The Warburg effect version 2.0: metabolic reprogramming of cancer stem cells

Exploring the interplay between triple-negative breast cancer stem cells and tumor microenvironment for effective therapeutic strategies

Triple-negative breast cancer (TNBC) is a highly aggressive and metastatic malignancy with poor treatment outcomes. The interaction between the tumor microenvironment (TME) and breast cancer stem cells (BCSCs) plays an important role in the development of TNBC. Owing to their ability of self-renewal and multidirectional differentiation, BCSCs maintain tumor growth, drive metastatic colonization, and facilitate the development of drug resistance. TME is the main factor regulating the phenotype and metastasis of BCSCs. Immune cells, cancer-related fibroblasts (CAFs), cytokines, mesenchymal cells, endothelial cells, and extracellular matrix within the TME form a complex communication network, exert highly selective pressure on the tumor, and provide a conducive environment for the formation of BCSC niches. Tumor growth and metastasis can be controlled by targeting the TME to eliminate BCSC niches or targeting BCSCs to modify the TME. These approaches may improve the treatment outcomes and possess great application potential in clinical settings. In this review, we summarized the relationship between BCSCs and the progression and drug resistance of TNBC, especially focusing on the interaction between BCSCs and TME. In addition, we discussed therapeutic strategies that target the TME to inhibit or eliminate BCSCs, providing valuable insights into the clinical treatment of TNBC.

Mitochondrial Dysfunction, Its Oxidative Stress-Induced Pathologies and Redox Bioregulation through Low-Dose Medical Ozone: A Systematic Review

Our hypothesis that controlled ozone applications interfere with the redox balance of a biological organism (first published in 1998 with a preclinical trial on protecting the liver from CCl4 intoxication) has been verified over the past two decades in reactive oxygen species (ROS)-induced mitochondrial pathologies, such as rheumatoid arthritis, osteoarthritis, aging processes and type 2 diabetes, and in the prevention of intoxications. Low-dose ozone acts as a redox bioregulator: the restoration of the disturbed redox balance is comprehensible in a number of preclinical and clinical studies by a remarkable increase in the antioxidant repair markers, here mainly shown as a glutathione increase and a reduction in oxidative stress markers, mainly malondialdehyde. The mechanism of action is shown, and relevant data are displayed, evaluated and comprehensively discussed: the repair side of the equilibrium increases by 21% up to 140% compared to the non-ozone-treated groups and depending on the indication, the stress markers are simultaneously reduced, and the redox system regains its balance.

Microglia and macrophage metabolism: a regulator of cerebral gliomas

Reciprocal interactions between the tumor microenvironment (TME) and cancer cells play important roles in tumorigenesis and progression of glioma. Glioma-associated macrophages (GAMs), either of peripheral origin or representing brain-intrinsic microglia, are the majority population of infiltrating immune cells in glioma. GAMs, usually classified into M1 and M2 phenotypes, have remarkable plasticity and regulate tumor progression through different metabolic pathways. Recently, research efforts have increasingly focused on GAMs metabolism as potential targets for glioma therapy. This review aims to delineate the metabolic characteristics of GAMs within the TME and provide a summary of current therapeutic strategies targeting GAMs metabolism in glioma. The goal is to provide novel insights and therapeutic pathways for glioma by highlighting the significance of GAMs metabolism.

Boosting immune responses in lung tumor immune microenvironment: A comprehensive review of strategies and adjuvants

The immune system has a substantial impact on the growth and expansion of lung malignancies. Immune cells are encompassed by a stroma comprising an extracellular matrix (ECM) and different cells like stromal cells, which are known as the tumor immune microenvironment (TIME). TME is marked by the presence of immunosuppressive factors, which inhibit the function of immune cells and expand tumor growth. In recent years, numerous strategies and adjuvants have been developed to extend immune responses in the TIME, to improve the efficacy of immunotherapy. In this comprehensive review, we outline the present knowledge of immune evasion mechanisms in lung TIME, explain the biology of immune cells and diverse effectors on these components, and discuss various approaches for overcoming suppressive barriers. We highlight the potential of novel adjuvants, including toll-like receptor (TLR) agonists, cytokines, phytochemicals, nanocarriers, and oncolytic viruses, for enhancing immune responses in the TME. Ultimately, we provide a summary of ongoing clinical trials investigating these strategies and adjuvants in lung cancer patients. This review also provides a broad overview of the current state-of-the-art in boosting immune responses in the TIME and highlights the potential of these approaches for improving outcomes in lung cancer patients.

Histone lactylation bridges metabolic reprogramming and epigenetic rewiring in driving carcinogenesis: Oncometabolite fuels oncogenic transcription

Heightened lactate production in cancer cells has been linked to various cellular mechanisms such as angiogenesis, hypoxia, macrophage polarisation and T-cell dysfunction. The lactate-induced lactylation of histone lysine residues is noteworthy, as it functions as an epigenetic modification that directly augments gene transcription from chromatin. This epigenetic modification originating from lactate effectively fosters a reliance on transcription, thereby expediting tumour progression and development. Herein, this review explores the correlation between histone lactylation and cancer characteristics, revealing histone lactylation as an innovative epigenetic process that enhances the vulnerability of cells to malignancy. Moreover, it is imperative to acknowledge the paramount importance of acknowledging innovative therapeutic methodologies for proficiently managing cancer by precisely targeting lactate signalling. This comprehensive review illuminates a crucial yet inadequately investigated aspect of histone lactylation, providing valuable insights into its clinical ramifications and prospective therapeutic interventions centred on lactylation.

Colorectal Cancer Stem Cell Biomarkers: Biological Traits and Prognostic Insights

Due to self-renewal, differentiation, and limitless proliferation properties, Cancer Stem Cells (CSCs) increase the probability of tumor development. These cells are identified by using CSC markers, which are highly expressed proteins on the cell surface of CSCs. Recently, the therapeutic application of CSCs as novel biomarkers improved both the prognosis and diagnosis outcome of colorectal Cancer. In the present review, we focused on a specific panel of colorectal CSC markers, including LGR5, ALDH, CD166, CD133, and CD44, which offers a targeted and comprehensive analysis of their functions. The selection criteria for these markers cancer were based on their established significance in Colorectal Cancer (CRC) pathogenesis and clinical outcomes, providing novel insights into the CSC biology of CRC. Through this approach, we aim to elevate understanding and stimulate further research for developing effective diagnostic and therapeutic strategies in CRC.

Exploring the promising potential of induced pluripotent stem cells in cancer research and therapy

The advent of iPSCs has brought about a significant transformation in stem cell research, opening up promising avenues for advancing cancer treatment. The formation of cancer is a multifaceted process influenced by genetic, epigenetic, and environmental factors. iPSCs offer a distinctive platform for investigating the origin of cancer, paving the way for novel approaches to cancer treatment, drug testing, and tailored medical interventions. This review article will provide an overview of the science behind iPSCs, the current limitations and challenges in iPSC-based cancer therapy, the ethical and social implications, and the comparative analysis with other stem cell types for cancer treatment. The article will also discuss the applications of iPSCs in tumorigenesis, the future of iPSCs in tumorigenesis research, and highlight successful case studies utilizing iPSCs in tumorigenesis research. The conclusion will summarize the advancements made in iPSC-based tumorigenesis research and the importance of continued investment in iPSC research to unlock the full potential of these cells.

Targeting redox regulation and autophagy systems in cancer stem cells

Cancer is a dysregulated cellular level pathological condition that results in tumor formation followed by metastasis. In the heterogeneous tumor architecture, cancer stem cells (CSCs) are essential to push forward the progression of tumors due to their strong pro-tumor properties such as stemness, self-renewal, plasticity, metastasis, and being poorly responsive to radiotherapy and chemotherapeutic agents. Cancer stem cells have the ability to withstand various stress pressures by modulating transcriptional and translational mechanisms, and adaptable metabolic changes. Owing to CSCs heterogeneity and plasticity, these cells display varied metabolic and redox profiles across different types of cancers. It has been established that there is a disparity in the levels of Reactive Oxygen Species (ROS) generated in CSCs vs Non-CSC and these differential levels are detected across different tumors. CSCs have unique metabolic demands and are known to change plasticity during metastasis by passing through the interchangeable epithelial and mesenchymal-like phenotypes. During the metastatic process, tumor cells undergo epithelial to mesenchymal transition (EMT) thus attaining invasive properties while leaving the primary tumor site, similarly during the course of circulation and extravasation at a distant organ, these cells regain their epithelial characteristics through Mesenchymal to Epithelial Transition (MET) to initiate micrometastasis. It has been evidenced that levels of Reactive Oxygen Species (ROS) and associated metabolic activities vary between the epithelial and mesenchymal states of CSCs. Similarly, the levels of oxidative and metabolic states were observed to get altered in CSCs post-drug treatments. As oxidative and metabolic changes guide the onset of autophagy in cells, its role in self-renewal, quiescence, proliferation and response to drug treatment is well established. This review will highlight the molecular mechanisms useful for expanding therapeutic strategies based on modulating redox regulation and autophagy activation to targets. Specifically, we will account for the mounting data that focus on the role of ROS generated by different metabolic pathways and autophagy regulation in eradicating stem-like cells hereafter referred to as cancer stem cells (CSCs).

Crosstalk between autophagy and CSCs: molecular mechanisms and translational implications

Cancer stem cells(CSCs) play a key role in regulating tumorigenesis, progression, as well as recurrence, and possess typical metabolic characteristics. Autophagy is a catabolic process that can aid cells to survive under stressful conditions such as nutrient deficiency and hypoxia. Although the role of autophagy in cancer cells has been extensively studied, CSCs possess unique stemness, and their potential relationship with autophagy has not been fully analyzed. This study summarizes the possible role of autophagy in the renewal, proliferation, differentiation, survival, metastasis, invasion, and treatment resistance of CSCs. It has been found that autophagy can contribute to the maintenance of CSC stemness, facilitate the tumor cells adapt to changes in the microenvironment, and promote tumor survival, whereas in some other cases autophagy acts as an important process involved in the deprivation of CSC stemness thus leading to tumor death. Mitophagy, which has emerged as another popular research area in recent years, has a great scope when explored together with stem cells. In this study, we have aimed to elaborate on the mechanism of action of autophagy in regulating the functions of CSCs to provide deeper insights for future cancer treatment.

The role of tumor microenvironment on cancer stem cell fate in solid tumors

In the last few decades, the role of cancer stem cells in initiating tumors, metastasis, invasion, and resistance to therapies has been recognized as a potential target for tumor therapy. Understanding the mechanisms by which CSCs contribute to cancer progression can help to provide novel therapeutic approaches against solid tumors. In this line, the effects of mechanical forces on CSCs such as epithelial-mesenchymal transition, cellular plasticity, etc., the metabolism pathways of CSCs, players of the tumor microenvironment, and their influence on the regulating of CSCs can lead to cancer progression. This review focused on some of these mechanisms of CSCs, paving the way for a better understanding of their regulatory mechanisms and developing platforms for targeted therapies. While progress has been made in research, more studies will be required in the future to explore more aspects of how CSCs contribute to cancer progression. Video Abstract.

Unrestricted Ketogenic Diet Feeding Enhances Epithelial Ovarian Cancer Growth In Vivo

The ketogenic diet (KD) is hypothesized to impact tumor progression by altering tumor metabolism. In this study, we assessed the impact of an unrestricted KD on epithelial ovarian cancer (EOC) tumor growth, gene expression, and metabolite concentration in a mouse model. ID8 EOC cells, which were syngeneic with C57Bl/6J mouse strain and transfected with luciferase (ID8-luc), were injectedand monitored for tumor development. Female mice were fed either a strict KD, a high fat/low carbohydrate (HF/LC) diet, or a low fat/high carbohydrate (LF/HC) diet (n = 10 mice per group) ad libitum. EOC tumor growth was monitored weekly, and tumor burden was determined based on luciferase fluorescence (photons/second). At the endpoint (42 days), tumors were collected and processed for RNA sequencing. Plasma and tumor metabolites were evaluated using LC-MS. The KD-fed mice exhibited a statistically significant increase in tumor progression in comparison to the HF/LC- and LF/HC-fed groups (9.1 vs. 2.0 vs. 3.1-fold, respectively, p < 0.001). The EOC tumors of the KD-fed mice exhibited significant enrichment of the peroxisome proliferator-activated receptor (PPAR) signaling and fatty acid metabolism pathways based on the RNA sequencing analysis when compared to the LF/HC- and HF/LC-fed mice. Thus, unrestricted KD diet enhanced tumor progression in our mouse EOC model. KD was associated with the upregulation of fatty acid metabolism and regulation pathways, as well as enrichment of fatty acid and glutamine metabolites.

Role of p53 suppression in the pathogenesis of hepatocellular carcinoma

In the world, hepatocellular carcinoma (HCC) is among the top 10 most prevalent malignancies. HCC formation has indeed been linked to numerous etiological factors, including alcohol usage, hepatitis viruses and liver cirrhosis. Among the most prevalent defects in a wide range of tumours, notably HCC, is the silencing of the p53 tumour suppressor gene. The control of the cell cycle and the preservation of gene function are both critically important functions of p53. In order to pinpoint the core mechanisms of HCC and find more efficient treatments, molecular research employing HCC tissues has been the main focus. Stimulated p53 triggers necessary reactions that achieve cell cycle arrest, genetic stability, DNA repair and the elimination of DNA-damaged cells’ responses to biological stressors (like oncogenes or DNA damage). To the contrary hand, the oncogene protein of the murine double minute 2 (MDM2) is a significant biological inhibitor of p53. MDM2 causes p53 protein degradation, which in turn adversely controls p53 function. Despite carrying wt-p53, the majority of HCCs show abnormalities in the p53-expressed apoptotic pathway. High p53 in-vivo expression might have two clinical impacts on HCC: (1) Increased levels of exogenous p53 protein cause tumour cells to undergo apoptosis by preventing cell growth through a number of biological pathways; and (2) Exogenous p53 makes HCC susceptible to various anticancer drugs. This review describes the functions and primary mechanisms of p53 in pathological mechanism, chemoresistance and therapeutic mechanisms of HCC.

Lin28 Regulates Cancer Cell Stemness for Tumour Progression

Tumours develop therapy resistance through complex mechanisms, one of which is that cancer stem cell (CSC) populations within the tumours present self-renewable capability and phenotypical plasticity to endure therapy-induced stress conditions and allow tumour progression to the therapy-resistant state. Developing therapeutic strategies to cope with CSCs requires a thorough understanding of the critical drivers and molecular mechanisms underlying the aforementioned processes. One such hub regulator of stemness is Lin28, an RNA-binding protein. Lin28 blocks the synthesis of let-7, a tumour-suppressor microRNA, and acts as a global regulator of cell differentiation and proliferation. Lin28also targets messenger RNAs and regulates protein translation. In this review, we explain the role of the Lin28/let-7 axis in establishing stemness, epithelial-to-mesenchymal transition, and glucose metabolism reprogramming. We also highlight the role of Lin28 in therapy-resistant prostate cancer progression and discuss the emergence of Lin28-targeted therapeutics and screening methods.

Assessment of the association of OCT3/4 with GLUT1 and CD105 in oral squamous cell carcinoma using dual immunohistochemistry

Background

Oral squamous cell carcinoma (OSCC) is the most common cancer affecting the oral and maxillofacial region. This study aimed to investigate the role of cancer stem cells (CSCs) in angiogenesis and hypoxic response in OSCC.

Methods

This retrospective observational study evaluated 56 cases of OSCC using dual immunohistochemistry. Octamer-binding transcription factor 3/4 (OCT3/4) marker was used to evaluate CSC activity. Glucose transporter 1 (GLUT1) marker was used to evaluate the hypoxic response and angiogenesis, while endoglin (CD105) was used to evaluate the late stage of angiogenesis and blood vessel formation.

Results

Co-expression of OCT3/4 and GLUT1 was noted in 11 of 12 patients with grade III OSCC. However, we did not observe co-expression of these markers in 13 of 22 patients with grade I OSCC. Although we observed a significant correlation between co-expression of GLUT1 and OCT3/4 and tumor grade, there was no significant correlation between co-expression of OCT3/4 and CD105 and different grades of OSCC.

Conclusions

CSCs could play important roles in the initial stages of hypoxic response and angiogenesis. Our result reported that in higher grades of OSCC, GLUT1 as a first response to hypoxic situations might be a result of CSCs. Further studies are required to discover other biomarkers, their roles, and associated pathways of CSCs in OSCC.

Tubulin Isotypes: Emerging Roles in Defining Cancer Stem Cell Niche

Although the role of microtubule dynamics in cancer progression is well-established, the roles of tubulin isotypes, their cargos and their specific function in the induction and sustenance of cancer stem cells (CSCs) were poorly explored. But emerging reports urge to focus on the transport function of tubulin isotypes in defining orchestrated expression of functionally critical molecules in establishing a stem cell niche, which is the key for CSC regulation. In this review, we summarize the role of specific tubulin isotypes in the transport of functional molecules that regulate metabolic reprogramming, which leads to the induction of CSCs and immune evasion. Recently, the surface expression of GLUT1 and GRP78 as well as voltage-dependent anion channel (VDAC) permeability, regulated by specific isotypes of β-tubulins have been shown to impart CSC properties to cancer cells, by implementing a metabolic reprogramming. Moreover, βIVb tubulin is shown to be critical in modulating EphrinB1signaling to sustain CSCs in oral carcinoma. These tubulin-interacting molecules, Ephrins, GLUT1 and GRP78, are also important regulators of immune evasion, by evoking PD-L1 mediated T-cell suppression. Thus, the recent advances in the field implicate that tubulins play a role in the controlled transport of molecules involved in CSC niche. The indication of tubulin isotypes in the regulation of CSCs offers a strategy to specifically target those tubulin isotypes to eliminate CSCs, rather than the general inhibition of microtubules, which usually leads to therapy resistance.

Suboptimal folic acid exposure rewires oncogenic metabolism and proteomics signatures to mediate human breast cancer malignancy

Whether treatment with folic acid (FA) affects human breast cancer positively or negatively remains unclear. We subjected human MCF-7 cells, a human breast cancer cell line, to suboptimal FA at low levels (10 nM; LF) and high levels (50 μM; HF) and investigated the molecular mechanisms underlying their effects through metabolic flux and systematic proteomics analyses. The data indicated that LF induced and HF aggravated 2-fold higher mitochondrial toxicity in terms of suppressed oxidative respiration, increased fermented glycolysis, and enhanced anchorage-independent oncospheroid formation. Quantitative proteomics and Gene Ontology enrichment analysis were used to profile LF- and HF-altered proteins involved in metabolism, apoptosis, and malignancy pathways. Through STRING analysis, we identified a connection network between LF- and HF-altered proteins with mTOR. Rapamycin-induced blockage of mTOR complex 1 (mTORC1) signaling, which regulates metabolism, differentially inhibited LF- and HF-modulated protein signatures of mitochondrial NADH dehydrogenase ubiquinone flavoprotein 2, mitochondrial glutathione peroxidase 4, kynureninase, and alpha-crystallin B chain as well as programmed cell death 5 in transcript levels; it subsequently diminished apoptosis and oncospheroid formation in LF/HF-exposed cells. Taken together, our data indicate that suboptimal FA treatment rewired oncogenic metabolism and mTORC1-mediated proteomics signatures to promote breast cancer development.

Breast cancer in the era of integrating “Omics” approaches

Worldwide, breast cancer is the leading cause of cancer-related deaths in women. Breast cancer is a heterogeneous disease characterized by different clinical outcomes in terms of pathological features, response to therapies, and long-term patient survival. Thus, the heterogeneity found in this cancer led to the concept that breast cancer is not a single disease, being very heterogeneous both at the molecular and clinical level, and rather represents a group of distinct neoplastic diseases of the breast and its cells. Indubitably, in the past decades we witnessed a significant development of innovative therapeutic approaches, including targeted and immunotherapies, leading to impressive results in terms of increased survival for breast cancer patients. However, these multimodal treatments fail to prevent recurrence and metastasis. Therefore, it is urgent to improve our understanding of breast tumor and metastasis biology. Over the past few years, high-throughput “omics” technologies through the identification of novel biomarkers and molecular profiling have shown their great potential in generating new insights in the study of breast cancer, also improving diagnosis, prognosis and prediction of response to treatment. In this review, we discuss how the implementation of “omics” strategies and their integration may lead to a better comprehension of the mechanisms underlying breast cancer. In particular, with the aim to investigate the correlation between different “omics” datasets and to define the new important key pathway and upstream regulators in breast cancer, we applied a new integrative meta-analysis method to combine the results obtained from genomics, proteomics and metabolomics approaches in different revised studies.

ADAPTOR PROTEIN Ruk/CIN85 PARTICIPATES IN THE METABOLIC CONTROL OF HUMAN BREAST ADENOCARCINOMA MCF-7 CELLS

Aim. To determine the role of Ruk/CIN85 in the control of breast adenocarcinoma cells metabolism, we performed systemic analysis of the activity levels/content of key enzymes/components of glycolysis and oxidative phosphorylation using as a model the weakly invasive human breast adenocarcinoma MCF-7 cell line (Mock); and its sublines with stable overexpression (G4 subline) and reverse down-regulation (G4vir subline) of the adaptor protein. Materials and methods. MCF-7 cells were cultured in the complete DMEM medium under standard conditions. Enzymes activity, content of metabolites and protein in cell extracts and the conditioned cell culture medium were estimated by spectrophotometric and fluorometric assays. Results. First of all, biochemical indexes of aerobic glycolysis, activity levels of some key glycolytic enzymes and metabolites were evaluated. A significant increase in the activity of these enzymes, aldolase A (ALDOA) and lactate dehydrogenase A (LDHA), was found in G4 cells compared to Mock by 1.3 and 1.6 times, respectively. In addition, in the conditioned medium of G4 cells, an increase in lactate content by 1.5 times compared with the control was found, which corresponded to a change in LDHA activity. Knockdown of Ruk/CIN85 expression level in G4 subline resulted in a significant decrease of these parameters compared to G4 cells, ALDOA – 4 times, LDHA - 1.4 times, and lactate production - 2.5 times. It should be noted that in G4vir cells, LDHA activity returned to level of control cells, while ALDOA activity and lactate content additionally decreased by 3 times and 1.6 times, respectively. Therefore, the observed changes in the intensity of glycolysis in MCF-7 sublines positively correlate with the expression level of adaptor protein studied. To assess the metabolic status of mitochondria, the level of activity of the Krebs cycle enzyme, NAD-dependent malate dehydrogenase (MDH2), the catalyst of last stage of the cycle, was determined. A 2-fold decrease in MDH2 activity was found in the MCF-7 G4 subline relative to control Mock cells, as well as an increase in this index by 2.4 times in G4vir cells to control values. Unlike glycolysis, we observed the opposite pattern with respect to the intensity of Krebs cycle reactions depending on the expression level of Ruk/CIN85. Conclusions. Use of limited proteolysis technique as the source of additional information for computer modeling allowed us to propose an improved model of 3D-structure of fibrinogen αC-regions. This model takes into account the behavior of αC-regions in the physiological condition and contributes to the general knowledge about fibrinogen structure.

Understanding autophagy role in cancer stem cell development

Cancer stem cells (CSCs) are a small subpopulation of immature cells located in the tumor mass. These cells are responsible for tumor development, proliferation, resistance and spreading. CSCs are characterized by three unique features: the ability to self-renew, differentiation and tumor formation. CSCs are similar to stem cells, but they differ in the malignant phenotype. CSCs become immortal and survive harsh environmental conditions such as hypoxia, starvation and oxidative stress. However, this harsh tumor microenvironment induces the activation of autophagy, which further increases the CSCs stemness profile, and all these features further increase tumorigenicity and metastasis capacity. Autophagy is induced by the extracellular and cellular microenvironment. Hypoxia is one of the most common factors that highly increases the activity of autophagy in CSCs. Therefore, hypoxia-induced autophagy and CSCs proliferation should be elucidated in order to find a novel cure to defeat cancer cells (CSCs and non-CSCs). The remaining challenges to close the gap between the laboratory bench and the development of therapies, to use autophagy against CSCs in patients, could be addressed by adopting a 3D platform to better-mimic the natural environment in which these cells reside. Ultimately allowing to obtain the blueprints for bioprocess scaling up and to develop the production pipeline for safe and cost-effective autophagy-based novel biologics.

Advancement in Cancer Stem Cell Biology and Precision Medicine-Review Article Head and Neck Cancer Stem Cell Plasticity and the Tumor Microenvironment

Head and Neck cancer survival has continued to remain around 50% despite treatment advances. It is thought that cancer stem cells play a key role in promoting tumor heterogeneity, treatment resistance, metastasis, and recurrence in solid malignancies including head and neck cancer. Initial studies identified cancer stem cell markers including CD44 and ALDH in head and neck malignancies and found that these cells show aggressive features in both in vitro and in vivo studies. Recent evidence has now revealed a key role of the tumor microenvironment in maintaining a cancer stem cell niche and promoting cancer stem cell plasticity. There is an increasing focus on identifying and targeting the crosstalk between cancer stem cells and surrounding cells within the tumor microenvironment (TME) as new therapeutic potential, however understanding how CSC maintain a stem-like state is critical to understanding how to therapeutically alter their function. Here we review the current evidence for cancer stem cell plasticity and discuss how interactions with the TME promote the cancer stem cell niche, increase tumor heterogeneity, and play a role in treatment resistance.

Autophagy Regulation on Cancer Stem Cell Maintenance, Metastasis, and Therapy Resistance

Simple Summary

Certain types of cancer have higher relapse rates compared to others, and cancer stem cells (CSCs) have been shown as the main drivers of cancer relapse and cancer severity. This subpopulation of cells displays stem-like characteristics which bolster tumorigenesis along with metastasis and lead to poorer prognoses. Autophagy has been studied as a mechanism by which CSCs maintain stemness and acquire resistance to chemotherapy and radiation. The aim of this review is to condense and organize what has been recently published on the connection between cancer stem cells (CSCs) and autophagy. Multiple studies on autophagy have suggested that the pathway is a double-edged sword, which can either undermine or enhance CSC characteristics depending on interactions with different pathways. Thus, future research should investigate regulation of autophagy in combination with traditional cancer therapies as a possible method to effectively eliminate CSCs and minimize cancer relapse.

Abstract

Cancer stem cells (CSCs) are a subset of the tumor population that play critical roles in tumorigenicity, metastasis, and relapse. A key feature of CSCs is their resistance to numerous therapeutic strategies which include chemotherapy, radiation, and immune checkpoint inhibitors. In recent years, there is a growing body of literature that suggests a link between CSC maintenance and autophagy, a mechanism to recycle intracellular components during moments of environmental stress, especially since CSCs thrive in a tumor microenvironment that is plagued with hypoxia, acidosis, and lack of nutrients. Autophagy activation has been shown to aid in the upkeep of a stemness state along with bolstering resistance to cancer treatment. However, recent studies have also suggested that autophagy is a double-edged sword with anti-tumorigenic properties under certain circumstances. This review summarizes and integrates what has been published in the literature in terms of what role autophagy plays in stemness maintenance of CSCs and suggests that there is a more complex interplay between autophagy and apoptosis which involves multiple pathways of regulation. Future cancer therapy strategies are needed to eradicate this resistant subset of the cell population through autophagy regulation.

Cancer Stem Cells: An Ever-Hiding Foe

Cancer stem cells are a population of cells enable to reproduce the original phenotype of the tumor and capable to self-renewal, which is crucial for tumor proliferation, differentiation, recurrence, and metastasis, as well as chemoresistance. Therefore, the cancer stem cells (CSCs) have become one of the main targets for anticancer therapy and many ongoing clinical trials test anti-CSCs efficacy of plenty of drugs. This chapter describes CSCs starting from general description of this cell population, through CSCs markers, signaling pathways, genetic and epigenetic regulation, role of epithelial-mesenchymal transition (EMT) transition and autophagy, cooperation with microenvironment (CSCs niche), and finally role of CSCs in escaping host immunosurveillance against cancer.

Compound Kushen Injection intervenes metabolic reprogramming and epithelial-mesenchymal transition of HCC via regulating β-catenin/c-Myc signaling

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the most extensive and most deadly cancers worldwide. The invasion and metastasis characteristics of HCC dramatically affect the prognosis and survival of HCC patients. Compound Kushen Injection (CKI) is a GMP produced, proverbially applied traditional Chinese medicine formula in China to treat cancer-associated pains, and used as an adjunctive therapy for HCC. Until so far, whether CKI could suppress the metastasis of HCC through regulation of epithelial-mesenchymal transition or metabolic reprogramming is still ambiguous.

PURPOSE

In this study, the anti-metastasis effects of CKI were clarified and its pharmacological mechanisms were systematically explored.

METHODS

Cell invasion and cell adhesion assay were performed in SMMC-7721 cells to assess the anti-metastasis role of CKI, and the histopathological evaluation and biochemical detection were utilized in DEN-induced HCC rats to verify the anti-HCC effect of CKI. Serum and liver samples were analyzed with ¹H NMR metabolomics approach to screen the differential metabolites and further target quantification the content of key metabolites. Finally, western blotting and immunofluorescence assay were applied to verify the crucial signaling pathway involved in metabolites.

RESULTS

CKI markedly repressed the invasion and adhesion in SMMC-7721 cells and significantly improved the liver function of DEN-induced HCC rats. CKI significantly regulated the expression of epithelial-mesenchymal transition (EMT) markers (Vimentin and E-cadherin). Metabolomics results showed that CKI regulated the metabolic reprogramming of HCC by inhibiting the key metabolites (citrate and lactate) and enzymes (HK and PK) in glycolysis process. Importantly, we found that c-Myc mediates the inhibitory effect of CKI on glycolysis. We further demonstrated that CKI inhibits c-Myc expression through modulating Wnt/β-catenin pathway in SMMC-7721 cells and DEN-induced HCC rats. Furthermore, through activating Wnt/β-catenin pathway with LiCl, the inhibitory effects of CKI on HCC were diminished.

CONCLUSION

Together, this study reveals that CKI intervenes metabolic reprogramming and epithelial-mesenchymal transition of HCC via regulating β-catenin/c-Myc signaling pathway. Our research provides a new understanding of the mechanism of CKI against invasion and metastasis of HCC from the perspective of metabolic reprogramming.

Reciprocal regulation of LOXL2 and HIF1α drives the Warburg effect to support pancreatic cancer aggressiveness

Hypoxic microenvironment is common in solid tumors, particularly in pancreatic ductal adenocarcinoma (PDAC). The Warburg effect is known to facilitate cancer aggressiveness and has long been linked to hypoxia, yet the underlying mechanism remains largely unknown. In this study, we identify that lysyl oxidase-like 2 (LOXL2) is a hypoxia-responsive gene and is essential for the Warburg effect in PDAC. LOXL2 stabilizes hypoxia-inducible factor 1α (HIF1α) from prolyl hydroxylase (PHD)-dependent hydroxylation via hydrogen peroxide generation, thereby facilitating the transcription of multiple glycolytic genes. Therefore, a positive feedback loop exists between LOXL2 and HIF1α that facilitates glycolytic metabolism under hypoxia. Moreover, LOXL2 couples the Warburg effect to tumor growth and metastasis in PDAC. Hijacking glycolysis largely compromises LOXL2-induced oncogenic activities. Collectively, our results identify a hitherto unknown hypoxia-LOXL2-HIF1α axis in regulating the Warburg effect and provide an intriguing drug target for PDAC therapy.

Metabostemness in cancer: Linking metaboloepigenetics and mitophagy in remodeling cancer stem cells

Cancer stem cells (CSCs) are rare populations of malignant cells with stem cell-like features of self-renewal, uninterrupted differentiation, tumorigenicity, and resistance to conventional therapeutic agents, and these cells have a decisive role in treatment failure and tumor relapse. The self-renewal potential of CSCs with atypical activation of developmental signaling pathways involves the maintenance of stemness to support cancer progression. The acquisition of stemness in CSCs has been accomplished through genetic and epigenetic rewiring following the metabolic switch. In this context, "metabostemness" denotes the metabolic parameters that essentially govern the epitranscriptional gene reprogramming mechanism to dedifferentiate tumor cells into CSCs. Several metabolites often referred to as oncometabolites can directly remodel chromatin structure and thereby influence the operation of epitranscriptional circuits. This integrated metaboloepigenetic dimension of CSCs favors the differentiated cells to move in dedifferentiated macrostates. Some metabolic events might perform as early drivers of epitranscriptional reprogramming; however, subsequent metabolic hits may govern the retention of stemness properties in the tumor mass. Interestingly, selective removal of mitochondria through autophagy can promote metabolic plasticity and alter metabolic states during differentiation and dedifferentiation. In this connection, novel metabostemness-specific drugs can be generated as potential cancer therapeutics to target the metaboloepigenetic circuitry to eliminate CSCs.

Sildenafil in ophthalmology: An update

Sildenafil citrate, a selective oral phosphodiesterase 5 inhibitor, is a widely used drug for erectile dysfunction that acts by elevating cGMP levels and causing smooth muscle relaxation. It also has 10% activity against PDE6, a key enzyme in phototransduction cascade in the retina. Recent ocular imaging developments have further revealed the influence of sildenafil on ocular hemodynamics, particularly choroidal perfusion. Choroidal thickness is increased, and choroidal perfusion is also enhanced by autoregulatory mechanisms that are further dependent on age and microvascular abnormalities. Studies demonstrating high intraocular pressure via a "parallel pathway" from increased choroidal volume and blood flow to the ciliary body have challenged previous concepts. Another new observation is the effect of sildenafil on bipolar cells and cyclic-nucleotide gated channels. We discuss potential deleterious effects (central serous chorioretinopathy, glaucoma, ischemic optic neuropathy, and risks to recessive carriers of retinitis pigmentosa), potential beneficial effects (ameliorate choroidal ischemia, prevent thickening of Bruch membrane, and promote recovery of the ellipsoid zone) in macular degeneration, as well as potential drug interactions of sildenafil.

BAI1 acts as a tumor suppressor in lung cancer A549 cells by inducing metabolic reprogramming via the SCD1/HMGCR module

Brain-specific angiogenesis inhibitor 1 (BAI1) is an important tumor suppressor in multiple cancers. However, the mechanisms behind its anti-tumor activity, particularly the relationship between BAI1 and metabolic aberrant of a tumor, remained unveiled. This study aimed to investigate whether BAI1 could inhibit biological functions in lung cancer A549 cells and the critical regulating molecules that induce metabolic reprogramming. Immunohistochemistry staining was performed to analyze whether variations in the expression of BAI1 in tumor tissues contributes to poor prognosis of lung cancer. Overexpressed BAI1 (BAI1-OE-A549) and control (Vector-NC-A549) were generated by lentiviral transfection. Biological function assays (proliferation, apoptosis, colony formation, invasion and in vivo metastasis), as well as metabolic reprogramming (by the Warburg effect and the glycolytic rate), were performed in both groups. Our results indicated that lower levels of BAI1 contributed to poor prognosis of lung cancer patients. Furthermore, overexpressed of BAI1 dramatically inhibited proliferation, migration, invasion, colony formation and in vivo metastasis of A549 cells. The Warburg effect and the Seahorse assay revealed that BAI1-OE induced metabolism reprogramming by inhibiting the Warburg effect and glycolysis. Further exploration indicated that BAI1 induced metabolic reprogramming by upregulating stearoyl-CoA desaturase 1 (SCD1) and inhibited 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR). Our study revealed a novel mechanism through which BAI1 acted as tumor suppressor by inducing metabolic reprogramming via the SCD1 and HMGCR module.

Identification and Development of Subtypes With Poor Prognosis in Pan-Gynecological Cancer Based on Gene Expression in the Glycolysis-Cholesterol Synthesis Axis

Objective: Metabolic reprogramming is an important biomarker of cancer. Metabolic adaptation driven by oncogenes allows tumor cells to survive and grow in a complex tumor microenvironment. The heterogeneity of tumor metabolism is related to survival time, somatic cell-driven gene mutations, and tumor subtypes. Using the heterogeneity of different metabolic pathways for the classification of gynecological pan-cancer is of great significance for clinical decision-making and prognosis prediction. Methods: RNA sequencing data for patients with ovarian, cervical, and endometrial cancer were downloaded from The Cancer Genome Atlas database. Genes related to glycolysis and cholesterol were extracted and clustered coherently by using ConsensusClusterPlus. The mutations and copy number variations in different subtypes were compared, and the immune scores of the samples were evaluated. The limma R package was used to identify differentially expressed genes between subtypes, and the WebGestaltR package (V0.4.2) was used to conduct Kyoto Encyclopedia of Genes and Genomes pathway and Gene Ontology functional enrichment analyses. A risk score model was constructed based on multivariate Cox analysis. Prognostic classification efficiency was analyzed by using timeROC, and internal and external cohorts were used to verify the robustness of the model. Results: Based on the expression of 11 glycolysis-related genes and seven cholesterol-related genes, 1,204 samples were divided into four metabolic subtypes (quiescent, glycolysis, cholesterol, and mixed). Immune infiltration scores showed significant differences among the four subtypes. Survival analysis showed that the prognosis of the cholesterol subtype was better than that of the quiescent subtype. A nine-gene signature was constructed based on differentially expressed genes between the cholesterol and quiescent subtypes, and it was validated by using an independent cohort of the International Cancer Genome Consortium. Compared with existing models, our nine-gene signature had good prediction performance. Conclusion: The metabolic classification of gynecological pan-cancer based on metabolic reprogramming may provide an important basis for clinicians to choose treatment options, predict treatment resistance, and predict patients' clinical outcomes.

Studying the Metabolism of Epithelial-Mesenchymal Plasticity Using the Seahorse XFe96 Extracellular Flux Analyzer

The critical role of metabolism in facilitating cancer cell growth and survival has been demonstrated by a combination of methods including, but not limited to, genomic sequencing, transcriptomic and proteomic analyses, measurements of radio-labelled substrate flux and the high throughput measurement of oxidative metabolism in unlabelled live cells using the Seahorse Extracellular Flux (XF) technology. These studies have revealed that tumour cells exhibit a dynamic metabolic plasticity, using numerous pathways including both glycolysis and mitochondrial oxidative phosphorylation (OXPHOS) to support cell proliferation, energy production and the synthesis of biomass. These advanced technologies have also demonstrated metabolic differences between cancer cell types, between molecular subtypes within cancers and between cell states. This has been exemplified by examining the transitions of cancer cells between epithelial and mesenchymal phenotypes, referred to as epithelial-mesenchymal plasticity (EMP). A growing number of studies are demonstrating significant metabolic alterations associated with these transitions, such as increased use of glycolysis by triple negative breast cancers (TNBC) or glutamine addiction in lung cancer. Models of EMP, including invasive cell lines and xenografts, isolated circulating tumour cells and metastatic tissue have been used to examine EMP metabolism. Understanding the metabolism supporting molecular and cellular plasticity and increased metastatic capacity may reveal metabolic vulnerabilities that can be therapeutically exploited. This chapter describes protocols for using the Seahorse Extracellular Flux Analyzer (XFe96), which simultaneously performs real-time monitoring of oxidative phosphorylation and glycolysis in living cells. As an example, we compare the metabolic profiles generated from two breast cancer sublines that reflect epithelial and mesenchymal phenotypes, respectively. We use this example to show how the methodology described can generate bioenergetic results that in turn can be correlated to EMP phenotypes. Normalisation of bioenergetic studies should be considered with respect to cell number, and to potential differences in mitochondrial mass, itself being an important bioenergetics endpoint.

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.

The mevalonate precursor enzyme HMGCS1 is a novel marker and key mediator of cancer stem cell enrichment in luminal and basal models of breast cancer

The definitive characterization of common cancer stem cell (CSCs) subpopulations in breast cancer subtypes with distinct genotypic and phenotypic features remains an ongoing challenge. In this study, we have used a non-biased genome wide screening approach to identify transcriptional networks that may be specific to the CSC subpopulations in both luminal and basal breast cancer subtypes. In depth studies of three CSC-enriched breast cancer cell lines representing various subtypes of breast cancer revealed a striking hyperactivation of the mevalonate metabolic pathway in comparison to control cells. The upregulation of metabolic networks is a key feature of tumour cells securing growth and proliferative capabilities and dysregulated mevalonate metabolism has been associated with tumour malignancy and cellular transformation in breast cancer. Furthermore, accumulating evidence suggests that Simvastatin therapy, a mevalonate pathway inhibitor, could affect breast cancer progression and reduce breast cancer recurrence. When detailing the mevalonate pathway in breast cancer using a single-cell qPCR, we identified the mevalonate precursor enzyme, HMGCS1, as a specific marker of CSC-enriched subpopulations within both luminal and basal tumour subtypes. Down-regulation of HMGCS1 also decreased the CSC fraction and function in various model systems, suggesting that HMGCS1 is essential for CSC-activities in breast cancer in general. These data was supported by strong associations between HMGCS1 expression and aggressive features, such as high tumour grade, p53 mutations as well as ER-negativity in lymph node positive breast cancer. Importantly, loss of HMGCS1 also had a much more pronounced effect on CSC-activities compared to treatment with standard doses of Simvastatin. Taken together, this study highlights HMGCS1 as a potential gatekeeper for dysregulated mevalonate metabolism important for CSC-features in both luminal and basal breast cancer subtypes. Pharmacological inhibition of HMGCS1 could therefore be a superior novel treatment approach for breast cancer patients via additional CSC blocking functions.

Co-expression based cancer staging and application

A novel method is developed for predicting the stage of a cancer tissue based on the consistency level between the co-expression patterns in the given sample and samples in a specific stage. The basis for the prediction method is that cancer samples of the same stage share common functionalities as reflected by the co-expression patterns, which are distinct from samples in the other stages. Test results reveal that our prediction results are as good or potentially better than manually annotated stages by cancer pathologists. This new co-expression-based capability enables us to study how functionalities of cancer samples change as they evolve from early to the advanced stage. New and exciting results are discovered through such functional analyses, which offer new insights about what functions tend to be lost at what stage compared to the control tissues and similarly what new functions emerge as a cancer advances. To the best of our knowledge, this new capability represents the first computational method for accurately staging a cancer sample. The R source code used in this study is available at GitHub (https://github.com/yxchspring/CECS).

Lipid metabolism alteration contributes to and maintains the properties of cancer stem cells

Lipids, the basic components of the cell membrane, execute fundamental roles in almost all the cell activities including cell-cell recognition, signalling transduction and energy supplies. Lipid metabolism is elementary for life sustentation that balances activity between synthesis and degradation. An accumulating amount of data has indicated abnormal lipid metabolism in cancer stem cells (CSCs), and that the alteration of lipid metabolism exerts a great impact on CSCs' properties such as the capability of self-renewal, differentiation, invasion, metastasis, and drug sensitivity and resistance. CSCs' formation and maintenance cannot do without the regulation of fatty acids and cholesterol. In normal cells and embryonic development, fatty acids and cholesterol metabolism are regulated by some important signalling pathways (such as Hedgehog, Notch, Wnt signalling pathways); these signalling pathways also play crucial roles in initiating and/or maintaining CSCs' properties, and such signalling is shown to be commonly modulated by the abnormal lipid metabolism in CSCs; on the other hand, the altered lipid metabolism in turn modifies the cell signalling and generates additional impacts on CSCs. Metabolic rewiring is considered as an ideal hallmark of CSCs, and metabolic alterations would be promising therapeutic targets of CSCs for aggressive tumors. In this review, we summarize the most updated findings of lipid metabolic abnormalities in CSCs and prospect the potential applications of targeting lipid metabolism for anticancer treatment.

Mitochondrial pH Nanosensors for Metabolic Profiling of Breast Cancer Cell Lines

The main role of mitochondria, as pivotal organelles for cellular metabolism, is the production of energy (ATP) through an oxidative phosphorylation system. During this process, the electron transport chain creates a proton gradient that drives the synthesis of ATP. One of the main features of tumoral cells is their altered metabolism, providing alternative routes to enhance proliferation and survival. Hence, it is of utmost importance to understand the relationship between mitochondrial pH, tumoral metabolism, and cancer. In this manuscript, we develop a highly specific nanosensor to accurately measure the intramitochondrial pH using fluorescence lifetime imaging microscopy (FLIM). Importantly, we have applied this nanosensor to establish differences that may be hallmarks of different metabolic pathways in breast cancer cell models, leading to the characterization of different metabophenotypes.

Metformin: Sentinel of the Epigenetic Landscapes That Underlie Cell Fate and Identity

The biguanide metformin is the first drug to be tested as a gerotherapeutic in the clinical trial TAME (Targeting Aging with Metformin). The current consensus is that metformin exerts indirect pleiotropy on core metabolic hallmarks of aging, such as the insulin/insulin-like growth factor 1 and AMP-activated protein kinase/mammalian Target Of Rapamycin signaling pathways, downstream of its primary inhibitory effect on mitochondrial respiratory complex I. Alternatively, but not mutually exclusive, metformin can exert regulatory effects on components of the biologic machinery of aging itself such as chromatin-modifying enzymes. An integrative metabolo-epigenetic outlook supports a new model whereby metformin operates as a guardian of cell identity, capable of retarding cellular aging by preventing the loss of the information-theoretic nature of the epigenome. The ultimate anti-aging mechanism of metformin might involve the global preservation of the epigenome architecture, thereby ensuring cell fate commitment and phenotypic outcomes despite the challenging effects of aging noise. Metformin might therefore inspire the development of new gerotherapeutics capable of preserving the epigenome architecture for cell identity. Such gerotherapeutics should replicate the ability of metformin to halt the erosion of the epigenetic landscape, mitigate the loss of cell fate commitment, delay stochastic/environmental DNA methylation drifts, and alleviate cellular senescence. Yet, it remains a challenge to confirm if regulatory changes in higher-order genomic organizers can connect the capacity of metformin to dynamically regulate the three-dimensional nature of epigenetic landscapes with the 4th dimension, the aging time.

Nonenzymatic function of Aldolase A downregulates miR-145 to promote the Oct4/DUSP4/TRAF4 axis and the acquisition of lung cancer stemness

Drug resistance remains a serious issue of clinical importance and is a consequence of cancer stemness. In this study, we showed that the level of Aldolase A (ALDOA) expression is significantly associated with the IC50 value of chemotherapy drugs in lung cancer. Our data revealed that ALDOA overexpression resulted in a significant increase of lung tumor spheres. The use of ingenuity pathway analysis (IPA) resulted in the identification of POU5F1 (Oct4) as the leading transcription factor of ALDOA. We observed high expression of ALDOA, Oct4 and stemness markers in collected spheroid cells. DUSP4 and TRAF4 were confirmed as major downstream targets of the ALDOA-Oct4 axis. Knockdown of these molecules significantly decreased the stemness ability of cells. In addition, we investigated whether miR-145 targets the 3′-UTR of Oct4 and is regulated by ALDOA due to the involvement of ALDOA in glycolysis and metabolic reprogramming. Furthermore, we constructed several mutant forms of ALDOA that disrupted its enzymatic activity and showed that they still induced significant in vitro sphere formation and in vivo tumorigenicity. These results demonstrated that ALDOA-mediated spheroid formation is independent of its enzymatic activity. In the clinical component, we also showed that the combination of ALDOA and TRAF4 or DUSP4 is positively correlated with poor overall survival in a xenograft model and cancer patients through immunohistochemical analyses. The results of our study revealed novel functional roles of ALDOA in inducing cancer stemness via the inhibition of miR-145 expression and the activation of Oct4 transcription. These findings offer new therapeutic strategies for modulation of lung cancer stemness to enhance chemotherapeutic responses in lung cancer patients.

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.

Metformin alleviates muscle wasting post-thermal injury by increasing Pax7-positive muscle progenitor cells

BACKGROUND

Profound skeletal muscle wasting and weakness is common after severe burn and persists for years after injury contributing to morbidity and mortality of burn patients. Currently, no ideal treatment exists to inhibit muscle catabolism. Metformin is an anti-diabetic agent that manages hyperglycemia but has also been shown to have a beneficial effect on stem cells after injury. We hypothesize that metformin administration will increase protein synthesis in the skeletal muscle by increasing the proliferation of muscle progenitor cells, thus mitigating muscle atrophy post-burn injury.

METHODS

To determine whether metformin can attenuate muscle catabolism following burn injury, we utilized a 30% total burn surface area (TBSA) full-thickness scald burn in mice and compared burn injuries with and without metformin treatment. We examined the gastrocnemius muscle at 7 and 14 days post-burn injury.

RESULTS

At 7 days, burn injury significantly reduced myofiber cross-sectional area (CSA) compared to sham, p < 0.05. Metformin treatment significantly attenuated muscle catabolism and preserved muscle CSA at the sham size. To investigate metformin's effect on satellite cells (muscle progenitors), we examined changes in Pax7, a transcription factor regulating the proliferation of muscle progenitors. Burned animals treated with metformin had a significant increase in Pax7 protein level and the number of Pax7-positive cells at 7 days post-burn, p < 0.05. Moreover, through BrdU proliferation assay, we show that metformin treatment increased the proliferation of satellite cells at 7 days post-burn injury, p < 0.05.

CONCLUSION

In summary, metformin's various metabolic effects and its modulation of stem cells make it an attractive alternative to mitigate burn-induced muscle wasting while also managing hyperglycemia.

Enhanced hexosamine metabolism drives metabolic and signaling networks involving hyaluronan production and O-GlcNAcylation to exacerbate breast cancer

The hexosamine biosynthetic pathway (HBP) metabolically regulates dynamic cellular events by linking nutrient availability to numerous signaling networks. Significant alterations in the HBP are often associated with cancer pathogenesis. In this study, we investigated the molecular events underlying cancer pathogenesis associated with enhanced HBP flux. Multidimensional analysis of microarray datasets demonstrated up-regulation of genes encoding HBP enzymes in clinical breast cancers and revealed that co-expression of hyaluronan synthase 2 (HAS2) and glutamine:fructose-6-phosphate amidotransferase (GFAT), a rate-limiting enzyme of the HBP, was strongly correlated with a poor prognosis in advanced cancer patients. Consistently with the clinical data, comparative analyses of distinct breast cancer mouse models demonstrated enhancement of the HBP gene expression in primary carcinoma cells, with elevation of Has2 expression and hyaluronan production in aggressive breast cancer cells. The silencing of GFAT reduced CD44high/CD24low cancer stem cell (CSC)-like subpopulations, aldehyde dehydrogenase-positive cell populations, and mammosphere size, which were further diminished by gene targeting of Has2. Has2 gene disruption reduced the in vivo growth of aggressive cancer cells and attenuated pro-tumorigenic Akt/GSK3β/β-catenin signaling and cisplatin resistance. Overall protein O-GlcNAcylation was also elevated in association with HBP enhancement in aggressive cancer cells, and the modification exhibited overlapping but distinct roles from the hyaluronan signal in the regulation of CSC-like features. The current data therefore demonstrate that enhanced hexosamine metabolism drives pro-tumorigenic signaling pathways involving hyaluronan and O-GlcNAcylation in aggressive breast cancer.

FRK plays an oncogenic role in non-small cell lung cancer by enhancing the stemness phenotype via induction of metabolic reprogramming

The role of Fyn-related kinase (FRK) in malignant tumors remains controversial. Our study investigated the function of FRK in lung cancer. Immunohistochemistry staining and generating a knockout of FRK by CRISPR/Cas9 in H1299 (FRK-KO-H1299) cells were strategies used to explore the role of FRK. Immunohistochemistry staining indicated that FRK expression was elevated in 223 lung cancer tissues compared to 26 distant normal lung tissues. FRK contributed to poor survival status in lung cancer patients and acted as a predictor for poor prognosis of lung cancer. Knockout of FRK by CRISPR/Cas9 markedly inhibited proliferation, invasion, colony formation and epithelial-mesenchymal transition (EMT) process in the lung cancer cell line H1299. Further exploration indicated that FRK-KO damaged the stemness phenotype of H1299 by inhibiting CD44 and CD133 expression. Seahorse detection and a U-¹³ C flux assay revealed that FRK-KO induced metabolism reprogramming by inhibiting the Warburg effect and changing the energy type in H1299 cells. Epidermal growth factor stimulation recovered the expression of FRK and biological functions, metabolic reprogramming and stemness phenotype of H1299 cells. FRK plays an oncogenic role in lung cancer cells via a novel regulation mechanism of enhancing the stemness of H1299 cells by inducing metabolism reprogramming, which finally promotes EMT and metastasis. Our study also indicates that FRK could be used as a potential therapeutic target for drug development.

P4HA1/HIF1α feedback loop drives the glycolytic and malignant phenotypes of pancreatic cancer

Hypoxia-inducible factor 1α (HIF1α) activation is profoundly implicated in the initiation and progression of multiple malignant tumors. Prolyl 4-hydroxylase subunit alpha 1 (P4HA1) is the active catalytic component of prolyl 4-hydroxylase and has been reported to promote tumor progression in several cancers. In this study, we revealed that P4HA1 was highly expressed in pancreatic ductal adenocarcinoma (PDAC) and predicted a poor clinical outcome. Notably, elevated expression of P4HA1 in PDAC cells was HIF1α-dependent. Gene set enrichment analysis of The Cancer Genome Atlas (TCGA) cohort demonstrated a close link between P4HA1 expression and glycolysis and hypoxia gene signatures in PDAC. Knockdown of P4HA1 significantly suppressed the glycolytic activity of PDAC cells as revealed by reduced glucose utilization and lactate production. Consistently, there was a close correlation between P4HA1 and glycolysis genes. Moreover, we found that P4HA1 can enhance HIF1α stability, indicating a positive feedback loop between HIF1α and P4HA1 in PDAC. Genetic silencing of P4HA1 significantly inhibited the cell proliferation, chemoresistance, and stemness of PDAC cells. Collectively, our findings identify the P4HA1-HIF1α loop as a critical regulator in glycolysis and oncogenic activities of PDAC and provide a potential target for pancreatic cancer treatment.

HSP90 Molecular Chaperones, Metabolic Rewiring, and Epigenetics: Impact on Tumor Progression and Perspective for Anticancer Therapy

Heat shock protein 90 (HSP90) molecular chaperones are a family of ubiquitous proteins participating in several cellular functions through the regulation of folding and/or assembly of large multiprotein complexes and client proteins. Thus, HSP90s chaperones are, directly or indirectly, master regulators of a variety of cellular processes, such as adaptation to stress, cell proliferation, motility, angiogenesis, and signal transduction. In recent years, it has been proposed that HSP90s play a crucial role in carcinogenesis as regulators of genotype-to-phenotype interplay. Indeed, HSP90 chaperones control metabolic rewiring, a hallmark of cancer cells, and influence the transcription of several of the key-genes responsible for tumorigenesis and cancer progression, through either direct binding to chromatin or through the quality control of transcription factors and epigenetic effectors. In this review, we will revise evidence suggesting how this interplay between epigenetics and metabolism may affect oncogenesis. We will examine the effect of metabolic rewiring on the accumulation of specific metabolites, and the changes in the availability of epigenetic co-factors and how this process can be controlled by HSP90 molecular chaperones. Understanding deeply the relationship between epigenetic and metabolism could disclose novel therapeutic scenarios that may lead to improvements in cancer treatment.

Hypoxia- and MicroRNA-Induced Metabolic Reprogramming of Tumor-Initiating Cells

Colorectal cancer (CRC), the second most common cause of cancer mortality in the Western world, is a highly heterogeneous disease that is driven by a rare subpopulation of tumorigenic cells, known as cancer stem cells (CSCs) or tumor-initiating cells (TICs). Over the past few years, a plethora of different approaches, aimed at identifying and eradicating these self-renewing TICs, have been described. A focus on the metabolic and bioenergetic differences between TICs and less aggressive differentiated cancer cells has thereby emerged as a promising strategy to specifically target the tumorigenic cell compartment. Extrinsic factors, such as nutrient availability or tumor hypoxia, are known to influence the metabolic state of TICs. In this review, we aim to summarize the current knowledge on environmental stress factors and how they affect the metabolism of TICs, with a special focus on microRNA (miRNA)- and hypoxia-induced effects on colon TICs.

Inhibition of FASN suppresses the malignant biological behavior of non-small cell lung cancer cells via deregulating glucose metabolism and AKT/ERK pathway

Background

Fatty acid synthase (FASN) is overexpressed in most human carcinomas, including non-small cell lung cancer (NSCLC), and contributes to poor prognosis. An increasing number of studies have highlighted the potential function of FASN as both a biomarker and therapeutic target for cancers. However, the underlying molecular mechanisms of FASN in glucose metabolism and the malignant biological behavior of NSCLC remain the subjects of intensive investigation.

Methods

FASN expression was depleted by FASN-siRNA in A549 and NCI-H1299 cell lines to detect the function of glucose metabolism and the malignant biological behavior of NSCLC cells. Western-blot and qPCR were applied to determine the expressions of FASN, t-AKT, p-AKT, t-ERK, p-ERK, PKM2, HK2 and AZGP1. ATP and lactate were detected to determine the activation of glucose metabolism. CCK8 and transwell assays were used to detect the proliferation, invasion, and migration capacity of the two types of NSCLC cells. The xenograft mouse model was used to evaluate tumor weights after suppression of FASN.

Results

LV-FASN-siRNA and its control lentiviral vector were successfully transfected into the two types of NSCLC cells (A549 and NCI-H1299). LV-FASN siRNA significantly suppressed FASN expression in both NSCLC cell types, and expressions of p-AKT, p-ERK, PKM2, and AZGP1 were also significantly decreased. Notably, the levels of ATP and lactate were significantly decreased after transfection with LV-FASN siRNA. The proliferation of both NSCLC cell types was decreased after suppression of FASN. The invasion and migration capacity of A549, but not NCI-H1299, were inhibited following down-regulation of FASN. In vivo, inhibition of FASN caused a marked animal tumor weight loss.

Conclusions

FASN was involved in glucose metabolism via down-regulation of the AKT/ERK pathway and eventually altered the malignant phenotype in lung cancer cells.

Long noncoding RNA MALAT1 mediates stem cell-like properties in human colorectal cancer cells by regulating miR-20b-5p/Oct4 axis

Cancer stem cells (CSCs) are crucial components of the tumor microenvironment that take part in tumor initiation, progression, recurrence, metastasis, and resistance to chemotherapy. This study explores the mechanisms through which CSCs maintain their stemness, especially in tumors of colorectal cancer (CRC), which thus far remain uncertain. Our findings indicated that the expression of miR-20b-5p is negatively correlated with that of metastasis-associated lung adenocarcinoma transcript-1 (MALAT1, r = -0.928, p = 0.023) and Oct4 (r = -0.894, p = 0.041) in CRC cells. We hypothesized that there may be some targeted regulatory relationships among MALAT1, miR-20b-5p, and Oct4. We proceeded to show that both si-MALAT1 and miR-20b-5p-mimic attenuated microsphere formation and self-renewal capacity, decreased the proportion of CSCs, and downregulated the expression of proteins associated with tumor cell stemness maintenance (Oct4, Nanog, sex-determining region Y-box 2, and Notch1) and cellular metabolism (glucose transporter 1, lactate dehydrogenase B, hexokinase 2, and pyruvate kinase isozyme M2) in HCT-116 cells in vitro. In addition, a xenograft model based on Balb/c mice demonstrated that the administration of either si-MALAT1 or miR-20b-5p-mimic suppressed the tumorigenicity of HCT-116 cells in vivo. The underlying mechanisms may involve the targeting of the tumor cell stemness maintenance-related factor Oct4 by miR-20b-5p. For the first time, we present the possible underlying effects of MALAT1 in influencing the stem cell-like properties of CRC cells. We propose that microRNAs and long noncoding RNAs have vital functions in mediating tumor stemness, which remain to be fully elucidated.

2-Deoxy-D-Glucose inhibits aggressive triple-negative breast cancer cells by targeting glycolysis and the cancer stem cell phenotype

Due to limited availability of pharmacological therapies, triple-negative breast cancer (TNBC) is the subtype with worst outcome. We hypothesised that 2-Deoxy-D-Glucose (2-DG), a glucose analogue, may hold potential as a therapy for particularly aggressive TNBC. We investigated 2-DG’s effects on TNBC cell line variants, Hs578T parental cells and their isogenic more aggressive Hs578Ts(i)₈ variant, using migration, invasion and anoikis assays. We assessed their bioenergetics by Seahorse. We evaluated metabolic alterations using a Seahorse XF Analyzer, citrate synthase assay, immunoblotting and flow cytometry. We assessed the cancer stem cell (CSC) phenotype of the variants and 2-DG’s effects on CSCs. 2-DG significantly inhibited migration and invasion of Hs578Ts(i)₈ versus Hs578T and significantly decreased their ability to resist anoikis. Investigating 2-DG’s preferential inhibitory effect on the more aggressive cells, we found Hs578Ts(i)₈ also had significantly decreased oxidative phosphorylation and increased glycolysis compared to Hs578T. This is likely due to mitochondrial dysfunction in Hs578Ts(i)₈, shown by their significantly decreased mitochondrial membrane potential. Furthermore, Hs578Ts(i)₈ had a significantly increased proportion of cells with CSC phenotype, which was significantly decreased by 2-DG. 2-DG may have benefit as a therapy for TNBC with a particularly aggressive phenotype, by targeting increased glycolysis. Studies of more cell lines and patients’ specimens are warranted.

Autophagy and cancer stem cells: molecular mechanisms and therapeutic applications

Autophagy and mitophagy act in cancer as bimodal processes, whose differential functions strictly depend on cancer ontogenesis, progression, and type. For instance, they can act to promote cancer progression by helping cancer cells survive stress or, instead, when mutated or abnormal, to induce carcinogenesis by influencing cell signaling or promoting intracellular toxicity. For this reason, the study of autophagy in cancer is the main focus of many researchers and several clinical trials are already ongoing to manipulate autophagy and by this way determine the outcome of disease therapy. Since the establishment of the cancer stem cell (CSC) theory and the discovery of CSCs in individual cancer types, autophagy and mitophagy have been proposed as key mechanisms in their homeostasis, dismissal or spread, even though we still miss a comprehensive view of how and by which regulatory molecules these two processes drive cell fate. In this review, we will dive into the deep water of autophagy, mitophagy, and CSCs and offer novel viewpoints on possible therapeutic strategies, based on the modulation of these degradative systems.