Pyruvate carboxylase (PC) is a mitochondrial enzyme that catalyzes the ATP-dependent carboxylation of pyruvate to oxaloacetate (OAA), serving to replenish the tricarboxylic acid (TCA) cycle. In nonmalignant tissue, PC plays an essential role in controlling whole-body energetics through regulation of gluconeogenesis in the liver, synthesis of fatty acids in adipocytes, and insulin secretion in pancreatic β cells. In breast cancer, PC activity is linked to pulmonary metastasis, potentially by providing the ability to utilize glucose, fatty acids, and glutamine metabolism as needed under varying conditions as cells metastasize. PC enzymatic activity appears to be of particular importance in cancer cells that are unable to utilize glutamine for anaplerosis. Moreover, PC activity also plays a role in lipid metabolism and protection from oxidative stress in cancer cells. Thus, PC activity may be essential to link energy substrate utilization with cancer progression and to enable the metabolic flexibility necessary for cell resilience to changing and adverse conditions during the metastatic process.

Vitamin D exerts anti‐cancer effects in recent clinical trials and preclinical models. The actions of vitamin D are primarily mediated through its hormonal form, 1,25‐dihydroxyvitamin D (1,25(OH)2D). Previous literature describing in vitro studies has predominantly focused on the anti‐tumourigenic effects of the hormone, such as proliferation and apoptosis. However, recent evidence has identified 1,25(OH)2D as a regulator of energy metabolism in cancer cells, where requirements for specific energy sources at different stages of progression are dramatically altered. The literature suggests that 1,25(OH)2D regulates energy metabolism, including glucose, glutamine and lipid metabolism during cancer progression, as well as oxidative stress protection, as it is closely associated with energy metabolism. Mechanisms involved in energy metabolism regulation are an emerging area in which vitamin D may inhibit multiple stages of cancer progression. LINKED ARTICLES This article is part of a themed issue on New avenues in cancer prevention and treatment (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.12/issuetoc

Regions of hypoxia are common in solid tumors and drive changes in gene expression that increase risk of cancer metastasis. Tumor cells must respond to the stress of hypoxia by activating genes to modify cell metabolism and antioxidant response to improve survival. The goal of the current study was to determine the effect of hypoxia on cell metabolism and markers of oxidative stress in metastatic (metM-Wntlung) compared with nonmetastatic (M-Wnt) murine mammary cancer cell lines. We show that hypoxia induced a greater suppression of glutamine to glutamate conversion in metastatic cells (13% in metastatic cells compared to 7% in nonmetastatic cells). We also show that hypoxia increased expression of genes involved in antioxidant response in metastatic compared to nonmetastatic cells, including glutamate cysteine ligase catalytic and modifier subunits and malic enzyme 1. Interestingly, hypoxia increased the mRNA level of the transaminase glutamic pyruvic transaminase 2 (Gpt2, 7.7-fold) only in metM-Wntlung cells. The change in Gpt2 expression was accompanied by transcriptional (4.2-fold) and translational (6.5-fold) induction of the integrated stress response effector protein activating transcription factor 4 (ATF4). Genetic depletion ATF4 demonstrated importance of this molecule for survival of hypoxic metastatic cells in detached conditions. These findings indicate that more aggressive, metastatic cancer cells utilize hypoxia for metabolic reprogramming and induction of antioxidant defense, including activation of ATF4, for survival in detached conditions.

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Several cancers, including breast cancers, show dependence on glutamine metabolism. The purpose of the present study was to determine the mechanistic basis and impact of differential glutamine metabolism in nonmetastatic and metastatic murine mammary cancer cells. Universally labeled 13C5-glutamine metabolic tracing, qRT-PCR, measures of reductive–oxidative balance, and exogenous ammonium chloride treatment were used to assess glutamine reprogramming. Results show that 4 mM media concentration of glutamine, compared with 2 mM, reduced viability only in metastatic cells, and that this decrease in viability was accompanied by increased incorporation of glutamine-derived carbon into the tricarboxylic acid (TCA) cycle. While increased glutamine metabolism in metastatic cells occurred in tandem with a decrease in the reduced/oxidized glutathione ratio, treatment with the antioxidant molecule N-acetylcysteine did not rescue cell viability. However, the viability of metastatic cells was more sensitive to ammonium chloride treatment compared with nonmetastatic cells, suggesting a role of metabolic reprogramming in averting nitrogen cytotoxicity in nonmetastatic cells. Overall, these results demonstrate the ability of nonmetastatic cancer cells to reprogram glutamine metabolism and that this ability may be lost in metastatic cells.

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Excess adiposity is thought to be associated with approximately 20% of all cancers, including breast cancer. However the mechanism underlying this relationship remains controversial. Adipocytes secrete a wide array of bioactive molecules which act as key mediators in several obesity‐associated diseases. Further, the active form of vitamin D, 1α,25dihydroxyvitamin D (1,25(OH)2D) regulates multiple aspects of adipocyte biology, including adipogenesis and adipocyte apoptosis, as well as modulating the release of factors associated with cancer promotion. The purpose of these studies was to investigate 1,25(OH)2D‐mediated regulation of differentiated adipocytes to determine the impact on breast cancer progression. Differentiated 3T3‐L1 adipocytes were treated with 1,25(OH)2D (10 nM) for 2 days, followed by harvesting the adipocytes and collection of adipocyte conditioned media (ACM). ACM from adipocytes treated with 1,25(OH)2D decreased cell proliferation in metastatic MDA‐MB‐231 and MCF10CA1a cells compared to vehicle treated ACM, (42% and 37% of vehicle ACM, respectively), as measured by an MTT assay. In addition, ACM from adipocytes treated with 1,25(OH)2D inhibited cell migration and wound healing in MDA‐MB‐231 cells (37% and 30% respectively relative to vehicle ACM). In order to explore the mechanism underlying these effects on breast cancer metastatic capability, the mRNA expression of IGF‐1, IL‐6 and leptin was measured in adipocytes treated with either vehicle or 1,25(OH)2D. Treatment of adipocytes with 1,25(OH)2D decreased mRNA expression of IGF‐1, IL‐6 and leptin by 23%, 85%, and 39%, respectively. Further studies aim at demonstrating the mechanism underlying the impact of 1,25(OH)2D on adipocytes to inhibit their capability of promoting breast cancer metastasis. In summary, these results suggest that 1,25(OH)2D alters adipocyte secretions to inhibit breast cancer metastasis.Support or Funding InformationThis work was supported in part by the Higher Education Challenge Grant from the National Institute of Food and Agriculture, United States Department of Agriculture (#2013‐70003‐20922).

For women, breast cancer is the most diagnosed cancer, with metastasis being the primary cause of most breast cancer-related deaths. During metastasis, cells detach from the extracellular matrix (ECM) to move to a secondary site. Unlike normal cells, metastatic cells are resistant to cell death upon ECM detachment. The amino acid glutamine is used as an energy source during metastatic progression via replenishing the TCA cycle. Breast cancer cells have decreased viability in the absence of glutamine, but the effect of glutamine in ECM detached conditions in metastatic cells is not known. We hypothesize that metastatic and non-metastatic cells have a decreased viability in ECM detachment in glutamine deprived conditions. In this study, metastatic MCF10CA1a cells and non-metastatic Harvey-ras oncogene transfected MCF10A-ras cells were employed. As expected, in ECM detached conditions, the MCF10A-ras cells had a greater decrease in viability (58.4%) in comparison to the MCF10CA1a cells (32.7%). However, in glutamine deprived conditions, the MCF10CA1a cells decrease in viability was 15.2% greater compared to the MCF10A-ras cells. mRNA expression of the major glutamine transporter, SLC1A5, was decreased in detached conditions in both cell lines, but to a greater extent in the MCF10A-ras cells (70.04%) compared to the MCF10CA1a cells (20.15%). Additionally, mRNA expression in detached conditions of glutamate dehydrogenase, the enzyme that metabolizes the downstream glutamine metabolite glutamate to α-ketoglutarate (αKG), was decreased by 77% in the non-metastatic cells, but increased by 23% in the metastatic cells. Additionally, mRNA expression of GOT1, a gene which encodes for the transaminase enzyme which synthesizes αKG and aspartate from glutamate and oxaloacetate, decreased 73% in detached conditions in the non-metastatic cells but was unchanged in the metastatic cells. Moreover, following detachment the glutamine synthesizing enzyme, glutamine synthetase mRNA expression was increased by 81.92% in the non-metastatic cells and 88.43% in the metastatic cells. In summary, the greater effect of glutamine depletion on viability, and the maintained expression of glutamine metabolizing enzymes in the metastatic cells suggest greater dependence on glutamine metabolism in ECM detached conditions compared to non-metastatic cells. Comparison of metastatic and non-metastatic breast cancer cells will provide insights to direct the development of new targets for the prevention of breast cancer metastasis. Citation Format: Kanika K. Garg, Madeline Sheeley, Dorothy Teegarden. Comparison of metastatic and nonmetastatic breast cancer cell survival in glutamine depleted extracellular matrix detached conditions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2873.