Macroautophagy (hereafter referred to as autophagy) is a process in which organelles termed autophagosomes deliver cytoplasmic constituents to lysosomes for degradation. Autophagy has a major role in cellular homeostasis and has been implicated in various forms of human disease. The role of autophagy in cancer seems to be complex, with reports indicating both pro-tumorigenic and tumour-suppressive roles. Here we show, in a humanized genetically-modified mouse model of pancreatic ductal adenocarcinoma (PDAC), that autophagy's role in tumour development is intrinsically connected to the status of the tumour suppressor p53. Mice with pancreases containing an activated oncogenic allele of Kras (also called Ki-Ras)--the most common mutational event in PDAC--develop a small number of pre-cancerous lesions that stochastically develop into PDAC over time. However, mice also lacking the essential autophagy genes Atg5 or Atg7 accumulate low-grade, pre-malignant pancreatic intraepithelial neoplasia lesions, but progression to high-grade pancreatic intraepithelial neoplasias and PDAC is blocked. In marked contrast, in mice containing oncogenic Kras and lacking p53, loss of autophagy no longer blocks tumour progression, but actually accelerates tumour onset, with metabolic analysis revealing enhanced glucose uptake and enrichment of anabolic pathways, which can fuel tumour growth. These findings provide considerable insight into the role of autophagy in cancer and have important implications for autophagy inhibition in cancer therapy. In this regard, we also show that treatment of mice with the autophagy inhibitor hydroxychloroquine, which is currently being used in several clinical trials, significantly accelerates tumour formation in mice containing oncogenic Kras but lacking p53.

SummaryA 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.

In response to tenacious stress signals, such as the unscheduled activation of oncogenes, cells can mobilize tumour suppressor networks to avert the hazard of malignant transformation. A large body of evidence indicates that oncogene-induced senescence (OIS) acts as such a break, withdrawing cells from the proliferative pool almost irreversibly, thus crafting a vital pathophysiological mechanism that protects against cancer. Despite the widespread contribution of OIS to the cessation of tumorigenic expansion in animal models and humans, we have only just begun to define the underlying mechanism and identify key players. Although deregulation of metabolism is intimately linked to the proliferative capacity of cells, and senescent cells are thought to remain metabolically active, little has been investigated in detail about the role of cellular metabolism in OIS. Here we show, by metabolic profiling and functional perturbations, that the mitochondrial gatekeeper pyruvate dehydrogenase (PDH) is a crucial mediator of senescence induced by BRAF(V600E), an oncogene commonly mutated in melanoma and other cancers. BRAF(V600E)-induced senescence was accompanied by simultaneous suppression of the PDH-inhibitory enzyme pyruvate dehydrogenase kinase 1 (PDK1) and induction of the PDH-activating enzyme pyruvate dehydrogenase phosphatase 2 (PDP2). The resulting combined activation of PDH enhanced the use of pyruvate in the tricarboxylic acid cycle, causing increased respiration and redox stress. Abrogation of OIS, a rate-limiting step towards oncogenic transformation, coincided with reversion of these processes. Further supporting a crucial role of PDH in OIS, enforced normalization of either PDK1 or PDP2 expression levels inhibited PDH and abrogated OIS, thereby licensing BRAF(V600E)-driven melanoma development. Finally, depletion of PDK1 eradicated melanoma subpopulations resistant to targeted BRAF inhibition, and caused regression of established melanomas. These results reveal a mechanistic relationship between OIS and a key metabolic signalling axis, which may be exploited therapeutically.

Previous work has shown that some cancer cells are highly dependent on serine/glycine uptake for proliferation. Although serine and glycine can be interconverted and either might be used for nucleotide synthesis and one-carbon metabolism, we show that exogenous glycine cannot replace serine to support cancer cell proliferation. Cancer cells selectively consumed exogenous serine, which was converted to intracellular glycine and one-carbon units for building nucleotides. Restriction of exogenous glycine or depletion of the glycine cleavage system did not impede proliferation. In the absence of serine, uptake of exogenous glycine was unable to support nucleotide synthesis. Indeed, higher concentrations of glycine inhibited proliferation. Under these conditions, glycine was converted to serine, a reaction that would deplete the one-carbon pool. Providing one-carbon units by adding formate rescued nucleotide synthesis and growth of glycine-fed cells. We conclude that nucleotide synthesis and cancer cell proliferation are supported by serine--rather than glycine--consumption.

Maddocks, O. D. K. et al. (2017) Modulating the therapeutic response of tumours to dietary serine and glycine starvation. Nature, 544(7650), pp. 372-376.There may be differences between this version and the published version. You are advised to consult the publisher's version if you wish to cite from it.http://eprints.gla.ac.uk/140432/ AbstractThe non-essential amino acids serine and glycine are used in multiple anabolic processes that support cancer cell growth and proliferation (reviewed in ref. 1). While some cancer cells upregulate de novo serine synthesis 2,3,4 , many others rely on exogenous serine for optimal growth 5,6,7 . Restriction of dietary serine and glycine can reduce tumour growth in xenograft and allograft models 7,8 . Here we show that this observation translates into more clinically relevant autochthonous tumours in genetically engineered mouse models of intestinal cancer (driven by Apc inactivation) or lymphoma (driven by Myc activation). The increased survival following dietary restriction of serine and glycine in these models was further improved by antagonizing the anti-oxidant response. Disruption of mitochondrial oxidative phosphorylation (using biguanides) led to a complex response that could improve or impede the anti-tumour effect of serine and glycine starvation. Notably, Krasdriven mouse models of pancreatic and intestinal cancers were less responsive to depletion of serine and glycine, reflecting an ability of activated Kras to increase the expression of enzymes that are part of the serine synthesis pathway and thus promote de novo serine synthesis.To assess the effect of dietary serine and glycine (SG) restriction in autochthonous tumour models, we used genetically engineered mouse models (GEMMs) of lymphoma (Eμ-Myc) and intestinal tumours (defective Apc). Eμ-Myc mice develop pre-neoplastic lesions within 28-42 days after birth 9 , and adenoma initiation is evident days after birth in Apc Min/+ mice 10 . Accordingly, Apc Min/+ mice carried high tumour numbers at 80 days, which subsequently increased in size but not number (Extended Data Fig. 1a). Transferring mice from normal chow diet to experimental diets 60-80 days after birth showed that an SG-free diet significantly extended survival in these models carrying pre-malignant lesions (Fig. 1a, b), with a slightly lower tumour burden in Apc Min/+ mice on the SG-free diet at clinical end point (Extended Data Fig. 1a). The diet reproducibly decreased serum SG from around 150 μM to 65 μM (Fig. 1c-e), while showing minimal or inconsistent impact on other amino acids, glucose and lactate (Fig. 1c, d and Extended Data Figs 1b, 2a, b), These results were further validated using an inducible intestinal tumour model (Lgr5-creER;Apc fl/fl ); transferring mice to the SG-free diet a week after induction. Again, the experimental diet caused a significant increase in survival compared to control diet (containing purified amino acids) or normal chow (containing whole protein as a source of amino acids) (Fig. 1f). (c, control, n = 14; control,...

Plasmax, a physiological cell culture medium, prevents metabolic artifacts imposed on cancer cells by commonly used media.

DeRossi, C. et al. Ablation of mouse phosphomannose isomerase (Mpi) causes mannose 6-phosphate accumulation, toxicity, and embryonic lethality.

Succinate dehydrogenase (SDH) is a hetero-tetrameric nuclear-encoded complex responsible for the oxidation of succinate to fumarate in the tricarboxylic acid (TCA) cycle. Loss-of-function mutations in any of the SDH genes are associated with cancer formation. However, the impact of SDH loss on cell metabolism and the mechanisms enabling growth of SDH-defective cells are largely unknown. Here, we generated Sdhb-ablated kidney mouse cells and employed comparative metabolomics and stable isotope-labelling approaches to identify nutritional requirements and metabolic adaptations to SDH loss. We found that lack of SDH activity commits cells to consume extracellular pyruvate, which sustains Warburg-like bioenergetic features. We further demonstrated that pyruvate carboxylation diverts glucose-derived carbons into aspartate biosynthesis, thus sustaining cell growth. By identifying pyruvate carboxylase as an essential gene for the proliferation and tumorigenic capacity of SDH-deficient cells, this study revealed a metabolic vulnerability for potential future treatment of SDH-associated malignancies.