A Novel Liver X Receptor Inverse Agonist Impairs Cholesterol and Phospholipid Metabolism and Induces Apoptosis and Necroptosis in Pancreatic Ductal Adenocarcinoma Cells

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease with a high mortality rate and few effective treatments. A growing area of cancer therapeutics seeks to exploit the metabolic dysregulation of cancer cells, such as glucose, amino acid, and fatty acid metabolism, to selectively target malignant cells. As ligand-dependent transcription factors and critical regulators of metabolism, liver X receptors (LXRs) are amenable to small-molecule targeting for such purposes. We have profiled the transcriptomic, metabolomic, and cytotoxic effects of a newly discovered small-molecule LXR modulator, GAC0003A4 (3A4), in PDAC cell lines. On the transcriptomic level, marked changes in gene expression were observed, including downregulation of LXR target genes and pathways. Gene set enrichment analysis determined downregulation of several metabolic pathways, such as fatty acid and cholesterol metabolism, while upregulated pathways involved TNFα/NF-κB and other stress-induced processes. Metabolomic analyses revealed altered metabolites in several pathways, the most enriched categories being lipids and amino acid metabolites, while phospholipids and sphingolipids, including ceramides, were also found to be significantly altered. Insights from transcriptomic and metabolomic studies helped guide the determination of alterations in cholesterol and ceramides as integral to the antiproliferative mechanisms of 3A4. Additionally, a concurrent programmed cell death mechanism involving apoptosis and necroptosis was shown to be activated. These studies provide novel insights into the effects of LXR modulation on gene expression, metabolism, and cell death induction in PDAC cells. The metabolic and cytotoxic effects of LXR modulation on the PDAC cell lines used in this study could also aid in the design and application of drugs to target other refractory cancers.