Low aerobic mitochondrial energy metabolism in poorly- or undifferentiated neuroblastoma

Expanding the phenotypic and biochemical spectrum of NDUFAF3-related mitochondrial disease

Recessive variants in NDUFAF3 are a known cause of complex I (CI)-related mitochondrial disorders (MDs). The seven patients reported to date exhibited severe neurologic symptoms and lactic acidosis, followed by a fatal course and death during infancy in most cases. We present a 10-year-old patient with a neurodevelopmental disorder, progressive exercise intolerance, dystonia, basal ganglia abnormalities, and elevated lactate concentration in blood. Trio-exome sequencing revealed compound-heterozygosity for a pathogenic splice-site and a likely pathogenic missense variant in NDUFAF3. Spectrophotometric analysis of fibroblast-derived mitochondria demonstrated a relatively mild reduction of CI activity. Complexome analyses revealed severely reduced NDUFAF3 as well as CI in patient fibroblasts. Accumulation of early sub-assemblies of the membrane arm of CI associated with mitochondrial complex I intermediate assembly (MCIA) complex was observed. The most striking additional findings were both the unusual occurrence of free monomeric CI holding MCIA and other assembly factors. Here we discuss our patient in context of genotype, phenotype and metabolite data from previously reported NDUFAF3 cases. With the atypical presentation of our patient, we provide further insight into the phenotypic spectrum of NDUFAF3-related MDs. Complexome analysis in our patient confirms the previously defined role of NDUFAF3 within CI biogenesis, yet adds new aspects regarding the correct timing of both the association of soluble and membrane arm modules and CI-maturation as well as respiratory supercomplex formation.

Metabolic protein kinase signalling in neuroblastoma

BACKGROUND

Neuroblastoma is a paediatric malignancy of incredibly complex aetiology. Oncogenic protein kinase signalling in neuroblastoma has conventionally focussed on transduction through the well-characterised PI3K/Akt and MAPK pathways, in which the latter has been implicated in treatment resistance. The discovery of the receptor tyrosine kinase ALK as a target of genetic alterations in cases of familial and sporadic neuroblastoma, was a breakthrough in the understanding of the complex genetic heterogeneity of neuroblastoma. However, despite progress in the development of small-molecule inhibitors of ALK, treatment resistance frequently arises and appears to be a feature of the disease. Moreover, since the identification of ALK, several additional protein kinases, including the PIM and Aurora kinases, have emerged not only as drivers of the disease phenotype, but also as promising druggable targets. This is particularly the case for Aurora-A, given its intimate engagement with MYCN, a driver oncogene of aggressive neuroblastoma previously considered 'undruggable.'

SCOPE OF REVIEW

Aided by significant advances in structural biology and a broader understanding of the mechanisms of protein kinase function and regulation, we comprehensively outline the role of protein kinase signalling, emphasising ALK, PIM and Aurora in neuroblastoma, their respective metabolic outputs, and broader implications for targeted therapies.

MAJOR CONCLUSIONS

Despite massively divergent regulatory mechanisms, ALK, PIM and Aurora kinases all obtain significant roles in cellular glycolytic and mitochondrial metabolism and neuroblastoma progression, and in several instances are implicated in treatment resistance. While metabolism of neuroblastoma tends to display hallmarks of the glycolytic "Warburg effect," aggressive, in particular MYCN-amplified tumours, retain functional mitochondrial metabolism, allowing for survival and proliferation under nutrient stress. Future strategies employing specific kinase inhibitors as part of the treatment regimen should consider combinatorial attempts at interfering with tumour metabolism, either through metabolic pathway inhibitors, or by dietary means, with a view to abolish metabolic flexibility that endows cancerous cells with a survival advantage.

Effect of cadmium in the gonads of mussel (Mytilus coruscus): an ionomics and proteomics study

The mussel Mytilus coruscus is an important and very popular seafood in China and widespread along the eastern coast of China. In this study, we investigated the molecular response of mussel gonads to cadmium accumulation at two concentrations (80 and 200 µg/L) for 30 days using ionomics and proteomics techniques. The shrinkage of the cells and moderate hemocytic infiltration were observed in the Cd-treated groups. The strontium, selenium (Se), and zinc contents were significantly altered, and the relationships between iron, copper, Se, manganese, calcium, sodium, and magnesium were also significantly altered. Label-free quantitative proteomics analysis revealed a total of 227 differentially expressed proteins. These proteins were associated with multiple biological processes, including the tricarboxylic acid cycle, structural reorganization of cells, biosynthesis of amino acids, inflammatory response of cells, and tumorigenesis. Nonetheless, our ionomics and proteomics analysis revealed that mussels could partly alleviate the adverse effects of Cd by altering the metal contents and correlations between minerals, thereby enhancing the biosynthesis of some amino acids and activity of antioxidant enzymes. Overall, this study provides an insight into the mechanism underlying Cd toxicity in mussel gonads from a metal and protein perspective.

Parkin exerts the tumor-suppressive effect through targeting mitochondria

The role of PARKIN in Parkinson's disease is well established but its role in cancer has recently emerged. PARKIN serves as a tumor suppressor in many cancers and loses the tumor-suppressive function due to loss of heterozygosity and DNA copy number. But how PARKIN protects against cancer is poorly understood. Through the analysis of PARKIN substrates and their association with mitochondria, this viewpoint discussed that PARKIN exerts its anti-cancer activity through targeting mitochondria. Mitochondria function as a convergence point for many signaling pathways and biological processes, including apoptosis, cell cycle, mitophagy, energy metabolism, oxidative stress, calcium homeostasis, inflammation, and so forth. PARKIN participates in these processes through regulating its mitochondrial targets. Conversely, these mitochondrial substrates also influence the function of PARKIN under different cellular circumstances. We believe that future studies in this area may lead to novel therapeutic targets and strategies for cancer therapy.

Impact of the m.13513G>A Variant on the Functions of the OXPHOS System and Cell Retrograde Signaling

Mitochondria are involved in many vital functions in living cells, including the synthesis of ATP by oxidative phosphorylation (OXPHOS) and regulation of nuclear gene expression through retrograde signaling. Leigh syndrome is a heterogeneous neurological disorder resulting from an isolated complex I deficiency that causes damage to mitochondrial energy production. The pathogenic mitochondrial DNA (mtDNA) variant m.13513G>A has been associated with Leigh syndrome. The present study investigated the effects of this mtDNA variant on the OXPHOS system and cell retrograde signaling. Transmitochondrial cytoplasmic hybrid (cybrid) cell lines harboring 50% and 70% of the m.13513G>A variant were generated and tested along with wild-type (WT) cells. The functionality of the OXPHOS system was evaluated by spectrophotometric assessment of enzyme activity and high-resolution respirometry. Nuclear gene expression was investigated by RNA sequencing and droplet digital PCR. Increasing levels of heteroplasmy were associated with reduced OXPHOS system complex I, IV, and I + III activities, and high-resolution respirometry also showed a complex I defect. Profound changes in transcription levels of nuclear genes were observed in the cell lines harboring the pathogenic mtDNA variant, indicating the physiological processes associated with defective mitochondria.

The opportunities and challenges for nutritional intervention in childhood cancers

Diet dictates nutrient availability in the tumor microenvironment, thus affecting tumor metabolic activity and growth. Intrinsically, tumors develop unique metabolic features and are sensitive to environmental nutrient concentrations. Tumor-driven nutrient dependencies provide opportunities to control tumor growth by nutritional restriction or supplementation. This review summarized the existing data on nutrition and pediatric cancers after systematically searching articles up to 2023 from four databases (PubMed, Web of Science, Scopus, and Ovid MEDLINE). Epidemiological studies linked malnutrition with advanced disease stages and poor clinical outcomes in pediatric cancer patients. Experimental studies identified several nutrient dependencies (i.e., amino acids, lipids, vitamins, etc.) in major pediatric cancer types. Dietary modifications such as calorie restriction, ketogenic diet, and nutrient restriction/supplementation supported pediatric cancer treatment, but studies remain limited. Future research should expand epidemiological studies through data sharing and multi-institutional collaborations and continue to discover critical and novel nutrient dependencies to find optimal nutritional approaches for pediatric cancer patients.

GAPDH in neuroblastoma: Functions in metabolism and survival

Neuroblastoma is a pediatric cancer of neural crest cells. It develops most frequently in nerve cells around the adrenal gland, although other locations are possible. Neuroblastomas rely on glycolysis as a source of energy and metabolites, and the enzymes that catalyze glycolysis are potential therapeutic targets for neuroblastoma. Furthermore, glycolysis provides a protective function against DNA damage, and there is evidence that glycolysis inhibitors may improve outcomes from other cancer treatments. This mini-review will focus on glyceraldehyde 3-phosphate dehydrogenase (GAPDH), one of the central enzymes in glycolysis. GAPDH has a key role in metabolism, catalyzing the sixth step in glycolysis and generating NADH. GAPDH also has a surprisingly diverse number of localizations, including the nucleus, where it performs multiple functions, and the plasma membrane. One membrane-associated function of GAPDH is stimulating glucose uptake, consistent with a role for GAPDH in energy and metabolite production. The plasma membrane localization of GAPDH and its role in glucose uptake have been verified in neuroblastoma. Membrane-associated GAPDH also participates in iron uptake, although this has not been tested in neuroblastoma. Finally, GAPDH activates autophagy through a nuclear complex with Sirtuin. This review will discuss these activities and their potential role in cancer metabolism, treatment and drug resistance.

Ketogenic Diet Treatment of Defects in the Mitochondrial Malate Aspartate Shuttle and Pyruvate Carrier

The mitochondrial malate aspartate shuttle system (MAS) maintains the cytosolic NAD+/NADH redox balance, thereby sustaining cytosolic redox-dependent pathways, such as glycolysis and serine biosynthesis. Human disease has been associated with defects in four MAS-proteins (encoded by MDH1, MDH2, GOT2, SLC25A12) sharing a neurological/epileptic phenotype, as well as citrin deficiency (SLC25A13) with a complex hepatopathic-neuropsychiatric phenotype. Ketogenic diets (KD) are high-fat/low-carbohydrate diets, which decrease glycolysis thus bypassing the mentioned defects. The same holds for mitochondrial pyruvate carrier (MPC) 1 deficiency, which also presents neurological deficits. We here describe 40 (18 previously unreported) subjects with MAS-/MPC1-defects (32 neurological phenotypes, eight citrin deficiency), describe and discuss their phenotypes and genotypes (presenting 12 novel variants), and the efficacy of KD. Of 13 MAS/MPC1-individuals with a neurological phenotype treated with KD, 11 experienced benefits—mainly a striking effect against seizures. Two individuals with citrin deficiency deceased before the correct diagnosis was established, presumably due to high-carbohydrate treatment. Six citrin-deficient individuals received a carbohydrate-restricted/fat-enriched diet and showed normalisation of laboratory values/hepatopathy as well as age-adequate thriving. We conclude that patients with MAS-/MPC1-defects are amenable to dietary intervention and that early (genetic) diagnosis is key for initiation of proper treatment and can even be lifesaving.

Characterising a homozygous two-exon deletion in UQCRH: comparing human and mouse phenotypes

Mitochondrial disorders are clinically and genetically diverse, with isolated complex III (CIII) deficiency being relatively rare. Here, we describe two affected cousins, presenting with recurrent episodes of severe lactic acidosis, hyperammonaemia, hypoglycaemia and encephalopathy. Genetic investigations in both cases identified a homozygous deletion of exons 2 and 3 of UQCRH, which encodes a structural complex III (CIII) subunit. We generated a mouse model with the equivalent homozygous Uqcrh deletion (Uqcrh-/- ), which also presented with lactic acidosis and hyperammonaemia, but had a more severe, non-episodic phenotype, resulting in failure to thrive and early death. The biochemical phenotypes observed in patient and Uqcrh-/- mouse tissues were remarkably similar, displaying impaired CIII activity, decreased molecular weight of fully assembled holoenzyme and an increase of an unexpected large supercomplex (SXL ), comprising mostly of one complex I (CI) dimer and one CIII dimer. This phenotypic similarity along with lentiviral rescue experiments in patient fibroblasts verifies the pathogenicity of the shared genetic defect, demonstrating that the Uqcrh-/- mouse is a valuable model for future studies of human CIII deficiency.

A comprehensive phenotypic characterization of a whole-body Wdr45 knock-out mouse

Pathogenic variants in the WDR45 (OMIM: 300,526) gene on chromosome Xp11 are the genetic cause of a rare neurological disorder characterized by increased iron deposition in the basal ganglia. As WDR45 encodes a beta-propeller scaffold protein with a putative role in autophagy, the disease has been named Beta-Propeller Protein-Associated Neurodegeneration (BPAN). BPAN represents one of the four most common forms of Neurodegeneration with Brain Iron Accumulation (NBIA). In the current study, we generated and characterized a whole-body Wdr45 knock-out (KO) mouse model. The model, developed using TALENs, presents a 20-bp deletion in exon 2 of Wdr45. Homozygous females and hemizygous males are viable, proving that systemic depletion of Wdr45 does not impair viability and male fertility in mice. The in-depth phenotypic characterization of the mouse model revealed neuropathology signs at four months of age, neurodegeneration progressing with ageing, hearing and visual impairment, specific haematological alterations, but no brain iron accumulation. Biochemically, Wdr45 KO mice presented with decreased complex I (CI) activity in the brain, suggesting that mitochondrial dysfunction accompanies Wdr45 deficiency. Overall, the systemic Wdr45 KO described here complements the two mouse models previously reported in the literature (PMIDs: 26,000,824, 31,204,559) and represents an additional robust model to investigate the pathophysiology of BPAN and to test therapeutic strategies for the disease.

Mitochondrial DNA Haplogroups and Susceptibility to Neuroblastoma

BACKGROUND

Neuroblastoma is a childhood malignancy that arises from the developing sympathetic nervous system. Although mitochondrial dysfunctions have been implicated in the pathophysiology of neuroblastoma, the role of mitochondrial DNA (mtDNA) has not been extensively investigated.

METHODS

A total of 2404 Caucasian children diagnosed with neuroblastoma and 9310 ancestry-matched controls were recruited at the Children's Hospital of Philadelphia. The mtDNA haplogroups were identified from SNP array data of two independent cohorts. We conducted a case-control study to explore potential associations of mtDNA haplogroups with the susceptibility of neuroblastoma. The genetic effect of neuroblastoma was measured by odds ratios (ORs) of mitochondrial haplogroups. All tests were two-sided.

RESULTS

Haplogroup K was statistically significantly associated with reduced risk of neuroblastoma in the discovery cohort consisting of 1474 cases and 5699 controls (OR = 0.72, 95% confidence interval [CI] = 0.57 to 0.90; P = 4.8 × 10-3). The association was replicated in an independent cohort (OR = 0.69, 95% CI = 0.53 to 0.92; P = .01) of 930 cases and 3611 controls. Pooled analysis was performed by combining the two data sets. The association remained highly statistically significant after correction for multiple testing (OR = 0.71, 95% CI = 0.59 to 0.84, P = 1.96 × 10-4, Pcorrected = .002). Further analysis focusing on neuroblastoma subtypes indicated haplogroup K was more associated with high-risk neuroblastoma (OR = 0.57, 95% CI = 0.43 to 0.76; P = 1.46 × 10-4) than low-risk and intermediate-risk neuroblastoma.

CONCLUSIONS

Haplogroup K is an independent genetic factor associated with reduced risk of developing neuroblastoma in European descents. These findings provide new insights into the genetic basis of neuroblastoma, implicating mitochondrial DNA encoded proteins in the etiology of neuroblastoma.

Catastrophic ATP loss underlies a metabolic combination therapy tailored for MYCN-amplified neuroblastoma

MYCN-amplified neuroblastoma is a lethal subset of pediatric cancer. MYCN drives numerous effects in the cell, including metabolic changes that are critical for oncogenesis. The understanding that both compensatory pathways and intrinsic redundancy in cell systems exists implies that the use of combination therapies for effective and durable responses is necessary. Additionally, the most effective targeted therapies exploit an "Achilles' heel" and are tailored to the genetics of the cancer under study. We performed an unbiased screen on select metabolic targeted therapy combinations and correlated sensitivity with over 20 subsets of cancer. We found that MYCN-amplified neuroblastoma is hypersensitive to the combination of an inhibitor of the lactate transporter MCT1, AZD3965, and complex I of the mitochondrion, phenformin. Our data demonstrate that MCT4 is highly correlated with resistance to the combination in the screen and lowly expressed in MYCN-amplified neuroblastoma. Low MCT4 combines with high expression of the MCT2 and MCT1 chaperone CD147 in MYCN-amplified neuroblastoma, altogether conferring sensitivity to the AZD3965 and phenformin combination. The result is simultaneous disruption of glycolysis and oxidative phosphorylation, resulting in dramatic disruption of adenosine triphosphate (ATP) production, endoplasmic reticulum stress, and cell death. In mouse models of MYCN-amplified neuroblastoma, the combination was tolerable at concentrations where it shrank tumors and did not increase white-blood-cell toxicity compared to single drugs. Therefore, we demonstrate that a metabolic combination screen can identify vulnerabilities in subsets of cancer and put forth a metabolic combination therapy tailored for MYCN-amplified neuroblastoma that demonstrates efficacy and tolerability in vivo.

Mitochondrial Inhibition: a Treatment Strategy in Cancer?

PURPOSE OF REVIEW

Mitochondria have a major impact on virtually all processes linked to oncogenesis. Thus, mitochondrial metabolism inhibition has emerged as a promising anticancer strategy. In this review, we discuss the anticancer potential of mitochondrial inhibitors, with particular focus on metformin, in the context of more effective, targeted therapeutic modalities, and diagnostic strategies for cancer patients.

RECENT FINDINGS

Metformin has gained interest as an antitumor agent. However, promising results have not been translated into remarkable advances in the clinical practice. Recent findings emphasize the need of providing a metabolic context in which mitochondrial inhibitors may elicit its anticancerous effects. In addition, mitochondria are critical regulators in orchestrating immune responses. Thus, the immunomodulatory effect of mitochondrial inhibitors should also be taken into account to optimize its clinical use. Targeting mitochondrial metabolic network represents a promising therapeutic strategy in cancer. However, there is a need to define the metabolic context in which mitochondrial inhibitors are more effective, as well as how the cross-talk between many immunological functions and mitochondrial functionality may be exploited for a therapeutic benefit in cancer patients.

Immunotherapeutic Strategies for Neuroblastoma: Present, Past and Future

Neuroblastoma is the most common extracranial pediatric solid tumor with a heterogeneous clinical course, ranging from spontaneous regression to metastatic disease and death, irrespective of intensive chemotherapeutic regimen. On the basis of several parameters, children affected by neuroblastoma are stratified into low, intermediate and high risk. At present, more than 50% of high-risk patients with metastatic spread display an overall poor long-term outcome also complicated by devastating long-term morbidities. Thus, novel and more effective therapies are desperately needed to improve lifespan of high-risk patients. In this regard, adoptive cell therapy holds great promise and several clinical trials are ongoing, demonstrating safety and tolerability, with no toxicities. Starting from the immunological and clinical features of neuroblastoma, we here discuss the immunotherapeutic approaches currently adopted for high-risk patients and different innovative therapeutic strategies currently under investigation. The latter are based on the infusion of natural killer (NK) cells, as support of consolidation therapy in addition to standard treatments, or chimeric antigen receptor (CAR) T cells directed against neuroblastoma associated antigens (e.g., disialoganglioside GD2). Finally, future perspectives of adoptive cell therapies represented by γδ T lymphocyes and CAR NK cells are envisaged.

Case Report and Review of the Literature: A New and a Recurrent Variant in the VARS2 Gene Are Associated With Isolated Lethal Hypertrophic Cardiomyopathy, Hyperlactatemia, and Pulmonary Hypertension in Early Infancy

Mitochondriopathies represent a wide spectrum of miscellaneous disorders with multisystem involvement, which are caused by various genetic changes. The establishment of the diagnosis of mitochondriopathy is often challenging. Recently, several mutations of the VARS2 gene encoding the mitochondrial valyl-tRNA synthetase were associated with early onset encephalomyopathies or encephalocardiomyopathies with major clinical features such as hypotonia, developmental delay, brain MRI changes, epilepsy, hypertrophic cardiomyopathy, and plasma lactate elevation. However, the correlation between genotype and phenotype still remains unclear. In this paper we present a male Caucasian patient with a recurrent c.1168G>A (p.Ala390Thr) and a new missense biallelic variant c.2758T>C (p.Tyr920His) in the VARS2 gene which were detected by whole exome sequencing (WES). VARS2 protein was reduced in the patient's muscle. A resulting defect of oxidative phosphorylation (OXPHOS) was proven by enzymatic assay, western blotting and immunohistochemistry from a homogenate of skeletal muscle tissue. Clinical signs of our patient included hyperlactatemia, hypertrophic cardiomyopathy (HCM) and pulmonary hypertension, which led to early death at the age of 47 days without any other known accompanying signs. The finding of novel variants in the VARS2 gene expands the spectrum of known mutations and phenotype presentation. Based on our findings we recommend to consider possible mitochondriopathy and to include the analysis of the VARS2 gene in the genetic diagnostic algorithm in cases with early manifesting and rapidly progressing HCM with hyperlactatemia.

On the Origin of ATP Synthesis in Cancer

ATP is required for mammalian cells to remain viable and to perform genetically programmed functions. Maintenance of the ΔG′_ATP hydrolysis of −56 kJ/mole is the endpoint of both genetic and metabolic processes required for life. Various anomalies in mitochondrial structure and function prevent maximal ATP synthesis through OxPhos in cancer cells. Little ATP synthesis would occur through glycolysis in cancer cells that express the dimeric form of pyruvate kinase M2. Mitochondrial substrate level phosphorylation (mSLP) in the glutamine-driven glutaminolysis pathway, substantiated by the succinate-CoA ligase reaction in the TCA cycle, can partially compensate for reduced ATP synthesis through both OxPhos and glycolysis. A protracted insufficiency of OxPhos coupled with elevated glycolysis and an auxiliary, fully operational mSLP, would cause a cell to enter its default state of unbridled proliferation with consequent dedifferentiation and apoptotic resistance, i.e., cancer. The simultaneous restriction of glucose and glutamine offers a therapeutic strategy for managing cancer.

Metabolic reprogramming related to whole-chromosome instability in models for Hürthle cell carcinoma

Hürthle cell carcinoma (HCC) is a recurrent subtype of non-medullary thyroid cancer. HCC is characterized by profound whole-chromosome instability (w-CIN), resulting in a near-homozygous genome (NHG), a phenomenon recently attributed to reactive oxygen species (ROS) generated during mitosis by malfunctioning mitochondria. We studied shared metabolic traits during standard and glucose-depleted cell culture in thyroid cancer cell lines (TCCLs), with or without a NHG, using quantitative analysis of extra and intracellular metabolites and ROS production following inhibition of complex III with antimycin A. We found that the XTC.UC1 and FTC-236 cell lines (both NHG) are functionally impaired in complex I and produce significantly more superoxide radicals than SW579 and BHP 2–7 (non-NHG) after challenge with antimycin A. FTC-236 showed the lowest levels of glutathione and SOD2. XTC.UC1 and FTC-236 both exhibited reduced glycolytic activity and utilization of alternative sources to meet energy demands. Both cell lines also shared low levels of α-ketoglutarate and high levels of creatine, phosphocreatine, uridine diphosphate-N-acetylglucosamine, pyruvate and acetylcarnitine. Furthermore, the metabolism of XTC.UC1 was skewed towards the de novo synthesis of aspartate, an effect that persisted even in glucose-free media, pointing to reductive carboxylation. Our data suggests that metabolic reprogramming and a subtle balance between ROS generation and scavenging/conversion of intermediates may be involved in ROS-induced w-CIN in HCC and possibly also in rare cases of follicular thyroid cancer showing a NHG.

From old to new - Repurposing drugs to target mitochondrial energy metabolism in cancer

Although we have entered the era of personalized medicine and tailored therapies, drugs that target a large variety of cancers regardless of individual patient differences would be a major advance nonetheless. This review article summarizes current concepts and therapeutic opportunities in the area of targeting aerobic mitochondrial energy metabolism in cancer. Old drugs previously used for diseases other than cancer, such as antibiotics and antidiabetics, have the potential to inhibit the growth of various tumor entities. Many drugs are reported to influence mitochondrial metabolism. However, here we consider only those drugs which predominantly inhibit oxidative phosphorylation.

Targeting metabolic dependencies in pediatric cancer

PURPOSE OF REVIEW

In an attempt to identify potential new therapeutic targets, efforts to describe the metabolic features unique to cancer cells are increasingly being reported. Although current standard of care regimens for several pediatric malignancies incorporate agents that target tumor metabolism, these drugs have been part of the therapeutic landscape for decades. More recent research has focused on the identification and targeting of new metabolic vulnerabilities in pediatric cancers. The purpose of this review is to describe the most recent translational findings in the metabolic targeting of pediatric malignancies.

RECENT FINDINGS

Across multiple pediatric cancer types, dependencies on a number of key metabolic pathways have emerged through study of patient tissue samples and preclinical modeling. Among the potentially targetable vulnerabilities are glucose metabolism via glycolysis, oxidative phosphorylation, amino acid and polyamine metabolism, and NAD metabolism. Although few agents have yet to move forward into clinical trials for pediatric cancer patients, the robust and promising preclinical data that have been generated suggest that future clinical trials should rationally test metabolically targeted agents for relevant disease populations.

SUMMARY

Recent advances in our understanding of the metabolic dependencies of pediatric cancers represent a source of potential new therapeutic opportunities for these diseases.

Mutations in NDUFS1 Cause Metabolic Reprogramming and Disruption of the Electron Transfer

Complex I (CI) is the first enzyme of the mitochondrial respiratory chain and couples the electron transfer with proton pumping. Mutations in genes encoding CI subunits can frequently cause inborn metabolic errors. We applied proteome and metabolome profiling of patient-derived cells harboring pathogenic mutations in two distinct CI genes to elucidate underlying pathomechanisms on the molecular level. Our results indicated that the electron transfer within CI was interrupted in both patients by different mechanisms. We showed that the biallelic mutations in NDUFS1 led to a decreased stability of the entire N-module of CI and disrupted the electron transfer between two iron–sulfur clusters. Strikingly interesting and in contrast to the proteome, metabolome profiling illustrated that the pattern of dysregulated metabolites was almost identical in both patients, such as the inhibitory feedback on the TCA cycle and altered glutathione levels, indicative for reactive oxygen species (ROS) stress. Our findings deciphered pathological mechanisms of CI deficiency to better understand inborn metabolic errors.

Low VDAC1 Expression Is Associated with an Aggressive Phenotype and Reduced Overall Patient Survival in Cholangiocellular Carcinoma

Cancer cells frequently exhibit dysfunctional oxidative phosphorylation (OXPHOS) and a concomitant increase in glycolytic flux. We investigated the expression of OXPHOS complex subunits and mitochondrial mass in 34 human cholangiocellular carcinomas (CCCs) and adjacent normal tissue by using tissue microarrays. In the tumor periphery, all OXPHOS complexes were reduced except complex I. In addition, significantly lower levels of complex IV were found at the tumor center (p < 0.0001). Mitochondrial mass, as indicated by VDAC1 expression, was significantly increased in CCCs compared to corresponding normal tissue (p < 0.0001). VDAC1 levels were inversely correlated with UICC (Union Internationale Contre le Cancer) cancer stage classification (p = 0.0065). Furthermore, significantly lower VDAC1 was present in patients with lymph node involvement (p = 0.02). Consistent with this, patients whose carcinomas expressed VDAC1 at low to moderate levels had significantly reduced survival compared to high expressors (p < 0.05). Therefore, low mitochondrial mass is associated with more aggressive CCC. These metabolic features are indicative of a Warburg phenotype in CCCs. This metabolic signature has potential therapeutic implications because tumors with low mitochondrial function may be targeted by metabolic therapies such as a high-fat, low-carbohydrate ketogenic diet.

Reduced Levels of ATP Synthase Subunit ATP5F1A Correlate with Earlier-Onset Prostate Cancer

Switching of cellular energy production from oxidative phosphorylation (OXPHOS) to aerobic glycolysis occurs in many types of tumors. However, the significance of energy metabolism for the development of prostate carcinoma is poorly understood. We investigated the expression of OXPHOS complexes in 94 human prostate carcinomas and paired benign tissue using immunohistochemistry. Overall mitochondrial mass was upregulated in carcinomas compared to benign prostate tissue in all Gleason grades. A significant direct correlation between the expression of OXPHOS complexes I, II, and V and the Gleason score was observed. However, 17% of prostate carcinomas and 18% of benign prostate tissues showed isolated or combined deficiency of OXPHOS complexes (one deficiency in 12% of the tumors, combined deficiencies in 5%). Complex I was absent in 9% of the samples, with only parts of the tumor affected. ATP5F1A, a complex V protein, was the most frequently affected subunit, in 10% of tumors and 11% of benign prostate tissues (but not both tissues in any single patient). A possible role of complex V in prostate cancer development is suggested by the significant positive correlation of ATP5F1A levels with earlier-onset prostate cancer (age at diagnosis and at prostatectomy) and free PSA percentage. The relatively high percentage (17%) of prostate carcinomas with regional foci of partial OXPHOS complex deficiencies could have important therapeutic implications.

A comprehensive characterization of rare mitochondrial DNA variants in neuroblastoma

Background

Neuroblastoma, a tumor of the developing sympathetic nervous system, is a common childhood neoplasm that is often lethal. Mitochondrial DNA (mtDNA) mutations have been found in most tumors including neuroblastoma. We extracted mtDNA data from a cohort of neuroblastoma samples that had undergone Whole Exome Sequencing (WES) and also used snap-frozen samples in which mtDNA was entirely sequenced by Sanger technology. We next undertook the challenge of determining those mutations that are relevant to, or arisen during tumor development. The bioinformatics pipeline used to extract mitochondrial variants from matched tumor/blood samples was enriched by a set of filters inclusive of heteroplasmic fraction, nucleotide variability, and in silico prediction of pathogenicity.

Results

Our in silico multistep workflow applied both on WES and Sanger-sequenced neuroblastoma samples, allowed us to identify a limited burden of somatic and germline mitochondrial mutations with a potential pathogenic impact.

Conclusions

The few singleton germline and somatic mitochondrial mutations emerged, according to our in silico analysis, do not appear to impact on the development of neuroblastoma. Our findings are consistent with the hypothesis that most mitochondrial somatic mutations can be considered as ‘passengers’ and consequently have no discernible effect in this type of cancer.

Mitochondrial translation requires folate-dependent tRNA methylation

Folates enable the activation and transfer of one-carbon units for biosynthesis of purines, thymidine and methionine^1–3. Antifolates are important immunosuppressive⁴ and anticancer agents⁵. In proliferating lymphocytes⁶ and human cancers^7,8, folate enzymes localizing to the mitochondria are particularly strongly upregulated. This in part reflects the need for mitochondria to generate one-carbon units and export them to the cytosol for anabolic metabolism^2,9. The full range of uses of folate-bound one-carbon units in the mitochondrial compartment itself, however, has not been thoroughly explored. Here we show that loss of catalytic activity of the mitochondrial folate enzyme serine hydroxymethyltransferase 2 (SHMT2), but not other folate enzymes, leads to defective oxidative phosphorylation due to impaired mitochondrial translation. We find that SHMT2, presumably by generating mitochondrial 5,10-methylenetetrahydrofolate, provides methyl donors for producing the taurinomethyluridine base at the wobble position of select mitochondrial tRNAs. Mitochondrial ribosome profiling reveals that SHMT2 knockout cells, due to lack of this modified base, suffer from defective translation with preferential mitochondrial ribosome stalling at certain lysine (AAG) and leucine (UUG) codons. This results in impaired respiratory chain enzyme expression. Stalling at these specific codons also occurs in certain mitochondrial inborn errors of metabolism. Disrupting whole-cell folate metabolism, by folate deficiency or antifolate therapy, also impairs the respiratory chain. In summary, mammalian mitochondria use folate-bound one-carbon units to methylate tRNA, and this modification is required for respiratory chain translation and thus oxidative phosphorylation.

Melanoma tumors exhibit a variable but distinct metabolic signature

The Warburg theory of cancer postulates that an important driver of tumorigenesis is insufficient respiration due to mitochondrial defects, and concomitant enhancement of lactate production due to increased aerobic glycolysis. We analysed 48 melanoma samples by immunohistochemistry and found that 38% of melanomas are characterized by areas of isolated or combined deficiencies of complexes of the oxidative phosphorylation (OXPHOS) system, whereby the incidence of OXPHOS-deficient areas is associated with an increased Breslow index; 62% of melanomas showed high expression of all OXPHOS complexes. Expression of carbonic anhydrase IX was low, indicating that melanomas generally are well-oxygenated. Expression of HIF-1α and MCT4 was high, which might be a consequence of increased lactate dehydrogenase A levels in melanomas. Our data indicate that there are two types of melanomas: one that features a classic Warburg effect, whereas the other one, despite being glycolytic, maintains a high level of OXPHOS complexes.

Combination of metronomic cyclophosphamide and dietary intervention inhibits neuroblastoma growth in a CD1-nu mouse model

BACKGROUND

MYCN-amplification in high-grade Neuroblastoma (NB) tumors correlates with increased vascularization and therapy resistance. This study combines an anti-angiogenic approach with targeting NB metabolism for treatment.

METHODS AND RESULTS

Metronomic cyclophosphamide (MCP) monotherapy significantly inhibited NB growth and prolonged host survival. Growth inhibition was more pronounced in MYCN-amplified xenografts. Immunohistochemical evaluation of this subtype showed significant decrease in blood vessel density and intratumoral hemorrhage accompanied by blood vessel maturation and perivascular fibrosis. Up-regulation of VEGFA was not sufficient to compensate for the effects of the MCP regimen. Reduced Bcl-2 expression and increased caspase-3 cleavage were evident. In contrast non MYCN-amplified tumors developed resistance, which was accompanied by Bcl-2-up-regulation. Combining MCP with a ketogenic diet and/or calorie-restriction significantly enhanced the anti-tumor effect. Calorie-restricted ketogenic diet in combination with MCP resulted in tumor regression in all cases.

CONCLUSIONS

Our data show efficacy of combining an anti-angiogenic cyclophosphamide dosing regimen with dietary intervention in a preclinical NB model. These findings might open a new front in NB treatment.

Biallelic C1QBP Mutations Cause Severe Neonatal-, Childhood-, or Later-Onset Cardiomyopathy Associated with Combined Respiratory-Chain Deficiencies

Complement component 1 Q subcomponent-binding protein (C1QBP; also known as p32) is a multi-compartmental protein whose precise function remains unknown. It is an evolutionary conserved multifunctional protein localized primarily in the mitochondrial matrix and has roles in inflammation and infection processes, mitochondrial ribosome biogenesis, and regulation of apoptosis and nuclear transcription. It has an N-terminal mitochondrial targeting peptide that is proteolytically processed after import into the mitochondrial matrix, where it forms a homotrimeric complex organized in a doughnut-shaped structure. Although C1QBP has been reported to exert pleiotropic effects on many cellular processes, we report here four individuals from unrelated families where biallelic mutations in C1QBP cause a defect in mitochondrial energy metabolism. Infants presented with cardiomyopathy accompanied by multisystemic involvement (liver, kidney, and brain), and children and adults presented with myopathy and progressive external ophthalmoplegia. Multiple mitochondrial respiratory-chain defects, associated with the accumulation of multiple deletions of mitochondrial DNA in the later-onset myopathic cases, were identified in all affected individuals. Steady-state C1QBP levels were decreased in all individuals' samples, leading to combined respiratory-chain enzyme deficiency of complexes I, III, and IV. C1qbp-/- mouse embryonic fibroblasts (MEFs) resembled the human disease phenotype by showing multiple defects in oxidative phosphorylation (OXPHOS). Complementation with wild-type, but not mutagenized, C1qbp restored OXPHOS protein levels and mitochondrial enzyme activities in C1qbp-/- MEFs. C1QBP deficiency represents an important mitochondrial disorder associated with a clinical spectrum ranging from infantile lactic acidosis to childhood (cardio)myopathy and late-onset progressive external ophthalmoplegia.

Transcriptome analysis of human colorectal cancer biopsies reveals extensive expression correlations among genes related to cell proliferation, lipid metabolism, immune response and collagen catabolism

Precise characterization of biological processes critical to proliferation and metastasis of colorectal cancer should facilitate the development of diagnostic and prognostic biomarkers as well as novel treatments. Using mRNA-Seq, we examined the protein coding messenger RNA (mRNA) expression profiles across different histologically defined stages of primary colon cancers and compared them to their patient matched normal tissue controls. In comparing 79 colorectal cancers to their matched normal mucosa, tumors were distinguished from normal non-malignant tissues not only in the upregulation of biological processes pertaining to cell proliferation, inflammation, and tissue remodeling, but even more strikingly, in downregulated biological processes including fatty acid beta oxidization for ATP production and epithelial cell differentiation and function. A network analysis of deregulated genes revealed newly described cancer networks and putative hub genes.

Taken together, our findings suggest that, within an inflammatory microenvironment, invasive, dedifferentiated and rapidly dividing tumor cells divert the oxidation of fatty acids and lipids from energy production into lipid components of cell membranes and organelles to support tumor proliferation. A gene co-expression network analysis provides a clear and broad picture of biological pathways in tumors that may significantly enhance or supplant current histopathologic studies.

A ketogenic diet supplemented with medium-chain triglycerides enhances the anti-tumor and anti-angiogenic efficacy of chemotherapy on neuroblastoma xenografts in a CD1-nu mouse model

Neuroblastoma (NB) is a pediatric malignancy characterized by a marked reduction in aerobic energy metabolism. Recent preclinical data indicate that targeting this metabolic phenotype by a ketogenic diet (KD), especially in combination with calorie restriction, slows tumor growth and enhances metronomic cyclophosphamide (CP) therapy of NB xenografts. Because calorie restriction would be contraindicated in most cancer patients, the aim of the present study was to optimize the KD such that the tumors are sensitized to CP without the need of calorie restriction. In a NB xenograft model, metronomic CP was combined with KDs of different triglyceride compositions and fed to CD1-nu mice ad libitum. Metronomic CP in combination with a KD containing 8-carbon medium-chain triglycerides exerted a robust anti-tumor effect, suppressing growth and causing a significant reduction of tumor blood-vessel density and intratumoral hemorrhage, accompanied by activation of AMP-activated protein kinase in NB cells. Furthermore, the KDs caused a significant reduction in the serum levels of essential amino acids, but increased those of serine, glutamine and glycine. Our data suggest that targeting energy metabolism by a modified KD may be considered as part of a multimodal treatment regimen to improve the efficacy of classic anti-NB therapy.

Effects of alpha-melanocyte-stimulating hormone on mitochondrial energy metabolism in rats of different age-groups

Hypothalamic alpha-melanocyte-stimulating hormone (α-MSH) is a key catabolic mediator of energy homeostasis. Its anorexigenic and hypermetabolic effects show characteristic age-related alterations that may be part of the mechanism of middle-aged obesity and geriatric anorexia/cachexia seen in humans and other mammals. We aimed to investigate the role of α-MSH in mitochondrial energy metabolism during the course of aging in a rodent model. To determine the role of α-MSH in mitochondrial energy metabolism in muscle, we administered intracerebroventricular (ICV) infusions of α-MSH for 7-days to different age-groups of male Wistar rats. The activities of oxidative phosphorylation complexes I to V and citrate synthase were determined and compared to those of age-matched controls. We also quantified mitochondrial DNA (mtDNA) copy number and measured the expression of the master regulators of mitochondrial biogenesis, peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and peroxisome proliferator-activated receptor gamma (PPARγ). The peptide reduced weight gain in juvenile rats to one fifth of that of controls and increased the weight loss in older animals by about five fold. Mitochondrial DNA copy number inversely correlated with changes in body weight in controls, but not in α-MSH-treated animals. The strong increase in body weight in young rats was associated with a low mtDNA copy number and high PPARγ mRNA levels in controls. Expression of PGC-1α and PPARγ declined with age, whereas OXPHOS and citrate synthase enzyme activities were unchanged. In contrast, α-MSH treatment suppressed OXPHOS enzyme and citrate synthase activity. In conclusion, our results showed age-related differences in the metabolic effects of α-MSH. In addition, administration of α-MSH suppressed citrate synthase and OXPHOS activities independent of age. These findings suggest that α-MSH exposure may inhibit mitochondrial biogenesis.

Combined Respiratory Chain Deficiency and UQCC2 Mutations in Neonatal Encephalomyopathy: Defective Supercomplex Assembly in Complex III Deficiencies

Vertebrate respiratory chain complex III consists of eleven subunits. Mutations in five subunits either mitochondrial (MT-CYB) or nuclear (CYC1, UQCRC2, UQCRB, and UQCRQ) encoded have been reported. Defects in five further factors for assembly (TTC19, UQCC2, and UQCC3) or iron-sulphur cluster loading (BCS1L and LYRM7) cause complex III deficiency. Here, we report a second patient with UQCC2 deficiency. This girl was born prematurely; pregnancy was complicated by intrauterine growth retardation and oligohydramnios. She presented with respiratory distress syndrome, developed epileptic seizures progressing to status epilepticus, and died at day 33. She had profound lactic acidosis and elevated urinary pyruvate. Exome sequencing revealed two homozygous missense variants in UQCC2, leading to a severe reduction of UQCC2 protein. Deficiency of complexes I and III was found enzymatically and on the protein level. A review of the literature on genetically distinct complex III defects revealed that, except TTC19 deficiency, the biochemical pattern was very often a combined respiratory chain deficiency. Besides complex III, typically, complex I was decreased, in some cases complex IV. In accordance with previous observations, the presence of assembled complex III is required for the stability or assembly of complexes I and IV, which might be related to respirasome/supercomplex formation.

The ketogenic diet is not feasible as a therapy in a CD-1 nu/nu mouse model of renal cell carcinoma with features of Stauffer's syndrome

The ketogenic diet (KD), a high-fat low-carbohydrate diet, has shown some efficacy in the treatment of certain types of tumors such as brain tumors and neuroblastoma. These tumors are characterized by the Warburg effect. Because renal cell carcinoma (RCC) presents similar energetic features as neuroblastoma, KD might also be effective in the treatment of RCC. To test this, we established xenografts with RCC 786-O cells in CD-1 nu/nu mice and then randomized them to a control diet or to KDs with different triglyceride contents. Although the KDs tended to reduce tumor growth, mouse survival was dramatically reduced due to massive weight loss. A possible explanation comes from observations of human RCC patients, who often experience secondary non-metastatic hepatic dysfunction due to secretion of high levels of inflammatory cytokines by the RCCs. Measurement of the mRNA levels of tumor necrosis factor alpha (TNFα) and interleukin-6 revealed high expression in the RCC xenografts compared to the original 786-O cells. The expression of TNFα, interleukin-6 and C-reactive protein were all increased in the livers of tumor-bearing mice, and KD significantly boosted their expression. KDs did not cause weight loss or liver inflammation in healthy mice, suggesting that KDs are per se safe, but might be contraindicated in the treatment of RCC patients presenting with Stauffer's syndrome, because they potentially worsen the associated hepatic dysfunction.

Oxidative Phosphorylation System in Gastric Carcinomas and Gastritis

Switching of cellular energy production from oxidative phosphorylation (OXPHOS) by mitochondria to aerobic glycolysis occurs in many types of tumors. However, the significance of this switching for the development of gastric carcinoma and what connection it may have to Helicobacter pylori infection of the gut, a primary cause of gastric cancer, are poorly understood. Therefore, we investigated the expression of OXPHOS complexes in two types of human gastric carcinomas ("intestinal" and "diffuse"), bacterial gastritis with and without metaplasia, and chemically induced gastritis by using immunohistochemistry. Furthermore, we analyzed the effect of HP infection on several key mitochondrial proteins. Complex I expression was significantly reduced in intestinal type (but not diffuse) gastric carcinomas compared to adjacent control tissue, and the reduction was independent of HP infection. Significantly, higher complex I and complex II expression was present in large tumors. Furthermore, higher complex II and complex III protein levels were also obvious in grade 3 versus grade 2. No differences of OXPHOS complexes and markers of mitochondrial biogenesis were found between bacterially caused and chemically induced gastritis. Thus, intestinal gastric carcinomas, but not precancerous stages, are frequently characterized by loss of complex I, and this pathophysiology occurs independently of HP infection.

Selective elimination of neuroblastoma cells by synergistic effect of Akt kinase inhibitor and tetrathiomolybdate

Neuroblastoma is the most common extracranial solid tumour of infancy. Pathological activation of glucose consumption, glycolysis and glycolysis‐activating Akt kinase occur frequently in neuroblastoma cells, and these changes correlate with poor prognosis of patients. Therefore, several inhibitors of glucose utilization and the Akt kinase activity are in preclinical trials as potential anti‐cancer drugs. However, metabolic plasticity of cancer cells might undermine efficacy of this approach. In this work, we identified oxidative phosphorylation as compensatory mechanism preserving viability of neuroblastoma cells with inhibited glucose uptake/Akt kinase. It was oxidative phosphorylation that maintained intracellular level of ATP and proliferative capacity of these cells. The oxidative phosphorylation inhibitors (rotenone, tetrathiomolybdate) synergized with inhibitor of the Akt kinase/glucose uptake in down‐regulation of both viability of neuroblastoma cells and clonogenic potential of cells forming neuroblastoma spheroids. Interestingly, tetrathiomolybdate acted as highly specific inhibitor of oxygen consumption and activator of lactate production in neuroblastoma cells, but not in normal fibroblasts and neuronal cells. Moreover, the reducing effect of tetrathiomolybdate on cell viability and the level of ATP in the cells with inhibited Akt kinase/glucose uptake was also selective for neuroblastoma cells. Therefore, efficient elimination of neuroblastoma cells requires inhibition of both glucose uptake/Akt kinase and oxidative phosphorylation activities. The use of tetrathiomolybdate as a mitochondrial inhibitor contributes to selectivity of this combined treatment, preferentially targeting neuroblastoma cells.

Deficiency of respiratory chain complex I in Hashimoto thyroiditis

Oncocytic cells (OCs) are characterized by an accumulation of mitochondria and their occurrence in the thyroid gland of patients with Hashimoto thyroiditis (HT) is well known. However, their properties and functional relevance are poorly understood. We investigated OC lesions (n=212) in the thyroid of 12 HT patients. Loss of complex I protein was observed in oncocytic lesions of each of the patients. In addition to isolated complex I deficiency, 25% of oncocytic lesions showed combined deficiency of complex I and IV. Thus, we demonstrate for the first time a defect of respiratory chain complex I in OCs of HT patients.

Clinical, morphological, biochemical, imaging and outcome parameters in 21 individuals with mitochondrial maintenance defect related to FBXL4 mutations

FBXL4 deficiency is a recently described disorder of mitochondrial maintenance associated with a loss of mitochondrial DNA in cells. To date, the genetic diagnosis of FBXL4 deficiency has been established in 28 individuals. This paper retrospectively reviews proxy-reported clinical and biochemical findings and evaluates brain imaging, morphological and genetic data in 21 of those patients. Neonatal/early-onset severe lactic acidosis, muscular hypotonia, feeding problems and failure to thrive is the characteristic pattern at first presentation. Facial dysmorphic features are present in 67% of cases. Seven children died (mean age 37 months); 11 children were alive (mean age at follow-up 46 months), three children were lost to follow-up. All survivors developed severe psychomotor retardation. Brain imaging was non-specific in neonates but a later-onset, rapidly progressive brain atrophy was noted. Elevated blood lactate and metabolic acidosis were observed in all individuals; creatine kinase was elevated in 45% of measurements. Diagnostic workup in patient tissues and cells revealed a severe combined respiratory chain defect with a general decrease of enzymes associated with mitochondrial energy metabolism and a relative depletion of mitochondrial DNA content. Mutations were detected throughout the FBXL4 gene albeit with no clear delineation of a genotype-phenotype correlation. Treatment with "mitochondrial medications" did not prove effective. In conclusion, a clinical pattern of early-onset encephalopathy, persistent lactic acidosis, profound muscular hypotonia and typical facial dysmorphism should prompt initiation of molecular genetic analysis of FBXL4. Establishment of the diagnosis permits genetic counselling, prevents patients undergoing unhelpful diagnostic procedures and allows for accurate prognosis.

Alterations of oxidative phosphorylation in meningiomas and peripheral nerve sheath tumors

BACKGROUND

Changes in the mode of aerobic energy production are observed in many solid tumors, though the kinds of changes differ among tumor types. We investigated mitochondrial energy metabolism in meningiomas and peripheral nerve sheath tumors, taking into consideration the histologic heterogeneity of these tumors.

METHODS

Oxidative phosphorylation (OXPHOS) complexes and porin (a marker for mitochondrial mass) were analyzed by immunohistochemical staining of meningiomas (n = 76) and peripheral nerve sheath tumors (schwannomas: n = 10; neurofibromas: n = 4). The enzymatic activities of OXPHOS complexes and citrate synthase were determined by spectrophotometric measurement. Western blot analysis of OXPHOS complexes, porin, and mitochondrial transcription factor A was performed. Furthermore, mitochondrial DNA copy number was determined.

RESULTS

The tumors differed with regard to mitochondrial energy metabolism. Low levels of a subset of OXPHOS complexes were frequently observed in World Health Organization grade I meningiomas (percent of cases with a reduction; complex I: 63%; complex II: 67%; complex IV: 56%) and schwannomas (complex III: 40%, complex IV: 100%), whereas in neurofibromas a general reduction of all complexes was observed. In contrast, expression of complexes III and V was similar to that in normal brain tissue in the majority of tumors. Mitochondrial mass was comparable or higher in all tumors compared with normal brain tissue, whereas mitochondrial DNA copy number was reduced.

CONCLUSIONS

The reduction of OXPHOS complexes in meningiomas and peripheral nerve sheath tumors has potential therapeutic implications, since respiratory chain-deficient tumor cells might be selectively starved by inhibitors of glycolysis or by ketogenic diet.

Inhibition of Neuroblastoma Tumor Growth by Ketogenic Diet and/or Calorie Restriction in a CD1-Nu Mouse Model

INTRODUCTION

Neuroblastoma is a malignant pediatric cancer derived from neural crest cells. It is characterized by a generalized reduction of mitochondrial oxidative phosphorylation. The goal of the present study was to investigate the effects of calorie restriction and ketogenic diet on neuroblastoma tumor growth and monitor potential adaptive mechanisms of the cancer's oxidative phosphorylation system.

METHODS

Xenografts were established in CD-1 nude mice by subcutaneous injection of two neuroblastoma cell lines having distinct genetic characteristics and therapeutic sensitivity [SH-SY5Y and SK-N-BE(2)]. Mice were randomized to four treatment groups receiving standard diet, calorie-restricted standard diet, long chain fatty acid based ketogenic diet or calorie-restricted ketogenic diet. Tumor growth, survival, metabolic parameters and weight of the mice were monitored. Cancer tissue was evaluated for diet-induced changes of proliferation indices and multiple oxidative phosphorylation system parameters (respiratory chain enzyme activities, western blot analysis, immunohistochemistry and mitochondrial DNA content).

RESULTS

Ketogenic diet and/or calorie restriction significantly reduced tumor growth and prolonged survival in the xenograft model. Neuroblastoma growth reduction correlated with decreased blood glucose concentrations and was characterized by a significant decrease in Ki-67 and phospho-histone H3 levels in the diet groups with low tumor growth. As in human tumor tissue, neuroblastoma xenografts showed distinctly low mitochondrial complex II activity in combination with a generalized low level of mitochondrial oxidative phosphorylation, validating the tumor model. Neuroblastoma showed no ability to adapt its mitochondrial oxidative phosphorylation activity to the change in nutrient supply induced by dietary intervention.

CONCLUSIONS

Our data suggest that targeting the metabolic characteristics of neuroblastoma could open a new front in supporting standard therapy regimens. Therefore, we propose that a ketogenic diet and/or calorie restriction should be further evaluated as a possible adjuvant therapy for patients undergoing treatment for neuroblastoma.

The single nucleotide polymorphism Gly482Ser in the PGC-1α gene impairs exercise-induced slow-twitch muscle fibre transformation in humans

PGC-1α (peroxisome proliferator-activated receptor γ co-activator 1α) is an important regulator of mitochondrial biogenesis and a master regulator of enzymes involved in oxidative phosphorylation. Recent evidence demonstrated that the Gly482Ser single nucleotide polymorphism (SNP) in the PGC-1α gene affects insulin sensitivity, blood lipid metabolism and binding to myocyte enhancer factor 2 (MEF2). Individuals carrying this SNP were shown to have a reduced cardiorespiratory fitness and a higher risk to develop type 2 diabetes. Here, we investigated the responses of untrained men with the Gly482Ser SNP to a 10 week programme of endurance training (cycling, 3 x 60 min/week, heart rate at 70-90% VO_2peak). Quantitative data from analysis of biopsies from vastus lateralis muscle revealed that the SNP group, in contrast to the control group, lacked a training-induced increase in content of slow contracting oxidative fibres. Capillary supply, mitochondrial density, mitochondrial enzyme activities and intramyocellular lipid content increased similarly in both groups. These results indicate that the impaired binding of MEF2 to PGC-1α in humans with this SNP impedes exercise-induced fast-to-slow muscle fibre transformation.

Clinical, biochemical, and genetic spectrum of seven patients with NFU1 deficiency

Disorders of the mitochondrial energy metabolism are clinically and genetically heterogeneous. An increasingly recognized subgroup is caused by defective mitochondrial iron–sulfur (Fe–S) cluster biosynthesis, with defects in 13 genes being linked to human disease to date. Mutations in three of them, NFU1, BOLA3, and IBA57, affect the assembly of mitochondrial [4Fe–4S] proteins leading to an impairment of diverse mitochondrial metabolic pathways and ATP production. Patients with defects in these three genes present with lactic acidosis, hyperglycinemia, and reduced activities of respiratory chain complexes I and II, the four lipoic acid-dependent 2-oxoacid dehydrogenases and the glycine cleavage system (GCS). To date, five different NFU1 pathogenic variants have been reported in 15 patients from 12 families. We report on seven new patients from five families carrying compound heterozygous or homozygous pathogenic NFU1 mutations identified by candidate gene screening and exome sequencing. Six out of eight different disease alleles were novel and functional studies were performed to support the pathogenicity of five of them. Characteristic clinical features included fatal infantile encephalopathy and pulmonary hypertension leading to death within the first 6 months of life in six out of seven patients. Laboratory investigations revealed combined defects of pyruvate dehydrogenase complex (five out of five) and respiratory chain complexes I and II+III (four out of five) in skeletal muscle and/or cultured skin fibroblasts as well as increased lactate (five out of six) and glycine concentration (seven out of seven). Our study contributes to a better definition of the phenotypic spectrum associated with NFU1 mutations and to the diagnostic workup of future patients.

Mitochondria: The ketogenic diet--A metabolism-based therapy

Mitochondria are the energy-producing organelles of the cell, generating ATP via oxidative phosphorylation mainly by using pyruvate derived from glycolytic processing of glucose. Ketone bodies generated by fatty acid oxidation can serve as alternative metabolites for aerobic energy production. The ketogenic diet, which is high in fat and low in carbohydrates, mimics the metabolic state of starvation, forcing the body to utilize fat as its primary source of energy. The ketogenic diet is used therapeutically for pharmacoresistant epilepsy and for "rare diseases" of glucose metabolism (glucose transporter type 1 and pyruvate dehydrogenase deficiency). As metabolic reprogramming from oxidative phosphorylation toward increased glycolysis is a hallmark of cancer cells; there is increasing evidence that the ketogenic diet may also be beneficial as an adjuvant cancer therapy by potentiating the antitumor effect of chemotherapy and radiation treatment. This article is part of a Directed Issue entitled: Energy Metabolism Disorders and Therapies.

Energy metabolism in neuroblastoma and Wilms tumor

To support high proliferation, the majority of cancer cells undergo fundamental metabolic changes such as increasing their glucose uptake and shifting to glycolysis for ATP production at the expense of far more efficient mitochondrial energy production by oxidative phosphorylation (OXPHOS), which at first glance is a paradox. This phenomenon is known as the Warburg effect. However, enhanced glycolysis is necessary to provide building blocks for anabolic growth. Apart from the generation of ATP, intermediates of glycolysis serve as precursors for a variety of biosynthetic pathways essential for cell proliferation. In the last 10-15 years the field of tumor metabolism has experienced an enormous boom in interest. It is now well established that tumor suppressor genes and oncogenes often play a central role in the regulation of cellular metabolism. Therefore, they significantly contribute to the manifestation of the Warburg effect. While much attention has focused on adult solid tumors, so far there has been comparatively little effort directed at elucidation of the mechanism responsible for the Warburg effect in childhood cancers. In this review we focus on metabolic pathways in neuroblastoma (NB) and Wilms tumor (WT), the two most frequent solid tumors in children. Both tumor types show alterations of the OXPHOS system and glycolytic features. Chromosomal alterations and activation of oncogenes like MYC or inactivation of tumor suppressor genes like TP53 can in part explain the changes of energy metabolism in these cancers. The strict dependence of cancer cells on glucose metabolism is a fairly common feature among otherwise biologically diverse types of cancer. Therefore, inhibition of glycolysis or starvation of cancer cells through glucose deprivation via a high-fat low-carbohydrate diet may be a promising avenue for future adjuvant therapeutic strategies.

Mitochondrial dysfunction: a neglected component of skin diseases

Aberrant mitochondrial structure and function influence tissue homeostasis and thereby contribute to multiple human disorders and ageing. Ten per cent of patients with primary mitochondrial disorders present skin manifestations that can be categorized into hair abnormalities, rashes, pigmentation abnormalities and acrocyanosis. Less attention has been paid to the fact that several disorders of the skin are linked to alterations of mitochondrial energy metabolism. This review article summarizes the contribution of mitochondrial pathology to both common and rare skin diseases. We explore the intriguing observation that a wide array of skin disorders presents with primary or secondary mitochondrial pathology and that a variety of molecular defects can cause dysfunctional mitochondria. Among them are mutations in mitochondrial- and nuclear DNA-encoded subunits and assembly factors of oxidative phosphorylation (OXPHOS) complexes; mutations in intermediate filament proteins involved in linking, moving and shaping of mitochondria; and disorders of mitochondrial DNA metabolism, fatty acid metabolism and heme synthesis. Thus, we assume that mitochondrial involvement is the rule rather than the exception in skin diseases. We conclude the article by discussing how improving mitochondrial function can be beneficial for aged skin and can be used as an adjunct therapy for certain skin disorders. Consideration of mitochondrial energy metabolism in the skin creates a new perspective for both dermatologists and experts in metabolic disease.

The LYR factors SDHAF1 and SDHAF3 mediate maturation of the iron-sulfur subunit of succinate dehydrogenase

Disorders arising from impaired assembly of succinate dehydrogenase (SDH) result in a myriad of pathologies, consistent with its unique role in linking the citric acid cycle and electron transport chain. In spite of this critical function, however, only a few factors are known to be required for SDH assembly and function. We show here that two factors, Sdh6 (SDHAF1) and Sdh7 (SDHAF3), mediate maturation of the FeS cluster SDH subunit (Sdh2/SDHB). Yeast and Drosophila lacking SDHAF3 are impaired in SDH activity with reduced levels of Sdh2. Drosophila lacking the Sdh7 ortholog SDHAF3 are hypersensitive to oxidative stress and exhibit muscular and neuronal dysfunction. Yeast studies revealed that Sdh6 and Sdh7 act together to promote Sdh2 maturation by binding to a Sdh1/Sdh2 intermediate, protecting it from the deleterious effects of oxidants. These studies in yeast and Drosophila raise the possibility that SDHAF3 mutations may be associated with idiopathic SDH-associated diseases.

Telomerase reverse transcriptase promoter mutations in tumors originating from the adrenal gland and extra-adrenal paraganglia

Hotspot mutations in the promoter of the telomerase reverse transcriptase (TERT) gene have been recently reported in human cancers and proposed as a novel mechanism of telomerase activation. To explore TERT promoter mutations in tumors originating from the adrenal gland and extra-adrenal paraganglia, a set of 253 tumors (38 adrenocortical carcinomas (ACCs), 127 pheochromocytomas (PCCs), 18 extra-adrenal paragangliomas (ea PGLs), 37 head and neck PGLs (HN PGLs), and 33 peripheral neuroblastic tumors) was selected along with 16 human neuroblastoma (NBL) and two ACC cell lines to assess TERT promoter mutations by the Sanger sequencing method. All mutations detected were confirmed by a SNaPshot assay. Additionally, 36 gastrointestinal stromal tumors (GISTs) were added to explore an association between TERT promoter mutations and SDH deficiency. TERT promoter mutations were found in seven out of 289 tumors and in three out of 18 human cell lines; four C228T mutations in 38 ACCs (10.5%), two C228T mutations in 18 ea PGLs (11.1%), one C250T mutation in 36 GISTs (2.8%), and three C228T mutations in 16 human NBL cell lines (18.75%). No mutation was detected in PCCs, HN PGLs, neuroblastic tumors as well as ACC cell lines. TERT promoter mutations preferentially occurred in a SDH-deficient setting (P=0.01) being present in three out of 47 (6.4%) SDH-deficient tumors vs zero out of 171 (0%) SDH-intact tumors. We conclude that TERT promoter mutations occur in ACCs and ea PGLs. In addition, preliminary evidence indicates a potential association with the acquisition of TERT promoter mutations in SDH-deficient tumors.

Metabolic therapy: a new paradigm for managing malignant brain cancer

Little progress has been made in the long-term management of glioblastoma multiforme (GBM), considered among the most lethal of brain cancers. Cytotoxic chemotherapy, steroids, and high-dose radiation are generally used as the standard of care for GBM. These procedures can create a tumor microenvironment rich in glucose and glutamine. Glucose and glutamine are suggested to facilitate tumor progression. Recent evidence suggests that many GBMs are infected with cytomegalovirus, which could further enhance glucose and glutamine metabolism in the tumor cells. Emerging evidence also suggests that neoplastic macrophages/microglia, arising through possible fusion hybridization, can comprise an invasive cell subpopulation within GBM. Glucose and glutamine are major fuels for myeloid cells, as well as for the more rapidly proliferating cancer stem cells. Therapies that increase inflammation and energy metabolites in the GBM microenvironment can enhance tumor progression. In contrast to current GBM therapies, metabolic therapy is designed to target the metabolic malady common to all tumor cells (aerobic fermentation), while enhancing the health and vitality of normal brain cells and the entire body. The calorie restricted ketogenic diet (KD-R) is an anti-angiogenic, anti-inflammatory and pro-apoptotic metabolic therapy that also reduces fermentable fuels in the tumor microenvironment. Metabolic therapy, as an alternative to the standard of care, has the potential to improve outcome for patients with GBM and other malignant brain cancers.