Dinner is served, sir: Fighting cancer with the right diet.

Altered metabolism of tumors offers an opportunity to use metabolic interventions as a therapeutic strategy. Lien et al. demonstrate that understanding how specific diets with different carbohydrate and fat composition affect tumor metabolism is essential in order to use this opportunity efficiently.

Evidence for an alternative fatty acid desaturation pathway increasing cancer plasticity.

Most tumours have an aberrantly activated lipid metabolism1,2 that enables them to synthesize, elongate and desaturate fatty acids to support proliferation. However, only particular subsets of cancer cells are sensitive to approaches that target fatty acid metabolism and, in particular, fatty acid desaturation3. This suggests that many cancer cells contain an unexplored plasticity in their fatty acid metabolism. Here we show that some cancer cells can exploit an alternative fatty acid desaturation pathway. We identify various cancer cell lines, mouse hepatocellular carcinomas, and primary human liver and lung carcinomas that desaturate palmitate to the unusual fatty acid sapienate to support membrane biosynthesis during proliferation. Accordingly, we found that sapienate biosynthesis enables cancer cells to bypass the known fatty acid desaturation pathway that is dependent on stearoyl-CoA desaturase. Thus, only by targeting both desaturation pathways is the in vitro and in vivo proliferation of cancer cells that synthesize sapienate impaired. Our discovery explains metabolic plasticity in fatty acid desaturation and constitutes an unexplored metabolic rewiring in cancers.

[18F]-(2S,4R)4-Fluoroglutamine PET Imaging of Glutamine Metabolism in Murine Models of Hepatocellular Carcinoma (HCC).

Purpose: Quantitative in vivo [18F]-(2S,4R)4-fluoroglutamine ([18F]4-FGln or more simply [18F]FGln) metabolic kinetic parameters are compared with activity levels of glutamine metabolism in different types of hepatocellular carcinoma (HCC). Methods: For this study, we used two transgenic mouse models of HCC induced by protooncogenes, MYC, and MET. Biochemical data have shown that tumors induced by MYC have increased levels of glutamine metabolism compared to those induced by MET. One-hour dynamic [18F]FGln PET data were acquired and reconstructed for fasted MYC mice (n = 11 tumors from 7 animals), fasted MET mice (n = 8 tumors from 6 animals), fasted FVBN controls (n = 8 normal liver regions from 6 animals), nonfasted MYC mice (n = 16 tumors from 6 animals), and nonfasted FVBN controls (n = 8 normal liver regions from 3 animals). The influx rate constants (K 1) using the one-tissue compartment model were derived for each tumor with the left ventricular blood pool input function. Results: Influx rate constants were significantly higher for MYC tumors (K 1 = 0.374 ± 0.133) than for MET tumors (K 1 = 0.141 ± 0.058) under fasting conditions (P = 0.0002). Rate constants were also significantly lower for MET tumors (K 1 = 0.141 ± 0.135) than normal livers (K 1 = 0.332 ± 0.179) under fasting conditions (P = 0.0123). Fasting conditions tested for MYC tumors and normal livers did not result in any significant difference with P values > 0.005. Conclusion: Higher influx rate constants corresponded to elevated levels of glutamine metabolism as determined by biochemical assays. The data showed that there is a distinctive difference in glutamine metabolism between MYC and MET tumors. Our study has demonstrated the potential of [18F]FGln PET imaging as a tool to assess glutamine metabolism in HCC tumors in vivo with a caution that it may not be able to clearly distinguish HCC tumors from normal liver tissue.

Defining a metabolic landscape of tumours: genome meets metabolism.

Cancer is a complex disease of multiple alterations occuring at the epigenomic, genomic, transcriptomic, proteomic and/or metabolic levels. The contribution of genetic mutations in cancer initiation, progression and evolution is well understood. However, although metabolic changes in cancer have long been acknowledged and considered a plausible therapeutic target, the crosstalk between genetic and metabolic alterations throughout cancer types is not clearly defined. In this review, we summarise the present understanding of the interactions between genetic drivers of cellular transformation and cancer-associated metabolic changes, and how these interactions contribute to metabolic heterogeneity of tumours. We discuss the essential question of whether changes in metabolism are a cause or a consequence in the formation of cancer. We highlight two modes of how metabolism contributes to tumour formation. One is when metabolic reprogramming occurs downstream of oncogenic mutations in signalling pathways and supports tumorigenesis. The other is where metabolic reprogramming initiates transformation being either downstream of mutations in oncometabolite genes or induced by chronic wounding, inflammation, oxygen stress or metabolic diseases. Finally, we focus on the factors that can contribute to metabolic heterogeneity in tumours, including genetic heterogeneity, immunomodulatory factors and tissue architecture. We believe that an in-depth understanding of cancer metabolic reprogramming, and the role of metabolic dysregulation in tumour initiation and progression, can help identify cellular vulnerabilities that can be exploited for therapeutic use.

Correction: Hopefully devoted to Q: targeting glutamine addiction in cancer.

This article was originally published under a CC BY NC SA License, but has now been made available under a CC BY 4.0 License.

Metabolic reprogramming and Notch activity distinguish between non-small cell lung cancer subtypes.

BACKGROUND: Previous studies suggested that the metabolism is differently reprogrammed in the major subtypes of non-small cell lung cancer (NSCLC), squamous cell carcinomas (SCC) and adenocarcinomas (AdC). However, a comprehensive analysis of this differential metabolic reprogramming is lacking. METHODS: Publicly available gene expression data from human lung cancer samples and cell lines were analysed. Stable isotope resolved metabolomics were performed on SCC and ADC tumours in human patients and in freshly resected tumour slices. RESULTS: Analysis of multiple transcriptomics data from human samples identified a SCC-distinguishing enzyme gene signature. SCC tumours from patients infused with [U-13C]-glucose and SCC tissue slices incubated with stable isotope tracers demonstrated differential glucose and glutamine catabolism compared to AdCs or non-cancerous lung, confirming increased activity through pathways defined by the SCC metabolic gene signature. Furthermore, the upregulation of Notch target genes was a distinguishing feature of SCCs, which correlated with the metabolic signature. Notch and MYC-driven murine lung tumours recapitulated the SCC-distinguishing metabolic reprogramming. However, the differences between SCCs and AdCs disappear in established cell lines in 2D culture. CONCLUSIONS: Our data emphasise the importance of studying lung cancer metabolism in vivo. They also highlight potential targets for therapeutic intervention in SCC patients including differentially expressed enzymes that catalyse reactions in glycolysis, glutamine catabolism, serine, nucleotide and glutathione biosynthesis.

Low catalytic activity is insufficient to induce disease pathology in triosephosphate isomerase deficiency.

Triosephosphate isomerase (TPI) deficiency is a fatal genetic disorder characterized by hemolytic anemia and neurological dysfunction. Although the enzyme defect in TPI was discovered in the 1960s, the exact etiology of the disease is still debated. Some aspects indicate the disease could be caused by insufficient enzyme activity, whereas other observations indicate it could be a protein misfolding disease with tissue-specific differences in TPI activity. We generated a mouse model in which exchange of a conserved catalytic amino acid residue (isoleucine to valine, Ile170Val) reduces TPI specific activity without affecting the stability of the protein dimer. TPIIle170Val/Ile170Val mice exhibit an approximately 85% reduction in TPI activity consistently across all examined tissues, which is a stronger average, but more consistent, activity decline than observed in patients or symptomatic mouse models that carry structural defect mutant alleles. While monitoring protein expression levels revealed no evidence for protein instability, metabolite quantification indicated that glycolysis is affected by the active site mutation. TPIIle170Val/Ile170Val mice develop normally and show none of the disease symptoms associated with TPI deficiency. Therefore, without the stability defect that affects TPI activity in a tissue-specific manner, a strong decline in TPI catalytic activity is not sufficient to explain the pathological onset of TPI deficiency.

De novo MYC addiction as an adaptive response of cancer cells to CDK4/6 inhibition.

Cyclin-dependent kinases (CDK) are rational cancer therapeutic targets fraught with the development of acquired resistance by tumor cells. Through metabolic and transcriptomic analyses, we show that the inhibition of CDK4/6 leads to a metabolic reprogramming associated with gene networks orchestrated by the MYC transcription factor. Upon inhibition of CDK4/6, an accumulation of MYC protein ensues which explains an increased glutamine metabolism, activation of the mTOR pathway and blunting of HIF-1α-mediated responses to hypoxia. These MYC-driven adaptations to CDK4/6 inhibition render cancer cells highly sensitive to inhibitors of MYC, glutaminase or mTOR and to hypoxia, demonstrating that metabolic adaptations to antiproliferative drugs unveil new vulnerabilities that can be exploited to overcome acquired drug tolerance and resistance by cancer cells.

Hopefully devoted to Q: targeting glutamine addiction in cancer.

Altered cell metabolism enables tumours to sustain their increased energetic and biosynthetic needs. Although tumour metabolism has long been considered a promising discipline in the development of cancer therapeutics, the majority of work has focused on changes in glucose metabolism. However, the complexity of cellular metabolism means that very rarely is an individual metabolite required for a single purpose, and thus understanding the overall metabolic requirements of tumours is vital. Over the past 30 years, increasing evidence has shown that many tumours require glutamine as well as glucose for their proliferation and survival. In this minireview, we explore the complexity of glutamine metabolism in tumour cells, discussing how the overall context of the tumour dictates the requirement for glutamine and how this can affect the design of effective therapeutic strategies.

Reciprocal regulation of microRNA-122 and c-Myc in hepatocellular cancer: role of E2F1 and transcription factor dimerization partner 2.

UNLABELLED: c-Myc is a well-known oncogene frequently up-regulated in different malignancies, whereas liver-specific microRNA (miR)-122, a bona fide tumor suppressor, is down-regulated in hepatocellular cancer (HCC). Here we explored the underlying mechanism of reciprocal regulation of these two genes. Real-time reverse-transcription polymerase chain reaction (RT-PCR) and northern blot analysis demonstrated reduced expression of the primary, precursor, and mature miR-122 in c-MYC-induced HCCs compared to the benign livers, indicating transcriptional suppression of miR-122 upon MYC overexpression. Indeed, chromatin immunoprecipitation (ChIP) assay showed significantly reduced association of RNA polymerase II and histone H3K9Ac, markers of active chromatin, with the miR-122 promoter in tumors relative to the c-MYC-uninduced livers, indicating transcriptional repression of miR-122 in c-MYC-overexpressing tumors. The ChIP assay also demonstrated a significant increase in c-Myc association with the miR-122 promoter region that harbors a conserved noncanonical c-Myc binding site in tumors compared to the livers. Ectopic expression and knockdown studies showed that c-Myc indeed suppresses expression of primary and mature miR-122 in hepatic cells. Additionally, Hnf-3ß, a liver enriched transcription factor that activates miR-122 gene, was suppressed in c-MYC-induced tumors. Notably, miR-122 also repressed c-Myc transcription by targeting transcriptional activator E2f1 and coactivator Tfdp2, as evident from ectopic expression and knockdown studies and luciferase reporter assays in mouse and human hepatic cells. CONCLUSION: c-Myc represses miR-122 gene expression by associating with its promoter and by down-regulating Hnf-3ß expression, whereas miR-122 indirectly inhibits c-Myc transcription by targeting Tfdp2 and E2f1. In essence, these results suggest a double-negative feedback loop between a tumor suppressor (miR-122) and an oncogene (c-Myc).

Multi-State Gene Cluster Switches Determine the Adaptive Mitochondrial And Metabolic Landscape of Breast Cancer.

Adaptive metabolic switches are proposed to underlie conversions between cellular states during normal development as well as in cancer evolution. Metabolic adaptations represent important therapeutic targets in tumors, highlighting the need to characterize the full spectrum, characteristics, and regulation of the metabolic switches. To investigate the hypothesis that metabolic switches associated with specific metabolic states can be recognized by locating large alternating gene expression patterns, we developed a method to identify interspersed gene sets by massive correlated biclustering (MCbiclust) and to predict their metabolic wiring. Testing the method on breast cancer transcriptome datasets revealed a series of gene sets with switch-like behavior that could be used to predict mitochondrial content, metabolic activity, and central carbon flux in tumors. The predictions were experimentally validated by bioenergetic profiling and metabolic flux analysis of 13C-labelled substrates. The metabolic switch positions also distinguished between cellular states, correlating with tumor pathology, prognosis, and chemosensitivity. The method is applicable to any large and heterogeneous transcriptome dataset to discover metabolic and associated pathophysiological states.

Therapeutic potential of a synthetic lethal interaction between the MYC proto-oncogene and inhibition of aurora-B kinase.

The Myc protein and proteins that participate in mitosis represent attractive targets for cancer therapy. However, their potential is presently compromised by the threat of side effects and by a lack of pharmacological inhibitors of Myc. Here we report that a circumscribed exposure to the aurora kinase inhibitor, VX-680, selectively kills cells that overexpress Myc. This synthetic lethal interaction is attributable to inhibition of aurora-B kinase, with consequent disabling of the chromosomal passenger protein complex (CPPC) and ensuing DNA replication in the absence of cell division; executed by sequential apoptosis and autophagy; not reliant on the tumor suppressor protein p53; and effective against mouse models for B-cell and T-cell lymphomas initiated by transgenes of MYC. Our findings cast light on how inhibitors of aurora-B kinase may kill tumor cells, implicate Myc in the induction of a lethal form of autophagy, indicate that expression of Myc be a useful biomarker for sensitivity of tumor cells to inhibition of the CPPC, dramatize the virtue of bimodal killing by a single therapeutic agent, and suggest a therapeutic strategy for killing tumor cells that overexpress Myc while sparing normal cells.

ALDH1L2 regulation of formate, formyl-methionine, and ROS controls cancer cell migration and metastasis.

Mitochondrial 10-formyltetrahydrofolate (10-formyl-THF) is utilized by three mitochondrial enzymes to produce formate for nucleotide synthesis, NADPH for antioxidant defense, and formyl-methionine (fMet) to initiate mitochondrial mRNA translation. One of these enzymes-aldehyde dehydrogenase 1 family member 2 (ALDH1L2)-produces NADPH by catabolizing 10-formyl-THF into CO2 and THF. Using breast cancer cell lines, we show that reduction of ALDH1L2 expression increases ROS levels and the production of both formate and fMet. Both depletion of ALDH1L2 and direct exposure to formate result in enhanced cancer cell migration that is dependent on the expression of the formyl-peptide receptor (FPR). In various tumor models, increased ALDH1L2 expression lowers formate and fMet accumulation and limits metastatic capacity, while human breast cancer samples show a consistent reduction of ALDH1L2 expression in metastases. Together, our data suggest that loss of ALDH1L2 can support metastatic progression by promoting formate and fMet production, resulting in enhanced FPR-dependent signaling.

Vitamin B5 supports MYC oncogenic metabolism and tumor progression in breast cancer.

Tumors are intrinsically heterogeneous and it is well established that this directs their evolution, hinders their classification and frustrates therapy1-3. Consequently, spatially resolved omics-level analyses are gaining traction4-9. Despite considerable therapeutic interest, tumor metabolism has been lagging behind this development and there is a paucity of data regarding its spatial organization. To address this shortcoming, we set out to study the local metabolic effects of the oncogene c-MYC, a pleiotropic transcription factor that accumulates with tumor progression and influences metabolism10,11. Through correlative mass spectrometry imaging, we show that pantothenic acid (vitamin B5) associates with MYC-high areas within both human and murine mammary tumors, where its conversion to coenzyme A fuels Krebs cycle activity. Mechanistically, we show that this is accomplished by MYC-mediated upregulation of its multivitamin transporter SLC5A6. Notably, we show that SLC5A6 over-expression alone can induce increased cell growth and a shift toward biosynthesis, whereas conversely, dietary restriction of pantothenic acid leads to a reversal of many MYC-mediated metabolic changes and results in hampered tumor growth. Our work thus establishes the availability of vitamins and cofactors as a potential bottleneck in tumor progression, which can be exploited therapeutically. Overall, we show that a spatial understanding of local metabolism facilitates the identification of clinically relevant, tractable metabolic targets.

Metabolic profiling stratifies colorectal cancer and reveals adenosylhomocysteinase as a therapeutic target.

The genomic landscape of colorectal cancer (CRC) is shaped by inactivating mutations in tumour suppressors such as APC, and oncogenic mutations such as mutant KRAS. Here we used genetically engineered mouse models, and multimodal mass spectrometry-based metabolomics to study the impact of common genetic drivers of CRC on the metabolic landscape of the intestine. We show that untargeted metabolic profiling can be applied to stratify intestinal tissues according to underlying genetic alterations, and use mass spectrometry imaging to identify tumour, stromal and normal adjacent tissues. By identifying ions that drive variation between normal and transformed tissues, we found dysregulation of the methionine cycle to be a hallmark of APC-deficient CRC. Loss of Apc in the mouse intestine was found to be sufficient to drive expression of one of its enzymes, adenosylhomocysteinase (AHCY), which was also found to be transcriptionally upregulated in human CRC. Targeting of AHCY function impaired growth of APC-deficient organoids in vitro, and prevented the characteristic hyperproliferative/crypt progenitor phenotype driven by acute deletion of Apc in vivo, even in the context of mutant Kras. Finally, pharmacological inhibition of AHCY reduced intestinal tumour burden in ApcMin/+ mice indicating its potential as a metabolic drug target in CRC.

Deficiency in glutamine but not glucose induces MYC-dependent apoptosis in human cells.

The idea that conversion of glucose to ATP is an attractive target for cancer therapy has been supported in part by the observation that glucose deprivation induces apoptosis in rodent cells transduced with the proto-oncogene MYC, but not in the parental line. Here, we found that depletion of glucose killed normal human cells irrespective of induced MYC activity and by a mechanism different from apoptosis. However, depletion of glutamine, another major nutrient consumed by cancer cells, induced apoptosis depending on MYC activity. This apoptosis was preceded by depletion of the Krebs cycle intermediates, was prevented by two Krebs cycle substrates, but was unrelated to ATP synthesis or several other reported consequences of glutamine starvation. Our results suggest that the fate of normal human cells should be considered in evaluating nutrient deprivation as a strategy for cancer therapy, and that understanding how glutamine metabolism is linked to cell viability might provide new approaches for treatment of cancer.

Cold exposure as anti-cancer therapy.

Seki et al. report in Nature that increasing glucose catabolism in brown adipose tissue by cold exposure lowers blood glucose and insulin tolerance. This systemic effect on body metabolism decreases glucose catabolism in tumors and arrests tumor progression, offering a novel alternative approach for metabolism-based cancer therapy.

Cysteine and Folate Metabolism Are Targetable Vulnerabilities of Metastatic Colorectal Cancer.

With most cancer-related deaths resulting from metastasis, the development of new therapeutic approaches against metastatic colorectal cancer (mCRC) is essential to increasing patient survival. The metabolic adaptations that support mCRC remain undefined and their elucidation is crucial to identify potential therapeutic targets. Here, we employed a strategy for the rational identification of targetable metabolic vulnerabilities. This strategy involved first a thorough metabolic characterisation of same-patient-derived cell lines from primary colon adenocarcinoma (SW480), its lymph node metastasis (SW620) and a liver metastatic derivative (SW620-LiM2), and second, using a novel multi-omics integration workflow, identification of metabolic vulnerabilities specific to the metastatic cell lines. We discovered that the metastatic cell lines are selectively vulnerable to the inhibition of cystine import and folate metabolism, two key pathways in redox homeostasis. Specifically, we identified the system xCT and MTHFD1 genes as potential therapeutic targets, both individually and combined, for combating mCRC.

Constitutive activation of the PI3K-Akt-mTORC1 pathway sustains the m.3243 A > G mtDNA mutation.

Mutations of the mitochondrial genome (mtDNA) cause a range of profoundly debilitating clinical conditions for which treatment options are very limited. Most mtDNA diseases show heteroplasmy - tissues express both wild-type and mutant mtDNA. While the level of heteroplasmy broadly correlates with disease severity, the relationships between specific mtDNA mutations, heteroplasmy, disease phenotype and severity are poorly understood. We have carried out extensive bioenergetic, metabolomic and RNAseq studies on heteroplasmic patient-derived cells carrying the most prevalent disease related mtDNA mutation, the m.3243 A > G. These studies reveal that the mutation promotes changes in metabolites which are associated with the upregulation of the PI3K-Akt-mTORC1 axis in patient-derived cells and tissues. Remarkably, pharmacological inhibition of PI3K, Akt, or mTORC1 reduced mtDNA mutant load and partially rescued cellular bioenergetic function. The PI3K-Akt-mTORC1 axis thus represents a potential therapeutic target that may benefit people suffering from the consequences of the m.3243 A > G mutation.

Adapt and conquer: Metabolic flexibility in cancer growth, invasion and evasion.

BACKGROUND: It has been known for close to a century that, on average, tumors have a metabolism that is different from those found in healthy tissues. Typically, tumors show a biosynthetic metabolism that distinguishes itself by engaging in large scale aerobic glycolysis, heightened flux through the pentose phosphate pathway, and increased glutaminolysis among other means. However, it is becoming equally clear that non tumorous tissues at times can engage in similar metabolism, while tumors show a high degree of metabolic flexibility reacting to cues, and stresses in their local environment. SCOPE OF THE REVIEW: In this review, we want to scrutinize historic and recent research on metabolism, comparing and contrasting oncogenic and physiological metabolic states. This will allow us to better define states of bona fide tumor metabolism. We will further contextualize the stress response and the metabolic evolutionary trajectory seen in tumors, and how these contribute to tumor progression. Lastly, we will analyze the implications of these characteristics with respect to therapy response. MAJOR CONCLUSIONS: In our review, we argue that there is not one single oncogenic state, but rather a diverse set of oncogenic states. These are grounded on a physiological proliferative/wound healing program but distinguish themselves due to their large scale of proliferation, mutations, and transcriptional changes in key metabolic pathways, and the adaptations to widespread stress signals within tumors. We find evidence for the necessity of metabolic flexibility and stress responses in tumor progression and how these responses in turn shape oncogenic progression. Lastly, we find evidence for the notion that the metabolic adaptability of tumors frequently frustrates therapeutic interventions.