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Purpose:Intratumoral hypoxia and immunity have been correlated with patient outcome in various tumor settings. However, these factors are not currently considered for treatment selection in head and neck cancer (HNC) due to lack of validated biomarkers. Here we sought to develop a hypoxia-immune classifier with potential application in patient prognostication and prediction of response to targeted therapy.Experimental Design:A 54-gene hypoxia-immune signature was constructed on the basis of literature review. Gene expression was analyzed in silico using the The Cancer Genome Atlas (TCGA) HNC dataset (n = 275) and validated using two independent cohorts (n = 130 and 123). IHC was used to investigate the utility of a simplified protein signature. The spatial distribution of hypoxia and immune markers was examined using multiplex immunofluorescence staining.Results:Unsupervised hierarchical clustering of TCGA dataset (development cohort) identified three patient subgroups with distinct hypoxia-immune phenotypes and survival profiles: hypoxialow/immunehigh, hypoxiahigh/immunelow, and mixed, with 5-year overall survival (OS) rates of 71%, 51%, and 49%, respectively (P = 0.0015). The prognostic relevance of the hypoxia-immune gene signature was replicated in two independent validation cohorts. Only PD-L1 and intratumoral CD3 protein expression were associated with improved OS on multivariate analysis. Hypoxialow/immunehigh and hypoxiahigh/immunelow tumors were overrepresented in “inflamed” and “immune-desert” microenvironmental profiles, respectively. Multiplex staining demonstrated an inverse correlation between CA-IX expression and prevalence of intratumoral CD3+ T cells (r = −0.5464; P = 0.0377), further corroborating the transcription-based classification.Conclusions:We developed and validated a hypoxia-immune prognostic transcriptional classifier, which may have clinical application to guide the use of hypoxia modification and targeted immunotherapies for the treatment of HNC.

Figure S1. Gene order within the cluster defined groups. Figure S2. Analysis of individual hypoxia and immune gene signatures. Figure S3. Flow diagram showing progress of patient samples through study for Correlate cohort Figure S4. Relationship between heatmap defined hypoxia-immune subgroups and T stage. Figure S5 Expression of individual hypoxia- or immune-response related genes within the heat-map defined subgroups. Figure S6. Correlation of PD-L1 or CA-IX protein expression with survival. Figure S7 Correlation of gene and protein expression. Figure S8. Spatial interactions of hypoxia and immune cells: Vectra images of multiplex stained HNC sections. Table S1 Treatment schedules Table S2. Genes in the RNASeq panel/TCGA dataset Table S3. Relationship of hypoxia-immune classifier to other prognostic variables Table S4. Summary of immunohistochemistry staining Table S5. Summary of statistical analyses for IHC staining

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Succinate dehydrogenase is a key enzyme in the tricarboxylic acid cycle and the electron transport chain. All four subunits of succinate dehydrogenase are tumor suppressor genes predisposing to paraganglioma, but only mutations in the SDHB subunit are associated with increased risk of metastasis. Here we generated an Sdhd knockout chromaffin cell line and compared it with Sdhb-deficient cells. Both cell types exhibited similar SDH loss of function, metabolic adaptation, and succinate accumulation. In contrast, Sdhb−/− cells showed hallmarks of mesenchymal transition associated with increased DNA hypermethylation and a stronger pseudo-hypoxic phenotype compared with Sdhd−/− cells. Loss of SDHB specifically led to increased oxidative stress associated with dysregulated iron and copper homeostasis in the absence of NRF2 activation. High-dose ascorbate exacerbated the increase in mitochondrial reactive oxygen species, leading to cell death in Sdhb−/− cells. These data establish a mechanism linking oxidative stress to iron homeostasis that specifically occurs in Sdhb-deficient cells and may promote metastasis. They also highlight high-dose ascorbate as a promising therapeutic strategy for SDHB-related cancers.Significance:Loss of different succinate dehydrogenase subunits can lead to different cell and tumor phenotypes, linking stronger 2-OG–dependent dioxygenases inhibition, iron overload, and ROS accumulation following SDHB mutation.

Supplementary Table 2 Related to Figure 2. Differentially methylated gene-based features in Sdhb-/- versus Sdhd-/- imCCs

Background Multiple Myeloma (MM) is a plasma cell malignancy that develops in the bone marrow. Function of T lymphocytes is impaired in patients with MM and the bone marrow microenvironment is described as hostile for T cell activity. Precise suppressive mechanisms within the bone marrow microenvironment remain poorly defined but will impact efficacy of bispecific T cell engager and chimeric antigen receptor (CAR) T cell therapies. Methods In this study T cell phenotype, function and metabolic activity were analysed within paired bone marrow aspirate and peripheral blood samples from 72 patients across the spectrum of MM, including individuals with premalignant and asymptomatic disease, alongside age-matched controls. This permitted assessment of effects of disease stage and the bone marrow microenvironment. The bone marrow microenvironment was also modelled in vitro using autologous plasma co-culture systems. Results Bone marrow CD8+ T cell function decreased with MM development and was consistently lower within bone marrow samples than matched peripheral blood. These changes were accompanied by decreased mitochondrial mass, which correlated tightly with T cell function. Conversely, long-chain fatty acid uptake and peroxidation was markedly elevated in bone marrow CD8+ T cells. In vitro modelling confirmed uptake of bone marrow lipids suppresses CD8+ T function, which was impaired in autologous bone marrow plasma, but rescued by both lipid removal and inhibition of lipid peroxidation. Analysis of single-cell RNA-sequencing data identified expression of fatty acid transport protein 1 (FATP1) in bone marrow CD8+ T cells in MM, and FATP1 blockade also rescued CD8+ T cell function. Finally, analysis of samples from treated patient cohorts identified CD8+ T cell metabolic dysfunction resolves in treatment-responsive but not relapsed MM patients and is associated with substantial functional restoration. Conclusions CD8+ T cells are functionally impaired within the MM bone marrow microenvironment. This is accompanied by decreased mitochondrial mass but elevated uptake of long-chain fatty acids. Blockade of FATP1 restores CD8+ T cell function in presence of BM lipids and may therefore represent a novel therapeutic target to augment their activity in the bone marrow in MM and improve efficacy of T cell-directed therapies.

Using13C6glucose labeling coupled to GC-MS and 2D1H-13C HSQC NMR spectroscopy, we have obtained a comparative high-resolution map of glucose fate underpinning steady state insulin release and β cell function. In both mouse and human islets, the contribution of glucose to the TCA cycle is similar. Pyruvate-fueling of the TCA cycle is found to be mediated primarily by the activity of pyruvate dehydrogenase (PDH), with only a limited contribution from pyruvate carboxylase (PC). While conversion of pyruvate to lactate by lactate dehydrogenase (LDH) can be detected in both species, lactate accumulation via this route is six-fold higher in human islets. Transcriptomic analysis reveals that human β cells specifically express lactate dehydrogenase B (LDHB) at high levels, in keeping with the phenotype of patients harboring gain-of-function mutations in MCT1/ SLC16A1 (HHF7). Thus, glycolytically-derived acetyl CoA preferentially feeds the TCA cycle in both mouse and human β cells. However, human β cells possess the machinery needed to generate extra-mitochondrial lactate, which might reflect a key mechanism to balance the reducing activity of NADH-producing pathways.

Chemotherapeutic drugs are used to treat almost all types of cancer, but the intended response, i.e., elimination, is often incomplete, with a subset of cancer cells resisting treatment. Two critical factors play a role in chemoresistance: the p53 tumour suppressor gene and the X-linked inhibitor of apoptosis (XIAP). These proteins have been shown to act synergistically to elicit cellular responses upon DNA damage induced by chemotherapy, yet, the mechanism is poorly understood. This study introduces a mathematical model characterising the apoptosis pathway activation by p53 before and after mitochondrial outer membrane permeabilisation upon treatment with the chemotherapy Doxorubicin (Dox).“In-silico”simulations show that the p53 dynamics change dose-dependently. Under medium to high doses of Dox, p53 concentration ultimately stabilises to a high level regardless of XIAP concentrations. However, caspase-3 activation may be triggered or not depending on the XIAP induction rate, ultimately determining whether the cell will perish or resist. Consequently, the model predicts that failure to activate apoptosis in some cancer cells expressing wild-type p53 might be due to heterogeneity between cells in upregulating the XIAP protein, rather than due to the p53 protein concentration. Our model suggests that the interplay of the p53 dynamics and the XIAP induction rate is critical to determine the cancer cells’ therapeutic response.

Proline is a non-essential amino acid with key roles in protein structure/function and maintenance of cellular redox homeostasis. It is available from dietary sources, generated de novo within cells, and released from protein structures; a noteworthy source being collagen. Its catabolism within cells can generate ATP and reactive oxygen species (ROS). Recent findings suggest that proline biosynthesis and catabolism are essential processes in disease; not only due to the role in new protein synthesis as part of pathogenic processes but also due to the impact of proline metabolism on the wider metabolic network through its significant role in redox homeostasis. This is particularly clear in cancer proliferation and metastatic outgrowth. Nevertheless, the precise identity of the drivers of cellular proline catabolism and biosynthesis, and the overall cost of maintaining appropriate balance is not currently known. In this review, we explore the major drivers of proline availability and consumption at a local and systemic level with a focus on cancer. Unraveling the main factors influencing proline metabolism in normal physiology and disease will shed light on new effective treatment strategies.

Anoxia halts oxidative phosphorylation (OXPHOS) causing an accumulation of reduced compounds in mitochondrial matrix which impedes dehydrogenases. By simultaneously measuring oxygen concentration, NADH autofluorescence, mitochondrial membrane potential and ubiquinone reduction extentin organelloin real-time, we show that Complex I utilized endogenous quinones to oxidize NADH under acute anoxia. Untargeted or [U-13C]glutamate-targeted metabolomic analysis of matrix and effluxed metabolites extracted during anoxia in the presence or absence of site-specific inhibitors of the electron transfer system inferred that NAD+regenerated by Complex I is reduced by the 2-oxoglutarate dehydrogenase complex yielding succinyl-CoA supporting mitochondrial substrate-level phosphorylation (mtSLP), releasing succinate. Yet, targeted metabolomic analysis using [U-13C]malate also revealed concomitant succinate dehydrogenase reversal during anoxia yielding succinate by reducing fumarate, albeit to a small extent. Our results highlight the importance of quinone availability to Complex I oxidizing NADH, thus maintaining glutamate catabolism and mtSLP in the absence of OXPHOS.

Description, Exchange of mitochondrial subunits C15ORF48 and NDUFA4 occurs during macrophage activation in vitro and in inflammatory disease., Dysregulated mitochondrial function is a hallmark of immune-mediated inflammatory diseases. Cytochrome c oxidase (CcO), which mediates the rate-limiting step in mitochondrial respiration, is remodeled during development and in response to changes of oxygen availability, but there has been little study of CcO remodeling during inflammation. Here, we describe an elegant molecular switch mediated by the bifunctional transcript C15orf48, which orchestrates the substitution of the CcO subunit NDUFA4 by its paralog C15ORF48 in primary macrophages. Expression of C15orf48 is a conserved response to inflammatory signals and occurs in many immune-related pathologies. In rheumatoid arthritis, C15orf48 mRNA is elevated in peripheral monocytes and proinflammatory synovial tissue macrophages, and its expression positively correlates with disease severity and declines in remission. C15orf48 is also expressed by pathogenic macrophages in severe coronavirus disease 2019 (COVID-19). Study of a rare metabolic disease syndrome provides evidence that loss of the NDUFA4 subunit supports proinflammatory macrophage functions.

Background The molecular profiling of glioblastoma (GBM) based on transcriptomic analysis could provide precise treatment and prognosis. However, current subtyping (classic, mesenchymal, neural, proneural) is time-consuming and cost-intensive hindering its clinical application. A simple and efficient method for classification was imperative. Methods In this study, to simplify GBM subtyping more efficiently, we applied a random forest algorithm to conduct 26 genes as a cluster featured with hub genes, OLIG2 and CD276. Functional enrichment analysis and Protein–protein interaction were performed using the genes in this gene cluster. The classification efficiency of the gene cluster was validated by WGCNA and LASSO algorithms, and tested in GSE84010 and Gravandeel’s GBM datasets. Results The gene cluster (n = 26) could distinguish mesenchymal and proneural excellently (AUC = 0.92), which could be validated by multiple algorithms (WGCNA, LASSO) and datasets (GSE84010 and Gravandeel’s GBM dataset). The gene cluster could be functionally enriched in DNA elements and T cell associated pathways. Additionally, five genes in the signature could predict the prognosis well (p = 0.0051 for training cohort, p = 0.065 for test cohort). Conclusions Our study proved the accuracy and efficiency of random forest classifier for GBM subtyping, which could provide a convenient and efficient method for subtyping Proneural and Mesenchymal GBM.

Mutations in succinate dehydrogenase (SDH) lead to the development of tumors in a restricted subset of cell types, including chromaffin cells and paraganglia. The molecular basis for this specificity is currently unknown. We show that loss of SDH activity in a chromaffin cell model does not perturb complex I function, retaining the ability to oxidize NADH within the electron transport chain. This activity supports continued oxidation of substrates within the tricarboxylic acid (TCA) cycle. However, due to the block in the TCA cycle at SDH, the high glutamine oxidation activity is only maintained through an efflux of succinate. We also show that although the mitochondria of SDH-deficient cells are less active per se, their higher mass per cell results in an overall respiratory rate that is comparable with wild-type cells. Finally, we observed that when their mitochondria are uncoupled, SDH-deficient cells are unable to preserve their viability, suggesting that the mitochondrial metabolic network is unable to compensate when exposed to additional stress. We therefore show that in contrast to models of SDH deficiency based on epithelial cells, a chromaffin cell model retains aspects of metabolic "health," which could form the basis of cell specificity of this rare tumor type.

Purpose: Intratumoral hypoxia and immunity have been correlated with patient outcome in various tumor settings. However, these factors are not currently considered for treatment selection in head and neck cancer (HNC) due to lack of validated biomarkers. Here we sought to develop a hypoxia-immune classifier with potential application in patient prognostication and prediction of response to targeted therapy. Experimental Design: A 54-gene hypoxia-immune signature was constructed on the basis of literature review. Gene expression was analyzed in silico using the The Cancer Genome Atlas (TCGA) HNC dataset (n = 275) and validated using two independent cohorts (n = 130 and 123). IHC was used to investigate the utility of a simplified protein signature. The spatial distribution of hypoxia and immune markers was examined using multiplex immunofluorescence staining. Results: Unsupervised hierarchical clustering of TCGA dataset (development cohort) identified three patient subgroups with distinct hypoxia-immune phenotypes and survival profiles: hypoxialow/immunehigh, hypoxiahigh/immunelow, and mixed, with 5-year overall survival (OS) rates of 71%, 51%, and 49%, respectively (P = 0.0015). The prognostic relevance of the hypoxia-immune gene signature was replicated in two independent validation cohorts. Only PD-L1 and intratumoral CD3 protein expression were associated with improved OS on multivariate analysis. Hypoxialow/immunehigh and hypoxiahigh/immunelow tumors were overrepresented in “inflamed” and “immune-desert” microenvironmental profiles, respectively. Multiplex staining demonstrated an inverse correlation between CA-IX expression and prevalence of intratumoral CD3+ T cells (r = −0.5464; P = 0.0377), further corroborating the transcription-based classification. Conclusions: We developed and validated a hypoxia-immune prognostic transcriptional classifier, which may have clinical application to guide the use of hypoxia modification and targeted immunotherapies for the treatment of HNC.

Brain tumours are the most common cause of cancer death in children. Molecular studies have greatly improved our understanding of these tumours but tumour metabolism is underexplored. Metabolites measured in vivo have been reported as prognostic biomarkers of these tumours but analysis of surgically resected tumour tissue allows a more extensive set of metabolites to be measured aiding biomarker discovery and providing validation of in vivo findings. In this study, metabolites were quantified across a range of paediatric brain tumours using 1H-High-Resolution Magic Angle Spinning nuclear magnetic resonance spectroscopy (HR-MAS) and their prognostic potential investigated. HR-MAS was performed on pre-treatment frozen tumour tissue from a single centre. Univariate and multivariate Cox regression was used to examine the ability of metabolites to predict survival. The models were cross validated using C-indices and further validated by splitting the cohort into two. Higher concentrations of glutamine were predictive of a longer overall survival, whilst higher concentrations of lipids were predictive of a shorter overall survival. These metabolites were predictive independent of diagnosis, as demonstrated in multivariate Cox regression models. Whilst accurate quantification of metabolites such as glutamine in vivo is challenging, metabolites show promise as prognostic markers due to development of optimised detection methods and increasing use of 3 T clinical scanners.

The demands of cancer cell proliferation alongside an inadequate angiogenic response lead to insufficient oxygen availability in the tumor microenvironment. Within the mitochondria, oxygen is the major electron acceptor for NADH, with the result that the reducing potential produced through tricarboxylic acid (TCA) cycle activity and mitochondrial respiration are functionally linked. As the oxidizing activity of the TCA cycle is required for efficient synthesis of anabolic precursors, tumoral hypoxia could lead to a cessation of proliferation without another means of correcting the redox imbalance. We show that in hypoxic conditions, mitochondrial pyrroline 5-carboxylate reductase 1 (PYCR1) activity is increased, oxidizing NADH with the synthesis of proline as a by-product. We further show that PYCR1 activity is required for the successful maintenance of hypoxic regions by permitting continued TCA cycle activity, and that its loss leads to significantly increased hypoxia in vivo and in 3D culture, resulting in widespread cell death.

Succinate dehydrogenase is a key enzyme in the tricarboxylic acid cycle and the electron transport chain. All four subunits of succinate dehydrogenase are tumor suppressor genes predisposing to paraganglioma, but only mutations in the SDHB subunit are associated with increased risk of metastasis. Here we generated an Sdhd knockout chromaffin cell line and compared it with Sdhb-deficient cells. Both cell types exhibited similar SDH loss of function, metabolic adaptation, and succinate accumulation. In contrast, Sdhb−/− cells showed hallmarks of mesenchymal transition associated with increased DNA hypermethylation and a stronger pseudo-hypoxic phenotype compared with Sdhd−/− cells. Loss of SDHB specifically led to increased oxidative stress associated with dysregulated iron and copper homeostasis in the absence of NRF2 activation. High-dose ascorbate exacerbated the increase in mitochondrial reactive oxygen species, leading to cell death in Sdhb−/− cells. These data establish a mechanism linking oxidative stress to iron homeostasis that specifically occurs in Sdhb-deficient cells and may promote metastasis. They also highlight high-dose ascorbate as a promising therapeutic strategy for SDHB-related cancers. Significance: Loss of different succinate dehydrogenase subunits can lead to different cell and tumor phenotypes, linking stronger 2-OG–dependent dioxygenases inhibition, iron overload, and ROS accumulation following SDHB mutation.

BACKGROUND Idiopathic intracranial hypertension (IIH) is a condition predominantly affecting obese women of reproductive age. Recent evidence suggests that IIH is a disease of metabolic dysregulation, androgen excess, and an increased risk of cardiovascular morbidity. Here we evaluate systemic and adipose specific metabolic determinants of the IIH phenotype. METHODS In fasted, matched IIH (n = 97) and control (n = 43) patients, we assessed glucose and insulin homeostasis and leptin levels. Body composition was assessed along with an interrogation of adipose tissue function via nuclear magnetic resonance metabolomics and RNA sequencing in paired omental and subcutaneous biopsies in a case-control study. RESULTS We demonstrate an insulin- and leptin-resistant phenotype in IIH in excess of that driven by obesity. Adiposity in IIH is preferentially centripetal and is associated with increased disease activity and insulin resistance. IIH adipocytes appear transcriptionally and metabolically primed toward depot-specific lipogenesis. CONCLUSION These data show that IIH is a metabolic disorder in which adipose tissue dysfunction is a feature of the disease. Managing IIH as a metabolic disease could reduce disease morbidity and improve cardiovascular outcomes. FUNDING This study was supported by the UK NIHR (NIHR-CS-011-028), the UK Medical Research Council (MR/K015184/1), Diabetes UK, Wellcome Trust (104612/Z/14/Z), the Sir Jules Thorn Award, and the Midlands Neuroscience Teaching and Research Fund.

Succinate dehydrogenase (SDH) loss-of-function mutations drive succinate accumulation in tumor microenvironments, for example in the neuroendocrine tumors pheochromocytoma (PC) and paraganglioma (PG). Control of innate immune cell activity by succinate is described, but effects on T cells have not been interrogated. Here we report that exposure of human CD4

SummaryNonalcoholic fatty liver disease (NAFLD) affects ~88% of obese individuals and is characterised by hepatic lipid accumulation. Mitochondrial metabolic dysfunction is a feature of NAFLD. We used a human pluripotent stem cell-based system to determine how mitochondrial dysfunction is linked to hepatic lipid accumulation. We induced lipid accumulation in hepatocyte-like cells (HLCs) using lactate, pyruvate and octanoate (LPO). Transcriptomic analysis revealed perturbation of mitochondrial respiratory pathways in LPO exposed cells. Using13C isotopic tracing, we identified truncation of the TCA cycle in steatotic HLCs. We show that increased purine nucleotide cycle (PNC) activity fuels fumarate accumulation and drives lipid accumulation in steatotic cells. These findings provide new insights into the pathogenesis of hepatic steatosis and may lead to an improved understanding of the metabolic and transcriptional rewiring associated with NAFLD.

The alpha ketoglutarate-dependent dioxygenase, prolyl-4-hydroxylase 3 (PHD3), is a Hypoxia-Inducible Factor (HIF) target that uses molecular oxygen to hydroxylate peptidyl prolyl residues. While PHD3 has been reported to influence cancer cell metabolism and liver insulin sensitivity, relatively little is known about effects of this highly conserved enzyme in insulin-secreting β-cells in vivo. Here, we show that deletion of PHD3 specifically in β-cells (βPHD3KO) is associated with impaired glucose homeostasis in mice fed high fat diet. In the early stages of dietary fat excess, βPHD3KO islets energetically rewire, leading to defects in the management of pyruvate fate and a shift from glycolysis to increased fatty acid oxidation (FAO). However, under more prolonged metabolic stress, this switch to preferential FAO in βPHD3KO islets is associated with impaired glucose-stimulated ATP/ADP rises, Ca2+ fluxes and insulin secretion. Thus, PHD3 might be a pivotal component of the β-cell glucose metabolism machinery in mice by suppressing the use of fatty acids as a primary fuel source during the early phases of metabolic stress.

Gliomas are highly malignant brain tumours characterised by extensive areas of poor perfusion which subsequently leads to hypoxia and reduced survival. Therapies that address the hypoxic microenvironment are likely to significantly improve patient outcomes. Verteporfin, a benzoporphyrin-like drug, has been suggested to target the Yes-associated protein (YAP). Increased YAP expression and transcriptional activity has been proposed in other tumour types to promote malignant cell survival and thus YAP-inhibitor, verteporfin, may be predicted to impact glioma cell growth and viability. Due to the extensive hypoxic nature of gliomas, we investigated the effect of hypoxia on YAP expression and found that YAP transcription is increased under these conditions. Treatment of both primary and immortalised glioblastoma cell lines with verteporfin resulted in a significant decrease in viability but strikingly only under hypoxic conditions (1% O2). We discovered that cell death occurs through a YAP-independent mechanism, predominately involving binding of free iron and likely through redox cycling, contributes to production of reactive oxygen species. This results in disruption of normal cellular processes and death in cells already under oxidative stress – such as those in hypoxia. We suggest that through repurposing verteporfin, it represents a novel means of treating highly therapy-resistant, hypoxic cells in glioma.

Advancements in prevention, detection and treatment over the last 40 years have significantly transformed cancer healthcare however there are a few cancers, such as brain tumours, which are consistently lagging behind. The most common adult brain tumour is glioma; a highly aggressive cancer that invades deep into the surrounding brain consequently making treatment challenging. The severe hypoxic nature of glioma adds further complications to therapeutic efficacy as hypoxia limits efficient drug delivery as well as increasing treatment resistance. Therapies that therefore target both the hypoxic tumour microenvironment and metabolic pathways that sustain growth have significant potential to improve patient prognosis. It is well known that cancer cells demonstrate an abnormal metabolism, resulting in an altered requirement for amino acids to aid uncontrolled proliferation. Furthermore, tumour metabolism can also be influenced by this hostile hypoxic microenvironment, leading to a more malignant phenotype. We are therefore interested in a family of mitochondrial transporters, SLC25A, which translocate numerous solutes across the mitochondrial membrane and are crucial for many metabolic reactions. TCGA analysis has shown that many of these amino acid carriers are upregulated in glioma. Remarkably however, around 23 of the 53 mammalian SLC25A members lack defined substrate selectivity and so we are interested in identifying which transporters are particularly important in the metabolic adaptation to hypoxia. Using CRISPR and siRNA technologies we have identified transporters that are functionally required to maintain cell proliferation of glioma cell lines and patient tumour cells. Furthermore, using stable isotope-enriched nutrients, we have identified novel means by which glioma cell metabolism can be perturbed by inhibition of these transporters. Characterising which SLC25A transporters are important for hypoxic tumour metabolism could therefore expose a way to exploit these hypoxic areas subsequently making them more vulnerable to treatment and thus impacting patient survival.

Glioblastoma is the most common primary brain tumour and has a poor prognosis. The median survival is less than two years despite clinical intervention that usually involves the resection of the tumour volume, chemotherapy and radiotherapy. Achieving gross-total resection is challenging due to poorly defined boundaries as a result of tumour infiltration. Fluorescence-guided surgery (FGS) utilises an apparently selective accumulation of protoporphyrin IX (PPIX) that occurs in areas of glioblastoma after administration of the metabolite, 5-aminolevulinic acid (5-ALA). 5-ALA and the fluorescent metabolite, PPIX, sit within the endogenous heme biosynthetic pathway, which suggests that FGS is not only an important clinical tool, but also highlights differing metabolic phenotypes naturally present throughout the tumour. Genetic and mechanistic studies into this phenomenon have shown that differential expression of metabolite transporters, altered activity of the heme pathway enzymes and variable nutrient availability are all factors in the accumulation of PPIX. However, little is known about the cellular driving force for the uptake of 5-ALA and subsequent conversion into PPIX. Our data suggest that different microenvironments within the tumour alter the activity of the heme biosynthetic pathway, resulting in differential fluorescence in glioblastoma. It paves the way for work to alter the glioblastoma microenvironment in order to further improve the use of FGS in guiding surgery across these devastating tumours.

Aims Glioblastoma is the most common primary brain tumour and has a poor prognosis. Standard clinical intervention involves the resection of the tumour volume, chemotherapy and radiotherapy. However, achieving gross-total resection is challenging due to poorly defined boundaries as a result of tumour infiltration. Fluorescence-guided surgery (FGS) utilises an apparently selective accumulation of protoporphyrin IX (PPIX) that occurs in areas of glioblastoma after systemic administration of the metabolite 5-aminolevulinic acid (5-ALA). We have investigated the metabolic basis for the heterogeneity of the PPIX fluorescent signal, and its implications for glioma biology. Method Using glioblastoma cell lines and patient-derived primary cells, we have monitored the uptake of 5-ALA and conversion to the fluorescent molecule PPIX. Stable isotope tracing coupled with GCMS and LCMS was used to analyse intra- and extracellular metabolite levels arising from exogenous 5-ALA administration under both normoxic (21% O2) and hypoxic (1% O2) conditions. Results Uptake of exogenous 5-ALA from culture media and conversion to PPIX is observed in a time and dose-dependent manner in both normoxia and hypoxia. High levels of PPIX accumulation are associated with reduced cell proliferation despite the majority of the PPIX synthesised not being retained within the tumour cell, but exported into the medium. Under hypoxic conditions, reduced fluorescence is observed as a result of the decrease in oxygen availability likely affecting the oxygen-dependent enzymes. Stable isotope tracing experiments indicate an increase in the glutamine-derived succinate pool in response to exogenous 5-ALA, which is dependent on flux through the heme pathway. Conclusion Our data suggest that different microenvironments within the tumour alter the activity of the heme biosynthetic pathway, resulting in differential fluorescence in glioblastoma. It paves the way by which we could work to alter the glioblastoma microenvironment in order to further improve the use of FGS in guiding surgery across these devastating tumours.

Cellular metabolism in mammalian cells represents a challenge for analytical chemistry in the context of current biomedical research. Mass spectrometry and NMR spectroscopy together with computational tools have been used to study metabolism in cells. Compartmentalization of metabolism complicates the interpretation of stable isotope patterns in mammalian cells owing to the superimposition of different pathways contributing to the same pool of analytes. This indicates a need for a model-free approach to interpret such data. Mass spectrometry and NMR spectroscopy provide complementary analytical information on metabolites. Herein an approach that simulates 13 C multiplets in NMR spectra and utilizes mass increments to obtain long-range information is presented. The combined information is then utilized to derive isotopomer distributions. This is a first rigorous analytical and computational approach for a model-free analysis of metabolic data applicable to mammalian cells.