MYC Upregulation Confers Resistance to Everolimus and Establishes Vulnerability to Cyclin-Dependent Kinase Inhibitors in Pancreatic Neuroendocrine Neoplasm Cells

Abstract

<b><i>Introduction:</i></b> Dysregulation of the mechanistic target of rapamycin complex 1 (mTORC1)-dependent pathways in pancreatic neuroendocrine neoplasms (PanNENs) underlies the introduction of the mTORC1 inhibitor everolimus as treatment of advanced progressive PanNENs. Although everolimus significantly increases progression-free survival, most patients acquire secondary resistance to the drug. This study aimed at identifying mechanisms involved in acquisition of resistance to everolimus. <b><i>Methods:</i></b> BON-1 and everolimus-resistant (ER) BON-1 cells were used as in vitro system of sensitivity and acquired resistance. Transcriptome changes occurring in BON-1 and ER-BON-1 were investigated by RNA sequencing and validated by quantitative PCR analysis. RNA extracted from patients’ biopsies was used to validate MYC upregulation. Drug screening and functional assays were performed using ER-BON-1 cells. Cell cycle progression was evaluated by FACS analysis. <b><i>Results:</i></b> Our results show that MYC overexpression is a key event in the development of secondary resistance to everolimus in PanNEN cell lines and in metastatic lesions from neuroendocrine neoplasm patients. MYC knockdown restored ER-BON-1 sensitivity to everolimus. Pharmacological inhibition of MYC mediated by the cyclin-dependent kinase inhibitor dinaciclib strongly reduced viability of ER-BON-1. Dinaciclib synergized with everolimus and inhibited ER-BON-1 cell cycle progression. <b><i>Discussion:</i></b> Our findings suggest that MYC upregulation drives the development of secondary resistance to everolimus in PanNENs and that its inhibition is an exploitable vulnerability. Indeed, our results indicate that combined treatments with cyclin-dependent kinase and mTOR inhibitors may counteract secondary resistance to everolimus in PanNENs and may pave the ground for new therapeutic regimens for these tumors.

Reciprocal Interactions between Fibroblast and Pancreatic Neuroendocrine Tumor Cells: Putative Impact of the Tumor Microenvironment

“…First, the fibroblast-conditioned medium does not play a role in the acquired resistance to everolimus, a statement which is further underlined by experiments demonstrating that resistance to everolimus, as obtained in vitro, is rather the consequence of chronic exposure to the drug with selection of a resistant clonal tumoral cell [ 25 , 47 , 48 ]. Moreover, this secondary resistance is likely constituted by the activation of alternative signaling pathways, as has been shown for MYC [ 49 ] and even SRC [ 50 , 51 ]. Second, the results of our functional studies, including those using Western blot analysis, suggest that the Pi3K/AKT/mTOR signaling pathway is not overactivated in the presence of fibroblast-conditioned medium.…”

Target c-Myc to treat pancreatic cancer

“…Further, decreased c-Myc expression improves cancer cells’ response to mTOR inhibition. 74 , 75 C-Myc enhances mTOR-mediated 4EBP1 phosphorylation in the first stages of tumorigenesis. 76 C-Myc blocks the inhibitory effect of tuberous sclerosis complex 2 (TSC2) on mTOR.…”

Functional Interaction Between the Oncogenic Kinase NEK2 and Sam68 Promotes a Splicing Program Involved in Migration and Invasion in Triple-Negative Breast Cancer

“…Comparison of enriched motif within NEK2-regulated cassette exons with the compendium of RNA-binding motif from ( 37 ) were performed using Tomtom Motif comparison tools from the MEME Suite Collection (RRID:SCR_001783) ( 38 , 39 ). Gene ontology (GO) analysis was performed as previously described, using topGO (RRID:SCR_014798) Bioconductor package, ranking and analyzing ontologies using the elim method ( 40 ).…”