Discovery of N-hydroxyindole-based inhibitors of human lactate dehydrogenase isoform A (LDH-A) as starvation agents against cancer cells

Discovery of 2-((3-cyanopyridin-2-yl)thio)acetamides as human lactate dehydrogenase A inhibitors to reduce the growth of MG-63 osteosarcoma cells: Virtual screening and biological validation

Lactate dehydrogenase A (LDHA) has emerged as an attractive target in the oncology field. In this paper, we present the identification of 2-((3-cyanopyridin-2-yl)thio)acetamide-containing compounds as LDHA inhibitors. The in vitro enzymatic assay suggested that inhibitor 9 had good inhibitory potency against LDHA with IC50 value as 1.24μM. Cytotoxicity assay showed that inhibitor 9 strongly inhibited the proliferation of cancer cell MG-63 (EC50=0.98μM). These findings indicated that inhibitor 9 could be employed as a lead for developing more potent LDHA inhibitor with anti-proliferative potency.

'Dual hit' metabolic modulator LDCA selectively kills cancer cells by efficient competitive inhibition of LDH-A

Herein, we synthesize and elucidate the potential of a novel 'dual hit' molecule, LDCA, to constitutively block lactate dehydrogenase isoform-A (LDH-A) to selectively subvert apoptosis and rigorously attenuate breast tumor progression in a mouse model, comprehensively delineating the therapeutic prospectus of LDCA in the field of cancer metabolics.

Tryptophan Biochemistry: Structural, Nutritional, Metabolic, and Medical Aspects in Humans

L-Tryptophan is the unique protein amino acid (AA) bearing an indole ring: its biotransformation in living organisms contributes either to keeping this chemical group in cells and tissues or to breaking it, by generating in both cases a variety of bioactive molecules. Investigations on the biology of Trp highlight the pleiotropic effects of its small derivatives on homeostasis processes. In addition to protein turn-over, in humans the pathways of Trp indole derivatives cover the synthesis of the neurotransmitter/hormone serotonin (5-HT), the pineal gland melatonin (MLT), and the trace amine tryptamine. The breakdown of the Trp indole ring defines instead the "kynurenine shunt" which produces cell-response adapters as L-kynurenine, kynurenic and quinolinic acids, or the coenzyme nicotinamide adenine dinucleotide (NAD(+)). This review aims therefore at tracing a "map" of the main molecular effectors in human tryptophan (Trp) research, starting from the chemistry of this AA, dealing then with its biosphere distribution and nutritional value for humans, also focusing on some proteins responsible for its tissue-dependent uptake and biotransformation. We will thus underscore the role of Trp biochemistry in the pathogenesis of human complex diseases/syndromes primarily involving the gut, neuroimmunoendocrine/stress responses, and the CNS, supporting the use of -Omics approaches in this field.

Discovery of a novel human lactate dehydrogenase A (LDHA) inhibitor as an anti-proliferation agent against MIA PaCa-2 pancreatic cancer cells

A potent LDHA inhibitor with anti-proliferation activity against MIA PaCa-2 cancer cells was first time reported.

Novel therapeutic targets of tumor metabolism

The study of tumor metabolism has resulted in new understandings of how cancer cells modify metabolic pathways that control cellular energetics to allow increased proliferation and survival. Tumor cells have been shown to alter metabolic pathways involved in glucose, glutamine, and mitochondrial metabolism to generate raw materials needed for rapid cellular proliferation, maintain favorable cellular redox environments, modify cellular epigenetics, and even promote and maintain oncogenic transformation. As a consequence, there has been intense scientific and clinical interest in targeting metabolic alterations that are commonly adopted by tumor cells for therapeutic purposes. In this review, we describe common metabolic alterations seen in tumor cells and discuss how these alterations are being investigated as potential targets for pharmacological intervention in preclinical and clinical settings. We also discuss some of the challenges associated with using tumor metabolism as a therapeutic target in cancer therapy, along with potential avenues to overcome these challenges.

NADH-linked metabolic plasticity of MCF-7 breast cancer cells surviving in a nutrient-deprived microenvironment

Characteristic of the tumor microenvironment are fluctuating gradients of reduced nutrient levels and released lactate. A fundamental issue is how tumor cells modulate their metabolic activity when both glucose and glutamine levels become limiting in the presence of high exogenous lactate. For functional analyses, the activities of pyruvate kinase, lactate dehydrogenase (LDH) and plasma membrane NADH oxidase (NOX) as well as cell growth were measured in breast cancer MCF-7 cells cultured in medium containing various concentrations of these metabolites. After 3 days at glucose concentrations below 2.5 mM, cell number was higher with 0.1 mM than with 1.0 mM glutamine, indicating that the glucose/glutamine balance is important for growth. On the other hand, NOX activity increased with increasing glucose >2.5 mM, but only with low glutamine (0.1 mM). Pyruvate kinase activity also increased, with LDH activity remaining 2-3-fold lower. Here NOX could have a complementary role in reoxidizing NADH for glycolysis. Exogenous lactate supported cell survival at limiting concentrations of glucose and glutamine while increasing NOX and pyruvate kinase activities as well as NADH levels. It is proposed that lactate supports cell survival by fuelling gluconeogenesis and/or the TCA cycle in mitochondria, from where NADH could be shuttled to the cytosol and reoxidized by NOX. Cell survival and the metabolic phenotype are thus interrelated to the dynamics of NADH and plasma membrane NOX activity, which are regulated by the balance of glucose/glutamine levels, in conjunction with lactate in a precarious tumor microenvironment.

Identification of a potent inhibitor targeting human lactate dehydrogenase A and its metabolic modulation for cancer cell line

Targeting LDHA represents a promising strategy for the development of new anti-cancer agents. We report herein the identification of a potent compound as a direct LDHA inhibitor. The in vitro enzymatic assay revealed that the VS-2 had good inhibitory potency (IC50=0.25μM) to LDHA. Cytotoxic assay suggested that the VS-2 could inhibit MCF-7 cancer cell growth, with the IC50 value low to 1.54μM. The seahorse XF24 experiment validated that the VS-2 served as a modulator to reprogram MCF-7 cancer cell metabolism from glycolysis to mitochondrial respiration.

Lactate dehydrogenase-A inhibition induces human glioblastoma multiforme stem cell differentiation and death

Therapies that target the signal transduction and metabolic pathways of cancer stem cells (CSCs) are innovative strategies to effectively reduce the recurrence and significantly improve the outcome of glioblastoma multiforme (GBM). CSCs exhibit an increased rate of glycolysis, thus rendering them intrinsically more sensitive to prospective therapeutic strategies based on the inhibition of the glycolytic pathway. The enzyme lactate dehydrogenase-A (LDH-A), which catalyses the interconversion of pyruvate and lactate, is up-regulated in human cancers, including GBM. Although several papers have explored the benefits of targeting cancer metabolism in GBM, the effects of direct LDH-A inhibition in glial tumours have not yet been investigated, particularly in the stem cell subpopulation. Here, two representative LDH-A inhibitors (NHI-1 and NHI-2) were studied in GBM-derived CSCs and compared to differentiated tumour cells. LDH-A inhibition was particularly effective in CSCs isolated from different GBM cell lines, where the two compounds blocked CSC formation and elicited long-lasting effects by triggering both apoptosis and cellular differentiation. These data demonstrate that GBM, particularly the stem cell subpopulation, is sensitive to glycolytic inhibition and shed light on the therapeutic potential of LDH-A inhibitors in this tumour type.

Accurate Binding Free Energy Predictions in Fragment Optimization

Predicting protein-ligand binding free energies is a central aim of computational structure-based drug design (SBDD)--improved accuracy in binding free energy predictions could significantly reduce costs and accelerate project timelines in lead discovery and optimization. The recent development and validation of advanced free energy calculation methods represents a major step toward this goal. Accurately predicting the relative binding free energy changes of modifications to ligands is especially valuable in the field of fragment-based drug design, since fragment screens tend to deliver initial hits of low binding affinity that require multiple rounds of synthesis to gain the requisite potency for a project. In this study, we show that a free energy perturbation protocol, FEP+, which was previously validated on drug-like lead compounds, is suitable for the calculation of relative binding strengths of fragment-sized compounds as well. We study several pharmaceutically relevant targets with a total of more than 90 fragments and find that the FEP+ methodology, which uses explicit solvent molecular dynamics and physics-based scoring with no parameters adjusted, can accurately predict relative fragment binding affinities. The calculations afford R(2)-values on average greater than 0.5 compared to experimental data and RMS errors of ca. 1.1 kcal/mol overall, demonstrating significant improvements over the docking and MM-GBSA methods tested in this work and indicating that FEP+ has the requisite predictive power to impact fragment-based affinity optimization projects.

Different effects of LDH-A inhibition by oxamate in non-small cell lung cancer cells

Higher rate of glycolysis has been long observed in cancer cells, as a vital enzyme in glycolysis, lactate dehydrogenase A (LDH-A) has been shown with great potential as an anti-cancer target. Accumulating evidence indicates that inhibition of LDH-A induces apoptosis mediated by oxidative stress in cancer cells. To date, it's still unclear that whether autophagy can be induced by LDH-A inhibition. Here, we investigated the effects of oxamate, one classic inhibitor of LDH-A in non-small cell lung cancer (NSCLC) cells as well as normal lung epithelial cells. The results showed that oxamate significantly suppressed the proliferation of NSCLC cells, while it exerted a much lower toxicity in normal cells. As previous studies reported, LDH-A inhibition resulted in ATP reduction and ROS (reactive oxygen species) burst in cancer cells, which lead to apoptosis and G₂/M arrest in H1395 cells. However, when being exposed to oxamate, A549 cells underwent autophagy as a protective mechanism against apoptosis. Furthermore, we found evidence that LDH-A inhibition induced G₀/G₁ arrest dependent on the activation of GSK-3β in A549 cells. Taken together, our results provide useful clues for targeting LDH-A in NSCLC treatment and shed light on the discovery of molecular predictors for the sensitivity of LDH-A inhibitors.

A comparative analysis of inhibitors of the glycolysis pathway in breast and ovarian cancer cell line models

Many cancer cells rely on aerobic glycolysis for energy production and targeting of this pathway is a potential strategy to inhibit cancer cell growth. In this study, inhibition of five glycolysis pathway molecules (GLUT1, HKII, PFKFB3, PDHK1 and LDH) using 9 inhibitors (Phloretin, Quercetin, STF31, WZB117, 3PO, 3-bromopyruvate, Dichloroacetate, Oxamic acid, NHI-1) was investigated in panels of breast and ovarian cancer cell line models. All compounds tested blocked glycolysis as indicated by increased extracellular glucose and decreased lactate production and also increased apoptosis. Sensitivity to several inhibitors correlated with the proliferation rate of the cell lines. Seven compounds had IC50 values that were associated with each other consistent with a shared mechanism of action. A synergistic interaction was revealed between STF31 and Oxamic acid when combined with the antidiabetic drug metformin. Sensitivity to glycolysis inhibition was also examined under a range of O2 levels (21% O2, 7% O2, 2% O2 and 0.5% O2) and greater resistance to the inhibitors was found at low oxygen conditions (7% O2, 2% O2 and 0.5% O2) relative to 21% O2 conditions. These results indicate growth of breast and ovarian cancer cell lines is dependent on all the targets examined in the glycolytic pathway with increased sensitivity to the inhibitors under normoxic conditions.

The Regulation and Function of Lactate Dehydrogenase A: Therapeutic Potential in Brain Tumor

There are over 120 types of brain tumor and approximately 45% of primary brain tumors are gliomas, of which glioblastoma multiforme (GBM) is the most common and aggressive with a median survival rate of 14 months. Despite progress in our knowledge, current therapies are unable to effectively combat primary brain tumors and patient survival remains poor. Tumor metabolism is important to consider in therapeutic approaches and is the focus of numerous research investigations. Lactate dehydrogenase A (LDHA) is a cytosolic enzyme, predominantly involved in anaerobic and aerobic glycolysis (the Warburg effect); however, it has multiple additional functions in non‐neoplastic and neoplastic tissues, which are not commonly known or discussed. This review summarizes what is currently known about the function of LDHA and identifies areas that would benefit from further exploration. The current knowledge of the role of LDHA in the brain and its potential as a therapeutic target for brain tumors will also be highlighted. The Warburg effect appears to be universal in tumors, including primary brain tumors, and LDHA (because of its involvement with this process) has been identified as a potential therapeutic target. Currently, there are, however, no suitable LDHA inhibitors available for tumor therapies in the clinic.

MYC, Metabolism, and Cancer

The MYC oncogene encodes a transcription factor, MYC, whose broad effects make its precise oncogenic role enigmatically elusive. The evidence to date suggests that MYC triggers selective gene expression amplification to promote cell growth and proliferation. Through its targets, MYC coordinates nutrient acquisition to produce ATP and key cellular building blocks that increase cell mass and trigger DNA replication and cell division. In cancer, genetic and epigenetic derangements silence checkpoints and unleash MYC's cell growth- and proliferation-promoting metabolic activities. Unbridled growth in response to deregulated MYC expression creates dependence on MYC-driven metabolic pathways, such that reliance on specific metabolic enzymes provides novel targets for cancer therapy.

SIGNIFICANCE

MYC's expression and activity are tightly regulated in normal cells by multiple mechanisms, including a dependence upon growth factor stimulation and replete nutrient status. In cancer, genetic deregulation of MYC expression and loss of checkpoint components, such as TP53, permit MYC to drive malignant transformation. However, because of the reliance of MYC-driven cancers on specific metabolic pathways, synthetic lethal interactions between MYC overexpression and specific enzyme inhibitors provide novel cancer therapeutic opportunities.

Recent Update on Human Lactate Dehydrogenase Enzyme 5 (hLDH5) Inhibitors: A Promising Approach for Cancer Chemotherapy

Human lactate dehydrogenase (hLDH5), a glycolytic enzyme responsible for the conversion of pyruvate to lactate coupled with oxidation of NADH to NAD(+), plays a crucial role in the promotion of glycolysis in invasive tumor cells. Recently, hLDH5 has been considered a vital therapeutic target for invasive cancers. Selective inhibition of hLDH5 using small molecules holds potential prospects for the treatment of cancer and associated diseases. Consequently, significant progress has been made in the discovery of selective small-molecule hLDH5 inhibitors displaying remarkable inhibitory potencies. The purpose of this review is to discuss briefly the roles of hLDH isoforms and to compile small hLDH5 inhibitors into groups based on their chemical classes and pharmacological applications.

Synthesis and biological evaluation of non-glucose glycoconjugated N-hydroyxindole class LDH inhibitors as anticancer agents

Inhibitors of human lactate dehydrogenase A (LDH-A) are promising therapeutic agents against cancer. The development of LDH-A inhibitors that possess cellular activities has so far proved to be particularly challenging, since the enzyme's active site is narrow and highly polar. In the recent past, we were able to develop a glucose-conjugated N-hydroxyindole-based LDH-A inhibitor designed to exploit the sugar avidity expressed by cancer cells (the Warburg effect). Herein we describe a structural modulation of the sugar moiety of this class of inhibitors, with the insertion of α-D-mannose, β-D-gulose, or β-N-acetyl-D-glucosamine portions in their structures. Their stereospecific chemical synthesis, which involves a substrate-dependent stereospecific glycosylation step, and their biological activity in reducing lactate production and proliferation in cancer cells are reported. Interestingly, the α-D-mannose conjugate displayed the best properties in the cellular assays, demonstrating an efficient antiglycolytic and antiproliferative activity in cancer cells.

Paper-Based Device for Rapid Visualization of NADH Based on Dissolution of Gold Nanoparticles

We describe a paper-based device that enables rapid and sensitive room-temperature detection of dihydronicotinamide adenine dinucleotide (NADH) via a colorimetric readout and demonstrate its value for monitoring NAD+-driven enzymatic reactions. Our system is based on NADH-mediated inhibition of gold nanoparticle (AuNPs) dissolution in a Au3+-cetyltrimethylammonium bromide (CTAB) solution. We fabricated a device consisting of a mixed cellulose ester paper featuring a wax-encircled, AuNP-coated film atop a cotton absorbent layer sandwiched between two plastic cover layers. In the absence of NADH, the Au3+-CTAB complex dissolves the AuNP layer completely, generating a white color in the test zone. In the presence of NADH, Au3+ is rapidly reduced to Au+, greatly decreasing the dissolution of AuNPs and yielding a red color that becomes stronger at increasing concentrations of NADH. This device exploits capillary force-assisted vertical diffusion, allowing us to apply a 25 μL sample to a surface-confined test zone to achieve a detection limit of 12.5 μM NADH. We used the enzyme glucose dehydrogenase as a model to demonstrate that our paper-based device can monitor NAD+-driven biochemical processes with and without selective dehydrogenase inhibitors by naked-eye observation within 4 min at room temperature in a small sample volume. We believe that our paper-based device could offer a valuable and low-cost analytical tool for monitoring NAD+-associated enzymatic reactions and screening for dehydrogenase inhibitors in a variety of testing contexts.

Prognostic role of lactate dehydrogenase in solid tumors: a systematic review and meta-analysis of 76 studies

BACKGROUND

In cancer cells, metabolism is shifted to aerobic glycolysis with lactate production coupled with a higher uptake of glucose as the main energy source. Lactate dehydrogenase (LDH) catalyzes the reduction of pyruvate to form lactate, and serum level is often raised in aggressive cancer and hematological malignancies. We have assessed the prognostic value of LDH in solid tumors.

MATERIAL AND METHODS

A systematic review of electronic databases was conducted to identify publications exploring the association of LDH with clinical outcome in solid tumors. Overall survival (OS) was the primary outcome, and cancer-specific survival (CSS), progression-free survival (PFS), and disease-free survival (DFS) were secondary outcomes. Data from studies reporting a hazard ratio (HR) and 95% confidence interval (CI) were pooled in a meta-analysis. Pooled HRs were computed and weighted using generic inverse-variance and random-effect modeling. All statistical tests were two-sided.

RESULTS

Seventy-six studies comprising 22 882 patients, mainly with advanced disease, were included in the analysis. Median cut-off of serum LDH was 245 U/L. Overall, higher LDH levels were associated with a HR for OS of 1.7 (95% CI 1.62-1.79; p < 0.00001) in 73 studies. The prognostic effect was highest in renal cell, melanoma, gastric, prostate, nasopharyngeal and lung cancers (all p < 0.00001). HRs for PFS was 1.75 (all p < 0.0001).

CONCLUSIONS

A high serum LDH level is associated with a poor survival in solid tumors, in particular melanoma, prostate and renal cell carcinomas, and can be used as a useful and inexpensive prognostic biomarker in metastatic carcinomas.

Development and validation of a docking-based virtual screening platform for the identification of new lactate dehydrogenase inhibitors

The human muscle isoform of lactate dehydrogenase (hLDH5) is one of the key enzymes of the glycolytic process. It is overexpressed in metastatic cancer cells and is linked to the vitality of tumors in hypoxic conditions. With the aim of identifying new hLDH5 inhibitors, a fully automated docking-based virtual screening platform was developed by considering different protein conformations and the consensus docking strategy. In order to verify the reliability of the reported platform, a small database of about 10,000 compounds was filtered by using this method, and the top-ranked compounds were tested for their hLDH5 inhibition activity. Enzymatic assays revealed that, among the ten selected compounds, two proved to efficiently inhibit enzyme activity with IC₅₀ values in the micromolar range. These results demonstrate the validity of the methodologies we followed, encouraging the application of larger virtual screening studies and further refinements of the platform. Furthermore, the two active compounds herein described may be considered as interesting leads for the development of new and more efficient LDH inhibitors.

Screening of novel inhibitors targeting lactate dehydrogenase A via four molecular docking strategies and dynamics simulations

Lactate dehydrogenase A (LDHA) is a metabolic enzyme which catalyzes the interconversion of lactate and pyruvate in the glycolysis pathway, thus playing key roles in aerobic glycolysis. The inhibition of LDHA by small molecules has become an attractive strategy for anticancer therapy in recent years. However, very few LDHA inhibitors have been reported, even though a great deal of effort has directed into identifying LDHA inhibitors using structure-based approaches. Therefore, high-throughput and high-accuracy screening approaches are still urgently needed in order to target LDHA effectively. In the present work, after establishing that our docking strategies performed well using test datasets, we screened 32791 Specs products for their docking scores with the substrate-binding pocket and, separately, the cofactor-binding pocket of LDHA. We subsequently identified 76 hits (i.e., ligands that show low docking scores) for the cofactor-binding pocket and 27 hits for the substrate-binding pocket. Two representative compounds, ZINC20036549 and ZINC19369718, were then chosen for further MD simulation analysis, and we found that these compounds maintained their inhibitory activity during the MD simulations. Meanwhile, we found that ZINC19369718 interacts with a novel binding site close to the active site, and that this interaction may inhibit the catalytic activity of LDHA. Together, these results offer not only a new paradigm for identifying Specs drug-like products for novel therapeutic use but they also provide further opportunity to adopt LDHA inhibition as a strategy for cancer therapy.

Epilepsy treatment. Targeting LDH enzymes with a stiripentol analog to treat epilepsy

Neuronal excitation is regulated by energy metabolism, and drug-resistant epilepsy can be suppressed by special diets. Here, we report that seizures and epileptiform activity are reduced by inhibition of the metabolic pathway via lactate dehydrogenase (LDH), a component of the astrocyte-neuron lactate shuttle. Inhibition of the enzyme LDH hyperpolarized neurons, which was reversed by the downstream metabolite pyruvate. LDH inhibition also suppressed seizures in vivo in a mouse model of epilepsy. We further found that stiripentol, a clinically used antiepileptic drug, is an LDH inhibitor. By modifying its chemical structure, we identified a previously unknown LDH inhibitor, which potently suppressed seizures in vivo. We conclude that LDH inhibitors are a promising new group of antiepileptic drugs.

Molecular Pathways: Targeting Cellular Energy Metabolism in Cancer via Inhibition of SLC2A1 and LDHA

Reprogramming of cellular energy metabolism is widely accepted to be one of the main hallmarks of cancer. The aberrant expression pattern of key regulators in the glycolysis pathway in cancer cells corroborates with the hypothesis that most cancer cells utilize aerobic glycolysis as their main ATP production method instead of mitochondrial oxidative phosphorylation. Overexpression of SLC2A1 and LDHA, both important regulators of the glycolysis pathway, was detected in the premalignant lesions and tumors of lung cancer patients, suggesting the involvement of these proteins in early carcinogenesis and tumor progression in cancer. Preclinical studies demonstrated that inhibiting SLC2A1 or LDHA led to diminished tumor growth in vitro and in vivo. SLC2A1 and LDHA inhibitors, when administered in combination with other chemotherapeutic agents, showed synergistic antitumor effects by resensitizing chemoresistant cancer cells to the chemotherapies. These results indicate that disrupting SLC2A1, LDHA, or other regulators in cancer cell energetics is a very promising approach for new targeted therapies.

Metabolic Consequences of LDHA inhibition by Epigallocatechin Gallate and Oxamate in MIA PaCa-2 Pancreatic Cancer Cells

Lactate dehydrogenase A (LDHA) is the enzyme that converts pyruvate to lactate and oxidizes the reduced form of nicotinamide adenine dinucleotide (NADH) to NAD⁺. Several human cancers including the pancreas display elevated expression of LDHA. Because of its essential role in cancer metabolism, LDHA has been considered to be a potential target for cancer therapy. Recently, we have shown that a green tea extract significantly down-regulated LDHA in HPAF-II pancreatic cancer cells using global proteomics profiling. The present study is to investigate how EGCG, a major biological active constituent of green tea, targets the metabolism of human pancreatic adenocarcinoma MIA PaCa-2 cells. We compared the effect of EGCG to that of oxamate, an inhibitor of LDHA, on the multiple metabolic pathways as measured by extracellular lactate production, glucose consumption, as well as intracellular aspartate and glutamate production, fatty acid synthesis, acetyl-CoA, RNA ribose and deoxyribose. Specific metabolic pathways were studied using [1, 2-¹³C₂]-d-glucose as the single precursor metabolic tracer. Isotope incorporations in metabolites were analyzed using gas chromatography/mass spectrometry (GC/MS) and stable isotope-based dynamic metabolic profiling (SiDMAP). We found that the EGCG treatment of MIA PaCa-2 cells significantly reduced lactate production, anaerobic glycolysis, glucose consumption and glycolytic rate that are comparable to the inhibition of LDHA by oxamate treatment. Significant changes in intracellular glucose carbon re-distribution among major glucose-utilizing macromolecule biosynthesis pathways in response to EGCG and oxamate treatment were observed. The inhibition of LDHA by EGCG or oxamate impacts on various pathways of the cellular metabolic network and significantly modifies the cancer metabolic phenotype. These results suggest that phytochemical EGCG and LDHA inhibitor oxamate confer their anti-cancer activities by disrupting the balance of flux throughout the cellular metabolic network.

Structures of lactate dehydrogenase A (LDHA) in apo, ternary and inhibitor-bound forms

Lactate dehydrogenase (LDH) is an essential metabolic enzyme that catalyzes the interconversion of pyruvate and lactate using NADH/NAD(+) as a co-substrate. Many cancer cells exhibit a glycolytic phenotype known as the Warburg effect, in which elevated LDH levels enhance the conversion of glucose to lactate, making LDH an attractive therapeutic target for oncology. Two known inhibitors of the human muscle LDH isoform, LDHA, designated 1 and 2, were selected, and their IC50 values were determined to be 14.4 ± 3.77 and 2.20 ± 0.15 µM, respectively. The X-ray crystal structures of LDHA in complex with each inhibitor were determined; both inhibitors bind to a site overlapping with the NADH-binding site. Further, an apo LDHA crystal structure solved in a new space group is reported, as well as a complex with both NADH and the substrate analogue oxalate bound in seven of the eight molecules and an oxalate only bound in the eighth molecule in the asymmetric unit. In this latter structure, a kanamycin molecule is located in the inhibitor-binding site, thereby blocking NADH binding. These structures provide insights into LDHA enzyme mechanism and inhibition and a framework for structure-assisted drug design that may contribute to new cancer therapies.

Detection of protein-small molecule binding using a self-referencing external cavity laser biosensor

High throughput screening of protein-small molecule binding interactions using label-free optical biosensors is challenging, as the detected signals are often similar in magnitude to experimental noise. Here, we describe a novel self-referencing external cavity laser (ECL) biosensor approach that achieves high resolution and high sensitivity, while eliminating thermal noise with sub-picometer wavelength accuracy. Using the self-referencing ECL biosensor, we demonstrate detection of binding between small molecules and a variety of immobilized protein targets with binding affinities or inhibition constants in the sub-nanomolar to low micromolar range. The demonstrated ability to perform detection in the presence of several interfering compounds opens the potential for increasing the throughput of the approach. As an example application, we performed a "needle-in-the-haystack" screen for inhibitors against carbonic anhydrase isozyme II (CA II), in which known inhibitors are clearly differentiated from inactive molecules within a compound library.

Synthetic applications of hypophosphite derivatives in reduction

The purpose of this review is to collect the applications in fine synthesis of hypophosphite derivatives as reducing agents.

Bioactive heterocycles containing endocyclic N-hydroxy groups

Drug-likeness rules consider N-O single bonds as "structural alerts" which should not be present in a perspective drug candidate. In most cases this concern is correct, since it is known that N-hydroxy metabolites of branded drugs produce reactive species that cause serious side effects. However, this dangerous reactivity of the N-OH species generally takes place when the nitrogen atom is not comprised in a cyclic moiety. In fact, the same type of metabolic behavior should not be expected when the nitrogen atom is included in the ring of an aromatic heterocyclic scaffold. Nevertheless, heterocycles bearing endocyclic N-hydroxy portions have so far been poorly studied as chemical classes that may provide new therapeutic agents. This review provides an overview of N-OH-containing heterocycles with reported bioactivities that may be considered as therapeutically relevant and, therefore, may extend the chemical space available for the future development of novel pharmaceuticals. A systematic treatment of the various chemical classes belonging to this particular family of molecules is described along with a discussion of the biological activities associated to the most important examples.

Cell-state-specific metabolic dependency in hematopoiesis and leukemogenesis

The balance between oxidative and nonoxidative glucose metabolism is essential for a number of pathophysiological processes. By deleting enzymes that affect aerobic glycolysis with different potencies, we examine how modulating glucose metabolism specifically affects hematopoietic and leukemic cell populations. We find that a deficiency in the M2 pyruvate kinase isoform (PKM2) reduces the levels of metabolic intermediates important for biosynthesis and impairs progenitor function without perturbing hematopoietic stem cells (HSCs), whereas lactate dehydrogenase A (LDHA) deletion significantly inhibits the function of both HSCs and progenitors during hematopoiesis. In contrast, leukemia initiation by transforming alleles putatively affecting either HSCs or progenitors is inhibited in the absence of either PKM2 or LDHA, indicating that the cell-state-specific responses to metabolic manipulation in hematopoiesis do not apply to the setting of leukemia. This finding suggests that fine-tuning the level of glycolysis may be explored therapeutically for treating leukemia while preserving HSC function.

Optimization of 5-(2,6-dichlorophenyl)-3-hydroxy-2-mercaptocyclohex-2-enones as potent inhibitors of human lactate dehydrogenase

Optimization of 5-(2,6-dichlorophenyl)-3-hydroxy-2-mercaptocyclohex-2-enone using structure-based design strategies resulted in inhibitors with considerable improvement in biochemical potency against human lactate dehydrogenase A (LDHA). These potent inhibitors were typically selective for LDHA over LDHB isoform (4–10 fold) and other structurally related malate dehydrogenases, MDH1 and MDH2 (>500 fold). An X-ray crystal structure of enzymatically most potent molecule bound to LDHA revealed two additional interactions associated with enhanced biochemical potency.

Inhibition of lactate dehydrogenase activity as an approach to cancer therapy

In the attempt of developing innovative anticancer treatments, growing interest has recently focused on the peculiar metabolic properties of cancer cells. In this context, LDH, which converts pyruvate to lactate at the end of glycolysis, is emerging as one of the most interesting molecular targets for the development of new inhibitors. In fact, because LDH activity is not needed for pyruvate metabolism through the TCA cycle, inhibitors of this enzyme should spare glucose metabolism of normal non-proliferating cells, which usually completely degrade the glucose molecule to CO2. This review is aimed at summarizing the available data on LDH biology in normal and neoplastic cells, which support the anticancer therapeutic approach based on LDH inhibition. These data encouraged pharmaceutical industries and academic institutions in the search of small-molecule inhibitors and promising candidates have recently been identified. The availability of inhibitors with drug-like properties will allow the evaluation in the near future of the real potential of LDH inhibition in anticancer treatment, also making the identification of the most responsive neoplastic conditions possible.

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.

Molecular and Kinetic Characterization of Babesia microti Gray Strain Lactate Dehydrogenase as a Potential Drug Target

Babesia microti is an emerging zoonotic protozoan organism that causes “malaria-like” symptoms that can be fatal in immunocompromised people. Owing to lack of specific therapeutic regiment against the disease, we cloned and characterized B. microti lactate dehydrogenase (BmLDH) as a potential molecular drug receptor. The in vitro kinetic properties of BmLDH enzyme was evaluated using nicotinamide adenine dinucleotide (NAD⁺) as a co-factor and lactate as a substrate. Inhibitory assay was also done using gossypol as BmLDH inhibitor to determine the inhibitory concentration 50 (IC₅₀). The result showed that the 0.99 kbp BmLDH gene codes for a barely soluble 36 kDa protein (332 amino acids) localized in both the cytoplasm and nucleus of the parasite. In vitro enzyme kinetic studies further revealed that BmLDH is an active enzyme with a high catalytic efficiency at optimal pH of 10.2. The K_m values of NAD⁺ and lactate were 8.7 ± 0.57 mM and 99.9 ± 22.33 mM, respectively. The IC₅₀ value for gossypol was 0.345 μM, while at 2.5 μM, gossypol caused 100% inhibition of BmLDH catalytic activity. These findings, therefore, provide initial evidence that BmLDH could be a potential drug target, although further in vivo studies are needed to validate the practical application of lactate dehydrogenase inhibitors against B. microti infection.

Quantitative determinants of aerobic glycolysis identify flux through the enzyme GAPDH as a limiting step

Aerobic glycolysis or the Warburg Effect (WE) is characterized by the increased metabolism of glucose to lactate. It remains unknown what quantitative changes to the activity of metabolism are necessary and sufficient for this phenotype. We developed a computational model of glycolysis and an integrated analysis using metabolic control analysis (MCA), metabolomics data, and statistical simulations. We identified and confirmed a novel mode of regulation specific to aerobic glycolysis where flux through GAPDH, the enzyme separating lower and upper glycolysis, is the rate-limiting step in the pathway and the levels of fructose (1,6) bisphosphate (FBP), are predictive of the rate and control points in glycolysis. Strikingly, negative flux control was found and confirmed for several steps thought to be rate-limiting in glycolysis. Together, these findings enumerate the biochemical determinants of the WE and suggest strategies for identifying the contexts in which agents that target glycolysis might be most effective.

DOI:http://dx.doi.org/10.7554/eLife.03342.001

Cells generate energy from a sugar called glucose via a process called glycolysis. This process involves many enzymes that catalyze 10 different chemical reactions, and it essentially converts glucose step-by-step into a simpler chemical called pyruvate.

Pyruvate is then normally transported into structures within the cell called mitochondria, where it is further broken down using oxygen to release more energy. However, in cells that are rapidly dividing, pyruvate is converted into another chemical called lactate—which releases energy more quickly, but releases less energy overall. Cancer cells often convert most of their glucose into lactate, rather than breaking down pyruvate in their mitochondria: an observation known as the ‘Warburg effect’. And while many factors affect how a cell releases energy from pyruvate, it remains unclear what regulates which of these biochemical processes is most common in a living cell.

In this study, Shestov et al. have developed a computational model for the process of glycolysis and used this to investigate the causes of the Warburg Effect. The model was based on the known characteristics of the enzymes and chemical reactions involved at each step. It predicted that the activity of the enzyme called GAPDH, which carries out the sixth step in glycolysis, in many cases affects how much lactate is produced. This suggests that this enzyme represents a bottleneck in the pathway.

Next, Shestov et al. performed experiments where they used drugs to block different stages of the glycolysis pathway, and confirmed that the GAPDH enzyme is important for regulating this pathway in living cancer cells too. In these treated cells, the levels of a chemical called fructose-1,6-biphosphate (which is made in a step in the pathway between glucose and pyruvate) were either very high or very low. Shestov et al. proposed that the flow of chemicals through the glycolysis pathway is controlled by the GAPDH enzyme when the chemicals used by the enzymes upstream of GAPDH in the pathway (which includes fructose-1,6-biphosphate) are plentiful. However, if these chemicals are limited, other enzymes that are involved in earlier steps of the pathway regulate the process instead.

The findings of Shestov et al. reveal that the regulation of glycolysis is more complex than previously thought, and is also very different when cells are undergoing the Warburg Effect. In the future, these findings might help to identify the types of cancer that could be effectively treated using drugs that target the glycolysis process, which are currently being tested in pre-clinical studies.

DOI:http://dx.doi.org/10.7554/eLife.03342.002

Small-molecule inhibitors of human LDH5

The latest findings on the role played by human LDH5 (hLDH5) in the promotion of glycolysis in invasive tumor cells indicates that this enzyme subtype is a promising therapeutic target for invasive cancer. Compounds able to selectively inhibit hLDH5 hold promise for the cure of neoplastic diseases. hLDH5 has so far been a rather unexplored target, since its importance in the promotion of cancer progression has been neglected for decades. This enzyme should also be considered as a challenging target due the high polar character (mostly cationic) of its ligand cavity. Recently, significant progresses have been reached with small-molecule inhibitors of hLDH5 displaying remarkable potencies and selectivities. This review provides an overview of the newly developed hLDH5 inhibitors. The roles of hLDH isoforms will be briefly discussed, and then the inhibitors will be grouped into chemical classes. Furthermore, general pharmacophore features will be emphasized throughout the structural subgroups analyzed.

Identification of LDH-A as a therapeutic target for cancer cell killing via (i) p53/NAD(H)-dependent and (ii) p53-independent pathways

Most cancer cells use aerobic glycolysis to fuel their growth. The enzyme lactate dehydrogenase-A (LDH-A) is key to cancer's glycolytic phenotype, catalysing the regeneration of nicotinamide adenine dinucleotide (NAD(+)) from reduced nicotinamide adenine dinucleotide (NADH) necessary to sustain glycolysis. As such, LDH-A is a promising target for anticancer therapy. Here we ask if the tumour suppressor p53, a major regulator of cellular metabolism, influences the response of cancer cells to LDH-A suppression. LDH-A knockdown by RNA interference (RNAi) induced cancer cell death in p53 wild-type, mutant and p53-null human cancer cell lines, indicating that endogenous LDH-A promotes cancer cell survival irrespective of cancer cell p53 status. Unexpectedly, however, we uncovered a novel role for p53 in the regulation of cancer cell NAD(+) and its reduced form NADH. Thus, LDH-A silencing by RNAi, or its inhibition using a small-molecule inhibitor, resulted in a p53-dependent increase in the cancer cell ratio of NADH:NAD(+). This effect was specific for p53(+/+) cancer cells and correlated with (i) reduced activity of NAD(+)-dependent deacetylase sirtuin 1 (SIRT1) and (ii) an increase in acetylated p53, a known target of SIRT1 deacetylation activity. In addition, activation of the redox-sensitive anticancer drug EO9 was enhanced selectively in p53(+/+) cancer cells, attributable to increased activity of NAD(P)H-dependent oxidoreductase NQO1 (NAD(P)H quinone oxidoreductase 1). Suppressing LDH-A increased EO9-induced DNA damage in p53(+/+) cancer cells, but importantly had no additive effect in non-cancer cells. Our results identify a unique strategy by which the NADH/NAD(+) cellular redox status can be modulated in a cancer-specific, p53-dependent manner and we show that this can impact upon the activity of important NAD(H)-dependent enzymes. To summarise, this work indicates two distinct mechanisms by which suppressing LDH-A could potentially be used to kill cancer cells selectively, (i) through induction of apoptosis, irrespective of cancer cell p53 status and (ii) as a part of a combinatorial approach with redox-sensitive anticancer drugs via a novel p53/NAD(H)-dependent mechanism.

Tumor aerobic glycolysis: new insights into therapeutic strategies with targeted delivery

INTRODUCTION

Cancer cells acclimatize to the harsh tumor microenvironment by altering cellular metabolism in favor of aerobic glycolysis. This process provides a source of energy and also generates essential components for macromolecular biosynthesis, which enables cellular survival. As the dependence of cancer cells on glycolysis affects tumorigenesis, it has become an attractive target for therapeutic intervention. Several preclinical studies have shown the effectiveness of using biological targets from the glycolytic pathway for anticancer therapy.

AREAS COVERED

This review provides an insight into the glycolytic pathway, highlighting potential targets for glycolytic inhibition. We then discuss recent advancement in delivery strategies that have the potential to circumvent some of the problems posed by current glycolytic inhibitors, enabling resurrection of abandoned therapeutic agents.

EXPERT OPINION

Targeting the glycolysis pathway is a tactical approach for cancer therapy. However, the current nonspecific therapeutic strategies have several drawbacks such as poor bioavailability, unfavorable pharmacokinetic profile and associated nonspecific toxicity, thereby limiting preclinical investigation. In recent years, nanoparticle systems have received recognition for the delivery of therapeutic agents directly to the tumor tissue. Thus, it is envisaged that this strategy can be expanded for the delivery of current glycolytic inhibitors specifically to tumor tissues providing improved anticancer activity.