Global, Regional, and National Economic Consequences of Stroke

BACKGROUND

An understanding of global, regional, and national macroeconomic losses caused by stroke is important for allocation of clinical and research resources. The authors investigated the macroeconomic consequences of stroke disease burden in the year 2019 in 173 countries.

METHODS

Disability-adjusted life year data for overall stroke and its subtypes (ischemic stroke, intracerebral hemorrhage, and subarachnoid hemorrhage) were collected from the GBD study (Global Burden of Disease) 2019 database. Gross domestic product (GDP, adjusted for purchasing power parity [PPP]) data were collected from the World Bank; GDP and disability-adjusted life year data were combined to estimate macroeconomic losses using a value of lost welfare (VLW) approach. All results are presented in 2017 international US dollars adjusted for PPP.

RESULTS

Globally, in 2019, VLW due to stroke was $2059.67 billion or 1.66% of the global GDP. Global VLW/GDP for stroke subtypes was 0.78% (VLW=$964.51 billion) for ischemic stroke, 0.71% (VLW=$882.81 billion) for intracerebral hemorrhage, and 0.17% (VLW=$212.36 billion) for subarachnoid hemorrhage. The Central European, Eastern European, and Central Asian GBD super-region reported the highest VLW/GDP for stroke overall (3.01%), ischemic stroke (1.86%), and for subarachnoid hemorrhage (0.26%). The Southeast Asian, East Asian, and Oceanian GBD super-region reported the highest VLW/GDP for intracerebral hemorrhage (1.48%).

CONCLUSIONS

The global macroeconomic consequences related to stroke are vast even when considering stroke subtypes. The present quantification may be leveraged to help justify increased spending of finite resources on stroke in an effort to improve outcomes for patients with stroke globally.

Integrative transcriptomic and metabolic analyses of the mammalian hibernating brain identifies a key role for succinate dehydrogenase in ischemic tolerance

Ischemic stroke results in a loss of tissue homeostasis and integrity, the underlying pathobiology of which stems primarily from the depletion of cellular energy stores and perturbation of available metabolites ¹ . Hibernation in thirteen-lined ground squirrels (TLGS), Ictidomys tridecemlineatus , provides a natural model of ischemic tolerance as these mammals undergo prolonged periods of critically low cerebral blood flow without evidence of central nervous system (CNS) damage ² . Studying the complex interplay of genes and metabolites that unfolds during hibernation may provide novel insights into key regulators of cellular homeostasis during brain ischemia. Herein, we interrogated the molecular profiles of TLGS brains at different time points within the hibernation cycle via RNA sequencing coupled with untargeted metabolomics. We demonstrate that hibernation in TLGS leads to major changes in the expression of genes involved in oxidative phosphorylation and this is correlated with an accumulation of the tricarboxylic acid (TCA) cycle intermediates citrate, cis-aconitate, and α-ketoglutarate-αKG. Integration of the gene expression and metabolomics datasets led to the identification of succinate dehydrogenase (SDH) as the critical enzyme during hibernation, uncovering a break in the TCA cycle at that level. Accordingly, the SDH inhibitor dimethyl malonate (DMM) was able to rescue the effects of hypoxia on human neuronal cells in vitro and in mice subjected to permanent ischemic stroke in vivo . Our findings indicate that studying the regulation of the controlled metabolic depression that occurs in hibernating mammals may lead to novel therapeutic approaches capable of increasing ischemic tolerance in the CNS.

Early Neutrophilia Marked by Aerobic Glycolysis Sustains Host Metabolism and Delays Cancer Cachexia

An elevated neutrophil-lymphocyte ratio negatively predicts the outcome of patients with cancer and is associated with cachexia, the terminal wasting syndrome. Here, using murine model systems of colorectal and pancreatic cancer we show that neutrophilia in the circulation and multiple organs, accompanied by extramedullary hematopoiesis, is an early event during cancer progression. Transcriptomic and metabolic assessment reveals that neutrophils in tumor-bearing animals utilize aerobic glycolysis, similar to cancer cells. Although pharmacological inhibition of aerobic glycolysis slows down tumor growth in C26 tumor-bearing mice, it precipitates cachexia, thereby shortening the overall survival. This negative effect may be explained by our observation that acute depletion of neutrophils in pre-cachectic mice impairs systemic glucose homeostasis secondary to altered hepatic lipid processing. Thus, changes in neutrophil number, distribution, and metabolism play an adaptive role in host metabolic homeostasis during cancer progression. Our findings provide insight into early events during cancer progression to cachexia, with implications for therapy.

A Novel Combination of Blood Biomarkers and Clinical Stroke Scales Facilitates Detection of Large Vessel Occlusion Ischemic Strokes

Acute ischemic stroke caused by large vessel occlusions (LVOs) is a major contributor to stroke deaths and disabilities; however, identification for emergency treatment is challenging. We recruited two separate cohorts of suspected stroke patients and screened a panel of blood-derived protein biomarkers for LVO detection. Diagnostic performance was estimated by using blood biomarkers in combination with NIHSS-derived stroke severity scales. Multivariable analysis demonstrated that D-dimer (OR 16, 95% CI 5–60; p-value < 0.001) and GFAP (OR 0.002, 95% CI 0–0.68; p-value < 0.05) comprised the optimal panel for LVO detection. Combinations of D-dimer and GFAP with a number of stroke severity scales increased the number of true positives, while reducing false positives due to hemorrhage, as compared to stroke scales alone (p-value < 0.001). A combination of the biomarkers with FAST-ED resulted in the highest accuracy at 95% (95% CI: 87–99%), with sensitivity of 91% (95% CI: 72–99%), and specificity of 96% (95% CI: 90–99%). Diagnostic accuracy was confirmed in an independent cohort, in which accuracy was again shown to be 95% (95% CI: 87–99%), with a sensitivity of 82% (95% CI: 57–96%), and specificity of 98% (95% CI: 92–100%). Accordingly, the combination of D-dimer and GFAP with stroke scales may provide a simple and highly accurate tool for identifying LVO patients, with a potential impact on time to treatment.

Transcriptomic analysis of human primary breast cancer identifies fatty acid oxidation as a target for metformin

BACKGROUND

Epidemiological studies suggest that metformin may reduce the incidence of cancer in patients with diabetes and multiple late phase clinical trials assessing the potential of repurposing this drug are underway. Transcriptomic profiling of tumour samples is an excellent tool to understand drug bioactivity, identify candidate biomarkers and assess for mechanisms of resistance to therapy.

METHODS

Thirty-six patients with untreated primary breast cancer were recruited to a window study and transcriptomic profiling of tumour samples carried out before and after metformin treatment.

RESULTS

Multiple genes that regulate fatty acid oxidation were upregulated at the transcriptomic level and there was a differential change in expression between two previously identified cohorts of patients with distinct metabolic responses. Increase in expression of a mitochondrial fatty oxidation gene composite signature correlated with change in a proliferation gene signature. In vitro assays showed that, in contrast to previous studies in models of normal cells, metformin reduces fatty acid oxidation with a subsequent accumulation of intracellular triglyceride, independent of AMPK activation.

CONCLUSIONS

We propose that metformin at clinical doses targets fatty acid oxidation in cancer cells with implications for patient selection and drug combinations.

CLINICAL TRIAL REGISTRATION

NCT01266486.

The potential of breath analysis to improve outcome for patients with lung cancer

Lung cancer remains the most common cause of cancer related death in both the UK and USA. Development of diagnostic approaches that have the ability to detect lung cancer early are a research priority with potential to improve survival. Analysis of exhaled breath metabolites, or volatile organic compounds (VOCs) is an area of considerable interest as it could fulfil such requirements. Numerous studies have shown that VOC profiles are different in the breath of patients with lung cancer compared to healthy individuals or those with non-malignant lung diseases. This review provides a scientific and clinical assessment of the potential value of a breath test in lung cancer. It discusses the current understanding of metabolic pathways that contribute to exhaled VOC production in lung cancer and reviews the research conducted to date. Finally, we highlight important areas for future research and discuss how a breath test could be incorporated into various clinical pathways.

NADH Shuttling Couples Cytosolic Reductive Carboxylation of Glutamine with Glycolysis in Cells with Mitochondrial Dysfunction

The bioenergetics and molecular determinants of the metabolic response to mitochondrial dysfunction are incompletely understood, in part due to a lack of appropriate isogenic cellular models of primary mitochondrial defects. Here, we capitalize on a recently developed cell model with defined levels of m.8993T>G mutation heteroplasmy, mTUNE, to investigate the metabolic underpinnings of mitochondrial dysfunction. We found that impaired utilization of reduced nicotinamide adenine dinucleotide (NADH) by the mitochondrial respiratory chain leads to cytosolic reductive carboxylation of glutamine as a new mechanism for cytosol-confined NADH recycling supported by malate dehydrogenase 1 (MDH1). We also observed that increased glycolysis in cells with mitochondrial dysfunction is associated with increased cell migration in an MDH1-dependent fashion. Our results describe a novel link between glycolysis and mitochondrial dysfunction mediated by reductive carboxylation of glutamine.

Integrated Pharmacodynamic Analysis Identifies Two Metabolic Adaption Pathways to Metformin in Breast Cancer

Late-phase clinical trials investigating metformin as a cancer therapy are underway. However, there remains controversy as to the mode of action of metformin in tumors at clinical doses. We conducted a clinical study integrating measurement of markers of systemic metabolism, dynamic FDG-PET-CT, transcriptomics, and metabolomics at paired time points to profile the bioactivity of metformin in primary breast cancer. We show metformin reduces the levels of mitochondrial metabolites, activates multiple mitochondrial metabolic pathways, and increases 18-FDG flux in tumors. Two tumor groups are identified with distinct metabolic responses, an OXPHOS transcriptional response (OTR) group for which there is an increase in OXPHOS gene transcription and an FDG response group with increased 18-FDG uptake. Increase in proliferation, as measured by a validated proliferation signature, suggested that patients in the OTR group were resistant to metformin treatment. We conclude that mitochondrial response to metformin in primary breast cancer may define anti-tumor effect.

mTORC1 Upregulation Leads to Accumulation of the Oncometabolite Fumarate in a Mouse Model of Renal Cell Carcinoma

Renal cell carcinomas (RCCs) are common cancers diagnosed in more than 350,000 people each year worldwide. Several pathways are de-regulated in RCCs, including mTORC1. However, how mTOR drives tumorigenesis in this context is unknown. The lack of faithful animal models has limited progress in understanding and targeting RCCs. Here, we generated a mouse model harboring the kidney-specific inactivation of Tsc1. These animals develop cysts that evolve into papillae, cystadenomas, and papillary carcinomas. Global profiling confirmed several metabolic derangements previously attributed to mTORC1. Notably, Tsc1 inactivation results in the accumulation of fumarate and in mTOR-dependent downregulation of the TCA cycle enzyme fumarate hydratase (FH). The re-expression of FH in cellular systems lacking Tsc1 partially rescued renal epithelial transformation. Importantly, the mTORC1-FH axis is likely conserved in human RCC specimens. We reveal a role of mTORC1 in renal tumorigenesis, which depends on the oncometabolite fumarate.

Breath biopsy for early detection and precision medicine in cancer

Breath biopsy enables the non-invasive collection and analysis of volatile organic compounds (VOCs) in exhaled breath, providing valuable information about disease processes occurring in the body. Metabolic changes occur in cancer cells at the earliest stages of disease. We discuss progress in the use of breath biopsy for discovery of breath-based biomarkers for early detection of cancer, and potential applications for breath biopsy in enabling precision medicine in cancer.

Mammalian Circadian Period, But Not Phase and Amplitude, Is Robust Against Redox and Metabolic Perturbations

AIMS

Circadian rhythms permeate all levels of biology to temporally regulate cell and whole-body physiology, although the cell-autonomous mechanism that confers ∼24-h periodicity is incompletely understood. Reports describing circadian oscillations of over-oxidized peroxiredoxin abundance have suggested that redox signaling plays an important role in the timekeeping mechanism. Here, we tested the functional contribution that redox state and primary metabolism make to mammalian cellular timekeeping.

RESULTS

We found a circadian rhythm in flux through primary glucose metabolic pathways, indicating rhythmic NAD(P)H production. Using pharmacological and genetic perturbations, however, we found that timekeeping was insensitive to changes in glycolytic flux, whereas oxidative pentose phosphate pathway (PPP) inhibition and other chronic redox stressors primarily affected circadian gene expression amplitude, not periodicity. Finally, acute changes in redox state decreased PER2 protein stability, phase dependently, to alter the subsequent phase of oscillation.

INNOVATION

Circadian rhythms in primary cellular metabolism and redox state have been proposed to play a role in the cellular timekeeping mechanism. We present experimental data testing that hypothesis.

CONCLUSION

Circadian flux through primary metabolism is cell autonomous, driving rhythmic NAD(P)⁺ redox cofactor turnover and maintaining a redox balance that is permissive for circadian gene expression cycles. Redox homeostasis and PPP flux, but not glycolysis, are necessary to maintain clock amplitude, but neither redox nor glucose metabolism determines circadian period. Furthermore, cellular rhythms are sensitive to acute changes in redox balance, at least partly through regulation of PER protein. Redox and metabolic state are, thus, both inputs and outputs, but not state variables, of cellular circadian timekeeping. Antioxid. Redox Signal. 28, 507-520.

Fumarate Hydratase Loss Causes Combined Respiratory Chain Defects

Fumarate hydratase (FH) is an enzyme of the tricarboxylic acid (TCA) cycle mutated in hereditary and sporadic cancers. Despite recent advances in understanding its role in tumorigenesis, the effects of FH loss on mitochondrial metabolism are still unclear. Here, we used mouse and human cell lines to assess mitochondrial function of FH-deficient cells. We found that human and mouse FH-deficient cells exhibit decreased respiration, accompanied by a varying degree of dysfunction of respiratory chain (RC) complex I and II. Moreover, we show that fumarate induces succination of key components of the iron-sulfur cluster biogenesis family of proteins, leading to defects in the biogenesis of iron-sulfur clusters that affect complex I function. We also demonstrate that suppression of complex II activity is caused by product inhibition due to fumarate accumulation. Overall, our work provides evidence that the loss of a single TCA cycle enzyme is sufficient to cause combined RC activity dysfunction.

Mitochondrial Metabolism: Yin and Yang for Tumor Progression

Altered metabolism is a distinct feature of cancer cells. During transformation, the entire metabolic network is rewired to efficiently convert nutrients to biosynthetic precursors to sustain cancer cell growth and proliferation. Whilst the molecular underpinnings of this metabolic reprogramming have been described, its role in tumor progression is still under investigation. Importantly, the mitochondrion is a central actor in many of the metabolic processes that are altered in tumors. Yet, we have only begun to understand the dualities of mitochondrial function during cancer metastasis and therapy resistance. Paradoxically, mitochondrial metabolism can be both advantageous and detrimental to these processes, highlighting the need for a better understanding of the molecular and microenvironmental cues that define the role of this fascinating organelle. In this review article, we present an updated view on the different mitochondrial metabolic strategies adopted by cancer cells to overcome the many hurdles faced during tumor progression.

Tissue-specific and convergent metabolic transformation of cancer correlates with metastatic potential and patient survival

Cancer cells undergo a multifaceted rewiring of cellular metabolism to support their biosynthetic needs. Although the major determinants of this metabolic transformation have been elucidated, their broad biological implications and clinical relevance are unclear. Here we systematically analyse the expression of metabolic genes across 20 different cancer types and investigate their impact on clinical outcome. We find that cancers undergo a tissue-specific metabolic rewiring, which converges towards a common metabolic landscape. Of note, downregulation of mitochondrial genes is associated with the worst clinical outcome across all cancer types and correlates with the expression of epithelial-to-mesenchymal transition gene signature, a feature of invasive and metastatic cancers. Consistently, suppression of mitochondrial genes is identified as a key metabolic signature of metastatic melanoma and renal cancer, and metastatic cell lines. This comprehensive analysis reveals unexpected facets of cancer metabolism, with important implications for cancer patients' stratification, prognosis and therapy.

Cancer cells reprogramme their metabolism with unclear clinical implications. Here, the authors analyse the expression of metabolic genes across 20 types of solid cancers and find that clinical aggressiveness, poor survival and metastasis are associated with the deregulation of mitochondrial metabolism.

Fumarate is an epigenetic modifier that elicits epithelial-to-mesenchymal transition

Mutations of the tricarboxylic acid cycle enzyme fumarate hydratase cause hereditary leiomyomatosis and renal cell cancer. Fumarate hydratase-deficient renal cancers are highly aggressive and metastasize even when small, leading to a very poor clinical outcome. Fumarate, a small molecule metabolite that accumulates in fumarate hydratase-deficient cells, plays a key role in cell transformation, making it a bona fide oncometabolite. Fumarate has been shown to inhibit α-ketoglutarate-dependent dioxygenases that are involved in DNA and histone demethylation. However, the link between fumarate accumulation, epigenetic changes, and tumorigenesis is unclear. Here we show that loss of fumarate hydratase and the subsequent accumulation of fumarate in mouse and human cells elicits an epithelial-to-mesenchymal-transition (EMT), a phenotypic switch associated with cancer initiation, invasion, and metastasis. We demonstrate that fumarate inhibits Tet-mediated demethylation of a regulatory region of the antimetastatic miRNA cluster mir-200ba429, leading to the expression of EMT-related transcription factors and enhanced migratory properties. These epigenetic and phenotypic changes are recapitulated by the incubation of fumarate hydratase-proficient cells with cell-permeable fumarate. Loss of fumarate hydratase is associated with suppression of miR-200 and the EMT signature in renal cancer and is associated with poor clinical outcome. These results imply that loss of fumarate hydratase and fumarate accumulation contribute to the aggressive features of fumarate hydratase-deficient tumours.

Inhibition of glucose-6-phosphate dehydrogenase sensitizes cisplatin-resistant cells to death

The mechanisms of cisplatin resistance, one of the major limitations of current chemotherapy, has only partially been described. We previously demonstrated that cisplatin-resistant ovarian cancer cells (C13), are characterized by reduced mitochondrial activity and higher glucose-dependency when compared to the cisplatin-sensitive counterpart (2008). In this work we further characterized the role of metabolic transformation in cisplatin resistance. By using transmitochondrial hybrids we show that metabolic reprogramming of cisplatin-resistant cell is not caused by inherent mtDNA mutations. We also found that C13 cells not only present an increased glucose-uptake and consumption, but also exhibit increased expression and enzymatic activity of the Pentose Phosphate pathway (PPP) enzyme Glucose-6-Phosphate Dehydrogenase (G6PDH). Moreover, we show that cisplatin-resistant cells are more sensitive to G6PDH inhibition. Even if the metabolomic fingerprint of ovarian cancer cells remains to be further elucidated, these findings indicate that PPP offers innovative potential targets to overcome cisplatin resistance.

Near-complete elimination of mutant mtDNA by iterative or dynamic dose-controlled treatment with mtZFNs

Mitochondrial diseases are frequently associated with mutations in mitochondrial DNA (mtDNA). In most cases, mutant and wild-type mtDNAs coexist, resulting in heteroplasmy. The selective elimination of mutant mtDNA, and consequent enrichment of wild-type mtDNA, can rescue pathological phenotypes in heteroplasmic cells. Use of the mitochondrially targeted zinc finger-nuclease (mtZFN) results in degradation of mutant mtDNA through site-specific DNA cleavage. Here, we describe a substantial enhancement of our previous mtZFN-based approaches to targeting mtDNA, allowing near-complete directional shifts of mtDNA heteroplasmy, either by iterative treatment or through finely controlled expression of mtZFN, which limits off-target catalysis and undesired mtDNA copy number depletion. To demonstrate the utility of this improved approach, we generated an isogenic distribution of heteroplasmic cells with variable mtDNA mutant level from the same parental source without clonal selection. Analysis of these populations demonstrated an altered metabolic signature in cells harbouring decreased levels of mutant m.8993T>G mtDNA, associated with neuropathy, ataxia, and retinitis pigmentosa (NARP). We conclude that mtZFN-based approaches offer means for mtDNA heteroplasmy manipulation in basic research, and may provide a strategy for therapeutic intervention in selected mitochondrial diseases.

Abstract LB-200: Integrating dynamic 18F-FDG PET-CT, tumor metabolomics and functional genomics to understand metformin's pharmacodynamic effects in breast cancer: results of a phase 0 clinical trial

There is growing interest in the anticancer effect of the diabetes drug, metformin, and over 100 clinical trials are underway worldwide. However it is still not determined as to whether metformin has significant direct effects on cancer cells or solely indirect effects via modulation of host metabolism.

We recruited 41 non-diabetic patients with primary breast cancer to a neoadjuvant window trial. Patients received an escalating dose of metformin (500mg up to 1500mg) for 2 weeks with pre- and post-metformin pharmacodynamic assessments including, dynamic 18F-FDG PET-CT scans, serum metabolic markers, and tumour biopsies for whole transcriptome RNASeq, tumour metabolomics and immunohistochemistry.

Assessment of tumour FDG kinetics using a classic 2-tissue compartment model with three rate constants showed a 1.3 fold change (FC) post-metformin in the composite 18F-FDG flux constant, Kflux (p = 0.041, on paired t-test). There was a non-statistically significant 1.1 fold increase in the variable, metabolic rate of glucose utilization (MRglu) (p = 0.141). Mass spectrometry analysis revealed a decrease in intra-tumoral levels of the short-chain acyl-carnitines, propionylcarnitine (FC -0.50, p = 0.039) and acetylycarnitine (FC -0.40, p = 0.046) consistent with inhibition of fatty acid oxidation (wilcoxon rank test). This effect on fatty acid oxidation was validated in pre-clinical in vitro and in vivo breast cancer cell line models. There was a statistically significant positive correlation between the actual difference in Kflux and intratumoral levels of acetylcarnitine (p = 0.012, Spearman's rank test). Small but consistent falls in the levels of serum glucose (p = 0.032), c-peptide (p = 0.001), insulin (p = 0.005), IGF1 (p = 0.048) and IGF2 (p = 0.040) were observed following metformin treatment (paired t-test) but there was no correlation with change in Kflux or short chain acyl-carnitine levels. Pathway annotation analysis using GeneCodis revealed several pathways associated with mitochondrial and fatty acid metabolism that were upregulated. Immunohistochemical intratumoral nuclear expression of pAMPK increased 1.5 fold (p = 0.037, paired t-test) but this did not correlate with change in Kflux or levels of short-chain acyl-carnitines. Peak serum metformin levels correlated with intratumoral metformin levels (p = 0.012, Spearman's rank test) but did not correlate with change in Kflux or short-chain acyl-carnitine levels.

Our data shows that metformin treatment alters FDG kinetics, inhibits fatty acid oxidation and leads to altered gene expression in the mitochondrial (nuclear encoded) transcriptome but that these effects do not correlate with changes in host metabolism. This data provides strong evidence that metformin has a direct effect on breast cancer metabolism at clinical doses.

Citation Format: Simon Lord, Daniel Liu, Syed Haider, Edoardo Gaude, Eugene Teoh, Patel Neel, Qifeng Zhang, Fergus Gleeson, Michael Wakelam, Christian Frezza, Francesca Buffa, Fenwick John, Adrian Harris. Integrating dynamic 18F-FDG PET-CT, tumor metabolomics and functional genomics to understand metformin's pharmacodynamic effects in breast cancer: results of a phase 0 clinical trial. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-200.

Hypoxia-induced nitric oxide production and tumour perfusion is inhibited by pegylated arginine deiminase (ADI-PEG20)

The hypoxic tumour microenvironment represents an aggressive, therapy-resistant compartment. As arginine is required for specific hypoxia-induced processes, we hypothesised that arginine-deprivation therapy may be useful in targeting hypoxic cancer cells. We explored the effects of the arginine-degrading agent ADI-PEG20 on hypoxia-inducible factor (HIF) activation, the hypoxia-induced nitric oxide (NO) pathway and proliferation using HCT116 and UMUC3 cells and xenografts. The latter lack argininosuccinate synthetase (ASS1) making them auxotrophic for arginine. In HCT116 cells, ADI-PEG20 inhibited hypoxic-activation of HIF-1α and HIF-2α, leading to decreased inducible-nitric oxide synthase (iNOS), NO-production, and VEGF. Interestingly, combining hypoxia and ADI-PEG20 synergistically inhibited ASS1. ADI-PEG20 inhibited mTORC1 and activated the unfolded protein response providing a mechanism for inhibition of HIF and ASS1. ADI-PEG20 inhibited tumour growth, impaired hypoxia-associated NO-production, and decreased vascular perfusion. Expression of HIF-1α/HIF-2α/iNOS and VEGF were reduced, despite an increased hypoxic tumour fraction. Similar effects were observed in UMUC3 xenografts. In summary, ADI-PEG20 inhibits HIF-activated processes in two tumour models with widely different arginine biology. Thus, ADI-PEG20 may be useful in the clinic to target therapy-resistant hypoxic cells in ASS1-proficient tumours and ASS1-deficient tumours.

A three-dimensional engineered tumour for spatial snapshot analysis of cell metabolism and phenotype in hypoxic gradients

The profound metabolic reprogramming that occurs in cancer cells has been investigated primarily in two-dimensional cell cultures, which fail to recapitulate spatial aspects of cell-to-cell interactions as well as tissue gradients present in three-dimensional tumours. Here, we describe an engineered model to assemble three-dimensional tumours by rolling a scaffold-tumour composite strip. By unrolling the strip, the model can be rapidly disassembled for snapshot analysis, allowing spatial mapping of cell metabolism in concert with cell phenotype. We also show that the establishment of oxygen gradients within samples that are shaped by oxygen-dependent signalling pathways, as well as the consequential variations in cell growth, response to hypoxic gradients extending from normoxia to severe hypoxia, and therapy responsiveness, are consistent with those of tumours in vivo. Moreover, by using liquid chromatography tandem mass spectrometry, we mapped cellular metabolism and identified spatially defined metabolic signatures of cancer cells to reveal both known and novel metabolic responses to hypoxia.

Abstract A24: Integration of tumor metabolomics, cancer genome sequencing and dynamic functional imaging to assess the metabolic effects of metformin in breast cancer

There is great interest in the effects on cancer metabolism of the diabetes drug, metformin and its potential as a cancer treatment. Despite intense investigation it is still not clear as to its metabolic effects on primary human cancer in vivo. 41 patients with primary breast cancer were recruited to a ‘window of opportunity study’ prior to neoadjuvant chemotherapy. Before and after 2 weeks of metformin, dynamic 18F-FDG PET-CT scans were carried out, breast core biopsies of the primary tumour taken for RNASeq, metabolomics and immunohistochemistry analysis and host serum metabolic markers assessed.

Metabolomic mass spectrometry analysis revealed an increase in the ADP/ATP and AMP/ATP ratio (fold change 8.6 and 24.9, respectively, p = 0.07 and p = 0.14) after metformin treatment.

RNA sequencing of the first 21 paired samples showed upregulation of many genes encoding components of complex 1, and the TCA cycle, glutaminolysis, and glycolysis pathways. Several genes encoding for glucose and glutamine transport were amongst those most consistently upregulated, including GLUT1, SLC38A1 and SLC7A5 (all p&lt;0.0001).

Dynamic PET-CT analysis of the first 17 paired scans demonstrated a trend toward a decrease in the variable K2 post-metformin (an estimate of 18F-FDG efflux from tumour intracellular pool back to blood), but with much variability between paired scans (0.70±0.11 vs 0.51±0.05 (p=0.14)).

There was a decrease in serum C-peptide (0.56±0.04nmol/L vs 0.48±0.02nmol/L, pre- and post-metformin, p=0.003) consistent with reduced host insulin secretion. This is the first study in the clinical setting to show that metformin can cause an energy stress in cancer cells. The effect on mRNA expression was compatible with direct mitochondrial effects on the cancer cell leading to upregulation of the glutaminolysis and glycolysis pathways. The decrease in efflux of radiolabelled glucose may indicate retention of glucose possibly secondary to changes in blood glucose availability. We expect this study will help define biomarker development and future treatment strategies for metformin, in particular potential combination therapy.

Note: This abstract was not presented at the conference.

Citation Format: Simon R. Lord, Nilay Patel, D. Liu, J. Fenwick, C. Frezza, S. Henriques da Costa, E. Gaude, Q. Zhang, M. Wakelam, F. Gleeson, S. Haider, F. Buffa, A. L. Harris. Integration of tumor metabolomics, cancer genome sequencing and dynamic functional imaging to assess the metabolic effects of metformin in breast cancer [abstract]. In: Proceedings of the Thirteenth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2014 Sep 27-Oct 1; New Orleans, LA. Philadelphia (PA): AACR; Can Prev Res 2015;8(10 Suppl): Abstract nr A24.

The metabolic alterations of cancer cells

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

Metabolic reprograming of mononuclear phagocytes in progressive multiple sclerosis

Multiple sclerosis (MS) is an inflammatory and demyelinating disease of the central nervous system (CNS). Accumulation of brain damage in progressive MS is partly the result of mononuclear phagocytes (MPs) attacking myelin sheaths in the CNS. Although there is no cure yet for MS, significant advances have been made in the development of disease modifying agents. Unfortunately, most of these drugs fail to reverse established neurological deficits and can have adverse effects. Recent evidence suggests that MPs polarization is accompanied by profound metabolic changes, whereby pro-inflammatory MPs (M1) switch toward glycolysis, whereas anti-inflammatory MPs (M2) become more oxidative. It is therefore possible that reprograming MPs metabolism could affect their function and repress immune cell activation. This mini review describes the metabolic changes underpinning macrophages polarization and anticipates how metabolic re-education of MPs could be used for the treatment of MS.

KEY POINTS

Inflammation in progressive MS is mediated primarily by MPs.Cell metabolism regulates the function of MPs.DMAs can re-educate the metabolism of MPs to promote healing.

Fumarate induces redox-dependent senescence by modifying glutathione metabolism

Mutations in the tricarboxylic acid (TCA) cycle enzyme fumarate hydratase (FH) are associated with a highly malignant form of renal cancer. We combined analytical chemistry and metabolic computational modelling to investigate the metabolic implications of FH loss in immortalized and primary mouse kidney cells. Here, we show that the accumulation of fumarate caused by the inactivation of FH leads to oxidative stress that is mediated by the formation of succinicGSH, a covalent adduct between fumarate and glutathione. Chronic succination of GSH, caused by the loss of FH, or by exogenous fumarate, leads to persistent oxidative stress and cellular senescence in vitro and in vivo. Importantly, the ablation of p21, a key mediator of senescence, in Fh1-deficient mice resulted in the transformation of benign renal cysts into a hyperplastic lesion, suggesting that fumarate-induced senescence needs to be bypassed for the initiation of renal cancers.

Phenotype-based cell-specific metabolic modeling reveals metabolic liabilities of cancer

Utilizing molecular data to derive functional physiological models tailored for specific cancer cells can facilitate the use of individually tailored therapies. To this end we present an approach termed PRIME for generating cell-specific genome-scale metabolic models (GSMMs) based on molecular and phenotypic data. We build >280 models of normal and cancer cell-lines that successfully predict metabolic phenotypes in an individual manner. We utilize this set of cell-specific models to predict drug targets that selectively inhibit cancerous but not normal cell proliferation. The top predicted target, MLYCD, is experimentally validated and the metabolic effects of MLYCD depletion investigated. Furthermore, we tested cell-specific predicted responses to the inhibition of metabolic enzymes, and successfully inferred the prognosis of cancer patients based on their PRIME-derived individual GSMMs. These results lay a computational basis and a counterpart experimental proof of concept for future personalized metabolic modeling applications, enhancing the search for novel selective anticancer therapies.

Ischaemic accumulation of succinate controls reperfusion injury through mitochondrial ROS

Ischaemia-reperfusion injury occurs when the blood supply to an organ is disrupted and then restored, and underlies many disorders, notably heart attack and stroke. While reperfusion of ischaemic tissue is essential for survival, it also initiates oxidative damage, cell death and aberrant immune responses through the generation of mitochondrial reactive oxygen species (ROS). Although mitochondrial ROS production in ischaemia reperfusion is established, it has generally been considered a nonspecific response to reperfusion. Here we develop a comparative in vivo metabolomic analysis, and unexpectedly identify widely conserved metabolic pathways responsible for mitochondrial ROS production during ischaemia reperfusion. We show that selective accumulation of the citric acid cycle intermediate succinate is a universal metabolic signature of ischaemia in a range of tissues and is responsible for mitochondrial ROS production during reperfusion. Ischaemic succinate accumulation arises from reversal of succinate dehydrogenase, which in turn is driven by fumarate overflow from purine nucleotide breakdown and partial reversal of the malate/aspartate shuttle. After reperfusion, the accumulated succinate is rapidly re-oxidized by succinate dehydrogenase, driving extensive ROS generation by reverse electron transport at mitochondrial complex I. Decreasing ischaemic succinate accumulation by pharmacological inhibition is sufficient to ameliorate in vivo ischaemia-reperfusion injury in murine models of heart attack and stroke. Thus, we have identified a conserved metabolic response of tissues to ischaemia and reperfusion that unifies many hitherto unconnected aspects of ischaemia-reperfusion injury. Furthermore, these findings reveal a new pathway for metabolic control of ROS production in vivo, while demonstrating that inhibition of ischaemic succinate accumulation and its oxidation after subsequent reperfusion is a potential therapeutic target to decrease ischaemia-reperfusion injury in a range of pathologies.

Germline FH mutations presenting with pheochromocytoma

CONTEXT

At least a third of the patients with pheochromocytoma (PCC) or paraganglioma (PGL) harbor an underlying germline mutation in a known PCC/PGL gene. Mutations in genes (SDHB, SDHD, SDHC, and SDHA) encoding a component of the tricarboxylic acid cycle, succinate dehydrogenase (SDH), are a major cause of inherited PCC and PGL. SDHB mutations are also, albeit less frequently, associated with inherited renal cell carcinoma. Inactivation of SDH and another tricarboxylic acid cycle component, fumarate hydratase (FH), have both been associated with abnormalities of cellular metabolism, responsible for the activation of hypoxic gene response pathways and epigenetic alterations (eg, DNA methylation). However, the clinical phenotype of germline mutations in SDHx genes and FH is usually distinct, with FH mutations classically associated with hereditary cutaneous and uterine leiomyomatosis and renal cell carcinoma, although recently an association with PCC/PGL has been reported.

OBJECTIVE AND DESIGN

To identify potential novel PCC/PGL predisposition genes, we initially undertook exome resequencing studies in a case of childhood PCC, and subsequently FH mutation analysis in a further 71 patients with PCC, PGL, or head and neck PGL.

RESULTS

After identifying a candidate FH missense mutation in the exome study, we then detected a further candidate missense mutation (p.Glu53Lys) by candidate gene sequencing. In vitro analyses demonstrated that both missense mutations (p.Cys434Tyr and p.Glu53Lys) were catalytically inactive.

CONCLUSIONS

These findings 1) confirm that germline FH mutations may present, albeit rarely with PCC or PGL; and 2) extend the clinical phenotype associated with FH mutations to pediatric PCC.

Defects in mitochondrial metabolism and cancer

Cancer is a heterogeneous set of diseases characterized by different molecular and cellular features. Over the past decades, researchers have attempted to grasp the complexity of cancer by mapping the genetic aberrations associated with it. In these efforts, the contribution of mitochondria to the pathogenesis of cancer has tended to be neglected. However, more recently, a growing body of evidence suggests that mitochondria play a key role in cancer. In fact, dysfunctional mitochondria not only contribute to the metabolic reprogramming of cancer cells but they also modulate a plethora of cellular processes involved in tumorigenesis. In this review, we describe the link between mutations to mitochondrial enzymes and tumor formation. We also discuss the hypothesis that mutations to mitochondrial and nuclear DNA could cooperate to promote the survival of cancer cells in an evolving metabolic landscape.

Nuclear ARRB1 induces pseudohypoxia and cellular metabolism reprogramming in prostate cancer

Tumour cells sustain their high proliferation rate through metabolic reprogramming, whereby cellular metabolism shifts from oxidative phosphorylation to aerobic glycolysis, even under normal oxygen levels. Hypoxia-inducible factor 1A (HIF1A) is a major regulator of this process, but its activation under normoxic conditions, termed pseudohypoxia, is not well documented. Here, using an integrative approach combining the first genome-wide mapping of chromatin binding for an endocytic adaptor, ARRB1, both in vitro and in vivo with gene expression profiling, we demonstrate that nuclear ARRB1 contributes to this metabolic shift in prostate cancer cells via regulation of HIF1A transcriptional activity under normoxic conditions through regulation of succinate dehydrogenase A (SDHA) and fumarate hydratase (FH) expression. ARRB1-induced pseudohypoxia may facilitate adaptation of cancer cells to growth in the harsh conditions that are frequently encountered within solid tumours. Our study is the first example of an endocytic adaptor protein regulating metabolic pathways. It implicates ARRB1 as a potential tumour promoter in prostate cancer and highlights the importance of metabolic alterations in prostate cancer.

Safety and efficacy of transcranial direct current stimulation in acute experimental ischemic stroke

BACKGROUND AND PURPOSE

Transcranial direct current stimulation is emerging as a promising tool for the treatment of several neurological conditions, including cerebral ischemia. The therapeutic role of this noninvasive treatment is, however, limited to chronic phases of stroke. We thus ought to investigate whether different stimulation protocols could also be beneficial in the acute phase of experimental brain ischemia.

METHODS

The influence of both cathodal and anodal transcranial direct current stimulation in modifying brain metabolism of healthy mice was first tested by nuclear magnetic resonance spectroscopy. Then, mice undergoing transient proximal middle cerebral artery occlusion were randomized and treated acutely with anodal, cathodal, or sham transcranial direct current stimulation. Brain metabolism, functional outcomes, and ischemic lesion volume, as well as the inflammatory reaction and blood brain barrier functionality, were analyzed.

RESULTS

Cathodal stimulation was able, if applied in the acute phase of stroke, to preserve cortical neurons from the ischemic damage, to reduce inflammation, and to promote a better clinical recovery compared with sham and anodal treatments. This finding was attributable to the significant decrease of cortical glutamate, as indicated by nuclear magnetic resonance spectroscopy. Conversely, anodal stimulation induced an increase in the postischemic lesion volume and augmented blood brain barrier derangement.

CONCLUSIONS

Our data indicate that transcranial direct current stimulation exerts a measurable neuroprotective effect in the acute phase of stroke. However, its timing and polarity should be carefully identified on the base of the pathophysiological context to avoid potential harmful side effects.

The stem cell secretome and its role in brain repair

Compelling evidence exists that non-haematopoietic stem cells, including mesenchymal (MSCs) and neural/progenitor stem cells (NPCs), exert a substantial beneficial and therapeutic effect after transplantation in experimental central nervous system (CNS) disease models through the secretion of immune modulatory or neurotrophic paracrine factors. This paracrine hypothesis has inspired an alternative outlook on the use of stem cells in regenerative neurology. In this paradigm, significant repair of the injured brain may be achieved by injecting the biologics secreted by stem cells (secretome), rather than implanting stem cells themselves for direct cell replacement. The stem cell secretome (SCS) includes cytokines, chemokines and growth factors, and has gained increasing attention in recent years because of its multiple implications for the repair, restoration or regeneration of injured tissues. Thanks to recent improvements in SCS profiling and manipulation, investigators are now inspired to harness the SCS as a novel alternative therapeutic option that might ensure more efficient outcomes than current stem cell-based therapies for CNS repair. This review discusses the most recent identification of MSC- and NPC-secreted factors, including those that are trafficked within extracellular membrane vesicles (EVs), and reflects on their potential effects on brain repair. It also examines some of the most convincing advances in molecular profiling that have enabled mapping of the SCS.