Identification of C/EBPδ-Modifying Compounds as Potential Anticancer Agents Using a High-Throughput Drug Screen

CCAAT/enhancer-binding protein delta (C/EBPδ) has been shown to promote tumour growth, drug resistance and metastasis formation in some cancers, whereas we have shown that its re-expression limits the features of tumour progression in pancreatic ductal adenocarcinoma (PDAC). The pharmacological targeting—either activation or inhibition—of C/EBPδ may therefore harbour clinical relevance and is desirable for preclinical studies on C/EBPδ in different contexts. Regrettably, to date, only few molecules have been identified that modify C/EBPδ. Here, we present a high-throughput compound screen in conjunction with a novel eGFP reporter to identify further compounds that either increase or decrease C/EBPδ transcriptional activity. Of 1402 small molecule inhibitors, we identified a total of 22 potent inducers and 18 inhibitors of C/EBPδ-mediated eGFP fluorescence. Using pathway enrichment analysis, we found that, generally, inhibition of the cell cycle elicits an increase in C/EBPδ activity whereas PI3K/Akt/mTOR-targeting compounds reduce C/EBPδ activity. We confirmed the potential importance of cell cycle-mediated regulation of C/EBPδ by showing that four of the most potent C/EBPδ activators—R547, PHA793387, AZD5438 and AT7519, all multi-cyclin-dependent kinase (CDK) inhibitors—limited the clonal expansion of PDAC cells. Next to providing a valuable selection of C/EBPδ-modulating compounds for the use in preclinical studies, this report contributes to our understanding of the molecular regulatory mechanisms of C/EBPδ in general and in PDAC in particular.