Abstract
Abstract Pancreatic ductal adenocarcinoma (PDAC) is the most prevalent form of pancreatic cancer. It is predicted to become the third leading cause of cancer-related deaths by 2030. PDAC has a poor survival rate of 5 years with a 7% success rate. Current treatments include nontargeted highly toxic chemotherapeutic agents. More than 95% of PDAC patients have activating mutations of Kristen RAt Sarcoma virus (KRAS) gene, and it is known to drive metabolic reprogramming that increases cancer cell survival and resistance against the chemotherapeutic drugs. KRAS promotes noncanonical consumption of glutamine by upregulating the expression of glutaminase 1 (GLS1) enzyme. This, in turn, supports PDAC growth and survival by maintaining redox homeostasis and also by replenishing citric acid cycle intermediates. Liver X receptor beta (LXRβ), a nuclear receptor, is a ligand-dependent transcription factor that is ubiquitously expressed in all tissues. It plays an important role in maintaining cholesterol, lipid, and glucose homeostasis under normal physiologic conditions. Agonist-bound LXRβ activates the transcription of genes involved in lipogenesis, reverse cholesterol transport, and glucose metabolism. Our group has previously shown that LXRβ is expressed in PDAC tissues, and treatment with GW3965, an LXRβ agonist, reduced PDAC proliferation. However, LXRβ agonists have adverse side effects of increasing liver and circulating triglycerides. This study identified a novel ligand of LXRβ 1E5, which significantly reduced PDAC cell proliferation. 1E5 decreased the basal expression of LXRβ target genes such as sterol regulatory element-binding protein 1 (SREBP1c) and ATP binding cassette subfamily A member 1 (ABCA1). It also increased the binding of co-repressor peptides such as nuclear receptor co-repressor (NCoR) and silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) to the LXRβ ligand binding domain, whereas it decreased the binding of the co-activator peptide as demonstrated by the time-resolved fluorescence energy transfer (TR-FRET) assay, thereby inhibiting the transcriptional activity of LXRβ. Therefore, 1E5 acts as an LXRβ inverse agonist. Furthermore, the metabolomics study revealed that 1E5 disrupts glutamine metabolism in PDAC cells by downregulating the glutamine, aspartate, and alpha-ketoglutarate levels in cells. Gene expression analysis showed that it significantly downregulated GLS1 expression. These results demonstrate that the novel inverse agonist is a candidate agent in the treatment of PDAC by targeting glutamine metabolism. Citation Format: Shivangi Srivastava, Scott Widmann, Chin-Yo Lin. Liver X receptor ligand targets glutamine metabolism in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr C53.
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