Monocarboxylate transporters 1-4 in NSCLC: MCT1 is an independent prognostic marker for survival

Developing technologies and areas of interest in lung cancer screening adjuncts

Lung cancer remains the leading cause of cancer mortality. Screening guidelines have been implemented in the past decade to aid in earlier detection of at-risk groups. Nevertheless, computed tomography (CT) scans, the principal screening modality in use today, are still low yield, with 3.6% of lung cancer confirmed amongst 39.1% of lesions detected over a 3-year period. They also carry relatively high false positive rates, between 9% and 27%, which can bear unnecessary financial and emotional costs to patients. As such, research efforts have been dedicated to the development of lung cancer screening adjuncts to improve detection reliability. We herein review several emerging technologies in this specific arena and their efficacy. These include plasma markers (microDNA, DNA methylation, and tumor-associated antibodies), breath/sputum biomarkers [volatile organic compounds (VOCs) and exhaled breath condensate (EBC)], proteomics, metabolomics, and machine learning, such as radiomics technology. We find that, across the board, they offer promising results in terms of non-invasive diagnostics, genetic sequencing for higher-risk individuals, and accessibility for a diverse cohort of patients. While these screening adjuncts are unlikely to completely replace the current standard of care at the moment, continued research into these technologies is crucial to improve and personalize the identification, treatment, and outcome of lung cancer patients in the near future.

A systemic analysis of monocarboxylate transporters in ovarian cancer and possible therapeutic interventions

Monocarboxylate transporters (MCTs) play an immense role in metabolically active solid tumors by regulating concentration-dependent transport of different important monocarboxylates including pyruvate and lactate and are encoded by the SLC16A family of genes. Given the vast array of functions, these transporters play in oncogenesis, our objective was to look into the association of MCT1 (SLC16A1), MCT2 (SLC16A7), MCT3 (SLC16A8), and MCT4 (SLC16A3) with Epithelial ovarian cancer (EOC) pathophysiology by exploiting various publicly available databases and web resources. Few of the in silico findings were confirmed via in vitro experiments in EOC cell lines, SKOV3 and OAW-42. MCT1 and MCT4 were found to be upregulated at the mRNA level in OC tissues compared to normal. However, only higher level of MCT4 mRNA was found to be associated with poor patient survival. MCT4 was positively correlated with gene families responsible for invasion, migration, and immune modification, proving it to be one of the most important MCTs for therapeutic intervention. We compared the effects of MCT1/2 blocker SR13800 and a broad-spectrum MCT blocker α-Cyano Hydroxy Cinnamic Acid (α-CHCA) and discovered that α-CHCA has a greater effect on diminishing the invasive behavior of the cancer cells than MCT1/2 blocker SR13800. From our study, MCT4 has emerged as a prospective marker for predicting poor patient outcomes and a potential therapeutic target.

The role of lactate in cardiovascular diseases

Cardiovascular diseases pose a major threat worldwide. Common cardiovascular diseases include acute myocardial infarction (AMI), heart failure, atrial fibrillation (AF) and atherosclerosis. Glycolysis process often has changed during these cardiovascular diseases. Lactate, the end-product of glycolysis, has been overlooked in the past but has gradually been identified to play major biological functions in recent years. Similarly, the role of lactate in cardiovascular disease is gradually being recognized. Targeting lactate production, regulating lactate transport, and modulating circulating lactate levels may serve as potential strategies for the treatment of cardiovascular diseases in the future. The purpose of this review is to integrate relevant clinical and basic research on the role of lactate in the pathophysiological process of cardiovascular disease in recent years to clarify the important role of lactate in cardiovascular disease and to guide further studies exploring the role of lactate in cardiovascular and other diseases. Video Abstract.

Role of Human Monocarboxylate Transporter 1 (hMCT1) and 4 (hMCT4) in Tumor Cells and the Tumor Microenvironment

In recent years, the abnormal glucose metabolism of tumor cells has attracted increasing attention. Abnormal glucose metabolism is closely related to the occurrence and development of tumors. Monocarboxylate transporters (MCTs) transport the sugar metabolites lactic acid and pyruvate, which affect glucose metabolism and tumor progression in a variety of ways. Thus, research has recently focused on MCTs and their potential functions in cancer. The MCT superfamily consists of 14 members. MCT1 and MCT4 play a crucial role in the maintenance of intracellular pH in tumor cells by transporting monocarboxylic acids (such as lactate, pyruvate and butyrate). MCT1 and MCT4 are highly expressed in a variety of tumor cells and are involved the proliferation, invasion and migration of tumor cells, which are closely related to the prognosis of cancer. Because of their important functions in tumor cells, MCT1 and MCT4 have become potential targets for cancer treatment. In this review, we focus on the structure, function and regulation of MCT1 and MCT4 and discuss the developed inhibitors of MCT1 and MCT4 to provide more comprehensive information that might aid in the development of strategies targeting MCTs in cancer.

Metabolic Heterogeneity, Plasticity, and Adaptation to "Glutamine Addiction" in Cancer Cells: The Role of Glutaminase and the GTωA [Glutamine Transaminase-ω-Amidase (Glutaminase II)] Pathway

Many cancers utilize l-glutamine as a major energy source. Often cited in the literature as "l-glutamine addiction", this well-characterized pathway involves hydrolysis of l-glutamine by a glutaminase to l-glutamate, followed by oxidative deamination, or transamination, to α-ketoglutarate, which enters the tricarboxylic acid cycle. However, mammalian tissues/cancers possess a rarely mentioned, alternative pathway (the glutaminase II pathway): l-glutamine is transaminated to α-ketoglutaramate (KGM), followed by ω-amidase (ωA)-catalyzed hydrolysis of KGM to α-ketoglutarate. The name glutaminase II may be confused with the glutaminase 2 (GLS2) isozyme. Thus, we recently renamed the glutaminase II pathway the "glutamine transaminase-ω-amidase (GTωA)" pathway. Herein, we summarize the metabolic importance of the GTωA pathway, including its role in closing the methionine salvage pathway, and as a source of anaplerotic α-ketoglutarate. An advantage of the GTωA pathway is that there is no net change in redox status, permitting α-ketoglutarate production during hypoxia, diminishing cellular energy demands. We suggest that the ability to coordinate control of both pathways bestows a metabolic advantage to cancer cells. Finally, we discuss possible benefits of GTωA pathway inhibitors, not only as aids to studying the normal biological roles of the pathway but also as possible useful anticancer agents.

Expression analysis of BACH1 with clinical variables using the US breast cancer patient cohort

Background

Studies on functional roles of BACH1 reveal that BACH1 promotes cancer metastasis and regulates metabolic networks for metastatic processes. However, little is known about BACH1 protein expression in breast tumors and its relevance to clinical variables as a biomarker for patients with breast tumors.

Methods

Using a tissue microarray (TMA) of breast tumor tissues isolated from a patient cohort (N = 130) expression of BACH1 and its target gene MCT1 (encoded by SLC16A1) were monitored by immunohistochemistry (IHC) assays and scored for further analyses. We examined the association between scores of BACH1 (Allredscoretotal) or MCT1 (Hscoretotal3×2×1x) with clinical variables including: breast cancer subtypes, tissue types, tumor size, patient's racial/ethnic background, and age group. Groups were compared using the Mann-Whitney U test (or the non-parametric Kruskal-Wallis test when appropriate) for numerical data. A proportional odds ordinal logistic model was used to examine multiple covariates. Associations between variables were evaluated with the Spearman's correlation coefficient.

Results

BACH1 and MCT1 expression were detected in 90.76% (N = 118/130) and 92.30% (N = 120/130) of patients by IHC, respectively, in our study. After dichotomizing tumor size (small: 3-25 in diameter vs. big: 27-85 mm in diameter), BACH1 expression scores were significantly higher (p = 0.015) in the bigger tumor group (mean [SD]; 4.20 [1.796]) compared with the smaller tumor group (3.920 [1.693]). Of interest, we also observed significantly higher BACH1 scores (p = 0.004) in tumors from Black women (3.971 [1.514]; N = 69) compared with those of White women (3.02 [1.942]; N = 49). Consistent with mRNA expression analysis, BACH1 expression is most abundant in the basal-like tumors among all subtypes, specifically in Black women, whereas MCT1 expression scores are considerably higher in the basal-like tumors regardless of race. In addition, there was a positive association between BACH1 and MCT1 IHC scores in tumors from Black women, although a weak association between them in tumors from White women. In general, we did not detect associations between MCT1 IHC scores and race, tumor size, tissue types, or patient's age.

Conclusions

We found strong associations of BACH1 expression with tumor size and the basal-like subtype, respectively. Importantly, BACH1 expresses significantly higher in tumors from Black women than White women, as well as in the basal-like subtype of breast tumors from Black women. Our study suggests that BACH1 expression could serve as a potential race-associated biomarker indicating poor prognosis.

Targeting monocarboxylate transporters (MCTs) in cancer: How close are we to the clinics?

As a result of metabolic reprogramming, cancer cells display high rates of glycolysis, causing an excess production of lactate along with an increase in extracellular acidity. Proton-linked monocarboxylate transporters (MCTs) are crucial in the maintenance of this metabolic phenotype, by mediating the proton-coupled lactate flux across cell membranes, also contributing to cancer cell pH regulation. Among the proteins codified by the SLC16 gene family, MCT1 and MCT4 isoforms are the most explored in cancers, being overexpressed in many cancer types, from solid tumours to haematological malignancies. Similarly to what occurs in particular physiological settings, MCT1 and MCT4 are able to mediate lactate shuttles among cancer cells, and also between cancer and stromal cells in the tumour microenvironment. This form of metabolic cooperation is responsible for important cancer aggressiveness features, such as cell proliferation, survival, angiogenesis, migration, invasion, metastasis, immune tolerance and therapy resistance. The growing understanding of MCT functions and regulation is offering a new path to the design of novel inhibitors that can be foreseen in clinical practices. This review provides an overview of the role of MCT isoforms in cancer and summarizes the recent advances in their pharmacological targeting, highlighting the potential of new potent and selective MCT1 and/or MCT4 inhibitors in cancer therapeutics, and anticipating its inclusion in clinical practice.

Hyperoxia induces glucose metabolism reprogramming and intracellular acidification by suppressing MYC/MCT1 axis in lung cancer

The perils and promises of inspiratory hyperoxia (IH) in oncology are still controversial, especially for patients with lung cancer. Increasing evidence shows that hyperoxia exposure is relevant to the tumor microenvironment. However, the detailed role of IH on the acid-base homeostasis of lung cancer cells remains unclear. In this study, the effects of 60% oxygen exposure on intra- and extracellular pH were systematically evaluated in H1299 and A549 cells. Our data indicate that hyperoxia exposure reduces intracellular pH, which might be expected to reduce the proliferation, invasion, and epithelial-to-mesenchymal transition of lung cancer cells. RNA sequencing, Western blot, and PCR analysis reveal that monocarboxylate transporter 1 (MCT1) mediates intracellular lactate accumulation and intracellular acidification of H1299 and A549 cells at 60% oxygen exposure. In vivo studies further demonstrate that MCT1 knockdown dramatically reduces lung cancer growth, invasion, and metastasis. The results of luciferase and ChIP-qPCR assays further confirm that MYC is a transcription factor of MCT1, and PCR and Western blot assays confirm that MYC is downregulated under hyperoxic conditions. Collectively, our data reveal that hyperoxia can suppress the MYC/MCT1 axis and cause the accumulation of lactate and intracellular acidification, thereby retarding tumor growth and metastasis.

Impact of microvessel patterns and immune status in NSCLC: a non-angiogenic vasculature is an independent negative prognostic factor in lung adenocarcinoma

Introduction

Non-small cell lung carcinomas (NSCLC) exhibit different microvessel patterns (MVPs). Basal (BA), diffuse (DA) and papillary (PA) patterns show signs of angiogenesis (new blood vessels), while an alveolar pattern indicates that tumors are co-opting existing normal vessels (non-angiogenic alveolar, NAA). NAA tumor growth is known to exist in NSCLC, but little is known about its prognostic impact in different histological subgroups, and about associations between MVPs and immune cell infiltration.

Methods

Detailed patterns of angiogenic and non-angiogenic tumor growth were evaluated by CD34 immunohistochemistry in whole tissue slides from 553 surgically treated patients with NSCLC stage I-IIIB disease. Associations with clinicopathological variables and markers related to tumor immunology-, angiogenesis- and hypoxia/metabolism were explored, and disease-specific survival (DSS) was analyzed according to histological subtypes.

Results

The predominant MVP was angiogenic in 82% of tumors: BA 40%, DA 34%, PA 8%, while a NAA pattern dominated in 18%. A contribution of the NAA pattern >5% (NAA+), i.e., either dominant or minority, was observed in 40.1% of tumors and was associated with poor disease-specific survival (DSS) (p=0.015). When stratified by histology, a significantly decreased DSS for NAA+ was found for adenocarcinomas (LUAD) only (p< 0.003). In multivariate analyses, LUAD NAA+ pattern was a significant independent prognostic factor; HR 2.37 (CI 95%, 1.50-3.73, p< 0.001). The immune cell density (CD3, CD4, CD8, CD45RO, CD204, PD1) added prognostic value in squamous cell carcinoma (LUSC) and LUAD with 0-5% NAA (NAA-), but not in LUAD NAA+. In correlation analyses, there were several significant associations between markers related to tumor metabolism (MCT1, MCT4, GLUT1) and different MVPs.

Conclusion

The NAA+ pattern is an independent poor prognostic factor in LUAD. In NAA+ tumors, several immunological markers add prognostic impact in LUSC but not in LUAD.

Targeted lactate dehydrogenase genes silencing in probiotic lactic acid bacteria: A possible paradigm shift in colorectal cancer treatment?

Even though the pathophysiology of colorectal cancer (CRC) is complicated and poorly understood, interactions between risk factors appear to be key in the development and progression of the malignancy. The popularity of using lactic acid bacteria (LAB) prebiotics and probiotics to modulate the tumor microenvironment (TME) has grown widely over the past decade. The objective of this study was therefore to determine the detrimental effects of LAB-derived lactic acid in the colonic mucosa in colorectal cancer management. Six library databases and a web search engine were used to execute a structured systematic search of the existing literature, considering all publications published up until August 2022. A total of 7817 papers were screened, all of which were published between 1995 and August 2022. However, only 118 articles met the inclusion criterion. Lactic acid has been directly linked to the massive proliferation of cancerous cells since the glycolytic pathway provides cancerous cells with not only ATP, but also biosynthetic intermediates for rapid growth and proliferation. Our research suggests that targeting LAB metabolic pathways is capable of suppressing tumor growth and that the LDH gene is critical for tumorigenesis. Silencing of Lactate dehydrogenase, A (LDHA), B (LDHB), (LDHL), and hicD genes should be explored to inhibit fermentative glycolysis yielding lactic acid as the by-product. More studies are necessary for a solid understanding of this topic so that LAB and their corresponding lactic acid by-products do not have more adverse effects than their widely touted positive outcomes in CRC management.

Comprehensive analysis of pan-cancer reveals the potential of SLC16A1 as a prognostic and immunological biomarker

SLC16A1 plays an important role in the development of multiple cancer types. Pan-cancer analysis may have significant impacts on the exploration of the relationship between SLC16A1 gene expression, prognosis and the molecular mechanisms of tumorigenesis. In this study, through the analysis of TCGA and GEO datasets, we explored the expression level and survival prognosis of SLC16A1 in pan-cancer, and further explored the differences in SLC16A1 gene mutation, methylation, and phosphorylation between tumor and normal tissues. In addition, we focused on the biological function of this gene and the relationship between the prognosis and immune infiltration by immune infiltration analysis and enrichment analysis, in order to evaluate the diagnostic and prognostic significance of SLC16A1 in carcinomas. The study found that SLC16A1 was highly expressed in 14 kinds of tumors, and there were statistically significant differences in the prognosis of 9 tumors. The phosphorylation level of S467 increased in OV, RCC, and UCEC. There was a statistically negative correlation between the CD8+ T-cell infiltration level and the SLC16A1 expression in HNSC, LUSC, SARC, TGCT, and KIRC. The cancer-related fibroblasts were positively correlated with SLC16A1 expression in BLCA, BRCA, KIRC, KIRP, PAAD, PCPG, and THCA. The enrichment analysis indicated that the tumorigenesis mechanism of this gene was mainly related to "glycolysis and glucose metabolism synthesis." SLC16A1 was a promising prognostic and immunological biomarker in pan-cancer.

Prognostic Value of Monocarboxylate Transporter 1 Overexpression in Cancer: A Systematic Review

Energy production by cancer is driven by accelerated glycolysis, independently of oxygen levels, which results in increased lactate production. Lactate is shuttled to and from cancer cells via monocarboxylate transporters (MCTs). MCT1 works both as an importer and an extruder of lactate, being widely studied in recent years and generally associated with a cancer aggressiveness phenotype. The aim of this systematic review was to assess the prognostic value of MCT1 immunoexpression in different malignancies. Study collection was performed by searching nine different databases (PubMed, EMBASE, ScienceDirect, Scopus, Cochrane Library, Web of Science, OVID, TRIP and PsycINFO), using the keywords "cancer", "Monocarboxylate transporter 1", "SLC16A1" and "prognosis". Results showed that MCT1 is an indicator of poor prognosis and decreased survival for cancer patients in sixteen types of malignancies; associations between the transporter's overexpression and larger tumour sizes, higher disease stage/grade and metastasis occurrence were also frequently observed. Yet, MCT1 overexpression correlated with better outcomes in colorectal cancer, pancreatic ductal adenocarcinoma and non-small cell lung cancer patients. These results support the applicability of MCT1 as a biomarker of prognosis, although larger cohorts would be necessary to validate the overall role of MCT1 as an outcome predictor.

Lithium: A Promising Anticancer Agent

Lithium is a therapeutic cation used to treat bipolar disorders but also has some important features as an anti-cancer agent. In this review, we provide a general overview of lithium, from its transport into cells, to its innovative administration forms, and based on genomic, transcriptomic, and proteomic data. Lithium formulations such as lithium acetoacetate (LiAcAc), lithium chloride (LiCl), lithium citrate (Li3C6H5O7), and lithium carbonate (Li2CO3) induce apoptosis, autophagy, and inhibition of tumor growth and also participate in the regulation of tumor proliferation, tumor invasion, and metastasis and cell cycle arrest. Moreover, lithium is synergistic with standard cancer therapies, enhancing their anti-tumor effects. In addition, lithium has a neuroprotective role in cancer patients, by improving their quality of life. Interestingly, nano-sized lithium enhances its anti-tumor activities and protects vital organs from the damage caused by lipid peroxidation during tumor development. However, these potential therapeutic activities of lithium depend on various factors, such as the nature and aggressiveness of the tumor, the type of lithium salt, and its form of administration and dosage. Since lithium has been used to treat bipolar disorder, the current study provides an overview of its role in medicine and how this has changed. This review also highlights the importance of this repurposed drug, which appears to have therapeutic cancer potential, and underlines its molecular mechanisms.

Research progress of abnormal lactate metabolism and lactate modification in immunotherapy of hepatocellular carcinoma

Tumors meet their energy, biosynthesis, and redox demands through metabolic reprogramming. This metabolic abnormality results in elevated levels of metabolites, particularly lactate, in the tumor microenvironment. Immune cell reprogramming and cellular plasticity mediated by lactate and lactylation increase immunosuppression in the tumor microenvironment and are emerging as key factors in regulating tumor development, metastasis, and the effectiveness of immunotherapies such as immune checkpoint inhibitors. Reprogramming of glucose metabolism and the "Warburg effect" in hepatocellular carcinoma (HCC) lead to the massive production and accumulation of lactate, so lactate modification in tumor tissue is likely to be abnormal as well. This article reviews the immune regulation of abnormal lactate metabolism and lactate modification in hepatocellular carcinoma and the therapeutic strategy of targeting lactate-immunotherapy, which will help to better guide the medication and treatment of patients with hepatocellular carcinoma.

Importance of lactate dehydrogenase (LDH) and monocarboxylate transporters (MCTs) in cancer cells

Background

In most regions, cancer ranks the second most frequent cause of death following cardiovascular disorders.

Aim

In this article, we review the various aspects of glycolysis with a focus on types of MCTs and the importance of lactate in cancer cells.

Results and Discussion

Metabolic changes are one of the first and most important alterations in cancer cells. Cancer cells use different pathways to survive, energy generation, growth, and proliferation compared to normal cells. The increase in glycolysis, which produces substances such as lactate and pyruvate, has an important role in metastases and invasion of cancer cells. Two important cellular proteins that play a role in the production and transport of lactate include lactate dehydrogenase and monocarboxylate transporters (MCTs). These molecules by their various isoforms and different tissue distribution help to escape the immune system and expansion of cancer cells under different conditions.

Targeting glycolysis for cancer therapy using drug delivery systems

There is close crosstalk between cancer metabolism and immunity. Cancer metabolism regulation is a promising therapeutic target for cancer immunotherapy. Warburg effect is characterized by abnormal glucose metabolism that includes common features of increased glucose uptake and lactate production. The aerobic glycolysis can reprogram the cancer cells and promote the formation of a suppressive immune microenvironment. As a case in point, lactate plays an essential role in tumorigenesis, which is the end product of glycolysis as well as serves as a fuel supporting cancer cell survival. Meanwhile, it is also an important immune regulator that drives immunosuppression in tumors. Immunometabolic therapy is to intervene tumor metabolism and regulate the related metabolites that participate in the innate and acquired immunity, thereby reinstalling the immune balance and eliciting anticancer immune responses. In this contribution to the Orations - New Horizons of the Journal of controlled Release I will provide an overview of glucose metabolism in tumors and its effects on drug resistance and tumor metastasis, and present the advance of glycolysis-targeting therapy strategies with drug delivery techniques, as well as discuss the challenges in glycolysis-targeting immunometabolic therapy.

The strategic roles of four enzymes in the interconnection between metabolism and oncogene activation in non-small cell lung cancer: Therapeutic implications

NSCLC is the leading cause of cancer mortality and represents a major challenge in cancer therapy. Intrinsic and acquired anticancer drug resistance are promoted by hypoxia and HIF-1α. Moreover, chemoresistance is sustained by the activation of key signaling pathways (such as RAS and its well-known downstream targets PI3K/AKT and MAPK) and several mutated oncogenes (including KRAS and EGFR among others). In this review, we highlight how these oncogenic factors are interconnected with cell metabolism (aerobic glycolysis, glutaminolysis and lipid synthesis). Also, we stress the key role of four metabolic enzymes (PFK1, dimeric-PKM2, GLS1 and ACLY), which promote the activation of these oncogenic pathways in a positive feedback loop. These four tenors orchestrating the coordination of metabolism and oncogenic pathways could be key druggable targets for specific inhibition. Since PFK1 appears as the first tenor of this orchestra, its inhibition (and/or that of its main activator PFK2/PFKFB3) could be an efficacious strategy against NSCLC. Citrate is a potent physiologic inhibitor of both PFK1 and PFKFB3, and NSCLC cells seem to maintain a low citrate level to sustain aerobic glycolysis and the PFK1/PI3K/EGFR axis. Awaiting the development of specific non-toxic inhibitors of PFK1 and PFK2/PFKFB3, we propose to test strategies increasing citrate levels in NSCLC tumors to disrupt this interconnection. This could be attempted by evaluating inhibitors of the citrate-consuming enzyme ACLY and/or by direct administration of citrate at high doses. In preclinical models, this "citrate strategy" efficiently inhibits PFK1/PFK2, HIF-1α, and IGFR/PI3K/AKT axes. It also blocks tumor growth in RAS-driven lung cancer models, reversing dedifferentiation, promoting T lymphocytes tumor infiltration, and increasing sensitivity to cytotoxic drugs.

Monocarboxylate Transporter 4 in Cancer-Associated Fibroblasts Is a Driver of Aggressiveness in Aerodigestive Tract Cancers

The most common cancers of the aerodigestive tract (ADT) are non-small cell lung cancer (NSCLC) and head and neck squamous cell carcinoma (HNSCC). The tumor stroma plays an important role in ADT cancer development and progression, and contributes to the metabolic heterogeneity of tumors. Cancer-associated fibroblasts (CAFs) are the most abundant cell type in the tumor stroma of ADT cancers and exert pro-tumorigenic functions. Metabolically, glycolytic CAFs support the energy needs of oxidative (OXPHOS) carcinoma cells. Upregulation of the monocarboxylate transporter 4 (MCT4) and downregulation of isocitrate dehydrogenase 3α (IDH3α) are markers of glycolysis in CAFs, and upregulation of the monocarboxylate transporter 1 (MCT1) and the translocase of the outer mitochondrial membrane 20 (TOMM20) are markers of OXPHOS in carcinoma cells. It is unknown if glycolytic metabolism in CAFs is a driver of ADT cancer aggressiveness. In this study, co-cultures in vitro and co-injections in mice of ADT carcinoma cells with fibroblasts were used as experimental models to study the effects of fibroblasts on metabolic compartmentalization, oxidative stress, carcinoma cell proliferation and apoptosis, and overall tumor growth. Glycolytic metabolism in fibroblasts was modulated using the HIF-1α inhibitor BAY 87-2243, the antioxidant N-acetyl cysteine, and genetic depletion of MCT4. We found that ADT human tumors express markers of metabolic compartmentalization and that co-culture models of ADT cancers recapitulate human metabolic compartmentalization, have high levels of oxidative stress, and promote carcinoma cell proliferation and survival. In these models, BAY 87-2243 rescues IDH3α expression and NAC reduces MCT4 expression in fibroblasts, and these treatments decrease ADT carcinoma cell proliferation and increase cell death. Genetic depletion of fibroblast MCT4 decreases proliferation and survival of ADT carcinoma cells in co-culture. Moreover, co-injection of ADT carcinoma cells with fibroblasts lacking MCT4 reduces tumor growth and decreases the expression of markers of metabolic compartmentalization in tumors. In conclusion, metabolic compartmentalization with high expression of MCT4 in CAFs drives aggressiveness in ADT cancers.

A Heme-Binding Transcription Factor BACH1 Regulates Lactate Catabolism Suggesting a Combined Therapy for Triple-Negative Breast Cancer

The oncogenic expression or mutation of tumor suppressors drives metabolic alteration, causing cancer cells to utilize diverse nutrients. Lactate is a known substrate for cancer cells, yet the regulatory mechanisms of lactate catabolism are limited. Here, we show that a heme-binding transcription factor, BACH1, negatively regulates lactate catabolic pathways in triple-negative breast cancer (TNBC) cells. BACH1 suppresses the transcriptional expression of monocarboxylate transporter 1 (MCT1) and lactate dehydrogenase B, inhibiting lactate-mediated mitochondrial metabolism. In our studies, the depletion of BACH1 either genetically or pharmacologically increased the lactate use of TNBC cells, increasing their sensitivity to MCT1 inhibition. Thus, small inhibitory molecules (SR13800 and AZD3965) blocking MCT1 better suppressed the growth of BACH1-depleted TNBC cells than did the controls. Particularly, hemin treatment degrading BACH1 proteins induced lactate catabolism in TNBC cells, generating synthetic lethality with MCT1 inhibition. Our data indicates that targeting BACH1 generates metabolic vulnerability and increases sensitivity to lactate transporter inhibition, suggesting a potential novel combination therapy for cancer patients with TNBC.

Visual analysis on the research of monocarboxylate transporters based on CiteSpace

BACKGROUND

Monocarboxylate transports (MCTs), a family of solute carrier protein, play an important role in maintenance of cellular stability in tumor cells by mediating lactate exchange across membranes. The objective of this paper is to evaluate the knowledge structure, development trend, and research hotspot of MCTs research field systematically and comprehensively.

METHODS

Based on the 1526 publications from 2010 to 2020 retrieved from "Web of Science Core Collection" (WoSCC), we visually analyzed the MCTs research in terms of subject category, scientific collaboration network, keywords, and high-frequency literature using CiteSpace.

RESULTS

The number of publications exhibits an upward trend from 2010 to 2020 and the top 5 countries in the MCTs research were the United States, China, Japan, Germany, and England. Visser TJ was the most prolific author, while Halestrap AP was the most influential author with the highest citations. Analysis of the 7 cluster units from the co-cited references and keywords revealed that high expression of MCTs induced by oxidative stress and glycolysis was the pivotal point in the MCTs research field, while regulation of metabolism in tumor microenvironment, prognostic markers of cancer, and targeted inhibitors are the top 3 research frontiers topics.

CONCLUSION

This study will help the new researcher to understand the MCTs related field, master the research frontier, and obtain valuable scientific information, thus providing directions for follow-up research.

MCT4 is induced by metastasis-enhancing pathogenic mitochondrial NADH dehydrogenase gene mutations and can be a therapeutic target

Pathogenic mitochondrial NADH dehydrogenase (ND) gene mutations enhance the invasion and metastasis of various cancer cells, and they are associated with metastasis in human non-small cell lung cancer (NSCLC). Moreover, monocarboxylate transporter 4 (MCT4) is overexpressed in solid cancers and plays a role in cancer cell proliferation and survival. Here, we report that MCT4 is exclusively expressed in mouse transmitochondrial cybrids with metastasis-enhancing pathogenic ND6 mutations. A high level of MCT4 is also detected in human NSCLC cell lines and tissues predicted to carry pathogenic ND mutations and is associated with poor prognosis in NSCLC patients. MCT4 expression in the cell lines is suppressed by N-acetyl-L-cysteine. Phosphatidylinositol-3 kinase (PI3K), AMP-activated protein kinase (AMPK) and mechanistic target of rapamycin (mTOR) are involved in the regulation of MCT4 expression in the transmitochondrial cybrid cells. An MCT1/4 inhibitor effectively kills NSCLC cells with predicted pathogenic ND mutations, but an MCT1/2 inhibitor does not have the same effect. Thus, MCT4 expression is augmented by pathogenic ND mutations and could be a biomarker and a therapeutic target in pathogenic ND mutation-harbouring metastatic tumours.

The tissue expression of MCT3, MCT8, and MCT9 genes in women with breast cancer

BACKGROUND

Breast cancer (BC) is a common malignancy with a high mortality rate. Malignant cell transformation is associated with metabolic changes. One group of proteins that are affected is the monocarboxylate transporters (MCTs-SLC16A). The MCTs comprise 14 members, and they play an important role in the growth, proliferation, and metabolism of cancer cells by transporting monocarboxylates such as lactate, pyruvate and thyroid hormones.

OBJECTIVE

We aimed to evaluate the expression of MCT3 (SLC16A8), MCT8 (SLC16A2) and MCT9 (SLC16A9) genes in breast cancer samples, comparing to normal adjacent tissues.

METHODS

Forty paired breast cancer tumor samples, the adjacent non-tumor and five healthy tissues were collected. Three cancer cell lines (MCF-7, MDA-MB-231, and SKBR3) were also analyzed. The expression of SLC16A8, SLC16A2 and SLC16A9 were assessed using quantitative real-time PCR. The relationship between gene expression with the pathological features of the tumors, and the hormone receptors status of the patient's tumors were also analyzed.

RESULTS

There was a significantly lower expression of the MCT3 gene in tumor samples compared to adjacent normal tissue and healthy samples (p value < 0.05). There was a significant difference in the expression of all three candidate genes between the BC tissues and normal tissues, and for the, tissues with different hormone receptor status and the molecular subtypes. Altered MCT8 and MCT9 gene expression was associated with a reduced survival CONCLUSION: MCT3 expression is significantly downregulated in breast cancer tissue. MCT3 may represent a novel therapeutic target in breast cancer patients, or in some hormone receptor subgroups.

Blocking Aerobic Glycolysis by Targeting Pyruvate Dehydrogenase Kinase in Combination with EGFR TKI and Ionizing Radiation Increases Therapeutic Effect in Non-Small Cell Lung Cancer Cells

Simple Summary

Non-small cell lung cancer (NSCLC) patients harboring oncogenic mutations in the epidermal growth factor receptor (EGFR) inevitably develop resistance to targeted EGFR tyrosine kinase inhibitors (TKI) therapy. To support malignant features associated with cancer development and therapy resistance, the cancer cells adapt their metabolic rate and pathways. As an example, aerobic glycolysis, where the cells use glycolysis in the presence of oxygen, is frequently seen. Here we show that targeting aerobic glycolysis represents a promising strategy in cancer therapeutics.

Abstract

Increased glycolytic activity is a hallmark of cancer initiation and progression and is often observed in non-small cell lung cancer (NSCLC). Pyruvate dehydrogenase (PDH) complex acts as a gatekeeper between glycolysis and oxidative phosphorylation, and activation of PDH is known to inhibit glycolytic activity. As part of a standard therapeutic regimen, patients with NSCLC harboring oncogenic mutations in the epidermal growth factor receptor (EGFR) are treated with EGFR tyrosine kinase inhibitors (EGFR TKIs). Independent of good initial response, development of resistance to this therapy is inevitable. In the presented work, we propose that inhibition of glycolysis will add to the therapeutic effects and possibly prevent development of resistance against both EGFR TKIs and ionizing radiation in NSCLC. Analysis of transcriptome data from two independent NSCLC patient cohorts identified increased expression of pyruvate dehydrogenase kinase 1 (PDHK1) as well as upregulated expression of genes involved in glucose metabolism in tumors compared to normal tissue. We established in vitro models of development of resistance to EGFR TKIs to study metabolism and determine if targeting PDHK would prevent development of resistance to EGFR TKIs in NSCLC cells. The PDHK1 inhibitor dichloroacetate (DCA) in combination with EGFR TKIs and/or ionizing radiation was shown to increase the therapeutic effect in our NSCLC cell models. This mechanism was associated with redirected metabolism towards pyruvate oxidation and reduced lactate production, both in EGFR TKI sensitive and resistant NSCLC cells. Using DCA, the intracellular pool of pyruvate available for lactic fermentation becomes limited. Consequently, pyruvate is redirected to the mitochondria, and reinforces mitochondrial activity. Addition of DCA to cell culture deacidifies the extracellular microenvironment as less lactate is produced and excreted. In our study, we find that this redirection of metabolism adds to the therapeutic effect of EGFR TKI and ionizing radiation in NSCLC.

Targeting Cancer Metabolism and Current Anti-Cancer Drugs

Several studies have exploited the metabolic hallmarks that distinguish between normal and cancer cells, aiming at identifying specific targets of anti-cancer drugs. It has become apparent that metabolic flexibility allows cancer cells to survive during high anabolic demand or the depletion of nutrients and oxygen. Cancers can reprogram their metabolism to the microenvironments by increasing aerobic glycolysis to maximize ATP production, increasing glutaminolysis and anabolic pathways to support bioenergetic and biosynthetic demand during rapid proliferation. The increased key regulatory enzymes that support the relevant pathways allow us to design small molecules which can specifically block activities of these enzymes, preventing growth and metastasis of tumors. In this review, we discuss metabolic adaptation in cancers and highlight the crucial metabolic enzymes involved, specifically those involved in aerobic glycolysis, glutaminolysis, de novo fatty acid synthesis, and bioenergetic pathways. Furthermore, we also review the success and the pitfalls of the current anti-cancer drugs which have been applied in pre-clinical and clinical studies.

Lactate in the Tumor Microenvironment: An Essential Molecule in Cancer Progression and Treatment

Simple Summary

The role of lactate in cancer described by Otto Warburg in 1927 states that cancer cells uptake high amount of glucose with a marked increase in lactate production, this is known as the “Warburg effect”. Since then lactate turn out to be a major signaling molecule in cancer progression. Its release from tumor cells is accompanied by acidification ranging from 6.3 to 6.9 in the tumor microenvironment (TME) which favors processes such as tumor promotion, angiogenesis, metastasis, tumor resistance and more importantly, immunosuppression which has been associated with a poor outcome. The goal of this review is to examine and discuss in deep detail the recent studies that address the role of lactate in all these cancerous processes. Lastly, we explore the efforts to target the lactate production and its transport as a promising approach for cancer therapeutics.

Abstract

Cancer is a complex disease that includes the reprogramming of metabolic pathways by malignant proliferating cells, including those affecting the tumor microenvironment (TME). The “TME concept” was introduced in recognition of the roles played by factors other than tumor cells in cancer progression. In response to the hypoxic or semi-hypoxic characteristic of the TME, cancer cells generate a large amount of lactate via the metabolism of glucose and glutamine. Export of this newly generated lactate by the tumor cells together with H+ prevents intracellular acidification but acidifies the TME. In recent years, the importance of lactate and acidosis in carcinogenesis has gained increasing attention, including the role of lactate as a tumor-promoting metabolite. Here we review the existing literature on lactate metabolism in tumor cells and the ability of extracellular lactate to direct the metabolic reprogramming of those cells. Studies demonstrating the roles of lactate in biological processes that drive or sustain carcinogenesis (tumor promotion, angiogenesis, metastasis and tumor resistance) and lactate’s role as an immunosuppressor that contributes to tumor evasion are also considered. Finally, we consider recent therapeutic efforts using available drugs directed at and interfering with lactate production and transport in cancer treatment.

Hyperpolarized [1-13C]pyruvate-to-[1-13C]lactate conversion is rate-limited by monocarboxylate transporter-1 in the plasma membrane

Hyperpolarized [1-¹³C]pyruvate magnetic resonance spectroscopic imaging (MRSI) is a noninvasive metabolic-imaging modality that probes carbon flux in tissues and infers the state of metabolic reprograming in tumors. Prevailing models attribute elevated hyperpolarized [1-¹³C]pyruvate-to-[1-¹³C]lactate conversion rates in aggressive tumors to enhanced glycolytic flux and lactate dehydrogenase A (LDHA) activity (Warburg effect). By contrast, we find by cross-sectional analysis using genetic and pharmacological tools in mechanistic studies applied to well-defined genetically engineered cell lines and tumors that initial hyperpolarized [1-¹³C]pyruvate-to-[1-¹³C]lactate conversion rates as well as global conversion were highly dependent on and critically rate-limited by the transmembrane influx of [1-¹³C]pyruvate mediated predominately by monocarboxylate transporter-1 (MCT1). Specifically, in a cell-encapsulated alginate bead model, induced short hairpin (shRNA) knockdown or overexpression of MCT1 quantitatively inhibited or enhanced, respectively, unidirectional pyruvate influxes and [1-¹³C]pyruvate-to-[1-¹³C]lactate conversion rates, independent of glycolysis or LDHA activity. Similarly, in tumor models in vivo, hyperpolarized [1-¹³C]pyruvate-to-[1-¹³C]lactate conversion was highly dependent on and critically rate-limited by the induced transmembrane influx of [1-¹³C]pyruvate mediated by MCT1. Thus, hyperpolarized [1-¹³C]pyruvate MRSI measures primarily MCT1-mediated [1-¹³C]pyruvate transmembrane influx in vivo, not glycolytic flux or LDHA activity, driving a reinterpretation of this maturing new technology during clinical translation. Indeed, Kaplan-Meier survival analysis for patients with pancreatic, renal, lung, and cervical cancers showed that high-level expression of MCT1 correlated with poor overall survival, and only in selected tumors, coincident with LDHA expression. Thus, hyperpolarized [1-¹³C]pyruvate MRSI provides a noninvasive functional assessment primarily of MCT1 as a clinical biomarker in relevant patient populations.

Lactic Acidosis in the Presence of Glucose Diminishes Warburg Effect in Lung Adenocarcinoma Cells

Lactic acidosis (3 to 40 mM, pH < 6.9) is a condition found in solid tumors because tumor cells have a high rate of glucose consumption and lactate production even in the presence of oxygen; nevertheless, the microenvironment might still provide a sufficient glucose supply. Lactic acidosis has been proposed to shift metabolism from aerobic glycolysis toward oxidative phosphorylation (OXPHOS). We tested if lung tumor cells cultured under lactic acidosis shift their metabolism from glycolysis to OXPHOS by consuming extracellular lactate, increasing growth rate. We analyzed lung adenocarcinoma (A-549, A-427) cell lines and non-transformed fibroblast cells (MRC-5), which were cultured using RPMI-1640 medium initially containing lactate (2 mM) and glucose (10 mM), at pH 7.2 or 6.2 and oxygen tension 21% O₂ (normoxia) or 2% O₂ (hypoxia). We obtained growth curves, as well as glucose consumption and lactate production rates (measured during exponential growth) for each cell line. HIF-1α (Hypoxia-inducible factor 1 α), CS (citrate synthase) and AMPK (AMP-activated protein kinase) transcript levels were analyzed using RT-qPCR. By flow cytometry, we determined: (a) expression of glucose transporters (GLUT)1 and 4; (b) lactate transporters (MCT)1 and 4; (c) cell cycle profile, and (d) protein levels of HIF-1α, total and phosphorylated AMPK (pAMPK). Mitochondrial functionality was evaluated by measuring O₂ consumption in tumor cells using polarography and a Clark-type electrode. Tumor and non-transformed cells used both aerobic glycolysis and OXPHOS for obtaining energy. As of 48 h of culture, lactate levels ranged from (4.5–14 mM), thus forming a lactic environment. Lactic acidosis diminished GLUT1/GLUT4 expression and glucose consumption in A-549, but not in A-427 cells, and induced differential expression of HIF-1α, AMPK, and CS transcripts. A-427 cells increased pAMPK and HIF-1α levels and shifted their metabolism increasing OXPHOS; thus supporting cell growth. Conversely, A-549 cells increased HIF-1α protein levels, but did not activate AMPK and diminished OXPHOS. A-549 cells survived by arresting cells in G1-phase. Our findings show that lactic acidosis diminishes Warburg effect in tumor cells, but this change does not necessarily promote a shift to OXPHOS. Hence, lung adenocarcinomas show a differential metabolic response even when they are under the same microenvironmental conditions.

Lactate: Fueling the fire starter

It is becoming increasingly appreciated that intermediates of metabolic pathways, besides their anabolic and catabolic functions, can act as signaling molecules and influence the outcome of immune responses. Although lactate was previously considered as a waste product of glucose metabolism, accumulating evidence has highlighted its pivotal role in regulating diverse biological processes, including immune cell polarization, differentiation and effector functions. In addition, lactate is a key player in modulating tumor immune surveillance. Hence, targeting lactate-induced signaling pathways is a promising tool to reduce inflammation, to prevent autoimmunity and to restore anti-tumor immune response. This article is characterized under: Biological Mechanisms > Metabolism.

Comprehensive analysis of the SLC16A gene family in pancreatic cancer via integrated bioinformatics

SLC16A family members play crucial roles in tumorigenesis and tumor progression. However, the exact role of distinct members in the SLC16A family in human pancreatic cancer remains unclear. Integrated bioinformatics analysis for the identification of therapeutic targets for certain cancers based on transcriptomics, proteomics and high-throughput sequencing could help us obtain novel information and understand potential underlying molecular mechanisms. In the present study, we investigated SLC16A family members in pancreatic cancer through accumulated data from GEO (Gene Expression Omnibus), TCGA (The Cancer Genome Atlas) and other available databases. The expression profile, clinical application significance and prognostic value of the SLC16A family for patients with pancreatic cancer were explored. SLC16A1, SLC16A3 and SLC16A13 exhibited biomarker potential for prognosis, and we further identified their related genes and regulatory networks, revealing core molecular pathways that require further investigation for pancreatic cancer.

Lactate Beyond a Waste Metabolite: Metabolic Affairs and Signaling in Malignancy

To sustain their high proliferation rates, most cancer cells rely on glycolytic metabolism, with production of lactic acid. For many years, lactate was seen as a metabolic waste of glycolytic metabolism; however, recent evidence has revealed new roles of lactate in the tumor microenvironment, either as metabolic fuel or as a signaling molecule. Lactate plays a key role in the different models of metabolic crosstalk proposed in malignant tumors: among cancer cells displaying complementary metabolic phenotypes and between cancer cells and other tumor microenvironment associated cells, including endothelial cells, fibroblasts, and diverse immune cells. This cell metabolic symbiosis/slavery supports several cancer aggressiveness features, including increased angiogenesis, immunological escape, invasion, metastasis, and resistance to therapy. Lactate transport is mediated by the monocarboxylate transporter (MCT) family, while another large family of G protein-coupled receptors (GPCRs), not yet fully characterized in the cancer context, is involved in lactate/acidosis signaling. In this mini-review, we will focus on the role of lactate in the tumor microenvironment, from metabolic affairs to signaling, including the function of lactate in the cancer-cancer and cancer-stromal shuttles, as well as a signaling oncometabolite. We will also review the prognostic value of lactate metabolism and therapeutic approaches designed to target lactate production and transport.

Intestinal OCTN2- and MCT1-targeted drug delivery to improve oral bioavailability

Various drug transporters are widely expressed throughout the intestine and play important roles in absorbing nutrients and drugs, thus providing high quality targets for the design of prodrugs or nanoparticles to facilitate oral drug delivery. In particular, intestinal carnitine/organic cation transporter 2 (OCTN2) and mono-carboxylate transporter protein 1 (MCT1) possess high transport capacities and complementary distributions. Therefore, we outline recent developments in transporter-targeted oral drug delivery with regard to the OCTN2 and MCT1 proteins in this review. First, basic information of the two transporters is reviewed, including their topological structures, characteristics and functions, expression and key features of their substrates. Furthermore, progress in transporter-targeting prodrugs and nanoparticles to increase oral drug delivery is discussed, including improvements in the oral absorption of anti-inflammatory drugs, antiepileptic drugs and anticancer drugs. Finally, the potential of a dual transporter-targeting strategy is discussed.

Effect of transforming growth factor-β1 on functional expression of monocarboxylate transporter 1 in alveolar epithelial A549 cells

Epithelial-mesenchymal transition (EMT) contributes to the development of severe lung diseases, such as pulmonary fibrosis. Recently, it has been reported that EMT involves complex metabolic reprogramming triggered by several factors including transforming growth factor (TGF-β1) and that monocarboxylate transporter (MCT1) plays an essential role in these metabolic changes. The aim of the present study was to clarify the functional expression of MCT1 during TGF-β1-induced EMT in alveolar epithelial A549 cells. The transport function of MCT1 in A549 cells was examined using [³H]γ-hydroxybutyrate (GHB) and [³H] lactic acid (LA) as substrates and α-cyano-4-hydroxycinnamate (CHC), lactic acid, phloretin, and AR-C155858 (AR) as inhibitors of MCT1. EMT was induced by treating the cells with TGF-β1. mRNA and protein expression levels were analyzed using real-time PCR and Western blotting, respectively. Time-, temperature-, and pH-dependent GHB and LA uptake were observed in A549 cells. CHC, lactic acid, phloretin, and AR significantly inhibited the uptake of GHB in a concentration-dependent manner, suggesting that MCT1 is primarily responsible for transport of monocarboxylates such as GHB and LA in A549 cells. TGF-β1 treatment significantly enhanced GHB and LA uptake as well as the mRNA and protein expression levels of MCT1 in A549 cells. These changes were neutralized by co-treatment with SB431542, an inhibitor for the TGF-β1 signaling pathway. CHC and AR had no effect on TGF-β1-induced EMT-related gene expression changes. Here, we have clearly characterized functional expression of MCT1 in A549 cells and have shown that MCT1 may be upregulated via the TGF-β1 signaling pathway.

Carbonic anhydrase IX and acid transport in cancer

Alterations in tumour metabolism and acid/base regulation result in the formation of a hostile environment, which fosters tumour growth and metastasis. Acid/base homoeostasis in cancer cells is governed by the concerted interplay between carbonic anhydrases (CAs) and various transport proteins, which either mediate proton extrusion or the shuttling of acid/base equivalents, such as bicarbonate and lactate, across the cell membrane. Accumulating evidence suggests that some of these transporters interact both directly and functionally with CAIX to form a protein complex coined the 'transport metabolon'. Transport metabolons formed between bicarbonate transporters and CAIX require CA catalytic activity and have a function in cancer cell migration and invasion. Another type of transport metabolon is formed by CAIX and monocarboxylate transporters. In this complex, CAIX functions as a proton antenna for the transporter, which drives the export of lactate and protons from the cell. Since CAIX is almost exclusively expressed in cancer cells, these transport metabolons might serve as promising targets to interfere with tumour pH regulation and energy metabolism. This review provides an overview of the current state of research on the function of CAIX in tumour acid/base transport and discusses how CAIX transport metabolons could be exploited in modern cancer therapy.

A novel MCT1 and MCT4 dual inhibitor reduces mitochondrial metabolism and inhibits tumour growth of feline oral squamous cell carcinoma

Monocarboxylate transporters (MCTs) support tumour growth by regulating the transport of metabolites in the tumour microenvironment. High MCT1 or MCT4 expression is correlated with poor outcomes in human patients with head and neck squamous cell carcinoma (HNSCC). Recently, drugs targeting these transporters have been developed and may prove to be an effective treatment strategy for HNSCC. Feline oral squamous cell carcinoma (OSCC) is an aggressive and treatment-resistant malignancy resembling advanced or recurrent HNSCC. The goals of this study were to investigate the effects of a previously characterized dual MCT1 and MCT4 inhibitor, MD-1, in OSCC as a novel treatment approach for feline oral cancer. We also sought to determine the potential of feline OSCC as a large animal model for the further development of MCT inhibitors to treat human HNSCC. In vitro, MD-1 reduced the viability of feline OSCC and human HNSCC cell lines, altered glycolytic and mitochondrial metabolism and synergized with platinum-based chemotherapies. While MD-1 treatment increased lactate concentrations in an HNSCC cell line, the inhibitor failed to alter lactate levels in feline OSCC cells, suggesting an MCT-independent activity. In vivo, MD-1 significantly inhibited tumour growth in a subcutaneous xenograft model and prolonged overall survival in an orthotopic model of feline OSCC. Our results show that MD-1 may be an effective therapy for the treatment of feline oral cancer. Our findings also support the further investigation of feline OSCC as a large animal model to inform the development of MCT inhibitors and future clinical studies in human HNSCC.

Expression of Monocarboxylate Transporter 1 Is Associated With Better Prognosis and Reduced Nodal Metastasis in Pancreatic Ductal Adenocarcinoma

OBJECTIVES

Because lactate is believed to support tumor growth, monocarboxylate transporters (MCTs), which transport lactate, have been investigated in multiple tumors. However, the significance of MCTs in pancreatic cancer is unclear.

METHODS

A retrospective survey was conducted on 240 patients who underwent surgical resection for pancreatic ductal adenocarcinoma without preoperative treatment. The expression of MCT1, MCT2, MCT3, MCT4, and the glucose transporter 1 (GLUT1) was assessed in tumor cells and cancer-associated fibroblasts (CAFs) by tissue microarrays and immunohistochemistry. The impact of their expression on patient outcome and clinicopathological characteristics was also analyzed.

RESULTS

In tumor cells, MCT1, MCT2, MCT3, MCT4, and GLUT1 were detected in 52 (22%), 31 (13%), 149 (62%), 204 (85%), and 235 (98%) cases, respectively. In CAFs, MCT2, MCT4, and GLUT1 were detected in 9 (3.8%), 178 (74%), and 36 (15%) cases, respectively. In tumor cells, MCT1 expression was associated with extended overall and progression-free survival and decreased nodal metastasis. Conversely, MCT4 expression in CAFs was associated with shortened survival.

CONCLUSIONS

In tumor cells, MCT1 expression is associated with better prognosis and reduced nodal metastasis in pancreatic cancer, contrary to findings of past in vitro studies. Conversely, MCT4 expression in CAFs is indicative of worse prognosis.

MCT4 has a potential to be used as a prognostic biomarker - a systematic review and meta-analysis

The role of several metabolic changes, such as hypoxia and acidosis, in the tumour environment has caught the attention of researchers in cancer progression and invasion. Lactate transport is one of the acidosis-enhancing processes that are mediated via monocarboxylate transporters (MCTs). We conducted a systematic review and meta-analysis to investigate the expression of two cancer-relevant MCTs (MCT1 and MCT4) and their potential prognostic significance in patients with metastasis of different types of cancer. Studies were included if they reported the number of metastatic tissue samples expressing either low or high levels of MCT1 and/or MCT4 or those revealing the hazard ratios (HRs) of the overall survival (OS) or disease-free survival (DFS) as prognostic indicators. During the period between 2010 and 2018, a total of 20 articles including 3831 patients (56.3% males) were identified. There was a significant association between MCT4 expression (high versus low) and lymph node metastasis [odds ratio (OR)=1.87, 95% confidence interval (CI)=1.10-3.17, P=0.02] and distant metastasis (OR=2.18, 95%CI=1.65-2.86, P<0.001) and the correlation remained significant for colorectal and hepatic cancer in subgroup analysis. For survival analysis, patients with shorter OS periods exhibited a higher MCT4 expression [hazard ratio (HR)=1.78, 95%CI=1.49-2.13, P<0.001], while DFS was shorter in patients with high MCT1 (HR=1.48, 95%CI=1.04-2.10, P=0.03) and MCT4 expression (HR=1.70, 95%CI=1.19-2.42, P=0.003) when compared to their counterparts with low expression levels. Future research studies should consider the pharmacologic inhibition of MCT4 to effectively inhibit cancer progression to metastasis.

Lactate transporters as therapeutic targets in cancer and inflammatory diseases

INTRODUCTION

Inflammation is associated with the accumulation of lactate at sites of tumor-growth and inflammation. Lactate initiates tissue-responses contributing to disease. We discuss the potential of targeting lactate transporters in the treatment of cancer and inflammatory conditions. Areas covered: Lactate is the end product of glycolysis, often considered a waste metabolite but also a fuel for oxidative cells. It is however an active signaling molecule with immunomodulatory and angiogenic properties. They are the consequence of lactate binding to membrane receptor(s) or being transported through specific carrier-mediated-transporters across the cellular membrane. Carriers are distinct in proton-linked-monocarboxylate-transporters (MCTs) and Na+-coupled- electrogenic-transporters, expressed by several tissues including immune-system, endothelium and epithelium. Several tumors and inflammatory sites show accumulation of lactate and altered expression of its transporters, thus suggesting a role of this metabolite in cancer and inflammation. We review the most recent evidence on lactate biology, focusing on transporter expression and function in health and disease. Expert opinion: Lactate-initiated signaling is gaining attention for its implications in cancer and inflammation. This review discusses the therapeutic potential of targeting lactate transporters and drugs that are already in clinical use for cancer and discusses the opportunity to develop new therapeutics for inflammation and cancer.

Loss of function of miR-342-3p results in MCT1 over-expression and contributes to oncogenic metabolic reprogramming in triple negative breast cancer

Triple-negative breast cancer (TNBC) is a heterogeneous and aggressive neoplasia lacking the expression of hormonal receptors and human epidermal growth factor receptor-2. Accumulating evidence has highlighted the importance of miRNAs dysregulation in the establishment of cancer programs, but the functional role of many miRNAs remains unclear. The description of miRNAs roles might provide novel strategies for treatment. In the present work, an integrated analysis of miRNA transcriptional landscape was performed (N = 132), identifying the significant down-modulation of miR-342-3p in TNBC, probably because of the aberrant activity of estrogen receptor, which serves as a transcription factor of the miRNA, as demonstrated by a siRNA-knockdown approach. The enhanced expression of miR-342-3p significantly decreased cell proliferation, viability and migration rates of diverse TN cells in vitro. Bioinformatic and functional analyses revealed that miR-342-3p directly targets the monocarboxylate transporter 1 (MCT1), which promotes lactate and glucose fluxes alteration, thus disrupting the metabolic homeostasis of tumor cells. Optical metabolic imaging assay defined a higher optical redox ratio in glycolytic cells overexpressing miR-342-3p. Furthermore, we found that hypoxic conditions and glucose starvation attenuate miR-342-3p expression, suggesting a crosstalk program between these metabolic factors. Consistently, miR-342-3p down-modulation is associated with an increased MCT1 expression level and glycolytic score in human triple negative tumors. Overall, we described for the first time the regulatory activity of miR-342-3p on relevant metabolic carcinogenic pathways in TN breast cancers.

Utilization of lactic acid in human myotubes and interplay with glucose and fatty acid metabolism

Once assumed only to be a waste product of anaerobe glycolytic activity, lactate is now recognized as an energy source in skeletal muscles. While lactate metabolism has been extensively studied in vivo, underlying cellular processes are poorly described. This study aimed to examine lactate metabolism in cultured human myotubes and to investigate effects of lactate exposure on metabolism of oleic acid and glucose. Lactic acid, fatty acid and glucose metabolism were studied in myotubes using [¹⁴C(U)]lactic acid, [¹⁴C]oleic acid and [¹⁴C(U)]glucose, respectively. Myotubes expressed both the MCT1, MCT2, MCT3 and MCT4 lactate transporters, and lactic acid was found to be a substrate for both glycogen synthesis and lipid storage. Pyruvate and palmitic acid inhibited lactic acid oxidation, whilst glucose and α-cyano-4-hydroxycinnamic acid inhibited lactic acid uptake. Acute addition of lactic acid inhibited glucose and oleic acid oxidation, whereas oleic acid uptake was increased. Pretreatment with lactic acid for 24 h did not affect glucose or oleic acid metabolism. By replacing glucose with lactic acid during the whole culturing period, glucose uptake and oxidation were increased by 2.8-fold and 3-fold, respectively, and oleic acid oxidation was increased 1.4-fold. Thus, lactic acid has an important role in energy metabolism of human myotubes.

Beta-hydroxybutyrate (3-OHB) can influence the energetic phenotype of breast cancer cells, but does not impact their proliferation and the response to chemotherapy or radiation

Background

Ketogenic diets (KDs) or short-term fasting are popular trends amongst supportive approaches for cancer patients. Beta-hydroxybutyrate (3-OHB) is the main physiological ketone body, whose concentration can reach plasma levels of 2–6 mM during KDs or fasting. The impact of 3-OHB on the biology of tumor cells described so far is contradictory. Therefore, we investigated the effect of a physiological concentration of 3 mM 3-OHB on metabolism, proliferation, and viability of breast cancer (BC) cells in vitro.

Methods

Seven different human BC cell lines (BT20, BT474, HBL100, MCF-7, MDA-MB 231, MDA-MB 468, and T47D) were cultured in medium with 5 mM glucose in the presence of 3 mM 3-OHB at mild hypoxia (5% oxygen) or normoxia (21% oxygen). Metabolic profiling was performed by quantification of the turnover of glucose, lactate, and 3-OHB and by Seahorse metabolic flux analysis. Expression of key enzymes of ketolysis as well as the main monocarboxylic acid transporter MCT2 and the glucose-transporter GLUT1 was analyzed by RT-qPCR and Western blotting. The effect of 3-OHB on short- and long-term cell proliferation as well as chemo- and radiosensitivity were also analyzed.

Results

3-OHB significantly changed the oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) in BT20 cells resulting in a more oxidative energetic phenotype. MCF-7 and MDA-MB 468 cells had increased ECAR only in response to 3-OHB, while the other three cell types remained uninfluenced. All cells expressed MCT2 and GLUT1, thus being able to uptake the metabolites. The consumption of 3-OHB was not strongly linked to mRNA overexpression of key enzymes of ketolysis and did not correlate with lactate production and glucose consumption. Neither 3-OHB nor acetoacetate did interfere with proliferation. Further, 3-OHB incubation did not modify the response of the tested BC cell lines to chemotherapy or radiation.

Conclusions

We found that a physiological level of 3-OHB can change the energetic profile of some BC cell lines. However, 3-OHB failed to influence different biologic processes in these cells, e.g., cell proliferation and the response to common breast cancer chemotherapy and radiotherapy. Thus, we have no evidence that 3-OHB generally influences the biology of breast cancer cells in vitro.

Electronic supplementary material

The online version of this article (10.1186/s40170-018-0180-9) contains supplementary material, which is available to authorized users.

Monocarboxylate Transporter 1 (MCT1) is an independent prognostic biomarker in endometrial cancer

BACKGROUND

Endometrial cancer (EC) is a major health concern due to its rising incidence. Whilst early stage disease is generally cured by surgery, advanced EC has a poor prognosis with limited treatment options. Altered energy metabolism is a hallmark of malignancy. Cancer cells drive tumour growth through aerobic glycolysis and must export lactate to maintain intracellular pH. The aim of this study was to evaluate the expression of the lactate/proton monocarboxylate transporters MCT1 and MCT4 and their chaperone CD147 in EC, with the ultimate aim of directing future drug development.

METHODS

MCT1, MCT4 and CD147 expression was examined using immunohistochemical analysis in 90 endometrial tumours and correlated with clinico-pathological characteristics and survival outcomes.

RESULTS

MCT1 and MCT4 expression was observed in the cytoplasm, the plasma membrane or both locations. CD147 was detected in the plasma membrane and associated with MCT1 (p = 0.003) but not with MCT4 (p = 0.207) expression. High MCT1 expression was associated with reduced overall survival (p = 0.029) and remained statistically significant after adjustment for survival covariates (p = 0.017).

CONCLUSION

Our data suggest that MCT1 expression is an important marker of poor prognosis in EC. MCT1 inhibition may have potential as a treatment for advanced or recurrent EC.

Glucose-dependent growth arrest of leukemia cells by MCT1 inhibition: Feeding Warburg's sweet tooth and blocking acid export as an anticancer strategy

This study aims to investigate the utilization of The Warburg Effect, cancer's "sweet tooth" and natural greed for glucose to enhance the effect of monocarboxylate transporter inhibition on cellular acidification. By simulating hyperglycemia with high glucose we may increase the effectiveness of inhibition of lactate and proton export on the dysregulation of cell pH homeostasis causing cell death or disruption of growth in cancer cells. MCT1 and MCT4 expression was determined in MCF7 and K562 cell lines using RT-PCR. Cell viability, growth, intracellular pH and cell cycle analysis was measured in the cell lines grown in 5 mM and 25 mM glucose containing media in the presence and absence of the MCT1 inhibitor AR-C155858 (1 μM) and the NHE1 inhibitor cariporide (10 μM). The MCT1 inhibitor, AR-C155858 had minimal effect on the viability, growth and intracellular pH of MCT4 expressing MCF7 cells. AR-C155858 had no effect on the viability of the MCT1 expressing K562 cells, but decreased intracellular pH and cell proliferation, by a glucose-dependent mechanism. Inhibition of NHE1 on its own had a no effect on cell growth, but together with AR-C155858 showed an additive effect on inhibition of cell growth. In cancer cells that only express MCT1, increased glucose concentrations in the presence of an MCT1 inhibitor decreased intracellular pH and reduced cell growth by G1 phase cell-cycle arrest. Thus we propose a transient hyperglycemic-clamp in combination with proton export inhibitors be evaluated as an adjunct to cancer treatment in clinical studies.

Metabolic coupling and the Reverse Warburg Effect in cancer: Implications for novel biomarker and anticancer agent development

Glucose is a key metabolite used by cancer cells to generate ATP, maintain redox state and create biomass. Glucose can be catabolized to lactate in the cytoplasm, which is termed glycolysis, or alternatively can be catabolized to carbon dioxide and water in the mitochondria via oxidative phosphorylation. Metabolic heterogeneity exists in a subset of human tumors, with some cells maintaining a glycolytic phenotype while others predominantly utilize oxidative phosphorylation. Cells within tumors interact metabolically with transfer of catabolites from supporting stromal cells to adjacent cancer cells. The Reverse Warburg Effect describes when glycolysis in the cancer-associated stroma metabolically supports adjacent cancer cells. This catabolite transfer, which induces stromal-cancer metabolic coupling, allows cancer cells to generate ATP, increase proliferation, and reduce cell death. Catabolites implicated in metabolic coupling include the monocarboxylates lactate, pyruvate, and ketone bodies. Monocarboxylate transporters (MCT) are critically necessary for release and uptake of these catabolites. MCT4 is involved in the release of monocarboxylates from cells, is regulated by catabolic transcription factors such as hypoxia inducible factor 1 alpha (HIF1A) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and is highly expressed in cancer-associated fibroblasts. Conversely, MCT1 is predominantly involved in the uptake of these catabolites and is highly expressed in a subgroup of cancer cells. MYC and TIGAR, which are genes involved in cellular proliferation and anabolism, are inducers of MCT1. Profiling human tumors on the basis of an altered redox balance and intra-tumoral metabolic interactions may have important biomarker and therapeutic implications. Alterations in the redox state and mitochondrial function of cells can induce metabolic coupling. Hence, there is interest in redox and metabolic modulators as anticancer agents. Also, markers of metabolic coupling have been associated with poor outcomes in numerous human malignancies and may be useful prognostic and predictive biomarkers.

High expression of monocarboxylate transporter 4 predicts poor prognosis in patients with lung adenocarcinoma

Monocarboxylate transporter 4 (MCT-4) serves a key function in transporting lactate across the plasma membrane in various types of human cancer. Evidence indicates that MCT-4 expression is associated with non-small cell lung cancer; however, the distribution and clinical significance of MCT-4 in the lung adenocarcinoma (AC) subtype remain unknown. Thus, the aim of the present study was to explore the clinicopathological significance and prognostic values of MCT-4 expression in lung AC. Quantum dots-based immunofluorescence histochemistry was performed to observe the expression of MCT-4 in 146 specimens of lung AC and corresponding normal lung tissues. MCT-4 protein and mRNA were detected by western blotting and reverse transcription-quantitative polymerase chain reaction from 30 fresh samples of lung AC and corresponding normal lung tissues. Of the 146 samples, 25 (17.1%) exhibited high and 121 (82.9%) exhibited low MCT-4 expression. MCT-4, at the protein and mRNA level, was significantly increased in tumor specimens compared with corresponding normal lung tissue (P<0.05). MCT-4 protein expression was significantly associated with depth of invasion (P=0.034). A survival curve analysis indicated that high MCT-4 expression in lung AC was associated with a decreased overall survival rate (P=0.001). Multivariate analysis demonstrated that high MCT-4 level was an independent prognostic factor (hazard ratio, 3.192; 95% confidence interval, 1.804–5.646; P=0.001) for patients with lung AC. The results have demonstrated that high MCT-4 expression is significantly associated with the poor prognosis and disease progression of patients with lung AC. Therefore, MCT-4 may be a candidate therapeutic target in lung AC.

Expression of enzymes related to glucose metabolism in non-small cell lung cancer and prognosis

Purpose/Aim: Cancer cells are addicted to glycolytic anaerobic pathways, in presence or in absence of a functional Krebs' cycle (phenomenon Warburg). This metabolic predilection relies on both extracellular (impaired vascularization and oxygenation) and intracellular (oncogenic activation of genes) causes.

MATERIALS AND METHODS

We investigated the expression and prognostic relevance of enzymes involved in the glucose absorption and metabolism, monocarboxylate transporter (MCT) expression, MCT1 and MCT2, pentose pathway (Glucose-6-phospahte dehydrogenase G6PD), glycogene synthesis (glycogene synthase GYS1), glycolysis (Hexokinase HXKII, phosphofructokinase PFK1, fructose biphosphate aldolase), fate of pyruvate (pyruvate dehydrogenase PDH, phosphorylated pPDH, PDH kinase PDK1, lactate dehydrogenase LDH5 and LDH1) and key Kreb's cycle enzymes (citrate synthase CSynth and isocitrate dehydrogenase IDH).

RESULTS

A strong overexpression of the above enzymes/proteins was noted in a varying percentage of cases examined. An interesting significant correlation between the enzymes involved in glycolysis and with the LDH5 was noted. Adenocarcinomas expressed higher levels of GLUT1 and MCT2 compared to other subtypes. Stage (p = 0.0001), aldolase (p = 0.004), LDH5 (p = 0.008), GLUT2 (p = 0.008), MCT2 (p = 0.009), GSYS1 (p = 0.04), and GLUT1 (p = 0.05) were significantly related with poor disease specific overall survival. In multivariate analysis stage (p = 0.001), LDH5 (p = 0.04), pPDH (p = 0.04), and aldolase (p = 0.04) were independent prognostic variables.

CONCLUSION

It is concluded that an orchestrated activation of glucose absorption and metabolism towards anaerobic pathways characterize the majority of NSCLC, and this phenotype is strongly linked with an aggressive clinical behavior. This glycolytic addiction of lung cancer cell is revealed as a key therapeutic target.

Tumor stroma interaction is mediated by monocarboxylate metabolism

Human breast tumors contain significant amounts of stromal cells. There exists strong evidence that these stromal cells support cancer development and progression by altering various pathways (e.g. downregulation of tumor suppressor genes or autocrine signaling loops). Here, we suggest that stromal carcinoma-associated fibroblasts (CAFs), shown to be generated from bone marrow-derived mesenchymal stem cells, may (i) recycle tumor-derived lactate for their own energetic requirements, thereby sparing glucose for neighboring glycolytic tumor cells, and (ii) subsequently secrete surplus energetically and biosynthetically valuable metabolites of lactate oxidation, such as pyruvate, to support tumor growth. Lactate, taken up by stromal CAFs, is converted to pyruvate, which is then utilized by CAFs for energy needs as well as excreted and shared with tumor cells. We have interrogated lactate oxidation in CAFs to determine what metabolites may be secreted, and how they may affect the metabolism and growth of MDA-MB-231 breast cancer cells. We found that CAFs secrete pyruvate as a metabolite of lactate oxidation. Further, we show that pyruvate is converted to lactate to promote glycolysis in MDA-MB-231 cells and helps to control elevated ROS levels in these tumor cells. Finally, we found that inhibiting or interfering with ROS management, using the naturally occurring flavonoid phloretin (found in apple tree leaves), adds to the cytotoxicity of the conventional chemotherapeutic agent doxorubicin. Our work demonstrates that a lactate-pyruvate, reciprocally-supportive metabolic relationship may be operative within the tumor microenvironment (TME) to support tumor growth, and may be a useful drug target.

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.

Intracellular lactate-mediated induction of estrogen receptor beta (ERβ) in biphasic malignant pleural mesothelioma cells

Biphasic malignant pleural mesothelioma (MPM) is the second most common histotype of MPM. It is histologically characterized by the concomitant presence of epithelioid and sarcomatoid features, the latter associated with worse prognosis.

In this report we describe that silencing of AKT1 in spindle-shaped biphasic MPM cells promotes the shift toward an epithelioid phenotype. Furthermore, AKT1 silencing resulted in decreased expression of the lactate/H+ symporter MCT4 and its chaperone CD147/Basigin, and in the induction of estrogen receptor β (ERβ) expression. We provide evidence that ERβ expression is induced by increased intracellular lactate concentration. Spheroid culturing and tumor growth of ERβ negative biphasic MPM in nude mice resulted in the induction of ERβ expression and response to the selective agonist KB9520. In both models, the treatment with the ERβ agonist results in reduced cell proliferation, decreased expression of MCT4 and CD147/Basigin and increased acetylation and inactivation of AKT1. Collectively, in response to metabolic changes, ERβ expression is induced and exerts an anti-tumor effect through selective agonist activation. The possibility to reverse the more aggressive biphasic mesothelioma histotype by targeting ERβ with a selective agonist could represent a new effective treatment strategy.