Oxime-based inhibitors of glucose transporter 1 displaying antiproliferative effects in cancer cells

Effects of lactate dehydrogenase A and GLUT1 inhibition on human endothelial cell migration in relation to their intracellular nucleotide pool

The expression of both lactate dehydrogenase A (LDH-A) and glucose transporter type 1 (GLUT1) is high in pancreatic, thoracic and many other types of cancer. GLUT1 is also highly expressed in endothelial cells (EC), that play an important role in tumor metastasis. We investigated the effect of inhibition of LDH-A by NHI-2 and GLUT1 by PGL14 on cellular migration, a hallmark of metastasis, in relation to changes in intracellular purine nucleotide and nicotinamide adenine dinucleotide pools in a human microvascular endothelial cell line (HMEC-1). HMEC-1 were treated with NHI-2 and PGL14 alone or in combination. Cell migration was tested by the wound healing assay. The intracellular purine nucleotides and NAD+/NADH concentrations were measured using Reversed-Phase High Performance Liquid Chromatography (RP-HPLC). Both NHI-2 at 15 µM and 45 µM and PGL14 at 10 µM and 30 µM inhibited migration by 5 to 28% while the combination led to 46% inhibition. The drugs also decreased intracellular nucleotide pools, but only 45 µM NHI-2 altered energy charge and redox status in HMEC-1 cells. Inhibitors of glycolysis attenuated migration and the energy charge of EC and support further development of LDH-A and GLUT1 inhibitors to target cancer aggressiveness and metastasis.

Cellular metabolism hijacked by viruses for immunoevasion: potential antiviral targets

Cellular metabolism plays a central role in the regulation of both innate and adaptive immunity. Immune cells utilize metabolic pathways to modulate the cellular differentiation or death. The intricate interplay between metabolism and immune response is critical for maintaining homeostasis and effective antiviral activities. In recent years, immunometabolism induced by viral infections has been extensively investigated, and accumulating evidence has indicated that cellular metabolism can be hijacked to facilitate viral replication. Generally, virus-induced changes in cellular metabolism lead to the reprogramming of metabolites and metabolic enzymes in different pathways (glucose, lipid, and amino acid metabolism). Metabolic reprogramming affects the function of immune cells, regulates the expression of immune molecules and determines cell fate. Therefore, it is important to explore the effector molecules with immunomodulatory properties, including metabolites, metabolic enzymes, and other immunometabolism-related molecules as the antivirals. This review summarizes the relevant advances in the field of metabolic reprogramming induced by viral infections, providing novel insights for the development of antivirals.

Metabolic Effects of New Glucose Transporter (GLUT-1) and Lactate Dehydrogenase-A (LDH-A) Inhibitors against Chemoresistant Malignant Mesothelioma

Malignant mesothelioma (MM) is a highly aggressive and resistant tumor. The prognostic role of key effectors of glycolytic metabolism in MM prompted our studies on the cytotoxicity of new inhibitors of glucose transporter type 1 (GLUT-1) and lactate dehydrogenase-A (LDH-A) in relation to ATP/NAD⁺ metabolism, glycolysis and mitochondrial respiration. The antiproliferative activity of GLUT-1 (PGL13, PGL14) and LDH-A (NHI-1, NHI-2) inhibitors, alone and in combination, were tested with the sulforhodamine-B assay in peritoneal (MESO-II, STO) and pleural (NCI-H2052 and NCI-H28) MM and non-cancerous (HMEC-1) cells. Effects on energy metabolism were measured by both analysis of nucleotides using RP-HPLC and evaluation of glycolysis and respiration parameters using a Seahorse Analyzer system. All compounds reduced the growth of MM cells in the µmolar range. Interestingly, in H2052 cells, PGL14 decreased ATP concentration from 37 to 23 and NAD⁺ from 6.5 to 2.3 nmol/mg protein. NHI-2 reduced the ATP/ADP ratio by 76%. The metabolic effects of the inhibitors were stronger in pleural MM and in combination, while in HMEC-1 ATP reduction was 10% lower compared to that of the H2052 cells, and we observed a minor influence on mitochondrial respiration. To conclude, both inhibitors showed cytotoxicity in MM cells, associated with a decrease in ATP and NAD⁺, and were synergistic in the cells with the highest metabolic modulation. This underlines cellular energy metabolism as a potential target for combined treatments in selected cases of MM.

SLC2As as diagnostic markers and therapeutic targets in LUAD patients through bioinformatic analysis

Facilitative glucose transporters (GLUTs), which are encoded by solute carrier 2A (SLC2A) genes, are responsible for mediating glucose absorption. In order to meet their higher energy demands, cancer cells are more likely than normal tissue cells to have elevated glucose transporters. Multiple pathogenic processes, such as cancer and immunological disorders, have been linked to GLUTs. Few studies, meanwhile, have been conducted on individuals with lung adenocarcinoma (LUAD) to evaluate all 14 SLC2A genes. We first identified increased protein levels of SLC2A1, SLC2A5, SLC2A6, and SLC2A9 via HPA database and downregulated mRNA levels of SLC2A3, SLC2A6, SLC2A9, and SLC2A14 by ONCOMINE and UALCAN databases in patients with LUAD. Additionally, lower levels of SLC2A3, SLC2A6, SLC2A9, SLC2A12, and SLC2A14 and higher levels of SLC2A1, SLC2A5, SLC2A10, and SLC2A11 had an association with advanced tumor stage. SLC2A1, SLC2A7, and SLC2A11 were identified as prognostic signatures for LUAD. Kaplan-Meier analysis, Univariate Cox regression, multivariate Cox regression and ROC analyses further revealed that these three genes signature was a novel and important prognostic factor. Mechanistically, the aberrant expression of these molecules was caused, in part, by the hypomethylation of SLC2A3, SLC2A10, and SLC2A14 and by the hypermethylation of SLC2A1, SLC2A2, SLC2A5, SLC2A6, SLC2A7, and SLC2A11. Additionally, SLC2A3, SLC2A5, SLC2A6, SLC2A9, and SLC2A14 contributed to LUAD by positively modulating M2 macrophage and T cell exhaustion. Finally, pathways involving SLC2A1/BUB1B/mitotic cell cycle, SLC2A5/CD86/negative regulation of immune system process, SLC2A6/PLEK/lymphocyte activation, SLC2A9/CD4/regulation of cytokine production might participate in the pathogenesis of LUAD. In summary, our results will provide the theoretical basis on SLC2As as diagnostic markers and therapeutic targets in LUAD.

An appraisal of the current status of inhibition of glucose transporters as an emerging antineoplastic approach: Promising potential of new pan-GLUT inhibitors

Neoplastic cells displayed altered metabolism with accelerated glycolysis. Therefore, these cells need a mammoth supply of glucose for which they display an upregulated expression of various glucose transporters (GLUT). Thus, novel antineoplastic strategies focus on inhibiting GLUT to intersect the glycolytic lifeline of cancer cells. This review focuses on the current status of various GLUT inhibition scenarios. The GLUT inhibitors belong to both natural and synthetic small inhibitory molecules category. As neoplastic cells express multiple GLUT isoforms, it is necessary to use pan-GLUT inhibitors. Nevertheless, it is also necessary that such pan-GLUT inhibitors exert their action at a low concentration so that normal healthy cells are left unharmed and minimal injury is caused to the other vital organs and systems of the body. Moreover, approaches are also emerging from combining GLUT inhibitors with other chemotherapeutic agents to potentiate the antineoplastic action. A new pan-GLUT inhibitor named glutor, a piperazine-one derivative, has shown a potent antineoplastic action owing to its inhibitory action exerted at nanomolar concentrations. The review discusses the merits and limitations of the existing GLUT inhibitory approach with possible future outcomes.

Glucose transporters as markers of diagnosis and prognosis in cancer diseases

The primary metabolic substrate for cells is glucose, which acts as both a source of energy and a substrate in several processes. However, being lipophilic, the cell membrane is impermeable to glucose and specific carrier proteins are needed to allow transport. In contrast to normal cells, cancer cells are more likely to generate energy by glycolysis; as this process generates fewer molecules of adenosine triphosphate (ATP) than complete oxidative breakdown, more glucose molecules are needed. The increased demand for glucose in cancer cells is satisfied by overexpression of a number of glucose transporters, and decreased levels of others. As specific correlations have been observed between the occurrence of cancer and the expression of glucose carrier proteins, the presence of changes in expression of glucose transporters may be treated as a marker of diagnosis and/or prognosis for cancer patients.

Structure-Activity Relationship of Cytotoxic Natural Products from Indonesian Marine Sponges

Indonesian marine natural products have been one of the most promising sources in the race to obtain potential drugs for cancer treatment. One of the primary producers of cytotoxic compounds is sponges. However, there are still limited sources of comprehensive reviews related to the relationship between the structure of isolated compounds and their cytotoxic activity. This review remarks the attempt to provide a preliminary guidance from the perspective of structure-activity relationship and its participation on marine natural products research. This guidance is segregated by the compound's classes and their cytotoxic targets to obtain and organized a reliable summary of inter-study of the isolated compounds and their cytotoxicity. Structure-activity relationship is well-known for its ability to tune the bioactivity of a specific compound, especially on synthetic organic chemistry and in silico study but rarely used on natural product chemistry. The present review is intended to narrow down the endless possibilities of cytotoxicity by giving a predictable structure-activity relationship for active compounds. In addition, bioactive framework leads were selected by uncovering a noticeable structure-activity relationship with the intervention of cytotoxic agents from natural sources, especially Indonesian marine sponge.

Graphical abstract

Glucose Transporters as a Target for Anticancer Therapy

Simple Summary

For mammalian cells, glucose is a major source of energy. In the presence of oxygen, a complete breakdown of glucose generates 36 molecules of ATP from one molecule of glucose. Hypoxia is a hallmark of cancer; therefore, cancer cells prefer the process of glycolysis, which generates only two molecules of ATP from one molecule of glucose, and cancer cells need more molecules of glucose in comparison with normal cells. Increased uptake of glucose by cancer cells is due to increased expression of glucose transporters. However, overexpression of glucose transporters, promoting the process of carcinogenesis, and increasing aggressiveness and invasiveness of tumors, may have also a beneficial effect. For example, upregulation of glucose transporters is used in diagnostic techniques such as FDG-PET. Therapeutic inhibition of glucose transporters may be a method of treatment of cancer patients. On the other hand, upregulation of glucose transporters, which are used in radioiodine therapy, can help patients with cancers.

Abstract

Tumor growth causes cancer cells to become hypoxic. A hypoxic condition is a hallmark of cancer. Metabolism of cancer cells differs from metabolism of normal cells. Cancer cells prefer the process of glycolysis as a source of ATP. Process of glycolysis generates only two molecules of ATP per one molecule of glucose, whereas the complete oxidative breakdown of one molecule of glucose yields 36 molecules of ATP. Therefore, cancer cells need more molecules of glucose in comparison with normal cells. Increased uptake of glucose by these cells is due to overexpression of glucose transporters, especially GLUT1 and GLUT3, that are hypoxia responsive, as well as other glucose transport proteins. Increased expression of these carrier proteins may be used in anticancer therapy. This phenomenon is used in diagnostic techniques such as FDG-PET. It is also suggested, and there are observations, that therapeutic inhibition of glucose transporters may be a method in treatment of cancer patients. On the other hand, there are described cases, in which upregulation of glucose transporters, as, for example, NIS, which is used in radioiodine therapy, can help patients with cancer. The aim of this review is the presentation of possibilities, and how glucose transporters can be used in anticancer therapy.

Identification of novel inhibitors of GLUT1 by virtual screening and cell-based assays

In order to fuel the uncontrolled cell proliferation and division, tumor cells reprogram the energy metabolism to Warburg effect, where glucose is preferably converted by glycolysis even in the presence of oxygen. However, the high energetic demand of tumor cells require upregulating the expression of glucose transporters, notably GLUT1, which substantially increases glucose uptake into cytoplasm. GLUT1 is overexpressed in a variety of tumor cells and is likely to be a potential drug target in the treatment of pan-cancers. Although many small molecules were reported to inhibit the glucose uptake function by various measurements, several shortcomings such as weak binding affinity, low specificity of the known inhibitors demand the identification of alternative inhibitors with novel scaffolds. In this study, we performed a virtual screening campaign by docking each compound from Chemdiv database to the glucose binding pocket based on the crystal structure of GLUT1 (PDB ID 4PYP) and four small molecules with novel scaffolds were identified to inhibit the glucose uptake of cancer cells at the sub-micromole level. The identified compounds may serve as starting points for the development of anti-cancer drugs via the manipulation of the energy metabolism.

A small-molecule pan-class I glucose transporter inhibitor reduces cancer cell proliferation in vitro and tumor growth in vivo by targeting glucose-based metabolism

BACKGROUND

Cancer cells drastically increase the uptake of glucose and glucose metabolism by overexpressing class I glucose transporters (GLUT1-4) to meet their energy and biomass synthesis needs and are very sensitive and vulnerable to glucose deprivation. Although targeting glucose uptake via GLUTs has been an attractive anticancer strategy, the relative anticancer efficacy of multi-GLUT targeting or single GLUT targeting is unclear. Here, we report DRB18, a synthetic small molecule, is a potent anticancer compound whose pan-class I GLUT inhibition is superior to single GLUT targeting.

METHODS

Glucose uptake and MTT/resazurin assays were used to measure DRB18's inhibitory activities of glucose transport and cell viability/proliferation in human lung cancer and other cancer cell lines. Four HEK293 cell lines expressing GLUT1-4 individually were used to determine the IC₅₀ values of DRB18's inhibitory activity of glucose transport. Docking studies were performed to investigate the potential direct interaction of DRB18 with GLUT1-4. Metabolomics analysis was performed to identify metabolite changes in A549 lung cancer cells treated with DRB18. DRB18 was used to treat A549 tumor-bearing nude mice. The GLUT1 gene was knocked out to determine how the KO of the gene affected tumor growth.

RESULTS

DRB18 reduced glucose uptake mediated via each of GLUT1-4 with different IC₅₀s, which match with the docking glidescores with a correlation coefficient of 0.858. Metabolomics analysis revealed that DRB18 altered energy-related metabolism in A549 cells by changing the abundance of metabolites in glucose-related pathways in vitro and in vivo. DRB18 eventually led to G1/S phase arrest and increased oxidative stress and necrotic cell death. IP injection of DRB18 in A549 tumor-bearing nude mice at 10 mg/kg body weight thrice a week led to a significant reduction in the tumor volume compared with mock-treated tumors. In contrast, the knockout of the GLUT1 gene did not reduce tumor volume.

CONCLUSIONS

DRB18 is a potent pan-class I GLUT inhibitor in vitro and in vivo in cancer cells. Mechanistically, it is likely to bind the outward open conformation of GLUT1-4, reducing tumor growth through inhibiting GLUT1-4-mediated glucose transport and metabolisms. Pan-class I GLUT inhibition is a better strategy than single GLUT targeting for inhibiting tumor growth.

Structure guided design and synthesis of furyl thiazolidinedione derivatives as inhibitors of GLUT 1 and GLUT 4, and evaluation of their anti-leukemic potential

Cancer cells increase their glucose uptake and glycolytic activity to meet the high energy requirements of proliferation. Glucose transporters (GLUTs), which facilitate the transport of glucose and related hexoses across the cell membrane, play a vital role in tumor cell survival and are overexpressed in various cancers. GLUT1, the most overexpressed GLUT in many cancers, is emerging as a promising anti-cancer target. To develop GLUT1 inhibitors, we rationally designed, synthesized, structurally characterized, and biologically evaluated in-vitro and in-vivo a novel series of furyl-2-methylene thiazolidinediones (TZDs). Among 25 TZDs tested, F18 and F19 inhibited GLUT1 most potently (IC50 11.4 and 14.7 μM, respectively). F18 was equally selective for GLUT4 (IC50 6.8 μM), while F19 was specific for GLUT1 (IC50 152 μM in GLUT4). In-silico ligand docking studies showed that F18 interacted with conserved residues in GLUT1 and GLUT4, while F19 had slightly different interactions with the transporters. In in-vitro antiproliferative screening of leukemic/lymphoid cells, F18 was most lethal to CEM cells (CC50 of 1.7 μM). Flow cytometry analysis indicated that F18 arrested cell cycle growth in the subG0-G1 phase and lead to cell death due to necrosis and apoptosis. Western blot analysis exhibited alterations in cell signaling proteins, consistent with cell growth arrest and death. In-vivo xenograft study in a CEM model showed that F18 impaired tumor growth significantly.

Isosteres of ester derived glucose uptake inhibitors

Glucose transporters (GLUTs) facilitate glucose uptake and are overexpressed in most cancer cells. Inhibition of glucose transport has been shown to be an effective method to slow the growth of cancer cells both in vitro and in vivo. We have previously reported on the anticancer activity of an ester derived glucose uptake inhibitor. Due to the hydrolytic instability of the ester linkage we have prepared a series of isosteres of the ester moiety. Of all of the isosteres prepared, the amine linkage showed the most promise. Several additional analogues of the amine-linked compounds were also prepared to improve the overall activity.

Dysregulation of the miR-148a-GLUT1 axis promotes the progression and chemoresistance of human intrahepatic cholangiocarcinoma

Intrahepatic cholangiocarcinoma (iCCA) is a highly fatal malignant cancer worldwide. Elucidating the underlying molecular mechanism of iCCA progression is critical for the identification of new therapeutic targets. The present study explored the role of the miR-148a-GLUT1 axis in the progression of iCCA. The expression of GLUT1 was detected by using immunohistochemistry, western blot assays, and real-time polymerase chain reaction. The effects of GLUT1 on cell proliferation, invasion, and chemoresistance were investigated both in vitro and in vivo. A luciferase reporter assay was used to explore the effect of miR-148a on GLUT1 expression. GLUT1 was overexpressed in iCCA tissues. GLUT1 overexpression was associated with shorter overall and disease-free survival. Knockdown of GLUT1 reduced, while overexpression of GLUT1 promoted, the proliferation, motility, and invasiveness of iCCA cells in vitro and in vivo. Silencing GLUT1 significantly sensitized iCCA cells to gemcitabine in vitro and in vivo. GLUT1 was directly regulated by miR-148a, whose downregulation was associated with the proliferation, migration, and invasion of iCCA cells. WZB117, a GLUT1 inhibitor, inhibited tumor growth in an iCCA patient-derived xenograft model. These results indicate that downregulation of miR-148a levels results in GLUT1 overexpression in iCCA, leading to iCCA progression and gemcitabine resistance.

Solute carrier transporters: the metabolic gatekeepers of immune cells

Solute carrier (SLC) transporters meditate many essential physiological functions, including nutrient uptake, ion influx/efflux, and waste disposal. In its protective role against tumors and infections, the mammalian immune system coordinates complex signals to support the proliferation, differentiation, and effector function of individual cell subsets. Recent research in this area has yielded surprising findings on the roles of solute carrier transporters, which were discovered to regulate lymphocyte signaling and control their differentiation, function, and fate by modulating diverse metabolic pathways and balanced levels of different metabolites. In this review, we present current information mainly on glucose transporters, amino-acid transporters, and metal ion transporters, which are critically important for mediating immune cell homeostasis in many different pathological conditions.

The influence of Echinacea purpurea leaf microbiota on chicoric acid level

The controversial anti-proliferative effects of Echinacea purpurea (L.) Moench (Asteraceae) might be related to different plant metabolites contained in plant samples, extracts and products. The influence of bacterial endophytes on the synthesis of bioactive compounds in the medicinal plants has been previously demonstrated but there are only few studies addressing anticancer effects and mechanisms of E. purpurea extracts following endophytic colonization. The present study aimed to test and compare the lactate dehydrogenase (LDH) inhibition potential of n-hexane and methanol extracts from in vitro endophyte non-inoculated and inoculated E. purpurea plants. An in vitro model was previously set up to perform the infection of axenic E. purpurea plants with bacterial endophytic strains isolated from E. purpurea aerial part. Only methanol extracts showed LDH5 inhibition, in particular the richest in chicoric acid and most strongly inhibiting extract was obtained from inoculated stem and leaves of E. purpurea (IC₅₀ = 0.9 mg/ml). Chicoric acid showed an IC₅₀ value (66.7 µM) in enzymatic assays better than that of the reference compound galloflavin. Modeling studies were carried out to suggest the putative interaction mode of chicoric acid in the enzyme active site. This in vitro model on plant-bacterial interaction may lead to obtain extracts from plants enriched in bioactive compounds and it is a new approach for the discovery of novel anticancer compounds.

Glucose transporters in cancer - from tumor cells to the tumor microenvironment

Solute carriers of the glucose transporter (GLUT) family mediate the first step for cellular glucose usage. The upregulation of GLUTs has been reported in numerous cancer types as a result of perturbation of gene expression or protein relocalization or stabilization. Because they enable to sustain the energy demand required by tumor cells for various biochemical programs, they are promising targets for the development of anticancer strategies. Recently, important biological insights have come from the fine crystal structure determination of several GLUTs; these advances will likely catalyze the development of new selective inhibitory compounds. Furthermore, deregulated glucose metabolism of nontumor cells in the tumor mass is beginning to be appreciated and could have major implications for our understanding of how glucose uptake by specific cell types influences the behavior of neighboring cells in the same microenvironment. In this review, we discuss some of the deregulation mechanisms of glucose transporters, their genetic and pharmacological targeting in cancer, and new functions they may have in nontumor cells of the tumor environment or beyond glucose uptake for glycolysis.

Binding investigation and preliminary optimisation of the 3-amino-1,2,4-triazin-5(2H)-one core for the development of new Fyn inhibitors

Fyn tyrosine kinase inhibitors are considered potential therapeutic agents for a variety of human cancers. Furthermore, the involvement of Fyn kinase in signalling pathways that lead to severe pathologies, such as Alzheimer's and Parkinson's diseases, has also been demonstrated. In this study, starting from 3-(benzo[d][1,3]dioxol-5-ylamino)-6-methyl-1,2,4-triazin-5(2H)-one (VS6), a hit compound that showed a micromolar inhibition of Fyn (IC₅₀ = 4.8 μM), we computationally investigated the binding interactions of the 3-amino-1,2,4-triazin-5(2H)-one scaffold and started a preliminary hit to lead optimisation. This analysis led us to confirm the hypothesised binding mode of VS6 and to identify a new derivative that is about 6-fold more active than VS6 (compound 3, IC₅₀ = 0.76 μM).

Anticancer Activity of Euplotin C, Isolated from the Marine Ciliate Euplotes crassus, Against Human Melanoma Cells

Cutaneous melanoma is the most serious type of skin cancer, so new cytotoxic weapons against novel targets in melanoma are of great interest. Euplotin C (EC), a cytotoxic secondary metabolite of the marine ciliate Euplotes crassus, was evaluated in the present study on human cutaneous melanoma cells to explore its anti-melanoma activity and to gain more insight into its mechanism of action. EC exerted a marked cytotoxic effect against three different human melanoma cell lines (A375, 501Mel and MeWo) with a potency about 30-fold higher than that observed in non-cancer cells (HDFa cells). A pro-apoptotic activity and a decrease in melanoma cell migration by EC were also observed. At the molecular level, the inhibition of the Erk and Akt pathways, which control many aspects of melanoma aggressiveness, was shown. EC cytotoxicity was antagonized by dantrolene, a ryanodine receptor (RyR) antagonist, in a concentration-dependent manner. A role of RyR as a direct target of EC was also suggested by molecular modelling studies. In conclusion, our data provide the first evidence of the anti-melanoma activity of EC, suggesting it may be a promising new scaffold for the development of selective activators of RyR to be used for the treatment of melanoma and other cancer types.

Design, Synthesis, and Evaluation of GLUT Inhibitors

The Warburg effect describes how most cancer cells exhibit higher-than-normal glucose consumption, not only under hypoxic conditions, but also when normal oxygen levels are present. Although glucose transporter 1 (GLUT1) has been found to play a key role in the cellular uptake of glucose, especially in cancer cells, where it is generally overexpressed, it has not been given consideration as a suitable target for the development of anticancer drugs. In this chapter, an example of molecular design and realization of novel GLUT1 inhibitors, including in silico modeling, chemical synthesis, and biological characterization, is provided. This process started with the identification of a focused series of oxime derivatives, originally designed as estrogen receptor (ER) ligands, which were structurally optimized in order to direct their activity towards GLUT1 and to minimize their binding to the ERs, leading to the production of efficient and selective inhibitors of glucose uptake in cancer cells.

Development of terphenyl-2-methyloxazol-5(4H)-one derivatives as selective reversible MAGL inhibitors

Monoacylglycerol lipase is a serine hydrolase that plays a major role in the degradation of the endocannabinoid neurotransmitter 2-arachidonoylglycerol. A wide number of MAGL inhibitors are reported in literature; however, many of them are characterised by an irreversible mechanism of action and this behavior determines an unwanted chronic MAGL inactivation, which acquires a functional antagonism of the endocannabinoid system. The possible use of reversible MAGL inhibitors has only recently been explored, due to the lack of known compounds possessing efficient reversible inhibitory activities. In this work, we report a new series of terphenyl-2-methyloxazol-5(4H)-one derivatives characterised by a reversible MAGL-inhibition mechanism. Among them, compound 20b showed to be a potent MAGL reversible inhibitor (IC₅₀ = 348 nM) with a good MAGL/FAAH selectivity. Furthermore, this compound showed antiproliferative activities against two different cancer cell lines that overexpress MAGL.

Molecular Tools for Facilitative Carbohydrate Transporters (Gluts)

Facilitative carbohydrate transporters-Gluts-have received wide attention over decades due to their essential role in nutrient uptake and links with various metabolic disorders, including diabetes, obesity, and cancer. Endeavors directed towards understanding the mechanisms of Glut-mediated nutrient uptake have resulted in a multidisciplinary research field spanning protein chemistry, chemical biology, organic synthesis, crystallography, and biomolecular modeling. Gluts became attractive targets for cancer research and medicinal chemistry, leading to the development of new approaches to cancer diagnostics and providing avenues for cancer-targeting therapeutics. In this review, the current state of knowledge of the molecular interactions behind Glut-mediated sugar uptake, Glut-targeting probes, therapeutics, and inhibitors are discussed.

Constituents of Polygala flavescens ssp. flavescens and Their Activity as Inhibitors of Human Lactate Dehydrogenase

Four new flavonol glycosides (1-4), two oligosaccharides (5, 6), one α-ionone (7), and three triterpenoid saponins (8-10), together with four known secondary metabolites (11-14), were isolated from the aerial parts of Polygala flavescens ssp. flavescens. All structures were elucidated on the basis of their spectroscopic and spectrometric data. The isolates were assayed for their inhibitory activity against isoform 5 of human lactate dehydrogenase, and compound 11 (3,6'-di-O-sinapoylsucrose) showed an IC₅₀ value of 90.4 μM. Modeling studies were carried out to suggest the putative interaction mode of compound 11 in the enzyme active site.

Phospho-Akt overexpression is prognostic and can be used to tailor the synergistic interaction of Akt inhibitors with gemcitabine in pancreatic cancer

Background

There is increasing evidence of a constitutive activation of Akt in pancreatic ductal adenocarcinoma (PDAC), associated with poor prognosis and chemoresistance. Therefore, we evaluated the expression of phospho-Akt in PDAC tissues and cells, and investigated molecular mechanisms influencing the therapeutic potential of Akt inhibition in combination with gemcitabine.

Methods

Phospho-Akt expression was evaluated by immunohistochemistry in tissue microarrays (TMAs) with specimens tissue from radically-resected patients (n = 100). Data were analyzed by Fisher and log-rank test. In vitro studies were performed in 14 PDAC cells, including seven primary cultures, characterized for their Akt1 mRNA and phospho-Akt/Akt levels by quantitative-RT-PCR and immunocytochemistry. Growth inhibitory effects of Akt inhibitors and gemcitabine were evaluated by SRB assay, whereas modulation of Akt and phospho-Akt was investigated by Western blotting and ELISA. Cell cycle perturbation, apoptosis-induction, and anti-migratory behaviors were studied by flow cytometry, AnnexinV, membrane potential, and migration assay, while pharmacological interaction with gemcitabine was determined with combination index (CI) method.

Results

Immunohistochemistry of TMAs revealed a correlation between phospho-Akt expression and worse outcome, particularly in patients with the highest phospho-Akt levels, who had significantly shorter overall and progression-free-survival. Similar expression levels were detected in LPC028 primary cells, while LPC006 were characterized by low phospho-Akt. Remarkably, Akt inhibitors reduced cancer cell growth in monolayers and spheroids and synergistically enhanced the antiproliferative activity of gemcitabine in LPC028, while this combination was antagonistic in LPC006 cells. The synergistic effect was paralleled by a reduced expression of ribonucleotide reductase, potentially facilitating gemcitabine cytotoxicity. Inhibition of Akt decreased cell migration and invasion, which was additionally reduced by the combination with gemcitabine. This combination significantly increased apoptosis, associated with induction of caspase-3/6/8/9, PARP and BAD, and inhibition of Bcl-2 and NF-kB in LPC028, but not in LPC006 cells. However, targeting the key glucose transporter Glut1 resulted in similar apoptosis induction in LPC006 cells.

Conclusions

These data support the analysis of phospho-Akt expression as both a prognostic and a predictive biomarker, for the rational development of new combination therapies targeting the Akt pathway in PDAC. Finally, inhibition of Glut1 might overcome resistance to these therapies and warrants further studies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-016-0371-1) contains supplementary material, which is available to authorized users.

Anticancer agents interacting with membrane glucose transporters

The altered metabolism observed in cancer cells generally consists in increased glucose uptake and glycolytic activity. This is associated with an overexpression of glucose transporter proteins (GLUTs), which facilitate glucose uptake across the plasma membrane and play a crucial role in the survival of cancer cells. Therefore GLUTs are considered as suitable targets for the treatment of cancer. Herein we review some of the most relevant GLUT inhibitors that have been recently developed as prospective anticancer agents.

Facilitative glucose transporters: Implications for cancer detection, prognosis and treatment

It is long recognized that cancer cells display increased glucose uptake and metabolism. In a rate-limiting step for glucose metabolism, the glucose transporter (GLUT) proteins facilitate glucose uptake across the plasma membrane. Fourteen members of the GLUT protein family have been identified in humans. This review describes the major characteristics of each member of the GLUT family and highlights evidence of abnormal expression in tumors and cancer cells. The regulation of GLUTs by key proliferation and pro-survival pathways including the phosphatidylinositol 3-kinase (PI3K)-Akt, hypoxia-inducible factor-1 (HIF-1), Ras, c-Myc and p53 pathways is discussed. The clinical utility of GLUT expression in cancer has been recognized and evidence regarding the use of GLUTs as prognostic or predictive biomarkers is presented. GLUTs represent attractive targets for cancer therapy and this review summarizes recent studies in which GLUT1, GLUT3, GLUT5 and others are inhibited to decrease cancer growth.

Inhibition of carbonic anhydrase isoforms I, II, IX and XII with secondary sulfonamides incorporating benzothiazole scaffolds

Carbonic anhydrases (CAs, EC 4.2.1.1) catalyze the fundamental reaction of CO2 hydration in all living organisms, being actively involved in the regulation of a plethora of patho/physiological conditions. A series of benzothiazole-based sulfonamides were synthesized and tested as possible CA inhibitors. Their inhibitory activity was assessed against the cytosolic human isoforms hCA I and hCA II and the transmembrane hCA IX and hCA XII. Several of the investigated derivatives showed interesting inhibition activity and selectivities for inhibiting hCA IX and hCA XII over the off-target ones hCA I and hCA II. Furthermore, computational procedures were used to investigate the binding mode of this class of compounds, within the active site of hCA IX.

Solvent-free mechanochemical synthesis of arylcyanomethylenequinone oximes from phenylacetonitriles and 4-unsubstituted nitroaromatic compounds using KF/nano-γ-Al2O3 as catalyst

Solvent-free condensation of phenylacetonitriles with 4-unsubstituted nitroaromatic compounds to produce arylcyanomethylenequinone oximes catalyzed by KF/nano-γ-Al₂O₃ under HSVM conditions in moderate to excellent yields at short reaction times.

Salicylketoximes That Target Glucose Transporter 1 Restrict Energy Supply to Lung Cancer Cells

The glucose transporter GLUT1 is frequently overexpressed in most tumor tissues because rapidly proliferating cancer cells rely primarily on glycolysis, a low-efficiency metabolic pathway that necessitates a very high rate of glucose consumption. Because blocking GLUT1 is a promising anticancer strategy, we developed a novel class of GLUT1 inhibitors based on the 4-aryl-substituted salicylketoxime scaffold. Some of these compounds are efficient inhibitors of glucose uptake in lung cancer cells and have a notable antiproliferative effect. In contrast to their 5-aryl-substituted regioisomers, the newly synthesized compounds reported herein do not display significant binding to the estrogen receptors. The inhibition of glucose uptake in cancer cells by these compounds was further observed by fluorescence microscopy imaging using a fluorescent analogue of glucose. Therefore, blocking the ability of tumor cells to take up glucose by means of these small molecules, or by further optimized derivatives, may be a successful approach in the development of novel anticancer drugs.

The Warburg effect: evolving interpretations of an established concept

Metabolic reprogramming and altered bioenergetics have emerged as hallmarks of cancer and an area of active basic and translational cancer research. Drastically upregulated glucose transport and metabolism in most cancers regardless of the oxygen supply, a phenomenon called the Warburg effect, is a major focuses of the research. Warburg speculated that cancer cells, due to defective mitochondrial oxidative phosphorylation (OXPHOS), switch to glycolysis for ATP synthesis, even in the presence of oxygen. Studies in the recent decade indicated that while glycolysis is indeed drastically upregulated in almost all cancer cells, mitochondrial respiration continues to operate normally at rates proportional to oxygen supply. There is no OXPHOS-to-glycolysis switch but rather upregulation of glycolysis. Furthermore, upregulated glycolysis appears to be for synthesis of biomass and reducing equivalents in addition to ATP production. The new finding that a significant amount of glycolytic intermediates is diverted to the pentose phosphate pathway (PPP) for production of NADPH has profound implications in how cancer cells use the Warburg effect to cope with reactive oxygen species (ROS) generation and oxidative stress, opening the door for anticancer interventions taking advantage of this. Recent findings in the Warburg effect and its relationship with ROS and oxidative stress controls will be reviewed. Cancer treatment strategies based on these new findings will be presented and discussed.

Glucose transporter 1-mediated glucose uptake is limiting for B-cell acute lymphoblastic leukemia anabolic metabolism and resistance to apoptosis

The metabolic profiles of cancer cells have long been acknowledged to be altered and to provide new therapeutic opportunities. In particular, a wide range of both solid and liquid tumors use aerobic glycolysis to supply energy and support cell growth. This metabolic program leads to high rates of glucose consumption through glycolysis with secretion of lactate even in the presence of oxygen. Identifying the limiting events in aerobic glycolysis and the response of cancer cells to metabolic inhibition is now essential to exploit this potential metabolic dependency. Here, we examine the role of glucose uptake and the glucose transporter Glut1 in the metabolism and metabolic stress response of BCR-Abl+ B-cell acute lymphoblastic leukemia cells (B-ALL). B-ALL cells were highly glycolytic and primary human B-ALL samples were dependent on glycolysis. We show B-ALL cells express multiple glucose transporters and conditional genetic deletion of Glut1 led to a partial loss of glucose uptake. This reduced glucose transport capacity, however, was sufficient to metabolically reprogram B-ALL cells to decrease anabolic and increase catabolic flux. Cell proliferation decreased and a limited degree of apoptosis was also observed. Importantly, Glut1-deficient B-ALL cells failed to accumulate in vivo and leukemic progression was suppressed by Glut1 deletion. Similarly, pharmacologic inhibition of aerobic glycolysis with moderate doses of 2-deoxyglucose (2-DG) slowed B-ALL cell proliferation, but extensive apoptosis only occurred at high doses. Nevertheless, 2-DG induced the pro-apoptotic protein Bim and sensitized B-ALL cells to the tyrosine kinase inhibitor Dasatinib in vivo. Together, these data show that despite expression of multiple glucose transporters, B-ALL cells are reliant on Glut1 to maintain aerobic glycolysis and anabolic metabolism. Further, partial inhibition of glucose metabolism is sufficient to sensitize cancer cells to specifically targeted therapies, suggesting inhibition of aerobic glycolysis as a plausible adjuvant approach for B-ALL therapies.

An update on therapeutic opportunities offered by cancer glycolytic metabolism

Almost all invasive cancers, regardless of tissue origin, are characterized by specific modifications of their cellular energy metabolism. In fact, a strong predominance of aerobic glycolysis over oxidative phosphorylation (Warburg effect) is usually associated with aggressive tumour phenotypes. This metabolic shift offers a survival advantage to cancer cells, since they may continue to produce energy and anabolites even when they are exposed to either transient or permanent hypoxic conditions. Moreover, it ensures a high production rate of glycolysis intermediates, useful as building blocks for fast cell proliferation of cancer cells. This peculiar metabolic profile may constitute an ideal target for therapeutic interventions that selectively hit cancer cells with minimal residual systemic toxicity. In this review we provide an update about some of the most recent advances in the discovery of new bioactive molecules that are able to interfere with cancer glycolysis.

Inhibitors of glucose transport and glycolysis as novel anticancer therapeutics

Metabolic reprogramming and altered energetics have become an emerging hallmark of cancer and an active area of basic, translational, and clinical cancer research in the recent decade. Development of effective anticancer therapeutics may depend on improved understanding of the altered cancer metabolism compared to that of normal cells. Changes in glucose transport and glycolysis, which are drastically upregulated in most cancers and termed the Warburg effect, are one of major focuses of this new research area. By taking advantage of the new knowledge and understanding of cancer’s mechanisms, numerous therapeutic agents have been developed to target proteins and enzymes involved in glucose transport and metabolism, with promising results in cancer cells, animal tumor models and even clinical trials. It has also been hypothesized that targeting a pathway or a process, such as glucose transport or glucose metabolism, rather than a specific protein or enzyme in a signaling pathway may be more effective. This is based on the observation that cancer somehow can always bypass the inhibition of a target drug by switching to a redundant or compensatory pathway. In addition, cancer cells have higher dependence on glucose. This review will provide background information on glucose transport and metabolism in cancer, and summarize new therapeutic developments in basic and translational research in these areas, with a focus on glucose transporter inhibitors and glycolysis inhibitors. The daunting challenges facing both basic and clinical researchers of the field are also presented and discussed.