Blockade of 6-phosphogluconate dehydrogenase generates CD8+ effector T cells with enhanced anti-tumor function

Plasma GPI and PGD are associated with vascular normalization and may serve as novel prognostic biomarkers for lung adenocarcinoma: Multi-omics and multi-dimensional analysis

The aim of this study was to explore potential novel plasma protein biomarkers for lung adenocarcinoma (LUAD). A plasma proteomics analysis was carried out and candidate protein biomarkers were validated in 102 LUAD cases and 102 matched healthy controls. The same LUAD tumor tissues were detected to explore the correlation between the expression of candidate proteins in tissues and plasma and vascular normalization. A LUAD active metastasis mice model was constructed to explore the role of candidate proteins for lung metastasis. GPI and PGD were verified to be upregulated in plasma from LUAD patients, and the expression of GPI in tumor tissue was positively correlated with the expression of GPI in plasma and negatively correlated with the normalization of tumor blood vessels. Meanwhile, a negative correlation between the expression of GPI and PGD in plasma and tumor vascular normalization was discovered. In the LUAD active metastasis model, the lowest levels of vascular normalization and the highest expression of GPI and PGD were found in mice with lung metastases. This study found that GPI and PGD may be potential plasma biomarkers for LUAD, and monitoring those may infer the risk of metastasis and malignancy of the tumor. SIGNIFICANT: We identified GPI and PGD as potential novel diagnostic and prognostic biomarkers for LUAD. PGD and GPI can be used as diagnostic biomarkers in combination with other available strategies to assist in the screening and diagnosis of LUAD, and as prognostic biomarkers aid in predict the risk of tumor metastasis and malignancy in patients with LUAD.

Disulfidptosis, A Novel Cell Death Pathway: Molecular Landscape and Therapeutic Implications

Programmed cell death is pivotal for several physiological processes, including immune defense. Further, it has been implicated in the pathogenesis of developmental disorders and the onset of numerous diseases. Multiple modes of programmed cell death, including apoptosis, pyroptosis, necroptosis, and ferroptosis, have been identified, each with their own unique characteristics and biological implications. In February 2023, Liu Xiaoguang and his team discovered "disulfidptosis," a novel pathway of programmed cell death. Their findings demonstrated that disulfidptosis is triggered in glucose-starved cells exhibiting high expression of a protein called SLC7A11. Furthermore, disulfidptosis is marked by a drastic imbalance in the NADPH/NADP+ ratio and the abnormal accumulation of disulfides like cystine. These changes ultimately lead to the destabilization of the F-actin network, causing cell death. Given that high SLC7A11 expression is a key feature of certain cancers, these findings indicate that disulfidptosis could serve as the basis of innovative anti-cancer therapies. Hence, this review delves into the discovery of disulfidptosis, its underlying molecular mechanisms and metabolic regulation, and its prospective applications in disease treatment.

Myeloid-derived suppressor cell mitochondrial fitness governs chemotherapeutic efficacy in hematologic malignancies

Myeloid derived suppressor cells (MDSCs) are key regulators of immune responses and correlate with poor outcomes in hematologic malignancies. Here, we identify that MDSC mitochondrial fitness controls the efficacy of doxorubicin chemotherapy in a preclinical lymphoma model. Mechanistically, we show that triggering STAT3 signaling via β2-adrenergic receptor (β2-AR) activation leads to improved MDSC function through metabolic reprograming, marked by sustained mitochondrial respiration and higher ATP generation which reduces AMPK signaling, altering energy metabolism. Furthermore, induced STAT3 signaling in MDSCs enhances glutamine consumption via the TCA cycle. Metabolized glutamine generates itaconate which downregulates mitochondrial reactive oxygen species via regulation of Nrf2 and the oxidative stress response, enhancing MDSC survival. Using β2-AR blockade, we target the STAT3 pathway and ATP and itaconate metabolism, disrupting ATP generation by the electron transport chain and decreasing itaconate generation causing diminished MDSC mitochondrial fitness. This disruption increases the response to doxorubicin and could be tested clinically.

Deficiency of metabolic regulator PKM2 activates the pentose phosphate pathway and generates TCF1+ progenitor CD8+ T cells to improve checkpoint blockade

TCF1high progenitor CD8+ T cells mediate the efficacy of PD-1 blockade, however the mechanisms that govern their generation and maintenance are poorly understood. Here, we show that targeting glycolysis through deletion of pyruvate kinase muscle 2 (PKM2) results in elevated pentose phosphate pathway (PPP) activity, leading to enrichment of a TCF1high central memory-like phenotype and increased responsiveness to PD-1 blockade in vivo. PKM2KO CD8+ T cells showed reduced glycolytic flux, accumulation of glycolytic intermediates and PPP metabolites, and increased PPP cycling as determined by 1,2 13C glucose carbon tracing. Small molecule agonism of the PPP without acute glycolytic impairment skewed CD8+ T cells towards a TCF1high population, generated a unique transcriptional landscape, enhanced tumor control in mice in combination with PD-1 blockade, and promoted tumor killing in patient-derived tumor organoids. Our study demonstrates a new metabolic reprogramming that contributes to a progenitor-like T cell state amenable to checkpoint blockade.

The pentose phosphate pathway in health and disease

The pentose phosphate pathway (PPP) is a glucose-oxidizing pathway that runs in parallel to upper glycolysis to produce ribose 5-phosphate and nicotinamide adenine dinucleotide phosphate (NADPH). Ribose 5-phosphate is used for nucleotide synthesis, while NADPH is involved in redox homoeostasis as well as in promoting biosynthetic processes, such as the synthesis of tetrahydrofolate, deoxyribonucleotides, proline, fatty acids and cholesterol. Through NADPH, the PPP plays a critical role in suppressing oxidative stress, including in certain cancers, in which PPP inhibition may be therapeutically useful. Conversely, PPP-derived NADPH also supports purposeful cellular generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) for signalling and pathogen killing. Genetic deficiencies in the PPP occur relatively commonly in the committed pathway enzyme glucose-6-phosphate dehydrogenase (G6PD). G6PD deficiency typically manifests as haemolytic anaemia due to red cell oxidative damage but, in severe cases, also results in infections due to lack of leucocyte oxidative burst, highlighting the dual redox roles of the pathway in free radical production and detoxification. This Review discusses the PPP in mammals, covering its roles in biochemistry, physiology and disease.

A Phase I-II multicenter trial with Avelumab plus autologous dendritic cell vaccine in pre-treated mismatch repair-proficient (MSS) metastatic colorectal cancer patients; GEMCAD 1602 study

BACKGROUND

Immune check-point blockade (ICB) has shown clinical benefit in mismatch repair-deficient/microsatellite instability high metastatic colorectal cancer (mCRC) but not in mismatch repair-proficient/microsatellite stable patients. Cancer vaccines with autologous dendritic cells (ADC) could be a complementary therapeutic approach to ICB as this combination has the potential to achieve synergistic effects.

METHODS

This was a Phase I/II multicentric study with translational sub-studies, to evaluate the safety, pharmacodynamics and anti-tumor effects of Avelumab plus ADC vaccine in heavily pre-treated MSS mCRC patients. Primary objective was to determine the maximum tolerated dose and the efficacy of the combination. The primary end-point was 40% progression-free survival at 6 months with a 2 Simon Stage.

RESULTS

A total of 28 patients were screened and 19 pts were included. Combined therapy was safe and well tolerated. An interim analysis (Simon design first-stage) recommended early termination because only 2/19 (11%) patients were disease free at 6 months. Median PFS was 3.1 months [2.1-5.3 months] and overall survival was 12.2 months [3.2-23.2 months]. Stimulation of immune system was observed in vitro but not clinically. The evaluation of basal RNA-seq noted significant changes between pre and post-therapy liver biopsies related to lipid metabolism and transport, inflammation and oxidative stress pathways.

CONCLUSIONS

The combination of Avelumab plus ADC vaccine is safe and well tolerated but exhibited modest clinical activity. Our study describes, for the first-time, a de novo post-therapy metabolic rewiring, that could represent novel immunotherapy-induced tumor vulnerabilities.

6-Phosphogluconate dehydrogenase inhibition arrests growth and induces apoptosis in gastric cancer via AMPK activation and oxidative stress

Poor outcomes in advanced gastric cancer necessitate alternative therapeutic strategies. 6-Phosphogluconate dehydrogenase (6-PGDH), an enzyme that catalyzes the decarboxylation step in the oxidative pentose phosphate pathway, has been identified as a promising therapeutic target in many cancers. In this study, we systematically investigated the expression and function of 6-PGDH in gastric cancer. We found that 6-PGDH expression and activity were aberrantly elevated in gastric cancer tissues compared to their adjacent normal tissues. 6-PGDH knockdown using two independent shRNAs resulted in minimal 6-PGDH levels and activity, decreased growth, and enhanced gastric cancer cell sensitivity to 5-flurorouracil. However, 6-PGDH knockdown did not affect the cancer cells. Mechanistic studies showed that 6-PGDH inhibition disrupted lipid biosynthesis and redox homeostasis in gastric cancer, inhibited growth, and induced apoptosis. Notably, the in vitro findings were validated using an in vivo gastric cancer xenograft mouse model. This study established that 6-PGDH is broadly elevated in gastric cancer patients and that 6-PGDH inhibition can sensitize gastric cancer cells in response to chemotherapy.

HDAC7 is an immunometabolic switch triaging danger signals for engagement of antimicrobial versus inflammatory responses in macrophages

The immune system must be able to respond to a myriad of different threats, each requiring a distinct type of response. Here, we demonstrate that the cytoplasmic lysine deacetylase HDAC7 in macrophages is a metabolic switch that triages danger signals to enable the most appropriate immune response. Lipopolysaccharide (LPS) and soluble signals indicating distal or far-away danger trigger HDAC7-dependent glycolysis and proinflammatory IL-1β production. In contrast, HDAC7 initiates the pentose phosphate pathway (PPP) for NADPH and reactive oxygen species (ROS) production in response to the more proximal threat of nearby bacteria, as exemplified by studies on uropathogenic Escherichia coli (UPEC). HDAC7-mediated PPP engagement via 6-phosphogluconate dehydrogenase (6PGD) generates NADPH for antimicrobial ROS production, as well as D-ribulose-5-phosphate (RL5P) that both synergizes with ROS for UPEC killing and suppresses selective inflammatory responses. This dual functionality of the HDAC7-6PGD-RL5P axis prioritizes responses to proximal threats. Our findings thus reveal that the PPP metabolite RL5P has both antimicrobial and immunomodulatory activities and that engagement of enzymes in catabolic versus anabolic metabolic pathways triages responses to different types of danger for generation of inflammatory versus antimicrobial responses, respectively.

PCNA regulates primary metabolism by scaffolding metabolic enzymes

The essential roles of proliferating cell nuclear antigen (PCNA) as a scaffold protein in DNA replication and repair are well established, while its cytosolic roles are less explored. Two metabolic enzymes, alpha-enolase (ENO1) and 6-phosphogluconate dehydrogenase (6PGD), both contain PCNA interacting motifs. Mutation of the PCNA interacting motif APIM in ENO1 (F423A) impaired its binding to PCNA and resulted in reduced cellular levels of ENO1 protein, reduced growth rate, reduced glucose consumption, and reduced activation of AKT. Metabolome and signalome analysis reveal large consequences of impairing the direct interaction between PCNA and ENO1. Metabolites above ENO1 in glycolysis accumulated while lower glycolytic and TCA cycle metabolite pools decreased in the APIM-mutated cells; however, their overall energetic status were similar to parental cells. Treating haematological cancer cells or activated primary monocytes with a PCNA targeting peptide drug containing APIM (ATX-101) also lead to a metabolic shift characterized by reduced glycolytic rate. In addition, we show that ATX-101 treatments reduced the ENO1 - PCNA interaction, the ENO1, GAPDH and 6PGD protein levels, as well as the 6PGD activity. Here we report for the first time that PCNA acts as a scaffold for metabolic enzymes, and thereby act as a direct regulator of primary metabolism.

Overcoming current challenges to T-cell receptor therapy via metabolic targeting to increase antitumor efficacy, durability, and tolerability

The antitumor potential of personalized immunotherapy, including adoptive T-cell therapy, has been shown in both preclinical and clinical studies. Combining cell therapy with targeted metabolic interventions can further enhance therapeutic outcomes in terms of magnitude and durability. The ability of a T cell receptor to recognize peptides derived from tumor neoantigens allows for a robust yet specific response against cancer cells while sparing healthy tissue. However, there exist challenges to adoptive T cell therapy such as a suppressive tumor milieu, the fitness and survival of transferred cells, and tumor escape, all of which can be targeted to further enhance the antitumor potential of T cell receptor-engineered T cell (TCR-T) therapy. Here, we explore current strategies involving metabolic reprogramming of both the tumor microenvironment and the cell product, which can lead to increased T cell proliferation, survival, and anti-tumor cytotoxicity. In addition, we highlight potential metabolic pathways and targets which can be leveraged to improve engraftment of transferred cells and obviate the need for lymphodepletion, while minimizing off-target effects. Metabolic signaling is delicately balanced, and we demonstrate the need for thoughtful and precise interventions that are tailored for the unique characteristics of each tumor. Through improved understanding of the interplay between immunometabolism, tumor resistance, and T cell signaling, we can improve current treatment regimens and open the door to potential synergistic combinations.

Polarization and β-Glucan Reprogram Immunomodulatory Metabolism in Human Macrophages and Ex Vivo in Human Lung Cancer Tissues

Immunomodulatory (IM) metabolic reprogramming in macrophages (Mϕs) is fundamental to immune function. However, limited information is available for human Mϕs, particularly in response plasticity, which is critical to understanding the variable efficacy of immunotherapies in cancer patients. We carried out an in-depth analysis by combining multiplex stable isotope-resolved metabolomics with reversed phase protein array to map the dynamic changes of the IM metabolic network and key protein regulators in four human donors' Mϕs in response to differential polarization and M1 repolarizer β-glucan (whole glucan particles [WGPs]). These responses were compared with those of WGP-treated ex vivo organotypic tissue cultures (OTCs) of human non-small cell lung cancer. We found consistently enhanced tryptophan catabolism with blocked NAD+ and UTP synthesis in M1-type Mϕs (M1-Mϕs), which was associated with immune activation evidenced by increased release of IL-1β/CXCL10/IFN-γ/TNF-α and reduced phagocytosis. In M2a-Mϕs, WGP treatment of M2a-Mϕs robustly increased glucose utilization via the glycolysis/oxidative branch of the pentose phosphate pathway while enhancing UDP-N-acetyl-glucosamine turnover and glutamine-fueled gluconeogenesis, which was accompanied by the release of proinflammatory IL-1β/TNF-α to above M1-Mϕ's levels, anti-inflammatory IL-10 to above M2a-Mϕ's levels, and attenuated phagocytosis. These IM metabolic responses could underlie the opposing effects of WGP, i.e., reverting M2- to M1-type immune functions but also boosting anti-inflammation. Variable reprogrammed Krebs cycle and glutamine-fueled synthesis of UTP in WGP-treated OTCs of human non-small cell lung cancer were observed, reflecting variable M1 repolarization of tumor-associated Mϕs. This was supported by correlation with IL-1β/TNF-α release and compromised tumor status, making patient-derived OTCs unique models for studying variable immunotherapeutic efficacy in cancer patients.

Immune cellular components and signaling pathways in the tumor microenvironment

During the past decade there has been a revolution in cancer therapeutics by the emergence of antibody-based and cell-based immunotherapies that modulate immune responses against tumors. These new therapies have extended and improved the therapeutic efficacy of chemo-radiotherapy and have offered treatment options to patients who are no longer responding to these classic anti-cancer treatments. Unfortunately, tumor eradication and long-lasting responses are observed in a small fraction of patients, whereas the majority of patients respond only transiently. These outcomes indicate that the maximum potential of immunotherapy has not been reached due to incomplete knowledge of the cellular and molecular mechanisms that guide the development of successful anti-tumor immunity and its failure. In this review, we discuss recent discoveries about the immune cellular composition of the tumor microenvironment (TME) and the role of key signaling mechanisms that compromise the function of immune cells leading to cancer immune escape.

Phosphogluconate dehydrogenase is a predictive biomarker for immunotherapy in hepatocellular carcinoma

Background

Phosphogluconate dehydrogenase (PGD) is involved in the regulation of various tumors. However, its role in hepatocellular carcinoma (HCC) is poorly understood. This study tried to determine the prognostic efficacy of PGD and its value for immunotherapy in HCC.

Methods

The data from the TCGA database was used to explore the predictive power of PGD expression and methylation on the overall survival (OS) of HCC through Cox regression and the Kaplan-Meier analysis. Then, we used the GEO and ICGC database to further verify the predictive power. Finally, the relationship between PGD and immune cells and the relationship between PGD and the efficacy of immunotherapy were explored through bioinformatics analysis in HCC.

Results

PGD is highly expressed in HCC tissues, which is negatively regulated by PGD methylation. Low PGD expression and PGD hypermethylation predict better OS in HCC patients. Besides, a meta-analysis based on the TCGA, GSE14520, and ICGC databases further confirms that low PGD expression is closely related to favorable OS. Then, we find significant differences of immune cell infiltrations between high and low PGD expression groups. Expressions of immune checkpoints, most HLA members and tumor mutation burden (TMB) are higher in the high PGD expression group, which indicates beneficial efficacy of immunotherapy in this group. And the potential mechanisms of PGD are exhibited.

Conclusion

PGD is an independent prognostic factor of HCC patients and plays an important role in immune cell infiltration and immunotherapy, which indicates that PGD can be used as a predictive biomarker for HCC immunotherapy.

Glutaminase inhibition impairs CD8 T cell activation in STK11-/Lkb1-deficient lung cancer

The tumor microenvironment (TME) contains a rich source of nutrients that sustains cell growth and facilitate tumor development. Glucose and glutamine in the TME are essential for the development and activation of effector T cells that exert antitumor function. Immunotherapy unleashes T cell antitumor function, and although many solid tumors respond well, a significant proportion of patients do not benefit. In patients with KRAS-mutant lung adenocarcinoma, KEAP1 and STK11/Lkb1 co-mutations are associated with impaired response to immunotherapy. To investigate the metabolic and immune microenvironment of KRAS-mutant lung adenocarcinoma, we generated murine models that reflect the KEAP1 and STK11/Lkb1 mutational landscape in these patients. Here, we show increased glutamate abundance in the Lkb1-deficient TME associated with CD8 T cell activation in response to anti-PD1. Combination treatment with the glutaminase inhibitor CB-839 inhibited clonal expansion and activation of CD8 T cells. Thus, glutaminase inhibition negatively impacts CD8 T cells activated by anti-PD1 immunotherapy.

Lupus Susceptibility Loci Predispose Mice to Clonal Lymphocytic Responses and Myeloid Expansion

Lupus susceptibility results from the combined effects of numerous genetic loci, but the contribution of these loci to disease pathogenesis has been difficult to study due to the large cellular heterogeneity of the autoimmune immune response. We performed single-cell RNA, BCR, and TCR sequencing of splenocytes from mice with multiple polymorphic lupus susceptibility loci. We not only observed lymphocyte and myeloid expansion, but we also characterized changes in subset frequencies and gene expression, such as decreased CD8 and marginal zone B cells and increased Fcrl5- and Cd5l-expressing macrophages. Clonotypic analyses revealed expansion of B and CD4 clones, and TCR repertoires from lupus-prone mice were distinguishable by algorithmic specificity prediction and unsupervised machine learning classification. Myeloid differential gene expression, metabolism, and altered ligand-receptor interaction were associated with decreased Ag presentation. This dataset provides novel mechanistic insight into the pathophysiology of a spontaneous model of lupus, highlighting potential therapeutic targets for autoantibody-mediated disease.

6-Phosphogluconate dehydrogenase and its crystal structures

6-Phosphogluconate dehydrogenase (6PGDH; EC 1.1.1.44) catalyses the oxidative decarboxylation of 6-phosphogluconate to ribulose 5-phosphate in the context of the oxidative part of the pentose phosphate pathway. Depending on the species, it can be a homodimer or a homotetramer. Oligomerization plays a functional role not only because the active site is at the interface between subunits but also due to the interlocking tail-modulating activity, similar to that of isocitrate dehydrogenase and malic enzyme, which catalyse a similar type of reaction. Since the pioneering crystal structure of sheep liver 6PGDH, which allowed motifs common to the β-hydroxyacid dehydrogenase superfamily to be recognized, several other 6PGDH crystal structures have been solved, including those of ternary complexes. These showed that more than one conformation exists, as had been suggested for many years from enzyme studies in solution. It is inferred that an asymmetrical conformation with a rearrangement of one of the two subunits underlies the homotropic cooperativity. There has been particular interest in the presence or absence of sulfate during crystallization. This might be related to the fact that this ion, which is a competitive inhibitor that binds in the active site, can induce the same 6PGDH configuration as in the complexes with physiological ligands. Mutagenesis, inhibitors, kinetic and binding studies, post-translational modifications and research on the enzyme in cancer cells have been complementary to the crystallographic studies. Computational modelling and new structural studies will probably help to refine the understanding of the functioning of this enzyme, which represents a promising therapeutic target in immunity, cancer and infective diseases. 6PGDH also has applied-science potential as a biosensor or a biobattery. To this end, the enzyme has been efficiently immobilized on specific polymers and nanoparticles. This review spans the 6PGDH literature and all of the 6PGDH crystal structure data files held by the Protein Data Bank.

Switching to the cyclic pentose phosphate pathway powers the oxidative burst in activated neutrophils

Neutrophils are cells at the frontline of innate immunity that can quickly activate effector functions to eliminate pathogens upon stimulation. However, little is known about the metabolic adaptations that power these functions. Here we show rapid metabolic alterations in neutrophils upon activation, particularly drastic reconfiguration around the pentose phosphate pathway, which is specifically and quantitatively coupled to an oxidative burst. During this oxidative burst, neutrophils switch from glycolysis-dominant metabolism to a unique metabolic mode termed 'pentose cycle', where all glucose-6-phosphate is diverted into oxidative pentose phosphate pathway and net flux through upper glycolysis is reversed to allow substantial recycling of pentose phosphates. This reconfiguration maximizes NADPH yield to fuel superoxide production via NADPH oxidase. Disruptions of pentose cycle greatly suppress oxidative burst, the release of neutrophil extracellular traps and pathogen killing by neutrophils. Together, these results demonstrate the remarkable metabolic flexibility of neutrophils, which is essential for their functions as the first responders in innate immunity.

Metabolic Reprogramming in Gastric Cancer: Trojan Horse Effect

Worldwide, gastric cancer (GC) represents the fifth most common cancer for incidence and the third leading cause of death in developed countries. Despite the development of combination chemotherapies, the survival rates of GC patients remain unsatisfactory. The reprogramming of energy metabolism is a hallmark of cancer, especially increased dependence on aerobic glycolysis. In the present review, we summarized current evidence on how metabolic reprogramming in GC targets the tumor microenvironment, modulates metabolic networks and overcomes drug resistance. Preclinical and clinical studies on the combination of metabolic reprogramming targeted agents and conventional chemotherapeutics or molecularly targeted treatments [including vascular endothelial growth factor receptor (VEGFR) and HER2] and the value of biomarkers are examined. This deeper understanding of the molecular mechanisms underlying successful pharmacological combinations is crucial in finding the best-personalized treatment regimens for cancer patients.

Aminopyridine analogs selectively target metastatic pancreatic cancer

Metastatic outgrowth is supported by metabolic adaptations that may differ from the primary tumor of origin. However, it is unknown if such adaptations are therapeutically actionable. Here we report a novel aminopyridine compound that targets a unique Phosphogluconate Dehydrogenase (PGD)-dependent metabolic adaptation in distant metastases from pancreatic cancer patients. Compared to structurally similar analogs, 6-aminopicolamine (6AP) potently and selectively reversed PGD-dependent metastatic properties, including intrinsic tumorigenic capacity, excess glucose consumption, and global histone hyperacetylation. 6AP acted as a water-soluble prodrug that was converted into intracellular bioactive metabolites that inhibited PGD in vitro, and 6AP monotherapy demonstrated anti-metastatic efficacy with minimal toxicity in vivo. Collectively, these studies identify 6AP and possibly other 6-aminopyridines as well-tolerated prodrugs with selectivity for metastatic pancreatic cancers. If unique metabolic adaptations are a common feature of metastatic or otherwise aggressive human malignancies, then such dependencies could provide a largely untapped pool of druggable targets for patients with advanced cancers.

Activation of the NRF2 antioxidant program sensitizes tumors to G6PD inhibition

The KEAP1/NRF2 pathway promotes metabolic rewiring to support redox homeostasis. Activation of NRF2 occurs in many cancers, often due to KEAP1 mutations, and is associated with more aggressive disease and treatment resistance. To identify metabolic dependencies in cancers with NRF2 activation, we performed a metabolism-focused CRISPR screen. Glucose-6-phosphate dehydrogenase (G6PD), which was recently shown to be dispensable in Ras-driven tumors, was a top dependency. G6PD catalyzes the committed step of the oxidative pentose phosphate pathway that produces NADPH and nucleotide precursors, but neither antioxidants nor nucleosides rescued. Instead, G6PD loss triggered tricarboxylic acid (TCA) intermediate depletion because of up-regulation of the alternative NADPH-producing enzymes malic enzyme and isocitrate dehydrogenase. In vivo, G6PD impairment markedly suppressed KEAP1 mutant tumor growth, and this suppression was further augmented by TCA depletion by glutaminase inhibition. Thus, G6PD inhibition–induced TCA depletion is a therapeutic vulnerability of NRF2-activated cancer.

Metabolism-Associated Epigenetic and Immunoepigenetic Reprogramming in Liver Cancer

Metabolic reprogramming and epigenetic changes have been characterized as hallmarks of liver cancer. Independently of etiology, oncogenic pathways as well as the availability of different energetic substrates critically influence cellular metabolism, and the resulting perturbations often cause aberrant epigenetic alterations, not only in cancer cells but also in the hepatic tumor microenvironment. Metabolic intermediates serve as crucial substrates for various epigenetic modulations, from post-translational modification of histones to DNA methylation. In turn, epigenetic changes can alter the expression of metabolic genes supporting on the one hand, the increased energetic demand of cancer cells and, on the other hand, influence the activity of tumor-associated immune cell populations. In this review, we will illustrate the most recent findings about metabolic reprogramming in liver cancer. We will focus on the metabolic changes characterizing the tumor microenvironment and on how these alterations impact on epigenetic mechanisms involved in the malignant progression. Furthermore, we will report our current knowledge about the influence of cancer-specific metabolites on epigenetic reprogramming of immune cells and we will highlight how this favors a tumor-permissive immune environment. Finally, we will review the current strategies to target metabolic and epigenetic pathways and their therapeutic potential in liver cancer, alone or in combinatorial approaches.