Argininosuccinate synthetase 1 (ASS1) is a common metabolic marker of chemosensitivity for targeted arginine- and glutamine-starvation therapy

Etoposide-induced protein 2.4 homolog promotes argininosuccinate synthase 1 and cancer cell survival upon arginine deprivation

BACKGROUND

Arginine auxotrophy has been reported in a subset of cancers with inherently defective de novo arginine synthesis. However, the use of arginine deprivation therapy seems to be unequally effective, partially owing to the resistance acquired by cancer cells. Study of underlying factors involved in this response thus becomes of utmost importance. Meanwhile, the function of etoposide-induced 2.4 homolog (EI24) in cancer metabolism, and specifically in arginine metabolism, remains unknown.

METHODS

EI24 was overexpressed in cancer cells using a doxycycline-inducible system or adenovirus transduction, while siRNA was used to knockdown EI24. Amino acid(s) deprivation medium was exploited with a cell viability assay to check the reliance of cancer cell survival on arginine. Protein expression and activation were examined through western blot and co-immunoprecipitation blot. Furthermore, global and specific protein translation were assessed through the SUnSET assay and polysome fractionation analysis. Gene expression and arginine level were downloaded from public cancer datasets for in silico validation including gene set enrichment and survival analysis to objectively evaluate the association between EI24 and arginine metabolism.

RESULTS

EI24 promoted cancer survival under arginine starvation. Mechanistically, EI24 replenished translation of argininosuccinate synthase 1 (ASS1) by inducing the inactive S-nitrosylated form of phosphatase and tensin homolog (PTEN), leading to release of the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) axis. This tumor-promoting action of EI24 could be found in multiple ASS1-deficient cancer cells regardless of p53 status. Furthermore, expression of EI24 was linked to enrichment of arginine metabolism pathway as well as poor survival of patients with cancer across various cancer types, suggesting its role in cancer resistance to arginine deprivation.

CONCLUSIONS

This study is the first to report the role of EI24 in promoting cancer survival via translational regulation of the metabolic enzyme ASS1, thus paving a route for further investigation into the link between EI24 and cancer metabolism.

The roles of enhancer, especially super-enhancer-driven genes in tumor metabolism and immunity

Abnormal metabolism is a characteristic of malignant tumors. Numerous factors play roles in the regulation of tumor metabolism. As epigenetic regulators, enhancers, especially the super-enhancers (SEs), serve as platforms for transcription factors that regulate the expression of metabolism-related enzymes or transporters at the gene level. In this study, we review the effects of enhancer/ SE-driven genes on tumor metabolism and immunity. Enhancers/SEs play regulatory roles in glucose metabolism (glycolysis, gluconeogenesis, tricarboxylic acid (TCA) cycle, pyruvate, and pentose phosphate pathway, lipid metabolism (cholesterol, fatty acid, phosphatide, and sphingolipid), and amino acid metabolism (glutamine, tryptophan, arginine, and cystine). By regulating tumor metabolism, enhancers and SEs can reprogram tumor microenvironment, especially the status of various immune cells. Therefore, interfering enhancers/SEs that regulate the tumor metabolism is likely to enhance the effectiveness of immunotherapy.

The Mechanism of TRIM21 Inhibiting the Invasion and Migration of ccRCC by Stabilizing ASS1

Clear cell renal cell carcinoma (ccRCC) is characterized by its aggressive invasion and metastasis, presenting significant clinical challenges. Gaining insights into the molecular mechanisms underlying its progression is crucial for the development of effective therapeutic strategies. Addressing a critical knowledge gap in understanding ccRCC tumorigenesis, this study aims to elucidate the expression patterns of TRIM21 in ccRCC, unravel its impact on ccRCC patient prognosis, and investigate the regulatory role of TRIM21 in ASS1 expression and urea cycle dysregulation within the context of ccRCC. The results demonstrate that TRIM21 is downregulated in ccRCC, and low expression of TRIM21 predicts an unfavorable prognosis for ccRCC patients. Furthermore, the upregulation of TRIM21 can inhibit the migration and invasion of ccRCC cells by regulating the ubiquitination modification of ASS1. This not only expands the functional role of TRIM21 in ccRCC tumorigenesis but also demonstrates its ability to reverse urea cycle dysregulation through stabilizing ASS1 expression. Specifically, abnormal downregulation of TRIM21 in ccRCC reduces K63 ubiquitination modification of ASS1, leading to decreased stability of the ASS1 protein, aggravated urea cycle dysregulation, and facilitated migration and invasion of ccRCC cells. Additionally, reduction in ASS1 reverses the depressed migration and invasion caused by overexpression of TRIM21 in ccRCC cells. In summary, our findings contribute to a deeper understanding of the functional role played by TRIM21 in ccRCC progression, pinpoint a unique and novel regulatory mechanism involving ectopic downregulation-mediated ASS1 ubiquitination modification and urea cycle dysfunction during ccRCC progression, and provide fresh insights for further investigation into the pathogenesis and metabolic reprogramming associated with ccRCC.

SLC7A5 is required for cancer cell growth under arginine-limited conditions

Tumor cells must optimize metabolite acquisition between synthesis and uptake from a microenvironment characterized by hypoxia, lactate accumulation, and depletion of many amino acids, including arginine. We performed a metabolism-focused functional screen using CRISPR-Cas9 to identify pathways and factors that enable tumor growth in an arginine-depleted environment. Our screen identified the SLC-family transporter SLC7A5 as required for growth, and we hypothesized that this protein functions as a high-affinity citrulline transporter. Using isotope tracing experiments, we show that citrulline uptake and metabolism into arginine are dependent upon expression of SLC7A5. Pharmacological inhibition of SLC7A5 blocks growth under low-arginine conditions across a diverse group of cancer cell lines. Loss of SLC7A5 reduces tumor growth and citrulline import in a mouse tumor model. We identify a conditionally essential role for SLC7A5 in arginine metabolism, and we propose that SLC7A5-targeting therapeutic strategies in cancer may be effective in the context of arginine limitation.

Long-term zinc treatment alters the mechanical properties and metabolism of prostate cancer cells

The failure of intracellular zinc accumulation is a key process in prostate carcinogenesis. Although prostate cancer cells can accumulate zinc after long-term exposure, chronic zinc oversupply may accelerate prostate carcinogenesis or chemoresistance. Because cancer progression is associated with energetically demanding cytoskeletal rearrangements, we investigated the effect of long-term zinc presence on biophysical parameters, ATP production, and EMT characteristics of two prostate cancer cell lines (PC-3, 22Rv1). Prolonged exposure to zinc increased ATP production, spare respiratory capacity, and induced a response in PC-3 cells, characterized by remodeling of vimentin and a shift of cell dry mass density and caveolin-1 to the perinuclear region. This zinc-induced remodeling correlated with a greater tendency to maintain actin architecture despite inhibition of actin polymerization by cytochalasin. Zinc partially restored epithelial characteristics in PC-3 cells by decreasing vimentin expression and increasing E-cadherin. Nevertheless, the expression of E-cadherin remained lower than that observed in predominantly oxidative, low-invasive 22Rv1 cells. Following long-term zinc exposure, we observed an increase in cell stiffness associated with an increased refractive index in the perinuclear region and an increased mitochondrial content. The findings of the computational simulations indicate that the mechanical response cannot be attributed exclusively to alterations in cytoskeletal composition. This observation suggests the potential involvement of an additional, as yet unidentified, mechanical contributor. These findings indicate that long-term zinc exposure alters a group of cellular parameters towards an invasive phenotype, including an increase in mitochondrial number, ATP production, and cytochalasin resistance. Ultimately, these alterations are manifested in the biomechanical properties of the cells.

Suppression of the KRAS-NRF2 axis shifts arginine into the phosphocreatine energy system in pancreatic cancer cells

In pancreatic ductal adenocarcinomas (PDAC), the KRASG12D-NRF2 axis controls cellular functions such as redox homeostasis and metabolism. Disruption of this axis through suppression of NRF2 leads to profound reprogramming of metabolism. Unbiased transcriptome and metabolome analyses showed that PDAC cells with disrupted KRASG12D-NRF2 signaling (NRF2-/- cells) shift from aerobic glycolysis to metabolic pathways fed by amino acids. Metabolome, RNA-seq and qRT-PCR analyses revealed a blockade of the urea cycle, making NRF2-/- cells dependent on exogenous arginine for survival. Arginine is channeled into anabolic pathways, including the synthesis of phosphocreatine, which generates an energy buffer essential for cell growth. A similar switch was observed in tumor clones that had survived FOLFIRINOX therapy or blockade of KRAS signaling. Inhibition of the creatine pathway with cyclocreatine reduced both ATP and invasion rate in 3D spheroids from NRF2-deficient PDAC cells. Our study provides basis for the rational development of combination therapies for pancreatic cancer.

Genetics of enzymatic dysfunctions in metabolic disorders and cancer

Inherited metabolic disorders arise from mutations in genes involved in the biogenesis, assembly, or activity of metabolic enzymes, leading to enzymatic deficiency and severe metabolic impairments. Metabolic enzymes are essential for the normal functioning of cells and are involved in the production of amino acids, fatty acids and nucleotides, which are essential for cell growth, division and survival. When the activity of metabolic enzymes is disrupted due to mutations or changes in expression levels, it can result in various metabolic disorders that have also been linked to cancer development. However, there remains much to learn regarding the relationship between the dysregulation of metabolic enzymes and metabolic adaptations in cancer cells. In this review, we explore how dysregulated metabolism due to the alteration or change of metabolic enzymes in cancer cells plays a crucial role in tumor development, progression, metastasis and drug resistance. In addition, these changes in metabolism provide cancer cells with a number of advantages, including increased proliferation, resistance to apoptosis and the ability to evade the immune system. The tumor microenvironment, genetic context, and different signaling pathways further influence this interplay between cancer and metabolism. This review aims to explore how the dysregulation of metabolic enzymes in specific pathways, including the urea cycle, glycogen storage, lysosome storage, fatty acid oxidation, and mitochondrial respiration, contributes to the development of metabolic disorders and cancer. Additionally, the review seeks to shed light on why these enzymes represent crucial potential therapeutic targets and biomarkers in various cancer types.

The amino-acid stress sensing eIF2α kinase GCN2 is a survival biomarker for malignant mesothelioma

BACKGROUND

Malignant mesothelioma is a tumour that is strongly associated with a history of asbestos exposure, and which derives from mesothelial cells that line the serous cavities of the body. The tumour most commonly arises in the pleural cavity, but can also arise in the pericardium, peritoneum, and tunica vaginalis. At present the lesion has a very poor prognosis and is an incurable form of cancer with median survival times of up to 19 months being quoted for some histological subtypes. A large proportion of mesotheliomas have been shown to be arginine auxotrophic, leading to new research for therapeutics which might exploit this potential vulnerability.

METHODS

We measured the levels of General Control Non-derepressible 2 (GCN2) protein in malignant mesothelioma tumour samples and determined whether these levels correlate with clinical outcomes.

RESULTS

We observed that the expression levels of GCN2 correlated with patient survival and was an independent prognostic variable in pairwise comparisons with all available clinical data.

CONCLUSION

These findings suggest that GCN2 levels provides prognostic information and may allow for stratification of care pathways. It may suggest that targeting GCN2 is a viable strategy for mesothelioma therapy development.

Arginine deprivation as a treatment approach targeting cancer cell metabolism and survival: A review of the literature

Amino acid requirement of metabolically active cells is a key element in cellular survival. Of note, cancer cells were shown to have an abnormal metabolism and high-energy requirements including the high amino acid requirement needed for growth factor synthesis. Thus, amino acid deprivation is considered a novel approach to inhibit cancer cell proliferation and offer potential treatment prospects. Accordingly, arginine was proven to play a significant role in cancer cell metabolism and therapy. Arginine depletion induced cell death in various types of cancer cells. Also, the various mechanisms of arginine deprivation, e.g., apoptosis and autophagy were summarized. Finally, the adaptive mechanisms of arginine were also investigated. Several malignant tumors had high amino acid metabolic requirements to accommodate their rapid growth. Antimetabolites that prevent the production of amino acids were also developed as anticancer therapies and are currently under clinical investigation. The aim of this review is to provide a concise literature on arginine metabolism and deprivation, its effects in different tumors, its different modes of action, as well as the related cancerous escape mechanisms.

Argininosuccinate synthase 1, arginine deprivation therapy and cancer management

Metabolic reprogramming is an emerging hallmark of tumor cells. In order to survive in the nutrient-deprived environment, tumor cells rewire their metabolic phenotype to provide sufficient energy and build biomass to sustain their transformed state and promote malignant behaviors. Amino acids are the main compositions of protein, which provide key intermediate substrates for the activation of signaling pathways. Considering that cells can synthesize arginine via argininosuccinate synthase 1 (ASS1), arginine is regarded as a non-essential amino acid, making arginine depletion as a promising therapeutic strategy for ASS1-silencing tumors. In this review, we summarize the current knowledge of expression pattern of ASS1 and related signaling pathways in cancer and its potential role as a novel therapeutic target in cancer. Besides, we outline how ASS1 affects metabolic regulation and tumor progression and further discuss the role of ASS1 in arginine deprivation therapy. Finally, we review approaches to target ASS1 for cancer therapies.

Amino acid restriction induces a long non-coding RNA UBA6-AS1 to regulate GCN2-mediated integrated stress response in breast cancer

Oncogene activation, massive proliferation, and increased nutrient demands often result in nutrient and oxygen deprivation in solid tumors including breast cancer (BC), leading to the induction of oxidative stress and endoplasmic reticulum (ER) stress, and subsequently triggering integrated stress response (ISR). To elucidate the role of long non-coding RNAs (lncRNAs) in the ISR of BC, we performed transcriptome analyses and identified a lncRNA, UBA6-AS1, which was upregulated upon amino acid deprivation and ER stress. UBA6-AS1 was preferentially induced in triple-negative BC (TNBC) cells deprived of arginine or glutamine, two critical amino acids required for cancer cell growth, or treated with ER stress inducers. Mechanistically, UBA6-AS1 was regulated through the GCN2/eIF2α/ATF4 pathway, one of the major routes mediating ISR in amino acid sensing. In addition, both in vitro and in vivo assays indicated that UBA6-AS1 promoted TNBC cell survival when cells encountered metabolic stress, implicating a regulatory role of UBA6-AS1 in response to intratumoral metabolic stress during tumor progression. Moreover, PARP1 expression and activity were positively regulated by the GCN2/UBA6-AS1 axis upon amino acid deprivation. In conclusion, our data suggest that UBA6-AS1 is a novel lncRNA regulating ISR upon metabolic stress induction to promote TNBC cell survival. Furthermore, the GCN2-ATF4 axis is important for UBA6-AS1 induction to enhance PARP1 activity and could serve as a marker for the susceptibility of PARP inhibitors in TNBC.

Integration of transcriptomics and metabolomics confirmed hepatoprotective effects of steamed shoot extracts of ginseng (Panax ginseng C.A. Meyer) on toxicity caused by overdosed acetaminophen

The study aimed, by integrating transcriptomics and metabolomics, to reveal novel biomarkers caused by overdosed acetaminophen (APAP) and liver protection substances procured by pre-administration of ginseng shoots extract (GSE). Totally 4918 genes and 127 metabolites were identified as differentially expressed genes and differential metabolites, respectively. According to KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment, such pathways as primary bile acid biosynthesis, bile secretion, retinol metabolism, histidine and several other amino-related metabolism were significantly altered by GSE and disturbed by subsequent overdosed APAP at the transcriptomic as well as metabolomic levels. Fifteen key biomarker metabolites related to these pathways were up-regulated in APAP-treated vs GSE-pretreated liver tissues, and were reported exerting anti-oxidant, anti-inflammatory, anti-apoptotic and/or immunomodulate functions, three of which even possessed direct hepatoprotection effects. Twenty five vital unigenes modulating these metabolites were further verified by correlation analysis and expression levels of fifteen of them were examined by qRT-PCR. Our findings indicate that GSE may be an effective dietary supplement for preventing the liver damage caused by the overdosed APAP.

The context-specific roles of urea cycle enzymes in tumorigenesis

The expression of the urea cycle (UC) proteins is dysregulated in multiple cancers, providing metabolic benefits to tumor survival, proliferation, and growth. Here, we review the main changes described in the expression of UC enzymes and metabolites in different cancers at various stages and suggest that these changes are dynamic and should hence be viewed in a context-specific manner. Understanding the evolvability in the activity of the UC pathway in cancer has implications for cancer-immune cell interactions and for cancer diagnosis and therapy.

NEI-01-Induced Arginine Deprivation Has Potent Activity Against Acute Myeloid Leukemia Cells Both In Vitro and In Vivo

Recent studies have revealed that targeting amino acid metabolic enzymes is a promising strategy in cancer therapy. Acute myeloid leukemia (AML) downregulates the expression of argininosuccinate synthase (ASS1), a recognized rate-limiting enzyme for arginine synthesis, and yet displays a critical dependence on extracellular arginine for survival and proliferation. This dependence on extracellular arginine, also known as arginine auxotrophy, suggests that arginine deprivation would be a treatment strategy for AML. NEI-01, a novel arginine-depleting enzyme, is capable of binding to serum albumin to extend its circulating half-life, leading to a potent anticancer activity. Here we reported the preclinical activity of NEI-01 in arginine auxotrophic AMLs. NEI-01 efficiently depleted arginine both in vitro and in vivo NEI-01-induced arginine deprivation was cytotoxic to arginine auxotrophic AML cells through induction of cell-cycle arrest and apoptosis. Furthermore, the potent anti-leukemia activities of NEI-01 were observed in three different types of mouse models including human cell line-derived xenograft, mouse cell line-derived homografts in syngeneic mice and patient-derived xenograft. This preclinical data provide strong evidence to support the potential use of NEI-01 as a therapeutic approach in AML treatment.

Arginine Signaling and Cancer Metabolism

Arginine is an amino acid critically involved in multiple cellular processes including the syntheses of nitric oxide and polyamines, and is a direct activator of mTOR, a nutrient-sensing kinase strongly implicated in carcinogenesis. Yet, it is also considered as a non- or semi-essential amino acid, due to normal cells' intrinsic ability to synthesize arginine from citrulline and aspartate via ASS1 (argininosuccinate synthase 1) and ASL (argininosuccinate lyase). As such, arginine can be used as a dietary supplement and its depletion as a therapeutic strategy. Strikingly, in over 70% of tumors, ASS1 transcription is suppressed, rendering the cells addicted to external arginine, forming the basis of arginine-deprivation therapy. In this review, we will discuss arginine as a signaling metabolite, arginine's role in cancer metabolism, arginine as an epigenetic regulator, arginine as an immunomodulator, and arginine as a therapeutic target. We will also provide a comprehensive summary of ADI (arginine deiminase)-based arginine-deprivation preclinical studies and an update of clinical trials for ADI and arginase. The different cell killing mechanisms associated with various cancer types will also be described.

Alterations in rat adipose tissue transcriptome and proteome in response to prolonged fasting

Various pathophysiological situations of negative energy balance involve the intense depletion of the body's energy reserves. White adipose tissue is a central place to store energy and a major endocrine organ. As a model of choice to better understand how the white adipose tissue dynamically responds to changes in substrate availability, we used the prolonged fasting paradigm, which is characterized by successive periods of stimulated (phase 2) and then reduced (phase 3) lipid mobilization/utilization. Using omics analyses, we report a regulatory transcriptional program in rat epididymal (EPI) adipose tissue favoring lipolysis during phase 2 and repressing it during phase 3. Changes in gene expression levels of lipases, lipid droplet-associated factors, and the proteins involved in cAMP-dependent and cAMP-independent regulation of lipolysis are highlighted. The mRNA and circulating levels of adipose-secreted factors were consistent with the repression of insulin signaling during prolonged fasting. Other molecular responses are discussed, including the regulation of leptin and adiponectin levels, the specific changes reflecting an increased fibrinolysis and a possible protein catabolism-related energy saving mechanism in late fasting. Finally, some differences between internal and subcutaneous (SC) adipose tissues are also reported. These data provide a comprehensive molecular basis of adipose tissue responses when facing a major energetic challenge.

Uncovering the antitumor effects and mechanisms of Shikonin against colon cancer on comprehensive analysis

BACKGROUND

Shikonin, a naphthoquinone compound extracted from the root of Lithospermum erythrorhizon, has been extensively studied for its antitumor activity. However, the systematic pathways involved in Shikonin intervention in human colon cancer has not yet clearly defined.

PURPOSE

This study was to evaluate the cytotoxic effects of Shikonin in colon cancer, as well as investigate the potential biomarkers from a global perspective and the possible antitumor mechanisms involved.

METHODS

In this work, cell viability, cell cycle and cell apoptosis in human colon cancer cells were assessed to evaluate the antitumor activity of Shikonin. Transcriptomics and metabolomics were integrated to provide the perturbed pathways and explore the potential mechanisms. The crucial proteins and genes involved were further validated by immunohistochemistry and real-time quantitative PCR.

RESULTS

Shikonin revealed a remarkable antitumor potency in colon cancer. Cell cycle was significantly arrested at the S phase as well as apoptosis was induced in SW480 cell line. Furthermore, a total of 1642 differentially expressed genes and 40 metabolites were detected after Shikonin intervention. The integrated analysis suggested that the antitumor effect was mainly attributed to purine metabolism, arginine biosynthesis, pyrimidine metabolism, urea cycle and metabolism of amino acids. The up-regulated expression of proteins vital for arginine biosynthesis was subsequently validated by immunohistochemistry in xenograft mice. Notably, supplemental dNTPs and arginine could significantly reverse the cytotoxic effect induced by Shikonin and the genes participating in purine metabolism and arginine biosynthesis were further determined by RT-qPCR.

CONCLUSION

Our findings provide a systematic perspective in the therapeutic effect of Shikonin which might lay a foundation for further research on Shikonin in colon cancer.

Targeting the Proline-Glutamine-Asparagine-Arginine Metabolic Axis in Amino Acid Starvation Cancer Therapy

Proline, glutamine, asparagine, and arginine are conditionally non-essential amino acids that can be produced in our body. However, they are essential for the growth of highly proliferative cells such as cancers. Many cancers express reduced levels of these amino acids and thus require import from the environment. Meanwhile, the biosynthesis of these amino acids is inter-connected but can be intervened individually through the inhibition of key enzymes of the biosynthesis of these amino acids, resulting in amino acid starvation and cell death. Amino acid starvation strategies have been in various stages of clinical applications. Targeting asparagine using asparaginase has been approved for treating acute lymphoblastic leukemia. Targeting glutamine and arginine starvations are in various stages of clinical trials, and targeting proline starvation is in preclinical development. The most important obstacle of these therapies is drug resistance, which is mostly due to reactivation of the key enzymes involved in biosynthesis of the targeted amino acids and reprogramming of compensatory survival pathways via transcriptional, epigenetic, and post-translational mechanisms. Here, we review the interactive regulatory mechanisms that control cellular levels of these amino acids for amino acid starvation therapy and how drug resistance is evolved underlying treatment failure.

Arginine deprivation as a strategy for cancer therapy: An insight into drug design and drug combination

Extensive studies have shown that cancer cells have specific nutrient auxotrophy and thus have much a higher demand for certain nutrients than normal cells. Amino acid deprivation has attracted much attention in cancer therapy with positive outcomes from clinical trials. Arginine, as one of the conditionally essential amino acids, plays a pivotal role in cellular division and metabolism. Since many types of cancer cells exhibit decreased expression of argininosuccinate synthetase and/or ornithine transcarbamylase, they are auxotrophic for arginine, which makes arginine deprivation an accessible choice for cancer treatment. Arginine deiminase (ADI) and human arginase (hArg) are the two major protein drugs used for arginine deprivation and are undergoing many clinical trials. However, the clinical application of ADI and hArg is facing some common problems, including their short half-lives, immunogenicity and inconsistent production, which underlines the importance of improving these drugs using protein engineering techniques. Thus, we systematically review the latest studies of protein engineering and anti-cancer studies based on in vitro, in vivo and clinical models of ADI and hArg, and we include the latest studies on drug combinations consisting of ADI/hArg with chemotherapeutic drugs.

Mechanism for hypoxia inducible factor-1α to promote immune escape and therapeutic tolerance in hepatocellular carcinoma under hypoxic microenvironment

The liver is the largest immune organ in the body, and immunologic tolerance and escape mechanisms play an important role in hepatocellular carcinoma (HCC) development. HCC has a complex tumor microenvironment (TME), and it is necessary to study the mechanism that causes HCC cells to escape the body immune surveillance and produce therapeutic resistance in HCC clinical treatment. Hypoxia inducible factor-1α (HIF-1α) is a transcription factor that contains α subunits regulated by hypoxia. Tumor cells highly express HIF-1α in a hypoxic environment, which participates in the processes of tumor cell proliferation and metastasis, microvascular production, immune escape, and therapeutic tolerance, ultimately promoting tumorigenesis and development. In this paper, we will elaborate on the mechanisms by which HCC cells activate HIF-1α expression to promote hypoxic adaptation in cancer cells and regulate immune escape and treatment tolerance in hypoxic TME.

Systems level profiling of arginine starvation reveals MYC and ERK adaptive metabolic reprogramming

Arginine auxotrophy due to the silencing of argininosuccinate synthetase 1 (ASS1) occurs in many carcinomas and in the majority of sarcomas. Arginine deiminase (ADI-PEG20) therapy exploits this metabolic vulnerability by depleting extracellular arginine, causing arginine starvation. ASS1-negative cells develop resistance to ADI-PEG20 through a metabolic adaptation that includes re-expressing ASS1. As arginine-based multiagent therapies are being developed, further characterization of the changes induced by arginine starvation is needed. In order to develop a systems-level understanding of these changes, activity-based proteomic profiling (ABPP) and phosphoproteomic profiling were performed before and after ADI-PEG20 treatment in ADI-PEG20-sensitive and resistant sarcoma cells. When integrated with metabolomic profiling, this multi-omic analysis reveals that cellular response to arginine starvation is mediated by adaptive ERK signaling and activation of the Myc–Max transcriptional network. Concomitantly, these data elucidate proteomic changes that facilitate oxaloacetate production by enhancing glutamine and pyruvate anaplerosis and altering lipid metabolism to recycle citrate for oxidative glutaminolysis. Based on the complexity of metabolic and cellular signaling interactions, these multi-omic approaches could provide valuable tools for evaluating response to metabolically targeted therapies.

Glucometabolic Reprogramming in the Hepatocellular Carcinoma Microenvironment: Cause and Effect

Hepatocellular carcinoma (HCC) is a tumor that exhibits glucometabolic reprogramming, with a high incidence and poor prognosis. Usually, HCC is not discovered until an advanced stage. Sorafenib is almost the only drug that is effective at treating advanced HCC, and promising metabolism-related therapeutic targets of HCC are urgently needed. The "Warburg effect" illustrates that tumor cells tend to choose aerobic glycolysis over oxidative phosphorylation (OXPHOS), which is closely related to the features of the tumor microenvironment (TME). The HCC microenvironment consists of hypoxia, acidosis and immune suppression, and contributes to tumor glycolysis. In turn, the glycolysis of the tumor aggravates hypoxia, acidosis and immune suppression, and leads to tumor proliferation, angiogenesis, epithelial-mesenchymal transition (EMT), invasion and metastasis. In 2017, a mechanism underlying the effects of gluconeogenesis on inhibiting glycolysis and blockading HCC progression was proposed. Treating HCC by increasing gluconeogenesis has attracted increasing attention from scientists, but few articles have summarized it. In this review, we discuss the mechanisms associated with the TME, glycolysis and gluconeogenesis and the current treatments for HCC. We believe that a treatment combination of sorafenib with TME improvement and/or anti-Warburg therapies will set the trend of advanced HCC therapy in the future.

Metabolic Reprogramming of Chemoresistant Cancer Cells and the Potential Significance of Metabolic Regulation in the Reversal of Cancer Chemoresistance

Metabolic reprogramming is one of the hallmarks of tumors. Alterations of cellular metabolism not only contribute to tumor development, but also mediate the resistance of tumor cells to antitumor drugs. The metabolic response of tumor cells to various chemotherapy drugs can be analyzed by metabolomics. Although cancer cells have experienced metabolic reprogramming, the metabolism of drug resistant cancer cells has been further modified. Metabolic adaptations of drug resistant cells to chemotherapeutics involve redox, lipid metabolism, bioenergetics, glycolysis, polyamine synthesis and so on. The proposed metabolic mechanisms of drug resistance include the increase of glucose and glutamine demand, active pathways of glutaminolysis and glycolysis, promotion of NADPH from the pentose phosphate pathway, adaptive mitochondrial reprogramming, activation of fatty acid oxidation, and up-regulation of ornithine decarboxylase for polyamine production. Several genes are associated with metabolic reprogramming and drug resistance. Intervening regulatory points described above or targeting key genes in several important metabolic pathways may restore cell sensitivity to chemotherapy. This paper reviews the metabolic changes of tumor cells during the development of chemoresistance and discusses the potential of reversing chemoresistance by metabolic regulation.

Arginine metabolism and deprivation in cancer therapy

Certain cancer cells with nutrient auxotrophy and have a much higher nutrient demand compared with normal human cells. Arginine as a versatile amino acid, has multiple biological functions in metabolic and signaling pathways. Depletion of this amino acid by arginine depletor is generally well tolerated and has become a targeted therapy for arginine auxotrophic cancers. However, the modulatory eff ;ect of arginine on cancer cells is very complicated and still controversial. Therefore, this article focuses on arginine metabolism and depletion therapy in cancer treatment to provide systemical review on this issue.

Effects of glutamine deprivation on oxidative stress and cell survival in breast cell lines

Background

Tumourigenic cells modify metabolic pathways in order to facilitate increased proliferation and cell survival resulting in glucose- and glutamine addiction. Previous research indicated that glutamine deprivation resulted in potential differential activity targeting tumourigenic cells more prominently. This is ascribed to tumourigenic cells utilising increased glutamine quantities for enhanced glycolysis- and glutaminolysis. In this study, the effects exerted by glutamine deprivation on reactive oxygen species (ROS) production, mitochondrial membrane potential, cell proliferation and cell death in breast tumourigenic cell lines (MCF-7, MDA-MB-231, BT-20) and a non-tumourigenic breast cell line (MCF-10A) were investigated.

Results

Spectrophotometry demonstrated that glutamine deprivation resulted in decreased cell growth in a time-dependent manner. MCF-7 cell growth was decreased to 61% after 96 h of glutamine deprivation; MDA-MB-231 cell growth was decreased to 78% cell growth after 96 h of glutamine deprivation, MCF-10A cell growth was decreased 89% after 96 h of glutamine deprivation and BT-20 cell growth decreased to 86% after 24 h of glutamine deprivation and remained unchanged until 96 h of glutamine deprivation. Glutamine deprivation resulted in oxidative stress where superoxide levels were significantly elevated after 96 h in the MCF-7- and MDA-MB-231 cell lines. Time-dependent production of hydrogen peroxide was accompanied by aberrant mitochondrial membrane potential. The effects of ROS and mitochondrial membrane potential were more prominently observed in the MCF-7 cell line when compared to the MDA-MB-231-, MCF-10A- and BT-20 cell lines. Cell cycle progression revealed that glutamine deprivation resulted in a significant increase in the S-phase after 72 h of glutamine deprivation in the MCF-7 cell line. Apoptosis induction resulted in a decrease in viable cells in all cell lines following glutamine deprivation. In the MCF-7 cells, 87.61% of viable cells were present after 24 h of glutamine deprivation.

Conclusion

This study demonstrates that glutamine deprivation resulted in decreased cell proliferation, time-dependent- and cell line-dependent ROS generation, aberrant mitochondrial membrane potential and disrupted cell cycle progression. In addition, the estrogen receptor positive MCF-7 cell line was more prominently affected. This study contributes to knowledge regarding the sensitivity of breast cancer cells and non-tumorigenic cells to glutamine deprivation.

Electronic supplementary material

The online version of this article (10.1186/s40659-019-0224-9) contains supplementary material, which is available to authorized users.

Dietary Supplementation with Trihexanoin Enhances Intestinal Function of Weaned Piglets

Trihexanoin is a short-chain triglyceride (SCT). Many studies have reported that SCTs play important roles in the maintenance of intestinal epithelial structure and function. The present work was to investigate the effects of trihexanoin on growth performance, carbohydrate and fat metabolism, as well as intestinal morphology and function in weaned piglets. Twenty weaned piglets (21 ± 2 d) were randomly allocated to one of two treatment groups: The control group (basal diet supplemented with 0.5% soya oil); the TH group (basal diet supplemented with 0.5% trihexanoin). Dietary trihexanoin supplementation significantly reduced diarrhea rate; increased the concentrations of LDL, HDL and total protein in plasma; decreased cholesterol concentrations and glutamyl transpeptidase activity in plasma; improved intestinal morphologic structure; altered the mRNA levels and abundances of proteins related to glycogen and fat metabolism, mucosal barrier function, antioxidant capacity and water transport capacity; and altered the community of intestinal microflora. These results indicate that dietary trihexanoin supplementation could reduce diarrhea, regulate carbohydrate and fat metabolism, exert beneficial effects on the intestinal mucosal barrier, protect the intestinal mucosa from injuries, improve intestinal transport and absorption, and enhance antioxidant capacity. In conclusion, dietary supplementation with 0.5% trihexanoin improves the intestinal function and health of weaned piglets.

Deciphering metabolic rewiring in breast cancer subtypes

Metabolic reprogramming, an emerging hallmark of cancer, is observed in breast cancer. Breast cancer cells rewire their cellular metabolism to meet the demands of survival, proliferation, and invasion. However, breast cancer is a heterogeneous disease, and metabolic rewiring is not uniform. Each subtype of breast cancer displays distinct metabolic alterations. Here, we focus on unique metabolic reprogramming associated with subtypes of breast cancer, as well as common features. Therapeutic opportunities based on subtype-specific metabolic alterations are also discussed. Through this discussion, we aim to provide insight into subtype-specific metabolic rewiring and vulnerabilities that have the potential to better guide therapy and improve outcomes for patients.

Chromatin remodeling system p300-HDAC2-Sin3A is involved in Arginine Starvation-Induced HIF-1α Degradation at the ASS1 promoter for ASS1 Derepression

Argininosuccinate synthetase 1 (ASS1) is the key enzyme that controls biosynthesis of arginine (Arg). ASS1 is silenced in many human malignancies therefore, these tumors require extracellular Arg for growth. The Arg-degrading recombinant protein, pegylated arginine deiminase (ADI-PEG20), has been in clinical trials for targeting Arg auxotrophic tumors by Arg starvation therapy. Resistance to Arg starvation is often developed through reactivation of ASS1 expression. We previously demonstrated that ASS1 silencing is controlled by HIF-1α and Arg starvation-reactivated ASS1 is associated with HIF-1α downregulation. However, mechanisms underlying ASS1 repression and HIF-1α turnover are not known. Here, we demonstrate that interplay of p300-HDAC2-Sin3A in the chromatin remodeling system is involved in HIF-1α degradation at the ASS1 promoter. The histone acetyltransferase p300 is normally associated with the ASS1 promoter to maintain acetylated H3K14ac and H3K27ac for ASS1 silencing. Arg starvation induces p300 dissociation, allowing histone HDAC2 and cofactor Sin3A to deacetylate these histones at the ASS1 promoter, thereby facilitating HIF-1α-proteasomal complex, driven by PHD2, to degrade HIF-1α in situ. Arg starvation induces PHD2 and HDAC2 interaction which is sensitive to antioxidants. This is the first report describing epigenetic regulation of chromosomal HIF-1α turnover in gene activation that bears important implication in cancer therapy.