Effect of diclofenac on SLC16A3/MCT4 by the Caco-2 cell line

Microglia lactylation in relation to central nervous system diseases

The development of neurodegenerative diseases is closely related to the disruption of central nervous system homeostasis. Microglia, as innate immune cells, play important roles in the maintenance of central nervous system homeostasis, injury response, and neurodegenerative diseases. Lactate has been considered a metabolic waste product, but recent studies are revealing ever more of the physiological functions of lactate. Lactylation is an important pathway in lactate function and is involved in glycolysis-related functions, macrophage polarization, neuromodulation, and angiogenesis and has also been implicated in the development of various diseases. This review provides an overview of the lactate metabolic and homeostatic regulatory processes involved in microglia lactylation, histone versus non-histone lactylation, and therapeutic approaches targeting lactate. Finally, we summarize the current research on microglia lactylation in central nervous system diseases. A deeper understanding of the metabolic regulatory mechanisms of microglia lactylation will provide more options for the treatment of central nervous system diseases.

A lactate-dependent shift of glycolysis mediates synaptic and cognitive processes in male mice

Astrocytes control brain activity via both metabolic processes and gliotransmission, but the physiological links between these functions are scantly known. Here we show that endogenous activation of astrocyte type-1 cannabinoid (CB1) receptors determines a shift of glycolysis towards the lactate-dependent production of D-serine, thereby gating synaptic and cognitive functions in male mice. Mutant mice lacking the CB1 receptor gene in astrocytes (GFAP-CB1-KO) are impaired in novel object recognition (NOR) memory. This phenotype is rescued by the gliotransmitter D-serine, by its precursor L-serine, and also by lactate and 3,5-DHBA, an agonist of the lactate receptor HCAR1. Such lactate-dependent effect is abolished when the astrocyte-specific phosphorylated-pathway (PP), which diverts glycolysis towards L-serine synthesis, is blocked. Consistently, lactate and 3,5-DHBA promoted the co-agonist binding site occupancy of CA1 post-synaptic NMDA receptors in hippocampal slices in a PP-dependent manner. Thus, a tight cross-talk between astrocytic energy metabolism and gliotransmission determines synaptic and cognitive processes.

pH regulators and their inhibitors in tumor microenvironment

As an important characteristic of tumor, acidic tumor microenvironment (TME) is closely related to immune escape, invasion, migration and drug resistance of tumor. The acidity of the TME mainly comes from the acidic products produced by the high level of tumor metabolism, such as lactic acid and carbon dioxide. pH regulators such as monocarboxylate transporters (MCTs), carbonic anhydrase IX (CA IX), and Na+/H+ exchange 1 (NHE1) expel protons directly or indirectly from the tumor to maintain the pH balance of tumor cells and create an acidic TME. We review the functions of several pH regulators involved in the construction of acidic TME, the structure and structure-activity relationship of pH regulator inhibitors, and provide strategies for the development of small-molecule antitumor inhibitors based on these targets.

Exploring monocarboxylate transporter inhibition for cancer treatment

Cells are separated from the environment by a lipid bilayer membrane that is relatively impermeable to solutes. The transport of ions and small molecules across this membrane is an essential process in cell biology and metabolism. Monocarboxylate transporters (MCTs) belong to a vast family of solute carriers (SLCs) that facilitate the transport of certain hydrophylic small compounds through the bilipid cell membrane. The existence of 446 genes that code for SLCs is the best evidence of their importance. In-depth research on MCTs is quite recent and probably promoted by their role in cancer development and progression. Importantly, it has recently been realized that these transporters represent an interesting target for cancer treatment. The search for clinically useful monocarboxylate inhibitors is an even more recent field. There is limited pre-clinical and clinical experience with new inhibitors and their precise mechanism of action is still under investigation. What is common to all of them is the inhibition of lactate transport. This review discusses the structure and function of MCTs, their participation in cancer, and old and newly developed inhibitors. Some suggestions on how to improve their anticancer effects are also discussed.

Diclofenac and metformin synergistic dose dependent inhibition of hamster fibrosarcoma, rescued with mebendazole

We examined whether combinig diclofenac and metformin in doses equivalent to human doses would synergize their anticancer activity on fibrosarcoma inoculated to hamsters and in vitro. Rescue experiment was performed to examine whether the prosurvival NF-κB stimulation by mebendazole can reverse anticancer effects of the treatment. BHK-21/C13 cell culture was subcutaneously inoculated to Syrian golden hamsters randomly divided into groups (6 animals per group): 1) untreated control; treated daily with 2) diclofenac; 3) metformin; 4) combinations of diclofenac and metformin at various doses; 5) combination of diclofenac, metformin and mebendazole; 6) mebendazole. Dose response curves were made for diclofenac and metformin combination. Tumor growth kinetics, biophysical, pathological, histological and immunohistochemical characteristics of excised tumors and hamster organs as well as biochemical and hematological blood tests were compared among the groups. Single treatments had no anticancer effects. Diclofenac (60 mg/kg/day) exhibited significant (P < 0.05) synergistic inhibitory effect with metformin (500 mg/kg/day) on all tumor growth parameters, without toxicity and influence on biochemical and hematological blood tests. The same results were obtained with double doses of diclofenac and metformin combination. The addition of mebendazole to the diclofenac and metformin combination rescued tumor expansion. Furthermore, diclofenac with metformin demonstrated antiproliferative effects in hamster fibrosarcoma BHK-21/C13, human lung carcinoma A549 (CCL-185), colon carcinoma HT-29 (HTB-38) and cervical carcinoma HeLa (CCL-2) cell cultures, with markedly lower cytotoxicity in the normal fetal lung MRC-5 cells. In conclusion, diclofenac and metformin combination may be recommended for potential use in oncology, due to synergistic anticancer effect in doses achievable in humans.

In Vitro and In Vivo Models for Drug Transport Across the Blood-Testis Barrier

The blood-testis barrier (BTB) is a selectively permeable membrane barrier formed by adjacent Sertoli cells (SCs) in the seminiferous tubules of the testes that develops intercellular junctional complexes to protect developing germ cells from external pressures. However, due to this inherent defense mechanism, the seminiferous tubule lumen can act as a pharmacological sanctuary site for latent viruses (e.g., Ebola, Zika) and cancers (e.g., leukemia). Therefore, it is critical to identify and evaluate BTB carrier-mediated drug delivery pathways to successfully treat these viruses and cancers. Many drugs are unable to effectively cross cell membranes without assistance from carrier proteins like transporters because they are large, polar, and often carry a charge at physiologic pH. SCs express transporters that selectively permit endogenous compounds, such as carnitine or nucleosides, across the BTB to support normal physiologic activity, although reproductive toxicants can also use these pathways, thereby circumventing the BTB. Certain xenobiotics, including select cancer therapeutics, antivirals, contraceptives, and environmental toxicants, are known to accumulate within the male genital tract and cause testicular toxicity; however, the transport pathways by which these compounds circumvent the BTB are largely unknown. Consequently, there is a need to identify the clinically relevant BTB transport pathways in in vitro and in vivo BTB models that recapitulate human pharmacokinetics and pharmacodynamics for these xenobiotics. This review summarizes the various in vitro and in vivo models of the BTB reported in the literature and highlights the strengths and weaknesses of certain models for drug disposition studies. SIGNIFICANCE STATEMENT: Drug disposition to the testes is influenced by the physical, physiological, and immunological components of the blood-testis barrier (BTB). But many compounds are known to cross the BTB by transporters, resulting in pharmacological and/or toxicological effects in the testes. Therefore, models that assess drug transport across the human BTB must adequately account for these confounding factors. This review identifies and discusses the benefits and limitations of various in vitro and in vivo BTB models for preclinical drug disposition studies.

Lactic Acidosis in Patients with Solid Cancer

Significance: Cancer-associated tissue-specific lactic acidosis stimulates and mediates tumor invasion and metastasis and is druggable. Rarely, malignancy causes systemic lactic acidosis, the role of which is poorly understood. Recent Advances: The understanding of the role of lactate has shifted dramatically since its discovery. Long recognized as only a waste product, lactate has become known as an alternative metabolism substrate and a secreted nutrient that is exchanged between the tumor and the microenvironment. Tissue-specific lactic acidosis is targeted to improve the host body's anticancer defense and serves as a tool that allows the targeting of anticancer compounds. Systemic lactic acidosis is associated with poor survival. In patients with solid cancer, systemic lactic acidosis is associated with an extremely poor prognosis, as revealed by the analysis of 57 published cases in this study. Although it is considered a pathology worth treating, targeting systemic lactic acidosis in patients with solid cancer is usually inefficient. Critical Issues: Research gaps include simple questions, such as the unknown nuclear pH of the cancer cells and its effects on chemotherapy outcomes, pH sensitivity of glycosylation in cancer cells, in vivo mechanisms of response to acidosis in the absence of lactate, and overinterpretation of in vitro results that were obtained by using cells that were not preadapted to acidic environments. Future Directions: Numerous metabolism-targeting anticancer compounds induce lactatemia, lactic acidosis, or other types of acidosis. Their potential to induce acidic environments is largely overlooked, although the acidosis might contribute to a substantial portion of the observed clinical effects. Antioxid. Redox Signal. 37, 1130-1152.

Combining metformin with lactate transport inhibitors as a treatment modality for cancer - recommendation proposal

Highly glycolytic cancer cells excrete lactate to maintain cellular homeostasis. Inhibiting lactate export by pharmacological targeting of plasma membrane lactate transporters is being pursued as an anti-cancer therapy. Work from many laboratories show that the simultaneous inhibition of lactate export and mitochondrial respiration elicits strong synthetic lethality. The mitochondrial inhibitor, metformin, has been the subject of numerous clinical trials as an anti-cancer agent. We propose that, in future clinical trials, metformin be combined with lactate transport inhibitors to exploit this synergistic interaction.

Monocarboxylate Transporter 1 (MCT1) Mediates Succinate Export in the Retina

Purpose

Succinate is exported by the retina and imported by eyecup tissue. The transporters mediating this process have not yet been identified. Recent studies showed that monocarboxylate transporter 1 (MCT1) can transport succinate across plasma membranes in cardiac and skeletal muscle. Retina and retinal pigment epithelium (RPE) both express multiple MCT isoforms including MCT1. We tested the hypothesis that MCTs facilitate retinal succinate export and RPE succinate import.

Methods

We assessed retinal succinate export and eyecup succinate import in short-term ex vivo culture using gas chromatography-mass spectrometry. We tested the dependence of succinate export and import on pH, proton ionophores, conventional MCT substrates, and the MCT inhibitors AZD3965, AR-C155858, and diclofenac.

Results

Succinate exits retinal tissue through MCT1 but does not enter the RPE through MCT1 or any other MCT. Intracellular succinate levels are a contributing factor that determines if an MCT1-expressing tissue will export succinate.

Conclusions

MCT1 facilitates export of succinate from retinas. An unidentified, non-MCT transporter facilitates import of succinate into RPE.

The effects of H22 tumor on the quality of oocytes and the development of early embryos from host mice: A single-cell RNA sequencing approach

The association between cancer and female reproduction remains largely unknown. Here we investigated the quality of oocytes and the developmental potential of zygotes using H22 tumor-bearing mice model. The results showed that the number of oocytes was decreased in tumor-bearing mice compared with the control mice, and accompanied scattered chromosomes was observed. Further study revealed an abnormal epigenetic reprogramming occurred in the zygotes from the H22 tumor-bearing mice, as exemplified by the aberrant 5hmC/5mC modifications in the pronuclei. Finally, single-cell RNA sequencing was performed on the oocytes collected from the H22 tumor-bearing mice. Our data showed that 45 of the 202 differentially expressed genes in tumor-bearing group were closely associated with oocyte quality. Protein interaction analysis indicated that the potential interaction among these 45 genes. Collectively, our study uncovered that the quality of oocytes and early embryonic development were affected by H22 tumor bearing via the altered expression patterns of genes related with reproduction, providing new insights into the reproductive capability of female cancer patients.

A Novel Metabolic Reprogramming Strategy for the Treatment of Diabetes-Associated Breast Cancer

Diabetes is directly related to the risk of breast cancer (BC) occurrence and worsened BC prognosis. Currently, there are no specific treatments for diabetes-associated BC. This paper aims to understand the fundamental mechanisms of diabetes-induced BC progression and to develop personalized treatments. It reports a metabolic reprogramming strategy (MRS) that pharmaceutical induction of glucose import and glycolysis with metformin and NF-κB inhibitor (NF-κBi) while blocking the export of excessive lactate via inhibiting monocarboxylate transporter 4 (MCT4) leads to a metabolic crisis within the cancer cells. It demonstrates that the MRS shifts the metabolism of BC cells toward higher production of lactate, blocks lactate secretion, prompts intracellular acidification and induces significant cytotoxicity. Moreover, a novel MCT4 inhibitor CB-2 has been identified by structure-based virtual screening. A triple combination of metformin, CB-2, and trabectedin, a drug that impedes NF-κB signaling, strongly inhibits BC cells. Compared to normal glucose condition, MRS elicits more potent cancer cell-killing effects under high glucose condition. Animal model studies show that diabetic conditions promote the proliferation and progression of BC xenografts in nude mice and that MRS treatment significantly inhibits HG-induced BC progression. Therefore, inhibition of MCT4 combined with metformin/NF-κBi is a promising cancer therapy, especially for diabetes-associated BC.

Current Treatments and New Possible Complementary Therapies for Epithelial Ovarian Cancer

Epithelial ovarian cancer (EOC) is one of the deadliest gynaecological malignancies. The late diagnosis is frequent due to the absence of specific symptomatology and the molecular complexity of the disease, which includes a high angiogenesis potential. The first-line treatment is based on optimal debulking surgery following chemotherapy with platinum/gemcitabine and taxane compounds. During the last years, anti-angiogenic therapy and poly adenosine diphosphate-ribose polymerases (PARP)-inhibitors were introduced in therapeutic schemes. Several studies have shown that these drugs increase the progression-free survival and overall survival of patients with ovarian cancer, but the identification of patients who have the greatest benefits is still under investigation. In the present review, we discuss about the molecular characteristics of the disease, the recent evidence of approved treatments and the new possible complementary approaches, focusing on drug repurposing, non-coding RNAs, and nanomedicine as a new method for drug delivery.

Matrix Stiffness Modulates Metabolic Interaction between Human Stromal and Breast Cancer Cells to Stimulate Epithelial Motility

Breast tumors belong to the type of desmoplastic lesion in which a stiffer tissue structure is a determinant of breast cancer progression and constitutes a risk factor for breast cancer development. It has been proposed that cancer-associated stromal cells (responsible for this fibrotic phenomenon) are able to metabolize glucose via lactate production, which supports the catabolic metabolism of cancer cells. The aim of this work was to investigate the possible functional link between these two processes. To measure the effect of matrix rigidity on metabolic determinations, we used compliant elastic polyacrylamide gels as a substrate material, to which matrix molecules were covalently linked. We evaluated metabolite transport in stromal cells using two different FRET (Fluorescence Resonance Energy Transfer) nanosensors specific for glucose and lactate. Cell migration/invasion was evaluated using Transwell devices. We show that increased stiffness stimulates lactate production and glucose uptake by mammary fibroblasts. This response was correlated with the expression of stromal glucose transporter Glut1 and monocarboxylate transporters MCT4. Moreover, mammary stromal cells cultured on stiff matrices generated soluble factors that stimulated epithelial breast migration in a stiffness-dependent manner. Using a normal breast stromal cell line, we found that a stiffer extracellular matrix favors the acquisition mechanistical properties that promote metabolic reprograming and also constitute a stimulus for epithelial motility. This new knowledge will help us to better understand the complex relationship between fibrosis, metabolic reprogramming, and cancer malignancy.

Transport function, regulation, and biology of human monocarboxylate transporter 1 (hMCT1) and 4 (hMCT4)

Human monocarboxylate transporter 1 (hMCT1) and 4 (hMCT4) are involved in the proton-dependent transport of monocarboxylates such as L-lactate, which play an essential role in cellular metabolism and pH regulation. hMCT1 and 4 are overexpressed in a number of cancers, and polymorphisms in hMCT1 have been reported to be associated with the prognosis of some cancers. Accordingly, recent advances have focused on the inhibition of these transporters as a novel therapeutic strategy in cancers. To screen for MCT inhibitors for clinical application, it is important to study MCT function and regulation, and the effect of compounds on them, using human-derived cells. In this review, we focus on the transport function, regulation, and biology of hMCT1 and hMCT4, and the effects of genetic variation in these transporters in humans.

Development and in vitro characterization of a novel pMDI diclofenac formulation as an inhalable anti-inflammatory therapy for cystic fibrosis

Anti-inflammatory treatment options for cystic fibrosis (CF) patients are currently limited and as such, there is an imperative need to develop new anti-inflammatory agents to reduce the persistent inflammation present within CF lungs. This study explored the potential of Diclofenac (DICLO) as a novel inhaled anti-inflammatory drug for CF treatment. The anti-inflammatory activity of DICLO on an air-liquid interface (ALI) cell culture model of healthy (NuLi-1) and CF (CuFi-1) airways showed a significant reduction in the secretion of pro-inflammatory cytokines, IL-6 and IL-8. Therefore, pressurized metered dose inhaler (pMDI) DICLO formulations were developed to allow targeted DICLO delivery to CF airways. As such, two pMDI DICLO formulations with varying ethanol concentrations: 5% (w/w) equating to 150 µg of DICLO per dose (Low dose), and 15% (w/w) equating to 430 µg of DICLO per dose (High dose) were developed and characterized to determine the optimum formulation. The Low dose pMDI DICLO formulation showed a significantly smaller particle diameter with uniform distribution resulting in a greater aerosol performance when compared to High dose formulation. Consequently, the Low dose pMDI DICLO formulation was further evaluated in terms of in vitro transport characteristics and anti-inflammatory activity. Importantly, the DICLO pMDI displayed anti-inflammatory activity in both healthy and CF in vitro models, highlighting the potential of an aerosolized low-dose DICLO formulation as a promising inhaled anti-inflammatory therapy for CF treatment.

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.

Restricting Glycolysis Preserves T Cell Effector Functions and Augments Checkpoint Therapy

Tumor-derived lactic acid inhibits T and natural killer (NK) cell function and, thereby, tumor immunosurveillance. Here, we report that melanoma patients with high expression of glycolysis-related genes show a worse progression free survival upon anti-PD1 treatment. The non-steroidal anti-inflammatory drug (NSAID) diclofenac lowers lactate secretion of tumor cells and improves anti-PD1-induced T cell killing in vitro. Surprisingly, diclofenac, but not other NSAIDs, turns out to be a potent inhibitor of the lactate transporters monocarboxylate transporter 1 and 4 and diminishes lactate efflux. Notably, T cell activation, viability, and effector functions are preserved under diclofenac treatment and in a low glucose environment in vitro. Diclofenac, but not aspirin, delays tumor growth and improves the efficacy of checkpoint therapy in vivo. Moreover, genetic suppression of glycolysis in tumor cells strongly improves checkpoint therapy. These findings support the rationale for targeting glycolysis in patients with high glycolytic tumors together with checkpoint inhibitors in clinical trials.

The immunological Warburg effect: Can a metabolic-tumor-stroma score (MeTS) guide cancer immunotherapy?

The "glycolytic switch" also known as the "Warburg effect" is a key feature of tumor cells and leads to the accumulation of lactate and protons in the tumor environment. Intriguingly, non-malignant lymphocytes or stromal cells such as tumor-associated macrophages and cancer-associated fibroblasts contribute to the lactate accumulation in the tumor environment, a phenomenon described as the "Reverse Warburg effect." Localized lactic acidosis has a strong immunosuppressive effect and mediates an immune escape of tumors. However, some tumors do not display the Warburg phenotype and either rely on respiration or appear as a mosaic of cells with different metabolic properties. Based on these findings and on the knowledge that T cell infiltration is predictive for patient outcome, we suggest a metabolic-tumor-stroma score to determine the likelihood of a successful anti-tumor immune response: (a) a respiring tumor with high T cell infiltration ("hot"); (b) a reverse Warburg type with respiring tumor cells but glycolytic stromal cells; (c) a mixed type with glycolytic and respiring compartments; and (d) a glycolytic (Warburg) tumor with low T cell infiltration ("cold"). Here, we provide evidence that these types can be independent of the organ of origin, prognostically relevant and might help select the appropriate immunotherapy approach.

Metformin as Potential Therapy for High-Grade Glioma

Metformin (MET), 1,1-dimethylbiguanide hydrochloride, is a biguanide drug used as the first-line medication in the treatment of type 2 diabetes. The recent years have brought many observations showing metformin in its new role. The drug, commonly used in the therapy of diabetes, may also find application in the therapy of a vast variety of tumors. Its effectiveness has been demonstrated in colon, breast, prostate, pancreatic cancer, leukemia, melanoma, lung and endometrial carcinoma, as well as in gliomas. This is especially important in light of the poor options offered to patients in the case of high-grade gliomas, which include glioblastoma (GBM). A thorough understanding of the mechanism of action of metformin can make it possible to discover new drugs that could be used in neoplasm therapy.

Dual Inhibition of the Lactate Transporters MCT1 and MCT4 Is Synthetic Lethal with Metformin due to NAD+ Depletion in Cancer Cells

Highly glycolytic cancer cells prevent intracellular acidification by excreting the glycolytic end-products lactate and H⁺ via the monocarboxylate transporters 1 (MCT1) and 4 (MCT4). We report that syrosingopine, an anti-hypertensive drug, is a dual MCT1 and MCT4 inhibitor (with 60-fold higher potency on MCT4) that prevents lactate and H⁺ efflux. Syrosingopine elicits synthetic lethality with metformin, an inhibitor of mitochondrial NADH dehydrogenase. NAD+, required for the ATP-generating steps of glycolysis, is regenerated from NADH by mitochondrial NADH dehydrogenase or lactate dehydrogenase. Syrosingopine treatment leads to high intracellular lactate levels and thereby end-product inhibition of lactate dehydrogenase. The loss of NAD+ regeneration capacity due to combined metformin and syrosingopine treatment results in glycolytic blockade, leading to ATP depletion and cell death. Accordingly, ATP levels can be partly restored by exogenously provided NAD+, the NAD precursor nicotinamide mononucleotide (NMN), or vitamin K2. Thus, pharmacological inhibition of MCT1 and MCT4 combined with metformin treatment is a potential cancer therapy.

Homology modeling and site-directed mutagenesis identify amino acid residues underlying the substrate selection mechanism of human monocarboxylate transporters 1 (hMCT1) and 4 (hMCT4)

Human monocarboxylate transporters (hMCTs/SLC16As) mediate the transport of monocarboxylic compounds across plasma membranes. Among the hMCTs, hMCT1 and hMCT4 are expressed in various tissues, and transport substrates involved in energy metabolism. Both transporters mediate L-lactate transport, but, although hMCT1 also transports L-5-oxoproline (L-OPro), this compound is minimally transported by hMCT4. Thus, we were interested in the molecular mechanism responsible for the difference in substrate specificity between hMCT1 and hMCT4. Therefore, we generated 3D structure models of hMCT1 and hMCT4 to identify amino acid residues involved in the substrate specificity of these transporters. We found that the substrate specificity of hMCT1 was regulated by residues involved in turnover number (M69) and substrate affinity (F367), and these residues were responsible for recognizing (directly or indirectly) the -NH- moiety of L-OPro. Furthermore, our homology model of hMCT1 predicted that M69 and F367 participate in hydrophobic interactions with another region of hMCT1, emphasizing its potentially important role in the binding and translocation cycle of L-OPro. Mutagenesis experiments supported this model, showing that efficient L-OPro transport required a hydrophobic, long linear structure at position 69 and a hydrophobic, γ-branched structure at position 367. Our work demonstrated that the amino acid residues, M69 and F367, are key molecular elements for the transport of L-OPro by hMCT1. These two residues may be involved in substrate recognition and/or substrate-induced conformational changes.

Monocarboxylate transporter 4 (MCT4) is a high affinity transporter capable of exporting lactate in high-lactate microenvironments

Monocarboxylate transporter 4 (MCT4) is an H⁺-coupled symporter highly expressed in metastatic tumors and at inflammatory sites undergoing hypoxia or the Warburg effect. At these sites, extracellular lactate contributes to malignancy and immune response evasion. Intriguingly, at 30-40 mm, the reported K_m of MCT4 for lactate is more than 1 order of magnitude higher than physiological or even pathological lactate levels. MCT4 is not thought to transport pyruvate. Here we have characterized cell lactate and pyruvate dynamics using the FRET sensors Laconic and Pyronic. Dominant MCT4 permeability was demonstrated in various cell types by pharmacological means and by CRISPR/Cas9-mediated deletion. Respective K_m values for lactate uptake were 1.7, 1.2, and 0.7 mm in MDA-MB-231 cells, macrophages, and HEK293 cells expressing recombinant MCT4. In MDA-MB-231 cells MCT4 exhibited a K_m for pyruvate of 4.2 mm, as opposed to >150 mm reported previously. Parallel assays with the pH-sensitive dye 2',7'-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) indicated that previous K_m estimates based on substrate-induced acidification were severely biased by confounding pH-regulatory mechanisms. Numerical simulation using revised kinetic parameters revealed that MCT4, but not the related transporters MCT1 and MCT2, endows cells with the ability to export lactate in high-lactate microenvironments. In conclusion, MCT4 is a high-affinity lactate transporter with physiologically relevant affinity for pyruvate.

Targeting L-Lactate Metabolism to Overcome Resistance to Immune Therapy of Melanoma and Other Tumor Entities

Although immunotherapy plays a significant role in tumor therapy, its efficacy is impaired by an immunosuppressive tumor microenvironment. A molecule that contributes to the protumor microenvironment is the metabolic product lactate. Lactate is produced in large amounts by cancer cells in response to either hypoxia or pseudohypoxia, and its presence in excess alters the normal functioning of immune cells. A key enzyme involved in lactate metabolism is lactate dehydrogenase (LDH). Elevated baseline LDH serum levels are associated with poor outcomes of current anticancer (immune) therapies, especially in patients with melanoma. Therefore, targeting LDH and other molecules involved in lactate metabolism might improve the efficacy of immune therapies. This review summarizes current knowledge about lactate metabolism and its role in the tumor microenvironment. Based on that information, we develop a rationale for deploying drugs that target lactate metabolism in combination with immune checkpoint inhibitors to overcome lactate-mediated immune escape of tumor cells.

Metabolic targeting synergizes with MAPK inhibition and delays drug resistance in melanoma

Tumors, including melanomas, frequently show an accelerated glucose metabolism. Mutations in the v-Raf murine sarcoma viral oncogene homolog B (BRAF), detected in about 50% of all melanomas, result in further enhancement of glycolysis. Therefore anti-metabolic substances might enhance the impact of RAF inhibitors. We have identified the two non-steroidal anti-inflammatory drugs (NSAIDs) diclofenac and lumiracoxib being able to restrict energy metabolism in human melanoma cells by targeting lactate release and oxidative phosphorylation (OXPHOS). In combination with the RAF inhibitor vemurafenib strong synergism was observed: Diclofenac as well as lumiracoxib increased the anti-glycolytic impact of vemurafenib and prevented RAF-inhibitor induced metabolic reprogramming towards OXPHOS. Consequently, both NSAIDs sensitized melanoma cells to vemurafenib triggered proliferation arrest and enhanced the anti-tumor effect of RAF inhibitors from cytostatic to cytotoxic. Furthermore the addition of NSAIDs delayed the onset of RAF inhibitor resistance, most likely by counteracting the upregulation of MITF. Our data suggest that selected NSAIDs could be a promising combination partner for MAPK pathway inhibitors for the treatment of BRAF^V600E mutated melanomas.

Combined Metabolic Targeting With Metformin and the NSAIDs Diflunisal and Diclofenac Induces Apoptosis in Acute Myeloid Leukemia Cells

The accelerated metabolism of tumor cells, inevitable for maintaining high proliferation rates, is an emerging target for tumor therapy. Increased glucose and lipid metabolism as well as mitochondrial activity have been shown in solid tumors but also in leukemic cells. As tumor cells are able to escape the blockade of one metabolic pathway by a compensatory increase in other pathways, treatment strategies simultaneously targeting metabolism at different sites are currently developed. However, the number of clinically applicable anti-metabolic drugs is still limited. Here, we analyzed the impact of the anti-diabetic drug metformin alone or in combination with two non-steroidal anti-inflammatory drugs (NSAIDs) diclofenac and diflunisal on acute myeloid leukemia (AML) cell lines and primary patient blasts. Diclofenac but not diflunisal reduced lactate secretion in different AML cell lines (THP-1, U937, and KG-1) and both drugs increased respiration at low concentrations. Despite these metabolic effects, both NSAIDs showed a limited effect on tumor cell proliferation and viability up to a concentration of 0.2 mM. In higher concentrations of 0.4–0.8 mM diflunisal alone exerted a clear effect on proliferation of AML cell lines and blocked respiration. Single treatment with the anti-diabetic drug metformin blocked mitochondrial respiration, but proliferation and viability were not affected. However, combining all three drugs exerted a strong cytostatic and cytotoxic effect on THP-1 cells. Comparable to the results obtained with THP-1 cells, the combination of all three drugs significantly reduced proliferation of primary leukemic blasts and induced apoptosis. Furthermore, NSAIDs supported the effect of low dose chemotherapy with cytarabine and reduced proliferation of primary AML blasts. Taken together we show that low concentrations of metformin and the two NSAIDs diclofenac and diflunisal exert a synergistic inhibitory effect on AML proliferation and induce apoptosis most likely by blocking tumor cell metabolism. Our results underline the feasibility of applying anti-metabolic drugs for AML therapy.

Combined Modulation of Tumor Metabolism by Metformin and Diclofenac in Glioma

Glioblastoma remains a fatal diagnosis. Previous research has shown that metformin, which is an inhibitor of complex I of the respiratory chain, may inhibit some brain tumor initiating cells (BTICs), albeit at dosages that are too high for clinical use. Here, we explored whether a combined treatment of metformin and diclofenac, which is a non-steroidal anti-inflammatory drug (NSAID) shown to inhibit glycolysis by interfering with lactate efflux, may lead to additive or even synergistic effects on BTICs (BTIC-8, -11, -13 and -18) and tumor cell lines (TCs, U87, and HTZ349). Therefore, we investigated the functional effects, including proliferation and migration, metabolic effects including oxygen consumption and extracellular lactate levels, and effects on the protein level, including signaling pathways. Functional investigation revealed synergistic anti-migratory and anti-proliferative effects of the combined treatment with metformin and diclofenac on BTICs and TCs. Signaling pathways did not sufficiently explain synergistic effects. However, we observed that metformin inhibited cellular oxygen consumption and increased extracellular lactate levels, indicating glycolytic rescue mechanisms. Combined treatment inhibited metformin-induced lactate increase. The combination of metformin and diclofenac may represent a promising new strategy in the treatment of glioblastoma. Combined treatment may reduce the effective doses of the single agents and prevent metabolic rescue mechanisms. Further studies are needed in order to determine possible side effects in humans.

Evaluation of Monocarboxylate Transporter 4 in Inflammatory Bowel Disease and Its Potential Use as a Diagnostic Marker

Background

Monocarboxylate transporter 4 (MCT4), encoded by SLC16A3 gene, is responsible for exporting lactic acid into the extracellular microenvironment, and an acidic microenvironment promotes cytokine production and remodels chronic inflammation, providing a link from glycolysis to inflammatory bowel disease (IBD).

Objective

The aim of this study is to explore the value of MCT4 as a potential biomarker in IBD.

Methods

The study group consisted of 39 cases with UC and 15 cases with CD. The centration of lactate level in serum was assessed by blood gas analysis, and MCT4 expression was analyzed by IHC.

Results

Lactate level was increased in the forty-three of 54 patients (79.6%) with IBD by blood gas analysis compared with normal level (P < 0.001), in line with the result that showed increased MCT4 expression in inflamed colonic mucosa analyzed by immunohistochemistry. Most importantly, abundance of MCT4 expression was significantly associated with mucosal inflammation, which could be a clinical prognosis marker.

Conclusion

The data suggested that increased lactate level in blood was possibly due to highly expressed MCT4 expression caused by inflammation in intestinal mucosal epithelial tissue, which could be a prognosis indicator of IBD in children.

Identification of a selective inhibitor of human monocarboxylate transporter 4

The human monocarboxylate transporters (hMCTs/SLC16As) mediate the uptake of various monocarboxylates. Several isoforms of hMCTs are expressed in cancerous tissue as well as in normal tissue. In cancerous tissue, hypoxia induces the expression of hMCT4, which transports the energetic metabolite l-lactate across the plasma membrane. Since hMCT4 is involved in pH regulation and the transport of l-lactate in cancer cells, an hMCT4 inhibitor could function as an anticancer agent. Although several non specific hMCT inhibitors have been developed, a selective hMCT4 inhibitor has not yet been identified. The aim of this study was therefore to identify a selective hMCT4 inhibitor for use as a pharmacological tool for studying hMCT4. The heterologous expression system of the Xenopus oocyte was used to assess the effects of test compounds on hMCT4, whereupon isobutyrate derivatives, fibrates, and bindarit (2-[(1-benzyl-1H-indazol-3-yl)methoxy]-2-methylpropanoic acid) were demonstrated to exhibit selective inhibitory effects against this transporter. It is suggested that the structure formed from the joining of an isobutyrate moiety and two aromatic rings by appropriate linkers is important for acquiring the selective hMCT4-inhibiting activity. These findings provide novel insights into the ligand recognition of hMCT4, and contribute to the development of novel anticancer agents.

Metabolic Hallmarks of Tumor and Immune Cells in the Tumor Microenvironment

Cytotoxic T lymphocytes and NK cells play an important role in eliminating malignant tumor cells and the number and activity of tumor-infiltrating T cells represent a good marker for tumor prognosis. Based on these findings, immunotherapy, e.g., checkpoint blockade, has received considerable attention during the last couple of years. However, for the majority of patients, immune control of their tumors is gray theory as malignant cells use effective mechanisms to outsmart the immune system. Increasing evidence suggests that changes in tumor metabolism not only ensure an effective energy supply and generation of building blocks for tumor growth but also contribute to inhibition of the antitumor response. Immunosuppression in the tumor microenvironment is often based on the mutual metabolic requirements of immune cells and tumor cells. Cytotoxic T and NK cell activation leads to an increased demand for glucose and amino acids, a well-known feature shown by tumor cells. These close metabolic interdependencies result in metabolic competition, limiting the proliferation, and effector functions of tumor-specific immune cells. Moreover, not only nutrient restriction but also tumor-driven shifts in metabolite abundance and accumulation of metabolic waste products (e.g., lactate) lead to local immunosuppression, thereby facilitating tumor progression and metastasis. In this review, we describe the metabolic interplay between immune cells and tumor cells and discuss tumor cell metabolism as a target structure for cancer therapy. Metabolic (re)education of tumor cells is not only an approach to kill tumor cells directly but could overcome metabolic immunosuppression in the tumor microenvironment and thereby facilitate immunotherapy.

Characterization of loxoprofen transport in Caco-2 cells: the involvement of a proton-dependent transport system in the intestinal transport of loxoprofen

Loxoprofen, a propionate non-steroidal anti-inflammatory drug (NSAID), is used widely in East Asian countries. However, little is known about the transport mechanisms contributing to its intestinal absorption. The objectives of this study were to characterize the intestinal transport of loxoprofen using the human intestinal Caco-2 cell model. The transport of loxoprofen was investigated in cellular uptake studies. The uptake of loxoprofen into Caco-2 cells was pH- and concentration-dependent, and was described by a Michaelis-Menten equation with passive diffusion (K_m : 4.8 mm, V_max : 142 nmol/mg protein/30 s, and K_d : 2.2 μl/mg protein/30 s). Moreover, the uptake of loxoprofen was inhibited by a typical monocarboxylate transporter (MCT) inhibitor as well as by various monocarboxylates. The uptake of [¹⁴ C] l-lactic acid, a typical MCT substrate, in Caco-2 cells was saturable with relatively high affinity for MCT. Because loxoprofen inhibited the uptake of [¹⁴ C] l-lactic acid in a noncompetitive manner, it was unlikely that loxoprofen uptake was mediated by high-affinity MCT(s). Our results suggest that transport of loxoprofen in Caco-2 cells is, at least in part, mediated by a proton-dependent transport system. Copyright © 2016 John Wiley & Sons, Ltd.