Epigenetic pathway inhibitors represent potential drugs for treating pancreatic and bronchial neuroendocrine tumors

Abstract

Cancer is associated with alterations in epigenetic mechanisms such as histone modifications and methylation of DNA, and inhibitors targeting epigenetic mechanisms represent a novel class of anti-cancer drugs. Neuroendocrine tumors (NETs) of the pancreas (PNETs) and bronchus (BNETs), which may have 5-year survivals of <50% and as low as 5%, respectively, represent targets for such drugs, as >40% of PNETs and ~35% of BNETs have mutations of the multiple endocrine neoplasia type 1 (MEN1) gene, which encodes menin that modifies histones by interacting with histone methyltransferases. We assessed 9 inhibitors of epigenetic pathways, for their effects on proliferation, by CellTiter Blue assay, and apoptosis, by CaspaseGlo assay, using 1 PNET and 2 BNET cell lines. Two inhibitors, referred to as (+)-JQ1 (JQ1) and PFI-1, targeting the bromo and extra terminal (BET) protein family which bind acetylated histone residues, were most effective in decreasing proliferation (by 40–85%, P<0.001) and increasing apoptosis (by 2–3.6 fold, P<0.001) in all 3 NET cell lines. The anti-proliferative effects of JQ1 and PFI-1 remained present for at least 48 hours after removal of the compound. JQ1, but not PFI-1, had cell cycle effects, assessed by propidium iodide staining and flow cytometry, resulting in increased and decreased proportions of NET cells in G1, and S and G2 phases, respectively. RNA Sequencing analysis revealed that these JQ1 effects were associated with increased histone 2B expression, and likely mediated through altered activity of bromodomain-containing (Brd) proteins. Assessment of JQ1 in vivo, using a pancreatic beta cell-specific conditional Men1 knockout mouse model that develops PNETs, revealed that JQ1 significantly reduced proliferation (by ~50%, P<0.0005), assessed by bromodeoxyuridine incorporation, and increased apoptosis (by ~3 fold, P<0.0005), assessed by terminal deoxynucleotidyl transferase dUTP nick end labelling, of PNETs. Thus, our studies demonstrate that BET protein inhibitors may provide new treatments for NETs.

Long Noncoding RNA MEG3 Is an Epigenetic Determinant of Oncogenic Signaling in Functional Pancreatic Neuroendocrine Tumor Cells

“…Chromatin-remodeling perturbations and concomitant transcriptional dysregulation as a consequence of MEN1 loss are now acknowledged as constituents of the genomic landscape of PNET pathogenesis and potential therapeutic targets (24,48,49). Whether histone acetyltransferases or the pioneering factors such as GATA2 and FOXA1 (50) are recruited to the c-Met genomic regions in the absence of menin and Meg3 to facilitate c-Met signaling and concomitant tumor development remains to be investigated.…”

Twenty years of menin: emerging opportunities for restoration of transcriptional regulation in MEN1

“…JQ1 reduced the proliferation rate and increased apoptosis in a MEN1 pNET mouse model. However, a MYC-dependent mechanism could not be confirmed in the NET cell lines (Lines et al 2017). …”

“…identified JQ1 as a potential treatment for neuroendocrine tumors (Lines, et al 2017). Of note, no H3K4 demethylase inhibitors were tested in this study.…”

Animal models of MEN1

“…These findings provide the rationale for the evaluation of compounds targeting epigenetic regulatory proteins in these tumors. Recently, Lines et al (2017b) tested several epigenetic drugs for efficacy on pancreatic NET cells in vitro, and the most promising one, JQ1, was then evaluated in vivo in Men1 l/l ;RIP2-Cre-ER mice. JQ1 is 24:10 an inhibitor of the bromo and extra-terminal motif (BET) proteins that bind acetylated lysine residues.…”