Loss of mitochondrial pyruvate carrier 1 supports proline-dependent proliferation and collagen biosynthesis in ovarian cancer

The pyruvate transporter MPC1 (mitochondrial pyruvate carrier 1) acts as a tumour-suppressor, loss of which correlates with a pro-tumorigenic phenotype and poor survival in several tumour types. In high-grade serous ovarian cancers (HGSOC), patients display copy number loss of MPC1 in around 78% of cases and reduced MPC1 mRNA expression. To explore the metabolic effect of reduced expression, we demonstrate that depleting MPC1 in HGSOC cell lines drives expression of key proline biosynthetic genes; PYCR1, PYCR2 and PYCR3, and biosynthesis of proline. We show that altered proline metabolism underpins cancer cell proliferation, reactive oxygen species (ROS) production, and type I and type VI collagen formation in ovarian cancer cells. Furthermore, exploring The Cancer Genome Atlas, we discovered the PYCR3 isozyme to be highly expressed in a third of HGSOC patients, which was associated with more aggressive disease and diagnosis at a younger age. Taken together, our study highlights that targeting proline metabolism is a potential therapeutic avenue for the treatment of HGSOC.

Ancient complexes of iron and sulfur modulate oncogenes and oncometabolism

Inorganic complexes of iron and sulfur, that is, iron-sulfur [FeS] clusters, have played a fundamental role in life on Earth since the prebiotic period. These clusters were involved in elementary reactions leading to the emergence of life and, since then, gained function in processes, such as respiration, replication, transcription, and the immune response. We discuss how three [FeS] proteins involved in the innate immune response play a role in oncogene expression/function and oncometabolism. Our analysis highlights the importance of future research into understanding the [FeS] clusters' roles in cancer progression and proliferation. The outcomes of these studies will help identify new targets and develop new anticancer therapeutics.

Cardio-Onco-Metabolism - Metabolic vulnerabilities in cancer and the heart

Cancer and cardiovascular diseases (CVDs) are the leading cause of death worldwide. Metabolic remodeling is a hallmark of both cancer and the failing heart. Tumors reprogram metabolism to optimize nutrient utilization and meet increased demands for energy provision, biosynthetic pathways, and proliferation. Shared risk factors for cancer and CVDs suggest intersecting mechanisms for disease pathogenesis and progression. In this review, we aim to highlight the role of metabolic remodeling in cancer and its potential to impair cardiac function. Understanding these mechanisms will help us develop biomarkers, better therapies, and identify patients at risk of developing heart disease after surviving cancer.

Metabostemness in cancer: Linking metaboloepigenetics and mitophagy in remodeling cancer stem cells

Cancer stem cells (CSCs) are rare populations of malignant cells with stem cell-like features of self-renewal, uninterrupted differentiation, tumorigenicity, and resistance to conventional therapeutic agents, and these cells have a decisive role in treatment failure and tumor relapse. The self-renewal potential of CSCs with atypical activation of developmental signaling pathways involves the maintenance of stemness to support cancer progression. The acquisition of stemness in CSCs has been accomplished through genetic and epigenetic rewiring following the metabolic switch. In this context, "metabostemness" denotes the metabolic parameters that essentially govern the epitranscriptional gene reprogramming mechanism to dedifferentiate tumor cells into CSCs. Several metabolites often referred to as oncometabolites can directly remodel chromatin structure and thereby influence the operation of epitranscriptional circuits. This integrated metaboloepigenetic dimension of CSCs favors the differentiated cells to move in dedifferentiated macrostates. Some metabolic events might perform as early drivers of epitranscriptional reprogramming; however, subsequent metabolic hits may govern the retention of stemness properties in the tumor mass. Interestingly, selective removal of mitochondria through autophagy can promote metabolic plasticity and alter metabolic states during differentiation and dedifferentiation. In this connection, novel metabostemness-specific drugs can be generated as potential cancer therapeutics to target the metaboloepigenetic circuitry to eliminate CSCs.

Otto Warburg: The journey towards the seminal discovery of tumor cell bioenergetic reprogramming

Metabolic reprogramming is now regarded as a hallmark of cancer. This phenomenon was first observed at the level of cellular energetics, in the form of very high rates of lactic acid fermentation, not only in anoxia, but also in the presence of oxygen levels that do not compromise respiration. This intriguing tumor phenotype, characterized by a very low energy yield, was unveiled, in the early 1920s, by Otto Warburg, one of the greatest biochemists of all time. This manuscript outlines aspects of Warburg's personal and research life that, in retrospect, might be viewed as a preparation for his successful approach to the cancer problem. It also discusses the experiments that led to the discovery and briefly presents Warburg's theory for the origin of tumors. Finally, it concludes with considerations regarding the novel avenues that this monumental and still intriguing discovery opened in terms of diagnosis and treatment of cancer.

Chemistry, biochemistry, metabolic fate and mechanism of action of 6-oxo-cholestan-3β,5α-diol (OCDO), a tumor promoter and cholesterol metabolite

Oxygenation products of cholesterol, named oxysterols, were suspected since the 20th century to be involved in carcinogenesis. Among the family of oxysterol molecules, cholesterol-5,6-epoxides (5,6-EC) retained the attention of scientists because they contain a putative alkylating epoxide group. However, studies failed into demonstrating that 5,6-EC were direct carcinogens and revealed a surprising chemical stability and unreactivity towards nucleophiles in standard conditions. Analyses of 5,6-EC metabolism in normal cells showed that they were extensively transformed into cholestane-3β,5α,6β-triol (CT) by the cholesterol-5,6-epoxide hydrolase (ChEH). Studies performed in cancer cells showed that CT was additionally metabolized into an oxysterol identified as the 6-oxo-cholestan-3β,5α-diol (OCDO), by the 11β-hydroxysteroid dehydrogenase of type 2 (HSD2), the enzyme which inactivates cortisol into cortisone. Importantly, OCDO was shown to display tumor promoter properties in breast cancers, by binding to the glucocorticoid receptor, and independently of their estrogen receptor status, revealing the existence of a new tumorigenic pathway centered on 5,6-EC. In breast tumors from patients, OCDO production as well as the expression of the enzymes involved in the pathway producing OCDO, namely ChEH subunits and HSD2, were higher compared to normal tissues, and overexpression of these enzymes correlate with a higher risk of patient death, indicating that this onco-metabolism is of major importance to breast cancer pathology. Herein, we will review the actual knowledge and the future trends in OCDO chemistry, biochemistry, metabolism and mechanism of action and will discuss the impact of OCDO discovery on new anticancer therapeutic strategies.

O-GlcNAc in cancer: An Oncometabolism-fueled vicious cycle. J Bioenerg Biomembr. 2018;50:155-173. [PMID: 29594839 DOI: 10.1007/s10863-018-9751-2]

Cancer cells exhibit unregulated growth, altered metabolism, enhanced metastatic potential and altered cell surface glycans. Fueled by oncometabolism and elevated uptake of glucose and glutamine, the hexosamine biosynthetic pathway (HBP) sustains glycosylation in the endomembrane system. In addition, the elevated pools of UDP-GlcNAc drives the O-GlcNAc modification of key targets in the cytoplasm, nucleus and mitochondrion. These targets include transcription factors, kinases, key cytoplasmic enzymes of intermediary metabolism, and electron transport chain complexes. O-GlcNAcylation can thereby alter epigenetics, transcription, signaling, proteostasis, and bioenergetics, key 'hallmarks of cancer'. In this review, we summarize accumulating evidence that many cancer hallmarks are linked to dysregulation of O-GlcNAc cycling on cancer-relevant targets. We argue that onconutrient and oncometabolite-fueled elevation increases HBP flux and triggers O-GlcNAcylation of key regulatory enzymes in glycolysis, Kreb's cycle, pentose-phosphate pathway, and the HBP itself. The resulting rerouting of glucose metabolites leads to elevated O-GlcNAcylation of oncogenes and tumor suppressors further escalating elevation in HBP flux creating a 'vicious cycle'. Downstream, elevated O-GlcNAcylation alters DNA repair and cellular stress pathways which influence oncogenesis. The elevated steady-state levels of O-GlcNAcylated targets found in many cancers may also provide these cells with a selective advantage for sustained growth, enhanced metastatic potential, and immune evasion in the tumor microenvironment.

The TCA cycle as a bridge between oncometabolism and DNA transactions in cancer

Cancer cells exploit metabolic rearrangements for sustaining their high proliferation rate and energy demand. The TCA cycle is a central metabolic hub necessary for ATP production and for providing precursors used in many biosynthetic pathways. Thus, dysregulation of the TCA cycle flux is frequently observed in cancer. The identification of mutations in several enzymes of the TCA cycle in human tumours demonstrated a direct connection between this metabolic pathway and cancer occurrence. Moreover, changes in the expression/activity of these enzymes were also shown to promote metabolic adaptation of cancer cells. In this review, the main genetic and non-genetic alterations of TCA cycle in cancer will be described. Particular attention will be given to extrametabolic roles of TCA cycle enzymes and metabolites underlying the regulation of nuclear and mitochondrial DNA transactions.

The metabolic alterations of cancer cells

Cancer cells exhibit profound metabolic alterations, allowing them to fulfill the metabolic needs that come with increased proliferation and additional facets of malignancy. Such a metabolic transformation is orchestrated by the genetic changes that drive tumorigenesis, that is, the activation of oncogenes and/or the loss of oncosuppressor genes, and further shaped by environmental cues, such as oxygen concentration and nutrient availability. Understanding this metabolic rewiring is essential to elucidate the fundamental mechanisms of tumorigenesis as well as to find novel, therapeutically exploitable liabilities of malignant cells. Here, we describe key features of the metabolic transformation of cancer cells, which frequently include the switch to aerobic glycolysis, a profound mitochondrial reprogramming, and the deregulation of lipid metabolism, highlighting the notion that these pathways are not independent but rather cooperate to sustain proliferation. Finally, we hypothesize that only those genetic defects that effectively support anabolism are selected in the course of tumor progression, implying that cancer-associated mutations may undergo a metabolically convergent evolution.

Luciferase-based reporter to monitor the transcriptional activity of the SIRT3 promoter

Sirtuin 3 (SIRT3) is a major regulator of oncometabolism. Indeed, the activity of SIRT3 significantly affects the response to oxidative stress, glycolytic proficiency, and tumorigenic potential of malignant cells. Thus, a system to accurately measure the transcriptional activity of the SIRT3 promoter could facilitate the identification of novel antineoplastic agents or have diagnostic applications. Here, we describe all the steps involved in the development of a luciferase-based reporter system to measure the activation of the human SIRT3 promoter, encompassing the design of appropriate primers, the cloning of the promoter fragment, and its site-directed mutagenesis. We validated this system in human embryonic kidney 293T cells, taking advantage of the renowned ability of the transcription factor estrogen-related receptor α to transactivate SIRT3. Moreover, here we demonstrate that SIRT3 expression is responsive to rapamycin, a small inhibitor of mammalian target of rapamycin that has been extensively employed as a caloric restriction mimetic. Finally, we provide an overview of the complementary molecular biology techniques that might be employed to further verify the reliability of this system.