Metabolic Plasticity as a Determinant of Tumor Growth and Metastasis

The Role of Metabolic Plasticity in Blood and Brain Stem Cell Pathophysiology

Our understanding of intratumoral heterogeneity in cancer continues to evolve, with current models incorporating single-cell signatures to explore cell-cell interactions and differentiation state. The transition between stem and differentiation states in nonneoplastic cells requires metabolic plasticity, and this plasticity is increasingly recognized to play a central role in cancer biology. The insights from hematopoietic and neural stem cell differentiation pathways were used to identify cancer stem cells in leukemia and gliomas. Similarly, defining metabolic heterogeneity and fuel-switching signals in nonneoplastic stem cells may also give important insights into the corresponding molecular mechanisms controlling metabolic plasticity in cancer. These advances are important, because metabolic adaptation to anticancer therapeutics is rooted in this inherent metabolic plasticity and is a therapeutic challenge to be overcome.

Melanoma plasticity and phenotypic diversity: therapeutic barriers and opportunities

An incomplete view of the mechanisms that drive metastasis, the primary cause of cancer-related death, has been a major barrier to development of effective therapeutics and prognostic diagnostics. Increasing evidence indicates that the interplay between microenvironment, genetic lesions, and cellular plasticity drives the metastatic cascade and resistance to therapies. Here, using melanoma as a model, we outline the diversity and trajectories of cell states during metastatic dissemination and therapy exposure, and highlight how understanding the magnitude and dynamics of nongenetic reprogramming in space and time at single-cell resolution can be exploited to develop therapeutic strategies that capitalize on nongenetic tumor evolution.

The role of polarisation of circulating tumour cells in cancer metastasis

Metastasis is the spread of cancer cells from a primary tumour to a distant site of the body. Metastasising tumour cells have to survive and readjust to different environments, such as heterogeneous solid tissues and liquid phase in lymph- or blood circulation, which they achieve through a high degree of plasticity that renders them adaptable to varying conditions. One defining characteristic of the metastatic process is the transition of tumour cells between different polarised phenotypes, ranging from differentiated epithelial polarity to migratory front-rear polarity. Here, we review the polarisation types adopted by tumour cells during the metastatic process and describe the recently discovered single-cell polarity in liquid phase observed in circulating tumour cells. We propose that single-cell polarity constitutes a mode of polarisation of the cell cortex that is uncoupled from the intracellular polarisation machinery, which distinguishes single-cell polarity from other types of polarity identified so far. We discuss how single-cell polarity can contribute to tumour metastasis and the therapeutic potential of this new discovery.

Development of Novel Irreversible Pyruvate Kinase M2 Inhibitors

As cancer cells undergo metabolic reprogramming in the course of tumorigenesis, targeting energy metabolism represents a promising strategy in cancer therapy. Among various metabolic enzymes examined, pyruvate kinase M2 type (PKM2) has received much attention in light of its multifaceted function in promoting tumor growth and progression. In this study, we reported the development of a novel irreversible inhibitor of PKM2, compound 1, that exhibits a differential tumor-suppressive effect among an array of cancer cell lines. We further used a clickable activity-based protein profiling (ABPP) probe and SILAC coupled with LC-MS/MS to identify the Cys-317 and Cys-326 residues of PKM2 as the covalent binding sites. Equally important, compound 1 at 10 mg/kg was effective in suppressing xenograft tumor growth in nude mice without causing acute toxicity by targeting both metabolic and oncogenic functions. Together, these data suggest its translational potential to foster new strategies for cancer therapy.

IDH2 reprograms mitochondrial dynamics in cancer through a HIF-1α-regulated pseudohypoxic state

The role of mitochondria in cancer continues to be debated and paradoxically implicated in opposing functions in tumor growth and tumor suppression. To understand this dichotomy, we explored the function of mitochondrial isocitrate dehydrogenase (IDH)2, a tricarboxylic acid cycle enzyme mutated in subsets of acute leukemias and gliomas, in cancer. Silencing of IDH2 in prostate cancer cells impaired oxidative bioenergetics, elevated reactive oxygen species (ROS) production, and promoted exaggerated mitochondrial dynamics. This was associated with increased subcellular mitochondrial trafficking, turnover of membrane focal adhesion complexes, and enhanced tumor cell migration and invasion, without changes in cell cycle progression. Mechanistically, loss of IDH2 caused ROS-dependent stabilization of hypoxia-inducible factor-1α in normoxia, which was required for increased mitochondrial trafficking and tumor cell movements. Therefore, IDH2 is a dual regulator of cancer bioenergetics and tumor cell motility. This pathway may reprogram mitochondrial dynamics to differentially adjust energy production or promote tumor cell invasion in response to microenvironment conditions.-Wang, Y., Agarwal, E., Bertolini, I., Ghosh, J. C., Seo, J. H., Altieri, D. C. IDH2 reprograms mitochondrial dynamics in cancer through a HIF-1α-regulated pseudohypoxic state.

Tracking Photodynamic- and Chemotherapy-Induced Redox-State Perturbations in 3D Culture Models of Pancreatic Cancer: A Tool for Identifying Therapy-Induced Metabolic Changes

The metabolic plasticity of cancer cells is considered a highly advantageous phenotype that is crucial for disease progression and acquisition of treatment resistance. A better understanding of cancer metabolism and its adaptability after treatments is vital to develop more effective therapies. To screen novel therapies and combination regimens, three-dimensional (3D) culture models of cancers are attractive platforms as they recapitulate key features of cancer. By applying non-perturbative intensity-based redox imaging combined with high-throughput image analysis, we demonstrated metabolic heterogeneity in various 3D culture models of pancreatic cancer. Photodynamic therapy and oxaliplatin chemotherapy, two cancer treatments with relevance to pancreatic cancer, induced perturbations in redox state in 3D microtumor cultures of pancreatic cancer. In an orthotopic mouse model of pancreatic cancer, a similar disruption in redox homeostasis was observed on ex vivo slices following photodynamic therapy in vivo. Taken together, redox imaging on cancer tissues combined with high-throughput analysis can elucidate dynamic spatiotemporal changes in metabolism following treatment, which will benefit the design of new metabolism-targeted therapeutic approaches.

Low profile high value target: The role of OxLDL in cancer

Unhealthy Western-type diet and physical inactivity are highly associated with the current obesity epidemic and its related metabolic diseases such as atherosclerosis and non-alcoholic steatohepatitis. In addition, increasing evidence indicates that obesity is also a major risk factor for several types of common cancers. Recent studies have provided correlative support that disturbed lipid metabolism plays a role in cancer risk and development, pointing towards parallels in metabolic derangements between metabolic diseases and cancer. An important feature of disturbed lipid metabolism is the increase in circulating low-density lipoproteins, which can be oxidized (oxLDL). Elevated oxLDL and the level of its receptors have been positively associated with increased risk of various types of cancer. This review discusses the pro-oncogenic role of oxLDL in tumor development, progression and potential therapies, and provides insights into the underlying mechanisms.

BET protein targeting suppresses the PD-1/PD-L1 pathway in triple-negative breast cancer and elicits anti-tumor immune response

Therapeutic strategies aiming to leverage anti-tumor immunity are being intensively investigated as they show promising results in cancer therapy. The PD-1/PD-L1 pathway constitutes an important target to restore functional anti-tumor immune response. Here, we report that BET protein inhibition suppresses PD-1/PD-L1 in triple-negative breast cancer. BET proteins control PD-1 expression in T cells, and PD-L1 in breast cancer cell models. BET protein targeting reduces T cell-derived interferon-γ production and signaling, thereby suppressing PD-L1 induction in breast cancer cells. Moreover, BET protein inhibition improves tumor cell-specific T cell cytotoxic function. Overall, we demonstrate that BET protein targeting represents a promising strategy to overcome tumor-reactive T cell exhaustion and improve anti-tumor immune responses, by reducing the PD-1/PD-L1 axis in triple-negative breast cancer.

Macrophage ABHD5 Suppresses NFκB-Dependent Matrix Metalloproteinase Expression and Cancer Metastasis

Metabolic reprogramming in tumor-associated macrophages (TAM) is associated with cancer development, however, the role of macrophage triglyceride metabolism in cancer metastasis is unclear. Here, we showed that TAMs exhibited heterogeneous expression of abhydrolase domain containing 5 (ABHD5), an activator of triglyceride hydrolysis, with migratory TAMs expressing lower levels of ABHD5 compared with the nonmigratory TAMs. ABHD5 expression in macrophages inhibited cancer cell migration in vitro in xenograft models and in genetic cancer models. The effects of macrophage ABHD5 on cancer cell migration were dissociated from its metabolic function as neither triglycerides nor ABHD5-regulated metabolites from macrophages affected cancer cell migration. Instead, ABHD5 deficiency in migrating macrophages promoted NFκB p65-dependent production of matrix metalloproteinases (MMP). ABHD5 expression negatively correlated with MMP expression in TAMs and was associated with better survival in patients with colorectal cancer. Taken together, our findings show that macrophage ABHD5 suppresses NFκB-dependent MMP production and cancer metastasis and may serve as a prognostic marker in colorectal cancer. SIGNIFICANCE: These findings highlight the mechanism by which reduced expression of the metabolic enzyme ABHD5 in macrophages promotes cancer metastasis.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/21/5513/F1.large.jpg.

Chemotherapeutic Targets in Osteosarcoma: Insights from Synchrotron-MicroFTIR and Quasi-Elastic Neutron Scattering

This study aimed at the development of improved drugs against human osteosarcoma, which is the most common primary bone tumor in children and teenagers with a low prognosis. New insights into the impact of an unconventional Pd(II) anticancer agent on human osteosarcoma cells were obtained by synchrotron radiation-Fourier transform infrared microspectroscopy and quasi-elastic neutron scattering (QENS) experiments from its effect on the cellular metabolism to its influence on intracellular water, which can be regarded as a potential secondary pharmacological target. Specific infrared biomarkers of drug action were identified, enabling a molecular-level description of variations in cellular biochemistry upon drug exposure. The main changes were detected in the protein and lipid cellular components, namely, in the ratio of unsaturated-to-saturated fatty acids. QENS revealed reduced water mobility within the cytoplasm for drug-treated cells, coupled to a disruption of the hydration layers of biomolecules. Additionally, the chemical and dynamical profiles of osteosarcoma cells were compared to those of metastatic breast cancer cells, revealing distinct dissimilarities that may influence drug activity.

Drugging cancer metabolism: Expectations vs. reality

As compared to their normal counterparts, neoplastic cells exhibit a variety of metabolic changes that reflect not only genetic and epigenetic defects underlying malignant transformation, but also the nutritional and immunobiological conditions of the tumor microenvironment. Such alterations, including the so-called Warburg effect (an increase in glucose uptake largely feeding anabolic and antioxidant metabolism), have attracted considerable attention as potential targets for the development of novel anticancer therapeutics. However, very few drugs specifically conceived to target bioenergetic cancer metabolism are currently approved by regulatory agencies for use in humans. This reflects the elevated degree of heterogeneity and redundancy in the metabolic circuitries exploited by neoplastic cells from different tumors (even of the same type), as well as the resemblance of such metabolic pathways to those employed by highly proliferating normal cells. Here, we summarize the major metabolic alterations that accompany oncogenesis, the potential of targeting bioenergetic metabolism for cancer therapy, and the obstacles that still prevent the clinical translation of such a promising therapeutic paradigm.

Myc-mediated transcriptional regulation of the mitochondrial chaperone TRAP1 controls primary and metastatic tumor growth

The role of mitochondria in cancer continues to be debated, and whether exploitation of mitochondrial functions is a general hallmark of malignancy or a tumor- or context-specific response is still unknown. Using a variety of cancer cell lines and several technical approaches, including siRNA-mediated gene silencing, ChIP assays, global metabolomics and focused metabolite analyses, bioenergetics, and cell viability assays, we show that two oncogenic Myc proteins, c-Myc and N-Myc, transcriptionally control the expression of the mitochondrial chaperone TNFR-associated protein-1 (TRAP1) in cancer. In turn, this Myc-mediated regulation preserved the folding and function of mitochondrial oxidative phosphorylation (OXPHOS) complex II and IV subunits, dampened reactive oxygen species production, and enabled oxidative bioenergetics in tumor cells. Of note, we found that genetic or pharmacological targeting of this pathway shuts off tumor cell motility and invasion, kills Myc-expressing cells in a TRAP1-dependent manner, and suppresses primary and metastatic tumor growth in vivo We conclude that exploitation of mitochondrial functions is a general trait of tumorigenesis and that this reliance of cancer cells on mitochondrial OXPHOS pathways could offer an actionable therapeutic target in the clinic.

Metabolic adaptability in metastatic breast cancer by AKR1B10-dependent balancing of glycolysis and fatty acid oxidation

The different stages of the metastatic cascade present distinct metabolic challenges to tumour cells and an altered tumour metabolism associated with successful metastatic colonisation provides a therapeutic vulnerability in disseminated disease. We identify the aldo-keto reductase AKR1B10 as a metastasis enhancer that has little impact on primary tumour growth or dissemination but promotes effective tumour growth in secondary sites and, in human disease, is associated with an increased risk of distant metastatic relapse. AKR1B10^High tumour cells have reduced glycolytic capacity and dependency on glucose as fuel source but increased utilisation of fatty acid oxidation. Conversely, in both 3D tumour spheroid assays and in vivo metastasis assays, inhibition of fatty acid oxidation blocks AKR1B10^High-enhanced metastatic colonisation with no impact on AKR1B10^Low cells. Finally, mechanistic analysis supports a model in which AKR1B10 serves to limit the toxic side effects of oxidative stress thereby sustaining fatty acid oxidation in metabolically challenging metastatic environments.

Cancer cells must develop distinct metabolic adaptations to survive in challenging metastatic environments. Here, the authors find, via an in vivo RNAi screen, that the aldo-keto reductase AKR1B10 limits the toxic side effects of oxidative stress to sustain fatty acid oxidation and promote metastatic colonisation.

HSP90 Molecular Chaperones, Metabolic Rewiring, and Epigenetics: Impact on Tumor Progression and Perspective for Anticancer Therapy

Heat shock protein 90 (HSP90) molecular chaperones are a family of ubiquitous proteins participating in several cellular functions through the regulation of folding and/or assembly of large multiprotein complexes and client proteins. Thus, HSP90s chaperones are, directly or indirectly, master regulators of a variety of cellular processes, such as adaptation to stress, cell proliferation, motility, angiogenesis, and signal transduction. In recent years, it has been proposed that HSP90s play a crucial role in carcinogenesis as regulators of genotype-to-phenotype interplay. Indeed, HSP90 chaperones control metabolic rewiring, a hallmark of cancer cells, and influence the transcription of several of the key-genes responsible for tumorigenesis and cancer progression, through either direct binding to chromatin or through the quality control of transcription factors and epigenetic effectors. In this review, we will revise evidence suggesting how this interplay between epigenetics and metabolism may affect oncogenesis. We will examine the effect of metabolic rewiring on the accumulation of specific metabolites, and the changes in the availability of epigenetic co-factors and how this process can be controlled by HSP90 molecular chaperones. Understanding deeply the relationship between epigenetic and metabolism could disclose novel therapeutic scenarios that may lead to improvements in cancer treatment.

Metabolic pathways regulating colorectal cancer initiation and progression

Colorectal cancer (CRC) is one of the most common types of cancer worldwide. Despite recent advances in the molecular genetics of CRC, poor treatment outcomes highlight the need for a better understanding of the underlying mechanisms accounting for tumor initiation and progression. Recently, deregulation of cellular metabolism has emerged as a key hallmark of cancer. Reprogramming of core cellular metabolic pathways by cancer cells provides energy, anaplerotic precursors and reducing equivalents required to support tumor growth. Here, we review key findings implicating cancer metabolism as a major contributor of tumor initiation, growth and metastatic dissemination in CRC. We summarize the metabolic pathways governing stem cell fate in the intestine, the metabolic adaptations of proliferating colon cancer cells and their crosstalk with oncogenic signaling, and how they fulfill the energetic demands imposed by the metastatic cascade. Lastly, we discuss how some of these metabolic pathways could represent new vulnerabilities of CRC cells with the potential to be targeted.

Critical role of the MCAM-ETV4 axis triggered by extracellular S100A8/A9 in breast cancer aggressiveness

Metastatic breast cancer is the leading cause of cancer-associated death in women. The progression of this fatal disease is associated with inflammatory responses that promote cancer cell growth and dissemination, eventually leading to a reduction of overall survival. However, the mechanism(s) of the inflammation-boosted cancer progression remains unclear. In this study, we found for the first time that an extracellular cytokine, S100A8/A9, accelerates breast cancer growth and metastasis upon binding to a cell surface receptor, melanoma cell adhesion molecule (MCAM). Our molecular analyses revealed an important role of ETS translocation variant 4 (ETV4), which is significantly activated in the region downstream of MCAM upon S100A8/A9 stimulation, in breast cancer progression in vitro as well as in vivo. The MCAM-mediated activation of ETV4 induced a mobile phenotype called epithelial-mesenchymal transition (EMT) in cells, since we found that ETV4 transcriptionally upregulates ZEB1, a strong EMT inducer, at a very high level. In contrast, downregulation of either MCAM or ETV4 repressed EMT, resulting in greatly weakened tumor growth and lung metastasis. Overall, our results revealed that ETV4 is a novel transcription factor regulated by the S100A8/A9-MCAM axis, which leads to EMT through ZEB1 and thereby to metastasis in breast cancer cells. Thus, therapeutic strategies based on our findings might improve patient outcomes.

"Locked" cancer cells are more sensitive to chemotherapy

The treatment of metastatic cancer is a great challenging issue throughout the world. Conventional chemotherapy can kill the cancer cells and, whereas, would exacerbate the metastasis and induce drug resistance. Here, a new combinatorial treatment strategy of metastatic cancer was probed via subsequentially dosing dual nanomedicines, marimastat-loaded thermosensitive liposomes (MATT-LTSLs) and paclitaxel nanocrystals (PTX-Ns), via intravenous and intratumoral injection. First, the metastasis was blocked and cancer cells were locked in the tumor microenvironment (TME) by delivering the matrix metalloproteinase (MMP) inhibitor, MATT, to the tumor with LTSLs, downregulating the MMPs by threefold and reducing the degradation of the extracellular matrix. And then, the "locked" cancer cells were efficiently killed via intratumoral injection of the other cytotoxic nanomedicine, PTX-Ns, along with no metastasis and 100% inhibition of tumor growth. This work highlights the importance of the TME's integrity in the chemotherapy duration. We believe this is a generalized strategy for cancer treatment and has potential guidance for the clinical administration.

Extracellular vesicles in the tumor microenvironment: old stories, but new tales

Mammalian cells synthesize and release heterogeneous extracellular vesicles (EVs) which can be generally recognized as subclasses including exosomes, microvesicles (MVs), and apoptotic bodies (ABs), each differing in their biogenesis, composition and biological functions from others. EVs can originate from normal or cancer cells, transfer bioactive cargoes to both adjacent and distant sites, and orchestrate multiple key pathophysiological events such as carcinogenesis and malignant progression. Emerging as key messengers that mediate intercellular communications, EVs are being paid substantial attention in various disciplines including but not limited to cancer biology and immunology. Increasing lines of research advances have revealed the critical role of EVs in the establishment and maintenance of the tumor microenvironment (TME), including sustaining cell proliferation, evading growth suppression, resisting cell death, acquiring genomic instability and reprogramming stromal cell lineages, together contributing to the generation of a functionally remodeled TME. In this article, we present updates on major topics that document how EVs are implicated in proliferative expansion of cancer cells, promotion of drug resistance, reprogramming of metabolic activity, enhancement of metastatic potential, induction of angiogenesis, and escape from immune surveillance. Appropriate and insightful understanding of EVs and their contribution to cancer progression can lead to new avenues in the prevention, diagnosis and treatment of human malignancies in future medicine.

S100A4 alters metabolism and promotes invasion of lung cancer cells by up-regulating mitochondrial complex I protein NDUFS2

It is generally accepted that alterations in metabolism are critical for the metastatic process; however, the mechanisms by which these metabolic changes are controlled by the major drivers of the metastatic process remain elusive. Here, we found that S100 calcium-binding protein A4 (S100A4), a major metastasis-promoting protein, confers metabolic plasticity to drive tumor invasion and metastasis of non-small cell lung cancer cells. Investigating how S100A4 regulates metabolism, we found that S100A4 depletion decreases oxygen consumption rates, mitochondrial activity, and ATP production and also shifts cell metabolism to higher glycolytic activity. We further identified that the 49-kDa mitochondrial complex I subunit NADH dehydrogenase (ubiquinone) Fe-S protein 2 (NDUFS2) is regulated in an S100A4-dependent manner and that S100A4 and NDUFS2 exhibit co-occurrence at significant levels in various cancer types as determined by database-driven analysis of genomes in clinical samples using cBioPortal for Cancer Genomics. Importantly, we noted that S100A4 or NDUFS2 silencing inhibits mitochondrial complex I activity, reduces cellular ATP level, decreases invasive capacity in three-dimensional growth, and dramatically decreases metastasis rates as well as tumor growth in vivo Finally, we provide evidence that cells depleted in S100A4 or NDUFS2 shift their metabolism toward glycolysis by up-regulating hexokinase expression and that suppressing S100A4 signaling sensitizes lung cancer cells to glycolysis inhibition. Our findings uncover a novel S100A4 function and highlight its importance in controlling NDUFS2 expression to regulate the plasticity of mitochondrial metabolism and thereby promote the invasive and metastatic capacity in lung cancer.

Mechanisms of Metastasis and Cell Mobility - The Role of Metabolism

Tumour metastasis is responsible for more than 90% of tumour-associated mortality. About one third of breast cancer patients in the early stage develop metastases. The transformation in tumour development referred to as the "metastatic cascade" or "metastatic cycle" is a complex and multi-stage event. While it is generally recognised that epithelial-mesenchymal transformation (EMT) plays a crucial role in cancer progression and metastasis, the metabolic events in this process have received little attention to date. We would therefore like to provide a brief overview here of the influence of the metabolism on the progression and metastasis of tumours.

Using an in-vivo syngeneic spontaneous metastasis model identifies ID2 as a promoter of breast cancer colonisation in the brain

Background

Dissemination of breast cancers to the brain is associated with poor patient outcome and limited therapeutic options. In this study we sought to identify novel regulators of brain metastasis by profiling mouse mammary carcinoma cells spontaneously metastasising from the primary tumour in an immunocompetent syngeneic host.

Methods

4T1 mouse mammary carcinoma sublines derived from primary tumours and spontaneous brain and lung metastases in BALB/c mice were subject to genome-wide expression profiling. Two differentially expressed genes, Id2 and Aldh3a1, were validated in in-vivo models using mouse and human cancer cell lines. Clinical relevance was investigated in datasets of breast cancer patients with regards to distant metastasis-free survival and brain metastasis relapse-free survival. The role of bone morphogenetic protein (BMP)7 in regulating Id2 expression and promoting cell survival was investigated in two-dimensional and three-dimensional in-vitro assays.

Results

In the spontaneous metastasis model, expression of Id2 and Aldh3a1 was significantly higher in 4T1 brain-derived sublines compared with sublines from lung metastases or primary tumour. Downregulation of expression impairs the ability of cells to colonise the brain parenchyma whereas ectopic expression in 4T1 and human MDA-MB-231 cells promotes dissemination to the brain following intracardiac inoculation but has no impact on the efficiency of lung colonisation. Both genes are highly expressed in oestrogen receptor (ER)-negative breast cancers and, within this poor prognosis sub-group, increased expression correlates with reduced distant metastasis-free survival. ID2 expression also associates with reduced brain metastasis relapse-free survival. Mechanistically, BMP7, which is present at significantly higher levels in brain tissue compared with the lungs, upregulates ID2 expression and, after BMP7 withdrawal, this elevated expression is retained. Finally, we demonstrate that either ectopic expression of ID2 or BMP7-induced ID2 expression protects tumour cells from anoikis.

Conclusions

This study identifies ID2 as a key regulator of breast cancer metastasis to the brain. Our data support a model in which breast cancer cells that have disseminated to the brain upregulate ID2 expression in response to astrocyte-secreted BMP7 and this serves to support metastatic expansion. Moreover, elevated ID2 expression identifies breast cancer patients at increased risk of developing metastatic relapse in the brain.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-1093-9) contains supplementary material, which is available to authorized users.

Translational and HIF-1α-Dependent Metabolic Reprogramming Underpin Metabolic Plasticity and Responses to Kinase Inhibitors and Biguanides

There is increasing interest in therapeutically exploiting metabolic differences between normal and cancer cells. We show that kinase inhibitors (KIs) and biguanides synergistically and selectively target a variety of cancer cells. Synthesis of non-essential amino acids (NEAAs) aspartate, asparagine, and serine, as well as glutamine metabolism, are major determinants of the efficacy of KI/biguanide combinations. The mTORC1/4E-BP axis regulates aspartate, asparagine, and serine synthesis by modulating mRNA translation, while ablation of 4E-BP1/2 substantially decreases sensitivity of breast cancer and melanoma cells to KI/biguanide combinations. Efficacy of the KI/biguanide combinations is also determined by HIF-1α-dependent perturbations in glutamine metabolism, which were observed in VHL-deficient renal cancer cells. This suggests that cancer cells display metabolic plasticity by engaging non-redundant adaptive mechanisms, which allows them to survive therapeutic insults that target cancer metabolism.

Colorectal Cancer and Metabolism

Purpose of Review

Metabolic reprogramming is essential for the rapid proliferation of cancer cells and is thus recognized as a hallmark of cancer. In this review, we will discuss the etiologies and effects of metabolic reprogramming in colorectal cancer.

Recent Findings

Changes in cellular metabolism may precede the acquisition of driver mutations ultimately leading to colonocyte transformation. Oncogenic mutations and loss of tumor suppressor genes further reprogram CRC cells to upregulate glycolysis, glutaminolysis, one-carbon metabolism, and fatty acid synthesis. These metabolic changes are not uniform throughout tumors, as subpopulations of tumor cells may rely on different pathways to adapt to nutrient availability in the local tumor microenvironment. Finally, metabolic cross-communication between stromal cells, immune cells, and the gut microbiota enable CRC growth, invasion, and metastasis.

Summary

Altered cellular metabolism occurs in CRC at multiple levels, including in the cells that make up the bulk of CRC tumors, cancer stem cells, the tumor microenvironment, and host-microbiome interactions. This knowledge may inform the development of improved screening and therapeutics for CRC.

NRH:quinone oxidoreductase 2 (NQO2) and glutaminase (GLS) both play a role in large extracellular vesicles (LEV) formation in preclinical LNCaP-C4-2B prostate cancer model of progressive metastasis

In the course of studies aimed at the role of oxidative stress in the development of metastatic potential in the LNCaP-C4-2B prostate cancer progression model system, we found a relative decrease in the level of expression of the cytoplasmic nicotinamide riboside: quinone oxidoreductase (NQO2) and an increase in the oxidative stress in C4-2B cells compared to that in LNCaP or its derivatives C4 and C4-2. It was also found that C4-2B cells specifically shed large extracellular vesicles (LEVs) suggesting that these LEVs and their cargo could participate in the establishment of the osseous metastases. The level of expression of caveolin-1 increased as the system progresses from LNCaP to C4-2B. Since NQO2 RNA levels were not changed in LNCaP, C4, C4-2, and C4-2B, we tested an altered cellular distribution hypothesis of NQO2 being compartmentalized in the membrane fractions of C4-2B cells which are rich in lipid rafts and caveolae. This was confirmed when the detergent resistant membrane fractions were probed on immunoblots. Moreover, when the LEVs were analyzed for membrane associated caveolin-1 as possible cargo, we noticed that the enzyme NQO2 was also a component of the cargo along with caveolin-1 as seen in double immunofluorescence studies. Molecular modeling studies showed that a caveolin-1 accessible site is present in NQO2. Specific interaction between NQO2 and caveolin-1 was confirmed using deletion constructs of caveolin-1 fused with glutathione S-transferase (GST). Interestingly, whole cell lysate and mitochondrial preparations of LNCaP, C4, C4-2, and C4-2B showed an increasing expression of glutaminase (GLS, kidney type). The extrusion of LEVs appears to be a specific property of the bone metastatic C4-2B cells and this process could be inhibited by a GLS specific inhibitor BPTES, suggesting the critical role of a functioning glutamine metabolism. Our results indicate that a high level of expression of caveolin-1 in C4-2B cells contributes to an interaction between caveolin-1 and NQO2 and to their packaging as cargo in the shed LEVs. These results suggest an important role of membrane associated oxidoreductases in the establishment of osseous metastases in prostate cancer.

SPARC Inhibits Metabolic Plasticity in Ovarian Cancer

The tropism of ovarian cancer (OvCa) to the peritoneal cavity is implicated in widespread dissemination, suboptimal surgery, and poor prognosis. This tropism is influenced by stromal factors that are not only critical for the oncogenic and metastatic cascades, but also in the modulation of cancer cell metabolic plasticity to fulfill their high energy demands. In this respect, we investigated the role of Secreted Protein Acidic and Rich in Cysteine (SPARC) in metabolic plasticity of OvCa. We used a syngeneic model of OvCa in Sparc-deficient and proficient mice to gain comprehensive insight into the paracrine effect of stromal-SPARC in metabolic programming of OvCa in the peritoneal milieu. Metabolomic and transcriptomic profiling of micro-dissected syngeneic peritoneal tumors revealed that the absence of stromal-Sparc led to significant upregulation of the enzymes involved in glycolysis, TCA cycle, and mitochondrial electron transport chain (ETC), and their metabolic intermediates. Absence of stromal-Sparc increased reactive oxygen species and perturbed redox homeostasis. Recombinant SPARC exerted a dose-dependent inhibitory effect on glycolysis, mitochondrial respiration, ATP production and ROS generation. Comparative analysis with human tumors revealed that SPARC-regulated ETC-signature inversely correlated with SPARC transcripts. Targeting mitochondrial ETC by phenformin treatment of tumor-bearing Sparc-deficient and proficient mice mitigated the effect of SPARC-deficiency and significantly reduced tumor burden, ROS, and oxidative tissue damage in syngeneic tumors. In summary, our findings provide novel insights into the role of SPARC in regulating metabolic plasticity and bioenergetics in OvCa, and shines light on its potential therapeutic efficacy.

Cervical squamous cell carcinoma-secreted exosomal miR-221-3p promotes lymphangiogenesis and lymphatic metastasis by targeting VASH1

Cancer-secreted exosomal miRNAs are emerging mediators of cancer-stromal cross-talk in the tumor environment. Our previous miRNAs array of cervical squamous cell carcinoma (CSCC) clinical specimens identified upregulation of miR-221-3p. Here, we show that miR-221-3p is closely correlated with peritumoral lymphangiogenesis and lymph node (LN) metastasis in CSCC. More importantly, miR-221-3p is characteristically enriched in and transferred by CSCC-secreted exosomes into human lymphatic endothelial cells (HLECs) to promote HLECs migration and tube formation in vitro, and facilitate lymphangiogenesis and LN metastasis in vivo according to both gain-of-function and loss-of-function experiments. Furthermore, we identify vasohibin-1 (VASH1) as a novel direct target of miR-221-3p through bioinformatic target prediction and luciferase reporter assay. Re-expression and knockdown of VASH1 could respectively rescue and simulate the effects induced by exosomal miR-221-3p. Importantly, the miR-221-3p-VASH1 axis activates the ERK/AKT pathway in HLECs independent of VEGF-C. Finally, circulating exosomal miR-221-3p levels also have biological function in promoting HLECs sprouting in vitro and are closely associated with tumor miR-221-3p expression, lymphatic VASH1 expression, lymphangiogenesis, and LN metastasis in CSCC patients. In conclusion, CSCC-secreted exosomal miR-221-3p transfers into HLECs to promote lymphangiogenesis and lymphatic metastasis via downregulation of VASH1 and may represent a novel diagnostic biomarker and therapeutic target for metastatic CSCC patients in early stages.

FR58P1a; a new uncoupler of OXPHOS that inhibits migration in triple-negative breast cancer cells via Sirt1/AMPK/β1-integrin pathway

Highly malignant triple-negative breast cancer (TNBC) cells rely mostly on glycolysis to maintain cellular homeostasis; however, mitochondria are still required for migration and metastasis. Taking advantage of the metabolic flexibility of TNBC MDA-MB-231 cells to generate subpopulations with glycolytic or oxidative phenotypes, we screened phenolic compounds containing an ortho-carbonyl group with mitochondrial activity and identified a bromoalkyl-ester of hydroquinone named FR58P1a, as a mitochondrial metabolism-affecting compound that uncouples OXPHOS through a protonophoric mechanism. In contrast to well-known protonophore uncoupler FCCP, FR58P1a does not depolarize the plasma membrane and its effect on the mitochondrial membrane potential and bioenergetics is moderate suggesting a mild uncoupling of OXPHOS. FR58P1a activates AMPK in a Sirt1-dependent fashion. Although the activation of Sirt1/AMPK axis by FR58P1a has a cyto-protective role, selectively inhibits fibronectin-dependent adhesion and migration in TNBC cells but not in non-tumoral MCF10A cells by decreasing β1-integrin at the cell surface. Prolonged exposure to FR58P1a triggers a metabolic reprograming in TNBC cells characterized by down-regulation of OXPHOS-related genes that promote cell survival but comprise their ability to migrate. Taken together, our results show that TNBC cell migration is susceptible to mitochondrial alterations induced by small molecules as FR58P1a, which may have therapeutic implications.

Eco-evolutionary causes and consequences of temporal changes in intratumoural blood flow

Temporal changes in blood flow are commonly observed in malignant tumours, but the evolutionary causes and consequences are rarely considered. We propose that stochastic temporal variations in blood flow and microenvironmental conditions arise from the eco-evolutionary dynamics of tumour angiogenesis in which cancer cells, as individual units of selection, can influence and respond only to local environmental conditions. This leads to new vessels arising from the closest available vascular structure regardless of the size or capacity of this parental vessel. These dynamics produce unstable vascular networks with unpredictable spatial and temporal variations in blood flow and microenvironmental conditions. Adaptations of evolving populations to temporally varying environments in nature include increased diversity, greater motility and invasiveness, and highly plastic phenotypes, allowing for broad metabolic adaptability and rapid shifts to high rates of proliferation and profound quiescence. These adaptive strategies, when adopted in cancer cells, promote many commonly observed phenotypic properties including those found in the stem phenotype and in epithelial-to-mesenchymal transition. Temporal variations in intratumoural blood flow, which occur through the promotion of cancer cell phenotypes that facilitate both metastatic spread and resistance to therapy, may have substantial clinical consequences.

Microenvironmental regulation of cancer cell metabolism: implications for experimental design and translational studies

Cancers have an altered metabolism, and there is interest in understanding precisely how oncogenic transformation alters cellular metabolism and how these metabolic alterations can translate into therapeutic opportunities. Researchers are developing increasingly powerful experimental techniques to study cellular metabolism, and these techniques have allowed for the analysis of cancer cell metabolism, both in tumors and in ex vivo cancer models. These analyses show that, while factors intrinsic to cancer cells such as oncogenic mutations, alter cellular metabolism, cell-extrinsic microenvironmental factors also substantially contribute to the metabolic phenotype of cancer cells. These findings highlight that microenvironmental factors within the tumor, such as nutrient availability, physical properties of the extracellular matrix, and interactions with stromal cells, can influence the metabolic phenotype of cancer cells and might ultimately dictate the response to metabolically targeted therapies. In an effort to better understand and target cancer metabolism, this Review focuses on the experimental evidence that microenvironmental factors regulate tumor metabolism, and on the implications of these findings for choosing appropriate model systems and experimental approaches.

The miR-15b-5p/PDK4 axis regulates osteosarcoma proliferation through modulation of the Warburg effect

Blocking aerobic glycolysis has been proposed as an attractive therapeutic strategy for impairing the proliferation of cancer cells. However, the underlying mechanisms are poorly understood. Here, we show that miR-15b-5p was downregulated in osteosarcoma (OS) and that lower expression of miR-15b-5p promoted proliferation and contributed to the Warburg effect in OS cells. Mechanistically, miR-15b-5p acted as a tumor suppressor in OS by directly targeting pyruvate dehydrogenase kinase-4 and inhibiting its expression. These results reveal a previously unknown function of miR-15b-5p in OS, which is associated with metabolic alterations that promote cancer progression. miR-15b-5p may play an essential role in the molecular therapy of patients with OS.

Metabolic Hallmarks of Metastasis Formation

Metastasis to distant organs is a predictor of poor prognosis. Therefore, it is of paramount importance to understand the mechanisms that impinge on the different steps of the metastatic cascade. Recent work has revealed that particular metabolic pathways are rewired in cancer cells to support their transition through the metastatic cascade, resulting in the formation of secondary tumors in distant organs. Indeed, metabolic rewiring induces signaling pathways during initial cancer invasion, circulating cancer cells depend on enhanced antioxidant defenses, and cancer cells colonizing a distant organ require increased ATP production. Moreover, the local environment of the metastatic niche dictates the metabolic pathways secondary tumors rely on. Here we describe mechanisms of metabolic rewiring associated with distinct steps of metastasis formation.

A new role for extracellular vesicles: how small vesicles can feed tumors' big appetite

Cancer cells must adapt their metabolism in order to meet the energy requirements for cell proliferation, survival in nutrient-deprived environments, and dissemination. In particular, FA metabolism is emerging as a critical process for tumors. FA metabolism can be modulated through intrinsic changes in gene expression or signaling between tumor cells and also in response to signals from the surrounding microenvironment. Among these signals, extracellular vesicles (EVs) could play an important role in FA metabolism remodeling. In this review, we will present the role of EVs in tumor progression and especially in metabolic reprogramming. Particular attention will be granted to adipocytes. These cells, which are specialized in storing and releasing FAs, are able to shift tumor metabolism toward the use of FAs and, subsequently, increase tumor aggressiveness. Recent work demonstrates the involvement of EVs in this metabolic symbiosis.

Inhibition of FASN and ERα signalling during hyperglycaemia-induced matrix-specific EMT promotes breast cancer cell invasion via a caveolin-1-dependent mechanism

Since disturbed metabolic conditions such as obesity and diabetes can be critical determinants of breast cancer progression and therapeutic failure, we aimed to determine the mechanism responsible for their pro-oncogenic effects. Using non-invasive, epithelial-like ERα-positive MCF-7 and T47D human breast cancer cells we found that hyperglycaemia induced epithelial to mesenchymal transition (EMT), a key programme responsible for the development of metastatic disease. This was demonstrated by loss of the epithelial marker E-cadherin together with increases in mesenchymal markers such as vimentin, fibronectin and the transcription factor SLUG, together with an enhancement of cell growth and invasion. These phenotypic changes were only observed with cells grown on fibronectin and not with those plated on collagen. Analyzing metabolic parameters, we found that hyperglycaemia-induced, matrix-specific EMT promoted the Warburg effect by upregulating glucose uptake, lactate release and specific glycolytic enzymes and transporters. We showed that silencing of fatty acid synthase (FASN) and the downstream ERα, which we showed previously to mediate hyperglycaemia-induced chemoresistance in these cells, resulted in suppression of cell growth: however, this also resulted in a dramatic enhancement of cell invasion and SLUG mRNA levels via a novel caveolin-1-dependent mechanism.

Metabolomics uncovers a link between inositol metabolism and osteosarcoma metastasis

Cancer development and progression are characterized by complex molecular events. The acquisition of these events is primarily believed to result from alterations in gene and protein expression/function. Recent studies have also suggested the role of metabolic alterations, or "metabolic reprogramming," that may similarly contribute to these events. Indeed, our previous investigations in osteosarcoma (OS) identified metabolic changes uniquely linked to metastasis. Based on those findings, here we sought to build a more detailed understanding of the specific alterations in metabolites or metabolic pathways that may be responsible for the observed metastasis-associated metabolic alterations, suggested by gene expression data. This was pursued using a combination of high-throughput liquid- and gas-chromatography-based mass spectrometry (LC/MS and GC/MS) for a global metabolic profiling/subtraction of four pairs of high/low metastatic OS cell lines. By comparing the identity and level of the metabolites between high/low metastatic cells, several metabolic pathways were identified to be differentially activated, such as arginine, glutathione, inositol and fatty acid metabolic pathways. To further interrogate these results, we investigated the effects of inositol pathway dysregulation, through the exposure of metastatic OS cells to IP6 (inositol hexaphosphate). Although IP6 exposures had modest to minimal effects on cell proliferation, we observed reduced cellular glycolysis, down-regulation of PI3K/Akt signaling and suppression of OS metastatic progression. Collectively these data supported further investigation of metabolic sensitivities as anti-metastatic strategies in a clinical setting as well as investigation of altered metabolomics associated with metastatic progression.

Translating Mechanism-Based Strategies to Break the Obesity-Cancer Link: A Narrative Review

Prevalence of obesity, an established risk factor for many cancers, has increased dramatically over the past 50 years in the United States and across the globe. Relative to normoweight cancer patients, obese cancer patients often have poorer prognoses, resistance to chemotherapies, and are more likely to develop distant metastases. Recent progress on elucidating the mechanisms underlying the obesity-cancer connection suggests that obesity exerts pleomorphic effects on pathways related to tumor development and progression and, thus, there are multiple opportunities for primary prevention and treatment of obesity-related cancers. Obesity-associated alterations, including systemic metabolism, adipose inflammation, growth factor signaling, and angiogenesis, are emerging as primary drivers of obesity-associated cancer development and progression. These obesity-associated host factors interact with the intrinsic molecular characteristics of cancer cells, facilitating several of the hallmarks of cancer. Each is considered in the context of potential preventive and therapeutic strategies to reduce the burden of obesity-related cancers. In addition, this review focuses on emerging mechanisms behind the obesity-cancer link, as well as relevant dietary interventions, including calorie restriction, intermittent fasting, low-fat diet, and ketogenic diet, that are being implemented in preclinical and clinical trials, with the ultimate goal of reducing incidence and progression of obesity-related cancers.

Unique Metabolic Adaptations Dictate Distal Organ-Specific Metastatic Colonization

Metastases arising from tumors have the proclivity to colonize specific organs, suggesting that they must rewire their biology to meet the demands of the organ colonized, thus altering their primary properties. Each metastatic site presents distinct metabolic challenges to a colonizing cancer cell, ranging from fuel and oxygen availability to oxidative stress. Here, we discuss the organ-specific metabolic adaptations that cancer cells must undergo, which provide the ability to overcome the unique barriers to colonization in foreign tissues and establish the metastatic tissue tropism phenotype.

The lncRNA MACC1-AS1 promotes gastric cancer cell metabolic plasticity via AMPK/Lin28 mediated mRNA stability of MACC1

Background

Metabolic plasticity has been increasingly thought to be a determinant of tumor growth and metastasis. MACC1, a transcriptional regulator of MET, was recognized as an oncogene in gastric cancer (GC); however, its transcriptional or post-translational regulation was not clear. We previously reported the metabolic role of MACC1 in glycolysis to promote GC progression. MACC1-AS1 is the antisense lncRNA of MACC1, yet its function was previously unknown.

Methods

We profiled and analyzed the expression of MACC1-AS1 utilizing the TCGA database as well as in situ hybridization using 123 pairs of GC tissues and matched adjacent normal gastric mucosa tissues (ANTs). The biological role of MACC1-AS1 in cell growth and metastasis was determined by performing in vitro and in vivo functional experiments. Glycolysis and antioxidant capabilities were assayed to examine its metabolic function. Further, the specific regulatory effect of MACC1-AS1 on MACC1 was explored transcriptionally and post-transcriptionally.

Results

MACC1-AS1 was shown to be expressed significantly higher in GC tissues than in ANTs, which predicted poor prognosis in GC patients. MACC1-AS1 promoted GC cell proliferation and inhibited cell apoptosis under metabolic stress. Mechanistically, MACC1-AS1 stabilized MACC1 mRNA and post-transcriptionally augmented MACC1 expression. Further, MACC1-AS1 was shown to mediate metabolic plasticity through MACC1 upregulation and subsequent enhanced glycolysis and anti-oxidative capabilities, and this was suggested to be coordinated by the AMPK/Lin28 pathway.

Conclusions

Elevated expression of MACC1-AS1 in gastric cancer tissues is linked to poor prognosis and promotes malignant phenotype upon cancer cells. MACC1-AS1 is elevated under metabolic stress and facilitates metabolic plasticity by promoting MACC1 expression through mRNA stabilization. Our study implicates lncRNA MACC1-AS1 as a valuable biomarker for GC diagnosis and prognosis.

Electronic supplementary material

The online version of this article (10.1186/s12943-018-0820-2) contains supplementary material, which is available to authorized users.

Perspective on Circulating Tumor Cell Clusters: Why It Takes a Village to Metastasize

Circulating tumor cell (CTC) clusters may represent one of the key mechanisms initiating the metastasis process. However, the series of pathophysiologic events by which CTC clusters originate, enter the circulation, and reach the distant sites remain to be identified. The cellular and molecular mechanisms that provide survival advantage for CTC clusters during the transit in the blood stream are also still largely unknown. Understanding the biology of CTC clusters is critical to assess this unified scheme employed by cancer and to device strategies to overcome key pathways responsible for their improved metastatic potential. CTC clusters remain an underdeveloped area of research begging the attention of multidisciplinary cancer research teams. Here, we provide insight on existing preclinical evidence on the potential mechanisms leading to CTC cluster formation and dissemination and on processes that may offer survival advantage. We also offer our perspective on future directions to delineate the role of CTC clusters in metastatic cascade and discuss their clinical significance. Cancer Res; 78(4); 845-52. ©2018 AACR.

PGC-1α Promotes Breast Cancer Metastasis and Confers Bioenergetic Flexibility against Metabolic Drugs

Metabolic adaptations play a key role in fueling tumor growth. However, less is known regarding the metabolic changes that promote cancer progression to metastatic disease. Herein, we reveal that breast cancer cells that preferentially metastasize to the lung or bone display relatively high expression of PGC-1α compared with those that metastasize to the liver. PGC-1α promotes breast cancer cell migration and invasion in vitro and augments lung metastasis in vivo. Pro-metastatic capabilities of PGC-1α are linked to enhanced global bioenergetic capacity, facilitating the ability to cope with bioenergetic disruptors like biguanides. Indeed, biguanides fail to mitigate the PGC-1α-dependent lung metastatic phenotype and PGC-1α confers resistance to stepwise increases in metformin concentration. Overall, our results reveal that PGC-1α stimulates bioenergetic potential, which promotes breast cancer metastasis and facilitates adaptation to metabolic drugs.

Near-simultaneous intravital microscopy of glucose uptake and mitochondrial membrane potential, key endpoints that reflect major metabolic axes in cancer

While the demand for metabolic imaging has increased in recent years, simultaneous in vivo measurement of multiple metabolic endpoints remains challenging. Here we report on a novel technique that provides in vivo high-resolution simultaneous imaging of glucose uptake and mitochondrial metabolism within a dynamic tissue microenvironment. Two indicators were leveraged; 2-[N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl) amino]-2-deoxy-D-glucose (2-NBDG) reports on glucose uptake and Tetramethylrhodamine ethyl ester (TMRE) reports on mitochondrial membrane potential. Although we demonstrated that there was neither optical nor chemical crosstalk between 2-NBDG and TMRE, TMRE uptake was significantly inhibited by simultaneous injection with 2-NBDG in vivo. A staggered delivery scheme of the two agents (TMRE injection was followed by 2-NBDG injection after a 10-minute delay) permitted near-simultaneous in vivo microscopy of 2-NBDG and TMRE at the same tissue site by mitigating the interference of 2-NBDG with normal glucose usage. The staggered delivery strategy was evaluated under both normoxic and hypoxic conditions in normal tissues as well as in a murine breast cancer model. The results were consistent with those expected for independent imaging of 2-NBDG and TMRE. This optical imaging technique allows for monitoring of key metabolic endpoints with the unique benefit of repeated, non-destructive imaging within an intact microenvironment.

Fatty acid synthase (FASN) as a therapeutic target in breast cancer

INTRODUCTION

Ten years ago, we put forward the metabolo-oncogenic nature of fatty acid synthase (FASN) in breast cancer. Since the conception of this hypothesis, which provided a model to explain how FASN is intertwined with various signaling networks to cell-autonomously regulate breast cancer initiation and progression, FASN has received considerable attention as a therapeutic target. However, despite the ever-growing evidence demonstrating the involvement of FASN as part of the cancer-associated metabolic reprogramming, translation of the basic science-discovery aspects of FASN blockade to the clinical arena remains a challenge. Areas covered: Ten years later, we herein review the preclinical lessons learned from the pharmaceutical liabilities of the first generation of FASN inhibitors. We provide an updated view of the current development and clinical testing of next generation FASN-targeted drugs. We also discuss new clinico-molecular approaches that should help us to convert roadblocks into roadways that will propel forward our therapeutic understanding of FASN. Expert opinion: With the recent demonstration of target engagement and early signs of clinical activity with the first orally available, selective, potent and reversible FASN inhibitor, we can expect Big pharma to revitalize their interest in lipogenic enzymes as well-credentialed targets for oncology drug development in breast cancer.

Physiologic Medium Rewires Cellular Metabolism and Reveals Uric Acid as an Endogenous Inhibitor of UMP Synthase

A complex interplay of environmental factors impacts the metabolism of human cells, but neither traditional culture media nor mouse plasma mimic the metabolite composition of human plasma. Here, we developed a culture medium with polar metabolite concentrations comparable to those of human plasma (human plasma-like medium [HPLM]). Culture in HPLM, relative to that in traditional media, had widespread effects on cellular metabolism, including on the metabolome, redox state, and glucose utilization. Among the most prominent was an inhibition of de novo pyrimidine synthesis-an effect traced to uric acid, which is 10-fold higher in the blood of humans than of mice and other non-primates. We find that uric acid directly inhibits uridine monophosphate synthase (UMPS) and consequently reduces the sensitivity of cancer cells to the chemotherapeutic agent 5-fluorouracil. Thus, media that better recapitulates the composition of human plasma reveals unforeseen metabolic wiring and regulation, suggesting that HPLM should be of broad utility.

The Mitochondrial Complex(I)ty of Cancer

Recent evidence highlights that the cancer cell energy requirements vary greatly from normal cells and that cancer cells exhibit different metabolic phenotypes with variable participation of both glycolysis and oxidative phosphorylation. NADH-ubiquinone oxidoreductase (Complex I) is the largest complex of the mitochondrial electron transport chain and contributes about 40% of the proton motive force required for mitochondrial ATP synthesis. In addition, Complex I plays an essential role in biosynthesis and redox control during proliferation, resistance to cell death, and metastasis of cancer cells. Although knowledge about the structure and assembly of Complex I is increasing, information about the role of Complex I subunits in tumorigenesis is scarce and contradictory. Several small molecule inhibitors of Complex I have been described as selective anticancer agents; however, pharmacologic and genetic interventions on Complex I have also shown pro-tumorigenic actions, involving different cellular signaling. Here, we discuss the role of Complex I in tumorigenesis, focusing on the specific participation of Complex I subunits in proliferation and metastasis of cancer cells.

Modeling the process of human tumorigenesis

Modelling the genesis of human cancers is at a scientific turning point. Starting from primary sources of normal human cells, it is now possible to reproducibly generate several types of malignant cell populations. Powerful methods for clonally tracking and manipulating their appearance and progression in serially transplanted immunodeficient mice are also in place. These developments circumvent historic drawbacks inherent in analyses of cancers produced in model organisms, established human malignant cell lines, or highly heterogeneous patient samples. In this review, we survey the advantages, contributions and limitations of current de novo human tumorigenesis strategies and note several exciting prospects on the horizon.

A better understanding of the earliest stages of human cancer formation can enable future improvements in early detection, diagnosis and treatment. In this review, the authors summarize the methods enabling de novo tumorigenesis protocols to be applied to human cells and the insights derived from them to date, as well as the exciting and relevant technical developments anticipated to extend even further the utility of these strategies.

The EMT-activator Zeb1 is a key factor for cell plasticity and promotes metastasis in pancreatic cancer

Metastasis is the major cause of cancer-associated death. Partial activation of the epithelial-to-mesenchymal transition program (partial EMT) was considered a major driver of tumour progression from initiation to metastasis. However, the role of EMT in promoting metastasis has recently been challenged, in particular concerning effects of the Snail and Twist EMT transcription factors (EMT-TFs) in pancreatic cancer. In contrast, we show here that in the same pancreatic cancer model, driven by Pdx1-cre-mediated activation of mutant Kras and p53 (KPC model), the EMT-TF Zeb1 is a key factor for the formation of precursor lesions, invasion and notably metastasis. Depletion of Zeb1 suppresses stemness, colonization capacity and in particular phenotypic/metabolic plasticity of tumour cells, probably causing the observed in vivo effects. Accordingly, we conclude that different EMT-TFs have complementary subfunctions in driving pancreatic tumour metastasis. Therapeutic strategies should consider these potential specificities of EMT-TFs to target these factors simultaneously.

Eradicating Quiescent Tumor Cells by Targeting Mitochondrial Bioenergetics

The presence of quiescent cell populations in solid tumors represents a major challenge for disease eradication. Such cells are generally present in poorly vascularized tumor areas, show limited sensitivity to traditional chemotherapeutical drugs, and tend to resume proliferation, resulting in tumor reseeding and growth. There is growing recognition of the importance of developing therapies that target these quiescent cell populations to achieve long-lasting remission. Recent studies have shown that the combination of hypoxia and reduced nutrient availability in poorly vascularized areas results in limited tumor metabolic plasticity coupled with an increased sensitivity to perturbations in mitochondrial flux. Targeting of mitochondrial bioenergetics in these quiescent cell tumor populations may enable tumor eradication and improve the prognosis of patients with cancer.

Optical redox ratio identifies metastatic potential-dependent changes in breast cancer cell metabolism

The development of prognostic indicators of breast cancer metastatic risk could reduce the number of patients receiving chemotherapy for tumors with low metastatic potential. Recent evidence points to a critical role for cell metabolism in driving breast cancer metastasis. Endogenous fluorescence intensity of nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) can provide a label-free method for assessing cell metabolism. We report the optical redox ratio of FAD/(FAD + NADH) of four isogenic triple-negative breast cancer cell lines with varying metastatic potential. Under normoxic conditions, the redox ratio increases with increasing metastatic potential (168FARN>4T07>4T1), indicating a shift to more oxidative metabolism in cells capable of metastasis. Reoxygenation following acute hypoxia increased the redox ratio by 43 ± 9% and 33 ± 4% in the 4T1 and 4T07 cells, respectively; in contrast, the redox ratio decreased 14 ± 7% in the non-metastatic 67NR cell line. These results demonstrate that the optical redox ratio is sensitive to the metabolic adaptability of breast cancer cells with high metastatic potential and could potentially be used to measure dynamic functional changes that are indicative of invasive or metastatic potential.