LKB1 and KEAP1/NRF2 Pathways Cooperatively Promote Metabolic Reprogramming with Enhanced Glutamine Dependence in KRAS-Mutant Lung Adenocarcinoma

In KRAS-mutant lung adenocarcinoma, tumors with LKB1 loss (KL) are highly enriched for concurrent KEAP1 mutations, which activate the KEAP1/NRF2 pathway (KLK). Here, we investigated the biological consequences of these cooccurring alterations and explored whether they conferred specific therapeutic vulnerabilities. Compared with KL tumors, KLK tumors exhibited increased expression of genes involved in glutamine metabolism, the tricarboxylic acid cycle, and the redox homeostasis signature. Using isogenic pairs with knockdown or overexpression of LKB1, KEAP1, and NRF2, we found that LKB1 loss results in increased energetic and redox stress marked by increased levels of intracellular reactive oxygen species and decreased levels of ATP, NADPH/NADP⁺ ratio, and glutathione. Activation of the KEAP1/NRF2 axis in LKB1-deficient cells enhanced cell survival and played a critical role in the maintenance of energetic and redox homeostasis in a glutamine-dependent manner. LKB1 and the KEAP1/NRF2 pathways cooperatively drove metabolic reprogramming and enhanced sensitivity to the glutaminase inhibitor CB-839 in vitro and in vivo. Overall, these findings elucidate the adaptive advantage provided by KEAP1/NRF2 pathway activation in KL tumors and support clinical testing of glutaminase inhibitor in subsets of KRAS-mutant lung adenocarcinoma. SIGNIFICANCE: In KRAS-mutant non-small cell lung cancer, LKB1 loss results in enhanced energetic/redox stress, which is tolerated, in part, through cooccurring KEAP1/NRF2-dependent metabolic adaptations, thus enhancing glutamine dependence and vulnerability to glutaminase inhibition.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/13/3251/F1.large.jpg.

Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging abnormalities

Polyamines serve a number of vital functions in humans, including regulation of cellular proliferation, intracellular signaling, and modulation of ion channels. Ornithine decarboxylase 1 (ODC1) is the rate-limiting enzyme in endogenous polyamine synthesis. In this report, we present four patients with a distinct neurometabolic disorder associated with de novo heterozygous, gain-of-function variants in the ODC1 gene. This disorder presents with global developmental delay, ectodermal abnormalities including alopecia, absolute or relative macrocephaly, and characteristic facial dysmorphisms. Neuroimaging variably demonstrates white matter abnormalities, prominent Virchow-Robin spaces, periventricular cysts, and abnormalities of the corpus callosum. Plasma clinical metabolomics analysis demonstrates elevation of N-acetylputrescine, the acetylated form of putrescine, with otherwise normal polyamine levels. Therapies aimed at reducing putrescine levels, including ODC1 inhibitors, dietary interventions, and antibiotics to reduce polyamine production by gastrointestinal flora could be considered as disease-modifying therapies. As the ODC1 gene has been implicated in neoplasia, cancer surveillance may be important in this disorder.

Transmembrane Protease TMPRSS11B Promotes Lung Cancer Growth by Enhancing Lactate Export and Glycolytic Metabolism

Pathways underlying metabolic reprogramming in cancer remain incompletely understood. We identify the transmembrane serine protease TMPRSS11B as a gene that promotes transformation of immortalized human bronchial epithelial cells (HBECs). TMPRSS11B is upregulated in human lung squamous cell carcinomas (LSCCs), and high expression is associated with poor survival of non-small cell lung cancer patients. TMPRSS11B inhibition in human LSCCs reduces transformation and tumor growth. Given that TMPRSS11B harbors an extracellular (EC) protease domain, we hypothesized that catalysis of a membrane-bound substrate modulates tumor progression. Interrogation of a set of soluble receptors revealed that TMPRSS11B promotes solubilization of Basigin, an obligate chaperone of the lactate monocarboxylate transporter MCT4. Basigin release mediated by TMPRSS11B enhances lactate export and glycolytic metabolism, thereby promoting tumorigenesis. These findings establish an oncogenic role for TMPRSS11B and provide support for the development of therapies that target this enzyme at the surface of cancer cells.

Isotope Tracing of Human Clear Cell Renal Cell Carcinomas Demonstrates Suppressed Glucose Oxidation In Vivo

Clear cell renal cell carcinoma (ccRCC) is the most common form of human kidney cancer. Histological and molecular analyses suggest that ccRCCs have significantly altered metabolism. Recent human studies of lung cancer and intracranial malignancies demonstrated an unexpected preservation of carbohydrate oxidation in the tricarboxylic acid (TCA) cycle. To test the capacity of ccRCC to oxidize substrates in the TCA cycle, we infused 13C-labeled fuels in ccRCC patients and compared labeling patterns in tumors and adjacent kidney. After infusion with [U-13C]glucose, ccRCCs displayed enhanced glycolytic intermediate labeling, suppressed pyruvate dehydrogenase flow, and reduced TCA cycle labeling, consistent with the Warburg effect. Comparing 13C labeling among ccRCC, brain, and lung tumors revealed striking differences. Primary ccRCC tumors demonstrated the highest enrichment in glycolytic intermediates and lowest enrichment in TCA cycle intermediates. Among human tumors analyzed by intraoperative 13C infusions, ccRCC is the first to demonstrate a convincing shift toward glycolytic metabolism.

Abstract IA23: Metabolic complexity in cancer cells and tumors

Metabolism is dynamic and responds to a wide range of cell-intrinsic and cell-extrinsic factors. In cancer, cell-intrinsic influences on metabolism include somatically acquired mutations in oncogenes and tumor suppressor genes, many of which regulate metabolic activity. Cell-extrinsic factors include nutrient access, which may become limiting due to inadequate vasculature and intense fuel utilization, and metabolic interactions with stromal and immune cells. A major challenge in cancer metabolism research is to understand how these various factors culminate in the metabolic phenotype of an intact tumor, and ultimately to identify which altered pathways represent potential therapeutic targets. We have taken two parallel approaches to understand metabolic complexity in human cancer. The first uses a combination of multiparametric imaging and intraoperative stable isotope infusions to assess metabolic fluxes in patients with solid tumors, and to compare fluxes between tumors and adjacent benign tissue. Genomic, histologic, and metabolic analysis of tumor samples allows us to correlate various intrinsic and extrinsic factors to specific aspects of the metabolic phenotype. The second approach uses standardized culture conditions to assess cell-intrinsic heterogeneity of metabolic preferences and dependencies in large panels of human cancer cell lines. This approach has uncovered liabilities associated with specific molecular subtypes of non-small cell and small cell lung cancer. I will discuss the application of these two approaches to metabolic heterogeneity in human cancer, with an emphasis on features relevant to intact tumors and therapeutic liabilities.

Citation Format: Ralph J. DeBerardinis. Metabolic complexity in cancer cells and tumors [abstract]. In: Proceedings of the AACR Special Conference: Pediatric Cancer Research: From Basic Science to the Clinic; 2017 Dec 3-6; Atlanta, Georgia. Philadelphia (PA): AACR; Cancer Res 2018;78(19 Suppl):Abstract nr IA23.

Abstract IA27: MYC drives molecular and therapeutically distinct subtype of SCLC

Small cell lung cancer (SCLC) has largely been treated in the clinic as a homogeneous disease for the last 40 years. However, it is become increasingly appreciated that SCLC exhibits both intra- and intertumoral heterogeneity. Genetic loss of the tumor suppressors RB1 and TP53 is nearly universal in SCLC, while amplifications in MYC family members including C-, L-, and N-MYC are mutually exclusive. Using genetically engineered mouse models (GEMMs), we show that MycT58A expression cooperates with Rb1 and Trp53 loss in the mouse lung to promote aggressive, highly metastatic tumors that are initially sensitive to chemotherapy followed by relapse, similar to human SCLC. Importantly, MYC drives a neuroendocrine-low ‘‘variant’’ subset of SCLC with low ASCL1 and high NEUROD1 expression corresponding to transcriptional profiles of human SCLC. The MYC-driven subset of SCLC is also low for other clinically relevant biomarkers such as TTF1/NKX2.1 and DLL3. Targeted drug screening reveals that SCLC with high MYC expression is vulnerable to Aurora kinase inhibition, which, combined with chemotherapy, strongly suppresses tumor progression and increases survival. These findings are consistent with the results of recent clinical trials in patients with relapsed SCLC who received paclitaxel with or without the AURKA inhibitor alisertib. Furthermore, recent preclinical studies demonstrate that the MYC-driven subset of SCLC is preferentially sensitive to CHK1 inhibition and other metabolic targets compared to MYCL-driven SCLC. These data identify molecular features for patient stratification and uncover potential targeted treatment approaches for MYC-driven SCLC.

Citation Format: Gurkan Mollaoglu, Matthew R. Guthrie, Stefanie Bohm, Johannes Bragelmann, Milind D. Chalishazar, Abbie S. Ireland, Fang Huang, Zeping Hu, Robert J. Cardnell, Triparna Sen, Jason Gertz, Jane E. Johnson, Adi F. Gazdar, Lauren A. Byers, Ralph J. DeBerardinis, Robert J. Wechsler-Reya, Martin Sos, Trudy G. Oliver. MYC drives molecular and therapeutically distinct subtype of SCLC [abstract]. In: Proceedings of the Fifth AACR-IASLC International Joint Conference: Lung Cancer Translational Science from the Bench to the Clinic; Jan 8-11, 2018; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(17_Suppl):Abstract nr IA27.

Applications of metabolomics to study cancer metabolism

Reprogrammed metabolism supports tumor growth and provides a potential source of therapeutic targets and disease biomarkers. Mass spectrometry-based metabolomics has emerged as a broadly informative technique for profiling metabolic features associated with specific oncogenotypes, disease progression, therapeutic liabilities and other clinically relevant aspects of tumor biology. In this review, we introduce the applications of metabolomics to study deregulated metabolism and metabolic vulnerabilities in cancer. We provide examples of studies that used metabolomics to discover novel metabolic regulatory mechanisms, including processes that link metabolic alterations with gene expression, protein function, and other aspects of systems biology. Finally, we discuss emerging applications of metabolomics for in vivo isotope tracing and metabolite imaging, both of which hold promise to advance our understanding of the role of metabolic reprogramming in cancer.

Metabolic regulation of transcription through compartmentalized NAD+ biosynthesis

NAD⁺ (nicotinamide adenine dinucleotide in its oxidized state) is an essential molecule for a variety of physiological processes. It is synthesized in distinct subcellular compartments by three different synthases (NMNAT-1, -2, and -3). We found that compartmentalized NAD⁺ synthesis by NMNATs integrates glucose metabolism and adipogenic transcription during adipocyte differentiation. Adipogenic signaling rapidly induces cytoplasmic NMNAT-2, which competes with nuclear NMNAT-1 for the common substrate, nicotinamide mononucleotide, leading to a precipitous reduction in nuclear NAD⁺ levels. This inhibits the catalytic activity of poly[adenosine diphosphate (ADP)-ribose] polymerase-1 (PARP-1), a NAD⁺-dependent enzyme that represses adipogenic transcription by ADP-ribosylating the adipogenic transcription factor C/EBPβ. Reversal of PARP-1-mediated repression by NMNAT-2-mediated nuclear NAD⁺ depletion in response to adipogenic signals drives adipogenesis. Thus, compartmentalized NAD⁺ synthesis functions as an integrator of cellular metabolism and signal-dependent transcriptional programs.

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field.

Lkb1 deficiency confers glutamine dependency in polycystic kidney disease

Polycystic kidney disease (PKD) is a common genetic disorder characterized by the growth of fluid-filled cysts in the kidneys. Several studies reported that the serine-threonine kinase Lkb1 is dysregulated in PKD. Here we show that genetic ablation of Lkb1 in the embryonic ureteric bud has no effects on tubule formation, maintenance, or growth. However, co-ablation of Lkb1 and Tsc1, an mTOR repressor, results in an early developing, aggressive form of PKD. We find that both loss of Lkb1 and loss of Pkd1 render cells dependent on glutamine for growth. Metabolomics analysis suggests that Lkb1 mutant kidneys require glutamine for non-essential amino acid and glutathione metabolism. Inhibition of glutamine metabolism in both Lkb1/Tsc1 and Pkd1 mutant mice significantly reduces cyst progression. Thus, we identify a role for Lkb1 in glutamine metabolism within the kidney epithelia and suggest that drugs targeting glutamine metabolism may help reduce cyst number and/or size in PKD.

Polycystic kidney disease (PKD) is characterized by the formation of large fluid-filled cysts. Here Flowers and colleagues show that loss of Lkb1, downregulated in PKD, renders kidney cells dependent on glutamine for growth, and suggest that inhibition of glutamine metabolism may prevent cyst development in PKD.

Metabolic strategies of melanoma cells: Mechanisms, interactions with the tumor microenvironment, and therapeutic implications

Melanomas are metabolically heterogeneous, and they are able to adapt in order to utilize a variety of fuels that facilitate tumor progression and metastasis. The significance of metabolism in melanoma is supported by growing evidence of impact on the efficacy of contemporary therapies for this disease. There are also data to support that the metabolic phenotypes of melanoma cells depend upon contributions from both intrinsic oncogenic pathways and extrinsic factors in the tumor microenvironment. This review summarizes current understanding of the metabolic processes that promote cutaneous melanoma tumorigenesis and progression, the regulation of cancer cell metabolism by the tumor microenvironment, and the impact of metabolic pathways on targeted and immune therapies.

Genomic regression analysis of coordinated expression

Co-expression analysis is widely used to predict gene function and to identify functionally related gene sets. However, co-expression analysis using human cancer transcriptomic data is confounded by somatic copy number alterations (SCNA), which produce co-expression signatures based on physical proximity rather than biological function. To better understand gene-gene co-expression based on biological regulation but not SCNA, we describe a method termed "Genomic Regression Analysis of Coordinated Expression" (GRACE) to adjust for the effect of SCNA in co-expression analysis. The results from analyses of TCGA, CCLE, and NCI60 data sets show that GRACE can improve our understanding of how a transcriptional network is re-wired in cancer. A user-friendly web database populated with data sets from The Cancer Genome Atlas (TCGA) is provided to allow customized query.

Lipoic acid metabolism and mitochondrial redox regulation

Lipoic acid is an essential cofactor for mitochondrial metabolism and is synthesized de novo using intermediates from mitochondrial fatty-acid synthesis type II, S-adenosylmethionine and iron-sulfur clusters. This cofactor is required for catalysis by multiple mitochondrial 2-ketoacid dehydrogenase complexes, including pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, and branched-chain ketoacid dehydrogenase. Lipoic acid also plays a critical role in stabilizing and regulating these multienzyme complexes. Many of these dehydrogenases are regulated by reactive oxygen species, mediated through the disulfide bond of the prosthetic lipoyl moiety. Collectively, its functions explain why lipoic acid is required for cell growth, mitochondrial activity, and coordination of fuel metabolism.

Liposuction: Extracellular Fat Removal Promotes Proliferation

In this issue of Cell Chemical Biology, Yao et al. (2016) investigate the makeup of lipid membranes of both cancer and non-transformed cells to reveal that doubling cells preferentially use exogenous fatty acids over de novo synthesis to proliferate.

The abundance of metabolites related to protein methylation correlates with the metastatic capacity of human melanoma xenografts

Metabolic reprogramming is a major factor in transformation, and particular metabolic phenotypes correlate with oncogenotype, tumor progression, and metastasis. By profiling metabolites in 17 patient-derived xenograft melanoma models, we identified durable metabolomic signatures that correlate with biological features of the tumors. BRAF mutant tumors had metabolomic and metabolic flux features of enhanced glycolysis compared to BRAF wild-type tumors. Tumors that metastasized efficiently from their primary sites had elevated levels of metabolites related to protein methylation, including trimethyllysine (TML). TML levels correlated with histone H3 trimethylation at Lys⁹ and Lys²⁷, and methylation at these sites was also enhanced in efficiently metastasizing tumors. Erasing either of these marks by genetically or pharmacologically silencing the histone methyltransferase SETDB1 or EZH2 had no effect on primary tumor growth but reduced cellular invasiveness and metastatic spread. Thus, metabolite profiling can uncover targetable epigenetic requirements for the metastasis of human melanoma cells.

Lactate Metabolism in Human Lung Tumors

Cancer cells consume glucose and secrete lactate in culture. It is unknown whether lactate contributes to energy metabolism in living tumors. We previously reported that human non-small-cell lung cancers (NSCLCs) oxidize glucose in the tricarboxylic acid (TCA) cycle. Here, we show that lactate is also a TCA cycle carbon source for NSCLC. In human NSCLC, evidence of lactate utilization was most apparent in tumors with high ¹⁸fluorodeoxyglucose uptake and aggressive oncological behavior. Infusing human NSCLC patients with ¹³C-lactate revealed extensive labeling of TCA cycle metabolites. In mice, deleting monocarboxylate transporter-1 (MCT1) from tumor cells eliminated lactate-dependent metabolite labeling, confirming tumor-cell-autonomous lactate uptake. Strikingly, directly comparing lactate and glucose metabolism in vivo indicated that lactate's contribution to the TCA cycle predominates. The data indicate that tumors, including bona fide human NSCLC, can use lactate as a fuel in vivo.

The NQO1 bioactivatable drug, β-lapachone, alters the redox state of NQO1+ pancreatic cancer cells, causing perturbation in central carbon metabolism

Many cancer treatments, such as those for managing recalcitrant tumors like pancreatic ductal adenocarcinoma, cause off-target toxicities in normal, healthy tissue, highlighting the need for more tumor-selective chemotherapies. β-Lapachone is bioactivated by NAD(P)H:quinone oxidoreductase 1 (NQO1). This enzyme exhibits elevated expression in most solid cancers and therefore is a potential cancer-specific target. β-Lapachone's therapeutic efficacy partially stems from the drug's induction of a futile NQO1-mediated redox cycle that causes high levels of superoxide and then peroxide formation, which damages DNA and causes hyperactivation of poly(ADP-ribose) polymerase, resulting in extensive NAD⁺/ATP depletion. However, the effects of this drug on energy metabolism due to NAD⁺ depletion were never described. The futile redox cycle rapidly consumes O₂, rendering standard assays of Krebs cycle turnover unusable. In this study, a multimodal analysis, including metabolic imaging using hyperpolarized pyruvate, points to reduced oxidative flux due to NAD⁺ depletion after β-lapachone treatment of NQO1+ human pancreatic cancer cells. NAD⁺-sensitive pathways, such as glycolysis, flux through lactate dehydrogenase, and the citric acid cycle (as inferred by flux through pyruvate dehydrogenase), were down-regulated by β-lapachone treatment. Changes in flux through these pathways should generate biomarkers useful for in vivo dose responses of β-lapachone treatment in humans, avoiding toxic side effects. Targeting the enzymes in these pathways for therapeutic treatment may have the potential to synergize with β-lapachone treatment, creating unique NQO1-selective combinatorial therapies for specific cancers. These findings warrant future studies of intermediary metabolism in patients treated with β-lapachone.

Control of intestinal stem cell function and proliferation by mitochondrial pyruvate metabolism

Most differentiated cells convert glucose to pyruvate in the cytosol through glycolysis, followed by pyruvate oxidation in the mitochondria. These processes are linked by the mitochondrial pyruvate carrier (MPC), which is required for efficient mitochondrial pyruvate uptake. In contrast, proliferative cells, including many cancer and stem cells, perform glycolysis robustly but limit fractional mitochondrial pyruvate oxidation. We sought to understand the role this transition from glycolysis to pyruvate oxidation plays in stem cell maintenance and differentiation. Loss of the MPC in Lgr5-EGFP-positive stem cells, or treatment of intestinal organoids with an MPC inhibitor, increases proliferation and expands the stem cell compartment. Similarly, genetic deletion of the MPC in Drosophila intestinal stem cells also increases proliferation, whereas MPC overexpression suppresses stem cell proliferation. These data demonstrate that limiting mitochondrial pyruvate metabolism is necessary and sufficient to maintain the proliferation of intestinal stem cells.

Addressing metabolic heterogeneity in clear cell renal cell carcinoma with quantitative Dixon MRI

BACKGROUND

Dysregulated lipid and glucose metabolism in clear cell renal cell carcinoma (ccRCC) has been implicated in disease progression, and whole tumor tissue-based assessment of these changes is challenged by the tumor heterogeneity. We studied a noninvasive quantitative MRI method that predicts metabolic alterations in the whole tumor.

METHODS

We applied Dixon-based MRI for in vivo quantification of lipid accumulation (fat fraction [FF]) in targeted regions of interest of 45 primary ccRCCs and correlated these MRI measures to mass spectrometry-based lipidomics and metabolomics of anatomically colocalized tissue samples isolated from the same tumor after surgery.

RESULTS

In vivo tumor FF showed statistically significant (P < 0.0001) positive correlation with histologic fat content (Spearman correlation coefficient, ρ = 0.79), spectrometric triglycerides (ρ = 0.56) and cholesterol (ρ = 0.47); it showed negative correlation with free fatty acids (ρ = -0.44) and phospholipids (ρ = -0.65). We observed both inter- and intratumoral heterogeneity in lipid accumulation within the same tumor grade, whereas most aggressive tumors (International Society of Urological Pathology [ISUP] grade 4) exhibited reduced lipid accumulation. Cellular metabolites in tumors were altered compared with adjacent renal parenchyma.

CONCLUSION

Our results support the use of noninvasive quantitative Dixon-based MRI as a biomarker of reprogrammed lipid metabolism in ccRCC, which may serve as a predictor of tumor aggressiveness before surgical intervention.

FUNDING

NIH R01CA154475 (YZ, MF, PK, IP), NIH P50CA196516 (IP, JB, RJD, JAC, PK), Welch Foundation I-1832 (JY), and NIH P01HL020948 (JGM).

Regulation of mitochondrial biogenesis in erythropoiesis by mTORC1-mediated protein translation

Advances in genomic profiling present new challenges of explaining how changes in DNA and RNA are translated into proteins linking genotype to phenotype. Here we compare the genome-scale proteomic and transcriptomic changes in human primary haematopoietic stem/progenitor cells and erythroid progenitors, and uncover pathways related to mitochondrial biogenesis enhanced through post-transcriptional regulation. Mitochondrial factors including TFAM and PHB2 are selectively regulated through protein translation during erythroid specification. Depletion of TFAM in erythroid cells alters intracellular metabolism, leading to elevated histone acetylation, deregulated gene expression, and defective mitochondria and erythropoiesis. Mechanistically, mTORC1 signalling is enhanced to promote translation of mitochondria-associated transcripts through TOP-like motifs. Genetic and pharmacological perturbation of mitochondria or mTORC1 specifically impairs erythropoiesis in vitro and in vivo. Our studies support a mechanism for post-transcriptional control of erythroid mitochondria and may have direct relevance to haematologic defects associated with mitochondrial diseases and ageing.

CPS1 maintains pyrimidine pools and DNA synthesis in KRAS/LKB1-mutant lung cancer cells

Metabolic reprogramming by oncogenic signals promotes cancer initiation and progression. The oncogene KRAS and tumour suppressor STK11, which encodes the kinase LKB1, regulate metabolism and are frequently mutated in non-small-cell lung cancer (NSCLC). Concurrent occurrence of oncogenic KRAS and loss of LKB1 (KL) in cells specifies aggressive oncological behaviour. Here we show that human KL cells and tumours share metabolomic signatures of perturbed nitrogen handling. KL cells express the urea cycle enzyme carbamoyl phosphate synthetase-1 (CPS1), which produces carbamoyl phosphate in the mitochondria from ammonia and bicarbonate, initiating nitrogen disposal. Transcription of CPS1 is suppressed by LKB1 through AMPK, and CPS1 expression correlates inversely with LKB1 in human NSCLC. Silencing CPS1 in KL cells induces cell death and reduces tumour growth. Notably, cell death results from pyrimidine depletion rather than ammonia toxicity, as CPS1 enables an unconventional pathway of nitrogen flow from ammonia into pyrimidines. CPS1 loss reduces the pyrimidine to purine ratio, compromises S-phase progression and induces DNA-polymerase stalling and DNA damage. Exogenous pyrimidines reverse DNA damage and rescue growth. The data indicate that the KL oncological genotype imposes a metabolic vulnerability related to a dependence on a cross-compartmental pathway of pyrimidine metabolism in an aggressive subset of NSCLC.

Understanding the Intersections between Metabolism and Cancer Biology

Transformed cells adapt metabolism to support tumor initiation and progression. Specific metabolic activities can participate directly in the process of transformation or support the biological processes that enable tumor growth. Exploiting cancer metabolism for clinical benefit requires defining the pathways that are limiting for cancer progression and understanding the context specificity of metabolic preferences and liabilities in malignant cells. Progress toward answering these questions is providing new insight into cancer biology and can guide the more effective targeting of metabolism to help patients.