by neuroendocrine cell hyperplasia, tumorlets, and eventually carcinoid tumors. Although it is regarded by some authors as a preneoplastic condition, this issue is controversial. New pathologic criteria have recently been proposed for the diagnosis of DIPNECH, and a subgroup of carcinoid tumors expressing developing neural transcription factors (DNTFs), with clinicopathologic features similar to those of DIPNECH, has been recognized. This paper reports on the clinical and pathological findings in three cases of DIPNECH and investigates the expression of three DNTFs (TTF1, ASCL1, and POU3F2). All patients were female, with a mean age of 63 years, and all lesions were located in the periphery of the lung. In two cases, typical carcinoids were associated with a spindle-cell component. All neuroendocrine proliferations were DNTF positive. The morphologic (spindle-cell component), phenotypic (DNTF expression), and clinicopathologic (peripheral tumors, female predominance) similarities suggest that DIPNECH may be a preneoplastic lesion for peripheral carcinoids.