Metformin-induced metabolic reprogramming of chemoresistant ALDHbright breast cancer cells

Non-coding RNAs as potential targets in metformin therapy for cancer

Metformin, a widely used oral hypoglycemic drug, has emerged as a potential therapeutic agent for cancer treatment. While initially known for its role in managing diabetes, accumulating evidence suggests that metformin exhibits anticancer properties through various mechanisms. Several cellular or animal experiments have attempted to elucidate the role of non-coding RNA molecules, including microRNAs and long non-coding RNAs, in mediating the anticancer effects of metformin. The present review summarized the current understanding of the mechanisms by which non-coding RNAs modulate the response to metformin in cancer cells. The regulatory roles of non-coding RNAs, particularly miRNAs, in key cellular processes such as cell proliferation, cell death, angiogenesis, metabolism and epigenetics, and how metformin affects these processes are discussed. This review also highlights the role of lncRNAs in cancer types such as lung adenocarcinoma, breast cancer, and renal cancer, and points out the need for further exploration of the mechanisms by which metformin regulates lncRNAs. In addition, the present review explores the potential advantages of metformin-based therapies over direct delivery of ncRNAs, and this review highlights the mechanisms of non-coding RNA regulation when metformin is combined with other therapies. Overall, the present review provides insights into the molecular mechanisms underlying the anticancer effects of metformin mediated by non-coding RNAs, offering novel opportunities for the development of personalized treatment strategies in cancer patients.

Silencing of Dicer enhances dacarbazine resistance in melanoma cells by inhibiting ADSL expression

Dacarbazine (DTIC) is the primary first-line treatment for advanced-stage metastatic melanoma; thus, DTIC resistance is poses a major challenge. Therefore, investigating the mechanism underlying DTIC resistance must be investigated. Dicer, a type III cytoplasmic endoribonuclease, plays a pivotal role in the maturation of miRNAs. Aberrant Dicer expression may contribute to tumor progression, clinical aggressiveness, and poor prognosis in various tumors. Dicer inhibition led to a reduction in DTIC sensitivity and an augmentation in stemness in melanoma cells. Clinical analyses indicated a low Dicer expression level as a predictor of poor prognosis factor. Metabolic alterations in tumor cells may interfere with drug response. Adenylosuccinate lyase (ADSL) is a crucial enzyme in the purine metabolism pathway. An imbalance in ADSL may interfere with the therapeutic efficacy of drugs. We discovered that DTIC treatment enhanced ADSL expression and that Dicer silencing significantly reduced ADSL expression in melanoma cells. Furthermore, ADSL overexpression reversed Dicer silencing induced DTIC resistance and cancer stemness. These findings indicate that Dicer-mediated ADSL regulation influences DTIC sensitivity and stemness in melanoma cells.

Interrogating colorectal cancer metastasis to liver: a search for clinically viable compounds and mechanistic insights in colorectal cancer Patient Derived Organoids

BACKGROUND

Approximately 20-50% of patients presenting with localized colorectal cancer progress to stage IV metastatic disease (mCRC) following initial treatment and this is a major prognostic determinant. Here, we have interrogated a heterogeneous set of primary colorectal cancer (CRC), liver CRC metastases and adjacent liver tissue to identify molecular determinants of the colon to liver spreading. Screening Food and Drug Administration (FDA) approved drugs for their ability to interfere with an identified colon to liver metastasis signature may help filling an unmet therapeutic need.

METHODS

RNA sequencing of primary colorectal cancer specimens vs adjacent liver tissue vs synchronous and asynchronous liver metastases. Pathways enrichment analyses. The Library of Integrated Network-based Cellular Signatures (LINCS)-based and Connectivity Map (CMAP)-mediated identification of FDA-approved compounds capable to interfere with a 22 gene signature from primary CRC and liver metastases. Testing the identified compounds on CRC-Patient Derived Organoid (PDO) cultures. Microscopy and Fluorescence Activated Cell Sorting (FACS) based analysis of the treated PDOs.

RESULTS

We have found that liver metastases acquire features of the adjacent liver tissue while partially losing those of the primary tumors they derived from. We have identified a 22-gene signature differentially expressed among primary tumors and metastases and validated in public databases. A pharmacogenomic screening for FDA-approved compounds capable of interfering with this signature has been performed. We have validated some of the identified representative compounds in CRC-Patient Derived Organoid cultures (PDOs) and found that pentoxyfilline and, to a minor extent, dexketoprofen and desloratadine, can variably interfere with number, size and viability of the CRC -PDOs in a patient-specific way. We explored the pentoxifylline mechanism of action and found that pentoxifylline treatment attenuated the 5-FU elicited increase of ALDHhigh cells by attenuating the IL-6 mediated STAT3 (tyr705) phosphorylation.

CONCLUSIONS

Pentoxifylline synergizes with 5-Fluorouracil (5-FU) in attenuating organoid formation. It does so by interfering with an IL-6-STAT3 axis leading to the emergence of chemoresistant ALDHhigh cell subpopulations in 5-FU treated PDOs. A larger cohort of CRC-PDOs will be required to validate and expand on the findings of this proof-of-concept study.

Metformin and Breast Cancer: Where Are We Now?

Breast cancer is the most prevalent cancer and the leading cause of cancer-related death among women worldwide. Type 2 diabetes–associated metabolic traits such as hyperglycemia, hyperinsulinemia, inflammation, oxidative stress, and obesity are well-known risk factors for breast cancer. The insulin sensitizer metformin, one of the most prescribed oral antidiabetic drugs, has been suggested to function as an antitumoral agent, based on epidemiological and retrospective clinical data as well as preclinical studies showing an antiproliferative effect in cultured breast cancer cells and animal models. These benefits provided a strong rationale to study the effects of metformin in routine clinical care of breast cancer patients. However, the initial enthusiasm was tempered after disappointing results in randomized controlled trials, particularly in the metastatic setting. Here, we revisit the current state of the art of metformin mechanisms of action, critically review past and current metformin-based clinical trials, and briefly discuss future perspectives on how to incorporate metformin into the oncologist’s armamentarium for the prevention and treatment of breast cancer.

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.

Enhanced Antiproliferation Potency of Electrical Pulse-Mediated Metformin and Cisplatin Combination Therapy on MDA-MB-231 Cells

We investigated the combined potency of metformin and cisplatin on the MDA-MB-231, triple-negative breast cancer (TNBC) cells with the application of electrical pulses. There are no targeted therapies for this subset of breast cancer because of the absence of specific biomarkers. Cytotoxic chemotherapy is the mainstream mode of treatment for TNBC, and cisplatin is the most commonly used chemotherapeutic drug. While there is a good response initially, TNBC cells develop drug resistance eventually. Thus, there is a need for alternate therapies. Toward this, we studied the antiproliferation characteristics of electrical pulse-mediated combination therapy using metformin, the commonly used Type-2 diabetes drug, along with cisplatin. We used metformin, as it has various anticancer properties caused by repressing energy pathways in a cancer cell. Application of 8 pulses of 1000 V/cm, 100 µs, at 1 Hz frequency, enhanced the drug uptake leading to cell viability as low as 25.86% at 30 µM cisplatin and 5 mM metformin in a 24 h study. Also, the same studies were conducted on MCF10A, a non-cancerous human epithelial cell. It aided in comparing the result for both MDA-MB-231 and MCF10A cell lines while establishing a better understanding of the experimental outcomes. Overall, the various experimental results from colony-forming assay, reactive oxidative analysis, and the intracellular glucose metabolic assay indicate the possibility of the electrical pulses-based cisplatin and metformin drug combination as a potential alternative to TNBC treatment.

Anticancer potential of metformin: focusing on gastrointestinal cancers

Gastrointestinal cancers are one of the most common types of cancer that have high annual mortality; therefore, identification and introduction of safe drugs in the control and prevention of these cancers are of particular importance. Metformin, a lipophilic biguanide, is the most commonly prescribed agent for type 2 diabetes management. In addition to its great effects on lowering the blood glucose concentrations, the anti-cancer properties of this drug have been reported in many types of cancers such as gastrointestinal cancers. Hence the effects of this agent as a safe drug on the reduction of gastrointestinal cancer risk and suppression of these types of cancers have been studied in different clinical trials. Furthermore, the proposed mechanisms of metformin in preventing the growth of these cancers have been investigated in several studies. In this review, we discuss recent advances in elucidating the molecular mechanisms that are relevant for metformin use in gastrointestinal cancer treatment.

The Chemosensitizing Role of Metformin in Anti-Cancer Therapy

Chemoresistance, which leads to the failure of chemotherapy and further tumor recurrence, presents the largest hurdle for the success of anti-cancer therapy. In recent years, metformin, a widely used first-line antidiabetic drug, has attracted increasing attention for its anti-cancer effects. A growing body of evidence indicates that metformin can sensitize tumor responses to different chemotherapeutic drugs, such as hormone modulating drugs, anti-metabolite drugs, antibiotics, and DNA-damaging drugs via selective targeting of Cancer Stem Cells (CSCs), improving the hypoxic microenvironment, and by suppressing tumor metastasis and inflammation. In addition, metformin may regulate metabolic programming, induce apoptosis, reverse Epithelial to Mesenchymal Transition (EMT), and Multidrug Resistance (MDR). In this review, we summarize the chemosensitization effects of metformin and focus primarily on its molecular mechanisms in enhancing the sensitivity of multiple chemotherapeutic drugs, through targeting of mTOR, ERK/P70S6K, NF-κB/HIF-1 α, and Mitogen- Activated Protein Kinase (MAPK) signaling pathways, as well as by down-regulating the expression of CSC genes and Pyruvate Kinase isoenzyme M2 (PKM2). Through a comprehensive understanding of the molecular mechanisms of chemosensitization provided in this review, the rationale for the use of metformin in clinical combination medications can be more systematically and thoroughly explored for wider adoption against numerous cancer types.>.

Metformin: Metabolic Rewiring Faces Tumor Heterogeneity

Tumor heterogeneity impinges on all the aspects of tumor history, from onset to metastasis and relapse. It is growingly recognized as a propelling force for tumor adaptation to environmental and micro-environmental cues. Metabolic heterogeneity perfectly falls into this process. It strongly contributes to the metabolic plasticity which characterizes cancer cell subpopulations-capable of adaptive switching under stress conditions, between aerobic glycolysis and oxidative phosphorylation-in both a convergent and divergent modality. The mitochondria appear at center-stage in this adaptive process and thus, targeting mitochondria in cancer may prove of therapeutic value. Metformin is the oldest and most used anti-diabetic medication and its relationship with cancer has witnessed rises and falls in the last 30 years. We believe it is useful to revisit the main mechanisms of action of metformin in light of the emerging views on tumor heterogeneity. We first analyze the most consolidated view of its mitochondrial mechanism of action and then we frame the latter in the context of tumor adaptive strategies, cancer stem cell selection, metabolic zonation of tumors and the tumor microenvironment. This may provide a more critical point of view and, to some extent, may help to shed light on some of the controversial evidence for metformin's anticancer action.

Pyntacle: a parallel computing-enabled framework for large-scale network biology analysis

BACKGROUND

Some natural systems are big in size, complex, and often characterized by convoluted mechanisms of interaction, such as epistasis, pleiotropy, and trophism, which cannot be immediately ascribed to individual natural events or biological entities but that are often derived from group effects. However, the determination of important groups of entities, such as genes or proteins, in complex systems is considered a computationally hard task.

RESULTS

We present Pyntacle, a high-performance framework designed to exploit parallel computing and graph theory to efficiently identify critical groups in big networks and in scenarios that cannot be tackled with traditional network analysis approaches.

CONCLUSIONS

We showcase potential applications of Pyntacle with transcriptomics and structural biology data, thereby highlighting the outstanding improvement in terms of computational resources over existing tools.

Metabolomic Approaches to Study Chemical Exposure-Related Metabolism Alterations in Mammalian Cell Cultures

Biological organisms are constantly exposed to an immense repertoire of molecules that cover environmental or food-derived molecules and drugs, triggering a continuous flow of stimuli-dependent adaptations. The diversity of these chemicals as well as their concentrations contribute to the multiplicity of induced effects, including activation, stimulation, or inhibition of physiological processes and toxicity. Metabolism, as the foremost phenotype and manifestation of life, has proven to be immensely sensitive and highly adaptive to chemical stimuli. Therefore, studying the effect of endo- or xenobiotics over cellular metabolism delivers valuable knowledge to apprehend potential cellular activity of individual molecules and evaluate their acute or chronic benefits and toxicity. The development of modern metabolomics technologies such as mass spectrometry or nuclear magnetic resonance spectroscopy now offers unprecedented solutions for the rapid and efficient determination of metabolic profiles of cells and more complex biological systems. Combined with the availability of well-established cell culture techniques, these analytical methods appear perfectly suited to determine the biological activity and estimate the positive and negative effects of chemicals in a variety of cell types and models, even at hardly detectable concentrations. Metabolic phenotypes can be estimated from studying intracellular metabolites at homeostasis in vivo, while in vitro cell cultures provide additional access to metabolites exchanged with growth media. This article discusses analytical solutions available for metabolic phenotyping of cell culture metabolism as well as the general metabolomics workflow suitable for testing the biological activity of molecular compounds. We emphasize how metabolic profiling of cell supernatants and intracellular extracts can deliver valuable and complementary insights for evaluating the effects of xenobiotics on cellular metabolism. We note that the concepts and methods discussed primarily for xenobiotics exposure are widely applicable to drug testing in general, including endobiotics that cover active metabolites, nutrients, peptides and proteins, cytokines, hormones, vitamins, etc.

Metformin as an adjuvant in breast cancer treatment

Breast cancer is one of the most common malignancies in females. It is an etiologically complex disease driven by a multitude of cellular pathways. The proliferation and spread of breast cancer is intimately linked to cellular glucose metabolism, given that glucose is an essential cellular metabolic substrate and that insulin signalling has mitogenic effects. Growing interest has focused on anti-diabetic agents in the management of breast cancer. Epidemiologic studies show that metformin reduces cancer incidence and mortality among type 2 diabetic patients. Preclinical in vitro and in vivo research provides intriguing insight into the cellular mechanisms behind the oncostatic effects of metformin. This article aims to provide an overview of the mechanisms in which metformin may elicit its anti-cancerous effects and discuss its potential role as an adjuvant in the management of breast cancer.

Metformin in breast cancer: preclinical and clinical evidence

Metformin, a well-acknowledged biguanide, safety profile and multiaction drug with low cost for management of type 2 diabetes, makes a first-class candidate for repurposing. The off-patent drug draws huge attention for repositioned for anticancer drug delivery recently. Still few unanswered questions are challenging, among them one leading question; can metformin use as a generic therapy for all breast cancer subtypes? And is metformin able to get over the problem of drug resistance? The review focused on the mechanisms of metformin action specifically for breast cancer therapy and overcoming the resistance; also discusses preclinical and ongoing and completed clinical trials. The existing limitation such as therapeutic dose specifically for cancer treatment, resistance of metformin in breast cancer and organic cation transporters heterogeneity of the drug opens up a new pathway for improved understanding and successful application as repurposed effective chemotherapeutics for breast cancer. However, much more additional research is needed to confirm the accurate efficacy of metformin treatment for prevention of cancer and its recurrence.

Metformin and Breast Cancer: Molecular Targets

Metformin has been the first-line drug for the treatment of type II diabetes mellitus for decades, being presently the most widely prescribed antihyperglycemic drug. Retrospective studies associate the use of metformin with a reduction in cancer incidence and cancer-related death. However, despite extensive research about the molecular effects of metformin in cancer cells, its mode of action remains controversial. The major molecular targets of metformin include complex I of the mitochondrial electron transport chain, adenosine monophosphate (AMP)-activated protein kinase (AMPK), and mechanistic target of rapamycin complex 1 (mTORC1), but AMPK-independent effects of metformin have also been described. Breast cancer is one of the leading causes of cancer-related morbidity and mortality among women worldwide. Several studies have reinforced a link between breast cancer risk and diabetes. Moreover, metformin significantly reduces breast cancer risk, compared to patients who are not using metformin and is independent of diabetes status. In this review, we summarize the current molecular evidence to elucidate metformin's mode of action against breast cancer cells.

Monitoring Vitamin B12 in Women Treated with Metformin for Primary Prevention of Breast Cancer and Age-Related Chronic Diseases

Metformin (MET) is currently being used in several trials for cancer prevention or treatment in non-diabetics. However, long-term MET use in diabetics is associated with lower serum levels of total vitamin B₁₂. In a pilot randomized controlled trial of the Mediterranean diet (MedDiet) and MET, whose participants were characterized by different components of metabolic syndrome, we tested the effect of MET on serum levels of B₁₂, holo transcobalamin II (holo-TC-II), and methylmalonic acid (MMA). The study was conducted on 165 women receiving MET or placebo for three years. Results of the study indicate a significant overall reduction in both serum total B₁₂ and holo-TC-II levels according with MET-treatment. In particular, in the MET group 26 of 81 patients and 10 of the 84 placebo-treated subjects had B₁₂ below the normal threshold (<221 pmol/L) at the end of the study. Considering jointly all B₁₂, Holo-TC-II, and MMA, 13 of the 165 subjects (10 MET and 3 placebo-treated) had at least two deficits in the biochemical parameters at the end of the study, without reporting clinical signs. Although our results do not affect whether women remain in the trial, B₁₂ monitoring for MET-treated individuals should be implemented.

Simulated microgravity promotes the formation of tridimensional cultures and stimulates pluripotency and a glycolytic metabolism in human hepatic and biliary tree stem/progenitor cells

Many pivotal biological cell processes are affected by gravity. The aim of our study was to evaluate biological and functional effects, differentiation potential and exo-metabolome profile of simulated microgravity (SMG) on human hepatic cell line (HepG2) and human biliary tree stem/progenitor cells (hBTSCs). Both hBTSCs and HepG2 were cultured in a weightless and protected environment SGM produced by the Rotary Cell Culture System (Synthecon) and control condition in normal gravity (NG). Self-replication and differentiation toward mature cells were determined by culturing hBTSCs in Kubota’s Medium (KM) and in hormonally defined medium (HDM) tailored for hepatocyte differentiation. The effects on the expression and cell exo-metabolome profiles of SMG versus NG cultures were analyzed. SMG promotes tridimensional (3D) cultures of hBTSCs and HepG2. Significative increase of stemness gene expression (p < 0.05) has been observed in hBTSCs cultured in SMG when compared to NG condition. At the same time, the expression of hepatocyte lineage markers in hBTSCs differentiated by HDM was significantly lower (p < 0.05) in SMG compared to NG, demonstrating an impaired capability of hBTSCs to differentiate in vitro toward mature hepatocytes when cultured in SMG condition. Furthermore, in HepG2 cells the SMG caused a lower (p < 0.05 vs controls) transcription of CYP3A4, a marker of late-stage (i.e. Zone 3) hepatocytes. Exo-metabolome NMR-analysis showed that both cell cultures consumed a higher amount of glucose and lower glutamate in SMG respect to NG (p < 0.05). Moreover, hBTSCs media cultures resulted richer of released fermentation (lactate, acetate) and ketogenesis products (B-hydroxybutyrate) in SGM (p < 0.05) than NG. While, HepG2 cells showed higher consumption of amino acids and release of ketoacids (3-Methyl-2-oxovalerate, 2-oxo-4-methyl-valerate) and formiate with respect to normogravity condition (p < 0.05). Based on our results, SMG could be helpful for developing hBTSCs-derived liver devices. In conclusion, SMG favored the formation of hBTSCs and HepG2 3D cultures and the maintenance of stemness contrasting cell differentiation; these effects being associated with stimulation of glycolytic metabolism. Interestingly, the impact of SMG on stem cell biology should be taken into consideration for workers involved in space medicine programs.

Intracellular redox status controls spherogenicity, an in vitro cancer stem cell marker, in thyroid cancer cell lines

Cancer stem cells (CSCs), a small fraction of a tumor mass, are proposed to be highly crucial for cancer initiation, recurrence and metastasis. We have recently found that aldehyde dehydrogenase (ALDH) 1A3 is a CSC marker in some thyroid cancer cell lines, whose functional activity is, however, not relevant for thyroid cancer stemness. Since previous studies on malignancies in other organs suggest that intracellular reactive oxygen species (ROS) might be a functional and targetable CSC marker, the present study was conducted to elucidate the significance of ROS as a functional CSC marker in thyroid cancer cell lines. We first found that ROS levels controlled spherogenicity; that is, ROS^low cells were more spherogenic than ROS^high cells. However, unlike typical CSCs in other cancers, CSC-like ROS^low cells in thyroid cancer cells were plastic and were not accompanied by de-differentiation status (i.e., expression of stemness markers/thyroid-specific transcription factors) or chemo-/radio-resistance. The lower levels of ROS were functionally critical because a forced increase in ROS levels by L-buthionine-S,R-sulfoximine, an inhibitor of glutathione (GSH) synthesis, and irradiation suppressed spherogenicity. ROS levels were also correlated with the number of double strand DNA breaks determined by 53BP1 staining. Lower ROS levels appear to be a result of decreased mitochondrial oxidative phosphorylation and elevated GSH contents. Given the importance of CSC-targeted therapy for achieving long-term disease eradication by exhausting self-renewal and growth potential of cancer tissues, ROS may be a good candidate for CSC-targeted therapy in thyroid cancer.

Metformin influences drug sensitivity in pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive, highly metastatic malignancy and accounts for 85% of pancreatic cancers. PDAC patients have poor prognosis with a five-year survival of only 5-10% after diagnosis and treatment. Pancreatic cancer has been associated with type II diabetes as the frequency of recently diagnosed diabetics that develop pancreatic cancer within a 10-year period of initial diagnosis of diabetes in increased in comparison to non-diabetic patients. Metformin is a very frequently prescribed drug used to treat type II diabetes. Metformin acts in part by stimulating AMP-kinase (AMPK) and results in the suppression of mTORC1 activity and the induction of autophagy. In the following studies, we have examined the effects of metformin in the presence of various chemotherapeutic drugs, signal transduction inhibitors and natural products on the growth of three different PDAC lines. Metformin, by itself, was not effective at suppressing growth of the pancreatic cancer cell lines at concentration less than 1000 nM, however, in certain PDAC lines, a suboptimal dose of metformin (250 nM) potentiated the effects of various chemotherapeutic drugs used to treat pancreatic cancer (e.g., gemcitabine, cisplatin, 5-fluorouracil) and other cancer types (e.g., doxorubicin, docetaxel). Furthermore, metformin could increase anti-proliferative effects of mTORC1 and PI3K/mTOR inhibitors as well as natural products such as berberine and the anti-malarial drug chloroquine in certain PDAC lines. Thus, metformin can enhance the effects of certain drugs and signal transduction inhibitors which are used to treat pancreatic and various other cancers.

Stromal miR-20a controls paracrine CXCL8 secretion in colitis and colon cancer

Inflammatory bowel disease (IBD) affects one million people in the US. Ulcerative colitis (UC) is a subtype of IBD that can lead to colitis-associated cancer (CAC). In UC, the rate of CAC is 3-5-fold greater than the rate of sporadic colorectal cancer (CRC). The pathogenesis of UC and CAC are due to aberrant interactions between host immune system and microenvironment, but precise mechanisms are still unknown. In colitis and CAC, microenvironmental fibroblasts exhibit an activated, inflammatory phenotype that contributes to tumorigenesis accompanied by excessive secretion of the chemokine CXCL8. However, mechanisms regulating CXCL8 secretion are unclear. Since it is known that miRNAs regulate chemokines such as CXCL8, we queried a microRNA library for mimics affecting CXCL8 secretion. Among the identified microRNAs, miR-20a/b was further investigated as its stromal expression levels inversely correlated with the amounts of CXCL8 secreted and predicted fibroblast tumor-promoting activity. Indeed, miR-20a directly bound to the 3′UTR of CXCL8 mRNA and regulated its expression by translational repression. In vivo co-inoculation studies with CRC stem cells demonstrated that fibroblasts characterized by high miR-20a expression had reduced tumor-promoting activities. These studies reveal that in stromal fibroblasts, miR-20a modulates CXCL8 function, therefore influencing tumor latency.

Metabolic Profiles Associated With Metformin Efficacy in Cancer

Metformin is one of the most commonly prescribed medications for the treatment of type 2 diabetes. Numerous reports have suggested potential anti-cancerous and cancer preventive properties of metformin, although these findings vary depending on the intrinsic properties of the tumor, as well as the systemic physiology of patients. These intriguing studies have led to a renewed interest in metformin use in the oncology setting, and fueled research to unveil its elusive mode of action. It is now appreciated that metformin inhibits complex I of the electron transport chain in mitochondria, causing bioenergetic stress in cancer cells, and rendering them dependent on glycolysis for ATP production. Understanding the mode of action of metformin and the consequences of its use on cancer cell bioenergetics permits the identification of cancer types most susceptible to metformin action. Such knowledge may also shed light on the varying results to metformin usage that have been observed in clinical trials. In this review, we discuss metabolic profiles of cancer cells that are associated with metformin sensitivity, and rationalize combinatorial treatment options. We use the concept of bioenergetic flexibility, which has recently emerged in the field of cancer cell metabolism, to further understand metabolic rearrangements that occur upon metformin treatment. Finally, we advance the notion that metabolic fitness of cancer cells increases during progression to metastatic disease and the emergence of therapeutic resistance. As a result, sophisticated combinatorial approaches that prevent metabolic compensatory mechanisms will be required to effectively manage metastatic disease.

Metabolic Portraits of Breast Cancer by HR MAS MR Spectroscopy of Intact Tissue Samples

Despite progress in early detection and therapeutic strategies, breast cancer remains the second leading cause of cancer-related death among women globally. Due to the heterogeneity and complexity of tumor biology, breast cancer patients with similar diagnosis might have different prognosis and response to treatment. Thus, deeper understanding of individual tumor properties is necessary. Cancer cells must be able to convert nutrients to biomass while maintaining energy production, which requires reprogramming of central metabolic processes in the cells. This phenomenon is increasingly recognized as a potential target for treatment, but also as a source for biomarkers that can be used for prognosis, risk stratification and therapy monitoring. Magnetic resonance (MR) metabolomics is a widely used approach in translational research, aiming to identify clinically relevant metabolic biomarkers or generate novel understanding of the molecular biology in tumors. Ex vivo proton high-resolution magic angle spinning (HR MAS) MR spectroscopy is widely used to study central metabolic processes in a non-destructive manner. Here we review the current status for HR MAS MR spectroscopy findings in breast cancer in relation to glucose, amino acid and choline metabolism.

Head and Neck Squamous Cell Carcinoma Metabolism Draws on Glutaminolysis, and Stemness Is Specifically Regulated by Glutaminolysis via Aldehyde Dehydrogenase

Cancer cells use alternate energetic pathways; however, cancer stem cell (CSC) metabolic energetic pathways are unknown. The purpose of this study was to define the metabolic characteristics of head and neck cancer at different points of its pathogenesis with a focus on its CSC compartment. UPLC-MS/MS-profiling and GC-MS-validation studies of human head and neck cancer tissue, saliva, and plasma were used in conjunction with in vitro and in vivo models to carry out this investigation. We identified metabolite biomarker panels that distinguish head and neck cancer from healthy controls, and confirmed involvement of glutamate and glutaminolysis. Glutaminase, which catalyzes glutamate formation from glutamine, and aldehyde dehydrogenase (ALDH), a stemness marker, were highly expressed in primary and metastatic head and neck cancer tissues, tumorspheres, and CSC versus controls. Exogenous glutamine induced stemness via glutaminase, whereas inhibiting glutaminase suppressed stemness in vitro and tumorigenesis in vivo. Head and neck CSC (CD44hi/ALDHhi) exhibited higher glutaminase, glutamate, and sphere levels than CD44lo/ALDHlo cells. Glutaminase drove transcriptional and translational ALDH expression, and glutamine directed even CD44lo/ALDHlo cells toward stemness. Glutaminolysis regulates tumorigenesis and CSC metabolism via ALDH. These findings indicate that glutamate is an important marker of cancer metabolism whose regulation via glutaminase works in concert with ALDH to mediate cancer stemness. Future analyses of glutaminolytic-ALDH driven mechanisms underlying tumorigenic transitions may help in the development of targeted therapies for head and neck cancer and its CSC compartment.

Aldehyde dehydrogenase 3A1 promotes multi-modality resistance and alters gene expression profile in human breast adenocarcinoma MCF-7 cells

Aldehyde dehydrogenases participate in a variety of cellular homeostatic mechanisms like metabolism, proliferation, differentiation, apoptosis, whereas recently, they have been implicated in normal and cancer cell stemness. We explored roles for ALDH3A1 in conferring resistance to chemotherapeutics/radiation/oxidative stress and whether ectopic overexpression of ALDH3A1 could lead to alterations of gene expression profile associated with cancer stem cell-like phenotype. MCF-7 cells were stably transfected either with an empty vector (mock) or human aldehyde dehydrogenase 3A1 cDNA. The expression of aldehyde dehydrogenase 3A1 in MCF-7 cells was associated with altered cell proliferation rate and enhanced cell resistance against various chemotherapeutic drugs (4-hydroxyperoxycyclophosphamide, doxorubicin, etoposide, and 5-fluorouracil). Aldehyde dehydrogenase 3A1 expression also led to increased tolerance of MCF-7 cells to gamma radiation and hydrogen peroxide-induced stress. Furthermore, aldehyde dehydrogenase 3A1-expressing MCF-7 cells exhibited gene up-regulation of cyclins A, B1, B2, and down-regulation of cyclin D1 as well as transcription factors p21, CXR4, Notch1, SOX2, SOX4, OCT4, and JAG1. When compared to mock cells, no changes were observed in mRNA levels of ABCA2 and ABCB1 protein pumps with only a minor decrease of the ABCG2 pump in the aldehyde dehydrogenase 3A1-expressing cells. Also, the adhesion molecules EpCAM and CD49F were also found to be up-regulated in aldehyde dehydrogenase 3A1expressing cells. Taken together, ALDH3A1 confers a multi-modality resistance phenotype in MCF-7 cells associated with slower growth rate, increased clonogenic capacity, and altered gene expression profile, underlining its significance in cell homeostasis.

Metformin induces apoptosis of human hepatocellular carcinoma HepG2 cells by activating an AMPK/p53/miR-23a/FOXA1 pathway

The antidiabetic drug metformin has been shown to possess antitumor functions in many types of cancers. Although studies have revealed its beneficial effects on the prognosis of hepatocellular carcinoma (HCC), the detailed molecular mechanism underlying this event remains largely unknown. In this work, we showed that miR-23a was significantly induced upon metformin treatment; inhibition of miR-23a abrogated the proapoptotic effect of metformin in HepG2 cells. We next established forkhead box protein A1 (FOXA1) as the functional target of miR-23a, and silencing FOXA1 mimicked the effect of metformin. Moreover, the phosphorylation of AMP-activated protein kinase (AMPK) and the expression of p53 were increased upon metformin treatment, and the inhibition of p53 abrogated the induction of miR-23a by metformin, suggesting that AMPK/p53 signaling axis is responsible for the induction of miR-23a by metformin. In summary, we unraveled a novel AMPK/p53/miR-23a/FOXA1 axis in the regulation of apoptosis in HCC, and the application of metformin could, therefore, be effective in the treatment of HCC.

PKM1 is involved in resistance to anti-cancer drugs

Resistance to chemotherapy is a crucial problem in the clinical situation. To overcome this issue, many mechanisms of chemoresistance have been elucidated so far. However, this problem still has not been solved completely. In this study, we investigated the mechanism of chemoresistance from the view of cancer metabolism-related genes, especially focusing on the expression profile of pyruvate kinase muscle (PKM) isoforms, which are rate-limiting enzymes in cancer-specific metabolism (Warburg effect). Herein, we showed that PKM1, which promotes oxidative phosphorylation (OXPHOS), was commonly up-regulated in various chemoresistant cells. To clarify the functions of PKM1 in chemoresistance, we investigated effects of PKM1 expression in DLD-1 parental, 5-FU-resistant and oxaliplatin-resistant DLD-1 cells. The overexpression of PKM1 resulted in resistance of the parental cells to 5-FU and oxaliplatin. Moreover, gene-silencing of PKM1 induced apoptosis in these cells including the resistant cells by causing a decrease in the mitochondrial membrane potential. Furthermore, combination therapy using 5-FU or oxaliplatin with siR-PKM1 was also effective against the resistant cells. Our findings should lead to the development of new agents that can cancel the chemoresistance from the view of cancer energy metabolism.

Disruption of BASIGIN decreases lactic acid export and sensitizes non-small cell lung cancer to biguanides independently of the LKB1 status

Most cancers rely on aerobic glycolysis to generate energy and metabolic intermediates. To maintain a high glycolytic rate, cells must efficiently export lactic acid through the proton-coupled monocarboxylate transporters (MCT1/4). These transporters require a chaperone, CD147/BASIGIN (BSG) for trafficking to the plasma membrane and function.

To validate the key role of these transporters in lung cancer, we first analysed the expression of MCT1/4 and BSG in 50 non-small lung cancer (NSCLC) cases. These proteins were specifically upregulated in tumour tissues. We then disrupted BSG in three NSCLC cell lines (A549, H1975 and H292) via ‘Zinc-Finger Nucleases’. The three homozygous BSG^−/− cell lines displayed a low MCT activity (10- to 5-fold reduction, for MCT1 and MCT4, respectively) compared to wild-type cells. Consequently, the rate of glycolysis, compared to the wild-type counterpart, was reduced by 2.0- to 3.5-fold, whereas the rate of respiration was stimulated in BSG^−/− cell lines. Both wild-type and BSG-null cells were extremely sensitive to the mitochondria inhibitor metformin/phenformin in normoxia. However, only BSG-null cells, independently of their LKB1 status, remained sensitive to biguanides in hypoxia in vitro and tumour growth in nude mice. Our results demonstrate that inhibiting glycolysis by targeting lactic acid export sensitizes NSCLC to phenformin.

(1)H NMR Metabolomic Footprinting Analysis for the In Vitro Screening of Potential Chemopreventive Agents

Metabolomics is the quantification and analysis of the concentration profiles of low-molecular-weight compounds present in biological samples. In particular metabolic footprinting analysis, based on the monitoring of metabolites consumed from and secreted into the growth medium, is a valuable tool for the study of pharmacological and toxicological effects of drugs. Mass spectrometry and nuclear magnetic resonance (NMR) are the two main complementary techniques used in this field. Although less sensitive, NMR gives a direct fingerprint of the system, and the spectra obtained contain metabolic information that can be distilled by chemometric techniques. In this chapter, we present how metabolomic footprinting can be used to assess in vitro a potential chemopreventive molecule as metformin.

Metabolic reprogramming orchestrates cancer stem cell properties in nasopharyngeal carcinoma

Cancer stem cells (CSCs) represent a subpopulation of tumor cells endowed with self-renewal capacity and are considered as an underlying cause of tumor recurrence and metastasis. The metabolic signatures of CSCs and the mechanisms involved in the regulation of their stem cell-like properties still remain elusive. We utilized nasopharyngeal carcinoma (NPC) CSCs as a model to dissect their metabolic signatures and found that CSCs underwent metabolic shift and mitochondrial resetting distinguished from their differentiated counterparts. In metabolic shift, CSCs showed a greater reliance on glycolysis for energy supply compared with the parental cells. In mitochondrial resetting, the quantity and function of mitochondria of CSCs were modulated by the biogenesis of the organelles, and the round-shaped mitochondria were distributed in a peri-nuclear manner similar to those seen in the stem cells. In addition, we blocked the glycolytic pathway, increased the ROS levels, and depolarized mitochondrial membranes of CSCs, respectively, and examined the effects of these metabolic factors on CSC properties. Intriguingly, the properties of CSCs were curbed when we redirected the quintessential metabolic reprogramming, which indicates that the plasticity of energy metabolism regulated the balance between acquisition and loss of the stemness status. Taken together, we suggest that metabolic reprogramming is critical for CSCs to sustain self-renewal, deter from differentiation and enhance the antioxidant defense mechanism. Characterization of metabolic reprogramming governing CSC properties is paramount to the design of novel therapeutic strategies through metabolic intervention of CSCs.

Metformin and erlotinib synergize to inhibit basal breast cancer

Basal-like breast cancers (BBCs) are enriched for increased EGFR expression and decreased expression of PTEN. We found that treatment with metformin and erlotinib synergistically induced apoptosis in a subset of BBC cell lines. The drug combination led to enhanced reduction of EGFR, AKT, S6 and 4EBP1 phosphorylation, as well as prevented colony formation and inhibited mammosphere outgrowth. Our data with other compounds suggested that biguanides combined with EGFR inhibitors have the potential to outperform other targeted drug combinations and could be employed in other breast cancer subtypes, as well as other tumor types, with activated EGFR and PI3K signaling. Analysis of BBC cell line alterations led to the hypothesis that loss of PTEN sensitized cells to the drug combination which was confirmed using isogenic cell line models with and without PTEN expression. Combined metformin and erlotinib led to partial regression of PTEN-null and EGFR-amplified xenografted MDA-MB-468 BBC tumors with evidence of significant apoptosis, reduction of EGFR and AKT signaling, and lack of altered plasma insulin levels. Combined treatment also inhibited xenografted PTEN null HCC-70 BBC cells. Measurement of trough plasma drug levels in xenografted mice and a separately performed pharmacokinetics modeling study support possible clinical translation.

Sendai virus-mediated expression of reprogramming factors promotes plasticity of human neuroblastoma cells

Neuroblastoma (NB) is the most common extracranial solid tumor that originates from multipotent neural crest cells. NB cell populations that express embryonic stem cell-associated genes have been identified and shown to retain a multipotent phenotype. However, whether somatic reprogramming of NB cells can produce similar stem-cell like populations is unknown. Here, we sought to reprogram NB cell lines using an integration-free Sendai virus vector system. Of four NB cell lines examined, only SH-IN cells formed induced pluripotent stem cell-like colonies (SH-IN 4F colonies) at approximately 6 weeks following transduction. These SH-IN 4F colonies were alkaline phosphatase-positive. Array comparative genomic hybridization analysis indicated identical genomic aberrations in the SH-IN 4F cells as in the parental cells. SH-IN 4F cells had the ability to differentiate into the three embryonic germ layers in vitro, but rather formed NBs in vivo. Furthermore, SH-IN 4F cells exhibited resistance to cisplatin treatment and differentiated into endothelial-like cells expressing CD31 in the presence of vascular endothelial growth factor. These results suggest that SH-IN 4F cells are partially reprogrammed NB cells, and could be a suitable model for investigating the plasticity of aggressive tumors.

Metformin and cancer: Between the bioenergetic disturbances and the antifolate activity

For decades, metformin has been the first-line drug for the treatment of type II diabetes mellitus, and it thus is the most widely prescribed antihyperglycemic drug. Retrospective studies associate the use of metformin with a reduction in cancer incidence and cancer-related death. However, despite extensive research about the molecular effects of metformin in cancer cells, its mode of action remains controversial. In this review, we summarize the current molecular evidence in an effort to elucidate metformin's mode of action against cancer cells. Some authors describe that metformin acts directly on mitochondria, inhibiting complex I and restricting the cell's ability to cope with energetic stress. Furthermore, as the drug interrupts the tricarboxylic acid cycle, metformin-induced alteration of mitochondrial function leads to a compensatory increase in lactate and glycolytic ATP. It has also been reported that cell cycle arrest, autophagy, apoptosis and cell death induction is mediated by the activation of AMPK and Redd1 proteins, thus inhibiting the mTOR pathway. Additionally, unbiased metabolomics studies have provided strong evidence to support that metformin alters the methionine and folate cycles, with a concomitant decrease in nucleotide synthesis. Indeed, purines such as thymidine or hypoxanthine restore the proliferation of tumor cells treated with metformin in vitro. Consequently, some authors prefer to refer to metformin as an "antimetabolite drug" rather than a "mitochondrial toxin". Finally, we also review the current controversy concerning the relationship between the experimental conditions of in vitro-reported effects and the plasma concentrations achieved by chronic treatment with metformin.

Glipizide, an antidiabetic drug, suppresses tumor growth and metastasis by inhibiting angiogenesis

Angiogenesis is involved in the development, progression and metastasis of various human cancers. Herein, we report the discovery of glipizide, a widely used drug for type 2 diabetes mellitus, as a promising anticancer agent through the inhibition of tumor angiogenesis. By high-throughput screening (HTS) of an FDA approved drug library utilizing our in vivo chick embryo chorioallantoic membrane (CAM) and yolk sac membrane (YSM) models, glipizide has been identified to significantly inhibit blood vessel formation and development. Moreover, glipizide was found to suppress tumor angiogenesis, tumor growth and metastasis using xenograft tumor and MMTV-PyMT transgenic mouse models. We further revealed that the anticancer capability of glipizide is not attributed to its antiproliferative effects, which are not significant against various human cancer cell lines. To investigate whether its anticancer efficacy is associated with the glucose level alteration induced by glipizide application, glimepiride, another medium to long-acting sulfonylurea antidiabetic drug in the same class, was employed for the comparison studies in the same fashion. Interestingly, glimepiride has demonstrated no significant impact on the tumor growth and metastasis, indicating that the anticancer effects of glipizide is not ascribed to its antidiabetic properties. Furthermore, glipizide suppresses endothelial cell migration and the formation of tubular structures, thereby inhibiting angiogenesis by up-regulating the expression of natriuretic peptide receptor A. These findings uncover a novel mechanism of glipizide as a potential cancer therapy, and also for the first time, provide direct evidence to support that treatment with glipizide may reduce the cancer risk for diabetic patients.

Recent advances in the use of metformin: can treating diabetes prevent breast cancer?

There is substantial epidemiological evidence pointing to an increased incidence of breast cancer and morbidity in obese, prediabetic, and diabetic patients. In vitro studies strongly support metformin, a diabetic medication, in breast cancer therapy. Although metformin has been heralded as an exciting new breast cancer treatment, the principal consideration is whether metformin can be used as a generic treatment for all breast cancer types. Importantly, will metformin be useful as an inexpensive therapy for patients with comorbidity of diabetes and breast cancer? In general, meta-analyses of clinical trial data from retrospective studies in which metformin treatment has been used for patients with diabetes and breast cancer have a positive trend; nevertheless, the supporting clinical data outcomes remain inconclusive. The heterogeneity of breast cancer, confounded by comorbidity of disease in the elderly population, makes it difficult to determine the actual benefits of metformin therapy. Despite the questionable evidence available from observational clinical studies and meta-analyses, randomized phases I-III clinical trials are ongoing to test the efficacy of metformin for breast cancer. This special issue review will focus on recent research, highlighting in vitro research and retrospective observational clinical studies and current clinical trials on metformin action in breast cancer.

microRNAs and cancer metabolism reprogramming: the paradigm of metformin

Increasing evidence witnesses that cancer metabolism alterations represent a critical hallmark for many types of human tumors. There is a strong need to understand and dissect the molecular mechanisms underlying cancer metabolism to envisage specific biomarkers and underpin critical molecular components that might represent novel therapeutic targets. One challenge, that is the focus of this review, is the reprogramming of the altered metabolism of a cancer cell toward that of un-transformed cell. The anti-hyperglicemic agent, metformin has proven to be effective in reprogramming the metabolism of cancer cells even from those subpopulations endowed with cancer stem like features and very high chemoresistenace to conventional anticancer treatments. A functional interplay involving selective modulation of microRNAs (miRNAs) takes place along the anticancer metabolic effects exerted by metformin. The implications of this interplay will be also discussed in this review.