Common responses of tumors and wounds to hypoxia

Research Progress on Mechanism and Management of Adverse Drug Reactions of Anlotinib

Anti-angiogenesis therapy plays a vital role in the treatment of tumors, with anlotinib as its representative targeted drug. Anlotinib is a novel oral tyrosine kinase inhibitor (TKI) with inhibitory effects on tumor growth tumor angiogenesis. In Phase III clinical trials, anlotinib demonstrated better overall survival and progression-free survival than placebo in patients with advanced non-small cell lung cancer (NSCLC), and was approved for the first time as a third-line treatment for refractory advanced NSCLC. Going far beyond that, anlotinib has shown encouraging results in a variety of malignancies, including medullary thyroid carcinoma, renal cell carcinoma, gastric cancer and esophageal squamous cell carcinoma. Nevertheless, anlotinib has been subject to some controversy in terms of adverse events due to its widespread use. In this review, the mechanism of action, pharmacokinetic characteristics, adverse reactions in clinical use and management of anlotinib were summarized.

SYVN1-mediated ubiquitylation directs localization of MCT4 in the plasma membrane to promote the progression of lung adenocarcinoma

Tumour cells mainly generate energy from glycolysis, which is commonly coupled with lactate production even under normoxic conditions. As a critical lactate transporter, monocarboxylate transporter 4 (MCT4) is highly expressed in glycolytic tissues, such as muscles and tumours. Overexpression of MCT4 is associated with poor prognosis for patients with various tumours. However, how MCT4 function is post-translationally regulated remains largely unknown. Taking advantage of human lung adenocarcinoma (LUAD) cells, this study revealed that MCT4 can be polyubiquitylated in a nonproteolytic manner by SYVN1 E3 ubiquitin ligase. The polyubiquitylation facilitates the localization of MCT4 into the plasma membrane, which improves lactate export by MCT4; in accordance, metabolism characterized by reduced glycolysis and lactate production is effectively reprogrammed by SYVN1 knockdown, which can be reversed by MCT4 overexpression. Biologically, SYVN1 knockdown successfully compromises cell proliferation and tumour xenograft growth in mouse models that can be partially rescued by overexpression of MCT4. Clinicopathologically, overexpression of SYVN1 is associated with poor prognosis in patients with LUAD, highlighting the importance of the SYVN1-MCT4 axis, which performs metabolic reprogramming during the progression of LUAD.

Biomedical applications of PLGA nanoparticles in nanomedicine: advances in drug delivery systems and cancer therapy

INTRODUCTION

During the last decades, the ever-increasing proportion of patients with cancer has been led to serious concerns worldwide. Therefore, the development and use of novel pharmaceuticals, like nanoparticles (NPs)-based drug delivery systems (DDSs), can be potentially effective in cancer therapy.

AREA COVERED

Poly lactic-co-glycolic acid (PLGA) NPs, as a kind of bioavailable, biocompatible, and biodegradable polymers, have approved by the Food and Drug Administration (FDA) for some biomedical and pharmaceutical applications. PLGA is comprised of lactic acid (LA) and glycolic acid (GA) and their ratio could be controlled during various syntheses and preparation approaches. LA/GA ratio determines the stability and degradation time of PLGA; lower content of GA results in fast degradation. There are several approaches for preparing PLGA NPs that can affect their various aspects, such as size, solubility, stability, drug loading, pharmacokinetics, and pharmacodynamics, and so on.

EXPERT OPINION

These NPs have indicated the controlled and sustained drug release in the cancer site and can use in passive and active (via surface modification) DDSs. This review aims to provide an overview of PLGA NPs, their preparation approach and physicochemical aspects, drug release mechanism and the cellular fate, DDSs for efficient cancer therapy, and status in the pharmaceutical industry and nanomedicine.

Proton-coupled monocarboxylate transporters in cancer: From metabolic crosstalk, immunosuppression and anti-apoptosis to clinical applications

The Warburg effect is known as the hyperactive glycolysis that provides the energy needed for rapid growth and proliferation in most tumor cells even under the condition of sufficient oxygen. This metabolic pattern can lead to a large accumulation of lactic acid and intracellular acidification, which can affect the growth of tumor cells and lead to cell death. Proton-coupled monocarboxylate transporters (MCTs) belong to the SLC16A gene family, which consists of 14 members. MCT1-4 promotes the passive transport of monocarboxylate (e.g., lactate, pyruvate, and ketone bodies) and proton transport across membranes. MCT1-4-mediated lactate shuttling between glycolytic tumor cells or cancer-associated fibroblasts and oxidative tumor cells plays an important role in the metabolic reprogramming of energy, lipids, and amino acids and maintains the survival of tumor cells. In addition, MCT-mediated lactate signaling can promote tumor angiogenesis, immune suppression and multidrug resistance, migration and metastasis, and ferroptosis resistance and autophagy, which is conducive to the development of tumor cells and avoid death. Although there are certain challenges, the study of targeted drugs against these transporters shows great promise and may form new anticancer treatment options.

Dual-Mode Tumor Imaging Using Probes That Are Responsive to Hypoxia-Induced Pathological Conditions

Hypoxia in solid tumors is associated with poor prognosis, increased aggressiveness, and strong resistance to therapeutics, making accurate monitoring of hypoxia important. Several imaging modalities have been used to study hypoxia, but each modality has inherent limitations. The use of a second modality can compensate for the limitations and validate the results of any single imaging modality. In this review, we describe dual-mode imaging systems for the detection of hypoxia that have been reported since the start of the 21st century. First, we provide a brief overview of the hallmarks of hypoxia used for imaging and the imaging modalities used to detect hypoxia, including optical imaging, ultrasound imaging, photoacoustic imaging, single-photon emission tomography, X-ray computed tomography, positron emission tomography, Cerenkov radiation energy transfer imaging, magnetic resonance imaging, electron paramagnetic resonance imaging, magnetic particle imaging, and surface-enhanced Raman spectroscopy, and mass spectrometric imaging. These overviews are followed by examples of hypoxia-relevant imaging using a mixture of probes for complementary single-mode imaging techniques. Then, we describe dual-mode molecular switches that are responsive in multiple imaging modalities to at least one hypoxia-induced pathological change. Finally, we offer future perspectives toward dual-mode imaging of hypoxia and hypoxia-induced pathophysiological changes in tumor microenvironments.

Construction of a Six-Gene Prognostic Risk Model Related to Hypoxia and Angiogenesis for Cervical Cancer

Background: The prognosis of cervical cancer (CC) is poor and not accurately reflected by the primary tumor node metastasis staging system. Our study aimed to develop a novel survival-prediction model.

Methods: Hallmarks of CC were quantified using single-sample gene set enrichment analysis and univariate Cox proportional hazards analysis. We linked gene expression, hypoxia, and angiogenesis using weighted gene co-expression network analysis (WGCNA). Univariate and multivariate Cox regression was combined with the random forest algorithm to construct a prognostic model. We further evaluated the survival predictive power of the gene signature using Kaplan-Meier analysis and receiver operating characteristic (ROC) curves.

Results: Hypoxia and angiogenesis were the leading risk factors contributing to poor overall survival (OS) of patients with CC. We identified 109 candidate genes using WGCNA and univariate Cox regression. Our established prognostic model contained six genes (MOCSI, PPP1R14A, ESM1, DES, ITGA5, and SERPINF1). Kaplan-Meier analysis indicated that high-risk patients had worse OS (hazard ratio = 4.63, p < 0.001). Our model had high predictive power according to the ROC curve. The C-index indicated that the risk score was a better predictor of survival than other clinicopathological variables. Additionally, univariate and multivariate Cox regressions indicated that the risk score was the only independent risk factor for poor OS. The risk score was also an independent predictor in the validation set (GSE52903). Bivariate survival prediction suggested that patients exhibited poor prognosis if they had high z-scores for hypoxia or angiogenesis and high risk scores.

Conclusions: We established a six-gene survival prediction model associated with hypoxia and angiogenesis. This novel model accurately predicts survival and also provides potential therapeutic targets.

Oxygen therapy in traditional and immunotherapeutic treatment protocols of cancer patients: current reality and future prospects

INTRODUCTION

The metabolic environment in ischemic and hypoxic tumors is known to contribute to cancer progression. Importantly, peculiar metabolic changes occurring in malignant cells (the increased glycolysis and the hampered Krebs cycle) may contribute to decreased antioxidant-dependent defense in ischemic and hypoxic tumors.

AREAS COVERED

In the clinic, oxygen saturation of tumors is usually achieved by the application of water-soluble ozone and hyperbaric oxygen therapy. Tumor oxygenation has been shown to inhibit tumor growth and potentiate anti-tumor effects of chemoradiotherapy in animal experiments and the clinical setting. Tumor oxygenation could enhance anti-tumor effects achieved by tumor blood vessel occlusion or angiostatic therapy.

EXPERT OPINION

Owing to a profound influence of ROS on both the innate and adaptive immunity, oxygen therapy, when combined simultaneously or sequentially with immunotherapeutic interventions (such as immune checkpoint inhibition, drug-induced immunostimulation, adoptive cell therapy, hyperthermia, etc.), could be considered as a novel highly-effective clinical biological approach to cancer treatment.

NADH dehydrogenase subunit 1/4/5 promotes survival of acute myeloid leukemia by mediating specific oxidative phosphorylation

Acute myeloid leukemia (AML) is a type of hematological malignancy caused by uncontrolled clonal proliferation of hematopoietic stem cells. The special energy metabolism mode of AML relying on oxidative phosphorylation is different from the traditional ‘Warburg effect’. However, its mechanism is not clear. In the present study, it was demonstrated that the mRNA expression levels of NADH dehydrogenase subunit 1, 4 and 5 (ND1, ND4 and ND5) were upregulated in AML samples from The Cancer Genome Atlas database using the limma package in the R programming language. Reverse transcription-quantitative PCR and ELISA were used to verify the upregulation of ND1, ND4 and ND5 in clinical samples. Pan-cancer analysis revealed that the expression of ND1 was upregulated only in AML, ND2 was upregulated only in AML and thymoma, and ND4 was upregulated only in AML and kidney chromophobe. In the present study, it was demonstrated that silencing of ND1/4/5 could inhibit the proliferation of AML cells in transplanted tumor of nude mice. Additionally, it was found that oxidative phosphorylation and energy metabolism of AML cells were decreased after silencing of ND1/4/5. In conclusion, the present study suggested that ND1/4/5 may be involved in the regulation of oxidative phosphorylation metabolism in AML as a potential cancer-promoting factor.

A Tumor Suppressor Gene, N-myc Downstream-Regulated Gene 1 (NDRG1), in Gliomas and Glioblastomas

The development of potent and selective therapeutic approaches to glioblastoma (GBM) requires the identification of molecular pathways that critically regulate the survival and proliferation of GBM. Glioblastoma stem-like cells (GSCs) possess stem-cell-like properties, self-renewal, and differentiation into multiple neural cell lineages. From a clinical point of view, GSCs have been reported to resist radiation and chemotherapy. GSCs are influenced by the microenvironment, especially the hypoxic condition. N-myc downstream-regulated gene 1 (NDRG1) is a tumor suppressor with the potential to suppress the proliferation, invasion, and migration of cancer cells. Previous studies have reported that deregulated expression of NDRG1 affects tumor growth and clinical outcomes of patients with GBM. This literature review aimed to clarify the critical role of NDRG1 in tumorigenesis and acquirement of resistance for anti-GBM therapies, further to discussing the possibility and efficacy of NDRG1 as a novel target of treatment for GBM. The present review was conducted by searching the PubMed and Scopus databases. The search was conducted in February 2022. We review current knowledge on the regulation and signaling of NDRG1 in neuro-oncology. Finally, the role of NDRG1 in GBM and potential clinical applications are discussed.

Unconventional roles of lactate along the tumor and immune landscape

The tumor ecosystem evolves with dynamic interactions between cancer and normal cells, and nutrients have emerged as new regulators of cancer hallmarks. Lactate has climbed the rankings as a multifunctional molecule orchestrating many aspects of the disease onset and progression. Here, we patchwork and discuss the main recent findings conferred during the EMBO workshop titled 'Lactate: Unconventional Roles of a Nutrient Along the Tumor Landscape.'

Metabolic response to radiation therapy in cancer

Tumor metabolism has emerged as a hallmark of cancer and is involved in carcinogenesis and tumor growth. Reprogramming of tumor metabolism is necessary for cancer cells to sustain high proliferation rates and enhanced demands for nutrients. Recent studies suggest that metabolic plasticity in cancer cells can decrease the efficacy of anticancer therapies by enhancing antioxidant defenses and DNA repair mechanisms. Studying radiation-induced metabolic changes will lead to a better understanding of radiation response mechanisms as well as the identification of new therapeutic targets, but there are few robust studies characterizing the metabolic changes induced by radiation therapy in cancer. In this review, we will highlight studies that provide information on the metabolic changes induced by radiation and oxidative stress in cancer cells and the associated underlying mechanisms.

4-Hexylresorcinol: pharmacologic chaperone and its application for wound healing

4-Hexylresorcinol (4HR) is amphiphilic organic chemical and auto-regulator for micro-organism. As 4HR administration induces the stress on the endoplasmic reticulum, 4HR changes protein folding. The application of 4HR inhibits NF-κB signal pathway and TNF-α production. In addition, 4HR administration increases VEGF, TGF-β1, and calcification associated proteins. As a consequence, 4HR administration increases angiogenesis and bone formation in wounded area. Strong anti-inflammatory reaction and capillary regeneration in diabetic model demonstrate that 4HR can be applied on many types of surgical wound.

Hypoxia boosts aerobic glycolysis of carcinoma：a complex process for tumor development

Hypoxia, a common feature in malignant tumors, is mainly caused by insufficient oxygen supply. Hypoxia is closely related to cancer development, affecting cancer invasion and metastasis, energy metabolism and other pathological processes, and is not conducive to cancer treatment and prognosis. Tumor cells exacerbate metabolic abnormalities to adapt to the hypoxic microenvironment, especially to enhance aerobic glycolysis. Glycolysis leads to an acidic microenvironment in cancer tissues, enhancing cancer metastasis, deterioration and drug resistance. Therefore, hypoxia is a therapeutic target that cannot be ignored in cancer treatment. The adaptation of tumor cells to hypoxia is mainly regulated by hypoxia inducible factors (HIFs), and the stability of HIFs is improved under hypoxic conditions. HIFs can promote the glycolysis of tumors by regulating glycolytic enzymes, transporters, and participates in regulating the TCA (tricarboxylic acid) cycle. In addition, HIFs indirectly affect glycolysis through its interaction with non-coding RNAs. Therefore, targeting hypoxia and HIFs are important tumor therapies.

Predictive and prognostic transcriptomic biomarkers in soft tissue sarcomas

Soft tissue sarcomas (STS) are rare and heterogeneous tumours comprising over 80 different histological subtypes. Treatment options remain limited in advanced STS with high rates of recurrence following resection of localised disease. Prognostication in clinical practice relies predominantly on histological grading systems as well as sarcoma nomograms. Rapid developments in gene expression profiling technologies presented opportunities for applications in sarcoma. Molecular profiling of sarcomas has improved our understanding of the cancer biology of these rare cancers and identified potential novel therapeutic targets. In particular, transcriptomic signatures could play a role in risk classification in sarcoma to aid prognostication. Unlike other solid and haematological malignancies, transcriptomic signatures have not yet reached routine clinical use in sarcomas. Herein, we evaluate early developments in gene expression profiling in sarcomas that laid the foundations for transcriptomic signature development. We discuss the development and clinical evaluation of key transcriptomic biomarker signatures in sarcomas, including Complexity INdex in SARComas (CINSARC), Genomic Grade Index, and hypoxia-associated signatures. Prospective validation of these transcriptomic signatures is required, and prospective trials are in progress to evaluate reliability for clinical application. We anticipate that integration of these gene expression signatures alongside existing prognosticators and other Omics methodologies, including proteomics and DNA methylation analysis, could improve the identification of 'high-risk' patients who would benefit from more aggressive or selective treatment strategies. Moving forward, the incorporation of these transcriptomic prognostication signatures in clinical practice will undoubtedly advance precision medicine in the routine clinical management of sarcoma patients.

Hypoxia Dictates Metabolic Rewiring of Tumors: Implications for Chemoresistance

Hypoxia is a condition commonly observed in the core of solid tumors. The hypoxia-inducible factors (HIF) act as hypoxia sensors that orchestrate a coordinated response increasing the pro-survival and pro-invasive phenotype of cancer cells, and determine a broad metabolic rewiring. These events favor tumor progression and chemoresistance. The increase in glucose and amino acid uptake, glycolytic flux, and lactate production; the alterations in glutamine metabolism, tricarboxylic acid cycle, and oxidative phosphorylation; the high levels of mitochondrial reactive oxygen species; the modulation of both fatty acid synthesis and oxidation are hallmarks of the metabolic rewiring induced by hypoxia. This review discusses how metabolic-dependent factors (e.g., increased acidification of tumor microenvironment coupled with intracellular alkalinization, and reduced mitochondrial metabolism), and metabolic-independent factors (e.g., increased expression of drug efflux transporters, stemness maintenance, and epithelial-mesenchymal transition) cooperate in determining chemoresistance in hypoxia. Specific metabolic modifiers, however, can reverse the metabolic phenotype of hypoxic tumor areas that are more chemoresistant into the phenotype typical of chemosensitive cells. We propose these metabolic modifiers, able to reverse the hypoxia-induced metabolic rewiring, as potential chemosensitizer agents against hypoxic and refractory tumor cells.

Imaging of Tumor Hypoxia for Radiotherapy: Current Status and Future Directions

Tumor regions that are transiently or chronically undersupplied with oxygen (hypoxia) and nutrients, and enriched with acidic waste products, are common due to an abnormal and inefficient tumor vasculature, and a deviant highly glycolytic energy metabolism. There is compelling evidence that tumor hypoxia is strongly linked to poor prognosis since oxygen-deprived cells are highly resistant to therapy including radio- and chemotherapy, and survival of such cells is a primary cause of disease relapse. Despite a general improvement in cancer survival rates, hypoxia remains a formidable challenge. Recent progress in radiation delivery systems with improved spatial accuracy that allows dose escalation to hypoxic tumors or even tumor subvolumes, and the development of hypoxia-selective drugs, including bioreductive prodrugs, holds great promise for overcoming this obstacle. However, apart from one notable exception, translation of promising preclinical therapies to the clinic have largely been disappointing. A major obstacle in clinical trials on hypoxia-targeting strategies has been the lack of reliable information on tumor hypoxia, which is crucial for patient stratification into groups of those that are likely to benefit from intervention and those who are not. Further, in many newer trials on hypoxia-selective drugs the choice of cancer disease and combination therapy has not always been ideal, especially not for clinical proof of principle trials. Clearly, there is a pending need for clinical applicable methodologies that may allow us to quantify, map and monitor hypoxia. Molecular imaging may provide the information required for narrowing the gap between potential and actual patient benefit of hypoxia-targeting strategies. The grand majority of preclinical and clinical work has focused on the usefulness of PET-based assessment of hypoxia-selective tracers. Since hypoxia PET has profound inherent weaknesses, the use of other methodologies, including more indirect methods that quantifies blood flow or oxygenation-dependent flux changes through ATP-generating pathways (eg, anaerobic glycolysis) is being extensively studied. In this review, we briefly discuss established and emerging hypoxia-targeting strategies, followed by a more thorough evaluation of strengths and weaknesses of clinical applicable imaging methodologies that may guide timely treatment intensification to overcome hypoxia-driven resistance. Historically, most evidence for the linkage between hypoxia and poor outcome is based on work in the field of radiotherapy. Therefore, main emphasis in this review is on targeting and imaging of hypoxia for improved radiotherapy.

Mitochondria in cancer

The rediscovery and reinterpretation of the Warburg effect in the year 2000 occulted for almost a decade the key functions exerted by mitochondria in cancer cells. Until recent times, the scientific community indeed focused on constitutive glycolysis as a hallmark of cancer cells, which it is not, largely ignoring the contribution of mitochondria to the malignancy of oxidative and glycolytic cancer cells, being Warburgian or merely adapted to hypoxia. In this review, we highlight that mitochondria are not only powerhouses in some cancer cells, but also dynamic regulators of life, death, proliferation, motion and stemness in other types of cancer cells. Similar to the cells that host them, mitochondria are capable to adapt to tumoral conditions, and probably to evolve to ‘oncogenic mitochondria' capable of transferring malignant capacities to recipient cells. In the wider quest of metabolic modulators of cancer, treatments have already been identified targeting mitochondria in cancer cells, but the field is still in infancy.

Interrogating the Lactate Dehydrogenase Tetramerization Site Using (Stapled) Peptides

Lactate dehydrogenases (LDHs) are tetrameric enzymes of major significance in cancer metabolism as well as promising targets for cancer therapy. However, their wide and polar catalytic sites make them a challenging target for orthosteric inhibition. In this work, we conceived to target LDH tetramerization sites with the ambition of disrupting their oligomeric state. To do so, we designed a protein model of a dimeric LDH-H. We exploited this model through WaterLOGSY nuclear magnetic resonance and microscale thermophoresis for the identification and characterization of a set of α-helical peptides and stapled derivatives that specifically targeted the LDH tetramerization sites. This strategy resulted in the design of a macrocyclic peptide that competes with the LDH tetramerization domain, thus disrupting and destabilizing LDH tetramers. These peptides and macrocycles, along with the dimeric model of LDH-H, constitute promising pharmacological tools for the de novo design and identification of LDH tetramerization disruptors. Overall, our study demonstrates that disrupting LDH oligomerization state by targeting their tetramerization sites is achievable and paves the way toward LDH inhibition through this novel molecular mechanism.

Early pH Changes in Musculoskeletal Tissues upon Injury-Aerobic Catabolic Pathway Activity Linked to Inter-Individual Differences in Local pH

Local pH is stated to acidify after bone fracture. However, the time course and degree of acidification remain unknown. Whether the acidification pattern within a fracture hematoma is applicable to adjacent muscle hematoma or is exclusive to this regenerative tissue has not been studied to date. Thus, in this study, we aimed to unravel the extent and pattern of acidification in vivo during the early phase post musculoskeletal injury. Local pH changes after fracture and muscle trauma were measured simultaneously in two pre-clinical animal models (sheep/rats) immediately after and up to 48 h post injury. The rat fracture hematoma was further analyzed histologically and metabolomically. In vivo pH measurements in bone and muscle hematoma revealed a local acidification in both animal models, yielding mean pH values in rats of 6.69 and 6.89, with pronounced intra- and inter-individual differences. The metabolomic analysis of the hematomas indicated a link between reduction in tricarboxylic acid cycle activity and pH, thus, metabolic activity within the injured tissues could be causative for the different pH values. The significant acidification within the early musculoskeletal hematoma could enable the employment of the pH for novel, sought-after treatments that allow for spatially and temporally controlled drug release.

Potential Therapeutic Strategies for Lung and Breast Cancers through Understanding the Anti-Angiogenesis Resistance Mechanisms

Breast and lung cancers are among the top cancer types in terms of incidence and mortality burden worldwide. One of the challenges in the treatment of breast and lung cancers is their resistance to administered drugs, as observed with angiogenesis inhibitors. Based on clinical and pre-clinical findings, these two types of cancers have gained the ability to resist angiogenesis inhibitors through several mechanisms that rely on cellular and extracellular factors. This resistance is mediated through angiogenesis-independent vascularization, and it is related to cancer cells and their microenvironment. The mechanisms that cancer cells utilize include metabolic symbiosis and invasion, and they also take advantage of neighboring cells like macrophages, endothelial cells, myeloid and adipose cells. Overcoming resistance is of great interest, and researchers are investigating possible strategies to enhance sensitivity towards angiogenesis inhibitors. These strategies involved targeting multiple players in angiogenesis, epigenetics, hypoxia, cellular metabolism and the immune system. This review aims to discuss the mechanisms of resistance to angiogenesis inhibitors and to highlight recently developed approaches to overcome this resistance.

Monocarboxylate transporters in cancer

Background

Tumors are highly plastic metabolic entities composed of cancer and host cells that can adopt different metabolic phenotypes. For energy production, cancer cells may use 4 main fuels that are shuttled in 5 different metabolic pathways. Glucose fuels glycolysis that can be coupled to the tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OXPHOS) in oxidative cancer cells or to lactic fermentation in proliferating and in hypoxic cancer cells. Lipids fuel lipolysis, glutamine fuels glutaminolysis, and lactate fuels the oxidative pathway of lactate, all of which are coupled to the TCA cycle and OXPHOS for energy production. This review focuses on the latter metabolic pathway.

Scope of review

Lactate, which is prominently produced by glycolytic cells in tumors, was only recently recognized as a major fuel for oxidative cancer cells and as a signaling agent. Its exchanges across membranes are gated by monocarboxylate transporters MCT1-4. This review summarizes the current knowledge about MCT structure, regulation and functions in cancer, with a specific focus on lactate metabolism, lactate-induced angiogenesis and MCT-dependent cancer metastasis. It also describes lactate signaling via cell surface lactate receptor GPR81.

Major conclusions

Lactate and MCTs, especially MCT1 and MCT4, are important contributors to tumor aggressiveness. Analyses of MCT-deficient (MCT^+/- and MCT^−/-) animals and (MCT-mutated) humans indicate that they are druggable, with MCT1 inhibitors being in advanced development phase and MCT4 inhibitors still in the discovery phase. Imaging lactate fluxes non-invasively using a lactate tracer for positron emission tomography would further help to identify responders to the treatments.

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In cancer, hypoxia and cell proliferation are associated to lactic acid production.

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Lactate exchanges are at the core of tumor metabolism.

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Transmembrane lactate trafficking depends on monocarboxylate transporters (MCTs).

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MCTs are implicated in tumor development and aggressiveness.

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Targeting MCTs is a therapeutic option for cancer treatment.

Monocarboxylate transporter 1 and monocarboxylate transporter 4 in cancer-endothelial co-culturing microenvironments promote proliferation, migration, and invasion of renal cancer cells

Background

The Warburg effect demonstrates the importance of glycolysis in the development of primary and metastatic cancers. We aimed to explore the role of monocarboxylate transporter 1 (MCT1) and MCT4, two essential transporters of lactate, in renal cancer progression during cancer-endothelial cell co-culturing.

Methods

Renal cancer cells (786-O) and human vascular endothelial cells (HUVECs) were single-cultured or co-cultured in transwell membranes in the presence or absence of a MCT-1/MCT-4 specific blocker, 7ACC1. Cell proliferation was evaluated with the CCK-8 kit, while cell migration, after a scratch and invasion in transwell chambers, was evaluated under a microscope. Real-time qPCR and western blot were employed to determine the mRNA and protein levels of MCT1 and MCT4, respectively. The concentration of lactic acid in the culture medium was quantified with an l-Lactic Acid Assay Kit.

Results

786-O cells and HUVECs in the co-culturing mode exhibited significantly enhanced proliferation and migration ability, compared with the cells in the single-culturing mode. The expression of MCT1 and MCT4 was increased in both 786-O cells and HUVECs in the co-culturing mode. Co-culturing promoted the invasive ability of 786-O cells, and markedly increased extracellular lactate. Treatments with 7ACC1 attenuated cell proliferation, migration, and invasion, and down-regulated the levels of MCT1/MCT4 expression and extracellular lactate.

Conclusions

The Warburg effect accompanied with high MCT1/MCT4 expression in the cancer-endothelial microenvironments contributed significantly to renal cancer progression, which sheds new light on targeting MCT1/MCT4 and glycolytic metabolism in order to effectively treat patients with renal cancers.

Hypoxia-induced upregulation of angiogenic factors in immortalized human periodontal ligament fibroblasts

Hypoxia induces complex cellular responses that are mediated by a key transcription factor, hypoxia-inducible factor-1 (HIF-1). HIF-1 promotes production of cytokines and angiogenic factors and contributes to recovery of injured tissues. In the present study, expressions of angiogenin (ANG) and vascular endothelial growth factor (VEGF), which are potent angiogenic factors in mammalian tissues, were examined in immortalized fibroblasts exposed to hypoxia. After 24 h of exposure to hypoxia, ANG and VEGF mRNAs expressions were significantly elevated in periodontal ligament (PDL) fibroblasts but not in embryonic fibroblasts. Hypoxia also increased productions of ANG and VEGF proteins in PDL fibroblasts. HIF-1α mRNA expression was not affected by hypoxia in either fibroblast, although HIF-1α protein expression was enhanced after exposure to hypoxia. Treatment of PDL fibroblasts with dimethyloxaloylglycine, a prolyl hydroxylase inhibitor that stabilizes the HIF-1α protein, significantly increased expressions of ANG and VEGF mRNAs under normoxia. This suggests that stabilization of HIF-1α is crucial for upregulation of ANG and VEGF in PDL fibroblasts. These results indicate that, under hypoxic conditions, HIF-1α upregulates synthesis of ANG and VEGF in PDL fibroblasts and promotes angiogenesis.

PLGA: From a classic drug carrier to a novel therapeutic activity contributor

Poly(lactic-co-glycolic acid) (PLGA) is well known for its biocompatibility and minimal toxicity. It is one of the most promising biodegradable polymeric drug delivery systems able to get endorsement from regulatory bodies to enter market. For many decades, PLGA has been functioning as an excipient, which by definition is pharmaceutically inert at a given dose of formulation. Lactate (one of the hydrolysis products of PLGA) has a key role in biochemical pathways and could improve physiological activities in certain illnesses by exerting therapeutic effects such as angiogenesis and promotion of healing. These activities, however, depend on the released amounts and metabolic clearance of lactate and route of formulation delivery. In the current commentary, along with several key notes on the lactate interactions, we would like to inform the PLGA research community that lactate (resulting from local delivery of physiologically significant amount of PLGA) may positively or negatively affect therapeutic efficacy of certain drugs. Hence, the excipient role of PLGA may be investigated for its potential pharmacological contributions in some biomedical applications.

Radiosynthesis and validation of (±)-[18F]-3-fluoro-2-hydroxypropionate ([18F]-FLac) as a PET tracer of lactate to monitor MCT1-dependent lactate uptake in tumors

Cancers develop metabolic strategies to cope with their microenvironment often characterized by hypoxia, limited nutrient bioavailability and exposure to anticancer treatments. Among these strategies, the metabolic symbiosis based on the exchange of lactate between hypoxic/glycolytic cancer cells that convert glucose to lactate and oxidative cancer cells that preferentially use lactate as an oxidative fuel optimizes the bioavailability of glucose to hypoxic cancer cells. This metabolic cooperation has been described in various human cancers and can provide resistance to anti-angiogenic therapies. It depends on the expression and activity of monocarboxylate transporters (MCTs) at the cell membrane. MCT4 is the main facilitator of lactate export by glycolytic cancer cells, and MCT1 is adapted for lactate uptake by oxidative cancer cells. While MCT1 inhibitor AZD3965 is currently tested in phase I clinical trials and other inhibitors of lactate metabolism have been developed for anticancer therapy, predicting and monitoring a response to the inhibition of lactate uptake is still an unmet clinical need. Here, we report the synthesis, evaluation and in vivo validation of (±)-[18F]-3-fluoro-2-hydroxypropionate ([18F]-FLac) as a tracer of lactate for positron emission tomography. [18F]-FLac offers the possibility to monitor MCT1-dependent lactate uptake and inhibition in tumors in vivo.

Anti-angiogenic agents for the treatment of solid tumors: Potential pathways, therapy and current strategies - A review

Recent strategies for the treatment of cancer, other than just tumor cell killing have been under intensive development, such as anti-angiogenic therapeutic approach. Angiogenesis inhibition is an important strategy for the treatment of solid tumors, which basically depends on cutting off the blood supply to tumor micro-regions, resulting in pan-hypoxia and pan-necrosis within solid tumor tissues. The differential activation of angiogenesis between normal and tumor tissues makes this process an attractive strategic target for anti-tumor drug discovery. The principles of anti-angiogenic treatment for solid tumors were originally proposed in 1972, and ever since, it has become a putative target for therapies directed against solid tumors. In the early twenty first century, the FDA approved anti-angiogenic drugs, such as bevacizumab and sorafenib for the treatment of several solid tumors. Over the past two decades, researches have continued to improve the performance of anti-angiogenic drugs, describe their drug interaction potential, and uncover possible reasons for potential treatment resistance. Herein, we present an update to the pre-clinical and clinical situations of anti-angiogenic agents and discuss the most recent trends in this field.

Time- and oxygen-dependent expression and regulation of NDRG1 in human brain cancer cells

N-myc downstream-regulated gene 1 (NDRG1) is a tumor suppressor with the potential to suppress metastasis, invasion and migration of cancer cells. It is regulated under stress conditions such as starvation or hypoxia. NDRG1 regulation is both induced and controlled by HIF-1α-dependent and -independent pathways under hypoxic conditions. However, there are profound differences in the way NDRG1 expression is regulated by HIF-1α and other transcription factors. Therefore, we aimed to define the time-dependent pattern of NDRG1 mRNA and protein expression in human glioblastoma cell lines in extreme hypoxia and after re-oxygenation as well as under normoxic conditions. Furthermore, we ascribe the regulation of NDRG1 to the transcription factors HIF-1α, SP1, CEBPα, YB-1 and Smad7 in a time-dependent manner. The human malignant glioma cell lines U87-MG, U373 and GaMG were cultured for 1, 6 and 24 h under hypoxic (0.1% O2) conditions and then they were re-oxygenated. The mRNA expression of NDRG1, HIF-1α SP1, CEBPα, YB-1 and Smad7 was measured using semi-quantitative RT-PCR analysis. Their protein expression was analyzed using western blotting. Our experiments revealed that long-term (24 h), but not short-term hypoxia led to the induction of NDRG1 expression in human glioma cell lines. NDRG1 expression was found to correlate with the protein expression of HIF-1α, SP1, CEBPα, YB-1 and Smad7. The present study suggests for the first time that SP1 regulates NDRG1 expression in glioma cells under hypoxia in a time-dependent manner along with HIF-1α, CEBPα, YB-1 and Smad7. These molecules, each separately or in combination, may possess the potential to become target molecules for antitumor therapeutic approaches particularly in human brain tumors.

Cancer heterogeneity is not compatible with one unique cancer cell metabolic map

The Warburg effect and its accompanying metabolic features (anaplerosis, cataplerosis) are presented in textbooks and reviews as a hallmark (general characteristic): the metabolic map of cancer. On the other hand, research articles on specific tumors since a few years emphasize various biological features of different cancers, different cells in a cancer and the dynamic heterogeneity of these cells. We have analysed the research literature of the subject and show the generality of a dynamic, evolving biological and metabolic, spatial and temporal heterogeneity of individual cancers. We conclude that there is no one metabolic map of cancer but several and describe the two extremes of a panel from the hypoxic to the normoxic state. The implications for the significance of general 'omic' studies, and on therapeutic conclusions drawn from them and for the diagnostic use of fractional biopsies is discussed.

Novel Epigenetic Controlling of Hypoxia Pathway Related to Overexpression and Promoter Hypomethylation of TET1 and TET2 in RPE Cells

CpG methylation of DNA takes part in a specific epigenetic memory that plays crucial roles in the differentiation and abnormality of the cells. The methylation pattern aberration of genomes is affected in three ways, namely DNA methyltransferase (DNMT), ten-eleven translocation (TET), and methyl-binding domain (MBD) proteins. Of these, TET enzymes have recently been demonstrated to be master modifier enzymes in the DNA methylation process. Additionally, recent studies emphasize that not only epigenetic phenomena play a role in controlling hypoxia pathway, but the hypoxia condition also triggers hypomethylation of genomes that may help with the expression of hypoxia pathway genes. In this study, we suggested that TET1 and TET2 could play a role in the demethylation of genomes under chemical hypoxia conditions. Herein, the evaluating methylation status and mRNA expression of mentioned genes were utilized through real-time PCR and methylation-specific PCR (MSP), respectively. Our results showed that TET1 and TET2 genes were overexpressed (P < 0.05) under chemical hypoxia conditions in Retinal Pigment Epithelial (RPE) cells, whereas the promoter methylation status of them were hypomethylated in the same condition. Therefore, chemical hypoxia not only causes overexpression of TET1 and TET2 but also could gradually do promoter demethylation of same genes. This is the first study to show the relationship between epigenetics and the expression of mentioned genes related to hypoxia pathways. Furthermore, it seems that these associations in RPE cells are subjected to chemical hypoxia as a mechanism that could play a crucial role in methylation pattern changes of hypoxia-related diseases such as cancer and ischemia. J. Cell. Biochem. 118: 3193-3204, 2017. © 2017 Wiley Periodicals, Inc.

Cancer metabolism in space and time: Beyond the Warburg effect

Altered metabolism in cancer cells is pivotal for tumor growth, most notably by providing energy, reducing equivalents and building blocks while several metabolites exert a signaling function promoting tumor growth and progression. A cancer tissue cannot be simply reduced to a bulk of proliferating cells. Tumors are indeed complex and dynamic structures where single cells can heterogeneously perform various biological activities with different metabolic requirements. Because tumors are composed of different types of cells with metabolic activities affected by different spatial and temporal contexts, it is important to address metabolism taking into account cellular and biological heterogeneity. In this review, we describe this heterogeneity also in metabolic fluxes, thus showing the relative contribution of different metabolic activities to tumor progression according to the cellular context. This article is part of a Special Issue entitled Mitochondria in Cancer, edited by Giuseppe Gasparre, Rodrigue Rossignol and Pierre Sonveaux.

Glutamine activates STAT3 to control cancer cell proliferation independently of glutamine metabolism

Cancer cells can use a variety of metabolic substrates to fulfill the bioenergetic and biosynthetic needs of their oncogenic program. Besides bioenergetics, cancer cell metabolism also directly influences genetic, epigenetic and signaling events associated with tumor progression. Many cancer cells are addicted to glutamine, and this addiction is observed in oxidative as well as in glycolytic cells. While both oxidative and bioreductive glutamine metabolism can contribute to cancer progression and glutamine can further serve to generate peptides (including glutathione) and proteins, we report that glutamine promotes the proliferation of cancer cells independently of its use as a metabolic fuel or as a precursor of glutathione. Extracellular glutamine activates transcription factor STAT3, which is necessary and sufficient to mediate the proliferative effects of glutamine in glycolytic and in oxidative cancer cells. Glutamine also activates transcription factors HIF-1, mTOR and c-Myc, but these factors do not mediate the effects of glutamine on cancer cell proliferation. Our findings shed a new light on the anticancer effects of L-asparaginase that possesses glutaminase activity and converts glutamine into glutamate extracellularly. Conversely, cancer resistance to treatments that block glutamine metabolism could arise from glutamine-independent STAT3 re-activation.

A prognostic profile of hypoxia-induced genes for localised high-grade soft tissue sarcoma

Background:

For decades, tumour hypoxia has been pursued as a cancer treatment target. However, prognostic and predictive biomarkers are essential for the use of this target in the clinic. This study investigates the prognostic value of a hypoxia-induced gene profile in localised soft tissue sarcoma (STS).

Methods:

The hypoxia-induced gene quantification was performed by real-time quantitative PCR (RT-qPCR) of formalin-fixed, paraffin-embedded tissue samples. The gene expression cut-points were determined in a test cohort of 55 STS patients and used to allocate each patient into a more or a less hypoxic group. The cut-points found in the test cohort were applied to a cohort of 77 STS patients for validation.

Results:

For patients with localised high-grade STS treated with surgery with or without postoperative radiation therapy, the prognostic value of the hypoxia-induced gene profile was proved in the test cohort and confirmed in the validation cohort. After adjustment for confounders, the hazard ratio (HR) was 3.2 (95% CI: 1.5; 7.0) for patients with more hypoxic tumours compared with patients with less hypoxic tumours regarding disease-specific survival. Moreover, for the development of metastatic disease, the HR was 2.61 (95% CI: 1.27; 5.33).

Conclusions:

The hypoxia-induced gene profile is a validated independent prognostic marker that may help identify STS patients needing more aggressive or different adjuvant treatment.

Monocarboxylate transporters in the brain and in cancer

Monocarboxylate transporters (MCTs) constitute a family of 14 members among which MCT1-4 facilitate the passive transport of monocarboxylates such as lactate, pyruvate and ketone bodies together with protons across cell membranes. Their anchorage and activity at the plasma membrane requires interaction with chaperon protein such as basigin/CD147 and embigin/gp70. MCT1-4 are expressed in different tissues where they play important roles in physiological and pathological processes. This review focuses on the brain and on cancer. In the brain, MCTs control the delivery of lactate, produced by astrocytes, to neurons, where it is used as an oxidative fuel. Consequently, MCT dysfunctions are associated with pathologies of the central nervous system encompassing neurodegeneration and cognitive defects, epilepsy and metabolic disorders. In tumors, MCTs control the exchange of lactate and other monocarboxylates between glycolytic and oxidative cancer cells, between stromal and cancer cells and between glycolytic cells and endothelial cells. Lactate is not only a metabolic waste for glycolytic cells and a metabolic fuel for oxidative cells, but it also behaves as a signaling agent that promotes angiogenesis and as an immunosuppressive metabolite. Because MCTs gate the activities of lactate, drugs targeting these transporters have been developed that could constitute new anticancer treatments. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou.

Metabolic changes associated with tumor metastasis, part 2: Mitochondria, lipid and amino acid metabolism

Metabolic alterations are a hallmark of cancer controlling tumor progression and metastasis. Among the various metabolic phenotypes encountered in tumors, this review focuses on the contributions of mitochondria, lipid and amino acid metabolism to the metastatic process. Tumor cells require functional mitochondria to grow, proliferate and metastasize, but shifts in mitochondrial activities confer pro-metastatic traits encompassing increased production of mitochondrial reactive oxygen species (mtROS), enhanced resistance to apoptosis and the increased or de novo production of metabolic intermediates of the TCA cycle behaving as oncometabolites, including succinate, fumarate, and D-2-hydroxyglutarate that control energy production, biosynthesis and the redox state. Lipid metabolism and the metabolism of amino acids, such as glutamine, glutamate and proline are also currently emerging as focal control points of cancer metastasis.

Metabolic changes associated with tumor metastasis, part 1: tumor pH, glycolysis and the pentose phosphate pathway

Metabolic adaptations are intimately associated with changes in cell behavior. Cancers are characterized by a high metabolic plasticity resulting from mutations and the selection of metabolic phenotypes conferring growth and invasive advantages. While metabolic plasticity allows cancer cells to cope with various microenvironmental situations that can be encountered in a primary tumor, there is increasing evidence that metabolism is also a major driver of cancer metastasis. Rather than a general switch promoting metastasis as a whole, a succession of metabolic adaptations is more likely needed to promote different steps of the metastatic process. This review addresses the contribution of pH, glycolysis and the pentose phosphate pathway, and a companion paper summarizes current knowledge regarding the contribution of mitochondria, lipids and amino acid metabolism. Extracellular acidification, intracellular alkalinization, the glycolytic enzyme phosphoglucose isomerase acting as an autocrine cytokine, lactate and the pentose phosphate pathway are emerging as important factors controlling cancer metastasis.

Overcoming Hypoxia-Mediated Tumor Progression: Combinatorial Approaches Targeting pH Regulation, Angiogenesis and Immune Dysfunction

Hypoxia is an important contributor to the heterogeneity of the microenvironment of solid tumors and is a significant environmental stressor that drives adaptations which are essential for the survival and metastatic capabilities of tumor cells. Critical adaptive mechanisms include altered metabolism, pH regulation, epithelial-mesenchymal transition, angiogenesis, migration/invasion, diminished response to immune cells and resistance to chemotherapy and radiation therapy. In particular, pH regulation by hypoxic tumor cells, through the modulation of cell surface molecules such as extracellular carbonic anhydrases (CAIX and CAXII) and monocarboxylate transporters (MCT-1 and MCT-4) functions to increase cancer cell survival and enhance cell invasion while also contributing to immune evasion. Indeed, CAIX is a vital regulator of hypoxia mediated tumor progression, and targeted inhibition of its function results in reduced tumor growth, metastasis, and cancer stem cell function. However, the integrated contributions of the repertoire of hypoxia-induced effectors of pH regulation for tumor survival and invasion remain to be fully explored and exploited as therapeutic avenues. For example, the clinical use of anti-angiogenic agents has identified a conundrum whereby this treatment increases hypoxia and cancer stem cell components of tumors, and accelerates metastasis. Furthermore, hypoxia results in the infiltration of myeloid-derived suppressor cells (MDSCs), regulatory T cells (Treg) and Tumor Associated Macrophages (TAMs), and also stimulates the expression of PD-L1 on tumor cells, which collectively suppress T-cell mediated tumor cell killing. Therefore, combinatorial targeting of angiogenesis, the immune system and pH regulation in the context of hypoxia may lead to more effective strategies for curbing tumor progression and therapeutic resistance, thereby increasing therapeutic efficacy and leading to more effective strategies for the treatment of patients with aggressive cancer.

Lactate does not activate NF-κB in oxidative tumor cells

The lactate anion is currently emerging as an oncometabolite. Lactate, produced and exported by glycolytic and glutaminolytic cells in tumors, can be recycled as an oxidative fuel by oxidative tumors cells. Independently of hypoxia, it can also activate transcription factor hypoxia-inducible factor-1 (HIF-1) in tumor and endothelial cells, promoting angiogenesis. These protumoral activities of lactate depend on lactate uptake, a process primarily facilitated by the inward, passive lactate-proton symporter monocarboxylate transporter 1 (MCT1); the conversion of lactate and NAD(+) to pyruvate, NADH and H(+) by lactate dehydrogenase-1 (LDH-1); and a competition between pyruvate and α-ketoglutarate that inhibits prolylhydroxylases (PHDs). Endothelial cells do not primarily use lactate as an oxidative fuel but, rather, as a signaling agent. In addition to HIF-1, lactate can indeed activate transcription factor nuclear factor-κB (NF-κB) in these cells, through a mechanism not only depending on PHD inhibition but also on NADH alimenting NAD(P)H oxidases to generate reactive oxygen species (ROS). While NF-κB activity in endothelial cells promotes angiogenesis, NF-κB activation in tumor cells is known to stimulate tumor progression by conferring resistance to apoptosis, stemness, pro-angiogenic and metastatic capabilities. In this study, we therefore tested whether exogenous lactate could activate NF-κB in oxidative tumor cells equipped for lactate signaling. We report that, precisely because they are oxidative, HeLa and SiHa human tumor cells do not activate NF-κB in response to lactate. Indeed, while lactate-derived pyruvate is well-known to inhibit PHDs in these cells, we found that NADH aliments oxidative phosphorylation (OXPHOS) in mitochondria rather than NAD(P)H oxidases in the cytosol. These data were confirmed using oxidative human Cal27 and MCF7 tumor cells. This new information positions the malate-aspartate shuttle as a key player in the oxidative metabolism of lactate: similar to glycolysis that aliments OXPHOS with pyruvate produced by pyruvate kinase and NADH produced by glyceraldehyde-3-phosphate dehydrogenase (GAPDH), oxidative lactate metabolism aliments OXPHOS in oxidative tumor cells with pyruvate and NADH produced by LDH1.

Cancer as a Proinflammatory Environment: Metastasis and Cachexia

The development of the syndrome of cancer cachexia and that of metastasis are related with a poor prognostic for cancer patients. They are considered multifactorial processes associated with a proinflammatory environment, to which tumour microenvironment and other tissues from the tumour bearing individuals contribute. The aim of the present review is to address the role of ghrelin, myostatin, leptin, HIF, IL-6, TNF-α, and ANGPTL-4 in the regulation of energy balance, tumour development, and tumoural cell invasion. Hypoxia induced factor plays a prominent role in tumour macro- and microenvironment, by modulating the release of proinflammatory cytokines.