ATP citrate lyase mediates resistance of colorectal cancer cells to SN38

Epigenetic-Transcriptional Regulation of Fatty Acid Metabolism and Its Alterations in Leukaemia

In recent years fatty acid metabolism has gained greater attention in haematologic cancers such as acute myeloid leukaemia. The oxidation of fatty acids provides fuel in the form of ATP and NADH, while fatty acid synthesis provides building blocks for cellular structures. Here, we will discuss how leukaemic cells differ from healthy cells in their increased reliance on fatty acid metabolism. In order to understand how these changes are achieved, we describe the main pathways regulating fatty acid metabolism at the transcriptional level and highlight the limited knowledge about related epigenetic mechanisms. We explore these mechanisms in the context of leukaemia and consider the relevance of the bone marrow microenvironment in disease management. Finally, we discuss efforts to interfere with fatty acid metabolism as a therapeutic strategy along with the use of metabolic parameters as biomarkers.

The role of metabolism and tunneling nanotube-mediated intercellular mitochondria exchange in cancer drug resistance

Intercellular communications play a major role in tissue homeostasis. In pathologies such as cancer, cellular interactions within the tumor microenvironment (TME) contribute to tumor progression and resistance to therapy. Tunneling nanotubes (TNTs) are newly discovered long-range intercellular connections that allow the exchange between cells of various cargos, ranging from ions to whole organelles such as mitochondria. TNT-transferred mitochondria were shown to change the metabolism and functional properties of recipient cells as reported for both normal and cancer cells. Metabolic plasticity is now considered a hallmark of cancer as it notably plays a pivotal role in drug resistance. The acquisition of cancer drug resistance was also associated to TNT-mediated mitochondria transfer, a finding that relates to the role of mitochondria as a hub for many metabolic pathways. In this review, we first give a brief overview of the various mechanisms of drug resistance and of the cellular communication means at play in the TME, with a special focus on the recently discovered TNTs. We further describe recent studies highlighting the role of the TNT-transferred mitochondria in acquired cancer cell drug resistance. We also present how changes in metabolic pathways, including glycolysis, pentose phosphate and lipid metabolism, are linked to cancer cell resistance to therapy. Finally, we provide examples of novel therapeutic strategies targeting mitochondria and cell metabolism as a way to circumvent cancer cell drug resistance.

When fats commit crimes: fatty acid metabolism, cancer stemness and therapeutic resistance

The role of fatty acid metabolism, including both anabolic and catabolic reactions in cancer has gained increasing attention in recent years. Many studies have shown that aberrant expression of the genes involved in fatty acid synthesis or fatty acid oxidation correlate with malignant phenotypes including metastasis, therapeutic resistance and relapse. Such phenotypes are also strongly associated with the presence of a small percentage of unique cells among the total tumor cell population. This distinct group of cells may have the ability to self-renew and propagate or may be able to develop resistance to cancer therapies independent of genetic alterations. Therefore, these cells are referred to as cancer stem cells/tumor-initiating cells/drug-tolerant persisters, which are often refractory to cancer treatment and difficult to target. Moreover, interconversion between cancer cells and cancer stem cells/tumor-initiating cells/drug-tolerant persisters may occur and makes treatment even more challenging. This review highlights recent findings on the relationship between fatty acid metabolism, cancer stemness and therapeutic resistance and prompts discussion about the potential mechanisms by which fatty acid metabolism regulates the fate of cancer cells and therapeutic resistance.

SCD1 Confers Temozolomide Resistance to Human Glioma Cells via the Akt/GSK3β/β-Catenin Signaling Axis

Resistance to temozolomide (TMZ), the standard chemotherapy agent for glioblastoma (GBM), poses a major clinical challenge to GBM prognosis. Understanding the mechanisms of TMZ resistance can help to identify novel drug targets and more effective therapies. Recent studies suggest that bioenergetic alterations of cancer cells play important roles in drug resistance. In our study, the altered metabolism of cancer cells was observed using a metabolic PCR array. We found that stearoyl-coenzyme A desaturase 1 (SCD1), a key rate-limiting enzyme for synthesis of monounsaturated fatty acids, was significantly upregulated in TMZ-resistant GBM cells compared to their parental counterparts. Overexpression of SCD1 promoted resistance to TMZ in parental GBM cells, whereas SCD1 downregulation by siRNA could re-sensitize TMZ-resistant cells in vitro. Combinational treatment of TMZ and an SCD1-specific inhibitor showed a combined inhibitory effect on TMZ-resistant glioma cells. We also observed that overexpression of SCD1 promoted Akt/GSK3β/β-catenin signaling, while silencing of SCD1 inhibited the signaling. The combination of an Akt activator with exogenous SCD1 or the combined inhibition of Akt and enforced expression of SCD1 resulted in the most significant changes of Akt signaling. Functionally, significantly lower viability and mobility rates were observed in TMZ-resistant cells when treated with Akt inhibitors and an SCD1 inhibitor simultaneously compared to when treated individually. In conclusion, our study identified SCD1 along with its functional pathway as a novel target in the development of TMZ resistance. SCD1 inhibition used alone or in combination with Akt inhibition could effectively overcome TMZ resistance in gliomas.

SN38-PEG-PLGA-verapamil nanoparticles inhibit proliferation and downregulate drug transporter ABCG2 gene expression in colorectal cancer cells

Nowadays, nanoparticle-based drug delivery systems are recognized to reduce the therapeutic side effects. One of the common problems in cancer treatment is cancer drug resistance, resulting from the over-expression of one energy-dependent transporter that enhances drug efflux. Irinotecan is used for metastatic colorectal cancer. The involvement of ABCG2 transporter in irinotecan resistance has been established. The current study was designed to characterize SN38-loaded pegylated (polyethylene glycol) PLGA [poly(lactic-co-glycolic acid)]-verapamil nanoparticles (NPs), and to distinguish the cytotoxic effect of SN38-PEG-PLGA-Ver NPs and the ability of SN38-PEG-PLGA-Ver NPs to inhibit drug resistance through the inhibition of ABCG2 expression. The surface morphology of nanoparticles was determined by scanning electron microscopy. The drug cytotoxicity of SN38-PEG-PLGA-verapamil nanoparticles was measured by MTT assay with desired concentrations and SN38-PEG-PLGA-Ver at different incubation times. Real-time PCR was used to determine the mRNA level of ABCG2, BAX, and BCL2. The cellular uptake assay was performed to show the cellular uptake of nanoparticles. The size of NPs used in this study was about 179 nm with surface charge of -17.1 mV. MTT assay results showed that 1 μmol/L of free drug and 3 μmol/L of NPs could reduce HT29 cells by half (IC50) after 48 and 96 h, respectively. An increase in expression of BAX and a decrease in expression of ABCG2 were observed according to the real-time PCR. No significant change was detected in expression of BCL2. In conclusion, sufficient uptake of SN38-PEG-PLGA-Ver NPs and a significant decrease in expression of ABCG2 and an increase in expression of BAX and BAX/BCL2 ratio was observed after treatment with nanoparticles compared with free SN38. These results reveal that SN38-PEG-PLGA-Ver NPs can be an effective therapeutic method in colon cancer treatments and also may prevent anticancer drug resistance.

Microscale Mass Spectrometry Analysis of Extracellular Metabolites in Live Multicellular Tumor Spheroids

Extracellular compounds in tumors play critical roles in intercellular communication, tumor proliferation, and cancer cell metastasis. However, the lack of appropriate techniques leads to limited studies of extracellular metabolite. Here, we introduced a microscale collection device, the Micro-funnel, fabricated from biocompatible fused silica capillary. With a small probe size (∼25 μm), the Micro-funnel can be implanted into live multicellular tumor spheroids to accumulate the extracellular metabolites produced by cancer cells. Metabolites collected in the Micro-funnel device were then extracted by a microscale sampling and ionization device, the Single-probe, for real-time mass spectrometry (MS) analysis. We successfully detected the abundance change of anticancer drug irinotecan and its metabolites inside spheroids treated under a series of conditions. Moreover, we found that irinotecan treatment dramatically altered the composition of extracellular compounds. Specifically, we observed the increased abundances of a large number of lipids, which are potentially related to the drug resistance of cancer cells. This study provides a novel way to detect the extracellular compounds inside live spheroids, and the successful development of our technique can benefit the research in multiple areas, including the microenvironment inside live tissues, cell-cell communication, biomarker discovery, and drug development.

Targeting metabolism and AMP-activated kinase with metformin to sensitize non-small cell lung cancer (NSCLC) to cytotoxic therapy: translational biology and rationale for current clinical trials

Lung cancer is the most fatal malignancy worldwide, in part, due to high resistance to cytotoxic therapy. There is need for effective chemo-radio-sensitizers in lung cancer. In recent years, we began to understand the modulation of metabolism in cancer and its importance in tumor progression and survival after cytotoxic therapy. The activity of biosynthetic pathways, driven by the Growth Factor Receptor/Ras/PI3k/Akt/mTOR pathway, is balanced by the energy stress sensor pathway of LKB1/AMPK/p53. AMPK responds both to metabolic and genotoxic stress. Metformin, a well-tolerated anti-diabetic agent, which blocks mitochondria oxidative phosphorylation complex I, became the poster child agent to elicit AMPK activity and tumor suppression. Metformin sensitizes NSCLC models to chemotherapy and radiation. Here, we discuss the rationale for targeting metabolism, the evidence supporting metformin as an anti-tumor agent and adjunct to cytotoxic therapy in NSCLC and we review retrospective evidence and on-going clinical trials addressing this concept.

ATP citrate lyase is increased in human breast cancer, depletion of which promotes apoptosis

Breast cancer is a malignant tumor that is harmful to women’s health around the world. Investigating the biological mechanism is, therefore, of pivotal importance to improve patients’ prognoses. Compared to non-neoplastic tissues, enhanced glucose and lipid metabolism is one of the most common properties of malignant breast cancer. Adenosine triphosphate (ATP) citrate lyase is a key enzyme linking aerobic glycolysis and fatty acid synthesis and is of high biological and prognostic significance in breast cancer. In our clinical study, fresh clinical tissues were used to analyze ATP citrate lyase expression by western blotting, and paraffin archived samples from 62 breast cancer patients were used to analyze ATP citrate lyase expression by immunohistochemistry. In the cellular study, following small interfering RNA–mediated inhibition of ATP citrate lyase in MCF-7 cells, cell viability and apoptosis were measured using the Cell Counting Kit-8 and flow cytometry, respectively. Breast cancer tissues showed strong expression of ATP citrate lyase, whereas adjacent normal tissues showed weak expression. Silencing of endogenous ATP citrate lyase expression by small interfering RNA in MCF-7 cells suppressed cell viability and increased cell apoptosis. Collectively, our study revealed that expression of ATP citrate lyase was significantly increased in breast cancer tissue compared with normal tissue. In addition, we found that depletion of ATP citrate lyase suppressed tumor growth, which suggests that ATP citrate lyase–related inhibitors might be potential therapeutic approaches for breast cancer.

TNF Signaling through RIP1 Kinase Enhances SN38-Induced Death in Colon Adenocarcinoma

Elucidation of TNF-directed mechanisms for cell death induction and maintenance of tumor growth has revealed a role for receptor-interacting protein kinases 1 and 3 (RIPK1/RIP1 and RIPK3/RIP3), components of the necrosome complex, as determinants of cell fate. Here, the participation of TNF signaling was analyzed with regard to the cytotoxic action of different DNA-damaging agents in a panel of colon cancer cells. While most of these cell lines were insensitive to TNF, combination with these drugs increased sensitivity by inducing cell death and DNA damage, especially in the case of the topoisomerase inhibitor SN38. Changes in levels of RIP1 and RIP3 occurred following monotherapy with SN38 or in combination with TNF. Downregulation of RIP1 resulted in increased resistance to SN38, implying a requirement for RIP1 in mediating cytotoxicity through the TNF/TNFR signaling pathway. Downregulation of RIP1 in a xenograft model impaired tumor growth inhibition from SN38 treatment, suggesting the potential of RIP1 to determine the clinical outcome of irinotecan treatment. These results indicate that TNF plays a key role in determining the cytotoxic effectiveness of SN38 in colorectal cancer and suggests a re-evaluation of TNF-based interventions to enhance therapeutic efficacy.Implications: The capacity of RIP1 to influence drug sensitivity suggests RIP1 may have biomarker potential. Mol Cancer Res; 15(4); 395-404. ©2017 AACR.

Targeting Lipid Metabolic Reprogramming as Anticancer Therapeutics

Cancer cells rewire their metabolism to satisfy the demands of growth and survival, and this metabolic reprogramming has been recognized as an emerging hallmark of cancer. Lipid metabolism is pivotal in cellular process that converts nutrients into energy, building blocks for membrane biogenesis and the generation of signaling molecules. Accumulating evidence suggests that cancer cells show alterations in different aspects of lipid metabolism. The changes in lipid metabolism of cancer cells can affect numerous cellular processes, including cell growth, proliferation, differentiation, and survival. The potential dependence of cancer cells on the deregulated lipid metabolism suggests that enzymes and regulating factors involved in this process are promising targets for cancer treatment. In this review, we focus on the features associated with the lipid metabolic pathways in cancer, and highlight recent advances on the therapeutic targets of specific lipid metabolic enzymes or regulating factors and target-directed small molecules that can be potentially used as anticancer drugs.

Design and synthesis of emodin derivatives as novel inhibitors of ATP-citrate lyase

Aberrant cellular metabolism drives cancer proliferation and metastasis. ATP citrate lyase (ACL) plays a critical role in generating cytosolic acetyl CoA, a key building block for de novo fatty acid and cholesterol biosynthesis. ACL is overexpressed in cancer cells, and siRNA knockdown of ACL limits cancer cell proliferation and reduces cancer stemness. We characterized a new class of ACL inhibitors bearing the key structural feature of the natural product emodin. Structure-activity relationship (SAR) study led to the identification of 1d as a potent lead that demonstrated dose-dependent inhibition of proliferation and cancer stemness of the A549 lung cancer cell line. Computational modeling indicates this class of inhibitors occupies an allosteric binding site and blocks the entrance of the substrate citrate to its binding site.

Reprogramming of glucose, fatty acid and amino acid metabolism for cancer progression

Metabolic reprogramming is widely observed during cancer development to confer cancer cells the ability to survive and proliferate, even under the stressed, such as nutrient-limiting, conditions. It is famously known that cancer cells favor the "Warburg effect", i.e., the enhanced glycolysis or aerobic glycolysis, even when the ambient oxygen supply is sufficient. In addition, deregulated anabolism/catabolism of fatty acids and amino acids, especially glutamine, serine and glycine, have been identified to function as metabolic regulators in supporting cancer cell growth. Furthermore, extensive crosstalks are being revealed between the deregulated metabolic network and cancer cell signaling. These exciting advancements have inspired new strategies for treating various malignancies by targeting cancer metabolism. Here we review recent findings related to the regulation of glucose, fatty acid and amino acid metabolism, their crosstalk, and relevant cancer therapy strategy.

Polymorphisms in genes of the de novo lipogenesis pathway and overall survival of hepatocellular carcinoma patients undergoing transarterial chemoembolization

Aberrant expression of genes in de novo lipogenesis (DNL) pathway were associated with various cancers, including hepatocellular carcinoma (HCC). Single nucleotide polymorphisms (SNPs) of DNL genes have been reported to be associated with prognosis of some malignancies. However, the effects of SNPs in DNL genes on overall survival of HCC patients receiving transarterial chemoembolization (TACE) treatment are still unknown. In present study, nine SNPs in three genes (ACLY, ACACA and FASN) in DNL pathway were genotyped using the Sequenom iPLEX genotyping system in a hospital-based cohort with 419 HCC patients treated with TACE, and their associations with HCC overall survival were evaluated by Cox proportional hazard regression analysis under three genetic models (additive, dominant and recessive). Although we did not find any significant results in total analysis (all p>0.05), our stratified data showed that SNP rs9912300 in ACLY gene was significantly associated with overall survival of HCC patients with lower AFP level and SNP rs11871275 in ACACA gene was significantly associated with overall survival of HCC patients with higher AFP level. We further identified the significant interactions between AFP level and SNP rs9912300 or rs11871275 in the joint analysis. Conclusively, our data suggest that genetic variations in genes of DNL pathway may be a potential biomarker for predicting clinical outcome of HCC patients treated with TACE.

The metabolic cooperation between cells in solid cancer tumors

Cancer cells cooperate with stromal cells and use their environment to promote tumor growth. Energy production depends on nutrient availability and O₂ concentration. Well-oxygenated cells are highly proliferative and reorient the glucose metabolism towards biosynthesis, whereas glutamine oxidation replenishes the TCA cycle coupled with OXPHOS-ATP production. Glucose, glutamine and alanine transformations sustain nucleotide and fatty acid synthesis. In contrast, hypoxic cells slow down their proliferation, enhance glycolysis to produce ATP and reject lactate which is recycled as fuel by normoxic cells. Thus, glucose is spared for biosynthesis and/or for hypoxic cell function. Environmental cells, such as fibroblasts and adipocytes, serve as food donors for cancer cells, which reject waste products (CO₂ , H⁺, ammoniac, polyamines…) promoting EMT, invasion, angiogenesis and proliferation. This metabolic-coupling can be considered as a form of commensalism whereby non-malignant cells support the growth of cancer cells. Understanding these cellular cooperations within tumors may be a source of inspiration to develop new anti-cancer agents.

Managing lipid metabolism in proliferating cells: new perspective for metformin usage in cancer therapy

Cancer cells metabolically adapt to undergo cellular proliferation. Lipids, besides their well-known role as energy storage, represent the major building blocks for the synthesis of neo-generated membranes. There is increasing evidence that cancer cells show specific alterations in different aspects of lipid metabolism. The changes of expression and activity of lipid metabolising enzymes are directly regulated by the activity of oncogenic signals. The dependence of tumour cells on the deregulated lipid metabolism suggests that proteins involved in this process could be excellent chemotherapeutic targets for cancer treatment. Due to its rare side effects in non-cancerous cells, metformin has been recently revaluated as a potential anti-tumourigenic drug, which negatively affects lipid biosynthetic pathways. In this review we summarised the emerging molecular events linking the anti-proliferative effect of metformin with lipid metabolism in cancer cells.