Abstract B76: Pyruvate dehydrogenase: A key to epigenetic regulation in CAFs

Cancer-associated fibroblasts (CAFs) play fundamental roles in cancer and are emerging as therapeutic target in tumors with extensive stromal regions and in those for which there are limited targeted therapies against the cancer cells, such as ovarian cancer. A unique feature of the CAFs is their ability to secrete abundant collagen-rich extracellular matrix (ECM) that promotes the desmoplastic reaction that accompanies tumor progression and drives tumor growth and metastasis. Altered tumor metabolism is a hallmark of cancer, and understanding whether and how metabolic pathways support protumorigenic and proinvasive CAF functions may identify ways to target these cells to effectively target tumors. Using global phosphoproteomics, we have found that the activity of the pyruvate dehydrogenase complex (PDC), which is the rate-limiting enzyme for the entry of glycolysis-derived metabolites into the TCA cycle by converting pyruvate into acetyl-CoA, is strongly increased in patient-derived CAFs compared to their normal fibroblast counterpart. Consistently, the expression of pyruvate dehydrogenase kinase (PDK), which phosphorylates and inhibits PDC activity, is downregulated in CAFs and in the stroma of tumor patient samples. We found that PDC activity in CAFs leads to increased acetyl-CoA production. Surprisingly, 13C-glucose tracing experiments showed that CAFs do not channel acetyl-CoA into the TCA cycle. Instead, CAFs use acetyl-CoA to activate an epigenetic switch triggered by acetylation of H3K27. H3K27 acetylation is a known marker of gene expression activation. In CAFs, it triggered the expression of several collagen genes. Interestingly, also the expression of enzymes of the proline synthesis pathway was induced following H3K27 acetylation. Collagens have an unusually high content of proline residues, and we show that enhanced proline synthesis is necessary to support the production of collagen-rich ECM in CAFs. Targeting the PDK/PDC pathway or H3K27 acetylation or the proline synthesis pathway was sufficient to inhibit collagen synthesis in CAFs in in vitro experiments. Targeting proline synthesis in the stroma was sufficient to reduce tumor growth in vivo. Our work provides a first evidence that metabolism and epigenetics are tightly intertwined in regulating CAF functions and that targeting the PDK/PDC pathway or the proline synthesis pathway in the stroma could halt the development of a desmoplastic reaction and tumor progression.

Citation Format: Emily Kay, Lisa Neilson, Claudia Boldrini, Juan Hernandez-Fernaud, Enio Gjerga, David Sumpton, Sandeep Dhayade, Grace McGregor, Grigorios Koulouras, Jurre Kamphorst, Karen Blyth, Julio Saez-Rodriguez, Gillian Mackay, Sara Zanivan. Pyruvate dehydrogenase: A key to epigenetic regulation in CAFs [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr B76.

Abstract B33: Assessing the role of DGAT activity on lipid homeostasis and cancer cell survival

Studies on the effects of modulating the lipid composition of cells have found that increases in saturated fatty acid levels can lead to ER stress, activation of the unfolded protein response (UPR) and cell death. These effects may occur through saturation of the phospholipid pool and subsequent deterioration of ER membrane function. Changes in the composition of the ER membrane can be sensed by the two UPR stress sensors IRE1 and PERK and lead to activation of UPR targets.

Rapidly proliferating cancer cells frequently exhibit elevated ER stress due to their increased protein translation rate. In addition, the tumor microenvironment is frequently hypoxic and a lack of oxygen can inhibit the activity of the fatty acid desaturase SCD1. This leads to saturation of the fatty acid pool and renders the ER less able to cope with high levels of protein synthesis, making the maintenance of adequate lipid homeostasis of paramount importance to cancer cells within hypoxic tumor domains. Tumor cells adapt to these conditions through a variety of mechanisms, including the uptake of exogenous unsaturated lipid. Both hypoxia and the presence of certain oncogenic drivers have been found to increase lipid uptake, which was found to protect cancer cells against inhibition of SCD1.

Since fatty acids can be converted to triglycerides and stored within lipid droplets, we asked whether cancer cells also cope with saturation of their fatty acid pool by storing excess saturated fatty acids as triglycerides. Clear cell renal cell carcinoma (ccRCC) tumors are very fatty and lipidomic analyses have found high levels of triglycerides in ccRCC compared to normal kidney tissue. We inhibited triglyceride synthesis in A498 ccRCC cells by shRNA –mediated knockdown of DGAT enzymes, which catalyze the final step in the synthesis of triglycerides from fatty acids. We tested whether loss of DGAT activity causes sensitivity to tumor-like stresses and investigated its effect on xenograft tumor growth. Remarkably, while loss of DGAT activity has little effect on cancer cell proliferation under oxygen- and nutrient-rich conditions, loss of DGAT activity has large effects on xenograft tumor growth. We also find that loss of DGAT activity is often accompanied by increases in markers of ER stress. We are currently assessing the lipid composition of these tumors and determining what aspects of the tumor microenvironment sensitize cells to loss of DGAT activity.

Citation Format: Daniel Ackerman, Bo Qiu, Hong Xie, Jurre Kamphorst, M. Celeste Simon. Assessing the role of DGAT activity on lipid homeostasis and cancer cell survival. [abstract]. In: Proceedings of the AACR Special Conference: Metabolism and Cancer; Jun 7-10, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(1_Suppl):Abstract nr B33.

Abstract LB-61: Targeting cancer cell metabolism in pancreatic cancer: p53, a key regulator of glycolysis and a major factor deciding the outcome of targeting the Warburg effect

Background and Aim: Tumor cells depend on metabolic alterations for their continued growth and survival, and such changes make cancer cells peculiarly addicted to the rapacious uptake of glucose. The Warburg effect is such a metabolic feature of cancers that helps to preferentially metabolize pyruvate via glycolytic pathway to lactate by lactate dehydrogenase A (LDHA). Our recent findings indicated that LDHA is required not only for tumor initiation but for tumor maintenance and progression (Le et al., PNAS, 2010). Here, we investigated the therapeutic potential of LDHA inhibition in pancreatic cancer, and attempt to delineate the factors responsible for tumor response. Methods: We evaluated the in vivo efficacy of FX11, a small molecule inhibitor of LDHA, in a panel of pancreatic cancer xenografts with annotated mutational status. Non-invasive quantitative assessment of lactate production was measured by real-time hyperpolarization experiments with 1-13C-labeled pyruvate using a DNP polarizer (HyperSense). [18F]-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET) combined with computed tomography (CT) imaging was conducted to evaluate the effect of FX11 treatment on glucose metabolism. Liquid chromatography - mass spectrometry (LC-MS) was used to quantify the tumor metabolites. Ki-67 and TUNEL staining were performed to determine the effect of FX11 treatment on apoptosis and tumor cell proliferation. Results: p53-deficient pancreatic cancer xenografts showed higher baseline metabolic activity and FX11 treatment down-regulated the tumor metabolic activity. Real-time imaging of pyruvate to lactate conversion using nuclear magnetic resonance (NMR) spectroscopy revealed that FX11 treatment inhibits pyruvate to lactate conversion in p53-deficient pancreatic cancer xenografts. Importantly, p53 promotes the expression of TP53-induced glycolysis regulator (TIGAR) and loss of p53 in tumors results in reduced TIGAR levels. The metabolic profiles of p53-deficient versus p53-proficient pancreatic cancer xenografts were remarkably different. FX11 treatment attenuates tumor progression, induces apoptosis and reduces tumor cell proliferation, preferentially in p53-deficient pancreatic cancer xenografts. Conclusions: Because the Warburg effect is characteristic of virtually all cancers and p53 is frequently mutated in vast majority of human cancers, our finding that p53, a key regulator of glycolysis and a major factor deciding the therapeutic outcome of targeting the Warburg effect may have broad clinical implications. Our findings may help to identify patient subsets that may be particularly responsive to LDHA targeted agents in clinical trials. Acknowledgement: Stand Up To Cancer-AACR Dream Team Translational Cancer Research Grant No. SU2C-AACR DT0509.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-61. doi:1538-7445.AM2012-LB-61

Microarray analysis indicates an important role for FABP5 and putative novel FABPs on a Western-type diet

Liver parenchymal cells play a dominant role in hepatic metabolism and thereby total body cholesterol homeostasis. To gain insight into the specific pathways and genes involved in the response of liver parenchymal cells to increased dietary lipid levels under atherogenic conditions, changes in parenchymal cell gene expression upon feeding a Western-type diet for 0, 2, 4, and 6 weeks were determined using microarray analysis in LDL receptor-deficient mice, an established atherosclerotic animal model. Using ABI Mouse Genome Survey Arrays, we were able to detect 7,507 genes (28% of the total number on an array) that were expressed in parenchymal cells isolated from livers of LDL receptor-deficient mice at every time point investigated. Time-dependent gene expression profiling identified fatty acid binding protein 5 (FABP5) and four novel FABP5-like transcripts located on chromosomes 2, 8, and 18 as important proteins in the primary response of liver parenchymal cells to Western-type diet feeding, because their expression was 16- to 22-fold increased within the first 2 weeks on the Western-type diet. The rapid substantial increase in gene expression suggests that these FABPs may play an important role in the primary protection against the cellular toxicity of cholesterol, free fatty acids, and/or lipid oxidants. Furthermore, as a secondary response to the Western-type diet, liver parenchymal cells of LDL receptor-deficient mice stimulated glycolysis and lipogenesis pathways, resulting in a steady, more atherogenic serum lipoprotein profile (increased VLDL/LDL).