The metabolic fate of acetate in cancer

Short-chain fatty acids reprogram metabolic profiles with the induction of reactive oxygen species production in human colorectal adenocarcinoma cells

Short-chain fatty acids (SCFAs) exhibit anticancer activity in cellular and animal models of colon cancer. Acetate, propionate, and butyrate are the three major SCFAs produced from dietary fiber by gut microbiota fermentation and have beneficial effects on human health. Most previous studies on the antitumor mechanisms of SCFAs have focused on specific metabolites or genes involved in antitumor pathways, such as reactive oxygen species (ROS) biosynthesis. In this study, we performed a systematic and unbiased analysis of the effects of acetate, propionate, and butyrate on ROS levels and metabolic and transcriptomic signatures at physiological concentrations in human colorectal adenocarcinoma cells. We observed significantly elevated levels of ROS in the treated cells. Furthermore, significantly regulated signatures were involved in overlapping pathways at metabolic and transcriptomic levels, including ROS response and metabolism, fatty acid transport and metabolism, glucose response and metabolism, mitochondrial transport and respiratory chain complex, one-carbon metabolism, amino acid transport and metabolism, and glutaminolysis, which are directly or indirectly linked to ROS production. Additionally, metabolic and transcriptomic regulation occurred in a SCFAs types-dependent manner, with an increasing degree from acetate to propionate and then to butyrate. This study provides a comprehensive analysis of how SCFAs induce ROS production and modulate metabolic and transcriptomic levels in colon cancer cells, which is vital for understanding the mechanisms of the effects of SCFAs on antitumor activity in colon cancer.

Regulation and function of the mammalian tricarboxylic acid cycle

The tricarboxylic acid (TCA) cycle, otherwise known as the Krebs cycle, is a central metabolic pathway that performs the essential function of oxidizing nutrients to support cellular bioenergetics. More recently, it has become evident that TCA cycle behavior is dynamic, and products of the TCA cycle can be co-opted in cancer and other pathologic states. In this review, we revisit the TCA cycle, including its potential origins and the history of its discovery. We provide a detailed accounting of the requirements for sustained TCA cycle function and the critical regulatory nodes that can stimulate or constrain TCA cycle activity. We also discuss recent advances in our understanding of the flexibility of TCA cycle wiring and the increasingly appreciated heterogeneity in TCA cycle activity exhibited by mammalian cells. Deeper insight into how the TCA cycle can be differentially regulated and, consequently, configured in different contexts will shed light on how this pathway is primed to meet the requirements of distinct mammalian cell states.

Metformin acts in the gut and induces gut-liver crosstalk

Metformin is the most prescribed drug for DM2, but its site and mechanism of action are still not well established. Here, we investigated the effects of metformin on basolateral intestinal glucose uptake (BIGU), and its consequences on hepatic glucose production (HGP). In diabetic patients and mice, the primary site of metformin action was the gut, increasing BIGU, evaluated through PET-CT. In mice and CaCo2 cells, this increase in BIGU resulted from an increase in GLUT1 and GLUT2, secondary to ATF4 and AMPK. In hyperglycemia, metformin increased the lactate (reducing pH and bicarbonate in portal vein) and acetate production in the gut, modulating liver pyruvate carboxylase, MPC1/2, and FBP1, establishing a gut-liver crosstalk that reduces HGP. In normoglycemia, metformin-induced increases in BIGU is accompanied by hypoglycemia in the portal vein, generating a counter-regulatory mechanism that avoids reductions or even increases HGP. In summary, metformin increases BIGU and through gut-liver crosstalk influences HGP.

Radiosynthesis, Preclinical, and Clinical Positron Emission Tomography Studies of Carbon-11 Labeled Endogenous and Natural Exogenous Compounds

The presence of positron emission tomography (PET) centers at most major hospitals worldwide, along with the improvement of PET scanner sensitivity and the introduction of total body PET systems, has increased the interest in the PET tracer development using the short-lived radionuclides carbon-11. In the last few decades, methodological improvements and fully automated modules have allowed the development of carbon-11 tracers for clinical use. Radiolabeling natural compounds with carbon-11 by substituting one of the backbone carbons with the radionuclide has provided important information on the biochemistry of the authentic compounds and increased the understanding of their in vivo behavior in healthy and diseased states. The number of endogenous and natural compounds essential for human life is staggering, ranging from simple alcohols to vitamins and peptides. This review collates all the carbon-11 radiolabeled endogenous and natural exogenous compounds synthesised to date, including essential information on their radiochemistry methodologies and preclinical and clinical studies in healthy subjects.

Simultaneous Quantification of Serum Lipids and Their Association with Type 2 Diabetes Mellitus-Positive Hepatocellular Cancer

Type 2 diabetes mellitus (T2DM) has been recognized as one of the most important and independent risk factors for hepatocellular cancer (HCC). However, there is still a lack of ideal tumor markers for HCC detection in the T2DM population. Serum lipids have been revealed as potential tumor markers for HCC. In this study, our objective was to develop a novel liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to detect several lipids including 8,15-dihydroxy-5,9,11,13-eicosatetraenoic acid (8,15-DiHETE), hexadecanedioic acid (HDA), 15-keto-13,14-dihydroprostaglandin A2 (DHK-PGA2), ricinoleic acid (RCL), octadecanedioic acid (OA) and 16-hydroxy hexadecanoic acid (16OHHA) in serum and explore their diagnostic potential for T2DM-positive [T2DM(+)] HCC. A robust LC-MS/MS method was established for the measurement of 8,15-DiHETE, HDA, DHK-PGA2, RCL, OA, and 16OHHA. The methodology validation was conducted, and the results suggested the reliability of this LC-MS/MS method for targeted lipids. Several serum lipids, including 8,15-DiHETE, HDA, DHK-PGA2, and OA were increased in T2DM(+) HCC patients. A biomarker signature that incorporated HDA, DHK-PGA2, and AFP was established and showed good diagnostic potential for T2DM(+) HCC, and the area under the ROC curve (AUC) was 0.87 for diagnosing T2DM(+) HCC from T2DM individuals. Additionally, the biomarker signature diagnosed small-size (AUC = 0.88) and early-stage (AUC = 0.79) tumors with high efficacy. Moreover, the biomarker signature could differentiate T2DM(+) HCC from other T2DM(+) tumors, including pancreatic, gastric and colorectal cancer (AUC = 0.88) as well. In conclusion, our study develops a novel tool for early diagnosis of T2DM(+) HCC in T2DM patients.

Acetate accumulation and regulation by process parameters control in Chinese hamster ovary cell culture

Chinese hamster ovary (CHO) cells represent a group of predominantly used mammalian hosts for producing recombinant therapeutic proteins. Known for their rapid proliferation rates, CHO cells undergo aerobic glycolysis that is characterized by fast glucose consumption, that ultimately gives rise to a group of small-molecule organic acids. However, only the function of lactate has been extensively studied in CHO cell culture. In this study, we observed the accumulation of acetate from the late exponential phase to harvest day, potentially contributing to the pH decline in late culture stage regardless of lactate consumption. In addition, we evaluated the acidification of the fresh media and the cell culture suspension, and the data revealed that acetate presented a lower acidification capacity compared to lactate and exhibited limited inhibitory effect on cells with less than 20 mM supplemented in the media. This study also explored the ways to control acetate accumulation in CHO cell culture by manipulating the process parameters such as temperature, glucose, and pH control. The positive correlation between the specific glucose consumption rate and acetate generation rate provides evidence of the endogenous acetate generation from overflow metabolism. Reducing these parameters (temperature, glucose consumption) and HCl-controlled low pH ultimately suppress acetate build-up. In addition, the specific acetate generation rate and relevant glucose consumption rate are found to be a metabolic trait associated with specific cell lines. Taken together, the results presented in these experiments provide a means to advance industrial CHO cell culture process control and development.

Association between human blood metabolome and the risk of breast cancer

BACKGROUND

Breast cancer is the most common cancer among women with limited treatment options. To identify promising drug targets for breast cancer, we conducted a systematical Mendelian randomization (MR) study to screen blood metabolome for potential causal mediators of breast cancer and further predict target-mediated side effects.

METHODS

We selected 112 unique blood metabolites from 3 large-scale European ancestry-based genome-wide association studies (GWASs) with a total of 147,827 participants. Breast cancer data were obtained from a GWAS in the Breast Cancer Association Consortium (BCAC), involving 122,977 cases and 105,974 controls of European ancestry. We conducted MR analyses to systematically assess the associations of blood metabolites with breast cancer, and a phenome-wide MR analysis was further applied to ascertain the potential on-target side effects of metabolite interventions.

RESULTS

Two blood metabolites were identified as the potential causal mediators for breast cancer, including high-density lipoprotein cholesterol (HDL-C) (odds ratio [OR], 1.09; 95% confidence interval [CI], 1.06-1.12; P = 9.67 × 10^-10) and acetate (OR, 1.24; 95% CI, 1.13-1.37; P = 1.35 × 10^-5). In the phenome-wide MR analysis, lowering HDL-C might have deleterious effects on the risk of the circulatory system and foreign body injury, while lowering acetate had deleterious effects on mental disorders disease.

CONCLUSIONS

The present systematic MR analysis revealed that HDL-C and acetate may be the causal mediators in the risk of developing breast cancer. Side-effect profiles were characterized to help inform drug target prioritization for breast cancer prevention. HDL-C and acetate might be promising drug targets for preventing breast cancer, but they should be applied under weighting advantages and disadvantages.

Application of Metabolic Reprogramming to Cancer Imaging and Diagnosis

Cellular metabolism governs the signaling that supports physiological mechanisms and homeostasis in an individual, including neuronal transmission, wound healing, and circadian clock manipulation. Various factors have been linked to abnormal metabolic reprogramming, including gene mutations, epigenetic modifications, altered protein epitopes, and their involvement in the development of disease, including cancer. The presence of multiple distinct hallmarks and the resulting cellular reprogramming process have gradually revealed that these metabolism-related molecules may be able to be used to track or prevent the progression of cancer. Consequently, translational medicines have been developed using metabolic substrates, precursors, and other products depending on their biochemical mechanism of action. It is important to note that these metabolic analogs can also be used for imaging and therapeutic purposes in addition to competing for metabolic functions. In particular, due to their isotopic labeling, these compounds may also be used to localize and visualize tumor cells after uptake. In this review, the current development status, applicability, and limitations of compounds targeting metabolic reprogramming are described, as well as the imaging platforms that are most suitable for each compound and the types of cancer to which they are most appropriate.

Ultrahigh resolution MS1/MS2-based reconstruction of metabolic networks in mammalian cells reveals changes for selenite and arsenite action

Metabolic networks are complex, intersecting, and composed of numerous enzyme-catalyzed biochemical reactions that transfer various molecular moieties among metabolites. Thus, robust reconstruction of metabolic networks requires metabolite moieties to be tracked, which cannot be readily achieved with mass spectrometry (MS) alone. We previously developed an Ion Chromatography-ultrahigh resolution-MS1/data independent-MS2 method to track the simultaneous incorporation of the heavy isotopes 13C and 15N into the moieties of purine/pyrimidine nucleotides in mammalian cells. Ultrahigh resolution-MS1 resolves and counts multiple tracer atoms in intact metabolites, while data independent-tandem MS (MS2) determines isotopic enrichment in their moieties without concern for the numerous mass isotopologue source ions to be fragmented. Together, they enabled rigorous MS-based reconstruction of metabolic networks at specific enzyme levels. We have expanded this approach to trace the labeled atom fate of [13C6]-glucose in 3D A549 spheroids in response to the anticancer agent selenite and that of [13C5,15N2]-glutamine in 2D BEAS-2B cells in response to arsenite transformation. We deduced altered activities of specific enzymes in the Krebs cycle, pentose phosphate pathway, gluconeogenesis, and UDP-GlcNAc synthesis pathways elicited by the stressors. These metabolic details help elucidate the resistance mechanism of 3D versus 2D A549 cultures to selenite and metabolic reprogramming that can mediate the transformation of BEAS-2B cells by arsenite.

Metabolomic and elemental profiling of blood serum in bladder cancer

Bladder cancer (BC) is one of the most frequently diagnosed types of urinary cancer. Despite advances in treatment methods, no specific biomarkers are currently in use. Targeted and untargeted profiling of metabolites and elements of human blood serum from 100 BC patients and the same number of normal controls (NCs), with external validation, was attempted using three analytical methods, i.e., nuclear magnetic resonance, gold and silver-109 nanoparticle-based laser desorption/ionization mass spectrometry (LDI-MS), and inductively coupled plasma optical emission spectrometry (ICP-OES). All results were subjected to multivariate statistical analysis. Four potential serum biomarkers of BC, namely, isobutyrate, pyroglutamate, choline, and acetate, were quantified with proton nuclear magnetic resonance, which had excellent predictive ability as judged by the area under the curve (AUC) value of 0.999. Two elements, Li and Fe, were also found to distinguish between cancer and control samples, as judged from ICP-OES data and AUC of 0.807 (in validation set). Twenty-five putatively identified compounds, mostly related to glycans and lipids, differentiated BC from NCs, as detected using LDI-MS. Five serum metabolites were found to discriminate between tumor grades and nine metabolites between tumor stages. The results from three different analytical platforms demonstrate that the identified distinct serum metabolites and metal elements have potential to be used for noninvasive detection, staging, and grading of BC.

Aspartate and Acetate Fuel Gastrointestinal Stromal Tumors Beyond the Warburg Effect

Metabolic reprogramming is closely linked to the tumorigenesis and drug resistance of gastrointestinal stromal tumors (GISTs). Mapping the metabolic orbit of GISTs is a prerequisite if intervention against the metabolic vulnerability of refractory GISTs is desirable.

Methods

A total of 43 patients with treatment-naïve GISTs who had undergone surgical resections were enrolled, on whom a metabolomics profile detected from surgical specimens was constructed based on the 1H-nuclear magnetic resonance (NMR) platform. The mRNA and protein levels of GLUT1, HK2, ACSS2, and FASN were assayed. Dual-tracer 18F-FDG/11C-acetate PET imaging was introduced before surgery in 15 patients.

Results

1H-NMR-based metabolomics revealed that GISTs were characterized by upregulation of glutamate, ascorbate, aspartate and glycine and downregulation of choline, creatine, glucose and glycerol. Bioinformatics analysis showed that the TCA cycle and alanine, aspartate, and glutamate metabolism were the two leading pathways. High- and nonhigh-risk (including intermediate-, low-, and very low-risk) GISTs preferentially displayed upregulation of HK2 and ACSS2, respectively, echoed by in vivo imaging that high- and nonhigh-risk GISTs preferentially exhibited higher uptake of 18F-FDG and 11C-acetate, respectively, while 18F-FDG and 11C-acetate were complementary to each other. Nuclear ACSS2 was exclusively identified in high-risk GISTs.

Conclusion

We describe a metabolic landscape of GISTs that read aspartate as a de facto "oncometabolite," which was replenished via the TCA cycle and alanine, aspartate, and glutamate metabolism. Glycolysis and ACSS2-mediated acetate metabolism competed and complemented fatty acid synthesis, although glycolysis remained an aggressive phenotype.

The roles of metabolic profiles and intracellular signaling pathways of tumor microenvironment cells in angiogenesis of solid tumors

Innate and adaptive immune cells patrol and survey throughout the human body and sometimes reside in the tumor microenvironment (TME) with a variety of cell types and nutrients that may differ from those in which they developed. The metabolic pathways and metabolites of immune cells are rooted in cell physiology, and not only provide nutrients and energy for cell growth and survival but also influencing cell differentiation and effector functions. Nowadays, there is a growing awareness that metabolic processes occurring in cancer cells can affect immune cell function and lead to tumor immune evasion and angiogenesis. In order to safely treat cancer patients and prevent immune checkpoint blockade-induced toxicities and autoimmunity, we suggest using anti-angiogenic drugs solely or combined with Immune checkpoint blockers (ICBs) to boost the safety and effectiveness of cancer therapy. As a consequence, there is significant and escalating attention to discovering techniques that target metabolism as a new method of cancer therapy. In this review, a summary of immune-metabolic processes and their potential role in the stimulation of intracellular signaling in TME cells that lead to tumor angiogenesis, and therapeutic applications is provided. Video abstract.

Druggable Metabolic Vulnerabilities Are Exposed and Masked during Progression to Castration Resistant Prostate Cancer

There is an urgent need for exploring new actionable targets other than androgen receptor to improve outcome from lethal castration-resistant prostate cancer. Tumor metabolism has reemerged as a hallmark of cancer that drives and supports oncogenesis. In this regard, it is important to understand the relationship between distinctive metabolic features, androgen receptor signaling, genetic drivers in prostate cancer, and the tumor microenvironment (symbiotic and competitive metabolic interactions) to identify metabolic vulnerabilities. We explore the links between metabolism and gene regulation, and thus the unique metabolic signatures that define the malignant phenotypes at given stages of prostate tumor progression. We also provide an overview of current metabolism-based pharmacological strategies to be developed or repurposed for metabolism-based therapeutics for castration-resistant prostate cancer.

CTpathway: a CrossTalk-based pathway enrichment analysis method for cancer research

BACKGROUND

Pathway enrichment analysis (PEA) is a common method for exploring functions of hundreds of genes and identifying disease-risk pathways. Moreover, different pathways exert their functions through crosstalk. However, existing PEA methods do not sufficiently integrate essential pathway features, including pathway crosstalk, molecular interactions, and network topologies, resulting in many risk pathways that remain uninvestigated.

METHODS

To overcome these limitations, we develop a new crosstalk-based PEA method, CTpathway, based on a global pathway crosstalk map (GPCM) with >440,000 edges by combing pathways from eight resources, transcription factor-gene regulations, and large-scale protein-protein interactions. Integrating gene differential expression and crosstalk effects in GPCM, we assign a risk score to genes in the GPCM and identify risk pathways enriched with the risk genes.

RESULTS

Analysis of >8300 expression profiles covering ten cancer tissues and blood samples indicates that CTpathway outperforms the current state-of-the-art methods in identifying risk pathways with higher accuracy, reproducibility, and speed. CTpathway recapitulates known risk pathways and exclusively identifies several previously unreported critical pathways for individual cancer types. CTpathway also outperforms other methods in identifying risk pathways across all cancer stages, including early-stage cancer with a small number of differentially expressed genes. Moreover, the robust design of CTpathway enables researchers to analyze both bulk and single-cell RNA-seq profiles to predict both cancer tissue and cell type-specific risk pathways with higher accuracy.

CONCLUSIONS

Collectively, CTpathway is a fast, accurate, and stable pathway enrichment analysis method for cancer research that can be used to identify cancer risk pathways. The CTpathway interactive web server can be accessed here http://www.jianglab.cn/CTpathway/ . The stand-alone program can be accessed here https://github.com/Bioccjw/CTpathway .

Metabolic Adaptation as Potential Target in Papillary Renal Cell Carcinomas Based on Their In Situ Metabolic Characteristics

Metabolic characteristics of kidney cancers have mainly been obtained from the most frequent clear cell renal cell carcinoma (CCRCC) studies. Moreover, the bioenergetic perturbances that affect metabolic adaptation possibilities of papillary renal cell carcinoma (PRCC) have not yet been detailed. Therefore, our study aimed to analyze the in situ metabolic features of PRCC vs. CCRCC tissues and compared the metabolic characteristics of PRCC, CCRCC, and normal tubular epithelial cell lines. The protein and mRNA expressions of the molecular elements in mammalian target of rapamycin (mTOR) and additional metabolic pathways were analyzed in human PRCC cases compared to CCRCC. The metabolic protein expression pattern, metabolite content, mTOR, and metabolic inhibitor sensitivity of renal carcinoma cell lines were also studied and compared with tubular epithelial cells, as “normal” control. We observed higher protein expressions of the “alternative bioenergetic pathway” elements, in correlation with the possible higher glutamine and acetate consumption in PRCC cells instead of higher glycolytic and mTOR activity in CCRCCs. Increased expression of certain metabolic pathway markers correlates with the detected differences in metabolite ratios, as well. The lower lactate/pyruvate, lactate/malate, and higher pyruvate/citrate intracellular metabolite ratios in PRCC compared to CCRCC cell lines suggest that ACHN (PRCC) have lower Warburg glycolytic capacity, less pronounced pyruvate to lactate producing activity and shifted OXPHOS phenotype. However, both studied renal carcinoma cell lines showed higher mTOR activity than tubular epithelial cells cultured in vitro, the metabolite ratio, the enzyme expression profiles, and the higher mitochondrial content also suggest increased importance of mitochondrial functions, including mitochondrial OXPHOS in PRCCs. Additionally, PRCC cells showed significant mTOR inhibitor sensitivity and the used metabolic inhibitors increased the effect of rapamycin in combined treatments. Our study revealed in situ metabolic differences in mTOR and metabolic protein expression patterns of human PRCC and CCRCC tissues as well as in cell lines. These underline the importance in the development of specific new treatment strategies, new mTOR inhibitors, and other anti-metabolic drug combinations in PRCC therapy.

NAD/NAMPT and mTOR Pathways in Melanoma: Drivers of Drug Resistance and Prospective Therapeutic Targets

Malignant melanoma represents the most fatal skin cancer due to its aggressive behavior and high metastatic potential. The introduction of BRAF/MEK inhibitors and immune-checkpoint inhibitors (ICIs) in the clinic has dramatically improved patient survival over the last decade. However, many patients either display primary (i.e., innate) or develop secondary (i.e., acquired) resistance to systemic treatments. Therapeutic resistance relies on the rewiring of multiple processes, including cancer metabolism, epigenetics, gene expression, and interactions with the tumor microenvironment that are only partially understood. Therefore, reliable biomarkers of resistance or response, capable of facilitating the choice of the best treatment option for each patient, are currently missing. Recently, activation of nicotinamide adenine dinucleotide (NAD) metabolism and, in particular, of its rate-limiting enzyme nicotinamide phosphoribosyltransferase (NAMPT) have been identified as key drivers of targeted therapy resistance and melanoma progression. Another major player in this context is the mammalian target of rapamycin (mTOR) pathway, which plays key roles in the regulation of melanoma cell anabolic functions and energy metabolism at the switch between sensitivity and resistance to targeted therapy. In this review, we summarize known resistance mechanisms to ICIs and targeted therapy, focusing on metabolic adaptation as one main mechanism of drug resistance. In particular, we highlight the roles of NAD/NAMPT and mTOR signaling axes in this context and overview data in support of their inhibition as a promising strategy to overcome treatment resistance.

MYCN and Metabolic Reprogramming in Neuroblastoma

Neuroblastoma is a pediatric cancer responsible for approximately 15% of all childhood cancer deaths. Aberrant MYCN activation, as a result of genomic MYCN amplification, is a major driver of high-risk neuroblastoma, which has an overall survival rate of less than 50%, despite the best treatments currently available. Metabolic reprogramming is an integral part of the growth-promoting program driven by MYCN, which fuels cell growth and proliferation by increasing the uptake and catabolism of nutrients, biosynthesis of macromolecules, and production of energy. This reprogramming process also generates metabolic vulnerabilities that can be exploited for therapy. In this review, we present our current understanding of metabolic reprogramming in neuroblastoma, focusing on transcriptional regulation as a key mechanism in driving the reprogramming process. We also highlight some important areas that need to be explored for the successful development of metabolism-based therapy against high-risk neuroblastoma.

Exosomal miR-155-5p derived from glioma stem-like cells promotes mesenchymal transition via targeting ACOT12

Tumor-associated exosomes play essential roles in intercellular communication and the foundation of cancer microenvironment in glioma. Many mRNAs, microRNAs (miRNAs) and proteins contained in tumor-associated exosomes can be transferred to recipient cells and contribute to the progression of tumor. Nevertheless, the cellular communication between malignant cells with different heterogeneities or characteristics and resultant tumor progression are still unclear in glioma. Here, we show that exosomes released from glioma stem-like cells (GSCs) contain a significant increasing level of miR-155-5p and could be horizontally transferred to surrounding glioma cells. High expression of miR-155-5p in plasma exosomes from patients was associated with glioma diagnosis and grading. Mechanically, we found that miR-155-5p markedly reduced the expression of acetyl-CoA thioesterase 12 (ACOT12), which played as a tumor suppressor in glioma. Furthermore, mesenchymal transition was significantly promoted in glioma cells treated with GSCs-derived exosomes. In conclusion, GSCs-derived exosomal miR-155-5p play a critical role in glioma progression and facilitating tumor aggressive growth by targeting ACOT12 and promoting mesenchymal transition. Exosomal miR-155-5p is also a potential predictive biomarker for glioma, which may provoke the development of novel diagnostic and therapeutic strategies against glioma.

Nanomedicines Targeting Metabolism in the Tumor Microenvironment

Cancer cells reprogram their metabolism to meet their growing demand for bioenergy and biosynthesis. The metabolic profile of cancer cells usually includes dysregulation of main nutritional metabolic pathways and the production of metabolites, which leads to a tumor microenvironment (TME) having the characteristics of acidity, hypoxic, and/or nutrient depletion. Therapies targeting metabolism have become an active and revolutionary research topic for anti-cancer drug development. The differential metabolic vulnerabilities between tumor cells and other cells within TME provide nanotechnology a therapeutic window of anti-cancer. In this review, we present the metabolic characteristics of intrinsic cancer cells and TME and summarize representative strategies of nanoparticles in metabolism-regulating anti-cancer therapy. Then, we put forward the challenges and opportunities of using nanoparticles in this emerging field.

Emerging roles of fatty acid metabolism in cancer and their targeted drug development

Metabolic reprogramming is now considered as one of hallmark of tumor cells and provides them with a selective survival/growth advantage to resist harsh micro-environmental stress. Fatty acid (FA) metabolism of tumor cells supports the biosynthetic needs and provides fuel sources for energy supply. Since FA metabolic reprogramming is a critical link in tumor metabolism, its various roles in tumors have attracted increasing interest. Herein, we review the mechanisms through which cancer cells rewire their FA metabolism with a focus on the pathway of FA metabolism and its targeting drug development. The failure and successful cases of targeting tumor FA metabolism are expected to bypass the metabolic vulnerability and improve the efficacy of targeted therapy.

Extracellular Citrate Treatment Induces HIF1α Degradation and Inhibits the Growth of Low-Glycolytic Hepatocellular Carcinoma under Hypoxia

HCC is well known for low glycolysis in the tumors, whereas hypoxia induces glycolytic phenotype and tumor progression. This study was conducted to evaluate the expression of SLCs in human HCCs and investigated whether extracellular nutrient administration related to SLCs in low-glycolytic HCC can prevent hypoxic tumor progression. SLCs expression was screened according to the level of glycolysis in HCCs. Then, whether extracellular nutrient treatment can affect hypoxic tumor progression, as well as the mechanisms, were evaluated in an in vitro cell line and an in vivo animal model. Low-glycolytic HCCs showed high SLC13A5/NaCT and SLC16A1/MCT1 but low SLC2A1/GLUT1 and HIF1α/HIF1α expression. Especially, high SLC13A5 expression was significantly associated with good overall survival in the Cancer Genome Atlas (TCGA) database. In HepG2 cells with the highest NaCT expression, extracellular citrate treatment upon hypoxia induced HIF1α degradation, which led to reduced glycolysis and cellular proliferation. Finally, in HepG2-animal models, the citrate-treated group showed smaller tumor with less hypoxic areas than the vehicle-treated group. In patients with HCC, SLC13A5/NaCT is an important SLC, which is associated with low glycolysis and good prognosis. Extracellular citrate treatment induced the failure of metabolic adaptation to hypoxia and tumor growth inhibition, which can be a potential therapeutic strategy in HCCs.

Differences in cognition, short-chain fatty acids and related metabolites in pregnant versus non-pregnant women: a cross-sectional study

Background

Pregnancy induces cognitive reorganization which can lead to mental disorders. The aim of this study is to determine differences in cognitive scores, short-chain fatty acids (SCFAs) and related metabolites between pregnant and non-pregnant participants.

Methods

This cross-sectional study included 67 full-term pregnant women and 31 non-pregnant women. We compared scores of mental state and cognitive assessment tests, as well as serum concentrations of SCFAs, hormones, inflammatory factors, and neurotransmitters between these groups.

Results

Scores for information processing speed, immediate visual memory, motor response speed and accuracy, execution ability and verbal use ability in the pregnant group were lower than those in the non-pregnant group (p < 0.05 for all tests). Total serum SCFAs in the pregnant group were significantly lower than those in the non-pregnant group (P = 0.031). Among them, acetate and propionate were significantly decreased (P = 0.013 and 0.037, respectively) whereas butyrate was significantly increased (P = 0.035). Serum peptide YY, glucagon-like peptide-1, γ-aminobutyric acid, and dopamine showed no differences between the two groups. However, cortisol, adrenocorticotropic hormone, and acetylcholine were significantly increased in the pregnant group as compared with the non-pregnant group (P = 0.039, 0.016, and 0.012, respectively). Tumor necrosis factor-α was increased and interleukin-10 significantly decreased in the pregnant group (P = 0.045 and 0.019, respectively).

Conclusion

According to our study findings, cognitive reorganization in the third trimester of pregnancy showed that both the passive storage capacity of working memory and the executive function of online information processing were decreased to varying degrees. At the same time, the changes in total SCFAs, the proportions of SCFAs and related metabolites were also detected. These changes in the internal environment may be increasing the risk of perinatal mental illness.

Acetyl-CoA Synthetase 2 as a Therapeutic Target in Tumor Metabolism

Simple Summary

Acetyl-CoA Synthetase 2 (ACSS2) is highly expressed in a variety of tumors, which is very important for tumor growth, proliferation, invasion, and metastasis in the nutritional stress microenvironment. Studies have proven that ACSS2 inhibitors can be effective in halting cancer growth and can be combined with other antineoplastic drugs to reduce drug resistance. This article mainly reviews the mechanism of ACSS2-promoting tumor growth from many aspects and the prospect of clinical application of targeted inhibitors.

Abstract

Acetyl-CoA Synthetase 2 (ACSS2) belongs to a member of the acyl-CoA short-chain synthase family, which can convert acetate in the cytoplasm and nucleus into acetyl-CoA. It has been proven that ACSS2 is highly expressed in glioblastoma, breast cancer, liver cancer, prostate cancer, bladder cancer, renal cancer, and other tumors, and is closely related to tumor stage and the overall survival rate of patients. Accumulating studies show that hypoxia and a low serum level induce ACSS2 expression to help tumor cells cope with this nutrient-poor environment. The potential mechanisms are associated with the ability of ACSS2 to promote the synthesis of lipids in the cytoplasm, induce the acetylation of histones in the nucleus, and facilitate the expression of autophagy genes. Novel-specific inhibitors of ACSS2 are developed and confirmed to the effectiveness in pre-clinical tumor models. Targeting ACSS2 may provide novel approaches for tumor treatment. This review summarizes the biological function of ACSS2, its relation to survival and prognosis in different tumors, and how ACSS2 mediates different pathways to promote tumor metastasis, invasion, and drug resistance.

Metabolic Alterations in Sputum and Exhaled Breath Condensate of Early Stage Non-Small Cell Lung Cancer Patients After Surgical Resection: A Pilot Study

Every year, close to two million people world-wide are diagnosed with and die of lung cancer. Most patients present with advanced-stage cancer with limited curative options and poor prognosis. Diagnosis of lung cancer at an early stage provides the best chance for a cure. Low- dose CT screening of the chest in the high-risk population is the current standard of care for early detection of lung cancer. However, CT screening is invasive due to radiation exposure and carries the risk of unnecessary biopsies in non-cancerous tumors. In this pilot study, we present metabolic alterations observed in sputum and breath condensate of the same population of early- stage non-small cell lung cancer (NSCLC) patients cancer before and after surgical resection (SR), which could serve as noninvasive diagnostic tool. Exhaled breath condensate (EBC) (n=35) and sputum (n=15) were collected from early-stage non-small cell lung cancer (NSCLC) patients before and after SR. Median number of days for EBC and sputum collection before and after SR were 7 and 42; and 7 and 36 respectively Nuclear magnetic resonance (NMR) and liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) were used to analyze the metabolic profile of the collected samples. A total of 26 metabolites with significant alteration post SR were identified, of which 14 (54%) were lipids and 12 constituted nine different chemical metabolite classes. Eighteen metabolites (69%) were significantly upregulated and 8 (31%) were downregulated. Median fold change for all the up- and downregulated metabolites (LC-QTOF-MS) were 10 and 8, respectively. Median fold change (MFC) in concentration of all the up- and downregulated metabolites (NMR) were 0.04 and 0.27, respectively. Furthermore, glucose (median fold change, 0.01, p=0.037), adenosine monophosphate (13 log fold, p=0.0037) and N1, N12- diacetylspermine (8 log fold p=0.011) sputum levels were significantly increased post-SR. These identified sputa and EBC indices of altered metabolism could serve as basis for further exploration of biomarkers for early detection of lung cancer, treatment response, and targets for drug discovery. Validation of these promising results by larger clinical studies is warranted.

Elevation of fatty acid desaturase 2 in esophageal adenocarcinoma increases polyunsaturated lipids and may exacerbate bile acid-induced DNA damage

Background

The risk of esophageal adenocarcinoma (EAC) is associated with gastro‐esophageal reflux disease (GERD) and obesity. Lipid metabolism‐targeted therapies decrease the risk of progressing from Barrett's esophagus (BE) to EAC, but the precise lipid metabolic changes and their roles in genotoxicity during EAC development are yet to be established.

Methods

Esophageal biopsies from the normal epithelium (NE), BE, and EAC, were analyzed using concurrent lipidomics and proteomics (n = 30) followed by orthogonal validation on independent samples using RNAseq transcriptomics (n = 22) and immunohistochemistry (IHC, n = 80). The EAC cell line FLO‐1 was treated with FADS2 selective inhibitor SC26196, and/or bile acid cocktail, followed by immunofluorescence staining for γH2AX.

Results

Metabolism‐focused Reactome analysis of the proteomics data revealed enrichment of fatty acid metabolism, ketone body metabolism, and biosynthesis of specialized pro‐resolving mediators in EAC pathogenesis. Lipidomics revealed progressive alterations (NE‐BE‐EAC) in glycerophospholipid synthesis with decreasing triglycerides and increasing phosphatidylcholine and phosphatidylethanolamine, and sphingolipid synthesis with decreasing dihydroceramide and increasing ceramides. Furthermore, a progressive increase in lipids with C20 fatty acids and polyunsaturated lipids with ≥4 double bonds were also observed. Integration with transcriptome data identified candidate enzymes for IHC validation: Δ4‐Desaturase, Sphingolipid 1 (DEGS1) which desaturates dihydroceramide to ceramide, and Δ5 and Δ6‐Desaturases (fatty acid desaturases, FADS1 and FADS2), responsible for polyunsaturation. All three enzymes showed significant increases from BE through dysplasia to EAC, but transcript levels of DEGS1 were decreased suggesting post‐translational regulation. Finally, the FADS2 selective inhibitor SC26196 significantly reduced polyunsaturated lipids with three and four double bonds and reduced bile acid‐induced DNA double‐strand breaks in FLO‐1 cells in vitro.

Conclusions

Integrated multiomics revealed sphingolipid and phospholipid metabolism rewiring during EAC development. FADS2 inhibition and reduction of the high polyunsaturated lipids effectively protected EAC cells from bile acid‐induced DNA damage in vitro, potentially through reduced lipid peroxidation.

GBP5 and ACSS3: two potential biomarkers of high-grade ovarian cancer identified through downstream analysis of microarray data

Among all malignancies of the reproductive organs, ovarian cancer is the sixth leading cause of death for women. Several factors contribute to the uncontrolled expression of certain genes in cancer thus making them act as oncogenes or tumour suppressors. In this study, we have examined four microarray datasets of high-grade ovarian cancer cells to identify differentially expressed genes (DEGs). 362 and 94 common DEGs were identified as up-regulated and down-regulated, respectively from 119 disease and 31 control samples. The DEGs were further analysed for their gene ontologies (GO), pathway, protein-protein interactions and co-expression. Most of the biological processes were associated with cellular processes, biological regulation, metabolic processes, and developmental processes. Further, regulatory networks were constructed by the DEGs which are also co-expressed and the hub genes were identified. The hub genes targeted by a large number of microRNAs (miRNAs) were further analyzed to reveal their role in the overall survival of cancer patients. Finally, GBP5 and ACSS3 were highlighted as potential biomarkers for ovarian cancer research.Communicated by Ramaswamy H. Sarma.

Molecular interactions between the intestinal microbiota and the host

The intestine is the most densely colonized region of the body, inhabited by a diverse community of microbes. The functional significance of the intestinal microbiota is not yet fully understood, but it is known that the microbiota is implicated in numerous physiological processes of the host, such as metabolism, nutrition, the immune system, and regulation of behavior and mood. This article reviews recent findings on how bacteria of the intestinal microbiota interact with the host.

Microbiota‐microbiota and microbiota‐host interactions are mediated by direct cell contact and by metabolites either produced by bacteria or produced by the host or the environment and metabolized by bacteria. Among them are short‐chain fatty, including butyrate, propionate, and acetate. Other examples include polyamines, linoleic acid metabolites, tryptophan metabolites, trimethylamine‐N‐oxide, vitamins, and secondary bile acids. These metabolites are involved in regulating the cell cycle, neurobiological signaling, cholesterol and bile acid metabolism, immune responses, and responses to antioxidants. Understanding the host‐microbiota pathways and their modulation will allow the identification of individualized therapeutic targets for many diseases. This overview helps to facilitate and promote further research in this field.

O-GlcNAc transferase regulates glioblastoma acetate metabolism via regulation of CDK5-dependent ACSS2 phosphorylation

Glioblastomas (GBMs) preferentially generate acetyl-CoA from acetate as a fuel source to promote tumor growth. O-GlcNAcylation has been shown to be elevated by increasing O-GlcNAc transferase (OGT) in many cancers and reduced O-GlcNAcylation can block cancer growth. Here, we identify a novel mechanism whereby OGT regulates acetate-dependent acetyl-CoA and lipid production by regulating phosphorylation of acetyl-CoA synthetase 2 (ACSS2) by cyclin-dependent kinase 5 (CDK5). OGT is required and sufficient for GBM cell growth and regulates acetate conversion to acetyl-CoA and lipids. Elevating O-GlcNAcylation in GBM cells increases phosphorylation of ACSS2 on Ser-267 in a CDK5-dependent manner. Importantly, we show that ACSS2 Ser-267 phosphorylation regulates its stability by reducing polyubiquitination and degradation. ACSS2 Ser-267 is critical for OGT-mediated GBM growth as overexpression of ACSS2 Ser-267 phospho-mimetic rescues growth in vitro and in vivo. Importantly, we show that pharmacologically targeting OGT and CDK5 reduces GBM growth ex vivo. Thus, the OGT/CDK5/ACSS2 pathway may be a way to target altered metabolic dependencies in brain tumors.

Hallmarks of Metabolic Reprogramming and Their Role in Viral Pathogenesis

Metabolic reprogramming is a hallmark of cancer and has proven to be critical in viral infections. Metabolic reprogramming provides the cell with energy and biomass for large-scale biosynthesis. Based on studies of the cellular changes that contribute to metabolic reprogramming, seven main hallmarks can be identified: (1) increased glycolysis and lactic acid, (2) increased glutaminolysis, (3) increased pentose phosphate pathway, (4) mitochondrial changes, (5) increased lipid metabolism, (6) changes in amino acid metabolism, and (7) changes in other biosynthetic and bioenergetic pathways. Viruses depend on metabolic reprogramming to increase biomass to fuel viral genome replication and production of new virions. Viruses take advantage of the non-metabolic effects of metabolic reprogramming, creating an anti-apoptotic environment and evading the immune system. Other non-metabolic effects can negatively affect cellular function. Understanding the role metabolic reprogramming plays in viral pathogenesis may provide better therapeutic targets for antivirals.

Lipid Metabolism Interplay in CRC—An Update

Colorectal cancer (CRC) to date still ranks as one of the deadliest cancer entities globally, and despite recent advances, the incidence in young adolescents is dramatically increasing. Lipid metabolism has recently received increased attention as a crucial element for multiple aspects of carcinogenesis and our knowledge of the underlying mechanisms is steadily growing. However, the mechanism how fatty acid metabolism contributes to CRC is still not understood in detail. In this review, we aim to summarize our vastly growing comprehension and the accompanied complexity of cellular fatty acid metabolism in CRC by describing inputs and outputs of intracellular free fatty acid pools and how these contribute to cancer initiation, disease progression and metastasis. We highlight how different lipid pathways can contribute to the aggressiveness of tumors and affect the prognosis of patients. Furthermore, we focus on the role of lipid metabolism in cell communication and interplay within the tumor microenvironment (TME) and beyond. Understanding these interactions in depth might lead to the discovery of novel markers and new therapeutic interventions for CRC. Finally, we discuss the crucial role of fatty acid metabolism as new targetable gatekeeper in colorectal cancer.

Abnormal lipid synthesis as a therapeutic target for cancer stem cells

Cancer stem cells (CSCs) comprise a subpopulation of cancer cells with stem cell properties, which exhibit the characteristics of high tumorigenicity, self-renewal, and tumor initiation and are associated with the occurrence, metastasis, therapy resistance, and relapse of cancer. Compared with differentiated cells, CSCs have unique metabolic characteristics, and metabolic reprogramming contributes to the self-renewal and maintenance of stem cells. It has been reported that CSCs are highly dependent on lipid metabolism to maintain stemness and satisfy the requirements of biosynthesis and energy metabolism. In this review, we demonstrate that lipid anabolism alterations promote the survival of CSCs, including de novo lipogenesis, lipid desaturation, and cholesterol synthesis. In addition, we also emphasize the molecular mechanism underlying the relationship between lipid synthesis and stem cell survival, the signal trans-duction pathways involved, and the application prospect of lipid synthesis reprogramming in CSC therapy. It is demonstrated that the dependence on lipid synthesis makes targeting of lipid synthesis metabolism a promising therapeutic strategy for eliminating CSCs. Targeting key molecules in lipid synthesis will play an important role in anti-CSC therapy.

Synthesis and Evaluation of 11C-Labeled Triazolones as Probes for Imaging Fatty Acid Synthase Expression by Positron Emission Tomography

Cancer cells require lipids to fulfill energetic, proliferative, and signaling requirements. Even though these cells can take up exogenous fatty acids, the majority exhibit a dependency on de novo fatty acid synthesis. Fatty acid synthase (FASN) is the rate-limiting enzyme in this process. Expression and activity of FASN is elevated in multiple cancers, where it correlates with disease progression and poor prognosis. These observations have sparked interest in developing methods of detecting FASN expression in vivo. One promising approach is the imaging of radiolabeled molecular probes targeting FASN by positron emission tomography (PET). However, although [11C]acetate uptake by prostate cancer cells correlates with FASN expression, no FASN-specific PET probes currently exist. Our aim was to synthesize and evaluate a series of small molecule triazolones based on GSK2194069, an FASN inhibitor with IC50 = 7.7 ± 4.1 nM, for PET imaging of FASN expression. These triazolones were labeled with carbon-11 in good yield and excellent radiochemical purity, and binding to FASN-positive LNCaP cells was significantly higher than FASN-negative PC3 cells. Despite these promising characteristics, however, these molecules exhibited poor in vivo pharmacokinetics and were predominantly retained in lymph nodes and the hepatobiliary system. Future studies will seek to identify structural modifications that improve tumor targeting while maintaining the excretion profile of these first-generation 11C-methyltriazolones.

Interplay between Dysbiosis of Gut Microbiome, Lipid Metabolism, and Tumorigenesis: Can Gut Dysbiosis Stand as a Prognostic Marker in Cancer?

The gut bacterial community is involved in the metabolism of bile acids and short-chain fatty acids (SCFAs). Bile acids are involved in the absorption of fat and the regulation of lipid homeostasis through emulsification and are transformed into unconjugated bile acids by the gut microbiota. The gut microbiota is actively involved in the production of bile acid metabolites, such as deoxycholic acid, lithocholic acid, choline, and SCFAs such as acetate, butyrate, and propionate. Metabolites derived from the gut microbiota or modified gut microbiota metabolites contribute significantly to host pathophysiology. Gut bacterial metabolites, such as deoxycholic acid, contribute to the development of hepatocellular carcinoma and colon cancer by factors such as inflammation and oxidative DNA damage. Butyrate, which is derived from gut bacteria such as Megasphaera, Roseburia, Faecalibacterium, and Clostridium, is associated with the activation of Treg cell differentiation in the intestine through histone acetylation. Butyrate averts the action of class I histone deacetylases (HDAC), such as HDAC1 and HDAC3, which are responsible for the transcription of genes such as p21/Cip1, and cyclin D3 through hyperacetylation of histones, which orchestrates G1 cell cycle arrest. It is essential to identify the interaction between the gut microbiota and bile acid and SCFA metabolism to understand their role in gastrointestinal carcinogenesis including colon, gastric, and liver cancer. Metagenomic approaches with bioinformatic analyses are used to identify the bacterial species in the metabolism of bile acids and SCFAs. This review provides an overview of the current knowledge of gut microbiota-derived bile acid metabolism in tumor development and whether it can stand as a marker for carcinogenesis. Additionally, this review assesses the evidence of gut microbiota-derived short-chain fatty acids including butyric acid in antitumor activity. Future research is required to identify the beneficial commensal gut bacteria and their metabolites which will be considered to be therapeutic targets in inflammation-mediated gastrointestinal cancers.

A two-front nutritional environment fuels colorectal cancer: perspectives for dietary intervention

Colorectal cancer (CRC) develops and progresses in a nutritional environment comprising a continuously changing luminal cocktail of external dietary and microbial factors on the apical side, and a dynamic host-related pool of systemic factors on the serosal side. In this review, we highlight how this two-front environment influences the bioenergetic status of colonocytes throughout CRC development from (cancer) stem cells to cancer cells in nutrient-rich and nutrient-poor conditions, and eventually to metastatic cells, which, upon entry to the circulation and during metastatic seeding, are forced to metabolically adapt. Furthermore, given the influence of diet on the two-front nutritional environment, we discuss dietary strategies that target the specific metabolic preferences of these cells, with a possible impact on colon cancer cell bioenergetics and CRC outcome.

Urinary Volatomic Expression Pattern: Paving the Way for Identification of Potential Candidate Biosignatures for Lung Cancer

The urinary volatomic profiling of Indian cohorts composed of 28 lung cancer (LC) patients and 27 healthy subjects (control group, CTRL) was established using headspace solid phase microextraction technique combined with gas chromatography mass spectrometry methodology as a powerful approach to identify urinary volatile organic metabolites (uVOMs) to discriminate among LC patients from CTRL. Overall, 147 VOMs of several chemistries were identified in the intervention groups-including naphthalene derivatives, phenols, and organosulphurs-augmented in the LC group. In contrast, benzene and terpenic derivatives were found to be more prevalent in the CTRL group. The volatomic data obtained were processed using advanced statistical analysis, namely partial least square discriminative analysis (PLS-DA), support vector machine (SVM), random forest (RF), and multilayer perceptron (MLP) methods. This resulted in the identification of nine uVOMs with a higher potential to discriminate LC patients from CTRL subjects. These were furan, o-cymene, furfural, linalool oxide, viridiflorene, 2-bromo-phenol, tricyclazole, 4-methyl-phenol, and 1-(4-hydroxy-3,5-di-tert-butylphenyl)-2-methyl-3-morpholinopropan-1-one. The metabolic pathway analysis of the data obtained identified several altered biochemical pathways in LC mainly affecting glycolysis/gluconeogenesis, pyruvate metabolism, and fatty acid biosynthesis. Moreover, acetate and octanoic, decanoic, and dodecanoic fatty acids were identified as the key metabolites responsible for such deregulation. Furthermore, studies involving larger cohorts of LC patients would allow us to consolidate the data obtained and challenge the potential of the uVOMs as candidate biomarkers for LC.

Tumor Microenvironment Features and Chemoresistance in Pancreatic Ductal Adenocarcinoma: Insights into Targeting Physicochemical Barriers and Metabolism as Therapeutic Approaches

Currently, the median overall survival of PDAC patients rarely exceeds 1 year and has an overall 5-year survival rate of about 9%. These numbers are anticipated to worsen in the future due to the lack of understanding of the factors involved in its strong chemoresistance. Chemotherapy remains the only treatment option for most PDAC patients; however, the available therapeutic strategies are insufficient. The factors involved in chemoresistance include the development of a desmoplastic stroma which reprograms cellular metabolism, and both contribute to an impaired response to therapy. PDAC stroma is composed of immune cells, endothelial cells, and cancer-associated fibroblasts embedded in a prominent, dense extracellular matrix associated with areas of hypoxia and acidic extracellular pH. While multiple gene mutations are involved in PDAC initiation, this desmoplastic stroma plays an important role in driving progression, metastasis, and chemoresistance. Elucidating the mechanisms underlying PDAC resistance are a prerequisite for designing novel approaches to increase patient survival. In this review, we provide an overview of the stromal features and how they contribute to the chemoresistance in PDAC treatment. By highlighting new paradigms in the role of the stromal compartment in PDAC therapy, we hope to stimulate new concepts aimed at improving patient outcomes.

Targeting cancer metabolism in the era of precision oncology

One hundred years have passed since Warburg discovered alterations in cancer metabolism, more than 70 years since Sidney Farber introduced anti-folates that transformed the treatment of childhood leukaemia, and 20 years since metabolism was linked to oncogenes. However, progress in targeting cancer metabolism therapeutically in the past decade has been limited. Only a few metabolism-based drugs for cancer have been successfully developed, some of which are in - or en route to - clinical trials. Strategies for targeting the intrinsic metabolism of cancer cells often did not account for the metabolism of non-cancer stromal and immune cells, which have pivotal roles in tumour progression and maintenance. By considering immune cell metabolism and the clinical manifestations of inborn errors of metabolism, it may be possible to isolate undesirable off-tumour, on-target effects of metabolic drugs during their development. Hence, the conceptual framework for drug design must consider the metabolic vulnerabilities of non-cancer cells in the tumour immune microenvironment, as well as those of cancer cells. In this Review, we cover the recent developments, notable milestones and setbacks in targeting cancer metabolism, and discuss the way forward for the field.

Transorgan short-chain fatty acid fluxes in the fasted and postprandial state in the pig

The short-chain fatty acids (SCFAs) acetate, propionate, butyrate, isovalerate, and valerate are end products of intestinal bacterial fermentation and important mediators in the interplay between the intestine and peripheral organs. To unravel the transorgan fluxes and mass balance comparisons of SCFAs, we measured their net fluxes across several organs in a translational pig model. In multicatheterized conscious pigs [n = 12, 25.6 (95% CI [24.2, 26.9]) kg, 8-12 wk old], SCFA fluxes across portal-drained viscera (PDV), liver, kidneys, and hindquarter (muscle compartment) were measured after an overnight fast and in the postprandial state, 4 h after administration of a fiber-free, mixed meal. PDV was the main releasing compartment of acetate, propionate, butyrate, isovalerate, and valerate during fasting and in the postprandial state (all P = 0.001). Splanchnic acetate release was high due to the absence of hepatic clearance. All other SCFAs were extensively taken up by the liver (all P < 0.05). Even though only 7% [4, 10] (propionate), 42% [23, 60] (butyrate), 26% [12, 39] (isovalerate), and 3% [0.4, 5] (valerate) of PDV release were excreted from the splanchnic area in the fasted state, splanchnic release of all SCFAs was significant (all P values ≤0.01). Splanchnic propionate, butyrate, isovalerate, and valerate release remained low but significant in the postprandial state (all P values <0.01). We identified muscle and kidneys as main peripheral SCFA metabolizing organs, taking up the majority of all splanchnically released SCFAs in the fasted state and in the postprandial state. We conclude that the PDV is the main SCFA releasing and the liver the main SCFA metabolizing organ. Splanchnically released SCFAs appear to be important energy substrates to peripheral organs not only in the fasted but also in the postprandial state.NEW & NOTEWORTHY Using a multicatheterized pig model, we identified the portal-drained viscera as the main releasing compartment of the short-chain fatty acids acetate, propionate, butyrate, isovalerate, and valerate in the fasted and postprandial states. Low hepatic acetate metabolism resulted in a high splanchnic release, whereas all other SCFAs were extensively cleared resulting in low but significant splanchnic releases. Muscle and kidneys are the main peripheral SCFA metabolizing organs during fasting and in the postprandial state.

Metabolite Biomarkers of Response (BoRs): Towards a fingerprint for the evolution of metastatic breast cancer

Breast cancer is the most common cancer in women worldwide and despite improved treatment strategies, it persists as the second leading cause of death of women globally. Overall prognosis drops drastically once the cancer has metastasized, which is also associated with resistance to therapy. The evolution from a localized breast cancer to metastatic disease is complex and multifactorial. Metabolic reprogramming is a pre-requisite for this transition. In this graphical review, we provide an overview of altered metabolic pathways observed in metastatic breast cancer (mBC) and detail how metabolite biomarkers could serve as a novel class of precision medicine tools to improve the diagnosis, monitoring, and treatment of mBC.

Mammalian SIRT6 Represses Invasive Cancer Cell Phenotypes through ATP Citrate Lyase (ACLY)-Dependent Histone Acetylation

The modulation of dynamic histone acetylation states is key for organizing chromatin structure and modulating gene expression and is regulated by histone acetyltransferase (HAT) and histone deacetylase (HDAC) enzymes. The mammalian SIRT6 protein, a member of the Class III HDAC Sirtuin family of NAD+-dependent enzymes, plays pivotal roles in aging, metabolism, and cancer biology. Through its site-specific histone deacetylation activity, SIRT6 promotes chromatin silencing and transcriptional regulation of aging-associated, metabolic, and tumor suppressive gene expression programs. ATP citrate lyase (ACLY) is a nucleo-cytoplasmic enzyme that produces acetyl coenzyme A (acetyl-CoA), which is the required acetyl donor for lysine acetylation by HATs. In addition to playing a central role in generating cytosolic acetyl-CoA for de novo lipogenesis, a growing body of work indicates that ACLY also functions in the nucleus where it contributes to the nutrient-sensitive regulation of nuclear acetyl-CoA availability for histone acetylation in cancer cells. In this study, we have identified a novel function of SIRT6 in controlling nuclear levels of ACLY and ACLY-dependent tumor suppressive gene regulation. The inactivation of SIRT6 in cancer cells leads to the accumulation of nuclear ACLY protein and increases nuclear acetyl-CoA pools, which in turn drive locus-specific histone acetylation and the expression of cancer cell adhesion and migration genes that promote tumor invasiveness. Our findings uncover a novel mechanism of SIRT6 in suppressing invasive cancer cell phenotypes and identify acetyl-CoA responsive cell migration and adhesion genes as downstream targets of SIRT6.

A Unique Urinary Metabolic Feature for the Determination of Bladder Cancer, Prostate Cancer, and Renal Cell Carcinoma

Prostate cancer (PCa), bladder cancer (BCa), and renal cell carcinoma (RCC) are the most prevalent cancer among urological cancers. However, there are no cancer-specific symptoms that can differentiate them as well as early clinical signs of urological malignancy. Furthermore, many metabolic studies have been conducted to discover their biomarkers, but the metabolic profiling study to discriminate between these cancers have not yet been described. Therefore, in this study, we aimed to investigate the urinary metabolic differences in male patients with PCa (n = 24), BCa (n = 29), and RCC (n = 12) to find the prominent combination of metabolites between cancers. Based on ¹H NMR analysis, orthogonal partial least-squares discriminant analysis was applied to find distinct metabolites among cancers. Moreover, the ranked analysis of covariance by adjusting a potential confounding as age revealed that 4-hydroxybenzoate, N-methylhydantoin, creatinine, glutamine, and acetate had significantly different metabolite levels among groups. The receiver operating characteristic analysis created by prominent five metabolites showed the great discriminatory accuracy with area under the curve (AUC) > 0.7 for BCa vs. RCC, PCa vs. BCa, and RCC vs. PCa. This preliminary study compares the metabolic profiles of BCa, PCa, and RCC, and reinforces the exploratory role of metabolomics in the investigation of human urine.

Metabolic Profiling of Praziquantel-mediated Prevention of Opisthorchis viverrini-induced Cholangiocyte Transformation in the Hamster Model of Cholangiocarcinoma

BACKGROUND

Opisthorchis viverrini (Ov) infection-induced cholangiocarcinoma (CCA) is a major public health problem in northeastern Thailand. Praziquantel was shown to prevent CCA development in an Ov-infected hamster model; however, the molecular mechanism remains unknown.

MATERIALS AND METHODS

In this study, we used a hamster model with Ov and N-nitrosodimethylamine-induced CCA to study the mechanisms of praziquantel action. The liver tissues from the hamsters with and without praziquantel treatment were analyzed using ¹H nuclear magnetic resonance spectroscopy.

RESULTS

A total of 14 metabolites were found to be significantly different between the two groups. Furthermore, the combination of acetate, inosine and sarcosine was shown to exert an anti-inflammatory effect through interleukin-6 inhibition in a macrophage cell line, suggesting a mechanism by which praziquantel may prevent inflammation caused by Ov, cholangiocyte transformation and further CCA develpoment.

CONCLUSION

These findings might avail the development of a preventive strategy for CCA in high-risk populations.

Structural Characterization of the Reaction and Substrate Specificity Mechanisms of Pathogenic Fungal Acetyl-CoA Synthetases

Acetyl CoA synthetases (ACSs) are Acyl-CoA/NRPS/Luciferase (ANL) superfamily enzymes that couple acetate with CoA to generate acetyl CoA, a key component of central carbon metabolism in eukaryotes and prokaryotes. Normal mammalian cells are not dependent on ACSs, while tumor cells, fungi, and parasites rely on acetate as a precursor for acetyl CoA. Consequently, ACSs have emerged as a potential drug target. As part of a program to develop antifungal ACS inhibitors, we characterized fungal ACSs from five diverse human fungal pathogens using biochemical and structural studies. ACSs catalyze a two-step reaction involving adenylation of acetate followed by thioesterification with CoA. Our structural studies captured each step of these two half-reactions including the acetyl-adenylate intermediate of the first half-reaction in both the adenylation conformation and the thioesterification conformation and thus provide a detailed picture of the reaction mechanism. We also used a systematic series of increasingly larger alkyl adenosine esters as chemical probes to characterize the structural basis of the exquisite ACS specificity for acetate over larger carboxylic acid substrates. Consistent with previous biochemical and genetic data for other enzymes, structures of fungal ACSs with these probes bound show that a key tryptophan residue limits the size of the alkyl binding site and forces larger alkyl chains to adopt high energy conformers, disfavoring their efficient binding. Together, our analysis provides highly detailed structural models for both the reaction mechanism and substrate specificity that should be useful in designing selective inhibitors of eukaryotic ACSs as potential anticancer, antifungal, and antiparasitic drugs.

The Crucial Roles of Intermediate Metabolites in Cancer

Metabolic alteration, one of the hallmarks of cancer cells, is important for cancer initiation and development. To support their rapid growth, cancer cells alter their metabolism so as to obtain the necessary energy and building blocks for biosynthetic pathways, as well as to adjust their redox balance. Once thought to be merely byproducts of metabolic pathways, intermediate metabolites are now known to mediate epigenetic modifications and protein post-transcriptional modifications (PTM), as well as connect cellular metabolism with signal transduction. Consequently, they can affect a myriad of processes, including proliferation, apoptosis, and immunity. In this review, we summarize multiple representative metabolites involved in glycolysis, the pentose phosphate pathway (PPP), the tricarboxylic acid (TCA) cycle, lipid synthesis, ketogenesis, methionine metabolism, glutamine metabolism, and tryptophan metabolism, focusing on their roles in chromatin and protein modifications and as signal-transducing messengers.

Glucose-sensitive acetylation of Seryl tRNA synthetase regulates lipid synthesis in breast cancer

Abnormally enhanced de novo lipid biosynthesis has been increasingly realized to play crucial roles in the initiation and progression of varieties of cancers including breast cancer. However, the mechanisms underlying the dysregulation of lipid biosynthesis in breast cancer remain largely unknown. Here, we reported that seryl tRNA synthetase (SerRS), a key enzyme for protein biosynthesis, could translocate into the nucleus in a glucose-dependent manner to suppress key genes involved in the de novo lipid biosynthesis. In normal mammary gland epithelial cells glucose can promote the nuclear translocation of SerRS by increasing the acetylation of SerRS at lysine 323. In SerRS knock-in mice bearing acetylation-defective lysine to arginine mutation, we observed increased body weight and adipose tissue mass. In breast cancer cells the acetylation and nuclear translocation of SerRS are greatly inhibited. Overexpression of SerRS, in particularly the acetylation-mimetic lysine to glutamine mutant, dramatically inhibits the de novo lipid synthesis and hence greatly suppresses the proliferation of breast cancer cells and the growth of breast cancer xenografts in mice. We further identified that HDAC4 and HDAC5 regulated the acetylation and nuclear translocation of SerRS. Thus, we identified a SerRS-meditated inhibitory pathway in glucose-induced lipid biosynthesis, which is dysregulated in breast cancer.

Disturbed mitochondrial acetylation in accordance with the availability of acetyl groups in hepatocellular carcinoma

As an essential post-translational modification, acetylation participates in various cellular processes and shows aberrances during tumorigenesis. Owing to its modification substrate, acetyl-CoA, acetylation is postulated as a depot for acetyl groups and evolve to build a connection between epigenetics and metabolism. Here we depict a distinct acetylome atlas of hepatocellular carcinoma from the perspectives of both protein acetylation and acetyl-CoA metabolism. We found that tumor acetylome demonstrated a compartment-dependent alteration that the acetylation level of mitochondrial proteins tended to be decreased while nuclear proteins were highly acetylated. In addition, elevated expression of ATP-citrate synthase (ACLY) was observed in tumors, which would facilitate histone acetylation by transporting mitochondrial acetyl coenzyme A to the nucleus. A hypothetical model of the oncogenic acetylome was proposed that growing demands for histone acetylation in tumor cells would drive the relocalization of acetyl-CoA to the nucleus, which may contribute to the global deacetylation of mitochondrial proteins to support the nuclear acetyl-CoA pool in an ACLY-dependent manner. Our findings are thought-provoking on the potential linkage between epigenetics and metabolism in the progression of tumorigenesis.