Metabolic Plasticity as a Determinant of Tumor Growth and Metastasis

Exosome-mediated metabolic reprogramming: the emerging role in tumor microenvironment remodeling and its influence on cancer progression

Metabolic reprogramming is reported to be one of the hallmarks of cancer, which is an adaptive mechanism by which fast-growing cancer cells adapt to their increasing energy demands. Recently, extracellular vesicles (EVs) known as exosomes have been recognized as crucial signaling mediators in regulating the tumor microenvironment (TME). Meanwhile, the TME is a highly heterogeneous ecosystem incorporating cancer cells, fibroblasts, adipocytes, endothelial cells, mesenchymal stem cells, and extracellular matrix. Accumulated evidence indicates that exosomes may transfer biologically functional molecules to the recipient cells, which facilitate cancer progression, angiogenesis, metastasis, drug resistance, and immunosuppression by reprogramming the metabolism of cancer cells and their surrounding stromal cells. In this review, we present the role of exosomes in the TME and the underlying mechanism of how exosomes exacerbate tumor development through metabolic reprogramming. In addition, we will also discuss the potential role of exosomes targeting metabolic process as biomarkers for tumor diagnosis and prognosis, and exosomes-mediated metabolic reprogramming as potential targets for cancer therapy. Furthermore, a better understanding of the link between exosomes and metabolic reprogramming, and their impact on cancer progression, would provide novel insights for cancer prevention and treatment in the future.

Dietary fats suppress the peritoneal seeding of colorectal cancer cells through the TLR4/Cxcl10 axis in adipose tissue macrophages

Peritoneal carcinomatosis (PC) of colorectal cancer (CRC) is a terminal phase of malignancy with no effective strategies for the prevention of this condition. Here we established PC models in mice by intraperitoneal engraftment of CRC cells and revealed an unexpected role for a high-fat diet (HFD) in preventing metastatic seeding in the visceral fat. Mechanistically, the HFD stimulated the activation of adipose tissue macrophages (ATMs) toward an M1-like phenotype and enhanced ATM tumor phagocytosis in a TLR4-dependent manner. Furthermore, the TLR4–Cxcl10 axis in ATMs promoted T cell recruitment, and M1-like macrophages stimulated T cell activation in tumor-seeded fats. The inhibitory effect of the HFD on tumor seeding was abolished with the ablation of macrophages, inactivation of T cells, or blockade of the TLR4–Cxcl10 axis in macrophages. Finally, we showed that a HFD and conventional chemotherapeutic agents (oxaliplatin or 5-fluorouracil) synergistically improved the survival of tumor-seeded mice. Collectively, our findings demonstrate that peritoneal seeding of CRC can be suppressed by short-term treatment with a HFD in the early phase, providing a novel concept for the management of these patients in the clinic.

Mitochondrial ROS1 Increases Mitochondrial Fission and Respiration in Oral Squamous Cancer Carcinoma

Simple Summary

The clinical efficacy of anti-epidermal growth factor receptor (EGFR) antibody cetuximab for oral squamous cell carcinomas (OSCCs) is low. We previously reported that an increased oncogenic ROS proto-oncogene 1 (ROS1) is responsible for the invasiveness and metastasis of OSCC. This study demonstrates for the first time that ROS1, a receptor tyrosine kinase, can localize to mitochondria. Mitochondrial ROS1 in the highly invasive OSCC promotes mitochondrial fission, enhances mitochondrial oxidative phosphorylation and ATP production but reduces mitochondrial biogenesis. These findings highlight the novel function of ROS1 in mitochondrial morphogenesis and metabolic adaptation to promote OSCC invasiveness.

Abstract

Increased ROS proto-oncogene 1 (ROS1) expression has been implicated in the invasiveness of human oral squamous cell carcinoma (OSCC). The cellular distribution of ROS1 has long-been assumed at the plasma membrane. However, a previous work reported a differential cellular distribution of mutant ROS1 derived from chromosomal translocation, resulting in increased carcinogenesis. We thus hypothesized that cellular distribution of upregulated ROS1 in OSCC may correlate with invasiveness. We found that ROS1 can localize to mitochondria in the highly invasive OSCC and identified a mitochondria-targeting signal sequence in ROS1. We also demonstrated that ROS1 targeting to mitochondria is required for mitochondrial fission phenotype in the highly invasive OSCC cells. OSCC cells expressing high levels of ROS1 consumed more oxygen and had increased levels of cellular ATP levels. Our results also revealed that ROS1 regulates mitochondrial biogenesis and cellular metabolic plasticity. Together, these findings demonstrate that ROS1 targeting to mitochondria enhances OSCC invasion through regulating mitochondrial morphogenesis and cellular respiratory.

The Metabolic Heterogeneity and Flexibility of Cancer Stem Cells

Simple Summary

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

Abstract

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

Metabolic Rewiring in Response to Biguanides Is Mediated by mROS/HIF-1a in Malignant Lymphocytes

Metabolic flexibility allows cells to adapt to various environments and limits the efficacy of metabolic drugs. Therapeutic targeting of cancer metabolism relies on defining limiting requirements and vulnerabilities in the highly dynamic metabolic network. Here, we characterize the metabolic reprogramming and identify cancer-specific metabolic vulnerabilities in response to the pharmacological inhibition of mitochondrial complex I. Our work reveals the adaptation mechanism in malignant lymphocytes providing resistance against the biguanides phenformin and metformin by transcriptionally reprogramming glucose metabolism. Metabolic adaptation to complex I inhibition is mediated by mitochondrial reactive oxygen species (mROS) serving as a mitochondrial stress signal activating hypoxia-inducible factor-1a (HIF-1a). Inhibition of the mROS/HIF-1a axis through antioxidants or direct suppression of HIF-1a selectively disrupts metabolic adaptation and survival during complex I dysfunction in malignant lymphocytes. Our results identify HIF-1a signaling as a critical factor in resistance against biguanide-induced mitochondrial dysfunction, allowing selective targeting of metabolic pathways in leukemia and lymphoma.

Manipulation of Mitochondrial Plasticity Changes the Metabolic Competition Between "Foe" and "Friend" During Tumor Malignant Transformation

Mitochondria as the cellular energy powerhouses provide a common site for multiple metabolic reactions in order to cover energy and biomolecule demands, thus integrating the diverse metabolic pathways to endow cells with metabolic adaptation. Mitochondrial plasticity is normally regulated by mitochondrial dynamics, mitochondrial metabolism and mitochondrial biogenesis. Given that tumor cells and T cells share the metabolic similarities of survival, proliferation, expansion as well as effector function, manipulation of mitochondrial plasticity would change the metabolic competition between “foe” and “friend” during tumor malignant progression. On the one hand, for “foe” tumor cells, mitochondrial plasticity provides the enhancement of tumor metastasis and the development of resistance to‘ diverse antitumor drugs. On the other hand, for “friend” T cells, mitochondrial plasticity promotes the generation of long-term memory T (T_M) cells and alleviates the exhaustion of tumor-infiltrating lymphocytes (TILs). Therefore, downregulation of mitochondrial plasticity of tumor cells through engineering tumor-targeting nanoparticles may effectively potentiate metabolic vulnerability and re-sensitize tumor to relevant therapeutic treatment. On the contrary, upregulation of mitochondrial plasticity of T cells through optimizing adoptive cellular immunotherapy (ACI) or chimeric antigen receptor (CAR)-T cell therapy would provide T cells with the robust metabolic fitness and the persistent immune function, thus blocking tumor metastasis and reoccurrence.

Exosomal microRNAs: novel players in cervical cancer

Cervical cancer ranks fourth for both mortality and morbidity in women globally. Exosomes are considered as extracellular vesicles, secreted continuously by many cells with a size range from 30 to 150 nm. Exosomes can encapsulate microRNAs (miRNAs) and release them for cellular communications. This exosome-induced miRNA transfer is a novel strategy for genetic exchange among cells. This trafficking modality affects many pathological as well as physiological conditions. Moreover, exosomes can protect the miRNAs against harsh environments and keep them very stable. Given that a variety of exosomal miRNAs derived from cervical cancer cells can be targeted to recipient cells and contribute to tumorgenesis, it has been documented that exosomal miRNAs could be applied as diagnostic and therapeutic biomarkers in the treatment of cervical cancer. Herein, we summarize the pathologic and diagnostic roles of exosomal miRNAs in the cervical cancer. Moreover, we highlight the roles of exosomal miRNAs in other cancers.

Lung mesenchymal cells elicit lipid storage in neutrophils that fuel breast cancer lung metastasis

Acquisition of a lipid-laden phenotype by immune cells has been defined in infectious diseases and atherosclerosis, but remains largely uncharacterized in cancer. Here, in breast cancer models we found that neutrophils are induced to accumulate neutral lipids upon interaction with resident mesenchymal cells (MCs) in the pre-metastatic lung. Lung MCs elicit this process through repressing the adipose triglyceride lipase (ATGL) activity in neutrophils in prostaglandin E2-dependent and -independent manners. In vivo, neutrophil-specific deletion of genes encoding ATGL or ATGL inhibitory factors altered neutrophil lipid profiles and breast tumor lung metastasis in mice. Mechanistically, lipids stored in lung neutrophils are transported to metastatic tumor cells through a macropinocytosis-lysosome pathway, endowing the tumor cells with augmented survival and proliferative capacities. Pharmacological inhibition of macropinocytosis significantly reduced metastatic colonization by breast tumor cells in vivo. Collectively, our work reveals that neutrophils serve as an energy reservoir to fuel breast cancer lung metastasis.

Role of intracellular water in the normal-to-cancer transition in human cells-insights from quasi-elastic neutron scattering

The transition from normal to malignant state in human cells is still a poorly understood process. Changes in the dynamical activity of intracellular water between healthy and cancerous human cells were probed as an innovative approach for unveiling particular features of malignancy and identifying specific reporters of cancer. Androgen-unresponsive prostate and triple-negative breast carcinomas were studied as well as osteosarcoma, using the technique of quasi-elastic neutron scattering. The cancerous cells showed a considerably higher plasticity relative to their healthy counterparts, this being more significant for the mammary adenocarcinoma. Also, the data evidence that the prostate cancer cells display the highest plasticity when compared to triple-negative mammary cancer and osteosarcoma, the latter being remarkably less flexible. Furthermore, the results suggest differences between the flexibility of different types of intracellular water molecules in normal and cancerous cells, as well as the number of molecules involved in the different modes of motion. The dynamics of hydration water molecules remain virtually unaffected when going from healthy to cancer cells, while cytoplasmic water (particularly the rotational motions) undergoes significant changes upon normal-to-cancer transition. The results obtained along this study can potentially help to understand the variations in cellular dynamics underlying carcinogenesis and tumor metastasis, with an emphasis on intracellular water.

Distribution and prognostic significance of gluconeogenesis and glycolysis in lung cancer

Inhibition of glycolysis has been considered as a therapeutic approach in aggressive cancers including lung cancer. Abbreviated gluconeogenesis, mediated by phosphoenolpyruvate carboxykinase (PEPCK), was recently discovered to partially circumvent the need for glycolysis in lung cancer cells. However, the interplay of glycolysis and gluconeogenesis in lung cancer is still poorly understood. Here, we analyzed the expression of GLUT1, the prime glucose transporter, and of PCK1 and PCK2, the cytoplasmic and mitochondrial isoforms of PEPCK, in 450 samples of non‐small cell lung cancer (NSCLC) and in 54 NSCLC metastases using tissue microarrays and whole tumor sections. Spatial distribution was assessed by automated image analysis. Additionally, glycolytic and gluconeogenic gene expression was inferred from The Cancer Genome Atlas (TCGA) datasets. We found that PCK2 was preferentially expressed in the lung adenocarcinoma subtype, while GLUT1 expression was higher in squamous cell carcinoma. GLUT1 and PCK2 were inversely correlated, GLUT1 showing elevated expression in larger tumors while PCK2 was highest in smaller tumors. However, a mixed phenotype showing the presence of both, glycolytic and gluconeogenic cancer cells was frequent. In lung adenocarcinoma, PCK2 expression was associated with significantly improved overall survival, while the opposite was found for GLUT1. The metabolic tumor microenvironment and the 3‐dimensional context play an important role in modulating both pathways, since PCK2 expression preferentially occurred at the tumor margin and hypoxia regulated both, glycolysis and gluconeogenesis, in NSCLC cells in vitro, albeit in opposite directions. PCK1/2 expression was enhanced in metastases compared to primary tumors, possibly related to the different environment. The results of this study show that glycolysis and gluconeogenesis are activated in NSCLC in a tumor size and oxygenation modulated manner and differentially correlate with outcome. The frequent co‐activation of gluconeogenesis and glycolysis in NSCLC should be considered in potential future therapeutic strategies targeting cancer cell metabolism.

Metabolic Remodeling Induced by Adipocytes: A New Achilles' Heel in Invasive Breast Cancer?

Metabolic reprogramming represents an important hallmark of cancer cells. Besides de novo fatty acid synthesis, it is now clear that cancer cells can acquire Fatty Acids (FA) from tumor-surrounding adipocytes to increase their invasive capacities. Indeed, adipocytes release FA in response to tumor secreted factors that are transferred to tumor cells to be either stored as triglycerides and other complex lipids or oxidized in mitochondria. Like all cells, FA can be released over time from triglyceride stores through lipolysis and then oxidized in mitochondria in cancer cells. This metabolic interaction results in specific metabolic remodeling in cancer cells, and underpins adipocyte stimulated tumor progression. Lipolysis and fatty acid oxidation therefore represent novel targets of interest in the treatment of cancer. In this review, we summarize the recent advances in our understanding of the metabolic reprogramming induced by adipocytes, with a focus on breast cancer. Then, we recapitulate recent reports studying the effect of lipolysis and fatty acid oxidation inhibitors on tumor cells and discuss the interest to target these metabolic pathways as new therapeutic approaches for cancer.

UCP2 Deficiency Increases Colon Tumorigenesis by Promoting Lipid Synthesis and Depleting NADPH for Antioxidant Defenses

Colorectal cancer (CRC) is associated with metabolic and redox perturbation. The mitochondrial transporter uncoupling protein 2 (UCP2) controls cell proliferation in vitro through the modulation of cellular metabolism, but the underlying mechanism in tumors in vivo remains unexplored. Using murine intestinal cancer models and CRC patient samples, we find higher UCP2 protein levels in tumors compared to their non-tumoral counterparts. We reveal the tumor-suppressive role of UCP2 as its deletion enhances colon and small intestinal tumorigenesis in AOM/DSS-treated and Apc^Min/+ mice, respectively, and correlates with poor survival in the latter model. Mechanistically, UCP2 loss increases levels of oxidized glutathione and proteins in tumors. UCP2 deficiency alters glycolytic pathways while promoting phospholipid synthesis, thereby limiting the availability of NADPH for buffering oxidative stress. We show that UCP2 loss renders colon cells more prone to malignant transformation through metabolic reprogramming and perturbation of redox homeostasis and could favor worse outcomes in CRC.

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UCP2 protein expression, but not mRNA, is increased in CRC in both mice and humans

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UCP2 loss promotes AOM/DSS-induced CAC and Apc^Min-dependent intestinal cancer

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UCP2 loss-induced oxidative stress contributes to increased colon tumorigenesis

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UCP2 deficiency drives an imbalance between lipid metabolism and NADPH homeostasis

GLUT1 inhibition blocks growth of RB1-positive triple negative breast cancer

Triple negative breast cancer (TNBC) is a deadly form of breast cancer due to the development of resistance to chemotherapy affecting over 30% of patients. New therapeutics and companion biomarkers are urgently needed. Recognizing the elevated expression of glucose transporter 1 (GLUT1, encoded by SLC2A1) and associated metabolic dependencies in TNBC, we investigated the vulnerability of TNBC cell lines and patient-derived samples to GLUT1 inhibition. We report that genetic or pharmacological inhibition of GLUT1 with BAY-876 impairs the growth of a subset of TNBC cells displaying high glycolytic and lower oxidative phosphorylation (OXPHOS) rates. Pathway enrichment analysis of gene expression data suggests that the functionality of the E2F pathway may reflect to some extent OXPHOS activity. Furthermore, the protein levels of retinoblastoma tumor suppressor (RB1) strongly correlate with the degree of sensitivity to GLUT1 inhibition in TNBC, where RB1-negative cells are insensitive to GLUT1 inhibition. Collectively, our results highlight a strong and targetable RB1-GLUT1 metabolic axis in TNBC and warrant clinical evaluation of GLUT1 inhibition in TNBC patients stratified according to RB1 protein expression levels.

In situ Metabolic Profiling of Ovarian Cancer Tumor Xenografts: A Digital Pathology Approach

Metabolic profiling of cancer is a rising interest in the field of biomarker development. One bottleneck of its clinical exploitation, however, is the lack of simple and quantitative techniques that enable to capture the key metabolic traits of tumor from archival samples. In fact, liquid chromatography associated with mass spectrometry is the gold-standard technique for the study of tumor metabolism because it has high levels of accuracy and precision. However, it requires freshly frozen samples, which are difficult to collect in large multi-centric clinical studies. For this reason, we propose here to investigate a set of established metabolism-associated protein markers by exploiting immunohistochemistry coupled with digital pathology. As case study, we quantified expression of MCT1, MCT4, GLS, PHGDH, FAS, and ACC in 17 patient-derived ovarian cancer xenografts and correlated it with survival. Among these markers, the glycolysis-associated marker MCT4 was negatively associated with survival of mice. The algorithm enabling a quantitative analysis of these metabolism-associated markers is an innovative research tool that can be exported to large sets of clinical samples and can remove the variability of individual interpretation of immunohistochemistry results.

Neutrophils: Orchestrators of the Malignant Phenotype

Neutrophils are the first leukocytes recruited to sites of inflammation, where they execute anti-microbial functions to eliminate infectious agents. These functions include phagocytosis, release of reactive oxygen species and the formation of neutrophil extracellular traps via NETosis. Neutrophils are receiving increasing attention in the context of cancer, where these same neutrophil-associated functions are also important for modulating tumor growth and metastatic progression. Neutrophils are phenotypically heterogeneous and, depending on the context, exert anti- or pro-tumorigenic functions. Increasing evidence also suggests an important role of neutrophils and their involvement in promoting multiple steps of the metastatic cascade. The steps include: (1) local invasion and intravasation of cancer cells into circulation, (2) survival of cancer cells in the bloodstream and extravasation at a distant site, (3) early cancer cell seeding/survival, and (4) progressive growth of cancer cells to form macroscopic metastases. Although neutrophil functions designed to eliminate infectious agents can also eliminate tumor cells, their dysregulation can promote tumor growth and enable metastasis at multiple steps along the metastatic cascade. In this review, we will provide an overview of the current advances in neutrophil biology in the context of cancer. We also discuss the emerging field of immunometabolism, in which the rewiring of alternative metabolic pathways within neutrophils can impact their pro-tumorigenic/pro-metastatic functions.

Small Extracellular Vesicle Regulation of Mitochondrial Dynamics Reprograms a Hypoxic Tumor Microenvironment

The crosstalk between tumor cells and the adjacent normal epithelium contributes to cancer progression, but its regulators have remained elusive. Here, we show that breast cancer cells maintained in hypoxia release small extracellular vesicles (sEVs) that activate mitochondrial dynamics, stimulate mitochondrial movements, and promote organelle accumulation at the cortical cytoskeleton in normal mammary epithelial cells. This results in AKT serine/threonine kinase (Akt) activation, membrane focal adhesion turnover, and increased epithelial cell migration. RNA sequencing profiling identified integrin-linked kinase (ILK) as the most upregulated pathway in sEV-treated epithelial cells, and genetic or pharmacologic targeting of ILK reversed mitochondrial reprogramming and suppressed sEV-induced cell movements. In a three-dimensional (3D) model of mammary gland morphogenesis, sEV treatment induced hallmarks of malignant transformation, with deregulated cell death and/or cell proliferation, loss of apical-basal polarity, and appearance of epithelial-to-mesenchymal transition (EMT) markers. Therefore, sEVs released by hypoxic breast cancer cells reprogram mitochondrial dynamics and induce oncogenic changes in a normal mammary epithelium.

The mitophagy effector FUNDC1 controls mitochondrial reprogramming and cellular plasticity in cancer cells

Mitochondria are signaling hubs in eukaryotic cells. Here, we showed that the mitochondrial FUN14 domain-containing protein-1 (FUNDC1), an effector of Parkin-independent mitophagy, also participates in cellular plasticity by sustaining oxidative bioenergetics, buffering ROS production, and supporting cell proliferation. Targeting this pathway in cancer cells suppressed tumor growth but rendered transformed cells more motile and invasive in a manner dependent on ROS-mediated mitochondrial dynamics and mitochondrial repositioning to the cortical cytoskeleton. Global metabolomics and proteomics profiling identified a FUNDC1 interactome at the mitochondrial inner membrane, comprising the AAA+ protease, LonP1, and subunits of oxidative phosphorylation, complex V (ATP synthase). Independently of its previously identified role in mitophagy, FUNDC1 enabled LonP1 proteostasis, which in turn preserved complex V function and decreased ROS generation. Therefore, mitochondrial reprogramming by a FUNDC1-LonP1 axis controls tumor cell plasticity by switching between proliferative and invasive states in cancer.

Associations between the Nrf2/Keap1 pathway and mitochondrial functions in colorectal cancer are affected by metastasis

BACKGROUND

Both mitochondria and the Nrf2/Keap1 pathway are targets of cancer therapy. Reactive oxygen species released from mitochondria can activate Nrf2, and the Nrf2/Keap1 pathway affects glycolysis, oxidative phosphorylation, mitochondrial biogenesis and mitophagy.

OBJECTIVE

This study investigates the associations between the expressions of proteins in the Nrf2/Keap1 pathway and those related to mitochondrial function and glycolysis in colorectal cancer (CRC) with or without metastasis.

METHODS

The protein levels of HO1, Nrf2, Keap1, Bach1, p21, p62, NRF1, LC3, ATP5B, HSP60 and GAPDH in the normal and tumor tissues of 60 CRC subjects were determined by Western blot.

RESULTS

The Keap1 protein levels, the ATP5B/HSP60 ratio and the BEC index were higher in the tumor than in the normal tissues of CRC with or without metastasis. The following clusters were found in the dendrogram: Nrf2 and p21 with ATP5B and GADPH in all the tissues and with NRF1 in all except the tumor tissues with metastasis; Bach1 with ATP5B and GAPDH in the tumor tissues; Keap1 with p62 in all the tissues, with LC3 in the tumor tissues and with NRF1 and HO1 in the tumor tissues with metastasis.

CONCLUSIONS

Nrf2, Keap1, Bach1 and p21 have the association with the proteins related to mitochondrial functions different among the tissues of CRC with or without metastasis.

Role of Mitochondrial Glycerol-3-Phosphate Dehydrogenase in Metabolic Adaptations of Prostate Cancer

Prostate cancer is one of the most prominent cancers diagnosed in males. Contrasting with other cancer types, glucose utilization is not increased in prostate carcinoma cells as they employ different metabolic adaptations involving mitochondria as a source of energy and intermediates required for rapid cell growth. In this regard, prostate cancer cells were associated with higher activity of mitochondrial glycerol-3-phosphate dehydrogenase (mGPDH), the key rate limiting component of the glycerophosphate shuttle, which connects mitochondrial and cytosolic processes and plays significant role in cellular bioenergetics. Our research focused on the role of mGPDH biogenesis and regulation in prostate cancer compared to healthy cells. We show that the 42 amino acid presequence is cleaved from N-terminus during mGPDH biogenesis. Only the processed form is part of the mGPDH dimer that is the prominent functional enzyme entity. We demonstrate that mGPDH overexpression enhances the wound healing ability in prostate cancer cells. As mGPDH is at the crossroad of glycolysis, lipogenesis and oxidative metabolism, regulation of its activity by intramitochondrial processing might represent rapid means of cellular metabolic adaptations.

Fibroblast Reprogramming in Gastrointestinal Cancer

Gastrointestinal cancers are a significant cause of cancer mortality worldwide and have been strongly linked with chronic inflammation. Current therapies focus on epithelial/cancer cells; however, the importance of the tumor microenvironment in the development and treatment of the disease is also now well established. Cancer-associated fibroblasts (CAFs) are a major component of the tumor microenvironment, and are actively participating in tumor initiation, promotion and metastasis. They structurally and functionally affect cancer cell proliferation, tumor immunity, angiogenesis, extracellular matrix remodeling and metastasis through a variety of signaling pathways. CAFs originate predominantly from resident mesenchymal cells, which are activated and reprogrammed in response to cues from cancer cells. In recent years, chronic inflammation of the gastrointestinal tract has also proven an important driver of mesenchymal cell activation and subsequent CAF development, which in turn are capable of regulating the transition from acute to chronic inflammation and cancer. In this review, we will provide a concise overview of the mechanisms that drive fibroblast reprogramming in cancer and the recent advances on the downstream signaling pathways that regulate the functional properties of the activated mesenchyme. This new mechanistic insight could pave the way for new therapeutic strategies and better prognosis for cancer patients.

Metabolism in the Tumor Microenvironment

From a general perspective, in the context of solid tumors, we can distinguish metabolic alterations of cancer cells from those of the stroma. These two components interact with each other and with the extracellular matrix (ECM), and these interactions can take the form of either metabolic competition or metabolic symbiosis. The aim of this chapter is to overview the canonical metabolic alterations of tumor and stroma cells and to present specific examples of metabolic competition and symbiosis. We will also discuss the complexity and plasticity of metabolism, which pose indeed a serious threat to our ability to target selective metabolic features of tumor microenvironment with drugs. Finally, we will highlight some limitations of state-of-the-art techniques used to study tumor metabolism and propose some innovative solutions to investigate the clinical relevance of metabolic alterations for patient management and treatment.

Cancer Cells Don't Live Alone: Metabolic Communication within Tumor Microenvironments

Solid tumors reside in harsh tumor microenvironments (TMEs) together with various stromal cell types. During tumor progression and metastasis, both tumor and stromal cells undergo rapid metabolic adaptations. Tumor cells metabolically coordinate or compete with their "neighbors" to maintain biosynthetic and bioenergetic demands while escaping immunosurveillance or therapeutic interventions. Here, we provide an update on metabolic communication between tumor cells and heterogeneous stromal components in primary and metastatic TMEs and discuss emerging strategies to target metabolic communications for improved cancer treatments.

Metformin induces a fasting- and antifolate-mimicking modification of systemic host metabolism in breast cancer patients

Certain dietary interventions might improve the therapeutic index of cancer treatments. An alternative to the “drug plus diet” approach is the pharmacological reproduction of the metabolic traits of such diets. Here we explored the impact of adding metformin to an established therapeutic regimen on the systemic host metabolism of cancer patients. A panel of 11 serum metabolites including markers of mitochondrial function and intermediates/products of folate-dependent one-carbon metabolism were measured in paired baseline and post-treatment sera obtained from HER2-positive breast cancer patients randomized to receive either metformin combined with neoadjuvant chemotherapy and trastuzumab or an equivalent regimen without metformin. Metabolite profiles revealed a significant increase of the ketone body β-hydroxybutyrate and of the TCA intermediate α-ketoglutarate in the metformin-containing arm. A significant relationship was found between the follow-up levels of homocysteine and the ability of treatment arms to achieve a pathological complete response (pCR). In the metformin-containing arm, patients with significant elevations of homocysteine tended to have a higher probability of pCR. The addition of metformin to an established anti-cancer therapeutic regimen causes a fasting-mimicking modification of systemic host metabolism. Circulating homocysteine could be explored as a clinical pharmacodynamic biomarker linking the antifolate-like activity of metformin and biological tumor response.

A Potential Role of YAP/TAZ in the Interplay Between Metastasis and Metabolic Alterations

Yes-Associated Protein (YAP) and Transcriptional Co-activator with PDZ-binding Motif (TAZ) are the downstream effectors of the Hippo signaling pathway that play a crucial role in various aspects of cancer progression including metastasis. Metastasis is the multistep process of disseminating cancer cells in a body and responsible for the majority of cancer-related death. Emerging evidence has shown that cancer cells reprogram their metabolism to gain proliferation, invasion, migration, and anti-apoptotic abilities and adapt to various environment during metastasis. Moreover, it has increasingly been recognized that YAP/TAZ regulates cellular metabolism that is associated with the phenotypic changes, and recent studies suggest that the YAP/TAZ-mediated metabolic alterations contribute to metastasis. In this review, we will introduce the latest knowledge of YAP/TAZ regulation and function in cancer metastasis and metabolism, and discuss possible links between the YAP/TAZ-mediated metabolic reprogramming and metastasis.

Metabolic Escape Routes of Cancer Stem Cells and Therapeutic Opportunities

Although improvement in early diagnosis and treatment ameliorated life expectancy of cancer patients, metastatic disease still lacks effective therapeutic approaches. Resistance to anticancer therapies stems from the refractoriness of a subpopulation of cancer cells-termed cancer stem cells (CSCs)-which is endowed with tumor initiation and metastasis formation potential. CSCs are heterogeneous and diverge by phenotypic, functional and metabolic perspectives. Intrinsic as well as extrinsic stimuli dictated by the tumor microenvironment (TME)have critical roles in determining cell metabolic reprogramming from glycolytic toward an oxidative phenotype and vice versa, allowing cancer cells to thrive in adverse milieus. Crosstalk between cancer cells and the surrounding microenvironment occurs through the interchange of metabolites, miRNAs and exosomes that drive cancer cells metabolic adaptation. Herein, we identify the metabolic nodes of CSCs and discuss the latest advances in targeting metabolic demands of both CSCs and stromal cells with the scope of improving current therapies and preventing cancer progression.

Non-Coding RNAs Operate in the Crosstalk Between Cancer Metabolic Reprogramming and Metastasis

Metastasis, the spread of cancer cells from a primary tumor to a secondary site, represents one of the hallmarks of malignancies and the leading cause of cancer-related death. The process of metastasis is a result of the interaction of genetic heterogeneity, abnormal metabolism, and tumor microenvironments. On the other hand, metabolic reprogramming, another malignancy hallmark, refers to the ability of cancer cells to alter metabolic and nutrient acquisition modes in order to support the energy demands for accomplishing the rapid growth, dissemination, and colonization. Cancer cells remodel metabolic patterns to supplement nutrients for their metastasis and also undergo metabolic adjustments at different stages of metastasis. Genes and signaling pathways involved in tumor metabolic reprogramming crosstalk with those participating in metastasis. Non-coding RNAs are a group of RNA molecules that do not code proteins but have pivotal biological functions. Some of microRNAs and lncRNAs, which are the two most extensively studied non-coding RNAs, have been identified to participate in regulating metabolic remodeling of glucose, lipid, glutamine, oxidative phosphorylation, and mitochondrial respiration, as well as the process of metastasis involving cell motility, transit in the circulation and growth at a new site. This article reviews recent progress on non-coding RNAs operating in the crosstalk between tumor metabolic reprogramming and metastasis, particularly those influencing metastasis through regulating metabolism, and the underlying mechanisms of how they exert their regulatory functions.

Progression-Dependent Altered Metabolism in Osteosarcoma Resulting in Different Nutrient Source Dependencies

Osteosarcoma (OS) is a primary malignant bone tumor and OS metastases are mostly found in the lung. The limited understanding of the biology of metastatic processes in OS limits the ability for effective treatment. Alterations to the metabolome and its transformation during metastasis aids the understanding of the mechanism and provides information on treatment and prognosis. The current study intended to identify metabolic alterations during OS progression by using a targeted gas chromatography mass spectrometry approach. Using a female OS cell line model, malignant and metastatic cells increased their energy metabolism compared to benign OS cells. The metastatic cell line showed a faster metabolic flux compared to the malignant cell line, leading to reduced metabolite pools. However, inhibiting both glycolysis and glutaminolysis resulted in a reduced proliferation. In contrast, malignant but non-metastatic OS cells showed a resistance to glycolytic inhibition but a strong dependency on glutamine as an energy source. Our in vivo metabolic approach hinted at a potential sex-dependent metabolic alteration in OS patients with lung metastases (LM), although this will require validation with larger sample sizes. In line with the in vitro results, we found that female LM patients showed a decreased central carbon metabolism compared to metastases from male patients.

Identifying inhibitors of epithelial-mesenchymal plasticity using a network topology-based approach

Metastasis is the cause of over 90% of cancer-related deaths. Cancer cells undergoing metastasis can switch dynamically between different phenotypes, enabling them to adapt to harsh challenges, such as overcoming anoikis and evading immune response. This ability, known as phenotypic plasticity, is crucial for the survival of cancer cells during metastasis, as well as acquiring therapy resistance. Various biochemical networks have been identified to contribute to phenotypic plasticity, but how plasticity emerges from the dynamics of these networks remains elusive. Here, we investigated the dynamics of various regulatory networks implicated in Epithelial–mesenchymal plasticity (EMP)—an important arm of phenotypic plasticity—through two different mathematical modelling frameworks: a discrete, parameter-independent framework (Boolean) and a continuous, parameter-agnostic modelling framework (RACIPE). Results from either framework in terms of phenotypic distributions obtained from a given EMP network are qualitatively similar and suggest that these networks are multi-stable and can give rise to phenotypic plasticity. Neither method requires specific kinetic parameters, thus our results emphasize that EMP can emerge through these networks over a wide range of parameter sets, elucidating the importance of network topology in enabling phenotypic plasticity. Furthermore, we show that the ability to exhibit phenotypic plasticity correlates positively with the number of positive feedback loops in a given network. These results pave a way toward an unorthodox network topology-based approach to identify crucial links in a given EMP network that can reduce phenotypic plasticity and possibly inhibit metastasis—by reducing the number of positive feedback loops.

An acylhydroquinone derivative produces OXPHOS uncoupling and sensitization to BH3 mimetic ABT-199 (Venetoclax) in human promyelocytic leukemia cells

Since cancer cells have different mitochondrial bioenergetic requirements than non-cancerous cells, therapeutic inhibition of its mitochondrial functionality continues to be an important target for anticancer drug discovery. In this study, a series of acylhydroquinones with different acyl-chain length, and their chlorinated derivatives, in the aromatic ring, synthesized by Fries rearrangement under microwave irradiation, were evaluated for their anticancer activity in two leukemia cell lines. Findings from the primary and secondary screening of the 18 acylhydroquinones, tested at 5 µM on acute promyelocytic leukemia HL-60 and acute lymphoblastic leukemia CEM cells lines, identified an acylchlorohydroquinone (12) with a highly selective anti-proliferative effect toward HL-60 cells. This compound induced S-phase arrest in the cell cycle progression of HL-60 cells with insignificant toxicity on leukemic CEM cells and non-cancerous Hs27 cells. In HL-60 leukemic cells, 12 triggered increased mitochondrial NADH oxidation, increased respiration in presence of oligomycin (state 4o), mitochondrial depolarization, and ROS production, suggesting an uncoupling of OXPHOS. This provoked a metabolic adaptation dependent on AMPK/ACC/autophagy axis, having the mitochondrial β-oxidation a pro-survival role since the combination of 12 and etomoxir, a carnitine palmitoyl-transferase (CPT) inhibitor promoted extensive HL-60 cell death. Finally, 12-induced metabolic stress sensitized to HL-60 cells to cell death by the FDA-approved anti-leukemic drug ABT-199, a BH3 mimetic. Therefore, our results suggest that acylchlorohydroquinone is a promising scaffold in anti-promyelocytic leukemia drug research.

STIM1 is a metabolic checkpoint regulating the invasion and metastasis of hepatocellular carcinoma

Background: Cancer cells undergoing invasion and metastasis possess a phenotype with attenuated glycolysis, but enhanced fatty acid oxidation (FAO). Calcium (Ca²⁺)-mediated signaling pathways are implicated in tumor metastasis and metabolism regulation. Stromal-interaction molecule 1 (STIM1) triggered store-operated Ca²⁺ entry (SOCE) is the major route of Ca²⁺ influx for non-excitable cells including hepatocellular carcinoma (HCC) cells. However, whether and how STIM1 regulates the invasion and metastasis of HCC via metabolic reprogramming is unclear.

Methods: The expressions of STIM1 and Snail1 in the HCC tissues and cells were measured by immunohistochemistry, Western-blotting and quantitative PCR. STIM1 knockout-HCC cells were generated by CRISPR-Cas9, and gene-overexpression was mediated via lentivirus transfection. Besides, the invasive and metastatic activities of HCC cells were assessed by transwell assay, anoikis rate in vitro and lung metastasis in vivo. Seahorse energy analysis and micro-array were used to evaluate the glucose and lipid metabolism.

Results: STIM1 was down-regulated in metastatic HCC cells rather than in proliferating HCC cells, and low STIM1 levels were associated with poor outcome of HCC patients. During tumor growth, STIM1 stabilized Snail1 protein by activating the CaMKII/AKT/GSK-3β pathway. Subsequently, the upregulated Snail1 suppressed STIM1/SOCE during metastasis. STIM1 restoration significantly diminished anoikis-resistance and metastasis induced by Snail1. Mechanistically, the downregulated STIM1 shifted the anabolic/catabolic balance, i.e., from aerobic glycolysis towards AMPK-activated fatty acid oxidation (FAO), which contributed to Snail1-driven metastasis and anoikis-resistance.

Conclusions: Our data provide the molecular basis that STIM1 orchestrates invasion and metastasis via reprogramming HCC metabolism.

Cancer Stem Cell Plasticity - A Deadly Deal

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

Uncovering the Underlying Mechanisms of Cancer Metabolism through the Landscapes and Probability Flux Quantifications

Cancer metabolism is critical for understanding the mechanism of tumorigenesis, yet the understanding is still challenging. We studied gene-metabolism regulatory interactions and quantified the global driving forces for cancer-metabolism dynamics as the underlying landscape and probability flux. We uncovered four steady-state attractors: a normal state attractor, a cancer OXPHOS state attractor, a cancer glycolysis state attractor, and an intermediate cancer state attractor. We identified the key regulatory interactions through global sensitivity analysis based on the landscape topography. Different landscape topographies of glycolysis switch between normal cells and cancer cells were identified. We uncovered that the normal state to cancer state transformation is associated with the peaks of the probability flux and the thermodynamic dissipation, giving dynamical and thermodynamic origin of cancer formation. We found that cancer metabolism oscillations consume more energy to support cancer malignancy. This study provides a quantitative understanding of cancer metabolism and suggests a metabolic therapeutic strategy.

Non-Coding RNAs in Lung Tumor Initiation and Progression

Lung cancer is one of the deadliest forms of cancer affecting society today. Non-coding RNAs, such as microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), through the transcriptional, post-transcriptional, and epigenetic changes they impose, have been found to be dysregulated to affect lung cancer tumorigenesis and metastasis. This review will briefly summarize hallmarks involved in lung cancer initiation and progression. For initiation, these hallmarks include tumor initiating cells, immortalization, activation of oncogenes and inactivation of tumor suppressors. Hallmarks involved in lung cancer progression include metastasis and drug tolerance and resistance. The targeting of these hallmarks with non-coding RNAs can affect vital metabolic and cell signaling pathways, which as a result can potentially have a role in cancerous and pathological processes. By further understanding non-coding RNAs, researchers can work towards diagnoses and treatments to improve early detection and clinical response.

Effects of folic acid withdrawal on transcriptomic profiles in murine triple-negative breast cancer cell lines

We have previously shown that withdrawal of folic acid led to metabolic reprogramming and a less aggressive phenotype in a mouse cell model of triple-negative breast cancer (TNBC). Herein, we evaluate the effects of folic acid withdrawal on transcriptomic profiles in these cells. Murine cell lines were originally derived from a pool of spontaneous mammary tumors grown in MMTV-Wnt1 transgenic mice. Based on their differential molecular characteristics and metastatic potential, these cell lines were previously characterized as non-metastatic epithelial (E-Wnt), non-metastatic mesenchymal (M-Wnt) and metastatic mesenchymal (metM-Wnt^liver) cells. Using custom two-color 180K Agilent microarrays, we have determined gene expression profiles for three biological replicates of each subtype kept on standard medium (2.2 μM folic acid) or folic acid-free medium for 72 h. The analyses revealed that more genes were differentially expressed upon folic acid withdrawal in M-Wnt cells (1884 genes; Benjamini-Hochberg-adjusted P-value <0.05) compared to E-Wnt and metM-Wnt^liver cells (108 and 222 genes, respectively). Pathway analysis has identified that type I interferon signaling was strongly affected by folic acid withdrawal, with interferon-responsive genes consistently being upregulated upon folic acid withdrawal in M-Wnt cells. Of note, repressed interferon signaling has been established as one of the characteristics of aggressive human TNBC, and hence reactivation of this pathway may be a promising therapeutic approach. Overall, while our study indicates that the response to folic acid withdrawal varies by molecular subtype and cellular phenotype, it also underscores the necessity to further investigate one-carbon metabolism as a potential therapeutic means in the treatment of advanced TNBC.

Potent Anticancer Effect of the Natural Steroidal Saponin Gracillin Is Produced by Inhibiting Glycolysis and Oxidative Phosphorylation-Mediated Bioenergetics

Metabolic rewiring to utilize aerobic glycolysis is a hallmark of cancer. However, recent findings suggest the role of mitochondria in energy generation in cancer cells and the metabolic switch to oxidative phosphorylation (OXPHOS) in response to the blockade of glycolysis. We previously demonstrated that the antitumor effect of gracillin occurs through the inhibition of mitochondrial complex II-mediated energy production. Here, we investigated the potential of gracillin as an anticancer agent targeting both glycolysis and OXPHOS in breast and lung cancer cells. Along with the reduction in adenosine triphosphate (ATP) production, gracillin markedly suppresses the production of several glycolysis-associated metabolites. A docking analysis and enzyme assay suggested phosphoglycerate kinase 1 (PGK1) is a potential target for the antiglycolytic effect of gracillin. Gracillin reduced the viability and colony formation ability of breast cancer cells by inducing apoptosis. Gracillin displayed efficacious antitumor effects in mice bearing breast cancer cell line or breast cancer patient-derived tumor xenografts with no overt changes in body weight. An analysis of publicly available datasets further suggested that PGK1 expression is associated with metastasis status and poor prognosis in patients with breast cancer. These results suggest that gracillin is a natural anticancer agent that inhibits both glycolysis and mitochondria-mediated bioenergetics.

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

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

Queuine Micronutrient Deficiency Promotes Warburg Metabolism and Reversal of the Mitochondrial ATP Synthase in Hela Cells

Queuine is a eukaryotic micronutrient, derived exclusively from eubacteria. It is incorporated into both cytosolic and mitochondrial transfer RNA to generate a queuosine nucleotide at position 34 of the anticodon loop. The transfer RNA of primary tumors has been shown to be hypomodified with respect to queuosine, with decreased levels correlating with disease progression and poor patient survival. Here, we assess the impact of queuine deficiency on mitochondrial bioenergetics and substrate metabolism in HeLa cells. Queuine depletion is shown to promote a Warburg type metabolism, characterized by increased aerobic glycolysis and glutaminolysis, concomitant with increased ammonia and lactate production and elevated levels of lactate dehydrogenase activity but in the absence of significant changes to proliferation. In intact cells, queuine deficiency caused an increased rate of mitochondrial proton leak and a decreased rate of ATP synthesis, correlating with an observed reduction in cellular ATP levels. Data from permeabilized cells demonstrated that the activity of individual complexes of the mitochondrial electron transport chain were not affected by the micronutrient. Notably, in queuine free cells that had been adapted to grow in galactose medium, the re-introduction of glucose permitted the mitochondrial F₁F_O-ATP synthase to operate in the reverse direction, acting to hyperpolarize the mitochondrial membrane potential; a commonly observed but poorly understood cancer trait. Together, our data suggest that queuosine hypomodification is a deliberate and advantageous adaptation of cancer cells to facilitate the metabolic switch between oxidative phosphorylation and aerobic glycolysis.

Phototherapy alters the oncogenic metabolic activity of breast cancer cells

BACKGROUND

Metabolic reprogramming in cancer cells is a strategy to attain a high proliferation rate, invasion, and metastasis. In this study, the effects of phototherapy at different wavelengths were investigated on the metabolic activity of breast cancer cells.

METHODS

The states of the MCF7 cells proliferation and viability were measured by the MTT assay. Glucose consumption and the lactate formation in the LED-irradiated cells culture were analyzed by biochemical assay kits. The Amino acid concentration in the culture media of the MCF7 cells was analyzed using HPLC. Moreover, the gene expression of some glycolytic, TCA cycle and pentose phosphate cycleenzymes were assessed by real time PCR.

RESULTS

Phototherapy at wavelength of 435 nm decreased the cell viability by 23 % when the energy dose was 17.5 J/cm² compared to the control group. The expression of the LDHA and GLS was up-regulated in 629 nm-treated cells while the expression of these genes was down-regulated in the MCF7 cells irradiated at 435 nm in comparison with the control group. Consequently, the glucose consumption and the lactate formation were diminished respectively by 22 % and 15 % in the 435 nm-irradiated cells while the glucose consumption and the lactate formation were increased in the 629 nm-irradiated cells by 112 % and 107 % in comparison with the control group. In addition, the analysis of the glutamine concentration by the HPLC indicated that the blue light irradiation decreased the glutamine consumption while the red light increased it in comparison with the control group.

Complex Mitochondrial Dysfunction Induced by TPP+-Gentisic Acid and Mitochondrial Translation Inhibition by Doxycycline Evokes Synergistic Lethality in Breast Cancer Cells

The mitochondrion has emerged as a promising therapeutic target for novel cancer treatments because of its essential role in tumorigenesis and resistance to chemotherapy. Previously, we described a natural compound, 10-((2,5-dihydroxybenzoyl)oxy)decyl) triphenylphosphonium bromide (GA-TPP⁺C₁₀), with a hydroquinone scaffold that selectively targets the mitochondria of breast cancer (BC) cells by binding to the triphenylphosphonium group as a chemical chaperone; however, the mechanism of action remains unclear. In this work, we showed that GA-TPP⁺C₁₀ causes time-dependent complex inhibition of the mitochondrial bioenergetics of BC cells, characterized by (1) an initial phase of mitochondrial uptake with an uncoupling effect of oxidative phosphorylation, as previously reported, (2) inhibition of Complex I-dependent respiration, and (3) a late phase of mitochondrial accumulation with inhibition of α-ketoglutarate dehydrogenase complex (αKGDHC) activity. These events led to cell cycle arrest in the G1 phase and cell death at 24 and 48 h of exposure, and the cells were rescued by the addition of the cell-penetrating metabolic intermediates l-aspartic acid β-methyl ester (mAsp) and dimethyl α-ketoglutarate (dm-KG). In addition, this unexpected blocking of mitochondrial function triggered metabolic remodeling toward glycolysis, AMPK activation, increased expression of proliferator-activated receptor gamma coactivator 1-alpha (pgc1α) and electron transport chain (ETC) component-related genes encoded by mitochondrial DNA and downregulation of the uncoupling proteins ucp3 and ucp4, suggesting an AMPK-dependent prosurvival adaptive response in cancer cells. Consistent with this finding, we showed that inhibition of mitochondrial translation with doxycycline, a broad-spectrum antibiotic that inhibits the 28 S subunit of the mitochondrial ribosome, in the presence of GA-TPP⁺C₁₀ significantly reduces the mt-CO1 and VDAC protein levels and the FCCP-stimulated maximal electron flux and promotes selective and synergistic cytotoxic effects on BC cells at 24 h of treatment. Based on our results, we propose that this combined strategy based on blockage of the adaptive response induced by mitochondrial bioenergetic inhibition may have therapeutic relevance in BC.

The fuel and engine: The roles of reprogrammed metabolism in metastasis of primary liver cancer

Metastasis and metabolism reprogramming are two major hallmarks of cancer. In the initiation and progression of cancer, tumor cells are known to undergo fundamental metabolic changes to sustain their development and progression. In recent years, much more attentions have been drawn to their important roles in facilitating cancer metastasis through regulating the biological properties. In this review, we summarized the recent progresses in the studies of metabolism reprogramming of cancer metastasis, particularly of primary liver cancer, and highlight their potential applications.

Understanding and Modeling Metastasis Biology to Improve Therapeutic Strategies for Combating Osteosarcoma Progression

Osteosarcoma is a malignant primary tumor of bone, arising from transformed progenitor cells with osteoblastic differentiation and osteoid production. While categorized as a rare tumor, most patients diagnosed with osteosarcoma are adolescents in their second decade of life and underscores the potential for life changing consequences in this vulnerable population. In the setting of localized disease, conventional treatment for osteosarcoma affords a cure rate approaching 70%; however, survival for patients suffering from metastatic disease remain disappointing with only 20% of individuals being alive past 5 years post-diagnosis. In patients with incurable disease, pulmonary metastases remain the leading cause for osteosarcoma-associated mortality; yet identifying new strategies for combating metastatic progression remains at a scientific and clinical impasse, with no significant advancements for the past four decades. While there is resonating clinical urgency for newer and more effective treatment options for managing osteosarcoma metastases, the discovery of druggable targets and development of innovative therapies for inhibiting metastatic progression will require a deeper and more detailed understanding of osteosarcoma metastasis biology. Toward the goal of illuminating the processes involved in cancer metastasis, a convergent science approach inclusive of diverse disciplines spanning the biology and physical science domains can offer novel and synergistic perspectives, inventive, and sophisticated model systems, and disruptive experimental approaches that can accelerate the discovery and characterization of key processes operative during metastatic progression. Through the lens of trans-disciplinary research, the field of comparative oncology is uniquely positioned to advance new discoveries in metastasis biology toward impactful clinical translation through the inclusion of pet dogs diagnosed with metastatic osteosarcoma. Given the spontaneous course of osteosarcoma development in the context of real-time tumor microenvironmental cues and immune mechanisms, pet dogs are distinctively valuable in translational modeling given their faithful recapitulation of metastatic disease progression as occurs in humans. Pet dogs can be leveraged for the exploration of novel therapies that exploit tumor cell vulnerabilities, perturb local microenvironmental cues, and amplify immunologic recognition. In this capacity, pet dogs can serve as valuable corroborative models for realizing the science and best clinical practices necessary for understanding and combating osteosarcoma metastases.

TGFβ2-induced formation of lipid droplets supports acidosis-driven EMT and the metastatic spreading of cancer cells

Acidosis, a common characteristic of the tumor microenvironment, is associated with alterations in metabolic preferences of cancer cells and progression of the disease. Here we identify the TGF-β2 isoform at the interface between these observations. We document that acidic pH promotes autocrine TGF-β2 signaling, which in turn favors the formation of lipid droplets (LD) that represent energy stores readily available to support anoikis resistance and cancer cell invasiveness. We find that, in cancer cells of various origins, acidosis-induced TGF-β2 activation promotes both partial epithelial-to-mesenchymal transition (EMT) and fatty acid metabolism, the latter supporting Smad2 acetylation. We show that upon TGF-β2 stimulation, PKC-zeta-mediated translocation of CD36 facilitates the uptake of fatty acids that are either stored as triglycerides in LD through DGAT1 or oxidized to generate ATP to fulfill immediate cellular needs. We also address how, by preventing fatty acid mobilization from LD, distant metastatic spreading may be inhibited.

The tumour microenvironment is known to have an acidic pH but how this influences cancer cell phenotype is unclear. Here, the authors show that tumour cells upregulate TGF-β2 under acidosis, which leads to the increased formation of lipid droplets allowing for invasiveness and metastases.

Metabolic Fitness and Plasticity in Cancer Progression

Cancer cells have enhanced metabolic needs due to their rapid proliferation. Moreover, throughout their progression from tumor precursors to metastases, cancer cells face challenging physiological conditions, including hypoxia, low nutrient availability, and exposure to therapeutic drugs. The ability of cancer cells to tailor their metabolic activities to support their energy demand and biosynthetic needs throughout disease progression is key for their survival. Here, we review the metabolic adaptations of cancer cells, from primary tumors to therapy resistant cancers, and the mechanisms underpinning their metabolic plasticity. We also discuss the metabolic coupling that can develop between tumors and the tumor microenvironment. Finally, we consider potential metabolic interventions that could be used in combination with standard therapeutic approaches to improve clinical outcome.

Mitochondrial Involvement in Migration, Invasion and Metastasis

Mitochondria in addition to be a main cellular power station, are involved in the regulation of many physiological processes, such as generation of reactive oxygen species, metabolite production and the maintenance of the intracellular Ca²⁺ homeostasis. Almost 100 years ago Otto Warburg presented evidence for the role of mitochondria in the development of cancer. During the past 20 years mitochondrial involvement in programmed cell death regulation has been clarified. Moreover, it has been shown that mitochondria may act as a switchboard between various cell death modalities. Recently, accumulated data have pointed to the role of mitochondria in the metastatic dissemination of cancer cells. Here we summarize the modern knowledge concerning the contribution of mitochondria to the invasion and dissemination of tumor cells and the possible mechanisms behind that and attempts to target metastatic cancers involving mitochondria.

Mutant p53 on the Path to Metastasis

Metastasis contributes to the vast majority of cancer-related mortality. Regulatory mechanisms of the multistep invasion-metastasis cascade are being unraveled. TP53 is the most frequently mutated gene across human cancers. Accumulating evidence has shown that mutations of TP53 not only lead to loss of function or dominant negative effects, but also promotes a gain of function. Specifically, gain of function mutant p53 promotes cancer cell motility, invasion, and metastasis. Here, we summarize the mechanisms and functions of mutant p53 that foster metastasis in different types of cancers. We also discuss the prognostic value of mutant p53 and current status of therapeutic strategies targeting mutant p53. Future studies will shed light on discovering novel mechanisms of mutant p53-driven cancer metastasis and developing innovative therapeutics to improve clinical outcomes in patients harboring p53 mutations.

New avenues in pancreatic cancer: exploiting microRNAs as predictive biomarkers and new approaches to target aberrant metabolism

Introduction: Most pancreatic cancer patients are diagnosed at advanced-stages and first-line regimens (FOLFIRINOX and gemcitabine/nab-paclitaxel) provide limited survival advantage and are associated with considerable toxicities. In this grim scenario, novel treatments and biomarkers are warranted.Areas covered: MicroRNAs (miRNAs) emerged as biomarkers for cancer prognosis and chemoresistance and blood-based miRNAs are being evaluated as indicators of therapeutic activity. Moreover, aberrant metabolism, such as aerobic glycolysis, has been correlated to tumor aggressiveness and poor prognosis. Against this background, innovative approaches to tackle metabolic aberrations are being implemented and glycolytic inhibitors targeting lactate dehydrogenase-A (LDH-A) showed promising effects in preclinical models. A PubMed search was used to compile relevant publications until February 2019.Expert opinion: Analysis of tissue/circulating miRNA might improve selection for optimal treatment regimens. For instance, miR-181a modulation seems to predict response to FOLFIRINOX. However, we need further studies to validate predictive miRNA profiles, as well as to exploit miRNAs for treatment-tailoring. Several miRNAs have also a key role in regulating metabolic aberrations. Since preliminary evidence supports the development of new agents targeting these aberrations, such as LDH-A inhibitors, the identification of biomarkers for these treatments, including the above-mentioned miRNAs, should shorten the gap between preclinical studies and personalized therapies.

EGFL9 promotes breast cancer metastasis by inducing cMET activation and metabolic reprogramming

The molecular mechanisms driving metastatic progression in triple-negative breast cancer (TNBC) patients are poorly understood. In this study, we demonstrate that epidermal growth factor-like 9 (EGFL9) is significantly upregulated in basal-like breast cancer cells and associated with metastatic progression in breast tumor samples. Functionally, EGFL9 is both necessary and sufficient to enhance cancer cell migration and invasion, as well as distant metastasis. Mechanistically, we demonstrate that EGFL9 binds cMET, activating cMET-mediated downstream signaling. EGFL9 and cMET co-localize at both the cell membrane and within the mitochondria. We further identify an interaction between EGFL9 and the cytochrome c oxidase (COX) assembly factor COA3. Consequently, EGFL9 regulates COX activity and modulates cell metabolism, promoting a Warburg-like metabolic phenotype. Finally, we show that combined pharmacological inhibition of cMET and glycolysis reverses EGFL9-driven stemness. Our results identify EGFL9 as a therapeutic target for combating metastatic progression in TNBC.

Triple-negative breast cancer is an aggressive form of the disease. Here, the authors identify EGFL9 as a mediator of metastasis in TNBC through interactions with cMET.

The natural compound gracillin exerts potent antitumor activity by targeting mitochondrial complex II

Mitochondria play a pivotal role in cancer bioenergetics and are considered a potential target for anticancer therapy. Considering the limited efficacy and toxicity of currently available mitochondria-targeting agents, it is necessary to develop effective mitochondria-targeting anticancer drugs. By screening a large chemical library consisting of natural products with diverse chemical entities, we identified gracillin, a steroidal saponin, as a mitochondria-targeting antitumor drug. Gracillin displayed broad-spectrum inhibitory effects on the viability of a large panel of human cancer cell lines, including those carrying acquired resistance to chemotherapy or EGFR-targeting drugs, by inducing apoptosis. We show that gracillin attenuates mitochondria-mediated cellular bioenergetics by suppressing ATP synthesis and by producing reactive oxygen species (ROS). Mechanistically, gracillin disrupts complex II (CII) function by abrogating succinate dehydrogenase (SDH) activity without affecting the succinate:ubiquinone reductase. The gracillin-induced cell death was potentiated by 3-nitropropionic acid (3-NPA) or thenoyltrifluoroacetone (TTFA), which inhibit CII by binding to the active site of SDHA or to the ubiquinone-binding site, respectively. Finally, we show that gracillin effectively suppressed the mutant-Kras-driven lung tumorigenesis and the growth of xenograft tumors derived from cell lines or patient tissues. Gracillin displayed no obvious pathophysiological features in mice. Collectively, gracillin has potential as a CII-targeting antitumor drug.