Defining molecular classifications and targets in gastroenteropancreatic neuroendocrine tumors through DNA microarray analysis

Abstract

Current classifications of human gastroenteropancreatic neuroendocrine tumors (NETs) are inconsistent and based upon histopathologic but not molecular features. We sought to compare a molecular classification with the World Health Organization (WHO) histologic classification, identify genes that may be important for tumor progression, and determine whether gastrointestinal NETs (GI-NETs) differ in their molecular profile from pancreatic NETs (PNETs). DNA microarray analysis was performed to identify differentially expressed genes in PNETs and GI-NETs. Confirmation of expression levels was obtained by quantitative real-time PCR. Immunoblotting and mutational analysis were performed for selected genes. Hierarchical clustering of 19 PNETs revealed a 'benign' and 'malignant' cluster that corresponded well with the WHO categories of welldifferentiated endocrine tumor (WDET) and well-differentiated endocrine carcinoma (WDEC) respectively. FEV, adenylate cyclase 2 (ADCY2), nuclear receptor subfamily 4, group A, member 2 (NR4A2), and growth arrest and DNA-damage-inducible, beta (GADD45b) were the most highly up-regulated genes in the malignant group of PNETs. Platelet-derived growth factor receptor (PDGFR) was expressed in both WDETs and WDECs, and phosphorylation of PDGFR-b was observed in 83% of all PNETs. Malignant ileal GI-NETs exhibited a distinctive gene expression profile, and extracellular matrix protein 1 (ECM), vesicular monoamine member 1 (VMAT1), galectin 4 (LGALS4), and RET Proto-oncogene (RET) were highly up-regulated genes. Gene expression profiles reflect the current WHO classification and can distinguish benign from malignant PNETs and also PNETs from GI-NETs. This suggests that molecular profiling may enhance tumor classification schemes. Potential gene targets have also been identified, and PDGFR and RET are candidates that may represent novel therapeutic targets.

Functional malignant cell heterogeneity in pancreatic neuroendocrine tumors revealed by targeting of PDGF-DD

“…Our findings are supported by previous studies showing that besides stromal cells, human primary PanNET and metastatic cells express high levels of PDGFRβ compared with normal tissue (51,52). Moreover, clinical reports show evidence of PDGFR activation and copy number alteration in small intestine, gastroenteropancreatic, and pancreatic NET, although the use of whole tumor cell lysates precludes identification of the cell type expressing PDGFRβ (21,53). The identification of PDGFRβ + tumor cells in human PanNET has important clinical implications, considering that sunitinib, a PDGFR/VEGFR small molecule inhibitor, was recently approved to treat patients with progressive well-differentiated PanNET (54).…”

“…We identified rare cells coexpressing PDGFRβ and insulin in primary tumors (Fig. 6A, Right), consistent with previous reports of activated PDGFRβ in whole tumor lysates of human PanNET lesions (21). Malignant cells expressing PDGFRβ were more prevalent in micrometastatic lesions in the liver (Fig.…”

Molecular pathology and genetics of pancreatic endocrine tumours

“…These studies are summarised in Table 4 (Maitra et al 2003, Bloomston et al 2004, Hansel et al 2004, Dilley et al 2005, Capurso et al 2006, Couvelard et al 2006, Duerr et al 2008, Missiaglia et al 2010. The different samples and methods account for the expected poor reproducibility of the results.…”

Genetics of neuroendocrine tumours, hereditary tumour syndromes

“…Az utóbbi években elterjedt nagy áteresztőképességű bioinformatikai vizsgálatok számos génexpressziós eltérést mutattak ki a neuroendokrin daganatokban, amelyek mind a patogenezis feltárása, mind potenciális új terápiás célpontok azonosítása szempontjából nagy jelentőségűek [19].…”