Metabolic scavenging by cancer cells: when the going gets tough, the tough keep eating

Cancer is fundamentally a disease of uncontrolled cell proliferation. Tumour metabolism has emerged as an exciting new discipline studying how cancer cells obtain the necessary energy and cellular ‘building blocks’ to sustain growth. Glucose and glutamine have long been regarded as the key nutrients fuelling tumour growth. However, the inhospitable tumour microenvironment of certain cancers, like pancreatic cancer, causes the supply of these nutrients to be chronically insufficient for the demands of proliferating cancer cells. Recent work has shown that cancer cells are able to overcome this nutrient insufficiency by scavenging alternative substrates, particularly proteins and lipids. Here, we review recent work identifying the endocytic process of macropinocytosis and subsequent lysosomal processing as an important substrate-acquisition route. In addition, we discuss the impact of hypoxia on fatty acid metabolism and the relevance of exogenous lipids for supporting tumour growth as well as the routes by which tumour cells can access these lipids. Together, these cancer-specific scavenging pathways provide a promising opportunity for therapeutic intervention

Crosstalk between purine nucleotide metabolism and mitochondrial pathways in Plasmodium falciparum

Metabolism is known for its intricate adjustments to meet the needs of an organism. Due to demands of adaptation, parasite metabolic pathways are greatly altered from those of their hosts. A key difference in metabolic pathways in Plasmodium spp, during the intra-erythrocytic stages, pertains to energy metabolism with the absence of a major role for the mitochondria in adenosine triphosphate (ATP) generation. In most organisms there exists a tight link between nucleotide and energy metabolism. An important feature of purine nucleotide metabolism in Plasmodium falciparum is the absence of the de novo pathway, with purine requirements being completely met by the salvage pathway. Presence of the enzymes adenylosuccinate lyase, adenylosuccinate synthetase and adenosine monophosphate (AMP) deaminase, involved in AMP metabolism, suggests the existence of a functional purine nucleotide cycle (PNC) in P. falciparum with fumarate, a tricarboxylic acid (TCA) cycle intermediate, and ammonia being the net output from the cycle. In the absence of a conventional TCA cycle, the fate of fumarate generated from PNC merits examination. In this review we cover ATP generation through glycolysis, key features of the TCA cycle, the role of electron transport chain and the link between PNC and the mitochondrion. Recent studies using genetic approaches highlight unexpected features that were hitherto unknown with respect to these pathways and these are also summarized in this review

A rapid method for quantifying free and bound acetate based on alkylation and GC-MS analysis

Background: Acetyl-CoA is a key metabolic intermediate with roles in the production of energy and biomass, as well as in metabolic regulation. It was recently found that acetate is crucial for maintaining acetyl-CoA production in hypoxic cancer cells. However, the availability of free acetate in the tumor environment and how much tumor cells consume remains unknown. Similarly, much is still to be learned about changes in the dynamics and distribution of acetylation in response to tumor-relevant conditions. The analysis of acetate is non-trivial, and to help address these topics, we developed a rapid and robust method for the analysis of both free and bound acetate in biological samples. Results: We developed a sensitive and high-throughput method for the analysis of acetate based on alkylation to its propyl derivative and gas chromatography-mass spectrometry. The method facilitates simultaneous quantification of both 12C- and 13C-acetate, shows high reproducibility (< 10 % RSD), and has a wide linear range of quantification (2–2000 μM). We demonstrate the method’s utility by measuring free acetate uptake by cultured cancer cells and by quantifying total acetylation (using hydrolysis) in separate cellular compartments. Additionally, we measure free acetate in tissues and bio-fluids and show that there are considerable differences in acetate concentrations between organs in vivo, providing insights into its complex systemic metabolism and availability for various types of tumors. Conclusions: Our approach for the quantification of acetate is straightforward to implement using widely available equipment and reagents, and will aid in in-depth investigation of various aspects of acetate metabolism. It is also readily adaptable to the analysis of formate and short-chain fatty acids, making it highly relevant to the cancer metabolism community

Macropinocytosis renders a subset of pancreatic tumor cells resistant to mTOR inhibition

Pancreatic ductal adenocarcinoma (PDAC) features a near-universal mutation in KRAS. Additionally, the tumor suppressor PTEN is lost in ∼10% of patients, and in mouse models, this dramatically accelerates tumor progression. While oncogenic KRAS and phosphatidylinositol 3-kinase (PI3K) cause divergent metabolic phenotypes individually, how they synergize to promote tumor metabolic alterations and dependencies remains unknown. We show that in KRAS-driven murine PDAC cells, loss of Pten strongly enhances both mTOR signaling and macropinocytosis. Protein scavenging alleviates sensitivity to mTOR inhibition by rescuing AKT phosphorylation at serine 473 and consequently cell proliferation. Combined inhibition of mTOR and lysosomal processing of internalized protein eliminates the macropinocytosis-mediated resistance. Our results indicate that mTORC2, rather than mTORC1, is an important regulator of protein scavenging and that protein-mediated resistance could explain the lack of effectiveness of mTOR inhibitors in certain genetic backgrounds. Concurrent inhibition of mTOR and protein scavenging might be a valuable therapeutic approach

Acetyl-CoA synthetase 2 promotes acetate utilization and maintains cancer cell growth under metabolic stress

A functional genomics study revealed that the activity of acetyl-CoA synthetase 2 (ACSS2) contributes to cancer cell growth under low-oxygen and lipid-depleted conditions. Comparative metabolomics and lipidomics demonstrated that acetate is used as a nutritional source by cancer cells in an ACSS2-dependent manner, and supplied a significant fraction of the carbon within the fatty acid and phospholipid pools. ACSS2 expression is upregulated under metabolically stressed conditions and ACSS2 silencing reduced the growth of tumor xenografts. ACSS2 exhibits copy-number gain in human breast tumors, and ACSS2 expression correlates with disease progression. These results signify a critical role for acetate consumption in the production of lipid biomass within the harsh tumor microenvironment

A stromal lysolipid-autotaxin signaling axis promotes pancreatic tumor progression

Pancreatic ductal adenocarcinoma (PDAC) develops a pronounced stromal response reflecting an aberrant wound-healing process. This stromal reaction features transdifferentiation of tissue-resident pancreatic stellate cells (PSC) into activated cancer-associated fibroblasts, a process induced by PDAC cells but of unclear significance for PDAC progression. Here, we show that PSCs undergo a dramatic lipid metabolic shift during differentiation in the context of pancreatic tumorigenesis, including remodeling of the intracellular lipidome and secretion of abundant lipids in the activated, fibroblastic state. Specifically, stroma-derived lysophosphatidylcholines support PDAC cell synthesis of phosphatidylcholines, key components of cell membranes, and also facilitate production of the potent wound-healing mediator lysophosphatidic acid (LPA) by the extracellular enzyme autotaxin, which is overexpressed in PDAC. The autotaxin–LPA axis promotes PDAC cell proliferation, migration, and AKT activation, and genetic or pharmacologic autotaxin inhibition suppresses PDAC growth in vivo. Our work demonstrates how PDAC cells exploit the local production of wound-healing mediators to stimulate their own growth and migration. Significance: Our work highlights an unanticipated role for PSCs in producing the oncogenic LPA signaling lipid and demonstrates how PDAC tumor cells co-opt the release of wound-healing mediators by neighboring PSCs to promote their own proliferation and migration

Metabolic control of cellular differentiation

The role of metabolic rewiring during cellular differentiation is under intense investigation. Reporting recently in Science, Peng et al. (2016) found that activation of glycolysis supports T helper cell differentiation by controlling acetyl-coA and histone acetylation levels, identifying a link between metabolic state and epigenetic control of gene activity

Mechanism of growth inhibition of intraerythrocytic stages of Plasmodium falciparum by 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR)

Purine nucleotide synthesis in Plasmodium falciparum takes place solely by the purine salvage pathway in which preformed purine base(s) are salvaged from the host and acted upon by a battery of enzymes to generate AMP and GMP. Inhibitors of this pathway have a potent effect on the in vitro growth of P. falciparum and are hence, implicated as promising leads for the development of new generation anti-malarials. Here, we describe the mechanism of inhibition of the intraerythrocytic growth of P. falciparum by the purine nucleoside precursor, 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR). Our results show that AICAR toxicity is mediated through the erythrocyte in which AICAR is phosphorylated to its nucleotide, ZMP. Further, purine metabolite labeling of the parasitized erythrocytes by H-3]-hypoxanthine, in the presence of AICAR, showed a significant decrease in radioactive counts in adenylate fractions but not in guanylate fractions. The most dramatic effect on parasite growth was observed when erythrocytes pretreated with AICAR were used in culture. Pretreatment of erythrocytes with AICAR led to significant intracellular accumulation of ZMP and these erythrocytes were incapable of supporting parasite growth. These results implicate that in addition to the purine salvage pathway in P. falciparum, AICAR alters the metabolic status of the erythrocytes, which inhibits parasite growth. As AICAR and ZMP are metabolites in the human serum and erythrocytes, our studies reported here throw light on their possible role in disease susceptibility, and also suggests the possibility of AICAR being a potential prophylactic or chemotherapeutic anti-malarial compound. (C) 2011 Elsevier B.V. All rights reserved

CommuterScanner: Towards Smart Indoor Positioning Systems in Urban Transportation

With the rapid growth of modern cities, public transportation systems require smart planning to provide effective and competitive services to the daily commuters. Due to the presence of Wireless LAN Network (WLAN), Wi-Fi access is available to commuters during their daily commute. The overarching goal of this work is to leverage infrastructure-based indoor positioning systems (IIPS) deployed at train stations to enable several smart transportation use cases by analyzing commuter traffic. Specifically, in this work we address identification of whether a user is in-train or on-platform by utilizing two types of passively sensed Wi-Fi data, namely, received signal strength (RSSI) and phase vectors (AoA) measured at the deployed access points from data received from mobile devices. We conduct structured analysis of each data source, to identify features that distinguish on-platform and in-train devices. OurCommuterScanner solution achieves up to 90% accuracy using random forest model. Our solution works for a variety of deployments including APs with RSSI-only or RSSI + AoA capabilities and irrespective of if the device is connected to the Wi-Fi

Adenine metabolism in Plasmodium falciparum

Plasmodium falciparum lacks the de novo purine biosynthesis pathway and relies entirely on the salvage pathway to meet its purine nucleotide requirements. The entire flux for purine nucleotide biosynthesis in the parasite is believed to be through hypoxanthine guanine phosphoribosyltransferase (HGPRT), with the enzymes, adenosine kinase and adenine phosphoribosyltransferase (APRT) being unannotated in the Plasmodium genome database. This manuscript reports on the studies carried out to explore bypass mechanisms, if any, for AMP synthesis in the intraerythrocyitc stages of the parasite life cycle. Uptake and subsequent incorporation of radiolabel adenine in the nucleotide pool of saponin released erythrocyte free parasites implicated the role of parasite encoded enzymes in adenine metabolism. To explore the route for AMP synthesis in the parasite, we have monitored adenine mediated supplementation of metabolic viability in saponin released hadacidin (N-formyl-N-hydroxyglycine) treated parasites. Our results implicate the role of an APRT like activity that enables parasite survival when the flux through the HGPRT pathway is blocked