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Supporting cell proliferation through nucleotide biosynthesis is an essential requirement for cancer cells. Hence, inhibition of folate-mediated one carbon (1C) metabolism, which is required for nucleotide synthesis, has been successfully exploited in anti-cancer therapy. Here, we reveal that mitochondrial folate metabolism is upregulated in patient-derived leukaemic stem cells (LSCs). We demonstrate that inhibition of mitochondrial 1C metabolism through impairment ofde novopurine synthesis has a cytostatic effect on chronic myeloid leukaemia (CML) cells. Consequently, changes in purine nucleotide levels lead to activation of AMPK signalling and suppression of mTORC1 activity. Notably, suppression of mitochondrial 1C metabolism increases expression of erythroid differentiation markers. Moreover, we find that increased differentiation occurs independently of AMPK signalling and can be reversed through reconstitution of purine levels and reactivation of mTORC1. Of clinical relevance, we identify that combination of 1C metabolism inhibition with imatinib, a frontline treatment for CML patients, decreases the number of therapy-resistant CML LSCs in a patient-derived xenograft model. Our results highlight a novel role for folate metabolism and purine sensing in stem cell fate decisions and leukaemogenesis.

Resistance to standard and novel therapies remains the main obstacle to cure in acute myeloid leukemia (AML) and is often driven by metabolic adaptations which are therapeutically actionable. Here we identify inhibition of mannose-6-phosphate isomerase (MPI), the first enzyme in the mannose metabolism pathway, as a sensitizer to both cytarabine and FLT3 inhibitors across multiple AML models. Mechanistically, we identify a connection between mannose metabolism and fatty acid metabolism, that is mediated via preferential activation of the ATF6 arm of the unfolded protein response (UPR). This in turn leads to cellular accumulation of polyunsaturated fatty acids, lipid peroxidation and ferroptotic cell death in AML cells. Our findings provide further support to the role of rewired metabolism in AML therapy resistance, unveil a novel connection between two apparently independent metabolic pathways and support further efforts to achieve eradication of therapy-resistant AML cells by sensitizing them to ferroptotic cell death.

Inhibition of autophagy has been proposed as a potential therapy for individuals with cancer. However, current lysosomotropic autophagy inhibitors have demonstrated limited efficacy in clinical trials. Therefore, validation of novel specific autophagy inhibitors using robust preclinical models is critical. In chronic myeloid leukemia (CML), minimal residual disease is maintained by persistent leukemic stem cells (LSCs), which drive tyrosine kinase inhibitor (TKI) resistance and patient relapse. Here, we show that deletion of autophagy-inducing kinase ULK1 (unc-51–like autophagy activating kinase 1) reduces growth of cell line and patient-derived xenografted CML cells in mouse models. Using primitive cells, isolated from individuals with CML, we demonstrate that pharmacological inhibition of ULK1 selectively targets CML LSCs ex vivo and in vivo, when combined with TKI treatment. The enhanced TKI sensitivity after ULK1-mediated autophagy inhibition is driven by increased mitochondrial respiration and loss of quiescence and points to oxidative stress–induced differentiation of CML LSCs, proposing an alternative strategy for treating patients with CML.

Objectives Fatty acid oxidation (FAO) and glycolysis have been implicated in immune regulation and activation of macrophages. However, investigation of human monocyte intracellular metabolism in the context of the hypoxic and inflammatory rheumatoid arthritis (RA) synovium is lacking. We hypothesized that exposure of monocytes to the hypoxic and inflammatory RA environment would have a profound impact on their metabolic state, and potential to contribute to disease pathology. Methods Human monocytes were isolated from buffy coats and exposed to hypoxia. Metabolic profiling of monocytes was carried out by LC-MS metabolomics. Inflammatory mediator release after LPS or RA-synovial fluid (RA-SF) stimulation was analysed by ELISA. FAO was inhibited by etomoxir or enhanced with exogenous carnitine supplementation. Transcriptomics of RA blood monocytes and RA-SF macrophages was carried out by microarray. Results Hypoxia exacerbated monocyte-derived CCL20 and IL-1β release in response to LPS, and increased glycolytic intermediates at the expense of carnitines. Modulation of carnitine identified a novel role for FAO in the production of CCL20 in response to LPS. Transcriptional analysis of RA blood monocytes and RA-SF macrophages revealed that fatty acid metabolism was altered and CCL20 increased when monocytes enter the synovial environment. In vitro analysis of monocytes showed that RA-SF increases carnitine abundance and CCL20 production in hypoxia, which was exacerbated by exogenous carnitine. Conclusion This work has revealed a novel inflammatory mechanism in RA that links FAO to CCL20 production in human monocytes, which could subsequently contribute to RA disease pathogenesis by promoting the recruitment of Th17 cells and osteoclastogenesis.

Metabolic rewiring is an important hallmark of cancer. The folate metabolism pathway, also known as one-carbon (1C) metabolism, allows for transfer of 1C units through folate intermediates for biosynthetic processes, including precursors for DNA synthesis. Recent studies have shown that enzymes involved in the mitochondrial arm of 1C metabolism are overexpressed in a subset of aggressive cancers and that their expression affects responses to anti-metabolite drug treatments. However, the role of 1C metabolism in therapy resistant leukemic stem cells (LSCs) is currently unknown. Therefore, we aimed to investigate the activity and the impact of genetic and pharmacological inhibition of folate enzymes in primitive chronic myeloid leukaemia (CML) cells. We initially performed transcriptomic analysis of CD34+38- cells, from individuals with chronic phase CML (E-MTAB-2581). This revealed a significant upregulation of folate metabolism genes in CML LSCs, including serine hydroxymethyltransferase (SHMT2; p≤0.05), a key mitochondrial enzyme. To assess the activity of 1C metabolism in primitive cells we performed gas chromatography-mass spectrometry-mediated secretomic analysis using patient-derived, c-KIT enriched CML cells, which revealed a significant increase in the exchange rate of formate (folate intermediate necessary for purine synthesis) in CML cells, when compared to the secretome of normal counterparts (p Following CRISPR-Cas9-mediated SHMT2 knockout (KO) in CML cell line, we observed a significant decrease in growth rate, together with a decrease in glycolytic capacity and oxygen consumption rate (p Phenotypically, both pharmacological and genetic inhibition of SHMT1/2 induced the expression of erythropoiesis markers CD71 and Glycophorin A, which was reversed following formate supplementation. CRISPR-Cas9-mediated double AMPKα1/α2 KO revealed that the increased expression of these erythropoiesis markers following SHMT1/2 inhibition was independent of AMPK activity. Conversely, while NIX KO had no effect, pharmacological inhibition of ULK1 kinase activity, or genetic inhibition of ULK1 and ATG7 (protein important for autophagosome formation), prevented increased expression of CD71/Glycophorin A following SHMT1/2 inhibition. We next investigated the effect of 1C metabolism inhibition on differentiation and survival of primary CML cells. Of clinical relevance, pharmacological inhibition of SHMT1/2 promoted erythroid maturation of CD34+ CML cells (measured by expression of CD71, CD44, CD36 and Glycophorin A) when challenged with erythropoietin, which sensitises primitive cells to erythroid lineage commitment. Lastly, pharmacological inhibition of 1C metabolism decreased the colony formation capacity of CD34+ CML by 50%, with minimum effect on normal CD34+ cells. Moreover, combination treatment of SHIN1 with imatinib, a frontline treatment for CML patients, further increased the sensitivity of primary CML cells to imatinib by 40%. Overall, our novel findings indicate that disruption of the folate metabolism pathway inhibits central carbon metabolism in CML cells, promotes autophagy dependent, but AMPK independent maturation phenotype and has detrimental effect on the survival of primitive CML cells. Disclosures No relevant conflicts of interest to declare.

Career situation of first and presenting author Post-doctoral fellow. Introduction Metabolic pathways are considered to have a governing role in inflammatory cascades in myeloid cells. This is particularly evident in murine macrophages where glycolysis and fatty acid oxidation (FAO) have been implicated in inflammatory cascades and immune regulation respectively.1 However, investigation of intracellular metabolism of human monocytes in the context of the hypoxic and inflammatory RA synovium is lacking. Objectives To mimic the hypoxic RA environment in vitro and metabolically profile human monocytes. Determine if altered metabolic pathways have a functional impact on monocytes under disease-relevant conditions. Methods Human monocytes were isolated from buffy coats and were exposed to hypoxia in vitro. Metabolic profiling of monocytes was carried out by LC-MS metabolomics. Inflammatory mediator release after LPS or RA-synovial fluid (RA-SF) stimulation was analysed by ELISA. FAO was inhibited by etomoxir or enhanced with exogenous carnitine supplements. Transcriptomics of RA blood monocytes and RA-SF macrophages was carried out by microarray. Results We report that hypoxia exacerbates CCL20 and IL-1β release in response to LPS and increases glycolytic intermediates at the expense of carnitines. Modulation of carnitine identified a novel role for FAO in the production of CCL20 in response to LPS. Transcriptomics of RA blood monocytes and RA-SF macrophages revealed that fatty acid metabolism was altered and CCL20 was increased when monocytes enter the RA milieu. In vitro analysis of monocytes showed that RA-SF increases carnitine abundance and CCL20 production in hypoxia, which was exacerbated by exogenous carnitine. Conclusions This work has revealed a novel inflammatory mechanism in RA which links FAO to CCL20 production in human monocytes. This may contribute to RA disease pathogenesis by promoting the recruitment of Th17 cells and osteoclastogenesis.2 3 References O’Neill LA, et al. Nat Rev Immunol 2016;16:553–565. Hirota K, et al. J Exp Med 2007;204:2803–2812. Lisignoli G, et al. J Cell Physiol 2009;221:154–160. Disclosure of Interest None declared.

Discovered over fifty years ago, autophagy is a double-edged blade. On one hand, it regulates cellular energy sources by “cannibalization” of its own cellular components, feeding on proteins and other unused cytoplasmic factors. On the other, it is a recycling process that removes dangerous waste from the cytoplasm keeping the cell clean and healthy. Failure of the autophagic machinery is translated in dysfunction of the immune response, in aging, and in the progression of pathologies such as Parkinson disease, diabetes, and cancer. Further investigation identified autophagy with a protective role in specific types of cancer, whereas in other cases it can promote tumorigenesis. Evidence shows that treatment with chemotherapeutics can upregulate autophagy in order to maintain a stable intracellular environment promoting drug resistance and cell survival. Leukemia, a blood derived cancer, represents one of the malignancies in which autophagy is responsible for drug treatment failure. Inhibition of autophagy is becoming a strategic target for leukemic stem cell (LSC) eradication. Interestingly, the latest findings demonstrate that LSCs show higher levels of mitochondrial metabolism compared to normal stem cells. With this review, we aim to explore the links between autophagy and metabolism in the hematopoietic system, with special focus on primitive LSCs.