Degeneration and regeneration of the nerves of the heart after transplantation. Transplantation. 1973;15:337-344. [PMID: 25032859 PMCID: PMC4123079 DOI: 10.1038/cddis.2014.285]

Targeting Cancer Stem Cells by Dietary Agents: An Important Therapeutic Strategy against Human Malignancies

As a multifactorial disease, treatment of cancer depends on understanding unique mechanisms involved in its progression. The cancer stem cells (CSCs) are responsible for tumor stemness and by enhancing colony formation, proliferation as well as metastasis, and these cells can also mediate resistance to therapy. Furthermore, the presence of CSCs leads to cancer recurrence and therefore their complete eradication can have immense therapeutic benefits. The present review focuses on targeting CSCs by natural products in cancer therapy. The growth and colony formation capacities of CSCs have been reported can be attenuated by the dietary agents. These compounds can induce apoptosis in CSCs and reduce tumor migration and invasion via EMT inhibition. A variety of molecular pathways including STAT3, Wnt/β-catenin, Sonic Hedgehog, Gli1 and NF-κB undergo down-regulation by dietary agents in suppressing CSC features. Upon exposure to natural agents, a significant decrease occurs in levels of CSC markers including CD44, CD133, ALDH1, Oct4 and Nanog to impair cancer stemness. Furthermore, CSC suppression by dietary agents can enhance sensitivity of tumors to chemotherapy and radiotherapy. In addition to in vitro studies, as well as experiments on the different preclinical models have shown capacity of natural products in suppressing cancer stemness. Furthermore, use of nanostructures for improving therapeutic impact of dietary agents is recommended to rapidly translate preclinical findings for clinical use.

Celecoxib and dimethylcelecoxib block oxidative phosphorylation, epithelial-mesenchymal transition and invasiveness in breast cancer stem cells

BACKGROUND

Drug resistance and invasiveness developed by breast cancer stem cells (BCSC) are considered the major hurdles for successful cancer treatment. <P> Objective: As these two processes are highly energy-dependent, the identification of the main ATP supplier required for stem cell viability may result advantageous in the design of new therapeutic strategies to deter malignant carcinomas. <P> Methods: The energy metabolism (glycolysis and oxidative phosphorylation, OxPhos) was systematically analyzed by assessing relevant protein contents, enzyme activities and pathway fluxes in BCSC. Once identified the main ATP supplier, selective energy inhibitors and canonical breast cancer drugs were used to block stem cell viability and their metastatic properties. <P> Results: OxPhos and glycolytic protein contents, as well as HK and LDH activities were several times higher in BCSC than in their parental line, MCF-7 cells. However, CS, GDH, COX activities and both energy metabolism pathway fluxes were significantly lower (38-86%) in BCSC than in MCF-7 cells. OxPhos was the main ATP provider (>85%) in BCSC. Accordingly, oligomycin (a specific and potent canonical OxPhos inhibitor) and other non-canonical drugs with inhibitory effect on OxPhos (celecoxib, dimethylcelecoxib) significantly decreased BCSC viability, levels of epithelial-mesenchymal transition proteins, invasiveness, and induced ROS over-production, with IC50 values ranging from 1 to 20 µM in 24 h treatment. In contrast, glycolytic inhibitors (gossypol, iodoacetic acid, 3-bromopyruvate, 2-deoxyglucose) and canonical chemotherapeutic drugs (paclitaxel, doxorubicin, cisplatin) were much less effective against BCSC viability (IC50> 100 µM). <P> Conclusion: These results indicated that the use of some NSAIDs may be a promising alternative therapeutic strategy to target BCSC.

Potential Therapies Targeting Metabolic Pathways in Cancer Stem Cells

Cancer stem cells (CSCs) are heterogeneous cells with stem cell-like properties that are responsible for therapeutic resistance, recurrence, and metastasis, and are the major cause for cancer treatment failure. Since CSCs have distinct metabolic characteristics that plays an important role in cancer development and progression, targeting metabolic pathways of CSCs appears to be a promising therapeutic approach for cancer treatment. Here we classify and discuss the unique metabolisms that CSCs rely on for energy production and survival, including mitochondrial respiration, glycolysis, glutaminolysis, and fatty acid metabolism. Because of metabolic plasticity, CSCs can switch between these metabolisms to acquire energy for tumor progression in different microenvironments compare to the rest of tumor bulk. Thus, we highlight the specific conditions and factors that promote or suppress CSCs properties to portray distinct metabolic phenotypes that attribute to CSCs in common cancers. Identification and characterization of the features in these metabolisms can offer new anticancer opportunities and improve the prognosis of cancer. However, the therapeutic window of metabolic inhibitors used alone or in combination may be rather narrow due to cytotoxicity to normal cells. In this review, we present current findings of potential targets in these four metabolic pathways for the development of more effective and alternative strategies to eradicate CSCs and treat cancer more effectively in the future.

Potential Therapies Targeting Metabolic Pathways in Cancer Stem Cells

Cancer stem cells (CSCs) are heterogeneous cells with stem cell-like properties that are responsible for therapeutic resistance, recurrence, and metastasis, and are the major cause for cancer treatment failure. Since CSCs have distinct metabolic characteristics that plays an important role in cancer development and progression, targeting metabolic pathways of CSCs appears to be a promising therapeutic approach for cancer treatment. Here we classify and discuss the unique metabolisms that CSCs rely on for energy production and survival, including mitochondrial respiration, glycolysis, glutaminolysis, and fatty acid metabolism. Because of metabolic plasticity, CSCs can switch between these metabolisms to acquire energy for tumor progression in different microenvironments compare to the rest of tumor bulk. Thus, we highlight the specific conditions and factors that promote or suppress CSCs properties to portray distinct metabolic phenotypes that attribute to CSCs in common cancers. Identification and characterization of the features in these metabolisms can offer new anticancer opportunities and improve the prognosis of cancer. However, the therapeutic window of metabolic inhibitors used alone or in combination may be rather narrow due to cytotoxicity to normal cells. In this review, we present current findings of potential targets in these four metabolic pathways for the development of more effective and alternative strategies to eradicate CSCs and treat cancer more effectively in the future.

Metabolic control of cancer progression as novel targets for therapy

Metabolism is an important part of tumorigenesis as well as progression. The various cancer metabolism pathways, such as glucose metabolism and glutamine metabolism, directly regulate the development and progression of cancer. The pathways by which the cancer cells rewire their metabolism according to their needs, surrounding environment and host tissue conditions are an important area of study. The regulation of these metabolic pathways is determined by various oncogenes, tumor suppressor genes, as well as various constituent cells of the tumor microenvironment. Expanded studies on metabolism will help identify efficient biomarkers for diagnosis and strategies for therapeutic interventions and countering ways by which cancers may acquire resistance to therapy.

PGC1α-Mediated Metabolic Reprogramming Drives the Stemness of Pancreatic Precursor Lesions

PURPOSE

Metabolic reprogramming and cancer stem cells drive the aggressiveness of pancreatic ductal adenocarcinoma (PDAC). However, the metabolic and stemness programs of pancreatic precursor lesions (PPL), considered early PDAC development events, have not been thoroughly explored.

EXPERIMENTAL DESIGN

Meta-analyses using gene expression profile data from NCBI Gene Expression Omnibus and IHC on tissue microarrays (TMA) were performed. The following animal and cellular models were used: cerulean-induced Kras^G12D; Pdx1 Cre (KC) acinar-to-ductal metaplasia (ADM) mice, Kras^G12D; Smad4^Loss; Pdx-1 Cre (KC^Smad4-) intraductal papillary mucinous neoplasm (IPMN) mice, LGKC1 cell line derived from the doxycycline-inducible Gnas IPMN model, and human IPMN organoids. Flow cytometry, Seahorse extracellular flux analyzer, qRT-PCR, and sphere assay were used to analyze metabolic and stemness features. SR18292 was used to inhibit PGC1α, and short hairpin RNA was used to knockdown (KD) PGC1α.

RESULTS

The meta-analysis revealed a significant upregulation of specific stemness genes in ADM-mediated pancreatic intraepithelial neoplasms (PanIN) and IPMN. Meta- and TMA analyses followed by in vitro and in vivo validation revealed that ADM/PanIN exhibit increased PGC1α and oxidative phosphorylation (OXPhos) but reduced CPT1A. IPMN showed elevated PGC1α, fatty acid β-oxidation (FAO) gene expression, and FAO-OXPhos. PGC1α was co-overexpressed with its coactivator NRF1 in ADM/PanINs and with PPARγ in IPMN. PGC1α KD or SR18292 inhibited the specific metabolic and stemness features of PPLs and repressed IPMN organoid growth.

CONCLUSIONS

ADM/PanINs and IPMNs show specific stemness signatures with unique metabolisms. Inhibition of PGC1α using SR18292 diminishes the specific stemness by targeting FAO-independent and FAO-dependent OXPhos of ADM/PanINs and IPMNs, respectively.

Plasticity of Cancer Stem Cell: Origin and Role in Disease Progression and Therapy Resistance

In embryonic development and throughout life, there are some cells can exhibit phenotypic plasticity. Phenotypic plasticity is the ability of cells to differentiate into multiple lineages. In normal development, plasticity is highly regulated whereas cancer cells re-activate this dynamic ability for their own progression. The re-activation of these mechanisms enables cancer cells to acquire a cancer stem cell (CSC) phenotype- a subpopulation of cells with increased ability to survive in a hostile environment and resist therapeutic insults. There are several contributors fuel CSC plasticity in different stages of disease progression such as a complex network of tumour stroma, epidermal microenvironment and different sub-compartments within tumour. These factors play a key role in the transformation of tumour cells from a stable condition to a progressive state. In addition, flexibility in the metabolic state of CSCs helps in disease progression. Moreover, epigenetic changes such as chromatin, DNA methylation could stimulate the phenotypic change of CSCs. Development of resistance to therapy due to highly plastic behaviour of CSCs is a major cause of treatment failure in cancers. However, recent studies explored that plasticity can also expose the weaknesses in CSCs, thereby could be utilized for future therapeutic development. Therefore, in this review, we discuss how cancer cells acquire the plasticity, especially the role of the normal developmental process, tumour microenvironment, and epigenetic changes in the development of plasticity. We further highlight the therapeutic resistance property of CSCs attributed by plasticity. Also, outline some potential therapeutic options against plasticity of CSCs. Graphical Abstract .

Conflicting metabolic alterations in cancer stem cells and regulation by the stromal niche

Recent studies have revealed that cancer stem cells (CSCs) undergo metabolic alterations that differentiate them from non-CSCs. Inhibition of specific metabolic pathways in CSCs has been conducted to eliminate the CSC population in many types of cancer. However, there is conflicting evidence about whether CSCs depend on glycolysis or mitochondrial oxidative phosphorylation (OXPHOS) to maintain their stem cell properties. This review summarizes the latest knowledge regarding CSC-specific metabolic alterations and offers recent evidence that the surrounding microenvironments may play an important role in the maintenance of CSC properties.

ETV4 promotes breast cancer cell stemness by activating glycolysis and CXCR4-mediated sonic Hedgehog signaling

Cancer stem cells (CSCs) are a major cause of tumor treatment resistance, relapse and metastasis. Cancer cells exhibit reprogrammed metabolism characterized by aerobic glycolysis, which is also critical for sustaining cancer stemness. However, regulation of cancer cell metabolism rewiring and stemness is not completely understood. Here, we report that ETV4 is a key transcription factor in regulating glycolytic gene expression. ETV4 loss significantly inhibits the expression of HK2, LDHA as well as other glycolytic enzymes, reduces glucose uptake and lactate release in breast cancer cells. In human breast cancer and hepatocellular carcinoma tissues, ETV4 expression is positively correlated with glycolytic signaling. Moreover, we confirm that breast CSCs (BCSCs) are glycolysis-dependent and show that ETV4 is required for BCSC maintenance. ETV4 is enriched in BCSCs, its knockdown and overexpression suppresses and promotes breast cancer cell stem-like traits, respectively. Mechanistically, on the one hand, we find that ETV4 may enhance glycolysis activity to facilitate breast cancer stemness; on the other, ETV4 activates Sonic Hedgehog signaling by transcriptionally promoting CXCR4 expression. A xenograft assay validates the tumor growth-impeding effect and inhibition of CXCR4/SHH/GLI1 signaling cascade after ETV4 depletion. Together, our study highlights the potential roles of ETV4 in promoting cancer cell glycolytic shift and BCSC maintenance and reveals the molecular basis.

Interplay between Metabolism Reprogramming and Epithelial-to-Mesenchymal Transition in Cancer Stem Cells

Simple Summary

Tumor cells display important plasticity potential. Notably, tumor cells have the ability to change toward immature cells called cancer stem cells under the influence of the tumor environment. Importantly, cancer stem cells are a small subset of relatively quiescent cells that, unlike rapidly dividing differentiated tumor cells, escape standard chemotherapies, causing relapse or recurrence of cancer. Interestingly, these cells adopt a specific metabolism. Most often, they mainly rely on glucose uptake and metabolism to sustain their energy needs. This metabolic reprogramming is set off by environmental factors such as pro-inflammatory signals or catecholamine hormones (epinephrine, norepinephrine). A better understanding of this process could provide opportunities to kill cancer stem cells. Indeed, it would become possible to develop drugs that act specifically on metabolic pathways used by these cells. These new drugs could be used to strengthen the effects of current chemotherapies and overcome cancers with poor prognoses.

Abstract

Tumor cells display important plasticity potential, which contributes to intratumoral heterogeneity. Notably, tumor cells have the ability to retrodifferentiate toward immature states under the influence of their microenvironment. Importantly, this phenotypical conversion is paralleled by a metabolic rewiring, and according to the metabostemness theory, metabolic reprogramming represents the first step of epithelial-to-mesenchymal transition (EMT) and acquisition of stemness features. Most cancer stem cells (CSC) adopt a glycolytic phenotype even though cells retain functional mitochondria. Such adaptation is suggested to reduce the production of reactive oxygen species (ROS), protecting CSC from detrimental effects of ROS. CSC may also rely on glutaminolysis or fatty acid metabolism to sustain their energy needs. Besides pro-inflammatory cytokines that are well-known to initiate the retrodifferentiation process, the release of catecholamines in the microenvironment of the tumor can modulate both EMT and metabolic changes in cancer cells through the activation of EMT transcription factors (ZEB1, Snail, or Slug (SNAI2)). Importantly, the acquisition of stem cell properties favors the resistance to standard care chemotherapies. Hence, a better understanding of this process could pave the way for the development of therapies targeting CSC metabolism, providing new strategies to eradicate the whole tumor mass in cancers with unmet needs.

Reactive oxygen species produced by altered tumor metabolism impacts cancer stem cell maintenance

Controlling reactive oxygen species (ROS) at sustainable levels can drive multiple facets of tumor biology, including within the cancer stem cell (CSC) population. Tight regulation of ROS is one key component in CSCs that drives disease recurrence, cell signaling, and therapeutic resistance. While ROS are well-appreciated to need oxygen and are a product of oxidative phosphorylation, there are also important roles for ROS under hypoxia. As hypoxia promotes and sustains major stemness pathways, further consideration of ROS impacts on CSCs in the tumor microenvironment is important. Furthermore, glycolytic shifts that occur in cancer and may be promoted by hypoxia are associated with multiple mechanisms to mitigate oxidative stress. This altered metabolism provides survival advantages that sustain malignant features, such as proliferation and self-renewal, while producing the necessary antioxidants that reduce damage from oxidative stress. Finally, disease recurrence is believed to be attributed to therapy resistant CSCs which can be quiescent and have changes in redox status. Effective DNA damage response pathways and/or a slow-cycling state can protect CSCs from the genomic catastrophe induced by irradiation and genotoxic agents. This review will explore the delicate, yet complex, relationship between ROS and its pleiotropic role in modulating the CSC.

Enhanced Glycolysis Is Required for Antileishmanial Functions of Neutrophils Upon Infection With Leishmania donovani

Visceral leishmaniasis (VL) is a fatal parasitic disease if untreated. Treatment options of VL diminish due to emerging drug resistance. Although the principal host cells for the multiplication of Leishmania are macrophages, neutrophils are the first cells infected with the parasites rapidly after parasite inoculation. Leishmania can survive in neutrophils despite the potent antimicrobial effector functions of neutrophils that can eliminate the parasites. Recently, the growing field of immunometabolism provided strong evidence for the therapeutic potential in targeting metabolic processes as a means of controlling immune effector functions. Therefore, the understanding of the immunometabolic profile of neutrophils during Leishmania infection could provide new promising targets for host-directed therapies against VL. To our knowledge, this is the first study addressing the bioenergetics profile of L. donovani-infected primary human neutrophils. Transcriptome analysis of L. donovani-infected neutrophils revealed an early significant upregulation of several glycolytic enzymes. Extracellular flux analysis showed that glycolysis and glycolytic capacity were upregulated in L. donovani-infected neutrophils at 6 h post infection. An increased glucose uptake and accumulation of glycolytic end products were further signs for an elevated glycolytic metabolism in L. donovani-infected neutrophils. At the same time point, oxidative phosphorylation provided NADPH for the oxidative burst but did not contribute to ATP production. Inhibition of glycolysis with 2-DG significantly reduced the survival of L. donovani promastigotes in neutrophils and in culture. However, this reduction was due to a direct antileishmanial effect of 2-DG and not a consequence of enhanced antileishmanial activity of neutrophils. To further address the impact of glucose metabolism during the first days of infection in vivo, we treated C57BL/6 mice with 2-DG prior to infection with L. donovani and assessed the parasite load one day and seven days post infection. Our results show, that seven days post-infection the parasite load of 2-DG treated animals was significantly higher than in mock treated animals. This data indicates that glycolysis serves as major energy source for antimicrobial effector functions against L. donovani. Inhibition of glycolysis abrogates important neutrophil effector functions that are necessary the initial control of Leishmania infection.

Novel molecular regulators of breast cancer stem cell plasticity and heterogeneity

Tumors consist of heterogeneous cell populations, and tumor heterogeneity plays key roles in regulating tumorigenesis, metastasis, recurrence and resistance to anti-tumor therapies. More and more studies suggest that cancer stem cells (CSCs) promote tumorigenesis, metastasis, recurrence and drug resistance as well as are the major source for heterogeneity of cancer cells. CD24^-CD44⁺ and ALDH⁺ are the most common markers for breast cancer stem cells (BCSCs). Previous studies showed that different BCSC markers label different BCSC populations, indicating the heterogeneity of BCSCs. Therefore, defining the regulation mechanisms of heterogeneous BCSCs is essential for precisely targeting BCSCs and treating breast cancer. In this review, we summarized the novel regulators existed in BCSCs and their niches for BCSC heterogeneity which has been discovered in recent years, and discussed their regulation mechanisms and the latest corresponding cancer treatments, which will extend our understanding on BCSC heterogeneity and plasticity, and provide better prognosis prediction and more efficient novel therapeutic strategies for breast cancer.

Targeting Energy Metabolism in Cancer Stem Cells: Progress and Challenges in Leukemia and Solid Tumors

Malignant stem cells have long been considered a key therapeutic target in leukemia. Therapeutic strategies designed to target the fundamental biology of leukemia stem cells while sparing normal hematopoietic cells may provide better outcomes for leukemia patients. One process in leukemia stem cell biology that has intriguing therapeutic potential is energy metabolism. In this article we discuss the metabolic properties of leukemia stem cells and how targeting energy metabolism may provide more effective therapeutic regimens for leukemia patients. In addition, we highlight the similarities and differences in energy metabolism between leukemia stem cells and malignant stem cells from solid tumors.

HDAC11 Regulates Glycolysis through the LKB1/AMPK Signaling Pathway to Maintain Hepatocellular Carcinoma Stemness

Hepatocellular carcinoma (HCC) contains a subset of cancer stem cells (CSC) that cause tumor recurrence, metastasis, and chemical resistance. Histone deacetylase 11 (HDAC11) mediates diverse immune functions and metabolism, yet little is known about its role in HCC CSCs. In this study, we report that HDAC11 is highly expressed in HCC and is closely related to disease prognosis. Depletion of HDAC11 in a conditional knockout mouse model reduced hepatocellular tumorigenesis and prolonged survival. Loss of HDAC11 increased transcription of LKB1 by promoting histone acetylation in its promoter region, thereby activating the AMPK signaling pathway and inhibiting the glycolysis pathway, which in turn leads to the suppression of cancer stemness and HCC progression. Furthermore, HDAC11 overexpression reduced HCC sensitivity to sorafenib. Collectively, these data propose HDAC11 as a new target for combination therapy in patients with kinase-resistant HCC. SIGNIFICANCE: This study finds that HDAC11 suppresses LKB1 expression in HCC to promote cancer stemness, progression, and sorafenib resistance, suggesting the potential of targeting HDAC11 to treat HCC and overcome kinase inhibitor resistance.

Cancer Stem Cell Metabolism

Cancer stem cells (CSCs), also known as tumorinitiating cells (TICs), are a group of cells found within cancer cells. Like normal stem cells, CSCs can proliferate, engage in self-renewal, and are often implicated in the recurrence of tumors after therapy [1, 2]. The existence of CSCs in various types of cancer has been proven, such as in acute myeloid leukemia (AML) [3], breast [4], pancreatic [5], and lung cancers [6], to name a few. There are two theories regarding the origin of CSCs. First, CSCs may have arisen from normal stem/progenitor cells that experienced changes in their environment or genetic mutations. On the other hand, CSCs may also have originated from differentiated cells that underwent genetic and/or heterotypic modifications [7]. Either way, CSCs reprogram their metabolism in order to support tumorigenesis.

Metabolic programming of distinct cancer stem cells promotes metastasis of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) metastasizes to distant organs, which is the primary cause of mortality; however, specific features mediating organ-specific metastasis remain unexplored. Emerging evidence demonstrates that cancer stem cells (CSCs) and cellular metabolism play a pivotal role in metastasis. Here we investigated the role of distinct subtypes of pancreatic CSCs and their metabolomic signatures in organ-specific metastatic colonization. We found that PDAC consists of ALDH+/CD133+ and drug-resistant (MDR1+) subtypes of CSCs with specific metabolic and stemness signatures. Human PDAC tissues with gemcitabine treatment, autochthonous mouse tumors from Kras^G12D; Pdx1-Cre (KC) and Kras^G12D; Trp53^R172H; Pdx-1 Cre (KPC) mice, and KPC- Liver/Lung metastatic cells were used to evaluate the CSC, EMT (epithelial-to-mesenchymal transition), and metabolic profiles. A strong association was observed between distinct CSC subtypes and organ-specific colonization. The liver metastasis showed drug-resistant CSC- and EMT-like phenotype with aerobic glycolysis and fatty acid β-oxidation-mediated oxidative (glyco-oxidative) metabolism. On the contrary, lung metastasis displayed ALDH+/CD133+ and MET-like phenotype with oxidative metabolism. These results were obtained by evaluating FACS-based side population (SP), autofluorescence (AF+) and Alde-red assays for CSCs, and Seahorse-based oxygen consumption rate (OCR), extracellular acidification rate (ECAR), and fatty acid β-oxidation (FAO)-mediated OCR assays for metabolic features along with specific gene signatures. Further, we developed in vitro human liver and lung PDAC metastasis models by using a combination of liver or lung decellularized scaffolds, a co-culture, and a sphere culture methods. PDAC cells grown in the liver-mimicking model showed the enrichment of MDR1+ and CPT1A+ populations, whereas the PDAC cells grown in the lung-mimicking environment showed the enrichment of ALDH+/CD133+ populations. In addition, we observed significantly elevated expression of ALDH1 in lung metastasis and MDR1/LDH-A expression in liver metastasis compared to human primary PDAC tumors. Our studies elucidate that distinct CSCs adapt unique metabolic signatures for organotropic metastasis, which will pave the way for the development of targeted therapy for PDAC metastasis.

CD44 in Ovarian Cancer Progression and Therapy Resistance-A Critical Role for STAT3

Despite significant progress in cancer therapy over the last decades, ovarian cancer remains the most lethal gynecologic malignancy worldwide with the five-year overall survival rate less than 30% due to frequent disease recurrence and chemoresistance. CD44 is a non-kinase transmembrane receptor that has been linked to cancer metastatic progression, cancer stem cell maintenance, and chemoresistance development via multiple mechanisms across many cancers, including ovarian, and represents a promising therapeutic target for ovarian cancer treatment. Moreover, CD44-mediated signaling interacts with other well-known pro-tumorigenic pathways and oncogenes during cancer development, such as signal transducer and activator of transcription 3 (STAT3). Given that both CD44 and STAT3 are strongly implicated in the metastatic progression and chemoresistance of ovarian tumors, this review summarizes currently available evidence about functional crosstalk between CD44 and STAT3 in human malignancies with an emphasis on ovarian cancer. In addition to the role of tumor cell-intrinsic CD44 and STAT3 interaction in driving cancer progression and metastasis, we discuss how CD44 and STAT3 support the pro-tumorigenic tumor microenvironment and promote tumor angiogenesis, immunosuppression, and cancer metabolic reprogramming in favor of cancer progression. Finally, we review the current state of therapeutic CD44 targeting and propose superior treatment possibilities for ovarian cancer.

Advance in metabolism and target therapy in breast cancer stem cells

Breast cancer, like many other cancers, is believed to be driven by a population of cells that display stem cell properties. Recent studies suggest that cancer stem cells (CSCs) are essential for tumor progression, and tumor relapse is thought to be caused by the presence of these cells. CSC-targeted therapies have also been proposed to overcome therapeutic resistance in breast cancer after the traditional therapies. Additionally, the metabolic properties of cancer cells differ markedly from those of normal cells. The efficacy of metabolic targeted therapy has been shown to enhance anti-cancer treatment or overcome therapeutic resistance of breast cancer cells. Metabolic targeting of breast CSCs (BCSCs) may be a very effective strategy for anti-cancer treatment of breast cancer cells. Thus, in this review, we focus on discussing the studies involving metabolism and targeted therapy in BCSCs.

Hyaluronan: Metabolism and Function

As a major polysaccharide component of the extracellular matrix, hyaluronan plays essential roles in the organization of tissue architecture and the regulation of cellular functions, such as cell proliferation and migration, through interactions with cell-surface receptors and binding molecules. Metabolic pathways for biosynthesis and degradation tightly control the turnover rate, concentration, and molecular size of hyaluronan in tissues. Despite the relatively simple chemical composition of this polysaccharide, its wide range of molecular weights mediate diverse functions that depend on molecular size and tissue concentration. Genetic engineering and pharmacological approaches have demonstrated close associations between hyaluronan metabolism and functions in many physiological and pathological events, including morphogenesis, wound healing, and inflammation. Moreover, emerging evidence has suggested that the accumulation of hyaluronan extracellular matrix and fragments due to the altered expression of hyaluronan synthases and hyaluronidases potentiates cancer development and progression by remodeling the tumor microenvironment. In addition to the well-known functions exerted by extracellular hyaluronan, recent metabolomic approaches have also revealed that its synthesis can regulate cellular functions via the reprogramming of cellular metabolism. This review highlights the current advances in knowledge on the biosynthesis and catabolism of hyaluronan and describes the diverse functions associated with hyaluronan metabolism.

Therapy Resistance, Cancer Stem Cells and ECM in Cancer: The Matrix Reloaded

The extracellular matrix (ECM) has remained an enigmatic component of the tumor microenvironment. It drives metastasis via its interaction with the integrin signaling pathway, contributes to tumor progression and confers therapy resistance by providing a physical barrier around the tumor. The complexity of the ECM lies in its heterogeneous composition and complex glycosylation that can provide a support matrix as well as trigger oncogenic signaling pathways by interacting with the tumor cells. In this review, we attempt to dissect the role of the ECM in enriching for the treatment refractory cancer stem cell population and how it may be involved in regulating their metabolic needs. Additionally, we discuss how the ECM is instrumental in remodeling the tumor immune microenvironment and the potential ways to target this component in order to develop a viable therapy.

Cancer Metabolism: Phenotype, Signaling and Therapeutic Targets

Aberrant metabolism is a major hallmark of cancer. Abnormal cancer metabolism, such as aerobic glycolysis and increased anabolic pathways, has important roles in tumorigenesis, metastasis, drug resistance, and cancer stem cells. Well-known oncogenic signaling pathways, such as phosphoinositide 3-kinase (PI3K)/AKT, Myc, and Hippo pathway, mediate metabolic gene expression and increase metabolic enzyme activities. Vice versa, deregulated metabolic pathways contribute to defects in cellular signal transduction pathways, which in turn provide energy, building blocks, and redox potentials for unrestrained cancer cell proliferation. Studies and clinical trials are being performed that focus on the inhibition of metabolic enzymes by small molecules or dietary interventions (e.g., fasting, calorie restriction, and intermittent fasting). Similar to genetic heterogeneity, the metabolic phenotypes of cancers are highly heterogeneous. This heterogeneity results from diverse cues in the tumor microenvironment and genetic mutations. Hence, overcoming metabolic plasticity is an important goal of modern cancer therapeutics. This review highlights recent findings on the metabolic phenotypes of cancer and elucidates the interactions between signal transduction pathways and metabolic pathways. We also provide novel rationales for designing the next-generation cancer metabolism drugs.

The Metabolic Heterogeneity and Flexibility of Cancer Stem Cells

Simple Summary

Cancer stem cells (CSCs) have been shown to be the main cause of therapy resistance and cancer recurrence. An analysis of their biological properties has revealed that CSCs have a particular metabolism that differs from non-CSCs to maintain their stemness properties. In this review, we analyze the flexible metabolic mechanisms of CSCs and highlight the new therapeutics that target CSC metabolism.

Abstract

Numerous findings have indicated that CSCs, which are present at a low frequency inside primary tumors, are the main cause of therapy resistance and cancer recurrence. Although various therapeutic methods targeting CSCs have been attempted for eliminating cancer cells completely, the complicated characteristics of CSCs have hampered such attempts. In analyzing the biological properties of CSCs, it was revealed that CSCs have a peculiar metabolism that is distinct from non-CSCs to maintain their stemness properties. The CSC metabolism involves not only the catabolic and anabolic pathways, but also intracellular signaling, gene expression, and redox balance. In addition, CSCs can reprogram their metabolism to flexibly respond to environmental changes. In this review, we focus on the flexible metabolic mechanisms of CSCs, and highlight the new therapeutics that target CSC metabolism.

Early Prediction of Tumor Response to Neoadjuvant Chemotherapy and Clinical Outcome in Breast Cancer Using a Novel FDG-PET Parameter for Cancer Stem Cell Metabolism

Cancer stem cells (CSCs) contribute to chemoresistance and tumor relapse. By using the distinct metabolic phenotype of CSC, we designed novel PET parameters for CSC metabolism and investigated their clinical values. Patients with breast cancer who underwent ¹⁸F-FDG PET/CT before neoadjuvant chemotherapy (NAC) were retrospectively included. We developed a method to measure CSC metabolism using standardized uptake value histogram data. The predictive value of novel CSC metabolic parameters for pathologic complete response (pCR) was assessed with multivariable logistic regression. The association between the CSC parameter and disease-free survival (DFS) was also determined. We identified 82 patients with HER2-positive/triple-negative subtypes and 38 patients with luminal tumors. After multivariable analysis, only metabolic tumor volume for CSC (MTVcsc) among metabolic parameters remained the independent predictor of pCR (OR, 0.12; p = 0.022). MTVcsc successfully predicted pathologic tumor response to NAC in HER2-positive/triple-negative subtypes (accuracy, 74%) but not in the luminal subtype (accuracy, 29%). MTVcsc was also predictive of DFS, with a 3-year DFS of 90% in the lower MTVcsc group (<1.75 cm³) versus 72% in the higher group (>1.75 cm³). A novel data-driven PET parameter for CSC metabolism provides early prediction of pCR after NAC and DFS in HER2-positive and triple-negative subtypes.

Newcastle disease virus suppress glycolysis pathway and induce breast cancer cells death

Newcastle disease virus (NDV) can modulate cancer cell signaling pathway and induce apoptosis in cancer cells. Cancer cells increase their glycolysis rates to meet the energy demands for their survival and generate ATP as the primary energy source for cell growth and proliferation. Interfering the glycolysis pathway may be a valuable antitumor strategy. This study aimed to assess the effect of NDV on the glycolysis pathway in infected breast cancer cells. Oncolytic NDV attenuated AMHA1 strain was used in this study. AMJ13 and MCF7 breast cancer cell lines and a normal embryonic REF cell line were infected with NDV with different multiplicity of infections (moi) to determine the IC50 of NDV through MTT assay. Crystal violet staining was done to study the morphological changes. NDV apoptosis induction was assessed using AO/PI assay. NDV interference with the glycolysis pathway was examined through measuring hexokinase (HK) activity, pyruvate, and ATP concentrations, and pH levels in NDV infected and non-infected breast cancer cells and in normal embryonic cells. The results showed that NDV replicates efficiently in cancer cells and spare normal cells and induce morphological changes and apoptosis in breast cancer cells but not in normal cells. NDV infected cancer cells showed decreased in the HK activity, pyruvate and ATP concentrations, and acidity, which reflect a significant decrease in the glycolysis activity of the NDV infected tumor cells. No effects on the normal cells were observed. In conclusion, oncolytic NDV ability to reduce glycolysis pathway activity in cancer cells can be an exciting module to improve antitumor therapeutics.

Hexokinase inhibition using D-Mannoheptulose enhances oncolytic newcastle disease virus-mediated killing of breast cancer cells

Background

Most cancer cells exhibit increased glycolysis and use this metabolic pathway cell growth and proliferation. Targeting cancer cells' metabolism is a promising strategy in inhibiting cancer cell progression. We used D-Mannoheptulose, a specific hexokinase inhibitor, to inhibit glycolysis to enhance the Newcastle disease virus anti-tumor effect.

Methods

Human breast cancer cells were treated by NDV and/or hexokinase inhibitor. The study included cell viability, apoptosis, and study levels of hexokinase enzyme, pyruvate, ATP, and acidity. The combination index was measured to determine the synergism of NDV and hexokinase inhibitor.

Results

The results showed synergistic cytotoxicity against breast cancer cells by combination therapy but no cytotoxic effect against normal cells. The effect was accompanied by apoptotic cell death and hexokinase downregulation and inhibition to glycolysis products, pyruvate, ATP, and acidity.

Conclusions

The combination treatment showed safe significant tumor cell proliferation inhibition compared to monotherapies suggesting a novel strategy for anti-breast cancer therapy through glycolysis inhibition by hexokinase downregulation.

Metabolic heterogeneity in cancer: An overview and therapeutic implications

Recent research on cancer metabolism has revealed that individual tumors have highly heterogeneous metabolic profiles that contribute to the connective metabolic networks within the tumor and its environment. Indeed, tumor-associated cells types, including tumor cells, cancer-associated fibroblasts (CAFs) and immune cells, reprogram their metabolism in many different ways due to diverse genetic backgrounds and complex environmental stimuli. This intratumoral metabolic heterogeneity and the derived metabolic interactions play an instrumental role in cancer progression. Understanding how this heterogeneity occurs may provide promising therapeutic strategies. Here, we review the diverse metabolic profiles of several important cell subpopulations in tumors and their impact on tumor progression and discuss the consequent metabolic interactions as well as the related therapeutic concerns.

Targeting Glucose Metabolism to Overcome Resistance to Anticancer Chemotherapy in Breast Cancer

Breast cancer (BC) is the most prevalent cancer in women. BC is heterogeneous, with distinct phenotypical and morphological characteristics. These are based on their gene expression profiles, which divide BC into different subtypes, among which the triple-negative breast cancer (TNBC) subtype is the most aggressive one. The growing interest in tumor metabolism emphasizes the role of altered glucose metabolism in driving cancer progression, response to cancer treatment, and its distinct role in therapy resistance. Alterations in glucose metabolism are characterized by increased uptake of glucose, hyperactivated glycolysis, decreased oxidative phosphorylation (OXPHOS) component, and the accumulation of lactate. These deviations are attributed to the upregulation of key glycolytic enzymes and transporters of the glucose metabolic pathway. Key glycolytic enzymes such as hexokinase, lactate dehydrogenase, and enolase are upregulated, thereby conferring resistance towards drugs such as cisplatin, paclitaxel, tamoxifen, and doxorubicin. Besides, drug efflux and detoxification are two energy-dependent mechanisms contributing to resistance. The emergence of resistance to chemotherapy can occur at an early or later stage of the treatment, thus limiting the success and outcome of the therapy. Therefore, understanding the aberrant glucose metabolism in tumors and its link in conferring therapy resistance is essential. Using combinatory treatment with metabolic inhibitors, for example, 2-deoxy-D-glucose (2-DG) and metformin, showed promising results in countering therapy resistance. Newer drug designs such as drugs conjugated to sugars or peptides that utilize the enhanced expression of tumor cell glucose transporters offer selective and efficient drug delivery to cancer cells with less toxicity to healthy cells. Last but not least, naturally occurring compounds of plants defined as phytochemicals manifest a promising approach for the eradication of cancer cells via suppression of essential enzymes or other compartments associated with glycolysis. Their benefits for human health open new opportunities in therapeutic intervention, either alone or in combination with chemotherapeutic drugs. Importantly, phytochemicals as efficacious instruments of anticancer therapy can suppress events leading to chemoresistance of cancer cells. Here, we review the current knowledge of altered glucose metabolism in contributing to resistance to classical anticancer drugs in BC treatment and various ways to target the aberrant metabolism that will serve as a promising strategy for chemosensitizing tumors and overcoming resistance in BC.

Photodynamic therapy regulates fate of cancer stem cells through reactive oxygen species

Photodynamic therapy (PDT) is an effective and promising cancer treatment. PDT directly generates reactive oxygen species (ROS) through photochemical reactions. This oxygen-dependent exogenous ROS has anti-cancer stem cell (CSC) effect. In addition, PDT may also increase ROS production by altering metabolism, endoplasmic reticulum stress, or potential of mitochondrial membrane. It is known that the half-life of ROS in PDT is short, with high reactivity and limited diffusion distance. Therefore, the main targeting position of PDT is often the subcellular localization of photosensitizers, which is helpful for us to explain how PDT affects CSC characteristics, including differentiation, self-renewal, apoptosis, autophagy, and immunogenicity. Broadly speaking, excess ROS will damage the redox system and cause oxidative damage to molecules such as DNA, change mitochondrial permeability, activate unfolded protein response, autophagy, and CSC resting state. Therefore, understanding the molecular mechanism by which ROS affect CSCs is beneficial to improve the efficiency of PDT and prevent tumor recurrence and metastasis. In this article, we review the effects of two types of photochemical reactions on PDT, the metabolic processes, and the biological effects of ROS in different subcellular locations on CSCs.

Oxidized ATM promotes breast cancer stem cell enrichment through energy metabolism reprogram-mediated acetyl-CoA accumulation

Cancer stem cell (CSC) is a challenge in the therapy of triple-negative breast cancer (TNBC). Intratumoral hypoxia is a common feature of solid tumor. Hypoxia may contribute to the maintenance of CSC, resulting in a poor efficacy of traditional treatment and recurrence of TNBC cases. However, the underlying molecular mechanism involved in hypoxia-induced CSC stemness maintenance remains unclear. Here, we report that hypoxia stimulated DNA double-strand breaks independent of ATM kinase activation (called oxidized ATM in this paper) play a crucial role in TNBC mammosphere formation and stemness maintenance by governing a specific energy metabolism reprogramming (EMR). Oxidized ATM up-regulates GLUT1, PKM2, and PDHa expressions to enhance the uptake of glucose and production of pyruvate rather than lactate products, which facilitates glycolytic flux to mitochondrial pyruvate and citrate, thus resulting in accumulation of cytoplasmic acetyl-CoA instead of the tricarboxylic acid (TCA) cycle by regulating ATP-citrate lyase (ACLY) activity. Our findings unravel a novel model of TNBC-CSC glucose metabolism and its functional role in maintenance of hypoxic TNBC-CSC stemness. This work may help us to develop new therapeutic strategies for TNBC treatment.

Energy metabolism in cancer stem cells

Normal cells mainly rely on oxidative phosphorylation as an effective energy source in the presence of oxygen. In contrast, most cancer cells use less efficient glycolysis to produce ATP and essential biomolecules. Cancer cells gain the characteristics of metabolic adaptation by reprogramming their metabolic mechanisms to meet the needs of rapid tumor growth. A subset of cancer cells with stem characteristics and the ability to regenerate exist throughout the tumor and are therefore called cancer stem cells (CSCs). New evidence indicates that CSCs have different metabolic phenotypes compared with differentiated cancer cells. CSCs can dynamically transform their metabolic state to favor glycolysis or oxidative metabolism. The mechanism of the metabolic plasticity of CSCs has not been fully elucidated, and existing evidence indicates that the metabolic phenotype of cancer cells is closely related to the tumor microenvironment. Targeting CSC metabolism may provide new and effective methods for the treatment of tumors. In this review, we summarize the metabolic characteristics of cancer cells and CSCs and the mechanisms of the metabolic interplay between the tumor microenvironment and CSCs, and discuss the clinical implications of targeting CSC metabolism.

Glycolytic inhibitor 2-deoxyglucose suppresses inflammatory response in innate immune cells and experimental staphylococcal endophthalmitis

Previously, we have shown that Staphylococcus (S) aureus induces a glycolytic response in retinal residential (microglia) and infiltrated cells (neutrophils and macrophages) during endophthalmitis. In this study, we sought to investigate the physiological role of glycolysis in bacterial endophthalmitis using a glycolytic inhibitor, 2-deoxyglucose (2DG). Our data showed that 2DG treatment attenuated the inflammatory responses of mouse bone marrow-derived macrophages (BMDM) and neutrophils (BMDN) when challenged with either live or heat-killed S. aureus (HKSA). Among the inflammatory mediators, 2DG caused a significant reduction in levels of cytokines (TNF-α, IL-1β, IL-6) and chemokines (CXCL1 and CXCL2). Western blot analysis of 2DG treated cells showed downregulation of bacterial-induced MEK/ERK pathways. In vivo, intravitreal administration of 2DG both pre- and post-bacterial infection resulted in a significant reduction in intraocular inflammation in C57BL/6 mouse eyes and downregulation of ERK phosphorylation in retinal tissue. Collectively, our study demonstrates that 2DG attenuates inflammatory response in bacterial endophthalmitis and cultured innate immune cells via inhibition of ERK signaling. Thus glycolytic inhibitors in combination with antibiotics could mitigate inflammation-mediated tissue damage in ocular infections.

Cancer Stem Cell Plasticity - A Deadly Deal

Intratumoral heterogeneity is a major ongoing challenge in the effective therapeutic targeting of cancer. Accumulating evidence suggests that a fraction of cells within a tumor termed Cancer Stem Cells (CSCs) are primarily responsible for this diversity resulting in therapeutic resistance and metastasis. Adding to this complexity, recent studies have shown that there can be different subpopulations of CSCs with varying biochemical and biophysical traits resulting in varied dissemination and drug-resistance potential. Moreover, cancer cells can exhibit a high level of plasticity or the ability to dynamically switch between CSC and non-CSC states or among different subsets of CSCs. In addition, CSCs also display extensive metabolic plasticity. The molecular mechanisms underlying these different interconnected axes of plasticity has been under extensive investigation and the trans-differentiation process of Epithelial to Mesenchymal transition (EMT) has been identified as a major contributing factor. Besides genetic and epigenetic factors, CSC plasticity is also shaped by non-cell-autonomous effects such as the tumor microenvironment (TME). In this review, we discuss the latest developments in decoding mechanisms and implications of CSC plasticity in tumor progression at biochemical and biophysical levels, and the latest in silico approaches being taken for characterizing cancer cell plasticity. These efforts can help improve existing therapeutic approaches by taking into consideration the contribution of cellular plasticity/heterogeneity in enabling drug resistance.

Shedding New Light on Cancer Metabolism: A Metabolic Tightrope Between Life and Death

Since the earliest findings of Otto Warburg, who discovered the first metabolic differences between lactate production of cancer cells and non-malignant tissues in the 1920s, much time has passed. He explained the increased lactate levels with dysfunctional mitochondria and aerobic glycolysis despite adequate oxygenation. Meanwhile, we came to know that mitochondria remain instead functional in cancer cells; hence, metabolic drift, rather than being linked to dysfunctional mitochondria, was found to be an active act of direct response of cancer cells to cell proliferation and survival signals. This metabolic drift begins with the use of sugars and the full oxidative phosphorylation via the mitochondrial respiratory chain to form CO₂, and it then leads to the formation of lactic acid via partial oxidation. In addition to oncogene-driven metabolic reprogramming, the oncometabolites themselves alter cell signaling and are responsible for differentiation and metastasis of cancer cells. The aberrant metabolism is now considered a major characteristic of cancer within the past 15 years. However, the proliferating anabolic growth of a tumor and its spread to distal sites of the body is not explainable by altered glucose metabolism alone. Since a tumor consists of malignant cells and its tumor microenvironment, it was important for us to understand the bilateral interactions between the primary tumor and its microenvironment and the processes underlying its successful metastasis. We here describe the main metabolic pathways and their implications in tumor progression and metastasis. We also portray that metabolic flexibility determines the fate of the cancer cell and ultimately the patient. This flexibility must be taken into account when deciding on a therapy, since singular cancer therapies only shift the metabolism to a different alternative path and create resistance to the medication used. As with Otto Warburg in his days, we primarily focused on the metabolism of mitochondria when dealing with this scientific question.

HNF4A-AS1/hnRNPU/CTCF axis as a therapeutic target for aerobic glycolysis and neuroblastoma progression

BACKGROUND

Aerobic glycolysis is a hallmark of metabolic reprogramming that contributes to tumor progression. However, the mechanisms regulating expression of glycolytic genes in neuroblastoma (NB), the most common extracranial solid tumor in childhood, still remain elusive.

METHODS

Crucial transcriptional regulators and their downstream glycolytic genes were identified by integrative analysis of a publicly available expression profiling dataset. In vitro and in vivo assays were undertaken to explore the biological effects and underlying mechanisms of transcriptional regulators in NB cells. Survival analysis was performed by using Kaplan-Meier method and log-rank test.

RESULTS

Hepatocyte nuclear factor 4 alpha (HNF4A) and its derived long noncoding RNA (HNF4A-AS1) promoted aerobic glycolysis and NB progression. Gain- and loss-of-function studies indicated that HNF4A and HNF4A-AS1 facilitated the glycolysis process, glucose uptake, lactate production, and ATP levels of NB cells. Mechanistically, transcription factor HNF4A increased the expression of hexokinase 2 (HK2) and solute carrier family 2 member 1 (SLC2A1), while HNF4A-AS1 bound to heterogeneous nuclear ribonucleoprotein U (hnRNPU) to facilitate its interaction with CCCTC-binding factor (CTCF), resulting in transactivation of CTCF and transcriptional alteration of HNF4A and other genes associated with tumor progression. Administration of a small peptide blocking HNF4A-AS1-hnRNPU interaction or lentivirus-mediated short hairpin RNA targeting HNF4A-AS1 significantly suppressed aerobic glycolysis, tumorigenesis, and aggressiveness of NB cells. In clinical NB cases, high expression of HNF4A-AS1, hnRNPU, CTCF, or HNF4A was associated with poor survival of patients.

CONCLUSIONS

These findings suggest that therapeutic targeting of HNF4A-AS1/hnRNPU/CTCF axis inhibits aerobic glycolysis and NB progression.

Targeting cancer stem cells from a metabolic perspective

The process of cancer development and progression is driven by distinct subsets of cancer stem cells (CSCs) that contribute the self-renewal capacity as the major impetus to the metastatic dissemination and main impediments in cancer treatment. Given that CSCs are so scarce in the tumor mass, there are debatable points on the metabolic signatures of CSCs. As opposed to differentiated tumor progenies, CSCs display exquisite patterns of metabolism that, depending on the type of cancer, predominately rely on glycolysis, oxidative metabolism of glutamine, fatty acids, or amino acids for ATP production. Metabolic heterogeneity of CSCs, which attributes to differences in type and microenvironment of tumors, confers CSCs to have the plasticity to cope with the endogenous mitochondrial stress and exogenous microenvironment. In essence, CSCs and normal stem cells are like mirror images of each other in terms of metabolism. To achieve reprogramming, CSCs not only need to upregulate their metabolic engine for self-renewal and defense mechanism, but also expedite the antioxidant defense to sustain the redox homeostasis. In the context of these pathways, this review portrays the connection between the metabolic features of CSCs and cancer stemness. Identification of the metabolic features in conferring resistance to anticancer treatment dictated by CSCs can enhance the opportunity to open up a new therapeutic dimension, which might not only improve the effectiveness of cancer therapies but also annihilate the whole tumor without recurrence. Henceforth, we highlight current findings of potential therapeutic targets for the design of alternative strategies to compromise the growth, drug resistance, and metastasis of CSCs by altering their metabolic phenotypes. Perturbing the versatile skills of CSCs by barricading metabolic signaling might bring about plentiful approaches to discover novel therapeutic targets for clinical application in cancer treatments.

Impact statement

This minireview highlights the current evidence on the mechanisms of pivotal metabolic pathways that attribute to cancer stem cells (CSCs) with a special focus on developing metabolic strategies of anticancer treatment that can be exploited in preclinical and clinical settings. Specific metabolic inhibitors that can overwhelm the properties of CSCs may impede tumor recurrence and metastasis, and potentially achieve a permanent cure of cancer patients.

Crosstalk between autophagy and metabolic regulation of cancer stem cells

Cancer is now considered as a heterogeneous ecosystem in which tumor cells collaborate with each other and with host cells in their microenvironment. As circumstances change, the ecosystem evolves to ensure the survival and growth of the cancer cells. In this ecosystem, metabolism is not only a key player but also drives stemness. In this review, we first summarize our current understanding of how autophagy influences cancer stem cell phenotype. We emphasize metabolic pathways in cancer stem cells and discuss how autophagy-mediated regulation metabolism is involved in their maintenance and proliferation. We then provide an update on the role of metabolic reprogramming and plasticity in cancer stem cells. Finally, we discuss how metabolic pathways in cancer stem cells could be therapeutically targeted.

Metformin as Potential Therapy for High-Grade Glioma

Metformin (MET), 1,1-dimethylbiguanide hydrochloride, is a biguanide drug used as the first-line medication in the treatment of type 2 diabetes. The recent years have brought many observations showing metformin in its new role. The drug, commonly used in the therapy of diabetes, may also find application in the therapy of a vast variety of tumors. Its effectiveness has been demonstrated in colon, breast, prostate, pancreatic cancer, leukemia, melanoma, lung and endometrial carcinoma, as well as in gliomas. This is especially important in light of the poor options offered to patients in the case of high-grade gliomas, which include glioblastoma (GBM). A thorough understanding of the mechanism of action of metformin can make it possible to discover new drugs that could be used in neoplasm therapy.

Therapeutic targeting of YY1/MZF1 axis by MZF1-uPEP inhibits aerobic glycolysis and neuroblastoma progression

As a hallmark of metabolic reprogramming, aerobic glycolysis contributes to tumorigenesis and aggressiveness. However, the mechanisms and therapeutic strategies regulating aerobic glycolysis in neuroblastoma (NB), one of leading causes of cancer-related death in childhood, still remain elusive.

Methods: Transcriptional regulators and their downstream glycolytic genes were identified by a comprehensive screening of publicly available datasets. Dual-luciferase, chromatin immunoprecipitation, real-time quantitative RT-PCR, western blot, gene over-expression or silencing, co-immunoprecipitation, mass spectrometry, peptide pull-down assay, sucrose gradient sedimentation, seahorse extracellular flux, MTT colorimetric, soft agar, matrigel invasion, and nude mice assays were undertaken to explore the biological effects and underlying mechanisms of transcriptional regulators in NB cells. Survival analysis was performed by using log-rank test and Cox regression assay.

Results: Transcription factor myeloid zinc finger 1 (MZF1) was identified as an independent prognostic factor (hazard ratio=2.330, 95% confidence interval=1.021 to 3.317), and facilitated glycolysis process through increasing expression of hexokinase 2 (HK2) and phosphoglycerate kinase 1 (PGK1). Meanwhile, a 21-amino acid peptide encoded by upstream open reading frame of MZF1, termed as MZF1-uPEP, bound to zinc finger domain of Yin Yang 1 (YY1), resulting in repressed transactivation of YY1 and decreased transcription of MZF1 and downstream genes HK2 and PGK1. Administration of a cell-penetrating MZF1-uPEP or lentivirus over-expressing MZF1-uPEP inhibited the aerobic glycolysis, tumorigenesis and aggressiveness of NB cells. In clinical NB cases, low expression of MZF1-uPEP or high expression of MZF1, YY1, HK2, or PGK1 was associated with poor survival of patients.

Conclusions: These results indicate that therapeutic targeting of YY1/MZF1 axis by MZF1-uPEP inhibits aerobic glycolysis and NB progression.

Gene signatures and prognostic analyses of the Tob/BTG pituitary tumor-transforming gene (PTTG) family in clinical breast cancer patients

Breast cancer is the most common cancer type in females, and exploring the mechanisms of disease progression is playing a crucial role in the development of potential therapeutics. Pituitary tumor-transforming gene (PTTG) family members are well documented to be involved in cell-cycle regulation and mitosis, and contribute to cancer development by their involvement in cellular transformation in several tumor types. The critical roles of PTTG family members as crucial transcription factors in diverse types of cancers are recognized, but how they regulate breast cancer development still remains mostly unknown. Meanwhile, a holistic genetic analysis exploring whether PTTG family members regulate breast cancer progression via the cell cycle as well as the energy metabolism-related network is lacking. To comprehensively understand the messenger RNA expression profiles of PTTG proteins in breast cancer, we herein conducted a high-throughput screening approach by integrating information from various databases such as Oncomine, Kaplan-Meier Plotter, Metacore, ClueGo, and CluePedia. These useful databases and tools provide expression profiles and functional analyses. The present findings revealed that PTTG1 and PTTG3 are two important genes with high expressions in breast cancer relative to normal breast cells, implying their unique roles in breast cancer progression. Results of our coexpression analysis demonstrated that PTTG family genes were positively correlated with thiamine triphosphate (TTP), deoxycytidine triphosphate (dCTP) metabolic, glycolysis, gluconeogenesis, and cell-cycle related pathways. Meanwhile, through Cytoscape analyzed indicated that in addition to the metastasis markers AURKA, AURKB, and NDC80, many of the kinesin superfamily (KIF) members including KIFC1, KIF2C, KIF4A, KIF14, KIF20A, KIF23, were also correlated with PTTG family transcript expression. Finally, we revealed that high levels of PTTG1 and PTTG3 transcription predicted poor survival, which provided useful insights into prospective research of cancer associated with the PTTG family. Therefore, these members of the PTTG family would serve as distinct and essential prognostic biomarkers in breast cancer.

Variation in energy metabolism arising from the effect of the tumor microenvironment on cell biological behaviors of bladder cancer cells and endothelial cells

Tumor energy metabolism and angiogenesis play significant roles in tumor genesis and development, while the effect of the tumor microenvironment (TME), which tumors rely on, is always ignored. In this research, we cocultured bladder cancer (BC) T24 cells with tumor-associated human umbilical vein endothelial cells (HUVECs) under normoxic and hypoxic conditions and detected proliferation, migration, oxidative phosphorylation (OXPHOS) and glycolysis to reveal the energy metabolism characteristics and their effect on cell biological behaviors (CBBs) in the TME. Compared with single-cultured cells, both cocultured T24 cells and HUVECs showed poor proliferation and migration in hypoxic environment, and OXPHOS was activated in cocultured T24 cells but weakened in cocultured HUVECs. However, in normoxic environment, cocultured T24 cells grew much faster while cocultured HUVECs grew slower compared with single-cultured cells. Additionally, glycolysis played a crucial role in energy metabolism and was inhibited in cocultured T24 cells but activated in cocultured HUVECs. In normoxic TME, OXPHOS take main responsibility of energy metabolism. T24 cells exhibited increased proliferation and migration with HUVECs support. In hypoxic TME, glycolysis may be the primary energy supply pathway. T24 cells then exhibit suppressed proliferation and migration, while HUVECs tend to promote angiogenesis to adapt to the harsh TME.

Novel therapies hijack the blood-brain barrier to eradicate glioblastoma cancer stem cells

Glioblastoma (GBM) is amongst the most aggressive brain tumors with a dismal prognosis. Despite significant advances in the current multimodality therapy including surgery, postoperative radiotherapy (RT) and temozolomide (TMZ)-based concomitant and adjuvant chemotherapy (CT), tumor recurrence is nearly universal with poor patient outcomes. These limitations are in part due to poor drug penetration through the blood-brain barrier (BBB) and resistance to CT and RT by a small population of cancer cells recognized as tumor-initiating cells or cancer stem cells (CSCs). Though CT and RT kill the bulk of the tumor cells, they fail to affect CSCs, resulting in their enrichment and their development into more refractory tumors. Therefore, identifying the mechanisms of resistance and developing therapies that specifically target CSCs can improve response, prevent the development of refractory tumors and increase overall survival of GBM patients. Small molecule inhibitors that can breach the BBB and selectively target CSCs are emerging. In this review, we have summarized the recent advancements in understanding the GBM CSC-specific signaling pathways, the CSC-tumor microenvironment niche that contributes to CT and RT resistance and the use of novel combination therapies of small molecule inhibitors that may be used in conjunction with TMZ-based chemoradiation for effective management of GBM.

2-Deoxyglucose and Newcastle Disease Virus Synergize to Kill Breast Cancer Cells by Inhibition of Glycolysis Pathway Through Glyceraldehyde3-Phosphate Downregulation

Targeting cancer cells metabolism is promising strategy in inhibiting cancer cells progression that are known to exhibit increased aerobic glycolysis. We used the glucose analog 2-Deoxyglucose (2-DG) as a competitor molecule of glucose. To further enhance the effectiveness of 2-DG, the Newcastle disease virus (NDV) was used as a combination virotherapy to enhance the anti-tumor effect. Human and mouse-breast cancer cells were treated by NDV and/or 2-DG. The effect was analyzed by study cell viability, apoptosis and level of glyceraldehyde3-phosphate (GAPDH) by ELISA and QPCR assays. Synergistic cytotoxicity was found after a 72-h treatment of human- and mouse-breast cancer cells with 2-DG in combination with NDV at different concentrations. The synergistic cytotoxicity was accompanied by apoptotic cell death and GAPDH downregulation and inhibition to glycolysis product pyruvate. The combination treatment showed significant tumor growth inhibition compared to single treatments in vivo. Our results suggest the effectiveness of a novel strategy for anti-breast cancer therapy through glycolysis inhibition and GAPDH downregulation.

Bioactive lipids in cancer stem cells

Tumours are known to be a heterogeneous group of cells, which is why they are difficult to eradicate. One possible cause for this is the existence of slow-cycling cancer stem cells (CSCs) endowed with stem cell-like properties of self-renewal, which are responsible for resistance to chemotherapy and radiotherapy. In recent years, the role of lipid metabolism has garnered increasing attention in cancer. Specifically, the key roles of enzymes such as stearoyl-CoA desaturase-1 and 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase in CSCs, have gained particular interest. However, despite accumulating evidence on the role of proteins in controlling lipid metabolism, very little is known about the specific role played by lipid products in CSCs. This review highlights recent findings on the role of lipid metabolism in CSCs, focusing on the specific mechanism by which bioactive lipids regulate the fate of CSCs and their involvement in signal transduction pathways.

Targeting cancer stem cells in drug discovery: Current state and future perspectives

In recent decades, cancer stem cells (CSCs) have been increasingly identified in many malignancies. CSC-related signaling pathways and their functions provide new strategies for treating cancer. The aberrant activation of related signaling pathways (e.g., Wnt, Notch, and Hedgehog pathways) has been linked to multiple types of malignant tumors, which makes these pathways attractive targets for cancer therapy. CSCs display many characteristic features, such as self-renewal, differentiation, high tumorigenicity, and drug resistance. Therefore, there is an urgent need to develop new therapeutic strategies to target these pathways to control stem cell replication, survival, and differentiation. Notable crosstalk occurs among different signaling pathways and potentially leads to compensatory escape. Therefore, multitarget inhibitors will be one of the main methods to overcome the drug resistance of CSCs. Many small molecule inhibitors of components of signaling pathways in CSCs have entered clinical trials, and some inhibitors, such as vismodegib, sonidegib, and glasdegib, have been approved. Tumor cells are susceptible to sonidegib and vismodegib resistance due to mutations in the Smo protein. The signal transducers and activators of transcription 3 (STAT3) inhibitor BBI608 is being evaluated in a phase III trial for a variety of cancers. Structural derivatives of BBI608 are the main focus of STAT3 inhibitor development, which is another strategy for CSC therapy. In addition to the potential pharmacological inhibitors targeting CSC-related signaling pathways, other methods of targeting CSCs are available, such as nano-drug delivery systems, mitochondrion targeting, autophagy, hyperthermia, immunotherapy, and CSC microenvironment targeting. In addition, we summarize the latest advances in the clinical development of agents targeting CSC-related signaling pathways and other methods of targeting CSCs.

Heat shock proteins in cancer stem cell maintenance: A potential therapeutic target?

Cancer stem cells (CSCs) are a subpopulation of tumor cells with unlimited self-renewal capability, multilineage differentiation potential and long-term tumor repopulation capacity. CSCs reside in anatomically distinct regions within the tumor microenvironment, called niches, and this favors the maintenance of CSC properties and preserves their phenotypic plasticity. Indeed, CSCs are characterized by a flexible state based on their capacity to interconvert between a differentiated and a stem-like phenotype, and this depends on the activation of adaptive mechanisms in response to different environmental conditions. Heat Shock Proteins (HSPs) are molecular chaperones, upregulated upon cell exposure to several stress conditions and are responsible for normal maturation, localization and activity of intra and extracellular proteins. Noteworthy, HSPs play a central role in several cellular processes involved in tumor initiation and progression (i.e. cell viability, resistance to apoptosis, stress conditions and drug therapy, EMT, bioenergetics, invasiveness, metastasis formation) and, thus, are widely considered potential molecular targets. Furthermore, much evidence suggests a key regulatory function for HSPs in CSC maintenance and their upregulation has been proposed as a mechanism used by CSCs to adapt to unfavorable environmental conditions, such as nutrient deprivation, hypoxia, inflammation. This review discusses the relevance of HSPs in CSC biology, highlighting their role as novel potential molecular targets to develop anticancer strategies aimed at CSC targeting.

Deoxyelephantopin suppresses hepatic stellate cells activation associated with inhibition of aerobic glycolysis via hedgehog pathway

Accumulating evidence suggests that hepatic stellate cells (HSCs) adopt aerobic glycolysis during activation. Hedgehog (Hh) pathway plays a vital role in the process of HSCs activation by regulating metabolism, and activation of the Hh pathway promotes transdifferentiation of HSCs into myofibroblasts. Deoxyelephantopin (DET), a naturally occurring sesquiterpene lactone from Elephantopus scaber, has been shown to exert hepatoprotective as well as anticancer effects. However, the effect of DET on hepatic fibrosis and glycolysis in HSCs have never been elucidated. Here, we studied the function of the DET on HSCs activation and investigated the anti-fibrogenic effects of DET was associated with interfering with glycolysis in HSCs. Our results first demonstrated that DET reduced the expression of a-smooth muscle actin (a-SMA) and a1(I)procollagen at both mRNA and protein levels, and restore lipogenesis in HSCs. Furthermore, DET decreased the expression of hexokinase (HK), phosphofructokinase-2 (PFK2), Glucose transporter 4 (Glut4), and reduced lactate production dose-dependently in HSCs. Moreover, we further revealed that DET reduced fibrotic gene expression, restored lipid accumulation in HSCs. However, the Hh pathway agonist SAG could reverse the above effect of DET. Together, these results indicate DET inhibits aerobic glycolysis in HSCs associated with inhibition of Hh pathway. Our results provided a novel mechanism for DET suppression of HSC activation implicated in antifibrotic therapy.

Redox regulation of cell state and fate

The failure in effective cancer treatment is thought to be attributed to a subpopulation of tumor cells with stem cell-like properties. These cancer stem cells (CSCs) are intimately linked to tumor initiation, heterogeneity, maintenance, recurrence and metastasis. Increasing evidence supports the view that a tight redox regulation is crucial for CSC proliferation, tumorigenicity, therapy resistance and metastasis in many cancer types. Since the distinct metabolic and epigenetic states of CSCs may influence ROS levels, and hence their malignancy, ROS modulating agents hold promise in their utility as anti-CSC agents that may improve the durability of current cancer treatments. This review will focus on (i) how ROS levels are regulated for CSCs to elicit their hallmark features; (ii) the link between ROS and metabolic plasticity of CSCs; and (iii) how ROS may interface with epigenetics that would enable CSCs to thrive in a stressful tumor microenvironment and survive therapeutic insults.

Targeting the ROS/PI3K/AKT/HIF-1α/HK2 axis of breast cancer cells: Combined administration of Polydatin and 2-Deoxy-d-glucose

It is well established that cancer cells depend upon aerobic glycolysis to provide the energy they need to survive and proliferate. However, anti-glycolytic agents have yielded few positive results in human patients, in part due to dose-limiting side effects. Here, we discovered the unexpected anti-cancer efficacy of Polydatin (PD) combined with 2-deoxy-D-glucose (2-DG), which is a compound that inhibits glycolysis. We demonstrated in two breast cell lines (MCF-7 and 4T1) that combination treatment with PD and 2-DG induced cell apoptosis and inhibited cell proliferation, migration and invasion. Furthermore, we determined the mechanism of PD in synergy with 2-DG, which decreased the intracellular reactive oxygen (ROS) levels and suppressed the PI3K/AKT pathway. In addition, the combined treatment inhibited the glycolytic phenotype through reducing the expression of HK2. HK2 deletion in breast cancer cells thus improved the anti-cancer activity of 2-DG. The combination treatment also resulted in significant tumour regression in the absence of significant morphologic changes in the heart, liver or kidney in vivo. In summary, our study demonstrates that PD synergised with 2-DG to enhance its anti-cancer efficacy by inhibiting the ROS/PI3K/AKT/HIF-1α/HK2 signalling axis, providing a potential anti-cancer strategy.

High metabolic rate and stem cell characteristics of esophageal cancer stem-like cells depend on the Hsp27-AKT-HK2 pathway

Tumor progression with chemoresistance and local recurrence is commonly happened during treatment of esophageal squamous cell carcinoma (ESCC). Cancer stem cells (CSC) may respond for tumor progression. However, there are few reports regarding metabolism of esophageal CSCs with clinical correlation. In this work, we demonstrated that ESCC cell lines in spheroid culture display CSC phenotypes, including increased ALDH activity, chemoresistance and tumor initiation, which are dependent on Hsp27 activation. Esophageal CSCs also exhibit reprogrammed metabolic features particularly higher glycolysis and oxidative phosphorylation, which are regulated via the Hsp27-AKT-HK2 pathway. Moreover, HK2 is required for maintenance of CSC phenotypes. Inhibition of CSC metabolism reduces cell growth and tumor formation. Clinically, patients who underwent surgical resection for esophageal cancer, and displayed overexpression of both Hsp27 and HK2, had the worst prognosis of all expression types. In conclusion, stem cells features and aberrant metabolic reprogramming of esophageal CSCs depend on the Hsp27-AKT-HK2 pathway. Targeting Hsp27 and HK2 could be novel therapeutic strategy for treating esophageal cancer and warrants further investigation.