Pancreatic ductal adenocarcinoma (PDAC) is difficult to detect early and is often resistant to standard chemotherapeutic options, contributing to extremely poor disease outcomes. Members of the nuclear receptor superfamily carry out essential biological functions such as hormone signaling and are successfully targeted in the treatment of endocrine-related malignancies. Liver X receptors (LXRs) are nuclear receptors that regulate cholesterol homeostasis, lipid metabolism, and inflammation, and LXR agonists have been developed to regulate LXR function in these processes. Intriguingly, these compounds also exhibit antiproliferative activity in diverse types of cancer cells. In this study, LXR agonist treatments disrupted proliferation, cell-cycle progression, and colony-formation of PDAC cells. At the molecular level, treatments downregulated expression of proteins involved in cell cycle progression and growth factor signaling. Microarray experiments further revealed changes in expression profiles of multiple gene networks involved in biological processes and pathways essential for cell growth and proliferation following LXR activation. These results establish the antiproliferative effects of LXR agonists and potential mechanisms of action in PDAC cells and provide evidence for their potential application in the prevention and treatment of PDAC.

Hereditary, hormonal, and behavioral factors contribute to the development of breast cancer. Alcohol consumption is a modifiable behavior that is linked to increased breast cancer risks and is associated with the development of hormone-dependent breast cancers as well as disease progression and recurrence following endocrine treatment. In this study we examined the molecular mechanisms of action of alcohol by applying molecular, genetic, and genomic approaches in characterizing its effects on estrogen receptor (ER)-positive breast cancer cells. Treatments with alcohol promoted cell proliferation, increased growth factor signaling, and up-regulated the transcription of the ER target gene GREB1 but not the canonical target TFF1/pS2. Microarray analysis following alcohol treatment identified a large number of alcohol-responsive genes, including those which function in apoptotic and cell proliferation pathways. Furthermore, expression profiles of the responsive gene sets in tumors were strongly associated with clinical outcomes in patients who received endocrine therapy. Correspondingly, alcohol treatment attenuated the anti-proliferative effects of the endocrine therapeutic drug tamoxifen in ER-positive breast cancer cells. To determine the contribution and functions of responsive genes, their differential expression in tumors were assessed between outcome groups. The proto-oncogene BRAF was identified as a novel alcohol- and estrogen-induced gene that showed higher expression in patients with poor outcomes. Knock-down of BRAF, moreover, prevented the proliferation of breast cancer cells. These findings not only highlight the mechanistic basis of the effects of alcohol on breast cancer cells and increased risks for disease incidents and recurrence, but may facilitate the discovery and characterization of novel oncogenic pathways and markers in breast cancer research and therapeutics.

Pancreatic ductal adenocarcinoma (PDAC) is the predominant form of pancreatic cancer. PDACs harbor oncogenic mutations in the KRAS gene, and ongoing efforts to directly target its mutant protein product to inhibit tumor growth are a priority not only in pancreatic cancer but in other malignancies such as lung and colorectal cancers where KRAS is also commonly mutated. An alternative strategy to directly targeting KRAS is to identify and target druggable receptors involved in dysregulated cancer hallmarks downstream of KRAS dysregulation. Liver X receptors (LXRs) are members of the nuclear receptor family of ligand-modulated transcription factors and are involved in the regulation of genes which function in key cancer-related processes, including cholesterol transport, lipid and glucose metabolism, and inflammatory and immune responses. Modulation of LXRs via small molecule ligands has emerged as a promising approach for directly targeting tumor cells or the stromal and immune cells within the tumor microenvironment. We have previously shown that only one of the two LXR subtypes (LXRβ) is expressed in pancreatic cancer cells, and targeting LXR with available synthetic ligands blocked the proliferation of PDAC cells and tumor formation. In a screen of a focused library of drug-like small molecules predicted to dock in the ligand-binding pocket of LXRβ, we identified two novel LXR ligands with more potent antitumor activity than current LXR agonists used in our published studies. Characterization of the two lead compounds (GAC0001E5 and GAC0003A4) indicates that they function as LXR inverse agonists which inhibit their transcriptional activity. Prolonged treatments with novel ligands further revealed their function as LXR "degraders" which significantly reduced LXR protein levels in all three PDAC cell lines tested. These findings support the utility of these novel inhibitors in basic research on ligand design, allosteric mechanisms, and LXR functions and their potential application as treatments for advanced pancreatic cancer and other recalcitrant malignancies.

Pancreatic cancer is the fourth leading cause of cancer deaths in the US and has the worst prognosis of the major cancers due to difficulties in early detection and limited treatment options. Nuclear receptors (NRs) are a family of ligand-dependent transcription factors which play key roles in regulating gene expression in normal development and physiology and in a number of human diseases, including cancers. These receptors and their ligands are involved in breast and prostate cancers, and they have been successfully targeted clinically in the prevention and treatment of these diseases. Liver X receptors (LXRs) are NRs which are known to regulate cholesterol, glucose, and fatty acid metabolism and inflammatory responses. Published reports of the ability of LXR agonists to block the growth and proliferation of breast, prostate, ovarian, lung, skin, and colorectal cancer cells suggest that LXRs are involved in regulating common pathways in cancer progression and tumor cell growth and proliferation found in these diverse cancers and perhaps other malignancies as well. To test this hypothesis, we treated pancreatic cancer cells (PANC-1, Mia-PaCa-2, and BxPC-3) with the synthetic LXR ligand GW3965, originally developed for the treatment of atherosclerosis, and measured the effects of ligand treatment on cell proliferation, survival, and cell cycle progression. Treatment with the LXR ligand disrupted cell proliferation as determined by trypan blue exclusion, clonogenic, bromodeoxyuridine incorporation, and tetrazolium salt reduction assays. Cell cycle analysis indicated an increase in cells in the G0 or G1 phase, suggestive of cell cycle arrest or withdrawal. To determine potential mechanisms underlying the observed effects, we performed microarray analysis of gene expression in response to ligand treatment and found that known LXR target genes and genes associated with a number of signaling pathways and molecular processes, including those involved in cell division, are differentially expressed in pancreatic cancer cells following treatment. These findings suggest that LXRs and their ligands target gene networks which are important for pancreatic cancer cell proliferation and warrant further study as potential therapeutic targets and agents, respectively, in the treatment of pancreatic cancer. Citation Format: Nicholes R. Candelaria, Sridevi Manchem, H Trang Vu, Jine Zheng, Chiara Gabbi, Prasenjit Dey, Husna Karaboga, Jean Lin, Lise-Lotte Vedin, Fei Su, Ka Liu, Philip Jonsson, Knut R. Steffensen, Jan-Åke Gustafsson, Chin-Yo Lin. Liver X receptor agonist blocks pancreatic cancer cell proliferation. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1310. doi:10.1158/1538-7445.AM2013-1310

No abstract